Synthesis of the hexasaccharide repeating unit corresponding to the cell wall lipopolysaccharide of Azospirillum irakense KBC1

Article abstract of DOI:10.1016/j.tetasy.2010.11.008

A convenient chemical synthesis of the hexasaccharide repeating unit of the cell wall lipopolysaccharide of Azospirillum irakense KBC1 has been successfully achieved. A stereo- and regioselective [4 + 2] block glycosylation strategy has been used to obtai

Full text of DOI:10.1016/j.tetasy.2010.11.008

Tetrahedron: Asymmetry 21 (2010) 2755–2761
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of the hexasaccharide repeating unit corresponding to the cell
wall lipopolysaccharide of Azospirillum irakense KBC1
⇑
Samir Ghosh, 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:
Received 22 June 2010
Revised 1 November 2010
Accepted 11 November 2010
Available online 4 December 2010
A convenient chemical synthesis of the hexasaccharide repeating unit of the cell wall lipopolysaccharide
of Azospirillum irakense KBC1 has been successfully achieved. A stereo- and regioselective [4 + 2] block
glycosylation strategy has been used to obtain the target hexasaccharide as its octyl glycoside. All syn-
thetic intermediates have been prepared in high yields from commercially available reducing sugars fol-
lowing a series of protection–deprotection reactions. An oxidation–reduction methodology has been
applied to convert b-
D-glucosidic unit to a b-
D-mannosidic moiety.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
In the current scenario, the development of plant growth-pro-
moting agents is highly essential to enhance the crop production.
In this context it is quite reasonable to understand the role of the
LPS of Azospirillum irakense KBC1 in the interaction of the bacteria
with plant roots. In order to carry out different biological experi-
ments, sufficient quantities of the hexasaccharide repeating unit
are required, which are not accessible from its natural source.
Therefore, the development of a convenient chemical synthetic
strategy is essential to provide the required quantity of the hexa-
saccharide repeating unit as well as its several analogs. Herein
we report a convenient chemical synthesis of the hexasaccharide
as its octyl glycoside found in the cell-wall lipopolysaccharide of
Azospirillum irakense KBC1 (Fig. 2). The presence of an octyl group
at the reducing end makes the purification of the target hexasac-
charide easier following solid phase extraction using reverse phase
C18 column.6
Bacteria belonging to the genus Azospirillum are known as plant
growth promoting rhizobacteria (PGPR) for their active role to pro-
mote plant growth by associating them with different plants in the
rhizosphere.1 Azospirilla are gram-negative, motile, free-living
nitrogen fixing rhizobacteria that exert beneficial effects on plant
growth and crop productions by producing several phytohor-
mones, vitamins, and bioactive substances.2 In general, PGPR
establish association with roots of cereals and other non-legumes
by symbiotic relationships.3 Macromolecules, such as exopolysac-
charides (EPS), lipopolysaccharides (LPS), and capsular polysaccha-
rides (CPS) present in the cell-wall of Azospirilla regulate their
interactions with the leguminous and non-leguminous roots of
plants.4 Among cell-wall polysaccharides, the role of LPS in the
plant-bacterial interactions is considered to be very important for
their survival in challenging environmental conditions. Although
the usefulness of the LPSs has been well documented, only a few
structures of the LPS have been reported from Azospirillum
strains.1b,5 Fedonenko et al. reported the structure of a hexasaccha-
ride repeating unit found in the LPS of Azospirillum irakense KBC1
(Fig. 1).1c
2. Results and discussion
The synthesis of the target hexasaccharide containing
a
b-
D
-mannose unit and an -galactofuranose moiety at the non-
a-D
reducing end, as its octyl glycoside (Fig. 2) has been accomplished
by exploiting a [4 + 2] block glycosylation strategy. Since, b-selec-
tive glycosylation of
blesome, a -glucose derivative 6 has been used as the precursor
of the -mannose moiety. A tetrasaccharide diol derivative 16
D-mannose derivatives is considered as trou-
α-D-Galf-(1→2)-α-L-Rhap-(1→3)-β-D-Manp-(1→3)-α-L-Rhap
D
1
↓
3
D
has been used as the glycosyl acceptor in the block glycosylation
step. Regio- and steroselective glycosylation of a tetrasaccharide
diol derivative 16 with a disaccharide thioglycoside derivative 17
furnished hexasaccharide derivative 18. Dess–Martin oxidation fol-
lowed by sodium borohydride reduction of the free hydroxyl group
of compound 18 gave hexasaccharide derivative 19, which was
finally deprotected to give target hexasaccharide 1. The key
→4)-α-L-Rhap-(1→3)-β-D-Galp-(1→
Figure 1. Hexasaccharide repeating unit corresponding to the cell-wall lipopoly-
saccharide of Azospirillum irakense KBC1.
⇑
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 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.11.008

2756
S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2755–2761
HO
HO
OH
HO
OH
OBn
O
a, b, c
O
O
A
HO
OC8H17
HO
OC8H17
OC8H17
O
HO
HO
OH
B
BnO
O
HO
8
9
O
C
O
O
OH
HO
d
HO
HO
HO
O
D
AcO
OBn
O
O
HO
OC8H17
O
E
HO
BnO
HO
HO
O
2
HO
OH
Scheme 1. Reagents and conditions: (a) 2,2-dimethoxypropane, p-TsOH, DMF,
room temperature, 12 h; (b) benzyl bromide, NaOH, DMF, room temperature, 6 h;
(c) 80% aq AcOH, 80 °C, 1.5 h, 72% overall; (d) triethylorthoacetate, p-TsOH, DMF,
2 h then H2O, room temperature, 30 min, 76%.
1
F
O
OH
directed the formation of 1,2-trans glycosylated product 10 by a
neighboring participation effect. One-pot deacetylation–benzyla-
tion13 of compound 10 using benzyl bromide and sodium hydrox-
ide afforded compound 11 in 80% yield. Oxidative removal of the
4-methoxybenzyl group of compound 11 using DDQ16 produced
compound 12 in 77% yield. The stereoselective glycosylation of
compound 12 with thioglycoside derivative 5 in the presence of
NIS-TMSOTf15 furnished trisaccharide derivative 13 in 77% yield,
which on deacetylation gave compound 14 in 95% yield. The pres-
ence of an 2-O-acetyl group in the thioglycoside donor 5 directed
the formation of the 1,2-trans glycosylated product 13 by neigh-
boring group participation. The structure of compound 13 was con-
firmed through spectral analysis [d 5.24 (br s, H-1B), 5.00 (br s, 1C),
4.33 (d, J = 7.2 Hz, H-1A) in 1H NMR and d 104.1 (C-1A), 98.8 (C-1B),
96.2 (C-1C) in 13C NMR spectra]. b-Selective glycosylation of com-
pound 14 with thioglycoside derivative 6 in the presence of NIS-
TMSOTf15 furnished tetrasaccharide derivative 15 in 71% yield,
which was deacetylated to give compound 16 in 92% yield. In this
case, the 1,2-trans glycosylated product 15 was obtained by apply-
ing the neighboring participation effect of 2-O-acetyl group present
in the thioglycoside donor 6. The appearance of signals corre-
sponding to compound 15 confirmed its formation [d 104.1
(C-1A), 102.9 (C-1D), 101.3 (PhCH), 101.2 (C-1C), 98.7 (C-1B) in the
13C NMR spectrum] (Scheme 2).
AcO
SEt
SEt
OBn
O
O
O
HO
OC8H17
BnO
MBnO
BnO
BnO
BnO
OAc
OH
4
3
2
OBn
O
SEt
Ph
O
O
O
O
OC(NH)CCl3
AcO
SEt
OBn
BnO
OAc
BnO
OBn
BnO
OAc
7
6
5
Figure 2. Structure of the synthesized hexasaccharide as its octyl glycoside 1
corresponding to the cell-wall lipopolysaccharide of Azospirillum irakense KBC1.
features of the synthetic strategy are: (a) a late-stage conversion of
the b-D-glucose to the b-D-mannose moiety after completion of the
glycosylation steps; (b) a highly regio- and stereoselective glyco-
sylation of a disaccharide thioglycoside 17 with a tetrasaccharide
diol 16; (c) the formation of
-rhamnosyl thioglycoside donor 17; (d) use of a thioglycoside
derivative 4 as an orthogonal glycosyl acceptor; (e) the use of a
per-O-benzylated -galactofuranosyl trichloroacetimidate deriva-
tive for the preparation of the -linked -galactofuranosylated
a-glycoside using C-2 glycosylated
L
D
a
D
compound; and (f) the use of an octyl group as an anomeric pro-
tecting group makes the purification of unprotected hexasaccha-
ride 1 easier using solid phase extraction over reverse-phase C18
silica gel.
In a separate experiment, L-rhamnose derived thioglycoside 4
was allowed to couple with the galactofuranosyl trichloroacetimi-
date donor 7 under Schmidt’s glycosylation conditions17 to give
disaccharide thioglycoside derivative 17 in 73% yield together with
some of the b-isomer (ꢀ10%), which was separated by flash col-
A dihydroxyl groups containing tetrasaccharide acceptor 16 and
a disaccharide thioglycoside derivative 17 have been synthesized
from suitably derivatized monosaccharide intermediates 2, 3,7 4,8
umn chromatography. The formation of the
a-linked galactofur-
anosyl disaccharide thioglycoside 17 was unambiguously
confirmed from its NMR spectroscopic analysis. The presence of
5,8 69 and 7.10 Octyl b-
D
-galactopyranoside 811 was subjected to a
series of reactions consisting of the acetonide formation using
2,2-dimethoxypropane and p-toluenesulfonic acid,12 benzylation
of the remaining hydroxyl groups using benzyl bromide and so-
dium hydroxide13 and finally acidic hydrolysis of the acetonide
signals at d 5.32 (br s, H-1E,
a-L-Rhap) and 5.23 (d, J = 4.3 Hz, H-
1F, a-
a-
D
-Galf) in the 1H NMR and d 98.0 (JC-1/H-1 = 170 Hz, C-1F,
D
-Galf) and 84.4 (JC-1/H-1 = 171 Hz, C-1E, a-L
-Rhap) in the 13C NMR
supported its structure. In earlier reports,18 it has been established
ring to give octyl 2,6-di-O-benzyl-b-
D
-galactopyranoside 9 in 72%
that the b-galactofuranosyl linkage has JH1/H2 = 0–2 Hz, whereas
yield. Compound 9 was selectively acetylated via orthoesterifica-
the
spectrum of compound 17, the appearance of the JH1,H2 = 4.3 Hz
for the galactofuranosyl moiety confirmed it as an -linkage.
a
-galactofuranosyl residue has JH1/H2 = 4–5 Hz. In the 1H NMR
tion14 to give octyl 4-O-acetyl-2,6-di-O-benzyl-b-
side 2 in 76% yield (Scheme 1).
D
-galactopyrano-
a
The stereoselective 1,2-trans glycosylation of
L
-rhamnose
Regio- and stereoselective glycosylation of compound 16 with
compound 17 in the presence of NIS-TMSOTf15 combination
furnished hexasaccharide derivative 18 in 70% yield together with
a minor quantity of (1?3)-linked b-glycosylation product (ꢀ10%),
which was separated by flash column chromatography. The forma-
tion of compound 18 was unambiguously confirmed from NMR
spectroscopic analysis. Appearance of signals at d 5.40 (br s,
H-1B), 5.37 (s, 1H, PhCH), 5.28 (d, J = 3.8 Hz, H-1E), 5.23 (br s,
derived thioglycoside 3 with compound 2 in the presence of a com-
bination of N-iodosuccinimide (NIS) and trimethylsilyl trifluome-
thanesulfonate (TMSOTf)15 furnished the disaccharide derivative
10 in 79% yield. Appearance of signals in the NMR spectra [d 5.05
(br s, H-1B), 4.35 (d, J = 7.0 Hz, H-1A) in 1H NMR and d 103.9
(C-1A), 99.2 (C-1B) in 13C NMR spectra] confirmed its formation.
The presence of a 2-O-acetyl group in the thioglycoside donor 3

S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2755–2761
2757
R2O
O
formation. The presence of signals at d 5.30 (br s, H-1C), 5.07 (br
s, H-1E), 4.94 (br s, H-1B), 4.83 (d, J = 4.8 Hz, H-1F), 4.46 (br s, H-
1D), 4.36 (d, J = 7.8 Hz, H-1F), 4.14 (d, J = 4.8 Hz, H-1F) in the 1H
OBn
a
O
2 + 3
A
OC8H17
BnO
NMR and d 105.5 (JC-1/H-1 = 158.5 Hz, C-1A, b-
1 = 156 Hz, C-1D, b- -Manp), 102.8 (JC-1/H-1 = 171 Hz, C-1B,
Rhap), 102.4 (JC-1/H-1 = 173.5 Hz, C-1C,
D-Galp), 104.0 (JC-1/H-
O
B
D
a-
L-
BnO
R1O
OR2
a-
L-Rhap), 101.8 (JC-1/H-
1 = 169 Hz, C-1F,
a-D-Galf), 100.1 (JC-1/H-1 = 172.3 Hz, C-1E, a
-
L
-
10: R1 = MBn; R2 = Ac
11:
Rhap) in the 13C NMR supported its formation (Scheme 3). The
appearance of coupling constants (JC-1/H-1) in the gated 1H coupled
13C NMR spectrum of compound 1 confirmed the presence of two
b
R
1 = MBn; R2 = Bn
12: R1 = H; R2 = Bn
c
a
5
equatorial (b-
D-Galp and b-D-Manp) and three axial glycopyranosyl
linkages (three
a-L a-D-galactofurano-
-Rhap).19 The presence of an
syl linkage was confirmed from the 1H NMR (JH-1/H-2 = 4.8 Hz) and
JC-1/H-1 = 169 Hz value.18
BnO
OBn
O
A
O
OC8H17
BnO
O
B
O
SEt
BnO
OBn
E
O
a
BnO
4 + 7
O
BnO
C
BnO
O
BnO
OBn
BnO
BnO
OR
13: R = Ac
14: R = H
F
O
d
OBn
6
a
17
BnO
O
OBn
16
b
O
A
BnO
OC8H17
OBn
BnO
O
O
B
A
O
OC8H17
BnO
BnO
O
OBn
O
B
O
BnO
O
C
OBn
BnO
D
BnO
O
O
C
O
BnO
R1
O
O
RO
BnO
Ph
O
O
O
O
O
OR
d
Ph
E
15:
16:
R = Ac
R = H
D
R2
Scheme 2. Reagents and conditions: (a) N-iodosuccinimide (NIS), TMSOTf, CH2Cl2,
MS 4 Å, ꢁ40 °C, 1 h, 79% for 10, 77% for 13 and 71% for 15; (b) benzyl bromide,
NaOH, TBAB, DMF, room temperature, 4 h, 80%; (c) DDQ, CH2Cl2, H2O, room
temperature, 3 h, 77%; (d) 0.1 M CH3ONa, CH3OH, room temperature, 2 h, 95% for 14
and 92% for 16.
O
BnO
BnO
BnO
OBn
O
18: R1 = H; R2 = OH
BnO
c
R
1 = OH; R2 = H
19:
F
O
OBn
H-1C), 5.05 (br s, H-1F), 4.30 (d, J = 9.1 Hz, H-1A), 4.18 (d, J = 7.5 Hz,
H-1D) in the 1H NMR and d 106.7 (JC-1/H-1 = 158.5 Hz, C-1A, b-
D-
d
Galp), 104.5 (JC-1/H-1 = 155.9 Hz, C-1D, b-
101.2 (JC-1/H-1 = 171 Hz, C-1E, -Rhap), 99.4 (JC-1/H-1 = 172.3 Hz,
C-1C, -Rhap), 98.3 (JC-1/H-1 = 168.5 Hz, C-1F, -Galf), 97.4
(JC-1/H-1 = 170 Hz, C-1B,
-Rhap) in the 13C NMR and gated 1H
D-Glcp), 101.7 (PhCH),
a-L
1
a-
L
a-D
a
-L
coupled 13C NMR spectra19 of compound 18 confirmed the
stereoselective [4 + 2] glycosylation to obtain compound 18. The
formation of regioselective (1?3)-glycosylation product 18 was
confirmed from its 2D HMBC NMR spectral analysis. The appear-
ance of three bond correlation peak (H-1E/C-3D) in the 2D HMBC
spectrum of compound 18 and also spectroscopic analysis of the
acetylated product of compound 18 (data not included) strongly
confirmed the formation of the regioselective (1?3)-glycosylation
product 18. Oxidation of the free hydroxyl group at the C-2D posi-
tion in compound 18 using Dess–Martin periodinane20 followed by
sodium borohydride reduction21 of the resulting ketone furnished
Scheme 3. Reagents and conditions: (a) TMSOTf, CH2Cl2, ꢁ15 °C, 1 h, 73%; (b) NIS,
TMSOTf, CH2Cl2, MS 4 Å, ꢁ40 °C, 70%; (c) (i) Dess–Martin periodinane, CH2Cl2, room
temperature, 18 h; (ii) NaBH4, CH3OH, room temperature, 4 h; (d) H2, 20% Pd(OH)2–
C, CH3OH, room temperature, 24 h, 62% overall.
3. Conclusion
In conclusion, an efficient synthetic strategy has been success-
fully developed for the preparation of the hexasaccharide repeating
unit of the lipopolysaccharide found in the cell wall of Azospirillum
irakense KBC1. Regio- and stereoselective [4 + 2] glycosylation
allowed us to achieve the target hexasaccharide in minimum
hexasaccharide derivative 19 containing a b-D-mannosidic moiety,
which was conventionally hydrogenolized over Pearlman’s catalyst
to give target hexasaccharide 1 in 62% overall yield as its octyl
glycoside. Spectroscopic analysis of compound 1 confirmed its
number of steps. The generation of b-
b- -glucosyl moiety in the late stage minimized the difficulties
D-mannosyl moiety from a
D

2758
S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2755–2761
for its formation. All intermediate steps were reasonably high
yielding and reproducible for a scale-up preparation.
PhCH2), 4.45 (d, J = 11.9 Hz, 1H, PhCH2), 4.36 (d, J = 7.7 Hz, 1H, H-
1), 3.97–3.93 (m, 1H, OCH2a), 3.74–3.71 (m, 2H, H-6ab), 3.56–3.48
(m, 3H, H-3, H-5, OCH2b), 3.47–3.44 (dd, J = 7.8, 7.8 Hz, 1H, H-2),
2.05 (s, 3H, COCH3), 1.30–1.25 [m, 12H, (CH2)6], 0.87 (t, J = 6.5 Hz,
3H, CH3); 13C NMR (75 MHz, CDCl3): d 171.1 (COCH3), 138.7–
128.2 (Ar-C), 104.1 (C-1), 79.6 (C-2), 75.1 (C-3), 74.0 (PhCH2),
72.9 (PhCH2), 72.4 (C-5), 70.7 (OCH2), 70.0 (C-6), 68.7 (C-4), 32.2
(CH2), 30.1 (CH2), 29.8 (CH2), 29.7 (CH2), 26.6 (CH2), 23.1 (CH2),
21.2 (COCH3), 14.5 (CH3); ESI-MS: m/z 537.2 [M+Na]+; Anal. Calcd
for C30H42O7 (514.29): C, 70.01; H, 8.23. Found: C, 69.78; H, 8.45.
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
in a hot plate. Silica gel 230–400 mesh was used for column chro-
matography. 1H and 13C NMR, 2D COSY, and HMQC spectra were
recorded on Brucker Avance DPX 500 MHz 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 re-
corded on a Micromass Quttro II mass spectrometer. Elementary
analysis was carried out on Carlo Erba-1108 analyzer. Optical rota-
tions were measured at 25 °C on a Jasco P-2000 polarimeter. Com-
mercially available grades of organic solvents of adequate purity
are used in all reactions.
4.4. Octyl [2-O-acetyl-4-O-benzyl-3-O-(4-methoxybenzyl)-a-L-
rhamnopyranosyl]-(1?3)-4-O-acetyl-2,6-di-O-benzyl-b-D-
galactopyranoside (10)
To a solution of compound 2 (2.0 g, 3.88 mmol) and compound
3 (2.1 g, 4.56 mmol) in anhydrous CH2Cl2 (20 mL) were added MS
4 Å (3 g) and reaction mixture was allowed to stir at room temper-
ature for 30 min under argon. The reaction mixture was cooled to
ꢁ40 °C and N-iodosuccinimide (NIS; 1.2 g, 5.33 mmol) followed by
TMSOTf (20 lL) were added to it. The reaction mixture was al-
lowed to stir at same temperature for 1 h, filtered through a Celite
bedÒ, and washed with CH2Cl2 (100 mL). The organic layer was
washed with 5% aq Na2S2O3, aq NaHCO3 and water, dried (Na2SO4)
and concentrated under reduced pressure. The crude product was
purified over SiO2 using hexane–EtOAc (6:1) as eluant to afford
4.2. Octyl 2,6-di-O-benzyl-b-D-galactopyranoside (9)
To a solution of compound 8 (3.0 g, 10.26 mmol) in dry DMF
(10 mL) were added 2,2-dimethoxypropane (4 mL, 32.53 mmol)
followed by p-TsOH (150 mg) and the reaction mixture was al-
lowed to stir at room temperature for 12 h. To the reaction mixture
were added powdered NaOH (4.0 g, 100 mmol) and benzyl bro-
mide (5.0 mL, 42.05 mmol) and it was allowed to stir at room tem-
perature for 6 h. The reaction mixture was poured into water
(200 mL) and extracted with EtOAc (100 mL). The organic layer
was washed with satd NaHCO3, dried (Na2SO4), and concentrated.
A solution of the crude product in 80% aq AcOH (100 mL) was al-
lowed to stir at 80 °C for 1.5 h. The solvents were removed under
reduced pressure and the crude product was purified over SiO2
using hexane–EtOAc (4:1) as eluant to give pure 9 (3.5 g, 72%). Col-
pure 10 (2.8 g, 79%). Colorless oil; ½a D25
¼ þ1:1 (c 1.2, CHCl3); mmax
ꢂ
(neat): 3031, 2929, 2858, 1746, 1613, 1514, 1455, 1370, 1237,
1174, 1140, 1099, 1078, 1060, 985, 823, 754, 699 cmꢁ1 1H NMR
;
(300 MHz, CDCl3): d 7.31–7.23 (m, 15H, Ar-H), 7.20 (d, J = 8.6 Hz,
2H, Ar-H), 6.79 (d, J = 8.6 Hz, 2H, Ar-H), 5.42–5.40 (m, 1H, H-2B),
5.31 (d, J = 3.1 Hz, 1H, H-4A), 5.05 (br s, 1H, H-1B), 4.89 (d,
J = 10.9 Hz, 1H, PhCH2), 4.85 (d, J = 11.7 Hz, 1H, PhCH2), 4.62 (d,
J = 10.9 Hz, 1H, PhCH2), 4.58 (d, J = 11.0 Hz, 2H, PhCH2), 4.54 (d,
J = 11.8 Hz, 1H, PhCH2), 4.45 (d, J = 11.8 Hz, 1H, PhCH2), 4.36 (d,
J = 10.9 Hz, 1H, PhCH2), 4.35 (d, J = 7.0 Hz, 1H, H-1A), 3.98–3.91
(m, 1H, OCH2a), 3.89–3.79 (m, 1H, H-5B), 3.76 (s, 3H, OCH3),
3.77–3.69 (m, 3H, H-3A, H-3B, H-5A), 3.63–3.56 (dd, J = 7.8 Hz each,
1H, H-2A), 3.53–3.47 (m, 3H, H-6abA, OCH2b), 3.32 (t, J = 9.4 Hz each,
1H, H-4B), 2.07 (s, 3H, COCH3), 2.00 (s, 3H, COCH3), 1.65–1.61 (m,
2H, CH2), 1.28–1.23 [m, 13H, (CH2)5, CH3], 0.87 (t, J = 4.0 Hz, 3H,
CH3); 13C NMR (75 MHz, CDCl3): d 169.7 (2C, 2COCH3), 159.2–
113.7 (Ar-C), 103.9 (C-1A), 99.2 (C-1B), 79.5 (C-4B), 79.4 (C-2A),
77.2 (C-3A), 75.4 (C-3B), 74.9 (PhCH2), 74.5 (PhCH2), 73.7 (PhCH2),
72.6 (C-5A), 71.4 (PhCH2), 70.3 (OCH2) 69.7 (C-5B), 68.9 (C-2B),
68.5 (C-4A), 68.4 (C-6A), 55.1 (OCH3), 31.8 (CH2), 29.8 (CH2), 29.5
(CH2), 29.3 (CH2), 26.2 (CH2), 22.7 (CH2), 21.0 (COCH3), 20.7
(COCH3), 18.1 (CH3), 14.2 (CH3); ESI-MS: m/z 935.4 [M+Na]+; Anal.
Calcd for C53H68O13 (912.46): C, 69.71; H, 7.51. Found: C, 69.50; H,
7.75.
orless oil; ½a 2D5
ꢂ
¼ ꢁ6:4 (c 1.2, CHCl3);
mmax (neat): 3418, 2927, 2857,
1722, 1603, 1585, 1453, 1374, 1316, 1275, 1115, 1069, 1028, 756,
712 cmꢁ1 1H NMR (300 MHz, CDCl3): d 7.33–7.25 (m, 10H, Ar-H),
;
4.94 (d, J = 11.5 Hz, 1H, PhCH2), 4.65 (d, J = 11.5 Hz, 1H, PhCH2),
4.57 (br s, 2H, PhCH2), 4.32 (d, J = 7.4 Hz, 1H, H-1), 4.03–3.90 (m,
2H, H-3, H-4), 3.78–3.63 (m, 2H, H-5, H-OCH2a), 3.59–3.34 (m,
4H, 2H-6ab, H-OCH2b, H-2), 2.59 (br s, 2H, 2 OH), 1.66–1.59 (m,
2H, CH2), 1.38–1.08 [m, 10H, (CH2)5], 0.87–0.85 (m, 3H, CH3); 13C
NMR (75 MHz, CDCl3): d 137.2–126.4 (Ar-C), 102.4 (C-1), 77.8 (C-
2), 73.2 (C-3), 72.4 (C-5), 72.1 (PhCH2), 71.9 (PhCH2), 69.9 (OCH2),
68.6 (C-4), 67.6 (C-6), 30.6 (CH2), 28.5 (CH2), 28.1 (CH2), 28.0
(CH2), 24.9 (CH2), 21.4 (CH2), 12.8 (CH3); ESI-MS: m/z 495.2
[M+Na]+; Anal. Calcd for C28H40O6 (472.28): C, 71.16; H, 8.53.
Found: C, 71.0; H, 8.75.
4.3. Octyl 4-O-acetyl-2,6-di-O-benzyl-b-D-galactopyranoside (2)
4.5. Octyl [2,4-di-O-benzyl-3-O-(4-methoxybenzyl)-
a
-L
-rham-
nopyranosyl]-(1?3)-2,4,6-tri-O-benzyl-b-
(11)
D-galactopyranoside
To a solution of compound 9 (3.0 g, 6.34 mmol) in dry DMF
(10 mL) were added triethyl orthoacetate (8.0 mL, 43.64 mmol) fol-
lowed by p-TsOH (100 mg) and the reaction mixture was allowed
to stir at room temperature for 2 h. To the reaction mixture was
added water (100 mL) and then was extracted with EtOAc
(100 mL) after stirring at room temperature for 30 min. The organic
layer was dried (Na2SO4) and concentrated. The crude product was
purified over SiO2 using hexane–EtOAc (5:1) as eluant to give pure
To a solution of compound 10 (2.6 g, 2.85 mmol) in dry DMF
(10 mL) were added powdered NaOH (1.0 g, 25.0 mmol), tetrabu-
tylammonium bromide (200 mg) and benzyl bromide (1.2 mL,
10.09 mmol) and the reaction mixture was allowed to stirred at
room temperature for 4 h. The reaction mixture was poured into
water and extracted with EtOAc (100 mL). The organic layer was
washed with water, dried (Na2SO4), and concentrated. The crude
product was purified over SiO2 using hexane–EtOAc (7:1) as eluant
2 (2.5 g, 76%). Colorless oil; ½a D25
ꢂ
¼ ꢁ9:1 (c 1.2, CHCl3);
mmax (neat):
3469, 3031, 2927, 2857, 1744, 1455, 1373, 11238, 1173, 1102,
1079, 752, 698 cmꢁ1 1H NMR (300 MHz, CDCl3): d 7.33–7.25 (m,
;
to give pure 11 (2.3 g, 80%). Colorless oil; ½a D25
¼ ꢁ7 (c 1.2, CHCl3);
ꢂ
10H, Ar-H), 5.36 (d, J = 3.2 Hz, 1H, H-4), 4.96 (d, J = 11.3 Hz, 1H,
PhCH2), 4.65 (d, J = 11.5 Hz, 1H, PhCH2), 4.54 (d, J = 11.9 Hz, 1H,
m
max (neat): 3031, 2929, 2858, 1746, 1613, 1514, 1455, 1370, 1237,
1174, 1099, 1078, 1060, 985, 823, 754, 699 cmꢁ1
;
1H NMR

S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2755–2761
2759
(300 MHz, CDCl3): d 7.34–7.18 (m, 25H, Ar-H), 7.15 (d, J = 8.5 Hz,
2H, Ar-H), 6.73 (d, J = 8.5 Hz, 2H, Ar-H), 5.27 (br s, 1H, H-1B), 4.98
(d, J = 12.0 Hz, 1H, PhCH2), 4.94 (d, J = 11.4 Hz, 1H, PhCH2), 4.83
(d, J = 11.7 Hz, 1H, PhCH2), 4.67–4.39 (m, 7H, PhCH2), 4.37–4.32
(m, 3H, H-1A, PhCH2), 3.97–3.87 (m, 1H, OCH2a), 3.84–3.74 (m,
6H, H-2A, H-2B, H-4A, H-5B, H-6abA), 3.69 (s, 3H, OCH3), 3.61–3.51
(m, 4H, H-3A, H-3B, H-4B, H-5A), 3.49–3.42 (m, 1H, OCH2b), 1.60–
1.56 (m, 2H, CH2), 1.33 (d, J = 6.1 Hz, 3H, CCH3), 1.32–1.20 [m,
10H, (CH2)5], 0.85 (t, J = 6.5 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3):
d 159.1–113.7 (Ar-C), 104.1 (C-1A), 99.4 (C-1B), 80.2 (C-4B), 79.7 (C-
2A), 79.3 (C-3A), 78.0 (C-3B),76.1 (C-2B), 75.5 (C-5B), 75.1 (PhCH2),
74.7 (PhCH2), 74.3 (PhCH2), 73.6 (C-5A), 73.5 (PhCH2), 72.3 (PhCH2),
71.5 (PhCH2), 70.1 (OCH2), 69.0 (C-4A), 68.9 (C-6A), 55.1 (OCH3),
31.8 (CH2), 29.7 (CH2), 29.4 (CH2), 29.2 (CH2), 26.1 (CH2), 22.6
(CH2), 18.2 (CH3), 14.1 (CH3); ESI-MS: m/z 1031.5 [M+Na]+; Anal.
Calcd for C63H76O11 (1008.54): C, 74.97; H, 7.59. Found: C, 74.80;
H, 7.85.
ride derivative 13 (1.3 g, 77%). Colorless oil; ½a D25
ꢂ
¼ ꢁ5:9 (c 1.2,
CHCl3); mmax (neat): 3089, 3064, 3031, 2926, 2858, 1744, 1606,
1497, 1454, 1369, 1235, 1079, 913, 840, 740, 699 cmꢁ1 1H NMR
;
(300 MHz, CDCl3): d 7.31–7.11 (m, 35H, Ar-H), 5.45–5.43 (m, 1H,
H-2C), 5.24 (br s, 1H, H-1B), 5.00 (br s, 1H, 1C), 4.97–4.85 (m, 3H,
PhCH2), 4.77 (d, J = 11.1 Hz, 1H, PhCH2), 4.61–4.56 (m, 5H, PhCH2),
4.48–4.36 (m, 3H, PhCH2), 4.33 (d, J = 7.2 Hz, 1H, H-1A), 4.20 (br s,
2H, PhCH2), 4.08–4.04 (dd, J = 9.2, 2.6 Hz, 1H, H-3A), 3.92–3.84 (m,
2H, H-3C, OCH2a), 3.82–3.74 (m, 5H, H-3B, H-4A, H-5A, H-6abA), 3.68
(br s, 1H, H-2B), 3.62–3.57 (m, 4H, H-2A, H-4B, H-5B, H-5C), 3.49–
3.41 (m, 1H, OCH2b), 3.36 (t, J = 9.4 Hz, 1H, H-4C), 2.07 (s, 3H,
COCH3), 1.58–1.53 (m, 2H, CH2), 1.28 (d, J = 6.1 Hz, 3H, CCH3),
1.27–1.20 (m, 10H, (CH2)5], 0.85 (t, J = 6.4 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d 169.7 (COCH3), 138.8–127.2 (Ar-C), 104.1 (C-
1A), 98.8 (C-1B), 96.2 (C-1C), 80.9 (C-4B), 80.0 (C-3A), 79.8 (C-4A),
78.3 (C-3B), 78.2 (C-3C), 77.9 (C-2A), 77.2 (C-4C), 76.0 (C-2C), 75.2
(PhCH2), 75.1 (PhCH2), 74.7 (PhCH2), 74.5 (PhCH2), 73.7 (C-2B),
73.5 (PhCH2), 72.1 (PhCH2), 71.6 (PhCH2), 69.9 (OCH2), 69.0 (C-
5B), 68.9 (C-5C), 68.8 (C-6A), 68.3 (C-5A), 31.8 (CH2), 29.7 (CH2),
29.4 (CH2), 29.2 (CH2), 26.1 (CH2), 22.7 (CH2), 20.9 (COCH3), 18.2
(CCH3), 18.1 (CCH3), 14.2 (CH3); ESI-MS: m/z 1279.6 [M+Na]+; Anal.
Calcd for C77H92O15 (1256.64): C, 73.54; H, 7.37. Found: C, 73.35; H,
7.60.
4.6. Octyl [2,4-di-O-benzyl-3-O-(4-methoxybenzyl)-a-L-
rhamnopyranosyl]-(1?3)-2,4,6-tri-O-benzyl-b-D-
galactopyranoside (12)
To a solution of compound 11 (2.2 g, 2.18 mmol) in CH2Cl2
(50 mL) was added a solution of DDQ (1.0 g, 4.40 mmol) in H2O
(20 mL) and the reaction mixture was allowed to stir at room tem-
perature for 3 h. The reaction mixture was diluted with CH2Cl2
(50 mL) and the organic layer was washed with satd NaHCO3 and
water, dried (Na2SO4), and concentrated. The crude product was
purified over SiO2 using hexane–EtOAc (5:1) as eluant to give pure
4.8. Octyl (3,4-di-O-benzyl-
di-O-benzyl- -rhamnopyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b-
-galactopyranoside (14)
a-L-rhamnopyranosyl)-(1?3)-(2,4-
a-L
D
A solution of compound 13 (1.2 g, 0.95 mmol) in 0.1 M CH3ONa
12 (1.5 g, 77%). Colorless oil; ½a D25
ꢂ
¼ ꢁ1:4 (c 1.2, CHCl3); mmax
in CH3OH (15 mL) was allowed to stir at room temperature for 2 h,
neutralized with Dowex 50W X8 (H+) resin. The reaction mixture
was filtered and the filtrate was concentrated to give crude prod-
uct, which was passed through a short pad of SiO2 using hexane–
EtOAc (3:1) as eluant to give pure 14 (1.1 g, 95%). Colorless oil;
(neat): 3556, 3064, 3031, 2927, 2857, 1497, 1455, 1371, 1209,
1101, 1029, 993, 912, 808, 753, 698 cmꢁ1 1H NMR (300 MHz,
;
CDCl3): d 7.36–7.10 (m, 25H, Ar-H), 5.30 (br s, 1H, H-1B), 5.07 (d,
J = 11.5 Hz, 1H, PhCH2), 4.89 (d, J = 12.5 Hz, 1H, PhCH2), 4.88 (d,
J = 12.5 Hz, 1H, PhCH2), 4.64–4.56 (m, 3H, PhCH2), 4.47 (d,
J = 11.9 Hz, 1H, PhCH2), 4.42 (d, J = 11.9 Hz, 1H, PhCH2), 4.36 (d,
J = 7.0 Hz, 1H, H-1A), 4.22 (d, J = 11.7 Hz, 1H, PhCH2), 4.00 (d,
J = 11.7 Hz, 1H, PhCH2), 3.96–3.86 (m, 2H, H-3A, OCH2a), 3.83–
3.77 (m, 4H, H-2A, H-3B, H-6abA), 3.69–3.68 (m, 1H, H-2B), 3.61–
3.58 (m, 3H, H-4A, H-5A, H-5B), 3.51–3.43 (m, 1H, OCH2b), 3.29 (t,
J = 9.4 Hz, 1H, H-4B), 1.62–1.59 (m, 2H, CH2), 1.32 (d, J = 6.2 Hz,
3H, CCH3), 1.30–1.20 [m, 10H, (CH2)5], 0.86 (t, J = 6.4 Hz, 3H,
CH3); 13C NMR (75 MHz, CDCl3): d 138.9–127.3 (Ar-C), 104.1 (C-
1A), 98.4 (C-1B), 82.1 (C-4B), 80.0 (C-3A), 78.8 (C-4A), 78.4 (C-2A),
76.1 (C-3B), 74.9 (PhCH2), 74.7 (PhCH2), 74.6 (PhCH2), 73.6 (C-2B),
73.5 (PhCH2), 72.2 (PhCH2), 71.5 (C-5B), 70.0 (OCH2), 68.8 (C-6A),
68.0 (C-5A), 31.7 (CH2), 29.6 (CH2), 29.3 (CH2), 29.2 (CH2), 26.1
(CH2), 22.6 (CH2), 18.1 (CCH3), 14.0 (CH3); ESI-MS: m/z 911.4
[M+Na]+; Anal. Calcd for C55H68O10 (888.48): C, 74.30; H, 7.71.
Found: C, 74.17; H, 7.95.
½
a 2D5
ꢂ
¼ ꢁ15:1 (c 1.2, CHCl3); mmax (neat): 3478, 3064, 3031, 2927,
2858, 1497, 1454, 1365, 1213, 1099, 1078, 1057, 1029, 994, 752,
735, 698 cmꢁ1 1H NMR (300 MHz, CDCl3): d 7.30–7.13 (m, 35H,
;
Ar-H), 5.24 (br s, 1H, H-1B), 5.06 (br s, 1H, H-1C), 4.99 (d,
J = 11.5 Hz, 1H, PhCH2), 4.90–4.84 (m, 2H, PhCH2), 4.70 (d,
J = 11.1 Hz, 1H, PhCH2), 4.63–4.53 (m, 6H, PhCH2), 4.47 (d,
J = 12.1 Hz, 1H, PhCH2), 4.42 (d, J = 12.1 Hz, 1H, PhCH2), 4.31 (d,
J = 7.0 Hz, 1H, H-1A), 4.25–4.17 (m, 2H, PhCH2), 4.06–4.02 (dd,
J = 9.3, 2.7 Hz, H-3A), 3.93–3.86 (m, 2H, H-3C, OCH2a), 3.84–3.71
(m, 7H, H-2A, H-2C, H-3B, H-4A, H-4B, H-5B, H-6abA), 3.60–3.52 (m,
4H, H-2B, H-2C, H-4A, H-5B), 3.49–3.37 (m, 2H, H-4C, H-OCH2b),
1.58–1.56 (m, 2H, CH2), 1.28–1.19 [m, 13H, (CH2)5, CCH3], 0.86 (t,
J = 6.4 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3): d 138.8–127.1
(Ar-C), 104.1 (C-1A), 100.6 (C-1C), 98.9 (C-1B), 80.8 (C-4B), 78.0
(C-4A), 79.9 (C-3A), 79.8 (C-3C), 78.3 (C-3B), 78.2 (C-2A), 77.5 (C-
2B), 76.2 (C-4C), 75.1 (PhCH2), 75.0 (PhCH2) 74.8 (PhCH2), 74.5
(PhCH2), 73.7 (C-2C), 73.5 (PhCH2), 72.0 (PhCH2), 71.9 (PhCH2),
69.9 (OCH2), 69.0 (C-5C), 68.8 (C-6A), 68.7 (C-5B), 68.0 (C-5A), 31.8
(CH2), 29.7 (CH2), 29.4 (CH2), 29.2 (CH2), 26.1 (CH2), 22.6 (CH2),
18.2 (CH3), 18.1 (CH3), 14.1 (CH3); ESI-MS: m/z 1237.6 [M+Na]+;
Anal. Calcd for C75H90O14 (1214.63): C, 74.11; H, 7.46. Found: C,
74.27; H, 7.70.
4.7. Octyl (2-O-acetyl-3,4-di-O-benzyl-
(1?3)-(2,4-di-O-benzyl- -rhamnopyranosyl)-(1?3)-2,4,6-tri-
O-benzyl-b- -galactopyranoside (13)
a-L-rhamnopyranosyl)-
a
-L
D
To a solution of compound 12 (1.2 g, 1.35 mmol) and compound
5 (700 mg, 1.62 mmol) in anhydrous CH2Cl2 (10 mL) were added
MS 4 Å (2 g) and reaction mixture was allowed to stir at room tem-
perature for 30 min under argon. The reaction mixture was cooled
4.9. Octyl (2,3-di-O-acetyl-4,6-O-benzylidene-b-
(1?2)-(3,4-di-O-benzyl- -rhamnopyranosyl)-(1?3)-(2,4-di-
O-benzyl- -rhamnopyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b-
galactopyranoside (15)
D-glucopyranosyl)-
a-L
to ꢁ40 °C and NIS (440 mg, 1.95 mmol) followed by TMSOTf (5
l
L)
a
-L
D-
were added to it. The reaction mixture was allowed to stir at same
temperature for 1 h, filtered through a Celite bedÒ, and washed
with CH2Cl2 (100 mL). The organic layer was washed with 5% aq
Na2S2O3, aq NaHCO3 and water, dried (Na2SO4), and concentrated
under reduced pressure. The crude product was purified over
SiO2 using hexane–EtOAc (6:1) as eluant to afford pure trisaccha-
To a solution of compound 14 (1.0 g, 0.82 mmol) and compound
6 (390 mg, 0.98 mmol) in anhydrous CH2Cl2 (5 mL) were added MS
4 Å (1 g) and the reaction mixture was allowed to stir at room tem-
perature for 30 min under argon. The reaction mixture was cooled

2760
S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2755–2761
to ꢁ40 °C and NIS (260 mg, 1.15 mmol) followed by TMSOTf (3
l
L)
(2C, 2 PhCH2), 73.7 (C-3D), 72.4 (PhCH2), 70.4 (PhCH2), 69.3 (C-
6A), 69.2 (2C, C-5A, OCH2), 68.8 (C-4C), 68.7 (C-6D), 66.9 (C-5D),
32.2 (CH2), 30.1 (CH2), 29.8 (CH2), 29.6 (CH2), 26.5 (CH2), 23.1
(CH2), 18.5 (CCH3), 18.4 (CCH3), 14.5 (CH2CH3); ESI-MS: m/z
1487.7 [M+Na]+; Anal. Calcd for C88H104O19 (1464.71): C, 72.11;
H, 7.15. Found: C, 71.88; H, 7.40.
were added to it. The reaction mixture was allowed to stir at same
temperature for 1 h, filtered through a Celite bedÒ and washed
with CH2Cl2 (50 mL). The organic layer was washed with 5% aq
Na2S2O3, aq NaHCO3 and water, dried (Na2SO4), and concentrated
under reduced pressure. The crude product was purified over
SiO2 using hexane–EtOAc (6:1) as eluant to afford pure tetrasac-
charide derivative 15 (900 mg, 71%). Colorless oil; ½a D25
ꢂ
¼ ꢁ16 (c
4.11. Ethyl (2,3,5,6-tetra-O-benzyl-a-D-galactofuranosyl)-(1?2)-
1.2, CHCl3); mmax (neat): 3485, 3089, 3064, 3031, 2925, 2856,
3,4-di-O-benzyl-1-thio- -rhamnopyranoside (17)
a-L
1753, 1497, 1455, 1370, 1239, 1218, 1082, 911, 819, 740,
698 cmꢁ1
;
1H NMR (300 MHz, CDCl3): d 7.38–7.12 (m, 40H, Ar-
A solution of compound 4 (500 mg, 1.29 mmol) and compound
7 (1.1 g, 1.60 mmol) in anhydrous CH2Cl2 (10 mL) was cooled to
ꢁ15 °C. To the cooled reaction mixture was added TMSOTf
H), 5.27 (s, 1H, PhCH), 5.22 (br s, 1H, H-1B), 5.21 (t, J = 9.4 Hz, H-
3D), 5.04 (br s, 1H, H-1C), 5.03 (d, J = 11.2 Hz, 1H, PhCH2), 4.99 (t,
J = 9.4 Hz, H-2D), 4.89 (d, J = 11.5 Hz, 1H, PhCH2), 4.80 (d,
J = 11.1 Hz, 1H, PhCH2), 4.68 (d, J = 11.5 Hz, 1H, PhCH2), 4.60–4.51
(m, 5H, PhCH2), 4.48–4.40 (m, 4H, H-1D, PhCH2), 4.32 (d,
J = 7.0 Hz, 1H, H-1A), 4.18–4.11 (m, 2H, PhCH2), 4.03–3.99 (dd,
J = 9.4, 2.7 Hz, H-3A), 3.93–3.87 (m, 1H, OCH2a), 3.81–3.63 (m, 9H,
H-2A, H-2C, H-3B, H-3C, H-4A, H-4B, H-5A, H-6abA), 3.57–3.53 (m,
3H, H-2B, H-6abD), 3.51–3.41 (m, 3H, H-5B, H-5C, OCH2b), 3.34 (t,
J = 9.4 Hz, 1H, H-4D), 3.22–3.10 (m, 2H, H-4C, H-5D), 2.04 (s, 3H,
COCH3), 1.84 (s, 3H, COCH3), 1.60–1.56 (m, 2H, CH2), 1.25–1.20
[m, 13H, (CH2)5, CCH3], 0.85 (t, J = 6.4 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3): d 169.8 (COCH3), 169.4 (COCH3), 138.8–126.1
(Ar-C), 104.1 (C-1A), 102.9 (C-1D), 101.3 (PhCH), 101.2 (C-1C),
98.7 (C-1B), 80.5 (C-4B), 80.3 (C-4A), 79.9 (C-3B), 79.5 (C-3C), 78.5
(C-3A), 78.4 (C-2A), 78.1 (C-2B), 77.9 (C-4D), 75.9 (C-5B), 75.1
(PhCH2), 75.0 (PhCH2), 74.6 (2C, 2 PhCH2), 73.6 (C-2C), 73.5
(PhCH2), 72.8 (PhCH2), 72.1 (C-2D), 72.0 (PhCH2), 71.4 (C-3D), 69.9
(OCH2), 68.8 (3C, C-5A, C-5C, C-6A), 68.6 (C-4C), 69.0 (C-6D), 66.0
(C-5D), 31.8 (CH2), 29.7 (CH2), 29.4 (CH2), 29.2 (CH2), 26.1 (CH2),
22.6 (CH2), 20.8 (COCH3), 20.6 (COCH3), 18.1 (2C, 2CH3), 14.1
(CH3); MALDI-MS: m/z 1571.7 [M+Na]+; Anal. Calcd for
(25 lL) and it was allowed to stir at same temperature for 1 h.
The reaction mixture was diluted with CH2Cl2 (100 mL) and the or-
ganic layer was washed with satd NaHCO3, water, dried (Na2SO4),
and concentrated. The crude product was purified over SiO2 using
hexane–EtOAc (5:1) as eluent to give pure 17 (860 mg, 73%). Color-
less oil; ½a 2D5
¼ þ16 (c 1.2, CHCl3); mmax (neat): 3087, 3032, 2856,
ꢂ
1742, 1739, 1615, 1560, 1475, 1372, 1239, 1173, 1097, 1072,
1059, 989, 911, 823, 755, 698 cmꢁ1 1H NMR (500 MHz, CDCl3): d
;
7.24–7.11 (m, 30H, Ar-H), 5.32 (br s, 1H, H-1E), 5.23 (d, J = 4.3 Hz,
1H, H-1F), 4.72 (d, J = 11.0 Hz, 1H, PhCH2), 4.70 (d, J = 11.4 Hz, 1H,
PhCH2), 4.65 (d, J = 11.6 Hz, 1H, PhCH2), 4.55 (d, J = 11.9 Hz, 1H,
PhCH2), 4.50–4.31 (m, 8H, PhCH2), 4.29–4.24 (m, 1H, H-3F), 4.20–
4.18 (m, 1H, H-2E), 4.05–4.02 (m, 1H, H-2F), 3.95–3.91 (m, 2H, H-
4F, H-5F), 3.73–3.69 (m, 2H, H-3E, H-5E), 3.55–3.44 (m, 3H, H-4E,
H-6abF), 2.54–2.49 (m, 2H, SCH2CH3), 1.19 (t, J = 7.4 Hz, 3H,
SCH2CH3), 1.11 (d, J = 6.2 Hz, 3H, CCH3); 13C NMR (125 MHz,
CDCl3): d 139.3–127.7 (Ar-C), 98.0 (JC-1/H-1 = 170 Hz, C-1F,
a-D-Galf),
84.4 (C-1E, JC-1/H-1 = 171 Hz, -Rhap), 81.4 (C-2F), 81.3 (C-4E), 81.2
a
-L
(C-3F), 81.1 (C-4F), 79.7 (C-5E), 79.4 (C-3E), 74.1 (C-2E), 73.7 (2C, 2
PhCH2), 72.9 (PhCH2), 72.5 (PhCH2), 72.3 (PhCH2), 71.9 (PhCH2),
70.4 (C-6F), 68.9 (C-5F), 26.1 (SCH2CH3), 18.5 (CCH3), 15.6
(SCH2CH3); ESI-MS: m/z 933.4 [M+Na]+; Anal. Calcd for C56H62O9S
(910.41): C, 73.82; H, 6.86. Found: C, 73.61; H, 7.10.
C92H108O21 (1548.73): C, 71.30; H, 7.02. Found: C, 71.12; H, 7.30.
4.10. Octyl (4,6-O-benzylidene-b-
D-glucopyranosyl)-(1?2)-(3,4-
di-O-benzyl- -rhamnopyranosyl)-(1?3)-(2,4-di-O-benzyl-a-L-
a-
L
rhamnopyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b-
galactopyranoside (16)
D
-
4.12. Octyl (2,3,5,6-tetra-O-benzyl-
(3,4-di-O-benzyl- -rhamnopyranosyl)-(1?3)-(4,6-O-
benzylidene-b- -glucopyranosyl)-(1?2)-(3,4-di-O-benzyl-
rhamnopyranosyl)-(1?3)-(2,4-di-O-benzyl-
rhamnopyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b-D-
galactopyranoside (18)
a-D-galactofuranosyl)-(1?2)-
a-L
D
a-L-
A solution of compound 15 (800 mg, 0.52 mmol) in 0.1 M CH3O-
Na in CH3OH (10 mL) was allowed to stir at room temperature for
2 h, neutralized with Dowex 50W X8 (H+) resin. The reaction mix-
ture was filtered and the filtrated was concentrated to give a crude
product, which was passed through a short pad of SiO2 using hex-
ane–EtOAc (3:1) as eluant to give pure 16 (700 mg, 92%). Colorless
a-L-
To a solution of compound 16 (600 mg, 0.41 mmol) and com-
pound 17 (400 mg, 0.44 mmol) in anhydrous CH2Cl2 (10 mL) were
added MS 4 Å (2 g) and reaction mixture was allowed to stir at
room temperature for 30 min under argon. The reaction mixture
was cooled to ꢁ40 °C and NIS (120 mg, 0.53 mmol) followed by
oil; ½a 2D5
¼ ꢁ9 (c 1.2, CHCl3); mmax (neat): 3478, 3469, 3031, 2925,
ꢂ
2858, 1606, 1496, 1454, 1365, 1213, 1099, 1056, 1030, 751, 736,
697 cmꢁ1 1H NMR (500 MHz, CDCl3): d 7.27–7.14 (m, 40H, Ar-
;
H), 5.30 (s, 1H, PhCH) 5.20 (br s, 1H, H-1B), 4.99 (br s, 1H, H-1C),
4.94 (d, J = 11.5 Hz, 1H, PhCH2), 4.79 (d, J = 11.6 Hz, 1H, PhCH2),
4.76 (d, J = 11.2 Hz, 1H, PhCH2), 4.60–4.44 (m, 7H, PhCH2), 4.39
(d, J = 11.9 Hz, 1H, PhCH2), 4.33 (d, J = 11.9 Hz, 1H, PhCH2), 4.25
(d, J = 7.0 Hz, 1H, H-1A), 4.13–4.05 (m, 2H, PhCH2), 4.08 (d,
J = 9.5 Hz, 1H, H-1D), 3.95–3.92 (dd, J = 9.4, 2.8 Hz, 1H, H-3A),
3.84–3.82 (m, 1H, OCH2a), 3.79–3.77 (dd, J = 9.4, 3.0 Hz, 1H, H-
3C), 3.73–3.65 (m, 8H, H-2A, H-2D, H-3B, H-4A, H-4B, H-5A, H-
TMSOTf (2 lL) were added to it. The reaction mixture was allowed
to stir at same temperature for 1 h, filtered through a Celite bedÒ,
and washed with CH2Cl2 (50 mL). The organic layer was washed
with 5% aq Na2S2O3, aq NaHCO3 and water, dried (Na2SO4), and
concentrated under reduced pressure. The crude product was puri-
fied over SiO2 using hexane–EtOAc (4:1) as eluant to afford pure
hexasaccharide derivative 18 (660 mg, 70%). Colorless oil;
½
a 2D5
ꢂ
¼ ꢁ7:2 (c 1.2, CHCl3); mmax (neat): 3666, 3064, 3030, 2926,
2857, 1951, 1728, 1611, 1585, 1511, 11496, 1454, 1371, 1311,
1238, 1175, 1081, 911, 818, 740, 698 cmꢁ1 1H NMR (500 MHz,
6abA), 3.63 (br s, 1H, H-2B), 3.57 (t, J = 9.1 Hz each, 1H, H-3D),
3.52–3.48 (m, 3H, H-2C, H-6abD), 3.46–3.38 (m, 3H, H-4D, H-5B,
OCH2b), 3.35–3.31 (m, 2H, H-4C, H-5C), 2.95–2.91 (m, 1H, H-5D),
1.54–1.49 (m, 2H, CH2), 1.26–1.14 [m, 16H, (CH2)5, 2CH3], 0.77 (t,
J = 6.8 Hz, 3H, CH3); 13C NMR (125 MHz, CDCl3): d 138.9–126.7
(Ar-C), 106.3 (C-1D), 104.5 (C-1A), 102.1 (2C, C-1C, PhCH), 99.2 (C-
1B), 81.1 (C-4B), 80.8 (C-4A), 80.5 (C-3B), 80.3 (2C, C-3A, C-3C),
79.9 (C-2A), 79.0 (C-2B), 78.9 (C-4D), 76.5 (C-5B), 75.5 (2C, C-2C,
PhCH2), 75.3 (C-5C), 75.1 (PhCH2), 75.0 (PhCH2), 74.1 (C-4D), 74.0
;
CDCl3): d 7.32–7.20 (m, 70H, Ar-C), 5.40 (br s, 1H, H-1B), 5.37 (s,
1H, PhCH), 5.28 (d, J = 3.8 Hz, 1H, H-1E), 5.23 (br s, 1H, H-1C),
5.05 (br s, 1H, H-1F), 5.19–4.29 (m, 27H, H-3F, PhCH2), 4.30 (d,
J = 9.1 Hz, 1H, H-1A), 4.20–4.19 (m, 1H, H-2E), 4.18 (d, J = 7.5 Hz,
1H, H-1D), 4.13–4.07 (m, 2H, H-2F, H-3A), 4.02–3.98 (m, 2H, H-4F,
H-5F), 3.91–3.87 (m, 2H, H-3C, OCH2a), 3.82–3.67 (m, 11H, H-2A,
H-2D, H-3B, H-3D, H-3E, H-4A, H-4B, H-5A, H-5E, H-6abA), 3.66–3.36

S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 2755–2761
2761
(m, 12H, H-2B, H-2C, H-4C, H-4D, H-4E, H-5B, H-2C, H-6abD, H-6abF
,
104.0 (JC-1/H-1 = 156 Hz, C-1D, b-
C-1B,
(JC-1/H-1 = 169 Hz, C-1F,
-Rhap), 83.5 (C-4F), 81.5 (C-4A), 81.4 (C-5F), 80.6 (C-5D), 79.8
D
-Manp), 102.8 (JC-1/H-1 = 171 Hz,
OCH2b), 3.08–3.04 (m, 1H, H-5D), 1.60–1.54 (m, 2H, CH2), 1.31–
1.20 (m, 16H, (CH2)5, 2CH3), 0.92 (d, J = 6.2 Hz, 1H, CH3), 0.85
(t, J = 6.9 Hz, CH3); 13C NMR (125 MHz, CDCl3): d 138.9–127.8
a-
L
-Rhap), 102.4 (JC-1/H-1 = 173.5 Hz, C-1C,
a-L-Rhap), 101.8
a-D
-Galf), 100.1 (JC-1/H-1 = 172.3 Hz, C-1E,
a-L
(Ar-C), 106.7 (JC-1/H-1 = 158.5 Hz, C-1A, b-
155.9 Hz, C-1D, b- -Glcp), 101.7 (PhCH), 101.2 (JC-1/H-1 = 171 Hz,
C-1E, -Rhap), 99.4 (JC-1/H-1 = 172.3 Hz, C-1C, -Rhap), 98.3
(JC-1/H-1 = 168.5 Hz, C-1F, -Galf), 97.4 (JC-1/H-1 = 170 Hz, C-1B,
-Rhap), 84.3 (C-4A), 82.9 (C-4B), 81.8 (C-3B), 81.2 (C-2A), 80.9
(2C, C-3A, C-3C), 80.5 (C-2F), 80.4 (C-4E), 80.3 (C-3F), 79.7 (C-4F),
79.1 (C-3D), 79.0 (C-2B), 78.9 (C-5E), 78.6 (C-3E), 77.0 (C-5B), 76.8
(C-2C), 76.5 (C-5A), 75.6 (PhCH2), 75.3 (C-2D), 75.1 (PhCH2), 75.0
(PhCH2), 74.1 (C-4D), 74.0 (2C, 2 PhCH2), 73.9 (PhCH2), 73.8 (C-
2E), 73.6 (PhCH2), 73.0 (PhCH2), 72.8 (PhCH2), 72.5 (PhCH2), 72.4
(PhCH2), 72.1 (PhCH2), 72.0 (PhCH2), 70.4 (OCH2), 70.3 (C-6F),
69.3 (C-6A), 69.3 (C-5C), 68.9 (C-6D), 68.2 (C-5F), 67.3 (C-4C), 66.2
(C-5D), 32.4 (CH2), 30.1 (CH2), 29.8 (CH2), 29.6 (CH2), 26.5 (CH2),
23.1 (CH2), 18.6 (CH3), 18.5 (CH3), 18.4 (CH3), 14.5 (CH3); MALDI-
MS: m/z 2336.1 [M+Na]+; Anal. Calcd for C142H160O28 (2313.11):
C, 73.68; H, 6.97. Found: C, 73.46; H, 7.20.
D
-Galp), 104.5 (JC-1/H-1
=
(C-3D), 78.9 (C-4D), 77.6 (C-4E), 77.1 (C-2A), 75.4 (C-5A), 75.1 (C-
4B), 73.7 (C-4C), 73.5 (C-2F), 73.2 (C-3B), 72.5 (C-3A), 71.1 (C-3F),
71.0 (C-3E), 70.8 (C-2C), 70.5 (C-2E), 70.4 (C-2D), 69.9 (OCH2), 69.4
(C-5C), 69.3 (C-2B), 69.1 (C-5E), 69.0 (C-5B), 68.8 (C-3C), 63.4 (C-
6A), 61.7 (C-6F), 61.2 (C-6D), 32.0 (CH2), 29.8 (CH2), 29.6 (CH2),
29.4 (CH2), 26.1 (CH2), 22.7 (CH2), 17.0 (2C, 2CH3), 16.8 (CH3),
13.4 (CH3); ESI-MS: m/z 1077.4 [M+Na]+; Anal. Calcd for
D
a-
L
a-L
a-D
a-L
C44H78O28 (1054.46): C, 50.09; H, 7.45. Found: C, 49.86; H, 7.72.
Acknowledgments
S.G. thanks UGC, New Delhi for providing a Senior Research Fel-
lowship. This work was supported by Ramanna Fellowship (AKM),
Department of Science and Technology, New Delhi (SR/S1/RFPC-
06/2006) and Bose Institute, Kolkata.
References
4.13. Octyl (
rhamnopyranosyl)-(1?3)-(b-
rhamnopyranosyl)-(1?3)-(
a
-
D
-galactofuranosyl)-(1?2)-(
-mannopyranosyl)-(1?2)-(
-rhamnopyranosyl)-(1?3)-b-D-
a-L-
D
a-L-
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a
-
L
galactopyranoside (1)
To a solution of compound 18 (550 mg, 0.24 mmol) in dry
CH2Cl2 (5 mL) was added Dess–Martin periodinane (200 mg,
0.47 mmol) and the reaction mixture was allowed to stir at room
temperature for 24 h. The reaction mixture was diluted with
CH2Cl2 (50 mL) and the organic layer was washed with 5% Na2S2O3
and water in succession. The organic layer was dried over Na2SO4,
filtered, and concentrated under reduced pressure to give the crude
ketone, which was used in the next step without purification. To a
solution of the crude ketone in CH3OH (10 mL) was slowly added
NaBH4 (100 mg, 2.64 mmol) portionwise at 0 °C. The reaction mix-
ture was allowed to stir at room temperature for 12 h and concen-
trated under reduced pressure. The crude product was dissolved in
CH2Cl2 (50 mL) and successively washed with 1 M HCl, satd NaH-
CO3 and water, dried (Na2SO4), and concentrated. The crude prod-
uct was purified over SiO2 using hexane–EtOAc (4:1) as eluant to
afford pure hexasaccharide derivative 19 (390 mg). To a solution
of the crude product (390 mg, 0.17 mmol) in CH3OH (10 mL) was
added 20% Pd(OH)2–C (100 mg) and the reaction mixture was al-
lowed to stir at room temperature under a positive pressure of
hydrogen for 24 h. The reaction mixture was filtered through a Cel-
iteÒ bed and then washed with CH3OH–H2O (60 mL; 4:1 v/v). The
combined filtrate was evaporated under reduced pressure to fur-
nish compound 1, which was purified through a Sep-PakÒ C18 col-
umn using water and CH3OH sequentially as eluant to give pure
compound 1 (110 mg, 62%). White powder; ½a D25
¼ ꢁ27 (c 1.0,
ꢂ
CH3OH); mmax (KBr): 3401, 2925, 2854, 1736, 1649, 1460, 1379,
1121, 1073, 1044, 985, 915, 805, 725 cmꢁ1 1H NMR (500 MHz,
;
CD3OD): d 5.30 (br s, 1H, H-1C), 5.07 (br s, 1H, H-1E), 4.94 (br s,
1H, H-1B), 4.83 (d, J = 4.8 Hz, 1H, H-1F), 4.46 (br s, 1H, H-1D), 4.36
(d, J = 7.8 Hz, 1H, H-1F), 4.14 (d, J = 4.8 Hz, 1H, H-1F), 3.97–3.96
(m, 2H, H-2B, H-2D), 3.91–3.87 (m, 2H, H-2C, H-3F), 3.84–3.81 (m,
2H, H-3C, H-3D), 3.80–3.74 (m, 4H, H-2E, H-3B, H-3E, H-6aD), 3.73–
3.69 (m, 3H, H-4D, H-5E, H-6aA), 3.64–3.61 (m, 3H, H-5B, H-6abF),
3.56–3.49 (m, 5H, H-3A, H-5C, H-6bA, H-6bD, OCH2a), 3.45–3.38
(m, 6H, H-4A, H-4F, H-5A, H-5D, H-5F, OCH2b), 3.29–3.23 (m, 4H,
H-2A, H-4B, H-4C, H-4E), 1.54–1.50 (m, 2H, CH2), 1.21–1.15 (m,
19H, (CH2)5, 3CH3), 0.80 (t, J = 6.7 Hz, 3H, CH3); 13C NMR
(125 MHz, CD3OD): d 105.5 (JC-1/H-1 = 158.5 Hz, C-1A, b-D-Galp),