Concise synthesis of a pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O102

Article abstract of DOI:10.1016/j.tetasy.2013.06.005

An efficient synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit of the O-antigen of Escherichia coli O102 strain. The target pentasaccharide 1 has been synthesized using a [2+3] block glycosylation strategy. All glycosylation steps are highly stereoselective and high yielding. Concept of armed-disarmed and orthogonal glycosylation strategies has been applied during the synthesis. The target compound has been synthesized using the minimum number of steps.

Full text of DOI:10.1016/j.tetasy.2013.06.005

Tetrahedron: Asymmetry 24 (2013) 942–946
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Concise synthesis of a pentasaccharide repeating unit corresponding
to the O-antigen of Escherichia coli O102
⇑
Abhijit Sau, Debashis Dhara, Anup Kumar Misra
Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata 700054, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit of
the O-antigen of Escherichia coli O102 strain. The target pentasaccharide 1 has been synthesized using a
[2+3] block glycosylation strategy. All glycosylation steps are highly stereoselective and high yielding.
Concept of armed-disarmed and orthogonal glycosylation strategies has been applied during the synthe-
sis. The target compound has been synthesized using the minimum number of steps.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 23 May 2013
Accepted 25 June 2013
Available online 24 July 2013
1. Introduction
α-L-Rhap-(1→4)-β-D-GalpNAc
1
Diarrheal infections in developing countries are a serious prob-
lem.1,2 In general, enteric infections and their associated problems
such as hemorrhagic colitis and hemorrhagic uremic syndrome,
spread through contaminated food and water.3,4 The major causa-
tive agent of the diarrheal disease is enteropathogenic Escherichia
coli (EPEC).5 Among several pathogenic strains of E. coli, Shiga toxin
producing E. coli (STEC) strains is most virulent.6 Among several
STEC strains, E. coli O157 is most often cited for its association with
several diarrheal outbreaks in developed countries.7,8 Recently,
E. coli O102 strain has been found to produce the Shiga toxin and
act as the causative agent of avian colibacillisis9 and STEC infec-
tions in humans.10 E. coli O102 strain has also been identified as
a multidrug-resistant pathogenic strain causing infections in hos-
pitals and social communities.11,12
↓
3
→4)-α-D-Galp-(1→6)-β-D-Glcp-(1→3)-β-D-GalpNAc-(1→
Figure 1. Structure of the pentasaccharide repeating unit of the O-antigen of
Escherichia coli O102.
has been undertaken. A convergent synthesis of the pentasaccha-
ride repeating unit of the O-antigen of E. coli O102 is reported here-
in (Fig. 2).
2. Results and discussion
The O-antigens of pathogenic Gram-negative bacteria exist in
the lipopolysaccharide chains of the cell wall and play important
roles in the initial stage of bacterial adhesion with the host.13,14
Therefore, the development of glycoconjugate based therapeutics
would be important to combat the battle against such infections.
A number of reports have appeared dealing with glycoconjugate
based vaccine preparations.15–19 Recently, Perepelov et al.20
reported on the structure of the O-antigen of E. coli O102, which
The target pentasaccharide 1 protected as its p-methoxyphenyl
glycoside has been synthesized by the stereoselective glycosyla-
tion of a trisaccharide acceptor 11 with a disaccharide thioglyco-
side donor 12 using a [2+3] block glycosylation strategy (Fig. 2).
The trisaccharide derivative 11 and the disaccharide derivative
12 were prepared from suitably protected monosaccharide inter-
mediates 2, 3,21 4,22 5, and 6,23 which were prepared from com-
mercially available reducing sugars using reported reaction
methodologies (Fig. 2).
is a pentasaccharide repeating unit consisting of
D-galactosamine,
D
-glucose, -galactose, and -rhamnose (Fig. 1). The development
D
L
p-Methoxyphenyl 4,6-O-benzylidene-2-deoxy-2-N-phthalimi-
do-b-D D-galactosamine
-galactopyranoside 724 (prepared from
of glycoconjugate derivatives corresponding to the O-antigen of
E. coli O102 and its biological studies requires large quantities of
pentasaccharide, which is difficult to isolate from a natural source.
Therefore, chemical synthesis of the pentasaccharide repeating
unit with the required stereochemistry at the glycosyl linkages
hydrochloride in six steps) was treated with sodium cyanoborohy-
dride in the presence of HCl–ether25 to furnish p-methoxyphenyl
6-O-benzyl-2-deoxy-2-N-phthalimido-b-
82% yield. Ethyl 3-O-acetyl-4,6-O-benzylidene-2-deoxy-2-N-
phthalimido-1-thio-b-
-galactopyranoside 826 (prepared from
D-galactopyranoside 2 in
D
D-
⇑
galactosamine hydrochloride in six steps) was subjected to acid
hydrolysis using 80% aq acetic acid to give diol derivative, which
Corresponding author. Tel.: +91 33 2569 3240; fax: +91 33 2355 3886.
E-mail address: akmisra69@gmail.com (A.K. Misra).
0957-4166/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2013.06.005

A. Sau et al. / Tetrahedron: Asymmetry 24 (2013) 942–946
943
OH
HO
HO
OBn
O
O
BzO
BzO
SEt
OPMP
NPhth
OBz
HO
E
3
HO
OH
OH
O
O
2
O
HO
O
O
OBn
OBz
HO
AcO
C
D
O
HO
HO
O
O
HO
NHAc
O
SEt
OH
HO
O
SEt
O
OBn
O
O
HO
HO
NPhth
B
A
OPMP
4
5
SEt
OH
NHAc
1
O
BnO
BnO
OBn
PMP: p-methoxyphenyl
6
Figure 2. Structure of the synthesized pentasaccharide 1 as its p-methoxyphenyl glycoside and synthetic intermediates.
was selectively benzoylated using benzoyl cyanide27 to furnish
compound 5 in 80% yield (Scheme 1).
fonate (TMSOTf)28,29 exploiting the ‘armed-disarmed’ glycosylation
strategy30 furnished disaccharide thioglycoside derivative 9 in 73%
yield. The anomeric thioethyl group of compound 3 also acted as
an orthogonal anomeric protecting group, which can be activated
in a later glycosylation reaction.31 The formation of compound 9
was confirmed by spectroscopic analysis [signals at d 4.79 (br s,
H-1C), 4.75 (d, J = 10 Hz, H-1B) and d 97.4 (C-1C), 83.5 (C-1B) in
the 1H and 13C NMR spectra, respectively]. Compound 9 was al-
Ph
O
HO
HO
OBn
O
O
a
lowed to couple regio- and stereoselectively with D-galactosamine
O
OPMP
derived diol derivative 2 in the presence of a combination of NIS-
TMSOTf28,29 to furnish trisaccharide derivative 10 in 71% yield.
Spectroscopic analysis of compound 10 supported its formation
[signals at d 5.64 (d, J = 8.5 Hz, H-1A), 5.06 (d, J = 8.0 Hz, each, 1
H, H-1B), 4.76 (br s, 1 H, H-1C) and d 101.3 (C-1B), 97.5 (C-1A),
97.2 (C-1C) in the 1H and 13C NMR spectra respectively]. Acetyla-
tion of compound 10 using acetic anhydride and pyridine followed
by acidic hydrolysis using 80% aq acetic acid led to the formation of
trisaccharide diol derivative 11 in 93% yield (Scheme 2).
In another experiment, thioglycoside derivative 5 was allowed
to condense with thioglycoside derivative 6 in the presence of a
combination of NIS-TMSOTf28,29 exploiting ‘armed-disarmed’ gly-
cosylation to furnish disaccharide thioglycoside derivative 12 in
74% yield (Scheme 2). The stereoselective formation of compound
12 was supported by its spectroscopic analysis [signals at d 5.52 (d,
J = 10.5 Hz, H-1D), 5.14 (d, J = 2.5 Hz, H-1E) and d 99.9 (C-1E), 81.3
(C-1D) in the 1H and 13C NMR spectra, respectively].
OPMP
HO
NPhth
NPhth
7
2
Ph
OBz
HO
AcO
O
b,c
O
O
SEt
O
SEt
NPhth
AcO
NPhth
5
8
Scheme 1. Reagents and conditions: (a) NaBH3CN, HCl–Et2O, 5 °C, 2 h, 82%; (b) 80%
aq AcOH, 80 °C, 1.5 h; (c) benzoyl cyanide, pyridine, CH2Cl2, room temperature, 2 h,
80% in two steps.
Finally, iodonium ion promoted regio- and stereoselective gly-
cosylation of disaccharide glycosyl donor 12 with the trisaccharide
glycosyl acceptor 13 in the presence of NIS-TMSOTf furnished
pentasaccharide derivative 13 in 74% yield. The formation of
The stereoselective glycosylation of thioglycoside derivative 3
with thioglycoside derivative 4 in the presence of a combination
of N-iodosuccinimide (NIS) and trimethylsilyl trifluoromethanesul-
O
OBn
O
R2O
OBn
C
O
O
a
2
a
C
BnO
O
R3O
3 + 4
BnO
R1O
O
OBn
O
BzO
BzO
O
B
SEt
O
BzO
BzO
O
B
A
OBz
OPMP
9
OBz
NPhth
10: R1 = H; R2,R3
=
(CH3)2C
b, c
BnO
11:
E
R
1 = Ac; R2,R3 = H
OBz
O
O
a
BnO
BnO
O
5 + 6
D
SEt
AcO
NPhth
12
Scheme 2. Reagents and conditions: (a) N-iodosuccinimide (NIS), TMSOTf, MS-4Å, CH2Cl2, ꢀ30 °C, 45 min, 73% for compound 9, 71% for compound 10 and 74% for compound
12; (b) acetic anhydride, pyridine, room temperature, 2 h; (c) 80% aq AcOH, 80 °C, 1.5 h, 93% over two steps.

944
A. Sau et al. / Tetrahedron: Asymmetry 24 (2013) 942–946
BnO
E
HO
OBn
O
OBz
O
BnO
BnO
O
b, c, d, e
a
O
1
C
11 + 12
D
O
AcO
BnO
NPhth
O
OBn
AcO
O
O
BzO
BzO
O
B
A
OPMP
OBz
NPhth
13
Scheme 3. Reagents and conditions: (a) NIS, TMSOTf, MS-4Å, CH2Cl2, ꢀ30 °C, 45 min, 74%; (b) NH2NH2ꢃH2O, CH3CH2OH, 80 °C, 8 h; (c) acetic anhydride, pyridine, room
temperature, 3 h; (d) Et3SiH, 10% Pd-C, CH3OH, room temperature, 12 h; (e) 0.1 M CH3ONa, CH3OH, room temperature, 4 h, 60% overall yield.
compound 13 was confirmed by its spectroscopic analysis [signals
at d 5.77 (d, J = 8.5 Hz, H-1A), 5.47 (d, J = 8.5 Hz, H-1D), 5.01 (br s, H-
1E), 4.87 (d, J = 8.0 Hz, H-1B), 4.47 (d, J = 3.5 Hz, H-1C) and d 101.4
(C-1A), 100.3 (C-1C), 98.7 (C-1D), 97.9 (C-1E), 97.2 (C-1B) in the 1H
and 13C NMR spectra, respectively]. Compound 13 was subjected
to a series of reactions involving (a) removal of N-phthalimido
group using hydrazine hydrate;32 (b) acetylation using acetic anhy-
dride and pyridine; (c) catalytic transfer hydrogenation using tri-
ethylsilane and Pd-C33 and (d) de-O-acetylation using sodium
methoxide to furnish compound 1, which was purified using
SephadexÒ LH-20 gel to give pure compound 1 in 60% yield. Spec-
troscopic analysis of compound 1 unambiguously confirmed its
formation [signals at d 5.12 (br s, H-1E), 5.05 (d, J = 8.5 Hz, H-1A),
4.90 (d, J = 8.5 Hz, H-1D), 4.87 (d, J = 3.0 Hz, H-1C), 4.62 (d,
J = 7.5 Hz, H-1B) and 104.0 (C-1B), 103.1 (C-1D), 101.7 (C-1E),
100.6 (C-1A), 98.6 (C-1C) in the 1H and 13C NMR spectra, respec-
tively] (Scheme 3).
layer was washed with water, dried (Na2SO4), and concentrated
to give the crude product, which was purified over SiO2 using hex-
ane/EtOAc (3:1) as eluant to give pure compound 2 (3.3 g, 82%).
White solid; mp 147–148 °C; ½a D25
¼ þ6 (c 1.0, CHCl3); IR (KBr):
ꢂ
3418, 3064, 2870, 1776, 1717, 1600, 1500, 1478, 1217, 1099,
914 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.79–7.25 (m, 9 H, Ar-H),
;
6.83 (d, J = 9.0 Hz, 2 H, Ar-H), 6.68 (d, J = 9.0 Hz, 2 H, Ar-H), 5.67
(d, J = 8.0 Hz, 1 H, H-1), 4.60 (d, J = 12.0 hz, 1 H, PhCH2), 4.55 (d,
J = 12.0 Hz, 1 H, PhCH2), 4.36–4.30 (m, 2 H, H-6ab), 3.80–3.75 (m,
2 H, H-4, H-5), 3.69 (s, 3 H, OCH3), 3.67–3.62 (m, 2 H, H-2, H-3);
13C NMR (125 MHz, CDCl3): d 168.3 (PhthCO), 155.4–114.4 (Ar-C),
97.5 (C-1), 74.4 (C-3), 73.7 (PhCH2), 73.3 (C-4), 71.7 (C-5), 70.0
(C-6), 56.3 (OCH3), 55.5 (C-2); ESI-MS: 528.1 [M+Na]+; Anal. Calcd
for C28H27NO8 (505.17): C, 66.53; H, 5.38. Found: C, 66.40; H, 5.60.
4.1.2. Ethyl 3-O-acetyl-6-O-benzoyl-2-deoxy-2-N-phthalimido-
1-thio-b-D-galactopyranoside 5
A solution of compound 8 (4 g, 8.27 mmol) in 80% aq AcOH
(100 mL) was allowed to stir at 80 °C for 1.5 h. The solvents were
then removed under reduced pressure and the reaction mixture
was co-evaporated with toluene. To a solution of the crude product
in CH2Cl2 (30 mL) were added pyridine (5 mL) and benzoyl cyanide
(1.1 g, 8.38 mmol) and the reaction mixture was stirred at room
temperature for 2 h. The reaction mixture was diluted with CH2Cl2
(100 mL) and successively washed with 1 M HCl, satd NaHCO3 and
water, dried (Na2SO4), and concentrated. The crude product was
purified over SiO2 using hexane/Et2O (3:1) as eluant to give pure
3. Conclusion
In conclusion, a convenient synthesis for the pentasaccharide
repeating unit of the O-antigen of E. coli O102 has been successfully
developed using a [2+3] block glycosylation strategy. The ‘arm-dis-
armed’ glycosylation and ‘orthogonal’ protecting group concept
has been applied during the synthesis of the target compound.
The yields and stereoselectivity of the glycosylation were excellent.
compound 5 (3.3 g, 80%). Yellow oil; ½a D25
ꢂ
¼ þ29 (c 1.0, CHCl3); IR
4. Experimental
4.1. General
(neat): 3443, 2926, 1718, 1638, 1219, 1080, 770 cmꢀ1
;
1H NMR
(500 MHz, CDCl3): d 8.08–7.40 (m, 9 H, Ar-H), 5.73 (dd, J = 11.0,
3.0 Hz, H, H-3), 5.47 (d, J = 10.5 Hz, H, H-1), 4.68 (t,
1
1
All reactions were monitored by thin layer chromatography over
silica gel-coated TLC plates. The spots on TLC were visualized by
warming ceric sulfate [2% Ce(SO4)2 in 2 N H2SO4]-sprayed plates
on a hot plate. Silica gel 230–400 mesh was used for column chro-
matography. 1H and 13C NMR, DEPT 135, 2D COSY, and 2D HSQC
NMR spectra were recorded on Brucker Avance DRX 500 MHz spec-
trometers using CDCl3 and D2O as solvents and TMS as the internal
reference unless stated otherwise. Chemical shift values are ex-
J = 11.0 Hz each, 1 H, H-2), 4.65 (dd, J = 11.5, 6.0 Hz, 1 H, H-6a),
4.55 (dd, J = 11.5, 6.0 Hz, 1 H, H-6b), 4.24 (d, J = 3.0 Hz, 1 H, H-4),
4.11–4.09 (m, 1 H, H-5), 2.73–2.60 (m, 2 H, SCH2CH3), 1.96 (s, 3
H, COCH3), 1.25 (t, J = 7.4 Hz each, 3 H, SCH2CH3); 13C NMR
(125 MHz, CDCl3): d 169.7 (COCH3), 167.9, 167.8 (PhthCO), 166.3
(PhCO), 134.2–123.6 (Ar-C), 81.3 (C-1), 76.1 (C-3), 71.2 (C-4),
66.8 (C-5), 63.1 (C-6), 50.1 (C-2), 24.2 (SCH2CH3), 20.7 (COCH3),
14.9 (SCH2CH3); ESI-MS: 522.1 [M+Na]+; Anal. Calcd for C25H25-
NO8S (499.13): C, 60.11; H, 5.04. Found: C, 59.93; H, 5.20.
pressed in
d ppm. MALDI-MS were recorded on a Bruker
Daltronics mass spectrometer. Elementary analysis was carried
out on a Carlo Erba analyzer. Optical rotations were measured at
25 °C on a Jasco P-2000 polarimeter. Commercially available grades
of organic solvents of adequate purity are used in all reactions.
4.1.3. Ethyl (2,6-di-O-benzyl-3,4-O-isopropylidene-
a
-
D
-galacto
pyranosyl)-(1?6)-2,3,4-tri-O-benzoyl-1-thio-b-D-glucopyranosi-
de 9
To a solution of compound 3 (2 g, 3.72 mmol) and compound 4
(1.7 g, 3.82 mmol) in anhydrous CH2Cl2 (10 mL) was added MS-4Å
(2 g) and the reaction mixture was stirred at ꢀ30 °C for 30 min un-
der argon. To the cooled reaction mixture was added NIS (0.9 g,
4.1.1. p-Methoxyphenyl 6-O-benzyl-2-deoxy-2-N-phthalimido-
b-D
-galactopyranoside 2
To a solution of compound 7 (4 g, 7.94 mmol) in anhydrous THF
(25 mL) were added NaBH3CN (3 g, 47.74 mmol) and MS-3Å (5 g)
and the reaction mixture was allowed to stir at 0 °C for 15 min.
To the cooled reaction mixture was added dropwise HCl–Et2O
(ꢁ10 mL) until the pH of the solution became ꢁ2. After stirring
the reaction mixture at 5 °C for 1 h, it was poured into a satd.
NaHCO3 solution and extracted with CH2Cl2 (150 mL). The organic
4.0 mmol) followed by TMSOTf (5 lL) and then allowed to stir at
the same temperature for 45 min. The reaction mixture was
poured into a 5% Na2S2O3 solution and extracted with CH2Cl2
(100 mL). The organic layer was washed with satd NaHCO3 and
water, dried (Na2SO4), and concentrated. The crude product was
purified over SiO2 using hexane/EtOAc (7:1) as eluant to give pure

A. Sau et al. / Tetrahedron: Asymmetry 24 (2013) 942–946
945
compound 9 (2.5 g, 73%). White solid; mp 55–56 °C; ½a D25
ꢂ
¼ þ30 (c
pressure to give the acetylated product. A solution of the acetylated
product in 80% aq AcOH (mL) was stirred at 80 °C for 1.5 h and the
solvents were removed under reduced pressure. The crude product
was purified over SiO2 using hexane/EtOAc (4:1) as eluant to give
1.0, CHCl3); IR (KBr): 3442, 3064, 2930, 1736, 1602, 1494, 1452,
1380, 1315, 1260, 1092, 872, 755, 709, 617, 510 cmꢀ1 1H NMR
;
(500 MHz, CDCl3): d 7.95–7.20 (m, 25 H, Ar-H), 5.85 (t, J = 9.5 Hz
each, 1 H, H-3B), 5.53 (t, J = 10.0 Hz, each, 1 H, H-2B), 5.49, (t,
J = 10.0 Hz each, 1 H, H-4B), 4.81 (d, J = 12.5 Hz, 1 H, PhCH2), 4.79
(br s, 1 H, H-1C), 4.75 (d, J = 10 Hz, 1 H, H-1B), 4.67 (d, J = 12.5 Hz,
1 H, PhCH2), 4.56 (d, J = 12.5 Hz, 1 H, PhCH2), 4.49 (d, J = 12.5 Hz,
1 H, PhCH2), 4.32 (dd, J = 9.0, 3.0 Hz, 1 H, H-3C), 4.26–4.24 (m, 1
H, H-5C), 4.09–4.05 (m, 2 H, H-4C, H-5B), 3.90 (dd, J = 12.0, 6.0 Hz,
1 H, H-6aC), 3.65–3.58 (m, 3 H, H-6bC, H-6abB), 3.48 (dd, J = 10.0,
3.5 Hz, 1 H, H-2C), 2.79–2.71 (m, 2 H, SCH2CH3), 1.38, 1.32 (2 s, 6
H, 2 COCH3), 1.23 (t, J = 7.4 Hz each, 3 H, SCH2CH3); 13C NMR
(125 MHz, CDCl3): d 165.7, 165.1, 165.1, 165.0, (3 PhCO), 138.4–
127.4 (Ar-C), 109.0 (C(CH3)2), 97.4 (C-1C), 83.5 (C-1B), 77.4 (C-4C),
76.6 (C-2C), 75.8 (C-3C), 74.4 (C-3B), 73.8 (C-5B), 73.1 (PhCH2),
72.4 (PhCH2), 70.5 (C-4B), 69.6 (C-2B), 69.4 (C-6C), 67.1 (C-6B),
66.5 (C-5C), 28.2 (CH3), 26.4 (CH3), 23.9 (SCH2CH3), 14.9 (SCH2CH3);
ESI-MS: 941.3 [M+Na]+; Anal. Calcd for C52H54O13S (918.32): C,
67.96; H, 5.92. Found: C, 67.80; H, 6.15.
pure compound 11 (1.4 g, 93%). Yellow oil; ½a D25
¼ þ12 (c 1.0,
ꢂ
CHCl3); IR (neat): 3480, 3064, 3017, 2926, 2854, 1778, 1720, 1602,
1585, 1507, 1453, 1386, 1316, 1281, 1094, 830, 759, 710 cmꢀ1
;
1H
NMR (500 MHz, CDCl3): 8.05–7.23 (m, 34 H, Ar-H), 6.76
d
(d, J = 9.0 Hz, 2 H, Ar-H), 6.61 (d, J = 9.0 Hz, 2 H, Ar-H), 5.86
(t, J = 9.0 Hz each, 1 H, H-3B), 5.73 (d, J = 2.5 Hz, 1 H, H-4A), 5.64
(d, J = 8.5 Hz, 1 H, H-1A), 5.56 (t, J = 10.0 Hz each, 1 H, H-4B), 5.42
(t, J = 9.0 Hz each, 1 H, H-2B), 5.02 (d, J = 7.5 Hz, 1 H, H-1B), 4.70
(dd, J = 8.5 Hz, each, 1 H, H-2A), 4.62 (br s, 2 H, PhCH2), 4.53–4.45
(dd, J = 11.5 Hz, each, 2 H, PhCH2), 4.43 (br s, 2 H, PhCH2), 4.31 (dd,
J = 10.0, 3.0 Hz, 1 H, H-3A), 3.93–3.87 (m, 5 H, H-4C, H-5A, H-5C, H-
6
abA), 3.84–3.76 (m, 3 H, H-5B, H-6aB, H-6aC), 3.69 (dd, J = 9.5,
3.0 Hz, 1 H, H-2C), 3.66 (s, 3 H, OCH3), 3.57–3.54 (m, 3 H, H-3C, H-
bB, H-6bC), 1.69 (s, 3 H, COCH3); 13C NMR (125 MHz, CDCl3): d
6
169.9 (COCH3), 165.7, 165.4, 165.0 (3 PhCO), 155.6–114.3 (Ar-C),
100.9 (C-1B), 97.5 (C-1C), 97.3 (C-1A), 76.6 (C-2C), 74.3 (C-4C), 73.5
(C-5C), 73.4 (2 C, 2 PhCH2), 73.2 (2 C, C-2B, C-3A), 72.8 (PhCH2),
72.7 (C-3B), 70.4 (C-4A), 70.0 (C-6C), 69.9 (C-4B), 69.8 (C-6A), 69.6
(C-5A), 69.0 (C-3C), 68.7 (C-5B), 66.7 (C-6B), 55.4 (OCH3), 51.4
(C-2A), 20.3 (COCH3); ESI-MS: 1386.4 [M+Na]+; Anal. Calcd for
4.1.4. p-Methoxyphenyl (2,6-di-O-benzyl-3,4-O-isopropylidene-
a-D-galactopyranosyl)-(1?6)-2,3,4-tri-O-benzoyl-b-D-glucopyr-
anosyl)-(1?3)-6-O-benzyl-2-deoxy-2-N-phthalimido-b-D-galac
topyranoside 10
C77H73NO22 (1363.46): C, 67.78; H, 5.39. Found: C, 67.60; H, 5.60.
To a solution of compound 2 (1 g, 1.97 mmol) and compound 9
(2 g, 2.17 mmol) in anhydrous CH2Cl2 (10 mL) was added MS-4Å
(2 g) and the reaction mixture was stirred at ꢀ30 °C for 30 min un-
der argon. To the cooled reaction mixture was added NIS (0.5 g,
4.1.6. Ethyl (2,3,4-tri-O-benzyl- -rhamnopyranosyl)-(1?4)-3-
O-acetyl-6-O-benzoyl-2-deoxy-2-N-phthalimido-1-thio-b-D-gala
ctopyranoside 12
a
-L
2.22 mmol) followed by TMSOTf (3
l
L) and then allowed to stir
To a solution compound 5 (2 g, 4.0 mmol) and compound 6 (2 g,
4.17 mmol) in anhydrous CH2Cl2 (10 mL) was added MS-4Å (2 g)
and the reaction mixture was stirred at ꢀ30 °C for 30 min under ar-
gon. To the cooled reaction mixture was added NIS (950 mg,
at the same temperature for 45 min. The reaction mixture was
poured into a 5% Na2S2O3 solution and extracted with CH2Cl2
(100 mL). The organic layer was washed with satd NaHCO3 and
water, dried (Na2SO4), and concentrated. The crude product was
purified over SiO2 using hexane/EtOAc (7:1) as eluant to give pure
4.22 mmol) followed by TMSOTf (5 lL) and it was allowed to stir
at the same temperature for 45 min. The reaction mixture was
poured into 5% Na2S2O3 solution and extracted with CH2Cl2
(100 mL). The organic layer was washed with satd NaHCO3 and
water, dried (Na2SO4), and concentrated. The crude product was
purified over SiO2 using hexane/EtOAc (7:1) as eluant to give pure
compound 10 (1.9 g, 71%). Yellow oil; ½a D25
¼ þ35 (c 1.0, CHCl3); IR
ꢂ
(neat): 3457, 3254, 2897, 2453, 1756, 1709, 1645, 1576, 1487,
1324, 1245, 1176, 1095, 765, 710 cmꢀ1; 1H NMR (500 MHz, CDCl3):
d 7.92–7.21 (m, 34 H, Ar-H), 6.77 (d, J = 9.0 Hz, 2 H, Ar-H), 6.62 (d,
J = 9.0 Hz, 2 H, Ar-H), 5.68 (t, J = 9.5 Hz each, 1 H, H-3B), 5.64 (d,
J = 8.5 Hz, 1 H, H-1A), 5.24 (t, J = 8.5 Hz each, 1 H, H-2B), 5.20 (t,
J = 8.5 Hz, each, 1 H, H-4B), 5.06 (d, J = 8.0 Hz, each, 1 H, H-1B),
4.78 (d, J = 10.5 Hz, 1 H, PhCH2), 4.76 (br s, 1 H, H-1C), 4.64–4.61
(m, 3 H, PhCH2), 4.55–4.48 (m, 2 H, PhCH2), 4.45 (dd, J = 8.5 each
1 H, H-2A), 4.41–4.35 (m, 1 H, H-5A), 4.27–4.24 (m, 2 H, H-3C, H-
5C), 4.15 (d, J = 2.5 Hz, 1 H, H-4A), 3.98–3.95 (m, 2 H, H-4C, H-
compound 12 (2.7 g, 74%). Yellow oil; ½a D25
¼ þ10 (c 1.0, CHCl3); IR
ꢂ
(neat): 3080, 2980, 1750, 1654, 1345, 1437, 1324, 1256, 1123,
1098, 1076, 789, 745, 710 cmꢀ1 1H NMR (500 MHz, CDCl3): d
;
8.05–7.26 (m, 24 H, Ar-H) 5.77 (dd, J = 11.0, 3.0 Hz, 1 H, H-3D),
5.52 (d, J = 10.5 Hz, 1 H, H-1D), 5.14 (d, J = 2.5 Hz, 1 H, H-1E),
4.87–4.71 (m, 6 H, PhCH2), 4.60–4.56 (m, 2 H, H-2D, H-6aD), 4.43
(dd, J = 11.5, 6.0 Hz, 1 H, H-6bD), 4.32 (d, J = 2.0 Hz, 1 H, H-4D),
4.15–4.12 (m, 1 H, H-5D), 4.09–4.08 (m, 1 H, H-2E), 3.96 (dd,
J = 8.0, 2.5 Hz, 1 H, H-3E), 3.84–3.78 (m, 1 H, H-5E), 3.58 (t,
J = 8.5 Hz each, 1 H, H-4E), 2.78–2.62 (m, 2 H, SCH2CH3), 1.76 (s, 3
H, COCH3), 1.26 (d, J = 6.0 Hz, 3 H, CH3), 1.23 (t, J = 7.4 Hz each, 3
H, SCH2CH3); 13C NMR (125 MHz, CDCl3): d 169.4 (COCH3), 165.9
(PhCO), 138.5–123.6 (Ar-C), 99.9 (C-1E), 81.3 (C-1D), 80.3
(C-4E), 79.5 (C-3E), 75.9 (C-2E), 75.8 (C-5D), 74.7 (PhCH2), 73.1
(PhCH2), 72.5 (C-4D), 72.3 (PhCH2), 71.9 (C-3D), 69.5 (C-5E), 63.1
(C-6D), 50.3 (C-2D), 24.2 (SCH2CH3), 20.5 (COCH3), 18.1 (CH3),
6aC), 3.87–3.81 (m, 2 H, H-6aA, H-6aB), 3.75–3.70 (m, H-5B, H-6bC),
3.68–3.66 (m, 1 H, H-6bB), 3.65 (s, 3 H, OCH3), 3.54 (dd, J = 10.0,
3.5 Hz, 1 H, H-3A), 3.51–3.47 (m, 1 H, H-6bA), 3.46 (dd, J = 10.0,
3.0 Hz, 1 H, H-2C), 1.31, 1.09 (2 s, 6 H, 2 CH3); 13C NMR
(125 MHz, CDCl3): d 165.7, 165.5, 165.0 (3 PhCO), 155.6–114.4
(Ar-C), 109.0 (C(CH3)2), 101.3 (C-1B), 97.5 (C-1A), 97.2 (C-1C), 77.3
(C-4A), 76.6 (C-3C), 75.9 (C-2C), 73.9 (C-4C), 73.7 (C-3B), 73.4
(PhCH2), 73.1 (C-5B), 73.0 (C-2B), 72.7 (C-4B), 72.4 (PhCH2), 72.3
(PhCH2), 69.5 (C-5C), 69.4 (C-6C), 68.9 (C-6A), 68.6 (C-3A), 66.9 (C-
6B), 66.1 (C-5A), 55.4 (OCH3), 54.6 (C-2A), 28.2 (CH3), 26.3 (CH3);
ESI-MS: 1384.4 [M+Na]+; Anal. Calcd for C78H75NO21 (1361.48):
C, 68.76; H, 5.55. Found: C, 68.58; H, 5.70.
15.0 (SCH2CH3); ESI-MS: 938.3 [M+Na]+; Anal. Calcd for C52H53
-
NO12S (915.32): C, 68.18; H, 5.83. Found: C, 68.00; H, 6.00.
4.1.7. p-Methoxyphenyl (2,3,4-tri-O-benzyl-
syl)-(1?4)-(3-O-acetyl-6-O-benzoyl-2-deoxy-2-N-phthalimido-
b- -galactopyranosyl)-(1?3)-(2,6-di-O-benzyl- -galactopyran
osyl)-(1?6)-(2,3,4-tri-O-benzoyl-b- -glucopyranosyl)-(1?3)-4-
a-L-rhamnopyrano
4.1.5. p-Methoxyphenyl (2,6-di-O-benzyl-
a-D-galactopyranosyl)
-(1?6)-2,3,4-tri-O-benzoyl-b- -glucopyranosyl)-(1?3)-4-O-
D
D
a-D
acetyl-6-O-benzyl-2-deoxy-2-N-phthalimido-b-
D-galactopyrano-
D
side 11
O-acetyl-6-O-benzyl-2-deoxy-2-N-phthalimido-b-D-galactopyra
A solution of compound 10 (1.5 g, 1.10 mmol) in acetic anhy-
dride (3 mL) and pyridine (3 mL) was allowed to stir at room tem-
perature for 2 h. The solvents were removed under reduced
noside 13
To a solution of compound 11 (1 g, 0.73 mmol) and compound
12 (0.7 g, 0.76 mmol) in anhydrous CH2Cl2 (10 mL) was added

946
A. Sau et al. / Tetrahedron: Asymmetry 24 (2013) 942–946
MS-4Å (2 g) and the reaction mixture was stirred at ꢀ30 °C for
2A), 4.17–4.13 (m, 2 H, H-4A, H-4D), 4.10 (br s, 1 H, H-4C), 4.08–
4.00 (m, 1 H, H-2D), 3.98–3.91 (m, 3 H, H-2E, H-3C, H-5C), 3.88–
3.78 (m, 6 H, H-3A, H-3D, H-4B, H-5B, H-5D, H-6aC), 3.76–3.55 (m,
9 H, H-3E, H-5E, H-6abA, H-6abB, H-6abD, H-6bC), 3.69 (s, 3 H,
OCH3), 3.44–3.32 (m, 5 H, H-2B, H-2C, H-3B, H-4E, H-5A), 2.11,
1.80 (2 s, 6 H, 2 COCH3), 1.19 (d, J = 6.0 Hz, 3 H, CCH3); 13C NMR
(125 MHz, D2O): d 175.8, 173.7 (2 COCH3), 154.8–115.0 (Ar-C),
104.0 (C-1B), 103.1 (C-1D), 101.7 (C-1E), 100.6 (C-1A), 98.6 (C-1C),
76.7 (C-4A), 75.7 (C-5A), 75.1 (C-3C), 74.8 (C-2E), 74.5 (C-3D), 74.4
(C-2B), 73.7 (C-2C), 72.1 (C-3E), 71.7 (C-4E), 71.4 (C-5C), 70.5 (C-
5E), 70.2 (C-3B), 70.0 (C-3A), 69.4 (C-4B), 69.2 (C-4C), 69.0 (C-4D),
67.2 (C-5B), 66.2 (C-5D), 61.4 (C-6C), 61.0 (2 C, C-6B, C-6D), 60.7
(C-6A), 55.8 (OCH3), 53.7 (C-2D), 53.4 (C-2A), 22.4, 20.0 (2 COCH3)
16.6 (CCH3); ESI-MS: 1023.3 [M+Na]+; Anal. Calcd for
30 min under argon. To the cooled reaction mixture was added
NIS (190 mg, 0.84 mmol) followed by TMSOTf (2 lL) and then al-
lowed to stir at the same temperature for 45 min. The reaction
mixture was poured into a 5% Na2S2O3 solution and extracted with
CH2Cl2 (50 mL). The organic layer was washed with satd. NaHCO3
and water, dried (Na2SO4), and concentrated. The crude product
was purified over SiO2 using hexane/EtOAc (7:1) as eluant to give
pure compound 13 (1.2 g, 74%). Yellow oil; ½a D25
¼ þ8 (c 1.0,
ꢂ
CHCl3); IR (neat): 3272, 3064, 3017, 2930, 1778, 1721, 1602,
1507, 1453, 1430, 1585, 1507, 1452, 1430, 1385, 1282, 1261,
1218, 1177, 1028, 919, 755, 710, 667 cmꢀ1 1H NMR (500 MHz,
;
CDCl3): d 8.07–6.97 (m, 58 H, Ar-H), 6.77 (d, J = 9.0 Hz, 2 H, Ar-
H), 6.48 (d, J = 9.0 Hz, 2 H, Ar-H), 5.86 (br s, 1 H, H-4A), 5.84 (t,
J = 10.5 Hz each, 1 H, H-3B), 5.77 (d, J = 8.5 Hz, 1 H, H-1A), 5.64
(dd, J = 10.0, 3.0 Hz, 1 H, H-3D), 5.47 (d, J = 8.5 Hz, 1 H, H-1D),
5.43 (t, J = 9.5 Hz each, 1 H, H-2B), 5.35 (t, J = 9.5 Hz each, 1 H, H-
4B), 5.01 (br s, 1 H, H-1E), 4.87 (d, J = 8.0 Hz, 1 H, H-1B), 4.82–4.76
(m, 5 H, PhCH2), 4.74–4.70 (m, 2 H, H-2A, H-2D), 4.59–4.51 (m, 4
H, PhCH2), 4.47 (d, J = 3.5 Hz, 1 H, H-1C), 4.41 (d, J = 11.5 Hz,
PhCH2), 4.34 (d, J = 11.5 Hz, 1 H, PhCH2), 4.28–4.17 (m, 4 H, H-4D,
H-6aB, H-6aD, PhCH2), 4.12–4.07 (m, 3 H, H-6abA, H-6bD), 4.06 (br
s, 1 H, H-2E), 3.95–3.89 (m, 4 H, H-5A, H-5E, H-6bB, H-6aC), 3.87–
3.75 (m, 2 H, H-3A, H-3E), 3.74–3.70 (m, 1 H, H-5B), 3.67–3.65 (m,
2 H, H-2C, H-4C), 3.57 (s, 3 H, OCH3), 3.56–3.51 (m, 2 H, H-5C, H-
5D), 3.40 (dd, J = 10.0, 3.0 Hz, 1 H, H-3C), 3.35–3.27 (m, 2 H, H-4E,
H-6bC), 1.77, 1.70 (2 s, 6 H, 2 COCH3), 0.87 (d, J = 6.0 Hz, 3 H,
CH3); 13C NMR (125 MHz, CDCl3): d 170.4, 170.0, (2 COCH3),
167.9, 167.8 (2 PhthCO), 165.6, 165.5, 165.3, 165.1 (4 PhCO),
155.6–114.2 (Ar-C), 101.4 (C-1A), 100.3 (C-1C), 98.7 (C-1D), 97.9
(C-1E), 97.2 (C-1B), 80.7 (C-5A), 80.5 (C-5D), 78.9 (C-3A), 76.7 (C-
3D), 76.1 (C-2E), 75.6 (C-4D), 74.7 (C-3E), 74.6 (PhCH2), 74.0 (C-
4C), 73.7 (PhCH2), 73.4 (C-3C), 73.2 (2 C, 2 PhCH2), 73.1 (PhCH2),
73.0 (PhCH2), 72.8 (C-4A), 72.3 (C-2B), 71.9 (C-4B), 70.0 (C-4E),
70.6 (C-6A), 70.3 (C-3B), 69.7 (C-6D), 69.5 (C-5C), 68.7 (C-5B), 68.5
(C-5E), 66.7 (C-6C), 62.8 (C-6B), 55.4 (OCH3), 51.4 (C-2A), 51.1 (C-
2D), 20.5 (COCH3), 20.4 (COCH3), 18.1 (CH3); MALDI-MS: 2239.7
[M+Na]+; Anal. Calcd for C127H120N2O34 (2216.77): C, 68.76; H,
5.45. Found: C, 68.57; H, 5.66.
C41H64N2O26 (1000.37): C, 49.20; H, 6.44. Found: C, 49.03; H, 6.66.
Acknowledgments
A.S. and D.D. thank CSIR, New Delhi for providing Senior and Ju-
nior Research Fellowships. This work was supported by DST, New
Delhi (Project No. SR/S1/OC-83/2010).
References
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4.1.8. p-Methoxyphenyl (
mido-2-deoxy-b- -galactopyranosyl)-(1?3)-(
osyl)-(1?6)-(b- -glucopyranosyl)-(1?3)-2-acetamido-2-deoxy-
b- -galactopyranoside 1
To a solution of compound 13 (1 g, 0.45 mmol) in EtOH (10 mL)
a
-
L
-rhamnopyranosyl)-(1?4)-(2-aceta
D
a-D-galactopyran-
D
D
was added NH2NH2ꢃH2O (0.5 mL, 10.3 mmol) and the reaction mix-
ture was allowed to stir at 80 °C for 8 h. The reaction mixture was
then evaporated to dryness and a solution of the crude mass in ace-
tic anhydride (2 mL) and pyridine (2 mL) was kept at room temper-
ature for 3 h and concentrated under reduced pressure. To a
solution of the crude acetylated product in CH3OH (10 mL) was
added 10% Pd-C (150 mg) followed by the dropwise addition of Et3-
SiH (1 mL, 6.26 mmol) and the reaction mixture was allowed to stir
at room temperature for 12 h. The reaction mixture was filtered
through a CeliteÒ bed and the filtrate was concentrated under re-
duced pressure. A solution of the crude product in 0.1 M CH3ONa
(10 mL) was allowed to stir at room temperature for 4 h, neutral-
ized with Dowex 50 W X8 (H+) resin, filtered, and concentrated.
The crude product was purified over SephadexÒ LH-20 gel using
CH3OH/H2O (4:1) as eluant to give pure compound 1 (270 mg,
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60%). Glass; ½a 2D5
ꢂ
¼ þ4 (c 1.0, H2O); IR (KBr): 3020, 2929, 1742,
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1367, 1214, 1066, 799 cmꢀ1
;
1H NMR (500 MHz, D2O): d 6.99 (d,
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J = 9.0 Hz, 2 H, Ar-H), 6.68 (d, J = 9.0 Hz, 2 H, Ar-H), 6.86 (d,
J = 9.0 Hz, 2 H, Ar-H), 5.12 (br s, 1 H, H-1E), 5.05 (d, J = 8.5 Hz, 1
H, H-1A), 4.90 (d, J = 8.5 Hz, 1 H, H-1D), 4.87 (d, J = 3.0 Hz, 1 H, H-
1C), 4.62 (d, J = 7.5 Hz, 1 H, H-1B), 4.20 (t, J = 8.5 Hz each, 1 H, H-
33. Santra, A.; Ghosh, T.; Misra, A. K.; Beilstein, J. Org. Chem. 2013, 9, 74–78.