Synthesis of tri- and pentasaccharide fragments corresponding to the O-antigen of Shigella boydii type 6

Article abstract of DOI:10.1016/j.tetasy.2010.10.032

A convenient synthetic strategy for the synthesis of the acidic pentasaccharide repeating unit and its trisaccharide fragment corresponding to the O-antigen of Shigella boydii type 6 has been successfully developed. A stereoselective sequential glycosylation method has been exploited to obtain the target tri- and pentasaccharide derivatives. Most of the synthetic intermediates were solid and prepared in high yields from commercially available reducing sugars following a series of protection-deprotection reactions. A late-stage TEMPO mediated selective oxidation reaction finally resulted in the pentasaccharide containing a glucuronic acid unit. A 2-(4-methoxyphenoxy) ethyl group has been chosen as the anomeric protecting group to provide trisaccharide and pentasaccharide derivatives linked to an ethylene glycol linker.

Full text of DOI:10.1016/j.tetasy.2010.10.032

Tetrahedron: Asymmetry 21 (2010) 2612–2618
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of tri- and pentasaccharide fragments corresponding
to the O-antigen of Shigella boydii type 6
⇑
Abhishek Santra, Anup Kumar Misra
Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata 700 054, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A convenient synthetic strategy for the synthesis of the acidic pentasaccharide repeating unit and its tri-
saccharide fragment corresponding to the O-antigen of Shigella boydii type 6 has been successfully devel-
oped. A stereoselective sequential glycosylation method has been exploited to obtain the target tri- and
pentasaccharide derivatives. Most of the synthetic intermediates were solid and prepared in high yields
from commercially available reducing sugars following a series of protection–deprotection reactions. A
late-stage TEMPO mediated selective oxidation reaction finally resulted in the pentasaccharide contain-
ing a glucuronic acid unit. A 2-(4-methoxyphenoxy) ethyl group has been chosen as the anomeric pro-
tecting group to provide trisaccharide and pentasaccharide derivatives linked to an ethylene glycol linker.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 28 July 2010
Revised 22 October 2010
Accepted 28 October 2010
1. Introduction
tant bacterial strains demands the development of alternative
methods toward the development of anti-shigellosis agents.7 Since,
Shigella is a well-documented human pathogen responsible for
diarrheal disease and bacilliary dysentery (shigellosis). Shigella
dysenteriae is the most virulent bacilli among the genus Shigella
and has the potential for causing devastating health problems in
developing countries.1 Shigella strains are divided into four species:
Shigella boydii, S. dysenteriae, Shigella flexneri, and Shigella sonnei,
which are also known as Shigella subgroups A, B, C, and D, respec-
tively.2 The first three species are typed into multiple serotypes,
based on the antigenic variation in their O-antigens.3 All Shigella
O-antigens, except for a few, are acidic due to the presence of
either a sugar acid (uronic or pseudaminic acid) or a noncarbohy-
drate acidic component, such as lactic acid ethers, pyruvic acid ace-
tals, or alanine.4 Recently Senchenkova et al. reported a revised
structure of the D-glucuronic acid containing pentasaccharide
repeating unit of the O-antigen of S. boydii type 6 (Fig. 1).5 Long
back, Dmitriev et al.6 had initially reported the structure of this
O-antigen, which was partially incorrect.
O-antigenic polysaccharides are highly immunogenic and impor-
tant virulence factors, antibodies against the O-specific polysac-
charide of a particular Shigella strain could have the potential to
protect the host from shigella infections.8 A number of reports have
already appeared in the literature for the development of glycocon-
jugate based therapy against Shigella infections.9 For detailed bio-
logical studies with the glycoconjugates derived from the
pentasaccharide O-antigen of S. boydii type 6, a large quantity of
pentasaccharide is required, which is not accessible from a natural
source. Hence, chemical synthesis is the only option to obtain large
quantities of the particular oligosaccharide and its smaller frag-
ments. The synthesis of smaller fragments of the oligosaccharide
repeating unit is useful for determining the immunodominant
fragment of the whole oligosaccharide repeating unit. In this con-
text, we herein report a convenient synthesis of a trisaccharide and
a pentasaccharide as their 2-(4-methoxyphenoxy) ethyl glycoside
(1 and 2) corresponding to the O-antigen of S. boydii type 6 using
a sequential glycosylation strategy (Fig. 2). The 4-methoxyphenyl
(PMP) group can be easily removed under oxidative conditions to
give trisaccharide and pentasaccharide derivatives linked to an
ethylene glycol linker useful for the preparation of glycoconjugate
derivatives.
→3)-α-D-Galp-(1→6)-α-D-Manp-(1→2)-α-D-Manp-(1→3)-β-D-GalpNAc-(1→
4
↑
1
β-D-GlcpA
Figure 1. Pentasaccharide repeating unit of the O-antigen of Shigella boydii type 6.
2. Results and discussion
Although, a number of effective therapeutics have appeared in
the past to control Shigella infections, the emergence of drug resis-
The synthesis of trisaccharide 1 and pentasaccharide 2 as their
2-(4-methoxyphenoxy) ethyl glycoside (Fig. 2) was achieved using
a sequential glycosylation strategy via stereoselective glycosyla-
tion of monosaccharide intermediates. For this purpose, a series
⇑
Corresponding author. Tel.: +91 33 25693240; fax: +91 33 2355 3886.
E-mail address: akmisra69@gmail.com (A.K. Misra).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.10.032

A. Santra, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2612–2618
2613
HO
OH
HO
HO
OAc
O
HO
HO
HO
O
O
O
a, b
O
C
H3CO
AcO
ONa
O
HO
O
O
SEt
SEt
HO
HO
HO
HO
HO
8
9
E
O
HO
OH
O
OH
B
HO
c, d
O
O
A
D
O
O
HO
OPMP
HO
NHAc
HO
O
OAc
O
1
MBnO
AcO
AcO
O
HO
C
HO
O
HO
HO
HO
SEt
MBn: 4-Methoxybenzyl
5
O
HO
OH
B
O
Scheme 1. Reagents and conditions: (a) p-anisaldehyde dimethyl acetal, p-TsOH,
CH3CN, room temperature, 12 h; (b) acetic anhydride, pyridine, room temperature,
2 h, overall yield 79%; (c) NaBH3CN, TFA, DMF, room temperature, 10 h; (d) acetic
anhydride, pyridine, room temperature, 1 h, over all 73%.
A
O
O
2
OPMP
NHAc
PMP: 4-Methoxyphenyl
of an O-acetyl group at the C-2 position of compound 5, which
Ph
directs the formation of an
a-mannosidic linkage through neigh-
OAc
OAc
Ph
O
O
BnO
MBnO
AcO
AcO
O
boring group participation. The presence of signals in the NMR
spectra confirmed the formation of compound 12 [signals at d
5.68 (s, PhCH), 5.39 (s, PhCH), 5.17 (br s, H-1C), 4.95 (br s, H-1B),
4.27 (d, J = 8.0 Hz, H-1A) in the 1H NMR and d 102.7 (PhCH),
102.0 (PhCH), 101.0 (C-1A), 100.6 (C-1B), 96.5 (C-1C) in the 13C
NMR spectra]. The removal of functional groups from compound
12 involving hydrogenolysis17 followed by N-acetylation and
O-deacetylation furnished trisaccharide derivative 1 as its 2-(4-
methoxyphenoxy) ethyl glycoside in 66% yield, which was sup-
ported by its spectroscopic analysis [Signals at d 5.16 (br s, H-1C),
4.85 (br s, H-1B), 4.43 (d, J = 8.4 Hz, H-1A) in the 1H NMR and d
103.2 (C-1B), 102.1 (C-1A), 94.9 (C-1C) in the 13C NMR spectra]
(Scheme 2).
O
O
O
O
N3
HO
O
SEt
SEt
OPMP
5
4
3
AcO
BnO
OBn
OBz
O
O
BzO
BzO
SEt
OC(NH)CCl3
BnO
OBz
7
6
Figure 2. Structure of the synthesized trisaccharide 1 and pentasaccharide 2 as
their 2-(4-methoxyphenoxy) ethyl glycoside.
In a separate experiment, the O-acetoxy groups of compound 12
were converted into O-benzyl ethers under one-pot deacetylation–
of monosaccharide intermediates 3,10 4,11 5, 6,12 and 713 were pre-
pared from the commercially available reducing sugars using a ser-
ies of protection and deprotection reaction methodologies. A late-
stage TEMPO mediated selective oxidation of a primary hydroxyl
group in the presence of secondary hydroxyl groups under a
biphasic reaction condition has been applied to achieve the target
pentasaccharide 2 containing a D-glucuronic acid moiety. Stereo-
selective glycosylation reactions were carried out using either thio-
glycoside or glycosyl trichloroacetimidate derivatives under
different glycosylation conditions.
Ph
OR
Ph
O
O
BnO
a
O
3 + 4
B
b
O
O
O
O
A
O
OPMP
N3
10: R = Ac
11: R = H
Ethyl 1-thio-a
-D-mannopyranoside 814 was subjected to a se-
a
5
quence of functional group transformations involving 4-methoxy-
benzylidene acetal formation15 and acetylation to give compound
9 in 79% yield. Compound 9 was converted into ethyl 2,3,4-tri-O-
OR1
R2O
R1O
R1O
O
acetyl-6-O-(4-methoxybenzyl)-1-thio-a-D-mannopyranoside 5 in
C
73% yield after reductive ring opening15 of the benzylidene acetal
of compound 9 followed by acetylation (Scheme 1).
Ph
O
Ph
O
O
O
The stereoselective glycosylation of compound 3 with thiogly-
coside derivative 4 in the presence of an N-iodosuccinimide (NIS)
and trifluoromethane sulfonic acid (TfOH) combination16 furnished
disaccharide derivative 10 in 75% yield, which was deacetylated to
give the disaccharide acceptor 11 in 97% yield. The presence of an
O-acetyl group at the C-2 position of compound 4 favored the for-
mation of 1,2-trans-glycoside 10, which was confirmed from its
NMR spectra [signals at d 5.61 (s, PhCH), 5.57 (s, PhCH), 5.02 (br
s, H-1B), 4.43 (d, J = 8.0 Hz, H-1A) in the 1H NMR and d 102.8
(PhCH), 102.1 (COCH3), 101.3 (C-1A), 95.5 (C-1B) in the 13C NMR
spectra]. The iodonium ion mediated stereoselective coupling of
compound 11 with the thioglycoside donor 5 in the presence of
NIS-TfOH16 furnished trisaccharide derivative 12 in 72% yield.
The formation of trisaccharide 12 was influenced by the presence
B
O
BnO
O
O
O
A
O
OPMP
N3
e, f
12: R1 = Ac; R2 = MBn
13: R1 = Bn; R2 = MBn
14: R1 = Bn; R2 = H
1
c
d
PMP: 4-Methoxyphenyl
Scheme 2. Reagents and conditions: (a) N-iodosuccinimide (NIS), TfOH, CH2Cl2, MS
4 Å, ꢀ40 °C, 1 h, 75% for 10 and 72% for 12; (b) 0.1 M CH3ONa, CH3OH, room
temperature, 1 h, 97%; (c) benzyl bromide, NaOH, DMF, TBAB, room temperature,
5 h, 76%; (d) DDQ, CH2Cl2, H2O, room temperature, 2 h, 72%; (e) H2, 20% Pd(OH)2–C,
CH3OH, room temperature, 24 h; (f) (i) acetic anhydride, pyridine, room temper-
ature, 2 h; (ii) 0.1 M CH3ONa, CH3OH, room temperature, 1 h, overall yield 6%.

2614
A. Santra, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2612–2618
benzylation conditions18 to give compound 13 in 76% yield. Oxida-
tive removal19 of 4-methoxybenzyl group from compound 13
using DDQ furnished trisaccharide acceptor 14 in 72% yield. Iodo-
nium ion mediated 1,2-cis glycosylation of compound 14 with thio-
glycoside derivative 6 in the presence of NIS-TfOH16 furnished
tetrasaccharide derivative 15 in 76% yield, which was quantita-
tively deacetylated to give tetrasaccharide acceptor 16. Due to
the presence of an O-benzyl group at the C-2 position of compound
14
a
6
RO
OBn
O
D
BnO
BnO
O
OBn
O
6, desired a-linked glycosylation product 15 was obtained as a major
BnO
BnO
C
product together with a minor quantity of its 1,2-trans glycosylation
product (ꢁ12%), which was separated by flash column chromatogra-
phy. The formation of compound 15 was confirmed from its 1D and
2D NMR spectroscopic analysis [signals at d 5.52 (s, PhCH), 5.42 (s,
PhCH), 5.11 (br s, H-1C), 4.95 (br s, H-1B), 4.32 (br s, H-1D), 4.26 (d,
J = 7.9 Hz, H-1A) in the 1H NMR and d 170.3 (COCH3), 154.2–114.7
(Ar-C), 104.4 (JC-1/H-1 = 155 Hz, C-1A), 102.4 (JC-1/H-1 = 172.8 Hz, C-
1D), 101.6 (PhCH), 101.0 (PhCH), 100.3 (JC-1/H-1 = 170.5 Hz, C-1B),
96.1 (JC-1/H-1 = 171.3 Hz, C-1C), in the 13C NMR spectra]. Unambigu-
ous assignment of the stereochemistry of the glycosyl linkages in
compound 15 was achieved using gated 1H coupled 13C NMR, 2D
HMBC, and HMQC NMR spectra.20 The appearance of anomeric
carbon atoms with JC-1/H-1 = 155 Hz (b-D-GalpN), JC-1/H-1 = 171.3 Hz
Ph
O
Ph
O
O
O
B
O
BnO
O
O
O
A
O
15: R = Ac
16: R = H
OPMP
b
N3
c
7
OBz
O
BzO
BzO
E
O
OBn
O
OBz
BnO
(a-D-Manp), JC-1/H-1 = 170.5 Hz (
a-D-Manp) and JC-1/H-1 = 172.8 Hz
D
(a-D-Galp) indicates the presence of three axial and one equatorial
BnO
O
glycosyl linkages. The three bond correlations in the 2D HMBC spec-
trum also supported the regioselectivity of the glycosylyl linkages.
Gated 1H coupled 13C NMR spectrum of compound 15 also
confirmed the achievement of the desired stereochemical outcome
of previous glycosylation reactions. The stereoselective coupling of
OBn
O
BnO
BnO
C
Ph
O
Ph
O
O
BnO
O
B
compound 16 with trichloroacetimidate derivative
7 under
O
O
Schmidt’s glycosylation conditions21 furnished pentasaccharide
derivative 17 in 72% yield. The presence of signals in the NMR spec-
tra [d 5.60 (s, PhCH), 5.58 (s, PhCH), 5.20 (d, J = 7.9 Hz, H-1E), 5.11 (br
s, H-1C), 5.07 (br s, H-1B), 4.46 (br s, H-1D), 4.14 (d, J = 7.8 Hz, H-1A) in
the 1H NMR and d 105.1 (C-1A), 102.6 (C-1E), 102.3 (PhCH), 101.8
(PhCH), 101.4 (C-1D), 101.0 (C-1B), 97.2 (C-1C) in the 13C NMR spec-
tra] confirmed its formation. The presence of a neighboring group
participating 2-O-benzoyl group in the trichloroacetimidate donor
7 directed the exclusive formation of 1,2-trans glycosyl product
17. It is worth mentioning that use of thioglycoside derivatives as
a glycosyl donor was unsuccessful in furnishing the glycosylation
product. Compound 17 was converted into the target pentasaccha-
ride derivative 2 following a series of reactions involving saponifica-
tion using sodium methoxide, chemoselective TEMPO mediated
oxidation22 of the primary hydroxyl group to a carboxylic group un-
der phase transfer reaction condition, hydrogenolysis over Pearl-
man’s catalyst, and N-acetylation followed by O-deacetylation in
64% over all yield. Spectroscopic analysis of compound 2 supported
its formation [signals at d 5.19 (s, H-1C), 4.77 (br s, H-1B), 4.62 (d,
J = 8.1 Hz, H-1E), 4.40 (d, J = 7.8 Hz, H-1A), 4.17 (br s, H-1D) in the
1H NMR and d 174.6 (COONa), 105.4 (C-1A), 105.0 (C-1D), 103.8
(C-1B), 101.6 (C-1E), 101.0 (C-1C)] (Scheme 3).
O
17
O
A
O
OPMP
N3
d, e
2
Scheme 3. Reagents and conditions: (a) N-iodosuccinimide (NIS), TfOH, CH2Cl2, MS
4 Å, ꢀ25 °C, 45 min, 76%; (b) 0.1 M CH3ONa, CH3OH, room temperature, 1 h,
quantitative; (c) TMSOTf, CH2Cl2, ꢀ10 °C, 1 h, 72%; (d) (i) 0.1 M CH3ONa, CH3OH,
room temperature, 3 h; (ii) NaBr, CH2Cl2, H2O, TBAB, TEMPO, NaHCO3, NaOCl, 0–
5 °C, 3 h; (iii) tert-butanol, 2-methyl-but-2-ene, NaClO2, NaH2PO4, room tempera-
ture, 3 h; (e) (i) H2, 20% Pd(OH)2–C, room temperature, 24 h; (ii) acetic anhydride,
pyridine, room temperature, 4 h; (iii) 0.1 M CH3ONa, CH3OH, room temperature,
2 h, overall yield 64%.
4. Experimental
4.1. General methods
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, HMQC, HMBC,
and gated 1H coupled 13C NMR spectra were recorded on Brucker
Avance DRX 300 and 500 MHz spectrometers using CDCl3 and
CD3OD as solvents and TMS as internal reference unless stated
otherwise. Chemical shift values are expressed in d ppm. ESI-MS
were recorded on a Micromass Quttro II mass spectrometer.
Elementary analysis was carried out on Carlo Erba-1108 analyzer.
Optical rotations were measured at 25 °C on a Jasco P-2000 polar-
imeter. Commercially available grades of organic solvents of
adequate purity are used in all reactions.
3. Conclusion
In conclusion, a convenient synthetic strategy for the prepara-
tion of tri- and pentasaccharide fragments corresponding to the
O-specific polysaccharide of S. boydii type 6 has been successfully
developed. Stereoselective sequential glycosylation reactions
allowed us to obtain the target tri- and pentasaccharides in mini-
mum number of steps. All intermediate steps were reasonably high
yielding and reproducible for a scale-up preparation. Oligosaccha-
rides as their 2-(4-methoxyphenoxy) ethyl glycoside provide
access to an ethylene glycol linked tri- and pentasaccharide deriv-
atives for their further use.

A. Santra, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2612–2618
2615
4.1.1. Ethyl 2,3-di-O-acetyl-4,6-O-(4-methoxy)benzylidene-1-
thio- -D-mannopyranoside 9
same temperature for 1 h the reaction mixture was filtered
through a CeliteÒ bed and washed with CH2Cl2 (100 mL). The com-
bined organic layer was washed with 5% Na2S2O3, satd. NaHCO3,
and water in succession, dried (Na2SO4), and concentrated under
reduced pressure. The crude product was purified over SiO2 using
hexane–EtOAc (7:1) as eluant to give pure 10 (2.8 g, 75%). White
a
To a solution of compound 8 (3.0 g, 13.37 mmol) in dry CH3CN
(15 mL) were added 4-methoxybenzaldehyde dimethylacetal
(3.4 mL, 20 mmol) and p-TsOH (400 mg) and the reaction mixture
was allowed to stir at room temperature for 12 h. The reaction
mixture was neutralized with Et3N (1.5 mL) and concentrated un-
der reduced pressure. A solution of the crude product in acetic
anhydride–pyridine (10 mL, 1:1 v/v) was kept at room temperature
for 2 h and the solvents were removed under reduced pressure. The
crude product was purified over SiO2 using toluene–EtOAc (3:1) as
eluant to give pure 9 (4.5 g, 79%). White solid; mp 82–84 °C;
solid; mp 152–154 °C; ½a D25
¼ þ21:8 (c 1.2, CHCl3); mmax (KBr):
ꢂ
3336, 2926, 2111, 1735, 1711, 1509, 1457, 1230, 1172, 1060,
753, 697 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.53–7.25 (m, 15H,
;
Ar-H), 6.86–6.79 (m, 4H, Ar-H), 5.61 (s, 1H, PhCH), 5.57 (s, 1H,
PhCH), 5.37–5.36 (m, 1H, H-2B), 5.02 (br s, 1H, H-1B), 4.61 (br s,
2H, PhCH2), 4.43 (d, J = 8.0 Hz, 1H, H-1A), 4.32–4.27 (m, 2H,
OCH2), 4.23 (d, J = 3.2 Hz, 1H, H-4A), 4.21–4.18 (m, 1H, H-3A),
4.15–4.13 (m, 2H, OCH2), 4.07–4.03 (m, 4H, H-4B, H-5B, H-6abB),
3.98–3.94 (m, 1H, H-6aA), 3.83–3.78 (m, 2H, H-2A, H-6bA), 3.75 (s,
3H, OCH3), 3.60 (dd, J = 10.4, 3.6 Hz, 1H, H-3B), 3.37 (br s, 1H, H-
5A), 2.15 (s, 3H, COCH3); 13C NMR (125 MHz, CDCl3): d 170.5
(COCH3), 154.4–115.0 (Ar-C), 102.8 (PhCH), 102.1 (COCH3), 101.3
(C-1A), 95.5 (C-1B), 78.6 (C-4B), 74.8 (C-3B), 74.2 (C-5B), 73.0
(PhCH2), 71.1 (C-3A), 70.7 (C-2B), 69.5 (C-6A), 68.9 (C-6B), 68.6
(OCH2), 68.4 (OCH2), 66.8 (C-5A), 65.0 (C-4A), 61.4 (C-2A), 56.0
(OCH3), 21.4 (COCH3); ESI-MS: 848.3 [M+Na]+; Anal. Calcd for
C44H47N3O13 (825.31): C, 63.99; H, 5.74. Found: C, 63.78; H, 5.96.
½
a 2D5
ꢂ
¼ þ95:3 (c 1.2, CHCl3); mmax (KBr): 3462, 2930, 1740, 1519,
1254, 1224, 1095, 1025, 834, 753 cmꢀ1; 1H NMR (500 MHz, CDCl3):
d 7.38 (d, J = 8.7 Hz, 2H, Ar-H), 6.88 (d, J = 8.7 Hz, 2H, Ar-H), 5.53 (s,
1H, PhCH), 5.44–5.43 (m, 1H, H-2), 5.33 (dd, J = 10.3, 3.4 Hz, 1H, H-
3), 5.23 (br s, 1H, H-1), 4.35–4.31 (m, 1H, H-5), 4.23 (dd, J = 10.3,
4.9 Hz, 1H, H-6a), 4.06 (t, J = 10.0 Hz each, 1H, H-4), 3.86 (t,
J = 10.3 Hz each, 1H, H-6b), 3.79 (s, 3H, OCH3), 2.68–2.60 (m, 2H,
SCH2CH3), 2.16 (s, 3H, COCH3), 2.00 (s, 3H, COCH3), 1.29 (t,
J = 7.4 Hz each, 3H, SCH2CH3); 13C NMR (125 MHz, CDCl3): d
170.2 (COCH3), 170.2 (COCH3), 160.6–114.0 (Ar-C), 102.3 (PhCH),
83.6 (C-1), 76.7 (C-5), 72.1 (C-3), 69.1 (C-2), 68.9 (C-6), 64.9 (C-
4), 55.6 (OCH3), 25.8 (SCH2CH3), 21.3 (COCH3), 21.2 (COCH3), 15.2
(SCH2CH3); ESI-MS: 449.1 [M+Na]+; Anal. Calcd for C20H26O8S
(426.13): C, 56.32; H, 6.14. Found: C, 56.10; H, 6.40.
4.1.4. 2-(4-Methoxyphenoxy)ethyl (3-O-benzyl-4,6-O-
benzylidene-a-D-mannopyranosyl)-(1?3)-2-azido-4,6-O-
benzylidene-2-deoxy-b-D-galactopyranoside 11
4.1.2. Ethyl 2,3,4-tri-O-acetyl-6-O-(4-methoxybenzyl)-1-thio-
D-mannopyranoside 5
a
-
A solution of compound 10 (2.5 g, 3.03 mmol) in 0.1 M CH3ONa
(25 mL) was allowed to stir at room temperature for 1 h and neu-
tralized with Amberlite IR 120 (H+) resin. The reaction mixture was
filtered and concentrated under reduced pressure to give the crude
product, which was purified over SiO2 using hexane–EtOAc (5:1) as
eluant to give pure 11 (2.3 g, 97%). White solid; mp 158–159 °C;
To an ice-cooled solution of 9 (4.0 g, 9.38 mmol) in dry DMF
(10 mL) were added MS 3 Å (3 g) and NaBH3CN (3.0 g, 47.74 mmol)
followed by TFA (3.0 mL, 40.38 mmol) and the reaction mixture
was allowed to stir at room temperature for 10 h. The reaction
mixture was diluted with water and extracted with CH2Cl2
(100 mL). The organic layer was successively washed with satd.
NaHCO3 and water, dried (Na2SO4), and concentrated under re-
duced pressure. A solution of the crude product in acetic anhy-
dride–pyridine (8.0 mL, 1:1 v/v) was kept at room temperature
for 1 h and the solvents were removed under reduced pressure.
The crude product was purified over SiO2 using toluene–EtOAc
½
a 2D5
ꢂ
¼ þ33:7 (c 1.2, CHCl3); mmax (KBr): 3540, 2926, 2111, 1711,
1509, 1458, 1327, 1231, 1172, 1060, 823, 753, 698 cmꢀ1 1H
;
NMR (500 MHz, CDCl3): d 7.44–7.17 (m, 15H, Ar-H), 6.81–6.74
(m, 4H, Ar-H), 5.54 (s, 1H, PhCH), 5.45 (s, 1H, PhCH), 5.04 (br s,
1H, H-1B), 4.78 (d, J = 11.5 Hz, 1H, PhCH2), 4.62 (d, J = 11.5 Hz, 1H,
PhCH2), 4.39 (d, J = 8.0 Hz, 1H, H-1A), 4.24–4.21 (m, 2H, OCH2),
4.19 (d, J = 3.2 Hz, 1H, H-4A), 4.18–4.13 (m, 1H, H-3A), 4.09–4.02
(m, 4H, H-2B, H-4B, OCH2), 3.99–3.94 (m, H-5B, H-6abB), 3.92–3.89
(m, 1H, H-6aA), 3.79–3.74 (m, H-2A, H-6bA), 3.68 (s, 3H, OCH3),
3.59 (dd, J = 10.4, 3.3 Hz, 1H, H-3B), 3.33 (br s, 1H, H-5A); 13C
NMR (125 MHz, CDCl3): d 154.4–115.0 (Ar-C), 102.9 (PhCH),
102.1 (PhCH), 101.4 (C-1A), 96.0 (C-1B), 79.0 (C-4B), 76.0 (C-3B),
73.8 (PhCH2), 73.4 (C-5B), 70.7 (C-3A), 70.4 (C-2B), 69.6 (C-6A),
69.1 (C-6B), 68.7 (OCH2), 68.4 (OCH2), 66.8 (C-5A), 64.3 (C-4A),
61.6 (C-2A), 56.1 (OCH3); ESI-MS: 806.3 [M+Na]+; Anal. Calcd for
(3:1) as eluant to give pure
¼ þ65:8 (c 1.2, CHCl3); mmax (neat): 3442, 3016, 2963, 2934,
1749, 1613, 1514, 1370, 1244, 1223, 1095, 1047, 756 cmꢀ1 1H
5 (3.2 g, 73%). Yellow oil;
½ ꢂ
a 2D5
;
NMR (500 MHz, CDCl3): d 7.26 (d, J = 8.6 Hz, 2H, Ar-H), 6.85 (d,
J = 8.6 Hz, 2H, Ar-H), 5.35 (t, J = 9.9 Hz each, 1H, H-4), 5.32–5.31
(m, 1H, H-2), 5.29 (br s, 1H, H-1), 5.24 (dd, J = 9.8, 3.4 Hz, 1H, H-
3), 4.52 (d, J = 11.6 Hz, 1H, PhCH2), 4. 39 (d, J = 11.6 Hz, 1H, PhCH2),
4.33–4.29 (m, 1H, H-5), 3.78 (s, 3H, OCH3), 3.57–3.49 (m, 2H, H-
6ab), 2.66–2.60 (m, 2H, SCH2CH3), 2.14 (s, 1H, COCH3), 1.98 (s, 1H,
C42H45N3O12 (783.30): C, 64.36; H, 5.79. Found: C, 64.15; H, 5.97.
COCH3), 1.90 (s, 1H, COCH3), 1.28 (t, J = 7.4 Hz each, 3H, SCH2CH3);
13C NMR (125 MHz, CDCl3): d 170.5 (COCH3), 170.3 (COCH3), 170.2
(COCH3), 159.6–114.0 (Ar-C), 82.4 (C-1), 73.5 (PhCH2), 71.7 (C-5),
70.4 (C-3), 70.1 (C-2), 68.8 (C-6), 67.4 (C-4), 55.7 (OCH3), 25.7
(SCH2CH3), 21.3 (COCH3), 21.1 (COCH3), 21.0 (COCH3), 15.1
(SCH2CH3); ESI-MS: 493.1 [M+Na]+; Anal. Calcd for C22H30O9S
(470.16): C, 56.16; H, 6.43. Found: C, 55.92; H, 6.66.
4.1.5. 2-(4-Methoxyphenoxy)ethyl [2,3,4-tri-O-acetyl-6-O-(4-
methoxybenzyl)- -D-mannopyranosyl]-(1?2)-(3-O-benzyl-4,6-
O-benzylidene- -D-mannopyranosyl)-(1?3)-2-azido-4,6-O-
a
a
benzylidene-2-deoxy-b-D-galactopyranoside 12
To a solution of compound 11 (2.2 g, 2.81 mmol) and compound
5 (1.5 g, 3.19 mmol) in anhydrous CH2Cl2 (10 mL) were added MS
4 Å (2 g) and the reaction mixture was allowed to stir at room tem-
perature for 30 min under argon. The reaction mixture was cooled
4.1.3. 2-(4-Methoxyphenoxy)ethyl (2-O-acetyl-3-O-benzyl-4,6-
O-benzylidene-
benzylidene-2-deoxy-b-D-galactopyranoside 10
a
-D-mannopyranosyl)-(1?3)-2-azido-4,6-O-
to ꢀ40 °C and NIS (850 mg, 3.77 mmol) followed by TfOH (10
lL)
were added to it. After stirring at the same temperature for 1 h
the reaction mixture was filtered through a CeliteÒ bed and
washed with CH2Cl2 (100 mL). The combined organic layer was
washed with 5% Na2S2O3, satd NaHCO3, and water in succession,
dried (Na2SO4), and concentrated under reduced pressure. The
crude product was purified over SiO2 using hexane–EtOAc (6:1)
as eluant to give pure 12 (2.4 g, 72%). White solid; mp 78–81 °C;
To a solution of compound 3 (2.0 g, 4.51 mmol) and compound
4 (2.4 g, 5.40 mmol) in anhydrous CH2Cl2 (10 mL) were added MS
4 Å (2 g) and the reaction mixture was allowed to stir at room
temperature for 30 min under argon. The reaction mixture was
cooled to ꢀ40 °C and N-iodosuccinimide (NIS; 1.4 g, 6.22 mmol)
followed by TfOH (25 lL) were added to it. After stirring at the

2616
A. Santra, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2612–2618
½
a 2D5
ꢂ
¼ þ23:5 (c 1.2, CHCl3); mmax (KBr): 3476, 2928, 2870, 2115,
1753, 1507, 1371, 1248, 1221, 1104, 1079, 1050, 822, 750, 737,
699 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.37–7.19 (m, 17H, Ar-
(DDQ, 500 mg, 2.20 mmol) in H2O (10 mL) and the biphasic reac-
tion mixture was allowed to stir at room temperature for 2 h.
The reaction mixture was diluted with H2O and extracted with
CH2Cl2 (100 mL). The organic layer was successively washed with
satd NaHCO3 and water, dried (Na2SO4), and concentrated. The
crude product was purified over SiO2 using hexane–EtOAc (6:1)
as eluant to give pure 14 (980 mg, 72%). White solid; mp 91–
;
H), 6.89–6.83 (m, 6H, Ar-H), 5.68 (s, 1H, PhCH), 4.43–4.40 (m, 2H,
H-2C, H-3C), 5.39 (s, 1H, PhCH), 5.20 (t, J = 9.8 Hz each, 1H, H-4C),
5.17 (br s, 1H, H-1C), 4.95 (br s, 1H, H-1B), 4.80 (d, J = 11.9 Hz,
1H, PhCH2), 4.55 (d, J = 11.9 Hz, 1H, PhCH2), 4.42 (d, J = 11.9 Hz,
1H, PhCH2), 4.33–4.30 (m, 1H, H-3A), 4.27 (d, J = 8.0 Hz, 1H, H-
1A), 4.21 (d, J = 11.6 Hz, 1H, PhCH2), 4.19–4.10 (m, 6H, H-2B, H-4B,
H-6abB, OCH2), 4.06–4.00 (m, 3H, H-5C, OCH2), 3.99 (br s, 1H, H-
4A), 3.95–3.91 (m, 2H, H-5B, H-6aA), 3.82–3.79 (m, 1H, H-6bA),
3.79 (s, 3H, OCH3), 3.75 (s, 3H, OCH3), 3.72 (dd, J = 8.0 Hz each,
1H, H-2A), 3.52–3.49 (m, 1H, H-6aC), 3.44 (dd, J = 10.4, 3.3 Hz, 1H,
H-3B), 3.33–3.31 (m, I H, H-6bC), 2.88 (br s, 1H, H-5A), 2.09 (s, 3H,
COCH3), 1.99 (s, 3H, COCH3), 1.95 (s, 3H, COCH3); 13C NMR
(125 MHz, CDCl3): d 170.4 (COCH3), 170.2 (COCH3), 170.1 (COCH3),
159.7–114.2 (Ar-C), 102.7 (PhCH), 102.0 (PhCH), 101.0 (C-1A),
100.6 (C-1B), 96.5 (C-1C), 79.0 (C-4B), 78.5 (C-4A), 75.9 (C-3A),
74.1 (C-3B), 73.7 (PhCH2), 73.4 (PhCH2), 70.8 (C-2B), 70.7 (C-5B),
69.8 (C-2C), 69.7 (C-6A), 69.5 (C-3C), 69.4 (C-6B), 69.0 (C-6C), 68.7
(OCH2), 68.8 (OCH2), 67.4 (C-4C), 66.7 (C-5A), 61.6 (C-2A), 56.1
(OCH3), 55.7 (OCH3), 21.3 (COCH3), 21.2 (COCH3), 21.1 (COCH3);
ESI-MS: 1214.4 [M+Na]+; Anal. Calcd for C62H69N3O21 (1191.44):
C, 62.46; H, 5.83. Found: C, 62.24; H, 6.05.
94 °C; ½a 2D5
¼ þ10:2 (c 1.2, CHCl3); mmax (KBr): 3470, 3064, 3031,
ꢂ
2926, 2872, 2114, 1509, 1454, 1311, 1233, 1176, 1105, 1075,
1028, 1002, 914, 823, 741, 698 cmꢀ1 1H NMR (500 MHz, CDCl3):
;
d 7.43–7.13 (m, 30H, Ar-H), 6.79–6.72 (m, 4H, Ar-H), 5.53 (s, 1H,
PhCH), 5.46 (s, 1H, PhCH), 5.05 (br s, 1H, H-1C), 4.94 (br s, 1H, H-
1B), 4.83 (d, J = 10.7 Hz, 1H, PhCH2), 4.75 (d, J = 11.4 Hz, 1H, PhCH2),
4.55–4.47 (m, 7H, PhCH2), 4.38 (d, J = 8.0 Hz, 1H, H-1A), 4.37–4.34
(m, 2H, PhCH2), 4.16–4.11 (m, 4H, H-3A, H-4B, OCH2), 4.08–4.05
(m, 2H, OCH2), 3.99–3.85 (m, 6H, H-2B, H-4A, H-5B, H-5C, H-6abB),
3.82–3.63 (m, 5H, H-2A, H-2B, H-2C, H-3C, H-6abA), 3.65 (s, 3H,
OCH3), 3.63–3.49 (m, 2H, H-4C, H-6aC), 3.48–3.44 (m, 2H, H-3B,
H-6bC), 3.25 (br s, 1H, H-5A); 13C NMR (125 MHz, CDCl3): d
154.5–115.0 (Ar-C), 102.8 (PhCH), 101.7 (PhCH), 101.3 (C-1A),
100.4 (C-1B), 95.4 (C-1C), 79.7 (C-4B), 79.5 (C-4A), 76.6 (C-3A),
76.3 (C-3B), 75.8 (PhCH2), 75.6 (C-2B), 75.2 (C-5B), 74.3 (PhCH2),
73.5 (C-2C), 73.3 (C-3C), 72.8 (PhCH2), 72.3 (PhCH2), 70.5 (C-4C),
69.4 (C-6A), 69.0 (C-6B), 68.6 (OCH2), 68.3 (OCH2), 66.8 (C-5A),
64.8 (C-5C), 62.9 (C-6C), 61.5 (C-2A), 56.0 (OCH3); ESI-MS: 1238.4
[M+Na]+; Anal. Calcd for C69H73N3O17 (1215.49): C, 68.13; H,
6.05. Found: C, 67.90.; H, 6.30.
4.1.6. 2-(4-Methoxyphenoxy)ethyl [2,3,4-tri-O-benzyl-6-O-(4-
methoxybenzyl)-
a-D-mannopyranosyl]-(1?2)-(3-O-benzyl-4,6-
O-benzylidene- -D-mannopyranosyl)-(1?3)-2-azido-4,6-O-
a
benzylidene-2-deoxy-b-D-galactopyranoside 13
4.1.8. 2-(4-Methoxyphenoxy)ethyl (4-O-acetyl-2,3,6-tri-O-
To a solution of 12 (2.0 g, 1.67 mmol) in dry DMF (15 mL) were
added benzyl bromide (1.2 mL, 10.08 mmol), crushed NaOH
(700 mg, 17.5 mmol) and TBAB (300 mg, 0.93 mmol) and the reac-
tion mixture was allowed to stir at room temperature for 5 h. The
reaction mixture was diluted with H2O (100 mL) and extracted
with CH2Cl2 (100 mL). The organic layer was washed with H2O,
dried (Na2SO4), and concentrated under reduced pressure. The
crude product was purified over SiO2 using hexane–EtOAc (9:1)
as eluant to give pure 13 (1.7 g, 76%). White solid; mp 86–88 °C;
benzyl-
a
-D-galactopyranosyl)-(1?6)-(2,3,4-tri-O-benzyl-
a
a
-D-
-D-
mannopyranosyl)-(1?2)-(3-O-benzyl-4,6-O-benzylidene-
mannopyranosyl)-(1?3)-2-azido-4,6-O-benzylidene-2-deoxy-b-
D-galactopyranoside 15
To a solution of compound 14 (900 mg, 0.74 mmol) and com-
pound 6 (475 mg, 0.88 mmol) in anhydrous CH2Cl2 (5 mL) were
added MS 4 Å (1 g) and the reaction mixture was allowed to stir
at room temperature for 30 min under argon. The reaction mixture
was cooled to ꢀ25 °C and NIS (240 mg, 1.06 mmol) followed by
½
a 2D5
ꢂ
¼ þ49:2 (c 1.2, CHCl3); mmax (KBr): 3488, 3034, 2920, 2871,
2113, 1611, 1509, 1457, 1370, 1288, 1239, 1073, 914, 824, 744,
697 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.51–6.80 (m, 38H, Ar-
TfOH (3 lL) were added to it. After stirring at the same tempera-
ture for 45 min the reaction mixture was filtered through a CeliteÒ
bed and washed with CH2Cl2 (50 mL). The combined organic layer
was washed with 5% Na2S2O3, satd NaHCO3, water in succession,
dried (Na2SO4), and concentrated under reduced pressure. The
crude product was purified over SiO2 using hexane–EtOAc (6:1)
as eluant to give pure 15 (950 mg, 76%). White solid; mp 71–
;
H), 5.60 (s, 1H, PhCH), 5.43 (s, 1H, PhCH), 5.18 (br s, 1H, H-1C),
4.96 (br s, 1H, H-1B), 4.88 (d, J = 10.7 Hz, 1H, PhCH2), 4.69 (d,
J = 11.6 Hz, 1H, PhCH2), 4.62–4.45 (m, 7H, PhCH2), 4.33–4.28 (m,
1H, H-3A), 4.23 (d, J = 11.2 Hz, 1H, PhCH2), 4.18–4.02 (m, 6H, H-
1A, H-2B, H-4B, H-5C, OCH2), 3.99–3.91 (m, 4H, H-6abB, OCH2),
3.90–3.88 (m, 3H, H-5B, H-6abA), 3.88 (br s, 1H, H-4A), 3.85–3.79
(m, 2H, H-2A, H-2C), 3.76 (s, 3H, OCH3), 3.74 (s, 3H, OCH3), 3.78–
3.63 (m, 3H, H-3C, H-4C, H-6aC), 3.56–3.53 (m, 1H, H-6bC), 3.34
(dd, J = 10.4, 3.3 Hz, 1H, H-3B), 2.70 (br s, 1H, H-5A); 13C NMR
(125 MHz, CDCl3): d 159.7–114.2 (Ar-C), 102.6 (PhCH), 101.9
(PhCH), 101.5 (C-1A), 101.1 (C-1B), 91.5 (C-1C), 79.9 (C-4B), 79.2
(C-4A), 78.7 (C-3A), 75.9 (C-3B), 75.7 (PhCH2), 75.4 (C-2B), 75.0 (C-
5B), 74.5 (C-2C), 73.5 (PhCH2), 73.4 (PhCH2), 72.8 (PhCH2), 72.7
(C-3C), 72.3 (PhCH2), 70.8 (C-4C), 70.7 (C-6A), 69.4 (C-6B), 69.1 (C-
6C), 68.5 (OCH2), 68.2 (OCH2), 66.6 (C-5A), 65.0 (C-5C), 61.5 (C-
2A), 56.0 (OCH3), 55.6 (OCH3); ESI-MS: 1358.5 [M+Na]+; Anal. Calcd
for C77H81N3O18 (1335.55): C, 69.20; H, 6.11. Found: C, 69.00; H,
6.35.
74 °C; ½a 2D5
¼ þ9:2 (c 1.2, CHCl3); mmax (KBr): 3345, 3031, 2926,
ꢂ
2113, 1730, 1507, 1659, 1375, 1284, 1228, 1064, 920, 824, 745,
699 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.46–7.05 (m, 45H, Ar-
;
H), 6.79–6.71 (m, 4H, Ar-H), 5.52 (s, 1H, PhCH), 5.45 (br s, 1H, H-
4D), 5.42 (s, 1H, PhCH), 5.11 (br s, 1H, H-1C), 4.95 (br s, 1H, H-1B),
5.74–4.66 (m, 3H, PhCH2), 4.60–4.35 (m, 9H, PhCH2), 4.34–4.27
(m, 3H, H-1D, PhCH2), 4.26 (d, J = 7.9 Hz, 1H, H-1A), 4.21–4.12 (m,
1H, H-6aB), 4.11–3.95 (m, 8H, H-3A, H-4A, H-5D, H-6bB, H-6abA
,
OCH2), 3.94–3.75 (m, 8H, H-2B, H-4B, H-5B, H-5C, H-6abD, OCH2),
3.74–3.55 (m, 3H, H-2A, H-3D, H-6aC), 3.66 (s, 3H, OCH3), 3.54–
3.50 (m, 1H, H-6bC), 3.49–3.37 (m, 2H, H-2C, H-3C), 3.36–3.30 (m,
2H, H-3B, H-4C), 3.28–3.26 (m, 1H, H-2D), 3.08 (br s, 1H, H-5A),
1.91 (s, 3H, COCH3); 13C NMR (125 MHz, CDCl3): d 170.3 (COCH3),
154.2–114.7 (Ar-C), 104.4 (JC-1/H-1 = 155 Hz, C-1A), 102.4
(JC-1/H-1 = 172.8 Hz, C-1D), 101.6 (PhCH), 101.0 (PhCH), 100.3
(JC-1/H-1 = 170.5 Hz, C-1B), 96.1 (JC-1/H-1 = 171.3 Hz, C-1C), 79.4 (2 C,
C-2D, C-4C), 79.0 (C-4B), 78.7 (C-4A), 76.6 (C-3C), 76.0 (C-3A), 75.4
(C-3B), 75.3 (C-2B), 74.8 (C-5B), 74.6 (C-3D), 73.7 (2 C, 2 PhCH2),
73.6 (PhCH2), 72.4 (PhCH2), 72.1 (C-2C), 72.0 (PhCH2), 71.7 (PhCH2),
70.4 (C-4D), 69.2 (C-6A), 69.0 (C-6C), 68.7 (C-6D), 68.3 (OCH2), 68.0
(OCH2), 67.8 (C-6B), 66.7 (C-5A), 66.4 (C-5D), 64.6 (C-5C), 61.1
4.1.7. 2-(4-Methoxyphenoxy)ethyl (2,3,4-tri-O-benzyl-
a-D-
mannopyranosyl)-(1?2)-(3-O-benzyl-4,6-O-benzylidene-
a-D-
mannopyranosyl)-(1?3)-2-azido-4,6-O-benzylidene-2-deoxy-b-
D-galactopyranoside 14
To a solution of 13 (1.5 g, 1.12 mmol) in CH2Cl2 (20 mL) was
added a solution of 2,3-dicholoro-5,6-dicyano-p-benzoquinone

A. Santra, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2612–2618
2617
(C-2A), 55.7 (OCH3), 20.9 (COCH3); ESI-MS: 1712.6 [M+Na]+; Anal.
H-5D, H-6bB, OCH2), 3.91–3.73 (m, 8H, H-2A, H-2D, H-5E, H-6abA,
Calcd for C98H103N3O23 (1689.69): C, 69.61; H, 6.14. Found: C,
69.43; H, 6.38.
H-6abD, H-6aC), 3.75 (s, 3H, OCH3), 3.71–3.60 (m, 3H, H-3C, H-4C,
H-6bC), 3.41–3.27 (m, 4H, H-2C, H-2D, H-3B, H-5A); 13C NMR
(125 MHz, CDCl3): d 166.3 (COPh), 166.1 (COPh), 166.4 (COPh),
165.3 (COPh), 154.4–115.0 (Ar-C), 105.1 (C-1A), 102.6 (C-1E),
102.3 (PhCH), 101.8 (PhCH), 101.4 (C-1D), 101.0 (C-1B), 97.2 (C-
1C), 81.6 (C-2D), 80.2 (C-4C), 79.6 (C-4B), 79.2 (C-4A), 76.1 (C-3A),
75.5 (2 C, C-2B, C-3B), 75.3 (2 C, C-5B, PhCH2), 75.2 (C-3D), 75.0
(C-2C), 74.0 (C-3C), 73.9 (PhCH2), 73.7 (PhCH2), 73.5 (PhCH2), 73.4
(C-2D), 73.0 (C-5E), 72.8 (C-5D), 72.6 (C-3E), 72.4 (PhCH2), 71.9 (C-
2E), 71.3 (2 C, 2 PhCH2), 70.1 (C-4E), 69.4 (3 C, C-6A, C-6C, C-6D),
69.0 (C-6B), 68.6 (OCH2), 68.4 (OCH2), 66.8 (C-5A), 65.0 (C-5C),
63.1 (C-6E), 61.6 (C-2A), 56.0 (OCH3); MALDI-MS: 2248.8
[M+Na]+; Anal. Calcd for C130H127N3O31 (2225.84): C, 70.10; H,
5.75. Found: C, 69.87; H, 6.00.
4.1.9. 2-(4-Methoxyphenoxy)ethyl (2,3,6-tri-O-benzyl-
galactopyranosyl)-(1?6)-(2,3,4-tri-O-benzyl- -D-
mannopyranosyl)-(1?2)-(3-O-benzyl-4,6-O-benzylidene-
a
-D-
a
a-D-
mannopyranosyl)-(1?3)-2-azido-4,6-O-benzylidene-2-deoxy-b-
D-galactopyranoside 16
A solution of compound 15 (900 g, 0.53 mmol) in 0.1 M CH3ONa
(10 mL) was allowed stir at room temperature for 1 h and neutral-
ized with Amberlite IR 120 (H+) resin. The reaction mixture was fil-
tered and concentrated under reduced pressure to give the crude
product, which was purified over SiO2 using hexane–EtOAc (3:1)
as eluant to give pure 16 (875 mg, quantitative). White solid; mp
77–79 °C; ½a 2D5
¼ þ15:4 (c 1.2, CHCl3); mmax (KBr): 3452, 3033,
ꢂ
2924, 2920, 2114, 1507, 1457, 1369, 1287, 1232, 1067, 915, 824,
4.1.11. 2-(4-Methoxyphenoxy)ethyl (
(1?2)-( -D-mannopyranosyl)-(1?3)-2-acetamido-2-deoxy-b-
D-galactopyranoside 1
a-D-mannopyranosyl)-
742, 697 cmꢀ1
;
1H NMR (500 MHz, CDCl3): d 7.35–7.17 (m, 41H,
a
Ar-H), 6.87–6.80 (m, 4H, Ar-H), 5.59 (s, 1H, PhCH), 5.57 (s, 1H,
PhCH), 5.10 (br s, 1H, H-1C), 5.08 (br s, 1H, H-1B), 4.82 (d,
J = 11.0 Hz, 1H, PhCH2), 4.75 (d, J = 10.8 Hz, 1H, PhCH2), 4.73–4.34
(m, 11H, PhCH2), 4.32–4.28 (m, 2H, H-1D, PhCH2), 4.24–4.16 (m,
1H, H-6aB), 4.20 (d, J = 7.8 Hz, 1H, H-1A), 4.15–4.10 (m, 3H, H-3A,
OCH2), 4.06 (br s, 1H, H-4A), 4.03–3.85 (m, 11H, H-2B, H-4B, H-4D,
H-5B, H-5C, H-5D, H-6abA, H-6abD, H-6bB), 3.78–3.69 (m, 4H, H-2A,
H-2C, H-3D, H-6aC), 3.73 (s, 3H, OCH3), 3.64–3.61 (m, 1H, H-6bC),
3.59 (dd, J = 10.3, 3.2 Hz, 1H, H-3C), 3.54 (t, J = 7.9 Hz each, 1H, H-
4C), 3.38–3.35 (m, 2H, H-2D, H-3B), 3.22 (br s, 1H, H-5A); 13C NMR
(125 MHz, CDCl3): d 153.3–115.0 (Ar-C), 105.8 (C-1A), 102.6 (C-
1D), 101.9 (PhCH), 101.3 (PhCH), 100.9 (C-1B), 96.9 (C-1C), 81.1
(C-2D), 79.8 (C-4C), 79.4 (C-4B), 79.1 (C-4A), 76.2 (C-3A), 75.6
(PhCH2), 75.4 (PhCH2), 75.3 (C-3B), 75.1 (C-2B), 74.8 (C-5B), 73.9
(2 C, PhCH2, C-3D), 73.4 (C-2C), 72.9 (C-3C), 72.7 (PhCH2), 72.6
(PhCH2), 72.0 (PhCH2), 71.9 (PhCH2), 71.1 (C-4D), 69.3 (C-6A), 69.1
(2 C, C-6C, C-6D), 69.0 (C-6B), 68.4 (OCH2), 68.3 (OCH2), 66.9 (C-
5D), 66.8 (C-5A), 64.9 (C-5C), 61.6 (C-2A), 56.0 (OCH3); ESI-MS:
1670.6 [M+Na]+; Anal. Calcd for C96H101N3O22 (1647.68): C,
69.93; H, 6.17. Found: C, 69.72; H, 6.40.
To a solution of compound 12 (300 mg, 0.25 mmol) in CH3OH
(10 mL) was added 20% Pd(OH)2–C (150 mg) and the reaction mix-
ture was allowed to stir at room temperature under a positive
pressure of hydrogen for 24 h. The reaction mixture was filtered
through a CeliteÒ bed and evaporated to dryness under reduced
pressure. A solution of the crude product in acetic anhydride–pyr-
idine (2 mL, 1:1 v/v) was kept at room temperature for 2 h and the
solvents were removed under reduced pressure. A solution of the
acetylated product in 0.1 M sodium methoxide (5 mL) was allowed
to stir at room temperature for 2 h and neutralized with Dowex
50 W X8 (H+) resin. The reaction mixture was filtered and evapo-
rated to dryness to give compound 1, which was purified over
SephadexÒ LH-20 using CH3OH (60 mL) as eluant to give pure 1
(115 mg, 66%). White powder; ½a D25
ꢂ
¼ þ16 (c 1.2, CH3OH); mmax
(KBr): 3434, 2945, 1628, 1378, 1148, 1078, 668 cmꢀ1
;
1H NMR
(500 MHz, CD3OD): d 6.88–6.83 (m, 6H, Ar-H), 5.16 (br s, 1H, H-
1C), 4.85 (br s, 1H, H-1B), 4.43 (d, J = 8.4 Hz, 1H, H-1A), 4.04–4.00
(m, 3H, H-3A, OCH2), 3.97 (m, 2H, OCH2), 3.88–3.87 (m, 1H, H-
2B), 3.82–3.81 (m, 1H, H-2C), 3.79–3.75 (m, 3H, H-4A, H-6abC),
3.70–3.64 (m, 4H, H-3C, H-4C, H-6abB), 3.63 (s, 3H, OCH3), 3.60–
3.52 (m, 4H, H-4B, H-5C, H-6abA), 3.48–3.39 (m, 3H, H-3B, H-5A,
H-5B), 3.25–3.21 (m, 1H, H-2A), 1.18 (s, 3H, COCH3); 13C NMR
(125 MHz, CD3OD): d 172.7 (COCH3), 103.2 (C-1B), 102.1 (C-1A),
94.9 (C-1C), 79.7 (C-2C), 75.7 (C-5A), 75.2 (C-5B), 74.0 (C-3B), 73.9
(C-2B), 71.4 (C-5C), 70.9 (C-4C), 70.8 (C-4B), 68.2 (OCH2), 68.1
(OCH2), 68.0 (C-4A), 67.7 (C-3C), 63.7 (C-3A), 62.4 (C-6B), 62.3 (C-
6A), 61.7 (C-6C), 55.1 (OCH3), 53.5 (C-2A), 22.2 (COCH3); ESI-MS:
718.2 [M+Na]+; Anal. Calcd for C29H45NO18 (695.26): C, 50.07; H,
6.52. Found: C, 49.85; H, 6.77.
4.1.10. 2-(4-Methoxyphenoxy)ethyl (2,3,4,6-tetra-O-benzoyl-b-
D-glucopyranosyl)-(1?4)-(2,3,6-tri-O-benzyl-
galactopyranosyl)-(1?6)-(2,3,4-tri-O-benzyl-
mannopyranosyl)-(1?2)-(3-O-benzyl-4,6-O-benzylidene-
a
-D-
a-D-
a-D-
mannopyranosyl)-(1?3)-2-azido-4,6-O-benzylidene-2-deoxy-b-
D-galactopyranoside 17
To a solution of compound 16 (850 mg, 0.51 mmol) and com-
pound 7 (530 mg, 0.71 mmol) in anhydrous CH2Cl2 (5 mL) was
added TMSOTf (15
l
L) at ꢀ10 °C under argon and the reaction mix-
ture was allowed to stir at the same temperature for 1 h. The reac-
tion mixture was quenched with Et3N (0.1 mL) and diluted with
CH2Cl2 (50 mL). The organic layer was successively washed with
satd NaHCO3 and water, dried (Na2SO4), and concentrated under
reduced pressure. The crude product was purified over SiO2 using
hexane–EtOAc (4:1) as eluant to give pure compound 17
4.1.12. 2-(4-Methoxyphenoxy)ethyl (sodium b-D-
glucopyranosyluronate)-(1?4)-( -D-galactopyranosyl)-(1?6)-
a
(a
-D-mannopyranosyl)-(1?2)-(a-D-mannopyranosyl)-(1?3)-2-
acetamido-2-deoxy-b-D-galactopyranoside 2
A solution of compound 17 (700 mg, 0.31 mmol) in 0.1 M CH3O-
Na (20 mL) was allowed stir at room temperature for 3 h and neu-
tralized with Dowex 50W X8 (H+) resin. The reaction mixture was
filtered and concentrated under reduced pressure. To a solution of
the crude product in CH2Cl2 (20 mL) and H2O (3.5 mL) were added
an aq solution of NaBr (1 mL; 1 M), an aq solution of TBAB (2 mL;
1 M), TEMPO (80 mg, 0.5 mmol), a satd aq solution of NaHCO3
(8 mL), and 4% aq NaOCl (10 mL) in succession and the reaction
mixture was allowed to stir at 0–5 °C for 3 h. The reaction mixture
was neutralized with the addition of 1 N aq HCl solution. To the
reaction mixture were added tert-butanol (25 mL), 2-methyl-but-
2-ene (30 mL; 2 M solution in THF), aq solution of NaClO2 (1 g in
(820 mg, 72%). White solid; mp 82–84 °C; ½a D25
¼ þ12:3 (c 1.2,
ꢂ
CHCl3); mmax (KBr): 3450, 3034, 2926, 2873, 2114, 1732, 1507,
1455, 1369, 1267, 1099, 916, 826, 741, 703 cmꢀ1
;
1H NMR
(500 MHz, CDCl3): d 8.16–6.82 (m, 65H, Ar-H), 5.92 (t, J = 9.6 Hz
each, 1H, H-3E), 5.72 (t, J = 9.6 Hz each, 1H, H-4E), 5.60 (s, 1H,
PhCH), 5.58 (s, 1H, PhCH), 5.50 (t, J = 8.0 Hz each, 1H, H-2E), 5.20
(d, J = 7.9 Hz, 1H, H-1E), 5.11 (br s, 1H, H-1C), 5.07 (br s, 1H, H-
1B), 4.73–4.61 (m, 4H, PhCH2), 4.58–4.47 (m, 7H, H-6abE, PhCH2),
4.46 (br s, 1H, H-1D), 4.44–4.32 (m, 5H, PhCH2), 4.30–4.18 (m,
3H, H-3A, OCH2), 4.16–4.08 (m, 5H, H-2B, H-4A, H-6abB), 4.14 (d,
J = 7.8 Hz, 1H, H-1A), 4.06–3.94 (m, 8H, H-4B, H-4D, H-5B, H-5C,

2618
A. Santra, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2612–2618
5 mL), and aq solution of NaH2PO4 (1 g in 5 mL) and the reaction
mixture was allowed to stir at room temperature for 3 h. The reac-
tion mixture was diluted with satd aq NaH2PO4 and extracted with
CH2Cl2 (100 mL). The organic layer was washed with water, dried
(Na2SO4) and concentrated to dryness. To a solution of the crude
product in CH3OH (30 mL) was added 20% Pd(OH)2–C (200 mg)
and the reaction mixture was allowed to stir at room temperature
under a positive pressure of hydrogen for 24 h. The reaction mix-
ture was filtered through a CeliteÒ bed and evaporated to dryness.
A solution of the crude product in acetic anhydride–pyridine (3 mL,
1:1 v/v) was kept at room temperature for 4 h and the solvents
were removed under reduced pressure. A solution of the acetylated
product in 0.1 M sodium methoxide (10 mL) was allowed to stir at
room temperature for 2 h and neutralized with Dowex 50W X8
(H+) resin. The reaction mixture was filtered and evaporated to
dryness to give compound 2, which was purified over SephadexÒ
LH-20 using CH3OH–H2O (60 mL; 4:1 v/v) as eluant to give pure
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(500 MHz, CD3OD): d 6.79–6.71 (m, 4H, Ar-H), 5.19 (s, 1H, H-1C),
4.77 (br s, 1H, H-1B), 4.62 (d, J = 8.1 Hz, 1H, H-1E), 4.48 (m, 2H,
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4.15–4.10 (m, 2H, H-4A, H-4D), 4.08–3.93 (m, 4H, H-4B, H-5D,
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3H, OCH3), 3.54–3.35 (m, 7H, H-3C, H-4C, H-4E, H-6abA, H-6abC),
3.31–3.23 (m, 2H, H-2A, H-3D), 3.21–3.10 (m, 4H, H-2C, H-2D, H-
3B, H-5A); 13C NMR (125 MHz, CD3OD): d 174.6 (COONa), 172.4
(COCH3), 105.4 (C-1A), 105.0 (C-1D), 103.8 (C-1B), 101.6 (C-1E),
101.0 (C-1C), 80.8 (C-2E), 78.6 (C-4B), 77.3 (C-4A), 77.1 (C-4C),
75.0 (C-3A), 74.8 (C-3B), 74.1 (C-2B), 73.9 (C-2D), 73.2 (C-2C), 72.5
(C-3D), 71.3 (C-4D), 71.1 (C-5E), 70.9 (2 C, C-5D, C-3E), 70.6 (2 C,
C-3C, C-4E), 68.2 (2 C, 2 OCH2), 67.6 (2 C, C-5A, C-5C), 66.9 (C-5B),
62.0 (C-6B), 61.8 (C-6D), 60.9 (C-6A), 60.5 (C-6C), 55.1 (OCH3), 53.4
(C-2A), 22.2 (COCH3); ESI-MS: 1056.3 [M+1]+; Anal. Calcd for
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Acknowledgments
A.S. thanks CSIR, New Delhi for providing a Junior Research Fel-
lowship. This work was partly supported by Ramanna Fellowship
(A.K.M.), Department of Science and Technology, New Delhi (SR/
S1/RFPC-06/2006) and Bose Institute, Kolkata.