DEVELOPMENT OF SYNTHETIC METHODOLOGIES TOWARDS CYCLIC
HYDROXAMIC ACID-BASED NATURAL PRODUCTS
BY
RANJAN BANERJEE
A Dissertation Submitted to the Graduate Faculty of
WAKE FOREST UNIVERSITY GRADUATE SCHOOL OF ARTS AND SCIENCES
in Partial Fulfillment of the Requirements
for the Degree of
DOCTOR OF PHILOSOPHY
Chemistry
December 2010
Winston-Salem, North Carolina
Approved By:
S. Bruce King, Ph.D., Advisor
Pradeep K. Garg, Ph.D., Chairman
Rebecca W. Alexander, Ph.D.
Christa L. Colyer, Ph.D.
Paul B. Jones, Ph.D.
ACKNOWLEDGEMENTS
I want to express my thanks and sincere gratitude to Dr. S. Bruce King, for all his
academic support and chemistry help, support, and advising throughout my Ph.D career. I
owe him a lot for helping me develop into an organic chemisty, guiding my projects and
his patience in helping me improve my scientific writing. I am really fortunate to have
shared his immense scientific knowledge and learn from his amazing mentoring ability. I
am also thankful to Dr. Paul Jones and Dr. Rebecca Alexander for being my committee
members.
I really want to thank Dr. Cynthia S. Day for crystallographic help and Dr. Marcus W.
Wright for NMR assistance. They have always been extremely helpful with any data
interpretation and experiment setup needed.
I thank my previous lab mates Dr. Sarah Knaggs, Dr. Weibin Chen, Dr. Mike Gorczyski,
Brad Poole and the present lab mates Mai Shoman, Raje Mukherjee, Dr. Richard Macri,
Dr. Mallinath Hadimani, Dr. Susan Mitroka, Craig Clodfelter, Julie Reisz and Jenna
DuMond for their assistance and friendship.
I appreciate the friendship and support I received from my Wake Forest friends Tanya
Pinder, Dr. Uli Bierbach, Lu Rao, Rajsekhar Guddneppanavar, Jayati Roychoudhuri,
Zhidong Ma, Samrat Dutta, Lindsey Davis, John Solano, R.P. Oates, Zhouli Zho and
Sandhya Bharti. I am really indebted to Subhasis De for his enormous help to start my
American life and really appreciate his friendship. I am also very thankful to my
roommates Saurav Sarma, Sebastial Berisha, Edison Munoz-Recuay, Angelo Malvestio,
Matt Koval, Joe Maye, Dhruv Gandhi, Anand Gondalerkar and Ben Rosenberg.
My very special thanks and love to my beautiful girlfriend Erika Bechtold for bringing so
much joy and happiness in life. Erika has always been an amazing support, my very best
friend and the sweetest thing I have ever known. She has changed my life and I enjoy it
every moment. I am also thankful to Erika’s roommates Charlie and Jeremy for their
friendship and support.
My sincere love and gratitude goes to my father and mother for being the best parent in
the world. Word cannot express my thankfulness for their endless love, countless
sacrifices and tremendous encouragement throughout my life. I will be indebted to them
forever and I thank God for blessing my life with their kind souls. I wish to dedicate this
work to my parents and Erika.
TABLE OF CONTENTS
LIST OF FIGURES……………………………………………………………………
LIST OF TABLES……………………………………………………………………..
ABSTRACT……………………………………………………………………………
CHAPTER 1: INTRODUCTION………………………………………………………...1
1.1 Hydroxamic Acids………………………………………………………..1
1.2 Basic Structure…………………………………………………………....2
1.3 Biological Importance of Hydroxamic Acids…………………………….2
1.3.1 Enzyme Inhibitors…………………………………………………2
1.3.1.1 Matrix Metalloproteinase Inhibition……………………..2
1.3.1.2 Histone Deacetylase Inhibition…………………………..4
1.3.1.3 TNF-Alpha Converting Enzyme Inhibition……………...5
1.3.2 Therapeutic Uses of Hydroxamic Acids…………………………..6
1.3.2.1 Antimalarial Activity…………………………………….6
1.3.2.2 Antimelanogenic Agents………………………………....7
1.3.2.3 NO Donors……………………………………………….7
1.4 Biological Importance of Cyclic Hydroxamic Acids……………………..8
1.4.1. Iron Uptake by Siderophores……………………………………...8
1.4.2 Lipoxygenase Inhibitory Activity………………………………….9
1.4.3 Therapeutic Application of Cycllic Hydroxamic Acids………….10
1.4.3.1 Prostate Cancer Therapeutics……………………………10
1.4.3.2 Growth Inhibitors Tumor Cell Lines…………………....11
1.4.3.3 Analgesic Activity………………………………………12
i 1.5 Synthetic Approaches to Hydroxamic Acids…………………………….12
1.5.1 Simple Hydroxamic Acids………………………………………..12
1.5.2 Angeli-Rimini Reaction…………………………………………..13
1.5.3 Solid Phase Modification…………………………………………13
1.5.4 Oxidation of N-Boc protected Amides…………………………...14
1.5.5 N-Substituted Hydroxamic Acids………………………………...15
1.5.6 Solid Phase Synthetic Approach………………………………….16
1.5.7 Nitroso-ene Reactions…………………………………………….17
1.5.7.1 Intermolecular Nitroso-ene Reactions…………………..18
1.6 Synthesis of Cyclic Hydroxamic Acids…………………………………..20
1.6.1 Reductive Cyclization of Aliphatic Nitro Acids…………………..20
1.6.2 Synthesis of the Cobactin Core……………………………………20
1.6.3 Heterocycle Based Synthesis: Tungstate Catalyzed Oxidation of
Tetrahydro Quinoline……………………………………………..21
1.6.4 Oxidation of Lactams to Cyclic Hydroxamic Acids……………...22
1.6.5 Phenyliodine(III) Bis Trifluoroacetate Mediated Ring-closure…...22
1.6.6 Photochemical Synthesis of Cyclic Hydroxamic Acids…………..23
1.6.7 Intramolecular Nitroso-ene Reaction……………………………...24
1.6.8 Ring Expansion of Cyclic Ketones ……………………………… 26
1.6.9 Piloty’s Acid-Based Rearrangements of Cyclic Ketones to Make
Cobactin…………………………………………………………...27
1.7
Piloty’s Acid: A Nitroxyl Donor…………………………………………27
1.7.1 Nitroxyl (HNO) Chemistry……………………………………….28
1.8
Mycobactin – S…………………………………………………………..30
ii 1.8.1 Biosynthesis of Mycobactins……………………………………………31
CHAPTER 2: SYNTHESIS OF CYCLIC HYDROXAMIC ACID THROUGH –NOH
INSERTION OF KETONES……………………………………………34 2.1 Introduction………………………………………………………………35
2.2 Synthesis of N-Hydroxy Benzenesulfohydroxamic Acid (Piloty’s acid)...36
2.3 -NOH Insertion Reaction of Cyclic Ketones…………………………….36
2.3.1
Synthesis of N-hydroxy Piperidone………………………………36
2.3.2 -NOH Insertion Reaction in Cyclobutanones…………………….38
2.3.3 Solid phase modification………………………………………….42
2.4 Mechanism of –NOH insertion reaction………………………………….43
2.5 Scope of –NOH Insertion Reaction………………………………………49
2.5.1
Synthesis of O-Protected Cyclic Hydroxamic Acids…………….49
2.5.2 –NOH Insertion Reaction in α-Substituted Cyclopentanone…….50
2.5.3
-NOH Insertion in Cyclohexenone……………………………….51
2.5.4
Investigation of a Cobactin Synthesis Using the –NOH Insertion
Reaction………………………………………………………...52
2.6 Experimental……………………………………………………………...54
CHAPTER 3:
3.1
PROGRESS TOWARDS THE SYNTHESIS OF THE COBACTIN
CORE AND MYCOBACTIC ACID UTILIZING NITROSO-ENE
REACTION………………………………………………………….71
Intramolecular Nitroso-ene Reaction Approach to the Synthesis of
Cobactin Core………………………………………………………….71
3.1.1 Retrosynthesis of Cobactin ……………………………………..71
3.1.2
Intramolecular Nitroso-ene Reactons: Results and Discussion…72
3.2 Structure Elucidation of Mycobactin …………………………………..76
iii 3.3
Investigation of Intermolecular Nitroso-ene Approach towards the
Synthesis of Cobactin and Mycobactic Acid…………………………...76
3.3.1 Synthesis of the Precursor Alkene and Diels-Alder Cycloadduct
(Acyl-nitroso Precursor) for a Nitroso-ene Reaction………………….78
3.3.2
Nitroso-ene Reaction…………………………………………...78
3.3.3 Progress Towards the Synthesis of Mycobactic Acid Utilizing a
Nitroso-ene Reaction…………………………………………..83
3.4
Nitroso-ene Reactions of Acetyl-Nitroso Compounds…………………86
3.5
Nitroso-ene Reactions of Benzoyl Nitroso compounds………………...87
3.6
Experimental……………………………………………………………90
CHAPTER 4: SUMMARY …………………………………………………………...114
REFERENCES……………………………………………………………………….117
APPENDIX…………………………………………………………………………..136
SCHOLASTIC VITA………………………………………………………………...181
iv LIST OF FIGURES
Figure 1. X-ray Diffraction structure of N-hydroxy piperidone (85) …………. 38
Figure 2. X-ray Diffraction Structure of 89 …………………………………… 39
Figure 3. Figure 3. X-ray Diffraction Structure of 94…………………………. 42
Figure 4. X-ray Diffraction Structure of Compound 127 …………………….. 75
v LIST OF TABLES
Table 1. Results of –NOH insertion with cyclopentanone towards N-hydroxy
piperidone synthesis…………………………………………………. 37
Table 2. Results of –NOH Insertion into cyclobutanone ………………………40
Table 3. Gas Chromatography Results: Hydrolysis of acyloxy nitroso ………. 47
vi LIST OF ABBREVIATION
Boc
tert-Butyloxy carbonyl
Cbz
Carboxybenzyl
DCC
DIBOA
N, N’-Dicyclohexylcabodiimide
2,4-dihydroxy-2H-1,4-benzooxazin-3(4H)-one
DMA
Dimehtylanthracene
DMAP
4-Dimethylaminopyridine
DMD
Dimethyldioxirane
DMF
Dimehtylformamide
DMSO
Dimehtylsulfoxide
DNA
Deoxyribonucleic Acid
E
EDC
Entgegen
1-Ethyl-3-(3-dimethylaminopropoyl)carbodiimide
FR900098
Fosmidomycin
GC
Gas chromatography
HCl
Hydrochloric acid
HDAC
Histone deacetylase
HETE
Hydroxyeicosatetraenoic acid
HNO
Nitroxyl
HOAt
1-Hydroxy-7-azabenzotriazole
Half maximal inhibitory activity
IC50
MMP
Matrix metalloproteinase
MS
Mass Spectrometry
NMR
Nuclear magnetic resonance
NO
Nitric Oxide
vii PIFA
Phenylidoine (III) bis(trifluoroacetate)
Ppm
Parts per million
SAHA
Suberoylanilide hydroxamic acid
TACE
Tumor necrosis factor alpha converting enzyme
TBDMSCl
tert-Butyl dimethylsilyl chloride
TBDPSCl
tert-Butyl chlorodiphenylsilane
TFA
Trifluoroacteic acid
THF
Tetrahydrofuran
TIMP
Tissue inhibitor of metalloproteinases
TLC
Thin layer chromatogrpahy
TMD
Trifluoromethyl dioxiranes
TNF
Tumor Necrosis Factor
TSA
Tricostatin A
Z
Zussamen
viii Abstract
Hydroxamic acids are an important class of bioactive compounds with wide uses as
anti-bacterial, or anti-inflammatory agents and a key component of many natural
products, mainly siderophores (low-molecular-weight iron sequestering agents) in lower
organisms. Hydroxamic acid based analogs may find potential therapeutic uses in the
inhibition of siderophore biosynthesis. Our research targets to develop new synthetic
methodology towards making cyclic hydroxamic acids in a stereoselective and
regioselective fashion. Basic decomposition of Piloty’s acid transforms cyclic ketones
(mainly four and five membered) into ring-expanded cyclic hydroxamic acids in 20-69%
yield (Scheme 1). Mechanistic study reveals this reaction involves a C-nitroso
intermediate 98 (Scheme 47) in the course of the rearrangement, which can also be
generated by a separate hydrolysis reaction of acyloxy nitroso intermediate 103 (Scheme
51) leading to the ring-expansion product in 75-80% yield.
Nitroso-ene reactions regioselectively and stereoselectively functionalize olefins in
the allylic position. We use various acyl nitroso species (general formula RCONO) as
enophiles in an ene reaction with olefins to produce hydroxamic acids substituted at the
nitrogen with an allylic group. This sequence allows the synthesis of many N-containing
products with diverse structures. Amino acid-based hydroxamic acids are important
components in mycobactin, hydroxamic acid-based siderophores produced by
Mycobacterium species. Mycobactin S inhibits growth against Mycobacterium
tuberculosis and it consists of cobactin and mycobactic acid (Scheme 38), which contain
ix a hydroxamic acid residue derived from NЄ-hydroxylysine. The intermolecular nitrosoene reaction between a Nα-acyl-homoallyl-glycine ester (149) and a t-butyl nitroso
formate (136), followed by reduction and deprotection, yields Nα-acyl-NЄ-hydroxylysine
(152, Scheme 68). This sequence provides a key intermediate in route to cobactin, the
seven-membered cyclic hydroxamic acid found in various mycobactins.
A similar
synthetic route using a long chain-derived acyl nitroso species supports a synthetic route
to mycobactic acid. This research also involves exploring the scope of the nitroso-ene
reaction of various acyl nitroso species with terminal alkene (149) to generate a series of
N-substituted hydroxamic acids.
x CHAPTER 1
INTRODUCTION
1.1
Hydroxamic acids ( RCONR'OH )
Hydroxamic acids have been known since 1869 with the discovery of
oxalohydroxamic acid by Lossen.1 Despite this early discovery, not much biological
information about these important molecules was known for a long time. A tremendous
amount of research attention has been given over the last couple of decades towards the
synthesis and biomedical applications of hydroxamic acid containing organic
molecules.2-5 Hydroxamic acids are powerful metal ion chelators,6 which possess a
wide spectrum of biological activities, such as anti-bacterial, anti-fungal, antiinflammatory, and anti-asthmatic properties,7-9 and are potent inhibitors of matrix
metalloproteinases, a family of zinc-dependent enzymes associated with diseases like
cancer, arthritis, nephritis and multiple sclerosis.10-13 Hydroxamic acids can find
therapeutic potential as ribonucleoside reductase inhibitors blocking DNA biosynthesis
and also act as histone deacetylase inhibitors, both common targets for cancer
treatment.14
Hydroxamic acids play key roles in microbial iron consumption as
siderophores, low molecular weight iron-sequestering agents produced by most
microorganisms, especially under iron deficient conditions.15 Finally, hydroxamic acids
have been shown to inhibit TNF (tumor necrosis factor)-alpha converting enzyme
(TACE),
16
to demonstrate anti-malarial activity and to act as donors of nitric oxide
(NO), an important biological signaling molecule.17
1
1.2
Basic Structure
Hydroxamic acids are N-hydroxy amides, derivatives of hydroxylamine and
carboxylic acids. Cyclic hydroxamic acids (1) are generally N-hydroxy lactams. Two
possible hydroxamic acid tautomers exist (Scheme 1), the keto isomer is predominant
under acidic or neutral conditions, and the enol form is stable in alkaline conditions.
NMR studies have shown the presence of (E) and (Z) isomers extending the structural
diversity. The structure of the hydroxamic acids allows these compounds to chelate
various metal ions strongly.
Scheme 1. Structure of hydroxamic acids
1.3 Biological Importance of Hydroxamic Acids
1.3.1
1.3.1.1
Enzyme Inhibitors
Matrix Metalloproteinase Inhibition
Matrix metalloproteinases (MMPs) are a family of structurally related zinc
containing enzymes that mediate the degradation of the extracellular matrix and tissue
remodeling and are therefore targets for therapeutic inhibitors in inflammatory,
malignant and degenerative diseases.18, 19 Under normal physiological conditions, the
proteolytic activity of MMPs are controlled at three stages: transcription, activation of
2
zymogens (inactive
(
enzzyme precurrsors) and innhibition off the active fforms by vaarious
tissue inhib
bitors (TIMP
Ps). Under pathologicaal conditionss this equiliibrium is shhifted
towards pro
oducing actiive MMPs leading
l
to bbreakdown oof connectivve tissues. M
MMPs
are involved in morpho
ogenesis, tissue remodelling (such aas wound heaaling), apopptosis,
cancer invaasion, and arthritis, deegradation oof the bloood - brain barrier, muultiple
schlerosis, dermatitis, congestive heart failurre and Alzhheimer’s dissease. Originnally,
MMPs were thought to be resp
ponsible foor invasion and metasstasis by m
matrix
or cells to aaccess bloodd and lymphhatic vessels. The
remodeling thereby allowing tumo
mechanism of action (Scheme 2)) as propossed by Lovvejoy et al, is mediateed by
coordination of the scisssile amide carbonyl
c
from
m the peptidde to the activve site zinc(III)
Scheeme 2. Mech
hanism of prroteolysis byy MMPs 19
ion and successive attacck of a waterr molecule oon the carbonnyl. Hydroxamic acids pplay a
significant role in inhiibition of MMPs
M
by sppecifically bbinding the Zn atom inn the
s
(3, Sccheme 3).20 A representtative hydroxxamic acid bbased
enzyme acttive site as shown
non-peptidy
yl MMP inhiibitor is also
o shown (4, S
Scheme 3).
3
Scheme 3. Model inhibitors of MMPs
1.3.1.2
Histone Deacetylase Inhibition
Histone deacetylase and histone acetyl transferase are involved in chromatin
structure modification and functional regulation of gene transcription.21 Reversible
acetylation of the side chain amino groups of specific histone lysine residue plays
important roles in chromatin remodeling. Evidence of aberrant histone deacetylase
activity in leukemia has established the focus on developing both natural and synthetic
histone decetylase inhibitors as potential therapeutic agents. Recent studies have shown
that inhibition of histone deactylase has pronounced anti-cancer effects in several tumor
cell lines by inhibiting cell growth and inducing apoptosis.22 One of the major families
of histone deacetylases is the zinc-containing amido hydrolases, suggesting that a
structural requirement for potent inhibitors is a specific Zn2+ binding functional group.
Indeed, one of the most effective naturally occurring histone deacetylase inhibitor is
tricostatin A (TSA) (5, Scheme 4) that mimics the substrate and chelates zinc in the
catalytic pocket as the main mechanism of inhibition.23 A major breakthrough in
synthetic histone deacetylase inhibitors was the discovery of suberoylanilide
hydroxamic acid (SAHA, 6, Scheme 4) which induces apoptosis in a variety of tumor
cells and is currently in phase I clinical trials.24 Oxamflatin (7, Scheme 4), an antitumor
4
compound containing a hydroxamic acid, was found to be an inhibitor of mammalian
histone deacetylase.25
Scheme 4. Natural and synthetic HDAC inhibitors
1.3.1.3
TNF-Alpha Converting Enzyme Inhibition (TACE)
Tumor necrosis factor-α (TNF-α) is a therapeutic target through inhibition of its
formation for treatment of rheumatoid arthritis, meningitis and several other
inflammatory diseases.26 Development of anti TNF-α agents has received tremendous
attention for small molecule drug discovery.26 One approach is to establish small
molecule inhibitors of the TNF-α converting enzyme (TACE) responsible for TNF
processing. TACE is a member of the metalloproteinase family and its active site
structure is very similar to MMPs. Hydroxamic acid based TACE inhibitors have been
proven to be a class of potent anti-inflammatory agents and may lead to effective
medicines in the future. Some of the representative examples are shown below.
Retrohydroxamates (N-substituted hydroxamic acids) are successfully incorporated in
designing TACE inhibitors (8, Scheme 5) In early 1998, Pfizer reported compound 9
(Scheme 6) showing nanomolar activity for the inhibition of TNF-α release in a human
blood assay.27 Macrocyclic hydroxamic acids (10, Scheme 5) with various aryl
5
substituents showed high selectivity for TACE inhibition over MMPs.28, 29 Anthranilic
acid derivatives (11, Scheme 5) bearing an additional amine moiety also show
promising results in a TACE inhibition study.28
Scheme 5. Different classes of TACE inhibitor templates
1.3.2.
Therapeutic Uses of Hydroxamic Acids
1.3.2.1 Antimalarial activity
Hydroxamic acids also exert anti-malarial activity. The first hydroxamic acid based
Scheme 6. Hydroxamic Acid Based Antimalarial Agents
6
compound (12, Scheme 6) with profound activity was well studied by Hynes.30
Hydroxamic acids retard parasite growth by selective inhibition of DNA synthesis or
protease activities. Phosphonohydroxamic acids, such as fosmidomycins (13, Scheme
6), are drug candidates for treatment of malaria, and are currently in phase II clinical
trial.31, 32
1.3.2.2 Anti-melanogenic agents
The production of melanin in our body is mainly regulated by the enzyme tyrosinase
Tyrosinase is involved in catalyzing the oxidation of phenols and the production of
melanin.33 Inhibitors of tyrosinase could be useful in the treatment of melanin
hyperpigmentation. Metal ion chelators like kojic acid,34 flavonol,35 and Nnitrosohydoxylamines36 are all known tyrosinase inhibitors with their inhibitory activity
coming from their binding Cu in the active site of tyrosinase. Kim et al exploited the
metal chelation ability of hydroxamic acids and evaluated the potency of a group of
anti-melanogenic agents (14 and 15) in a murine melanocyte cell line (Scheme 7).37
Scheme 7. Hydroxamic acids as anti-melanogenic agents
1.3.2.3 NO Donors
While most physiological roles of hydroxamic acids are due to their metal chelation
ability, they were also found to be nitric oxide (NO) donors in recent studies.14
Hydroxamic acids readily transfers NO in presence of Ru(III) forming a stable
7
ruthenium-nitrosyl (II) complex (18, Scheme 8). These complexes result in
vasorelaxation of rat aorta by NO mediated activation of guanylate cyclase.14
[Ru(HEDTA)Cl]- + RCONHOH
16
[Ru(EDTA)(NO)Cl]2- + RCOOH
17
18
19
Scheme 8. Hydroxamic acids as NO Donor
1.4 Biological Importance of Cyclic Hydroxamic Acids
1.4.1 Iron Uptake by Siderophores
Iron plays crucial roles in almost every form of life on the earth. Although iron is
one of the most abundant elements in Nature, its importance in physiological processes
depends upon its assimilation. The most stable ionic form of iron is Fe (III), which is
insoluble under physiological conditions. To circumvent this solubility problem many
microbes, plants and even higher organisms synthesize low molecular weight, very
specific iron-chelators called siderophores.38 Cyclic hydroxamic acids are the most
common residues of the siderophores that scavenge iron in an iron-deficient
environment. The competition for iron between host and bacteria is an important factor
for determining bacterial infection. Structurally modified siderophores, may serve as
antagonists of microbial growth by competitive iron-binding or inhibiting iron
assimilation and show potential therapeutic value. This property was exploited to bring
revolutionary changes in anti-bacterial and anti-fungal drug discovery.39 Naturally
occurring siderophores such as mycobactine and pseudobactines (20, Scheme 9) are
finding medicinal application as antibiotics.40 Biological studies have shown that
mycobactin-S (21, Scheme 9) inhibits 99% growth of M.tuberculosis H37Rv at a
8
concentration of 12.5 µg/mL.41 Apart from their use as broad-spectrum antibiotics,
siderophores could also be used for treatment of iron overload in the human body.
Desferrioxamine (22, Scheme 9) is still the drug of choice to remove excess iron
(binding specifically Fe (III)) for blood transfusions in thalassemic patients.42
O
O
H
N
NH
NH2
N
H
O
NH
H
O
O
O N
O
Fe
NH3+ O
O
O
O
O
O O HN
H
NH
HN
H HN
HN
N
HO O HN
5
NH
O
O
HO N
O
2
R''
O
N OH
O
20
NHR'
H
HO
22
Desferrioxamines
Fe(III) bound Pseudobactine
Scheme 9. Representative examples of siderophores
1.4.2
Lipoxygenase Inhibitory Activity
Lipoxygenases are enzymes involved in the oxidative metabolic pathway of
unsaturated fatty acids. 5-, 8- and 12-Lipoxygenases are well characterized enzymes in
the lipoxygenase enzyme family and a specific lipoxygenase oxidizes a specific
position of the fatty acid to a produce a specific metabolite. Hydroxyeicosatetraenoic or
12-HETE (12(S)-5(Z),8(Z),10(E),14(Z)-), a metabolite produced by 12-lipoxygenase
acid, exhibits a variety of biological activities. Cancer cells induce the release of this
9
arachidonate metabolite 12-HETE in high amounts. Cyclic hydroxamic acids are
reported to be active inhibitors of 12-lipoxygenase and are useful for the treatment and
prevention of cancer metastasis, inflammation, immune diseases and ischemic
cardiovascular diseases.43 Some representative structures are shown below (23 and 24,
Scheme 10).
Scheme 10. Lipoxygenase inhibitors
1.4.3 Therapeutic Application of Cyclic Hydroxamic acids
1.4.3.1 Prostate Cancer Therapeutics
The development of new pharmacological agents to combat prostate cancer is a
great challenge in biomedical research. The water soluble pollen extract Cernitin T-60,
which contains the cyclic hydroxamic acid based structure DIBOA (2,4-dihydroxy-2H1,4-benzooxazin-3(4H)-one), shows striking growth inhibitory activity to a prostate
cancer cell line.44 The chemical structure of DIBOA (25) and other analogous synthetic
structures (26 and 27, Scheme 11) with potential inhibitory activity are shown in
Scheme 8. Natural and synthetic cyclic hydroxamic acid based structures are potential
drug candidates for the clinical symptoms of prostatitis, prostatodynia and prostate
cancer.
10
Scheme 11. Prostate Cancer Drug Candidates
1.4.3.2 Growth Inhibitors of Tumor Cell Lines
Amamistatin A and B (28 and 29, Scheme 12), cyclic hydroxamic acid containing
natural products isolated from a strain of Nocardia, show antiproliferative activity
against three human tumor cell lines (IC50 0.24-0.56 µM).
45
These linear lipopeptides
contain a seven membered cyclic and a straight chain hydroxamic acid, similar in
structure to formobactin and mycobactin. 46 47
Scheme 12. Tumor growth inhibitor Amamistatin A and B
11
1.4.3.3 Analgesic Activity
The elevated level of copper in blood relates to inflammation and arthritic
diseases.48 Cyclic hydroxamic acids, such as 30 and 31 (Scheme 13) play an important
role in chelating the copper (II) ion thereby alleviate inflammation and acts as analgesic
agents. 49
Scheme 13. Cyclic hydroxamic acids for analgesic activity
1.5.
1.5.1
Synthetic Approaches to Hydroxamic Acids
Simple Hydroxamic Acids
A common practice in the chemical synthesis of unsubstituted linear hydroxamic
acids is to react an activated carboxylic acid with an O-protected hydroxylamine to
produce a conveniently protected form of a hydroxamic acid (32, Scheme 14).
Scheme 14. General synthetic route to hydroxamic acids
12
1.5.2
Angeli-Rimini Reaction
In 1896, Angeli and Rimini discovered that benzenesulfohydroxamic acid (Piloty’s
acid, named after O. Piloty) decomposes in basic condition in the presence of an
aldehyde to yield the corresponding hydroxamic acid.50 This reaction is primarily
known in the literature for detection of aldehydes but has never enjoyed preparative
synthetic success because of low yields and purification problems. The mechanism of
the reaction is also not well understood, but a proposed mechanism (Scheme 15) for
this unique reaction describes nucleophilic attack of the N-anion of Piloty’s acid to an
aldehyde followed by rearrangement to yield the desired product.51
O
R
PhSO2NHOH
H
OR CH NSO2Ph
OH
OH-
34
33
R
NHOH
R CH N O
OH
O
35
Scheme 15. Angeli-Rimini reaction
1.5.3 Solid Phase Modification
While the Angeli-Rimini reaction has not found synthetic attention as a standard
procedure to make hydroxamic acids, Andrea et al reported a solid state modification of
this reaction to afford fair yields of hydroxamic acids.52 This methodology reported a
solid-supported Piloty’s acid reagent (36, Scheme 16) that makes purification easier.
This new reagent can be prepared by shaking a pyridine solution of hydroxylamine
hydrochloride with polystyrene sulfonyl chloride in dichloromethane at room
13
Scheme 16. Solid phase modification
temperature. Once the reaction between the poly-sulfohydroxamic acid polymer and
aldehyde is done, the polymer can be filtered off and acidic work up yields the
hydroxamic acid. This method is the only successful use of the Angeli-Rimini reaction
to produce hydroxamic acids in organic synthesis.
1.5.4
Oxidation of N-Boc Protected Amides
Dimethyldioxirane (DMD) or methyl(trifluoromethyl)dioxiranes (TFD) are well
known effective reagents for C-H or hetereoatom oxidation under mild conditions.53, 54
N-Boc protected peptides are reported to be oxidized by DMD or TFD (6 eq.) at 0ºC in
H
N
O
O
N
H
O
O
O
DMD or TFD in DCM
O
O
78%
N
OH O
H
N
37
Scheme 17. Oxidation of amides to make hydroxamic acids
14
O
O
chlorinated solvents to generate N-hydroxy amides or hydroxamic acids (37, Scheme
17). These reactions are representative examples of amide oxidation to prepare
hydroxamic acids.55
1.5.5
N-Substituted Hydroxamic Acids
Preparation of N-substituted hydroxamic acids follows a limited number of
literature procedures.56, 57 One simple method is to prepare the O-protected analog (38,
Scheme 18) of the correctly N-substituted hydroxylamine followed by a substitution
reaction with an acid halide (39, Scheme 18).
BnO
N
H
38
O
X
R'
O
Base
X
R'
X
N
OBn
39
40
Scheme 18. Preparation of N-substituted hydroxamic acid
Various synthetic pathways exist to make functionalized hydroxylamines. Using Nprotected hydroxylamines as starting materials generally improves the yield. Scheme 19
shows different routes to functionalized hydroxylamines 38, which are difficult to
prepare through the reaction of hydroxylamine and organic halides, especially if
additional functional groups are present. Hydroxylamine 38 can be prepared from
substituted aldehyde [42, X = CH2CO2Et ] by an imination reaction with NH2OBn and
further reduction of the intermediate 43 by NaBH3CN (Route A).58
Functionalized
alkyl bromides [44, X= CHRP(O)(OEt)2] can be transformed into hydroxylamine 38 by
substitution reactions with a protected hydroxylamine (NH2OBn, Route B).59 Oxidation
15
of functionalized amines [45, X = R(NHR’)CO2Me) with dimethyldioxirane (Route
C)60 or imines [46, (X=(CH2)3COOH)] with peracid followed by a reaction with TFA
(Route D), also gives unprotected N-substituted hydroxylamines.61, 62
Scheme 19. Existing approaches to N-functionalized hydroxylamines 63
1.5.6 Solid Phase Synthetic Approach
Polymeric solid phase reagents are useful to synthesize substituted hydroxamic acids
because of the easy separation of low-molecular weight products by filtration or
selective precipitation. Usually O-linked polymer bound hydroxylamine (48, Scheme
20) is treated with ketones to form the corresponding oxime (49), which is subsequently
reduced and acylated to give (51). Reductive cleavage of 51 would give the desired the
desired N-substituted hydroxamic acid (52, Scheme 20). 64
16
Scheme 20. Solid State Synthesis of N-substituted Hydroxamic Acids
1.5.7 Nitroso-Ene Reactions
Over the last couple of decades, nitroso-ene reactions have been extensively used to
synthesize various hydroxamic acids.65-69 This reaction typically involves a transient
acyl nitroso species and an allylic component. Kirby et al reported a variety of Cnitroso carbonyl enophiles reacting in both intermolecular and intramolecular fashion
giving a variety of hydroxamic acids.66, 67 Recent progress in the nitroso ene reactions
has also been exploited to make hydroxamic acids such as FR900098 (55, Scheme 21),
a N-substituted hydroxamic acid-containing antimalarial drug.34 Fokin and coworkers
suggested this reaction typically involves a six membered transition state between an
acyl nitroso component and the allylic part of an active alkene (Scheme 21).
17
Scheme 21. Nitroso-ene Route to Antimalerial Agent FR900098
Both intra and intermolecular ene reactions offer a useful way to make hydroxamic
acids. Acyl nitroso intermediates are very reactive in nature and are generated in situ by
the oxidation of corresponding hydroxamic acid by oxidants like NaIO4, Bu4NIO4,
PhI(OAc)2, PhIO and stored as the Diels-Alder adducts of 9,10-dimethylanthracene or
cyclopentadiene.
70
Heat exposure to these Diels-Alder adducts usually liberates the
acyl nitroso component through a retro Diels-Alder reaction.
1.5.7.1 Intermolecular Nitroso-ene Reaction
The bimolecular ene reaction of an acyl nitroso species and a separate allylic
component constitutes an efficient route to straight chain N-hydroxy amides by allylic
N-hydroxy amidation. The Kirby and Keck groups have done comprehensive research
on these reactions.67,
71
C-Nitroso carbonyl compounds usually include acyl nitroso
ketones,71 esters 67 or formamides 66 as enophiles (Scheme 22). The general procedure
18
Scheme 22. Intermolecular nitroso-ene route to N-subsituted hydroxamic acid
of the bimolecular nitroso ene typically involves dissolving the acyl-nitroso precursor
in the olefin as solvent and heating at reflux under an inert atmosphere until TLC
monitoring indicates consumption of the precursor.71
The regiochemistry of intermolecular ene reaction is of special interest, since
literature results demonstrate the possibility of multiple ene products from one
substrate. Theoretical calculations reveal the nitroso-ene reaction could proceed
through stepwise biradical intermediates instead of a typical concerted path.72, 73 Fokin
and coworkers
showed that
allylic hydrogen abstraction in the case of
mono
substituted olefins renders a mixture of 1:1 (E : Z) hydroxamic acid products after the
nitroso-ene between compound 53 and 54 (Scheme 23).63 However, with di, tri or tetrasubstituted olefins where several allylic hydrogens from different substituents are
available, regiochemical issues become apparent. Tsutsumi and coworkers show that
trisusbtituted olefins like 2-methyl-2 butene (55) yields the twix hydrogen (Scheme 23)
abstraction product as the major regioisomer. 74
19
Scheme 23. Regiochemistry of intermolecular nitroso-ene reaction
1.6
Synthesis of Cyclic Hydroxamic Acids
1.6.1
Reductive Cyclization of Aliphatic Nitro Acids
The reductive cyclization of linear alkyl nitro compounds with a terminal acid group
(56, Scheme 24) is another method to synthesize five membered cyclic hydroxamic
acids.75 This method is limited to the synthesis of five membered α-substituted cyclic
hydroxamic acids from aliphatic nitro compounds.
O
R1
Zn,Ac2O,AcOH
NO2
R2
N OH
CO2H
60 -75 C
46%
56
R1
R2
57
Scheme 24. Nitro-reduction and cyclization route to a cyclic hydroxamic acid
20
1.6.2
Synthesis of the Cobactin Core
The Miller group reported the first total synthesis of mycobactin-S (21, Scheme 9), a
biologically important bacterial siderophore that showed significant inhibitory activity
in a human tuberculosis cell line.76 Mycobactin-S has a seven membered ring cyclic
hydroxamic acid, the cobactin core, as a part of its structure. Miller’s reported method
includes a six step synthesis from the Nα-Cbz-L-lysine (58, Scheme 25) as starting
material. N-Cbz-lysine was converted to the tert-butyl ester (59) and then DMD
oxidation provided nitrone (60, Scheme 25). Treatment of the nitrone with
hydroxylamine hydrochloride followed by basic work-up, extraction and TFA
hydrolysis gave hydroxylamine (62, Scheme 25). DCC-coupled ring closure in the
presence of DMAP·HCl yielded 3-amino N-hydroxy azepanone (63, Scheme 25) in
very low yield. O-Protection of the desired hydroxamic acid 63 with TBDMSCl or
Scheme 25. Synthesis of cobactin core76
TBDPSCl (for easy chromatographic purification) rendered the targeted cobactin
hydroxamic acid residue 64 in moderate yield (50%, in last four steps). Miller’s
21
reported method for cobactin synthesis remains unclear as the key intermediate 62 was
not characterized or isolated and the DCC cyclization to cobactin leads to poor yield.
1.6.3
Heterocycle Based Synthesis: Tungstate Catalyzed Oxidation of Tetrahydro
quinoline
Catalytic oxidation of certain aromatic secondary amines (65, Scheme 26) can
produce hydroxamic acids (66, Scheme 26).77
This method is limited to reduced
quinoline systems.
Scheme 26. Catalytic oxidation of secondary amine yields hydroxamic acid
1.6.4 Oxidation of Lactams to Cyclic Hydroxamic Acids
Oxidation of cyclic amides produces cyclic hydroxamic acids.78 Sammes et al
reported the synthesis of DIBOA (25) by the oxidation of the silylated lactam with a
peroxo-molybdenum complex (Scheme 27) in the presence of dimethylformamide. This
method produced the targeted hydroxamic acid in 33% yield and is mainly applicable
to aromatic lactams.79
Scheme 27. Peroxo-molybdenum oxidation of lactams
22
1.6.5. Phenyliodine(III) Bis Trifluoroacetate Mediated Ring-closure
N-Acyl-N-alkyloxy nitrenium ions, which can be generated under mild conditions
by treating N-methoxyamides with the hypervalent iodine compound, PIFA
[phenyliodine(III) bis trifluoroacetate], is another literature route to make cyclic
hydroxamic acids. Work done by Wardrop et al demonstrates the PIFA mediated ringclosure method to build the bicylic five membered N-hydroxy lactam 67 (Scheme 28).80
Synthesis of a spirocyclic hydroxamic 68 (Scheme 28) was also reported by the same
group of researchers using this method.80,
81
This method is limited to the use of
disubstituted alkenes as substrates and trifluoroacetic acid as catalyst.
Scheme 28. PIFA mediated cyclization of nitrenium ion
1.6.6 Photochemical Synthesis of Cyclic Hydroxamic Acids
The photolysis of cyclic α-nitro ketones 69, which predominantly exist as the enol
form in ethanol, generates cyclic hydroxamic acid 70 as one of the photo rearrangement
products (11%).
82
According to this study with the steroidal α-nitro ketone (Scheme
23
29), the photoreaction proceeds through nitrogen insertion into the ring bearing the
nitro group. Previous studies done by Reid et al suggested a nitro-nitrite rearrangement
for the formation of the N-hydroxy imide.83, 84 Since this reaction suffers from a poor
yield, it has not found larger synthetic attention.
Scheme 29. Photolysis of a α-nitroketone
1.6.7 Intramolecular Nitroso-ene Reaction
Intramolecular nitroso-ene reactions are a convenient way of making 5 and 6
membered cyclic hydroxamic acids (Scheme 30). These reactions find tremendous
application in the total synthesis of Amaryllidaceae alkaloids and other cyclic
hydroxamic acid- based natural products.85 Intramolecular nitroso-ene methodology is a
two-step procedure to construct cyclic hydroxamic ring systems, the first step being the
generation of the acyl-nitroso species and store it as a Diels-Alder cycloadduct,
followed by a second step of thermal release of the acycl-nitroso species with the
concomitant ene reaction.
24
Scheme 30. Intramolecular nitroso-ene reaction yields cyclic hydroxamic acids
However, synthetic application of this unique cyclization to build complex natural
product requires some understanding of the regiochemical features of this reaction.
Keck et al reported the synthesis of five membered cyclic hydroxamic acid 71 (Scheme
30) and a bicyclic hydroxamic acid 72 being a key intermediate for (±) crinane
synthesis.86 Two sets of allylic methylene groups (A and B) exist in compound 73,
which gives two possible ene results (Scheme 30 ) corresponding to Type I and
Type II ene reactions according to the hypothesis of Oppolzer and Sneickus (Scheme
31).87
25
Scheme 31. Variants of the intramolecular nitroso-ene reaction
Type I generates the isolated fused spiro structure 74 (path A, Scheme 30) while the
Type II product or the fused bicycle 75 (path B, Scheme 30) has not been observed.
The nitroso-ene reaction of compound 76 generates the fused spirocyclic hydroxamic
acid 77 in 85% yield and compound 78 in 15% yield (Scheme 30), suggesting the
synthesis of seven membered ring hydroxamic acid by intramolecular nitroso-ene is
achievable albeit in poor yield.
1.6.8 Ring Expansion of Cyclic Ketones
The Angeli-Rimini reaction generates hydroxamic acids from aldehydes and early
Italian literature reports cyclic ketones act in a similar fashion to make the
corresponding ring-expanded cyclic hydroxamic acids.88,
89
An early patent indicates
this method is useful for making 6 membered cyclic hydroxamic acids with or without
substitution. The synthesis describes alkali metal hydroxide decomposition of Piloty’s
acid in protic solvents to produce ring expanded hydroxamic acids (80, Scheme 32)
after –NOH insertion in presence of saturated cyclic ketone .
26
Scheme 32. –NOH insertion into cyclic ketones under basic conditions
Interestingly the patent proposed a mechanism (Scheme 33) that features the anion of
nitroxyl (HNO/NO-) attacking the ketone to yield a tetrahedral intermediate that
rearranges to the product. However this mechanism differs from the proposed AngeliRimini’s reaction as described before (Scheme 15). 90
Scheme 33. Proposed mechanism of ring-expansion
1.6.9
Piloty’s Acid-Based Rearrangements of Cyclic Ketones to Make Cobactin
Basic decomposition of Piloty’s acid in the presence of 2-bromo cyclohexanone
yields the cobactin precursor 3-bromo-1-hydroxyazepanone in very low yield (1-2%)
(Scheme 34).91 These results show that while this pathway exists for seven membered
ring formation, the yields are extremely low.
Scheme 34. –NOH insertion route to Cobactin
27
1.7
Piloty’s Acid: A nitroxyl donor
Benzenesulfohydroxamic acid or Piloty’s acid (33, Scheme 35) is known to
decompose under basic conditions to produce nitroxyl (HNO) and a benzenesulfinic
acid salt.92 It was first postulated by Angeli that the reaction might occur via
elimination of HNO from the conjugate anion of Piloty’s acid in an analogy to
nitrohydroxamates or Angeli’s salt (Na2N2O3), another known source of HNO.29
Scheme 35. Basic decomposition of Piloty’s acid : Generation of HNO
1.7.1
Nitroxyl (HNO) Chemistry
Nitroxyl (HNO), the one-electron reduced and protonated form of nitric oxide
(NO), (in HNO, N is in +1, formal oxidation state), has recently garnered increased
attention based on its unique chemical and biological properties. Extensive theoretical
and experimental studies indicate that singlet HNO, with a pKa = 11.4, exists as the
dominant species of the HNO/NO- conjugate acid/base pair under physiological
conditions (Scheme 36).93-95 Calculations predict NO- exists as a triplet species
isoelectronic with oxygen. The spin change between 1HNO and 3NO- retards proton
transfer from HNO and the high reduction potential eliminates the direct reduction of
NO as a source of in vivo HNO formation (Scheme 36).93, 94, 96
28
Scheme 36. Equilibrium predominance of 1HNO
Nitroxyl (HNO) represents the simplest possible nitroso compound (X-N=O, X = H)
and demonstrates reactivity similar to C-nitroso compounds. The chemical reactions of
HNO have been reviewed and HNO generally reacts as an electrophile.96-99 Nitroxyl
reacts rapidly with thiols as an electrophile to give N-hydroxysulfenamides that react
with excess thiol to give disulfides and hydroxylamine or rearranges to sulfinamides
(Scheme 37). Calculations support the rapid reactions of HNO with thiols and other soft
nucleophiles. HNO dimerizes to yield hyponitrous acid that dehydrates to nitrous
oxide. Finally, nitroxyl reacts with oxidized metals (especially iron) to yield reduced
nitrosyl complexes 93,96, 97
.
Scheme 37. Reactivity of nitroxyl with thiol
29
1.8
Mycobactin S
Mycobactins are a family of siderophores produced by mycobacteria including M.
tuberculosis and M. smegmatis for promoting the iron uptake process and bacterial
growth. All mycobactins have a nearly identical molecular nucleus, which includes two
hydroxamic acid residues cobactin and mycobactic acid (83 and 84, Scheme 38) and a
2-hydroxyphenyl-oxazoline residue (Scheme 38). Detailed studies on mycobacterial
growth factors and the structural elucidation of mycobactins led G. A. Snow to
conclude that alternate or modified forms of the mycobactins could have antituberculosis activity.47,
76
Mycobactin S acts as an antimycobacterial agent by
disrupting the iron acquisition process in bacteria and hence finds tremendous
therapeutic attention for mycobacterial infectious diseases. Mycobactin S also qualifies
for better drug-delivery across the mycobacterial cell envelope. The Miller group
verified the growth inhibitory activity of mycobactin S in a human tuberculosis cell
line. Mycobactin S, isolated from M. smegmatis, consists of a seven membered cyclic
hydroxamic acid residue cobactin (83) and a long chain hydroxamic acid residue
mycobactic acid (84, Scheme 38).
Scheme 38. Structure of mycobactin S
30
This background work suggests that cyclic hydroxamic acids are biologically
important molecules and potentially useful therapeutic agents but existing chemical
methods to synthesize them are somewhat difficult and limited. Our research focuses on
the development of synthetic methodology towards making cyclic hydroxamic acids
and related natural products.
1.8.1
Biosynthesis of Mycobactins
Iron is essential for bacterial survival and is a seminal growth factor during infectious
diseases in vertebrates.100 Under iron deficient condition, bacteria up-regulates the
production of the enzymes that synthesize the siderophore mycobactin. The Walsh and
coworkers have done a detailed study on identifying the mycobactin T biosynthetic
(mbt) gene clusters.101 The gene clusters, designated mbtA-J, contain isochorismate
synthase, acetyl hydrolase, salicylate-AMP ligase, polyketide synthase, lysine-Noxygenase and nonribosomal peptide synthatase. A major biosynthetic strategy in
mycobactin synthesis is the use of non-ribosomal peptide synthatase assembly logic to
assemble the hydroxmate and the oxazoline moieties. The non-ribosomal peptide
synthetases are made during post translational modification of peptide carrier proteins
and these enzymes mediate the generation of mycobactin peptide backbone. It is
unknown whether lysine-N-oxygenase oxidizes the terminal amine of lysine residues
befoe or after incorporation into mycobactin T The proposed linear biosynthesis is
initiated with salicylic acid and terminated with intramolecular cyclization forming the
seven membered ring hydroxamic acid.102
31
Research goals of this dissertation
1) Investigate the Piloty’s acid based –NOH insertion reaction methodology to
synthesize cyclic hydroxamic acid (mainly five and six membered) by –NOH
insertion and ring-expansion of a cyclic ketone as substrate
Scheme 39. Piloty’s acid based –NOH insertion of cyclic ketones
This –NOH insertion methodology research particularly aims to:
a) optimize the reaction conditions, yield and purification of the ring-expanded
cyclic hydroxamic acid as a –NOH insertion product
b) explore the regioselectivity and stereoselectivity of the insertion reaction using a
set of syn-bicyclic ketones as substrates
c) establish the mechanism of the insertion-ring expansion reaction, examining any
role of HNO
d) examine the scope of this unique ring-expansion reaction and study the
synthetic application to a cobactin core synthesis
2) Utilize nitroso-ene reactions towards the formal synthesis of cobactin and
mycobactic acid.
a) Investigate the scope of intramolecular nitroso-ene reactions towards cobactin
core synthesis. This research particularly aims to explore the alkene chain
lengths of different acyl nitroso intermediates
32
b) Investigate intermolecular nitroso-ene reactions towards the formal synthesis
of cobactin and mycobactic acid. This research mainly aims to:
I.
explore the structure and chain lengths of different acyl nitroso species and
study their nitroso-ene reactions
II. investigate the nitroso-ene reactions of different acyl-nitroso enophiles to
synthesize the cobactin and mycobactic acid precursors from Nα-acylhomoallyl-glycine ester as the alkene substrate (scheme 40)
Scheme 40. Intermolecular nitroso-ene approach towards formal synthesis of cobactin
and mycobactic acid
33
CHAPTER 2
SYNTHESIS OF CYCLIC HYDROXAMIC ACID THROUGH –NOH INSERTION OF
KETONES
Ranjan Banerjee and S. Bruce King*
Department of Chemistry,Salem Hall, Box 7486, Wake Forest University, Winston Salem,
North Carolina 27109
The work contained in this chapter was initially published in Organic Letters 2009, 11,
4580-4583. The manuscript, including figures and schemes, was drafted by Ranjan
Banerjee and edited by S. Bruce King. Since publication, changes in both format and
content were made to adapt this work for the dissertation format. The research described
herein was performed by Ranjan Banerjee.
Crystal structure determination was
performed by Dr. Cynthia S. Day. This work was supported by the American Chemical
Society Petroleum Research Fund (PRF 48660-AC1).
34
2.1 Introduction
Recent studies demonstrate the distinct biological character of nitroxyl (HNO)
compared to its redox partner nitric oxide (NO) as a signaling agent in the vascular
system.103,
104
Nitroxyl exhibits different chemistry from NO by dimerizing and
dehydrating to nitrous oxide, by reacting with heme proteins through separate
mechanisms to NO and by rapidly condensing with thiols to yield disulfides and
sulfenamides.97,
98
This chemistry requires the use of HNO donors in fundamental
chemical and biochemical studies and focuses attention on these donors as potential
therapies for various conditions including congestive heart failure, cancer, alcoholism and
hemolytic disorders.103
Angeli’s salt (Na2N2O3) and Piloty’s acid (PhSO2NHOH, N-hydroxybenzene
sulfonamide, 33, Scheme 15) represent the two most widely used HNO sources for
routine study. In addition to releasing HNO, Piloty’s acid reacts with aldehydes under
basic conditions to give the corresponding hydroxamic acid and benzenesulfinic acid and
this reaction forms the basis of the Angeli-Rimini test for the colorimetric identification
of aldehydes (Scheme 15 and Scheme 41).52, 105 Early reports indicate that Piloty’s acid
reacts with cyclopentanone to yield the corresponding cyclic hydroxamic acid (85,
Scheme 41) in low yield.88
Scheme 41. Angeli-Rimini reaction of aldehydes and ketones
35
Given our interest in the chemistry of HNO donors, we further examined this unusual
reaction of Piloty’s acid with cyclic ketones and showed that under basic conditions Nhydroxybenzenesulfonamide reacts with small (four and five-membered) cyclic ketones
to give the cyclic hydroxamic acid in moderate yields through a mechanism that includes
a C-nitroso intermediate.
2.2
Synthesis of N-Hydroxy Benzenesulfohydroxamic Acid (Piloty’s acid)
Piloty’s acid is a commercially available compound, but we observed better results
when freshly prepared and purified in the laboratory. It can be synthesized by dropwise
addition of benzenesulfonyl chloride (86, Scheme 42) to a neutralized solution of
hydroxylamine hydrochloride (87, Scheme 42) in methanol at 0°C with stirring at room
temperature overnight.106 The crude Piloty’s acid (33) was purified by flash
chromatography and stored in an airtight glass container in the freezer as it is vulnerable
to air oxidation and decomposition at room temperature.
Scheme 42. Synthesis of Piloty’s Acid
2.3
-NOH Insertion Reaction of Cyclic Ketones
2.3.1
Synthesis of N-hydroxy Piperidone
Basic decomposition of Piloty’s acid was performed in the presence of
cyclopentanone to yield the ring expanded N-hydroxy piperidone (85, Scheme 41). As
36
earlier reported,107 treatment of cyclopentanone with Piloty’s acid (0.9 equiv.) in ethanol
with excess sodium hydroxide at room temperature yields 1-hydroxy piperdine-2-one
(85, Scheme 41, Entry 1, Table 1) in 18% yield. Table 1 shows that increasing the molar
equivalents of Piloty’s acid increases the yield of 85 with two equivalents more than
doubling and greater equivalents furthering increasing the isolated yield of 85 (Table 1,
Entries 5-8).
The use of sodium methoxide as base or sodium hydride in a polar aprotic
solvent (THF or DMF) results in product but does not improve the observed yield (Table
1, Entries 2-4).
Table 1. Results of –NOH insertion into cyclopentanone
Entry
Equivalents of PA
Base / Solvents
Yield
1
0.9
2N NaOH / EtOH
18%
2
1.1
NaH / THF
11%
3
2
NaH / DMF
2%
4
2
NaOMe / MeOH
33%
5
2
2N NaOH / EtOH
40%
6
4
2N NaOH / EtOH
44%
7
6
2N NaOH / EtOH
59%
8
10
2N NaOH / EtOH
69%
37
Figure 1. X-ray Diffraction structure of N-hydroxy piperidone (85)
The structure of the N-hydroxy piperidone (85, Figure 1) was confirmed by NMR and
X-ray crystallography. Intermolecular H-bonding was observed between the carbonyl
oxygen and the H atom attached to the N-hydroxy oxygen of another molecule in the
same unit cell.
2.3.2 -NOH Insertion Reaction in Cyclobutanones
While treatment of cyclohexanone with Piloty’s acid in basic ethanol yields less than
5% of the corresponding cyclic hydroxamic acid (88, N-hydroxycaprolactam, Scheme
43), exposure of cyclobutanone to these conditions gives the five-membered ring
hydroxamic acid in 39% yield (89, Scheme 43). X-ray diffraction studies on crystalline
89 further confirms the structure of the ring-expanded hydroxamic acid (Figure 2).
Higher equivalents of Piloty’s acid yields a higher amount amount of 89 (Entry 1-2,
Table 2) in ethanol with excess sodium hydroxide as base. The use of sodium methoxide
as base did not improve the yield (Entry 3, Table 2). Given the fact that Piloty’s acid
decomposes to nitroxyl (HNO), the slow addition of Piloty’s acid (same equivalents) to
38
the reaction mixture does not improve yield. The volatility of cyclobutanone and the
water solubility of 89 hinders isolation and purification, which account for the limited
yield of 89, and these results suggest a relationship between ring size and yield.
Attempts to convert 2-hexanone to the corresponding hydroxamic acid under identical
conditions gives less than 5% of N-hydroxy-N-propylacetamide (Scheme 43).
Scheme 43. –NOH insertion with various ketones
Figure 2. X-ray Diffraction Structure of 89
39
Table 2. Results of –NOH insertion into cyclobutanone
Entry
Equivalents of PA
Base / Solvents
Yield
1
1.1
2N NaOH / EtOH
29%
2
2
2N NaOH / EtOH
39%
3
2
NaOMe / MeOH
32%
This success with cyclobutanone encouraged the application of this sequence to more
substituted less-volatile cyclobutanones (Scheme 45). A standard two step sequence of a
[2 + 2] cycloaddition between an alkene and dichloroketene followed by Zn / AcOH
O
O
a
b
Cl
Cl
48%
33%
O
a
Cl
Cl
28%
90
O
b
34%
91
O
O
b
a
46%
Cl
Cl
Ph
79%
Ph
92
O
a
5
b
Cl
19%
5
Cl
74%
5
93
a = i) Zn,ii) POCl3,iii) Cl3CCOCl, reflux /ether
b = i) Zn ii) CH3COOH, stirring at 600C for 2hrs
40
O
Scheme 44. Synthesis of substituted cyclobutanones
reduction of the α,α-dichloroketone intermediate generates various substituted
cyclobutanone substrates (90 - 93 , Scheme 44).108, 109
Treatment of these cyclobutanones with Piloty’s acid (2 equiv.) in base forms the
corresponding cyclic hydroxamic acids in 30-59% yield ( 94 – 97, Scheme 45). The
decreased volatility of the substituted cyclobutanone substrates (compared to
cyclobutanone) and the decreased water solubility of the products likely improve the
isolated yields and facilitate purification. This sequence yields cyclic five-membered
ring hydroxamic acids derived from two unsymmetric bicyclic cyclobutanones (94 and
95) and from two symmetric substituted cyclobutanones (96 and 97).
1
H and 13C NMR
spectroscopy and high resolution mass spectrometry support the structures of 94-97 and
X-ray diffraction studies on crystals of 94 confirm the structure of this bicyclic
hydroxamic acid (Figure 3). In addition to structural confirmation, the crystallography
Scheme 45. Reaction of Piloty’s acid with substituted cyclobutanones
41
studies also reveal two important features of this reaction 1) the –NOH inserts to the
more substituted side of the ketone demonstrating regioselectivity and 2) the –NOH
group adds stereoselectively with the overall ring juncture relative stereochemistry
remaining cis. NMR and chromatographic analysis of the crude reaction mixture do not
reveal the presence of any other hydroxamic acids. These results appear similar to the
Baeyer-Villiger oxidation of ketones with migration
of the more electron-donating
branch with retention of configuration.110
Figure 3. X-ray Diffraction Structure of 94
2.3.3
Solid phase modification
Despite success in developing this method to synthesize cyclic hydroxamic acids, the
target molecules’ high polarity and difficulty in being chromatographed or recrystallized
complicated purification. In an attempt to solve this problem, we explored the solid-phase
Angeli-Rimini reaction with polymer bound sulfohydroxamic acid as the reagent and
cyclic ketones as substrate (Scheme 46). The reactions were done at room temperature, in
dry THF using sodium methoxide as a base. Acidic work up was done with Dowex42
50WX2 ion exchange resin after filtration of the polymer bound reagent. The resinsupported N-hydroxybenzene sulfonamide (36) was prepared as described before.52 Two
equivalents of the modified reagent 36 reacted with cyclopentanone and cyclobutanone
(Scheme 46) to produce the corresponding hydroxamic acids in 9% and 35% yield
respectively (Scheme 46). These results suggest solid phase modification does not
improve the yield of the product over regular Piloty’s acid based ring-expansion
reactions.
Scheme 46. Solid phase modification of –NOH insertion reaction
2.4
Mechanism of –NOH insertion reaction
Early work proposes two mechanistic possibilities for this unsual transformation. The
first includes the direct addition of HNO or –NO to the ketone to form a C-nitroso
intermediate 98 that rearranges to the observed product (85, Scheme 47, path a). Further
experiments argue against this route and suggest instead that a nucleophilic addition of
the N-anion of Piloty’s acid to the cyclic ketone gives a tetrahedral intermediate 99 that
rearranges to the ring-expanded hydroxamic acid with the loss of benzenesulfinic acid
43
(Scheme 47, path b).111,
112
Such a mechanism finds direct precedence in the known
reaction of aldehydes with Piloty’s acid to form hydroxamic acids (the Angeli-Rimini
reaction, Scheme 41).112
Scheme 47. Proposed Mechanisms for Formation of 85
Experiments with O-benzyl p-toluene N-hydroxysulfonamide (100, Scheme 48),
prepared by the treatment of p-tosyl chloride with O-benzylhydroxylamine, provide
insight into the mechanism (Scheme 47). This compound cannot decompose to HNO
(Scheme 47, path a) but can form an N-anion that should react to give an O-alkyl cyclic
hydroxamate (Scheme 47, path b).
Reaction of 100 with cyclobutanone or
cyclopentanone fails to yield any insertion product arguing against path a (Schemes 47
and 48) as the mechanism of product formation.
44
SO2NHOBn
Na
aOH
No Re
eaction
O
Scheeme 48. Reacction of O-p
protected Pilooty’s Acid w
with Cyclopeentanone
Treatmentt of 100 wiith NaH in THF follow
wed by metthyl iodide produces thhe Nmethylated
m
prroduct (101
1, Scheme 49)
4 verifyingg the nucleoophilic abiltiyy of the anion of
100. X-ray diiffraction stu
udies on com
mpound 101 cconfirms thee structure (S
Scheme 49). This
SO2NMeOCH2Ph
h
SO
O2NHOCH2Ph
h
1. 1.1 eq.
e NaH in TH
HF
2. MeI, 74%
10
00
101
Scheme
S
49. N-methylatio
N
on and X-rayy diffractionn structure off 101
reesult also elliminates th
he potential invovlemennt of O-nitreene intermeddiates that ccould
fo
orm through
h the dissocciation of th
he N-anion oof Piloty’s acid and w
would give thhe 1(b
benzyloxy) piperidin-2-o
p
one product, which was not observedd.
45
Further treatment of smaller O-protected Piloty’s acid analogs such as O-benzyl
methansulfonamide113 or O-methyl benzenesulfohydroxamic acid with cyclopentanone
under basic condition fails to yield any insertion product, indicating sterics do not play a
crucial role in tetrahedral intermediate (99, Scheme 47) formation during the insertion
reaction. In addition, incubation of cyclopentanone with Angeli’s salt in a
methanol/buffer mixture, conditions that clearly generate HNO as judged by gas
chromatographic identification of nitrous oxide, fail to produce 85 arguing against path a
(Scheme 50).114, 115 Previous pKa calculations also disfavor the direct reaction of –NO
with cyclic ketones to form a C-nitroso intermediate and product (Scheme 47, path a).116
Scheme 50. Synthesis and reactions of other O-protected sulfonamides
These results led to the examination of acyloxy nitroso compounds as precursors to
the C-nitroso intermediate (98, Scheme 51) and cyclic hydroxamic acids. Our previous
work shows that hydrolysis of the cyclohexyl-derived acetoxy nitroso compound (102,
Scheme 51) forms cyclohexanone and HNO (as judged by nitrous oxide generation)
through a C-nitroso intermediate and highlights these compounds as new HNO donors.117
GC data (Table 3) depicts a direct correlation between the ring size and HNO donating
properties of 5-6 membered cyclic acyloxy-nitroso compounds. These GC data suggest
46
cyclopentyl derived acetoxy nitroso compounds are more prone to give ring-expanded
hydroxamic acids upon hydrolysis, while cyclohexyl-derived acetoxy nitroso compounds
are not because of low ring strain.
____________________________________________________________
Table 3. Gas Chromatography Results: Hydrolysis of acyloxy nitroso
Entry
O N
OAc
Time
Mols of N2O
% yield
2 hrs
3.70E-08
6.81%
24hrs
3.55E-08
6.53%
2 hrs
2.89E-07
53.15%
24 hrs
2.71E-07
49.82%
Hydrolysis of the cyclopentyl-derived acetoxy nitroso compound (103), generated by
the lead tetra-acetate oxidation of cyclopentanone oxime, yields cyclic hydroxamate (85,
Scheme 51) in 75% yield and only trace amounts of nitrous oxide (indicating little HNO
formation, Scheme 51). These results provide evidence of a C-nitroso intermediate
during the formation of 85 (Scheme 51) from cyclopentanone and Piloty’s acid in basic
conditions and also show a ring size dependency on the reaction pathway. Scheme 47
depicts a mechanism where addition of the N-anion of Piloty’s acid generates a
tetrahedral intermediate (99) that eliminates benzenesulfinic acid to give the C-nitroso
47
intermediate (98, path c, Scheme 47 and Scheme 51). This mechanism produces the
orignially proposed C-nitroso intermediate (98) through this tetrahedral intermediate.
This C-nitroso intermediate either eliminates HNO to give the ketone (cyclohexyl) or
rearranges to the cyclic hydroxamic acid (cyclobutyl, cyclopentyl).
Scheme 51. Modified Reaction Mechanism
Increasing the amount of Piloty’s acid would increase the amount of the reactive Nanion under equilibrium conditions and result in an increased yield of the observed
product (Table 1). Previous results show slow addition of Piloty’s acid does not alter the
yield of the product, suggesting the efficient generation of the N-anion of Piloty’s acid is
critical to this method as the anion also decomposes to nitroxyl.92 The C-nitroso
interemediate (98) shows structural similarity to the accepted peroxy intermediates in the
Baeyer-Villiger reaction and the observed regiochemistry and stereochemistry appears
48
consistent. Obviously, the ring strain of the C-nitroso intermediate plays a major
determinant in the product outcome. Unfavorable eclipsing interactions leading to ring
strain likely drive rearrangement of the smaller membered rings (cyclobutyl, cyclopentyl)
to larger rings that relieve these interactions.
In summary, these results show that the N-anion of Piloty’s acid reacts with four and
five-membered ring cyclic ketones to form tetrahedral intermediates that rearrange to Cnitroso species and ultimately a cyclic hydroxamic acid (depending on ring size) in
moderate yields. These experiments suggest a regio and stereoselective rearrangement
similar to the Baeyer-Villiger reaction.
This chemistry shows the complexity of the
reactions of N-hydroxysulfonamides and may prove useful for the synthesis of various
cyclic hydroxamic acid containing compounds, such as siderophores,9, 102, 118, 119 natural
iron-chelating compounds that show promise as new antibiotics. As such, these studies
also compliment other methods for the direct conversion of ketones to the corresponding
N-OH amides.120-123 This work aids in the structural development of new HNO (both
Piloty’s acid and acyloxy nitroso-based) donors as the reactivity of the N-anion must be
considered for Piloty’s acid-based donors and the structures, particularly ring size, must
be taken into account for new acyloxy nitroso compounds.
2.5
Scope of –NOH Insertion Reaction
2.5.1
Synthesis of O-Protected Cyclic Hydroxamic Acids
Initial ring-expansion of cyclopentanone generates N-hydroxy piperidone (85), which
was used for further transformations including O-acylation and O-alkylation reactions
(Scheme 52) to prepare O-protected cyclic hydroxamic acids. Treatment of N-hydroxy
49
piperidone (85) with acetic anhydride in the presence of DMAP produces O-acetoxy
piperidone (104, Scheme 52) in 63% yield. Treatment of N-hydroxy piperidone with
methyl iodide in the presence of sodium hydride produces O-methyl piperidone (105,
Scheme 52) in 58% yield. Cyclic Weinreb amides 124, 125 such as compound 105 (Scheme
52) are useful synthetic intermediates for ring-opening transformations by Grignard
reagents or other nucleophiles.
Scheme 52. O-protection of N-hydroxy piperidone
2.5.2 –NOH Insertion Reaction in α-Substituted Cyclopentanone
Preliminary results show that an excess of Piloty’s acid greatly increases yield (Table
1), which indicates inefficiencies in generating the reactive species. Apart from the use of
excess amounts of Piloty’s acid another limitation is that these –NOH insertions show the
best results with unsubstituted cyclic ketones as substrates. Treatment of Piloty’s acid
with 2-methyl cyclopentanone under identical –NOH insertion condition yields only trace
amounts of ring expanded cyclic hydroxamic acid 106 (Scheme 53). However this
problem may be overcome through the hydrolysis of the acyloxy nitroso compounds of
the corresponding cyclic ketone. Previous results (Scheme 51) demonstrate that the
50
hydrolysis of the cyclopentyl-derived acetoxy-nitroso compound 103 produces the ringexpanded hydroxamic acid 85.
Treatment of hydroxylamine hydrochloride with 2-
methyl cyclopentanone yields 2-methyl cyclopentanone oxime (Scheme 53) and
Pb(OAc)4 oxidation gives the corresponding acetoxy nitroso compound (107, Scheme
53). Hydrolysis of 107 gives 6-methyl-N-hydroxy-piperidone (106, Scheme 53) in 77%
yield.
Scheme 53. –NOH Insertion in 2-Methyl Cyclopentanone
2.5.3 -NOH Insertion in Cyclohexenone
Treatment of cyclohexenone (108, Scheme 54) with Piloty’s acid under the identical –
NOH insertion conditions installs an oxime group at the 3-position of the ketone and
generates 3-hydroxyimino cyclohexanone (109, Scheme 54). This reaction provides
support for the –NOH insertion mechanism (Scheme 47) and validates the generation of a
C-nitroso intermediate after Michael addition of the N-anion of Piloty’s acid (Scheme
54). This reaction is a unique example of introducing an oxime group at the 3-position of
cyclohexenone and opens a new avenue of oxo-amination reactions of cyclic ketones.
51
Scheme 54. Piloty’s acid based –NOH insertion reaction of cyclohexenones
2.5.4
Investigation of a Cobactin Synthesis Using the –NOH Insertion Reaction
The final objective of this project was to apply the –NOH insertion methodology to
the preparation of a small biologically relevant natural product, cobactin (83, Scheme
38). We proposed a short synthesis of cobactin from an α-amino cyclohexanone using
this Piloty’s acid based –NOH insertion methodology (Scheme 55). This synthesis would
consist of three steps, aminohydroxylation126, 127 of cyclohexene to give a cyclic amino
alcohol (110, Scheme 55) followed by oxidation to yield an α-amino cyclohexanone
(111) and finally the –NOH insertion reaction with the precursor ketone to yield the
cobactin core 112 (Scheme 55).
Scheme 55. Prosposed route to cobactin core using Piloty’s acid based –NOH insertion
method
52
Previous results describe that the –NOH insertion works best with four and five
memebered ring ketones. To explore this pathway in a five membered substrate a new
route was designed, where Sharpless aminohydroxylation of cyclopentene provided the
N-Boc protected α-amino alcohol (113, Scheme 56) in 76% yield and Dess-Martin
oxidation gave the precursor ketone (114, Scheme 56) in 40% yield. Treatment of 114
with Piloty’s acid under identical –NOH insertion condition afforded only trace amounts
of the ring-expanded hydroxamic acid (115, Scheme 56). These results show the Piloty’s
acid based –NOH insertion method may not be an efficient route for the ring-expansion
of an α-subsituted cyclic ketones, suggesting the cobactin synthesis will not be an
efficient synthetic application of this method.
Scheme 56. Exploring Piloty’s acid rearrnagement reaction with α-amino-substituted
cyclopentanones
53
2.6
Experimental
General. Melting points (mp) were measured on a Mel-Temp capillary melting point
apparatus and are uncorrected. Analytical TLC was performed on silica gel plates with
QF-254
indicator.
phosphomolybdic
Visualization
acid,
and/or
was
accomplished
dinitrophenylhydrazine
with
UV
stain.
light,
Extraction
FeCl3,
and
chromatography solvents were technical grade. All reactions were performed under an
inert atmosphere of dry argon. 1H NMR and
13
C NMR were recorded in CDCl3 and
deuterated DMSO on a Bruker Avance 300 MHz and 500 MHz NMR Spectrometer.
Chemical shifts are given in ppm (δ); multiplicities are indicated by s (singlet), d
(doublet), t (triplet), q (quartet), m (multiplet) and b (broadened). Low resolution mass
spectra were obtained using an Agilent GC/MS system consisting of a 5973 mass
selective detector interfaced to a 6850 gas chromatograph or from HT Laboratories (San
Diego, CA) and data are reported in m/z. Elemental analysis were performed by Atlantic
Microlab, Inc. (Atlanta, GA).
54
N-Hydroxybenzene sulfonamide (Piloty’s Acid, 33).128 A solution of potassium
carbonate (27.7 g, 0.2 mol) in water (30 mL) was added dropwise to a solution of
hydroxylamine hydrochloride (13.6 g, 0.2 mol) in water: methanol (3:2, 50 mL) at 0°C
with vigorous magnetic stirring for 1 h. Ice cold methanol (200 mL) was added in a
single portion to this mixture followed by dropwise addition of benzenesulfonyl chloride
(35.3 g, 0.2 mol) over 1 h. After 18 h of stirring the mixture was filtered and the methanol
was removed under vacuum. The water residue was acidified to neutral pH, extracted
with ethyl acetate (300 mL), concentrated under vacuum and purified by flash
chromatography on SiO2 to give 33 as a white solid (9.25 g, 27%); Rf = 0.176 (3:1 pet.
ether : EtOAc); mp 108°C. 1H NMR (DMSO-d6) 9.62-9.68 (m, 2H), 7.85-7.92 (m, 2H),
7.61-7.78 (m, 3H); 13C NMR (DMSO-d6) 137.12, 133.01, 128.84, 127.98.
1-Hydroxypiperidine-2-one (85).107, 129 A solution of degassed sodium hydroxide (2N,
80 mmol, 40 mL) was added to a solution of cyclopentanone (1 mL, 11.3 mmol) in EtOH
(20 mL) at 0°C. To this mixture, a solution of Piloty’s acid (3.91 g, 22.6 mmol) in EtOH
(20 mL) was added dropwise over 30 min and the reaction mixture was stirred at room
55
temperature for 18 h. The ethanol was removed under vacuum and the water layer was
extracted with diethyl ether to remove unreacted ketone. The aqueous layer was acidified
to pH 5.5 with 2N HCl and extracted with CHCl3 (6 x 50 mL). The CHCl3 layer was
dried with MgSO4 and concentrated to give a semisolid crude residue that was purified by
flash chromatography to give 85 as a reddish white solid (0.52 g, 40%); Rf = 0.37 (95:5
CHCl3 : MeOH). Pure white crystals of N-hydroxy piperidone were obtained by
subliming the product (45°C, 0.05mm); mp 48-50°C. 1H NMR (CDCl3) 9.39 (1H, b),
3.63 (t, J = 5.93 Hz, 2H), 2.45 (t, J = 6.47 Hz, 2H), 1.95 (m, 2H), 1.82 (m, 2H);
13
C
(CDCl3) NMR 165.39, 49.96, 31.54, 23.58, 21.13; GC MS m/z 115 (M+). Anal. Calcd.
for (C5H9NO2. 0.5H2O) : C 48.36%, H 8.12%, N 11.29%. Found: C 48.36%, H 8.11%, N
11.19%.
O
N
OH
88
1-Hydroxyazepan-2-one (88).119 A solution of degassed sodium hydroxide (2N, 80
mmol, 40 mL) was added to a solution of cyclohexanone (1.11 g, 11.3 mmol) in EtOH
(20 mL) at 0°C. To this mixture, a solution of Piloty’s acid (3.91 g, 22.6 mmol) in EtOH
(20 mL) was added dropwise over 30 min and the reaction mixture was stirred at room
temperature for 18 h. The ethanol was removed under vacuum and the water layer was
extracted with diethyl ether to remove the unreacted ketone. The aqueous layer was
56
acidified to pH 5.5 with 2N HCl and extracted with CHCl3 (5 x 50 mL). The CHCl3 layer
was dried with MgSO4 and concentrated to give a solid crude residue that was purified by
flash chromatography to give the hydroxamic acid 88 as a reddish white solid (60 mg,
4%) ; Rf = 0.41 (95:5 CHCl3 : MeOH). 1H NMR (CDCl3) 8.13 (b, 1H), 3.72 (b, 2H),
2.54-2.52 (m, 2H), 1.77-1.65 (m, 6H);
13
C NMR (CDCl3) 166.93, 50.51, 34.1, 29.69,
26.65, 22.94; GC MS m/z 129 (M+).
1-Hydroxypyrrolidine-2-one (89). A solution of degassed sodium hydroxide (2N, 80
mmol, 40 mL) was added to a solution of cyclobutanone (1 g, 14.27 mmol) in EtOH (20
mL) at 0°C. To this mixture, a solution of Piloty’s acid (4.94 g, 28.53 mmol) in EtOH (20
mL) was added drop wise over 30 min. The reaction mixture was stirred at 0°C for 4 h
and at room temperature for another 18 h. The ethanol was removed under vacuum and
the water layer was extracted with diethyl ether to remove the unreacted cyclobutanone.
The aqueous layer was acidified to pH 5.5 with 2N HCl and extracted with CHCl3 (6 x 50
mL). The CHCl3 layer was dried with MgSO4 and was concentrated to a solid crude
residue that was purified by flash chromatography to give 89 as a pale white solid
product (0.565 g, 39%) ; Rf = 0.4 (95:5 CHCl3 : MeOH). Pure white crystals were
collected after sublimation (40°C, 0.05mm); mp 77-79°C. 1H NMR (CDCl3) 10.41 (b,
1H), 3.67 (t, J = 7.19 Hz, 2H), 2.41 (t, J = 7.57 Hz, 2H), 2.061 (q, J = 7.26 Hz, 2H); 13C
57
NMR (CDCl3) 170.92, 49.16, 28.55, 15.56; GC MS m/z 101(M+). Anal. Calcd. for
C4H7NO2 : C 47.50%, H 6.98%, N 13.86%, Found : C 47.72%, H 7.08%, N 13.75%.
2-Hydroxyhexhydrocyclopenta[c]pyrrole-1(2H)-one (94). A solution of degassed
sodium hydroxide (2N, 80 mmol, 40 mL) was added to a solution of
bicylco[3.2.0]heptane-6-one (0.68 g, 6.18 mmol) in EtOH (20 mL) at 0°C. To this
mixture, a solution of Piloty’s acid (2.14 g, 12.36 mmol) in EtOH (20 mL) was added
dropwise over 30 min. The reaction was stirred at 0°C over 4 h and over 18 h at room
temperature. The ethanol was removed under vacuum and the water layer was extracted
with diethyl ether to remove unreacted ketone. The aqueous layer was acidified to pH 5.5
with 2N HCl and extracted with CHCl3 (6 x 50 mL).The CHCl3 layer was dried and
concentrated to give a solid crude residue that was purified by flash chromatography to
give 94 as a pale white solid product (0.35 g, 41%); Rf = 0.45 (95:5 CHCl3: MeOH,). The
product was further purified by sublimation (50°C, 0.05mm) to give white crystalline
solid; mp 76°C. 1H NMR (CDCl3) 10.39 (b, 1H), 4.21 (b, 1H), 2.29-2.1 (m, 2H), 2.782.63 (m, 1H), 2.076-1.97 (m, 1H), 1.8-1.48 (m, 5H);
13
C NMR (CDCl3) 169.52, 65.59,
35.89, 35.03, 32.67, 30.61, 23.72; GC MS m/z 141 (M+). Anal. Calcd. for C7H11NO2 : C
59.54% , H 7.86%, N 9.93%, Found : 59.57%, 7.99%, 9.90%.
58
OH
N
O
95
2-Hydroxyoctahydro-1H-isoindol-1-one (95). A solution of degassed sodium hydroxide
(2N, 80 mmol, 40 mL) was added to a solution of octahydro-1H-inden-1-one (0.69 g,
5.56 mmol) in EtOH (20 mL) at 0°C. To this reaction mixture, a solution of Piloty’s acid
(1.926 g, 11.1 mmol) in EtOH (20 mL) was added dropwise over 30 min and the reaction
mixture was stirred at 0°C for 4 h and for 18 h at room temperature. The ethanol was
removed under vacuum and the water layer washed with diethyl ether. The aqueous layer
was acidified to pH 5.5 with 2N HCl and extracted with CHCl3 (6 x 50 mL). After drying
with MgSO4, the CHCl3 layer was concentrated to give a solid crude residue that was
purified by flash chromatography to give 95 (0.41 g, yield 48%); Rf = 0.46 (95:5 CHCl3:
MeOH). Sublimation (55°C, 0.05mm) afforded a white crystalline solid; m.p 78°C. 1H
NMR (CDCl3) 9.56 (b, 1H), 3.74 (q, J = 4.95 Hz, 2H), 2.45-2.25 (m, 2H), 2.12-1.92 (m,
2H), 1.76-1.64 (m, 2H), 1.59-1.25 (m, 5H); 13C NMR (CDCl3) 172.53, 59.1, 35.79, 29.8,
28.39, 25.83, 23.24, 20.69; GC MS 155 (M+). Anal. Calcd. for C8H13NO2 : C 61.95%, H
8.45%, N 9.03%, Found : C 61.60%, H 8.62%, N 8.93%.
59
1-Hydroxy-4-phenylpyrrolidin-2-one (96). A solution of degassed sodium hydroxide
(2N, 80 mmol, 40 mL) was added to a solution of 3-phenyl cyclobutanone (0.67 g, 4.6
mmol) in EtOH (20 mL) at 0°C. To this mixture a solution of Piloty’s acid (1.59 g, 9.2
mmol) in EtOH (20 mL) was added dropwise over 30 min, stirred at 0°C for 4 h and at
room temperature overnight. The ethanol was removed under vacuum and the water layer
washed with diethyl ether to remove the unreacted ketone. The aqueous layer was
acidified to pH 5.5 with 2N HCl and extracted with CHCl3 (5 x 50 mL), was dried and
concentrated to give a solid crude residue that was purified by flash chromatography to
give 96 as a reddish product (0.3 g, 37%); Rf = 0.65 (95:5 CHCl3: MeOH). Sublimation
(60°C, 0.05 mm); mp 84°C. 1H NMR (CDCl3) 9.94 (b, 1H), 7.38-7.23 (m, 5H), 3.67-3.56
(pentet, J = 8.21 Hz, 1H), 4.04 (t, J = 8.78 Hz, 1H), 3.76-3.71 (dd, J = 22.29, 7.18 Hz,
1H), 2.82-2.92 (dd, J =17.04, 9.26 Hz, 1H), 2.52-2.60 (dd, J = 17.04, 7.73 Hz, 1H) ; 13C
NMR (CDCl3) 169.63, 141.64, 129.05, 127.42, 126.76, 55.63, 36.67, 34.68. GC MS m/z
177 (M+). Anal. Calcd. for (C10H11NO2, 0.1H2O): C 67.08%, H 6.31%, N 7.82%, Found :
C 67.17%, H 6.31%, N 7.62%.
60
4-Hexyl-1-hydroxypyrrolidine-2-one (97). A solution of degassed sodium hydroxide
(2N, 80 mmol, 40 mL) was added to a solution of 3-hexyl cyclobutanone (0.892 g, 5.79
mmol) in EtOH (20 mL) at 0°C. A solution of Piloty’s acid (1.926 g, 11.1 mmol) in
EtOH (20 mL) was added dropwise over 30 min and the reaction mixture was stirred at
0°C over 4 h and then over 18 h at room temperature. The ethanol was removed under
vacuum and the water layer washed with diethyl ether. The aqueous layer was acidified
to pH 5.5 by 2N HCl and extracted with CHCl3 (5 x 50 mL), dried with MgSO4 and
concentrated to give a liquid residue that was purified by flash chromatography to afford
97 as a liquid (0.64 g, yield 59%); Rf = 0.65 (95:5 CHCl3: MeOH). 1H NMR (CDCl3)
10.49 (b,1H), 3.74 (t, J = 8.79 Hz, 1H), 3.37-3.23 (dd, J = 9.1, 6.75 Hz, 1H), 2.58-2.48
(dd, J = 16.49, 8.89 Hz, 1H), 2.43-2.26 (septet, J = 7.24 Hz, 1H), 2.12-2.01 (dd, J
=16.486, 7.085 Hz, 1H),1.58-1.35 (m, 2H), 1.34-1.15 (m, 8H), 0.92-0.84 (m, J = 6.52 Hz,
3H);
13
C NMR (CDCl3) 170.17, 54.61, 35.08, 34.92, 31.71,29.17, 29.14,27.09, 22.59;
ESI MS m/z 187.2 (M+2H+). Anal. Calcd. for (C10H19NO2, 0.1 mol H2O): C 64.19%, H
10.35%, N 7.49%, Found : C 64.32%, H 10.36%, N 7.19%.
61
N-(Benzyloxy)-4-methylbenzenesulfonamide (100). A solution of potassium carbonate
(1.38 g, 10 mmol) in water (15 mL) was added dropwise to a solution of O-benzyl
hydroxylamine hydrochloride (1.59 g, 10 mmol) in water: methanol (3:2, 25 mL) at 0°C.
After stirring vigorously for 1 h, ice cold MeOH (100 mL) was added in a single portion
followed by dropwise addition of benzenesulfonyl chloride (1.90 g, 10 mmol). After 24 h
at room temperature, the methanol was removed; the water layer acidified to neutral pH
and extracted with ethyl acetate. The organic layer was dried over MgSO4, filtered and
concentrated to give a crude residue that was purified by flash chromatography to give
100 as a white solid (1.39 g, 51%); Rf = 0.46 (85:15 pet. ether : EtOAc). mp 72°C, 1H
NMR 7.8 (d, J = 8.25 Hz, HA and HA’ of AA’BB’ spin-system), 7.34-7.31 (m, 7H), 6.89
(b, 1H), 4.97 (s, 1H), 2.43 (s, 1H);
13
C NMR 145.53, 135.92, 134.33, 130.38, 129.96,
129.29, 129.20, 129.15, 80.02, 22.30. ESI MS m/z 276 (M-H-) Anal. Calcd. for
C14H15NSO3 : C 60.63%, H 5.46%, N 5.05%; Found: C 60.66%, H 5.35%, N 4.87%.
62
N-(Benzyloxy)-N,4-dimethylbenzenesulfonamide (101). A solution of MeI (0.068 g,
0.48 mmol) in THF (10 mL) was added dropwise into a mixture of NaH (0.014 g, 0.58
mmol) and 100 (0.134 g, 0.48 mmol) in dry THF (40 mL) that had stirred for 30 min..
The reaction mixture was stirred for 18 h and quenched with water (10 mL). The THF
was removed under vacuum and the aqueous layer acidified to pH 7 and extracted with
EtOAc (2 x 30 mL). The organic layer was dried, filtered and concentrated to give a solid
residue that was purified by flash chromatography to give 101 as a white solid (0.109 g,
78%); Rf = 0.4 (90:10 pet. ether: EtOAc). The product was crystallized from pet. ether /
EtOAc (95:5). mp 57°C, 1H NMR (CDCl3) 8.29 (d, J = 8.29 Hz, 2H), 7.4-7.32 (m, 7H),
5.02 (s, 2H), 2.66 (s, 3H), 2.43 (s, 3H);
13
C NMR (CDCl3) 144.79, 135.6, 129.78,
129.54, 129.49, 129.34, 128.58, 128.49, 78.62, 40.14, 21.69.
1-Nitroso-cyclohexyl-acetate (102).117 A solution of cyclohexanone oxime (2.73 g,
24.12 mmol) in CH2Cl2 (50 mL) was added drop wise with stirring to a solution of lead
63
tetraacetate (10.69 g, 24.12 mmol) in DCM (100 mL) at 0°C. A blue color gradually
appeared with the addition of the oxime. After 1 h at 0°C, the reaction mixture was
warmed to room temperature and stirred for another 2 h, water (30 mL) was added, and
the organic layer was washed with (2 x 30 mL) water and saturated sodium bicarbonate
solution (2 x 30 mL). The organic layer was dried over MgSO4, the solvent evaporated
and the residue purified by flash chromatography to give 102 as a bright blue liquid (2.09
g, 51%); Rf = 0.68 (20:1 pet.ether : EtOAc).1H NMR (CDCl3) 2.19-1.29 (m, 13H);
13
C
NMR (CDCl3) 21.68 (CH2), 21.99 (2CH2), 25.09 (2CH2), 29.72 (CH3), 124.09 (O-C-N),
169.28 (C=O) Anal. Calcd. for C8H13NO3 : C 56.13%, H 7.65%, N 8.18%; Found: C
56.07%, H 7.84%, N 8.05%.
1-Nitroso-cyclopentyl-acetate (103). A solution of cyclopentanone oxime (0.495 g, 5
mmol) in CH2Cl2 (10 mL) was added dropwise with stirring to a solution of lead
tetraacetate (2.216 g, 5 mmol) in DCM (20 mL) at 0°C. A blue color gradually appeared
with the addition of the oxime. After 1 h at 0°C, the reaction mixture was warmed to
room temperature. After 2 h at room temperature, water (10 mL) was added, and the
organic layer was washed with water (2 x 10 mL) and saturated sodium bicarbonate
solution (2 x 10 mL).The organic layer was dried over MgSO4, the solvent evaporated
and the residue purified by flash chromatography to give 103 as a bright blue liquid
(0.360 g, 49%); Rf = 0.62 (20:1 pet. ether: EtOAc). 1H NMR (CDCl3) 2.28-1.81 (m,
64
11H);
13
C NMR (CDCl3) 21.38 (2CH2), 25.73 (2CH2), 34.21 (CH3), 131.19 (O-C-N),
169.67 (C=O) Anal. Calcd. for C7H11NO3 : C 53.49%, H 7.05%, N 8.91%; Found: C
53.89%, H 7.29%, N 8.69%.
2-Oxopiperidin-1-yl acetate (104). A solution of acetic anhydride (0.709 g, 5 mmol) in
CH2Cl2 (10 mL) was added dropwise into a mixture of DMAP (0.027 g, 0.22 mmol) and
N-hydroxy piperidone (0.51 g, 4.43 mmol) in dry CH2Cl2 (150 mL) over 30 min. The
reaction mixture was stirred for another 12 h. This solution was thoroughly washed with
water, brine (30 mL). The organic layer was dried over MgSO4, the solvent was removed
under vacuum and the residue was purified by flash chromatography to give 104 as a
white solid (0.39 g, 63%); Rf = 0.81 (95:5 CHCl3:MeOH). 1H NMR (CDCl3) 3.565 (t, J =
5.99 Hz, 2H), 2.47 (t, J = 6.56 Hz, 2H), 2.15 (s, 3H), 2.02-1.885 (m, 2H), 1.86-1.75 (m,
2H); 13C NMR (CDCl3) 166.44, 164.83, 51.72, 33.45, 24.42, 21.62, 19.07.
65
1-Methoxypiperidin-2-one (105). A solution of MeI (0.709 g, 5 mmol) in THF (10 mL)
was added dropwise into a mixture of NaH (0.12 g, 4.98 mmol) and N-hydroxy
piperidone (0.521 g, 4.53 mmol) in dry THF (40 mL) that had stirred for 30 min. The
reaction mixture was stirred for 12 h and quenched with water (10 mL). The THF was
removed under vacuum and the aqueous layer acidified to pH 7 and extracted with CHCl3
(3 x 40 mL). The organic layer was dried, filtered and concentrated to give a solid residue
that was purified by flash chromatography to give 105 as a reddish liquid (0.339 g,
58%); Rf = 0.32 (EtOAc). 1H NMR (CDCl3) 3.79 (s, 3H), 3.61 (t, J = 6.01 Hz, 2H), 2.47
(t, J = 6.46 Hz, 2H), 2.01-1.93 (m, 2H), 1.87-1.74 (m, 2H);
13
C NMR (CDCl3) 167.48,
62.77, 50.75, 35.33, 26.21, 23.42.
2-Methyl-1-nitrosocyclopentyl acetate (107). A solution of 2-methyl cyclopentanoneoxime (0.97 g, 8.58 mmole) in CH2Cl2 (10 mL) was added dropwise with stirring to a
solution of lead tetraacetate (3.805 g, 8.58 mmole) in CH2Cl2 (20 mL) at 0°C. A blue
66
color gradually appeared with the addition of the oxime. After 1 h at 0°C, the reaction
mixture was warmed to room temperature. After 2 h at room temperature, water (10 mL)
was added, and the organic layer washed with water (2 x 10 mL) and saturated sodium
bicarbonate solution (2 x 10 mL).The organic layer was dried over MgSO4, the solvent
evaporated under vacuum and the residue purified by flash chromatography to give 107
as a bright blue liquid (0.968 g, 66%); Rf = 0.44 (20:1 pet. ether: EtOAc). 1H NMR
(CDCl3) 2.92-2.71 (m, 1H), 2.47-1.77 (m, 11H);
13
C NMR (CDCl3) 168.91, 130.68,
46.21, 32.67, 23.53, 20.9, 12.12.
1-Hydroxy-6-methylpiperidin-2-one (106). A solution of 2-methyl-1-nitrosocyclopentyl
acetate (0.524 g, 4.07 mmol) in MeOH (10 mL) was added to an aqueous solution of 2M
NaOH (10 mL). The blue color gradually disappeared and after 18 h stirring at room
temperature, the MeOH was removed under vacuum. The aqueous layer was acidified to
pH 6 and extracted with CHCl3 (3 x 50 mL). The organic layer was washed with water,
brine and dried over MgSO4. The solvent was removed under vacuum and the residue
was purified by flash chromatography to give 106 as a reddish brown solid (0.335 g,
78%); Rf = 0.62 (20:1 pet. ether: EtOAc). 1H NMR (CDCl3) 8.45 (b, 1H), 3.89-3.77 (m,
1H), 2.6-2.29 (m, 2H), 2.12-1.92 (m, 1H), 1.89-1.77 (m, 1H), 1.75-1.55 (m, 2H), 1.35 (d,
J = 6.34 Hz, 3H); 13C NMR (CDCl3) 164.82, 55.16, 31.05, 30.82, 19.18, 18.206.
67
3-(Hydroxyimino)cyclohexanone (109). A solution of degassed sodium hydroxide (2N,
40 mmol, 20 mL) was added to a solution of cyclohexenone (0.238 g, 2.5 mmol) in EtOH
(20 mL) at 0°C. To this mixture, a solution of Piloty’s acid (0.866 g, 5 mmol) in EtOH
(20 mL) was added dropwise over 30 min and the reaction mixture was stirred at room
temperature for 18 h. The ethanol was removed under vacuum and the water layer was
extracted with diethyl ether to remove unreacted ketone. The aqueous layer was acidified
to pH 6 with 2N HCl and extracted with CHCl3 (3 x 50 mL). The CHCl3 layer was dried
with MgSO4 and concentrated to give a semisolid crude residue that showed a brown spot
in FeCl3 stain by TLC. The residue was purified by flash chromatography to give a
yellow liquid (0.063 g, 20%) as an inseparable mixture of syn and anti oxime product
(109); Rf = 0.45 (EtOAc). 1H NMR (CDCl3) 8.39 (b, 1H), 3.48 (s, 1H), 3.22 (s, 1H), 2.73
(t, J = 6.57 Hz, 1H), 2.565-2.47 (m, 2H), 2.41-2.37 (m, 1H), 1.99-1.85 (m, 2H); 13C NMR
(CDCl3) 206.96, 206.02, 155.58, 155.13, 45.95, 40.98, 40.84, 30.05, 24.00, 21.37, 19.34.
68
tert-Butyl (1-hydroxy-2-oxopiperidin-3yl)carbamate (115). A solution of degassed
sodium hydroxide (2N, 80 mmol, 40 mL) was added to a solution of tert-butyl (2oxocyclopentyl)carbamate (113, Scheme 56) (0.6 g, 3.015 mmol) in EtOH (20 mL) at
0°C. To this mixture a solution of Piloty’s acid (1.044 g, 6.03 mmol) in EtOH (20 mL)
was added dropwise over 30 min and the reaction mixture was stirred at room
temperature for 18 h. The ethanol was removed under vacuum and the water layer was
extracted with diethyl ether to remove the unreacted ketone. The aqueous layer was
acidified to pH 5.5 with 2N HCl and extracted with CHCl3 (5 x 50 mL). The CHCl3 layer
was dried with MgSO4 and concentrated to give a solid crude residue that was purified by
flash chromatography to give 115 as a reddish solid (0.06 g, 4%) ; Rf = 0.24 (95:5 CHCl3
: MeOH). 1H NMR (CDCl3) 5.46 (b,1H), 5.24 (b, 1H), 2.475 (t, J = 5.61 Hz, 2H),
13
C-
NMR (CDCl3) 165.85, 155.55, 79.7, 68.14, 34.46, 32.24, 30.52, 19.01, LCMS m/z 229
(M+).
N-hydroxy-N-propylacetamide. A solution of degassed sodium hydroxide (2N, 80
mmol, 40 mL) was added to a solution of 2-pentanone (1.13 g, 11.3 mmol) in EtOH (20
69
mL) at 0°C. To this reaction mixture, a solution of Piloty’s acid (3.91 g, 22.6 mmol) in
EtOH (20 mL) was added dropwise over 30 min and this mixture was stirred at 0°C for 4
h and for 18 h at room temperature. The ethanol was removed under vacuum and the
water layer washed with diethyl ether. The aqueous layer was acidified to pH 5.5 with 2N
HCl and extracted with CHCl3 (6 x 50 mL). After drying with MgSO4, the CHCl3 layer
was concentrated to a solid crude residue and purified by flash chromatography to give
the N-hydroxy-N-propylacetamide as a thick red liquid (.04 g, 3%); Rf = 0.44 ( EtOAc);
1
H NMR (CDCl3) 3.60 (t, J = 6.69 Hz, 2H), 2.1 (s, 3H), 1.76-1.62 (m, 2H), 1.45-1.28 (m,
2H), 0.95 (t, J = 7.23 Hz, 3H).
70
CHAPTER 3
PROGRESS TOWARDS THE SYNTHESIS OF THE COBACTIN CORE AND
MYCOBACTIC ACID UTILIZING NITROSO-ENE REACTION
Ring-expansion reactions of cyclic ketones through –NOH insertion fails to generate the
seven-membered ring cobactin core (Scheme 55 and Scheme 56). As an alternative
approach, this research focuses on investigating the nitroso-ene reaction for making a
synthetic cobactin analog. The basics of the nitroso ene reaction have already been
discussed in the context of making linear and cyclic hydroxamic acid analogs in the
introduction.34 Our research goal is to utilize this reaction to synthesize cobactin and
mycobactic acid analogs. The specific aims of this project include investigating both the
intramolecular and intermolecular nitroso-ene reaction towards the formal synthesis of
cobactin and mycobactic acid.
3.1
3.1.1
Intramolecular Nitroso-ene Reaction Approach to the Synthesis of Cobactin Core
Retrosynthesis of Cobactin
A synthesis of the cobactin core (83, Scheme 57), a seven membered ring hydroxamic
acid residue of the natural product mycobactin S, would be approached using nitroso-ene
cyclization methodology. We envisioned that the cobactin core A could arise by
reduction of the unsaturated analog B, which could be synthesized in one step using an
intramolecular nitroso-ene cyclization of the linear hydroxamic acid C (Scheme 57).
71
Scheme 57. Retrosynthesis of cobactin using intramolecular nitroso-ene reaction
3.1.2 Intramolecular Nitroso-ene Reactons : Results and Discussion
The intramolecular nitroso-ene cyclization is one of the most useful tools to synthesize
cyclic hydroxamic acid frameworks. While nitroso-ene reactions are immensely useful to
make five or six membered ring hydroxamic acids, only a few reports exist for the sevenmembered ring synthesis.65, 71, 86
To explore the proposed retrosynthetic route (Scheme 58), the initial group of
experiments were directed to generate the proper chain length acyl nitroso species 116
(Scheme 58) and evaluate the nitroso-ene cyclization to construct a cobactin core.
Scheme 58. Proposed synthesis of cobactin core
To investigate this pathway with the α-unsubstituted acylnitroso species 116 (Scheme
58), the synthetic scheme began with the esterification of commercially available 572
hexenoic acid (118, Scheme 59) to the corresponding methyl ester (119) by treatment of
methyl iodide and potassium carbonate in acetone. Treatment of 119 with excess
hydroxylamine hydrochloride in base gave the corresponding hydroxamic acid (120,
Scheme 59).130 Oxidation of 120 with tetrabutylammonium periodate generates the
acylnitroso intermediate (116) which was trapped by 9, 10-dimethylanthracene (9,10O
1. K2CO3 (3eq.)
3
118
OH
O
O
1. NH2OH HCl
3 OMe 2. K2CO3, MeOH
2. MeI (5eq.),
Acetone
35%
119
55%
NHOH
3
120
1. Bu4NIO4
2. 9,10-DMA
52%
O
O
OH
N
+
Reflux in benzene or toluene
N
O
3
or sealed tube heating
117
121
X
Scheme 59. Attempted synthesis of cobactin core
DMA) to give a Diels-Alder bicycloadduct (121). Thermolysis of the cycloadduct 121
did not produce the seven membered hydroxamic acid 117 (Scheme 59).
O
N
O
H
Scheme 60. Nitroso-ene mechanism: Improper alignment
The failure of this cyclization may be due to the unfavorable deformation needed to
attain the intramolecular nitroso ene geometry required for the desired product (Scheme
73
60). The alkyl chain may not be long enough to allow proper alignment of the nitroso
species and the bridging alkene group in 116 (Scheme 58) for a productive nitroso-ene
reaction.
In order to circumvent this problem, we examined an alternative pathway where the
acyl nitroso species is derived from a 6-octenoic hydroxamic acid (124, Scheme 61). This
substrate has added flexibility with an extra methylene group and two carbon
homologous alkyl chain (123, Scheme 61). Ozonolysis of cyclohexene using the
procedure reported by Li et. al, yields 122 (Scheme 61) in 52% yield.131 Compound 122
was converted to the homologous two carbon (Z) alkene 123 by Wittig olefination.132
Treatment of 123 with
Scheme 61. Intramolecular nitroso-ene reaction of 126 generates eight membered ring
hydroxamic acids
74
ex
xcess hydro
oxylamine hydrochlorid
h
de in the prresence of excess K2C
CO3 affordedd the
hy
ydroxamic acid
a
(124) in
n 77% yield
d. Tetrabutyylammonium
m periodate ooxidation off 124,
fo
ollowed by the
t Diels-Allder reaction
n with 9,10--DMA gave the cycloaddduct (125, 56%,
(125) in reefluxing tolluene yieldeed an
Scheme 61). Thermolyssis of the cycloadduct
c
un
nusual eightt membered ring hydrox
xamic acid ppresumably as a nitroso-ene producct 127
(P
Path a, Scheeme 61) in 40%
4
yield, while
w
the forrmation of tthe vinyl subbstituted cobbactin
co
ore 128 (Patth b, Schem
me 61) was not
n observedd. X-ray diffr
fraction studiies on crystaals of
127 (Figure 4) confirmss the structu
ure, which is also suppported by N
NMR and m
masssp
pectroscopicc data. Whilee this intram
molecular nitrroso-ene reacction schem
me doesn’t suupport
th
he synthesis of a cobactiin core, it prrovides a unnique route too make eighht memberedd ring
hy
ydroxamic acid.
a
4 X-ray difffraction struucture of com
mpound 127
Figure 4.
75
3.2 Structure Elucidation of Mycobactin
The first structure elucidation of the hydroxamic acid-based siderophore mycobactin
was achieved by G. A. Snow in 1954.133 Amino acid-based hydroxamic acids are
important components in mycobactin. Mycobactin S exhibits growth inhibitory activity
against Mycobacterium tuberculosis and it consists of cobactin and mycobactic acid
(Scheme 62), both of which contain a hydroxamic acid residue derived from
NЄ-hydroxylysine. Mycobactin S is the closest structural relative of mycobactin T (found
in tuberculosis causing bacteria), differing in variable long chain substituents R1 (Scheme
62).76
Scheme 62. Structure elucidation of mycobactin S
3.3
Investigation of Intermolecular Nitroso-ene Approach towards the Synthesis of
Cobactin and Mycobactic Acid
Since the intramolecular nitroso-ene reactions failed to give an efficient formal
synthesis of the cobactin core, we proposed an intermolecular nitroso-ene methodology
76
as an alternative. Scheme 63 shows this route to cobactin and mycobactic acid using the
intermolecular nitroso-ene reaction. The ene reaction between a Nα-protected homoallylglycine ester 129 and a tert-butyl C-nitroso formate ester would generate the hydroxamic
acid (130, Scheme 63). Hydrogenation of 130 would yield the saturated hydroxamic acid
derivative (131) and deprotection by HCl would give the Nα-protected NЄ-hydroxylysine
(132, Scheme 63).
A DCC-DMAP coupled cyclization should generate the seven
membered ring hydroxamic acid (133, Scheme 63) as reported.76 This sequence provides
a short route to a key intermediate of cobactin synthesis. A similar synthetic route using
a long chain-derived acyl nitroso species supports the synthesis of a precursor of
mycobactic acid (84, Scheme 63).
Scheme 63. Intermolecular nitroso-ene reaction route to cobactin and mycobactic acid
77
3.3.1
Synthesis of the Precursor Alkene and Diels-Alder Cycloadduct ( Acyl-nitroso
Precursor) for a Nitroso-ene Reaction
To investigate the proposed synthetic route to cobactin (Scheme 63), we started with
the synthesis of a properly substituted alkene (135, Scheme 64) and a precursor of an acyl
nitroso compound (136, Scheme 64). Alkylation of the Schiff base protected glycine
ethyl ester with 4-bromo-1-butene (Scheme 64) gave the precursor alkene (ethyl 2((diphenylmethylene)amino)hex-5-enoate)
in
89%
yield.134
Tetrabutylammonium
periodate oxidation of tert-butyl hydroxycarbamate followed by a Diels-Alder reaction
with 9,10-DMA yielded the cycloadduct (136) as a precursor acyl nitroso species (71%,
Scheme 64).
Scheme 64. Synthesis of the precursor alkene and acyl nitroso component
78
3.3.2
Nitroso-ene Reaction
Intermolecular nitroso-ene reactions were performed by heating a solution of ethyl 2((diphenylmethylene)amino)hex-5-enoate and the precursor acylnitroso compound (136)
in toluene at reflux in a sealed tube for 4 h. This nitroso-ene reaction successfully
generates the hydroxamic acid (137) in 45% yield (Scheme 65). The best results were
obtained using an excess (4 eq.) amount of alkene to trap the in situ generated tert-butyl
C-nitrosoformate ester species (Scheme 65). Nitroso-ene reactions of terminal alkenes are
reported to produce a mixture of E and Z regioisomers and these reactions appears to give
inseparable mixtures of E/Z stereoisomers.63 The nitroso-ene product 137 (Scheme 65)
was isolated as a mixture of E/Z stereoisomers after chromatographic purification. As the
next synthetic step requires reduction, chromatographic separation or determination of
the stereochemistry of the alkene (137) was not performed.
Scheme 65. Intermolecular nitroso-ene reaction
Hydrogenation of 137 in presence of Pd/C (10 wt. %) catalyst in MeOH reduced the
olefin as well as the imino protecting group, giving a mixture of 138 and 139 (Scheme
66). Deprotection of the imino group of 137 with strong acid in MeOH yielded 140 which
failed to generate the hydrogenated product (141, Scheme 66), as the unprotected
hydroxylamine group may poison the hydrogenation catalyst.
79
Scheme 66. Results of hydrogenation on the nitroso-ene product
These results led to the design of an alkene with a different N-protecting group. NAcetyl homoallyl glycine ester (145, Scheme 67) was synthesized from diethyl
acetamidomalonate (142) by alkylation with 1-bromo butene followed by β-ketodecarboxylation and esterification of the free acid 144 (Scheme 67).135 The nitroso-ene
reaction of 145 with the cycloadduct (136, Scheme 67) afforded 146 in 46% yield as a
mixture of E/Z stereoisomers after chromatographic separation. Hydrogenation of 146
with Pd/C catalyst yielded the saturated hydroxamic acid (147, 89%, Scheme 66).
However, acid hydrolysis failed to generate the free acid needed for cyclization from 147
and only produced the hydroxylamine (148).
80
Scheme 67. Synthesis and nitroso-ene reactions of N-acetyl homo allyl glycine ethyl ester
The precursor alkene (144) was modified to an acid cleavable N-acetyl tert-butyl
homoallyl glycine ester (149, Scheme 68) using a published method.70 The nitroso-ene
reaction of 149 with the cycloadduct (136) under identical conditions afforded the
hydroxamic acid (150, Scheme 68) as a mixture of E and Z stereoisomers in 46% yield.
Hydrogenation of 150 under 2.5 atm pressure with Pd/C (10 wt.%) catalyst led to the
saturated hydroxamic acid (151, Scheme 68, 89%). Treatment of 151 with TFA in
CH2Cl2 (1:1) at room temperature for 3 h yields the deprotected precursor hydroxylamine
(152, Scheme 68), which failed to generate a seven membered cobactin core 153 after
either a DCC-DMAP (dicyclohexylcarbodiimide - dimethyl aminopyridine) or EDC–
81
HOAt
(1-ethyl-3-(3-dimethylaminopropyl)
carbodiimide
–
1-hydroxy-7-aza
benzotriazole) coupled cyclization, both methods reported by Miller.60, 136 Nevertheless,
these results show that the intermolecular nitroso-ene reactions provides a short route to
generate the key intermediate 152, which could be potentially useful to make the cobactin
core.
Scheme 68. Synthetic approach to the cobactin core using an intermolecular nitroso ene
reaction
The nitroso-ene product (150, Scheme 68), with its high polarity and iron chelating
ability, was difficult to purify by chromatography. Moreover mass-spectroscopic data
(see experimental) reveals 152 also binds iron strongly. To make a less polar nonchelating tert-Butyl dimethyl silyl (TBDMS) protected analog of 152, 150 was treated
with TBDMSCl in presence of imidazole as base to give the O-protected hydroxamic
acid (154, Scheme 69). Hydrogenation of 154 under 1.5 atm. pressure with Pd/C (10 wt.
82
%) yielded the saturated O-protected hydroxamic acid (155, Scheme 69), which failed to
produce the TBDMS protected hydroxylamine (156) under mild orthophosphoric acid
deprotection condition.
Scheme 69. Attempted synthesis of TBDMS protected hydroxylamine
3.3.3
Progress Towards the Synthesis of Mycobactic Acid Utilizing a Nitroso-ene
reaction
Mycobactic acid consists of a long chain derived [R1 = -(CH2)12CH3] N-substituted
hydroxamic acid along with a 2-hydroxyphenyl oxazoline residue. Both residues are
essential for bacterial siderophore activity and the long alkyl chain is important for lipid
solubility of mycobactins during iron transport through the cell membrane.102
Intermolecular nitroso-ene reactions between the precursor alkene (149, Scheme 70) and
a long chain derived acyl nitroso species provides a key intermediate 161 towards the
synthesis of mycobactic acid 84 (Scheme 63). The synthesis of the long chain N83
Scheme 70. Intermolecular nitroso-ene route to formal synthesis of mycobactic acid
substituted hydroxamic acid residue started with the acyl nitroso precursor (159, Scheme
70). Ethyl myristate (157, Scheme 70) was converted to N-hydroxy tetradecanamide
(158, Scheme 70) by treatment with a large excess of hydroxylamine hydrochloride and
potassium hydroxide in EtOH at room temperature. Tetrabutylammonium periodate
84
oxidation of 158 and Diels-Alder reaction with 9,10-DMA gave the cycloadduct (159,
Scheme 70). Thermolysis and concomitant nitroso-ene reaction of 159 with 149 (Scheme
70) under identical conditions for 6 h provided the hydroxamic acid (160) in 23% yield.
After chromatographic purification, 160 appeared to be a mixture of E and Z
stereoisomers. Hydrogenation of 160 gave the saturated long chain hydroxamic acid
(161), which is a precursor of mycobactic acid (84, Scheme 70).
Since the long chain derived acyl-nitroso-ene product 160 is difficult to
chromatograph and this complicated purification led to a poor yield, we tried protecting
the hydroxamic acid as a TBDMS ester. tert-Butyl dimethylsilyl (TBDMS) protection of
the hydroxamic acid group of cobactin has been reported by Miller.76 Using this method,
treatment of 160 with TBDMSCl resulted in a stable O-protected nitroso-ene product
(162, Scheme 71) in 30% yield with improved chromatographic purification still as a
mixture of E/Z stereoisomers.
Scheme 71. TBDMS protection of hydroxamic acid group in long chain derived
nitroso-ene product
85
3.3.4
The Nitroso-ene Chemistry of Long Chain-Derived Acyl Nitroso Species
The next set of experiments verifies the reactivity of the long chain-derived acyl nitroso
species. Treatment of the long chain derived acyl-nitroso cycloadduct (159, Scheme 72)
with cyclohexene as solvent under identical nitroso-ene reaction conditions afforded 163
(Scheme 72) in 33% yield, further proving the ability of the long chain- derived acyl
nitroso species to undergo nitroso-ene reactions, however the yield remained below 40%.
Scheme 72. Nitroso-ene reaction of a long chain-derived acyl nitroso species with
cyclohexene
3.4
Nitroso-ene Reactions of Acetyl-Nitroso Compounds
A small acyl nitroso compound was screened as an enophile in the nitroso-ene
reaction with the N-acetyl tert-butyl homoallyl glycine ester (149, Scheme 73).
Tetrabutylammonium periodate oxidation of acetohydroxamic acid generates the acetyl
nitroso intermediate that reacts with 9,10-DMA to give a Diels-Alder cycloadduct (164,
Scheme 73). The nitroso-ene reaction between 164 and alkene (149) under identical
nitroso-ene conditions afforded the hydroxamic acid after chromatographic purification
(165, 29%, Scheme 73), as a mixture of E and Z stereoisomers. The nitroso-ene product
(165) being highly polar, complicated purification and resulted in low isolation. TBDMS
protection of the hydroxamic acid (165) gave the O-protected product (166, 33%, Scheme
73) with ease in purification, still as a mixture of E/Z stereoisomers.
86
Scheme 73. Nitroso-ene reactions of acyl-nitroso species with the precursor alkene 149
3.5
Nitroso-ene reactions of Benzoyl nitroso compounds
Benzoyl nitroso compounds were screened to examine the scope of the nitroso-ene
reactions. Oxidation of benzohydroxamic acid with tetrabutylammonium periodate gave
the benzoyl nitroso intermediate and the in situ Diels-Alder reaction with 9,10-DMA
yields the cycloadduct (167, 53%, Scheme 74). The nitroso-ene reaction between 167 and
the alkene (149) generates the hydroxamic acid (168, 20%, Scheme 74) as a mixture of
E/Z stereoisomers. These results demonstrate poor nitroso-ene ability of the benzoyl
nitroso species.
87
Scheme 74. The nitroso-ene reaction of benzoyl nitroso species
Given the research goal of a short synthetic route to cobactin core and mycobactic
acid using nitroso-ene reactions, we wanted to examine the general ability of the acyl
nitroso compounds to undergo ene reactions. The last two experiments reveal the scope
of the nitroso-ene reactions of a short acetyl-nitroso and benzoyl nitroso intermediates,
with benzoyl nitroso compounds being the least efficient. In each case the hydroxamic
acids (165 and 168) are difficult to purify and complicated chromatographic separation
results in low yield.
TBDMS protection of the hydroxamic acid in 165 facilitates
purification, while it has not been attempted for 168. Previous results towards cobactin
and mycobactic acid synthesis suggest the tert-butyl C-nitroso formate esters show the
best nitroso-ene reactivity with 149, while the long chain derived acyl nitroso
intermediates are not very efficient enophiles. This failure to afford an efficient nitrosoene reaction could be attributed to the fact that the folding of the long chain alkyl group
may hinder the acyl nitroso fragment accessing the alkene, thus affecting its nitroso-ene
ability. In general acyl nitroso species are transient, exceptionally reactive and
88
electrophiles.137 All nitroso-ene reactions were performed in non-nucleophilic solvents
like toluene and benzene under inert atmosphere. This study shows the nitroso-ene
reactivity profile of a series of acyl nitroso intermediates with terminal alkenes generating
a series of N-substituted hydroxamic acids, which could further be useful for synthesizing
various substituted hydroxylamine derivatives.
89
3.6
Experimental
General. Analytical TLC was performed on silica gel plates with QF-254 indicator.
Visualization was accomplished with UV light, FeCl3, bromocresol green, potassium
permanganate, phosphomolybdic acid, and/or dinitrophenylhydrazine stain. Extraction
and chromatography solvents were technical grade. All reactions were performed under
an inert atmosphere of dry argon. 1H NMR and 13C NMR were recorded in CDCl3 and
deuterated DMSO on a Bruker Avance 300 MHz and 500 MHz NMR Spectrometer.
Chemical shifts are given in ppm (δ); multiplicities are indicated by s (singlet), d
(doublet), t (triplet), q (quartet), m (multiplet) and b (broadened). Low resolution mass
spectra were obtained using an Agilent LCMS system consisting of an 1100 LC/MSD
detector or from the UNC Mass Spectrometry Laboratories (UNC-Chapel Hill, NC)
using a BioToF-NT instrument and data are reported in m/z.
90
1-(9,10-dimethyl-9,10-dihydro-9,10-(epoxyimino)anthracen-11-yl)hex-5-en-1-one
(121). A solution of 120 (0.133 g, 1.03 mmol) in CHCl3 (9 mL) was added dropwise to
a solution of 9, 10-dimethylanthracene (0.53 g, 2.57 mmol) and Bu4NIO4 (0.49 g, 1.13
mmol) in CHCl3 (13 mL). The solution was stirred for 90 min and poured into aq.
Na2S2O3 solution (20 mL) and extracted with CH2Cl2 (2 x 20 mL). The extracts were
dried over MgSO4 and purified by flash chromatography (15% EtOAc : 85% pet.ether,
Rf = 0.74) to give as 121 a white solid ( 0.18 g, 52%); 1H-NMR (CDCl3, 300 MHz)
7.49-7.46 (m, 2H), 7.38-7.36 (m, 2H), 7.30-7.26 (m, 4H), 5.75-5.54 (m, 1H), 4.91-4.79
(m, 2H), 2.71 (s, 3H), 2.23 (s, 3H), 2.16 (t, J = 7.42 Hz, 2H), 1.81 (q, J = 7.16 Hz,
2H), 1.55 (s, 2H), 1.39 (p, J = 7.35 Hz, 2H);
13
C-NMR (CDCl3, 300 MHz) 178.52,
140.54, 140.42, 138.07, 138.00, 126.9, 126.59, 120.09, 120.01, 113.94, 113.89, 79.60,
64.15, 36.74, 34.12, 24.15, 17.66, 15.92.
Methyl-6-oxo-hexanoate (122).138 Ozone was bubbled through a mixture of
cyclohexene (2.46 g, 3.04 mL, 30 mmol) and anhydrous sodium carbonate (0.82 g, 7.74
91
mmol) in CH2Cl2 (90 mL) and methanol (18 mL) was added at -78°C until a faint blue
color appeared.139,
140
Argon was bubbled through the mixture until the blue color
discharged. The cooling bath was removed and the mixture was allowed to warm-up to
room temperature. After filtration, benzene (30 mL) was added and the mixture was
concentrated to a volume of ~20 mL. The resulting viscous liquid was diluted with
CH2Cl2 (80 mL) and cooled to 0°C. Et3N (4.5 g, 6.2 mL, 44.48mmol) and Ac2O (8.53 g
7.59 mL, 83.57 mmol) were sequentially added dropwise and the mixture was stirred at
0°C for 30 min and then at room temperature overnight. The organic phase was
washed with 0.1M aq. HCl (2 x 60 mL), 10% aq. NaOH (2 x 60 mL), water (60 ml) and
dried over MgSO4. After filtration, solvent was removed under vacuum and the product
was isolated as a crude oil and purified by flash chromatography (30% EtOAc : 70%
pet. Ether, Rf = 0.65) to give a colorless oil (2.25 g, 52%) with spectroscopic and
analytical details were identical to those reported.138
(Z)-Methyl oct-6-enoate (123). A NaHMDS solution in THF (1.1 g, 6 mmol) was
added to a suspension of ethyl triphenyl phosphonium bromide (1.86 g, 5 mmol) in
distilled THF (50 mL) under nitrogen and was stirred at room temperature for 30 min.
After 30 min, the solution color changed from red to orange, and the solution was
cooled to -80°C and methyl-6-oxohexanoate (0.72 g, 5 mmol) was added. After 16 h at
room temperature, the solution was heated to reflux for 3 h, the THF was evaporated
92
under vacuum and water (20 mL) added to the residue. The mixture was extracted with
Et2O (3 x 50mL) and dried over magnesium sulfate to give a crude mixture that was
purified by flash chromatography (25% Et2O:75% pet. ether, Rf = 0.95) to give 123 as a
colorless volatile liquid (0.45 g, 58%); 1H-NMR (CDCl3, 300 MHz) 5.54-5.34 (m, 2H),
3.7 (s, 3H), 2.35 (t, J = 7.5 Hz, 2H), 2.08 (q, J = 7.35 Hz, 2H), 1.74-1.6 (m, 5H), 1.471.37 (m, 2H);
13
C-NMR (CDCl3, 300 MHz) 173.36, 129.78, 123.96, 52.12, 34.88,
29.95, 27.4, 25.56, 14.49.
(Z)-N-Hydroxyoct-6-enamide (124). A solution of potassium hydroxide (12.12 g.,
216 mmol) in MeOH (70 mL) was added dropwise to a solution of hydroxylamine
hydrochloride (7.5 g, 108 mmol) in MeOH (70 mL) at 0°C. This solution was stirred
for 20 min and a solution of methyl-5-heptenoate (1.69g, 10.8 mmol) in MeOH (35
mL) was added dropwise and stirred for 2 h. Water (45 mL) was added and the pH of
the solution adjusted to 6 with conc. HCl. This acidified solution was extracted with
CHCl3 (3 x 50 mL), dried over MgSO4 and the solvent was removed under vacuum. The
crude mixture was purified by flash chromatography (1:1 EtOAc : pet. ether, Rf = 0.48)
to give 124 as a light brown thick liquid (1.3 g, 77%); 1H-NMR (CDCl3, 500MHz) 9.03
(b, 1H), 5.49-5.28 (m, 2H), 2.16 (t, J = 7.36 Hz, 2H), 2.04 (q, J = 7.21 Hz, 2H), 1.681.58 (m, 5H), 1.42-1.31 (m, 2H); 13C-NMR (CDCl3, 300 MHz) 172.44, 130.99, 125.49,
93
35.19, 31.27, 28.77, 27
7.39, 15.28. Homonuclea
H
ar decouplinng NMR expperiment revvealed
the Z config
guration of th
he alkene (124).
94
(Z)-1-(9,10-Dimethyl-dihydro-9,10-(epoxyimino)anthracen-11-yl)oct-6-en-1-one
(125). A solution of (Z)-N-hydroxy-6-octenamide (124, 0.338 g, 2.15 mmol) in CHCl3
(9 mL) was added dropwise to a solution of 9, 10-dimethylanthracene (1.11 g, 5.38
mmol) and Bu4NIO4 (1.02 g, 2.36 mmol) in CHCl3 (13 mL). The solution was stirred
for 90 min and poured into an aq. Na2S2O3 solution (20 mL) and extracted with CH2Cl2
(2 x 20 mL). The extracts were dried over MgSO4, solvent was removed under vacuum
and purified by flash chromatography (15% EtOAc : 85% pet.ether, Rf = 0.78) to give
125 as a white solid ( 0.438 g, 56%); 1H-NMR (CDCl3, 300 MHz) 7.51-7.48 (m, 2H),
7.41-7.37 (m, 2H), 7.32-7.27 (m, 4H), 2.74 (s, 3H), 2.27 (s, 3H), 2.19 (t, J = 7.17 Hz,
2H), 1.96-1.89 (dd, J = 7.32, 7.07 Hz, 2H), 1.56 (d, J = 6 Hz, 3H), 1,38-1.28 (m, 2H),
1.2-1.1 (m, 2H); 13C-NMR (CDCl3, 300 MHz) 180.07, 142.17, 142.06, 131.50, 128.56,
128.25, 124.93, 122.58, 121.75, 81.25, 65.78, 38.50, 31.20, 28.93, 25.91, 19.32, 17.58,
15.28.
(Z)-1-Hydroxy-8-methyl-1,4,5,8-tetrahydroazocin-2(3H)-one (127). A solution of
125 (0.198 g, 0.54 mmol) in toluene (250 mL) was refluxed for 20 min until TLC
95
revealed a high Rf UV active spot corresponding to 9,10-DMA and a broad polar spot
that turned purple in FeCl3 stain. After solvent evaporation under vacuum, the
remaining crude yellow solid was purified by flash chromatography (a gradient of 35%
EtOAc : 65% pet. ether to 95% CHCl3: 5% MeOH, Rf = 0.22) to give a reddish brown
thick liquid that was further purified by sublimation at 45°C under reduced pressure
(0.05 mm) to give 127 as a white crystalline solid (0.026 g, 30%); 1H-NMR (CDCl3,
300 MHz) 7.87 (b, 1H), 5.86-5.69 (m, 2H), 4.82-4.73 (m, 1H), 2.68-2.6 (m, 2H), 2.452.25 (m, 2H), 1.94-1.84 (m, 1H), 1.5 (d, J = 6.75 Hz, 3H),
13
C-NMR (CDCl3, 300
MHz) 172.35, 134.66, 130.70, 53.39, 34.54, 28.38, 23.66, 18.72. HRMS (ESI) m/z
156.1025 (M+H)+ Expected 155.0946
tert-Butyl-9,10-dimethyl-9,10-dihydro-9,10-(epoxyimino)anthracene-11-carboxy
latE (136).70 A solution of tert-butyl N-hydroxycarbamate (0.5 g, 3.75 mmol) in DMF
(5 mL) was added to a solution of 9,10-dimethylanthracene (0.516 g, 2.5 mmol) and
tetrabutylammonium periodate (1.625 g, 3.75 mmol) in CHCl3 (13 mL) at 5°C. This
solution was allowed to warm to room temperature, stirred for 24 h, poured into ethyl
acetate (100 mL) and washed with saturated sodium thiosulphate, brine and water. The
organic extract was dried over MgSO4 and filtered to give a crude yellow solid that was
purified by flash chromatography (5% EtOAc : 95% pet.ether, Rf = 0.38) to give an off
96
white solid 136 (0.6 g, 71%) with spectroscopic and analytical details identical to those
reported.70
Ethyl-6-((tert-butoxycarbonyl)(hydroxyl)amino)-2-((diphenylmethylene)amino)
hex-4-enoate (137). A solution of ethyl 2-((diphenylmethylene)amino)hex-5-enoate
(135, 2.65 g, 8.26 mmol) and 136 (0.696 g, 2.07 mmol) in toluene (5 mL) was heated
in a sealed tube to reflux for 4 h. The reaction mixture was cooled in an ice bath to
crystallize 9,10-DMA, which was filtered. The dark brown filtrate showed a crude
mixture of the excess alkene and a hydroxamic acid by TLC. The crude mixture was
purified by flash chromatography (25% EtOAc : 75% pet. ether, Rf = 0.26) to give 137
as a thick red liquid (0.417 g, 45%); 1H-NMR (CDCl3, 300 MHz) 7.63-7.02 (m, 10H),
5.64-5.49 (m, 2H), 4.22-4.09 (m, 4H), 3.98-3.96 (m, 1H), 2.71-2.57 (m, 2H), 1.47-1.44
(m, 10H), 1.28-1.23 (t, J = 7.14, 3H);
13
C-NMR (CDCl3, 500 MHz) 172.12, 171.16,
157.18, 139.83, 136.70, 130.91, 130.74, 129.27, 129.16, 129.03, 128.86, 128.41,
128.17, 128.12, 127.23, 82.20, 65.60, 61.33, 52.64, 37.01, 28.64, 28.59, 28.53, 14.55.
MS (ESI) m/z 453 (M)+.
97
Ethyl-6-((tert-butoxycarbonyl)(hydroxy)amino)-2-((diphenylmethylene)amino)
hexanoate (139). A solution of 137 (0.1 g, 0.22 mmol) in MeOH (20 mL) was slowly
added to 10 wt. % Pd/C (0.009 g) in a hydrogenation flask. This reaction mixture was
subjected to hydrogenation using a Parr-hydrogenator under 2.5 atm. pressure for 24 h.
The reaction mixture was filtered through celite and the filtrate concentrated to give a
crude mixture of hydroxamic acid products (TLC revealed two violet spots in FeCl3).
The crude product was purified by flash chromatography (25% EtOAc : 75% pet. ether,
Rf = 0.42) to give 139 as a thick red liquid (0.02 g, 20%); 1H-NMR (CDCl3, 500 MHz)
7.92-7.16 (m, 10H), 4.80 (s, 1H), 4.24-4.18 (q, J = 7.22Hz, 2H), 3.54-3.43 (m, 1H),
3.24-3.17 (m, 1H), 1.77-1.16 (m, 18H); 13C-NMR (CDCl3 , 500 MHz) 172.12, 171.17,
157.17, 139.84, 136.70, 130.90, 130.75, 129.16, 128.86, 128.41, 128.17, 128.12,
127.23, 82.21, 65.6, 61.33, 52.64, 37.01, 28.597, 14.54; MS (ESI) m/z 457 (M+2)+
98
Ethyl 2-amino-6-(hydroxyamino)hex-4-enoate (140). A solution of HCl (1.25M) in
MeOH (16 mL) was added to 139 (0.441 g, 1.33 mmol) and stirred at room temperature
for 12 h. The solution was concentrated under vacuum, dissolved in water (5 mL), and
extracted with diethyl ether (20 mL). The water layer was lyophilized to give 140 as a
dark brown liquid (0.076 g, 30%). 1H-NMR (MeOD, 300 MHz) 6.09-5.95 (m, 1H),
5.92-5.78 (m, 1H), 4.33 (q, J = 7.14, 2H), 4.2 (t, J = 6.3, 1H), 3.91-3.82 (m, 2H), 2.912.67 (m, 2H), 1.33 (t, J = 7.12, 3H);
13
C-NMR (CDCl3 , 300 MHz) 168.11, 133.77,
123.87, 63.68, 53.52, 53.21, 34.51, 14.83. MS (ESI) m/z 189 (M)+.
Ethyl 2-acetamido-6-((tert-butoxycarbonyl)(hydroxy)amino)hex-4-enoate (146). A
solution of ethyl 2-acetamidohex-5-enoate (145, 1.64 g, 8.24 mmol) and 136 (0.634 g,
2.059 mmol) in toluene (5 mL) was heated to reflux for 4 h in a sealed tube. The
reaction mixture was cooled in an ice bath to crystallize the 9, 10-DMA, which was
filtered. The reddish brown filtrate showed a crude mixture of the excess alkene and a
99
hydroxamic acid by TLC. The crude mixture was purified by flash chromatography
(1:1 EtOAc : pet. ether, Rf = 0.19) to yield 146 as a thick brown liquid (0.3 g, 45%);
1
H-NMR (CDCl3, 300 MHz) 6.18 (d, J = 7.85 Hz, 1H), 5.7-5.49 (m, 2H), 4.76-4.58 (m,
1H), 4.21 (q, J = 7.14 Hz, 1H), 4.11-3.9 (m, 2H) 2.69-2.55 (1H, m), 2.47-2.34 (m, 1H),
2.01 (s, 3H), 1.49 (s, 9H), 1.286 (t, J = 7.13 Hz, 3H);
13
C-NMR (CDCl3, 500 MHz)
172.13, 170.64, 157.10, 129.17, 128.57, 82.14, 62.05, 52.35, 52.22, 36.02, 28.66, 23.53,
14.52; HRMS (ESI) m/z (M+Na)+ 353.1689 Expected 330.3767.
Ethyl 2-acetamido-6-((tert-butoxycarbonyl)(hydroxy)amino)hexanoate (147). A
solution of 146 (0.175 g, 0.53 mmol) in MeOH (34 mL) was slowly added to 10 wt. %
Pd/C (0.02 g) in a hydrogenation flask. This reaction mixture was subjected to
hydrogenation using a Parr-hydrogenator under 2.5 atm. pressure for 24 h. The reaction
mixture was filtered through celite and the isolated extract gave pure product (147)
after solvent evaporation (0.172 g, 98%); 1H-NMR (CDCl3, 300 MHz) 6.22 (d, J = 8.08
Hz, 1H), 4.69-4.53 (m, 1H), 4.175 (q, J = 7.15 Hz, 2H), 3.61-3.35 (m, 2H), 2.02 (s,
3H), 1.94-1.32 (m, 15H), 1.27 (t, J = 7.13, 3H); 13C-NMR (CDCl3, 500 MHz) 172.85,
170.53, 157, 81.50, 61.66, 51.76, 49.71, 32.47, 28.47, 26.14, 23.24, 22.12, 14.28.
100
tert-Butyl-2-acetamidohex-5-enoate (149). A solution of 2-acetamidohex-5-enoic acid
(144, 0.495 g, 2.89 mmol)135 in dry toluene (20 mL) was added to N, N-dimethyl
formamide di-tert butyl acetal (2.78 mL, 11.608 mmol) at 80°C. The solution was
stirred at 80°C for 20 min and allowed to cool to room temperature.127 The reaction
mixture was concentrated under
reduced pressure and purified by flash
chromatography (1:1 EtOAc : pet.ether, Rf = 0.46) to give 149 as a colorless oil (0.48 g,
73%) that solidified in the freezer. 1H-NMR (CDCl3, 300 MHz) 6.02 (d, J = 7.42 Hz,
1H), 5.86-5.73 (m, 1H), 5.12-4.95 (m, 2H), 4.56-4.49 (m, 1H), 2.15-1.87 (m, 5H), 1.811.67 (m, 2H), 1.48 (s, 9H);
13
C-NMR (CDCl3, 300 MHz) 170.75, 168.64, 136.64,
115.10, 82.25, 52.76, 32.67, 32.6, 30.08, 28.74, 24.05. MS (ESI) m/z 227 (M)+.
tert-Butyl-2-acetamido-6-((tert-butoxycarbonyl)(hydroxyl)amino)hex-4-enoate
(150). A solution of tert-butyl-2-acetamidohex-5-enoate (149) (2.42 g, 10.68 mmol)
and 136 (0.9 g, 2.67 mmol) in toluene (5 mL) in a sealed tube was heated to reflux for 4
101
h. The reaction mixture was cooled in an ice bath to crystallize the 9,10-DMA, which
was filtered. The dark brown filtrate showed a crude mixture of the excess alkene and a
hydroxamic acid by TLC. The crude mixture was purified by flash chromatography
(1:1 EtOAc : pet. ether, Rf = 0.5) to yield 150 as a thick brown liquid ( 0.4 g, 41%); 1HNMR (CDCl3, 300 MHz) 6.18 (d, J = 7.63 Hz, 1H), 5.73-5.51 (m, 2H), 4.65-4.48 (m,
1H), 4.17-3.91 (m, 2H), 2.68-2.53 (m, 1H), 2.42-2.3 (m, 1H), 2.01 (s, 3H), 1.48 (s, 9H),
1.46 (s, 9H) ;
13
C-NMR (CDCl3, 300 MHz) 170.15, 169.51, 156.2, 128.38, 127.83,
82.73, 81.86, 52.87, 52.74, 36.5, 29.21, 28.89, 24.15; MS (ESI) m/z 391 (M+Na)+.
tert-Butyl 2-acetamido-6-(tertbutoxycarbonyl)(hydroxyamino)hexanoate (151). A
solution of 150 (0.458 g, 1.28 mmol) in MeOH (40 mL) was slowly added to 10 wt. %
Pd/C (0.051 g) in a hydrogenation flask. This reaction mixture was subjected to
hydrogenation using a Parr-hydrogenator under 2.5 atm. pressure for 24 h. The reaction
mixture was filtered through celite and the filtrate gave 151 after solvent evaporation
(0.455 g, 99%); 1H-NMR (CDCl3, 300 MHz) 6.12 (d, J = 8.11 Hz, 1H), 4.58-4.49 (m,
1H), 3.6-3.36 (m, 2H), 2.02 (s, 3H), 1.88-1.69 (m, 2H), 1.64-1.56 (m, 1H), 1.47-1.33
(m, 21H);
13
C-NMR (CDCl3, 300 MHz) 170.9, 169.29, 159.99, 82.35, 81.41, 52.42,
50.03, 33.29, 29.1, 28,74, 26.71, 24.03, 22.71; HRMS (ESI) m/z 383.2158 (M+Na)+
Expected 360.2260.
102
tert-Butyl-2-acetamido-6-(hydroxyamino)hexanoic acid (152). A solution of
TFA/CH2Cl2 (5.5mL / 5.5mL) was added to 151 (0.441g, 1.33 mmol) and stirred at
room temperature for 1.5 h. The solution was concentrated under vacuum, dissolved in
water (5mL), and extracted with diethyl ether (20mL). The water layer was lyophilized
to give 152 as a foamy brown solid (0.25 g, 92%); 1H-NMR (MeOD, 300 MHz) 4.5-4.4
(m, 1H), 3.29-3.23 (t, J = 7.67 Hz, 2H), 2.07-1.25 (m, 6H);
13
C-NMR (MeOD,
300MHz) 173.64, 172.06, 53.32, 51.84, 32.24, 24.37, 24.15, 22.68, HRMS (ESI) m/z
206.1561 (M+2)+ Expected (M)+ 204.1110, MS (ESI) m/z 204 (M)+, 260 (M+Fe)+.
tert-Butyl-2-acetamido-6-((tert-butoxycarbonyl)((tert-butyldimethylsilyl)oxy)
amino) hex-4-enoate (154). A solution of 150 (0.325 g, 0.91 mmol) in DMF (5 mL)
was added to a mixture of TBDMSCl (0.34 g, 2.26 mmol) and imidazole (0.306 g, 4.5
mmol).76 After stirring the reaction mixture overnight at 35°C, EtOAc (40 mL) was
added and the organic layer was washed with water and brine, dried over MgSO4 and
103
filtered to give a brown crude product that was purified by flash chromatography (25%
EtOAc :75% pet. ether, 0.3) to yield 154 as a colorless liquid (0.17g, 40%); 1H-NMR
(CDCl3, 500 MHz) 5.87 (d, J = 7.82 Hz, 1H), 5.56-5.47 (m, 1H), 5.41-5.31 (m, 1H),
4.43-4.41 (m, 1H), 3.88-3.69 (m, 2H), 2.40-2.35 (m, 2H), 1.89 (3H, s), 1.36-1.34 (m,
18H), 0.83 (s, 9H), 0.04 (s, 6H); 13C-NMR (CDCl3, 300 MHz) 170.866, 169.76, 158.45,
128.95, 128.42, 82.42, 81.71, 55.1, 52.39, 35.38, 28.58, 28.39, 26.18, 23.61, 18.04, 4.74; MS (ESI) m/z 497 (M+Na)+.
tert-Butyl-2-acetamido-6-((tert-butoxycarbonyl)((tert-butyldimethylsilyl)oxy)
amino) hexanoate (155). A solution of 154 (0.14 g, 0.296 mmol) in MeOH (20 mL)
was slowly added to 10 wt. % Pd/C (0.016 g) in a hydrogenation flask. This reaction
mixture was subjected to hydrogenation using a Parr-hydrogenator under 2.5 atm.
pressure for 24 h. The reaction mixture was filtered through celite and the filtrate
concentrated to give 155 (0.135 g, 96%) after solvent evaporation ; 1H-NMR (CDCl3,
300 MHz) 6.01 (d, J = 7.74 Hz, 1H), 4.50-4.44 (m, 1H), 3.42-3.37(m, 2H), 2.0 (s, 3H),
1.89-1.74 (m, 1H), 1.75-1.57 (m, 3H), 1.47 (s, 9H), 1.45 (s, 9H), 1.35-1.24 (m, 2H),
0.94 (s, 8H), 0.14 (s, 5H), 0.002 (s, 1H); 13C-NMR (CDCl3, 300 MHz) 170.73, 166.65,
104
157.04, 82.09, 81.17, 53.04, 53.04, 52.45, 33.06, 28.98, 28.73, 26.57, 24.02, 23.16,
18.64, -3.95; HRMS (ESI) m/z 497.3023 (M)+ expected 474.3125.
N-Hydroxytetradecanamide (158). A solution of KOH (4.49 g, 80 mmol) in EtOH
(50 mL) was added dropwise to a solution of hydroxylamine hydrochloride (2.64 g, 80
mmol) in EtOH (50 mL) at 0°C. This reaction mixture was stirred for 30min and ethyl
myristate (2.048 g, 8 mmol) in ethanol (25 mL) was added dropwise. After 4 h the
EtOH was removed under vacuum and water (30 mL) was added into it. The aqueous
solution was neutralized to pH 6 with 2N HCl and extracted with EtOAc : CHCl3
(150:150 mL). The organic layer was concentrtated under vacuum and purified by flash
chromatography (1:1 EtOAc : hexane, Rf = 0.44) to give 158 as a white flaky solid
(0.68 g, 35%); 1H-NMR (MeOD, 300 MHz) 2.08 (t, J = 7.57 Hz, 2H), 1.68-1.53 (m,
2H), 1.29 (b, 20H), 0.93-0.88 (m, 3H);
13
C-NMR (MeOD, 300 MHz) 171.50, 33.99,
33.27, 30.99, 30.85, 30.70, 30.63, 30.51, 30.41, 27.06, 24.04, 14.86.
105
1-(9,10-Dimethyl-9,10-dihydro-9,10-(epoxyimino)anthracen-11-yl)tetradecan-1one (159). A solution of 158 (0.329 g, 1.357 mmol) in DMF (5 mL) was added
dropwise to a solution of 9, 10-dimethylanthracene (0.7 g, 3.39 mmol) and Bu4NIO4
(0.644 g, 1.487 mmol) in CHCl3 (13 mL). The solution was stirred for 90 min and then
poured into a Na2S2O3 solution (20 mL) and extracted with EtOAc : CHCl3 (100:100
mL). The extracts were dried over MgSO4, concentrated under vacuum to a yellow
solid residue and purified by flash chromatography (silica gel, 5% EtOAc : 95%
pet.ether, Rf = 0.69) to give 159 as a white solid (0.35 g, 58%); 1H-NMR (CDCl3, 300
MHz) 7.47-7.41 (m, 2H), 7.37–7.32 (m, 2H), 7.26-7.20 (m, 4H), 2.7 (s, 3H), 2.21 (s,
3H), 2.13 (t, J = 7.36 , 2H), 1.24 (b, 22H), 0.89-0.85 (m, 3H); 13C-NMR (CDCl3, 300
MHz) 179.89, 141.35, 141.23, 127.56, 127.24, 121.51, 120.67, 79.65, 63.99, 36.50,
32.07, 29.82, 29.80, 29.75, 29.57, 29.55, 29.50, 29.15, 24.02, 22.84, 16.99, 15.23,
14.29; MS (ESI) m/z 446 (M)+.
106
tert-Butyl
2-acetamido-6-(N-hydroxyteradecanamido)hex-4-enoate
(160).
A
solution of tert-butyl 2-acetamidohex-5-enoate (149, 0.198 g, 0.88 mmol) and 159
(0.98 g, 0.22 mmol) in toluene (5 mL) in a sealed tube was heated to reflux for 4 h. The
reaction mixture was cooled in an ice bath to crystallize the 9,10-DMA, which was
filtered. The brown filtrate showed a crude mixture of the excess alkene and a
hydroxamic acid by TLC. The crude mixture was purified by flash chromatography
(eluted with a gradient of 1:1 EtOAc : pet.ether to 95% CHCl3 : 5% MeOH, Rf = 0.35
in EtOAc) to yield 160 as a brown liquid product (0.022 g, 23%); 1H-NMR (CDCl3,
500 MHz) 6.01-6.55 (m, 1H), 5.95-5.23 (m, 2H), 4.9-4.45 (m, 1H), 4.32-3.57 (m, 2H),
2.69-1.96 (m, 6H), 1.71-1.57 (m, 2H), 1.57-1.41 (m, 9H), 1.39-1.13 (m, 21H), 0.9 (t, J
= 6.8 Hz, 3H); 13C-NMR (CDCl3, 500 MHz) 175.98, 173.13, 171.05, 169.73, 130.25,
127.92, 127.02, 114.01, 82.57, 68.79, 52.378, 41.95, 41.18, 36.93, 36.093, 35.61, 32.06,
29.81, 29.79, 29.74, 29.61, 29.47, 29.38, 29.28, 28.23, 28.16, 26.68, 22.83, 14.26; MS
(ESI) m/z 467.5 (M)+.
107
tert-butyl 2-acetamido-6-(N-hydroxytetradecanamido)hexanoate (161). A solution
of 160 (0.015 g, 0.032 mmol) in MeOH (20 mL) was slowly added to 10 wt. % Pd/C
(0.003 g) in a hydrogenation flask. This reaction mixture was subjected to
hydrogenation using a Parr-hydrogenator under 2.5 atm. pressure for 24 h. The reaction
mixture was filtered through celite and the filtrate gave pure 161 after solvent
evaporation (0.016 g, 99%, Rf = 0.43 in EtOAc); 1H-NMR (CDCl3, 300 MHz) 6.5-5.92
(m, 1H), 4.68-4.23 (m, 1H), 3.79-3.41 (m, 2H), 2.70-1.92 (m, 6H), 1.91-1.01 (m, 34H),
0.96-0.73 (m, 5H); 13C-NMR (CDCl3, 300 MHz) 173.38, 171.75, 169.93, 82.14, 72.15,
52.3, 42.85, 31.89, 29,62, 29.45, 29.32, 29.22, 27.98, 22.66, 14.08.
tert-Butyl 2-acetamido-6-(N-((tert-butyldimethylsilyl)oxy)tetradecanamido) hex-4enoate (162). A solution of 160 (0.065 g, 0.128 mmol) in DMF (5 mL) was added to a
mixture of TBDMSCl (0.048 g, 0.32 mmol) and imidazole (0.044 g, 0.64 mmol).76
108
After stirring the reaction mixture overnight at 35°C, EtOAc (40 mL) was added and
the organic layer was washed with water and brine, dried over MgSO4, filtered and
concentrated under vacuum to give a brown crude product that was purified by flash
chromatography (silica gel, 50% EtOAc : 50% pet. ether, 0.23) to give 162 as a
yellowish liquid (0.22 g, 30%); 1H-NMR (CDCl3, 500 MHz) 6.023 (d, J = 7.9 Hz, 1H),
5.83-5.4 (m, 2H), 4.69-4.43 (m, 1H), 4.36-3.84 (m, 3H), 2.99-3.75 (m, 2H), 2.73-2.4
(m, 2H), 2.39-2.2 (m, 1H), 2.01 (s, 3H), 1.85-1.74 (m, 1H), 1.7-1.54 (m, 3H), 1.52-1.08
(m, 29H), 1.025-0.73 (8H), 0.213 (s, 3H), 0.0.15 (3H);
13
C-NMR (CDCl3, 500 MHz)
175.23, 174.78, 174. 21, 171.58, 171.04, 170.91, 169.75, 130.50, 128.48, 128.05,
128.035, 83.19, 82.37, 71.66, 71.30, 70.89, 55.71, 53.82, 53.09, 52.13, 38.51, 38.19,
37.33, 35.24, 34.28, 33.21, 32.78, 32.485, 32.06, 29.83, 29.79, 29.66, 29.58, 29.56,
29.5, 29.46, 28.50, 28.16, 28.12, 25.89, 25.79, 23.36, 22.84, 22.6, 19.98, 14.8, 14.28,
13.96, 0.14, -3.43, -4.49; MS (ESI) m/z 583 (M)+.
N-(cyclohex-2-en-1-yl)-N-hydroxytetradecanamide (163). A solution of cyclohexene
(5 mL) and 159 (0.2 g, 0.45 mmol) was heated in a sealed tube to reflux for 4 h. The
reaction mixture was cooled in an ice bath to crystallize the 9,10-DMA, which was
filtered. The filtrate showed a crude mixture of the excess alkene and a hydroxamic
acid by TLC (purple spot in FeCl3).
The crude mixture was purified by flash
chromatography (25% EtOAc: 75% pet.ether, Rf = 0.0.63 ) to yield 163 as a reddish
white solid (0.048 g, 33%); 1H-NMR (CDCl3, 300 MHz) 6.00 (d, J = 8.53 Hz, 1H),
109
5.58 (d, J = 8.52 Hz, 1H), 4.45 (b, 1H), 2.55-2.33 (m, 1H), 2.23-1.8 (m, 5H), 1.77-1.61
(m, 3H), 1.43-1.17 (m, 20H), 1.00-0.833 (m, 4H);
13
C-NMR (CDCl3, 300 MHz)
172.57, 169.92, 167.47, 141.03, 132.31, 131.19, 127.96, 126.02, 125.18, 71.73, 70.06,
55.04, 53.37, 46.37, 44.55, 34.66, 31.91, 29.64, 29.49, 29.35, 26.85, 25.56, 24.22,
22.67, 21.05, 14.1 MS (ESI) m/z 324 (M+1)+.
1-(9,10-Dimethyl-9,10-dihydro-9,10-(epoxyimino)anthracen-11-yl)ethanone
(164)
A solution of acetohydroxamic acid (0.437 g, 5.82 mmol) in DMF (5 mL) was added
dropwise to a solution of 9, 10-dimethylanthracene (0.8 g, 3.88 mmol) and Bu4NIO4
(0.644 g, 5.82 mmol) in CHCl3 (30 mL). The solution was stirred for 90 min and then
poured into a Na2S2O3 solution (20 mL) and extracted with EtOAc:CHCl3 (200:200
mL). The extracts were dried over MgSO4, concentrated under vacuum to a solid
residue and purified by flash chromatography (25% EtOAc :75% pet.ether, Rf = 0.5) to
give 164 as a white solid (0.852 g, 52%) with spectroscopic and analytical details were
identical to those reported.70
110
tert-Butyl 2-acetamido-6-(N-hydroxyacetamido)hex-4-enoate (165). A solution of
tert-butyl 2-acetamidohex-5-enoate (0.88 g, 3.88 mmol) and 164 (0.255 g, 0.97 mmol)
in toluene (5 mL) was heated in a sealed tube to reflux for 4 h. The reaction mixture
was cooled down in an ice bath to crystallize the 9,10-DMA and it was filtered. The
filtrate showed a crude mixture of the excess alkene and a hydroxamic acid by TLC
(purple spot in FeCl3 stain due to the presence of hydroxamic acid). The crude mixture
was purified by flash chromatography (a gradient of 1:1 EtOAc: pet.ether to 5% MeOH
in CHCl3, Rf = 0.20 in EtOAc) to yield 165 as a thick brown oil (0.084 g, 29%); 1HNMR (500 MHz, CDCl3) 6.11 (d, J =7.69 Hz, 1H), 5.69-5.50 (m, 2H), 4.89-4.37 (m,
2H), 4.23-4.04 (m, 1H), 2.77-2.43 (m, 1H), 2.36-1.91(m, 7H), 1.48 (s, 9H) ; 13C-NMR
(CDCl3, 300 MHz) 169.96, 169.90, 168.89, 128.89, 128.39, 127.30,125.53, 82.57,
52.61, 35.88, 29.96, 24.13, 21.35, 19.47; MS (ESI) m/z 323 (M+Na)+.
tert-Butyl-2-acetamido-6-(N-((tert-butyldimethylsilyl)oxy)acetamido)hex-4-enoate
(166) A solution of 165 (0.075 g, 0.25 mmol) in DMF (5 mL) was added to a solid
111
mixture of TBDMSCl (0.112 g, 0.75 mmol) and imidazole (0.102 g, 1.5 mmol). After
stirring the reaction mixture overnight at 35°C, EtOAc (40 mL) was added to dilute it.
The organic layer was washed with water and brine, dried over MgSO4 , filtered and
concentrated under vacuum to give a brown crude product that was purified by flash
chromatography (95% CHCl3 : 5% pet. ether, Rf = 0.53) to yield 166 as a yellow liquid
(0.035 g, 33%); 1H-NMR (CDCl3, 300 MHz) 6.04 (d, J = 6.56 Hz, 1H), 5.63-5.44 (m,
2H), 4.59-4.46 (m, 1H), 4.2-3.95 (m, 2H), 2.65-2.44 (m, 2H), 2.08-2.01 (m, 6H), 1.47
(s, 9H), 0.97 (s, 9H), 0.22 (m, 5H), 0.013 (s, 1H);
13
C-NMR (CDCl3, 300 MHz)
170.31, 169.90, 168.8, 127.76, 127.69, 82.42, 60.86, 52.61, 35.88, 30.55, 28.91, 26.64,
24.12, 22.32, 22.00, 18.83, 15.25, -3.29, -3.38, MS (ESI) m/z 414 (M)+.
(9,10-Dimethyl-9,10-dihydro-9,10-(epoxyimino)anthracen-11-yl)(phenyl)
methanone (167) A solution of benzohydroxamic acid (0.559 g, 4.08 mmol) in DMF
(5 mL) was added dropwise to a solution of 9, 10-dimethylanthracene (0.56 g, 2.72
mmol) and Bu4NIO4 (1.77 g, 4.08 mmol) in CHCl3 (20 mL). The solution was stirred
for 90 min and then poured into a Na2S2O3 solution (20 mL) and extracted with EtOAc
(200 mL). The extracts were dried over MgSO4, filtered, concentrated under vacuum to
give a solid residue that was purified by flash chromatography (5% EtOAc : 95%
pet.ether, Rf = 0.5) to give 167 as a white solid ( 0.528 g, 38%) with spectroscopic and
analytical details were identical to those reported.70
112
tert-Butyl 2-acetamido-6-(N-hydroxybenzamido)hex-4-enoate (168). A solution of
tert-butyl 2-acetamidohex-5-enoate (149, 0.687 g, 3.026 mmol) and 167 (0.258 g, 0.75
mmol) in toluene (5 mL) was heated in a sealed tube to reflux for 4 h. The reaction
mixture was cooled in an ice bath to crystallize 9,10-DMA, which was filtered. The
filtrate showed a crude mixture of the excess alkene and a hydroxamic acid by TLC
(purple spot in FeCl3 due to presence of hydroxamic acid). The crude mixture was
concentrated under vacuum and purified by flash chromatography (gradient of 1:1
EtOAc: pet.ether to 5% MeOH in CHCl3, Rf = 0.34 in EtOAc) to yield 168 as a thick
brown liquid (0.049 g, 20%); 1H-NMR (CDCl3, 500 MHz) 8.20-7.8 (m, 1H), 7.73-7.33
(m, 4H), 6.47-5.98 (b, 1H), 5.95-5.25 (m, 2H), 4.73-3.97 (m, 2H), 3.87-3.36 (m, 1H),
1.98 (s, 3H), 1.55-1.069 (m, 10H), 0.97-0.76 (m, 1H) MS (ESI) m/z 361.5 (M)+.
113
CHAPTER 4
SUMMARY
To summarize, this dissertation shows a detailed study of developing methods towards
the synthesis of cyclic hydroxamic acids and its application to cobactin synthesis. The
first stage of the research project featured the development of synthetic methodology
towards making cyclic hydroxamic acids from cyclic ketones by –NOH insertion and the
mechanistic details of this method. Basic decomposition of Piloty’s acid in presence of
cyclic ketones yields cyclic hydroxamic acids (mainly five and six membered) in 20-69%
yield with stoichiometric increase in Piloty’s acid amounts. Piloty’s acid-based
rearrangement reaction with two unsymmetric bicyclic ketones (90 and 91, Scheme 44)
reveals the regioselective nature of the reaction as the –NOH insertion always happens
from the most substituted side of the substrate ketones. The reaction is stereoselective in
nature as the syn configuration of the substrates (90, Scheme 44) retained after the –NOH
insertion. Mechanistic studies show that the –NOH insertion reaction involves a C-nitroso
intermediate (98). The C-nitroso intermediate can be generated by the hydrolysis of
acyloxy nitroso compound (103, Scheme 51) forming the N-hydroxypiperidone in 75%
yield. This discovery is seminal to perform an efficient synthesis of cyclic hydroxamic
acids (five and six membered) and could serve as a potential alternative of Piltoy’s acid
based -NOH insertion reaction. Piloty’s acid-based –NOH insertion did not work with αsubstituted ketones and failed to generate seven membered rings like cobactin. However,
hydrolysis of acyloxy nitroso intermediate generated from α-methyl cyclopentanones
114
(107, Scheme 53) makes the ring-expanded product in 78% yield. Overall, –NOH
insertion fails to generate cobactin, still it is widely applicable to synthesize weinreb
amides, selective oxoaminated products and could be vastly useful to make various
amino acids and diverse group of hydroxylamines.
The second part of the developmental research featured the general application of
intramolecular and intermolecular nitroso-ene reactions to make various hydroxamic
acids based structures and their potential uses in the synthesis of siderophore mycobactin
S. Intramolecular nitroso-ene reaction of acyl-nitroso species derived from 6-hexenoic
hydroxamic acid (120, Scheme 59) failed to generate any cyclized product, while the two
carbon homologous acyl nitroso species (124, Scheme 61) derived from (Z)-NHydroxyoct-6-enamide (126, Scheme 61) gave an unprecedented eight membered ring
hydroxamic acid (127, Scheme 61). The next developmental stage of this project was
exploring inter-molecular nitroso-ene reactions between model alkene 149 and acyl
nitroso precursor 136 towards generating the key intermediate N€-hydroxy lysine (152,
Scheme 68). Unfortunately, the key intermediate 152 failed to produce cobactin core
after DCC-DMAP coupled cyclization. The long chain hydroxamic residue of
mycobactin, mycobactic acid synthesis was approached using this nitroso-ene technology
with the model alkene 149 and a long chain-derived acyl nitroso precursor (159, Scheme
70). This method successfully generated the key intermediate 161 which can be useful to
make mycobactic acid. Nitroso-ene reactions of acyl nitroso and benzoyl nitroso species
with the model alkene 149 to produce the corresponding linear unsaturated hydroxamic
acids in 29% and 20% yields.
115
Overall, this research establishes a new method to make cyclic hydroxamic acids using –
NOH insertion technique into cyclic ketones, its potential synthetic applications and
utilization of nitroso-ene reactions to build hydroxamic acid components of siderophore
Mycobactin S.
116
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APPENDIX A
CRYSTAL STRUCTURE ANALYSIS REPORT AND TABLES FOR COMPOUND
C5H9NO2 (85)
Wake Forest X-Ray Facility Reference Code a52m
Performed by Dr. Cynthia Day
Wake Forest University
136
EXPERIMENTAL
Colorless rectangular-parallelepiped-shaped crystals of C5H9NO2 are, at 193(2)
K, orthorhombic, space group Pbca – D 15
2h (No. 61) (1) with a = 15.900(3) Å, b =
7.187(1) Å, c = 19.995(4) Å, V = 2284.9(8) Å3 and Z = 16 molecules {dcalcd = 1.339
g/cm3; a(MoK  ) = 0.103 mm-1}.
A full hemisphere of diffracted intensities (1868
20-second frames with a  scan width of 0.30) was measured for a single-domain
specimen using graphite-monochromated MoK radiation (= 0.71073 Å) on a Bruker
SMART APEX CCD Single Crystal Diffraction System (2). X-rays were provided by
a fine-focus sealed x-ray tube operated at 50kV and 30mA. Lattice constants were
determined with the Bruker SAINT software package using peak centers for 5101
reflections. A total of 21446 integrated reflection intensities having 2((MoK  )<
58.70 were produced using the Bruker program SAINT(3); 3116 of these were unique
and gave Rint = 0.058 with a coverage which was 99.6% complete. The relative
transmission factors ranged from 0.966 to 0.990.
The Bruker software package
SHELXTL was used to solve the structure using “direct methods” techniques. All
stages of weighted full-matrix least-squares refinement were conducted using Fo2 data
with the SHELXTL Version 6.12 software package(4).
The final structural model incorporated anisotropic thermal parameters for all
nonhydrogen atoms and isotropic thermal parameters for all hydrogen atoms.
Hydroxyl hydrogen atoms were located from a difference Fourier map and refined as
independent isotropic atoms. The remaining hydrogen atoms were included into the
structural model as idealized atoms (assuming sp3-hybridization of the carbon atoms
and C-H bond lengths of 0.99 Å). The isotropic thermal parameters for H2O and H4O
refined to final values of 0.069(5) and 0.066(5)Å2, respectively. The isotropic thermal
parameters of the remaining hydrogen atoms were fixed at values 1.2 times the
equivalent isotropic thermal parameter of the carbon atom to which they are covalently
bonded.
One of the two independent molecules shows disorder involving two of the ring
carbon atoms with two orientations in the crystal; the major orientation is adopted 71
137
% of the time and the minor orientation is adopted 29 % of the time. The major (71%)
orientation is specified by carbon atoms C8 and C9 and hydrogen atoms H7A, H7B, H8A,
H8B, H9A, H9B, H10A and H10B; the minor (29%) orientation is specified by carbon
atoms C8’ and C9’ and hydrogen atoms H7C, H7D, H8’A, H8’B, H9’A, H9’B, H10C and H10D,
respectively.
A total of 172 parameters were refined using no restraints, 3116 data and weights
of w = 1/ [2(F2) + (0.0816 P)2], where P = [Fo2 + 2Fc2] / 3. Final agreement factors
at convergence are:
R1(unweighted, based on F) = 0.048 for 2332 independent
“observed” reflections having 2(MoK  )< 58.70 and I>2(I); R1(unweighted,
based on F) = 0.062 and wR2(weighted, based on F2) = 0.130 for all 3116 independent
reflections having 2(MoK  )< 58.70. The largest shift/s.u. was 0.000 in the final
refinement cycle. The final difference map had maxima and minima of 0.30 and -0.16
e-/Å3, respectively.
Acknowledgment
The authors thank the National Science Foundation (grant CHE-0234489) for
funds to purchase the x-ray instrument and computers.
References
(1) International Tables for Crystallography, Vol A, 4th ed., Kluwer: Boston (1996).
(2) Data Collection: SMART Software Version 5.628 (2002). Bruker-AXS, 5465 E.
Cheryl Parkway, Madison, WI 53711-5373 USA.
(3) Data Reduction: SAINT Software Version 6.36a (2002). Bruker-AXS, 5465 E.
Cheryl Parkway, Madison, WI 53711-5373 USA.
(4) G. M. Sheldrick (2000). SHELXTL Version 6.12 Reference Manual. Bruker-AXS,
5465 E. Cheryl Parkway, Madison, WI 53711-5373 USA.
138
Table 1. Crystal data and structure refinement for C5H9NO2
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a52m2m
C5 H9 N O2
115.13
193(2) K
0.71073 Å
Orthorhombic
Pbca – D 15
(No. 61)
2h
Unit cell dimensions
a = 15.900(3) Å
b = 7.187(1) Å
c = 19.995(4) Å
2284.9(8) Å3
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 29.35°
Absorption correction
Max. and min. transmission
Refinement method
Data / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
16
1.339 g/cm3
0.103 mm-1
992
0.34 x 0.13 x 0.10 mm3
3.82 to 29.35°
-20≤h≤21, -9≤k≤9, -27≤l≤27
21446
3116 [R(int) = 0.0576]
99.6 %
None
0.9897 and 0.9657
Full-matrix least-squares on F2
3116 / 172
0.980
R1 = 0.0478, wR2 = 0.1214
R1 = 0.0620, wR2 = 0.1295
0.304 and -0.165 e-/Å3
--------------------------------------------------------------------------------------------------------R1 =  ||Fo| - |Fc|| /  |Fo|
wR2 = {  [w(Fo2 - Fc2)2] /  [w(Fo2)2] }1/2
139
Table 2. Atomic coordinates (x 104) and equivalent isotropic displacement parameters
(Å2x 103) for C5H9NO2. U(eq) is defined as one third of the trace of the
orthogonalized Uij tensor.
______________________________________________________________________
x
y
z
U(eq)
______________________________________________________________________
O(1)
771(1)
-1432(1)
1876(1)
51(1)
O(2)
1634(1)
441(1)
958(1)
42(1)
N(1)
1448(1)
1205(1)
1583(1)
32(1)
C(1)
1045(1)
131(2)
2020(1)
33(1)
C(2)
1867(1)
2964(2)
1714(1)
45(1)
C(3)
1534(1)
3864(2)
2342(1)
58(1)
C(4)
1473(1)
2487(2)
2905(1)
50(1)
C(5)
899(1)
926(2)
2704(1)
44(1)
O(3)
656(1)
1986(1)
69(1)
38(1)
O(4)
-278(1)
3562(1)
-876(1)
45(1)
N(2)
-609(1)
3080(1)
-254(1)
36(1)
C(6)
-95(1)
2329(2)
193(1)
31(1)
C(7)
-1490(1)
3599(2)
-171(1)
47(1)
C(8)
-1727(1)
3574(3)
593(1)
50(1)
C(9)
-1378(1)
1853(4)
925(1)
45(1)
C(10)
-458(1)
1901(2)
872(1)
38(1)
C(8')
-1920(3)
2496(7)
316(2)
40(1)
C(9')
-1411(3)
2866(10)
928(3)
41(1)
______________________________________________________________________
140
Table 3. Bond lengths [Å] and angles [°] for C5H9NO2
______________________________________________________________________
O(1)-C(1)
1.239(1)
O(3)-C(6)
1.245(1)
O(2)-N(1)
1.397(1)
O(4)-N(2)
1.394(1)
O(2)-H(2O)
0.88(2)
O(4)-H(4O)
0.87(2)
N(1)-C(1)
N(1)-C(2)
1.329(2)
1.453(2)
N(2)-C(6)
N(2)-C(7)
1.325(2)
1.459(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
1.501(2)
1.508(2)
1.501(2)
1.502(2)
C(6)-C(10)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
1.506(2)
1.572(3)
1.510(3)
1.467(3)
C(7)-C(8')
C(8')-C(9')
1.430(5)
1.492(7)
C(10)-C(9')
1.670(6)
N(1)-O(2)-H(2O)106.4(12)
N(2)-O(4)-H(4O)
105.7(12)
C(1)-N(1)-O(2) 117.46(10)
C(1)-N(1)-C(2) 127.41(10)
O(2)-N(1)-C(2) 113.98(9)
C(6)-N(2)-O(4)
C(6)-N(2)-C(7)
O(4)-N(2)-C(7)
118.00(10)
128.25(11)
113.62(10)
O(1)-C(1)-N(1)
O(1)-C(1)-C(5)
N(1)-C(1)-C(5)
N(1)-C(2)-C(3)
C(4)-C(3)-C(2)
C(3)-C(4)-C(5)
C(1)-C(5)-C(4)
O(3)-C(6)-N(2)
O(3)-C(6)-C(10)
N(2)-C(6)-C(10)
N(2)-C(7)-C(8)
C(9)-C(8)-C(7)
C(10)-C(9)-C(8)
C(9)-C(10)-C(6)
122.47(11)
120.49(11)
117.04(11)
109.75(12)
110.38(18)
108.4(2)
116.85(13)
122.96(11)
120.10(11)
116.90(10)
111.24(11)
111.34(13)
109.32(12)
115.72(11)
C(8')-C(7)-N(2) 113.3(2)
C(7)-C(8')-C(9') 101.5(4)
____________________________
C(8')-C(9')-C(10)
111.3(4)
C(6)-C(10)-C(9')
108.9(2)
____________________________
141
Anisotropic displacement parameters (Å2x 103) for C5H9NO2. The
anisotropic displacement factor exponent takes the form: -22[ h2 a*2U11 + ... + 2 h
k a* b* U12 ]
Table 4.
___________________________________________________________________
U11
U22
U33
U23
U13
U12
___________________________________________________________________
O(1) 70(1)
38(1)
46(1)
-6(1)
5(1)
-18(1)
O(2) 40(1)
55(1)
30(1)
0(1)
3(1)
10(1)
N(1) 31(1)
36(1)
29(1)
1(1)
1(1)
-1(1)
C(1) 33(1)
31(1)
35(1)
1(1)
0(1)
-2(1)
C(2) 47(1)
38(1)
49(1)
8(1)
1(1)
-11(1)
C(3) 70(1)
36(1)
69(1)
-9(1)
3(1)
-11(1)
C(4) 54(1)
53(1)
43(1)
-14(1)
0(1)
-6(1)
C(5) 55(1)
42(1)
36(1)
-4(1)
9(1)
-8(1)
O(3) 36(1)
42(1)
35(1)
-1(1)
2(1)
1(1)
O(4) 63(1)
41(1)
31(1)
5(1)
-4(1)
-11(1)
N(2) 42(1)
33(1)
33(1)
2(1)
-2(1)
-1(1)
C(6) 37(1)
24(1)
31(1)
-5(1)
-2(1)
-3(1)
C(7) 42(1)
41(1)
59(1)
3(1)
-10(1)
8(1)
C(8) 43(1)
54(1)
53(1)
4(1)
1(1)
19(1)
C(9) 37(1)
49(1)
49(1)
10(1)
5(1)
7(1)
C(10) 42(1)
39(1)
31(1)
-1(1)
2(1)
1(1)
C(8') 33(2)
44(3)
45(3)
-8(2)
-3(2)
-2(2)
C(9') 36(3)
43(3)
44(3)
0(3)
7(2)
9(3)
___________________________________________________________________
142
Table 5. Hydrogen coordinates (x 104) and isotropic displacement parameters (Å2x
10 3) for C5H9NO2.
______________________________________________________________________
x
y
z
U(eq)
______________________________________________________________________
H(2O)
1288(12)
970(30)
672(9)
69(5)
H(2A)
1780
3812
1331
54
H(2B)
2479
2747
1762
54
H(3A)
1911
4895
2475
70
H(3B)
971
4394
2252
70
H(4A)
1251
3109
3310
60
H(4B)
2038
1990
3010
60
H(5A)
957
-90
3035
53
H(5B)
311
1379
2727
53
H(4O)
-458(11)
2720(30)
-1152(8)
66(5)
H(7A)
-1852
2714
-418
57
H(7B)
-1585
4859
-356
57
H(7C)
-1521
4923
-36
57
H(7D)
-1780
3471
-606
57
H(8A)
-1497
4697
814
60
H(8B)
-2347
3596
642
60
H(9A)
-1548
1820
1401
54
H(9B)
-1600
724
703
54
H(10A)
-238
677
1017
45
H(10B)
-245
2843
1191
45
H(10C)
-87
2405
1226
45
H(10D)
-501
537
934
45
H(8'A)
-1912
1160
196
48
H(8'B)
-2510
2908
373
48
H(9'A)
-1707
2359
1324
49
H(9'B)
-1351
4226
991
49
______________________________________________________________________
143
Table 6. Torsion angles [°] for C5H9NO2
________________________________________________________________
O(2)-N(1)-C(1)-O(1)
-6.27(17)
C(2)-N(1)-C(1)-O(1)
-173.16(12)
O(2)-N(1)-C(1)-C(5)
176.17(10)
C(2)-N(1)-C(1)-C(5)
9.27(18)
C(1)-N(1)-C(2)-C(3)
-22.01(18)
O(2)-N(1)-C(2)-C(3)
170.71(11)
N(1)-C(2)-C(3)-C(4)
46.37(17)
C(2)-C(3)-C(4)-C(5)
-59.18(17)
O(1)-C(1)-C(5)-C(4)
160.80(13)
N(1)-C(1)-C(5)-C(4)
-21.57(18)
C(3)-C(4)-C(5)-C(1)
46.40(18)
O(4)-N(2)-C(6)-O(3)
-2.47(16)
C(7)-N(2)-C(6)-O(3)
-178.17(12)
O(4)-N(2)-C(6)-C(10)
177.28(9)
C(7)-N(2)-C(6)-C(10)
1.58(18)
C(6)-N(2)-C(7)-C(8')
-28.4(3)
O(4)-N(2)-C(7)-C(8')
155.8(2)
C(6)-N(2)-C(7)-C(8)
13.0(2)
O(4)-N(2)-C(7)-C(8)
-162.85(13)
N(2)-C(7)-C(8)-C(9)
-44.4(2)
C(7)-C(8)-C(9)-C(10)
61.8(3)
C(8)-C(9)-C(10)-C(6)
-48.1(3)
O(3)-C(6)-C(10)-C(9)
-163.59(17)
N(2)-C(6)-C(10)-C(9)
16.7(2)
O(3)-C(6)-C(10)-C(9')
169.6(3)
N(2)-C(6)-C(10)-C(9')
-10.1(3)
N(2)-C(7)-C(8')-C(9')
59.2(4)
C(7)-C(8')-C(9')-C(10)
-69.3(5)
C(6)-C(10)-C(9')-C(8')
46.0(5)
________________________________________________________________
144
Table 7. Hydrogen bonds for C5H9NO2 [Å and °]
______________________________________________________________________
D-H...A
d(D-H)
d(H...A)
d(D...A)
<(DHA)
______________________________________________________________________
O(2)-H(2O)...O(3)
0.88(2)
1.73(2)
2.6101(13)
176.3(18)
O(4)-H(4O)...O(1)#1 0.868(18)
1.789(18)
2.6383(14)
165.4(18)
______________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x,-y,-z
145
APPENDIX B
CRYSTAL STRUCTURE ANALYSIS REPORT AND TABLE FOR COMPOUND
C4H7NO2
Wake Forest X-Ray Facility Reference Code: a66n-2008
Performed by Dr. Cynthia Day
Wake Forest University
146
EXPERIMENTAL
Colorless single crystals of C4H7NO2 are, at 193(2) K, monoclinic, space group
P21/n (an alternate setting of P21/c – C 52h (No. 14)) with a = 10.471(1) Å, b = 7.0758(9)
Å, c = 12.929(2) Å, β = 95.461(2)° , V = 953.6(2) Å3, and Z = 8 {dcalcd = 1.409gcm-3;
μa(MoK  ) = 0.113 mm-1}. A full hemisphere of diffracted intensities (1968 30-second
frames with an  scan width of 0.30) was measured for a single-domain specimen
using graphite-monochromated MoK  radiation (= 0.71073 Å) on a Bruker SMART
APEX CCD Single Crystal Diffraction System. X-rays were provided by a fine-focus
sealed x-ray tube operated at 50kV and 30mA.
Lattice constants were determined with the Bruker SAINT software package
using peak centers for 4024 reflections having 7.82˚ ≤ 2θ ≤ 60.01˚. A total of 9994
integrated reflection intensities having 2((MoK  )≤ 60.10 were produced using the
Bruker program SAINT; 2756 of these were unique and gave Rint = 0.033 with a
coverage which was 98.7% complete. The data were corrected empirically (SADABS)
for variable absorption effects using equivalent reflections; the transmission factors
ranged from 0.8179 to 0.8925.
The Bruker software package SHELXTL was used to solve the structure using
“direct methods” techniques.
All stages of weighted full-matrix least-squares
refinement were conducted using Fo2 data with the SHELXTL Version 6.12 software
package. The resulting structural parameters have been refined to convergence {R1
(unweighted, based on F) = 0.0465 for 2330 independent reflections having 2Θ(MoK  ) <
60.10o and F2>2σ(F2)} {R1 (unweighted, based on F) = 0.0530 and wR2 (weighted, based
on F2) = 0.1261 for all 2756 reflections} using counter-weighted full-matrix least-squares
techniques and a structural model which incorporated anisotropic thermal parameters for
all nonhydrogen atoms. Hydrogen atoms were located from a difference Fourier map and
refined as independent isotropic atoms whose parameters were allowed to vary in leastsquares refinement cycles. A total of 183 parameters were refined using no restraints
and 2756 data. The largest shift/s.u. was 0.000 in the final refinement cycle. The final
147
3
difference map had maxima and minima of 0.405 and -0.199 e-/Å , respectively.
Acknowledgment
The authors thank the National Science Foundation (grant CHE-0234489) for
funds to purchase the x-ray instrument and computers.
References
(5) International Tables for Crystallography, Vol A, 4th ed., Kluwer Academic
Publishers: Boston (1996).
(6) Data Collection: SMART (Version 5.628) (2002). Bruker-AXS, 5465 E. Cheryl
Parkway, Madison, WI 53711-5373 USA.
(7) Data Reduction: SAINT (Version 6.36A) (2003). Bruker-AXS, 5465 E. Cheryl
Parkway, Madison, WI 53711-5373, USA.
(8) G. M. Sheldrick (2006). SADABS-2006/3. BRUKER AXS Inc., 5465 East Cheryl
Parkway, Madison, WI 53711-5373 USA
(9) G. M. Sheldrick (2001). SHELXTL (Version 6.12). Bruker-AXS, 5465 E. Cheryl
Parkway, Madison, WI 53711-5373 USA.
148
Table 1. Crystal data and structure refinement for C4H7NO2
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a66n2m
C4 H7 N O2
101.11
193(2) K
0.71073 Å
Monoclinic
P21/n (an alternate setting of P21/c – C 52h
(No. 14))
Unit cell dimensions
a = 10.4711(13) Å
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 30.05°
Absorption correction
Max. and min. transmission
Refinement method
Data / parameters
Goodness-of-fit on F2
Final R indices [2330 I>2σ(I)]
R indices (all 2756 data)
Largest diff. peak and hole
b = 7.0758(9) Å, β = 95.461(2)°
c = 12.9288(16) Å
953.6(2) Å3
8
1.409 g/cm3
0.113 mm-1
432
0.26 x 0.21 x 0.06 mm3
3.91 to 30.05°
-14≤h≤14, -9≤k≤9, -18≤l≤17
9994
2756 [R(int) = 0.0328]
98.7 %
Multi-scan (SADABS)
0.9932 and 0.9712
Full-matrix least-squares on F2
2756 / 183
1.032
R1 = 0.0465, wR2 = 0.1199
R1 = 0.0530, wR2 = 0.1261
0.405 and -0.199 e- /Å3
-----------------------------------------------------------------------------------------------------------------------R1 =  ||Fo| - |Fc|| /  |Fo|
2
2 2
2 2
wR2 = {  [w(Fo - Fc ) ] /  [w(Fo ) ] }
1/2
149
Table 2. Atomic coordinates
a,b
( x 104) and equivalent isotropic displacement
parameters (Å2x 103) for C4H7NO2
a
b
______________________________________________________________________
x
y
z
U(eq) c
______________________________________________________________________
O(1A)
5748(1)
2949(1)
5550(1)
34(1)
O(2A)
3323(1)
1280(1)
5476(1)
37(1)
N(1A)
3885(1)
2008(1)
4637(1)
31(1)
C(1A)
5070(1)
2692(1)
4719(1)
28(1)
C(2A)
3312(1)
1639(2)
3588(1)
36(1)
C(3A)
4136(1)
2903(2)
2956(1)
35(1)
C(4A)
5412(1)
3080(2)
3632(1)
32(1)
O(1B)
1813(1)
3593(1)
6404(1)
40(1)
O(2B)
2043(1)
5393(1)
4507(1)
36(1)
N(1B)
1552(1)
6200(1)
5360(1)
31(1)
C(1B)
1414(1)
5212(2)
6218(1)
30(1)
C(2B)
912(1)
8021(2)
5273(1)
34(1)
C(3B)
689(1)
8398(2)
6407(1)
38(1)
C(4B)
661(1)
6436(2)
6897(1)
37(1)
______________________________________________________________________
The numbers in parentheses are the estimated standard deviations in the last
significant digit.
Atoms are labeled in agreement with Figures 1 and 2.
c
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
150
Table 3. Bond lengths [Å] and angles [°] for C4H7NO2
a,b
___________________________________________________________________
O(1B)-C(1B)
1.2356(14)
O(1A)-C(1A)
1.2433(12)
O(2B)-N(1B)
1.3830(11)
O(2A)-N(1A)
1.3820(11)
O(2B)-H(2B)
0.887(18)
O(2A)-H(2A)
0.873(19)
N(1B)-C(1B)
1.3309(13)
N(1A)-C(1A)
1.3267(14)
N(1B)-C(2B)
1.4519(14)
N(1A)-C(2A)
1.4527(14)
C(1B)-C(4B)
1.5070(15)
C(1A)-C(4A)
1.5081(14)
C(2B)-C(3B)
1.5306(16)
C(2A)-C(3A)
1.5315(16)
C(2B)-H(2B1)
0.957(16)
C(2A)-H(2A1)
0.981(15)
C(2B)-H(2B2)
0.992(15)
C(2A)-H(2A2)
0.984(16)
C(3A)-C(4A)
C(3A)-H(3A1)
C(3A)-H(3A2)
C(4A)-H(4A1)
C(4A)-H(4A2)
1.5310(16)
0.979(16)
0.995(16)
0.980(16)
0.965(14)
C(3B)-C(4B)
C(3B)-H(3B1)
C(3B)-H(3B2)
C(4B)-H(4B1)
C(4B)-H(4B2)
1.5270(17)
0.974(16)
1.022(18)
0.989(17)
0.89(2)
N(1A)-O(2A)-H(2A) 103.7(12)
N(1B)-O(2B)-H(2B)
102.6(11)
C(1A)-N(1A)-O(2A) 122.53(9)
C(1A)-N(1A)-C(2A) 116.12(9)
O(2A)-N(1A)-C(2A) 119.80(9)
C(1B)-N(1B)-O(2B)
C(1B)-N(1B)-C(2B)
O(2B)-N(1B)-C(2B)
121.76(9)
116.40(9)
120.54(8)
O(1A)-C(1A)-N(1A) 125.16(9)
O(1A)-C(1A)-C(4A) 127.68(9)
N(1A)-C(1A)-C(4A) 107.17(8)
N(1A)-C(2A)-C(3A) 100.93(9)
N(1A)-C(2A)-H(2A1)109.4(9)
C(3A)-C(2A)-H(2A1)114.9(9)
O(1B)-C(1B)-N(1B)
O(1B)-C(1B)-C(4B)
N(1B)-C(1B)-C(4B)
N(1B)-C(2B)-C(3B)
N(1B)-C(2B)-H(2B1)
C(3B)-C(2B)-H(2B1)
125.97(10)
127.27(10)
106.75(9)
101.05(9)
108.3(9)
113.1(9)
N(1A)-C(2A)-H(2A2)111.1(9)
C(3A)-C(2A)-H(2A2)111.2(8)
H(2A1)-C(2A)-H(2A2)
C(4A)-C(3A)-C(2A)104.39(9)
C(4A)-C(3A)-H(3A1)110.6(9)
C(2A)-C(3A)-H(3A1)114.1(9)
N(1B)-C(2B)-H(2B2)
C(3B)-C(2B)-H(2B2)
H(2B1)-C(2B)-H(2B2)
C(4B)-C(3B)-C(2B)
C(4B)-C(3B)-H(3B1)
C(2B)-C(3B)-H(3B1)
107.9(9)
114.2(8)
111.4(13)
104.44(9)
114.1(10)
111.3(10)
151
a
b
C(4A)-C(3A)-H(3A2) 109.4(9)
C(2A)-C(3A)-H(3A2) 108.0(8)
H(3A1)-C(3A)-H(3A2) 110.2(12)
C(1A)-C(4A)-C(3A) 104.17(9)
C(1A)-C(4A)-H(4A1) 108.8(9)
C(3A)-C(4A)-H(4A1) 112.1(9)
C(1A)-C(4A)-H(4A2) 109.9(7)
C(3A)-C(4A)-H(4A2) 113.7(8)
H(4A1)-C(4A)-H(4A2) 108.0(11)
C(4B)-C(3B)-H(3B2) 108.5(10)
C(2B)-C(3B)-H(3B2) 109.1(9)
H(3B1)-C(3B)-H(3B2) 109.3(13)
C(1B)-C(4B)-C(3B)
104.45(9)
C(1B)-C(4B)-H(4B1) 107.3(10)
C(3B)-C(4B)-H(4B1) 113.7(10)
C(1B)-C(4B)-H(4B2) 112.4(12)
C(3B)-C(4B)-H(4B2) 114.5(12)
H(4B1)-C(4B)-H(4B2) 104.5(15)
______________________________________________________________________
The numbers in parentheses are the estimated standard deviations in the last
significant digit.
Atoms are labeled in agreement with Figures 1 and 2.
152
Table 4. Anisotropic displacement parameters (Å2x 103) for C4H7NO2 a,b,c
_____________________________________________________________________
U11
U22
U33
U23
U13
U12
_____________________________________________________________________
O(1A) 35(1)
36(1)
29(1)
-2(1)
0(1)
0(1)
O(2A) 43(1)
31(1)
38(1)
5(1)
13(1)
-1(1)
N(1A) 34(1)
30(1)
29(1)
0(1)
5(1)
-2(1)
C(1A) 31(1)
22(1)
29(1)
-2(1)
3(1)
4(1)
C(2A) 36(1)
36(1)
34(1)
-4(1)
-2(1)
-4(1)
C(3A) 41(1)
37(1)
27(1)
-1(1)
0(1)
1(1)
C(4A) 34(1)
33(1)
28(1)
-1(1)
5(1)
1(1)
O(1B) 45(1)
35(1)
40(1)
7(1)
7(1)
6(1)
O(2B) 38(1)
40(1)
30(1)
-6(1)
5(1)
-1(1)
N(1B) 32(1)
32(1)
29(1)
0(1)
4(1)
3(1)
C(1B) 27(1)
33(1)
30(1)
1(1)
-1(1)
-3(1)
C(2B) 36(1)
28(1)
36(1)
1(1)
-1(1)
-1(1)
C(3B) 41(1)
33(1)
41(1)
-5(1)
7(1)
1(1)
C(4B) 41(1)
39(1)
32(1)
0(1)
6(1)
2(1)
______________________________________________________________________
a
The numbers in parentheses are the estimated standard deviations in the last significant
digit.
b
The form of the anisotropic thermal parameter is: exp[-22 (U11h2a*2 + U22k2b*2 +
U33l2c*2 + 2U12hka*b* + 2U13hla*c* + 2U23klb*c*)].
c
Atoms are labeled in agreement with Figures 1 and 2.
153
Table 5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x
10 3)
for C4H7NO2 a,b
a
_____________________________________________________________________
x
y
z
U(eq)
_____________________________________________________________________
H(2A)
2833(17)
2200(30)
5656(15)
55(5)
H(2A1)
2398(14)
1970(20)
3538(12)
39(4)
H(2A2)
3400(14)
300(20)
3403(11)
43(4)
H(3A1)
4273(15)
2400(20)
2270(13)
47(4)
H(3A2)
3718(14)
4170(20)
2884(12)
42(4)
H(4A1)
6038(15)
2140(20)
3451(12)
44(4)
H(4A2)
5804(12)
4310(20)
3603(10)
30(3)
H(2B)
2796(17)
5970(30)
4500(13)
58(5)
H(2B1)
133(15)
7880(20)
4830(12)
40(4)
H(2B2)
1502(14)
8930(20)
4980(11)
37(3)
H(3B1)
-89(15)
9130(20)
6458(12)
49(4)
H(3B2)
1457(16)
9120(30)
6758(13)
52(4)
H(4B1)
-210(16)
5890(20)
6884(13)
52(4)
H(4B2)
967(18)
6390(30)
7561(16)
61(5)
______________________________________________________________________
All hydrogen atoms were located in a difference Fourier map and included in the
structural model as independent isotropic atoms whose parameters were allowed to
vary in least-squares refinement cycles.
b
Hydrogen atoms are labeled with the same numerical and literal subscript(s) as their
respective oxygen or carbon atoms.
154
Table 6. Torsion angles [°] for C4H7NO2
________________________________________________________________
O(2A)-N(1A)-C(1A)-O(1A)
-8.16(15)
C(2A)-N(1A)-C(1A)-O(1A)
-173.88(10)
O(2A)-N(1A)-C(1A)-C(4A)
171.81(8)
C(2A)-N(1A)-C(1A)-C(4A)
6.09(12)
C(1A)-N(1A)-C(2A)-C(3A)
-20.91(12)
O(2A)-N(1A)-C(2A)-C(3A)
172.96(9)
N(1A)-C(2A)-C(3A)-C(4A)
25.99(11)
O(1A)-C(1A)-C(4A)-C(3A)
-168.30(10)
N(1A)-C(1A)-C(4A)-C(3A)
11.74(11)
C(2A)-C(3A)-C(4A)-C(1A)
-23.67(11)
O(2B)-N(1B)-C(1B)-O(1B)
8.15(16)
C(2B)-N(1B)-C(1B)-O(1B)
175.15(10)
O(2B)-N(1B)-C(1B)-C(4B)
-170.82(9)
C(2B)-N(1B)-C(1B)-C(4B)
-3.82(12)
C(1B)-N(1B)-C(2B)-C(3B)
18.93(12)
O(2B)-N(1B)-C(2B)-C(3B)
-173.91(9)
N(1B)-C(2B)-C(3B)-C(4B)
-25.20(11)
O(1B)-C(1B)-C(4B)-C(3B)
167.76(11)
N(1B)-C(1B)-C(4B)-C(3B)
-13.29(12)
C(2B)-C(3B)-C(4B)-C(1B)
24.10(12)
________________________________________________________________
155
Table 7. Inter-molecular Hydrogen bonds for C4H7NO2 [Å and °]
______________________________________________________________________
D-H...A
d(D-H)
d(H...A)
d(D...A)
<(DHA)
______________________________________________________________________
O(2A)-H(2A)...O(1B) 0.873(19)
1.802(19)
2.6419(12)
160.8(18)
O(2B)-H(2B)...O(1A)#10.887(18) 1.714(18)
2.6007(12)
178.4(17)
______________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x+1,-y+1,-z+1
156
APPENDIX C
CRYSTAL STRUCTURE ANALYSIS REPORT AND TABLE FOR COMPOUND
C7H11NO2
Wake Forest X-Ray Facility Reference Code: a11m
Performed by Dr. Cynthia Day
Wake Forest University
157
EXPERIMENTAL
Table 1. Crystal data and structure refinement for C7H11NO2
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a11m
C7 H11 N O2
141.17
193(2) K
0.71073 Å
Monoclinic
P2(1)/c - C 52h (No. 14)
Unit cell dimensions
a = 13.040(3) Å
b = 10.086(3) Å, β = 92.336(3)°
c = 10.802(3) Å
1419.5(6) Å3
8
1.321 g/cm3
0.097 mm-1
608
0.18 x 0.12 x 0.08 mm3
4.03 to 25.00°
-15≤h≤15, 0≤k≤11, 0≤l≤12
3820
3822 [R(int) = 0.0000]
99.6 %
Full-matrix least-squares on F2
3822 / 190
1.194
R1 = 0.0684, wR2 = 0.1301
R1 = 0.0845, wR2 = 0.1365
0.213 and -0.172 e-/Å3
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 25.00°
Refinement method
Data / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
-----------------------------------------------------------------------------------------------------------------------R1 =  ||Fo| - |Fc|| /  |Fo|
2
2 2
2 2
wR2 = {  [w(Fo - Fc ) ] /  [w(Fo ) ] }
1/2
158
Table 3. Bond lengths [Å] and angles [°] for C7H11NO2
a,b
______________________________________________________________________
O(1B)-N(1B)
1.383(2)
O(1A)-N(1A)
1.387(2)
0.94(2)
O(1B)-H(1B)
0.90(3)
O(2A)-C(1A)
1.237(2)
O(2B)-C(1B)
1.230(3)
N(1A)-C(1A)
1.327(3)
N(1B)-C(1B)
1.321(3)
N(1A)-C(2A)
1.454(3)
N(1B)-C(2B)
1.456(3)
C(1A)-C(4A)
1.495(3)
C(1B)-C(4B)
1.496(3)
C(2A)-C(5A)
C(2A)-C(3A)
C(3A)-C(7A)
C(3A)-C(4A)
C(5A)-C(6A)
C(6A)-C(7A)
1.519(3)
1.549(3)
1.524(3)
1.528(3)
1.518(3)
1.519(3)
C(2B)-C(5B)
C(2B)-C(3B)
C(3B)-C(7B)
C(3B)-C(4B)
C(5B)-C(6B)
C(6B)-C(7B)
1.520(3)
1.553(3)
1.520(3)
1.529(3)
1.518(4)
1.506(4)
O(1A)-H(1A)
N(1A)-O(1A)-H(1A)
N(1B)-O(1B)-H(1B)
104.9(18)
C(1A)-N(1A)-O(1A)
C(1A)-N(1A)-C(2A)
O(1A)-N(1A)-C(2A)
C(1B)-N(1B)-O(1B)
C(1B)-N(1B)-C(2B)
O(1B)-N(1B)-C(2B)
121.56(17)
117.72(18)
120.34(18)
O(2A)-C(1A)-N(1A)
O(2B)-C(1B)-N(1B)
126.4(2)
O(2A)-C(1A)-C(4A)
N(1A)-C(1A)-C(4A)
O(2B)-C(1B)-C(4B)
N(1B)-C(1B)-C(4B)
126.2(2)
107.37(19
159
a
b
N(1A)-C(2A)-C(5A) 111.66(18)
N(1A)-C(2A)-C(3A) 102.36(17)
C(5A)-C(2A)-C(3A) 106.47(18)
C(7A)-C(3A)-C(4A) 114.47(19)
N(1B)-C(2B)-C(5B)
112.04(19)
N(1B)-C(2B)-C(3B) 102.35(18)
C(5B)-C(2B)-C(3B)
105.7(2)
C(7B)-C(3B)-C(4B)
113.6(2)
C(7A)-C(3A)-C(2A) 104.70(18)
C(4A)-C(3A)-C(2A) 105.73(17)
C(1A)-C(4A)-C(3A) 106.69(18)
C(6A)-C(5A)-C(2A) 103.55(19)
C(5A)-C(6A)-C(7A) 102.39(19)
C(6A)-C(7A)-C(3A) 104.17(19)
C(7B)-C(3B)-C(2B)
104.7(2)
C(4B)-C(3B)-C(2B)
105.41(17)
C(1B)-C(4B)-C(3B)
106.87(19)
C(6B)-C(5B)-C(2B)
104.6(2)
C(7B)-C(6B)-C(5B)
102.0(2)
C(6B)-C(7B)-C(3B)
104.6(2)
______________________________________________________________________
The numbers in parentheses are the estimated standard deviations in the last
significant digit.
Atoms are labeled in agreement with Figures 1 and 2.
160
Table 7. Inter-molecular Hydrogen bonds for C7H11NO2 [Å and °]
______________________________________________________________________
D-H...A
d(D-H)
d(H...A)
d(D...A)
<(DHA)
______________________________________________________________________
O(1A)-H(1A)...O(2B)#10.94(2)
1.71(3)
2.648(2)
178(2)
O(1B)-H(1B)...O(2A) 0.90(3)
1.69(3)
2.584(2)
173(3)
_____________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x+1,y+1/2,-z+1/2
161
APPENDIX D
CRYSTAL STRUCTURE ANALYSIS REPORT AND TABLE FOR COMPOUND
C15H17SO3N
Wake Forest X-Ray Facility Reference Code: a92ktab
Performed by Dr. Cynthia Day
Wake Forest University
162
Table 1. Crystal data and structure refinement for C15H17SO3N
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a92k
C15 H17 N O3 S
291.36
193(2) K
0.71073 Å
Monoclinic
P21/c - C 52h (No. 14)
Unit cell dimensions
a = 16.8053(17) Å
b = 7.8504(8) Å, β = 105.649(2)°
c = 11.6413(12) Å
1478.9(3) Å3
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 30.04°
Absorption correction
Max. and min. transmission
Refinement method
Data / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
4
1.309 g/cm3
0.225 mm-1
616
0.29 x 0.26 x 0.19 mm3
4.16 to 30.04°
-23≤h≤23, -10≤k≤11, -16≤l≤16
14854
4292 [R(int) = 0.0321]
99.1 %
Multi-scan (SADABS)
0.9585 and 0.9376
Full-matrix least-squares on F2
4292 / 183
1.139
R1 = 0.0579, wR2 = 0.1444
R1 = 0.0635, wR2 = 0.1485
0.552 and -0.246 e-/Å-3
163
Table 2. Atomic coordinates (x 104) and equivalent isotropic displacement parameters
(Å2x 103) for C15H17SO3N. U(eq) is defined as one third of the trace of the
orthogonalized Uij tensor.
______________________________________________________________________
x
y
z
U(eq)
______________________________________________________________________
S(1)
2242(1)
3423(1)
3160(1)
30(1)
O(1)
2640(1)
1791(2)
3364(1)
45(1)
O(2)
2129(1)
4251(2)
2035(1)
41(1)
O(3)
2420(1)
6311(1)
4073(1)
34(1)
N(1)
2843(1)
4712(2)
4179(1)
31(1)
C(1)
1281(1)
3303(2)
3482(1)
28(1)
C(2)
636(1)
4344(2)
2874(1)
34(1)
C(3)
-115(1)
4255(2)
3145(2)
41(1)
C(4)
-231(1)
3173(2)
4030(2)
39(1)
C(5)
429(1)
2178(2)
4644(2)
39(1)
C(6)
1182(1)
2214(2)
4371(1)
34(1)
C(7)
-1054(1)
3078(3)
4315(2)
58(1)
C(8)
3033(1)
4141(3)
5425(2)
44(1)
C(9)
2932(1)
7609(2)
3738(2)
37(1)
C(10)
3662(1)
8065(2)
4755(1)
31(1)
C(11)
4443(1)
7464(3)
4803(2)
46(1)
C(12)
5106(1)
7893(4)
5763(2)
64(1)
C(13)
4987(2)
8920(4)
6652(2)
67(1)
C(14)
4209(2)
9511(3)
6615(2)
55(1)
C(15)
3545(1)
9085(2)
5666(2)
38(1)
_____________________________________________________________________
164
Table 3. Bond lengths [Å] and angles [°] for C15H17SO3N
______________________________________________________________________
S(1)-O(2)
1.4277(13)
S(1)-N(1)
1.6748(14)
S(1)-O(1)
1.4341(13)
S(1)-C(1)
1.7565(16)
O(3)-N(1)
N(1)-C(8)
1.4309(17)
1.468(2)
O(3)-C(9)
1.453(2)
C(1)-C(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.387(2)
1.389(2)
1.383(3)
1.389(3)
1.387(3)
1.385(2)
C(10)-C(11)
C(10)-C(15)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
1.382(2)
1.384(2)
1.389(3)
1.369(4)
1.376(4)
1.383(3)
C(4)-C(7)
1.509(3)
C(9)-C(10)
1.500(2)
O(2)-S(1)-O(1)
O(2)-S(1)-N(1)
O(1)-S(1)-N(1)
119.97(9)
106.30(7)
104.94(8)
N(1)-O(3)-C(9) 108.77(12)
O(3)-C(9)-C(10) 111.90(14)
C(6)-C(1)-C(2) 120.56(15)
C(6)-C(1)-S(1) 119.67(12)
C(2)-C(1)-S(1) 119.73(12)
C(3)-C(2)-C(1) 119.31(16)
C(2)-C(3)-C(4) 121.25(17)
C(5)-C(4)-C(3) 118.32(16)
C(5)-C(4)-C(7) 120.78(19)
C(3)-C(4)-C(7) 120.91(19)
C(6)-C(5)-C(4) 121.54(16)
C(5)-C(6)-C(1) 118.99(16)
C(11)-C(10)-C(15) 119.69(17)
O(2)-S(1)-C(1)
O(1)-S(1)-C(1)
N(1)-S(1)-C(1)
108.50(8)
109.29(8)
107.08(7)
O(3)-N(1)-C(8)
O(3)-N(1)-S(1)
C(8)-N(1)-S(1)
108.95(13)
106.19(9)
116.39(11)
C(11)-C(10)-C(9)
C(15)-C(10)-C(9)
C(10)-C(11)-C(12)
C(13)-C(12)-C(11)
C(12)-C(13)-C(14)
C(13)-C(14)-C(15)
C(14)-C(15)-C(10)
121.05(17)
119.25(16)
119.7(2)
120.2(2)
120.3(2)
119.9(2)
120.12(19)
165
Anisotropic displacement parameters (Å2x 103) for C15H17SO3N. The
anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k
Table 4.
a* b* U12 ]
___________________________________________________________________
U11
U22
U33
U23
U13
U12
___________________________________________________________________
S(1) 35(1)
24(1)
31(1)
-2(1)
9(1)
-2(1)
O(1) 47(1)
27(1)
63(1)
-5(1)
16(1)
4(1)
O(2) 51(1)
44(1)
30(1)
-2(1)
14(1)
-9(1)
O(3) 32(1)
24(1)
44(1)
-3(1)
7(1)
0(1)
N(1) 31(1)
24(1)
35(1)
-1(1)
4(1)
0(1)
C(1) 32(1)
24(1)
25(1)
-1(1)
4(1)
-4(1)
C(2) 41(1)
30(1)
30(1)
3(1)
4(1)
2(1)
C(3) 37(1)
39(1)
43(1)
-5(1)
2(1)
4(1)
C(4) 37(1)
38(1)
41(1)
-16(1)
11(1)
-10(1)
C(5) 46(1)
38(1)
34(1)
-1(1)
11(1)
-13(1)
C(6) 39(1)
30(1)
31(1)
5(1)
3(1)
-5(1)
C(7) 46(1)
65(1)
70(2)
-29(1)
27(1)
-15(1)
C(8) 47(1)
42(1)
34(1)
5(1)
-4(1)
-4(1)
C(9) 45(1)
26(1)
36(1)
2(1)
3(1)
-5(1)
C(10) 36(1)
25(1)
33(1)
1(1)
9(1)
-5(1)
C(11) 42(1)
52(1)
49(1)
5(1)
19(1)
3(1)
C(12) 33(1)
87(2)
69(2)
26(1)
8(1)
-2(1)
C(13) 60(1)
79(2)
46(1)
19(1)
-13(1)
-33(1)
C(14) 80(2)
47(1)
32(1)
-3(1)
5(1)
-18(1)
C(15) 48(1)
31(1)
36(1)
-1(1)
12(1)
-2(1)
___________________________________________________________________
166
Table 5. Hydrogen coordinates (x 104) and isotropic displacement parameters (Å2x
10 3) for C15H17SO3N
______________________________________________________________________
x
y
z
U(eq)
______________________________________________________________________
H(2)
710
5108
2279
41
H(3)
-560
4948
2717
49
H(5)
363
1454
5266
47
H(6)
1624
1504
4787
41
H(7A)
-966
2790
5159
87
H(7B)
-1396
2199
3820
87
H(7C)
-1334
4182
4151
87
H(8A)
3262
2985
5487
66
H(8B)
2527
4142
5689
66
H(8C)
3439
4913
5928
66
H(9A)
2595
8642
3470
44
H(9B)
3129
7188
3062
44
H(11)
4527
6761
4181
55
H(12)
5642
7473
5802
77
H(13)
5444
9226
7299
80
H(14)
4129
10211
7240
66
H(15)
3008
9493
5639
46
______________________________________________________________________
167
Table 6. Torsion angles [°] for C15H17SO3N
________________________________________________________________
C(9)-O(3)-N(1)-C(8)
115.63(14)
C(9)-O(3)-N(1)-S(1)
-118.29(11)
O(2)-S(1)-N(1)-O(3)
57.37(12)
O(1)-S(1)-N(1)-O(3)
-174.55(10)
C(1)-S(1)-N(1)-O(3)
-58.46(11)
O(2)-S(1)-N(1)-C(8)
178.79(13)
O(1)-S(1)-N(1)-C(8)
-53.12(15)
C(1)-S(1)-N(1)-C(8)
62.96(14)
O(2)-S(1)-C(1)-C(6)
164.73(13)
O(1)-S(1)-C(1)-C(6)
32.25(15)
N(1)-S(1)-C(1)-C(6)
-80.92(14)
O(2)-S(1)-C(1)-C(2)
-17.58(15)
O(1)-S(1)-C(1)-C(2)
-150.06(13)
N(1)-S(1)-C(1)-C(2)
96.78(13)
C(6)-C(1)-C(2)-C(3)
-1.5(2)
S(1)-C(1)-C(2)-C(3)
-179.18(13)
C(1)-C(2)-C(3)-C(4)
1.4(3)
C(2)-C(3)-C(4)-C(5)
0.2(3)
C(2)-C(3)-C(4)-C(7)
-179.65(17)
C(3)-C(4)-C(5)-C(6)
-1.6(3)
C(7)-C(4)-C(5)-C(6)
178.16(17)
C(4)-C(5)-C(6)-C(1)
1.5(3)
C(2)-C(1)-C(6)-C(5)
0.1(2)
S(1)-C(1)-C(6)-C(5)
177.74(12)
N(1)-O(3)-C(9)-C(10)
-72.79(17)
O(3)-C(9)-C(10)-C(11)
103.30(19)
O(3)-C(9)-C(10)-C(15)
-75.81(19)
C(15)-C(10)-C(11)-C(12)
-0.2(3)
C(9)-C(10)-C(11)-C(12)
-179.28(18)
C(10)-C(11)-C(12)-C(13)
-0.6(3)
C(11)-C(12)-C(13)-C(14)
1.2(4)
C(12)-C(13)-C(14)-C(15)
-0.8(3)
C(13)-C(14)-C(15)-C(10)
0.0(3)
C(11)-C(10)-C(15)-C(14)
0.5(3)
168
C(9)-C(10)-C(15)-C(14)
179.60(17)
________________________________________________________________
169
APPENDIIX E
CRYSTA
AL STRUCTU
URE ANAL
LYSIS REPO
ORT AND T
TABLE FOR
R COMPOU
UND
C8H13NO
O2
Wake Foreest X-Ray Facility
F
Reeference Coode: a71q--2010
Perform
med by Dr. C
Cynthia Dayy
Waake Forest U
University
170
EXPERIMENTAL
Crystals of C8H13NO2 are, at 173(2) K, monoclinic, space group P21/c – C 52h (No. 14)
with a = 4.8089(12) Å, b = 21.598(5) Å, c = 8.156(2) Å, β = 106.278(3)°, V =
813.1(3)Å3, and Z = 4 {dcalcd = 1.268gcm-3; μa(MoK  ) = 0.091 mm-1}.
A full
hemisphere of diffracted intensities (1968 30-second frames with an  scan width of
0.30) was measured for a single-domain specimen using graphite-monochromated
MoK  radiation (= 0.71073 Å) on a Bruker SMART APEX CCD Single Crystal
Diffraction System. X-rays were provided by a fine-focus sealed x-ray tube operated at
50kV and 30mA.
Lattice constants were determined with the Bruker APEX2 software package
using peak centers for 1087 reflections having 7.69˚ ≤ 2θ ≤ 42.80˚. A total of 7741
integrated reflection intensities having 2((MoK  )≤ 55.74 were produced using the
Bruker program SAINT; 1938 of these were unique and gave Rint = 0.051 with a
coverage which was 99.8% complete. The data were corrected empirically for variable
scaling and absorption effects using the SADABS program; the estimated minimum
and maximum transmission values reported were 0.6422 and 0.7460.
The Bruker software package SHELXTL was used to solve the structure using
“direct methods” techniques.
All stages of weighted full-matrix least-squares
refinement were conducted using Fo2 data with the SHELXTL software package. The
resulting structural parameters have been refined to convergence {R1 (unweighted, based
on F) = 0.0488 for 1354 independent reflections having 2Θ(MoK  ) < 55.74o and
F2>2σ(F2)} {R1 (unweighted, based on F) = 0.0787 and wR2 (weighted, based on F2) =
0.1152 for all 1938 reflections} using counter-weighted full-matrix least-squares
techniques and a structural model which incorporated anisotropic thermal parameters for
all nonhydrogen atoms. All hydrogen atoms were located from a difference Fourier map
and included in the structural model as individual isotropic atoms whose parameters
were allowed to vary in least-squares refinement cycles. A total of 152 parameters
were refined using no restraints and 1938 data. The largest shift/s.u. was 0.000 in the
final refinement cycle. The final difference map had maxima and minima of 0.228 and
171
3
-0.169 e-/Å , respectively.
Acknowledgment
The authors thank the National Science Foundation (grant CHE-0234489) for
funds to purchase the x-ray instrument and computers.
References
International Tables for Crystallography, Vol A, 4th ed., Kluwer Academic Publishers:
Boston (1996). Data Collection: SMART (Version 5.628) (2002). Bruker-AXS, 5465 E.
Cheryl Parkway, Madison, WI 53711-5373 USA.
(10)
Data Reduction: SAINT (Version 7.66A)
(2009). Bruker-AXS, 5465 E. Cheryl Parkway, Madison, WI 53711-5373, USA.
(11)
G. M. Sheldrick (2008). SADABS (Version
2008/1). Program for Empirical Absorption Correction of Area Detector Data.
University of Göttingen, Germany.
(12)
G. M. Sheldrick (2008). SHELXTL. Bruker-AXS, 5465 E. Cheryl Parkway,
Madison, WI 53711-5373 USA.
.
172
Table 1. Crystal data and structure refinement for C8H13NO2
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a71q
C8 H13 N O2
155.19
173(2) K
0.71073 Å
Monoclinic
P21/c – C 52h (No. 14)
Unit cell dimensions
a = 4.8089(12) Å
b = 21.598(5) Å, β = 106.278(3)°
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 27.87°
Absorption correction
Max. and min. transmission
Refinement method
Data / parameters
Goodness-of-fit on F2
Final R indices [1354 I>2σ(I) data]
R indices (all data)
Largest diff. peak and hole
c = 8.156(2) Å
813.1(3) Å3
4
1.268 g/cm3
0.091 mm-1
336
0.17 x 0.10 x 0.03 mm3
3.85 to 27.87°
-6≤h≤6, -28≤k≤28, -10≤l≤10
7741
1938 [R(int) = 0.0506]
99.8 %
Multi-scan (SADABS)
0.7460 and 0.6422
Full-matrix least-squares on F2
1938 / 152
1.018
R1 = 0.0488, wR2 = 0.1030
R1 = 0.0787, wR2 = 0.1152
0.228 and -0.169e-/Å3
-----------------------------------------------------------------------------------------------------------------------R1 =  ||Fo| - |Fc|| /  |Fo|
2
2 2
2 2
wR2 = {  [w(Fo - Fc ) ] /  [w(Fo ) ] }
1/2
173
Table 2. Atomic coordinates
a,b
( x 104) and equivalent isotropic displacement
parameters (Å2x 103) for C8H13NO2
a
b
______________________________________________________________________
x
y
z
U(eq) c
______________________________________________________________________
O(1)
5896(2)
3237(1)
5685(2)
32(1)
O(2)
5023(2)
2519(1)
3050(2)
36(1)
N(1)
3277(3)
3271(1)
4387(2)
27(1)
C(1)
3143(3)
2911(1)
3008(2)
27(1)
C(2)
1960(3)
3892(1)
4263(2)
27(1)
C(3)
3590(4)
4328(1)
3432(2)
31(1)
C(4)
2975(4)
4419(1)
1762(2)
37(1)
C(5)
565(4)
4123(1)
426(2)
40(1)
C(6)
1001(4)
3435(1)
105(2)
35(1)
C(7)
566(4)
2983(1)
1468(2)
31(1)
C(8)
1842(4)
4110(1)
6010(2)
36(1)
______________________________________________________________________
The numbers in parentheses are the estimated standard deviations in the last
significant digit.
Atoms are labeled in agreement with Figures 1 and 2.
c
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
174
Table 3. Bond lengths [Å] and angles [°] for C8H13NO2
a,b
______________________________________________________________________
O(1)-N(1)
1.4018(16)
O(1)-H(1)
0.91(2)
O(2)-C(1)
1.2324(19)
C(3)-C(4)
1.325(2)
N(1)-C(1)
1.355(2)
N(1)-C(2)
1.474(2)
C(1)-C(7)
C(2)-C(3)
C(4)-C(5)
1.505(2)
1.503(2)
1.494(3)
C(2)-C(8)
C(5)-C(6)
C(6)-C(7)
1.516(2)
1.533(3)
1.537(2)
C(2)-H(2)
C(3)-H(3)
C(4)-H(4)
C(5)-H(5A)
C(5)-H(5B)
C(6)-H(6A)
0.937(16)
0.975(18)
0.97(2)
0.992(19)
0.982(19)
0.973(18)
C(6)-H(6B)
C(7)-H(7A)
C(7)-H(7B)
C(8)-H(8A)
C(8)-H(8B)
C(8)-H(8C)
0.963(18)
0.969(18)
0.973(17)
0.95(2)
0.989(18)
0.982(18)
N(1)-O(1)-H(1)103.8(14)
C(1)-N(1)-O(1)114.87(13)
C(1)-N(1)-C(2)123.13(13)
O(1)-N(1)-C(2)112.18(11)
O(2)-C(1)-N(1)120.56(14)
O(2)-C(1)-C(7)121.33(15)
N(1)-C(1)-C(7)118.04(15)
C(4)-C(3)-C(2)
C(4)-C(3)-H(3)
C(2)-C(3)-H(3)
C(3)-C(4)-C(5)
C(3)-C(4)-H(4)
C(5)-C(4)-H(4)
175
124.19(17)
121.0(11)
114.7(11)
126.18(18)
118.1(12)
115.7(12)
N(1)-C(2)-C(3) 109.40(13)
N(1)-C(2)-C(8) 110.29(14)
C(3)-C(2)-C(8) 112.98(15)
N(1)-C(2)-H(2) 105.1(10)
C(3)-C(2)-H(2) 111.1(10)
C(8)-C(2)-H(2) 107.6(10)
C(4)-C(5)-C(6) 115.11(15)
C(4)-C(5)-H(5A) 109.9(10)
C(6)-C(5)-H(5A) 109.7(10)
C(4)-C(5)-H(5B) 110.1(11)
C(6)-C(5)-H(5B) 106.4(11)
H(5A)-C(5)-H(5B)105.1(14)
C(5)-C(6)-C(7) 116.07(15)
C(5)-C(6)-H(6A) 109.8(10)
C(7)-C(6)-H(6A) 109.9(10)
C(5)-C(6)-H(6B) 108.2(10)
C(7)-C(6)-H(6B) 105.0(10)
H(6A)-C(6)-H(6B)107.5(14)
C(1)-C(7)-C(6) 114.95(14)
C(1)-C(7)-H(7A) 111.8(10)
C(6)-C(7)-H(7A) 108.2(10)
C(1)-C(7)-H(7B) 106.1(10)
C(6)-C(7)-H(7B) 107.0(10)
a
b
H(7A)-C(7)-H(7B)108.5(14)
C(2)-C(8)-H(8A) 110.5(11)
C(2)-C(8)-H(8B) 109.7(11)
H(8A)-C(8)-H(8B)111.1(16)
C(2)-C(8)-H(8C) 110.4(10)
H(8A)-C(8)-H(8C)106.6(15)
H(8B)-C(8)-H(8C)108.5(15)
__________________________________________________________________
The numbers in parentheses are the estimated standard deviations in the last
significant digit.
Atoms are labeled in agreement with Figures 1 and 2.
176
Table 4. Anisotropic displacement parameters (Å2x 103) for C8H13NO2
a,b,c
______________________________________________________________________
U11
U22
U33
U23
U13
U12
______________________________________________________________________
O(1) 29(1)
34(1)
26(1)
3(1)
-1(1)
-3(1)
O(2) 38(1)
37(1)
32(1)
-2(1)
7(1)
6(1)
N(1) 26(1)
28(1)
23(1)
0(1)
0(1)
-1(1)
C(1) 29(1)
27(1)
24(1)
3(1)
9(1)
-6(1)
C(2) 25(1)
30(1)
26(1)
0(1)
7(1)
0(1)
C(3) 36(1)
25(1)
34(1)
-2(1)
13(1)
2(1)
C(4) 46(1)
29(1)
39(1)
5(1)
20(1)
6(1)
C(5) 48(1)
44(1)
27(1)
10(1)
11(1)
14(1)
C(6) 36(1)
44(1)
22(1)
-2(1)
4(1)
3(1)
C(7) 30(1)
34(1)
28(1)
-5(1)
6(1)
-5(1)
C(8) 39(1)
38(1)
31(1)
-4(1)
11(1)
-3(1)
______________________________________________________________________
a
The numbers in parentheses are the estimated standard deviations in the last significant
digit.
b
The form of the anisotropic thermal parameter is: exp[-22 (U11h2a*2 + U22k2b*2 +
U33l2c*2 + 2U12hka*b* + 2U13hla*c* + 2U23klb*c*)].
c
Atoms are labeled in agreement with Figures 1 and 2.
177
Table 5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x
10 3) for C8H13NO2 a,b
a
______________________________________________________________________
x
y
z
U(eq)
______________________________________________________________________
H(1)
5510(50)
2968(10)
6450(30)
59(7)
H(2)
50(40)
3839(7)
3590(20)
25(4)
H(3)
5240(40)
4531(8)
4220(20)
38(5)
H(4)
4210(40)
4695(9)
1350(20)
48(6)
H(5A)
210(40)
4356(8)
-660(20)
38(5)
H(5B)
-1250(40)
4152(8)
750(20)
39(5)
H(6A)
2900(40)
3372(7)
-70(20)
29(4)
H(6B)
-420(40)
3315(7)
-930(20)
34(5)
H(7A)
-1150(40)
3108(8)
1780(20)
32(5)
H(7B)
220(30)
2576(8)
940(20)
32(5)
H(8A)
940(40)
3809(9)
6530(20)
44(5)
H(8B)
810(40)
4511(9)
5900(20)
37(5)
H(8C)
3810(40)
4168(8)
6770(20)
36(5)
______________________________________________________________________
All hydrogen atoms were located from a difference Fourier map and included in the
structural model as individual isotropic atoms whose parameters were allowed to
vary in least-squares refinement cycles.
b
Hydrogen atoms are labeled with the same numerical subscript(s) as their respective
oxygen or carbon atoms with an additional literal subscript (a, b or c) to distinguish
between hydrogens bonded to the same carbon atom.
178
Table 6. Torsion angles [°] for C8H13NO2 a
________________________________________________________________
O(1)-N(1)-C(1)-O(2)
10.7(2)
C(2)-N(1)-C(1)-O(2)
153.80(14)
O(1)-N(1)-C(1)-C(7)
-172.23(13)
C(2)-N(1)-C(1)-C(7)
-29.2(2)
C(1)-N(1)-C(2)-C(3)
-68.76(19)
O(1)-N(1)-C(2)-C(3)
75.17(16)
C(1)-N(1)-C(2)-C(8)
166.38(14)
O(1)-N(1)-C(2)-C(8)
-49.69(17)
N(1)-C(2)-C(3)-C(4)
88.99(19)
C(8)-C(2)-C(3)-C(4)
-147.73(17)
C(2)-C(3)-C(4)-C(5)
1.4(3)
C(3)-C(4)-C(5)-C(6)
-72.4(2)
C(4)-C(5)-C(6)-C(7)
75.3(2)
O(2)-C(1)-C(7)-C(6)
-89.25(19)
N(1)-C(1)-C(7)-C(6)
93.74(19)
C(5)-C(6)-C(7)-C(1)
-82.4(2)
______________________________________________________________________
a
The numbers in parentheses are the estimated standard deviations in the last significant
digit.
179
Table 7. Hydrogen bonds for C8H13NO2 [Å and °]
______________________________________________________________________
d(D-H)
d(H...A)
d(D...A)
<(DHA)
______________________________________________________________________
O(1)-H(1)...O(2)#1
0.91(2)
1.74(2)
2.6485(18)
175(2)
______________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 x,-y+1/2,z+1/2
180
SCHOLASTIC VITA
RANJAN BANERJEE
BORN
December, 1980
Howrah, West Bengal, India
EDUCATION
Ph.D, Organic Chemistry, Wake Forest University
Winston Salem, NC, December 2010
MS, Inorganic Chemistry, Indian Institute of
Technology-Kharagpur, June 2005
B.Sc., University of Calcutta, Kolkata, July 2003
SCHOLASTIC AND PROFESSIONAL EXPERIENCE
Research Assistant
2006-2010
Teaching Assistant
2005-2006
AWARDS AND HONORS
Royal Society of Science Summer Research Fellowship,
IISc Bangalore, India
2004
“First Class” recognition from the University of Calcutta
for outstanding undergraduate academic performance
2003
PROFESSIONAL SOCIETIES:
American Chemical Society
2007-present
181
CONFERENCE PRESENTATIONS
Ranjan Banerjee and S. Bruce King “Utilizing the Nitroso-ene Reaction for the
Synthesis of Hydroxamic Acid-Based Natural Products” Abstract Submitted for 240th
ACS National Meeting, Boston, MA, August 22-26, 2010
Ranjan Banerjee and S. Bruce King. “Synthesis of Cyclic
Hydroxamic Acids through –
NOH Insertion of Ketones” Oral presentation at 61st Southeast Regional Meeting of the
American Chemical Society, San Juan, PR, October 21-24, 2009
Ranjan Banerjee and S. Bruce King. “New Synthetic
Approaches Towards The Natural
Hydroxamic Acid Cobactin Core” Presented at 41st National Organic Symposium,
Boulder, CO, June 7-11, 2009
Ranjan Banerjee and S.thBruce King. “A New Synthetic Route to Cyclic Hydroxamic
Acids” Presented at 40 National Organic Symposium, Durham, NC, June 3-7, 2007
PEER-REVIEWED PUBLICATIONS
R. Banerjee and S. Bruce King “Synthesis of Cyclic Hydroxamic Acids through –NOH
Insertion of Ketones” Org. Lett. 2009, 11 (20), 4580-4583
182