Name__________Key________________
215 F12-Exam No. 3
Page 2
I. (26 points) Raffinose is a trisaccharide occurring in cottonseed meal. Answer the following questions as
directed in the boxes.
(1) (3 points) Label each of the glycosidic bonds in
raffinose using a small arrow (
).
HO
(2) (3 points) Classify each glycosidic bond in raffinose
as α or β right next to each of the arrows you have shown.
α
H
HO
no (circle one)
1
2
1
2
CH2
O
H
H
H
OH
α
3 (circle one)
3
H
H
OH
HO
β
H
HO
HO
H
H
(circle one)
O
O
HOH2C
(5) (2 points) How many reducing sugars are formed upon
complete acid hydrolysis of raffinose?
0
O
B
(4) (2 points) How many D sugars are formed upon complete
acid hydrolysis of raffinose?
0
A
H
H
(3) (2 points) Is raffinose a reducing sugar?
yes
CH2OH
O
H
H
OH
CH2OH
C
raffinose
(6) (2 points) Describe the glycosidic linkage between the sugar
units B and C [e.g., β(1->6)]:
α(1<-->2)β
14
(7) (12 points) Draw Fischer projections for the open chain forms of the carbohydrates produced when
raffinose is treated with excess dimethyl sulfate and NaOH, and then the permethylated product is
hydrolyzed with warm dilute acid.
raffinose
(C18H32O16)
(CH3)2SO4
(excess)
H
permethylated
raffinose
(C29H54O16)
From sugar unit B
From sugar unit A
NaOH
(excess)
H2O
(solvent)
H3O+
H2O
Δ
H
H3CO
H3CO
H
H
O
OCH3
H
H
OH
+
H
H3CO
H
H
From sugar unit C
O
CH2OCH3
OCH3
H
OCH3
OH
+
CH2OCH3
CH2OH
CH2OCH3
4
H3CO
H
H
O
H
OCH3
OH
4
4
Name____________Key______________
215 F12-Exam No. 3
Page 3
II. (8 points) Narbosine is a naturally occurring disaccharide. It is a dimer of L-rhodinose (as pyranose
forms) joined together by an α(1→4) glycosidic linkage. Draw in the box below the structure of narbosine
having the equatorial anomeric OH, using a conformational representation.
O
H
2
H
H
H
HO
H3C
H
H
OH
H
CH3
O
OH
O
H3C
O
OH
L-rhodinose
8
III. (14 points) Vancosamine is a small portion of vancomycin, one of the most powerful antibiotics that are
effective against drug-resistant bacteria. Show in the boxes provided below: i) if the vancosamine structure
given is a D- or L-sugar; ii) draw an open-chain Fischer projection formula of vancosamine; and iii) draw its
two pyranose chair conformations.
ii) Draw in a Fischer open- iii) Draw two chair
chain form.
conformations of
H3C
vancosamine.
CH3 OH
O
HO
H3C
OH
H3C
H
NH2
H
H3C
H
HO
vancosamine
i) stereochemical
designation:
O
H
NH2
OH
H
CH3
HO
-1 point for a wrong st
at each C.
D ; L
NH2
3
O
HO
H3C
Changed to 6 pts.
2
Circle the one that
applies.
O
OH
CH3
NH2
4
3
IV. (9 points) Using the pKa and structure information given on page 11, answer the following questions.
(1) (6 points) Draw the structure of the major species for each of the following three amino acids at pH 5.
aspartic acid at pH 5
histidine at pH 5
O
O
O
H3N
arginine at pH 5
H3N
O
H3N
O
H
H
HN
N H
H
O
H
O
O
2
2
N
H
N
H
NH2
(2) (3 points) The amino acid among above three (i.e., histidine, aspartic acid, and arginine) that has the
highest isoelectric point (pI) is:
arginine
3
2
Name___________Key_______________
215 F12-Exam No. 3
Page 4
V. (22 points) In a recent publication, an interesting sequence of the Dieckmann condensationdecarboxylation reactions was used in the synthesis of a pharmacologically significant alkaloid molecule
[Org. Lett. 2012, 14, 852].
O
Ph2CH
1. LHMDS
(1 euiv), 0 °C
OCH3
N
O
O
OH O
2. H3O+ workup
Ph2CH
OCH2CH3
N
OCH2CH3
O
(1) (18 points) Draw in the box below a step-by-step, curved-arrow mechanism for the above Dieckmann
condensation reaction, including the last protonation step. Use LiNRR' for LHMDS.
O
Ph2CH
OCH3
N
H3CO
O
O
Ph2CH
OCH2CH3
N
O
O
H H
OCH2CH3
H
Li NRR'
O
Ph2CH
O
OCH3
O
N
H
O
OCH2CH3
O
Ph2CH
O
H
O H
N
OCH2CH3
O
O
Ph2CH
O
OCH2CH3
N
OH O
H
O
2 pts for each intermediate
2 pts for each set of mechanism
arrows.
OCH3
Ph2CH
N
OCH2CH3
O
18
(2) Treatment of the product shown above with H3O+/H2O with heat produces a ketone product. Draw in
the box the structure of the expected product from the reaction below.
OH O
Ph2CH
N
OCH2CH3
O
O
H3O+, H2O
Δ
Ph2CH
+ CO2 + CH3CH2OH
N
O
4
Name___________Key_______________
215 F12-Exam No. 3
Page 5
VI. (20 points) Complete the following reactions by providing in each of the boxes the structure of the
starting compound, intermediate, or product. Indicate stereochemistry for the product/intermediate and if
more than one stereoisomer is formed, draw one structure and write “+ enantiomer” or “+ diastereomer.”
(1) [Synlett 2012, 2785]
O
O
1. NaH
OCH2CH3
+
OCH2CH3
2. H3O+-workup
O
O
O
O
C11H16O4
4
(2) [J. Mol. Catal. A: Chemical 2013, 366, 36]
O
NH
N
MgCO3 (mild base)
+
H2O, 40 °C
O
H
+ enantiomer
C11H19NO
4
(3) [Org Lett. 2004, 6, 3719]
O
1.
CuLi
O
2. H3O+-workup
+ diastereomer
C14H20O
(4)
4
OCH2CH3
O
O
OCH2CH3
1.
Ph
O
NaH
2. H3O+-workup
O
O
OCH2CH3
O
H3O+, H2O
Δ
H
O
O
Ph
Ph
OH
or
O
OCH2CH3
+ enantiomer
Ph
4
O
OH
4
+ CO2 + 2 CH3CH2OH
Name__________Key________________
215 F12-Exam No. 3
Page 6
VII. (21 points) Complete the following reactions by providing in each of the boxes the structure of the
intermediate or product. Indicate stereochemistry for the product/intermediate and if more than one
stereoisomer is formed, draw one structure and write “+ enantiomer” or “+ diastereomer.”
(1) [Synlett 2012 2789]
HO
OH
O
HO
O
(excess)
O
O
O
N
O
O
OH
OH
O
O
O
O
O
(solvent)
HBr
CH2Cl2
(solvent)
O
O
O
3
S
O
O
O
O
O
O
O
O
HN(CH2CH3)3
O
N
S
O
O
N
S
O
O
O
SN2!
O
O
S
O
Br
O
axial
4
4
(2) [ACS Catal. 2012, in press]
L-sugar!
O
O
O
O
O
O
O
BF3•O(CH2CH3)2
O
O
β
SH
or
O
O
S
O
TsOH
β anomer
4
NaOCH3 (catalytic)
HOCH3 (solvent)
NaH (2 equiv)
O
O
Br (2 equiv)
S
O
HO
O
S
HO
3
3
+ 2 NaBr
+ 2
O
OCH3