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UNIVERSITY OF SOUTHAMPTON
Faculty of Natural and Environmental Science
School of Chemistry
The Synthesis of Fluorinated Carbohydrates and Fluorinated
Cyclohexanols
by
Lewis Atugonza Mtashobya
A Thesis Submitted for the Degree of Doctor of Philosophy
April 2014
UNIVERSITY OF SOUTHAMPTON
ABSTRACT
FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCE
Chemistry
Thesis for the Degree of Doctor of Philosophy
The Synthesis of Fluorinated Carbohydrates and Fluorinated
Cyclohexanols
By Lewis Atugonza Mtashobya
Carbohydrates are central to many fundamental processes. However, their
interactions to proteins are characterized by low binding affinity. An attractive
strategy to improve this affinity is polyfluorination of carbohydrates. This
thesis describes the synthesis and extensive NMR characterisation of monoand difluorinated 2,3-dideoxysugars in which a sugar (CHOH)(CHOH) section
was replaced with the more hydrophobic CH2CHF, CH2CF2 and CHFCHF groups.
An important consequence of sugar fluorination is that the hydrogen bond
properties of the adjacent alcohol group(s) are modified. Part of this thesis
describes the synthesis of a number of fluorinated cyclohexanol and benzyl
alcohol derivatives as probes to investigate the influence of fluorination on the
alcohol hydrogen bond donating capacity.
Contents
ABSTRACT ................................................................................................................................ i
Contents ................................................................................................................................... i
DECLARATION OF AUTHORSHIP ............................................................................. vii
Acknowledgements..........................................................................................................ix
Abbreviations ......................................................................................................................xi
1
Introduction ................................................................................................................... 1
1.1
Fluorine Chemistry ............................................................................. 1
1.2
Influence of Fluorination on Molecular Properties ............................... 3
1.2.1
Physical Properties ....................................................................... 3
1.2.2
Lipophilicity ................................................................................. 4
1.2.3
Influence of Fluorination on pKa.................................................... 5
1.2.4
H−Bonding Interactions Involving Fluorine .................................... 6
1.2.5
H−Bonding of Fluorohydrins in the Linclau Group ......................... 8
1.2.6
Dipolar Interactions ...................................................................... 9
1.3
1.3.1
DiMagno: Hexafluorinated Pyranose ............................................. 9
1.3.2
Membrane Transport Studies ...................................................... 10
1.3.3
Previous Work in the Linclau Group ............................................ 11
1.4
2
Polar Hydrophobicity .......................................................................... 9
Aim and Objectives ........................................................................... 11
1.4.1
Synthesis of the Mono-and Difluorinated Sugars ......................... 12
1.4.2
Synthesis of Fluorohydrins ......................................................... 12
Results and Discussion: Synthesis of monofluorinated
Carbohydrates................................................................................................................... 14
2.1
Introduction ..................................................................................... 14
2.2
Synthesis of Monofluorinated Sugars 2.1 and 2.2 ............................. 14
2.2.1
Introduction ............................................................................... 14
2.2.2
Synthesis of 1,2,4,6-Tetra-O-acetyl-3-deoxy-3-fluoro-Dglucopyranose (2.1) ................................................................................. 15
2.2.3
Synthesis of 1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-Dglucopyranose (2.2) ................................................................................. 17
2.3
Synthesis of 3-Deoxy-3-fluorogalactopyranose (2.3) .......................... 18
2.3.1
2.4
Introduction ............................................................................... 18
Conclusion ....................................................................................... 23
i
3
Results and Discussion: Synthesis of Fluorosugars with Modified
Hydrophobic Domain .................................................................................................... 25
3.1
Introduction ...................................................................................... 25
3.2
Synthesis of 2,3-Dideoxy-2,3-difluorosugars ..................................... 25
3.2.1
Synthesis of 2,3-Dideoxy-2,3-difluoro-D-glucopyranose 1.45 ....... 26
3.2.2
Synthesis of 2,3-Dideoxy-2,3-difluoro-D-galactopyranose 1.46 .... 30
3.3
4
Synthesis of 2,3-Dideoxy-3-fluorosugars ........................................... 35
3.3.1
Synthesis of 2,3-Dideoxy-3-fluoro-D-glucopyranose 1.49............. 35
3.3.2
Synthesis of 2,3-Dideoxy-3-fluoro-α,β-D-galactopyranose 1.50 .... 36
3.4
Synthesis of 2,3-Dideoxy-3,3-difluoro-D-glucopyranose 1.47 ............. 38
3.5
Conclusion........................................................................................ 40
Results and Discussion: NMR Investigations on the
Conformationally Rigid Levoglucosan Derivatives..................................... 43
4.1
4.1.1
Introduction ............................................................................... 43
4.1.2
19
4.1.3
Our Levoglucosan Derivatives ..................................................... 44
4.1.4
Assignment of the Protons H6 and H6' ....................................... 46
4.1.5
5
4.1.6
4
4.1.7
Coupling Through the Heteroatom Oxygen ................................. 49
4.2
F NMR and the Coupling Constants ........................................... 43
JH6'-F3 Coupling ............................................................................ 48
JC6–F3 Coupling ............................................................................ 48
Intramolecular Hydrogen Bonding ..................................................... 50
4.2.1
Introduction ............................................................................... 50
4.2.2
Hydrogen Bonding Observations on Levoglucosans .................... 51
4.3
5
Long Range Coupling ........................................................................ 43
Conclusion........................................................................................ 52
Synthesis of Fluorohydrins................................................................................ 53
5.1
Introduction ...................................................................................... 53
5.2
Synthesis of the Fluorohydrins .......................................................... 53
5.2.1
Synthesis of Cis- and Trans-4-(tert-butyl)-1fluoromethylcyclohexanol (1.51 and 1.52) ............................................... 53
5.2.2
Synthesis of Cis- and Trans-4-(tert-butyl)-1difluoromethylcyclohexanol (1.53 and 1.54) ............................................ 56
5.2.3
Synthesis of Cis- and Trans-4-(tert-butyl)-1trifluoromethylcyclohexanol (1.55 and 1.56) ............................................ 59
5.2.4
Synthesis of Cis- and Trans-4-(tert-butyl)-1-methylcyclohexanol
(1.57 and 1.58) ........................................................................................ 59
5.2.5
Attempted Ssynthesis of Trans-4-(tert-butyl)-3-fluoro and Trans-4(tert-butyl)-3,3-difluorocyclohexanol (1.66 and 1.68) ............................... 60
ii
5.2.5.1
Deoxyfluorination Approach ................................................ 60
5.2.5.2
Attempts to Monofluorination through Mesylation ............... 61
5.2.6
Attempted Synthesis of Cis-4-(tert-butyl)-3-fluoro- and Cis-4-(tertbutyl)-3,3-difluorocyclohexanol (1.65 and 1.67)....................................... 62
5.2.6.1
Hydrogenation and Birch Reduction of a Resorcinol Derivative
62
5.2.6.2
Attempted Birch Reduction of a 3-fluorophenol Derivative .... 63
5.2.7
Synthesis of Trans- and Cis-2-fluorocyclohexanol (1.59 and 1.60)
65
5.2.8
Synthesis of Trans-and Cis-4-fluorocyclohexanol (1.63 and 1.64) 68
5.2.8.1
5.2.9
Birch Reduction of 3-fluorophenyl Acetate ............................ 72
5.2.9.2
ol
Synthesis of 3-Fluorocyclohexanol (1.62) from 2-Cyclohexen-172
5.2.9.3
Alternative Synthesis through Iodofluorination ..................... 73
Synthesis of 2-Fluorobenzyl Alcohols (1.69-1.71) ....................... 76
Results of H–bond Acidity of Fluoroalcohols ..................................... 78
5.3.1
Introduction ............................................................................... 78
5.3.2
Results of H−bond Acidity .......................................................... 78
5.4
6
Synthesis of Trans-and Cis-3-fluorocyclohexanol (1.61 and 1.62) 72
5.2.9.1
5.2.10
5.3
Attempt to Fluorination through SN2 Substitution ................. 70
5.3.2.1
Observations on Fluorohydrins............................................. 78
5.3.2.2
Observations on Benzyl Alcohols .......................................... 79
Conclusion ....................................................................................... 80
Experimental ............................................................................................................... 83
6.1
General Method ................................................................................ 83
6.2
Synthesis of Tetra-O-acetyl-3-fluoro-D-glucopyranose 2.1 .................. 84
6.2.1
1,2:5,6-Di-O-isopropylidene-3-keto-α-D-glucofuranose ................ 84
6.2.2
1,2:5,6-Di-O-isopropylidene-α-D-allofuranose .............................. 84
6.2.3
3-Deoxy-3-fluoro-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose 85
6.2.4
1,2,4,6-Tetra-O-acetyl-3-fluoro-D-glucopyranose ......................... 86
6.3
Synthesis of Tetra-O-acetyl -6-fluoro-D-glucopyranose 2.2 ................. 87
6.3.1
Methyl-6-fluoro-α-D-glucotopyranoside ....................................... 87
6.3.2
1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-D-glucotopyranose ........ 87
6.4
Synthesis of 3-Deoxy-3-fluorogalactopyranose 2.3 ............................ 88
6.4.1
3-O-acetyl-1,2:5,6-Di-O-isopropylidene-α-D-erythrohex-3-enose .. 88
6.4.2
3-O-acetyl-1,2:5,6-di-O-isopropylidene-α-D-gulofuranose ............ 89
6.4.3
1,2:5,6-Di-O-isopropylidene-α-D-gulofuranose ............................ 90
6.4.4
3-Deoxy-3-fluoro-1,2;5,6-di-O-isopropylidene-α-D-galactofuranose
90
6.4.5
1,2,4,6-Tetra-O-acetyl-3-deoxy-3-fluoro-D-galactopyranose ......... 91
iii
6.4.6
6.5
3-Deoxy-3-fluoro-D-galactopyranose ........................................... 92
Synthesis of 2,3-Dideoxy-2,3-difluoro-α,β-D-glucopyranose 1.45........ 93
6.5.1
1,6-Anhydro-2-deoxy-2-iodo-β-D-glucopyranose .......................... 93
6.5.2
1,6:2,5-Dianhydro-4-O-benzyl-β-D-mannopyranose...................... 94
6.5.3
1,6-Anhydro-4-O-benzyl-2-fluoro-β-D-glucopyranose ................... 94
6.5.4
1,6-Anhydro-4-O-benzyl-2,3-difluoro-β-D-glucopyranose ............. 95
6.5.5
1,6-Anhydro-2,3-dideoxy-2,3-difluoro-β-D-glucopyranose ............ 96
6.5.6
1,4,6-Tri-O-acetyl-2,3-dideoxy-2,3-difluoro-D-glucopyranose ....... 97
6.5.7
2,3-Dideoxy-2,3-difluoro-α,β-D-glucopyranose ............................. 98
6.6
Synthesis of 2,3-Dideoxy-2,3-difluoro-D-galactopyranose 1.46 .......... 99
6.6.1
1,6-Anhydro-2,3-dideoxy-2,3-difluoro[trifluoromethyl-sulfonyl]-Dglucopyranose ......................................................................................... 99
6.6.2
1,6-Anhydro-4-benzoyl-2,3-dideoxy-2,3-difluoro-D-galactopyranose
100
6.6.3
1,6-Di-O-acetyl-4-benzoyl-2,3-dideoxy-2,3-D-galactopyranose ... 100
6.6.4
1,6-Anhydro-2,3-dideoxy-2,3-difluoro-D-galactopyranose .......... 101
6.6.5
1,4,6-Tri-O-acetyl-2,3-dideoxy-2,3-difluoro-D-galactopyranose .. 102
6.6.6
2,3-Dideoxy-2,3-difluoro-D-galactopyranose ............................. 103
6.6.7
Methyl-2,3-dideoxy-2,3-difluoro-D-galactopyranose................... 103
6.7
Synthesis of 2,3-Dideoxy-3-fluoro-D-glucopyranose 1.49 ................. 104
6.7.1
1,6-Anhydro-4-benzyl-2-deoxy-D-arabino-hexopyranose............ 104
6.7.2
1,6-Anhydro-4-benzyl-2,3-dideoxy-3-fluoro-D-glucopyranose .... 105
6.7.3
1,6-Anhydro-2,3-dideoxy-3-fluoro-D-glucopyranose .................. 106
6.7.4
2,3-Dideoxy-3-fluoro-D-glucopyranose ...................................... 106
6.8
Synthesis of 2,3-Dideoxy-3-fluoro-α,β-D-galactopyranose 1.50 ......... 108
6.8.1
1,6-Anhydro-2,3-dideoxy-3-fluoro-(trifluoromethyl)-Dglucopyranose ....................................................................................... 108
6.8.2
1,6-Anhydro-4-benzoyl-2,3-dideoxy-3-fluoro-D-galactopyranose 108
6.8.3
1,6-Anhydro-2,3-dideoxy-3-fluoro-D-galactopyranose ................ 109
6.8.4
2,3-Dideoxy-3-fluoro-α,β-D-galactopyranose .............................. 110
6.8.5
Methyl-2,3-dideoxy-3-fluorogalactopyranoside.......................... 111
6.9
Synthesis of 2,3-Dideoxy-3,3-difluoro-D-glucopyranose 1.47 ........... 112
6.9.1
1,6-Anhydro-4-benzyl-2,3-dideoxy-3-keto-D-glucopyranose ....... 112
6.9.2
1,6-Anhydro-4-benzyl-2,3-dideoxy-3-difluoro-D-glucopyranose . 112
6.9.3
2,3-Dideoxy-3,3-difluoro-D-glucopyranose ................................ 113
6.9.4
Methyl-2,3-dideoxy-3,3-difluoro-α- and β-D-glucopyranoside ..... 114
6.10
Synthesis of 1,6-Anhydro-2-deoxy-2-fluoro-D-glucopyranose 4.5 .. 116
6.11
Synthesis of Trans- and Cis-4-(tert-butyl)-1-fluoromethylcyclohexanol
117
6.11.1
Cis- and trans-4-(tert-butyl)-1-oxiranecyclohexane .................... 117
iv
6.11.2
Trans- and cis-4-(tert-butyl)-1-fluoromethylcyclohexanol .......... 118
6.12
Synthesis of Trans- and Cis-4-(tert-butyl)-1difluoromethylcyclohexanol...................................................................... 119
6.12.1 Trans- and Cis-4-(tert-butyl)-1hydroxycyclohexyl(difluoromethyl)phosphonate .................................... 119
6.12.2
The phosphates 5.6 and 5.7 ..................................................... 120
6.12.3
cis- and Trans-4-(tert-butyl)-1-difluoromethylcyclohexanol ....... 121
6.13
Trans- and Cis-4-(tert-butyl)-1-trifluoromethylcyclohexanol ......... 122
6.14
Trans- and Cis-4-(tert-butyl)-1-methylcyclohexanol ...................... 123
6.15
Synthesis of Trans-4-(tert-butyl)-3-fluoro and -3,3difluorocyclohexanol ................................................................................ 124
6.15.1
2-bromo-4-(tert-butyl)cyclohexanone........................................ 124
6.15.2
Synthesis of 4-(Tert-butyl)cyclohex-2-enone ............................. 124
6.15.3
(1S,3S,4S)-4-(Tert-butyl)cyclohexane-1, 3-diol ........................... 125
6.15.4
2-(Tert-butyl)-5-(trityroxy)cyclohexanol ..................................... 126
6.15.5
2-(Tert-butyl)-5-(trityroxy)cyclohexanone .................................. 126
6.15.6
(1R,2R) and (1S,2R)-2-(Tert-butyl)cyclohexyl methanesulfonate . 127
6.15.7
4-(Tert-butyl) resorcinol............................................................ 128
6.15.8
(1R,3R, 4R)-4-(Tert-butyl)cyclohexane-1,3-diol .......................... 129
6.15.9
3-Fluoromethoxybenzene (3–Fluoroanisole).............................. 129
6.15.10
2-Tert-butyl-5-fluoro-1-methoxybenzene ............................... 130
6.15.11
3-Fluorophenyl acetate .......................................................... 130
6.15.12
2-Tert-butyl-5-fluorophenol ................................................... 131
6.16
Synthesis of Trans- and Cis-2-fluorocyclohexanol ........................ 131
6.16.1
Trans- 2-fluorocyclohexanol ..................................................... 131
6.16.2
(S)- 2-Fluorocyclohexanone....................................................... 132
6.16.3
Trans-2-fluorocyclohexyl trifluoromethanesulfonate................. 133
6.16.4
Cis-2-Fluorocyclohexyl acetate.................................................. 133
6.16.5
Cis-2-fluorocyclohexanol .......................................................... 134
6.17
Synthesis of Trans-and Cis-4-fluorocyclohexanol ......................... 135
6.17.1
Cis- and Trans-1-acetoxycyclohexanol ...................................... 135
6.17.2
Trans-and Cis-4-methylsulfonylcyclohexyl acetate .................... 136
6.18
Synthesis of Trans-and Cis-3-fluorocyclohexanol ......................... 136
6.18.1
Trans- and Cis-3-fluorocyclohexanol ........................................ 136
6.18.2
Trans-3-fluorocyclohexyl acetate .............................................. 137
6.18.3
Trans and Cis-3-fluoro-2-iodocyclohexanol ............................... 138
6.18.4
Trans-3-fluorocyclohexanol ...................................................... 139
6.19
Synthesis of 2-Fluorobenzyl Alcohols 5.66-5.68 ........................... 139
6.19.1
2-Fluorobenzyl alcohol ............................................................. 139
6.19.2
2-Fluoro-5-methylbenzyl alcohol............................................... 140
v
6.19.3
2-Fluoro-5-nitrobenzyl alcohol .................................................. 140
7
List of References..................................................................................................141
8
Appendix ....................................................................................................................149
8.1
X-ray Crystallography Data .............................................................. 149
8.2
Publication ...................................................................................... 155
vi
DECLARATION OF AUTHORSHIP
I, Lewis Atugonza Mtashobya declare that the thesis entitled “The synthesis of
fluorinated carbohydrates and fluorinated cyclohexanols” and the work
presented in the thesis are both my own, and have been generated by me as
the result of my own original research. I confirm that:
•
this work was done wholly while in candidature for a research degree at this
University;
•
where any part of this thesis has previously been submitted for a degree or
any other qualification at this University or any other institution, this has
been clearly stated;
•
where I have consulted the published work of others, this is always clearly
attributed;
•
Where I have quoted from the work of others, the source is always given.
With the exception of such quotations, this thesis is entirely my own work;
•
I have acknowledged all main sources of help;
•
where the thesis is based on work done by myself jointly with others, I have
made clear exactly what was done by others and what I have contributed
myself;
•
part of this work has been published as:
Lucas, R.; Peñalver, P.; Gómez-Pinto, I.; Vengut-Climent, E.; Mtashobya, L.;
Cousin, J.; Maldonado, O. S.; Perez, V.; Reynes, V.; Aviñó, A.; Eritja, R.;
González, C.; Linclau, B.; Morales, J. C. J. Org. Chem. 2014, 79, 2419–2429.
Signed: ………………………………………………………………………..
Date: …………………………………………………………………………
vii
Acknowledgements
I would first like to thank God the almighty, for giving me the opportunity to
live on this Earth and to have performed all that I have done up to this year,
2014 at my 40th year. “We are not saying that we can do this work ourselves. It
is God who makes us able to do all that we do.” 2 Corinthians 3:5. Also my
trust is built on the other word from the Bible that “I can do all things through
Christ because He gives me strength”, Philippians 4:13.
Second and most important, I would like to thank Dr Bruno Linclau for giving
me opportunity to join his research group particularly on the subject area of
“fluorine chemistry”. I have thoroughly enjoyed fluorine chemistry! Your full
commitment, guidance, enthusiasm and encouragement on a daily basis have
been incredible and much appreciated. I also thank Dr Eugen Stulz for being
my advisor.
A special thank has to go to Mkwawa University College of Education for
sponsoring my PhD studies. It has been very expensive, but thanks God that
they have finally managed.
I would like to thank all Linclau group members, past and present that have
assisted, advised, helped and entertained me throughout the three years.
These include in no particular order Konrad, Cath, Nathan, Sam, Carole,
Clement, Craig, Florent, Leona, Zhong, Stephanie, Giullaume, Julien, Joe,
Gemma, Kane, Lucas, Sarah, Anton, Vincent, Jonathan, and Krunal.
My thanks go to the service staff including Neil (NMR), John and Julie (MS), Karl
and others in stores; Mark in X-ray structures and all the guys in the
glassblowing workshop.
Finally, very special thanks go to my lovely wife Rehema, our children Meshach
and Ebenezer for their support and putting up with my absence at home in
Tanzania, for all the three years I have been in the UK. Last but not least, to my
mother (Ma Frida), Emmanuel Kagashe (my late father, may your soul rest in
peace), brothers and sisters and my uncle Benezeth for his daily updates about
all that was going on in our entire family.
ix
Abbreviations
d
DAST
DBU
DCM
DMAP
DMF
DMSO
ESI
EXSY
NBS
NMR
PDC
PE
TBAF
TEA
TFA
THF
TLC
Doublet
Diethylaminosulfur trifluoride
1,8-Diazobicylo[5.4.0]undec-7-ene
Dichloromethane
Dimethylaminopyridine
Dimethylformamide
Dimethylsulfoxide
Electrospray Ionisation
Exchange spectroscopy
N-bromosuccinimide
Nuclear Magnetic Resonance
Pyridinium Dichromate
Petroleum ether
Tetra-n-butylammonium fluoride
Triethylamine
Trifluoroacetic acid
Tetrahydrofuran
Thin-Layer Chromatography
xi
Chapter 1: Introduction
1 Introduction
1.1 Fluorine Chemistry
Fluorine is the most abundant halogen and the 13th most abundant element in
the earth’s crust.1-3 However, very few organic compounds possessing fluorine
atom(s) have been found in nature (Figure 1.1).4,5 The first organofluorine
compound, identified in 1943, was fluoroacetate (1.1), a metabolite of the
Southern African plant Dichapetalum cymosum. In East Africa, especially in
some places of Tanzania, many other fluoroacetate-accumulating plants were
found, most of them belonging to the genus Dichapetalum. D.5,6 The cell
extract of S. cattleya have been found to have very efficient NADH-dependent
fluoroacetaldehyde dehydrogenase which oxidises fluoroacetaldehyde (1.2) to
fluoroacetate.5,7 Fluorocitrate (1.3) is a potent inhibitor of the enzyme aconitase
and was first reported by Rudolph Peter in 1953 through conversion of
fluoroacetate. Fluoroacetate is toxic because it is converted in vivo to
fluorocitrate by condensation of fluoroacetyl-CoA with oxaloacetate by citrate
synthetase.
Therefore,
many
plants
which
accumulate
low
levels
of
fluoroacetate also contain fluorocitrate.5
Figure 1.1: Some naturally occurring fluorine-containing compounds4,5
The main fluorinated component (80%) of the seeds of a shrub, Dichapetalum
toxicarium, indigenous to Sierra Leone and other parts of West Africa was
found by Peter and co-workers to contain ω-fluorooleic acid (1.4). The plant D.
1
Chapter 1: Introduction
toxicarium is very toxic and has been frequently responsible for livestock
losses. When ingested the seeds cause loss of coordination, paralysis of lower
limbs and ultimately death.8 The nucleocidin (1.5) was isolated in 1957 from
Streptomyces calvus, an organism obtained from an Indian soil sample. It is
known to possess a broad spectrum of antibiotic activity.5,9,10
For a number of years, organofluorine chemistry has been a major field in the
life sciences.11 In 1954, Fried and Sabo showed that fludrocortisone 1.6 (Figure
1.2), the first synthetic cortisone with a fluorine atom to the 9α position of
cortisol improved its therapeutic index as an anti-inflammatory agent by two
fold.12,13
Figure 1.2: The first fluorinated pharmaceutical
Another landmark example is 2-deoxy-2-fluoro-D-glucose (1.7), which was
reported to cause a significant inhibition of glycolysis in tumour cell growth,14,15
but is currently an important cancer imaging agent (as its 18F derivative).16
Figure 1.3: 2-deoxy-2-fluoro-D-glucose
Currently, it has been estimated that 30-40% of agrochemicals and 25% of
pharmaceuticals on the market contain at least one fluorine atom.3,17 It is also
quite remarkable that three out of the five top-selling pharmaceuticals and
about one-third of the top-performing drugs, currently on the market, contain
fluorine atoms in their structure.3 For example, in 2006, the best and second
best-selling drugs in the world were Lipitor® 1.8 (by Pfizer/Astellas; $14.4
billion/year) and Advair® 1.9 (by GlaxoSmithKline; $6.1 billion/year), which
contain one and three fluorine atoms, respectively (Figure 1.4).4 In addition, in
2
Chapter 1: Introduction
2008, among the top 30 best-selling pharmaceutical products in the US, 10
have at least one fluorine atom.13
Figure 1.4: Top-2 best-selling drugs in 2006
From these and many other remarkable contributions, fluorine has been
highlighted as the second most utilised hetero-element (after nitrogen) in life
science oriented research.18
1.2 Influence of Fluorination on Molecular Properties
The unique atomic properties of fluorine which include: high electronegativity,
relatively small size, very low polarisability, tightly bound three non-bonding
electron pairs and excellent overlap between its 2s and 2p orbitals, have made
it very interesting in the life science oriented research.19
1.2.1 Physical Properties
Some atomic physical properties of fluorine in comparison with other halogens
that contribute to its special molecular properties are provided in Table 1.1.
Table 1.1: Atomic physical properties of halogens19
Entry
F
Cl
Br
I
Ionization potential
401.8
299.0
272.4
242.2
Van der Waals radius (rv)
1.47
1.75
1.85
1.98
Atomic polarizability (A3)
0.5
2.2
3.1
4.7
Electronegativity (Pauling)
4.0
3.2
3.0
2.7
Atomic fluorine has the smallest size and atomic polarizability among the
halogens. It is the most electronegative element according to the Pauling’s
scale and also, has the largest ionization potential value compared to the other
3
Chapter 1: Introduction
halogens as shown in Table 1.1. Due to high electronegativity of fluorine, the
C−F bond is one of the strongest and is capable of strengthening the adjacent
C−C single bond, and at the same time weakening the C=C bonds in allylic
systems.20,21
1.2.2 Lipophilicity
Lipophilicity, defined as the ability to penetrate the lipid bilayer membrane of a
cell, is a physicochemical property that plays a crucial role in determining
absorption, distribution, metabolism, excretion and toxicity properties22 which
all together determine the bioavailability of a compound.23 Lipophilicity
contributes to the drug solubility and permeability through membranes,
potency and selectivity.24,25 The logarithmic partition coefficient log P (1octanol/water), is currently the widely accepted lipophilicity parameter.26
Some general rules on the effects of fluorination on lipophilicity have been
established and include: fluorination usually but not always increases
lipophilicity;
aromatic
polyfluorination
fluorination
increases
always
lipophilicity.19
increases
However,
lipophilicity
there
is
a
and
complex
relationship between fluorination and lipophilicity as shown in Tables 1.2 and
1.3.
Table 1.2: Lipophilicity decreased by fluorination19
Entry
Log P (octanol-H2O)
CH3CH3
1.81
CH3CHF2
0.75
CH3(CH2)3CH3
3.11
CH3(CH2)3CH2F
2.33
Fluorination of alkanes decreases lipophilicity (Table 1.2), likely because of the
introduction of a large dipole moment. A trifluoromethyl group in the α
position of alcohols (Table 1.3) leads to an increase in lipophilicity, but a CF3group at the δ position causes a significant decrease in lipophilicity. The
former is difficult to rationalise but the changes in hydrogen bond properties,
as well as the ‘hardening’ of the alcohol lone pairs (less polarisable) is usually
invoked.
4
Chapter 1: Introduction
Table 1.3: Lipophilicity of alcohols27
Entry
Log P (octanol-H2O)
CH3CH2 OH
−0.32
CF3CH2 OH
0.36
CH3(CH2)2 OH
0.34
CF3(CH2)2 OH
0.39
CH3(CH2)3OH
0.88
CF3(CH2)3OH
0.90
CH3(CH2)4OH
1.40
CF3(CH2)4OH
1.15
Indeed, the highly dipolar C−F bond contributes to a reduced overall molecular
polarisability of organic molecules, by increasing the hardness of the carbon
framework.28 This also helps to account for the general increase in lipophilicity
of fluorinated aromatics (not shown).29,30 However, with fluorination far away
from heteroatom and π-systems, such as in the bottom example of Table 1.3,
the introduction of a dipole moment causes a decrease in lipophilicity
1.2.3 Influence of Fluorination on pKa
Fluorination modulates the acid dissociation constants (pKa) of adjacent acidic
and basic functional groups.31 As a general rule, fluorination increases
Bronsted acidity (some carbon acid exceptions), and decreases Bronsted
basicity.19 Table 1.4 shows decrease of the acid dissociation constant, pKa and
basicity, pKBH+ with introduction of the CF3 group into the carboxylate, alcohol
and amines functional groups.
5
Chapter 1: Introduction
Table 1.4: Influence of fluorination on pKa19
Acid
pKa
Amines
pKBH+
CH3CO2H
4.76
CH3CH2NH2
10.7
CF3CO2H
0.52
CF3CH2NH2
5.9
C6 H5CO2H
4.21
C6H5NH2
4.6
C6 F5CO2H
1.75
C6F5NH2
-0.36
CH3CH2OH
15.9
CF3CH2OH
12.4
(CH3)2CH2OH
16.1
(CF3)2(CH2)4OH
9.3
1.2.4 H−Bonding Interactions Involving Fluorine
A Hydrogen bond is an attractive interaction of a hydrogen atom and an
electronegative atom such as nitrogen, oxygen or fluorine (from a different
functional group). It is an electrostatic interaction with partial covalent
character.32 It is an important specific interaction between a molecule and its
local environment. These interactions have important functions in bioactive
molecules including the binding of ligands to protein receptors, promotion of
enzyme catalysis and (as intramolecular H–bonds) increasing membrane
permeability.2,33,34 They are well known key interactions in stabilizing tertiary
structures of peptides and nucleic acid and so are essential in molecular
recognition.35 These interactions can be examined by X-ray diffraction when in
solid state, computational methods in gas phase and by IR and NMR
spectroscopy when in the liquid phase. NMR spectroscopy can disclose the
existence of C−F···H−X H−bonds between carbon bound fluorine and
intramolecular hydrogen bond donor. In general, these interactions to fluorine
are much weaker than those observed on other heteroatoms such as oxygen
and nitrogen. The C−F is a weak H–bond acceptor because fluorine has a very
low proton affinity and is weakly polarizable.21 However, they can be
unambiguously observed in crystal structures which lack heteroatoms that
6
Chapter 1: Introduction
would compete for the hydrogen bond.19 Some examples of the interactions
previously reported are as shown in Figure 1.5.
Figure 1.5: Examples of H−bonding involving fluorine19
Examples of these interactions have been determined by Bernet in some
carbohydrate derivatives (Figure 1.6).35,36 The existence of a hydrogen bond to
fluorine was deduced from a
JOH,F coupling constant in compounds 1.16-1.22.
1h
In addition, the 3JH-OH coupling constant, which reveals the position of the O–H,
and which value can support the existence of such hydrogen bonding.
Figure 1.6: Previously observed C−F···H−O bonds in fluorinated
carbohydrates.35
7
Chapter 1: Introduction
1.2.5 H−Bonding of Fluorohydrins in the Linclau Group
The influence of fluorination on hydrogen bond properties is a topic of interest
in our group. In particular, the effect of relative configuration was investigated.
For this purpose, a number of fluorohydrins (Figure 1.7) have been
synthesised.34
The
non-fluorinated
alcohols
cis-
and
trans-4-tert-
butylcyclohexanol 1.31 and 1.32 did not show significant difference in their H–
bond acidity. With a single trans-diaxial vicinal fluorine, as in 1.23, the H–bond
acidity was increased, as expected. The difluorohydrins 1.29 and 1.30 showed
also greater H–bond acidity than the non-fluorinated alcohols; however, with
not as much as could be expected compared to the mono-fluorinated 1.23. The
fluorohydrins 1.24-1.27 showed a decrease in H-bond acidity compared to their
corresponding non-fluorinated alcohols. The decreased H–bond acidity may be
due to intramolecular F···H−O interactions, as indicated by the increased
energy barrier to rotation (∆GTS) of O−H bond. For example, the energy barrier
for 1.27 is 18 kJ mol-1 compared to only 3-5 kJ mol-1 for the fluorohydrins 1.23,
1.28, 1.31 and 1.32.
In general these results demonstrate the importance of relative fluorohydrin
configuration on H−bond acidity, and that the fluorine inductive effect cannot
be the only factor determining the magnitude of acidity.34
Figure 1.7: Previously synthesized fluorohydrins34
8
Chapter 1: Introduction
1.2.6 Dipolar Interactions
The highly polarised C–F bond is able to engage in stabilising electrostatic
interactions with various cationic or polar protein residues, present in a
protein, examples of which have been described by Diederich (Figure 1.8).21
Figure 1.8: C−F···C=O contact with the backbone amide of Trp332 (proteins Cs
are shown in grey)21
1.3 Polar Hydrophobicity
1.3.1 DiMagno: Hexafluorinated Pyranose
Hydrophobic desolvation is known to increase affinity, and perfluoroalkyl
desolvation energy is higher compared to that of hydrocarbons, due to their
larger surface.37 In addition, as mentioned above, there are possible stabilising
electrostatic interactions of the highly polarised C–F bond with various cationic
or polar protein residues. These are weak interactions, but negligible in
aqueous medium (when in the unbound state). The combination of these two
effects has been coined ‘polar hydrophobicity’, and has been proposed as an
appealing strategy to increase protein-carbohydrate affinity by replacing
multiple CHOH groups in the sugar ring with CHF or with CF2 groups.28,38 Thus
hydrophobic environment is created without significantly altering the shape of
the sugar. This led to the synthesis of 1.33 (Figure 1.9).
Figure 1.9: Hexafluorinated pyranose
9
Chapter 1: Introduction
1.3.2 Membrane Transport Studies
Transport studies of fluorosugars across the red blood cell membrane have
been performed to probe their binding requirement for transmembrane
transport.28 Red blood cells have been recognised to have a transport capability
for D-glucose across their cell membrane.39
F NMR and
19
F-2D EXSY NMR
19
experiments are used to study the efflux rate on the human erythrocytes.
Usually the human red blood cells are suspended in a D2O solution containing
the sample under study into the NMR tube. The
F NMR spectrum is used to
19
identify the signals for the intra- and extra-cellular anomers. The
F -2D EXSY
19
NMR exchange experiments are then used to measure the retained nuclear (19F)
polarization from the intra-cellular to the extra-cellular molecular population
(efflux rate). The intensity of the cross peak is proportional to the efflux rate
constant (kef).
Previous research has shown that 2-deoxy-2-fluoro-D-glucose (1.7) and 3deoxy-3-fluoro-D-glucose (1.34) have a transport efficiency similar to glucose.28
It has been found that the α-anomer of each mono-fluorinated glucose isomer
is transported more rapidly than the β-anomer. Also, while substitution of
fluorine on glucose has thus a relatively small effect on transport rate,
alteration of configuration of a single hydroxyl group on the ring has profound
effects; for example galactose which is epimeric to glucose at C4 is
transported over ten times slower than glucose.28,40
The hexafluorinated pyranose 1.33 was found to be transported across the
erythrocyte membrane as much as 10 times faster than D-glucose. This was
ascribed to a higher affinity to the relevant transporter protein due to the polar
hydrophobicity effect.41.
O’Hagan et al.39, reported that the 2,3,4-trideoxy-2,3,4-trifluoro glucose 1.35
has a somewhat lower transport rate than glucose itself. Interestingly, the
transport
rate
appeared
dependent
on
the
stereochemistry,
diastereoisomer 1.36 had a lower transport rate compared to 1.35.
10
as
the
Chapter 1: Introduction
Figure 1.10: Fluorinated carbohydrates
1.3.3 Previous Work in the Linclau Group
Our group has been involved in investigating the polar hydrophobicity effect as
a strategy to increase carbohydrate-protein affinity. The replacement of all
three ring-alcohols to CF2 was deemed detrimental to the selectivity of binding
(as hydrogen bonding is directional). Hence, an important element of our
substrates is the presence of a stereogenic alcohol group as part of the sugar
ring structure, which is deemed essential to impart binding selectivity, leading
to the synthesis of tetrafluorinated sugars. Several heavily fluorinated
carbohydrates (Figure 1.11) have been synthesised in our research group.
Some of these include 2,3-dideoxy-2,2,3,3-tetrafluororibose (1.37),42-44 -glucose
(1.38-1.40)42,43
and
tetrafluoroglucose
-galactose
(1.42),
(1.41);44,45
others
are
3,4-dideoxy-3,3,4,4-
2,3,4-trideoxy-3,3,4,4-tetrafluoro-D-glycerohexose
(1.43), and 3,4-dideoxy-3,3,4,4-tetrafluoromannose (1.44).
Figure 1.11: Tetrafluorinated carbohydrates
1.4 Aim and Objectives
The main objective of this project is the synthesis of fluorinated molecules that
will be used to extend our investigations. This project will mainly focus on the
synthesis of 2,3-dideoxygenated mono-and difluorinated sugars. In addition,
we provide a contribution to the related matter of the group’s investigation of
the hydrogen bond properties of fluorohydrins.
11
Chapter 1: Introduction
1.4.1 Synthesis of the Mono-and Difluorinated Sugars
The erythrocyte membrane transport experiments by DiMagno and O’Hagan
are
important
as
they indicate
a
fundamental
difference
between
a
perfluorinated ring moiety (as in 1.33), and a partially fluorinated moiety (as in
1.7 and 1.34). This led to our interest in investigating sugars that have other
hydrophobic moieties than a tetrafluoroethylidene group. Hence, the aim of
this
work
is to
synthesise
carbohydrate
derivatives
with
mono- and
difluorinated dideoxy fragments, by replacing the sugar (CHOH)(CHOH) with
CH2CHF, CH2CF2 and CHFCHF groups. The sugar derivatives 2,3-dideoxy-2,3difluoro, 2,3-dideoxy-3,3-difluoro glucose (1.45 and 1.47) and their galactose
derivatives (1.46, and 1.48) will be synthesised, as well as the lighter
fluorinated 2,3-dideoxy-3-fluoro glucose (1.49) and its galactose derivative
1.50 as shown in Figure 1.12. Efforts will be directed towards the
determination of their erythrocyte membrane transport rates and lipophilicity;
and in addition some other biological evaluations.
Figure 1.12: Fluorinated carbohydrate targets
1.4.2 Synthesis of Fluorohydrins
Part of this work will also be on synthesis of the fluorohydrins/fluoroalcohols
1.51-1.56, and 1.59-164 (Figure 1.13), altogether in gram scale which will then
be used to extend our investigation on H–bond acidity using Fourier Transform
Infrared (FTIR) spectroscopy. They will be synthesised along with their
corresponding non-fluorinated alcohols 1.57 and 1.58 that will be used as
reference compounds.
The series 1.51–1.58 are proposed in order to investigate the influence of a
trifluoromethyl group on the hydrogen bond donating capacity of an alcohol,
12
Chapter 1: Introduction
compared to that of a difluoromethyl and monofluoromethyl group, in a
conformationally restricted setting. The monofluorohydrins 1.59–1.64 are
proposed
to
investigate
the
influence
of
monofluorination
across
a
conformationally unrestricted six-membered ring. Compounds 1.65–1.68
further complete the conformationally restricted 1,3-fluorohydrin series, and
finally, a number of benzylic alcohols were also proposed.
Figure 1.13: Fluoroalcohol targets
13
Chapter 2: Results and Discussion
2 Results and Discussion: Synthesis of
monofluorinated Carbohydrates
2.1 Introduction
This section describes the synthesis of a number of known monofluorosugars,
which were required in certain properties, and which were deemed ideal for me
to gain practical experience in synthetic fluorine chemistry. The following three
monofluorinated sugar derivatives (2.1-2.3) as shown in Figure 2.1 have been
synthesised.
Figure 2.1: Known monofluorinated sugar derivatives
2.2 Synthesis of Monofluorinated Sugars 2.1 and 2.2
2.2.1 Introduction
Carbohydrate-aromatic interactions are an important contribution to the
binding affinity of sugars to proteins. Carbohydrate-aromatic stacking
interactions have been studies with a range of approaches, including molecular
biology tools,46 NMR and IR spectroscopy47-49 and computational methods.50,51
Morales and co-workers52 have used a model based on carbohydrate
oligonucleotide conjugates (COCs) to study carbohydrate-aromatic stacking
interactions. They have shown that carbohydrate-DNA interactions are
observed in a sugar-capped DNA double helix (Figure 2.2). In this model the
monosaccharide-aromatic interactions are measured and calculated using a
double dangling motif at 5’-end of a self-complementary CGCGCG sequence.53
Energies of -0.15 to -0.4 kcal mol-1 were found depending on the
stereochemistry and number of hydroxyl groups of the sugar.
14
Chapter 2: Results and Discussion
Figure 2.2: CH/π interactions observed by NOEs52
They also observed mono- and disaccharide stacking on top of DNA base pair
in COCs where the sugar is directly linked to the 5’ –end to DNA via ethylene
glycol spacer.52 According Morales, the mono- and disaccharide-DNA base
stacking interactions are energetically stabilizing and therefore are important
in designing of new carbohydrate-based RNA binders. It was deemed of
interest to compare these experiments using normal sugars with fluorinated
ones to investigate the influence of fluorination on carbohydrate-aromatic
interactions. Hence the sugar derivatives 2.1 and 2.2 were synthesised to
further investigate these CH/π interactions.
2.2.2 Synthesis of 1,2,4,6-Tetra-O-acetyl-3-deoxy-3-fluoro-D-glucopyranose
(2.1)
This sugar derivative has been synthesised by various authors using different
approaches. Withers et al.,54 prepared the β-anomer from acetylation of 3deoxy-3-fluoro-D-glucose which is commercially available, but currently very
expensive (from Sigma Aldrich, 50 mg cost £220). Using fluorination
strategies, the common intermediate for synthesis of this sugar derivative
would be the allofuranose 2.4.
Figure 2.3: Allofuranose 2.4
15
Chapter 2: Results and Discussion
The authors Jeong,55 Raju56 and Fairbanks57 have used DAST fluorination of 2.4
while Egli et al., used a fluoride displacement (cesium fluoride) on the
corresponding triflate.58 In this work, the DAST fluorination strategy was used.
However, on economic grounds compound 2.5 was an appropriate starting
material and we followed the four-step methodology as was also used by
Fairbanks. In this synthesis, the product was afforded in 25% overall yield
(same as for Fairbanks) as shown in Scheme 2.1.
Scheme 2.1: Synthesis of 1,2,4,6-tetra-O-acetyl-3-deoxy-3-fluoro-Dglucopyranose
The synthesis started with oxidation of 2.5, a commercially available
glucofuranose derivative, using pyridinium dichromate (PDC) and acetic
anhydride.59 This produced ketone 2.6 in good yield (71%) on gram scale.
Selective reduction using sodium borohydride in a mixture of ethanol and
water59 (4:1) afforded the allofuranose 2.4 in a reasonable yield (62%) and
complete diastereoselectivity. Fluorination with DAST and pyridine in DCM55
proceeded with expected inversion of configuration at C3 to the known C3fluorinated glucofuranose 2.7, in a reasonable yield (61%). This was followed
by deprotection using a mixture of water/ethanol (1:2), and then acetylation
with pyridine and acetic anhydride56 that afforded the mono-fluorosugar 2.1 as
a mixture of α and β anomers (1:1 ratio) in excellent yield (92%). Withers and
Egli reported only the 1H and
F NMR characterization of the β-anomer, which
19
corresponded to the data for the β-anomer obtained in this work. The 1H NMR
and
C NMR data for the mixture of anomers for this compound was not
13
reported in the literature.
16
Chapter 2: Results and Discussion
2.2.3 Synthesis of 1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-D-glucopyranose
(2.2)
This derivative has been synthesised by Elchert et al.,60 by fluorination of
methyl-α-D-glucopyranoside with DAST followed by acetylation with acetic
anhydride, however the characterization was not reported. Ambrose61 and
Withers54 have reported the β-anomer with limited characterization. Ambrose et
al., prepared the compound through triflation using a relatively expensive
base, 2,6-di tert-butyl-4-methylpyridine which is less nucleophilic due to steric
hindrance, required to avoid formation of pyridinium salts. This was followed
by SN2 displacement of the triflate with fluoride as shown in Scheme 2.2.
Scheme 2.2: Synthesis of 2.2 through triflation by Ambrose61
Scheme 2.3: Our synthesis of 1,2,3,4-tetra-O-acetyl-6-deoxy-6-fluoro-Dglucopyranose
The compound was prepared in a similar two-step process as used by Elchert
et al.,60 (Scheme 2.3). The synthesis started by treating a commercially
available methyl-α-D-glucopyranoside 2.10 with DAST that selectively afforded
2.11 in reasonable yield (53%). Interestingly, no other fluorinated products
were observed, which is explained by the higher reactivity of the primary
alcohol. Acetylation/acetolysis with acetic anhydride and catalytic amount of
sulfuric acid afforded the target monofluorosugar derivative 2.2 as a mixture
of α and β anomers (1:7 ratio, Figure 2.4 right) in good yield (77%). This is an
improved yield compared to Elchert, who obtained 48% yield of 2.2 from 2.11.
The 1H and
C NMR of the β-anomer in the mixture corresponded to those
13
reported by Ambrose. However, the
F NMR for the β and α anomers were
19
reported by Withers and Hara62 and were characterised as dt, JF,6 47, JF,5 25 Hz
17
Chapter 2: Results and Discussion
and dt, J 47.0, 22.6 Hz, respectively. These data are only different in the
assignment of the coupling, a dt instead of a td observed in this thesis: a td, 2JFH6
and 2JF-H6‫ ׳‬47.3 Hz, 3JF-H5 22.6 Hz; and td, 2JF-H6 and 2JF-H6‫ ׳‬46.2 Hz, 3JF-H5 23.6 Hz.
The F non-decoupled spectrum shows the α- and β-anomers overlapped and
could be clearly observed on F-decoupling as shown in Figure 2.4 right. Our
assignment is confirmed by the 1H NMR which clearly shows both the H6 and
H6‫ ׳‬protons displaying a 47.3 and 46.2 coupling respectively. Surprisingly, the
complete characterization of the mixture of α and β anomers has not been
reported in the literature.
Figure 2.4: 19F NMR and F-decoupled spectrum of 2.2
2.3 Synthesis of 3-Deoxy-3-fluorogalactopyranose (2.3)
2.3.1 Introduction
The galactose derivative is obtained by a C4 epimerization strategy of a Dglucose derivative. The Linclau group has reported a study of tetrafluorinated
galactose derivative 1.41 as substrate for galactose oxidase enzyme (GOase).63
The enzyme is capable of catalysing the oxidation of the 6OH of the Dgalactose to the corresponding aldehyde (Scheme 2.4), and has been used to
investigate the effect of fluorination on binding of different substrates to the
enzymes.63-65
18
Chapter 2: Results and Discussion
Scheme 2.4: Oxidation of galactose by galactose oxidase
Studies have shown that GOase can oxidise several fluorinated galactose
analogue, and recently the enzyme was found capable of even distinguishing
between the 2,3-dideoxy-2,2,3,3-tetrafluorinated glucose 1.38 and its epimeric
galactose analogue 1.41.63 For these experiments, 3-deoxy-3-fluorogalactose
2.3 was required as a control, and for future work in this area, more quantities
were required.
This 3-fluoro galactose sugar has been reported by several authors including
Blanchard66 and Hoffmann-Roder.67 Blanchard prepared it for the synthesis of
UDP-(3-deoxy-3-fluoro)-D-galactose
and
reported
only
the
H
1
NMR
characterization, however did not show the procedure. Hoffmann-Roder
synthesised the compound in 8 steps (16% overall yield) from D-glucopyranose.
This is the modified procedure from the one used by Howell et al.,56 who did
not
hydrolyse
the
corresponding
1,2,4,6-tetra-O-acetyl-3-fluoro-D-
galactopyranose to the final product 3-deoxy-3-fluoro-α,β-D-galactopyranose.
Hoffmann used the crude product to the next steps without purification and so
no characterization was reported. The compound had been prepared early in
the Linclau group in four steps (10.2% overall yield) from 1,2:5,6-di-Ocyclohexylidine-α-D-galactofuranose.63
The current synthesis of this compound as shown in Scheme 2.5 followed the
same methodology as one used by Howell. This process has been further
optimized leading to an improved overall yield to 26%. The intermediate 2.6
was converted to the corresponding enol acetate 2.14, using acetic anhydride
in pyridine, in excellent yield (94%). This was followed by reduction with
palladium hydroxide on charcoal under hydrogen atmosphere to the monoacetate 2.15, a white solid which was reasonably afforded in 64%.
19
Chapter 2: Results and Discussion
Scheme 2.5: Synthesis of 3-deoxy-3-fluoro-D-galactopyranose
This reduction effectively inverted the stereochemistry at C4 leading to the
gulose configuration. Deacetylation with sodium methoxide (0.5M) in methanol
afforded the expected gulose derivative 2.16, a white solid, in excellent yield
(87%). Compound 2.16 was then fluorinated using DAST and pyridine in DCM
using a procedure well described by Jeong et al.55 Substitution of hydroxyl
group by fluorine atom was achieved through inversion of configuration to give
the 3-fluorinated galactofuranose derivative 2.17 in 72%.
The fluorinated galactofuranoside 2.17 was first deprotected to give 3-deoxy-3fluorogalactose, 2.3 by the reaction with trifluoroacetic acid, TFA/H2O (9:1).
However, though analysis of the crude product showed that TFA was a major
impurity which could not be removed by evaporation. Filtration over silica
gel/K2CO3 did not show any improvement. Thus, the impure 2.3 was converted
to the corresponding tetraacetate 2.18 (87%) by a combination of procedures
from Withers et al.54 and Raju et al.,56 using pyridine and acetic anhydride. The
product formed still contained some TFA and furanose anomers. Crystallization
(EA/PE) afforded the pure compound and we obtained its first crystal structure
(Figure 2.5). The compound was formed as a mixture of α and β anomer in the
ratio 1:100 as seen in Figure 2.6 C.
20
Chapter 2: Results and Discussion
Figure 2.5: Crystal structure of 1,2,4,6-tetra-O-acetyl-3-deoxy-3-fluoro-β-Dgalactopyranose 2.18
Hydrolysis68 of the pure crystals of 2.18
afforded a mixture of α and β
anomers, 3-deoxy-3-fluoro-D-galactopyranose, 2.3 (80%) in a 1:1.3 ratio in
MeOH-d4 (Figure 2.6 A); free from TFA, but still with another impurity.
The presence of the signal at δ -190 and -196 ppm (Figure 2.6 A) upon
deprotection of the purified tetraacetate 2.18 was interesting and it was
proposed that these could belong to the corresponding furanose anomers.
Comparison with
F NMR of the furanoside 2.17 (Figure 2.6 B) appears to
19
confirm this. Fluorine in this compound has a signal at δ -187 ppm which
corresponded well to the chemical shift of the unknown compound. For
comparison, the 19F NMR spectrum of corresponding tetraacetate pyranoside is
also shown in Figure 2.6 C.
The furanose anomers can result from equilibration of α and β forms of sugars
that occur by opening the pyranose to give the open chain aldehyde, which is
followed by the ring closure of the C4 hydroxyl group onto C1 as shown in
Scheme 2.6.
Scheme 2.6: Formation of furanose anomers by equilibration of α and β forms
of pyranose sugar
21
Chapter 2: Results and Discussion
Figure 2.6: 19F NMR spectrum of 2.3 and its furanose anomer (A) 2.17 (B) and
2.18 (C)
22
Chapter 2: Results and Discussion
2.4 Conclusion
Figure 2.7: Accomplished targets
The synthesis of monofluorinated glucose derivatives 2.1 and 2.2 was
successful. Results of these samples that were sent to our collaborator Prof.
Juan Morales, University of Sevilla in Spain have revealed that the presence of
fluorine atom within the pyranose ring slightly increases the carbohydratearomatic interaction within the C−G DNA base pair.46 The synthesis of 3-deoxy3-fluoro-D-galactose was also successful. Investigation of the effect of
fluorination on the substrate 2.3 on the enzyme galactose oxidase is still on
progress.
23
Chapter 3: Results and Discussion
3 Results and Discussion: Synthesis of
Fluorosugars with Modified Hydrophobic
Domain
3.1 Introduction
This section describes the synthesis of the sugar derivatives in which a
(CHOH)(CHOH)
section
has
been
replaced
with
partially
fluorinated
hydrophobic motifs such as FHC−CHF, FHC−CH2 and F2C−CH2 leading to the
following novel fluorinated sugar derivatives 1.45-1.50 were envisioned (Figure
3.1).
Figure 3.1: The synthesised fluorinated sugar derivatives
In contrast to the tetrafluorinated sugars synthesised in our group, which were
synthesised via a de novo fluorinated building block approach, the synthesis of
the sugars listed in Figure 3.1 was planned using a sugar fluorination
approach. In all cases, D-glucal was used as starting material, which was
commercially available, or was synthesised from the cheaper D-glucal
triacetate. In the latter case, careful purification leading to crystalline glucal
was necessary to ensure good yield in the subsequent step.
3.2 Synthesis of 2,3-Dideoxy-2,3-difluorosugars
The complete syntheses of these difluorosugar derivatives has not yet been
described in the literature, though some late stage intermediates have been
reported by various authors.69-73 Where appropriate, we have followed the
literature procedures, and modified/extended as described.
25
Chapter 3: Results and Discussion
3.2.1 Synthesis of 2,3-Dideoxy-2,3-difluoro-D-glucopyranose 1.45
Scheme 3.1: Synthesis of 2,3-dideoxy-2,3-difluoro-D-glucopyranose
In the first step, 1,6-anhydro-2-iodo-β-D-glucopyranose 3.2 was prepared in
89% yield by iodocyclization of O-tributylstannyl-D-glucal, in-situ prepared by
treatment of D-glucal with bis(tributyltin) oxide in acetonitrile.69 The possible
mechanism for iodocyclization is described in Scheme 3.2, and starts with
stannylation of the alcohol groups. The subsequently formed iodonium species
is then regioselectively opened by the nucleophilic stannylate group to give the
1,6-anhydro sugar derivative. Purification of 3.2 has been problematic due to
formation of tin residues which were not easily completely removed by column
chromatography. The second one-pot procedure enabled preparation of the
epoxide, 3.3. By using an excess of NaH, the procedure simultaneously allowed
for the introduction of the protecting group at C4 using benzyl chloride and
the epoxide, leading to the product in good yield (85%).
In this synthesis,
benzyl chloride was used instead of paramethoxybenzyl chloride which was
used by Arndt et al. (75%).74 The next operation was regioselective epoxide
opening with potassium bifluoride in refluxing ethylene glycol,70 and that
afforded 3.4 in 65%. Recently, Jensen reported 40% yield of the epoxide under
these conditions which they could improve to 69% after only 20 min when
conducted in sealed vessel under microwave conditions at 220 ºC.72 However,
this improved yield under microwave conditions was done on small scale (0.49
g) compared to 2.3 g that was used in Scheme 3.1.
26
Chapter 3: Results and Discussion
Scheme 3.2: Possible mechanism for iodocyclization
This was followed by DAST-mediated deoxofluorination74 of the 3−OH in
toluene and successfully afforded the known difluoroglucosan 3.5 in excellent
yield (86%), with retention of configuration.75 This is confirmed by the large
coupling constant (2JC4-F3 26.3) (Figure 3.2), given the presence of a vicinal
electronegative substituent in the axial position.76
Figure 3.2: 13C NMR spectrum of 3.5
This stereochemical outcome is likely due to neighbouring group participation
by the axial benzyloxy group as shown in Figure 3.3. The thus formed
epoxonium 3.9 would then react regioselectively at C3 due to steric hindrance
of the C5 bridge.
27
Chapter 3: Results and Discussion
Scheme 3.3: Fluorination by anchimeric assistance.
..
However, if this mechanism would be operating, reaction of fluoride at the
benzylic position could also be expected, leading to the epoxide 3.10, which
then could further react to give 3.6 (Scheme 3.3). However, this was not
observed. An alternative pathway explaining the retention of configuration
could involve an SNi (nucleophilic substitution with internal return) type
fluorination of the intermediate 3.8 as shown in Scheme 3.4.
Scheme 3.4: SNi mechanism
Hydrogenolysis of the benzyl ether71 gave 3.6 in excellent yield (90%). With 3.6
in hand, final hydrolysis was then attempted. Aqueous HCl in 1,4-dioxane, as
was used by Matsumoto,77 returned only the starting material. This illustrates
the destabilizing effect of the fluorination on acid catalysed acetal hydrolysis.
However, acetolysis with catalytic H2SO4 and Ac2O proceeded with reasonable
yield (60%) to the triacetate 3.7 in a 1:6.7 (α:β) anomeric ratio as shown in
Figure 3.3.
28
Chapter 3: Results and Discussion
Figure 3.3: 19F-decoupled NMR spectrum of 3.7
The final step, hydrolysis of 3.7, afforded the final compound 2,3-difluoro-α,βD-glucopyranose
1.45 in good yield (81%) as a 1:1.6 (α:β) anomeric (in acetone-
d6). Only the pyranose anomers were observed as seen from the
F NMR
19
spectrum (Figure 3.4). Also, the α-anomer proton (δ 5.38 ppm) is deshielded
compared to the β-anomer proton (δ 4.83 ppm) in accordance with the general
rule.
The resulting chair inversion in comparison with the levoglucosan 3.6 was
clearly observed from
C NMR analysis in that the
13
JC4-F3 value in 1.45
2
(equatorial F gauche to C4−OH) reduced to a value of 17.6 Hz, from 27.4 Hz of
3.6 (axial F antiperiplanar to C4−OH). The 3JC5-F3 which was not observed in 3.6
(axial C3–F gauche to C4−C5), increased to 8.0 Hz in 1.45 in which the C3–F is
antiperiplanar to C4−C5 (Figure 3.5). All these are indicative of an equatorial
C–F bond in 1.45.
It is also interesting to observe that the chemical shift of the two fluorine
atoms of the β-anomer is much closer in chemical shift compared to those of
the α-anomer.
29
Chapter 3: Results and Discussion
Figure 3.4: 19F-decoupled NMR spectrum of 1.45
Figure 3.5: Conformational effects on the dihedral angle and coupling constant
3.2.2 Synthesis of 2,3-Dideoxy-2,3-difluoro-D-galactopyranose 1.46
This fluorosugar, not described in the literature, was synthesised from an
intermediate 3.6 in the synthesis of 2,3-difluoro glucose. It is epimeric to 1.45
at C4 position and was obtained by inversion of configuration through
triflation followed by benzoylation (Scheme 3.5), as described by Sarda.71
Triflation with trifluoromethanesulfonic anhydride in dry pyridine afforded 3.11
in excellent yield (94%). Benzoylation with sodium benzoate afforded 3.12 with
the expected inversion of configuration at C4 in very good yield (84%).
30
Chapter 3: Results and Discussion
Scheme 3.5: Synthesis of 2,3-dideoxy-2,3-difluoro-D-galactopyranose
Evidence of inversion of configuration at C4 was shown by the 2JC4-F3 coupling
constant, as already pointed out early by Sarda et al,71,76 which is larger when
the electronegative substituent (the triflate 3.11 and benzoate 3.12 in this
case) is axial to the fluorine atom on C3 (as in 3.11, 2JC4-F3 = 31.5 Hz) compared
to the equatorial (as in 3.12,
JC4-F3=15.8 Hz) as shown in Figure 3.6.
2
Interestingly, The C4 in 3.11 appears as a dd (small coupling with F2), while in
3.12, C4 appears only as a doublet.
Figure 3.6: 13C NMR spectrum showing evidence of inversion of configuration
Acetolysis of 3.12 using acetic anhydride containing sulfuric acid71 afforded the
anomeric mixture of acetylated novel compound 3.13 in 41% yield (1:14.3 α:β
anomeric ratio in CDCl3, Figure 3.7).
31
Chapter 3: Results and Discussion
Figure 3.7: 19F-decoupled NMR spectrum of 3.13
Deprotection of 3.13 with NaOMe gave the 2,3-dideoxy-2,3-difluorinated
galactose sugar 1.46, but together with a further mixture of compounds as
clearly observed from the
F-decoupled NMR spectrum in Figure 3.8. Apart
19
from the expected pyranose anomers, it is conceivable that the furanose
anomers 3.14 were also present.
Figure 3.8: 19F-decoupled NMR spectrum of impure 1.46.
32
Chapter 3: Results and Discussion
We also attempted prior debenzoylation of 3.12 to give 3.15 (Scheme 3.6), and
then performed the acetylation/acetolysis to 3.16. However, hydrolysis of 3.16
gave the same results as in Figure 3.8. Deprotection of 3.15 using the strong
Lewis acid, BCl3 followed by aqueous workup also ended with the same
products.
In order to avoid the formation of the suspected furanose anomers, we finally
tried to effect acetal methanolysis using a strong Lewis acid, BCl3, in MeOH
(Scheme 3.7), which gave the corresponding methyl glycoside anomers (α:β
ratio 1:5.5 in acetone-d6) in low yield (22%).
Scheme 3.6: Synthesis of 2,3-dideoxy-2,3-difluoro-D-galactopyranose
Scheme 3.7: Methanolysis with BCl3 and MeOH
Comparison of the 19F NMR spectrum of the mixture of 1.46 and 3.14 with the
galactopyranoside 3.17 confirmed the presence of the pyranose anomer in the
mixture as shown in Figure 3.9, and indicates the presence of furanose
anomers.
33
Chapter 3: Results and Discussion
Figure 3.9: 19F-decoupled NMR spectrum of a mixture of 1.46 and 3.14 (top)
and 3.17 (bottom)
34
Chapter 3: Results and Discussion
3.3 Synthesis of 2,3-Dideoxy-3-fluorosugars
3.3.1 Synthesis of 2,3-Dideoxy-3-fluoro-D-glucopyranose 1.49
Scheme 3.8: Synthesis of 2,3-dideoxy-3-fluoro-D-glucopyranose
O
BnO
O
O
LiAlH4, THF
O
reflux
87%
O
BnO
reflux
73%
OH
3.3
3.18
p-TSOH,
THF:H2O HO
34%
O
O
DAST,toluene
O
BnO
F
O
Pd/C, H2 (1 atm)
MeOH
74%
O
HO
3.19
F
3.20
OH
HO
F
1.49
The synthesis of this monofluorinated sugar started by regioselective opening
of the epoxide 3.3 with refluxing LiAlH4 in THF and afforded 3.18 in excellent
yield (87%). This is a known compound which was also synthesised by Thiem et
al.78 and Sviridov et al.,79 (42%), however neither provided the procedure nor
the NMR characterization.
Deoxofluorination reaction with DAST then gave 3.19 in good yield (73%),
again with overall retention of configuration. This was clearly proven by the
small 3JH3-H coupling values (<5 Hz). In addition, given the axial position of the
OBn substituent, the 2JC4-F value of 26.3 Hz clearly indicates an axial C–F bond,
and the very small (in this case unobserved) 3JC5-F value indicates a gauche
dihedral angle between C3–F and C4–C5. Debenzylation to 3.20 (74%), and
final hydrolysis with p-toluenesulfonic acid in THF:H2O (1:1)80 then led to 2,3dideoxy-3-fluoroglucose 1.49 in low yield of 34% as a mixture of α and β
anomers (1:2 ratio in CDCl3). The resulting chair inversion was obvious from 13C
NMR analysis, in that the 2JC4-F value reduced to a value of 17.6 Hz, and the 3JC5-F
value increased to 8.0 Hz, all indicative of an equatorial C–F bond.
35
Chapter 3: Results and Discussion
3.3.2 Synthesis of 2,3-Dideoxy-3-fluoro-α,β-D-galactopyranose 1.50
Scheme 3.9: Synthesis of 2,3-dideoxy-3-fluoro-α,β-D-galactopyranose
The synthesis of this galactose derivative followed the same methodology used
for 1.46. Triflation of the intermediate 3.20 (87%) was followed by benzoylation
to 3.22 (79%), which proceeded with the expected inversion of configuration at
C4. The next step was hydrolysis with K2CO3 in MeOH and afforded 3.23 in
excellent yield (96%). Hydrolysis using p-toluenesulfonic acid in THF/H2O (1:1)
afforded an inseparable anomeric mixture (Figure 3.10 top), including the
presumed furanose isomers, just as was observed on the other galactose
derivatives in Section 2.3 and 3.2.2. However, hydrolysis using BCl3 in
methanol
gave
the
corresponding
methyl-2,3-dideoxy-3-
fluorogalactopyranoside 3.25 (51%) as mixture of α and β anomer (ratio 1:12.5
in acetone-d6) as shown in Figure 3.10 bottom. The correspondence of the
signals in the
F NMR at δ -188 and -191 HZ (Figure 3.10) gives evidence for
19
the formation of 2,3-dideoxy-3-fluoro-α,β-D-galactopyranose, 1.50.
36
Chapter 3: Results and Discussion
Figure 3.10: 19F NMR spectrum of a mixture of 1.50 and 3.24 (top) and 3.25
(bottom)
37
Chapter 3: Results and Discussion
3.4 Synthesis of 2,3-Dideoxy-3,3-difluoro-D-glucopyranose
1.47
Scheme 3.10: Synthesis of 2,3-dideoxy-3,3-difluoro-D-glucopyranose
The synthesis of this difluorosugar as described in Scheme 3.10 started with
oxidation of the intermediate 3.18 using pyridinium dichromate and acetic
anhydride in refluxing DCM. This gave the ketone 3.26, a novel compound, in
reasonable
yield
(73%).
Fluorination
of
this
ketone
has
not
been
straightforward. Several attempts with different fluorinating reagents such as
deoxo-Fluor®81, XtalFluor-E®, TEA.3HF82 and refluxing DAST in toluene71 failed
to give the desired product. Fluorination of the compound was finally achieved
in low yield (23-25%) by a mixture of DAST, 1,3-dimethyl-3,4,5,6-tetrahydro2(1H) pyrimidinone (DMPU) and HF-pyridine in refluxing DCM at 45 ºC. This is a
similar procedure except use of HF-py (Scheme 3.11 bottom),instead of HF as
described by Gong et al. (Scheme 3.11 top),83 which achieved fluorination to
3.32.
Attempts to debenzylation of 3.27 through hydrogenolysis with H2, 10% Pd/C
were not successful. So an alternative deprotection of the benzyl ether and
hydrolysis with the strong Lewis acid BCl3 and quench with water84 afforded the
difluorosugar 1.47 in low yield of 11%. This difluorosugar, which is not
reported in the literature, was formed as a 1:20 mixture of α and β anomers as
shown in Figure 3.11. No furanose isomers were observed.
38
Chapter 3: Results and Discussion
Scheme 3.11: (a) Gong’s fluorination on 3.31 (top), and (b) our achieved
fluorination (bottom).
O
O
DAST/DMPU, HF
MeO
OMe
DCM
OMe
F F
3.32
O
DAST,DMPU, HF-py
25%
BnO
O
MeO
O
3.31
O
O
O
O
BnO
F F
3.27
O
3.26
.
Figure 3.11: 19F-decoupling NMR spectrum of 1.47
Furthermore, debenzylation and quenching with methanol gave two separable
α- and β-anomers 3.29 and 3.30 in 57% yield. These two anomers were
separable by column chromatography and could be clearly distinguished by the
H1 coupling and their chemical shift. The proton H1 for the α-anomer shows a
dd with small coupling constants at δ 4.86 (J 4.6, 0.9 Hz) ppm compared to the
coupling of the same proton in the β-anomer at δ 4.57 (dd, J 9.7, 2.3 Hz) ppm
39
Chapter 3: Results and Discussion
(Figure 3.12). The large coupling 3JH1–H2 =9.7 Hz for the β-anomer is due to
diaxial coupling which is missing in the α-anomer. The H1 of the α-anomer is
also deshielded at δ 4.86 ppm compared to δ 4.57 ppm for the β-anomer
according to the general rule.
Figure 3.12: Anomeric determination of 3.29 and 3.30 from 1H-decoupling
NMR spectrum
3.5 Conclusion
Figure 3.13: Accomplished targets
The fluorinated sugar derivatives 1.45, 1.47, 1.49 have been successfully
synthesised in this work. Their synthesis was accomplished on small scale and
while in some cases yields still need optimisation, the amount available was
sufficient for the determination of the intended physical and biological
properties including erythrocyte membrane transport, partition coefficient log
P (octanol/water), carbohydrate-aromatic interactions to mention a few.
Optimization of the methodologies is on progress to have more of the required
quantities.
40
Chapter 3: Results and Discussion
Preliminary results on erythrocyte membrane transport studies have shown
that the fluorosugar derivative 1.45 has the same transport rate as D-glucose.
Synthesis of the galactose derivatives has not been straightforward. We have
managed to get 1.46 and 1.50 as mixtures of α and β anomers, but together
with
their
corresponding
galactofuranose
anomers.
However,
the
galactopyranosides 3.17 and 3.25 were afforded pure and could confirm the
formation of the galactose 1.46 and 1.50 in the mixture. Both these galactose
derivatives will be sent to Professor Sabine Flitsch, University of Manchester for
investigations as substrates for galactose oxidase enzyme. The galactose
derivative 1.48 could not be synthesised following failure of the deprotection
of the benzyl ether on 3.27.
41
Chapter 4: Results and Discussion
4 Results and Discussion: NMR
Investigations on the Conformationally
Rigid Levoglucosan Derivatives
4.1 Long Range Coupling
4.1.1 Introduction
Coupling of over more than three bonds are in most cases too small to be
detected. However, there are situations where such coupling are significant
and can provide useful structural information. The 4J coupling constant in
aromatic systems is a typical example. The 4-bond coupling in allylic systems
and across saturated carbons (sp3) are normally observed when there is
favourable geometric arrangement along the H−C−C−C−H chain (W-coupling) as
shown in Figure 4.1.85
Figure 4.1: Long range coupling in aromatic, allylic and the W-coupling
For saturated systems, a 4-bond coupling is usually only observed in
conformationally well-defined systems, such as six-membered rings.86
4.1.2 19F NMR and the Coupling Constants
Apart from hydrogen and carbon,
F is perhaps the most studied nucleus in
19
NMR. It has a 100% natural abundance (no other isotopes of fluorine exist in
significant quantities) and a high gyromagnetic ratio (ratio of magnetic dipole
moment to its angular momentum) about 0.94 times that of 1H. The chemical
shift range of fluorine is very large (>350 ppm) compared to H and thus,
43
Chapter 4: Results and Discussion
resonances of different fluorine nuclei in fluorinated compounds are usually
well separated.23
Fluorine spin-spin coupling constants to other F nuclei, neighbouring H and C
nuclei are highly variable in magnitude and also highly characteristic of their
environments. The magnitude of coupling constant is dependent on the
dihedral angle, which has a maximum value of around 45 Hz at 180º and J~0
at 90º as shown in 4.4 in Figure 4.2.
Figure 4.2: Coupling in fluorinated molecules23
For some molecules, very large JH-F values are sometimes observed, for example
compounds 4.5-4.8. This has been attributed to the so called “through space”
coupling. This type of coupling has been explained by the exchange of spininformation when two nuclei are close together in space, regardless of how
many bonds separate them (Dolbier,23 2009, pg 19).
Examples of “through-bond” long range couplings
JF-H are reported, for
5
example in sugar 4.9, reported by Nakai et al.,87 with a coupling of the
magnitude 5JH1-F4 ~ 4.0 Hz as shown in Figure 4.3.
Figure 4.3: Long range coupling 5JH1-F4 of the free sugar 4.9
4.1.3 Our Levoglucosan Derivatives
Upon characterisation of the various fluorinated levoglucosan derivatives (see
Chapter 3), we have observed a range of significant and unexpected long range
44
Chapter 4: Results and Discussion
coupling constants involving the fluorine atom(s) and H6 (5J), C6 (4J), and CPh
(4J) (Figure 4.4). This is no doubt due to the configurationally rigid and
compact levoglucosan scaffold, although the
JF3-OCH2Ph coupling constant
4
involves a (potentially) flexible benzyloxy substituent.
Figure 4.4: Long range coupling in levoglucosan 3.27
Some interesting variations have been observed due to the selective orientation
of the substituents. An overview of the observed coupling constants is given in
Figure 4.5. This chapter will discuss how these long range coupling constants
have been assigned using selected examples. First the unambiguous
assignment of the two H6 protons is shown.
Figure 4.5: Long range coupling on levoglucosans
45
Chapter 4: Results and Discussion
4.1.4 Assignment of the Protons H6 and H6'
Initial assignment of the endo (H6) and the exo (H6') could be made by their
respective vicinal coupling constants to H5. The respective dihedral angles are
shown in Figure 4.6.
90
H H
H
BnO
H6
O
F
O
H5
H6
30
O O
F
3.27
3
J H6-H5 =1.3 Hz
3
J H6 -H5 =6.0 Hz
Figure 4.6: Dihedral angles between H5 and both H6 protons
Figure 4.7: 1H NMR and 1H NMR F-decoupling spectrum of 3.27
46
Chapter 4: Results and Discussion
Inspection of molecular model showed a dihedral angle between H5 and H6 of
around 90º, resulting in a very small coupling constant 3JH5-H6 =1.3 Hz, while the
dihedral angle between H5 and H6' appeared around 30º, consistent with a
coupling constant 3JH5-H6‫ = ׳‬6.0 Hz as shown in the 1H NMR spectra (Figure 4.7).
Further confirmation could be obtained by 1H-19F selective one dimensional
heteronuclear NOESY (HOESY) experiments. As shown in Figure 4.8 there is a
cross peak between the axial fluorine atom and the endo H6 proton, while the
equatorial fluorine does not show a cross peak to either H6/H6'. Both fluorines
show a cross peak with H2 and H4. Interestingly, the equatorial fluorine shows
cross peaks with the benzylic protons, but not with the same intensity.
Figure 4.8: (a) 1H NMR spectrum (CDCl3, 500 MHz) (b) 1D 1H-19F selective HOESY
spectrum (CDCl3, 500 MHz) (Selection of the signal at -88.9 ppm – axial
fluorine) (c) 1D 1H-19F selective HOESY spectrum (CDCl3, 500 MHz) (Selection of
the signal at -98 ppm) – equatorial fluorine)
47
Chapter 4: Results and Discussion
4.1.5 5JH6'-F3 Coupling
The magnitude of this 5-bond coupling to the exo H6' (see Figure 4.5) appears
to depend on the relative configuration of the electronegative substituent at
C4.
For 3.19, 3.20, 3.21, and 3.27, with an axial electronegative C4
substituent, a large
JH6'-F3 coupling constant of 3.7, 3.8, 3.8 and 4.1 Hz
5
respectively was found. A geminal fluorine substituent did not reduce the
magnitude of this coupling constant (compare 3.27 with 3.19), but a vicinal
trans-diaxial fluorine substituent at C2 caused such a reduction that this
coupling constant was not observed any more (compare 3.5 with 3.19 and 3.15
with 3.23).
Interestingly, with an equatorial substituent at C4, the coupling constant was
significantly reduced compared to the substrates with an axial C4-substituent.
For example in the levoglucosan 3.20 (4-OH), 5JH6–F3 =3.8 was reduced to 1.4 Hz
in 3.23. This is also observed with 3.21 and 3.22 where the C4 substituents are
not the same but still the coupling was reduced with inversion of configuration
at C4 from 3.8 Hz to 1.3 Hz.
An illustration of how these coupling constants were obtained is shown in
Figure 4.7. The protons H6 and H6' of 3.27 at δ =3.96 and 3.69 ppm feature
as a dt, J =7.8, 1.3 Hz and ddd, J =7.8, 6.0, 4.1 Hz, which upon F-decoupling
were reduced to dd, J 7.8, 1.3 Hz, and dd, J 7.8, 6.1 Hz showing a respective
loss of 5JH6–F3 =1.3 Hz and 5JH6‫–׳‬F3 =4.1 Hz respectively.
4.1.6 4JC6–F3 Coupling
This work also reports the coupling constant 4JC6–F3 between the axial fluorine
and C6 as shown by the 13C NMR spectrum in Figure 4.9. All the levoglucosans
in Figure 4.5 show this coupling constant which ranges from 2.5 to 6.2 Hz.
48
Chapter 4: Results and Discussion
Figure 4.9: 13C NMR spectrum showing 4JC6–F3 of 3.27
This coupling is also (marginally) affected by the presence of vicinal fluorine at
C2 as observed for 5JH6'-F3. We observe the coupling reduced from 5.5 Hz in 3.20
to 4.4 Hz in 3.6. Similar trend is seen in 3.19 where the coupling of 5.1 Hz is
reduced to 2.5 Hz in 3.5. We could also observe the effect of inversion of
configuration at C4 on the 13C NMR where the coupling of 4JC6–F3 =5.5 Hz in 3.20
was reduced to 4.0 Hz in 3.23. Also, 4JC6–F3 =4.8 Hz in 3.21 was reduced to 4.4
Hz in 3.22.
4.1.7 Coupling Through the Heteroatom Oxygen
Furthermore, we have observed an interesting long range coupling between a
fluorine atom at C3, and the benzylic carbon atom. For example, the
difluorosugar 3.5 has a 4JCPh-F3ax = 2.5 Hz (not reported by Sarda)71, which is
interesting as the coupling goes through the heteroatom oxygen. The sugar
3.27 also shows a 4JCPh-F3 coupling constant (4.4 Hz), though it is unclear which
fluorine atom is involved. We propose that this coupling occurs due to a certain
rotational restriction of the benzyl ether substituent, either by the axial or the
equatorial F3, which perhaps leads to a well-defined W arrangement as shown
in Figure 4.10.
49
Chapter 4: Results and Discussion
Figure 4.10: 4J F3ax -C7 coupling through heteroatom
4.2 Intramolecular Hydrogen Bonding
4.2.1 Introduction
The Linclau group is interested in using NMR data relating to O−H···F
interactions. This section discusses the competition observed between O−H···O
and O−H···F interactions in some of our conformationally locked fluorinated
levoglucosans, which can be grouped from certain coupling constants.
Cyclic carbohydrates especially the rigid pyranosides as in Figure 4.11, have
been found ideal for investigation of intramolecular O−H···F interactions as
they allow access to epimers with desired orientation of the F and the
secondary OH substituents.35
Figure 4.11: Intramolecular H–bonds of carbohydrates in CDCl335
Bernet has described the involvement of OH in an intramolecular H−bond that
usually gives large or small 3JH–OH (>5.5 and <3 Hz) whereas a freely rotating OH
show intermediate values.88 These O−H···O and O−H···F intramolecular
interactions can be detected by the 1H NMR, in which the coupling constant 3JH,
OH
is increased/decreased upon the presence of the H−bond acceptor such as
fluorine.88 The strongest intramolecular interactions JF–OH =7.5 and 7.8 Hz were
detected in 1,3-diaxial fluoro alcohols in Bernet’s work as shown in
compounds 4.17 and 4.18 (Figure 4.12).
50
Chapter 4: Results and Discussion
Figure 4.12: Intramolecular H−bonds and 3JH-OH values35,88
Examination
of
the
O−H···F
interactions
on
a
range
of
fluorinated
carbohydrates has shown quite interesting results of hJH–OH and hJF–OH ranging from
12-7.5 Hz as shown in Figure 4.12 and these are comparable to the results in
this work.
4.2.2 Hydrogen Bonding Observations on Levoglucosans
The levoglucosans synthesised in chapter 3 provided a unique opportunity to
study such intramolecular hydrogen bonding. NMR analysis in CDCl3 has shown
that the O−H···F interaction influences the coupling constant 3JH-OH. We have
observed that the competition between O−H···O and O−H···F interactions can
increase/decrease the magnitude of the coupling constant. An illustration is
the 3JH-OH in 3.20 and 3.6 (Figure 4.13): this value is 9.9 Hz for 3.20, which is
explained by an approximate 150º dihedral angle caused by intramolecular
hydrogen bonding to the endo oxygen. In 3.6, the axial C2 fluorine now
competes with the endo oxygen for hydrogen bonding, resulting in an increase
in dihedral angle, thus the coupling constant of 10.9 Hz.
Figure 4.13: Influence of fluorine on the coupling constant.
51
Chapter 4: Results and Discussion
The preference to form these intramolecular interactions are significantly
observed in solvents of low polarity like CDCl3 and get reduced in polar
solvents such as acetone−d6 as observed in 4.19, where 3JH3-OH3 =6.2 in CDCl3 is
reduced to 4.4 Hz in acetone−d6, and 4JH4-OH4 =10.9 Hz in CDCl3 is reduced to
6.8 Hz in acetone−d6. This is even more pronounced as polarity of solvent
increases such as in DMSO-d6 where they get replaced by the intermolecular
H−bond; the effect which has also been critically evidenced by Bernet and coworkers.35,88
4.3 Conclusion
NMR observations on the conformationally rigid levoglucosans have given
substantial facts to the existence of the long range couplings. We have
observed long range coupling of the magnitude: 5JH–F = 1.3 to 4.1 Hz and 4JC–F =
2.5 to 6.2 Hz. Interestingly, the coupling constant in both cases appeared to be
dependent on the relative stereochemistry. The presence of the C4 substituent
in the equatorial position significantly reduced the magnitude of the coupling
constant. Also, the presence of the axial F at C2 has reduced the coupling
constant of the 4JC–F and in the 5JH–F it was even not observed.
We have observed existence of intramolecular H−bond and the competition
that exist between O−H···O and O−H···F interactions, and that has influence on
the coupling constant. These interactions get more pronounced in apolar
solvent such as CDCl3 and decreases as polarity of solvent increases as
observed in acetone-d6. We have also observed only one case of the 1JF–OH,
however with a small coupling constant of 1.3 Hz compared to those observed
in Bernet’s work(s).
52
Chapter 5: Results and Discussion
5 Synthesis of Fluorohydrins
5.1 Introduction
The fluorohydrins/fluoroalcohols 1.51–1.56, 1.59-1.64 and the non-fluorinated
alcohols 1.57 and 1.58 (see Figure 1.13) were synthesised with aim of
extending our investigations on the influence of fluorination on the H–bond
donating capacity (H–bond acidity) of fluoroalcohols in comparison with their
corresponding non fluorinated alcohols. This is a collaboration with Dr Jerome
Graton and Prof Jean-Yves Le Questel (University of Nantes), who will determine
the
hydrogen
bond
acidity
using
Fourier
Transform
Infrared
(FTIR)
spectroscopy. To achieve this, all the target fluorohydrins have to be prepared
in gram quantities.
5.2 Synthesis of the Fluorohydrins
5.2.1 Synthesis of Cis- and Trans-4-(tert-butyl)-1-fluoromethylcyclohexanol
(1.51 and 1.52)
Scheme 5.1: Synthesis of cis- and trans-4-(tert-butyl)-1fluoromethylcyclohexanol
The two diastereoisomers 1.51 and 1.52 were synthesised by Akiyama et al.
and selectively obtained the cis-isomer as a major (99:1 ratio) from the pure
cis-epoxide by using TBAF-KHF2.89 This was not our preference as we needed
both isomers in large quantities, so the two were synthesised as a mixture in
two-steps, first by epoxidation to 5.2 and 5.3 from the commercially available
4-tert-butylcyclohexanone 5.1 (Scheme 5.1). Two different procedures were
investigated which both formed an inseparable mixture of diastereomeric
epoxides. In the first approach we used trimethylsulfonium iodide and
potassium tert-butoxide90 that afforded the diastereomeric mixture (89% yield)
53
Chapter 5: Results and Discussion
in a 1:1.6 ratio for the cis- and trans- epoxides respectively (Figure 5.1 left).
Epoxidation of the same ketone by trimethyloxosulfonium iodide and sodium
hydride91 improved selectivity and afforded the inseparable diastereomeric
mixture (84% yield) in the ratio 10:1 for the cis- and trans- epoxide respectively
(Figure 5.1 right). For our purpose of large scale synthesis of both
diastereoisomers, the sulfonium ylide reagent was preferred, as the final
compounds could be separated (see below).
Figure 5.1: 1H NMR spectrum of epoxides 5.2 and 5.3
The selectivity of oxosulfonium ylide and its preference to equatorial addition
is due to its large size as compared to sulfonium ylide.91 In Scheme 5.2 a
mechanism for the epoxide formation by the two ylides is shown.
Scheme 5.2: Possible mechanism for epoxidation
54
Chapter 5: Results and Discussion
The mixture of epoxides was opened by potassium hydrogen difluoride and
tetrabutylammonium dihydrogen trifluoride (Landini reagent) in the absence of
solvent, as was used by Lundt et al92, and also well described in Linclau
group.31 This afforded the two separable diastereoisomers 1.51 and 1.52, in
25% yield each. Interestingly, the trans-diastereoisomer gave a triplet of triplet
on the 19F NMR (Figure 5.2 left) which may be due coupling with the protons on
CH2F and the long range coupling with protons on C2 as shown by the 48.4
and 5.4 Hz coupling constant respectively. However, the 1H NMR couldn’t
confirm the particular protons involved as it gave a complicated multiplets.
This
observation
has
not
been
reported
in
the
literature.
The
cis-
diastereoisomer gave only a triplet as shown in Figure 5.2 right.
Figure 5.2: 19F NMR spectrum of the trans- and cis- diastereoisomers 1.52 and
1.51
55
Chapter 5: Results and Discussion
5.2.2 Synthesis of Cis- and Trans-4-(tert-butyl)-1difluoromethylcyclohexanol (1.53 and 1.54)
Scheme 5.3: Synthesis of trans- and cis-4-(tert-butyl)-1difluoromethylcyclohexanol
The two diastereoisomers (1.53 and 1.54) were previously synthesised by Surya
et al.,93 however reductive desulfonylation was achieved using Na/Hg amalgam
which we avoided due to extreme toxicity of Hg. They obtained the cis- and
trans-diastereoisomers
in
85%
and
88%
respectively
and
their
NMR
characterisation corresponded with that obtained in this work. A two-step
procedure for synthesis of these fluorohydrins (1.53 and 1.54) was used and
that went through formation of the phosphonates 5.4 and 5.5, as was also
described by Beier et al.94 The hydroxy phosphonates were separable, with
difficulties, by column chromatography, and were afforded in 25% (5.4) and
32% (5.5) yield. Waschbüsch et al.,95 only reported the cis-diastereoisomer (5.4),
however, with limited characterisation. Dephosphonylation using sodium
methoxide in methanol afforded 1.53 and 1.54 in low yield, 14% and 8%
respectively. The cause of low yield was due to formation of phosphates 5.6
and 5.7 (Scheme 5.4). This was also pointed out by Beier et al.,94 though no
NMR data of these hydroxyphosphates are available. Increasing the amount of
base was not helpful. Phosphate cleavage using lithium aluminium hydride96
gave the desired compounds 1.53 and 1.54 in an improved yield, 45% and 47%
respectively. However, on large scale we were able to hydrolysise the crude
phosphates, a procedure that helped reduce complexity in separation and
purification, especially of the phosphonates.
56
Chapter 5: Results and Discussion
Scheme 5.4: Mechanism for the formation of the phosphate by products
The cis- and trans-isomers of the phosphates 5.6 and 5.7 could be
distinguished
by
gradient-enhanced
nuclear
overhauser
effect
(GOESY)
experiments. The phosphate 5.6 shows cross peaks between the CHF2 and the
OCH2, CH3, H3ax, H3‫׳‬ax, and all the H2 and H2‫ ׳‬protons (Figure 5.3). On the other
hand, the phosphate 5.7 shows cross peaks between the CHF2 and all the H2
and H2‫ ׳‬protons only (Figure 5.4). The presence of the cross peaks between
CHF2 and H3ax, H3‫׳‬ax, confirms 5.6 to be the trans-isomer, and 5.7 to be its
corresponding cis-isomer as these cross peaks could not be observed due to
the protons being far away from each other.
57
Chapter 5: Results and Discussion
Figure 5.3: 1H NMR and GOESY of 5.6 after irradiation of CHF2 proton
Figure 5.4: 1H NMR and GOESY of 5.7 after irradiation of CHF2 proton
58
Chapter 5: Results and Discussion
5.2.3 Synthesis of Cis- and Trans-4-(tert-butyl)-1trifluoromethylcyclohexanol (1.55 and 1.56)
Scheme 5.5: Cis- and Trans-4-(tert-butyl)-1-trifluoromethylcyclohexanol
The two diastereoisomers were also synthesised by Diter in the same way as
shown in Scheme 5.5 and were obtained 73% overall yield.97 The ketone 5.1
was reacted with (trifluoromethyl) trimethylsilane and a substoichiometric
amount of tetrabutylammonium fluoride initiator (Scheme 5.5). The cis- and
trans-diastereoisomers were formed in 13% and 75% yield respectively.
5.2.4 Synthesis of Cis- and Trans-4-(tert-butyl)-1-methylcyclohexanol (1.57
and 1.58)
Scheme 5.6: Synthesis of trans- and cis-4-(tert-butyl)-1-methylcyclohexanol
Senda et al.,98 used MeMgI to synthesis the two diastereoisomers (1.57 and
1.58), however did not report the yield. The NMR characterisation reported by
Senda corresponded to one obtained in this work. We synthesised the two
diastereoisomers by addition of the methyl group to the ketone 5.1 using two
different procedures. Using methyl lithium/FeCl3,99 1.58 was obtained in 71%
yield, with only trace quantities of the other distaereomer (±1%). The second
approach using methylmagnesium bromide100 was less selective, and gave the
two separable diastereoisomers 1.57 in 19%, and 1.58 in 32% yield.
59
Chapter 5: Results and Discussion
5.2.5 Attempted Ssynthesis of Trans-4-(tert-butyl)-3-fluoro and Trans-4(tert-butyl)-3,3-difluorocyclohexanol (1.66 and 1.68)
5.2.5.1 Deoxyfluorination Approach
The synthesis of these fluorohydrins started with bromination of the
commercially available ketone 5.1, leading to an inseparable diastereomeric
mixture of 2-bromo-4-(tert-butyl)cyclohexanone 5.8 and 5.9.101 The reaction
goes through keto-enol tautomerism (Scheme 5.7) which is initiated by
ammonium ion.
Scheme 5.7: Synthesis of trans-4-(tert-butyl)-3-fluoro and -3,3difluorocyclohexanol
Scheme 5.8: Bromination mechanisn via keto-enol tautomerisation
The crude product (5.8 and 5.9) was used directly in the next step where it was
dehydrobrominated into a known enone 5.10 in 57% yield by magnesium
oxide, a procedure well described by Fujiko et al.102 Given E2-elimination with
60
Chapter 5: Results and Discussion
magnesium oxide is only possible for an axial bromide we propose the most
likely mechanism to be through carbene formation as shown in Scheme 5.8.
Scheme 5.9: Mechanism of enone formation
Selective hydroboration of the enone using borane tetrahydrofuran103 afforded
the known compound, 5.11 in low yield (24%). This was followed by selective
protection of the hydroxyl group at C1 using triphenylmethy chloride (trityl
chloride) that afforded 5.12 in excellent yield (86%). Attack by the hydroxyl at
C3 did not occur probably due to steric hindrance by the 4-tert-butyl group.
Oxidation of 5.12 in basic medium using sulfur trioxide pyridine complex and
triethylamine104 afforded the ketone 5.13 in reasonable yield (65%). As far as we
know, compounds 5.12 and 5.13 have not been reported in the literature.
Fluorination of 5.12 and 5.13 was not successful. Several methods proved
ineffective including use of DAST (neat),105 DAST with a strong base 2,4,6trimethyl pyridine (collidine),106 deoxofluor® and XtalFluor-E®82 under harsh
conditions of temperature up to 80 ºC. This is probably due to steric hindrance
by the 4-tert-butyl group.
5.2.5.2 Attempts to Monofluorination through Mesylation
After failure to direct fluorination of compound 5.12 (Scheme 5.7), we opted
for monofluorination through mesylation. The optimisation reaction was first
attempted with a model compound 5.16, which was mesylated using
methanesulfonyl chloride and triethylamine in DCM107 to give a mixture of
inseparable diastereoisomers 5.17 and 5.18 in 23% yield (Scheme 5.10).
Scheme 5.10: Fluorination through mesylation
61
Chapter 5: Results and Discussion
Attempt to fluorinate the obtained mesylates to the desired products 5.19 and
5.20
was
not
fruitful
tetrabutylammonium
for
both
fluoride
fluorinating
reagents
(commercially
that
we
available)
used:
and
tetrabutylammonium tetra tert-butanol coordinated fluoride which we prepared
using the procedure well described by Kim et al.108 Failure of this last attempt
has made us unsuccessful to our final desired compound, the fluoroalcohol
1.66.
5.2.6 Attempted Synthesis of Cis-4-(tert-butyl)-3-fluoro- and Cis-4-(tertbutyl)-3,3-difluorocyclohexanol (1.65 and 1.67)
5.2.6.1 Hydrogenation and Birch Reduction of a Resorcinol Derivative
Scheme 5.11: Synthesis of cis-4-(tert-butyl)-3-fluoro- and cis-4-(tert-butyl)-3,3difluorocyclohexanol
For the synthesis of the cis-4-(tert-butyl)-3-fluoro- and cis-4-(tert-butyl)-3,3difluorocyclohexanol (1.65 and 1.67), the synthesis of the 4-(tert-butyl)cyclohexane-1,3-diol 5.27 was investigated by reduction of tert-butylated
resorcinol. This started with introduction of the tert-butyl group to the
commercially available resorcinol 5.21 using tert-butanol, glacial acetic acid
and sulfuric acid.109 This gave a known compound 4-tert-butylresorcinol,109 5.22
in 45% yield. Lots of efforts to achieve hydrogenation using H2 (1−20 atm) and
5% Ru/C only afforded 5.23 in low yield (8%). The unformed compounds 5.2462
Chapter 5: Results and Discussion
5.27 were also not described in the literature. We also tried hydrogenation
through Birch reduction110 which in all cases afforded the starting material.
5.2.6.2 Attempted Birch Reduction of a 3-fluorophenol Derivative
Scheme 5.12: Synthesis of fluoroalcohols from fluorinated substrate
We also tried a starting material 5.28, as shown in Scheme 5.12 and that
already had a fluorine atom in the preferred position. The target was to
introduce the tert-butyl group next to fluorine in a less hindered position,
which could be achieved after protection of the hydroxyl group using methyl
iodide and sodium hydride in THF111 to afford 5.29 in 76% yield. This
compound was also synthesised by Kim et al.112. This was followed by
introduction of the tert-butyl group using tert-butanol, glacial acetic acid and
sulfuric acid109 which unfortunately didn’t give the desired product. We suggest
the unexpected product to be 5.31 which was not reported in the literature.
The evidence for this product include a triplet 3JH-F=13.9 Hz shown by the
F
19
NMR (Figure 5.5) which we believe is the coupling of F to H2 and H4.
Interestingly, we have observed long range coupling 6JF-tBu= 3.3 Hz and 5JF-CtBu=
2.9 Hz for the C−tBu and the 3C’s of tert-butyl group respectively which we
have not observed to the rest of our compounds.
We further tried to protect the hydroxyl group by acetylation using acetic
anhydride and triethylamine54 in order to increase steric hindrance at the ortho
positions. Acetylation afforded a known compound 5.33113-115 in excellent yield
(88%) as shown in Scheme 5.13.
63
Chapter 5: Results and Discussion
Figure 5.5: 19F NMR spectrum of 5.31
Scheme 5.13: Synthesis of fluoroalcohols from fluorinated substrate: second
attempt
The tert-butyl group was once again directed to the ortho position as in 5.31;
however, unexpectedly, the acetyl group was also hydrolysed to the
corresponding hydroxyl group. The NMR data of this compound corresponded
64
Chapter 5: Results and Discussion
to 5.31;
coupling
F has also given a triplet 3JH-F=12.9 Hz (Figure 5.6). Additionally, the
19
JF-tBu= 3.3 Hz and
JF-CtBu= 2.8 Hz for the C−tBu and the 3C’s
6
5
respectively were also clearly observed and that was exactly the same as in
5.31.
Figure 5.6: 19F NMR spectrum of 5.35
5.2.7 Synthesis of Trans- and Cis-2-fluorocyclohexanol (1.59 and 1.60)
Scheme 5.14: Synthesis of trans-and cis-2-fluorocyclohexanol
O
OH
KHF2, Bu4NH2F3
115°C, 2.5 days
96%
5.37
F
O
PDC, Ac2O
87%
1.59
5.38
L-selectride
F THF, -78°C
50%
O
PhCOCl, Et3N, DMAP
OH
O
68%
K2CO3, MeOH
F
29%
F
(impure)
5.39
(impure)
1.60
65
OH
F
(impure)
1.60
Chapter 5: Results and Discussion
As shown in Scheme 5.14, this five-step synthesis started with opening of the
epoxide (5.37) using two different procedures. In the first attempt, potassium
hydrogen
difluoride
and
tetrabutylammonium
dihydrogen
trifluoride31
selectively opened the epoxide and gave 1.59 in 96% yield. Because of the long
reaction time (2.5 days), an alternative procedure using potassium hydrogen
difluoride in ethylene glycol, which was reported to go to completion after
1h,116 was tried but the yield was reduced to 41%. To get to 1.60, the
fluorocyclohexanol 1.59 was first oxidised to 5.38 (87%) with pyridinium
dichromate59 followed by selective reduction of the ketone using lithium trisec-butyl borohydride (L-selectride)117 that gave an impure product even after
HPLC purification. Efforts to purify 1.60 through protection of the hydroxyl
with benzoyl chloride gave impure compound 5.39 which was not possible to
clean even after HPLC. Hydrolysis using potassium carbonate in methanol gave
the impure product 1.60 as well (Figure 5.7).
Figure 5.7: 19F NMR of impure 1.60
Attempt to invert the stereochemistry through Mitsunobu reaction34 was not
successful as we only obtained a crude product showing no peaks in the
F
19
NMR spectrum. That indicated an elimination side reaction that removed the
fluoride. Further attempt to getting 1.60 pure continued through inversion of
configuration via SN2 substitution of the triflate 5.48 with cesium acetate as
shown in Scheme 5.15.
66
Chapter 5: Results and Discussion
Scheme 5.15: Inversion of configuration via SN2 substitution
Reaction of 1.59 with trifluoromethanesulfonic anhydride and pyridine in
DCM118 gave pure 5.40 (86%), a novel and clean crude product that did not need
any purification. Inversion of the stereochemistry at the sulfonate was afforded
by SN2 substitution with cesium acetate119 and afforded 5.41 (59%), a compound
which was not reported in literature. Hydrolysis of the acetate using potassium
carbonate in methanol afforded pure 1.60 in low yield of 17%. The low yield
may due to elimination reaction forming an alkene that could not be isolated
due to being volatile. These fluorohydrins are known to the literature,120,121
however limited characterisation have been reported. Our 1H and
C NMR
13
spectra of 1.60 correspond to those reported by Basso et al,121 except the
F
19
NMR which was not reported and has shown a broad peak at 25 ºC which was
narrowed at 50 ºC (Figure 5.8).
Figure 5.8: 19F NMR spectra of 1.60 at 25 ºC and 50 ºC.
67
Chapter 5: Results and Discussion
5.2.8 Synthesis of Trans-and Cis-4-fluorocyclohexanol (1.63 and 1.64)
Scheme 5.16: Synthesis of trans- and cis-4-fluorocyclohexanol
The synthesis of these fluoroalcohols started with acetylation54 of 1,4cyclohexanediol 5.42 (mixture of isomers) with acetic anhydride and
triethylamine in DCM. Unfortunately, an inseparable mixture of 5.43 and 5.44
was isolated in 45% together with the mixture of diacetylated product cis-and
trans-1,4-diacetoxycyclohexane (5.45 and 5.46). Mixtures of these isomers
were clearly observed from their 1H NMR as shown in Figure 5.9. The cis- and
trans- diacetylated product were formed in 1:1.5 ratio respectively with the
protons 1 and 4 overlaped in each case (Figure 5.9 left). This diacetylated
product is known to the literature but was not fully characterised by Musher et
al.122 The monoacetylated products (Figure 5.9 right), not reported in the
literature as a mixture of isomers were obtained in 1:1 ratio, and the two
protons in each isomer occurred at different chemical shift in the 1H NMR as
expected. The trans- isomer was also synthesised by Hatano et al.123
68
Chapter 5: Results and Discussion
Figure 5.9: 1H NMR spectrum of the acetylated product 5.43-5.44
The next step was fluorination of the monoacetylated compounds (5.43 and
5.44). Direct fluorination with refluxing DAST in toluene as described by Sarda
et al,71 and DAST in DCM at 0 ºC, a procedure used by Van et al,124 were not
successful with these substrates. Procedure using the fluorinating reagents:
XtalFluor-E, Deoxo-Fluor and KF as described by L’Heureux et al,82 Lal et al,81
and Bandgar et al125 respectively were also not successful. In both cases we had
elimination product to the known alkene cyclohex-3-en-1-yl acetate 5.49126
(Figure 5.10). Formation of this alkene is not surprising because the fluoride
ion also behave as a strong base as was pointed out by Bangdar et al.125 Further
attempts with DAST and TBAF(tBuOH)4 in DCM at 0 ºC124;
and DAST and
hydrogen fluoride pyridine complex in DCM at 0 ºC gave elimination product
as well but with some trace amount of the expected products in 1:1 ratio as
observed in the crude 19F NMR (Figure 5.11) at δ -180.4 ppm for the cis-isomer
5.48 which is similar to one reported by Liu et al.,127 and -181.3 ppm for 5.47
that was not reported in literature. The traces were so minimal that we thought
could not end up with significant amount after purification by column
chromatography.
69
Chapter 5: Results and Discussion
Figure 5.10: Cyclohex-3-en-1-yl acetate
Figure 5.11:Crude 19F NMR spectrum showing 5.47 at δ -180.4 ppm and 5.48 at
δ -181.3 ppm
We also tried to add 1 equivalent of TBAF (tBuOH)4 and hydrogen fluoride
pyridine complex to the reactions with DAST in DCM at 0 ºC, in an attempt to
reduce basicity and so to avoid elimination effect; but was also not helpful.
5.2.8.1 Attempt to Fluorination through SN2 Substitution
We further tried to make the hydroxyl group a good leaving group by
mesylation as shown in Scheme 5.17.
70
Chapter 5: Results and Discussion
Scheme 5.17: Fluorination through mesylation
Mesylation
of
the
inseparable
diastereoisomers
5.43
and
5.44
with
methanesulfonyl chloride and triethylamine in DCM107 gave quantitatively a
mixture of inseparable diastereoisomers 5.50 and 5.51 that were not reported
in literature. The four protons at carbon 1 and 4 in the 1H NMR for these
mesylates overlapped as shown in Figure 5.12 and that made it difficult to
assign protons for these two diastereoisomers.
Figure 5.12: The four protons (at C1 and C4) in the 1H NMR spectrum of the
mesylates of 5.50 and 5.51
Fluorination of the mesylates using tetrabutylammonium tetra (tert-butyl
alcohol) coordinated fluoride which is described as a good nucleophile with
low basicity to avoid elimination side reaction,108 still gave the alkene cyclohex3-en-1-yl acetate 5.49 as for the other fluorinating reagents. Our further
attempt to fluorination was through introduction of a much better leaving
group, the triflate, using a procedure well described by Wang et al.,118 but also
ended up with the elimination product as well.
71
Chapter 5: Results and Discussion
5.2.9 Synthesis of Trans-and Cis-3-fluorocyclohexanol (1.61 and 1.62)
5.2.9.1 Birch Reduction of 3-fluorophenyl Acetate
Scheme 5.18: Synthesis of 1.61 through Birch reduction
Birch reduction using sodium and ethanol in refluxing ammonia to the
fluorobenzyl acetate, 5.33 that already have fluorine in the desired position
was not successful (Scheme 5.18). All our efforts ended only recovering the
starting material and sometimes the deacetylated product, the 3-fluorophenol.
3-Fluorophenol could be obtained due to cleavage of the acetyl by the sodium
ethoxide formed in situ.
5.2.9.2 Synthesis of 3-Fluorocyclohexanol (1.62) from 2-Cyclohexen-1-ol
Scheme 5.19: Synthesis of 3-fluorocyclohexanol from 2-cyclohexen-1-ol
2-Cyclohexen-1-ol 5.54, a commercially available compound, was reacted with
iron (III) nitrate nonahydrate, selectfluorTM and sodium borohydride in water
and acetonitrile.128 This gave a mixture of inseparable diastereoisomers 1.61 (at
δ 180 ppm) and 1.62 (at δ 173 ppm) in the ratio of 4.5:1 (Figure 5.13) and was
formed in 34% yield. Acetylation129 of the diastereoisomers gave 5.53 and 5.55
which on HPLC separation using 1% EtOAc/PE afforded 5.61 in low yield (20%),
72
Chapter 5: Results and Discussion
but 5.55 was not isolated after evaporation of solvent collected from the minor
peaks, may be it is volatile.
Figure 5.13: 19F NMR spectrum of mixture of diastereoisomers 1.61 and 1.62.
5.2.9.3 Alternative Synthesis through Iodofluorination
Scheme 5.20: Synthesis of 1.61 and 1.62 through iodofluorination
We then tried a synthetic route through iodofluorination,34 as shown in Scheme
5.20. The allylic alcohol 5.54 was reacted with N-iodosuccinimide and
hydrogen
fluoride
pyridine
complex
and
gave
the
two
separable
diastereoisomers 5.56 and 5.57 (1:2 ratio) in small yield (8-9%). The two
73
Chapter 5: Results and Discussion
diastereoisomers could be distinguished from the
H NMR and GOESY
1
experiments. The cis-isomer 5.57 has the equatorial H1 showing cross peaks
with H3eq, H2eq, OH, H4ax and H6ax (Figure 5.14). The absence of the cross peak
between H1 with the H5ax confirms the isomer to be cis-3-fluoro-2iodocyclohexanol.
Figure 5.14: 1H NMR and GOESY (top) of 5.57 after irradiation of H1
In Figure 5.15, the cross peaks between H1ax with 2Heq, OH, H5ax and H6eq can
be observed, though the H4eq, 5, 6 protons appeared a complex multiplet. The
absence of the cross peaks between H1 with H3eq and H4ax which are clearly
observed in 5.57, confirms 5.56 to be the trans-isomer as these protons are
now quite far apart in this trans-isomer as compared to the cis-isomer.
74
Chapter 5: Results and Discussion
Figure 5.15: 1H NMR and GOESY (top) of 5.56 after irradiation of H1
Radical
reduction
(Scheme
5.21)
with
tributyltin
hydride
and
azobisisobutyronitrile proceeded well and afforded 1.61 in reasonable yield
(64%).
Scheme 5.21: Mechanism of radical reduction
Attempt to reduce 5.57 using the same methodology as for 5.56 ended with an
inseparable mixture which was observed from the
that corresponded to Figure 5.13.
75
F NMR in Figure 5.16 and
19
Chapter 5: Results and Discussion
Figure 5.16: 19F NMR spectrum of the product from reduction of 5.57
5.2.10 Synthesis of 2-Fluorobenzyl Alcohols (1.69-1.71)
The three fluorobenzyl alcohols (Figure 5.17) were also important key
compounds for the determination of hydrogen bond acidities.
Figure 5.17: Target fluorobenzyl alcohols
These
fluorobenzyl
alcohols
commercially available
were
synthesized
2-fluorobenzaldehydes
from
5.69,
their
5.70
and
respective
5.71
by
reduction with sodium borohydride (Scheme 5.22). In both cases the yields
were very good, 94%, 84% and 84% respectively.
76
Chapter 5: Results and Discussion
Scheme 5.22: Synthesis of 2-fluorobenzyl alcohols
The fluorobenzyl alcohols 1.69, was also synthesised by Beller et al.,130 through
iron catalysed hydrosilylation of benzaldehyde and afforded the product in
81% yield. The 1H and 13C NMR reported by Beller corresponded to one obtained
F NMR was not reported. The 2-fluoro-5-
in this work. However, the
19
methoxybenzyl alcohol 1.70 was early synthesised by Luxen131 and afforded it
in 78% using the above procedure.
Luxen reported only the 1H NMR which
corresponded to one obtained in this work. Also it was synthesised by Lee et
al.,132 through indium tri(isopropoxide)-catalysed selective meerwein-ponndorfverley reduction of 2-fluoro-5-methoxybenzaldehyde but did not report the
yield. Lee reported the 1H and
C NMR that corresponded to ours however;
13
they could not show important JF-C coupling constants and the 19F NMR was not
reported. Andre et al.,133 reported the synthesis of 1.71 in the same procedure
as used in this work. The
H and
1
C NMR of 1.71 reported by Andre
13
corresponded to one obtained in this work. However, as for the other authors
who synthesised 5.66 and 5.67, Andre also did not report the
of 1.71.
77
F NMR details
19
Chapter 5: Results and Discussion
5.3 Results of H–bond Acidity of Fluoroalcohols
5.3.1 Introduction
The fluoroalcohols shown in Figure 5.18 were subjected to FTIR (Fourier
Transform Infrared) spectroscopy for determination of H−bond acidity.
Experiments
and
calculations
of
the
equilibrium
constant
for
these
fluoroalcohols were performed by our collaborators: Dr Jérôme Graton and Prof
Jean-Yves Le Questel from the University of Nantes in France.
5.3.2 Results of H−bond Acidity
5.3.2.1 Observations on Fluorohydrins
The results of the measurements of H–bond acidity are shown in Figure 5.18.
The non-fluorinated alcohols cis- and trans-4-tert-butylcyclohexanol 1.57 and
1.58, have shown a significant difference (0.7) in their H−bond acidity
compared to their counterpart 1.31 and 1.32 (0.04). All the fluorohydrins
except 1.52 have shown increased H−bond acidity compared to the nonfluorinated analogue. Also most of these fluorohydrins have given the values
close to the predicted H−bond acidity with exception of 1.55 and 1.59;
however, the predicted value for 1.55 using the general alcohol relationship is
33.3 which is close to the experimental value.
These results clearly show the influence of fluorination on the H–bond acidity
of the nearby hydroxyl functional group. In contrast to the earlier investigated
gauche monofluorohydrins, the monofluorohydrins 1.51 has a higher H–bond
donating capacity than the non-fluorinated alcohols 1.57. It is not clear what
the reason is for this. In contract, the difluoromethyl and trifluoromethyl
substituted cyclohexanols 1.53-1.56 have a higher H–bond donating capacity.
78
Chapter 5: Results and Discussion
Figure 5.18: Results of H-bond acidities of fluoroalcohols
Interestingly, the trend on these fluoroalcohols shows all the cis-fluorinated
isomers have high values of H−bond acidity compared to their trans-isomers
(Figure 5.18). However, the explanation for this observation has not yet been
established. Equally, it is not yet explained why 1.55 has a markedly higher
experimentally observed value compared to the predicted one.
5.3.2.2 Observations on Benzyl Alcohols
This investigation has shown fluorobenzyl alcohols (Figure 5.19) to have in
general larger equilibrium constants in comparison with the monofluorinated
cyclohexanols. In addition, the three fluorobenzyl alcohols have shown
increased value of the H−bond acidity. The equilibrium constant for 1.69 and
1.70 are comparable, however a decrease in the value could be expected on
1.70 due to the presence of OMe electron donating group, which increases
electron density on the fluorine atom and therefore likely to decrease its
H−bond acceptor ability. The nitro group in 1.71 has caused a significant fold
79
Chapter 5: Results and Discussion
increase in H–bond acidity which may be due to its strong electron withdrawing
effect that in turn decreases electron density on F and therefore decreasing
H−bond acceptor capacity of fluorine.
F
F
F
OH
OH
OH
OH
OMe
NO2
5.61
1.69
1.70
1.71
Measured KAHY
10.80
14.40
16.20
96.20
Predicted KAHY
14.80
15.50
13.70
108.20
Figure 5.19: Results of H-bond acidity on benzyl alcohols
5.4 Conclusion
Figure 5.20: Accomplished targets
The fluorohydrins 1.51-1.56 and 1.59 were successful synthesised, each in
gram quantities except 1.60 and 1.61 which were obtained in small yield not
sufficient for the H−bond determination. These fluorohydrins have given
interesting results on the H−bond acidities. They have in general given
increased H−bond acidities compared to their corresponding non-fluorinated
analogues. Interestingly, most of them gave the values very close to the
predicted one. We have observed the values of the equilibrium constant
increasing with increasing number of fluorines substituting for hydrogen, a
factor attributed by increased electron withdrawing effects of fluorine.
Furthermore, the increased values of H−bond acidity were more pronounced on
the cis-isomers than the trans-counterpart. The cause of this trend has not
been established.
80
Chapter 5: Results and Discussion
As for the fluorohydrins, the fluorobenzyl alcohols have also given very
interesting results. All the used substrates showed increased H−bond acidities
compared to the non-fluorinated benzyl alcohol, 5.61. The presence of
electronegative substituent in the fluorobenzyl alcohol (1.70 and 1.71) has
shown influence on the H−bond acidity. H−bond acidity increased significantly
particularly with the introduction of the nitro group in 1.71 which cause
multiple fold increase.
The fluorinated alcohols 1.62-1.68 were not afforded due to difficulties in
fluorination of the intermediates using available fluorinating reagents.
81
Chapter 6: Experimental
6 Experimental
6.1 General Method
In general all chemicals were obtained from commercial sources and were used
without further purification. All the experiments were carried out in glassware
flame dried in vacuum, cooled and taken under nitrogen or Argon. Anhydrous
solvents for the reactions were distilled with exception of DMF which was
purchased dried in sealed containers from commercial sources; diethyl ether
over Na/benzophenone, triethylamine over CaH2, pyridine over CaH2, methanol
over CaH2, and dichloromethane over CaH2. Water and air sensitive reactions
were carried out under inert atmosphere, using dry solvents.
Completion of reactions and column chromatography separations/purifications
were monitored by TLC silica gel 60 F254 Merck KGaA, aluminium sheet,
Darmstadt, Germany. Detection of the compounds on TLC was done using
mostly KMnO4 drying reagent prepared by dissolving a mixture of 1.5 g KMnO4,
10 g K2CO3 and 1.25 mL 10% NaOH in 200 mL of water.
The
compounds
obtained
were
separated
and
purified
by
column
chromatography in silica gel technical grade 60Å particle size 40-63 µm and
sometimes for further purification on high performance liquid chromatography
(HPLC).
All 1H NMR, 13C NMR,
F NMR and
19
P NMR spectra were carried out at room
31
temperature in CDCl3, acetone–d6, DMSO-d6, and MeOH-d4; Bruker av 300 and
400 MHz for 1H NMR, 75 and 101 MHz for 13C NMR , 282 MHz for 19F NMR and
121 MHz for 31P NMR spectrometer. The chemical shifts (δ) were in ppm relative
to residue solvent peaks. The coupling constants were recorded in Hertz (Hz).
The NMR signals were labelled as s (singlet), d (doublet), t (triplet), q (quartet),
quin (quintet), m (multiplet) or a combination of the above.
IR spectra were recorded as neat films on a Nicolet 380 FT-IR. Absorption
peaks are given in cm-1 and intensities were designated as w (weak), m
(medium), s (strong) and br (broad).
83
Chapter 6: Experimental
Optical rotations were recorded on an OPTICAL ACTIVITY POLAAR 2001
polarimeter at 589nm. Mass spectra were recorded on a WATERS ZMD single
quadrupole system and Bruker Apex III FT-ICR-MS.
6.2 Synthesis of Tetra-O-acetyl-3-fluoro-D-glucopyranose
2.1
6.2.1
1,2:5,6-Di-O-isopropylidene-3-keto-α-D-glucofuranose
Ac2O (11.53 mL, 122.17 mmol) was added to PDC (14.60 g, 38.80 mmol) in dry
DCM (200 mL). Then 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose, 2.5 (10.00
g, 38.42 mmol) was added in a minimal amount of the solvent and the mixture
boiled at 75 ºC for 4 h. After completion of the reaction (monitored by TLC),
the mixture was diluted with EtOAc (120 mL) and the precipitate filtered
through celite. After evaporation of the solvent, Et2O (80 mL) was added and
the mixture filtered through celite again, dried over MgSO4, filtered, evaporated
of solvent and dried under vacuum. The crude mixture was then purified by
column chromatography (EtOAc/hexane 50:50 mixture containing 0.5% TEA to
basify silica gel) that afforded 2.6, 7.0 g (71%). Mw 258.26 (C12H18O6); Rf 0.31
(EtOAc /hexane 50:50); 1H NMR (400 MHz, CDCl3) δ 6.14 (1H, dd, J 4.4, 1.8
Hz), 4.39 (1H, dd, J 4.5, 1.8 Hz), 4.34–4.37 (2H, m), 4.01–4.06 (2H, m), 1.46
(3H, s), 1.44 (3H, s), 1.34 (6H, s) ppm;
C NMR (101 MHz, CDCl3) δ 208.8 (s),
13
114.3 (s), 110.4 (s), 103.1 (s), 78.9 (s), 77.2 (s), 76.3 (s), 64.3 (s), 27.5 (s),
27.1 (s), 25.9 (s), 25.3 (s) ppm. These spectra data corresponded to those
reported by Guo.59
6.2.2 1,2:5,6-Di-O-isopropylidene-α-D-allofuranose
84
Chapter 6: Experimental
The ketone 2.6 (7.0 g, 27.10 mmol) was dissolved in a mixture of EtOH (40 mL)
and H2O (10 mL) and the solution cooled to 0 ºC. NaBH4 (2.65 g, 69.93 mmol)
was added and the mixture stirred at 0 ºC for 1h. This was followed by
addition of excess NH4Cl (30 mL) to destroy the unreacted borohydride. The
resulting mixture was concentrated and the residue extracted with DCM (3×30
mL). The extract was combined and washed with
H2O (2×30 mL), dried over
MgSO4, filtered, concentrated and purified on column chromatography
(EtOAc/PE 50:50 mixture containing 0.5% TEA) that afforded the allofuranose
2.4, 4.34g (62%). Mw 260.28 (C12H20O6); Rf 0.37 (EtOAc/PE 50:50); 1H NMR
(300 MHz, CDCl3) δ 5.81 (1H, d, J 4.0 Hz), 4.61 (1H, dd, J 5.1, 3.7 Hz), 4.30
(1H, td, J 6.6, 4.8 Hz), 3.97–4.12 (3 H, m), 3.82 (1H, dd, J 8.6, 4.6 Hz), 2.56
(1H, d, J 8.1 Hz), 1.58 (3H, s), 1.46 (3H, s), 1.38 (3H, s), 1.37 (3H, s) ppm;
C
13
NMR (75 MHz, CDCl3) δ 112.8 (s), 109.8 (s), 103.9 (s), 79.7 (s), 78.9 (s), 75.6
(s), 72.5 (s), 65.8 (s), 26.5 (s), 26.5 (s), 26.3 (s), 25.2 (s) ppm. These spectra
data match with those reported by Guo.59
6.2.3 3-Deoxy-3-fluoro-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose
To a solution of 2.4 (1.69 g, 6.49 mmol) in anhydrous DCM (40 mL) was added
pyridine (1.70 mL, 20.77 mmol) followed by drop wise additional of DAST
(1.37 mL, 10.39 mmol) at 0 ºC. The mixture was stirred at rt for 15h and
carefully poured onto saturated NaHCO3 solution (40 mL). After completion of
the reaction (monitored by TLC), the organic layer was separated, washed with
brine (20 mL), dried (MgSO4), filtered and evaporated of solvent. The resulting
residue was purified by silica gel column chromatography (EtOAc/PE 10:90
mixture containing 0.5% TEA) that afforded 2.7, 1.036 g (61%). Mw 262.27
(C12H19FO5); Rf 0.28 (EtOAc/PE 05:95); 1H NMR (300 MHz, CDCl3) δ 5.96 (1H, d, J
3.7 Hz, H1), 5.01 (1H, dd, J 49.9, 1.8 Hz, H3), 4.70 (1H, dd, J 10.7, 3.7 Hz,
H4), 4.24–4.34 (1H, m, H2), 4.00–4.20 (3H, m, H5,6), 1.51 (3H, s, CH3), 1.45
(3H, s, CH3), 1.37 (3H, s, CH3), 1.33 (3H, s, CH3) ppm;
C NMR (75 MHz, CDCl3)
13
δ 112.4 (s, C1), 109.5 (s), 105.2 (s), 93.8 (d, J 183.3 Hz, C3), 82.6 (d, J 32.9
85
Chapter 6: Experimental
Hz, C2), 80.7 (d, J 19.1 Hz, C4), 71.9 (d, J 7.2 Hz), 67.2 (d, J 1.1 Hz), 26.8 (s,
CH3), 26.7 (s, CH3), 26.2 (s, CH3), 25.2 (s, CH3) ppm;
F NMR (282 MHz, CDCl3)
19
δ -207.8 (1F, ddd, J 49.4, 29.0, 10.7 Hz) ppm. These spectra details
corresponded to those reported by Tewson et al.,134 except the
C NMR which
13
was not reported.
6.2.4 1,2,4,6-Tetra-O-acetyl-3-fluoro-D-glucopyranose
The glucofuranose 2.7 was dissolved in EtOH (50 mL) and water (100 mL).
Amberlite® IR-120 (H+) (ca. 10 mL) was added and the mixture stirred at 60-65
ºC for 12h. The reaction mixture was then filtered and concentrated to give
yellow solid. The solid was dissolved in pyridine (10 mL) and the solution
cooled to 0 ºC. Ac2O (3.14 mL, 30.77 mmol) was added and the reaction
mixture allowed to warm to rt and stirred overnight. Water (50 mL) and EtOAc
(100 mL) were added and the layers separated. The organic layer was washed
with water (50 mL) and brine (50 mL), dried (MgSO4), filtered and evaporated of
solvent. The residue was dissolved in pyridine/toluene (1:1) and the volatiles
removed under vacuum. The resulting solid was dissolved in DCM and a
spoonful of charcoal (decolorizing powder) was added, stirred for 15 min and
filtered over celite. The sample was then evaporated (×3) in DCM that afforded
2.1, 1.23 g (92%). MW 350.29 (C14H19FO9); Rf 0.10 (EtOAc/ PE 20:80);
H NMR
1
(400 MHz, CDCl3) δ 6.35 (1H, t, J 3.7 Hz, H1α), 5.66 (1H, d, J 8.3 Hz, H1β),
5.13–5.34 (4H, m, H2,4α,β), 4.83 (1H, dt, J 53.3, 9.4 Hz, H3α), 4.61 (1H, dt, J
51.8, 9.2 Hz, H3β), 4.21–4.31 (2H, m, H6α,β), 4.08–4.17 (2H, m, H6‫׳‬α,β), 3.99–
4.08 (1H, m, H5α), 3.72–3.78 (1H, m, H5β), 2.13 (6H, s, CH3), 2.13 (3H, s, CH3),
2.12 (3H, s, CH3), 2.11 (3H, s, CH3), 2.10 (3H, s, CH3), 2.10 (3H, s, CH3), 2.09
(3H, s, CH3), ppm; 13C NMR (101 MHz, CDCl3) δ 170.6 (s, C=O), 170.6 (s, C=O),
169.5 (s, C=O), 169.1 (s, C=O), 169.1 (s, C=O), 169.0 (s, C=O), 168.9 (s, C=O),
168.5 (s, C=O), 91.2 (d, J 11.0 Hz, C1β), 91.6 (d, J 191.5 Hz, C3β), 89.3 (d, J
9.5 Hz, C1α), 89.0 (d, J 190.0 Hz, C3α), 71.9 (d, J 7.7 Hz, C5β), 70.2 (d, J 19.1
Hz, 2Cβ), 69.7 (s, 5α), 69.6 (d, J 11.0 Hz, C2α), 67.8 (d, J 3.7 Hz, C4β), 67.6 (d, J
4.0 Hz, C4α), 61.3 (2C, s, C6α,β), 20.8 (s, CH3), 20.7 (s, CH3), 20.7 (2C, s, CH3),
86
Chapter 6: Experimental
20.6 (s, CH3), 20.6 (s, CH3), 20.6 (s, CH3), 20.5 (s, CH3) ppm; 19F NMR (376 MHz,
CDCl3) δ -196.1 (1F, dt, J 52.0, 12.1 Hz), -200.2 (1F, dt, J 52.0, 12.1 Hz) ppm.
6.3 Synthesis of Tetra-O-acetyl -6-fluoro-D-glucopyranose
2.2
6.3.1 Methyl-6-fluoro-α-D-glucotopyranoside
A suspension of 2.10 (2.0 g, 10.41 mmol) in dry DCM (40 mL) at -40 ºC was
added DAST (8.25 mL, 62.46 mmol). The cooling bath was removed and the
mixture allowed to stir at rt for 1h. After completion of reaction, the mixture
was cooled to -10 ºC and quenched via additional of MeOH (20 mL) and then
evaporated of solvent under reduced pressure. The crude was purified by
column chromatography (MeOH/DCM 10:90) that afforded off white solid 2.11,
1.08 g, (53%). Mw 196.17 (C7H13FO5); Rf 0.33 (MeOH/DCM 10:90); 1H NMR (300
MHz, acetone-d6) δ 4.68 (1H, d, J 3.8 Hz), 4.58 (2H, m, J 43.4 Hz, observed,
H6), 4.34 (1H, d, J 4.4 Hz, OH), 4.22 (1H, d, J 2.9 Hz, OH), 3.57–3.75 (3H, m),
3.35 (4H, m), 2.90 (1H, s, OH); 13C NMR (75 MHz, acetone-d6) d ppm 101.1 (s,
C1), 83.5 (d, J 171.4 Hz, C6), 75.3 (s, C3), 73.4 (s, C2), 71.9 (d, J 17.7 Hz, C5),
70.4 (d, J 7.2 Hz, C4), 55.4 (s, CH3); 19F NMR (282 MHz, acetone-d6) δ -234.53
(1F, td, J 47.3, 25.8 Hz) ppm. These spectra data correspond to those reported
by Ritter135 and Card et al.136
6.3.2 1,2,3,4-Tetra-O-acetyl-6-deoxy-6-fluoro-D-glucotopyranose
To a solution of 2.11 (0.5 g, 2.57 mmol) in Ac2O (2.43 mL, 25.75 mmol) was
added catalytic amount of concentrated H2SO4 (5 drops) slowly for 6h. After
87
Chapter 6: Experimental
completion of reaction, the reaction mixture was poured into a solution of
saturated NaHCO3 (10 mL) and EtOAc (10 mL). After the mixture was stirred
overnight, the organic layer was separated, washed with water (20 mL) and
brine (20 mL); dried over anhydrous MgSO4 and evaporated of solvent.
Purification by column chromatography (hexane/EtOAc 90:10-40:60) afforded
2.2 0.692 g (77%). Mw 350.29 (C14H19FO9); 1H NMR (400 MHz, CDCl3) δ 6.35
(1H, d, J 3.2 Hz, H1α), 5.74 (1H, d, J 8.1 Hz, H1β), 5.49 (2H, t, J 10.0 Hz, H3α,β),
5.28 (1H, t, J 9.2 Hz, H4α), 5.08 (1H, dd, J 10.4, 3.4 Hz, H4β), 5.15 (2H, t, J 9.9
Hz, H2α,β), 4.46 (2H, m, J 46.9 Hz, observed, H6α,β), 4.50 (2H, m, J 47.4 Hz,
H6‫׳‬α,β), 4.10 (1H, dd, J 23.3, 10.2 Hz, H5α), 3.84 (1H, dd, J 22.1, 9.6 Hz, H5β),
2.18 (6H, s), 2.06 (6H, br. s.), 2.03 (6H, br. s.), 2.02 (6H, br. s.) ppm;
C NMR
13
(101 MHz, CDCl3) δ 170.2 (s, C=O), 170.1 (s, C=O), 169.6 (s, C=O), 169.3 (s,
C=O), 169.3 (s, C=O), 169.1 (s, C=O), 168.9 (s, C=O), 168.7 (s, C=O), 91.6 (s,
C1β), 88.9 (s, C1α), 80.8 (d, J 176.4 Hz, C6α), 80.6 (d, J 176.8 Hz, C6β), 73.2 (d,
J 19.4 Hz, C5β), 72.7 (s, C3β), 70.5 (d, J 19.1 Hz, C5α), 70.1 (s, C3α), 69.7 (s,
C2β), 69.1 (s, C2α), 67.6 (d, J 7.0 Hz, C4α), 67.5 (d, J 6.6 Hz C4β), 20.8 (s, CH3),
20.7 (s, CH3), 20.6 (2C, s, CH3), 20.5 (s, CH3), 20.5 (s, CH3), 20.4 (2C, s, CH3)
ppm; 19F NMR (282 MHz, CDCl3) δ -233.4 (1F, td, 2JF-H6 47.3, 2JF-H6‫ ׳‬47.3, 3JF-H5 22.6),
-233.6 (1F, td, 2JF-H6 46.2, 2JF-H6‫ ׳‬46.2, 3JF-H5 23.6 Hz) ppm;
F NMR [1H] (282 MHz,
19
CDCl3) δ -233.4 (1F, br. s.), -233.6 (1F, s) ppm.
6.4 Synthesis of 3-Deoxy-3-fluorogalactopyranose 2.3
6.4.1
3-O-acetyl-1,2:5,6-Di-O-isopropylidene-α-D-erythrohex-3-enose
The ketone 2.6 (2.3g, 8.905 mmol) was dissolved in pyridine (5.049 mL,
62.432 mmol) and Ac2O (2.524 mL, 26.756mmol) was added drop wise to the
reaction mixture at 60 ºC. The reaction mixture was cooled to rt after 14h
when the reaction was complete (monitored by TLC), and the mixture was
poured onto ice (20 g). The aqueous layer was washed with DCM (3×60 mL)
and extracted. Pouring over ice, washing with DCM (3×60 mL) and extraction
was repeated to get rid of more pyridine. The organic layer was then washed
88
Chapter 6: Experimental
with saturated NaHCO3 to neutralize any formed acetic acid. The combined
organic extracts were dried over MgSO4 and concentrated to remove all the
volatiles. During concentration minimal amounts of toluene and chloroform
were added to further remove the remaining pyridine and finally afforded 2.14,
2.25 g (94%). Mw 300.30 (C14H20O7); Rf 0.20 (EtOAc/PE 30:70); 1H NMR (300
MHz, CDCl3) δ 6.03 (1H, d, J 5.5 Hz), 5.40 (1H, d, J 5.4 Hz), 4.71 (1H, t, J 6.4
Hz), 4.08 (1H, d, J 2.9 Hz), 4.06 (1H, d, J 2.6 Hz), 2.22 (3H, s), 1.54 (3H, s),
1.47 (3H, s), 1.45 (3H, s), 1.38 (3H, s) ppm;
C NMR (75 MHz, CDCl3) δ 168.9
13
(s), 145.3 (s), 129.0 (s), 113.4 (s), 110.4 (s), 104.0 (s), 80.8 (s), 68.6 (s), 65.9
(s), 27.9 (s), 27.8 (s), 25.8 (s), 25.6 (s), 20.5 (s) ppm. 1HNMR data corresponded
to those reported by Raju et al.56 13C NMR was not reported in the literature.
6.4.2 3-O-acetyl-1,2:5,6-di-O-isopropylidene-α-D-gulofuranose
To a solution of 3-O-acetyl-1,2:5,6-di-O-isopropylidine-α-D-erythrohex-3-enose,
2.14 (1.0 g, 3.33 mmol) in CH3OH (23 mL) was added 20% Pd(OH)2 on charcoal
(0.031 g). The mixture was cooled to -25 ºC and rapidly stirred under H2. The
temperature was then raised slowly and maintained between -15 ºC and -10 ºC.
The reduction was complete after 7h (monitored by TLC). The residue was
purified on silica gel column chromatography (EtOAc/PE 30:70 mixture
containing 0.5% TEA). The eluent was concentrated and dried under vacuum to
afford a white solid 2.15, 0.65 g (64%). Mw 302.32 (C14H22O7);
Rf 0.25
(EtOAc/PE 30:70); 1H NMR (400 MHz, CDCl3) δ 5.82 (1H, d, J 4.0 Hz), 5.07 (1H,
t, J 6.3 Hz), 4.81 (1H, dd, J 5.3, 4.3 Hz), 4.62 (1H, dt, J 9.0, 6.9 Hz), 4.04–4.14
(2H, m), 3.53 (1H, t, J 7.8 Hz), 2.13 (3H, s), 1.58 (3H, s), 1.44 (3H, s), 1.39 (3H,
s), 1.35 (3H, s) ppm;
C NMR (101 MHz, CDCl3) δ 169.6 (s), 114.4 (s), 109.2
13
(s), 105.0 (s), 81.3 (s), 78.4 (s), 75.1 (s), 71.7 (s), 66.3 (s), 26.7 (2C, s) 26.6 (s)
25.2 (s) 20.6 (s) ppm. The 1HNMR data corresponded to those reported by Raju
et al.56 13C NMR details were not reported.
89
Chapter 6: Experimental
6.4.3 1,2:5,6-Di-O-isopropylidene-α-D-gulofuranose
The gulofuranose, 2.15 (0.62 g, 2.050 mmol) was dissolved in CH3OH (20 mL)
and CH3ONa (1.8 mL, 0.5M in CH3OH) was added drop wise and stirred at rt.
After 2h the reaction was complete. The mixture was concentrated in vacuum
followed by purification on silica gel column chromatography (EtOAc/PE 50:50
mixture containing 0.5% TEA that afforded a white solid 2.16, 0.46 g (87%).
Mw 260.28 (C12H20O6); Rf 0.28 (EtOAc/PE 50:50); 1H NMR (400 MHz, CDCl3) δ
5.78 (1H, d, J 4.0 Hz), 4.66 (1H, dd, J 6.3, 4.1 Hz), 4.48 (1H, dt, J 8.4, 7.1 Hz),
4.17–4.26 (2H, m), 3.90 (1H, dd, J 8.6, 5.8 Hz), 3.71 (1H, dd, J 8.5, 7.3 Hz),
2.67 (1H, d, J 6.4 Hz), 1.63 (3H, s), 1.45 (3H, s), 1.42 (3H, s), 1.38 (3H, s) ppm;
C NMR (101 MHz, CDCl3) δ 115.0 (s), 109.2 (s), 105.3 (s), 84.3 (s), 79.9 (s),
13
75.5 (s), 69.7 (s), 66.3 (s), 27.1 (s), 27.1 (s), 26.7 (s), 25.2 (s) ppm. The 1HNMR
details corresponded with the one reported by Raju et al.56 13CNMR details were
not reported.
6.4.4 3-Deoxy-3-fluoro-1,2;5,6-di-O-isopropylidene-α-D-galactofuranose
To a solution of 2.16 (0.46 g, 1.77 mmol) in dry DCM (10 mL) was added
pyridine (0.46 mL, 5.65 mmol). This was followed by drop wise addition of
DAST (0.37 mL, 2.83 mmol) at 0 ºC. The mixture was stirred at rt for 15h when
TLC indicated the reaction complete and then carefully poured onto NaHCO3
solution (10 mL). The organic layer was separated, washed with brine (10 mL),
dried over MgSO4, filtered and concentrated. Toluene was added and
evaporated to get rid of the remaining pyridine. The resulting residue was
purified by silica gel column chromatography (EtOAc/PE 05:95 mixture
containing 0.5% Et3N that afforded a white solid 2.17, 0.33 g (72%). Mw 262.27
(C12H19FO5); Rf 0.22 (EtOAc/PE 05:95); 1H NMR (300 MHz, CDCl3) δ 5.92 (1H, d,
J 3.8 Hz), 4.84 (1H, dd, J 42.7, 3.4 Hz, H3), 4.72 (1H, dd, J 6.1, 3.7 Hz), 4.34
(1H, q, J 6.7 Hz), 4.15 (1H, dd, J 7.2, 3.3 Hz), 4.05–4.12 (1H, m), 3.83 (1H, dd,
90
Chapter 6: Experimental
J 8.4, 6.5 Hz), 1.55 (3H, s), 1.44–1.48 (3H, s), 1.38 (3H, s), 1.36 (3H, s) ppm;
C NMR (75 MHz, CDCl3) δ 113.8 (s), 110.1 (s), 105.0 (s), 94.7 (d, J 181.9 Hz,
13
C3), 84.7 (d, J 25.7 Hz), 84.5 (d, J 30.7 Hz, C2), 74.9 (d, J 7.7 Hz), 65.6 (s),
27.1 (s), 26.5 (s), 26.4 (s), 25.2 (s) ppm; 19F NMR (282 MHz, CDCl3) δ -187.5
(1F, ddd, J 51.8, 24.7, 15.0 Hz) ppm. The 1HNMR and
CNMR corresponded
13
with those reported by Raju et al.56 19F NMR details were not reported.
6.4.5 1,2,4,6-Tetra-O-acetyl-3-deoxy-3-fluoro-D-galactopyranose
A combination of procedures by Withers et al.54 and Raju et al.,56 was followed.
A solution of 2.3 (impure) (1.0 g, 5.49 mmol) in dry pyridine (8.89 mL) was
cooled to 0 ºC. Ac2O (5.28 mL) was slowly added and the mixture kept stirring
for 48h at rt. It was then cooled to 0 ºC and MeOH (5 mL) was added. After 1h
the solution was evaporated and dried in vacuum for 18h. Water (15mL) and
EtOAc (30 mL) were added, shaken and the layers separated. The organic layer
was washed with water (15 mL) and brine (15 mL), separated, dried over MgSO4
and filtered. The residue was dissolved in pyridine/toluene (1:1) and
evaporated. Purification by silica gel column chromatography (EtOAc/PE 30:70
mixture containing 0.5% TEA), followed by crystallization using the same
eluent afforded 2.18, 1.67 g (87%). MW 350.29 (C14H19FO9); Rf 0.26 (EtOAc/PE
30:70); 1H NMR (400 MHz, CDCl3) δ 6.40 (1H, t, J 4.2 Hz, H1), 5.68 (1H, ddd, J
6.0, 3.9, 1.0 Hz, H4), 5.40 (1H, td, J 10.6, 3.8 Hz, H2), 4.95 (1H, ddd, J 48.7,
10.2, 3.7 Hz, H3), 4.29 (1H, br. t, J 6.6, 6.6 Hz, H5), 4.16 (1H, dd, J 11.4, 6.5
Hz, H6), 4.08 (1H, ddd, J 11.2, 6.7, 1.0 Hz, H6‫)׳‬, 2.18 (3H, s, CH3), 2.16 (3H, s,
CH3), 2.08 (3H, s, CH3), 2.07 (3H, s, CH3) ppm;
C NMR (101 MHz, CDCl3) δ
13
ppm 170.4 (s, C=O), 169.8 (s, C=O), 169.8 (s, C=O), 168.7 (s, C=O), 89.9 (d, J
9.5 Hz, C1), 85.5 (d, J 192.9 Hz, C3), 68.7 (d, J 5.5 Hz, C5), 67.6 (d, J 19.1 Hz,
C2), 67.3 (d, J 16.9 Hz, C4), 61.3 (d, J 2.2 Hz, C6), 20.8 (s, CH3), 20.6 (s, CH3),
20.6 (s, CH3 ), 20.5 (s, CH3) ppm;
F NMR (376 MHz, CDCl3) δ -200.30 (1Fβ,
19
ddd, J 47.3, 11.5, 5.2 Hz), -204.13 (1Fα, ddt, J 48.5, 10.7, 5.2, 5.2 Hz) ppm.
Before crystallization, furanose anomers were observed:
91
F NMR (282 MHz,
19
Chapter 6: Experimental
CDCl3) δ -188.3 (1F, ddd, J 51.6, 23.6, 16.1 Hz), -199.0 (1F, dt, J 55.9, 21.5
Hz), -200.3 (1F, ddd, J 47.3, 11.8, 5.4 Hz), -204.1 (1F, ddt, J 48.4, 10.7, 5.4,
5.4 Hz) ppm; These NMR data corresponded with those reported by Kovac
68
and Hoffmann-Roder.67
6.4.6 3-Deoxy-3-fluoro-D-galactopyranose
Sodium methoxide (0.31mL, 0.5M in MeOH) was added to 2.18 (1.10 g, 3.14
mmol) in dry MeOH (20 mL). The mixture was stirred overnight at rt when TLC
showed the reaction complete. The reaction mixture was then neutralized with
dowex 50-W (H+) resin (1.0 g), filtered through celite and concentrated. The
resulting crude was purified by silica gel column chromatography (DCM/MeOH
80:20) that afforded 2.3, 0.457 g (80%). Crystallization obtained 2.3 with some
traces of furanose anomers which were not separated even on further
purification by HPLC. MW 182.15 (C6H11FO5); Rf 0.20 (DCM/MeOH 80:20); 1H
NMR (300 MHz, MEOH-d4) δ 3.66 (1H, t, J 3.9 Hz, H1α), 3.11 (1H, ddd, J 50.1,
9.3, 2.9 Hz, H3α), 2.93 (1H, d, J 7.3 Hz, H1β), 2.68 (1H, ddd, J 45.5, 9.1, 3.3
Hz, H3β), 2.52 (4H, m, H2,4, OH), 2.21 (4H, m, 6α,β), 2.00 (2H, t, J 5.8 Hz,
H5α,β), 1.79 (8H, br. s, OH) ppm;
C NMR (75 MHz, MEOH-d4) δ 98.4 (d, J 11.9
13
Hz, C1β), 95.2 (d, J 184.4 Hz, C3β), 94.6 (d, J 10.2 Hz, C1α), 92.9 (d, J 183.5
Hz, C3α), 75.5 (d, J 6.9 Hz, , C5β), 72.3 (d, J 18.0 Hz, C2β), 71.2 (d, J 6.1 Hz,
C5α), 69.3 (d, J 16.9 Hz, C4α), 69.0 (d, J 17.7 Hz, C2α), 68.6 (d, J 16.9 Hz, C4β),
62.4 (d, J 2.2 Hz, C6α), 62.3 (d, J 2.8 Hz, C6β) ppm; 19F NMR (282 MHz, MeOHd4) δ -200.20 (1F, dd, J 43.0, 12.9 Hz), -204.93 (1F, d, J 51.6 Hz) ppm. These
spectra details corresponded to those reporteded by Ioannou et al.63
92
Chapter 6: Experimental
6.5 Synthesis of 2,3-Dideoxy-2,3-difluoro-α,β-Dglucopyranose 1.45
6.5.1 1,6-Anhydro-2-deoxy-2-iodo-β-D-glucopyranose
D-Glucal
3.1 (2.0 g, 13.70 mmol) and molecular sieves were placed into a flask
under nitrogen and dry acetonitrile (80 mL) was added. The mixture was
stirred with warming until D-glucal dissolved. Bis (tributyltin) oxide (5.5 mL,
10.93 mmol) was added and the colourless solution heated under reflux for 3h
until the solution became opaque. The mixture was allowed to cool to rt and
solvent removed by evaporation under vacuum. The residue was taken up in
dry DCM (80 mL) under nitrogen at rt and subsequently cooled in an ice/water
bath. Iodine (4.2 g, 16.44 mmol) was added to the DCM solution and the
mixture stirred at 0 ºC for 15 min and then filtered through celite with several
rinse with DCM. The filtrate and DCM washings were combined and their
volume reduced to 5 mL by evaporation. The concentrated DCM was diluted
with hexane (50 mL) and stirred with aqueous sodium thiosulfate (50 mL) for
12h. The aqueous phase was extracted with EtOAc (6×100 mL), dried (MgSO4)
and evaporated of solvent. The crude was purified by column chromatography
(hexane/acetone 70:30 mixture containing 0.5% TEA) that afforded 3.2, 3.31 g
(89%). Mw 272.04 (C6H9IO4); Rf 0.26 (hexane/acetone 70:30); 1H NMR (300
MHz, DMSO-d6) δ 5.61 (1H, s, H1), 5.50 (1H, d, J 3.3 Hz, OH3), 5.18 (1H, d, J
3.0 Hz, OH4), 4.42 (1H, d, J 4.1 Hz, H5), 4.01 (1H, d, J 6.8 Hz, H6), 3.94 (1H,
br. s., H3), 3.82 (1H, br. s., H2), 3.52 (1H, t, J 5.9 Hz, H6‫)׳‬, 3.45 (1 H, br. s.,
H4) ppm;
C NMR (75 MHz, DMSO-d6) δ ppm 102.6 (s, C1), 76.0 (s, C5), 74.7
13
(s, C6), 72.0 (s, C3), 65.2 (s, C4), 45.7 (s, C2). The 1H NMR data matched with
those reported by Lateux et al.137 The
C NMR details were not reported in the
13
literature.
93
Chapter 6: Experimental
6.5.2 1,6:2,5-Dianhydro-4-O-benzyl-β-D-mannopyranose
O
O
HO
O
BnCl, NaH,
DMF
I
85%
OH
3.2
BnO
O
O
3.3
The iodide, 3.2 (0.87 g, 3.20 mmol) twice evaporated from acetonitrile was
dissolved in DMF (20 mL) and cooled to -20 ºC. Benzyl chloride (1.84 mL,
16.00 mmol) and sodium hydride (0.31, 12.8 mmol, 60% in mineral oil) were
added and reaction stirred for 2h (-20 ºC to rt). After completion of the
reaction (monitored by TLC), water (10 mL) was added carefully and the
mixture diluted with Et2O (10 mL). The aqueous layer was extracted four times
with Et2O (50 mL). The combined organic layers were washed with brine, dried
over MgSO4, filtered and evaporated of solvent. Column chromatography
(EtOAc/PE 30:70 mixture containing 0.5% TEA) afforded 3.3, 0.549 g (85%). Mw
234.25 (C13H14O4); Rf 0.43 (EtOAc/PE 30:70); 1HNMR (300 MHz, CDCl3) δ ppm
7.29–7.49 (5H, m, HAr), 5.72 (1H, d, J 2.2 Hz, H1), 4.72 (2H, s, CH2Ph), 4.52
(1H, d, J 5.7 Hz, H4), 3.62–3.77 (3H, m, H5,6), 3.46 (1H, t, J 3.6 Hz, H2), 3.20
(1H, d, J2.2 Hz, H3);
C NMR (75 MHz, CDCl3) δ 137.3 (s, CAr), 128.6 (2C, s,
13
CAr), 128.1 (s, CAr), 127.8 (2C, s, CAr), 97.6 (s, C1), 73.7 (s, C2), 72.1 (s, C7),
71.6 (s, C3), 65.8 (s, C6), 54.4 (s, C4), 47.8 (s, C5) ppm. These NMR details
corresponded to those reported by Mabashery et al.73
6.5.3 1,6-Anhydro-4-O-benzyl-2-fluoro-β-D-glucopyranose
The epoxide 3.3 (2.3 g, 9.82 mmol) was boiled with potassium hydrogen
difluoride (10.28 g, 131.57 mmol) in ethylene glycol (40 mL) for 6h under
nitrogen. After completion of the reaction, the mixture was cooled and then
poured into 5% K2CO3 (20 mL). The mixture was then extracted with chloroform
(5×30 mL). After drying over MgSO4 and evaporation of solvent, the obtained
syrup was chromatographed on silica gel (chloroform/acetone 95:05 with
addition of 0.5% TEA and afforded 3.4, 1.63 g (65%). Mw 254.25 (C13H15FO4);
Rf 0.32 (chloroform/acetone 95:05); 1H NMR (400 MHz, CDCl3) δ 7.29–7.43
94
Chapter 6: Experimental
(5H, m, HAr), 5.55 (1H, d, J 5.3 Hz, H1), 4.73 (1H, d, J 12.1 Hz, CHPh ), 4.68
(1H, d, J 12.3 Hz, CH‫׳‬Ph), 4.62 (1H, d, J 5.3 Hz, H5), 4.27 (1H, dd, J 47.4, 3.3
Hz, H2), 4.00 (1H, dt, J 20.0, 5.5 Hz, H3), 3.88 (1H, d, J 7.5 Hz, H6), 3.69 (1H,
dd, J 7.3, 5.5 Hz, H6‫)׳‬, 3.35 (1H, br. d, J 3.4 Hz, H4), 2.33 (1H, br. d, J 5.4 Hz,
OH) ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 7.29–7.42 (5H, m, HAr), 5.55 (1H, s,
H1), 4.73 (1H, d, J 12.3 Hz, CHPh), 4.68 (1H, d, J 12.1 Hz, CH‫׳‬Ph), 4.62 (1H,
dd, J 5.3, 0.9 Hz, H5), 4.24–4.29 (1H, m, H2), 4.00 (1H, t, J 5.0 Hz, H3), 3.88
(1H, d, J 7.5 Hz, H6), 3.69 (1H, dd, J 7.5, 5.4 Hz, H6‫)׳‬, 3.35 (1H, br. d, J 3.5 Hz,
H4), 2.33 (1H, d, J 5.5 Hz, OH) ppm; 13C NMR (75 MHz, CDCl3) δ ppm 137.4 (s,
CAr), 128.5 (2C, s, CAr), 128.0 (s, CAr), 127.9 (2C, s, CAr), 99.5 (d, J 30.1 Hz, C1),
89.8 (d, J 183.5 Hz, C2), 78.2 (d, J 6.4 Hz, C4), 75.0 (s, C5), 71.7 (s, CH2Ph),
70.0 (d, J 26.8 Hz, C3), 66.2 (s, C6);
F NMR (282 MHz, CDCl3) δ -187.7 (1F,
19
ddd, J 47.3, 21.5, 4.3 Hz) ppm. The 1H and
C NMR details corresponded to
13
those reported by Jensen et al.
72
6.5.4 1,6-Anhydro-4-O-benzyl-2,3-difluoro-β-D-glucopyranose
O
O
O
F
BnO
OH
3.4
O
DAST,
Toluene
BnO
86%
F
F
3.5
To a solution of 3.4 (4.3 g, 16.91 mmol) in dry toluene (80.0 mL) was added
slowly at rt DAST (11.17 mL, 84.56 mmol). The mixture was refluxed under
nitrogen atmosphere for 24h when TLC indicated completion of the reaction.
Destruction of excess reagent was carried out by adding dry MeOH (10 mL)
very slowly at -20 ºC. The solvent was evaporated and the sample dried under
high vacuu. Column chromatography (EtOAc/PE 20:80 with addition of 0.5%
TEA afforded a colourless liquid 3.5, 3.67 g (86%). Mw 256.25 (C13H14F2O3); Rf
0.38 (EtOAc/PE 20:80); ES+MS: m/z 320.1: [M+ MeCN+Na]+ (83%); 1H NMR (300
MHz, CDCl3) δ 7.38 (5H, br. s., HAr), 5.58 (1H, br. s., H1), 4.76 (4H, dd, J 48.2,
17.0 Hz, H2, 5, 7; coupling for H2 observed), 4.42 (1H, dd, J 45.9, 15.6 Hz,
H3), 3.87 (1H, br. d, J 7.3 Hz, H6), 3.76 (1H, br. t, J 5.9, 5.9 Hz, H6‫)׳‬, 3.49 (1H,
br. d, J 16.8 Hz, H4) ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 7.30– 7.44 (5H, m,
HAr), 5.57 (1H, s, H1), 4.59– 4.84 (4H, m, 2,5,7), 4.42 (1H, br. d, J 16.0 Hz, H3),
3.87 (1H, d, J 7.5 Hz, H6), 3.76 (1H, t, J 6.6 Hz, H6‫)׳‬, 3.49 (1H, br. s., H4) ppm;
95
Chapter 6: Experimental
C NMR (75 MHz, CDCl3) δ 137.0 (1C, s, CAr), 128.6 (2C, s, CAr), 128.2 (1C, s,
13
CAr), 127.9 (2C, s, CAr), 98.7 (1C, dd, J 29.3, 2.5 Hz, C1), 88.6 (1C, dd, J 180.2,
31.0 Hz, C2), 85.8 (1C, dd, J 183.0, 27.4 Hz, C3), 74.8 (1C, dd, J 26.3, 5.0 Hz,
C4), 74.2 (1C, d, J 2.5 Hz, C5), 71.7 (1C, s, C7), 65.5 (1C, d, J 2.5 Hz, C6) ppm;
F NMR (282 MHz, CDCl3) δ -187.2 (1F, tt, J 29.0, 15.0 Hz), -192.4 (1F, dt, J
19
46.2, 14.0 Hz) ppm; 19FNMR [1H] (282 MHz, CDCl3) δ -187.2 (1F, d, J 12.9 Hz), 192.4 (1F, d, J 12.9 Hz) ppm.
C NMR spectra details corresponded to those
13
reported by Sarda et al .71 The 1H NMR and 19F NMR data were not reported.
6.5.5 1,6-Anhydro-2,3-dideoxy-2,3-difluoro-β-D-glucopyranose
O
O
10% Pd/C,
H2 (atm)
F
BnO
O
O
F
HO
90%
F
F
3.5
3.6
To a solution of 3.5 (0.66 g, 0.23 mmol) in EtOAc (2.0 mL) was added 10%
Pd/C (0.03 g, 0.03 mmol). The mixture was stirred overnight in a hydrogen
atmosphere when TLC indicated completion of the reaction. The catalyst was
filtered through celite and the solvent evaporated. This afforded a white solid
α]D: -68.7 (c 0.94 , CHCl3, 28oC); Rf
3.6, 0.038 g (90%). Mw 256.25 (C6H8F2O3); [α
0.13 (EtOAc/ PE 20:80); 1H NMR (300 MHz, CDCl3) δ 5.57 (1H, br. s., H1), 4.63
(1H, br. d, J 5.2 Hz, H5), 4.70 (1H, br. dd, J 43.9, 12.4 Hz, H3), 4.42 (1H, dd, J
44.3, 12.2 Hz, H2), 4.06 (1H, d, J 7.7 Hz, H6), 3.68–3.92 (2H, m, H4, 6‫)׳‬, 2.78
(1H, d, J 10.9 Hz, OH) ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 5.57 (1H, s, H1),
4.69 (1H, br. s., H5), 4.63 (1H, d, J 5.0 Hz, H3), 4.43 (1H, d, J 6.6 Hz, H2), 4.07
(1H, d, J 7.6 Hz, H6), 3.85 (1H, t, J 6.7 Hz, H6‫)׳‬, 3.78 (1H, br. d, J 11.1 Hz,
H4), 2.72 (1H, d, J 11.2 Hz, OH) ppm;
C NMR (75 MHz, CDCl3) δ 98.5 (1C, d,
13
J 27.6 Hz, C1), 88.1 (1C, dd, J 181.1, 29.6 Hz, C3), 84.3 (1C, dd, J 180.2, 29.0
Hz, C2), 75.7 (1C, s, C5), 67.6 (1C, d, J 27.4 Hz, C4), 64.7 (1C, d, J 4.4 Hz,
C6) ppm; 19F NMR (282 MHz, CDCl3) δ-187.53 (1F, ddd, J 43.0, 25.8, 12.9 Hz),
-193.92 (1F, dt, J 47.3, 12.9 Hz) ppm;
F [1H] NMR (282 MHz, CDCl3) δ-187.5
19
(1F, d, J 12.9 Hz), -193.9 (1F, d, J
12.9 Hz) ppm. The
C NMR data
13
corresponded to those reported by Sarda et al.71 The 1H NMR and
spectra details were not reported.
96
F NMR
19
Chapter 6: Experimental
6.5.6 1,4,6-Tri-O-acetyl-2,3-dideoxy-2,3-difluoro-D-glucopyranose
To a solution of 3.6 (0.35 g, 2.11 mmol) in Ac2O (2.0 mL) was added a solution
of Ac2O (2.0 mL) containing sulfuric acid (98%, 0.4 mL). The mixture was
stirred at rt for 7 days. After neutralization with 5% cold solution of NaHCO3 (5
mL), the organic layer was extracted with EtOAc (30 mL × 2), washed with
water (30 mL), brine (30 mL), dried over MgSO4 and evaporated of solvent. The
crude was purified by column chromatography (EtOAc/PE 20:80) that afforded
a novel compound, 3.7, 0.39 g, (60%). Mw 310.24 (C12H16F2O7); Rf 0.32
(EtOAc/PE 20:80); IR (neat) 1743 (s, C=O), 1368 (m), 1202 (s), 1149 (m), 1009
(s) cm-1; ES+MS: m/z 374.1 [M + MeCN + Na] + (100%); 1H NMR (400 MHz, CDCl3)
δ 6.43 (1H, t, J 3.7 Hz, simplifies to d, J 4.1 Hz upon F-decoupling, H1α), 5.74
(0.2H, dd, J 8.1, 3.4 Hz, simplifies to d, J 8.2 Hz upon F-decoupling, H1β), 5.24
(1.2H, m (Σ32.2 Hz, major isomer), changes to t, J 10.3 Hz) upon F-decoupling,
H4α; and t, J 9.0 Hz, H-4β becomes visible), 4.88 (2H, dddd, J 53.4, 13.1, 9.1,
4.2 Hz, H3α,β), 4.61 (2H, dddd, J 50.9, 13.1, 8.9, 4.2 Hz, H2α,β), 4.27 (1H, dd, J
12.6, 4.2 Hz, H6β, signal for H6α is underneath), 4.08 (1H, dt, J 12.6, 1.9 Hz,
simplifies to dd, J 12.7, 2.4 Hz upon F-decoupling, H6‫׳‬β, signal for H6’α is
underneath), 4.01 (1H, dtd, J 10.1, 3.4, 3.4, 1.9 Hz, H5α), 3.76 (1H, ddd, J
10.2, 7.8, 3.5 Hz, H5β), 2.19 (6H, s, CH3), 2.13 (6H, s, CH3), 2.09 (6H, s, CH3)
ppm;
C NMR (101 MHz, CDCl3, major isomer only) δ 170.6 (C=O), 169.1
13
(C=O), 168.4 (C=O), 89.8 (dd, J 189.9, 19.4 Hz, C3), 88.5 (dd, J 22.0, 9.9 Hz,
C1), 86.5 (dd, J 194.7, 17.9 Hz, C2), 69.3 (d, J 7.3 Hz, C5), 67.1 (dd, J 19.0,
7.7 Hz, C4), 61.2 (C6), 20.71 (CH3), 20.63 (CH3), 20.58 (CH3), ppm;
F NMR
19
(282 MHz, CDCl3) δ-195.9 (0.15F, dq, J 52.7, 12.9 Hz, simplifies to d, J 14.0 Hz
upon H-decoupling, F3β), -200.4 (1F, dq, J 53.7, 12.9 Hz, simplifies to d, J 12.9
Hz upon H-decoupling, F3α), -201.2 (0.15F, dt, J 49.4, 14.0 Hz, simplifies to J
14.0 Hz upon H-decoupling, F2β), -203.0 (1F, dt, J 49.4, 12.9 Hz, simplifies to
d, J 12.9 Hz upon H-decoupling, F2α) ppm. This acetylated difluorosugar was
not reported in the literature.
97
Chapter 6: Experimental
6.5.7 2,3-Dideoxy-2,3-difluoro-α,β-D-glucopyranose
A solution of NaOMe (0.11 mL, 2 mmol, 0.5M in MeOH) was added to a
solution of 3.7 (0.36 g. 1.16 mmol) in dry MeOH. The mixture was stirred
overnight at rt. The reaction mixture was neutralized with Dowex 50-W (H+)
resin (0.5 g). Resin was filtered and the filtrate concentrated to get rid of
solvents.
The crude product was purified by column chromatography
(MeOH/DCM 10:90) and further purified by HPLC using the same eluent
afforded a colourless oily 1.45, 0.173g, (81%). Mw 184.14 (C6H10F2O4); Rf 0.30
(MeOH/DCM 10:90); [α
α]D: +50.6 (c 0.08, acetone, 19oC); IR (neat) 3315 (br.,
OH), 1024 (s, C–O) cm-1; ESI- -MS: m/z 183[M-H]- (35%); 1H NMR (400 MHz,
acetone-d6) δ 6.28 (1H, d, J 6.3 Hz, OHβ), 6.05 (1H, d, J 4.2 Hz, OHα), 5.38 (1H,
ddd, J 4.2, 3.9, 3.3 Hz, H1α), 4.90 (1H, d, J 5.3 Hz, OH), 4.83 (1H, ddd, J 8.6,
6.3, 4.3 Hz, H1β), 4.76 (1H, ddt, J 55.2, 14.0, 8.7, 8.7 Hz, H3α), 4.56 (1H, ddt, J
53.7, 16.0, 8.6, 8.6 Hz, H3β), 4.45 (1H, dddd, J 50.8, 13.4, 9.2, 3.9 Hz, H2α),
4.17 (1H, dddd, J 52.2, 14.5, 8.6, 7.7 Hz, H2β), 3.65–3.88 (5H, m, H4α,β5α,6α, β),
3.61 (2H, t, J 6.2 Hz, H6‫׳‬α,β), 3.35–3.41 (1H, m, H5β), 2.94 (3H, s, OH); 1H NMR
[19F] (400 MHz, acetone-d6) δ 6.24 (1H, br. d, J 5.6 Hz, OHβ), 6.01 (1H, br. d, J
3.4 Hz, OHα), 5.35 (1H, br. s., H1α), 4.86 (1H, br. d, J 5.1 Hz, OH), 4.66–4.83
(2H, m, H1β, 3α), 4.47–4.59 (1H, m, H3β), 4.34–4.47 (1H, m, H2α), 4.05–4.24
(1H, m, H2β), 3.61–3.86 (5H, m, H4α,β, 5α, 6α,β), 3.57 (2H, t, J 5.8 Hz, H6‫׳‬α,β),
3.24–3.39 (1H, m, H5β), 2.90 (3H, s, OH) ppm;
C NMR (101 MHz, acetone-d6)
13
δ 96.4 (dd, J 183.7, 17.6 Hz, C3β), 94.8 (dd, J 22.7, 11.0 Hz, C1β ), 94.6 (dd, J
179.7, 15.0 Hz, C3α), 92.7 (dd, J 182.2, 16.8 Hz, C2β) 91.3 (dd, J 20.9, 10.2
Hz, C1α), 89.7 (dd, J 191.4, 17.9 Hz, C2α), 76.3 (d, J 8.1 Hz, C5β), 72.2 (d, J 7.0
Hz, C5α), 69.7 (2C, dd, J 17.4, 6.4 Hz, C4α,β), 62.1 (2C, br. s., C6α+β), ppm;
F
19
NMR (282 MHz, acetone-d6) δ -195.6 (dq, J 53.7, 14.0 Hz, F3α), -199.7 (dt, J
51.6, 15.0 Hz, F2α), -201.6– -201.0 (m, F2+F3β), ppm;
F NMR [1H] (282 MHz,
19
acetone d6) δ -195.6 (d, J 14.0 Hz, F3α), -199.8 (d, J 14.0 Hz, F2α), -201.1 (d, J
14.0 Hz, Fβ), -201.4 (d, J 12.9 Hz, Fβ) ppm.
98
Chapter 6: Experimental
6.6 Synthesis of 2,3-Dideoxy-2,3-difluoro-Dgalactopyranose 1.46
6.6.1 1,6-Anhydro-2,3-dideoxy-2,3-difluoro[trifluoromethyl-sulfonyl]-Dglucopyranose
To a solution of 3.6 (0.38 g, 2.29 mmol) in dry DCM (4 mL) was added a
solution of trifluoromethanesulfonic anhydride (2.25 mL, 2.25 mmol, 1M in
DCM) in dry pyridine. The mixture was stirred for 3h at rt in nitrogen
atmosphere. After completion of reaction, the reaction mixture was diluted
with water (5 mL). The organic layer was extracted with DCM (20 mL × 2), dried
over MgSO4, filtered and concentrated. The obtained residue was purified by
column chromatography (EtOAc/PE 20:80) and afforded 3.11, 0.64 g, (94%).
Mw 298.18 (C7H7F5O5S); Rf 0.48 (EtOAc/PE 20:80); [α
α]D : -66.2 (c 0.94 , CHCl3,
30 oC); 1H NMR (300 MHz, CDCl3) δ 5.65 (1H, br. s, H1), 4.70–5.02 (3H, m, H–
3,4,5 ), 4.47 (1H, dd, J 45.3, 14.2 Hz, H2), 4.06 (1H, br. d, J 8.2 Hz, H6), 3.89
(1H, t, J 6.7 Hz, H6‫ )׳‬ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 5.56–5.73 (1H, br.
s, H1), 4.76–4.94 (3H, m, H3, 4, 5), 4.47 (1H, d, J 17.5 Hz, H2), 4.06 (1H, d, J
8.3 Hz, H6), 3.89 (1 H, dd, J 8.3, 6.1 Hz, H6‫ )׳‬ppm; 13C NMR (100 MHz, CDCl3)
δ 118.4 (d, J 319.1 Hz, CF3), 98.79 (d, J 28.2 Hz, C1), 87.16 (dd, J 183.0, 33.7
Hz, C3), 84.24 (dd, J 184.8, 26.0 Hz, C2), 80.35 (dd, J 31.5, 5.1 Hz, C4), 73.82
(s, C5), 65.12 (s, C6) ppm; 19F NMR (282 MHz, CDCl3) δ -74.8 (3F, s, CF3) -188.6
(1F, dtd, J 43.0, 27.9, 27.9, 14.0 Hz) -193.8 (1F, dt, J 45.1, 14.0 Hz) ppm;
F
19
NMR [1H] (282 MHz, CDCl3) δ -74.5 (3F, s), -188.3 (1F, d, J 14.0 Hz), -193.5 (1F,
d, J 14.0 Hz) ppm. This compound was synthesized by Sarda et al.,71 but no
identification details were reported.
99
Chapter 6: Experimental
6.6.2 1,6-Anhydro-4-benzoyl-2,3-dideoxy-2,3-difluoro-D-galactopyranose
To a solution of 3.11 (0.62 g, 2.08 mmol) in DMF was added sodium benzoate
(1.5 g, 10.40 mmol).The mixture was heated to 80 ºC for 24h under nitrogen
atmosphere. After completion of reaction (monitored by TLC) water (10 mL)
was added and the solution extracted with Et2O (30 mL × 3). The organic layer
was dried over anhydrous Na2SO4, filtered, evaporated of solvent and dried
under vacuum. The crude product was purified by column chromatography
(EtOAc/PE 10:90) followed by HPLC purification using the same eluent that
gave a white solid 3.12, 0.474 g, 84%. Mw 270.23 (C13H12F5O4); Rf 0.41
(EtOAc/PE 10:90); [α
α]D -31.3° (c 0.42 , CHCl3, 29 oC); 1H NMR (400 MHz, CDCl3)
δ 8.07–8.09 (1H, m, HAr), 8.05–8.07 (1H, m, HAr), 7.62 (1H, tt, J 7.6, 1.5 Hz, HAr),
7.45–7.52 (2H, m, HAr), 5.60–5.62 (1H, m, H1), 5.37 (1H, dt, J 25.8, 4.5 Hz,
H4), 5.14 (1H, m, J 47.0 Hz observed, H2), 4.69–4.72 (1H, m, H5), 4.67 (1H,
ddt, J 44.5, 11.1, 1.5, 1.5 Hz, H3), 4.41 (1H, d, J 7.6 Hz, H6), 3.83 (1H, t, J 6.3
Hz, H6‫ )׳‬ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 8.01–8.13 (2H, m, HAr), 7.62
(1H, t, J 7.0 Hz, HAr), 7.42–7.54 (2H, m, HAr), 5.61 (1H, s, H1), 5.31–5.45 (1H, m,
H4), 5.14 (1H, s, H2), 4.59– 4.76 (2H, m, H3,5), 4.41 (1H, d, J 7.6 Hz, H6), 3.83
(1H, t, J 6.2 Hz, H6‫ )׳‬ppm; 13C NMR (75 MHz, CDCl3) δ 165.1 (s, C=O), 133.7 (s,
CAr), 129.9 (2C, s, CAr), 128.8 (s, CAr), 128.6 (2C, s, CAr), 98.5 (d, J 26.0 Hz, C1),
86.1 (dd, J 183.3, 27.4 Hz, C3), 85.1 (dd, J 185.2, 32.6 Hz, C2), 71.8 (s, C5),
66.1 (d, J 15.8 Hz, C4), 64.5 (d, J 3.3 Hz, C6) ppm; 19F NMR (282 MHz, CDCl3) δ
-194.9 (1F, ddd, J 44.1, 15.0, 9.7 Hz), -205.9 (1F, m, J 47.3 Hz observed) ppm;
F NMR (282 MHz, CDCl3) δ -194.9 (1F, d, J 12.9 Hz), -205.9 (1F, d, J 17.2 Hz)
19
ppm. 13C NMR and [α]D data corresponded to those reported by Sarda et al.71
The 1H and 13C NMR data were not reported.
6.6.3 1,6-Di-O-acetyl-4-benzoyl-2,3-dideoxy-2,3-D-galactopyranose
100
Chapter 6: Experimental
To a solution of 3.12 (0.07 g, 0.26 mmol) in Ac2O (0.24 mL, 2.6 mmol) was
added a solution of Ac2O (0.24 mL) containing H2SO4 (98%, 0.1 mL). The
mixture was stirred at rt for 7 days. After completion of reaction, the reaction
mixture was neutralized with 5% cold solution of NaHCO3 (5 mL). The organic
layer was extracted with EtOAc (10 mL × 2), washed with water (10 mL), brine
(10 mL), dried over MgSO4, evaporated of solvent and dried under high
vacuum. The crude obtained was purified by column chromatography
(EtOAc/PE 20:80) that afforded a white solid 0.039 g, 41% yield of a novel
compound 3.13. Mw 372.32 (C17H18F2O7); Rf 0.23 (EtOAc/PE 20:80); IR (neat)
1724 (s, C=O), 1372 (m), 1213 (s), 1062 (m), 922 (s) cm-1; ES+MS: m/z
395.1[M + Na] + (100%); 436.1[M + MeCN + Na] + (46.6%);
H NMR (400 MHz,
1
CDCl3) δ 8.03–8.09 (2H, m, HAr), 7.59–7.65 (1H, m, HAr), 7.46–7.51 (2H, m, HAr),
6.57 (1H, t, J 4.0 Hz, H1), 5.93–5.99 (1H, m, H4) 5.13 (2H, m, J 52.0 Hz
observed, H2,3) 4.38 (1H, t, J 6.6 Hz, H5) 4.07–4.22 (2H, m, H6) 2.20 (3H, s,
CH3) 2.02 (3H, s, CH3) ppm; 13C NMR (75 MHz, CDCl3) δ 170.3 (s,C=O), 168.6 (s,
C=O), 165.2 (s, C=O), 133.8 (s, CAr), 133.7 (s, CAr), 129.9 (2C, s, CAr), 128.6 (2C,
s, CAr), 89.1 (dd, J 22.1, 9.1 Hz, C1), 86.4 (dd, J 192.9, 19.1 Hz, C2), 85.3 (dd, J
191.8, 19.6 Hz, C3), 68.8 (d, J 4.7 Hz, C5), 68.4 (dd, J 17.0, 7.9 Hz, C4), 61.3
(s, C6), 20.8 (s, CH3), 20.6 (s, CH3) ppm. Only the major isomer could be
observed in the 1H and
C NMR;
13
F NMR (282 MHz, CDCl3) δ -200.6 (1F, m, J
19
50.5 Hz observed), -204.7 (1F, m, J 46.2 Hz observed) -208.1 (1F, dt, J 54.8,
10.7 Hz), -209.7 (1F, dt, J 50.5, 9.7 Hz) ppm; 19F NMR [1H] (282 MHz, CDCl3) δ 209.7 (1F, d, J 14.0 Hz), -208.1 (1F, d, J 14.0 Hz), -204.7 (1F, d, J 12.9 Hz), 200.6 (1F, d, J 12.9 Hz) ppm.
6.6.4 1,6-Anhydro-2,3-dideoxy-2,3-difluoro-D-galactopyranose
O
O
BzO
K2CO3,
MeOH
F
96%
F
3.12
O
O
HO
F
F
3.15
A mixture of 3.12 (0.3 g, 1.19 mmol), K2CO3 (0.02 g, 0.12 mmol) and MeOH (2
mL) was stirred at rt for 3h. After completion of reaction, the solvent was
evaporated
in
vacuum
to
give
crude
that
was
purified
by
column
chromatography (acetone/PET 20:80) and afforded 0.546 g (96%) of 3.15. Mw
101
Chapter 6: Experimental
166.12 (C6H8F2O3); Rf 0.2 (acetone/PET 20:80); IR (neat) 3448 (br., OH), 1406
(s, C–F), 1130 (s, C–O) cm-1; LR-EI/CI MS: m/z: 166 [M+•]; 1H NMR (300 MHz,
CDCl3) δ 5.51 (1H, br. d, J 0.7 Hz, H1), 4.88 (1H, m, J 47.1 Hz observed, H3),
4.63 (1H, m, J 44.2 Hz observed, H2), 4.46–4.55 (1H, m, H5), 4.04–4.23 (2H,
m, H4,6), 3.73 (1H, br. t, J 6.4, 6.4 Hz, H6‫)׳‬, 2.44 (1H, dd, J 9.1, 3.7 Hz, OH)
ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 5.51 (1H, br. t, J 1.3, 1.3 Hz, H1), 4.88
(1H, dtt, J 6.3, 3.1, 3.1, 1.5, 1.5 Hz, H3), 4.60–4.65 (1H, m, H2), 4.52 (1H, br.
t, J 4.7, 4.7 Hz, H5), 4.10–4.17 (2H, m, H4,6), 3.73 (1H, ddd, J 7.9, 5.3, 0.6 Hz,
H6‫)׳‬, 2.48 (1H, d, J 7.7 Hz, OH) ppm; 13C NMR (75 MHz, CDCl3) δ 98.0 (d, J 26.0
Hz, C1), 87.2 (dd, J 177.7, 33.2 Hz, C3), 86.0 (dd, J 182.2, 27.6 Hz, C2), 73.9
(s, C5), 64.6 (d, J 17.7 Hz, C4), 63.4 (d, J 3.3 Hz, C6) ppm; 19F NMR (282 MHz,
CDCl3) δ -195.2 (1F, m, J 43.0 Hz, observed), -208.5 (1F, m, J 51.6 Hz,
observed) ppm;
F NMR [1H] (282 MHz, CDCl3) δ -195.2 (1F, d, J 12.9 Hz), -
19
208.5 (1F, d, J 17.2 Hz) ppm. The compound was also synthesised by Sarda et
al,71 but no NMR details were reported.
6.6.5 1,4,6-Tri-O-acetyl-2,3-dideoxy-2,3-difluoro-D-galactopyranose
Acetylation/acetolysis of 3.15 (0.5 g, 3.01 mmol) followed the same procedure
as for 3.7 and afforded a colourless oil 3.16, 0.39 g (42%). Mw 310.24
(C12H16F2O7); Rf 0.34 (acetone/PET 20:80); IR (neat) 1743 (s, C=O), 1372 (m, C–
F), 1206 (s, C–O) cm-1; ESI+MS: m/z 333 [M+Na]+ (100%); 1H NMR (300 MHz,
CDCl3) δ 6.47 (1H, br. t, J 4.2, 4.2 Hz, H1), 5.59–5.77 (1H, m, H4), 4.83–5.17
(2H, m, H2,3), 4.27 (1H, br. t, J 6.6, 6.6 Hz, H5), 3.96–4.22 (2H, m, H6), 2.18
(3 H, s, CH3), 2.17 (3H, s, CH3), 2.06 (3H, s, CH3) ppm; 13C NMR (75 MHz, CDCl3)
δ 170.3 (s, C=O), 169.6 (s, C=O), 168.6 (s, C=O), 89.1 (dd, J 22.4, 9.4 Hz, C1),
86.2 (dd, J 192.4, 19.1 Hz, C2), 85.1 (dd, J 191.6, 19.9 Hz, C3), 68.5 (dd, J
4.8, 1.0 Hz, C5), 67.7 (dd, J 17.1, 8.0 Hz, C4), 61.0 (d, J 1.7 Hz, C6), 20.8 (s,
CH3), 20.6 (s, CH3), 20.5 (s, CH3) ppm. Only the major isomer could be
observed in the 1H and
C NMR;
13
F NMR (282 MHz, CDCl3) δ -201.0 (1F, m, J
19
46.2 Hz, observed), -205.2 (1F, m, J 47.3 Hz, observed), -208.4 (1F, m, J 51.6
Hz, observed), -210.0 (1F, m, J 51.6 Hz, observed) ppm;
102
F NMR [1H] (282
19
Chapter 6: Experimental
MHz, CDCl3) δ -201.0 (1F, d, J 12.9 Hz), -205.2 (1F, d, J 12.9 Hz), -208.4 (1F, d,
J 14.0 Hz), -210.0 (0F, d, J 12.9 Hz) ppm.
6.6.6 2,3-Dideoxy-2,3-difluoro-D-galactopyranose
Hydrolysis procedure on 3.7 was applied on 3.16 (0.3 g, 0.97 mmol) and
afforded a mixture of compounds which were not separated even by HPLC. We
propose the mixture to be of the galactopyranose and galactofuranose
anomers 1.46 as the
F NMR shows important peaks of the 2,3-dideoxy-2,3-
19
difluoro-D-galactopyranose that corresponded to the Methyl-2,3-dideoxy-2,3difluoro-D-galactopyranoside that was made later. Mw 184.14 (C6H10F2O4); Rf
0.26 (MeOH/DCM 10:90);
F NMR (282 MHz, acetone-d6) δ -201.1 (1F, m, J
19
49.4 Hz observed) -206.5 (1F, m, J 48.4 Hz observed) -209.2 (1F, dt, J 53.7,
14.0 Hz) -210.5 (1F, m, J 50.5 Hz observed) ppm;
F NMR (282 MHz, acetone-
19
d6) δ -201.1 (1F, d, J 12.9 Hz), -206.5 (1F, d, J 17.2 Hz), -209.2 (1F, d, J 17.2
Hz), -210.6 (1F, d, J 17.2 Hz) ppm.
6.6.7 Methyl-2,3-dideoxy-2,3-difluoro-D-galactopyranose
A solution of 3.15 (0.1 g, 0.86 mmol) in DCM (4 mL) was stirred at 0 ºC. BCl3
(2.58 mL, 2.58 mmol; 1M solution in DCM) was added and the mixture stirred
at 0 ºC for 30 min, and then at rt for 1h. After total consumption of the
starting material, MeOH (3.5 mL) was added and stirred for 2h. The solvent
was evaporated and the crude product purified by column chromatography
that gave a yellow oil 3.17, 0.04 g (22%). Mw 198.16 (C7H12F2O4); Rf 0.3
(acetone/PET 40:60); IR (neat) 3372 (br., OH) 2945 (m, C–H) 1138-1361(s, C–F)
1028 (s, C–O) cm-1; ESI+-MS: m/z 221 [M+Na]+ (100%); 1H NMR (400 MHz,
acetone-d6) δ 4.96 (1H, d, J 4.3 Hz, 1Hα), 4.86 (2H, m, J 53.3 Hz, observed,
103
Chapter 6: Experimental
H2α,3α), 4.58 (3H, m, J 54.7 Hz observed, H1,2β,3β), 4.21–4.36 (2H, m, H4α,β),
3.97 (1H, t, J 5.6 Hz, H5β), 3.90 (1H, t, J 5.4 Hz, 5Hα), 3.71–3.83 (2H, m, H6α),
3.63 (2H m, H6β), 3.49 (3H, s, CH3β), 3.38 (3H, s, CH3α), 2.90 (2H, s, OHα), 2.60
(2H, s, OHβ) ppm;
H NMR [19F] (400 MHz, acetone-d6) δ 4.96 (1H, d, J 3.8 Hz,
1
H1α), 4.80-4.90 (2H, m, H3α,β), 4.73 (1H, dd, J 8.8, 3.5 Hz, H1β), 4.45–4.57 (2H,
m, H2α,β), 4.32 (1H, t, J 3.5 Hz, H5α), 4.26 (1H, t, J 3.9 Hz, H5β), 3.96 (1H, t, J
5.3 Hz, H4β), 3.90 (1H, t, J 5.3 Hz, H4α), 3.72–3.83 (2H, m, H6α), 3.60-3.65 (2H,
m, 6β), 3.56 (2H, br.,s, OHα), 3.49 (3H, s, CH3β), 3.38 (3H, s, CH3α), 2.91 (2H, br.
s., OHβ) ppm;
C NMR (101 MHz, acetone-d6) δ 101.9 (dd, J 22.4, 11.0 Hz, 1α),
13
98.6 (dd, J 20.2, 9.5 Hz, 1β), 92.8 (dd, J 185.6, 16.9 Hz), 91.0 (dd, J 179.4,
18.7 Hz), 90.3 (dd, J 184.1, 17.2 Hz), 88.0 (dd, J 187.8, 18.0 Hz), 74.9 (dd, J
6.4, 0.9 Hz, C5α), 71.3 (dd, J 5.5, 1.1 Hz, C5β), 69.3 (dd, J 16.5, 7.7 Hz, C4β),
68.6 (dd, J 16.5, 8.4 Hz, C4α), 61.9 (dd, J 2.8, 0.9 Hz, C6β), 61.6 (dd, J 3.1, 0.9
Hz, 6α), 56.8 (br. s, CH3α), 55.4 (s, CH3β) ppm;
F NMR (376 MHz, acetone-d6) δ
19
-201.1 (1F, m, J 48.6 Hz observed) -205.0 (1F, m, J 53.8 Hz, observed) -209.7
(1F, m, J 53.8, observed) -212.3 (138 F, m, J 50.3 Hz, observed) ppm; 19F NMR
[1H] (376 MHz, acetone-d6) δ -201.1 (1F, d, J 13.9 Hz) -205.0 (1F, d, J 13.9 Hz)
-209.7 (1F, d, J 13.9 Hz) -212.3 (1F, d, J 13.9 Hz) ppm.
6.7 Synthesis of 2,3-Dideoxy-3-fluoro-D-glucopyranose 1.49
6.7.1 1,6-Anhydro-4-benzyl-2-deoxy-D-arabino-hexopyranose
To a refluxing solution of LiAlH4 (2.82 mL, 2.82 mmol; 1M solution in THF) in
THF (6 mL) was added drop wise a solution of 3.3 (0.6 g, 2.56 mmol) in THF (3
mL) in 30 min. Refluxing was continued for 2h. The reaction mixture was
cooled to rt and quenched by successive addition of water (2 mL), aqueous
NaOH solution (15%, 2 mL) and again water (2 mL). More water (20 mL) was
added to dissolve more of the aluminium salts and this was followed by
extraction with EtOAc (3×20 mL). The combined organic phases were washed
with water, dried (MgSO4) and evaporated in vacuum to give a crude product
that was purified by column chromatography (acetone/PE 30:70) resulting to a
104
Chapter 6: Experimental
as a brown liquid 3.18, 0.52 g, (87%). Mw 236.26 (C13H16O4); Rf 0.23
(acetone/PE 30:70); IR (neat) 3451 (br., OH), 1452 (s, CH), 1126 (s, CO) cm1;
ESI+MS: m/z 275.2 (M+K)+ (53%); 1H NMR (400 MHz, CDCl3) δ ppm 7.28–7.41
(5H, m, HAr), 5.65 (1H, br. s, H1), 4.71 (1H, d, J 12.2 Hz, CHPh), 4.66 (1H, d, J
12.3 Hz, CH‫׳‬Ph), 4.60 (1H, br. d, J 5.4 Hz, H5), 4.18 (1H, d, J 7.6 Hz, H6), 3.93
(1H, br. s., H3), 3.72 (1H, dd, J 7.5, 5.4 Hz, H6‫)׳‬, 3.46 (1H, d, J 1.1 Hz, H4),
2.71 (1H, d, J 4.4 Hz, OH), 2.22 (1H, ddd, J 15.0, 5.3, 1.4 Hz, H2), 1.84 (1H, d,
J 15.0 Hz, H2‫ )׳‬ppm;
13
C NMR (101 MHz, , CDCl3) δ 137.8 (s, CAr), 128.5 (2C, s,
CAr), 127.9 (s, CAr), 127.8 (2C, s, CAr), 101.0 (s, C1), 77.8 (s, C4), 74.5 (s, C5),
71.6 (s, CH2Ph), 66.6 (s, C3), 65.2 (s, C6), 35.9 (s, C2) ppm. The compound
was synthesised by Kochetkov et al.,138 but no characterisation was reported.
6.7.2 1,6-Anhydro-4-benzyl-2,3-dideoxy-3-fluoro-D-glucopyranose
To a solution of 3.18 (2.6 g, 11.0 mmol) in dry toluene (40.0 mL) was added
slowly at rt DAST (7.3 mL, 55.02 mmol). The mixture was refluxed under argon
for 24h. Destruction of excess reagent was carried out by adding dry MeOH (10
mL) very slowly at -20 ºC. The solvent was evaporated and the sample dried
under vacuum. Column chromatography (EA/PE 20:80) afforded a brown liquid
of 3.19, 1.9 g (73%). Mw 256.25 (C13 H14F2O3); Rf 0.3 (EA/PE 20:80); [α
α]D: -55.6
(c 0.25, CHCl3, 19oC); IR (neat) 2952 (m), 1493 (w), 1452 (w), 1039 (s) cm-1;
EI-MS: m/z 238, (M+•); 1H NMR (300 MHz, CDCl3) δ 7.28–7.44 (5H, m, HAr), 5.58
(1H, br. s, H1), 4.72 (1H, d, J 12.1 Hz, CHPh), 4.72 (1H, m, coupling of 46.5
can be observed, reduced to m upon F-decoupling, simplified to dd, J 45.9, 4.9
Hz upon H4-decoupling, H3), 4.68 (1H, d, J 12.1 Hz, CH‫׳‬Ph), 4.61 (1H, d, J 6.3
Hz, H5, no change upon H4-decoupling), 4.06 (1H, d, J 7.4 Hz, H6), 3.77 (1H,
ddd , J 6.7, 6.3, 3.7 Hz, simplifies to dd, J 6.7, 6.3 Hz upon F-decoupling,
simplifies to dd, J 5.7, 3.3 Hz upon H6-decoupling, H6‫)׳‬, 3.53 (H, br. d, J 13.3
Hz, simplifies to br.s upon F-decoupling, H4), 2.15 (1H, dddd, J 40.0, 15.5,
4.9, 1.6 Hz, reduces to m upon F-decoupling), 2.03 (1H, dd, J 22.7, 15.4 Hz,
simplifies to d, J 15.8 Hz upon F-decoupling, H2) ppm;
105
C NMR (101 MHz,
13
Chapter 6: Experimental
CDCl3) δ 137.3 (s, CAr), 128.6 (2C, s, CAr), 128.1 (s, CAr), 127.8 (2C, s, CAr), 99.4
(d, J 1.5 Hz, C1), 86.5 (d, J 175.6 Hz, C3), 75.1 (d, J 26.3 Hz, C4), 73.4 (s, C5),
71.7 (s, CH2Ph), 64.5 (d, J 5.1 Hz, C6), 33.9 (1 C, d, J 20.1 Hz, C2) ppm;
F
19
NMR (282 MHz, CDCl3) δ -176.5 (ddddd, J 46.5, 40.0, 22.7, 14.0, 3.7 Hz) ppm.
This compound has not been reported in the literature.
6.7.3 1,6-Anhydro-2,3-dideoxy-3-fluoro-D-glucopyranose
To a solution of 3.19 (0.24 g, 1.0 mmol) in MeOH (3.0 mL) was added 10%
Pd/C (0.2 g, 0.15 mmol).139 The mixture was degassed with H2 (1 atm) for about
30 min and then stirred under hydrogen atmosphere at rt for 24h. The catalyst
was filtered through celite and the solvent evaporated in vacuum. The crude
was purified by column chromatography (acetone/PE 30:70) to give a white
solid 0.11 g (74%) of 3.20. Mw 148.13 (C6H9FO3); Rf 0.16 (acetone/ PE 30:70);
[α
α]D: -101.6 (c 0.25, CHCl3, 19oC); IR (neat) 3391 (br., OH), 2964 (m, C–H), 1334
(s, C–F), 1126 (s, C–O) cm-1; EI-MS: m/z 148, (M+•); 1H NMR (400 MHz, CDCl3) δ
5.56 (1H, br., s, H1), 4.67 (1H, ddd, J 46.4, 8.5, 1.3 Hz, H3), 4.54 (1H, br. d, J
5.8 Hz, H5), 4.20 (1H, d, J 7.6 Hz, H6), 3.77–3.87 (2H, m, H4, 6), 2.51 (1H, d, J
9.9 Hz, OH), 2.00–2.19 (2H, m, H2), ppm; 1H NMR [19F NMR] (400 MHz, CDCl3) δ
5.56 (1H, br. s, H1), 4.63–4.68 (1H, m, H–3), 4.54 (1H, br. d, J 5.8 Hz, H5),
4.20 (1H, d, J 7.6 Hz, H6), 3.78–3.86 (2H, m, H–4, 6‫)׳‬, 2.54 (1H, d, J 9.7 Hz,
OH), 1.98–2.15 (2H, m, H2), ppm; 13C NMR (75 MHz, CDCl3) δ 99.7 (br. d, J 1.7
Hz, C1), 88.1 (d, J 176.9 Hz, C3), 75.3 (s, C5), 68.6 (d, J 26.8 Hz, C4), 64.3 (d,
J 5.5 Hz, C–6), 33.2 (1C, d, J 20.7 Hz, C2) ppm;
F NMR (282 MHz, CDCl3) δ -
19
177.4 (1F, ddddd, J 46.0, 38.1, 23.7, 11.0, 3.9 Hz) ppm; This compound has
not been reported in the literature.
6.7.4 2,3-Dideoxy-3-fluoro-D-glucopyranose
106
Chapter 6: Experimental
A solution of 3.20 (0.05 g, 0.34 mmol) in THF:water (1:1, 3 mL) and ptoluenesulfonic acid (9.4 mg, 0.054 mmol) was refluxed for 48h. The mixture
was cooled to rt and partitioned between EtOAc and saturated NaHCO3. The
layers were separated and the aqueous phase was extracted with EtOAc (3×10
mL). The combined organic extract was dried (MgSO4) and evaporated in
vacuum to give crude product that was purified by column chromatography
(MeOH/DCM 10:90) to give brown oil of 1.49, 0.019 g (34%). Mw 166.15 (C6
H11FO4); Rf 0.23 (MeOH/DCM 20:80); [α
α]D +78.8
(c 0.60, acetone, 20oC); IR
(neat) 3312 (br., OH), 1244 (s, C–F), 1058 (s, C–O) cm-1; EI-MS: m/z 166, (M+•);
1H NMR (400 MHz, acetone-d6) δ 5.78 (0.5H, bd, J 5.7 Hz, OH1β), 5.39 (1H,
bs, OH1α), 5.34 (1H, bs – d, J 2.3 Hz can be observed, H1α), 4.84 (0.5H, m
(Σ10 Hz), H1β, becomes visible upon F-decoupling), 4.78 (1H, dddd, J 52.6,
11.4, 8.6, 5.4 Hz, simplifies to ddd, J 11.4, 8.6, 5.5 Hz upon F-decoupling,
H3α), 4.63 (0.5H, bd, J 4.9 Hz, OH4β), 4.61 (1H, d, J 5.1 Hz, OH4α), 4.52 (0.5H,
dddd, J 50.9, 11.6, 8.5, 5.4 Hz, simplifies to ddd, J 11.7, 8.6, 5.6 Hz upon Fdecoupling H3β), 3.86–3.65 (4H, m, H6α,β + H5α), 3.63–3.48 (3H, m, H4α,β +
OH6α+β), 3.18–3.25 (1H, m, simplifies to ddd, J 9.5, 5.1, 3.0 Hz upon Fdecoupling, H5α), 2.31 (1H, dddd, J 12.0, 5.7, 4.5, 1.9 Hz, simplifies to, J 12.0,
5.6, 1.9 Hz upon F-decoupling, H2eq,α), 2.19 (1H, m (Σ 23.6 Hz), Hz, simplifies
to ddd, J 12.3, 5.5, 1.4 Hz upon F-decoupling, H2eq,β), 1.69 (1H, qd, J 11.6, 3.5
Hz, simplifies to td, J 11.9, 3.4 Hz upon F-decoupling, H2ax,α), 1.58 (1 H, qd, J
11.5, 9.7 Hz, simplifies to td, J 11.8, 9.6 Hz upon F-decoupling, H2ax,β);
C
13
NMR (101 MHz, acetone-d6) δ 94.2 (d, J 16.1 Hz, C1β), 93.8 (d, J 177.8 Hz,
C3β), 92.5 (d, J 14.6 Hz, C1α), 92.4 (d, J 176.0 Hz, C3α), 76.3 (d, J 8.0 Hz, C5β),
72.8 (d, J 7.3 Hz, C5α), 71.6 (d, J 17.6 Hz, C4α), 71.1 (d, J 17.6 Hz, C4β), 62.8
(d, J 2.2 Hz, C6β), 62.7 (d, J 1.8 Hz, C6α), 39.8 (d, J 17.6 Hz, C2β), 37.3 (d, J
17.2 Hz, C2α) ppm;
19
F NMR (282 MHz, acetone-d6) δ -184.5 (0.5F, dt, J 51.6,
12.9 Hz), -188.9 (1F, dt, J 51.6, 12.9 Hz) ppm.
107
Chapter 6: Experimental
6.8 Synthesis of 2,3-Dideoxy-3-fluoro-α,β-Dgalactopyranose 1.50
6.8.1 1,6-Anhydro-2,3-dideoxy-3-fluoro-(trifluoromethyl)-D-glucopyranose
To a solution of 3.20 (0.7 g, 4.72 mmol) in dry DCM (10 mL) was added a
solution of trifluoromethanesulfonic anhydride (0.9 mL, 5.2 mmol) in pyridine
(15 mL). The mixture was stirred for 3h at rt in argon atmosphere. After
completion of reaction, the mixture was diluted with water (10 mL). The
organic layer was extracted with DCM (3×20 mL), dried (MgSO4), filtered and
solvent
evaporated
in
vacuum.
The
crude
was
purified
by
column
chromatography (acetone/PE 20:80) and afforded a white solid 3.21, 1.15 g
(87%). MW C7H8F4O5S: 280.19, Rf 0.46 (acetone / PE20:80); [α
α]D: -81.3 (c 0.60,
CHCl3, 20oC); IR (neat) 2975 (m, C–H), 1410 (s, C–F), 1130 (s, C–O) cm-1; EI-MS:
m/z 280, (M+•); 1H NMR (400 MHz, CDCl3) δ 5.65 (1H, s, H1), 4.88–4.92 (1H, m,
H4), 4.77-4.81 (1H, m, H5), 4.79 (1H, m, J 49.8 Hz observed H3), 4.18 (1H, d, J
8.2 Hz, H6), 3.88 (1H, ddd, J 8.2, 6.0, 3.8 Hz, H6‫)׳‬, 2.06–2.29 (2H, m, H2),
ppm;1H NMR [19F] (400 MHz, CDCl3) δ 5.65 (1H, br. s), 4.88 (1H, br. s, H4),
4.82–4.86 (1H, m, H5), 4.73–4.77 (1H, m, H3), 4.18 (1H, dd, J 8.2, 1.1 Hz, H6),
3.88 (1H, dd, J 8.3, 6.1 Hz, H6‫)׳‬, 2.09–2.22 (2H, m, H2) ppm;
C NMR (101
13
MHz, CDCl3) δ 118.4 (q, 2J C–F 319.7 Hz, CF3), 99.4 (s, C1), 85.5 (d, 1JC3–F3 178.8
Hz, C3), 80.8 (d, 2JC4–F3 31.7 Hz, C4), 73.2 (s, C5), 64.2 (d, 5JC6–F3 4.8 Hz, C6),
33.2 (d, 3JC2–F3 20.5 Hz, C2) ppm;
F NMR (376 MHz, CDCl3) δ -74.9 (3F, s) -
19
176.9 (1F, ddddd, J 48.5, 35.4, 23.4, 10.6, 3.7 Hz) ppm. This compound was
not reported in the literature.
6.8.2 1,6-Anhydro-4-benzoyl-2,3-dideoxy-3-fluoro-D-galactopyranose
108
Chapter 6: Experimental
To a solution of 3.21 (1.0 g, 3.57 mmol) in DMF (15 mL) was added sodium
benzoate (2.57 g, 17.85 mmol). The mixture was heated to 80 ºC for 24h
under argon. Water (20 mL) was then added and the solution extracted with
EtOAc (3×30 mL). The organic layer was dried (Na2SO4), filtered and evaporated
of
solvent.
The
crude
was
purified
by
column
chromatography
(acetone/PE20:80) followed by HPLC to afford 3.22, 0.71 g (79%).
MW
C13H13FO4: 252.24, Rf 0.36 (acetone/PE 20:80); IR (neat) 2960 (m, C–H), 1712
(s, C=O), 1266 (s, C–F), 1111 (s, C–O) cm-1; EI-MS: m/s 252, (M+•); 1H NMR (400
MHz, CDCl3) δ 8.04–8.14 (2H, m, HAr), 7.57–7.66 (1H, m, HAr), 7.43–7.53 (2H, m,
HAr), 5.63 (1H, s, H1), 5.22–5.32 (1H, m, H4), 5.13 (1H, m, 2JH3–F 50.6 Hz
observed, H3), 4.63 (1H, br. t, J 4.6, 4.6 Hz, H5), 4.57 (1H, d, J 7.5 Hz, H6),
3.85 (1H, ddt, J 7.0, 5.5, 1.3, 1.3 Hz, H6‫)׳‬, 2.29–2.41 (1H, m, H2), 2.02–2.20
(1H, m, H2‫ )׳‬ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 8.05–8.12 (2H, m, HAr),
7.58–7.64 (1H, m, HAr), 7.44–7.51 (2H, m, HAr), 5.63 (1H, d, J 1.1 Hz, H1), 5.26
(1H, td, J 4.1, 1.2 Hz, H4), 5.15 (1H, tq, J 4.1, 1.4 Hz, H3), 4.63 (1H, t, J 4.7
Hz, H5), 4.57 (1H, br. d, J 7.5 Hz, H6), 3.82–3.87 (1H, m, H6‫)׳‬, 2.35 (1H, dt, J
15.6, 1.6 Hz, H2), 2.11 (1H, ddd, J 15.5, 4.0, 1.8 Hz, H2‫ )׳‬ppm;
13
C NMR (101
MHz, CDCl3) δ 165.3 (s, C=O), 133.6 (s, CAr), 129.9 (2C, s, CAr), 129.2 (s, CAr),
128.5 (2C, s, CAr), 99.7 (d, J 1.5 Hz, C1), 85.5 (d, 1JC3–F181.6 Hz, C3), 72.2 (d, J
1.1 Hz, C5), 68.9 (d, J 15.8 Hz, C4), 65.5 (d, J 4.4 Hz, C6), 37.0 (d, J 19.8 Hz,
C2) ppm;
F NMR (376 MHz, CDCl3) δ -196.0 (dddd, J 52.3, 38.1, 25.4, 19.1
19
Hz) ppm.
6.8.3 1,6-Anhydro-2,3-dideoxy-3-fluoro-D-galactopyranose
A mixture of 3.22 (0.3 g, 1.19 mmol), K2CO3 (0.02 g, 0.12 mmol) and MeOH (2
mL) was stirred at rt for 3h. After completion of reaction, the solvent was
evaporated in vacuum and the crude purified by column chromatography
(acetone/PE 20:80) that gave a white solid of 3.23, 0.2 g (96%). MW C6H9FO3:
148.13, Rf 0.2 (acetone/PE 20:80); IR (neat) 3414 (br., OH), 2967 (m, C–H),
1417(s, C–F), 1126 (s, C–O) cm-1; ESI-MS: m/z 147.1 (M-H)- (34%); 1H NMR (400
109
Chapter 6: Experimental
MHz, CDCl3) δ 5.53 (1H, s, H1), 4.92 (1H, m J 50.2 Hz observed, H3), 4.45 (1H,
br. t, J 4.7, 4.7 Hz, H5), 4.27 (1H, d, J 7.8 Hz, H6), 3.97 (1H, m, J 25.5 Hz
observed, H4), 3.74 (1H, tt, J 7.5, 1.4 Hz, H6‫)׳‬, 2.57 (1H, dd, J 9.7, 5.0 Hz, OH),
2.30 (1H, br. dd, J 20.3, 15.7 Hz, H2), 2.00 (1H, dddd, J 41.3, 15.9, 4.2, 1.8
Hz, H2‫ )׳‬ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 5.51–5.54 (1H, m, H1), 4.92
(1H, tq, J 4.2, 1.3 Hz, H3), 4.45 (1H, br. t, J 4.8, 4.8 Hz, H5), 4.27 (1H, d, J 7.7
Hz, H6), 3.97 (1H, dt, J 9.3, 4.3, 4.3 Hz, H4), 3.72–3.77 (1H, m, H6‫)׳‬, 2.60 (1H,
d, J 9.5 Hz, OH), 2.30 (1H, dt, J 15.7, 1.5 Hz, H2), 2.00 (1H, ddd, J 15.7, 4.2,
2.0 Hz, H2‫ )׳‬ppm; 13C NMR (101 MHz, CDCl3) δ 99.0 (d, J 1.1 Hz, C1), 88.2 (d, J
173.5 Hz, C3), 74.3 (d, J 0.7 Hz, C5), 67.5 (d, J 18.0 Hz, C4), 64.3 (d, J 4.0 Hz,
C6), 36.7 (d, J 20.2 Hz, C2) ppm;
F NMR (282 MHz, CDCl3) δ -198.7 (1F, m J
19
52.0 Hz, observed) ppm.
6.8.4 2,3-Dideoxy-3-fluoro-α,β-D-galactopyranose
Similar procedure as for synthesis of 1.49 was used on 3.23 (0.125 g, 0.84
mmol) and afforded after column chromatography and HPLC purification an
inseparable anomeric mixture of galactopyranose 1.50 and galactofuranose
3.24, 0.012 g, (9%). MW C6H11FO4: 166.15, Rf 0.2 (MeOH / DCM 10:90); IR
(neat) 3312 (br., OH), 2941 (m, C–H), 1240 (s, C–F), 1013 (s, C–O) cm-1; 1H NMR
(400 MHz, acetone-d6) δ 5.68 (1H, d, J 7.1 Hz), 5.60–5.66 (1H, m), 5.57 (1H, t, J
5.1 Hz), 5.35 (1H, q, J 3.6 Hz), 5.33 (1H, ddt, J 45.4, 6.2, 1.4, 1.4 Hz), 5.22
(1H, dd, J 3.4, 1.8 Hz), 5.19 (1H, ddt, J 46.7, 6.5, 1.7, 1.7 Hz), 5.03 (1H, dd, J
4.8, 1.0 Hz), 4.90 (1H, dddd, J 48.1, 11.9, 5.1, 3.1 Hz), 4.71–4.79 (1H, m),
4.67 (1H, ddddd, J 54.9, 13.8, 10.9, 7.6, 4.9 Hz), 4.43 (1H, t, J 2.3 Hz), 4.35–
4.39 (1H, m), 4.30–4.33 (1H, m), 4.08–4.17 (2H, m), 3.90–4.03 (6H, m), 3.63–
3.79 (7H, m), 3.51–3.62 (2H, m), 3.27–3.44 (1H, m), 2.84 (4H, s), 2.27–2.44
(1H, m), 2.10–2.27 (2H, m), 2.07–2.09 (1H, m), 1.94–2.03 (2H, m), 1.82–1.91
(2H, m) ppm; 13C NMR (101 MHz, Acetone) δ 99.8 (s), 99.7 (s) 99.7 (s), 97.2 (d,
JC-F 175.0 Hz), 96.1 (d, 1JC-F 175.7 Hz), 94.8 (d, J 16.5 Hz), 92.8 (d, J 14.3 Hz),
1
90.8 (d, 1JC-F 180.5 Hz), 89.0 (d, 1JC-F 177.9 Hz), 85.9 (d, J 23.5 Hz), 85.0 (d, J
25.3 Hz), 75.1 (d, J 7.3 Hz), 72.7 (d, J 8.8 Hz), 72.2 (d, J 9.9 Hz), 71.1 (d, J 6.2
110
Chapter 6: Experimental
Hz), 67.7 (d, J 16.9 Hz), 66.4 (d, J 16.1 Hz), 64.0 (d, J 2.9 Hz), 62.7 (d, J 3.3
Hz), 62.4 (d, J 3.7 Hz), 42.8 (d, J 21.3 Hz), 41.6 (d, J 19.8 Hz), 35.2 (d, J 18.0
Hz), 32.2 (d, J 18.3 Hz) ppm;
F NMR (282 MHz, acetone-d6) δ -174.0–173.4
19
(1F, m), -174.7–174.1 (1F, m), -188.0 (1F, dd, J 47.3, 6.4 Hz), -191.2 (1F, d, J
48.4 Hz) ppm;
F NMR (376 MHz, acetone-d6) d -172.7 (1F, s), -173.3 (1F, s), -
19
186.9 (1F, s), -190.1 (1F, s) ppm
6.8.5 Methyl-2,3-dideoxy-3-fluorogalactopyranoside
Hydrolysis of 3.23 0.125 g (0.84 mmol) using BCl3 in MeOH (same procedure as
for
synthesis
of
3.17)
gave
the
corresponding
methyl-2,3-dideoxy-3-
fluorogalactopyranoside 3.25, 0.074 g in 51% yield. MW C7H13FO4: 180.17, Rf
0.4 (MeOH / DCM 10:90); IR (neat) 3383 (br., OH) 2835-2952 (m, C–H), 12021436 (s, C–F), 1016-1035 (s, C–O) cm-1; ESI+-MS: m/z 203 [M+Na] (100%); 1H
NMR (400 MHz, acetone-d6) δ 4.83 (1H, t, J 3.9 Hz, H1), 4.79 (1H, dddd, J
48.1, 12.1, 5.3, 3.2 Hz, H3), 4.08 (1H, m, H4), 3.71–3.84 (2H, m, H6), 3.68
(1H, q, J 5.4 Hz, H5), 3.42 (1H, s, OH), 3.28 (3H, s, CH3), 2.89 (1H, s, OH), 2.19
(1H, tdd, J 12.0, 12.0, 9.7, 3.8 Hz, H2ax), 1.87 (1H, dddt, J 12.1, 5.3, 4.1, 1.1,
1.1 Hz, H2eq) ppm;
1
H NMR [19F] (400 MHz, acetone-d6) δ 4.76–4.85 (2H, m,
H1,3), 4.00–4.12 (1H, m, H4), 3.71–3.80 (2H, m, H6), 3.68 (1H, q, J 5.4 Hz,
H5), 3.42 (1H, s, OH), 3.28 (3H, s, CH3), 2.85 (1H, br. s, OH), 2.19 (1H, td, J
12.0, 3.9 Hz, H2ax), 1.87 (1H, ddt, J 12.1, 5.3, 1.2, 1.2 Hz, H2eq) ppm, only
protons of the major isomer were observed;
C NMR (101 MHz, acetone-d6) δ
13
101.4 (d, J 16.9 Hz, C1α), 99.5 (d, J 14.3 Hz, C1β), 90.6 (d, J 170.2 Hz, C3α),
88.8 (d, J 178.6 Hz, C3β), 75.2 (d, J 7.0 Hz, C5α), 71.5 (d, J 6.2 Hz, C5β), 67.4
(d, J 16.5 Hz, C4β), 66.6 (d, J 16.5 Hz, C4α), 62.7 (d, J 2.9 Hz, C6β) 62.3 (d, J
3.7 Hz, C6α) 56.4 (s, CH3α), 54.8 (s, CH3β), 33.3 (d, J 19.1 Hz, C2α), 31.4 (d, J
19.4 Hz, C2β) ppm;
19
F NMR (376 MHz, acetone-d6) δ -188.2 (1F, ddd, J 46.8,
13.9, 6.9 Hz), -190.2 (1F, br. d, J 48.6 Hz) ppm.
111
Chapter 6: Experimental
6.9 Synthesis of 2,3-Dideoxy-3,3-difluoro-D-glucopyranose
1.47
6.9.1 1,6-Anhydro-4-benzyl-2,3-dideoxy-3-keto-D-glucopyranose
Ac2O (1.3 mL, 13.46 mmol) was added to PDC (1.6 g, 4.27 mmol) in DCM (20
mL). There after 3.18 (1.0 g, 4.23 mmol) in DCM (2 mL) was added and the
mixture stirred at 75 ºC for 4h. The mixture was then diluted with EtOAc (20
mL) and the precipitate filtered. After evaporation of EtOAc, Et2O (20 mL) was
added and the mixture filtered again. Evaporation of solvents and drying under
vacuum followed by column chromatography purification (acetone/PE 20:80)
afforded 3.26 (0.79g, 73%). MW C13H14O4: 234.25, Rf 0.36 (acetone /PE 20:80);
[α
α]D: -10.5 (c 0.8, CHCl3, 19 oC); IR (neat) 2971 (m, CH), 1724 (s, C=O), 1111
(s, C–O) cm-1; ESI+-MS: m/z 257 (M+Na)+ (100%); H NMR (400 MHz, CDCl3) δ
7.29–7.39 (5H, m, HAr), 5.80 (1H, t, J 1.8 Hz, H1), 4.79 (1H, br., d, J 5.9 Hz,
H5), 4.71 (1H, d, J 12.1 Hz, CHPh), 4.50 (1H, d, J 12.1 Hz, CH‫׳‬Ph), 3.83 (1H,
dd, J 8.2, 5.9 Hz, H6), 3.71 (1H, dd, J 8.3, 1.3 Hz, H6‫)׳‬, 3.53 (1H, br. s, H4),
2.90 (1H, dd, J 16.1, 2.3 Hz, H2), 2.57 (1H, ddd, J 16.1, 2.1, 1.3 Hz, H2‫ )׳‬ppm;
C NMR (101 MHz, CDCl3) δ 202.4 (s, C3), 136.7 (s, CAr), 128.5 (2C, s, CAr),
13
128.3 (2C, s, CAr), 128.2 (s, CAr), 100.8 (s, C1), 80.8 (s, C4), 76.1 (s, C5), 71.6
(s, CH2Ph), 65.1 (s, C6), 47.0 (s, C2) ppm. This compound has not been
reported in the literature.
6.9.2 1,6-Anhydro-4-benzyl-2,3-dideoxy-3-difluoro-D-glucopyranose
A solution of 3.26 (1.36 g, 5.8 mmol) in DCM (15 mL), DAST (4.68 mL, 29.03
mmol), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) (0.07 mL,
0.58 mmol) and HF-py (0.01 mL, 0.58 mmol) were stirred at 45 ºC for 48h.
112
Chapter 6: Experimental
Cold saturated NaHCO3 (10 mL) was slowly added and the mixture extracted
with DCM (3×20 mL). The combined organic phases were washed with water
(20 mL) and brine (20 mL), dried over MgSO4 and then evaporated of solvent in
vacuum. The crude was purified by column chromatography (acetone/PE
05:95) and afforded a novel compound 3.27, 0.37 g (25%). MW C13H14F2O3:
256.25, Rf 0.33 (acetone/PE 10:90); [α
α]D: -27.2 (c 0.3, CHCl3, 19oC); IR (neat)
2979 (m, CH), 1334 (s, CF), 1073 (s, CO) cm-1; ESI+: m/z 320.2 (M + MeCN
+Na)+ (20%); 1H NMR (300 MHz, CDCl3) δ 7.29–7.45 (5H, m, HAr), 5.65 (1H, br. d,
J 6.9 Hz, H1), 4.95 (1H, d, J 12.2 Hz, CHPh), 4.70 (1H, d, J 12.2 Hz, CH‫׳‬Ph),
4.61 (1H, br. t, J 6.0, 6.0 Hz, H5), 3.96 (1H, dt, J 7.8, 1.3 Hz, H6), 3.69 (1H,
ddd, J 7.7, 6.0, 4.1 Hz, H6‫)׳‬, 3.55 (1H, br. d, J 12.3 Hz, H4), 2.15–2.35 (2H, m,
H2) ppm; 1H NMR [19F] (400 MHz, CDCl3) δ 7.29–7.44 (5H, m, HAr), 5.64 (1H, t, J
1.8 Hz, H1), 4.95 (1H, d, J 12.2 Hz, CHPh), 4.70 (1H, d, J 12.2 Hz, CH‫׳‬Ph),
4.59–4.63 (1H, m, H5), 3.96 (1H, dd, J 7.8, 1.3 Hz, H6), 3.69 (1H, dd, J 7.8, 6.1
Hz, H6‫)׳‬, 3.55 (1H, d, J 2.1 Hz, H4), 2.27 (2H, m, H2) ppm; 13C NMR (101 MHz,
CDCl3) δ 137.1 (s, CAr), 128.6 (2C, s, CAr), 128.2 (s, CAr), 128.1 (2C, s, CAr), 119.7
(dd, J 256.4, 245.0 Hz, C3), 99.0 (dd, J 11.6, 0.9 Hz, C1), 76.1 (dd, J 33.4,
19.1 Hz, C4), 75.4 (d, J 5.5 Hz, C5), 73.7 (d, J 4.4 Hz, CHPh), 64.5 (d, J 6.2 Hz,
C6), 38.6 (t, J 21.6 Hz, C2) ppm;
F NMR (282 MHz, CDCl3) δ -89.0 (1F, m, J
19
260.6 Hz, observed), -98.2 (1F, m, J 259.0 Hz, observed) ppm;
F NMR [1H]
19
(376 MHz, CDCl3) δ -88.9 (1F, d, J 260.1 Hz), -98.1 (1F, d, J 260.1 Hz) ppm.
This difluorosugar has not been reported in the literature.
6.9.3 2,3-Dideoxy-3,3-difluoro-D-glucopyranose
A solution of 3.27 (0.19 g, 0.74 mmol) in DCM (7 mL) was stirred at 0 ºC. BCl3
(2.2 mL, 2.2 2 mmol; 1M solution in DCM) was added and continued stirring at
0 ºC for 30 min and then at rt for 90 min. The mixture was then quenched with
100 equivalent of water (2 mL) and stirred at rt for 1h. The mixture was
concentrated in vacuum and the resulting residue immediately purified by
column chromatography (acetone/PET 30:70) that gave 1.47 0.015 g (11%).
113
Chapter 6: Experimental
MW C6H10F2O4: 184.14, Rf 0.3 (acetone/PE 50:50); [α
α]D: +42.6 (c 0.3, acetone,
19oC); IR (neat) 3330 (br., OH) 2941, 2877 (m, C–H), 1240 (s, C–F), 1073, 1017
(s, C–O) cm-1; ESI+-MS: m/z 207, (M+Na)+ (100%); 1H NMR (400 MHz, acetoned6) δ 5.98 (1H, br. s., OH1β), 5.39 (1H, q, J 4.2 Hz, H1α), 5.33 (1H, br. s.,
OH1α), 4.88–4.97 (1H, m, H1β), 4.71 (1H, d, J 6.2 Hz, H5β), 4.63 (1H, d, J 6.5
Hz, H5α), 3.60–4.02 (4H, m, H4,6α,β), 3.35–3.59 (2H, m, H6‫׳‬α,β), 2.80–2.90 (4H,
m, OH), 2.35 (1H, dddd, J 13.4, 12.2, 5.9, 2.2 Hz, H2βeq), 2.07–2.30 (2H, m,
H2α), 1.87 (1H, dddd, J 35.5, 13.3, 9.5, 3.9 Hz, H2βax) ppm;
H NMR [19F] (400
1
MHz, acetone-d6) δ 5.96 (1H, br. d, J 5.9 Hz, OH1β), 5.39 (1H, br. t, J 4.0, 4.0
Hz, H1α), 5.29–5.33 (1H, m, OH1α), 4.92 (1H, ddd, J 9.4, 5.6, 1.9 Hz, H1β), 4.69
(1H, d, J 6.7 Hz, H5β), 4.61 (1H, d, J 7.2 Hz, H5α), 3.99 (1H, dt, J 9.9, 3.6 Hz,
6α), 3.68–3.86 (2H, m, 4α,β), 3.55–3.66 (1H, m, H6β), 3.46 (1H, t, J 6.2 Hz, 6‫׳‬α),
3.40 (1H, ddd, J 9.9, 4.6, 2.7 Hz, 6‫׳‬β), 2.84 (4H, s, OH), 2.35 (1H, dd, J 13.5,
2.3 Hz, H2βeq), 2.26 (1H, dd, J 14.2, 1.2 Hz, H2α eq), 2.06–2.14 (1H, m, H2αax),
1.87 (1H, dd, J 13.4, 9.7 Hz, H2βax) ppm;
C NMR (101 MHz, acetone-d6) δ
13
122.0 (dd, J 247.6, 240.3 Hz, C3), 93.8 (d, J 13.6 Hz, C1), 76.1 (d, J 7.0 Hz,
C5), 69.2 (t, J 20.0 Hz, C4), 62.3 (d, J 1.8 Hz, C6), 42.5 (dd, J 22.7, 19.1 Hz,
C2) ppm; Only carbons of the β anomers were clearly seen. 19F NMR (282 MHz,
acetone-d6) δ -100.1 (1Fα, dt, J 237.6, 5.2 Hz), -102.5 (1Fβ, br. d, J 241.0 Hz), 113.0 (1 Fα, dddd, J 237.6, 32.9, 19.1, 12.1 Hz), -117.9 (1Fβ, dddd, J 241.0,
36.4, 20.8, 12.1 Hz) ppm;19F NMR [1H] (282 MHz, acetone-d6) δ -100.1 (1Fα, d, J
237.6 Hz), -102.6 (1Fβ, d, J 241.0 Hz), -113.0 (1Fα, d, J 237.6 Hz), -117.9 (1Fβ,
d, J 241.0 Hz) ppm.
6.9.4 Methyl-2,3-dideoxy-3,3-difluoro-α- and β-D-glucopyranoside
The procedure in Section 8.93 was repeated on 3.27 (0.13 g, 0.5 mmol)
however the workup was done by quenching with 100 equivalent of MeOH (7
mL) and afforded the two separable glucopyranoside anomers 3.29 and 3.30
0.035 g (35%) and 0.022 g (22%) respectively.
MW C7H12F2O4: 198.16, Rf 0.33 (acetone / PE 40:60); [α
α]D:
+138.1 (c 1.2, acetone, 19 oC); IR (neat) 3380 (br., OH) 2922 (m,
114
Chapter 6: Experimental
C–H), 1202 (s, C–F), 1028 (s, C–O) cm-1; ESI+-MS: m/z 278, (M + MeCN + K)+
(40%); 1H NMR (300 MHz, acetone-d6) δ 4.86 (1H, t, J 4.0 Hz, H1), 4.66 (1H, d,
J 6.3 Hz, OH), 3.62–3.87 (4H, m, 4,5,6), 3.29 (3H, s, CH3), 2.89 (1H, br. s, OH),
2.07–2.35 (2H, m, H2) ppm; 1H NMR [19F] (400 MHz, acetone-d6) δ 4.86 (1H, dd,
J 4.6, 0.9 Hz, H1), 4.67 (1H, d, J 6.2 Hz, OH), 3.64–3.86 (4H, m, H4,5,6), 3.29
(3H, s, CH3), 2.91 (1H, s, OH), 2.27 (1H, dd, J 14.4, 0.9 Hz, H2eq), 2.11–2.18 (1
H, m, H2ax) ppm; 13C NMR (75 MHz, acetone-d6) δ 121.2 (dd, J 246.8, 242.7 Hz,
C3), 97.9 (dd, J 13.3, 1.4 Hz, C1), 71.9 (d, J 6.4 Hz, C5), 69.2 (t, J 20.7 Hz,
C4), 62.1 (d, J 1.4 Hz, C6), 55.0 (s, CH3), 38.9 (dd, J 23.2, 22.1 Hz, C2) ppm;
F NMR (282 MHz, acetone-d6) δ -100.9 (1F, br. d, J 238.6 Hz), -113.5 (1F,
19
dddd, J 238.6, 34.4, 20.4, 14.0 Hz) ppm; 19F NMR [1H] (282 MHz, acetone-d6) δ
-100.9 (1F, d, J 238.6 Hz), -113.5 (1F, d, J 237.5 Hz) ppm.
MW C7H12F2O4: 198.16, Rf 0.33 (acetone/PE 40:60); [α
α]D: -5.65 (c
0.9, acetone, 19 oC); IR (neat) 3489 (br.,OH) 2926 (m, C–H),
1255 (s, C–F), 1104 (s, C–O) cm-1; EI-MS: m/z 198, (M+•); 1H NMR
(400 MHz, acetone-d6) δ 4.76 (1H, d, J 7.0 Hz, H5), 4.57 (1H, ddd, J 9.7, 2.1,
1.2 Hz, H1), 3.67–3.92 (4H, m, H4,6,OH), 3.45 (3H, s, CH3), 2.82–2.96 (1H, m,
OH), 2.33 (1H, dddd, J 13.5, 12.3, 5.8, 2.2 Hz, H2eq), 1.86 (1H, dddd, J 35.5,
13.2, 9.7, 3.7 Hz, H2ax) ppm; 1H NMR [19F] (400 MHz, acetone-d6) δ 4.77 (1H, d,
J 7.0 Hz, H5), 4.57 (1H, dd, J 9.7, 2.3 Hz, H1), 3.87 (1H, br. dd, J 11.5, 2.1 Hz,
H4), 3.71–3.79 (3H, m, H6,OH), 3.45 (3H, s, CH3), 2.80–3.00 (1H, m, OH), 2.33
(1H, dd, J 13.4, 2.2 Hz, H2eq), 1.86 (1H, dd, J 13.4, 9.7 Hz, H2ax) ppm; 13C NMR
(101 MHz, acetone-d6) δ 121.8 (dd, J 246.9, 240.6 Hz, C3), 100.4 (d, J 13.9
Hz, C1), 76.2 (d, J 7.0 Hz, C5), 69.2 (t, J 20.2 Hz, C4), 62.2 (d, J 1.8 Hz, C6),
56.6 (d, J 0.7 Hz, CH3), 40.9 (dd, J 22.7, 20.2 Hz, C2) ppm; 19F NMR (376 MHz,
acetone-d6) δ -102.7 (1F, dd, J 241.0, 3.5 Hz), -117.3 (1F, dddd, J 242.8, 34.7,
20.8, 12.1 Hz) ppm;
F NMR [1H] (376 MHz, acetone-d6) δ -102.7 (1F, d, J
19
242.8 Hz), -117.3 (1F, d, J 241.0 Hz) ppm.
115
Chapter 6: Experimental
6.10
Synthesis of 1,6-Anhydro-2-deoxy-2-fluoro-D-
glucopyranose 4.5
To a solution of 3.4 (0.2 g, 0.78 mmol) in MeOH (3 mL) was added 10% Pd/C
(0.02 g, 0.19 mmol). The mixture was degased with H2 for 15 min and then
stirred under 1 atmosphere of H2 at rt for 24h. The mixture was filtered
through a small plug of celite and concentrated in vacuum. The crude was
purified by column chromatography (acetone/PE 50:50) and afforded 4.5 0.12
g (91%). MW C6H9FO4: 164.13, Rf 0.26 (acetone / PE 40:60); IR (neat) 3308 (br.,
OH) 2967 (m, C–H), 1334 (s, C–F), 1039 (s, C–O) cm-1; ES+MS: m/z 203 (M + K)+
(100%); 1H NMR (400 MHz, acetone-d6) δ 5.40 (1H, d, J 5.0 Hz, H1), 4.56 (1H,
d, J 4.5 Hz, OH3), 4.51 (1H, dd, J 5.6, 1.0 Hz, H5) 4.17 (1H, dt, 1JH2-F 47.0, 1.3
Hz), 4.08 (1H, d, J 6.7 Hz, OH4), 4.03 (1H, d, J 7.2 Hz, H6), 3.78 (1H, ddd, J
20.2, 2.8, 1.2 Hz, H3) 3.63 (1H, t, J 6.5 Hz, H6‫ )׳‬3.54 (1H, br. d, J 6.8 Hz, H4)
ppm; 1H NMR [19F] (400 MHz, acetone-d6) δ 5.40 (1H, s, H1) 4.56 (1H, d, J 4.4
Hz, OH3), 4.51 (1H, dq, J 5.7, 1.4 Hz, H5), 4.15–4.18 (1H, m, H2), 4.08 (1H, d,
J 6.8 Hz, OH4) 4.01–4.04 (1H, m, H6), 3.78 (1H, dtt, J 4.4, 2.9, 2.9, 1.4, 1.4
Hz, H3), 3.63 (1H, ddd, J 7.1, 5.7, 0.4 Hz, 6‫)׳‬, 3.50–3.57 (1H, m, H4) ppm;
C
13
NMR (101 MHz, acetone-d6) δ 100.3 (d, J 30.1 Hz, C1) 91.2 (d, J 179.0 Hz, C2)
77.9 (s, C5) 72.9 (d, J 26.0 Hz, C3) 72.6 (d, J 5.5 Hz, C4) 66.3 (s, C6) ppm; 19F
NMR (376 MHz, acetone-d6) δ -186.9 (1F, ddd, J 46.8, 19.1, 5.2 Hz) ppm.
In CDl3
H NMR (400 MHz, CDCl3) δ 5.58 (1H, q, J 2.0 Hz, H1), 4.62 (1H, m, J 5.4 Hz,
1
observed, H5), 4.32 (1H, dq, J 45.2, 1.7 Hz, H2), 4.19 (1H, dd, J 7.6, 0.7 Hz,
H6), 4.00 (1H, dddt, J 15.8, 6.1, 3.9, 1.8, 1.8 Hz, H3), 3.81 (1H, ddd, J 7.3,
5.9, 0.9 Hz, H6‫)׳‬, 3.64 (1H, dq, J 10.8, 1.8 Hz, H4), 2.62 (1H, dd, J 10.8, 1.3
Hz, OH4), 2.23 (1H, d, J 6.4 Hz, OH3) ppm; 1H NMR [19F] (400 MHz, CDCl3) δ
5.58 (1H, t, J 1.7 Hz, H1), 4.62 (1H, m, J 5.4 Hz, observed, H5), 4.32 (1H, q, J
1.5 Hz, H2), 4.19 (1H, dd, J 7.6, 0.9 Hz, H6), 4.00 (1H, ddt, J 6.3, 3.7, 1.9, 1.9
Hz, H3), 3.81 (1H, dd, J 7.6, 5.6 Hz, H6‫)׳‬, 3.64 (1H, dq, J 10.9, 1.7 Hz, H4),
2.61 (1 H, d, J 10.9 Hz, OH4), 2.22 (1H, d, J 6.2 Hz, OH3) ppm;
116
19
F NMR (376
Chapter 6: Experimental
MHz, CDCl3) δ -187.6 ( br. dd, J 45.1, 15.6 Hz) ppm. No peaks were observed
for 13C NMR due to low concentration caused by low solubility in CDCl3.
6.11
Synthesis of Trans- and Cis-4-(tert-butyl)-1-
fluoromethylcyclohexanol
6.11.1 Cis- and trans-4-(tert-butyl)-1-oxiranecyclohexane
The procedure followed is the same as one used by Corey et al.91 Sodium
hydride (0.25 g, 10.5 mmol (0.42 g 60% mineral oil) was placed in a three neck
reaction flask fitted with a stirrer and stopper. It was then washed three times
with 10 mL portions of PE by swirling, allowing the hydride to settle and
decanting to remove the mineral oil. The flask was immediately taken to
vacuum to remove traces of PE. Then trimethyloxosulfonium iodide (2.31 g,
10.5 mmol) and dry THF (30 mL) were introduced and the system placed under
nitrogen. With stirring, the mixture was heated to reflux during which
evolution of hydrogen gas was observed rapidly at first and ceased after some
minutes. After 2-3 hours, rapid evolution of hydrogen gas began and after 4h
the reaction was complete shown by lack of hydrogen evolution. A solution of
the ketone, 5.1, (1.54 g, 10.0 mm0l) in dry THF (5 mL) was added to the
solution above and the mixture heated at reflux for 1h. The mixture was
evaporated to remove THF, and water (20 mL) was added and the mixture
extracted with pentane (2×30 mL). The extracts were washed with water (20
mL), dried over anhydrous Na2SO4 and evaporated of solvent to give the crude
product which was purified by column chromatography (EtOAc/PE 05:95) that
gave a mixture of the diastereoisomeric epoxides 5.2 and 5.3 (1.418 g). The
two diastereoisomers (cis- and trans- in the ratio 10:1 respectively) could not
be separated even on further purification by HPLC. Mw: 168.28 (C11H20O); Rf
0.38 (EtOAc/PE 05:95); 1H NMR (300 MHz, CDCl3) δ 2.64 (2H, s), 1.74–1.94
(4H, m), 1.25–1.46 (4H, m), 1.02–1.13 (1H, m), 0.89 (9H, s, HtBu) ppm; 13C NMR
117
Chapter 6: Experimental
(75 MHz, CDCl3) δ 58.3 (s), 53.8 (s), 47.2 (s), 33.4 (2C,s), 32.5 (s), 27.6 (3C, s,
CtBu), 24.8 (2C, s) ppm. These spectra details corresponded to those reported
by Franssen et al.140
6.11.2 Trans- and cis-4-(tert-butyl)-1-fluoromethylcyclohexanol
Potassium hydrogen difluoride (2.69 g, 34.47 mmol) was added to the
diastereoisomeric mixture of the epoxides 5.2 and 5.3 (2.9 g, 17.23 mmol) and
tetrabutylammonium dihydrogen trifluoride (2.96 g, 9.82 mmol). The mixture
was stirred at 115 ºC for 2.5 days. Et2O (50 mL) was added and the solution
poured into saturated NaHCO3 (50 mL) and extracted. The organic layer was
washed successfully with NaHCO3 (20 mL) and brine (20 mL); dried over
anhydrous MgSO4, filtered and evaporated of solvent. The crude product was
purified and separated by column chromatography (EtOAc/PE 05, 10, 20, 50:
95, 90, 80, 50 mixtures) that afforded 0.81 g (25%) and 0.80 g (25%) of 1.52
and 1.51 respectively.
Mw: 188.28 (C11H21FO); Rf 0.16 (EtOAc/PE 10:90); IR (neat) 3338 (br.,
OH), 2941 (m, CH3), 1361 (m, C–O) cm-1;
H NMR (300 MHz, CDCl3) δ
1
4.41 (2H, d, J 47.6 Hz, CH2F) 2.13 (1H, d, J 1.3 Hz, OH) 1.94 (2H, m, J
12.3, 1.9 Hz observed, H2eq,2‫׳‬eq) 1.67–1.82 (2H, m, H3eq,3‫׳‬eq) 1.35–1.53 (2H, m,
H2,2‫׳‬ax) 0.93–1.13 (3H, m, H3ax,3‫׳‬ax,4 ) 0.86 (9H, s, HtBu) ppm;
C NMR (75 MHz,
13
CDCl3) δ 86.4 (d, J 170.6 Hz, CH2F), 71.5 (d, J 17.1 Hz, C1), 47.3 (s, C4), 34.4
(s, C2) 34.4 (s, C2‫ )׳‬32.2 (s, CtBu), 27.5 (3C, s, tBu), 24.3 (2C, s, C3,3‫ )׳‬ppm; 19F
NMR (282 MHz, CDCl3) δ -235.0 (1F, tt, J 47.3, 5.4 Hz) ppm.
Mw: 188.28 (C11H21FO); Rf 0.28 (EtOAc/PE 10:90); IR (neat) 3380 (br.,
OH), 2945 (m, CH3), 1365 (m, C–O) cm-1; 1H NMR (300 MHz, CDCl3) δ
4.17 (2H, d, J 47.8 Hz, CH2F), 1.73 (2H, m, H2,2‫׳‬eq), 1.60–1.69 (3H,
m, H3, 3‫׳‬eq, OH), 1.25–1.48 (4H, m, H2,2‫׳‬,3,3‫׳‬ax), 0.92–1.04 (1H, m, H4), 0.88
(9H, s, HtBu) ppm;
C NMR (75 MHz, CDCl3) δ 90.9 (d, J 171.9 Hz, CH2F), 70.2
13
(d, J 17.7 Hz, C1), 47.9 (s, C4), 33.1 (2C, d, J 3.6 Hz, C2,2‫)׳‬, 32.4 (s, CtBu),
27.5 (3C, s, tBu), 21.6 (2C, d, J 1.1 Hz, C3,3‫ )׳‬ppm; 19F NMR (282 MHz, CDCl3) δ
118
Chapter 6: Experimental
-230.1 (1F, t, J 47.3 Hz) ppm. These two compounds were also synthesized by
Akiyama et al.89, but no identification details were given.
6.12
Synthesis of Trans- and Cis-4-(tert-butyl)-1-
difluoromethylcyclohexanol
6.12.1 Trans- and Cis-4-(tert-butyl)-1hydroxycyclohexyl(difluoromethyl)phosphonate
O
HO
CF2PO(OEt)2
BuLi, i-(Pr)2NH,
CHF2PO(OEt)2
tBu
THF, -74 °C
5.1
HO
CF2PO(OEt)2
+
tBu
5.4 (25%)
tBu
5.5 (32%)
The procedure used was as described by Beier et al.94 A solution of butyllithium
(6.30 mL, 15.75 mmol; 2.5M solution in hexane) was added drop wise to a
stirred solution of diisopropylamine (2.2 mL, 15.75 mmol) in THF (30 mL)
cooled at 0 ºC. The mixture was stirred at 0 ºC for 20 min and then cooled to 74 ºC. A solution of diethyldifluoromethylphosphonate (2.34 mL, 14.98 mmol)
in THF (8 mL) was added drop wise followed by stirring at this temperature for
30 min. A solution of the ketone 5.1, (3.0 g, 19.45 mmol) in THF (10 mL) was
then added and the mixture stirred for 4h at -74 ºC before being warmed up
to 0 ºC for 10 min. Saturated aqueous solution of NH4Cl (30 mL) was added
and the product extracted with Et2O (4×100 mL). The combined organic
extracts were washed with brine (20 mL), dried over anhydrous MgSO4, filtered
and concentrated under reduced pressure. The crude product was purified by
column chromatography (EtOAc/PE 10, 15, 20: 90, 85, 80 mixtures) and
afforded 5.4, 1.33 g and 5.5, 1.72 g.
Mw: 342.36 (C15H29F2O4P); Rf 0.27 (EtOAc/PE 20:80); IR (neat)
3391 (br., OH), 2956 (m, CH3), 1361 (m, C–O) cm-1. 1H NMR (300
MHz, CDCl3) δ 4.29 (4H, quin, J 7.2 Hz, OCH2), 2.92 (1H, s, OH),
1.94 (2H, m, H2), 1.43–1.70 (6H, m, H2‫׳‬,3, 3‫)׳‬, 1.39 (6H, t, 3JH–H
7.1 Hz, CH3), 0.99 (1H, tt, J 11.7, 3.0 Hz, H4), 0.87 (9H, s, HtBu) ppm ;
C NMR
13
(101 MHz, CDCl3) δ 120.3 (td, 1JC–F 269.0, 1JC–P 200.2 Hz, CF2P), 73.6 (td, J 20.9,
119
Chapter 6: Experimental
13.5 Hz, C1), 64.8 (2C, d, 2JC–P 7.0 Hz, OCH2), 47.4 (s, C4), 32.4 (s, CtBu), 30.2
(2C, q, J 2.9 Hz, C2,2‫)׳‬, 27.5 (3C, s, tBu), 21.3 (2C, s, C–3,3‫)׳‬, 16.3 (2C, d, 3JC–P
5.5 Hz, CH3) ppm;
ppm;
F NMR (282 MHz, CDCl3) δ -121.4 (2F, d, 2JF–P 106.4 Hz)
19
P NMR (121 MHz, CDCl3) δ 8.1 (1P, tt, J 106.9, 6.7 Hz) ppm. These
31
spectral details match with limited characterisation reported by Waschbüsch et
al.95
Mw: 342.36 (C15H29F2O4P); Rf 0.13 (EtOAc/PE 20:80); 1H NMR
HO CF2PO(OEt)2
(400 MHz, CDCl3) δ 6.04 (1H, br. s., OH), 4.30 (2H, q, J 7.1, 7.1,
7.1 Hz, OCH2), 3.74 (2H, q, J 7.1 Hz, CH2), 2.44 (2H, dd, J 24.8,
tBu
5.5
12.6 Hz, H2eq,2‫׳‬eq), 1.67 (2H, d, J 11.4 Hz, H3eq,3‫׳‬eq), 1.39 (3H, t, J
7.2, 7.2 Hz, CH3), 1.30–1.54 (4H, m, H2ax,2‫׳‬ax3ax,3‫׳‬ax), 1.25 (3H, t, J 7.1 Hz, CH3),
1.05–1.19 (1H, m, H4), 0.85 (9H, s, tBu) ppm;
122.0 (td, 1JC–F
273.0, 1JC–P
C NMR (101 MHz, CDCl3) δ
13
202.7 Hz, CF2PO), 72.7 (td, J 20.9, 12.4 Hz, C1),
65.0 (2C, d, 2JC–P 7.0 Hz, OCH2), 46.2 (d, J 6.2 Hz, C4) 33.4–34.0 (2C, m, C
C2,2‫)׳‬, 32.4 (s, C(CH3)3), 27.5 (3C, s, tBu) 23.0–23.1 (2C, m, 3,3‫)׳‬, 16.3 (2C, d, J
5.9 Hz, CH3) ppm;
ppm;
F NMR (282 MHz, CDCl3) δ -113.1 (2F, d, 2JF–P 106.4 Hz)
19
P NMR (121 MHz, CDCl3) δ 7.6 (1P, t, J 109.2 Hz) ppm. Spectra details
31
for this compound have not been reported in the literature.
6.12.2 The phosphates 5.6 and 5.7
Mw: 342.36 (C15H29F2O4P); Rf 0.27 (EtOAc/PE 30:70); 1H NMR
(400 MHz, CDCl3) δ 6.16 (1H, t, 2JH–F 54.7 Hz, CHF2), 4.12 (4H,
quin, J 7.2 Hz, OCH2), 2.17–2.26 (2H, m, H2eq,2‫׳‬eq), 1.68–1.77
(2H, m, H3eq,3‫׳‬eq), 1.49–1.60 (2H, m, H3ax,3‫׳‬ax), 1.39–1.48 (2H, m,
H2ax,2‫׳‬ax), 1.34 (6H, td, J 7.1, 1.0 Hz, CH3), 1.06 (1H, tt, J 12.0, 3.2 Hz, H4),
0.88 (9H, s, tBu) ppm;
C NMR (101 MHz, CDCl3) δ 115.0 (t, 1JC–F 244.4 Hz,
13
CHF2), 82.9 (td, 2JC–F 23.4, 2JC–P 8.8 Hz, C1), 63.8 (2C, d, 1JC–P 5.9 Hz, CH2), 46.9
(s, C4), 32.4 (s, CtBu), 29.0 (2C, dd, J 5.9, 2.9 Hz, C2,2‫)׳‬, 27.4 (3C, s, tBu), 21.2
(2C, s, C3,3‫)׳‬, 16.0 (2C, d, 2JC–P 7.3 Hz, CH3) ppm; 19F NMR (282 MHz, CDCl3) δ 133.4 (1F, d, J 55.9 Hz) ppm;
31
P NMR (121 MHz, CDCl3) δ -4.8
(1P, br. s.) ppm.
Mw: 342.36 (C15H29F2O4P); Rf 0.36 (EtOAc/PE 30:70); 1H NMR (400
MHz, CDCl3) δ 5.99 (1H, td, J 54.9, 1.8 Hz, CHF2), 4.09 (4H, quin,
J 7.3 Hz, OCH2), 2.29–2.37 (2H, m, H2ax, H2eq ), 2.00–2.11 (2H, m,
H3ax, H3‫׳‬eq), 1.75–1.83 (2H, m, H3eq, H3‫׳‬eq ), 1.33 (6H, td, J 7.1, 1.0 Hz, CH3),
120
Chapter 6: Experimental
1.17–1.29 (3H, m, H2‫׳‬ax, H2‫׳‬eq, H4 ), 0.86 (9H, s, tBu) ppm;
CDCl3) δ 115.0 (td, 1JC–F, 3JC–P
C NMR (101 MHz,
13
248.5, 7.3 Hz, CHF2), 82.3 (td, 2JC–F, C–P
20.5, 6.6
Hz, C1), 63.7 (2C, d, 2JC–P 6.2 Hz, CH2), 46.2 (s, C4), 32.2 (s, CtBu), 31.6 (2C, q,
JC–F 2.6 Hz, C2, 2‫)׳‬, 27.5 (3C, s, tBu), 23.7 (2C, s, C3, 3‫)׳‬, 16.0 (2C, d, 3JC–P 7.0
3
Hz, CH3) ppm;
F NMR (282 MHz, CDCl3) δ -135.5 (2F, d, J 55.9 Hz) ppm;
19
P
31
NMR (121 MHz, CDCl3) δ -6.1 (1P, t, J 6.7 Hz) ppm. These NMR details for the
phosphates 5.6 and 5.7 were not reported in the literature.
6.12.3 cis- and Trans-4-(tert-butyl)-1-difluoromethylcyclohexanol
Sodium methoxide (1.32 mL, 4M, 3.50 mmol) in MeOH was added to a solution
of phosphonate 5.5 (0.6 g, 175 mmol) in THF (20 mL). The mixture was stirred
at rt to 40 ºC for 6h followed by addition of saturated NH4Cl (20 mL). The
solution was extracted into DCM (4×20 mL) and the combined extract was
washed with brine (15 mL), dried over anhydrous MgSO4, filtered and
concentrated under reduced pressure. The crude product was purified on silica
gel column chromatography (EtOAc/PE 20:80) and afforded white solid of 1.54,
0.03 g (8%). Mw: 206.27 (C11H20F2O); Rf 0.30 (EtOAc/PE 10:90); IR (neat)
3296 (br., OH), 2945 (m, CH3), 1361 (m, C–O) cm-1;
H NMR (400 MHz,
1
CDCl3) δ 5.83 (1H, d, 2JH–F 56.0 Hz, CHF2), 2.03–2.15 (2H, m, H2eq,2‫׳‬eq), 1.95 (1H,
t, J 1.4 Hz, OH), 1.72–1.81 (2H, m, H3eq,3‫׳‬eq), 1.42–1.54 (2H, m, H2ax,2‫׳‬ax), 1.08–
1.24 (3H, m, H3ax,3‫׳‬ax, 4), 0.87 (9H, s, tBu) ppm;
116.3 (t, 1JC–F
C NMR (101 MHz, CDCl3) δ
13
246.6 Hz, CHF2), 71.2 (t, 2JC–F 19.2 Hz, C1), 46.8 (s, C4), 33.6
(2C, t, J 2.9 Hz, C2,2‫)׳‬, 32.3 (s, CtBu), 27.5 (3C, s, tBu), 23.5 (2C, s, C3,3‫ )׳‬ppm;
F NMR (282 MHz, CDCl3) δ -135.5 (2F, d, J 55.9 Hz) ppm.
19
The hydrolysis procedure as above was used for on 5.4 and gave a
white solid of 1.53, 0.108 g (14%). Mw: 206.27 (C11H20F2O); Rf 0.43
(EtOAc/PE 10:90); IR (neat) 3398 (br., OH), 2949 (m, CH3), 1361 (m, C–
O) cm ; H NMR (400 MHz, CDCl3) δ 5.46 (1H, t, 2JH–F 56.5 Hz, CHF2), 1.61–1.77
-1 1
121
Chapter 6: Experimental
(4H, m, H2eq,2eq‫ ׳‬, 3eq,3‫׳‬eq), 1.57 (1H, s, OH), 1.32–1.53 (4H, m, H2ax,2ax‫ ׳‬,3ax 3‫׳‬ax),
0.95–1.05 (1H, m, H–4), 0.88 (9H, s, tBu) ppm ;
C NMR (101 MHz, CDCl3) δ
13
118.0 (t, 2JC-F 252.8 Hz, CHF2), 71.3 (d, 3JC-F 21.2 Hz, C1), 47.6 (s, C4), 32.4 (s,
CtBu), 30.3 (2C, t, J 2.4 Hz, C2,2‫)׳‬, 27.5 (3C, s, tBu), 21.1 (2C, s, C3,3‫ )׳‬ppm; 19F
NMR (282 MHz, CDCl3) δ -134.0 (1F, d, 2JH-F 55.9 Hz) ppm. Spectra details for
these two compounds, 1.56 and 1.57 corresponded to those reported by Surya
et al.93
6.13
Trans- and Cis-4-(tert-butyl)-1-
trifluoromethylcyclohexanol
A
mixture
of
the
ketone
5.1
(1.0
g,
6.5
mmol)
and
(trifluoromethyl)trimethylsilane (15.60 mL, 7.8 mmol; 0.5M solution in THF)
was treated with a catalytic amount of tetrabutylammonium fluoride (ca. 0.1
mL, 1M in THF). The reaction mixture was stirred for 1h at rt. The resulting
silyloxy compounds were hydrolysed with aqueous HCl (3 mL, 6M) and left
stirring for 1h. After completion of the reaction, the mixture was extracted
with Et2O (3×30 mL). The combined organic phases were washed with a
solution of NaHCO3 (20 mL), brine (20 mL), dried over MgSO4 and evaporated of
solvents. The residue was separated and purified by flash chromatography
(EtOAc/PE 02:98) and gave 0.18 g (11%) of 1.55 and 1.09 g (39%) of 1.56.
Mw: 224.26 (C11H19F3O); Rf 0.26 (EtOAc/Hexane 05:95); IR (neat) 3383
(br., OH), 2949 (m, CH3), 1308 (m, C–O) cm-1; 1H NMR (300 MHz,
CDCl3) δ 1.79–1.89 (2H, m, H2ax,3ax), 1.63–1.75 (3H, m, 3eq,3‫׳‬eq, OH),
1.54–1.63 (2H, m, H2eq,2‫׳‬eq), 1.30–1.47 (2H, m, 2ax‫ ׳‬,3‫׳‬ax), 0.95–1.10 (1H, m, H4),
0.89 (9H, s, tBu) ppm;
C NMR (75 MHz, CDCl3) δ 126.5 (q, 1JC–F 286.1 Hz,
13
CF3), 72.3 (q, 2JC–F 27.9 Hz, C1), 47.2 (s, C4), 32.4 (s, CtBu), 30.3 (2C, q, 3JC–F
1.2 Hz, C2,2‫)׳‬, 27.4 (3 C, s, tBu), 21.1 (2C, s, C3,3‫ )׳‬ppm;
CDCl3) δ -85.0 (3F, s) ppm.
122
F NMR (282 MHz,
19
Chapter 6: Experimental
Mw: 224.26 (C11H19F3O); Rf 0.23 (EtOAc/PE 10:90); IR (neat) 3289 (br.,
OH), 2949 (m, CH3), 1368 (m, C–O) cm-1;
H NMR (300 MHz, CDCl3)δ
1
2.17–2.30 (2H, m, H2eq,2‫׳‬eq), 2.04 (1H, s, OH), 1.73 (2H, m, H3eq,3‫׳‬eq),
1.42–1.59 (2H, m, H2ax,2‫׳‬ax), 1.23–1.42 (2H, m, H3ax,3‫׳‬ax), 1.03–1.17 (1H, m, H4
C NMR (75 MHz, CDCl3) δ 127.0 (q, 1JC–F
), 0.87 (9H, s, tBu) ppm;
13
284.2 Hz,
‫׳‬
CF3), 72.1 (q, JC–F 27.1 Hz, C1), 46.3 (s, C4), 33.3 (2C, s, C2,2 ), 32.3 (s, CtBu),
2
27.5 (3C, s, tBu), 23.0 (2C, q, 4JC–F 1.4 Hz, C3,3‫ )׳‬ppm;
F NMR (282 MHz,
19
CDCl3) δ -78.0 (3F, br. s.) ppm. These spectra details for 1.58 and 1.59
corresponded to those reported by Diter et al.97
6.14
Trans- and Cis-4-(tert-butyl)-1-methylcyclohexanol
A solution of the ketone 5.1 (3.0 g, 19.45 mmol) in THF (50 mL) was cooled to
0 ºC and methylmagnesium bromide (7.78 mL, 3M solution in Et2O, 23.34
mmol) was added. The reaction mixture was stirred at 0 ºC for 1h and then left
to stir at rt until the reaction was complete. The reaction mixture was diluted
with EtOAc and water (50 mL, 1:1) and the layers separated. The organic layer
was washed with saturated NaHCO3 (20 mL), HCl (20 mL, 2M solution) and
brine (20 mL). It was then dried over anhydrous MgSO4, filtered and
concentrated under reduced pressure to give the crude that was purified by
column chromatography (EtOAc/PE 07:93) and afforded 1.07 g (32%) of 1.58
and 0.62 g (19%) of 1.57.
Mw: 170.29 (C11H22O); Rf 0.2 (EtOAc/PE 10:90); IR (neat) 3334 (br.,
OH), 2933 (m, CH3), 1361 (m, C–O) cm-1; 1H NMR (300 MHz, CDCl3) δ
1.64–1.74 (2H, m, H2ax,2‫׳‬ax), 1.54–1.62 (2H, m, H3ax,3‫׳‬ax), 1.26–1.42
(4H, m, H2eq,2eq‫ ׳‬, 3eq,3‫׳‬eq), 1.17–1.23 (4H, m, CH3, OH), 0.90–0.98 (1H, m, H4),
0.87 (9H, s, tBu) ppm;
C NMR (75 MHz, CDCl3) δ 68.9 (s, C1), 47.6 (s, C4),
13
39.3 (2C, s, C2,2‫)׳‬, 32.4 (s, CtBu), 31.3 (s, CH3), 27.6 (3C, s, C–tBu), 22.6 (2C, s,
C3,3‫ )׳‬ppm.
123
Chapter 6: Experimental
Mw: 170.29 (C11H22O); Rf 0.33 (EtOAc/PE 10:90); IR (neat) 3368 (br.,
OH), 2945 (m, CH3), 1361 (m, C–O) cm-1; 1H NMR (400 MHz, CDCl3) δ
1.67–1.78 (4H, m, H2eq,2‫׳‬eq, 3eq,3‫׳‬eq), 1.36–1.48 (3H, m, 2ax,2‫׳‬ax, OH),
1.21 (3H, s, CH3), 0.98–1.17 (3H, m, 3ax,3‫׳‬ax, 4), 0.86 (9H, s, tBu) ppm; 13C NMR
(101 MHz, CDCl3) δ 71.0 (s, C1), 47.7 (s, C4), 40.9 (2C, s, C2,2‫)׳‬, 32.2 (s, CtBu),
27.6 (3C, s, tBu), 25.3 (s, CH3), 25.0 (2C, s, C3,3‫ )׳‬ppm; These spectral details
of 1.61, and 1.62 corresponded to the limited characterization reported by
Senda et al.98
6.15
Synthesis of Trans-4-(tert-butyl)-3-fluoro and -3,3-
difluorocyclohexanol
6.15.1 2-bromo-4-(tert-butyl)cyclohexanone
The procedure used by Tenemura et al.,101 was followed in which to a mixture
of the ketone (5.1), (20 g, 129.76 mmol) and N-bromosuccinamide (24.24 g,
136.24 mmol) in dry Et2O (120 mL) was added NH4OAc (1.0 g, 12.98 mmol).
The mixture was put under water bath and allowed to stir, after about 15 min
the mixture refluxed and immediately was added ice into the water bath to
stop refluxing. The reaction mixture was then allowed to stir at rt for 1h after
which was filtered with PE and the filtrate evaporated to half the volume;
filtered again and evaporated of solvents. The obtained crude 32.23 g of the
diastereomeric mixture of 5.8 and 5.9 was used directly in the next step.
6.15.2 Synthesis of 4-(Tert-butyl)cyclohex-2-enone
A suspension of MgO (7.35 g, 182.48 mmol) in DMF (50 mL) was stirred at 140
ºC. The crude (mixture of 5.8 and 5.9) (32.23 g, 138.24 mmol) in DMF (100
124
Chapter 6: Experimental
mL) was added and the mixture continued stirring for 1h. The reaction mixture
was cooled in an ice bath and HCl (1M, 100 mL) was added to dissolve the
MgO. The resulting mixture was extracted with Et2O (3×200 mL). The combined
ether extract was washed with brine (20 mL), saturated NaHCO3 (20 mL); dried
over MgSO4 and evaporated of solvent. The crude product was purified on
column chromatography (EtOAc/PE 05:95) and afforded 11.17g (57.3%) of
5.10.
Mw 152.23 (C10 H16O); Rf 0.26 (EtOAc/PE 10:90); 1H NMR (300 MHz,
CDCl3) δ 7.02 (1H, d, J 10.3 Hz, H2), 6.04 (1H, d, J 10.1 Hz, H3), 2.44–2.61
(1H, m, H6eq), 2.26–2.43 (1H, m, H6ax), 2.02–2.26 (2H, m, H5), 1.75 (1H, m,
H4), 0.98 (9H, s, tBu) ppm; 13C NMR (75 MHz, CDCl3) δ 200.0 (s, C1), 152.9 (s,
C2), 130.0 (s, C3), 46.8 (s, C4), 37.8 (s, C6), 32.9 (s, C tBu), 27.3 (3C, s, tBu),
24.3 (s, C5) ppm. These spectral details corresponded to those reported by List
et al.141
6.15.3 (1S,3S,4S)-4-(Tert-butyl)cyclohexane-1, 3-diol
The enone 5.10 (11.10 g, 72.12 mmol) in THF (30 mL) was cooled to 0 ºC.
Borane tetrahydrofurane complex (160.42 mL, 160.42 mmol; 1M in TH) was
added drop wise and the mixture stirred for 12h at rt. After completion of
reaction, excess borane was decomposed by careful adding ice and the
mixture oxidized with 10% NaOH (20 mL) and 30% H2O2 (20 mL) for 12h. Solid
K2CO3 was added to saturation and the layers separated. The aqueous layer was
extracted with DCM (4×100 mL). The combined organic layers were then dried
with MgSO4 and evaporated of solvents to give the crude product that was
purified by column chromatography (acetone/PE 10-30:90-70) and afforded a
white solid of 5.11, 2.96 g (24%). Mw 172.26 (C10H20O2); Rf 0.20 (EtOAc/PE
50:50); IR (neat) 1077(s, C–O), 2930 (m, CH3), 3319 (br., OH). ES+MS: m/z
236.3 [M + MeCN + Na] + (73.7%); 1H NMR (400 MHz, CDCl3) δ 3.52–3.69 (2H, m,
H 1,3), 2.18–2.27 (1H, m, H2), 1.91–2.01 (1H, m, H6), 1.72–1.87 (2H, m, H5),
1.43–1.50 (2H, m, OH), 1.38 (1H, dd, J 22.2, 10.9 Hz, H2‫)׳‬, 1.14–1.27 (1H, m,
H6‫)׳‬, 1.08 (1H, dd, J 9.4, 3.3 Hz, H4), 0.96–1.04 (9H, s, t-Bu) ppm;
125
C NMR
13
Chapter 6: Experimental
(101 MHz, CDCl3) δ 71.1 (s, C1), 68.8 (s, C3), 52.6 (s, C4), 46.2 (s, C2), 35.1 (s,
C6), 32.8 (s, CtBu), 29.2 (3C, s, tBu), 23.1 (s, C5) ppm. Dunkelblum et al103 only
reported the 1H NMR that corresponded with this data.
6.15.4 2-(Tert-butyl)-5-(trityroxy)cyclohexanol
The diol 5.11 (0.4 g, 2.32 mmol) was added to a solution of triphenylmethyl
chloride (0.8 g, 2.79 mmol) and 1, 8-diazabicyclo[5.4.0]undec-7-ene (DBU), (0.5
mL, 3.25 mmol) in DCM (20 mL). The mixture was stirred at rt for 48h. After
completion of the reaction, the reaction mixture was washed with cold water
(20 mL) and extracted the aqueous layer with DCM (2×50 mL). The combined
organic extracts were dried over anhydrous Na2SO4 and evaporated of solvents.
The obtained crude product was purified by column chromatography on silica
gel (acetone/PE 10-50:90-50 mixture containing 0.5% TEA) and afforded 0.83 g
(86%) white solid of a novel compound 5.12. Mw 414.58 (C29 H34O2); Rf 0.20
(EtOAc/PE 05:95); IR (neat) 1444 (s, C=CAr), 3421 (br., OH); ES+MS: m/z 473.3
[M + MeCN + NH4] + (100%); 1H NMR (400 MHz, CDCl3) δ 7.50–7.58 (6H, m, HAr),
7.22–7.35 (9H, m, HAr), 3.45 (1H, tt, J 10.1, 4.3 Hz, H1), 3.22–3.33 (1H, m,
H3), 1.53–1.68 (2H, m, H2,5), 1.27–1.43 (2H, m, H–2‫׳‬,6), 1.15–1.25 (1H, m,
H6‫ )׳‬1.12 (1H, d, J 6.6 Hz, OH), 0.96–1.05 (1H, m, H4), 0.92 (9H, s, tBu), 0.57–
0.69 (1H, m, H5‫ )׳‬ppm;
C NMR (101 MHz, CDCl3) δ 145.3 (3C, s, CAr), 128.9
13
(6C, s, CAr), 127.7 (6C, s, CAr), 126.9 (3C, s, CAr), 86.7 (s, CPh3) 71.2 (s, C3) 71.0
(s, C1) 52.9 (s, C4) 44.6 (s, C2) 33.4 (s, C6) 32.7 (s, CtBu) 29.1 (3C, s, tBu) 23.2
(s, C5) ppm. This compound was not reported in the literature.
6.15.5 2-(Tert-butyl)-5-(trityroxy)cyclohexanone
126
Chapter 6: Experimental
A suspension of sulfurtrioxide pyridine complex (0.6 g, 3.63 mmol) in DCM (3
mL) was dissolved in DMSO (8 mL) and Et3N (0.45 mL, 4.32 mmol). The solution
was immediately added drop wise to a stirred solution of 5.12 (0.47 g, 1.13
mmol) in DCM (10 mL) and DMSO (20 mL) at -5 ºC. The reaction mixture was
stirred at O ºC for 6h. After completion of reaction, the reaction mixture was
poured into a solution of saturated aqueous NH4Cl: H2O: Et2O: pentane (1:1:1:1,
100mL) and separated. The aqueous phase was extracted with Et2O: pentane
(1:1, 3×50). The combined organic phases were dried over Na2SO4, filtered and
evaporated
of
solvents.
The
crude
product
was
purified
by
column
chromatography (EtOAc/PET 05:95 mixture with 0.5% TEA) to give a white solid
of 5.13, 0.304 g (65%). Mw: 412.56 (C29H32O2); Rf 0.40 (EtOAc/PET 05:95); IR
(neat) 1055 (s, C–O), 1709(s, C=O); ES+MS: m/z 454.2 [M + MeCN + H] + (100%);
H NMR (400 MHz, CDCl3) δ 7.48–7.57 (6H, m, HAr), 7.23–7.37 (9H, m, HAr), 3.75
1
(1H, tt, J 10.0, 5.0 Hz, H1), 2.34 (1H, t, J 11.1 Hz, H2ax), 1.97–2.08 (2H, m,
H2eq,4), 1.88 (1H, ddd, J 13.3, 8.6, 3.8 Hz, H5ax), 1.48–1.63 (2H, m, H6), 0.99–
1.10 (1H, m, H5eq), 0.93 (9H, s, tBu) ppm; 13C NMR (101 MHz, CDCl3) δ 209.0 (s,
C=O), 144.8 (3C, s, CAr), 128.8 (6C, s, CAr), 127.8 (6C, s, CAr), 127.1 (3C, s, CAr),
87.0 (s, CPh3), 73.0 (s, C1), 59.1 (s, C4), 51.8 (s, C2), 33.4 (s, C6), 31.7 (s, C
tBu), 27.6 (3C, s, tBu ), 23.1 (s, C5) ppm. This compound was not reported in
the literature.
6.15.6 (1R,2R) and (1S,2R)-2-(Tert-butyl)cyclohexyl methanesulfonate
Methanesulfonyl chloride (3.1 mL, 40 mmol) was added drop wise over 30 min
to a stirred solution of 5.16 (5.0 g, 32 mmol) and Et3N (7.0 mL, 50 mmol) in
DCM (50 mL) at 0 ºC under argon. The mixture was stirred at 0 ºC for a further
3h. The solvent was removed in vacuum to leave a crude residue which was
partitioned between water (50 mL) and Et2O (2×50 mL). The combined organic
extracts were washed with brine (50 mL), dried over MgSO4, filtered and
concentrated in vacuum to give the crude which was purified by column
chromatography (EtOAc/PET 02:98 containing 0.5% mixture of Et3N). This
127
Chapter 6: Experimental
afforded 1.728 g, 23% of the diastereomeric mixtures of 5.17 and 5.18 that
could
not
be
separated
by
HPLC.
Mw
234.36
(C11H22O3S);
Rf
0.33
(EtOAc/hexane 07:93); 1H NMR (300 MHz, CDCl3) δ 4.72 (1H, td, J 10.0, 4.3 Hz,
H1ax), 3.68 (1H, br. s, H1eq), 3.00 (6H, s, CH3), 2.22–2.39 (2H, m, H2), 1.04–
1.97 (16H, m, H3,4,5,6), 1.00 (18H, s, tBu) ppm;
C NMR (75 MHz, CDCl3) δ
13
84.5 (s), 80.8 (s), 52.5 (s), 51.0 (s), 40.2 (s), 39.8 (s), 34.3 (s), 32.9 (s), 32.5 (s),
28.9 (6C, s), 28.1 (s), 26.7 (s), 26.2 (s), 25.3 (s), 24.3 (s), 21.8 (s), 20.0 (s)
ppm. These spectra details were not in the literature.
6.15.7 4-(Tert-butyl) resorcinol
To a solution of resorcinol 5.21 (20 g, 181.64 mmol), tert-butanol (17 mL,
177.80 mmol) and glacial acetic acid (30 mL) was added H2SO4 (10 mL) over a
period of 10 min with ice bath cooling. The reaction mixture was then allowed
to stir at rt for 30 min. After completion of the reaction, a solution of saturated
NaCl (40 mL) was added with stirring, and the mixture after diluting with water
(150 mL) was extracted with Et2O (150 mL). The ether layer was washed with
12% aqueous NaOH (100 mL), and the aqueous layer was acidified with 6M HCl
to pH 6. After extraction of the aqueous layer with Et2O, the combined ether
extract were dried over anhydrous Na2SO4 and evaporated of solvent. The crude
product was purified by column chromatography (EtOAc/PET 05, 10, 20: 95,
90. 80) and gave 5.22, 13.64 g (45%). Mw: 166.10 (C10H14O2);
Rf 0.25
(acetone/PE 20:80); 1H NMR (400 MHz, CDCl3) δ 7.10 (1H, d, J 8.5 Hz, H5),
6.36 (1H, dd, J 8.5, 2.5 Hz, H6), 6.27 (1H, d, J 2.5 Hz, H2), 5.66 (1H, br. s.,
OH), 5.44 (1H, br. s, OH), 1.38 (9H, s, tBu) ppm;
C NMR (101 MHz, CDCl3) δ
13
155.3 (s, C1), 154.5 (s, C3), 128.7 (s, C4), 127.7 (s, C5), 106.8 (s, C6), 104.1
(s, C2), 33.9 (s, CtBu), 29.8 (3C, s, tBu) ppm. These spectral details
corresponded to those reported by Lee et al109.
128
Chapter 6: Experimental
6.15.8 (1R,3R, 4R)-4-(Tert-butyl)cyclohexane-1,3-diol
A mixture of 5.22 (3.0 g, 18.05 mmol) and a catalyst 5% Ru/C (0.6 g, 20%
weight of the substrate) in isopropanol (15 mL) in a sealed reaction tube was
stirred at 120 ºC under hydrogen (20 atm) for 36h. The reaction mixture was
cooled to rt and then diluted with MeOH (10 mL) and the catalyst removed
through celite with several rinse with MeOH. Evaporation of solvent and
purification on column chromatography (EtOAc/PET 20, 30, 80: 80, 70, 20)
afforded 5.23, 0.25 g (8%). Mw: 172.26 (C10H20O2); Rf 0.33 (EtOAc/PET 30:70);
IR (neat) 1092(s, C–O), 1361 (s, C-H), 2933 (m, CH3), 3327 (br., OH); ES+MS:
m/z 236.3 [M + MeCN + Na] + (100%); 1H NMR (300 MHz, CDCl3) δ 4.28 (1H, br.
s., H3), 4.12 (1H, br. s., H1), 3.22 (1H, d, J 4.8 Hz, OH1), 3.12 (1H, d, J 7.0 Hz,
OH3), 2.10 (1H, dq, J 14.6, 2.8 Hz, H2ax), 1.82–2.01 (2H, m, H5ax,6ax), 1.45–1.59
(3H, m, H2eq,5eq,6eq), 1.05 (1H, d, J 12.9 Hz, H4), 0.97 (9H, s, tBu) ppm; 13C NMR
(75 MHz, CDCl3) 69.1 (s, C3), 67.6 (s, C1), 50.9 (s, C4), 39.1 (s, C2), 33.8 (s,
C6), 32.7 (s, C tBu), 28.5 (3C, s, tBu), 15.4 (s, C5) δ ppm. This compound was
also synthesised by Evans et al.,142 but no identification details were given.
6.15.9 3-Fluoromethoxybenzene (3–Fluoroanisole)
A solution of 3-fluorophenol (5 mL, 55.22 mmol) in THF (20 mL) was added
drop wise over 1h to a precooled (0 ºC) suspension of
NaH (1.6 g, 66.26
mmol; 2.67 g 60 weight % in mineral oil) prewashed with hexane in THF (10
mL). The resulting solution was stirred for 10 min then iodomethane (25 mL,
176.7 mmol) was added rapidly. The reaction was warmed to rt then refluxed
for 19h. The cooled reaction mixture was diluted with water (100 mL) and
extracted with Et2O (2×100 mL). The extract was dried over Na2SO4, filtered and
129
Chapter 6: Experimental
evaporated
of
solvent.
The
crude
product
was
purified
by
column
chromatography (EtOAc/PET 20/80) and afforded a yellow liquid of 5.29, 2.093
g (30%). Mw: 126.13 (C7H7FO), Rf 0.5 (EtOAc/hexane 02:98);
1
H NMR (300
MHz, CDCl3) δ 7.2–7.4 (1H, m, HAr), 6.6–6.9 (3H, m, HAr), 3.9 (3H, s, OMe) ppm;
C NMR (75 MHz, CDCl3) δ 163.7 (d, J 244.4 Hz), 161.0 (d, J 11.1 Hz), 130.2
13
(d, J 10.0 Hz), 109.8 (d, J 2.8 Hz), 107.4 (d, J 21.3 Hz), 101.6 (d, J 24.9 Hz),
55.4 (s) ppm;
F NMR (282 MHz, CDCl3) δ-112.0 (1F, m) ppm. The 1H NMR
19
data corresponded to those reported by Kim et al.112 13C NMR was not reported
in the literature.
6.15.10
2-Tert-butyl-5-fluoro-1-methoxybenzene
The same procedure used for synthesis of 5.22 was applied on 5.29 (3.0 g,
18.05 mmol) and afforded 0.460 g (16 %) of 5.31. Mw: 182.23 (C11H15FO), Rf
(Pentane 100%): 0.3; 1H NMR (300 MHz, CDCl3) δ 7.14–7.24 (1H, m, H4), 6.54–
6.67 (2H, m, H2,5), 3.80 (3H, s, CH3), 1.36 (9H, s, tBu) ppm; 1H NMR [19F] (400
MHz, CDCl3) δ 7.19 (1H, dd, J 8.6, 1.7 Hz, H2) 6.62 (1H, dd, J 11.6, 3.1 Hz, H4)
6.60 (1H, dd, J 8.6, 2.6 Hz, H5) 3.79 (3H, s, CH3) 1.36 (9H, s, tBu) ppm;
C
13
NMR (101 MHz, CDCl3) δ 162.3 (d, J 247.7 Hz, C3), 158.9 (d, J 11.7 Hz, C1),
129.2 (d, J 12.1 Hz, C2), 127.4 (d, J 7.7 Hz, C6), 108.8 (d, J 2.6 Hz, C5),
102.6 (d, J 27.8 Hz, C4), 55.5 (s, OMe), 33.7 (d, J 2.9 Hz, CtBu), 30.1 (3C, d, J
3.3 Hz, tBu) ppm;
F NMR (376 MHz, CDCl3) δ -107.8 (1F, t, J 13.9 Hz) ppm.
19
This compound has not been reported in the literature.
6.15.11
3-Fluorophenyl acetate
OH
Ac2O, Et3N
F
OAc
DCM
88%
5.28
F
5.33
A solution of 3-fluorophenol (4.04 mL, 44.6 mmol) in DCM (20 mL) was cooled
to 0 ºC, Ac2O (4.21 mL, 44.6 mmol) and Et3N (6.22 mL, 44.6 mmol) were added
and the mixture stirred at rt for 24h. After completion of the reaction, the
130
Chapter 6: Experimental
mixture was cooled to 0 ºC and MeOH (10 mL) was added and after stirring for
1h, the solvent was evaporated. The crude was purified by column
chromatography (EtOAc/PET 10:90) and gave 5.33, 6.061 g (88%). Mw 154.14
(C8H7FO2), Rf 0.36 (EtOAc/PET 05:95); 1H NMR (400 MHz, CDCl3) δ 7.30–7.39
(1H, m, HAr), 6.84–7.01 (3H, m, HAr), 2.31 (3H, s, CH3) ppm; 13C NMR (101 MHz,
CDCl3) δ 168.9 (s), 162.9 (d, J 247.4 Hz), 151.5 (d, J 10.6 Hz), 130.1 (d, J 9.1
Hz), 117.4 (d, J 3.7 Hz), 112.8 (d, J 20.9 Hz), 109.7 (d, J 24.5 Hz), 21.0 (s)
ppm;
F NMR (282 MHz, CDCl3) δ -111.3 (1F, dd, J 17.2, 8.6 Hz) ppm. This
19
compound was also synthesised by Brownlee,113 Shawcross,114 and Sheppard,115
but not spectral details were reported.
6.15.12
2-Tert-butyl-5-fluorophenol
The same procedure used for synthesis of 5.22 was applied on 5.33 (1 g, 6.49
mmol) and afforded 5.35, 0.06 g. Mw: 168.21 (C10H13FO), Rf (EtOAc/PET 10:90):
0.20; 1H NMR (400 MHz, CDCl3) δ 7.09–7.20 (1H, m, H2), 6.48–6.62 (2H, m,
H4,5), 4.90 (1H, br. s., OH), 1.33–1.38 (9H, s, tBu) ppm;
C NMR (75 MHz,
13
CDCl3) δ 162.2 (d, J 248.2 Hz, C3), 154.7 (d, J 12.2 Hz, C1), 129.5 (d, J 11.9
Hz, C2), 127.7 (d, J 8.0 Hz, C6), 110.3 (d, J 3.0 Hz, C5), 104.1 (d, J 27.6 Hz,
C4), 33.7 (d, J 2.8 Hz, CtBu), 30.1 (3C, d, J 3.3 Hz, tBu) ppm;
19
F NMR (282
MHz, CDCl3) δ -107.8 (1F, t, J 12.9 Hz) ppm. No spectra details for this
compound have been reported in the literature.
6.16
Synthesis of Trans- and Cis-2-fluorocyclohexanol
6.16.1 Trans- 2-fluorocyclohexanol
131
Chapter 6: Experimental
KHF2 (15.92 g, 203.8 mmol) was added to the mixture of the epoxide, 5.37
(10.3 g, 101.9 mmol) and Bu4NH2F3 (17.51 g, 58.1 mmol). The mixture was
stirred at 115 ºC for 2.5 days when TLC showed the reaction complete. Et2O
(100 mL) was added and the solution poured into NaHCO3 (100 mL) and
carefully extracted to manage the built up pressure. The organic layer was
washed successfully with saturated NaHCO3 (80 mL), brine (80 mL); dried
(MgSO4) and evaporated of solvent. The crude was purified by column
chromatography (EtOAc/PET 10:90) and afforded a colourless oil which
solidifies on standing, 11.6 g (96%) of 1.59; Mw 118.15 (C6 H11FO); Rf 0.30
(EtOAc/PET 20:80); IR (neat) 3364 (br., OH), 2937 (m, C–H), 1452 (s, C–F)1073
(m, C–O) cm-1; 1H NMR (300 MHz, CDCl3) δ ppm 4.25 (1H, dddd, J 51.4, 10.8,
8.5, 4.9 Hz, H2) 3.62 (1H, m, H1) 2.58 (1H, s, OH) 1.93–2.15 (2H, m, H–3eq,
6eq), 1.61–1.81 (2H, m, H4), 1.15–1.53 (4H, m, H5, 3ax, 6ax) ppm; 1H NMR [19F]
(400 MHz, CDCl3) δ 4.16–4.34 (1H, m, H2), 3.54–3.69 (1H, m, H1), 2.60 (1H,
br. s., OH), 1.94–2.14 (2H, m, H3eq,6eq), 1.60–1.80 (2H, m, H4), 1.36–1.50 (1H,
m, H5ax), 1.16–1.35 (3H, m, H5eq, 3ax, 6ax) ppm;
C NMR (75 MHz, CDCl3) δ 96.7
13
(d, J 173.9 Hz, C2), 73.2 (d, J 18.2 Hz, C1) 31.7 (d, J 6.9 Hz, C6) 30.3 (d, J
17.4 Hz, C3) 23.5 (d, J 1.9 Hz, C5) 23.5 (d, J 10.8 Hz, C4) ppm;
19
F NMR (282
MHz, CDCl3) δ -182.1 (1F, br. d, J 51.6 Hz) ppm. These 1H and
C NMR
13
corresponded to those reported by Abraham et al.120
6.16.2 (S)- 2-Fluorocyclohexanone
Ac2O (2.54 mL, 26.9 mmol) was added drop wise to PDC (3.22 g, 8.55 mmol) in
dry DCM (20 mL). Then 1.59 (1 g, 8.46 mmol) was added in a minimum DCM (5
mL) and the mixture boiled at 75 ºC for 4h. The mixture was diluted with Et2O
(20 mL) and the filtrate filtered. After evaporation of solvent, Et2O (20 mL) was
added and the mixture filtered again, dried over MgSO4, filtered and
concentrated at reduced pressure. The crude was purified by column
chromatography (Et2O/PE 20:80) that afforded 5.38, 0.87 g (87%). Mw 116.13
(C6H9FO); Rf 0.33 (EtOAc/PE 20:80); IR (neat) 2952 (m, C–H), 1727 (m, C═O),
1448 (m, C–F) cm-1; 1H NMR (400 MHz, CDCl3) δ 4.88 (1H, dddd, J 49.1, 11.5,
6.2, 1.0 Hz, H2) 2.50–2.60 (1H, m) 2.27–2.47 (2H, m) 1.93–2.10 (2H, m) 1.78–
132
Chapter 6: Experimental
1.93 (1H, m) 1.60–1.77 (2H, m,) ppm;
C NMR (75 MHz, CDCl3) δ 205.6 (d, J
13
14.6 Hz, C1), 92.7 (d, J 190.7 Hz, C2), 40.2 (, br. s), 34.2 (d, J 18.5 Hz), 26.9
(d, J 1.1 Hz), 22.7 (d, J 9.7 Hz) ppm;
m, 52.7 Hz, observed) ppm.
Jantzen et al,143 1H and
F NMR (282 MHz, CDCl3) δ -188.48 (1F,
19
C NMR details corresponded to one reported by
13
F NMR details were not reported in literature.
19
6.16.3 Trans-2-fluorocyclohexyl trifluoromethanesulfonate
To a mixture of 1.59 (1.0 g, 8.46 mmol) and pyridine (0.68 mL, 8.46 mmol) in
DCM
(34
mL,
4
mL
per
mmol
of
alcohol)
was
added
drop
wise
trifluoromethanesulfonic anhydride (10.2 mL, 10.2 mmol; 1M solution in DCM)
at 0 ºC. The mixture was stirred at 0 ºC for 2h when the reaction was complete.
The mixture was then diluted and extracted with ether (3×30 mL). The organic
layer was washed with water (25 mL), HCl (25 mL, 1M), NaHCO3 (3×20 mL) and
brine (25 mL); dried (MgSO4), filtered and evaporated of solvent that afforded
5.40, 1.83 g (86%). Mw 250.21 (C7H10F4O3S); Rf 0.5 (acetone/PE20:80); IR (neat)
2956 (m, C–H), 1402 (s, C–F), 1198 (m, C–O), cm-1; 1H NMR (400 MHz, CDCl3) δ
4.83 (1H, ddd, J 18.5, 10.2, 5.1 Hz, H1) 4.53 (1H, dddd, J 50.0, 10.6, 8.3, 4.9
Hz, H2) 2.19–2.34 (2H, m, H3eq,6eq) 1.76–1.88 (2H, m, H4eq,5eq) 1.52–1.76 (2H,
m, H3ax,6ax) 1.25–1.46 (2H, m, H4ax,5ax) ppm; 13C NMR (101 MHz, CDCl3) δ 118.5
(d, J 319.1 Hz, CF3) 90.7 (d, J 182.6 Hz, C2) 88.9 (d, J 19.0 Hz, C1) 30.7 (d, J
4.8 Hz, C6) 30.4 (d, J 17.9 Hz, C3) 23.1 (d, J 1.8 Hz, C5) 22.3 (d, J 9.5 Hz, C4)
ppm; 19F NMR (282 MHz, CDCl3) δ -75.3 (3F, br. s.) -180.8 (1F, br. d, J 47.3 Hz)
ppm. This compound was not reported in the literature.
6.16.4 Cis-2-Fluorocyclohexyl acetate
133
Chapter 6: Experimental
To the triflate 5.40 (0.8 g, 3.2 mmol) in anhydrous DMF (16.6 mL, 5.2 mL per
mmol) was added cesium acetate (3.1 g, 16 mmol). The mixture was stirred at
140 ºC for 20h. After completion of reaction, the mixture was cooled to rt and
diluted with water (60 mL) and ether (30 mL), and extracted with ether (3×50
mL). The combined organic extract were washed with brine (50 mL), dried over
MgSO4, filtered and evaporated of solvent. The crude was purified by column
chromatography acetone/PE 10:90 and afforded 5.41, 0.3 g, (59%). Mw 160.19
(C8H13FO2); Rf 0.5 (acetone/PE 20:80); IR (neat) 2941–2862 (m, C–H), 1731 (m,
C=O), 1444 (s, C–F), 1228 (m, C–O), cm-1; 1H NMR (400 MHz, CDCl3) δ 4.88
(1H, m, H1), 4.75 (1H, d, J 51.0 Hz observed, H2), 2.10 (3H, s, CH3), 2.00–2.09
(1H, m), 1.79–1.91 (1H, m), 1.52–1.78 (4H, m), 1.32–1.51 (2H, m) ppm;
C
13
NMR (101 MHz, CDCl3) δ 170.5 (s, C=O), 89.5 (d, J 176.7 Hz, C2), 72.3 (d, J
17.6 Hz, C1), 29.1 (d, J 20.5 Hz, C3), 26.3 (d, J 3.3 Hz, C6), 22.6 (s, C5), 21.2
(s, CH3), 19.9 (d, J 4.4 Hz, C4) ppm; 19F NMR (282 MHz, CDCl3) δ -197.8 (1F, br.
s.) ppm. This compound was not reported in the literature.
6.16.5 Cis-2-fluorocyclohexanol
A mixture of the acetate 5.41 (0.3 g, 1.87 mmol), K2CO3 (0.03 g, 0.187 mmol)
and MeOH (2 mL) was stirred at rt for 3h. After completion of reaction, the
mixture was diluted with water (4 mL) and extracted with Et2O (3×10 mL). The
organic layer was dried over MgSO4 and evaporated of solvent to give the crude
that was purified by column chromatography (acetone/PE 08:92) and afforded
1.60, 0.038 g (17%). Mw 118.15 (C6H11FO); Rf 0.30 (EtOAc/PE 20:80); IR (neat)
3372 (br., OH), 2933 (m, C–H), 1448 (s, C–F), 1081 (m, C–O) cm-1; 1H NMR (300
MHz, CDCl3) δ 4.68 (1H, ddt, J 49.8, 7.0, 2.3, 2.3 Hz, H2), 3.68–3.87 (1H, m),
1.84–2.13 (2H, m), 1.48–1.81 (5H, m), 1.24–1.46 (2H, m) ppm;
C NMR (75
13
MHz, CDCl3) δ 92.7 (d, J 171.1 Hz, C2), 69.8 (d, J 18.8 Hz, C1), 29.9 (d, J 3.9
Hz, C6), 28.3 (d, J 19.9 Hz, C3), 21.7 (s, C5), 20.7 (d, J 5.8 Hz, C4) ppm;
NMR (282 MHz, CDCl3) δ -196.5 (1F, br. s.) ppm; The 1H and
corresponded to those reported by Basso et al.121
the literature.
134
F
19
C NMR data
13
F NMR was not reported in
19
Chapter 6: Experimental
6.17
Synthesis of Trans-and Cis-4-fluorocyclohexanol
6.17.1 Cis- and Trans-1-acetoxycyclohexanol
A solution of 5.42 (mixture of isomers) (10 g, 86.1 mmol) in DCM (50 mL) was
cooled to 0 ºC. Ac2O (9.75 mL, 103.3 mmol) and Et3N (14.42, 103.3 mmol)
were added and the mixture stirred at rt for 24h. After completion of the
reaction, the mixture was cooled to 0 ºC and MeOH (30 mL) was added and
stirred for 1h. Water (50 mL) was added and the mixture extracted with Et2O
(2×100 mL). The organic layer was dried (MgSO4), filtered and evaporated of
solvent. The crude was purified by column chromatography (EtOAc/PE 30:70,
50:50, 70:30) and afforded a colourless liquid, 6.193 g (45%) of a mixture of
inseparable diastereoisomers 5.43 and 5.44 along with white solid of the
diacetylated product 5.45 and 5.46, 5.26 g (31%).
Mw 158.19 (C8H14O3); Rf 0.16 (EtOAc/PE 30:70); IR (neat) 3395
(br., OH), 2937 (m, C–H), 1731 (m, C=O),1062 (m, C–O) cm-1; 1H
NMR (400 MHz, CDCl3) δ ppm 4.84 (1H, tt, J 6.4, 3.2 Hz), 4.73
(1H, tt, J 10.2, 3.0 Hz), 3.78 (1H, tt, J 7.1, 3.7 Hz), 3.71 (1H, tt, J
7.6, 4.2 Hz), 2.05 (3H, s, CH3), 2.02 (3H, s, CH3), 1.93–2.01 (4H, m), 1.82–1.91
(2H, m), 1.55–1.77 (8H, m), 1.36–1.50 (4H, m);
C NMR (75 MHz, CDCl3) δ
13
170.6 (s, C=O), 170.6 (s, C=O), 71.7 (2C, s,) 69.9 (s), 68.9 (2C, s,), 67.7 (s),
32.2 (s), 30.4 (2C, s), 28.6 (s), 27.3 (2C, s), 21.4 (s, CH3), 21.3 (s, CH3) ppm. No
identification details for these compounds have been reported in the literature.
Mw 200.23 (C10H16O4); Rf 0.6 (EtOAc/PE 30:70); IR (neat) 2945 (m,
CH3), 1720 (m, C=O),1043 (m, C–O) cm-1; 1H NMR (400 MHz,
CDCl3) δ 4.81–4.89 (2H, m), 4.74–4.81 (2H, m), 2.05 (6H, s, CH3),
2.03 (6H, s, CH3), 1.92–2.01 (4H, m), 1.75–1.89 (4H, m), 1.65–
1.75 (4H, m), 1.52 (4H, m) ppm;
C NMR (101 MHz, CDCl3) δ 170.5 (2C, s,
13
C=O), 170.4 (2C, s, C=O), 70.9 (2C, s), 70.0 (2C, s), 28.1 (4C, s), 27.2 (4C, s),
135
Chapter 6: Experimental
21.3 (2C, s, CH3), 21.3 (2C, s, CH3) ppm. The complete characterization of this
mixture of compounds was not reported in the literature.
6.17.2 Trans-and Cis-4-methylsulfonylcyclohexyl acetate
OAc
OAc
OAc
MsCl, Et3N
+
OAc
+
DCM, 3h
OH
OH
5.43
5.44
100%
OMs
5.50
OMs
5.51
Methanesulfonyl chloride (1.5 mL, 19.38 mmol) was added drop wise over 30
min to a stirred solution of 5.43 and 5.44 (0.5 g, 3.16 mmol) and Et3N (0.6 mL,
4.9 mmol) in DCM (10 mL) at 0 ºC under argon. The mixture was stirred at 0 ºC
for a further 3h. The solvent was removed in vacuum to leave a crude residue
which was partitioned between water (10 mL) and Et2O (10 mL) and the
aqueous layer extracted with Et2O (2×10 mL). The combined organic extracts
were washed with brine (10 mL), dried over MgSO4, filtered and evaporated of
solvent to give the crude which was purified by column chromatography and
afforded a white solid 0.746 g (100%) of a mixture of diastereoisomers 5.50
and 5.51. Mw 236.29 (C9H16O5S); Rf 0.13 (EtOAc/PE 20:80); IR (neat) 2949 (m,
CH3), 2862 (m, C–H), 1716 (s, C=O),1244 (m, C–O) cm-1; 1H NMR (400 MHz,
CDCl3) δ 4.74–4.89 (4H, m), 3.02 (3H, s), 3.02 (3H, s), 1.95–2.14 (12H, m),
1.70–1.92 (8H, m), 1.53–1.66 (2H, m) ppm;
C NMR (75 MHz, CDCl3) δ 170.4
13
(s, C=O), 170.4 (s, C=O), 78.8 (s), 78.3 (s), 69.8 (s), 69.2 (s), 38.7 (s), 38.7 (s),
28.6 (2C, s), 28.5 (2C, s), 27.1 (2C, s), 26.9 (2c, s), 21.3 (s), 21.2 (s) ppm. No
complete characterization of these compounds has been reported in the
literature.
6.18
Synthesis of Trans-and Cis-3-fluorocyclohexanol
6.18.1 Trans- and Cis-3-fluorocyclohexanol
Iron (III) nitrate nonahydrate (16.47 g, 40.76 mmol) was stirred in water (200
mL) until completely dissolved. The clear solution was cooled to 0 ºC and
136
Chapter 6: Experimental
degased for 10 min. Selectfluor TM (14.44 g, 40.76 mmol) and MeCN (200 mL)
were added to the reaction mixture. A solution of the allylic alcohol 5.54 (2 mL,
20.38 mmol) in MeCN (20 mL) was added to the mixture and NaBH4 (2.47 g,
65.22 mmol) was added at 0 ºC. After 2 min, the mixture was treated with
addition of NaBH4 (2.47 g, 65.22 mmol) and the resulting mixture stirred
overnight. After completion of reaction, the mixture was quenched by adding
35% aqueous NH4OH (163 mL) and then extracted with 10% MeOH in DCM
(3×200 mL) and further extraction with Et2O (2×200 mL). The combined
organic layers were dried over Na2SO4 and evaporated of solvents to give a
crude product that was purified by column chromatography (acetone/PE 10:90)
and afforded 0.826 g (34%), a mixture of 1.61 and 1.62 that turned out to be
inseparable and was used directly in the next step.
6.18.2 Trans-3-fluorocyclohexyl acetate
To a mixture of diastereoisomers 1.61 and 1.62 (0.17 g, 1.44 mmol), pyridine
(0.17 mL, 2.1 mmol) and catalytic amount of dimethylaminopyridine (DMAP)
(0.018 g, 10% mmol) in Et2O (5 mL) was added Ac2O (0.27 mL, 2.88 mmol). The
mixture was stirred at rt for 12h and after completion of reaction was
quenched with water (10 mL) and extracted with Et2O (2×10 mL). The combined
organic layers were washed with 10% CuSO4 solution (5 mL), water (10 mL) and
brine (10 mL); dried over MgSO4 and evaporated of solvent. The crude was
purified by HPLC 1% EtOAc/PE and afforded 5.53, 0.046 g, (20%). The cisisomer was not isolated. Mw 160.19 (C8H13FO2); Rf 0.16 (1% EtOAc/PET 10:90);
IR (neat) 2945(m, C–H), 1721 (m, C=O), 1225 (s, C–F), 1024 (m, C–O), cm-1; 1H
NMR (300 MHz, CDCl3) δ 5.11 (1H, ddd, J 11.3, 8.1, 4.0 Hz, H1), 4.89 (1H,
dddd, J 48.3, 9.5, 6.2, 2.9 Hz, H3), 1.98–2.13 (4H, m) 1.58–1.92 (6H, m) 1.42–
1.57 (1H, m) ppm; 13C NMR (101 MHz, CDCl3) δ 170.2 (s, C=O) 89.4 (d, J 167.2
Hz, C3) 69.7 (d, J 5.5 Hz, C1) 36.5 (d, J 20.5 Hz, C2) 30.8 (d, J 20.1 Hz, C4)
30.3 (br., s, C5) 21.3 (s, CH3) 18.7 (s, C6) ppm;
F NMR (282 MHz, CDCl3) δ -
19
180.2 (1F, m) ppm. This fluorocyclohexyl acetate was not reported in the
literature.
137
Chapter 6: Experimental
6.18.3 Trans and Cis-3-fluoro-2-iodocyclohexanol
To a solution of 5.54 (1 mL, 10.18 mmol) in DCM (10 mL) at -60 ºC was added
hydrogen fluoride pyridine complex 70% (0.37 mL, 20.36 mmol), immediately
followed by N-iodosuccinimide (4.58 g, 20.36 mmol). The reaction mixture was
stirred at -60 ºC for 2h and then allowed to warm up to rt for 24h. 17% solution
of aqueous ammonia (20 mL) was added and the mixture extracted with Et2O
(3×20 mL). The organic phases were combined, washed with saturated Na2S2O3
solution (15 mL) and brine (20 mL); dried (MgSO4) and evaporated of solvent.
The crude was purified by column chromatography (acetone/PE 10:90) and
HPLC (acetone/hexane 05:95) that afforded 5.56, 0.16 g (6%) and 5.57, 0.038
g (2%).
Mw 244.05 (C6H10FIO); Rf 0.43 (EtOAc/PE 20:80); IR (neat) 3414
(br.,OH) 2945 (m, C–H), 1444 (m, C–f), 1058 (m, C–O), cm-1; EI MS: m/z
117.1 [M+ = (M-I)] (48%). 1H NMR (300 MHz, CDCl3) δ 4.93 (1H, dtd, J
47.5, 7.7, 7.7, 3.6 Hz, H3), 4.43 (1H, td, J 7.7, 2.9 Hz, H2), 3.70–3.82 (1H, m,
H1), 2.14–2.36 (1H, m, H4ax), 2.06 (1H, br. d, J 4.8 Hz, OH) 1.59–1.87 (5H, m,
H4eq, 5,6) ppm; 13C NMR (101 MHz, CDCl3) δ 92.6 (d, J 177.1 Hz, C3), 70.3 (d, J
4.0 Hz, C1), 42.7 (d, J 18.7 Hz, C2), 31.2 (d, J 1.5 Hz, C6), 29.7 (d, J 22.7 Hz,
C4), 18.3 (d, J 7.3 Hz, C5) ppm;
F NMR (282 MHz, CDCl3) δ -166.0 (1F, m, J
19
46.2 Hz observed) ppm.
Mw 244.05 (C6H10FIO); Rf 0.20 (EtOAc/PE 20:80); 1H NMR (300 MHz,
CDCl3) δ 4.56 (1H, dtd, J 47.1, 10.2, 10.2, 4.7 Hz, H3), 3.93 (1H, td, J
9.9, 7.1 Hz, H2), 3.64–3.78 (1H, m, H1) 2.41 (1H, d, J 2.9 Hz, OH)
1.99–2.19 (2H, m, H4ax, 6eq) 1.77–1.96 (1H, m, H5ax) 1.40–1.62 (1H, m, H4eq)
1.25–1.39 (2H, m, H5eq, 6ax) ppm;
C NMR (101 MHz, CDCl3) δ 93.6 (d, J 182.2
13
Hz, C3) 73.8 (d, J 6.2 Hz, C1) 44.5 (d, J 15.4 Hz, C2) 32.4 (d, J 1.5 Hz, C6)
32.0 (d, J 19.0 Hz, C4) 18.8 (d, J 12.1 Hz, C5) ppm; 19F NMR (282 MHz, CDCl3)
δ -162.7 (1F, d, J 47.3 Hz) ppm. The compounds 5.68 and 5.69 were not
reported in the literature.
138
Chapter 6: Experimental
6.18.4 Trans-3-fluorocyclohexanol
To a solution of 5.56 (0.14 g, 0.57 mmol) in degassed benzene (5 mL) was
added tributyltin hydride (0.31 mL, 1.14 mmol) and azobisisobutyronitrile
(0.007 g, 0.046 mmol). The mixture was heated to reflux for 3h after which the
solvent was removed under vacuum.
The residue was purified by column
chromatography (acetone/PE 07-20:93-80) to give yellow oil of 1.61, 0.043 g
(64%). Mw 118.15 (C6H11FO); Rf 0.33 (EtOAc/PET 20:80); 1H NMR (400 MHz,
CDCl3) δ 4.95 (1H, dddd, J 47.7, 8.3, 5.6, 2.9 Hz, H3) 4.05 (1H, tdd, J 8.7, 8.4,
8.4, 3.9 Hz, H1) 2.09–2.20 (1H, m) 1.76–1.92 (2H, m) 1.50–1.74 (4H, m) 1.47
(1H, d, J 4.2 Hz, OH) 1.31–1.44 (1H, m) ppm; 13C NMR (101 MHz, CDCl3) δ 90.0
(d, J 167.2 Hz, C3) 66.7 (d, J 4.4 Hz, C1) 39.8 (d, J 19.8 Hz, C2) 34.2 (s, C6)
30.6 (d, J 20.5 Hz, C4) 18.7 (d, J 4.4 Hz, C5) ppm; 19F NMR (282 MHz, CDCl3) δ
-180.9 (1F, br. d, J 42.3 Hz) ppm.
6.19
Synthesis of 2-Fluorobenzyl Alcohols 5.66-5.68
6.19.1 2-Fluorobenzyl alcohol
2-Fluorobenzaldehyde 5.58 (2.55 mL, 24.17 mmol) was dissolved in THF (25
mL) and sodium borohydride (0.914, 24.17 mmol) was added to the reaction
mixture. MeOH (5 mL) was then added drop wise and the mixture stirred at 70
ºC for 4h. After total consumption of the starting material, the reaction mixture
was washed with water (2×10 mL) and brine (2×10 mL). The obtained organic
layer was dried (MgSO4), filtered, concentrated under reduced pressure and
purified by column chromatography (EtOAc/PET 20:80). This afforded 1.69,
2.869 g (94%). Mw: 126.13 (C7H7FO), Rf 0.16 (EtOAc/PET 10:90); 1H NMR (300
MHz, CDCl3) δ 7.44 (1H, td, J 7.5, 1.6 Hz, HAr) 7.25–7.35 (1H, m, HAr) 7.16 (1H,
139
Chapter 6: Experimental
td, J 7.4, 0.9 Hz, HAr) 7.02–7.11 (1H, m, HAr) 4.78 (2H, d, J 5.8 Hz, CH2) 1.93
(1H, t, J 6.0 Hz, OH) ppm;
C NMR (75 MHz, CDCl3) δ 160.6 (d, J 246.6 Hz),
13
129.3 (s), 129.3 (d, J 12.7 Hz), 127.8 (d, J 14.7 Hz), 124.2 (d, J 3.6 Hz), 115.2
(d, J 21.3 Hz), 59.4 (d, J 4.4 Hz) ppm;
F NMR (282 MHz, CDCl3) δ -120.1 (1F,
19
br. s.) ppm.
6.19.2 2-Fluoro-5-methylbenzyl alcohol
Similar procedure as for synthesis of 1.69 was used on 5.59 (3.0 g, 19.46
mmol) and afforded a colourless liquid of 1.70, 2.57 g (84%). Mw: 156.15
(C8H9FO2), Rf 0.23 (EtOAc/PET 20:80);
(EtOAc/PET 20:80);
1
Mw: 156.15 (C8H9FO2), Rf 0.23
H NMR (300 MHz, CDCl3) δ 6.92–7.01 (2H, m, HAr), 6.77
(1H, s, HAr), 4.73 (2H, br. d, J 5.5 Hz, CH2), 3.79 (3H, s, OMe), 2.00 (1H, t, J 5.9
Hz, OH) ppm;
C NMR (75 MHz, CDCl3) δ 155.8 (d, J 2.2 Hz) 154.8 (d, J 238.0
13
Hz) 128.4 (d, J 16.6 Hz) 115.7 (d, J 22.9 Hz) 114.1 (d, J 8.0 Hz) 113.8 (d, J 4.7
Hz) 59.4 (d, J 3.9 Hz) 55.7 (s, CH3) ppm;
F NMR (282 MHz, CDCl3) δ -130.9
19
(1F, br. s.) ppm.
6.19.3 2-Fluoro-5-nitrobenzyl alcohol
Similar procedure as for synthesis of 1.69 was used on 5.60 (3.0 g, 17.74
mmol) and afforded a pale yellow solid of 1.71, 2.55 g (84%); Mw: 171.13
(C7H6FNO3), Rf 0.26 (EtOAc/PET 20:80),
H NMR (300 MHz, CDCl3) δ 8.42 (1H,
1
dd, J 6.1, 2.8 Hz), 8.19 (1H, ddd, J 8.8, 4.2, 3.2 Hz), 7.19 (1H, t, J 8.9 Hz),
4.85 (2H, d, J 5.9 Hz, CH2), 2.24 (1H, t, J 5.9 Hz, OH) ppm,13C NMR (75 MHz,
CDCl3) δ 163.5 (d, J 257.4 Hz), 129.8 (d, J 16.9 Hz), 125.0 (d, J 10.2 Hz),
124.7 (d, J 6.6 Hz), 116.1 (d, J 24.0 Hz), 58.3 (d, J 4.1 Hz) ppm;
(282 MHz, CDCl3) δ -108.7 (1F, br. s.) ppm.
140
F NMR
19
Chapter 7: References
7 List of References
(1)
Murphy, C. D.; Schaffrath, C.; O’Hagan, D. Chemosphere 2003, 52,
455-461.
(2)
Dalvit, C.; Vulpetti, A. ChemMedChem 2012, 7, 262-272.
(3)
Wang, J.; Sánchez-Roselló, M.; Aceña, J. L.; del Pozo, C.; Sorochinsky,
A. E.; Fustero, S.; Soloshonok, V. A.; Liu, H. Chem. Rev. 2013, 114,
2432-2506.
(4)
Ojima, I. Fluorine in Medicinal Chemistry and Chemical Biology;
Blackwell Publishing Ltd: New York, USA, 2009.
(5)
O’Hagan, D.; Harper, D. B. J. Fluorine Chem. 1999, 100, 127-133.
(6)
Marais, J. C. S. Onderstepoort J. Vet. Sci Anim. Ind. 1944, 20, 67-73.
(7)
Lovelace, J.; Miller, G. W.; Welkie, G. W. Atmos Environ (1967) 1968,
2, 187-190.
(8)
Ward, P. F. V.; Hall, R. J.; Peters, R. J. Nature 1964, 201, 611-612.
(9)
Thomas, S. O.; Singleton, V. L.; Lowery, J. A.; Sharpe, R. W.; Preuss,
L. M.; Porter, J. N.; Mowat, J. H.; Bohonos, N. Antibiotics Ann 1956,
1956-1957, 716.
(10) Tannock, J.; Rhod, J. Agric. Res 1975, 13, 67-71.
(11) Begue, J.-P.; Bonnet-Delpon, D. Bioorganic and Medicinal Chemistry
of Fluorine John Wiley & Sons: Canada, 2008.
(12) Fried, J.; Sabo, E. F. J. Am. Chem. Soc. 1954, 76, 1455-1456.
(13) O’Hagan, D. J. Fluorine Chem. 2010, 131, 1071-1081.
(14) Elmon L, C. Biochim. Biophys. Acta, Gen. Subj. 1972, 264, 319-327.
(15) Som, P.; Atkins, H. L.; Bandoypadhyay, D.; Fowler, J. S.; MacGregor,
R. R.; Matsui, K.; Oster, Z. H.; Sacker, D. F.; Shiue, C. Y.; Turner, H.;
Wan, C.-N.; Wolf, A. P.; Zabinski, S. V. J. Nucl. Med. 1980, 21, 670675.
(16) Moadel1, R. M.; Nguyen, A. V.; Lin, E. Y.; Lu, P.; Mani1, J.; Blaufox, M.
D.; Pollard, J. W.; Dadachova1, E. Breast Cancer Res 2003, R199R205.
(17) Ni, C.; Wang, F.; Hu, J. Beilstein J. Org. Chem. 2008, 4, 21.
(18) Cottet, F.; Marull, M.; Lefebvre, O.; Schlosser, M. Eur. J. Org. Chem.
2003, 2003, 1559-1568.
141
Chapter 7: References
(19) Smart, B. E. J. Fluorine Chem. 2001, 109, 3-11.
(20) Banks, R. E.; Smart, B. E.; Tatlow, J. C. Organofluorine Chemistry:
Principles and Commercial Applications; Plenum, New York, 1994.
(21) Müller, K.; Faeh, C.; Diederich, F. Science 2007, 317, 1881-1886.
(22) Arnott, J. A.; Planey, S. L. Expert Opinion on Drug Discovery 2012, 7,
863-875.
(23) Dolbier, W. R. Guide to Fluorine NMR for Organic Chemists John
Wiley & Sons, Inc., Hoboken New Jersey, 2009.
(24) Liu, X.; Testa, B.; Fahr, A. Pharm. Res. 2011, 28, 962-977.
(25) Waring, M. J. Bioorg. Med. Chem. Lett. 2009, 19, 2844-2851.
(26) Yamagami, C.; Takao, N. Chem. Pharm. Bull. 1993, 41, 694-698.
(27) Muller, N. J. Pharm. Sci. 1986, 75, 987-991.
(28) Biffinger, J. C.; Kim, H. W.; DiMagno, S. G. ChemBioChem 2004, 5,
622-627.
(29) Leo, A. J. Chem. Soc. Perkin Trans. 2 1983, 825-838.
(30) Menger, F. M.; Venkataram, U. V. J. Am. Chem. Soc. 1986, 108,
2980-2984.
(31) Linclau, B.; Leung, L.; Nonnenmacher, J.; Tizzard, G. Beilstein J. Org.
Chem. 2010, 6, 62.
(32) Gold, V.; 2nd ed.; International Union of Pure and Applied
Chemistry: 1997.
(33) Kuhn, B.; Mohr, P.; Stahl, M. J. Med. Chem. 2010, 53, 2601-2611.
(34) Graton, J.; Wang, Z.; Brossard, A.-M.; Gonçalves Monteiro, D.; Le
Questel, J.-Y.; Linclau, B. Angew. Chem., Int. Ed. 2012, 51, 61766180.
(35) Giuffredi, G. T.; Gouverneur, V.; Bernet, B. Angew. Chem., Int. Ed.
2013, 52, 10524-10528.
(36) Giuffredi, G. T.; Bernet, B.; Gouverneur, V. Eur. J. Org. Chem. 2011,
2011, 3825-3836.
(37) Mecinović, J.; Snyder, P. W.; Mirica, K. A.; Bai, S.; Mack, E. T.; Kwant,
R. L.; Moustakas, D. T.; Héroux, A.; Whitesides, G. M. J. Am. Chem.
Soc. 2011, 133, 14017-14026.
(38) Kim, H. W.; Rossi, P.; Shoemaker, R. K.; DiMagno, S. G. J. Am. Chem.
Soc. 1998, 120, 9082-9083.
(39) Bresciani, S.; Lebl, T.; Slawin, A. M. Z.; O'Hagan, D. Chem. Commun
2010, 46, 5434-5436.
142
Chapter 7: References
(40) Riley, G. J.; Taylor, N. F. Biochem. J. 1973, 135, 773-777.
(41) Choo, H.; Chong, Y.; Choi, Y.; Mathew, J.; Schinazi, R. F.; Chu, C. K.
J. Med. Chem. 2003, 46, 389-398.
(42) Linclau, B.; Boydell, A. J.; Timofte, R. S.; Brown, K. J.; Vinader, V.;
Weymouth-Wilson, A. C. Org. Biomol. Chem. 2009, 7, 803-814.
(43) Boydell, A. J.; Vinader, V.; Linclau, B. Angew. Chem., Int. Ed. 2004,
43, 5677-5679.
(44) Golten, S. B., University of Southampton, 2012.
(45) Timofte, R. S.; Linclau, B. Org. Lett. 2008, 10, 3673-3676.
(46) Lucas, R.; Peñalver, P.; Gómez-Pinto, I.; Vengut-Climent, E.;
Mtashobya, L.; Cousin, J.; Maldonado, O. S.; Perez, V.; Reynes, V.;
Aviñó, A.; Eritja, R.; González, C.; Linclau, B.; Morales, J. C. J. Org.
Chem. 2014, 79, 2419-2429.
(47) Terraneo, G.; Potenza, D.; Canales, A.; Jiménez-Barbero, J.;
Baldridge, K. K.; Bernardi, A. J. Am. Chem. Soc. 2007, 129, 28902900.
(48) Ramirez-Gualito, K.; Alonso-Rios, R.; Quiroz-Garcia, B.; Rojas-Aguilar,
A.; Diaz, D.; Jimenez-Barbero, J.; Cuevas, G. J. Am. Chem. Soc. 2009,
131, 18129-18138.
(49) Screen, J.; Stanca-Kaposta, E. C.; Gamblin, D. P.; Liu, B.; Macleod, N.
A.; Snoek, L. C.; Davis, B. G.; Simons, J. P. Angew. Chem., Int. Ed.
2007, 46, 3644-3648.
(50) Kozmon, S.; Matuška, R.; Spiwok, V.; Koča, J. Chem. Eur. J. 2011, 17,
5680-5690.
(51) Fernández-Alonso, M. d. C.; Cañada, F. J.; Jiménez-Barbero, J.;
Cuevas, G. J. Am. Chem. Soc. 2005, 127, 7379-7386.
(52) Lucas, R.; Gómez-Pinto, I.; Aviñó, A.; Reina, J. J.; Eritja, R.; González,
C.; Morales, J. C. J. Am. Chem. Soc. 2011, 133, 1909-1916.
(53) Morales, J. C.; Reina, J. J.; Díaz, I.; Aviñó, A.; Nieto, P. M.; Eritja, R.
Chem. Eur. J. 2008, 14, 7828-7835.
(54) Withers, S. G.; MacLennan, D. J.; Street, I. P. Carbohydr. Res. 1986,
154, 127-144.
(55) Jeong, L. S.; Lim, B. B.; Marquez, V. E. Carbohydr. Res. 1994, 262,
103-114.
143
Chapter 7: References
(56) Raju, R.; Castillo, B. F.; Richardson, S. K.; Thakur, M.; Severins, R.;
Kronenberg, M.; Howell, A. R. Bioorg. Med. Chem. Lett. 2009, 19,
4122-4125.
(57) Danac, R.; Ball, L.; Gurrb, S. J.; Antony J. Fairbanksa Carbohydr. Res.
2008, 343, 1012–1022.
(58) Egli, M.; Pallan, P. S.; Allerson, C. R.; Prakash, T. P.; Berdeja, A.; Yu,
J.; Lee, S.; Watt, A.; Gaus, H.; Bhat, B.; Swayze, E. E.; Seth, P. P. J. Am.
Chem. Soc. 2011, 133, 16642-16649.
(59) Guo, J.; Frost, J. W. J. Am. Chem. Soc. 2002, 124, 10642-10643.
(60) Elchert, B.; Li, J.; Wang, J.; Hui, Y.; Rai, R.; Ptak, R.; Ward, P.;
Takemoto, J. Y.; Bensaci, M.; Chang, C.-W. T. J. Org. Chem. 2004,
69, 1513-1523.
(61) Ambrose, M. G.; Binkley, R. W. J. Org. Chem. 1983, 48, 674-677.
(62) Kobayashi, S.; Yoneda, A.; Fukuhara, T.; Hara, a. S. Tetrahedron
2004, 60, 6923-6930.
(63) Ioannou, A.; Cini, E.; Timofte, R. S.; Flitsch, S. L.; Turner, N. J.;
Linclau, B. Chem. Commun 2011, 47, 11228-11230.
(64) Avigad, G.; Amaral, D.; Asensio, C.; Horecker, B. L. J. Biol. Chem.
1962, 237, 2736-2743.
(65) Whittaker, J. W. Chem. Rev. 2003, 103, 2347-2364.
(66) Barlow, J. N.; Blanchard, J. S. Carbohydr. Res. 2000, 328, 473-480.
(67) Hoffmann-Roder, A.; Johannes, M. Chem. Commun 2011, 47, 99039905.
(68) Kováč, P.; Glaudemans, C. P. J. Carbohydr. Res. 1983, 123, 326-331.
(69) Hawley, J.; Bampos, N.; Aboitiz, N.; Jiménez-Barbero, J.; Paz,
Manuela López de l.; Sanders, Jeremy K. M.; Carmona, P.; Vicent, C.
Eur. J. Org. Chem. 2002, 2002, 1925-1936.
(70) Pacak, J.; Podesva, J.; Tocik, Z.; Cerny, M. Collect. Czech. Chem.
Commun 1972, 37, 2589-2599.
(71) Sarda, P.; Escribano, F. C.; José Alves, R.; Olesker, A.; Lukacs, G. J.
Carbohydr. Chem. 1989, 8, 115-123.
(72) Viuff, A. H.; Hansen, J. C.; Christiansen, A. B.; Jensen, H. H. Synth.
Commun. 2012, 43, 1557-1562.
(73) Hesek, D.; Lee, M.; Zhang, W.; Noll, B. C.; Mobashery, S. J. Am.
Chem. Soc. 2009, 131, 5187-5193.
(74) Arndt, S.; Hsieh-Wilson, L. C. Org. Lett. 2003, 5, 4179-4182.
144
Chapter 7: References
(75) Ballereau, S.; Guedat, P.; Spiess, B.; Rehnberg, N.; Schlewer, G.
Tetrahedron Lett. 1995, 36, 7449-7450.
(76) Wray, V. J. Chem. Soc., Perkin Trans. 2 1976, 1598-1605.
(77) Matsumoto, K.; Ebata, T.; Koseki, K.; Okano, K.; Kawakami, H.;
Matsushita, H. Carbohydr. Res. 1993, 246, 345-352.
(78) Thiem, J.; Elvers, J.; Lorentzen, J. P. Chem. Ber. 1980, 113, 28272831.
(79) Sviridov, A. F.; Berdimbetova, G. E.; Kochetkov, N. K. Bulletin of the
Academy of Sciences of the USSR, Division of chemical science 1982,
31, 2273-2277.
(80) White, J. D.; Bolton, G. L.; Dantanarayana, A. P.; Fox, C. M. J.; Hiner,
R. N.; Jackson, R. W.; Sakuma, K.; Warrier, U. S. J. Am. Chem. Soc.
1995, 117, 1908-1939.
(81) Lal, G. S.; Pez, G. P.; Pesaresi, R. J.; Prozonic, F. M.; Cheng, H. J. Org.
Chem. 1999, 64, 7048-7054.
(82) L’Heureux, A.; Beaulieu, F.; Bennett, C.; Bill, D. R.; Clayton, S.;
LaFlamme, F. o.; Mirmehrabi, M.; Tadayon, S.; Tovell, D.; Couturier,
M. J. Org. Chem. 2010, 75, 3401-3411.
(83) Gong, C.; Shenzhen; C07H 19/12 (2006.01), A61K 31/7072
(2006.01) ed. United State, 2006; Vol. US 20060003963 A1.
(84) Boydell, J., University of Southampton, 2006.
(85) Reich, H. J. University of Wisconsin, 2010, p 6.1-6.5.
(86) Bifulco, G.; Dambruoso, P.; Gomez-Paloma, L.; Riccio, R. Chem. Rev.
2007, 107, 3744-3779.
(87) Nakai, K.; Takagi, Y.; Tsuchiya, T. Carbohydr. Res. 1999, 316, 4757.
(88) Bernet, B.; Vasella, A. Helv. Chim. Acta 2007, 90, 1874-1888.
(89) Akiyama, Y.; Fukuhara, T.; Hara, S. Synlett 2003, 2003, 1530-1532.
(90) Shao, L.; Wang, F.; Marcolm, S., Christopher; Hewitt, M., Charles;
Bush, L., R; MA, J.; Varney, M., A; Compbell, U.; Engel, S., Rae; Hardy,
L., Wendell; Koch, P.; Campbell, J., E In Sepracor Inc; A61K31/18
(2006.01) ed.; Inc, S., Ed. US, 2007; Vol. WO 2007/081857 A2.
(91) Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1965, 87, 1353-1364.
(92) Lundt, I.; Albanese, D.; Landini, D.; Penso, M. Tetrahedron 1993, 49,
7295-7300.
145
Chapter 7: References
(93) Surya Prakash, G. K.; Hu, J.; Wang, Y.; Olah, G. A. Eur. J. Org. Chem.
2005, 2005, 2218-2223.
(94) Beier, P.; Alexandrova, A. V.; Zibinsky, M.; Surya Prakash, G. K.
Tetrahedron 2008, 64, 10977-10985.
(95) Waschbüsch, R.; Samadi, M.; Savignac, P. J. Organomet. Chem.
1997, 529, 267-278.
(96) Baeza, A.; Nájera, C.; Sansano, J. M.; Saá, J. M. Chem. Eur. J. 2005,
11, 3849-3862.
(97) Carcenac, Y.; Tordeux, M.; Wakselman, C.; Diter, P. J. Fluorine Chem.
2005, 126, 1347-1355.
(98) Senda, Y.; Ishiyama, J.; Imaizumi, S. Tetrahedron 1975, 31, 16011605.
(99) Reetz, M. T.; Stanchev, S. J. Chem. Soc., Chem. Commun. 1993, 328330.
(100)Zhang, C.; Burke, M.; Chen, Z.; Dumas, J.; Fan, D.; Fan, J.; HatoumMokdad, H.; Jones, B. D.; Ladouceur, G.; Lee, W.; Phillips, B.; Corp, B.
P., Ed. US, 2003; Vol. WO03072561 (A1)
(101)Tanemura, K.; Suzuki, T.; Nishida, Y.; Satsumabayashi, K.;
Horaguchi, T. Chem. Commun 2004, 470-471.
(102)Fujiko, Y.; Shozo, Y.; Masayuki, T. Bull. Chem. Soc. Jpn 1991, 64,
3390-3394.
(103)Dunkelblum, E.; Levene, R.; Klein, J. Tetrahedron 1972, 28, 10091024.
(104)Linclau, B.; Boydell, A. J.; Clarke, P. J.; Horan, R.; Jacquet, C. J. Org.
Chem. 2003, 68, 1821-1826.
(105)Bird, T. G. C.; Fredericks, P. M.; Jones, E. R. H.; Meakins, G. D. J.
Chem. Soc., Chem. Commun. 1979, 65-66.
(106)Michaela, B.; Hanspeter, K.; Georg, K.; Michael , F.; Toshinari, K.; ,
R., Konrat; Walther, S. Beilstein J. Org. Chem 2012, 8, 448-455.
(107)Adams, D. R.; Duncton, M. A. J. Synth. Commun. 2001, 31, 20292036.
(108)Kim, D. W.; Jeong, H.-J.; Lim, S. T.; Sohn, M.-H. Angew. Chem., Int.
Ed. 2008, 47, 8404-8406.
(109)Lee, Y.; Jeon, H.-B.; Huang, H.; Sayre, L. M. J. Org. Chem. 2001, 66,
1925-1937.
146
Chapter 7: References
(110)Hannedouche, J.; Clarkson, G. J.; Wills, M. J. Am. Chem. Soc. 2004,
126, 986-987.
(111) Kendall, J. T. J. Labelled Compd. Radiopharm. 2000, 43, 917-924.
(112)Kim, A.; Powers, J. D.; Toczko, J. F. J. Org. Chem. 2006, 71, 21702172.
(113) Brownlee, R.; Sadek, M. Aust. J. Chem. 1981, 34, 1593-1602.
(114) Shawcross, F.; Sard, H. J. Heterocycl. Chem. 1995, 32, 1393-1395.
(115) Sheppard, W. A.; Taft, R. W. J. Am. Chem. Soc. 1972, 94, 1919-1923.
(116)Ando, T.; Ishihara, T.; Ohtani, E.; Sawada, H. J. Org. Chem. 1981, 46,
4446-4450.
(117) Spiniello, M.; White, J. M. Org. Biomol. Chem. 2003, 1, 3094-3101.
(118) Wang, S.; Zhang, A. Org. Prep. Proced. Int. 2008, 40, 293-301.
(119) Huffman, J. W.; Desai, R. C. Synth. Commun. 1983, 13, 553-557.
(120)Abraham, R. J.; Smith, T. A. D.; Thomas, W. A. J. Chem. Soc., Perkin
Trans. 2 1996, 1949-1955.
(121)Basso, E. A.; Abiko, L. A.; Gauze, G. F.; Pontes, R. M. J. Org. Chem.
2011, 76, 145-153.
(122) Musher, J. I.; Corey, E. J. Tetrahedron 1962, 18, 791-809.
(123)Hatano, M.; Kamiya, S.; Moriyama, K.; Ishihara, K. Org. Lett. 2010,
13, 430-433.
(124)Van, W. B.; Radhakrishnan, U.; Joshua, C.; Ian, E.; R, E. J.; Methvin, I.;
Fupeng, M.; Abdelmalik, S.; Gary, S.; Rebecca, U.; Sally, W.; Van, W.
B.; Radhakrishnan, U.; Joshua, C.; Ian, E.; R, E. J.; Methvin, I.; Fupeng,
M.; Abdelmalik, S.; Gary, S.; Rebecca, U.; Sally, W.; Bradford, V. W.;
James, E.; A61K31/4015; A61K31/496; A61P25/00; C07D209/34;
C07D401/14 ed.; +, A. A. S., Ed. 2009; Vol. US2009111830 (A1).
(125)Bandgar, B. P.; Kamble, V. T.; Biradar, A. V. Monatshefte für Chemie
/ Chemical Monthly 2005, 136, 1579-1582.
(126)Choudhari, M. K.; Punekar, S. A.; Ranade, R. V.; Paknikar, K. M. J.
Ethnopharmacol. 2012, 141, 363-367.
(127)Liu, W.; Huang, X.; Cheng, M.-J.; Nielsen, R. J.; Goddard, W. A.;
Groves, J. T. Science 2012, 337, 1322-1325.
(128)Barker, T. J.; Boger, D. L. J. Am. Chem. Soc. 2012, 134, 1358813591.
(129)Hayashi, T.; Kawatsura, M.; Uozumi, Y. J. Am. Chem. Soc. 1998, 120,
1681-1687.
147
Chapter 7: References
(130) Shaikh, N. S.; Junge, K.; Beller, M. Org. Lett. 2007, 9, 5429-5432.
(131)Monclus, M.; Masson, C.; Luxen, A. J. Fluorine Chem. 1995, 70, 3943.
(132)Lee, J.; Ryu, T.; Park, S.; Lee, P. H. J. Org. Chem. 2012, 77, 48214825.
(133)Andre, D.; Patricia, M.; Stephane, B.; Nicolas, L. 2001; Vol.
WO2011073322 (A1)
(134) Tewson, T. J.; Welch, M. J. J. Org. Chem. 1978, 43, 1090-1092.
(135)Sladojevich, F.; Arlow, S. I.; Tang, P.; Ritter, T. J. Am. Chem. Soc.
2013, 135, 2470-2473.
(136) Card, P. J. J. Org. Chem. 1983, 48, 393-395.
(137)Leteux, C.; Veyrières, A.; Robert, F. Carbohydr. Res. 1993, 242, 119130.
(138)Sviridov, A. F.; Borodkin, V. S.; Ermolenko, M. S.; Yashunsky, D. V.;
Kochetkov, N. K. Tetrahedron 1991, 47, 2291-2316.
(139) Jin, J.; Weinreb, S. M. J. Am. Chem. Soc. 1997, 119, 5773-5784.
(140)Weijers, C. A. G. M.; Konst, P. M.; Franssen, M. C. R.; Sudholter, E. J.
R. Org. Biomol. Chem. 2007, 5, 3106-3114.
(141)Lifchits, O.; Mahlau, M.; Reisinger, C. M.; Lee, A.; Farès, C.; Polyak, I.;
Gopakumar, G.; Thiel, W.; List, B. J. Am. Chem. Soc. 2013, 135,
6677-6693.
(142)Evans, D. A.; Chapman, K. T.; Carreira, E. M. J. Am. Chem. Soc. 1988,
110, 3560-3578.
(143)Jantzen, R.; Tordeux, M.; de Villardi, G.; Chachaty, C. Org. Magn.
Resonance 1976, 8, 183-186.
148
Chapter 8: Appendix
8 Appendix
8.1 X-ray Crystallography Data
Details of X-ray crystal Structure Determination of X
Table 1. Crystal data and structure refinement details
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal
Crystal size
θ range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to θ = 27.48°
Absorption correction
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [F2 > 2σ(F2)]
R indices (all data)
Largest diff. peak and hole
2011sot0763 (LM6136-93)
C14H19FO9
350.29
100(2) K
0.71075 Å
Monoclinic
P21
a = 8.146(3) Å
b = 12.669(3) Å
β = 111.677(4)°
c = 8.241(3) Å
790.3(4) Å3
2
1.472 Mg / m3
0.131 mm−1
368
Fragment; Colourless
0.22 × 0.13 × 0.04 mm3
3.00 − 27.48°
−10 ≤ h ≤ 10, −16 ≤ k ≤ 14, −10 ≤ l ≤ 10
5119
1884 [Rint = 0.0287]
99.3 %
Semi−empirical from equivalents
0.9948 and 0.9718
Full-matrix least-squares on F2
1884 / 1 / 221
1.011
R1 = 0.0325, wR2 = 0.0525
R1 = 0.0377, wR2 = 0.0544
0.178 and −0.182 e Å−3
Diffractometer: Rigaku AFC12 goniometer equipped with an enhanced sensitivity (HG) Saturn724+ detector
mounted at the window of an FR-E+ SuperBright molybdenum rotating anode generator with HF Varimax optics
(100µm focus). Cell determination, Data collection, Data reduction and cell refinement & Absorption
correction: CrystalClear-SM Expert 2.0 r7 (Rigaku, 2011) , Structure solution: SHELXS97 (G. M. Sheldrick, Acta
Cryst. (1990) A46 467−473). Structure refinement: SHELXL97 (G. M. Sheldrick (1997), University of Göttingen,
Germany). Graphics: CrystalMaker: a crystal and molecular structures program for Mac and Windows. CrystalMaker
Software Ltd, Oxford, England (www.crystalmaker.com)
Special details: All hydrogen atoms were located from the difference map and placed in idealised positions and
refined using a riding model, methyl torsion angles were allowed to refine.
149
Chapter 8: Appendix
Table 2. Atomic coordinates [× 104], equivalent isotropic displacement
parameters [Å2 × 103] and site occupancy factors. Ueq is defined as one third of
the trace of the orthogonalized Uij tensor.
Atom
x
y
z
Ueq
S.o.f.
F3
O1
O2
O4
O5
O6
O7
O8
O9
O10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
5680(1)
1934(2)
5354(2)
4849(2)
2557(2)
−521(2)
1324(2)
8127(2)
5445(2)
−1275(2)
3272(2)
4776(3)
4205(3)
3469(2)
1962(3)
1203(3)
997(3)
−465(3)
7095(3)
7488(3)
5786(3)
7272(3)
−1663(3)
−3429(3)
169(1)
947(1)
281(1)
2266(1)
2457(1)
3169(1)
1910(1)
916(1)
1544(1)
3977(1)
1699(2)
1104(2)
638(2)
1496(2)
2038(2)
2943(2)
1173(2)
412(2)
286(2)
−587(2)
2173(2)
2948(2)
3673(2)
3807(2)
669(2)
−4277(2)
−2860(2)
1023(2)
−2555(2)
−1870(2)
−6729(2)
−1746(3)
3691(2)
171(2)
−3348(3)
−1997(3)
−608(3)
212(3)
−1225(3)
−549(3)
−5994(3)
−6769(3)
−2650(3)
−3650(3)
2760(3)
3337(3)
−1303(3)
−2733(3)
22(1)
20(1)
20(1)
19(1)
19(1)
22(1)
32(1)
44(1)
29(1)
36(1)
19(1)
18(1)
17(1)
17(1)
18(1)
21(1)
21(1)
28(1)
24(1)
26(1)
20(1)
24(1)
21(1)
25(1)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
150
Chapter 8: Appendix
Table 3. Bond lengths [Å] and angles [°]
F3−C3
O1−C7
O1−C1
O2−C9
O2−C2
O4−C11
O4−C4
O5−C1
O5−C5
O6−C13
O6−C6
O7−C7
O8−C9
O9−C11
O10−C13
C1−C2
C2−C3
C3−C4
C4−C5
C5−C6
C7−C8
C9−C10
C11−C12
C13−C14
C7−O1−C1
C9−O2−C2
C11−O4−C4
C1−O5−C5
C13−O6−C6
O5−C1−O1
O5−C1−C2
O1−C1−C2
O2−C2−C3
O2−C2−C1
C3−C2−C1
F3−C3−C2
F3−C3−C4
C2−C3−C4
O4−C4−C3
O4−C4−C5
C3−C4−C5
O5−C5−C6
O5−C5−C4
C6−C5−C4
O6−C6−C5
O7−C7−O1
O7−C7−C8
O1−C7−C8
O8−C9−O2
O8−C9−C10
1.404(2)
1.367(3)
1.437(2)
1.364(2)
1.435(2)
1.356(3)
1.452(2)
1.403(2)
1.453(2)
1.347(2)
1.452(2)
1.196(3)
1.198(3)
1.208(3)
1.200(3)
1.517(3)
1.506(3)
1.516(3)
1.518(3)
1.505(3)
1.481(3)
1.482(3)
1.493(3)
1.495(3)
115.89(16)
116.77(16)
117.76(15)
114.33(14)
115.71(17)
109.80(14)
111.10(17)
108.03(16)
110.02(16)
108.74(17)
111.09(15)
108.47(14)
109.85(17)
110.03(16)
108.69(14)
108.72(16)
108.37(18)
107.33(16)
110.79(15)
112.34(18)
106.78(17)
122.9(2)
125.7(2)
111.28(19)
122.6(2)
126.62(19)
151
Chapter 8: Appendix
O2−C9−C10
O9−C11−O4
O9−C11−C12
O4−C11−C12
O10−C13−O6
O10−C13−C14
O6−C13−C14
110.73(18)
123.8(2)
125.5(2)
110.66(18)
123.1(2)
125.4(2)
111.5(2)
Table 4. Anisotropic displacement parameters [Å2× 103]. The anisotropic
displacement factor exponent takes the form: −2π 2[h2a*2U11 + ... + 2 h k a* b*
U12 ].
Atom
U11
U22
U33
U23
U13
U12
F3
O1
O2
O4
O5
O6
O7
O8
O9
O10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
19(1)
18(1)
14(1)
20(1)
22(1)
18(1)
31(1)
20(1)
26(1)
26(1)
18(1)
18(1)
12(1)
15(1)
17(1)
19(1)
19(1)
22(1)
17(1)
22(1)
18(1)
23(1)
20(1)
21(1)
24(1)
23(1)
22(1)
19(1)
20(1)
27(1)
37(1)
41(1)
39(1)
57(1)
18(1)
16(1)
17(1)
19(1)
19(1)
24(1)
25(1)
31(1)
26(1)
32(1)
23(1)
27(1)
21(1)
29(1)
21(1)
16(1)
21(1)
14(1)
15(1)
18(1)
24(1)
68(2)
20(1)
23(1)
20(1)
20(1)
20(1)
17(1)
18(1)
16(1)
19(1)
26(2)
26(1)
26(2)
17(1)
17(1)
24(1)
24(2)
5(1)
−1(1)
−4(1)
1(1)
1(1)
1(1)
9(1)
−24(1)
8(1)
−11(1)
−1(1)
−2(1)
2(1)
1(1)
1(1)
0(1)
0(1)
−3(1)
4(1)
0(1)
2(1)
−4(1)
1(1)
0(1)
5(1)
3(1)
5(1)
3(1)
6(1)
4(1)
5(1)
14(1)
7(1)
5(1)
7(1)
6(1)
3(1)
3(1)
6(1)
3(1)
7(1)
3(1)
6(1)
10(1)
5(1)
2(1)
9(1)
6(1)
6(1)
−2(1)
0(1)
−1(1)
3(1)
7(1)
−4(1)
−9(1)
2(1)
12(1)
−2(1)
1(1)
1(1)
−1(1)
1(1)
5(1)
6(1)
1(1)
2(1)
4(1)
8(1)
2(1)
−1(1)
−1(1)
152
Chapter 8: Appendix
Table 5. Hydrogen coordinates [× 104] and isotropic displacement parameters
[Å2 × 103].
Atom
x
y
z
Ueq
S.o.f.
H1
3719
2057
−4186
23
1
H2
5778
1602
−1438
21
1
H3
3277
91
−1141
21
1
H4
3040
1187
1099
21
1
H5
1007
1509
−1778
22
1
H6A
1087
2749
567
25
1
H6B
1979
3570
−349
25
1
H8A
−1464
608
−6441
42
1
H8B
−62
−299
−6334
42
1
H8C
−835
422
−8043
42
1
H10A
8769
−687
−3254
39
1
H10B
7018
−412
−4896
39
1
H10C
6936
−1238
−3459
39
1
H12A
6800
3660
3337
36
1
H12B
7907
2925
2533
36
1
H12C
8082
2769
4518
36
1
H14A
−4347
3831
−2231
38
1
H14B
−3652
3211
−3544
38
1
H14C
−3444
4466
−3360
38
1
153
Chapter 8: Appendix
Thermal ellipsoids drawn at the 35% probability level
154
Chapter 8: Appendix
8.2 Publication
155
Article
pubs.acs.org/joc
Effects of Sugar Functional Groups, Hydrophobicity, and Fluorination
on Carbohydrate−DNA Stacking Interactions in Water
Ricardo Lucas,† Pablo Peñalver,† Irene Gómez-Pinto,‡ Empar Vengut-Climent,† Lewis Mtashobya,§
Jonathan Cousin,§ Olivia S. Maldonado,† Violaine Perez,† Virginie Reynes,† Anna Aviño,́ ∥ Ramón Eritja,∥
Carlos González,‡ Bruno Linclau,§ and Juan C. Morales*,†
†
Department of Bioorganic Chemistry, Instituto de Investigaciones Químicas, CSIC−Universidad de Sevilla, 49 Américo Vespucio,
41092, Sevilla, Spain
‡
Instituto de Química Física “Rocasolano”, CSIC, C. Serrano 119, 28006 Madrid, Spain
§
Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom
∥
Instituto de Química Avanzada de Cataluña (IQAC), CSIC, CIBER−BBN Networking Centre on Bioengineering, Biomaterials and
Nanomedicine, Jordi Girona 18-26, E-08034 Barcelona, Spain
S Supporting Information
*
ABSTRACT: Carbohydrate−aromatic interactions are highly relevant for
many biological processes. Nevertheless, experimental data in aqueous
solution relating structure and energetics for sugar−arene stacking
interactions are very scarce. Here, we evaluate how structural variations in
a monosaccharide including carboxyl, N-acetyl, fluorine, and methyl groups
affect stacking interactions with aromatic DNA bases. We find small
differences on stacking interaction among the natural carbohydrates
examined. The presence of fluorine atoms within the pyranose ring slightly
increases the interaction with the C−G DNA base pair. Carbohydrate
hydrophobicity is the most determinant factor. However, gradual increase in
hydrophobicity of the carbohydrate does not translate directly into a steady
growth in stacking interaction. The energetics correlates better with the
amount of apolar surface buried upon sugar stacking on top of the aromatic DNA base pair.
■
INTRODUCTION
Molecular interactions between biomolecules rule most of the
biological processes inside the cell. A detailed understanding of
these interactions provides information on these processes, and
also allows their exploitation in a variety of applications such as
in protein engineering or drug design. Stacking between
aromatics is among the most studied interactions, whereas full
comprehension of carbohydrate−aromatic stacking interactions
is still to be reached.1 This binding motif is commonly found in
carbohydrate−protein interactions such as in lectins2 and is also
found in aminoglycoside-RNA recognition.3
Approaches to study carbohydrate−aromatic stacking interactions include molecular biology tools,4 NMR spectroscopy,5
IR spectroscopy,6 computational methods,7 and model systems
based in supramolecular architectures8 or in biomolecules.9
These studies have revealed that the hydrophobic effect and
CH−π interactions comprising dispersion and electrostatic
forces play a critical role. A recent work by Chen et al.10 has
used an enhanced aromatic sequon (sequence of amino acids
with an attached oligosaccharide) to study the relative
contributions of each of these forces. The authors have found
that the hydrophobic effect contributes significantly to
carbohydrate−aromatic stacking and is supplemented by
CH−π interactions with a dominating dispersive component.
© 2014 American Chemical Society
A model based on carbohydrate−oligonucleotide conjugates
(COCs) has been employed by our group to study
carbohydrate−aromatic stacking interactions. We calculated
monosaccharide−phenyl interactions using a double dangling
motif at the 5′-end of a self-complementary CGCGCG
sequence.11 Energies of −0.15 to −0.4 kcal mol−1 were found
depending on the stereochemistry and number of hydroxyl
groups of the sugar. We have also observed mono- and
disaccharide stacking on top of DNA base pairs in COCs where
the sugar is directly linked to the 5′-end to DNA via an
ethylene glycol spacer.12 Extra stabilization of the DNA duplex
due to sugar stacking was observed on sequences with terminal
C−G and G−C base pairs (e.g., up to −0.25 kcal mol−1 for
glucose/DNA unit and −0.45 kcal mol−1 for cellobiose/DNA
unit). However, no stabilization was found on top of terminal
A−T or T−A base pairs most probably due to the enhanced
entropic cost of reducing the breathing of these more flexible
terminal pairs.
In an effort to increase the energetics of carbohydrate−DNA
stacking, we synthesized COCs containing hydrophobic
versions of natural sugars (permethylated glucose or cellobiose)
Received: December 5, 2013
Published: February 19, 2014
2419
dx.doi.org/10.1021/jo402700y | J. Org. Chem. 2014, 79, 2419−2429
The Journal of Organic Chemistry
Article
Figure 1. Description of the oligonucleotide conjugates under study. (a) Schematic drawing of the dangling-ended DNA designed to study
carbohydrate−DNA interactions. (b) Enlarged view of the dangling-end area of a monosaccharide−oligonucleotide conjugate. (c) Carbohydrate−
oligonucleotide conjugates included in the study. R = −OCH2CH2−OPO2−−CGCGCG.
Figure 2. Top view of self-complementary DNA conjugates forming a double helix, permethylated glucose−CH2CH2−OPO2−−CGCGCG (left)
and permethylated glucose−CH2CH2−OPO2−−AGCGCT (right). The apolar carbohydrate stacks on top of a C−G base pair (left) and the apolar
carbohydrate stacks on top of an A−T base pair (right).
at the edge.13 In this case, the stability of the DNA double helix
increased significantly (e.g., up to −0.8 kcal mol−1 for glc(Me)/
DNA unit and −0.9 kcal mol−1 for cellob(Me)/DNA unit).
Additionally, these apolar carbohydrates were able also to
stabilize dsDNA with A−T or T−A terminal base-pairs. We
postulate that CH−π interactions together with the higher
hydrophobicity imparted by the methyl groups are responsible
for duplex stabilization.
In this work we decided to deepen our understanding
carbohydrate−DNA stacking interactions by studying three
different groups of carbohydrates in our dangling end COC
model (Figure 1). First, we studied a group of COCs
containing natural monosaccharides 5−8 (rhamnose, xylose,
N-acetylglucosamine, and glucuronic acid) to explore the
relevance of other functionalities on the pyranose. Second,
the influence on carbohydrate−DNA stacking of increasing
hydrophobicity in the pyranose unit was studied with a series of
COCs with partially hydrophobic glucose units 9−12. We have
observed in the NMR structures of permethylated glucose−
DNA conjugates (Figure 2) that one or two methyl groups
apparently do not participate contacting the DNA base pair
during stacking. The question arising was whether a gradual
increase in hydrophobicity of the sugar will gradually increase
stacking or whether the hydrophobic area contacting the
aromatic DNA bases will be more determinant. Finally, we
selected a group of COCs with fluorinated sugars 13−17 in
order to study the influence of this electron-withdrawing group
in the stacking interaction. At the same time, the reduced
hydrophilicity upon OH → F change could also have a role in
the carbohydrate−DNA interactions.
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Article
corresponding trichloroacetimidate glycosyl donor 32.16 When
ethylene glycol was used as the glycosyl acceptor, very low
yields of glycosylated product were obtained. Then, 2benzyloxyethanol was reacted with 32 to give 33 (30% yield)
and subsequent hydrogenation resulted in alcohol 33 (46%
yield). Synthesis of the corresponding phosphoramidite
compound 35 was carried out as described above.
The synthesis of 6-O-acetyl-2,3,4-O-trimethyl glucose
phosphoramidite 41 started by differentiating the primary
hydroxyl group of 2-benzyloxyethyl β-D-glucopyranoside 3613
with a TBDPS group (Scheme 2). Further methylation of the
remaining OH groups, hydrogenation and phosphoramidite
synthesis yielded derivative 41. In the case of 2,3-O-diacetyl4,6-O-dimethyl glucose phosphoramidite 44 its preparation was
carried out from the reported 1,2,3-O-triacetyl-4,6-O-dimethyl
α,β-glucopyranoside 4217 by reaction of its corresponding αbromo derivative with ethylene glycol. Then, hydrogenation
and phosphoramidite preparation in similar conditions as
described above resulted in compound 44.
Several mono- and difluorinated carbohydrate phosphoramidite derivatives were synthesized from the corresponding
acetylated α-bromide compounds (Scheme 3).18 Again classical
Koenigs−Knorr glycosylation was used and the alcohol
derivatives were obtained in moderate to good yields (44−
78%). The phosphoramidite derivatives of 3-fluoro-3-deoxyglucose 47, 4-fluoro-4-deoxy-glucose 50, 6-fluoro-6-deoxyglucose 53, 4-fluoro-4-deoxy-galactose 56, and 4,6-difluoro4,6-dideoxy-galactose 59 were synthesized using the same
reaction conditions used previously.
After standard solid phase automated oligonucleotide
synthesis, the resulting carbohydrate oligonucleotide conjugates
were cleaved from the resin, deprotected with ammonia, HPLC
purified, and characterized by MALDI-TOF mass spectrometry
(Supporting Information). In the case of glucuronic acid DNA
conjugate 8, preliminary treatment with Na2CO3 in MeOH/
H2O (2:1) for 24 h was carried out followed by normal
treatment with ammonia and HPLC purification.
Energetics of Carbohydrate−DNA Interactions. DNA
duplex stability was measured by UV-monitored thermal
denaturation experiments in a pH 7.0 phosphate buffer
containing 1 M NaCl. Thermodynamic parameters were
calculated from melting curve fitting and from van’t Hoff
plots (1/Tm versus ln[conjugate]).19 Thermodynamic parameters for the carbohydrate−oligonucleotide conjugates containing natural sugars at the 5′-end 1−8 are shown in Table 1. It is
important to clarify that the thermodynamic results obtained
are for each COC double helix that incorporates two
carbohydrate−DNA binding motifs within its structure. We
observed previously that the presence of glucose, galactose, and
fucose at the edge stabilized the DNA duplex by 3.1−3.5 °C
and by 0.3−0.6 kcal·mol−1.12 DNA stabilization by xylose and
N-acetylglucosamine is in the same range as for the previous
monosaccharides, whereas rhamnose and glucuronic acid are
less stabilizing, possibly due to the presence of an axial OH and
a negative charge in the pyranose, respectively.
In the series of hydrophobic glucose DNA conjugates 9−12,
all carbohydrates increased DNA stability with respect to the
natural glucose DNA conjugate 2 (Table 2). Whereas COC
double helix containing 6-deoxyglucose units showed a small
increase in Tm of 0.7 °C and 0.2 kcal·mol−1 with respect to
glucose, the other apolar sugar DNA conjugates containing 4,6dimethylated glucose, 2,3,4-trimethylated glucose, and 2,3,4,6-
RESULTS AND DISCUSSION
Synthesis of Carbohydrate−Oligonucleotide Conjugates. The preparation of carbohydrate−oligonucleotide
conjugates was carried out using standard solid phase
automated oligonucleotide synthesis as reported previously.11,12
Different monosaccharides were attached via an ethylene glycol
spacer to the 5′-end of the self-complementary CGCGCG
sequence using the corresponding protected carbohydrate
phosphoramidite derivatives. Their synthesis was carried out
by glycosylation of the spacer followed by standard
phosphoramidite preparation (Scheme 1).
Scheme 1. Synthesis of Rhamnose, Xylose, 6-Deoxyglucose,
N-Acetylglucosamine and Glucuronate Methyl Ester
Phophoramidites 20, 23, 26, 31, and 35a
a
Reagents and conditions: (a) ethylene glycol, Ag2CO3, CH2Cl2; (b)
2-cyanoethyl-N,N′-diisopropyamino-chlorophosphoramidite, DIPEA,
CH2Cl2; (c) 2-benzyloxyethanol, Ag2CO3, CH2Cl2; (d) MeNH2,
THF then pyridine/acetic anhydride, DMAP; (e) H2, Pd(OH)2,
EtOAc/MeOH (1:1); (f) ethylene glycol, BF3·OEt2, CH2Cl2.
In the case of the rhamnose, xylose, and 6-deoxyglucose,
their sugar phosphoramidites 20, 23, and 26 were synthesized
by attachment of ethylene glycol by Koenigs−Knorr glycosylation with the corresponding acetobromosugars.11,14 The
promoter used was silver carbonate, and the isolated yields
were between 44 to 83% (Scheme 1). Reaction of the obtained
alcohols with 2-cyanoethyl-N,N′-diisopropylamino-chlorophosphoramidite in the presence of base resulted in the
carbohydrate phosphoramidite derivatives 20, 23, and 26 in
high yields (75−90%).
The N-acetylglucosamine phosphoramidite 31 was synthesized by glycosylation of 2-benzyloxyethanol with acetobromo
N-phthalimide glucose 27.15 Next, phthalimide deprotection
with methylamine in THF and acetylation yielded the
corresponding N-acetamido derivative 29. Finally, hydrogenation of the benzyl protecting group and phosphoramidite
incorporation produced GlcNAc derivative 31. Glucuronate
methyl ester phosphoramidite 35 was synthesized from the
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Scheme 2. Synthetic Route for the Preparation of Partially Methylated Glucose Phophoramidites 41 and 44a
a
Reagents and conditions: (a) TBDPSCl, DIPEA, NEt3, DMF; (b) NaH, MeI, DMF; (c) TBAF 1.0 M, THF then pyridine/acetic anhydride,
DMAP; (d) H2, Pd(OH)2, EtOAc/MeOH (8:1); (e) 2-cyanoethyl-N,N′-diisopropyamino-chlorophosphoramidite, DIPEA, CH2Cl2; (f) HBr, AcOH,
CH2Cl2 then ethylene glycol, Ag2CO3, CH2Cl2.
tetramethylated glucose derivatives were more stable than 2 by
3.7−4.7 °C and by 0.7−0.9 kcal·mol−1.
It is interesting to observe that the large increase in DNA
stability from the dimethylated glucose does not correlate with
the gradual increase in hydrophobicity in this series as can be
deduced from the log P values of the glucose derivatives (Table
3). In fact, it does not correlate either with the increase in
surface area of the apolar sugars. We estimated the actual
surface area buried as the result of the sugar stacking on top of
the C−G final DNA base pair for each of the glucose
derivatives. A good correlation between the buried surface and
the DNA stability is found since adding third and fourth methyl
groups to the glucose unit does not increase the stacking area in
the conjugate but slightly reduces it. In fact, a graph plotting
free energy of COCs (containing glucose, 2, and hydrophobic
sugars, 9−12) versus stacking area showed a good linear fit (the
coefficient of determination is R2 = 0.9193; see Figure S4,
Supporting Information). This seems to indicate that the free
energy of the conjugate is also directly related with the number
of water molecules displaced by the hydrophobic carbohydrates
from the area of contact with the DNA base pair and not with
the hydrophobicity of the carbohydrates. A similar result was
found by Kool et al. when studying π−π aromatic interactions
with nonpolar DNA bases (e.g., benzene, naphthalene, pyrene,
etc.) at the edge of dsDNA.20 Log P values were a poor
predictor of stacking interaction, whereas surface area of
Scheme 3. Synthetic Route for the Preparation of Fluoro
Monosaccharide Phophoramidites 47, 50, 53, 56, and 59a
a
Reagents and conditions: (a) ethylene glycol, Ag2CO3, CH2Cl2; (b)
2-cyanoethyl-N,N′-diisopropyamino-chlorophosphoramidite, DIPEA,
CH2Cl2.
Table 1. Melting Temperatures and Thermodynamic Parameters for Carbohydrate Oligonucleotide Conjugate Duplexes
Containing Natural Carbohydrates and the CGCGCG Sequence
dangling moiety in
5′-CGCGCGa,b,c
(none) 1
β-D-glucose-C2e 2
β-D-galactose-C2e 3
β-L-fucose-C2e 4
α-L-rhamnose-C2 5
β-D-xylose-C2 6
N-acetyl-β-D-glucosamineC2 7
β-D-glucuronic acid-C2 8
a
Tm (°C)
40.9
44.0
44.4
44.4
42.7
43.6
44.6
±
±
±
±
±
±
±
0.4
0.7
0.4
0.4
0.2
0.4
0.3
42.4 ± 0.7
−ΔS° (van’t Hoff)
(cal/k mol)
114
140
113
136
137
156
136
±
±
±
±
±
±
±
5
4
8
3
7
9
7
141 ± 2
−ΔH° (van’t Hoff)
(kcal/mol)
43.5
52.1
43.5
51.1
50.9
57.2
50.8
±
±
±
±
±
±
±
2
2
3
1
2
3
3
52.2 ± 1
−ΔG°37 (van’t Hoff)
(kcal/mol)
8.2
8.7
8.5
8.8
8.6
8.8
8.7
±
±
±
±
±
±
±
0.3
0.3
0.5
0.2
0.4
0.6
0.5
8.5 ± 0.1
ΔG°37 (fits)
(kcal/mol)
ΔΔG°37d
(kcal/mol)
±
±
±
±
±
±
±
0.1
0.0
0.1
0.0
0.0
0.1
0.0
−
−0.5
−0.3
−0.6
−0.4
−0.6
−0.5
8.5 ± 0.0
−0.3
8.2
8.7
8.7
8.8
8.5
8.6
8.7
C2 stands for −CH2−CH2−. bBuffer: 10 mM Na phosphate, 1 M NaCl, pH 7.0. cAverage value of three experiments measured at 5 μM conc.
ΔΔG°37 = ΔGvh − ΔG (CGCGCG control). eData from Lucas et al.12
d
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Table 2. Melting Temperatures and Thermodynamic Parameters for Carbohydrate Oligonucleotide Conjugate Duplexes
Containing Hydrophobic Sugars and the CGCGCG Sequence
dangling moiety in
5′-CGCGCGa,b,c
(none) 1
β-D-glucose-C2e 2
β-D-6-deoxyglucose-C2 9
β-D-4,6-dimethyl-glc-C2 10
β-D-2,3,4-trimethyl-glc-C2
11
β-D-2,3,4,6-tetramethyl-glcC2f 12
a
Tm (°C)
40.9
44.0
44.7
47.7
48.2
±
±
±
±
±
0.4
0.7
0.2
0.2
0.1
48.7 ± 0.2
−ΔS° (van’t Hoff)
(cal/k mol)
114
140
145
157
146
±
±
±
±
±
−ΔH° (van’t Hoff)
(kcal/mol)
5
4
5
11
11
43.5
52.1
53.8
58.3
54.7
147 ± 10
±
±
±
±
±
2
2
2
4
4
55.1 ± 4
−ΔG°37 (van’t Hoff)
(kcal/mol)
8.2
8.7
8.9
9.6
9.4
±
±
±
±
±
0.3
0.3
0.3
0.8
0.8
ΔG°37 (fits)
(kcal/mol)
ΔΔG°37d
(kcal/mol)
±
±
±
±
±
0.1
0.0
0.0
0.1
0.1
−
−0.5
−0.7
−1.4
−1.2
9.4 ± 0.1
−1.2
8.2
8.7
8.8
9.4
9.4
9.4 ± 0.6
C2 stands for −CH2−CH2−. bBuffer: 10 mM Na phosphate, 1 M NaCl, pH 7.0. cAverage value of three experiments measured at 5 μM conc.
ΔΔG°37 = ΔGvh − ΔG (CGCGCG control). eData from Lucas et al.12 fData from Lucas et al.13
d
Table 3. Molecular Weight and Partition Coefficient Data for Dangling Moieties Studied
dangling moiety in 5′-CGCGCG
glucose
6-deoxyglucose
4,6-dimethyl-glucose
2,3,4-trimethyl-glucose
2,3,4,6-tetramethyl-glucose
2
9
10
11
12
MW
calc log Pa
surface area (Å2)b
S-area folded
S-area unfolded
stacking area (Å2)c
194.2
178.2
222.2
236.3
250.3
−2.01
−1.16
−1.29
−0.93
−0.57
186
179
207
227
243
2918
2905
2946
2954
2981
3093
3082
3147
3143
3170
175
177
201
189
189
a
Log P values were calculated using the Crippen’s fragmentation21 in the ChemBioDraw Ultra 11.0 software. bHalf of the calculated surface area of
base as Connolly accessible area using Chem 3D Pro software. cEstimated as buried surface by subtracting the unfolded from the folded
carbohydrate−DNA base pair.
Table 4. Melting Temperatures and Thermodynamic Parameters for Carbohydrate Oligonucleotide Conjugate Duplexes
Containing Fluorosugars and the CGCGCG Sequence
dangling moiety in
5′-CGCGCGa,b,c
(none) 1
β-D-glc-C2 2
3-F-β-D-glc-C2 13
4-F-β-D-glc-C2 14
6-F-β-D-glc-C2 15
β-D-gal-C2 3
4-F-β-D-gal-C2 16
4,6-diF-β-D-gal-C2 17
a
Tm (°C)
40.9
44.0
44.5
44.7
44.3
44.4
44.6
45.0
±
±
±
±
±
±
±
±
0.4
0.7
0.1
1.3
0.0
0.4
0.9
0.5
−ΔS° (van’t Hoff)
(cal/k mol)
114
140
141
141
150
113
138
135
±
±
±
±
±
±
±
±
−ΔH° (van’t Hoff)
(kcal/mol)
5
4
2
6
5
8
14
9
43.5
52.1
52.4
52.5
55.3
43.6
51.2
50.4
±
±
±
±
±
±
±
±
2
2
1
2
2
3
5
3
−ΔG°37 (van’t Hoff)
(kcal/mol)
8.2
8.7
8.8
8.9
8.9
8.5
8.6
8.6
±
±
±
±
±
±
±
±
0.3
0.3
0.1
0.4
0.3
0.5
1.0
0.6
ΔG°37 (fits)
(kcal/mol)
ΔΔG°37d
(kcal/mol)
±
±
±
±
±
±
±
±
−
−0.5
−0.6
−0.7
−0.7
−0.3
−0.4
−0.4
8.2
8.7
8.8
8.9
8.8
8.7
8.6
8.6
0.1
0.0
0.0
0.1
0.0
0.1
0.0
0.1
C2 stands for −CH2−CH2−. bBuffer: 10 mM Na phosphate, 1 M NaCl, pH 7.0. cAverage value of three experiments measured at 5 μM conc.
ΔΔG°37 = ΔGvh − ΔG (CGCGCG control).
d
since the values are within the experimental error. This is a
similar situation to that found when comparing glucose and
galactose.
Finally, a couple of explicit comparisons between the three
groups of monosaccharides may yield some information on the
relevance of different modifications in the carbohydrate when
stacking with DNA bases. If we compare glucose, 6deoxyglucose and 6-fluoroglucose, we observe that replacement
of the 6-OH with a proton or a fluorine atom yields only a
small increase in stability, probably due to the small decrease in
hydrophilicity with this modification. In contrast, a large
difference in energetics is observed between 4,6-difluorogalactose and 4,6-dimethyl-glucose (the latest 1.0 kcal·mol−1 in
ΔG more stable). Bearing in mind the different stereochemistry
of the carbohydrate, the increased hydrophobic surface in the
apolar carbohydrate has much more influence in the stacking
interaction than increasing the polarity of the −CH− protons
of the pyranose by the presence of the fluorine atoms.
Structural Features of Carbohydrate Oligonucleotide
Conjugates. As in previous NMR studies in related
systems,12,13 no distortion of the DNA double helix due to
overlap (buried surface by aromatic stacking) was a much
better predictor.
In the series of fluorinated sugars 13−17, DNA stability of
the carbohydrate oligonucleotide conjugates showed a minor
increase with respect to glucose and galactose derivatives 2 and
3 (0.3−0.7 °C in Tm and 0.1−0.2 kcal·mol−1 in ΔG, see Table
4). The incorporation of one or two electron-withdrawing
agents such as fluorine atoms in the pyranose could modify
CH−π interactions between the pyranose ring and the aromatic
DNA bases, but this effect seems to have little influence in the
carbohydrate−aromatic stacking interaction observed. These
results fit well with those obtained recently by Asensio et al.22
in a dynamic combinatorial approach using a disaccharide
model system. The authors observe a minor strengthening of
the carbohydrate/aromatic forces by incorporating electronwithdrawing substituents at the anomeric position (−F or
−CH2CF3).
If we consider the relevance of stereochemistry of
fluorosugars in the interaction with the DNA base pair, for
example by comparison of 4-fluoroglucose (4FGlc) and 4fluorogalactose (4FGal), we observe no difference in energetics
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solvent was removed, and the crude product was purified by flash
column chromatography (hexane:ethyl acetate mixtures) to afford the
corresponding glycosylated ethylene glycol.
2-Hydroxyethyl 2,3,4-tri-O-acetyl-β-L-rhamnopyranose (19).
2,3,4-Tri-O-acetyl-α-L-rhamnopyranosyl bromide 18 (972 mg, 2.76
mmol) was reacted following the general glycosylation procedure. The
crude product was purified by flash column chromatography
(hexane:ethyl acetate from 2:1 to 1:2) to afford 19 (592 mg, 64%)
as glassy solid: [α]D22 −3.3 (c 1 in CHCl3); 1H NMR (300 MHz,
CDCl3) δ ppm 5.26−5.19 (m, 1H, H2), 5.02−4.96 (t, J = 9.8 Hz, 1H,
H3), 4.72 (s, 1H, H1), 3.90−3.83 (m, 1H, H4), 3.74−3.69 (m, 3H, H5,
CH2), 3.51−3.55 (m, 2H, CH2), 2.08, 1.99, 1.92 (3s, 9H, 3 ×
OCOCH3), 1.17−1.15 (d, J = 8 Hz, 3H, CH3); 13C NMR (75 MHz,
CDCl3) δ = 170.1, 170.0, 169.9 (3 × CO), 97.6 (C1), 70.9 (C3), 69.7
(C2), 69.6 (CH2), 69.10 (C5), 66.4 (C4), 61.3 (CH2), 20.8, 20.7, 20.6
(3 × OCH3), 17.3 (CH3); HRMS (FAB+) Calcd. for C14H22O9Na (M
+ Na) 357.1162, found 357.1152.
2-Hydroxyethyl 2,3,4-tri-O-acetyl-β-D-xylopyranose (22). 2,3,4Tri-O-acetyl-α-D-xylopyranosyl bromide 21 (850 mg, 2.50 mmol) was
reacted following the general glycosylation procedure. The crude
product was purified by flash column chromatography (hexane:ethyl
acetate from 2:1 to 1:2) to afford 22 (540 mg, 66%) as glassy solid:
[α]D22 −48.5 (c 1 in CHCl3); 1H NMR (300 MHz, CDCl3) δ ppm
5.18−5.12 (t, J = 9.0 Hz, 1H, H3), 4.97−4.88 (m, 2H, H2, H4), 4.50−
4.48 (d, J = 7.2 Hz, 1H, H1), 4.14−4.08 (dd, J = 5.4/5.1 Hz, 1H, H5),
3.84−3.79 (m, 4H, 2 × CH2), 3.39−3.32 (dd, J = 5.3 Hz, 1H, H5′),
2.03−2.00 (3s, 9H, 3 × OCOCH3); 13C NMR (75 MHz, CDCl3) δ =
170.4, 170.3, 169.9 (3 × CO), 100.5 (C1), 72.0 (C3), 71.8 (C2), 71.3
(CH2), 69.1 (C4), 62.5 (CH2), 61.9 (C5), 21.0. 20.9 (OCCH3);
HRMS (FAB+) Calcd. for C13H20O9Na (M + Na) 343.0999, found
343.1005.
2-Hydroxyethyl 2,3,4-tri-O-acetyl-β-D-6-deoxyglucopyranose
(25). 2,3,4-Tri-O-acetyl-6-deoxy-α-D-glucosylbromide 24 (0.5 g, 1.50
mmol) was reacted following the general glycosylation procedure. The
crude product was purified by flash column chromatography
(hexane:ethyl acetate from 1:1 to 1:2) to afford 25 (196 mg, 44%)
as glassy solid: [α]D22 −23.8 (c 1 in CHCl3); 1H NMR (300 MHz,
CDCl3) δ ppm 5.11 (t, J = 9.0 Hz, 1H, H3), 4.92 (dd, J = 9.6 Hz, 1H,
H2), 4.77 (t, J = 9.5 Hz, 1H, H4), 4.46 (d, J = 8.1 Hz, 1H, H1), 3.72−
3.69 (m, 2H, CH2), 3.57−3.52 (m, 1H, H5), 2.40 (s, 1H, OH), 1.98,
1.97, 1.93 (3 × OCOCH3), 1.18 (d, 3H, J = 6.3 Hz, CH3) ; 13C NMR
(75 MHz, CDCl3) δ = 170.2, 169.6, 169.5 (CO), 100.9 (C1), 73.2
(C4), 72.7 (C3), 72.1 (CH2), 71.7 (C2), 70.0 (C5), 61.7 (CH2), 20.7,
20.6, 20.5 (OCCH3), 17.3 (CH3); HRMS (FAB+) Calcd. for
C14H22O9Na (M + Na) 357.1162, found 357.1168.
2-Benzyloxyethyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-Dglucopyranose (28). Ag2CO3 (1.38 g, 5.01 mmol) was added to a
solution of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide 2715 (1 g, 2.0 mmol) and 2-benzyloxyethanol (2.85 mL,
20.0 mmoL) in anhydrous CH2Cl2 (12 mL). The reaction was stirred
for 16 h and the mixture was then filtered over Celite and washed with
CH2Cl2. The solvent were removed and the crude purified by flash
column chromatography (hexane:ethyl acetate from 4:1 to 1:1) to
afford 28 (800 mg, 70%) as glassy solid: [α]D22 +19.7 (c 1 in CHCl3);
1
H NMR (300 MHz, CDCl3) δ ppm 7.74−7.71 (m, 2H, Harom,
Phth), 7.63−7.59 (m, 2H, Harom, Phth), 7.17−7.00 (m, 5H, Ph), 5.74
(dd, J = 9.0/10.8 Hz, 1H, H3), 5.39 (d, J = 8.4 Hz, 1H, H1), 5.11 (dd, J
= 9.0/10.0 Hz, 1H, H4), 4.32−4.22 (m, 2H, H2, H6), 4.17 (s, 2H,
CH2Ph), 4.09 (dd, J = 2.4/12.3 Hz, 1H, H6′), 3.92−3.77 (m, 2H, CH2,
H5), 3.69−3.60 (m, 1H, CH2), 3.42−3.39 (m, 2H, CH2), 2.03, 1.95,
1.80 (3s, 9H, 3 × OCOCH3); 13C NMR (75 MHz, CDCl3) δ = 170.7,
170.2, 169.5 (3 × CO), 138.0, 134.2, 131.4, 128.4, 128.3, 127.8, 127.4,
127.3, 123.5, 98.3 (C1), 72.9 (CH2), 71.8 (C5), 70.7 (C3), 69.3 (C4),
69.0, 68.7 (2 × CH2), 62.0 (C6), 54.6 (C2), 20.8. 20.6, 20.5 (OCCH3);
HRMS (FAB+) Calcd. for C29H31NO11Na (M + Na) 592.1795, found
592.1786.
2-Benzyloxyethyl 3,4,6-tri-O-acetyl-2-acetylamino-2-deoxy-β-Dglucopyranose (29). MeNH2 (40% aq, 3 mL) was added to a
solution of 28 (390 mg, 0.68 mmol) in THF (6 mL). The reaction was
stirred for 16 h. The solvent was then removed and the reaction
the presence of the fluorinated carbohydrates is observed. Two
dimensional NMR spectra were recorded for conjugates 13 to
16. Complete resonance assignment was performed, and we
found significant chemical shift differences with the control
duplex only for some protons of the terminal base pair.
Observed NOEs between the sugar units and the terminal C−
G base pair were very similar to those observed for the
corresponding nonfluorinated natural sugars (see Table S2,
Supporting Information). A structural model of conjugate 13
was built on the basis of the observed experimental NOEs (see
Figure S5, Supporting Information). The carbohydrate stacks
on top of the terminal C−G base pairs mainly through its alpha
face. The fluorine atom is oriented toward the solvent and does
not participate in the interaction with the DNA, explaining the
little effect of the fluorine substitutions in the thermal stability
of these conjugates. Consequently, we conclude that the
structures of the fluorinated conjugates are very similar to those
reported previously, and no further modeling was carried out.
■
CONCLUSION
Evaluation of stacking of natural monosaccharides on top of a
DNA base pair in water using our COC model system have
shown small differences due to changes in sugar stereochemistry and to the presence of typical functional groups such
as N-acetyl or carboxylic acid in the pyranose ring. At the same
time, replacement of a hydroxyl group with a fluorine atom
should increase −CH− polarization and local hydrophobicity,
but none of these aspects showed large differences on stacking
of the carbohydrate derivatives. Finally, increasing the hydrophobicity of the sugars through methylation exhibited a
considerable enhancement in carbohydrate aromatic stacking.
Nevertheless, it is important to emphasize that energetics seem
to correlate better with the amount of surface contact area
between the carbohydrate and the aromatic DNA base pair
than with a net increase in sugar hydrophobicity. These results
appear to point out the relevance of the number of water
molecules displaced from the surface of contact between the
carbohydrate and the aromatics.
■
EXPERIMENTAL SECTION
General Methods. All chemicals were obtained and used without
further purification, unless otherwise noted. All reactions were
monitored by TLC on precoated silica gel 60 plates F254 and
detected by heating with 5% sulfuric acid in ethanol or Mostain (500
mL of 10% H2SO4, 25 g of (NH4)6Mo7O24·4H2O, 1 g of Ce(SO4)2·
4H2O). Products were purified by flash chromatography with silica gel
60 (200−400 mesh). Low resolution mass spectra were obtained on an
ESI/ion trap mass spectrometer. High resolution mass spectra were
obtained on an ESI/quadrupole mass spectrometer. NMR spectra
were recorded on a 300, 400, or 500 MHz [300 or 400 MHz (1H), 75
or 100 (13C)] NMR spectrometers, at room temperature for solutions
in CDCl3, D2O, or CD3OD. Chemical shifts are referred to the solvent
signal. 2D experiments (COSY, TOCSY, ROESY, and HMQC) were
done when necessary to assign the carbohydrate derivatives and the
conjugates. Chemical shifts are in ppm. In all experiments the 1H
carrier frequency was kept at the water resonance. Data were
processed using manufacturer software, raw data were multiplied by
shifted exponential window function prior to Fourier transform, and
the baseline was corrected using polynomial fitting.
Synthetic Procedures. General Procedure for Glycosylation of
Ethylene Glycol. Ag2CO3 (1.7 g, 6.25 mmol) was added to a solution
of the acetyl protected glycosylbromide (2.5 mmol) and ethylenglycol
(1.3 mL, 25 mmoL) previously dried over molecular sieves, in
anhydrous CH2Cl2 (10 mL). The reaction was stirred for 24 h; the
mixture was then filtered over Celite and washed with CH2Cl2. The
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(0. 476 mL, 4.64 mmoL) were added to a cooled solution of 2benzyloxyethyl β-D-glucopyranoside 3613 (1.325 g, 4.22 mmol) in
anhydrous DMF under argon atmosphere. Then tert-butyldiphenylsilyl
chloride (1.21 mL, 4.64 mmoL) was slowly added to the mixture and
the reaction was left to at room temperature until starting material had
disappeared in 1h. Ethyl acetate (300 mL) was then added to the
mixture and the organic layer was washed with brine (2 × 100 mL),
dried with anhydrous Na2SO4 and concentrated to dryness. The crude
product was purified by silica gel column chromatography using ethyl
acetate 100% as eluent to give 37 (1.3 g, 57%) as a white solid: 1H
NMR (400 MHz, CDCl3) δ ppm 7.63−7.57 (m, 5H, Ph), 7.32−7.25
(m, 5H, Ph), 7.23−7.14 (m, 5H, Ph), 4.52−4.35 (m, 2H, CH2), 4.20
(d, J = 7.6 Hz, 1H, H1) 3.84 (m, 2H, CH2), 3.76 (dd, J = 10.9, 5.3 Hz,
1H), 3.64−3.36 (m, 5H, CH2, H5, H6, H6′), 3.35−3.25 (m, 2H, H2,
H), 0.95 (s, 9H, 3 × CH3isopropyl); 13C NMR (101 MHz, CDCl3) δ =
137.7 (Cq-arom), 135.7 (2 × Carom), 135.6 (2 × Carom),133.3(Carom),
129.8(2 × Carom), 128.5 (2 × Carom), 127.9 (2 × Carom), 127.8 (2 ×
Carom), 127.7 (4 × Carom), 102.6 (C1), 76.4(CH2), 75.4, 73.4, 73.1,
71.4, 69.0, 68.3, 64.5 (C2−C5, 2 × CH2), 26.8 (3 × CH3 iPr),
19.3(CCH3 iPr); HRMS (FAB+) Calcd. for C31H40O7Na Si (M + Na)
575.2441, found 575.2451.
2-Benzyloxyethyl 2,3,4-tri-O-methyl-6-tert-butyldiphenylsilyl-β-Dglucopyranose (38). Sodium hydride (1.25g, 60% conc., 30.8 mmol)
was slowly added to a cooled (0 °C) solution of 2-benzyloxyethyl 6-Otert-butyldiphenylsilyl-β-D-glucopyranose (37) (2.13 g, 3.86 mmol) in
anhydrous DMF (20 mL). After stirring at 0 °C for 10 min under
argon atmosphere, methyl iodide (3.6 mL, 58 mmol) was added and
the reaction was left to process overnight at room temperature. The
reaction was quenched with 2-propanol and treated with 50 mL sat.
NH4Cl. The aqueous layer was extracted with ethyl acetate (2 × 50
mL). The organic layer was then washed with brine and Na2S2O3,
dried with anhydrous Na2SO4 and concentrated to dryness. The crude
product was purified by silica gel column chromatography
(hexane:ethyl acetate, from 4:1 to 2:1) to give 38 (1.5 g, 67%) as a
white solid: 1H NMR (400 MHz, CDCl3) δ ppm 7.68−7.59 (m, 5H,
Ph), 7.33−7.14 (m, 10H, Ph), 4.49 (s, 2H, CH2), 4.22 (d, J = 7.6 Hz,
1H, H1) 3.95 (m, 1H), 3.79 (d, J = 2.8 Hz, 2H, CH2), 3.68−3.59 (m,
3H), 3.55 (s, 3H, OCH3), 3.52 (s, 3H, OCH3), 3.47 (s, 3H, OCH3),
3.27 (t, 1H,), 3.09 (ddd, J = 8.9, 5.7, 2.8 Hz, 2H), 2.97 (t, 1H, H2),
0.96 (s, 9H, 3 × CH3 iPr); 13C NMR (101 MHz, CDCl3) δ =, 138.4
(Cq-arom), 135.9 (2 × Carom), 135.6 (2 × Carom),133.8(Carom),
133.3(Carom), 129.6(2 × Carom), 128.4 (2 × Carom), 127.8 (2 ×
Carom), 127.72 (2 × Carom), 127.69 (2 × Carom), 127.6 (3 × Carom),
103.4 (C1), 86.6, 83.8 (C2), 79.1, 75.6, 73.2, 69.4, 68.7, 62.8, 60.9,
60.5(2 × C), 26.8 (3 × CH3 iPr), 19.4(CCH3 iPr); HRMS (FAB+)
Calcd. for C34H46O7NaSi (M + Na) 617.2911, found 617.2899.
2-Benzyloxyethyl 2,3,4-tri-O-methyl-6-O-acetyl-β-D-glucopyranose (39). TBAF (1 M in THF, 4.38 mL, 4.38 mmol) was slowly
added to a solution of 2-benzyloxyethyl 2,3,4-tri-O-methyl-6-O-tertbutyldiphenylsilyl-β-D-glucopyranose (38) (1.3 g, 2.19 mmol) in
anhydrous THF (10 mL). The reaction was stirred for 90 min under
argon atmosphere at room temperature. 50 mL of CH2Cl2 were added
to the reaction mixture and the organic layer was then washed with
brine and NH4Cl, dried with anhydrous MgSO4 and concentrated to
dryness. The crude product was purified by silica gel column
chromatography using as eluent (hexane:ethyl acetate, from 1:2 to
1:4) to give 2-benzyloxyethyl 2,3,4-tri-O-methyl-β-D-glucopyranose
(650 mg, 1.83 mmol, 83%) as a white solid. The product was then
solved in anhydrous pyridine (10 mL) and acetic anhydride (1.38 mL,
14.6 mmol) and dimethylaminopyridine (catalytic amount) was added
to the reaction mixture. The reaction was left to process overnight at
room temperature under argon atmosphere. CH2Cl2 was then added
to the reaction mixture (50 mL) and the organic layer was washed with
brine and HCl (5% v/v), dried with anhydrous Na2SO4 and
concentrated to dryness. The crude product was purified by silica
gel column chromatography (hexane:ethyl acetate, from 1:1 to 1:3) to
give 39 (705 mg, 97%) as a white solid: 1H NMR (400 MHz, CDCl3)
δ ppm 7.35−7.13 (m, 5H, Ph), 4.48 (s, 2H, CH2), 4.26 (d, J = 4.8 Hz,
1H, H1), 4.22 (d, 1H), 4.11 (dd, 1H), 3.99−3.86 (m, 1H), 3.66 (dd,
1H), 3.62−3.56 (m, 2H), 3.54 (s, 3H, OCH3), 3.50 (s, 3H, OCH3),
mixture was coevaporated with dry toluene. The crude was dissolved
in dry pyridine (10 mL) and acetic anhydride (3 mL) and a catalytic
amount of DMAP was added. The reaction mixture was stirred at
room temperature for 24 h. The solvent was removed in vacuo and the
crude product was purified by flash column chromatography
(hexane:ethyl acetate from 1:4 to 0:1) to afford 29 (200 mg, 62%
two steps) as a brown solid: [α]D22 −24.5 (c 1 in MeOH); 1H NMR
(300 MHz, CDCl3) δ ppm 7.30−7.19 (m, 5H, Ph), 5.76 (d, J = 8.7 Hz,
1H, NH), 5.16 (t, J = 9.3 Hz, 1H, H3), 4.99 (t, J = 9.3 Hz, 1H, H4),
4.69 (d, J = 7.2 Hz, 1H, H1), 4.46 (s, 2H, CH2Ph), 4.21−4.18 (m, 1H,
H6), 4.03−3.92 (m, 1H, H6′), 3.95−3.50 (m, 6H, 2 × CH2, H2, H5),
1.99, 1.95, 1.94, 1.78 (3s, 12H, 3 × OCOCH3, N-COCH3); 13C NMR
(75 MHz, CDCl3) δ = 170.8, 170.7, 170.3, 169.4 (4 × CO), 138.0,
128.5, 127.8, 127.6 (Carom), 100.9 (C1), 73.1 (CH2), 72.6 (C3), 71.8
(C5), 69.3 (CH2), 68.8 (C4), 68.6 (CH2), 62.1 (C6), 54.5 (C2), 23.2
(NCOCH3), 20.8. 20.7, 20.6 (OCCH3); HRMS (FAB+) Calcd. for
C23H31NO10Na (M + Na) 504.1846, found 504.1852.
2-Hydroxyethyl 3,4,6-tri-O-acetyl-2-acetylamino-2-deoxy-β-Dglucopyranose (30). A solution of compound 29 (180 mg, 0.37
mmol) in ethyl acetate-MeOH (1:1, 6 mL) and Pd(OH)2 in catalytic
amount was stirred under an atmosphere of hydrogen for 48 h. The
mixture was filtered off over Celite and solvents were removed. The
crude product was purified by silica gel column chromathography
using as eluent (hexane:ethyl acetate, from 1:4 to 0:1) to give 30 (120
mg, 83%): [α]D22 −2.4 (c 1 in CHCl3); 1H NMR (400 MHz, CD3OD)
δ ppm 5.22 (t, J = 9.6 Hz, 1H, H3), 5.00 (t, J = 9.6 Hz, 1H, H4), 4.70
(d, J = 8.4 Hz, 1H, H1), 4.29 (d, J = 4.8/12.4 Hz, 1H, H6), 4.15 (d, J =
2.0/12.4 Hz, 1H, H6′), 3.91−3.80 (m, 3H, H2, H5, OCH2), 3.70−3.64
(m, 3H, OCH2, CH2OH), 2.08, 2.02, 1.99, 1.93 (4s, 12H, 3 ×
OCOCH3, N-COCH3); 13C NMR (75 MHz, CDCl3) δ = 172.2,
170.9, 170.4, 169.9 (4 × CO), 100.8 (C1), 72.8 (C3), 71.5 (C5), 70.9
(CH2O), 68.8 (C4), 61.9 (C6), 60.8 (CH2OH), 54.1 (C2), 21.4, 19.3,
19.2, 19.1; HRMS (FAB+) Calcd. for C16H25NO10Na (M + Na)
414.1376, found 414.1375.
2-Benzyloxyethyl-(methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate) (33). BF3·OEt2 (50 mL, 0.67 mmol) was added to a
solution of trichloroacetimidate 3216 (800 mg, 1.67 mmol) and 2benzyloxyethanol (356 mL, 2.50 mmol) in anhydrous CH2Cl2 (8 mL).
After stirring at room temperature for 1 h under argon atmosphere,
triethylamine (0.3 mL) was added. Solvents were removed and the
crude product was purified by silica gel column chromatography
(toluene:acetone, from 10:1 to 6:1) to give the 33 (240 mg, 30%) as
glassy solid: [α]D22 −20.1 (c 1 in CHCl3); 1H NMR (300 MHz,
CDCl3) δ ppm 7.35−7.28 (m, 5H, Ph), 5.27−5.23 (m, 2H, H4, H3),
5.05 (t, J = 8.4 Hz, 1H, H2), 4.67(d, J = 7.8 Hz, 1H, H1), 4.58−4.50
(m, 2H, CH2Ph), 4.06−3.96 (m, 2H, CH2, H5), 3.81−3.75 (m, 4H,
CH3O, CH2), 3.66−3.63 (m, 2H, CH2), 2.06, 2.03, 199 (3s, 9H, 3 ×
OCOCH3); 13C NMR (75 MHz, CDCl3) δ = 170.0, 169.3, 169.2,
167.1 (4 × CO), 137.9 (Cq-arom), 128.3, 127.5, 127.4 (Carom), 101.9
(C1), 73.1 (CH2), 72.4 (C5), 71.9 (C3), 71.0 (C2), 70.3 (C4), 69.9,
69.3 (2 × CH2), 52.7 (CH3O), 20.5. 20.4 (OCCH3); HRMS (FAB+)
Calcd. for C13H20O9Na (M + Na) 343.0999, found 343.1005.
2-Hydroxyethyl-(methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate) (34). A solution of compound 33 (480 mg, 1.024 mmol) in
ethyl acetate-MeOH (1:1, 10 mL) and Pd(OH)2 in catalytic amount
was stirred under an atmosphere of hydrogen for 18 h. The mixture
was filtered off over Celite and solvents were removed. The crude
product was purified by silica gel column chromathography using as
eluent (hexane:ethyl acetate, 1:2) to give 34 (180 mg, 46%) as a syrup:
[α]D22 −19.0 (c 1 in CHCl3); 1H NMR (500 MHz, CDCl3) δ ppm
5.31−5.23 (m, 2H, H4, H3), 5.04 (t, J = 8.0 Hz, 1H, H2), 4.63 (d, J =
7.5 Hz, 1H, H1), 4.10 (d, J = 9.0 Hz, 1H, H5), 3.90−92 (m, 2H, CH2),
3.77 (s, 3H, CH3O) 3.76−3.73 (m, 2H, CH2), 2.07, 2.05, 2.04 (3s, 9H,
3 × OCOCH3); 13C NMR (125 MHz, CDCl3) δ = 170.1, 169.5,
169.4, 167.1 (4 × CO), 101.2 (C1), 72.9 (C5), 72.3 (C3), 71.9 (C2),
71.3 (C4), 69.1, 61.9 (2 × CH2), 53.0 (CH3O), 20.7, 20.6, 20.5
(OCCH3); HRMS (FAB+) Calcd. for C15H22O11Na (M + Na)
401.1060, found 401.1060.
2-Benzyloxyethyl 6-tert-butyldiphenylsilyl-β-D-glucopyranose
(37). Dimethylaminopyridine (catalytic amount) and triethylamine
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H NMR (300 MHz, CDCl3) δ ppm 5.03 (dt, JH,F= 15.0, J = 9.0 Hz,
1H, H3), 4.63 (dd, J= 7.8/9.6 Hz, 1H, H2), 4.30 (d, J= 7.8 Hz, 1H,
H1), 4.26−4.07 (m, 2H, H6, H4), 3.94−3.88 (ddd, J= 1.1/5.5/12.2 Hz,
1H, H6′), 3.58−3.47 (m, 4H, 2 × CH2), 3.41−3.38 (m, 1H, H5), 2.43
(br.s, 1H, OH), 1.80, 1.75, 1.73 (3 × OCOCH3); 13C NMR (75 MHz,
CDCl3) δ = 170.7, 170.1, 169.8 (CO), 101.3 (C1), 87.0 (d, JC,F = 184.0
Hz, C4), 72.9 (OCH2), 72.6 (d, JC,F = 19.6 Hz, C3), 71.5 (d, JC,F =
10.05 Hz, C5), 71.3 (d, JC,F = 5.47 Hz, C2), 62.2 (C6), 61.9 (CH2OH),
20.8 (OCCH3); 19F NMR (CDCl3, 323.6 MHz) −123.75 ppm;
HRMS (FAB+) Calcd. for C14H21O9FNa (M + Na) 375.1067, found
375.1073.
2-Hydroxyethyl 2,3,4-tri-O-acetyl-6-deoxy-6-fluoro-β-D-glucopyranose (52). 2,3,4-Tri-O-acetyl-6-deoxy-6-fluoro-α-D-glucopyranosyl
bromide 5118e (742 mg, 2.00 mmol) was reacted following the
general glycosylation procedure. The crude product was purified by
flash column chromatography (hexane:ethyl acetate, from 1:2 to 1:3)
to afford 52 (310 mg, 44%) as glassy solid: [α]D22 −2.2 (c 1 in
CHCl3); 1H NMR (300 MHz, CDCl3) δ ppm 5.08 (t, J = 9.5 Hz, 1H,
H3), 4.90−4.79 (m, 2H, H4, H2), 4.44 (d, J= 8.0 Hz, 1H, H1), 4.40−
4.22 (dm, JH,F= 47.0 Hz, 2H, H6, H6′), 3.75−3.53 (m, 5H, 2 × CH2,
H5), 2.46 (br.s, 1H, OH), 1.90, 1.88, 1.84 (3 × OCOCH3); 13C NMR
(75 MHz, CDCl3) δ = 170.0, 169.4, 169.3 (CO), 100.9 (C1), 81.1 (d,
JC,F = 174.0 Hz, C6), 72.5 (d, JC,F = 19.3 Hz, C5), 72.4 (C3), 72.1
(OCH2), 71.1 (C2), 67.8 (d, JC,F = 6.82 Hz, C4), 61.5 (CH2OH), 20.5,
20.4 (OCCH3); 19F NMR (CDCl3, 323.6 MHz) −155.60 ppm;
HRMS (FAB+) Calcd. for C14H21O9FNa (M + Na) 375.1067, found
375.1071.
2-Hydroxyethyl 2,3,6-tri-O-acetyl-4-deoxy-4-fluoro-β-D-galactopyranose (55). 2,3,6-Tri-O-acetyl-4-deoxy-4-fluoro-α-D-galactopyranosyl bromide 5418a,c (600 mg, 1.62 mmol) was reacted following the
general glycosylation procedure. The crude product was purified by
flash column chromatography (hexane:ethyl acetate, from 2:3 to 1:3)
to afford 55 (447 mg, 78%) as an oil: 1H NMR (400 MHz, CDCl3) δ
ppm 5.22 (dd, J = 8.0, 10.4 Hz,1H, H2), 4.94 (ddd, J = 2.4, 10.4, 27.6
Hz, 1H, H3), 4.81 (dd, J = 2.8, 50 Hz, 1H, H4), 4.51 (d, J = 7.9 Hz,
H1), 4.32−4.20 (m, 2H, H6, H6′), 3.89−3.75 (m, 5H, 2 × CH2, H5),
2.74 (s, 1H, OH), 2.04, 2.02, 2.00 (3s, 9H, 3 × OCOCH3); 13C NMR
(100 MHz, CDCl3) δ = 170.5, 170.3, 169.5 (CO), 101.4 (C1), 85.8 (d,
JC,F = 185.1 Hz, C4), 72.6 (CH2), 71.2 (d, JC,F = 17.6 Hz, C5), 70.9 (d,
JC,F = 18.1 Hz, C3), 68.7 (C2), 61.8 (CH2), 61.5 (d, JC,F = 5.6 Hz, C6),
20.7, 20.6 (OCCH3); 19F NMR (CDCl3, 323.6 MHz, internal
reference TFT) −216.1 ppm; HRMS (FAB+) Calcd. for C14H21O9FNa
(M + Na) 375.1067, found 375.1075.
2-Hydroxyethyl 2,3-di-O-acetyl-4,6-dideoxy-4,6-difluoro-β-D-galactopyranose (58). 2,3-Di-O-acetyl-4,6-dideoxy-4,6-difluoro-α-D-galactopyranosyl bromide 5718b (253 mg, 0.77 mmol) was reacted
following the general glycosylation procedure. The crude product was
purified by flash column chromatography (hexane:ethyl acetate, from
1:1 to 1:2) to afford 58 (158 mg, 66%): [α]D22 +5.8 (c 1 in CHCl3);
1
H NMR (400 MHz, CDCl3) δ ppm 5.20 (t, J = 9.6 Hz, 1H, H2),
5.011−4.79 (m, 2H, H3, H4), 4.56 (dd, JH,F= 46.4, J= 6.4 Hz, 2H, H6,
H6′), 4.55 (d, J= 8.0 Hz, 1H, H1), 3.96−3.83 (m, 2H, H5, CH), 3.74−
3.66 (m, 3H, CH2), 2.72 (br.s, 1H, OH), 2.07, 2.03 (2 × OCOCH3);
13
C NMR (100 MHz, CDCl3) δ = 170.3, 169.6 (CO), 101.2 (C1), 85.5
(dd, J = 186.0, 5.0 Hz, C4), 80.4 (dd, J = 170.0, 6.0 Hz, C6), 72.9
(OCH2), 72.1 (CH2), 71.6 (dd, J = 24.0, 18.0 Hz, C5), 71.0 (d, J =
17.0 Hz, C3), 68.7 (C2), 61.6 (CH2OH), 20.7, 20.6 (OCH3); 19F
NMR (CDCl3, 323.6 MHz) −140.7, −155.1 ppm; HRMS (FAB+)
Calcd. for C12H18O7F2Na (M + Na) 335.0918, found 335.0917.
General Procedure for Synthesis of Carbohydrate Phosphoramidites. To a solution of 2-hydroxyethyl acetyl protected
carbohydrate (0.5 mmol) in dry CH2Cl2 (5 mL), DIEA (0.35 mL,
2.0 mmol) and 2-cyanoethyl-N,N′-diisopropylamino-chlorophosphoramidite (0.174 mL, 0.76 mmoL) were added at room temperature
under argon atmosphere. After 1 h the solvent was evaporated to
dryness. The product was purified by silica gel column chromathography using a mixture of hexane, ethyl acetate and triethylamine.
2-(2,3,4-Tri-O-acetyl-β- L-rhamnopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (20). 2-Hydroxyethyl 2,3,4tri-O-acetyl-β-L-rhamnopyranose 19 (0.12 g, 0.358 mmol) was reacted
1
3.48 (s, 3H, OCH3), 3.28 (ddd, 1H, H5), 3.14−2.90 (m, 3H), 1.98 (s,
3H, OCOCH3); 13C NMR (101 MHz, CDCl3) δ = 170.7 (CO), 138.2
(Cq-arom), 128.3 (2 × Carom), 127.6 (2 × Carom), 127.55 (Carom), 103.5
(C1), 86.3(CH2), 83.6, 79.4, 73.1, 72.7, 69.25, 69.05, 63.3 (C2), 60. 8,
60.44, 60.37, 24.7, 20.8(OCOCH3); HRMS (FAB+) Calcd. for
C20H30O8Na (M + Na) 421.1838, found 421.1850.
2-Hydroxyethyl 2,3,4-tri-O-methyl-6-O-acetyl-β-D-glucopyranose
(40). Palladium hydroxyde (catalytic amount) was added to a solution
of 2-benzyloxyethyl 2,3,4-tri-O-methyl-6-O-acetyl-β-D-glucopyranose
(39) (705 mg, 1.77 mmol) in ethyl acetate (4 mL) and methanol
(0.5 mL). The reaction was stirred at room temperature under H2 (g)
atmosphere (4 psi) for 3 h. The mixture was then filtered over Celite
and washed with CH2Cl2 and methanol. The solvents were then
removed and the crude product was purified by flash column
chromatography (hexane:ethyl acetate, from 2:1 to 1:20) to afford 40
(518 mg, 95%) as a white solid: 1H NMR (400 MHz, CDCl3) δ ppm
4.32 (dd, 1H, H6′), 4.22 (d, J = 7.8 Hz, 1H, H1), 4.07 (dd, 1H, H6),
3.87 (ddd, 1H), 3.76 (ddd, 1H), 3.70−3.61 (m, 2H), 3.56 (s, 3H,
OCH3), 3.53 (s, 3H, OCH3), 3.45 (s, 3H, OCH3), 3.37 (ddd, 1H, H5),
3.12 (t, 1H, H3), 3.04−2.91 (m, 2H, H2, H4), 2.03 (s, 3H, OCOCH3);
13
C NMR (101 MHz, CDCl3) δ = 170.8 (CO), 104.0 (C1), 86.4(C3),
83.6 (C2), 79.7 (C4), 73.7 (CH2), 72.8 (C5), 63.3 (C6), 62.4 (CH2),
60.9, 60.7, 60.6 (3 × OCH3), 20.7 (OCOCH3); HRMS (FAB+) Calcd.
for C13H24O8Na (M + Na) 331.1369, found 331.1367.
2-Hydroxyethyl 2,3-di-O-acetyl-4,6-di-O-methyl-β-D-glucopyranose (43). HBr (2 mL, 33% in AcOH) were added dropwise to a
solution of 1,2,3-tri-O-acetyl-4,6-di-O-methyl-α/β-D-glucopyranose
4217 (1.0 g, 2.99 mmol) in anhydrous CH2Cl2 (5 mL). The reaction
was stirred at room temperature for 2 h. The mixture was then washed
with ice−water and NaHCO3, dried over Na2SO4 and concentrated.
2,3-Di-O-acetyl-4,6-di-O-methyl-β-D-glucopyranose bromide 42b (1.06
g) was obtained as a white solid and used without further purification
for next step. Ag2CO3 (2.06 g, 7.48 mmol) was added to a solution of
2,3-di-O-acetyl-4,6-di-O-methyl-β-D-glucopyranose bromide 42b (1.06
g, 2.99 mmol) and ethylene glycol (167 μL, 2.99 mmol), previously
dried over molecular sieves, in anhydrous CH2Cl2 (10 mL). The
reaction was then stirred at room temperature for 16 h under argon
atmosphere. The mixture was then filtered over Celite and washed
with CH2Cl2. The solvent was then removed and the crude purified by
flash column chromatography (hexane:ethyl acetate, from 1:2 to 1:20)
to afford 43 (520 mg, 52%) as white solid: 1H NMR (400 MHz,
CDCl3) δ ppm 5.15 (t, 1H, H3), 4.90 (t, 1H, H2), 4.48 (d, J= 7.96 Hz,
1H, H1), 3.89−3.76 (m, 2H, CH2), 3.76−3.55 (m, 4H, CH2, H6, H6′),
3.49 (m, 1H, H5), 3.43−3.41 (m, 6H, 2 × OCH3), 3.40−3.35 (m, 1H,
H4), 2.89 (t, 1H, OH), 2.07−2.04 (m, 6H, 2 × OCOCH3); 13C NMR
(101 MHz, CDCl3) δ = 170.1, 169.8, (CO), 101.2 (s, C1), 77.6 (s, C4),
74.9 (s, C3), 74.4 (s, C5), 73.3 (s, CH2), 72.0 (s, C2), 71.0 (s, C6), 62.2
(CH2), 60.3, 59.3 (OCH3), 20.8, 20.7 (OCOCH3); HRMS (FAB+)
Calcd. for C14H24O9 (M + Na) 359.1318, found 359.1313.
2-Hydroxyethyl 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-β-D-glucopyranose (46). 2,4,6-Tri-O-acetyl-3-deoxy-3-fluoro-α-D-glucopyranosyl
bromide 4518d (1.05 g, 2.85 mmol) was reacted following the general
glycosylation procedure. The crude product was purified by flash
column chromatography (hexane:ethyl acetate, from 1:2 to 1:3) to
afford 46 (688 mg, 68%) as a glassy solid: [α]D22 −14.6 (c 1 in
CHCl3); 1H NMR (300 MHz, CDCl3) δ ppm 5.06−4.93 (m, 2H, H4,
H2), 4.37−4.31 (m, 2H, H1, H3), 4.06−4.04 (m, 2H, H6, H6′), 3.70−
3.52 (m, 5H, 2 × CH2, H5), 2.53 (s, 1H, OH), 1.98, 1.97, 1.95 (3 ×
OCOCH3); 13C NMR (75 MHz, CDCl3) δ = 170.9, 169.6, 169.5
(CO), 101.0 (d, JC,F = 11.1 Hz, C1), 91.8 (d, JC,F = 189.9 Hz, C3), 73.1
(CH2), 71.5 (d, JC,F = 18.7 Hz, C4), 71.2 (d, JC,F = 7.65 Hz, C5), 68.6
(d, JC,F = 18.6 Hz, C2), 62.1 (C6), 62.0 (CH2), 20.9, 20.8 (OCCH3);
19
F NMR (CDCl3, 323.6 MHz) −119.6 ppm; HRMS (FAB+) Calcd.
for C14H21O9FNa (M + Na) 375.1067, found 375.1075.
2-Hydroxyethyl 2,3,6-tri-O-acetyl-4-deoxy-4-fluoro-β-D-glucopyranose (49). 2,3,6-Tri-O-acetyl-4-deoxy-4-fluoro-α-D-glucopyranosyl
bromide 4818f (2.0 g, 5.00 mmol) was reacted following the general
glycosylation procedure. The crude product was purified by flash
column chromatography (hexane:ethyl acetate, from 1:2 to 1:4) to
afford 49 (1.06 g, 60%) as glassy solid: [α]D22 −12.5 (c 1 in CHCl3);
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2H, H3, H4), 4.97−4.90 (m, 2H, H2), 4.61 (dd, J = 7.8/9.6 Hz, 1H,
H1), 4.00−3.65 (m, 10H, 2 × OCH2, OCH2CH2CN, CH3O, H5),
3.60−3.48 (m, 2H, 2 × CHisopropyl), 2.59−2.55 (m, 2H, CH2CN), 2.04,
1.99 (2s, 9H, 3 xOCOCH3), 1.15−1.09 (m, 12H, 4 × CH3isopropyl); 13C
NMR (100 MHz, CDCl3) δ = 170.1, 169.4, 169.3, 167.2 (4 × CO),
117.8 (CN), 100.8 (C1), 72.5 (C5), 72.0 (C3), 71.1 (C2), 69.6 (CH2),
69.4 (C4), 62.4, 58.5, 52.8 (3 × CH2), 43.0 (NCHisopropyl), 24.6, 24.5
(CH3isopropyl), 20.7, 20.5, 20.4 (OCCH3), 20.3 (CH2CN); HRMS
(FAB+) Calcd. for C24H39N2O12PNa (M + Na) 601.2134, found
601.2138.
2-(2,3,4-Tri-O-methyl-6-O-acetyl-β-D-glucopyranosyloxy)ethyl(2cyanoethyl)(N,N-diisopropyl)phosphoramidite (41). 2-Hydroxyethyl
2,3,4-tri-O-methyl-6-O-acetyl-β-D-glucopyranose 40 (165 mg, 0.535
mmol) was reacted following the general procedure. The crude
product was purified by silica gel column chromatography
(hexane:ethyl acetate, from 3:2 to 1:2 with 1% NEt3) to give
compound 41 as a white foam (155 mg, 57%): 1H NMR (400 MHz,
CDCl3) δ ppm 4.30−4.20 (m, 2H, H6′, H1), 4.13 (dd, 1H, H6), 3.90
(m, 1H, CH2), 3.85−3.73 (m, 3H, CH iPr, CH2), 3.67 (dtt, 2H, CH2),
3.55 (s, 5H, OCH3+2H), 3.51 (s, 3H, OCH3), 3.44 (s, 3H, OCH3),
3.30 (ddd, 1H, H5), 3.10 (t, 1H, H3), 3.02 (t, 1H, H4), 2.92 (ddd, 1H,
H2), 2.58 (t, 2H, CH2), 2.02 (s, 3H, OCOCH3), 1.14−1.08 (m, 12H,
4 × CH3 isopropyl); 13C NMR (101 MHz, CDCl3) δ = 170.8 (CO),
117.7 (CN), 103.5 (C1), 86.3, 83.6, 79.4, 72.7, 69.6 (dd), 63.3, 62.4
(dd), 60.8, 60.6−60.2 (m, 2C), 58.4 (dd), 43.0 (dd, 2C), 24.7−24.4
(m, 4C), 20.8, 20.3; HRMS (FAB+) Calcd. for C22H42N2O9P (M + H)
509.2628, found 509.2653.
2-(2,3-Di-O-acetyl-4,6-di-O-methyl-β-D-glucopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (44). 2-Hydroxyethyl 2,3-di-O-acetyl-4,6-di-O-methyl-β-D-glucopyranose 43 (0.150
g, 0.45 mmol) was reacted following the general procedure. The crude
product was purified by silica gel column chromathography
(hexane:ethyl acetate, 1:1 with 1% NEt3) to give compound 44 as a
white foam (111 mg, 53%): 1H NMR (400 MHz, CDCl3) δ ppm 5.14
(m, 1H, H3), 4.89 (ddd, 1H, H2), 4.55 (dd, 1H, H1), 3.98 (m, 2H,
CH2), 3.83 (m, 2H, CH2), 3.73 (m, 2H, CH2), 3.68−3.56 (m, 5H, H5,
H6/H6′, 2 × CHisopropyl), 3.48−3.40 (m, 7H, H4, 2 × OCH3), 2.66 (m,
2H, CH2), 2.06 (m, 6H, 2 × OCOCH3), 1.19 (m, 12H, 4 ×
CH3isopropyl); 13C NMR (101 MHz, CDCl3) δ = 170.2, 169.7 (CO),
117.8 (CN), 100.7 (C1), 75.1, 74.7, 71.9, 70.8, 69.3, 69.1, 62.5, 62.3,
60.3, 59.4, 58.6, 58.4, 43.1, 43.0, 24.7, 24.6, 24.5, 20.8, 20.4; HRMS
(FAB+) Calcd. for C23H41N2O10PNa (M + Na) 559.2392, found
559.2397.
2-(2,4,6-Tri-O-acetyl-3-deoxy-3-fluoro-β-D-glucopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (47). 2-Hydroxyethyl 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-β-D-glucopyranose 46
(0.220 g, 0.62 mmol) was reacted following the general procedure.
The crude product was purified by silica gel column chromathography
(hexane:ethyl acetate, from 3:2 to 1:1 with 1% NEt3) to give
compound 47 as a syrup (260 mg, 76%): 1H NMR (300 MHz,
CDCl3) δ ppm 5.11−4.91 (m, 2H, H4, H2), 4.53−4.28 (m, 2H, H1,
H3), 4.12 (ddd, J= 2.0/4.7/12.4 Hz, 1H, H6), 3.99 (br. d, J= 12.3 Hz,
1H, H6′), 3.86−3.53 (m, 6H, 2 × OCH2, OCH2CH2CN) 3.52−3.40
(m, 3H, 2 × CHisopropyl, H5), 2.53−2.49 (m, 2H, CH2CN), 1.99, 1.97,
1.96 (s, 9H, 3 × OCOCH3), 1.05, 1.03 (2d, 12H, 4CH3isopropyl); 13C
NMR (75 MHz, CDCl3) δ = 170.9, 169.5, 169.4 (CO), 118.0 (CN),
101.0 (d, JC,F = 10.65 Hz, C1), 91.9 (d, JC,F = 189.1 Hz, C3), 71.4 (d,
JC,F = 18.5 Hz, C2), 71.1 (d, JC,F = 7.65 Hz, C5), 69.8 (CH2), 68.5 (d,
JC,F = 18.3 Hz, C4), 62.6 (CH2), 62.0 (C6), 58.6 (CH2), 43.3
(NCHisopropyl), 24.9, 24.8 (CH3 isopropyl), 21.1, 21.0, 20.9 (OCCH3),
20.6 (CH2CN). 19F NMR (CDCl3, 323.6 MHz, internal reference
TFT) −195.3 ppm; HRMS (FAB+) Calcd. for C23H38N2O10FNaP (M
+ Na) 575.2146, found 575.2158.
2-(2,3,6-Tri-O-acetyl-4-deoxy-4-fluoro-β-D-glucopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (50). 2-Hydroxyethyl 2,3,6-tri-O-acetyl-4-deoxy-4-fluoro-β-D-glucopyranose 49
(0.365 g, 1.036 mmol) was reacted following the general procedure.
The crude product was purified by silica gel column chromathography
(hexane:ethyl acetate, from 3:2 to 1:1 with 1% NEt3) to give
compound 50 as a syrup (434 mg, 76%): 1H NMR (300 MHz,
following the general procedure. The crude product was purified by
flash column chromatography (hexane:ethyl acetate, 1:1 with 1%
NEt3) to obtain compound 20 as a syrup (165 mg, 86%): 1H NMR
(300 MHz, CDCl3) δ 5.25−5.16 (m, 2H, H2, H3), 4.99 (t, J = 9.9 Hz,
1H, H4), 4.71 (dd, J = 3.7/1.6 Hz, 1H, H1), 3.94−3.48 (m, 9H, 2 ×
OCH2, OCH2CH2CN, 2 × CHisopropyl, H5), 2.63−2.57 (m, 2H,
CH2CN), 2.07, 1.98, 1.91 (3s, 3H, 3 × OCOCH3), 1.19−1.11 (m,
15H, CH3, 4 × CH3isopropyl); 13C NMR (75 MHz, CDCl3) δ = 170.1,
170.0, 169.9 (CO), 117.8 (CN), 97.7 (C1), 71.1, 69.7, 69.0, 67.8, 67.5,
63.3, 62.4, 62.2, 58.5, 43.2 (NCHisopropyl), 24.6, 24.5 (CH3isopropyl), 20.9,
20.8 (OCCH3), 20.6 (CH2CN), 17.4 (CH3); HRMS (FAB+) Calcd.
for C23H39N2O10PNa (M + Na) 557.2240, found 557.2222.
2-(2,3,4-Tri-O-acetyl-β-D-xylopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (23). 2-Hydroxyethyl 2,3,4-tri-Oacetyl-β-D-xylopyranose 22 (0.06 g, 0.197 mmol) was reacted
following the general procedure. The crude product was purified by
silica gel column chromathography (hexane:ethyl acetate, 1:1 with 1%
NEt3) to give compound 23 as a syrup (80 mg, 83%): 1H NMR (300
MHz, CDCl3) δ ppm 5.08 (t, J = 8.5 Hz, 1H, H3), 4.88−4.82 (m, 2H,
H2, H4), 4.51 (m, 1H, H1), 4.06 (dd, J = 5.3/11.8 Hz, 1H, H5), 3.89−
3.46 (m, 8H, 2 × OCH2, OCH2CH2CN, 2 × CHisopropyl), 3.34−3.26
(m, 1H, H5′), 2.61−2.54 (m, 2H, CH2CN), 1.99, 1.98, 1.97 (3s, 9H, 3
× OCOCH3), 1.11, 1.10 (2d, 12H, 4 × CH3isopropyl); 13C NMR (75
MHz, CDCl3) δ = 170.1, 169.9, 169.4 (3 × CO), 117.7 (CN), 100.7
(C1), 71.4, 70.6, 69.1, 68.8, 62.5, 62.3, 61.9, 58.5, 58.3, 43.1
(NCHisopropyl), 24.6, 24.5 (CH3isopropyl), 20.8, 20.6 (OCCH3), 20.5
(CH2CN); HRMS (FAB+) Calcd. for C22H37KN2O10P (M + K)
559.1823, found 559.1827.
2-(2,3,4-Tri-O-acetyl-6-deoxy-β-D -glucopyranosyloxy)ethyl(2cyanoethyl)(N,N-diisopropyl)phosphoramidite (26). 2-Hydroxyethyl
2,3,4-tri-O-acetyl-6-deoxy-β-D-glucopyranoside 25 (0.140 g, 0.418
mmol) was reacted following the general procedure. The crude
product was purified by silica gel column chromathography using as
eluent (hexane:ethyl acetate, 1:1 with 1% NEt3) to give compound 26
as a syrup (200 mg, 90%): 1H NMR (500 MHz, CDCl3) δ 4.90 (t, J =
9.6 Hz, 1H, H3), 4.74−4.680 (m, 1H, H2), 4.57 (t, J = 9.6 Hz, 1H, H4),
4.36 (dd, JH,P= 14.5, J = 8.1 Hz, 1H, H1), 3.70−3.40 (m, 6H, 2 ×
OCH2, OCH2CH2CN), 3.39−3.29 (m, 3H, 2 × CHisopropyl, H5), 2.67−
2.62 (m, 2H, CH2CN), 2.05, 2.03, 1.99 (3s, 3H, 3 × OCOCH3), 1.23
(d, 3H, J = 6.0 Hz, CH3), 1.17 (t, 12H, 4CH3isopropyl); 13C NMR (75
MHz, CDCl3) δ = 170.2, 169.9, 169.6 (CO), 118.0 (CN), 100.8 (C1),
73.6 (C4), 73.1 (C3), 71.9 (C2), 70.2 (C5), 69.5, 62.8, 58.7 (3 × CH2),
43.3 (NCHisopropyl), 25.0, 24.9, 24.8, 24.7 (CH3isopropyl), 21.0, 20.9, 20.8
(OCCH3), 20.6 (CH2CN), 17.6 (CH3); HRMS (FAB+) Calcd. for
C23H39N2O10PNa (M + Na) 557.2240, found 557.2243.
2-(3,4,6-Tri-O-acetyl-2-acetamido-2-deoxy-β- D-glucopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (31).
2-Hydroxyethyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranoside 30 (0.20 g, 0.50 mmol) was reacted following the general
procedure. The crude product was purified by silica gel column
chromathography (hexane:ethyl acetate, 1:1 with 1% NEt3) to give
compound 31 as a syrup (265 mg, 90%): 1H NMR (300 MHz,
CDCl3) δ 5.92 (dd, J = 3.0/8.7 Hz, 1H, NH), 4.96 (t, J = 9.6 Hz, 1H,
H3), (td, J = 2.7/9.6 Hz, 1H, H4), 4.61 (t, J = 8.4 Hz, 1H, H1), 3.98
(dd, J = 4.8/12.3 Hz, 1H, H6), 3.84 (dd, J = 2.7/12.3 Hz, 1H, H6′),
3.72−3.40 (m, 9H, 2 × OCH2, OCH2CH2CN, H2, H5), 3.37−3.26 (m,
2H, 2 × CHisopropyl), 2.43−2.39 (m, 2H, CH2CN), 1.81, 1.73, 1.67 (3s,
12H, 3 × OCOCH3), 0.92−0.89 (m, 12H, 4 × CH3isopropyl); 13C NMR
(75 MHz, CDCl3) δ = 170.9, 170.6, 169.6 (CO), 118.4 (CN), 101.3
(C1), 73.0 (C3), 72.0 (C4), 69.6, 68.9 (CH2), 62.9 (CH2), 62.4 (C6),
58.5 (CH2), 54.6 (C2), 43.3 (NCHisopropyl), 24.9 (CH3isopropyl), 21.0,
20.9, 20.8 (OCCH3), 20.7 (CH2CN); HRMS (FAB+) Calcd. for
C25H42N3NaO11P (M + Na) 614.2455, found 614.2440.
2-(Methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate-oxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (35). 2-Hydroxyethyl methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate 34
(0.14 g, 0.37 mmol) was reacted following the general procedure.
The crude product was purified by silica gel column chromathography
(hexane:ethyl acetate, 1:1 with 1% NEt3) to give compound 35 as a
syrup (160 mg, 75%): 1H NMR (300 MHz, CDCl3) δ 5.21−5.11 (m,
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CDCl3) δ ppm 5.03 (dt, JH,F= 15.0, J = 9.0 Hz, 1H, H3), 4.68 (dd, J=
7.8/9.6 Hz, 1H, H2), 4.40 (dd, J= 7.8/10.5 Hz, 1H, H1), 4.37−4.13
(m, 2H, H6, H4), 4.02−3.97 (dd, J= 5.5/12.2 Hz, 1H, H6′), 3.74−3.43
(m, 7H, 2 × OCH2, OCH2CH2CN, H5), 3.40−3.28 (m, 2H, 2 ×
CHisopropyl), 2.43−2.37 (m, 2H, CH2CN), 1.87, 1.83, 1.80 (3s, 9H, 3 ×
OCOCH3), 0.95, 0.93 (m, 12H, 4CH3isopropyl); 13C NMR (75 MHz,
CDCl3) δ = 170.4, 169.8, 169.3 (CO), 117.7 (CN), 101.6 (C1), 86.6
(d, JC,F = 186.7 Hz, C4), 72.4 (d, JC,F = 19.5 Hz, C3), 71.2 (d, JC,F =
11.1 Hz, C5), 70.9 (d, JC,F = 4.35 Hz, C2), 69.5, 62.3 (CH2), 61.9 (C6),
58.3 (CH2), 42.9 (NCHisopropyl), 24.5, 24.4 (CH3isopropyl), 20.6, 20.3
(OCCH3), 20.2 (CH2CN). 19F NMR (CDCl3, 323.6 MHz, internal
reference TFT) −199.9 ppm; HRMS (FAB + ) Calcd. for
C23H38N2O10FNaP (M + Na) 575.2146, found 575.2164.
2-(2,3,4-Tri-O-acetyl-6-deoxy-6-fluoro-β-D-glucopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (53). 2-Hydroxyethyl 2,3,4-tri-O-acetyl-6-deoxy-6-fluoro-β-D-glucopyranose 52
(0.150 g, 0.42 mmol) was reacted following the general procedure.
The crude product was purified by silica gel column chromathography
(hexane:ethyl acetate, from 3:2 to 1:1 with 1% NEt3) to give
compound 53 as a syrup (150 mg, 65%): 1H NMR (500 MHz,
CDCl3) δ ppm 5.08 (td, J = 3.0/9.5 Hz, 1H, H3), 5.05 (t, J = 9.5 Hz,
1H, H4), 5.00−4.97 (m, 1H, H2), 4.66 (dd, J= 8.0/12.0 Hz, 1H, H1),
4.40−4.22 (dm, JH,F= 47.0 Hz, 2H, H6, H6′), 4.00−3.69 (m, 7H, 2 ×
OCH2, OCH2CH2CN, H5), 3.64−3.57 (m, 2H, 2 × CHisopropyl), 2.67−
2.63 (m, 2H, CH2CN), 2.08, 2.06, 2.02 (3 × OCOCH3), 1.19 (t, 12H,
4CH3isopropyl); 13C NMR (125 MHz, CDCl3) δ = 170.3, 169.5, 169.3
(CO), 118.0 (CN), 100.9 (C1), 81.1 (d, JC,F = 174.0 Hz, C6), 72.7 (d,
JC,F = 4.3 Hz, C3), 72.5 (d, JC,F = 19.6 Hz, C5), 71.2 (C2), 69.4 (CH2),
68.1 (d, JC,F = 6.75 Hz, C4), 62.4, 58.5 (CH2), 43.3 (NCHisopropyl), 24.6,
24.5 (CH3isopropyl), 20.7, 20.6 (OCCH3), 20.4 (CH2CN). 19F NMR
(CDCl3, 323.6 MHz, internal reference TFT) −231.4 ppm; HRMS
(FAB+) Calcd. for C23H38N2O10FNaP (M + Na) 575.2146, found
575.2117.
2-(2,3,6-Tri-O-acetyl-4-deoxy-4-fluoro-β-D-galactopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (56). 2-Hydroxyethyl 2,3,6-tri-O-acetyl-4-deoxy-4-fluoro-β-D-galactopyranose 55
(0.120 g, 0.34 mmol) was reacted following the general procedure.
The crude product was purified by silica gel column chromathography
(hexane:ethyl acetate, 1:1 with 1% NEt3) to give compound 56 as a
syrup (121 mg, 64%): 1H NMR (400 MHz, CDCl3) δ ppm 5.25−5.22
(m, 1H, H2), 5.01−4.90 (m, 1H, H3), 4.83 (d, J= 50.4 Hz, 1H, H4),
4.60 (dd, J= 8.0/11.8 Hz, 1H, H1), 4.37−4.32 (m, 1H, H5), 4.23−4.18
(dd, J= 6.8/11.3 Hz, 1H, H6), 3.96−3.70 (m, 7H, 2 × OCH2,
OCH2CH2CN, H6′), 3.62−3.54 (m, 2H, 2 × CHisopropyl), 2.66−2.62
(m, 2H, CH2CN), 2.1, 2.08, 2.06 (3s, 9H, 3 × OCOCH3), 1.17 (t, J =
6.6 Hz, 12H, 4 × CH3isopropyl); 13C NMR (100 MHz, CDCl3) δ =
170.4, 170.3, 169.3 (CO), 117.7 (CN), 100.9 (C1), 85.8 (dd, JC,P = 6.8
Hz, JC,F = 185.1 Hz, C4), 71.3 (dd, J = 4.7 Hz, J = 19.5 Hz), 70.8 (d, J =
18.0 Hz), 69.1 (dd, J = 25.2, 7.37 Hz), 68.6 (d, J = 4.8 Hz), 62.5 (dd, J
= 7.7, 16.6 Hz), 61.3, 58.4 (d, J = 19.0 Hz, CH2), 42.9 (dd, J = 4.2,
12.39 Hz, NCHisopropyl), 24.5, 24.4 (CH3isopropyl), 20.6, 20.3 (OCCH3),
20.2 (CH2CN). 19F NMR (CDCl3, 323.6 MHz, internal reference
TFT) −216.1 ppm; HRMS (FAB+) Calcd. for C23H38N2FO10NaP (M
+ Na) 575.2161, found 575.2146.
2-(2,3-Di-O-acetyl-4,6-dideoxy-4,6-difluoro-β- D -galactopyranosyloxy)ethyl(2-cyanoethyl)(N,N-diisopropyl)phosphoramidite (59). 2-Hydroxyethyl 2,3-di-O-acetyl-4,6-dideoxy-4,6difluoro-β-D-galactopyranose 58 (0.120 g, 0.38 mmol) was reacted
following the general procedure. The crude product was purified by
silica gel column chromathography (hexane:ethyl acetate, 1:1 with 1%
NEt3) to give compound 59 as a syrup (125 mg, 62%): 1H NMR (400
MHz, CDCl3) δ ppm 5.23−5.21 (m, 1H, H2), 5.00−4.93 (m, 1H, H3),
4.86 (d, J= 50.4 Hz, 1H, H4), 4.62−4.52 (m, 3H, H6, H1, H6′), 3.97−
3.65 (m, 7H, H5, 2 × OCH2, OCH2CH2CN), 3.63−3.53 (m, 2H, 2 ×
CHisopropyl), 2.66−2.61 (m, 2H, CH2CN), 2.09−2.07 (m, 6H, 2 ×
OCOCH3), 1.20 (t, J = 6.6 Hz, 12H, 4CH3isopropyl); 13C NMR (100
MHz, CDCl3) δ = 170.3, 169.3 (CO), 117.9 (CN), 100.9 (C1), 85.7
(dd, J = 5.0 Hz, 186 Hz, C4), 71.3 (dd, J = 4.7, 19.5 Hz, C6), 71.6, 71.4,
71.3, 71.2, 69.3, 68.2, 62.5, 58.4 (d, J = 19.6 Hz, CH2), 42.9
(NCHisopropyl), 24.6, 24.5 (CH3isopropyl), 20.8, 20.7 (OCCH3), 20.3
(CH2CN). 19F NMR (CDCl3, 323.6 MHz, internal reference TFT)
−217.1, −231.0 ppm; HRMS (FAB+) Calcd. for C21H35N2O8F2NaP
(M + Na) 535.1997, found 535.2005.
Synthesis of Carbohydrate−Oligonucleotide Conjugates.
Carbohydrate−oligonucleotide conjugates 6, 8, and 14 were
synthesized on a DNA automatic synthesizer by using standard βcyanoethylphosphoramidite chemistry. Conjugate 5, 7, 9, 10, 11, and
13−17 were prepared by Biomers following the same methodology.
Oligonucleotide conjugates were synthesized either on low-volume
200 nmols (LV200) or 1.0 μmol scale and using the DMT-off
procedure. Oligonucleotide supports were treated with 33% aqueous
ammonia for 16 h at 55 °C, and then the ammonia solutions were
evaporated to dryness and the conjugates were purified by reversedphase HPLC in a Waters Alliance separation module with a PDA
detector. HPLC conditions were as follows: Nucleosil 120 C18, 250 ×
8 mm, 10 μm column; flow rate: 3 mL/min. A 27 min linear gradient
0−30% B (solvent A: 5% CH3CN/95% 100 mM triethylammonium
acetate (TEAA; pH 6.5); solvent B: 70% CH3CN/30% 100 mM
TEAA (pH 6.5)).
Thermodynamic Measurements. Melting curves for the DNA
conjugates were measured in an UV/vis spectrophotometer at 280 nm
while the temperature was raised from 10 to 80 °C at a rate of 1.0 °C
min−1. Curve fits were excellent, with c2 values of 106 or better, and the
van’t Hoff linear fits were quite good (r2 = 0.98) for all
oligonucleotides. ΔH, ΔS, and ΔG errors were calculated as described
previously.19
NMR Spectroscopy. Samples of all the conjugates were purified
by HPLC, ion-exchanged with Dowex 50W resin and then suspended
in 500 μL of either D2O or H2O/D2O 9:1 in phosphate buffer, 100
mM NaCl, pH 7. NMR spectra were acquired in 600 or 800 MHz
NMR spectrometers. DQF-COSY, TOCSY and NOESY experiments
were recorded in D2O. The NOESY spectra were acquired with mixing
times of 150 and 300 ms, and the TOCSY spectra were recorded with
standard MLEV-17 spin-lock sequence, and 80-ms mixing time.
NOESY spectra in H2O were acquired with 100 ms mixing time. In 2D
experiments in H2O, water suppression was achieved by including a
WATERGATE23 module in the pulse sequence prior to acquisition.
Two-dimensional experiments in D2O were carried out at temperatures ranging from 5 to 25 °C, whereas spectra in H2O were recorded
at 5 °C to reduce the exchange with water. The spectral analysis
program Sparky24 was used for semiautomatic assignment of the
NOESY cross-peaks and quantitative evaluation of the NOE
intensities.
Conjugate Modeling and Buried Surface Area Calculations.
Computer models of conjugates 9−12 were built from the solution
structure of the permethylated conjugate 12 determined in a previous
study.13 The computer package Sybyl was used to perform the
adequate −CH3 to −OH substitutions. The coordinates were energy
minimized before surface area calculations. Models of the “open”
conjugates were built by manually changing the torsion angles of the
linking phosphate to locate the carbohydrate in a position where it is
completely exposed to the solvent.
The buried surface area is obtained as the difference between de
surface area of the “open” and the “folded” model of the
corresponding conjugate. Surface areas were calculated with the
program MOLMOL.25
■
ASSOCIATED CONTENT
S Supporting Information
*
Copies of 1H NMR and 13C NMR spectra for compounds 19−
59. HPLC traces of carbohydrate oligonucleotide conjugates
(COCs) 5−17. Melting and van’t Hoff curves of the COCs.
NMR proton assignments, relevant NOEs, and chemical shift
changes for COCs 13−17. This material is available free of
charge via the Internet at http://pubs.acs.org.
2428
dx.doi.org/10.1021/jo402700y | J. Org. Chem. 2014, 79, 2419−2429
The Journal of Organic Chemistry
■
Article
(16) Fischer, B.; Nudelman, A.; Ruse, M.; Herzig, J.; Gottlieb, H;
Keinan, E. J. Org. Chem. 1984, 49, 4988.
(17) Kovac, P.; Longauerova, Z. Chem. Zvesti 1972, 26, 179.
(18) (a) Koch, K.; Chambers, R. J. Carbohydr. Res. 1993, 241, 295.
(b) Withers, S. G.; Percival, M. D.; Street, I. P. Carbohydr. Res. 1989,
187, 43. (c) Xia, J.; Xue, J.; Locke, R. D.; Chandrasekaran, E. V.;
Srikrishnan, T.; Matta, K. L. J. Org. Chem. 2006, 71, 3696. (d) Csuk,
R.; Albert, S. Z. Naturforsch., B: J. Chem. Sci. 2011, 66b, 311.
(e) Nieschalk, J.; O’Hagan, D. J. Fluorine Chem. 1998, 91, 159.
(f) Berven, L. A.; Dolphin, D.; Withers, S. G. Can. J. Chem. 1990, 68,
1859.
(19) (a) Petersheim, M.; Turner, D. H. Biochemistry 1983, 22, 256.
(b) Ohmichi, T.; Nakano, S.; Miyoshi, D.; Sugimoto, N. J. Am. Chem.
Soc. 2002, 124, 10367.
(20) Guckian, K. M.; Schweitzer, B. A.; Ren, R. X. F.; Sheils, C. J.;
Tahmassebi, D. C.; Kool, E. T. J. Am. Chem. Soc. 2000, 122, 2213.
(21) Ghose, A. K.; Crippen, G. M. J. Chem. Inf. Comput. Sci. 1987, 27,
21.
(22) Santana, A. G.; Jimenez-Moreno, E.; Gomez, A. M.; Corzana, F.;
Gonzalez, C.; Jimenez-Oses, G.; Jimenez-Barbero, J.; Asensio, J. L. J.
Am. Chem. Soc. 2013, 135, 3347.
(23) Piotto, M.; Saudek, V.; Sklenar, V. J. Biomol. NMR 1992, 2, 661.
(24) Goddard, D. T., Kneller, D. G., SPARKY 3; University of
California: San Francisco.
(25) Koradi, R.; Billeter, M.; Wuthrich, K. J. Mol. Graphics 1996, 14,
29.
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected].
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
Financial support by Ministerio de Economiá y Competitividad
(Grants CTQ2007-68014-C02-02, CTQ2009-13705,
CTQ2010-20541-C03-01, CTQ2012-35360), Generalitat de
Catalunya (2009/SGR/208), and Instituto de Salud Carlos III
(CIBER-BNN, CB06_01_0019) is gratefully acknowledged.
E.V.C. thanks Ministerio de Educación for a FPU fellowship.
■
REFERENCES
(1) (a) Asensio, J. L.; Arda, A.; Canada, F. J.; Jimenez-Barbero, J. Acc.
Chem. Res. 2013, 46, 946. (b) Nishio, M. Phys. Chem. Chem. Phys.
2011, 13, 13873.
(2) (a) Gabius, H.-J.; Siebert, H.-C.; André, S.; Jiménez-Barbero, J.;
Rüdiger, H. ChemBioChem 2004, 5, 740. (b) Lis, H.; Sharon, N. Chem.
Rev. 1998, 98, 637. (c) Sharon, N.; Lis, H. Glycobiology 2004, 14, 53R.
(3) Vicens, Q.; Westhof, E. Biopolymers 2003, 70, 42.
(4) (a) Piotukh, K.; Serra, V.; Borriss, R.; Planas, A. Biochemistry
1999, 38, 16092. (b) Flint, J.; Nurizzo, D.; Harding, S. E.; Longman,
E.; Davies, G. J.; Gilbert, H. J.; Bolam, D. N. J. Mol. Biol. 2004, 337,
417.
(5) (a) Kogelberg, H.; Solis, D.; Jimenez-Barbero, J. Curr. Opin.
Struct. Biol. 2003, 13, 646. (b) Terraneo, G.; Potenza, D.; Canales, A.;
Jimenez-Barbero, J.; Baldridge, K. K.; Bernardi, A. J. Am. Chem. Soc.
2007, 129, 2890. (c) Ramirez-Gualito, K.; Alonso-Rios, R.; QuirozGarcia, B.; Rojas-Aguilar, A.; Diaz, D.; Jimenez-Barbero, J.; Cuevas, G.
J. Am. Chem. Soc. 2009, 131, 18129.
(6) (a) Screen, J.; Stanca-Kaposta, E. C.; Gamblin, D. P.; Liu, B.;
Macleod, N. A.; Snoek, L. C.; Davis, B. G.; Simons, J. P. Angew. Chem.,
Int. Ed. Engl. 2007, 46, 3644. (b) Su, Z.; Cocinero, E. J.; StancaKaposta, E. C.; Davis, B. G.; Simons, J. P. Chem. Phys. Lett. 2009, 471,
17.
(7) (a) Tsuzuki, S.; Fujii, A. Phys. Chem. Chem. Phys. 2008, 10, 2584.
(b) Fernandez-Alonso, M. C.; Canada, F. J.; Jimenez-Barbero, J.;
Cuevas, G. J. Am. Chem. Soc. 2005, 127, 7379. (c) Sujatha, M. S.;
Sasidhar, Y. U.; Balaji, P. V. Protein Sci. 2004, 13, 2502. (d) Kozmon,
S.; Matuska, R.; Spiwok, V.; Koca, J. Phys. Chem. Chem. Phys. 2011, 13,
14215. (e) Kozmon, S.; Matuska, R.; Spiwok, V.; Koca, J. Chem.Eur.
J. 2011, 17, 5680.
(8) (a) Kobayashi, K.; Asakawa, Y.; Kato, Y.; Aoyama, Y. J. Am. Chem.
Soc. 1992, 114, 10307. (b) Morales, J. C.; Penadés, S. Angew. Chem.,
Int. Ed. 1998, 37, 654. (c) Ke, C.; Destecroix, H.; Crump, M. P.; Davis,
A. P. Nat. Chem. 2012, 4, 718.
(9) (a) Laughrey, Z. R.; Kiehna, S. E.; Riemen, A. J.; Waters, M. L. J.
Am. Chem. Soc. 2008, 130, 14625. (b) Chavez, M. I.; Andreu, C.; Vidal,
P.; Aboitiz, N.; Freire, F.; Groves, P.; Asensio, J. L.; Asensio, G.;
Muraki, M.; Canada, F. J.; Jimenez-Barbero, J. Chem.Eur. J. 2005, 11,
7060.
(10) Chen, W.; Enck, S.; Price, J. L.; Powers, D. L.; Powers, E. T.;
Wong, C. H.; Dyson, H. J.; Kelly, J. W. J. Am. Chem. Soc. 2013, 135,
9877.
(11) Morales, J. C.; Reina, J. J.; Díaz, I.; Aviño,́ A.; Nieto, P. M.;
Eritja, R. Chem.Eur. J. 2008, 14, 7828.
(12) Lucas, R.; Gómez-Pinto, I.; Avinnó, A.; Reina, J. J.; Eritja, R.;
González, C.; Morales, J. C. J. Am. Chem. Soc. 2011, 133, 1909.
(13) Lucas, R.; Vengut-Climent, E.; Gómez-Pinto, I.; Avinnó, A.;
Eritja, R.; González, C.; Morales, J. C. Chem. Commun. 2012, 48, 2991.
(14) Sorg, B. L.; Hull, W. E.; Kliem, H. C.; Mier, W.; Wiessler, M.
Carbohydr. Res. 2005, 340, 181.
(15) (a) Kochetkov, N. K.; Byramova, N. E.; Tsvetkov, Y. E.;
Backinovskii, L. V. Tetrahedron 1985, 41, 3363. (b) Lemieux, R. U.;
Takwa, T.; Chung, B. Y. ACS Symp. SW 1976, 39, 90.
2429
dx.doi.org/10.1021/jo402700y | J. Org. Chem. 2014, 79, 2419−2429