Concise synthesis of two trisaccharides related to the saponin isolated from Centratherum anthelminticum

Article abstract of DOI:10.1016/j.tet.2007.08.077

Chemical synthesis of two trisaccharides related to the saponin isolated from Centratherum anthelminticum is reported. Stereoselective, high-yielding glycosylation strategies were developed using H₂SO₄ immobilized on silica for activ

Full text of DOI:10.1016/j.tet.2007.08.077

Tetrahedron 63 (2007) 11363–11370
Concise synthesis of two trisaccharides related to the
saponin isolated from Centratherum anthelminticum*
*
Santanu Mandal and Balaram Mukhopadhyay
Medicinal and Process Chemistry Division, Central Drug Research Institute, Chattar Manzil Palace,
Lucknow 226001, UP, India
Received 14 June 2007; revised 31 July 2007; accepted 23 August 2007
Available online 30 August 2007
Dedicated to Dr. C. M. Gupta, Director, CDRI on the occasion of his superannuation
Abstract—Chemical synthesis of two trisaccharides related to the saponin isolated from Centratherum anthelminticum is reported. Stereo-
selective, high-yielding glycosylation strategies were developed using H2SO4 immobilized on silica for activation of trichloroacetimidate
donors, or in conjunction with N-iodosuccinimide for activation of a thioglycoside. A late stage TEMPO-mediated oxidation was performed
for the formation of the required uronic acid moiety.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
important plant.6 It is well known as an ingredient of various
folk medicines for the treatment of fever, cough, diarrhoea or
used as general tonic. Medicinally attractive properties it
possesses include anthelminthic, antiphlegmatic, cardiac,
diuretic, febrifugal, alterative and digestive.7 Recently, Mehta
et al.8 reported the isolation and structure elucidation of
a new acetylated saponin from the methanol extract of
the plant C. anthelminticum. In continuation to our effort
towards the synthesis of various carbohydrate-based bio-
dynamic molecules, here we report convergent chemical
synthesis of two trisaccharides (1 and 2, Fig. 1) from com-
mercially available monosaccharides through rational pro-
tecting group manipulations and sequential glycosylations.
Saponins, the glycosylated secondary metabolites in plants,
are important for growth and development.1 Besides their
roles in the plant kingdom, they often possess important
biological activities that make them attractive medicinal
targets for drug discovery against various diseases, for exam-
ple, ginseng and liquorice.2 As the saponins possess antifun-
gal properties, they occur in high concentration in healthy
plants acting as a preformed chemical barrier for fungal
infections.3 Although saponins earned a great deal of attrac-
tion for their biological properties with many of them in
use commercially, detailed genetic machinery behind their
formation in plants is not clearly understood. One common
feature of all saponins is the presence of a sugar chain at
3-O-position mainly consisting of glucose, arabinose, glu-
curonic acid, xylose and rhamnose.4 The glycosylation on
the 3-O-position of the saponin aglycone, believed to be
the terminal stage of its formation, is important for saponin
bioactivities.5 Therefore, in order to establish the order of
events in saponin biosynthesis and elucidate the roles of gly-
cosyltransferases involved, synthesis of the saccharide frag-
ments becomes a useful target. Moreover, a synthetic route
will in turn provide an alternative way to get hold of the bi-
ologically potent saponins, which require a rigorous exercise
of isolation and chromatographic purification to obtain from
natural sources. Therefore, chemical synthesis of such struc-
tures offers the scope of their use as medicines in future.
OH
O
O
OH
O
OMP
HO
HO
O
O
OH
HO
O
Me
HO
O
OMe
O
Me
O
O
HO
HO
HO
HO
HO
O
HO
OH
OH
OH
OH
2
1
Figure 1. Target structure of the trisaccharides related to the saponin iso-
lated from C. anthelminticum.
2. Results and discussion
The plant, Centratherum anthelminticum, known as ‘Som-
raj’ and the seeds as ‘kalijiri’ in India, is a medicinally
2.1. Synthesis of the trisaccharide 1
*
CDRI Communication No. 7248.
* Corresponding author. E-mail: sugarnet73@hotmail.com
Synthesis of the trisaccharide 1 was planned through the syn-
thesis of Rha–Glc disaccharide from suitably protected
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.077

11364
S. Mandal, B. Mukhopadhyay / Tetrahedron 63 (2007) 11363–11370
AcO
AcO
monosaccharide building blocks and final glycosylation
with a suitable arabinopyranosyl acceptor. Thus, known
p-methoxyphenyl a-L-rhamnopyranoside (3)9 was subjected
to sequential one-pot ortho-esterification–benzylation–
ortho-ester rearrangement10 to afford suitably protected
acceptor 4 in 85% yield. Glycosylation of acceptor 4 with
the known p-tolyl 2,3,4,6-tetra-O-acetyl-1-thio-b-D-gluco-
pyranoside (5)11 donor was achieved by N-iodosuccinimide
in the presence of H2SO4 immobilized on silica to afford the
protected disaccharide (6) in 91% isolated yield on the basis
of the acceptor used. Use of H2SO4–silica12 instead of clas-
sical Lewis acid catalysts such as TfOH or TMSOTf proved
to be advantageous as this solid acid source is much easier to
handle and can be weighed neatly as required. Next, removal
of the p-methoxyphenyl group using CAN in CH3CN–H2O
(9:1)13 followed by DBU catalyzed trichloroacetimidate for-
mation14 furnished the activated disaccharide donor 7 in
79% overall yield. For the preparation of the arabinose ac-
ceptor, known per-O-acetylated L-arabinopyranose (8)11
was converted to the corresponding p-methoxyphenyl glyco-
side (9) through BF3$Et2O catalyzed glycosylation with
O
STol
OMP
OMP
a
AcO
OAc
5
Me
BnO
Me
HO
O
O
b
HO
HO
OAc
OH
4
3
NH
O
CCl3
OMP
c
Me
Me
O
O
BnO
O
BnO
O
AcO
AcO
AcO
AcO
AcO
O
O
OAc
OAc
O
Ac
OAc
OAc
6
7
OAc
AcO
OAc
O
d
e
O
O
O
OAc
OMP
OMP
OMP
AcO
O
OAc
OAc
OH
10
9
8
O
OH
O
O
O
O
OMP
O
HO
f
g
O
7 + 10
p-cresol in 87% yield. Zemplen de-O-acetylation15 followed
Me
ꢀ
O
Me
HO
O
BnO
by acid catalyzed acetonation using 2,2-DMP16 afforded the
required acceptor 10 in 83% yield over two steps. For the fi-
nal glycosylation through trichloroacetimidate activation of
the disaccharide donor 7, H2SO4–silica has been used suc-
cessfully to afford the protected trisaccharide 11 in 89%
yield. Global deprotection of 11, Pd–C catalyzed hydrogena-
tion followed by opening of isopropylidene acetal using 80%
AcOH at 80 ꢀC17 and de-O-acylation, furnished the target
trisaccharide 1 in 78% yield over three steps (Scheme 1).
AcO
O
O
HO
HO
HO
AcO
OAc
O
OH
AcO
OAc
OH
11
1
Scheme 1. Synthesis of trisaccharide 1. Reagents and conditions: (a) (i)
trimethyl ortho-acetate, CSA, CH3CN, rt, 45 min; (ii) BnBr, NaH, rt,
45 min; (iii) 80% AcOH, rt, 1 h; (b) NIS, H2SO4–silica, CH2Cl2, MS 4 A,
10 ꢀC, 45 min; (c) (i) CAN, CH3CN–H2O, rt, 30 min; (ii) CCl3CN, DBU,
CH2Cl2, rt, 1 h; (d) p-cresol, BF3$Et2O, CH2Cl2, rt, 3 h; (e) (i) NaOMe,
MeOH; (ii) 2,2-DMP, CSA, acetone, rt, 30 min; (f) H2SO4–silica,
CH2Cl2, ꢁ40 ꢀC, 5 h; (g) (i) H2, Pd–C, MeOH, rt, 6 h; (ii) 80% AcOH,
80 ꢀC, 2 h; (iii) NaOMe, MeOH, rt, 3 h.
˚
One can argue with the fact that the best possible way to
make the trisaccharide 1 would be to prepare the Ara–Rha
disaccharide followed by glycosylation with a suitable Glc
donor. Initially we tried that route but found it to be unsuc-
cessful with the choice of a suitable temporary protection
at 3-OH of rhamnose moiety. Although chloroacetyl and
p-methoxybenzyl groups are found to be suitable for making
the Ara–Rha disaccharide, their selective deprotection was
not compatible with the isopropylidene moiety on arabinose.
Protection of the arabinose moiety with groups other than
isopropylidene means increase in total number of steps.
Therefore, we discarded that route.
pyridine to afford the disaccharide 17 in 85% yield over
two steps. Removal of the isopropylidene protection was
necessary to avoid loss of compounds during later acid cat-
alyzed transformations. CAN-mediated removal of the
p-methoxyphenyl group13 followed by DBU catalyzed
trichloroacetimidate formation14 led to the disaccharide
donor 18 in 81% yield. Glycosylation of disaccharide donor
18 with known methyl 2-O-benzoyl-4,6-O-benzylidene-b-
D-glucopyranoside (19) in the presence of H2SO4–silica
afforded the trisaccharide 20 in 84% yield. Selective
removal of the TBDPS group using Bu4NF in THF produced
the required trisaccharide 21 that is ready for oxidation to
furnish the uronic acid moiety of the target molecule.
At this stage, TEMPO-mediated oxidation of the primary
hydroxyl to uronic acid was the target. Among different
TEMPO-mediated19 protocols available in the literature
including the late stage oxidation approach by Nepogodiev
et al.,20 the procedure developed by Huang et al.21 was
particularly attractive for us as this protocol uses phase-
transfer conditions suitable for protected oligosaccharides.
Therefore, oxidation of compound 21 using similar con-
ditions afforded the required uronic acid derivative 22 in
78% yield. Removal of the benzylidene acetal using 80%
AcOH at 80 ꢀC followed by de-O-acylation gave the target
trisaccharide 2 as its methyl ester form in 81% yield
(Scheme 2).
2.2. Synthesis of the trisaccharide 2
In a similar fashion as for the synthesis of trisaccharide 1,
synthesis of trisaccharide 2 was planned through the forma-
tion of non-reducing end Rha–Glc disaccharide and final
glycosylation with a suitably protected glucosyl acceptor
to furnish the targeted scaffold. Thus, known p-tolyl
1-thio-b-D-glucopyranoside (12) was converted to the corre-
sponding 6-O-tert-butyldiphenylsilyl derivative (13) using
TBDPS-Cl in pyridine.18 Per-O-acetylation of 13 with
Ac2O–pyridine afforded the protected donor 14 in 89%
yield. Glycosylation of 14 with known p-methoxyphenyl
2,3-isopropylidene-a-L-rhamnopyranoside (15)9 using NIS
in the presence of H2SO4–silica furnished the protected
disaccharide 16 in 86% yield.
At this point the isopropylidene group was deprotected using
80% AcOH at 80 ꢀC followed by acetylation with Ac2O–

S. Mandal, B. Mukhopadhyay / Tetrahedron 63 (2007) 11363–11370
11365
HO
HO
HO
TBDPSO
HO
TBDPSO
AcO
O
a
O
O
b
STol
STol
STol
HO
AcO
OH
OH
OAc
12
13
14
OMP
Me
HO
O
O
OMP
O
TBDPSO
AcO
AcO
Me
O
O
d
O
15
O
c
O
OAc
NH
CCl3
16
O
OMP
TBDPSO
AcO
Me
O
TBDPSO
AcO
Me
O
O
O
e
O
O
AcO
AcO
AcO
AcO
OAc
OAc
OAc
OAc
18
17
Ph
O
Ph
O
O
O
O
O
O
HO
BzO
BzO
OMe
OMe
g
Me
TBDPSO
AcO
O
19
O
O
AcO
AcO
20
f
OAc
OAc
Ph
O
O
Ph
O
O
O
O
O
O
OH
BzO
h
BzO
OMe
AcO
HO
AcO
AcO
Me
O
OMe
Me
O
O
O
O
O
O
AcO
AcO
AcO
22
OAc
OAc
OAc
OAc
21
HO
O
HO
O
OH
HO
i
OMe
Me
O
O
O
O
HO
HO
HO
OH
OH
2
ꢀ
˚
Scheme 2. Synthesis of trisaccharide 2. Reagents and conditions: (a) TBDPS-Cl, Py, rt, 6 h; (b) Ac2O, Py, rt, 2 h; (c) NIS, H2SO4–silica, CH2Cl2, MS 4 A, 10 C,
45 min; (d) (i) 80% AcOH, 80 ꢀC, 2 h; (ii) Ac2O, Py, rt, 2 h; (e) (i) CAN, CH3CN–H2O, rt, 30 min; (ii) CCl3CN, DBU, CH2Cl2, rt, 1 h; (f) H2SO4–silica, CH2Cl2,
ꢁ40 ꢀC, 6 h; (g) Bu4NF–THF, rt, 12 h; (h) TEMPO, NaOCl, NaOCl2, CH2Cl2–H2O, rt, 6 h; (i) (i) 80% AcOH, 80 ꢀC, 2 h; (ii) NaOMe, MeOH, rt, 3 h.
3. Conclusion
following immersion in a 10% ethanolic solution of sulfuric
acid. An orcinol dip, prepared by the careful addition of con-
centrated sulfuric acid (20 cm3) to an ice-cold solution of
3,5-dihydroxytoluene (360 mg) in EtOH (150 cm3) and
water (10 cm3), was used to detect deprotected compounds
by charring. Flash chromatography was performed with
silica gel 60 (Qualigens). Optical rotations were measured
at the sodium D-line at ambient temperature, with a Perkin
We have developed convergent and efficient synthetic strat-
egies for two trisaccharide fragments related to the saponin
isolated from the methanol extract of the plant C. anthelmin-
ticum. H2SO4–silica has been used for the activation of
glycosyl trichloroacetimidate and in conjunction with NIS
for thioglycoside activation. This has proved to be an
efficient and useful alternative to the classical Lewis acid
catalysts that are corrosive and difficult to handle. The tri-
saccharides produced will be evaluated for their biological
activities in due course.
1
Elmer 141 polarimeter. H NMR and 13C NMR spectra
were recorded on a Bruker Avance spectrometer at 300
and 75 MHz, respectively, using Me4Si or CH3OH as inter-
nal standard, as appropriate.
Preparation of H2SO4–silica: To a slurry of silica gel (10 g,
200–400 mesh) in dry diethyl ether (50 mL) was added com-
mercially available concd H2SO4 (1 mL) and shaken for
5 min. Solvents were evaporated under reduced pressure
resulting in free flowing H2SO4–silica. It was then dried at
110 ꢀC for 3 h and used for the reaction.
4. Experimental
4.1. General methods
All reagents and solvents were dried prior to use according to
standard methods.22 Commercial reagents were used with-
out further purification unless otherwise stated. Analytical
TLC was performed on silica gel 60-F254 (Merck or What-
man) with detection by fluorescence and/or by charring
4.1.1. p-Methoxyphenyl 2-O-acetyl-4-O-benzyl-a-L-
rhamnopyranoside (4). To a solution of 3 (3 g, 11 mmol)
in dry CH3CN (20 mL), trimethyl ortho-acetate (2.1 mL,

11366
S. Mandal, B. Mukhopadhyay / Tetrahedron 63 (2007) 11363–11370
16.5 mmol) was added followed by CSA (20 mg). The mix-
ture was stirred at room temperature until complete conver-
sion of the starting material to a faster moving spot on TLC
(w45 min). Then the solution was cooled on an ice-bath.
NaH (790 mg, 60% in mineral wax) was added followed
by slow addition of BnBr (1.6 mL, 13.2 mmol) and the mix-
ture was allowed to stir at room temperature for another
45 min. Excess NaH was neutralized by MeOH (1 mL)
and the solvents were evaporated in vacuo. The residue
was dissolved in AcOH–H2O (9:1, 30 mL) and stirred at
room temperature for 1 h. Next, the solvents were evapo-
rated in vacuo and the residue was purified by flash chroma-
tography using n-hexane–EtOAc (3:1) as eluent to get pure
compound 4 (3.8 g, 85%) as a colourless gel. [a]2D5 +39 (c
1.0, CHCl3). IR (neat): 2943, 2371, 1693, 1589, 1281,
4.1.3. p-Methoxyphenyl 3,4-isopropylidene-a-L-arabino-
pyranoside (10). To a solution of 8 (3 g, 9.4 mmol) and
p-cresol (1.75 g, 14.1 mmol) in dry CH2Cl2 (30 mL),
BF3$Et2O (2.3 mL, 18.8 mmol) was added dropwise at
0 ꢀC. After complete addition, the solution was stirred at
the same temperature for 2 h. Then the solution was diluted
with CH2Cl2 (20 mL) and washed successively with H2O
(2ꢂ50 mL), NaHCO3 (2ꢂ50 mL) and brine (50 mL). The
organic layer was separated, dried (Na2SO4) and evaporated
to afford 9 (3.1 g, 87%) as light yellow syrup which was pure
enough to proceed with. After dissolving the syrup in dry
MeOH (40 mL), NaOMe (0.5 M in MeOH, 400 mL) was
added and the solution was stirred at room temperature for
2 h. After complete conversion of the starting material, the
solution was neutralized with DOWEX 50W H+ resin,
filtered and evaporated to an amorphous mass. It was sus-
pended in acetone (30 mL), 2,2-DMP (1.2 mL, 9.7 mmol)
was added followed by CSA (20 mg) and the mixture was
stirred at room temperature for 30 min until the starting
material was completely disappeared (TLC). The solution
was neutralized with Et3N and the solvents were evaporated
to give the crude product as light brown syrup. It was purified
by flash chromatography using n-hexane–EtOAc (4:1) to
afford pure 10 (2 g, 83%) a colourless glass. [a]2D5 +103 (c
1.0, CHCl3). IR (neat): 2360, 1598, 1373, 1226,
1075 cmꢁ1; 1H NMR (300 MHz, CDCl3) d: 6.94, 6.76 (2d,
4H, C6H4OCH3), 4.73 (d, 1H, J 7.2 Hz, H-1), 4.27 (m, 1H,
H-4), 4.10 (dd, 1H, J 2.4 Hz, 7.8 Hz, H-3), 4.08 (dd, 1H, J
7.2 Hz, 7.8 Hz, H-2), 3.86 (dd, 1H, J 2.1, 12.9 Hz, H-5a),
3.81 (dd, 1H, J 4.2 Hz, 12.9 Hz, H-5b), 3.75 (s, 3H,
C6H4OCH3), 2.93 (br d, 1H, OH), 1.54, 1.36 (2s, 6H,
2ꢂisopropylidene-CH3). 13C NMR (75 MHz, CDCl3) d:
148.8, 136.6, 118.7(2), 114.7(2) (ArC), 110.2 (isopropyl-
idene-C), 101.5 (C-1), 77.9, 72.9, 72.4, 62.7, 55.4
(C6H4OCH3), 27.8, 25.8 (2ꢂisopropylidene-CH3). HRMS
calcd for C15H24O6N (M+NH4): 314.1604; found 314.1602.
1097, 1012, 708 cmꢁ1 1H NMR (300 MHz, CDCl3) d:
;
7.33–7.24 (m, 5H, ArH), 6.91, 6.77 (2d, 4H, C6H4OCH3),
5.29 (s, 1H, H-1), 5.24 (br s, 1H, H-2), 4.85, 4.70 (2d, 2H,
AB system, CH2Ph), 4.26 (dd, 1H, J 3.3 Hz, 9.3 Hz, H-3),
3.88 (m, 1H, H-5), 3.73 (s, 3H, C6H4OCH3), 3.38 (t, 1H, J
9.3 Hz, H-4), 2.48 (br s, 1H, OH), 2.17 (s, 3H, OCOCH3),
1.30 (d, 3H, J 6.0 Hz, C–CH3). 13C NMR (75 MHz,
CDCl3) d: 170.5 (COCH3), 155.1, 150.1, 138.3, 128.5,
127.8, 117.7, 114.6 (ArC), 96.4 (C-1), 81.5, 75.2, 72.6,
70.0, 68.1, 55.5 (C6H4OCH3), 21.0 (COCH3), 18.1 (C–
CH3). HRMS calcd for C22H30O7N (M+NH4): 420.2022;
found 420.2024.
4.1.2. p-Methoxyphenyl 2,3,4,6-tetra-O-acetyl-b-D-gluco-
pyranosyl-(1/3)-2-O-acetyl-4-O-benzyl-a-L-rhamno-
pyranoside (6). A mixture of compound 4 (2 g, 5.0 mmol),
˚
compound 5 (2.9 g, 6.5 mmol) and MS 4 A (2 g) in dry
CH2Cl2 (30 mL) was stirred under nitrogen for 1 h. NIS
(1.75 g, 7.8 mmol) was added and the mixture was cooled
to 10 ꢀC using ice-water bath. After stirring for 15 min,
H2SO4–silica (25 mg) was added and the mixture was al-
lowed to stir at 10 ꢀC until complete consumption of the
acceptor 4 was evident by TLC (45 min). The mixture was
immediately filtered through a pad of Celite and the filtrate
was washed successively with Na2S2O3 (2ꢂ30 mL),
NaHCO3 (2ꢂ30 mL) and brine (30 mL). Organic phase
was collected, dried (Na2SO4) and evaporated to syrup.
The crude product thus obtained was purified by flash chro-
matography using n-hexane–EtOAc (3:1) to afford pure
compound 6 (3.3 g, 91%) as white foam. [a]2D5 +62 (c 1.1,
CHCl3). IR (neat): 2934, 2367, 1751, 1597, 1376, 1227,
4.1.4. p-Methoxyphenyl 2,3,4,6-tetra-O-acetyl-b-D-gluco-
pyranosyl-(1/3)-2-O-acetyl-4-O-benzyl-a-L-rhamno-
pyranosyl-(1/2)-3,4-isopropylidene-a-L-arabinopyr-
anoside (11). To a solution of compound 6 (3 g, 4.1 mmol)
in CH3CN–H2O (9:1, 30 mL), CAN (4.5 g, 8.2 mmol) was
added and the mixture was stirred at room temperature for
30 min when all starting material was converted to a slower
moving spot (TLC). After evaporating the solvents in vacuo,
the residue was partitioned with CH2Cl2 and water. The or-
ganic phase was collected, dried (Na2SO4) and evaporated.
The crude product thus obtained was purified by flash chro-
matography using n-hexane–EtOAc (2:1). The resulting
product was dissolved in CH2Cl2 (25 mL), CCl3CN
(616 mL, 6.15 mmol) was added followed by DBU (674 mL,
4.5 mmol) and the solution was stirred at room temperature
for 1 h until the starting material was converted completely
to a faster running spot (TLC). After evaporation of the
solvents, the crude product was purified by flash chromato-
graphy to afford pure compound 7 (2.5 g, 79%) as a white
foam. This compound was used for the next step without
any further characterization, as glycosyl trichloroacet-
imidates are relatively unstable on storing.
1
1049 cmꢁ1; H NMR (200 MHz, CDCl3) d: 7.33–7.26 (m,
5H, ArH), 6.94, 6.78 (2d, 4H, C6H4OCH3), 5.30 (dd, 1H, J
1.8 Hz, 3.3 Hz, H-2), 5.27 (d, 1H, J 1.8 Hz, H-1), 5.14 (t,
1H, J 9.6 Hz, H-40), 5.09 (t, 1H, J 9.6 Hz, H-30), 5.03 (dd,
1H, J 7.5 Hz, 9.6 Hz, H-20), 4.81 (d, 1H, J 7.5 Hz, H-10),
4.79, 4.54 (2d, 2H, J 11.4 Hz, AB system, CH2Ph), 4.24
(m, 2H, H-3, H-6a0), 4.07 (dd, 1H, J 2.1 Hz, 12.3 Hz, H-
6b0), 3.85 (m, 1H, H-5), 3.75 (s, 3H, C6H4OCH3), 3.68 (m,
1H, H-50), 3.48 (t, 1H, J 9.6 Hz, H-4), 2.15, 2.07, 2.04,
1.98, 1.70 (5s, 15H, 5ꢂCOCH3), 1.24 (d, 3H, J 6.3 Hz, C–
CH3). 13C NMR (75 MHz, CDCl3) d: 169.9, 169.8, 169.7,
169.0(2) (5ꢂCOCH3), 155.0, 149.8, 138.1, 128.3, 127.6,
127.5, 127.2, 117.7, 114.5 (ArC), 100.9 (C-10), 96.0 (C-1),
79.2, 78.8, 74.8, 73.0, 71.7, 71.5, 71.4, 68.0, 61.4 (C-60),
55.3 (C6H4OCH3), 20.9, 20.7, 20.5(2), 20.4 (5ꢂCOCH3),
17.9 (C–CH3). HRMS calcd for C36H48O16N (M+NH4):
750.2973; found 750.2971.
A solution of 7 (2.5 g, 3.2 mmol), 10 (870 mg, 2.9 mmol)
˚
and MS 4 A (1.5 g) in dry CH2Cl2 (25 mL) was stirred under
nitrogen for 1 h. After cooling the mixture at ꢁ40 ꢀC,

S. Mandal, B. Mukhopadhyay / Tetrahedron 63 (2007) 11363–11370
11367
H2SO4–silica (20 mg) was added and the mixture was
allowed to stir at the same temperature for 5 h until the
acceptor 10 was completely consumed (TLC). The mixture
was neutralized with Et3N and filtered through a pad of
Celite. The filtrate was evaporated in vacuo and the crude
product was purified by flash chromatography using
n-hexane–EtOAc (1.5:1) to afford pure trisaccharide 11
(2.4 g, 89%) as a white foam. [a]2D5 +48 (c 1.1, CHCl3). IR
was stirred for 6 h at room temperature until the starting
material was completely consumed (TLC). Then Ac2O
(2.4 mL, 25.0 mmol) was added and stirring was continued
for another 2 h at room temperature. The solvents were evap-
orated in vacuo and the residue was dissolved in CH2Cl2
(30 mL), washed successively with ice-cold 1 M HCl
(2ꢂ30 mL), NaHCO3 (2ꢂ30 mL) and brine (30 mL). The
organic layer was separated, dried (Na2SO4) and evaporated
to syrup. The crude product was purified by flash chromato-
graphy using n-hexane–EtOAc (5:1) to afford pure 14 (4 g,
89%) as a colourless syrup. [a]2D5 +83 (c 1.0, CHCl3). IR
(KBr): 1751, 1724, 1635, 1601, 1363, 1221, 1042 cmꢁ1
;
1H NMR (300 MHz, CDCl3) d: 7.32–7.24 (m, 5H, ArC),
6.97, 6.75 (2d, 4H, C6H4OCH3), 5.28 (br s, 2H, H-10,
H-20), 5.08–5.01 (m, 3H, H-2000, H-3000, H-4000), 4.87 (d, 1H,
J 6.9 Hz, H-1000), 4.77, 4.55 (2d, 2H, J 11.4 Hz, AB system,
CH2Ph), 4.67 (d, 1H, J 7.5 Hz, H-1), 4.33 (m, 1H, H-4),
4.24–4.17 (m, 2H, H-2, H-3), 4.13–3.96 (m, 5H, H-5a, H-
30, H-50, H-6a00, H-6b00), 3.91 (dd, 1H, J 4.8 Hz, 12.6 Hz,
H-5b), 3.74 (s, 3H, C6H4OCH3), 3.59 (m, 1H, H-500), 3.44
(t, 1H, J 9.3 Hz, H-40), 2.13, 2.07, 1.99, 1.95, 1.65 (5s,
15H, 5ꢂCOCH3), 1.53, 1.31 (2s, 6H, 2ꢂisopropylidene-
CH3), 1.30 (d, 3H, J 6.0 Hz, C–CH3). 13C NMR (75 MHz,
CDCl3) d: 170.2, 169.8(2), 168.9(2) (5ꢂCOCH3), 155.1,
151.2, 138.4, 128.2(2), 127.4, 127.0(2), 118.0(2), 114.4(2)
(ArC), 110.6 (isopropylidene-C), 100.7 (C-100), 99.8 (C-1),
95.8 (C-100), 79.3, 78.8, 77.9, 75.2, 74.5, 72.9, 72.3, 71.6,
71.5, 71.0, 67.8, 67.4, 62.4 (C-5), 61.3 (C-600), 55.3
(C6H4OCH3), 27.6, 25.8 (2ꢂisopropylidene-CH3), 20.9,
20.5(3), 20.4 (5ꢂCOCH3), 17.8 (C–CH3). HRMS calcd for
C44H60O20N (M+NH4): 922.3709; found 922.3707.
(neat): 1751, 1373, 1228, 1063, 772 cmꢁ1 1H NMR
;
(300 MHz, CDCl3) d: 7.63–7.00 (m, 14H, ArH), 5.16 (t, 1H,
J 9.3 Hz, H-4), 5.11 (t, 1H, J 9.3 Hz, H-3), 4.92 (t, 1H, J
9.3 Hz, H-2), 4.62 (d, 1H, J 9.3 Hz, H-1), 3.77 (dd, 1H,
J 1.5 Hz, 11.4 Hz, H-6a), 3.69 (dd, 1H, J 4.5 Hz, 11.4 Hz,
H-6b), 3.55 (m, 1H, H-5), 2.30 (s, 3H, SC6H4CH3), 2.07,
2.01, 1.86 (3s, 9H, 3ꢂCOCH3), 1.05 (s, 9H, C(CH3)3). 13
C
NMR (75 MHz, CDCl3) d: 169.9, 168.7, 168.6 (3ꢂCOCH3),
138.2, 135.6, 135.5, 133.7, 132.9, 132.8, 129.6, 129.5, 127.7
(ArC), 96.1 (C-1), 85.5, 78.6, 74.5, 69.9, 68.0, 62.3 (C-6),
26.7 (C(CH3)3), 21.1, 20.6, 20.5 (3ꢂCOCH3), 18.5
(C(CH3)3). HRMS calcd for C35H46O8NSSi (M+NH4):
668.2713; found 668.2714.
4.1.7. p-Methoxyphenyl 2,3,4-tri-O-acetyl-6-O-tert-butyl-
diphenylsilyl-b-D-glucopyranosyl-(1/4)-2,3-isopropyli-
dene-a-L-rhamnopyranoside (16). A mixture of compound
14 (3.7 g, 5.8 mmol), compound 15 (1.5 g, 4.8 mmol) and
˚
4.1.5. p-Methoxyphenyl b-D-glucopyranosyl-(1/3)-a-L-
rhamnopyranosyl-(1/2)-a-L-arabinopyranoside (1). To
a solution of compound 11 (2 g, 2.2 mmol) in MeOH
(20 mL) was added Pd–C (10% Pd on activated charcoal,
50 mg) and the mixture was stirred under hydrogen (40 psi)
for 6 h until the starting material was completely converted
to a slower running spot (TLC). The mixture was filtered
through a pad of Celite and washed with hot MeOH to extract
the product completely from the charcoal. The filtrate was
evaporated in vacuo and the residue was dissolved in
AcOH–H2O (9:1, 30 mL) and the solution was stirred at
80 ꢀC for 2 h. After evaporating the solvents and co-evapo-
rating with toluene, the residue was dissolved in dry MeOH
(30 mL). NaOMe (0.5 M in MeOH) was added and the solu-
tion was allowed to stir at room temperature for 3 h. Then the
solution was neutralized with DOWEX 50W H+, filtered and
evaporated in vacuo to furnish pure compound 1 (970 mg,
78%) as amorphous white powder. [a]2D5 +82 (c 1.0, H2O);
1H NMR (300 MHz, D2O) d: 7.03, 6.88 (2d, 4H,
C6H4OCH3), 5.27 (d, 1H, J 1.5 Hz, H-10), 4.63 (d, 1H, J
7.8 Hz, H-100), 4.57 (d, 1H, J 7.2 Hz, H-1), 4.20 (m, 2H,
H-2, H-30), 4.02–3.77 (m, 8H, H-20, H-4, H-40, H-5a, H-5b,
H-50, H-6a00, H-6b00), 3.63 (m, 2H, H-3, H-400), 3.52 (m, 3H,
H-200, H-300, H-500), 3.72 (s, 3H, C6H4OCH3), 1.16 (d, 3H, J
6.0 Hz, C–CH3). 13C NMR (75 MHz, D2O) d: 151.4, 148.3,
115.0, 113.8 (ArC), 101.0 (C-100), 99.7 (C-1), 98.0 (C-10),
78.8, 76.0(2), 75.8(2), 72.9(2), 71.4, 69.7, 68.7, 68.5, 61.6,
60.9, 54.5 (C6H4OCH3), 15.5 (C–CH3). HRMS calcd for
C24H36O15Na (M+Na): 587.1952; found 587.1949.
MS 4 A (2 g) in dry CH2Cl2 (40 mL) was stirred under nitro-
gen for 1 h. NIS (1.6 g, 7.0 mmol) was added and the mix-
ture was cooled to 10 ꢀC using ice-water bath. After
stirring for 15 min, H2SO4–silica (25 mg) was added and
stirring was continued for another 45 min when the acceptor
15 was completely consumed (TLC). The mixture was im-
mediately filtered through a pad of Celite and the filtrate
was washed successively with Na2S2O3 (2ꢂ30 mL),
NaHCO3 (2ꢂ30 mL) and brine (30 mL). The organic layer
was collected, dried (Na2SO4) and evaporated in vacuo.
The crude product was purified by flash chromatography us-
ing n-hexane–EtOAc (3:1) as eluent to afford pure 16 (3.5 g,
86%) as white foam. [a]2D5 +46 (c 1.1, CHCl3). IR (KBr):
1763, 1723, 1639, 1598, 1367, 1235, 1047 cmꢁ1; 1H NMR
(300 MHz, CDCl3) d: 7.67–7.32 (m, 10H, ArH), 6.96, 6.80
(2d, 4H, C6H4OCH3), 5.57 (s, 1H, H-1), 5.25 (t, 1H, J
9.3 Hz, H-40), 5.22 (t, 1H, J 9.3 Hz, H-30), 5.00 (d, 1H, J
6.3 Hz, H-10), 4.99 (dd, 1H, J 6.3 Hz, 9.3 Hz, H-20), 4.29
(br d, 1H, J 6.3 Hz, H-2), 4.22 (t, 1H, J 7.2 Hz, H-4),
3.83–3.64 (m, 7H, H-3, H-5, H-6a00, H-6b00, C6H4OCH3),
3.52 (m, 1H, H-50), 2.09, 2.00, 1.91 (3s, 9H, 3ꢂCOCH3),
1.44, 1.35 (2s, 6H, 2ꢂisopropylidene-CH3), 1.26 (d, 3H, J
6.3 Hz, C–CH3), 1.04 (s, 9H, C(CH3)3). 13C NMR
(75 MHz, CDCl3) d: 170.0, 169.0, 168.7 (3ꢂCOCH3),
154.9, 150.0, 135.5, 135.4, 132.9, 132.6, 129.7, 127.7,
117.7, 114.5 (ArC), 109.2 (isopropylidene-C), 99.6 (C-10),
96.0 (C-1), 79.2, 78.2, 76.0, 74.3, 73.4, 71.7, 68.4, 64.8,
61.9 (C-60), 55.3 (C6H4OCH3), 27.9, 26.4 (2ꢂisopropyl-
idene-CH3), 26.6 (C(CH3)3), 20.6, 20.5, 20.4 (3ꢂCOCH3),
19.1 (C(CH3)3), 17.4 (C–CH3). HRMS calcd for
C44H60O14NSi (M+NH4): 854.3783; found 854.3785.
4.1.6. p-Tolyl 2,3,4-tri-O-acetyl-6-O-tert-butyldiphenyl-
silyl-1-thio-b-D-glucopyranoside (14). To a solution of
compound 12 (2 g, 7.0 mmol) in dry pyridine (30 mL),
TBDPS-Cl (2.4 mL, 9.1 mmol) was added and the solution
4.1.8. p-Methoxyphenyl 2,3,4-tri-O-acetyl-6-O-tert-butyl-
diphenylsilyl-b-D-glucopyranosyl-(1/4)-2,3-di-O-acetyl-

11368
S. Mandal, B. Mukhopadhyay / Tetrahedron 63 (2007) 11363–11370
a-L-rhamnopyranoside (17). A solution of compound 16
(3 g, 3.6 mmol) in AcOH–H2O (8:1, 30 mL) was stirred
at 80 ꢀC for 2 h. After evaporating the solvents, the resi-
due was dissolved in pyridine (15 mL), Ac2O (850 mL,
9.0 mmol) was added and the solution was stirred at room
temperature for 3 h. Then the solvents were evaporated
and the residue was dissolved in CH2Cl2 (30 mL). The solu-
tion was washed successively with ice-cold 1 M HCl
(2ꢂ30 mL), NaHCO3 (2ꢂ30 mL) and brine (30 mL). The
organic layer was separated, dried (Na2SO4) and evaporated
in vacuo. The crude product was purified by flash chromato-
graphy using n-hexane–EtOAc (2:1) as eluent to give pure
17 (2.7 g, 85%) as white foam. [a]2D5 +59 (c 1.1, CHCl3).
1.0, CHCl3). IR (KBr): 1757, 1721, 1636, 1593, 1364, 1230,
1
1043 cmꢁ1; H NMR (300 MHz, CDCl3) d: 8.01–7.29 (m,
20H, ArH), 5.61 (s, 1H, CHPh), 5.19 (t, 1H, J 9.6 Hz,
H-400), 5.16 (dd, 1H, J 3.6 Hz, 9.6 Hz, H-30), 5.06 (m, 3H,
H-10, H-20, H-300), 4.92 (m, 3H, H-1, H-200, H-2), 4.56 (d,
1H, J 7.8 Hz, H-100), 4.33 (m, 2H, H-40, H-50), 4.08 (m,
1H, H-500), 3.88 (m, 1H, H-5), 3.79 (m, 2H, H-6a, H-6b),
3.68 (dd, 1H, J 2.1 Hz, 11.4 Hz, H-6a00), 3.64 (dd, 1H, J
4.2 Hz, 11.4 Hz, H-6b00), 3.49 (t, 2H, H-3, H-4), 3.38 (s,
3H, OCH3), 1.99, 1.98(2), 1.86, 1.84 (5s, 15H, 5ꢂCOCH3),
1.05 (s, 9H, C(CH3)3), 0.85 (d, 3H, J 6.0 Hz, C–CH3). 13C
NMR (75 MHz, CDCl3) d: 170.2, 169.2, 168.9, 168.8,
168.7 (5ꢂCOCH3), 165.3 (COPh), 136.9, 135.5, 133.1,
132.8, 132.7, 129.9, 129.8, 129.7, 129.3, 129.1, 128.2,
128.1, 127.7, 126.2 (ArC), 101.7 (CHPh), 100.8 (C-100),
98.2 (C-1), 97.8 (C-10), 79.4, 76.7, 74.6, 74.3, 73.9, 73.5,
71.3, 71.2, 70.0, 68.8, 68.4, 66.9, 62.9 (C-6), 62.0 (C-600),
55.3 (OCH3), 26.7 (C(CH3)3), 20.9, 20.6, 20.5, 20.4, 20.3
(5ꢂCOCH3), 19.2 (C(CH3)3), 16.9 (C–CH3). HRMS calcd
for C59H74O21NSi (M+NH4): 1160.4523; found 1160.4525.
1
IR (KBr): 1754, 1378, 1226, 1067, 763 cmꢁ1; H NMR
(300 MHz, CDCl3) d: 7.66–7.34 (m, 10H, ArH), 6.98, 6.77
(2d, 4H, C6H4OCH3), 5.43 (dd, 1H, J 3.6 Hz, 9.9 Hz, H-3),
5.31 (dd, 1H, J 1.5 Hz, 3.6 Hz, H-2), 5.27 (br s, 1H, H-1),
5.11 (t, 1H, J 9.3 Hz, H-40), 5.06 (t, 1H, J 9.3 Hz, H-30), 4.94
(t, 1H, J 9.3 Hz, H-20), 4.69 (d, 1H, J 7.8 Hz, H-10), 3.95
(m, 1H, H-5), 3.75 (s, 3H, C6H4OCH3), 3.73–3.69 (m,
3H, H-4, H-6a0, H-6b0), 3.56 (m, 1H, H-50), 2.13 (2), 2.02,
2.00, 1.86 (4s, 15H, 5ꢂCOCH3), 1.38 (d, 3H, J 6.0 Hz,
C–CH3), 1.06 [s, 9H, C(CH3)3]. 13C NMR (75 MHz,
CDCl3) d: 170.3, 169.6, 169.4, 169.1, 168.8 (5ꢂCOCH3),
155.2, 150.0, 135.6, 133.0, 132.8, 129.9, 129.8, 127.8,
117.9, 114.5 (ArC), 100.9 (C-10), 96.5 (C-1), 76.8, 74.5,
73.4, 71.4, 71.3, 70.2, 68.5, 67.5, 62.3 (C-60), 55.4
(C6H4OCH3), 26.8 [C(CH3)3], 21.0, 20.9, 20.6, 20.4(2)
(5ꢂCOCH3), 18.5 [C(CH3)3], 17.7 (C–CH3). HRMS
calcd for C45H60O16NSi (M+NH4): 898.3681; found
898.3683.
4.1.10. Methyl 2,3,4-tri-O-acetyl-b-D-glucopyranosyl-
(1/4)-2,3-di-O-acetyl-a-L-rhamnopyranosyl-(1/3)-2-
O-benzyl-4,6-O-benzylidene-a-D-glucopyranoside (21).
To a stirred solution of compound 20 (1.5 g, 1.3 mmol) in
dry THF (20 mL) at 0 ꢀC was added AcOH (82 mL,
1.4 mmol) followed by Bu4NF (1 N in THF, 6.6 mL) and
the solution was allowed to stir at room temperature for
12 h when the starting material was completely converted
to a slower moving spot (TLC). The solvents were evapo-
rated at temperature <30 ꢀC in vacuo. The crude product
was purified by flash chromatography using n-hexane–
EtOAc (1:1) as eluent to afford pure compound 21 (985 mg,
83%) as a colourless glass. [a]2D5 +83 (c 1.1, CHCl3). IR
4.1.9. Methyl 2,3,4-tri-O-acetyl-6-O-tert-butyldiphenyl-
silyl-b-D-glucopyranosyl-(1/4)-2,3-di-O-acetyl-a-L-
rhamnopyranosyl-(1/3)-2-O-benzyl-4,6-O-benzyli-
dene-a-D-glucopyranoside (20). To a solution of compound
17 (2.5 g, 2.8 mmol) in CH3CN–H2O (9:1, 30 mL), CAN
(3 g, 5.6 mmol) was added and the mixture was stirred at
room temperature for 30 min when the starting material
was completely converted to slower moving component
(TLC). The solvents were evaporated and residue was dis-
solved in CH2Cl2 (30 mL), washed with H2O (30 mL),
NaHCO3 (30 mL) and brine (30 mL). The organic layer
was collected, dried (Na2SO4) and evaporated in vacuo.
The residue was dissolved in dry CH2Cl2 (20 mL) followed
by the addition of CCl3CN (420 mL, 4.2 mmol) and DBU
(465 mL, 3.1 mmol). The solution was stirred at room tem-
perature for 1 h when the starting material was completely
converted to a faster running spot (TLC). Solvents were
evaporated and the residue was charged on a flash column
directly and eluted with n-hexane–EtOAc (3:1) to afford
pure 18 (2.1 g, 81%).
(neat): 1754, 1719, 1634, 1597, 1367, 1223, 1039 cmꢁ1
;
1H NMR (300 MHz, CDCl3) d: 7.99–7.34 (m, 10H, ArH),
5.60 (s, 1H, CHPh), 5.28 (dd, 1H, J 1.8 Hz, 9.6 Hz, H-30),
5.12 (m, 3H, H-10, H-20, H-400), 4.91 (m, 3H, H-1, H-200,
H-300), 4.77 (dd, 1H, J 1.8 Hz, 9.6 Hz, H-2), 4.50 (d, 1H, J
7.8 Hz, H-100), 4.28 (m, 2H, H-40, H-50), 4.01 (m, 1H,
H-500), 3.81 (m, 1H, H-5), 3.78–3.70 (m, 2H, H-6a, H-6b),
3.61–3.42 (m, 4H, H-3, H-4, H-6a00, H-6b00), 3.38 (s, 3H,
OCH3), 2.10, 2.07, 1.98(2), 1.88 (5s, 15H, 5ꢂCOCH3),
0.81 (d, 3H, J 6.0 Hz, C–CH3). 13C NMR (75 MHz,
CDCl3) d: 171.0, 169.3(2), 168.8(2) (5ꢂCOCH3), 165.3
(COPh), 133.2, 129.9, 129.2, 128.3, 128.1, 126.3 (ArC),
101.6 (CHPh), 100.4 (C-100), 98.2 (C-1), 97.7 (C-10), 79.4,
76.7, 75.6, 74.6, 73.9, 73.6, 71.2, 71.0, 69.9, 69.0, 68.8,
62.8(2), 55.3 (OCH3), 20.8, 20.7, 20.6, 20.5, 20.4
(5ꢂCOCH3), 17.1 (C–CH3). HRMS calcd for C43H56O21N
(M+NH4): 922.3345; found 922.3343.
4.1.11. Methyl 2,3,4-tri-O-acetyl-b-D-glucopyranosyl-
(1/4)-2,3-di-O-acetyl-a-L-rhamnopyranosyl-(1/3)-2-
O-benzyl-4,6-O-benzylidene-a-D-glucopyranosiduronic
acid (22). To a solution of compound 21 (520 mg, 0.6 mmol)
in CH2Cl2 (14 mL) and H2O (3 mL) was added aq NaBr
(1 M, 320 mL), aq tetrabutylammonium bromide (1 M,
640 mL), TEMPO (30 mg, 0.3 equiv) and saturated aq
NaHCO3 (1.6 mL) at 0 ꢀC. To the resulting mixture, aq
NaOCl (1.9 mL) was added and the mixture was allowed
to stir for 1.5 h when the temperature was raised from 0 ꢀC
to room temperature. At this point TLC showed complete
A mixture of compound 18 (2 g, 2.2 mmol), compound 19
(695 mg, 1.8 mmol) and MS 4 A (2 g) was stirred under ni-
˚
trogen for 1 h. After cooling the mixture to ꢁ40 ꢀC, H2SO4–
silica (20 mg) was added and the mixture was allowed to stir
at the same temperature for another 6 h when the starting
acceptor 19 was completely consumed. The mixture was
neutralized with Et3N and filtered through Celite and the fil-
trate was evaporated in vacuo. The residue was purified by
flash chromatography using n-hexane–EtOAc (2:1) to afford
pure compound 20 (1.7 g, 84%) as white foam. [a]2D5 +78 (c

S. Mandal, B. Mukhopadhyay / Tetrahedron 63 (2007) 11363–11370
11369
conversion of the starting material to a faster moving spot,
presumably the corresponding aldehyde derivative. The
mixture was neutralized with 1 M HCl (w150 mL) to keep
the pH of the mixture at 6–7. Then tert-butanol (8.8 mL),
2-methyl-but-2-ene (2 M in THF, 18 mL), NaOCl2
(640 mg) and NaH2PO4 (510 mg) were added and the mix-
ture was allowed to stir at room temperature for another
4 h when TLC showed complete conversion. The mixture
was diluted with saturated NaH2PO4 (30 mL) and the prod-
uct was extracted with EtOAc (3ꢂ20 mL). The combined or-
ganic layer was dried (Na2SO4) and evaporated. The crude
product thus obtained was purified by flash chromatography
using n-hexane–EtOAc (1:4) to neat EtOAc to afford pure
compound 22 (410 mg, 78%) as a light yellow syrup. [a]D25
+68 (c 1.0, CHCl3). IR (neat): 2365, 1754, 1597, 1381,
gratefully acknowledged. The work is funded by Depart-
ment of Science and Technology, New Delhi, India through
SERC Fast-Track Grant SR/FTP/CS-110/2005.
Supplementary data
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2007.08.077.
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2002, 1621–1623; (b) Zolfigol, M. A. Tetrahedron 2001, 57,
9509–9511; (c) Zolfigol, M. A.; Shirini, F.; Ghorbani
Choghamarani, A.; Mohammadpoor-Baltork, I. Green Chem.
2002, 4, 562–564; (d) Shirini, F.; Zolfigol, M. A.;
Mohammadi, K. Bull. Korean Chem. Soc. 2004, 25, 325–
327; For similar type of glycosylations using HClO4–silica,
see: (a) Mukhopadhyay, B.; Maurer, S. V.; Rudolph, N.; van
Well, R.; Russell, D. A.; Field, R. A. J. Org. Chem. 2005, 70,
9059–9062; (b) Mukhopadhya, B.; Collet, B.; Field, R. A.
1226, 1046, 734 cmꢁ1
;
1H NMR (300 MHz, CDCl3) d:
7.97–7.30 (m, 10H, ArH), 5.55 (s, 1H, CHPh), 5.26 (dd,
1H, J 1.8 Hz, 9.6 Hz, H-30), 5.13 (m, 3H, H-10, H-20,
H-400), 4.88 (m, 3H, H-1, H-200, H-300), 4.78 (dd, 1H, J
1.8 Hz, 9.6 Hz, H-2), 4.62 (d, 1H, J 7.8 Hz, H-100), 4.33
(m, 2H, H-40, H-50), 4.03 (m, 1H, H-500), 3.88 (m, 1H,
H-5), 3.81–3.70 (m, 3H, H-6a, H-6b, H-3), 3.61 (t, 1H, J
9.6 Hz, H-4), 3.38 (s, 3H, OCH3), 2.03, 2.00, 1.97(2), 1.90
(5s, 15H, 5ꢂCOCH3), 0.84 (d, 3H, J 6.0 Hz, C–CH3). 13C
NMR (75 MHz, CDCl3) d: 171.4 (COOH), 169.8, 169.5,
169.1(3) (5ꢂCOCH3), 165.4 (COPh), 133.2, 129.8, 129.1,
128.9, 128.3, 128.1, 126.1 (ArC), 101.5 (CHPh), 100.5
(C-100), 98.2 (C-1), 97.7 (C-10), 79.4, 74.7, 73.6, 72.8, 71.2,
71.1, 69.7, 69.6, 68.8, 62.7, 55.3 (OCH3), 20.8, 20.5,
20.4(2), 20.3 (5ꢂCOCH3), 16.7 (C–CH3). HRMS calcd for
C43H50O22Na (M+Na): 941.2691; found 941.2693.
4.1.12. Methyl b-D-glucopyranosyl-(1/4)-a-L-rhamno-
pyranosyl-(1/3)-a-D-glucopyranosiduronic acid (2). A
solution of compound 22 (400 mg, 0.4 mmol) in AcOH–
H2O (9:1, 10 mL) was stirred at 80 ꢀC for 2 h when the start-
ing material was completely converted to a slower moving
spot (TLC). The solvents were evaporated and co-evaporated
with toluene to remove AcOH and H2O completely. Then the
residue was dissolved in dry MeOH (10 mL) and NaOMe
(0.5 M in MeOH) was added and the solution was stirred at
room temperature for 3 h. Then after neutralizing with
DOWEX 50W H+, the solvents were evaporated in vacuo
to afford pure compound 2 (180 mg, 81%) as white amor-
phous powder. [a]2D5 +69 (c 1.1, H2O). IR (KBr): 2353,
1
1687, 1197, 785 cmꢁ1; H NMR (300 MHz, D2O) d: 4.96
(br s, 1H, H-10), 4.65 (d, 1H, J 1.8 Hz, H-1), 4.63 (d, 1H, J
8.1 Hz, H-100), 3.94 (m, 2H, H-20, H-3), 3.82 (dd, 1H, J
3.3 Hz, 9.6 Hz, H-30), 3.72 (dd, 1H, J 1.8 Hz, 12.3 Hz,
H-6a), 3.67–3.53 (m, 6H, H-2, H-20, H-200, H-300, H-4,
H-400), 3.43 (m, 1H, H-500), 3.40 (t, 1H, J 9.6 Hz, H-40),
3.31 (s, 3H, C6H4OCH3), 3.28 (m, 1H, H-50), 3.18 (m, 1H,
H-5), 1.19 (d, 3H, J 6.3 Hz, C–CH3). 13C NMR (75 MHz,
D2O) d: 171.5 (COOH), 102.9 (C-100), 100.9 (C-1), 99.4
(C-10), 81.0, 80.1, 75.5, 73.6, 71.7(3), 71.5, 70.3, 70.2,
67.9, 67.2, 60.5 (C-6), 55.0 (OCH3), 16.6 (C–CH3). HRMS
calcd for C19H32O16Na (M+Na): 539.1588; found 539.1586.
Acknowledgements
S.M. is thankful to CSIR, New Delhi for providing
fellowship. Instrumentation facilities from SAIF, CDRI are

11370
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