Synthesis of two trisaccharides related to the triterpenoid saponins isolated from Solanum lycocarpum

Article abstract of DOI:10.1016/j.carres.2011.08.004

Chemical synthesis of two trisaccharides related to the triterpenoid saponins isolated from Solanum lycocarpum from commercially available D-Glc, D-Gal and L-Rha have been achieved by following concise and high-yielding route. The target trisaccharide 1 h

Full text of DOI:10.1016/j.carres.2011.08.004

Carbohydrate Research 346 (2011) 2342–2347
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of two trisaccharides related to the triterpenoid saponins
isolated from Solanum lycocarpum
⇑
Priya Verma, Vipin Kumar Kabra, Balaram Mukhopadhyay
Indian Institute of Science Education and Research-Kolkata, Mohanpur Campus, Mohanpur, Nadia, 741 252 W.B., India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 June 2011
Received in revised form 16 July 2011
Accepted 2 August 2011
Available online 10 August 2011
Chemical synthesis of two trisaccharides related to the triterpenoid saponins isolated from Solanum lyco-
carpum from commercially available D-Glc, D-Gal and L-Rha have been achieved by following concise and
high-yielding route. The target trisaccharide 1 has been made by following a bis-glycosylation approach
that has minimized the protecting group manipulations up to great extent. The trisaccharides have been
synthesized in the form of their p-methoxyphenyl (OMP) glycosides to leave the scope for further glyco-
conjugates formation by the selective removal of the OMP glycoside and trichloroacetimidate chemistry.
La(OTf)3 has been used successfully as the promoter for the NIS mediated activation of thioglycosides.
Ó 2011 Elsevier Ltd. All rights reserved.
Dedicated to Professor Brindaban Chandra
Ranu, Organic Chemistry Department,
Indian Association for the Cultivation of
Science, Jadavpur, Kolkata
Keywords:
Saponin
Oligosaccharide
Bis-glycosylation
La(OTf)3
1. Introduction
isolated from S. lycocarpum in the form of their p-methoxyphenyl
glycosides (Fig. 1).
Steroidal saponins are secondary metabolites produced in
plants in their regular growth and development programme. It is
believed that this class of compounds helps to form a chemical bar-
rier against fungal attack, and thus is very important for the de-
fence mechanism in plants.1 Although the biological importance
of steroidal saponins has been recognised, the biosynthesis of
saponins is still not understood completely. Saponins have also
served as a source of medicines for a long time. One of the common
features shared by this class of molecules is the presence of a
branched oligosaccharide at the 3-OH position of the aglycon
moiety.2,3 It is evident that the glycosylation happens in a mature
stage of the saponin biosynthesis and the oligosaccharides have a
clear role to regulate the bioactivity of the saponin concerned.
Therefore, chemical synthesis of saponins is required to elucidate
the biosynthetic pathway and the activity.4,5 Recently, Yoshikawa
et al.6 reported the structures of two new steroidal saponins,
robenoside A and B from the Brazilian medicinal plant Solanum
lycocarpum that showed reasonable antidiabetic properties. In
continuation to our effort towards the synthesis of the oligosaccha-
rides related to the bioactive saponins,7 here we report the total
synthesis of two trisaccharides related to the steroidal saponins
2. Results and discussion
Synthesis of the target trisaccharide 1 was commenced with
the known p-methoxyphenyl 4,6-O-benzylidene-b-D-glucopyran-
oside (3)8 (Scheme 1). p-Methoxyphenyl glycoside was preferred
as the reducing end glycoside as it can be selectively converted
to the corresponding trichloroacetimidate derivative after the
formation of the target structure and allows further glycoconju-
gates formation. Compound 3 was selectively benzylated at the
3-position via stannylene chemistry by using Bu2SnO in MeOH9
followed by BnBr in the presence of CsF to afford p-methoxy-
phenyl 3-O-benzyl-4,6-O-benzylidene-b-D-glucopyranoside (4) in
73% yield. Further regioselective opening of the benzylidene ace-
tal using triethylsilane in the presence of BF3ꢀEt2O10 furnished
the required diol, p-methoxyphenyl 3,6-di-O-benzyl-b-D-glucopy-
ranoside (5) in 86% yield. At this point, a bis-glycosylation with
two suitably protected rhamnose moieties would result the tar-
get trisaccharide 1. Therefore, the diol 5 was reacted with excess
(3 mol equiv) of known donor, p-tolyl 2,3,4-tri-O-acetyl-a-L-
rhamnopyranoside (6)11 in the presence of N-iodosuccinimide
(NIS) and La(OTf)3.12 The glycosylation reaction afforded the de-
sired trisaccharide 7 in 62% isolated yield along with the (1?2)-
disaccharide 8 in 20% yield. Surprisingly, no (1?4)-disaccharide
⇑
Corresponding author.
E-mail address: sugarnet73@hotmail.com (B. Mukhopadhyay).
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.08.004

P. Verma et al. / Carbohydrate Research 346 (2011) 2342–2347
2343
H
N
R
OH
O
HO
HO
OH
HO
O
Me
OH
O
HO
O
Me
OH
O
OMP
HO
O
O
O
HO
O
Me
O
HO
Me
HO
O
HO
OH
HO
OH
H
1
N
R
HO
OH
O
OH
O
OMP
HO
HO
HO
O
O
OH
O
OH
O
OH
Me
HO
O
O
HO
O
HO
O
OH
HO
OH
Me
O
HO
2
HO
OH
Figure 1. Structure of the triterpenoid saponins from Solanum lycocarpum and the synthetic targets.
STol
Me
AcO
O
AcO
OBn
O
O
Ph
OAc
O
O
Et3SiH
6
OMP
HO
R2O
OMP
BnO
BF3.Et2O, CH2Cl2
NIS, La(OTf)3
OR1
OH
5
i. Bu2SnO, MeOH 3 R1 = R2 = H
ii. BnBr, CsF
4 R1 = H, R2 = Bn
OAc
AcO
OBn
O
AcO
HO
O
OMP
Me
OBn
O
BnO
O
O
+
OMP
BnO
Me
O
O
AcO
AcO
Me
OAc
O
AcO
8
AcO
OAc
7
OH
HO
HO
O
Me
OH
O
O
OMP
HO
i. H2, Pd-C
O
7
ii. NaOMe, MeOH
Me
HO
O
HO
OH
1
Scheme 1. Synthesis of the trisaccharide 1.
could be isolated that indicates the greater reactivity of 2-OH of
the glucoside moiety in comparison to the 4-OH of the same. Fi-
nally, protected trisaccharide 7 upon catalytic hydrogenation
using Pd-C under H2 atmosphere13 followed by transesterifica-
tion using NaOMe in MeOH14 afforded the target trisaccharide,
For the synthesis of the target trisaccharide 2, known p-
methoxyphenyl 3,4-O-isopropylidene-b-
-galactopyranoside (9)15
was selectively benzoylated at the primary position by using an
equimolar amount of BzCN in the presence of catalytic Et3N in
CH3CN16 to furnish the desired 2-ol derivative, p-methoxyphenyl
D
p-methoxyphenyl
a-
L-rhamnopyranosyl-(1?2)-4-O-(
a-
L-rhamno-
6-O-benzoyl-3,4-O-isopropylidene-b-D-galactopyranoside (10) in
pyranosyl)-b-
1).
D
-glucopyranoside (1) in 72% overall yield (Scheme
88% yield (Scheme 2). Glycosylation of rhamnosyl donor 6 with
2-ol acceptor 10 in the presence of NIS and La(OTf)3 afforded the

2344
P. Verma et al. / Carbohydrate Research 346 (2011) 2342–2347
STol
Me
AcO
O
O
OBz
O
O
O
AcO
OH
O
OBz
O
OAc
OMP
O
BzCN
6
O
OMP
OMP
O
O
Et3N, CH3CN
NIS, La(OTf)3
OH
Me
AcO
OH
10
O
9
AcO
OAc
11
OAc
O
AcO
AcO
R1O
OR2
O
R2O
R1O
AcO
OBz
O
OR1
O
O
CCl3
R1O
OMP
O
14
OMP
R1O
NH
80% AcOH
80 oC
O
O
OR1
Me
R1O
H2SO4-silica
O
Me
O
AcO
R1O
AcO
OR1
OAc
15 R1 = Ac, R2 = Bz
2 R1, R2 = H
12 R1, R2 = H
13 R1 = H, R2 = Ac
i. trimethyl orthoacetate, CSA
ii.aq. HCl work-up
Scheme 2. Synthesis of the trisaccharide 2.
disaccharide 11 in 83% yield. Further, hydrolysis of the isopropyli-
dene ketal using 80% aq. AcOH at 80 °C17 followed by orthoesteri-
fication with trimethyl orthoacetate18 in the presence of CSA and
subsequent rearrangement of the orthoester by aq HCl work-up
furnished the disaccharide acceptor, p-methoxyphenyl 2,3,4-tri-
formed on Silica Gel 60-F254 with detection by fluorescence and/
or by charring following immersion in a 10% ethanolic solution of
sulfuric acid. An orcinol dip, prepared by the careful addition of
concentrated sulfuric acid (20 mL) to an ice-cold solution of 3,5-
dihydroxytoluene (360 mg) in EtOH (150 mL) and H2O (10 mL),
was used to detect deprotected compounds by charring. Flash
chromatography was performed with Silica Gel 230–400. Optical
rotations were measured at the sodium D-line at ambient temper-
ature. 1H NMR and 13C NMR spectra were recorded on a Bruker
Avance spectrometer at 500 MHz and 125 MHz, respectively.
O-acetyl-
a-L-rhamnopyranosyl-(1?2)-4-O-acetyl-6-O-benzoyl-b-
D
-galactopyranoside (13). Glycosylation of the disaccharide
acceptor 13 with known 2,3,4,6-tetra-O-acetyl-a-D-glucopyrano-
syl trichloroacetimidate (14)19 in the presence of H2SO4–silica20
afforded the protected trisaccharide p-methoxyphenyl 2,3,4-tri-
O-acetyl-
O-(2,3,4,6-tetra-O-acetyl-b-
a
-
L
-rhamnopyranosyl-(1?2)-4-O-acetyl-6-O-benzoyl-3-
-glucopyranosyl)-b- -galactopyrano-
D
D
4.2. p-Methoxyphenyl 3-O-benzyl-4,6-O-benzylidene-b-D-
side (15) in 81% yield. It is worth noting that when the final
glycosylation was tried with p-tolyl 2,3,4,6-tetra-O-acetyl-1-
glucopyranoside (4)
thio-b-
D
-glucopyranoside (16), only >15% isolated yield of the
A mixture of known p-methoxyphenyl-4,6-O-benzylidene-b-
D-
desired trisaccharide was obtained from a very messy product
mixture. Finally, global deprotection of the trisaccharide 15
through transesterification using NaOMe in MeOH furnished the
glucopyranoside (3) (5.0 g, 13.3 mmol) and Bu2SnO
(3.6 g,14.7 mmol) in dry MeOH (30 mL) was refluxed for 3 h.
The resulting solution was concentrated in vacuo, co-evaporated
with toluene and the residue was dried under vacuum for
30 min. The residue was dissolved in dry DMF (20 mL) and BnBr
(2.1 mL, 13.3 mmol) was added followed by CsF (2.0 g,
13.3 mmol) and the solution was stirred at 80 °C for 6 h. After
evaporating the solvents in vacuo the residue was dissolved in
CH2Cl2 (40 mL) and washed successively with H2O (50 mL) and
brine (50 mL). The organic layer was collected, dried (Na2SO4)
and evaporated in vacuo. The crude product thus obtained was
purified by flash chromatography using n-hexane–EtOAc (3:1)
as eluent to afford pure compound 4 (4.3 g, 73%) as white foam.
target trisaccharide, p-methoxyphenyl
a
-
L
-rhamnopyranosyl-
(1?2)-3-O-(b-D-glucopyranosyl)-b-D-galactopyranoside (2) in
83% yield.
3. Conclusion
In conclusion, we have synthesized two trisaccharides related
to the triterpenoid saponin isolated from S. lycocarpum. The trisac-
charides have been synthesized as their p-methoxyphenyl glyco-
sides to leave the scope open for further glycoconjugates
formation. Synthesis of the trisaccharide 1 has been accomplished
by following a bis-glycosylation strategy that minimized the pro-
tecting group manipulations.
½
a 2D5 +92 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.50–7.28
(m, 10H, ArH), 7.02 (d, 2H, J 9.0 Hz, C6H4OMe), 6.83 (d, 2H,
C6H4OMe), 5.59 (s, 1H, CHPh), 4.96 (d, 1H, J 11.5 Hz, CH2Ph),
4.89 (d, 1H, J1,2 7.5 Hz, H-1), 4.85 (d, 1H, J 11.5 Hz, CH2Ph),
ꢁ
4.36 (dd, 1H, J5,6a 4.5 Hz, J6a,6b 11.5 Hz, H-6a), 3.82 (t, 1H, J3,4
,
4. Experimental
4.1. General
J4,5 10.5 Hz, H-4), 3.77 (s, 3H, C6H4OCH3), 3.75 (m, 3H, H-2, H-
3, H-6b), 3.54 (m, 1H, H-5). 13C NMR (125 MHz, CDCl3) d:
155.4, 151.0, 138.1, 137.0, 128.9, 128.2 (2 ꢂ C), 128.1 (2 ꢂ C),
127.9 (2 ꢂ C), 127.6, 125.9 (2 ꢂ C), 118.6 (2 ꢂ C), 114.4 (2 ꢂ C)
(ArC), 102.7 (CHPh), 101.2 (C-1), 81.0, 80.5, 74.6, 73.7, 68.5,
66.2, 55.4 (C6H4OCH3). HRMS calcd for C27H28O7Na (M+Na)+:
487.1733, found: 487.1731.
All reagents and solvents were dried prior to use according to
standard methods.21 Commercial reagents were used without fur-
ther purification unless otherwise stated. Analytical TLC was per-

P. Verma et al. / Carbohydrate Research 346 (2011) 2342–2347
2345
C6H4OMe), 5.33 (dd, 1H, J1 ,2 1.5 Hz, J2 ,3 3.0 Hz, H-20), 5.26 (d,
0
0
0
0
4.3. p-Methoxyphenyl 3,6-di-O-benzyl-b-
D-glucopyranoside (5)
1H, J1 ,2 1.5 Hz, H-10), 5.24 (dd, 1H, J2 ,3 3.0 Hz, J3 ,4 10.0 Hz, H-30),
0
0
0
0
0
0
5.06 (t, 1H, J3 ,4 , J4 ,5 10.0 Hz, H-40), 4.89 (d, 1H, J1,2 7.5 Hz, H-1),
4.83 (2d, 2H, AB system, J 11.5 Hz, CH2Ph), 4.55 (2d, 2H, AB system,
J 12.0 Hz, CH2Ph), 4.34 (m, 1H, H-50), 3.86 (dd, 1H, J1,2 7.5 Hz, J2,3
9.0 Hz, H-2), 3.78 (s, 3H, C6H4OCH3), 3.72 (m, 3H, H-4, H-6a, H-
6b), 3.62 (t, 1H, J2,3, J3,4 8.5 Hz, H-3), 3.57 (m, 1H, H-5), 2.62 (br s,
1H, OH), 2.07, 2.01, 1.97 (3s, 9H, 3 ꢂ COCH3), 1.19 (d, 3H, J
6.0 Hz, C–CH3). 13C NMR (125 MHz, CDCl3) d: 170.1, 170.0, 169.9
(3 ꢂ COCH3), 155.3, 151.0, 138.1, 137.6, 128.5 (2 ꢂ C), 128.4
(2 ꢂ C), 127.9 (2 ꢂ C), 127.9, 127.8, 127.7 (2 ꢂ C), 118.1 (2 ꢂ C),
114.6 (2 ꢂ C) (ArC), 100.1 (C-1), 98.0 (C-10), 85.5, 76.6, 75.5, 73.9,
73.7, 72.5, 71.0, 70.3, 69.6, 69.2, 66.5, 55.6 (C6H4OCH3), 20.8,
20.7, 20.6 (3 ꢂ COCH3), 17.2 (C–CH3). HRMS calcd for C39H46O14Na
(M+Na)+: 761.2785, found: 761.2787.
0
0
0
0
To a solution of compound 4 (1.5 g, 3.2 mmol) in dry CH2Cl2
(15 mL) at 0 °C, triethylsilane (6.0 mL, 38 mmol) was added fol-
lowed by addition of BF3.Et2O (790 lL, 6.4 mmol). The reaction
was stirred at 0 °C till the TLC showed the complete conversion
of the reactant (2 h). The reaction mixture was diluted with CH2Cl2
(15 mL) and successively washed with H2O (30 mL) and NaHCO3
(30 mL). The organic layer was collected, dried over anhydrous
Na2SO4 and filtered. The solvent was evaporated and the crude
material was purified by flash chromatography using n-hexane–
EtOAc (2:1) to afford pure compound 5 (1.3 g, 86%). ½a D25
ꢁ
+101 (c
1.1, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.40–7.32 (m, 10H,
ArH), 7.02 (d, 2H, J 9.0 Hz, C6H4OMe), 6.80 (d, 2H, C6H4OMe),
4.99 (d, 1H, J 11.5 Hz, CH2Ph), 4.85 (d, 1H, J 11.5 Hz, CH2Ph), 4.77
(d, 1H, J1,2 7.5 Hz, H-1), 4.60 (d, 1H, J 12.0 Hz, CH2Ph), 4.55 (d,
1H, J 12.0 Hz, CH2Ph), 4.36 (dd, 1H, J5,6a 4.5 Hz, J6a,6b 11.5 Hz, H-
6a), 3.78 (s, 3H, C6H4OCH3), 3.76 (m, 2H, H-2, H-6b), 3.73 (t, 1H,
J2,3, J3,4 10.0 Hz, H-3), 3.58 (m, 1H, H-5), 3.48 (t, 1H, J3,4, J4,5
10.0 Hz, H-4), 2.73 (br s, 1H, OH), 2.61 (br s, 1H, OH). 13C NMR
(125 MHz, CDCl3) d: 155.4, 151.1, 138.5, 137.8, 128.6 (2 ꢂ C),
128.4 (2 ꢂ C), 128.0 (2 ꢂ C), 127.9, 127.6, 127.4 (2 ꢂ C), 118.6
(2 ꢂ C), 114.5 (2 ꢂ C) (ArC), 102.0 (C-1), 83.6, 74.8, 74.4, 74.0,
73.6, 71.3, 70.1, 55.6 (C6H4OCH3). HRMS calcd for C27H30O7Na
(M+Na)+: 489.1889, found: 489.1887.
4.5. p-Methoxyphenyl
rhamnopyranosyl)-b-
a
-
L
-rhamnopyranosyl-(1?2)-4-O-(
a-L-
D
-glucopyranoside (1)
The protected trisaccharide 7 (1 g, 1.0 mmol) was dissolved in
CH3OH and 20% Pd-C (150 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-
ite bed and evaporated to dryness. The residue was dissolved in dry
MeOH (10 mL), NaOMe (0.5 M in MeOH, 1.0 mL) was added and
the solution was stirred at room temperature for 4 h. The solution
was neutralised with DOWEX 50 W H+ resin and filtered through a
cotton plug. The filtrate was evaporated and washed with CH2Cl2
(5 ml) removing the methyl benzoate impurity to afford the target
4.4. p-Methoxyphenyl 2,3,4-tri-O-acetyl-
(1?2)-3,6-di-O-benzyl-4-O-(2,3,4-tri-O-acetyl-
pyranosyl)-b- -glucopyranoside (7)
a
-
L
-rhamnopyranosyl-
a-L-rhamno-
D
trisaccharide 1 (412 mg, 72%). ½a D25
ꢁ
+102 (c 0.8, H2O). 1H NMR
(500 MHz, D2O) d: 6.96 (d, 2H, J 9.0 Hz, C6H4OMe), 6.88 (d, 2H, J
A mixture of compound 5 (1.0 g, 2.1 mmol), compound 6 (2.5 g,
0
0
0
9.0 Hz, C6H4OMe), 5.06 (d, 1H, J1,2 8.0 Hz, H-1), 5.03 (d, 1H, J1 ,2
6.3 mmol) and MS 4 ÅA (2 g) in dry CH2Cl2 (30 mL) was stirred under
nitrogen for 1 h. NIS (1.8 g, 8.2 mmol) was added and the mixture
was cooled to 0 °C followed by addition of La(OTf)3 (100 mg). The
mixture was allowed to stir at 0 °C for 30 min when TLC showed
complete consumption of the acceptor 5. The mixture was imme-
diately filtered through a pad of Celite. The filtrate was diluted
with CH2Cl2 (20 mL) and washed successively with Na2S2O3
(2 ꢂ 50 mL), NaHCO3 (2 ꢂ 50 mL) and brine (50 mL). The organic
layer was collected, dried (Na2SO4) and evaporated in vacuo. The
residue was purified by flash chromatography using n-hexane–
EtOAc (2:1 to 1:1) to afford pure compound 7 (1.3 g, 62%) as col-
ourless foam and 8 (315 mg, 20%) as light yellow oil.
1.5 Hz, H-10), 4.75 (d, 1H, J1 ,2 1.5 Hz, H-100), 3.95 (dd, 1H, J1 ,2
00 00
0
0
1.5 Hz, J2 ,3 3.0 Hz, H-20), 3.91 (m, 1H, H-50), 3.87 (dd, 1H, J1 ,2
0
0
00 00
1.5 Hz, J2 ,3 3.5 Hz, H-200), 3.81 (m, 1H, H-500), 3.73 (dd, 1H, J5,6a
00 00
2.0 Hz, J6a,6b12.5 Hz, H-6a), 3.69 (s 3H, C6H4OCH3), 3.68 (t, 1H,
J2,3, J3,4 9.0 Hz, H-3), 3.63 (m, 2H, H-30, H-300), 3.58 (t, 1H, J3,4, J4,5
9.0 Hz, H-4), 3.54 (dd, 1H, J5,6b 2.5 Hz, J6a,6b12.5 Hz, H-6b), 3.52
(dd, 1H, J1,2 8.0 Hz, J2,3 9.0 Hz, H-2), 3.47 (m, 1H, H-5), 3.35 (t,
1H, J3 ,4 , J4 ,5 10.0 Hz, H-40), 3.32 (t, 1H, J3 ,4 , J4 ,5 10.0 Hz, H-400),
1.15 (d, 3H, J 6.5 Hz, C–CH3), 1.09 (d, 3H, J 6.5 Hz, C–CH3). 13C
NMR (125 MHz, D2O) d: 154.8, 150.5, 117.9 (2 ꢂ C), 115.3 (2 ꢂ C)
(ArC), 101.6 (C-1), 101.0 (C-10), 99.2 (C-100), 79.9, 76.9, 75.2, 75.0,
72.0, 70.5, 70.3, 70.2, 69.1, 69.0, 60.1, 55.9 (C6H6OCH3), 49.0, 16.7
(C–CH3), 16.5 (C–CH3). HRMS calcd for C25H38O15Na (M+Na)+:
601.2108, found: 601.2105.
0
0
0
0
00 00
00 00
Compound 7: ½a 2D5
ꢁ
+73 (c 0.9, CHCl3). 1H NMR (500 MHz, CDCl3)
d: 7.31–7.27 (m, 10H, ArH), 6.98 (d, 2H, J 9.0 Hz, C6H4OMe), 6.82 (d,
2H, J 9.0 Hz, C6H4OMe), 5.24 (dd, 1H, J1 ,2 1.5 Hz, J2 ,3 5.0 Hz, H-20),
0
0
0
0
5.22 (dd, 1H, J2 ,3 5.0 Hz, J3 ,4 10.0 Hz, H-30), 5.20 (m, 2H, H-200, H-
0
0
0
0
300), 5.19 (d, 1H, J1 ,2 1.5 Hz, H-10), 5.02 (d, 1H, J1 ,2 1.5 Hz, H-100),
5.01 (d, 1H, 12.0 Hz, CH2Ph), 4.97 (t, 2H, J 10.0 Hz, H-40, H-400),
4.91 (d, 1H, J1,2 7.5 Hz, H-1), 4.85 (d, 1H, J 12.0 Hz, CH2Ph), 4.56
(2d, 2H, AB system, J 12.0 Hz, CH2Ph), 4.34 (m, 1H, H-50), 4.05 (t,
1H, J3,4, J4,5 8.5 Hz, H-4), 4.01 (m, 2H, H-2, H-500), 3.79 (s, 3H,
C6H4OCH3), 3.78–3.73 (m, 3H, H-3, H-6a, H-6b), 3.56 (m, 1H, H-
5), 2.09, 2.01, 1.99, 1.92, 1.87, 1.85 (6s, 18H, 6 ꢂ COCH3), 1.21 (d,
3H, J 6.0 Hz, C–CH3), 0.86 (d, 3H, C–CH3). 13C NMR (125 MHz,
CDCl3) d: 170.2, 170.1, 170.0, 169.9, 169.8, 169.4 (6 ꢂ COCH3),
155.3, 151.0, 137.9, 137.5, 128.2 (2 ꢂ C), 128.0 (2 ꢂ C), 127.5
(2 ꢂ C), 127.4, 127.1, 126.1 (2 ꢂ C), 118.2 (2 ꢂ C), 114.6 (2 ꢂ C)
(ArC), 100.2 (C-1), 98.2 (C-10), 97.2 (C-100), 83.8, 75.1, 74.4, 74.3,
73.1, 70.8, 70.6, 69.9, 69.3, 69.2, 68.9, 68.1, 66.8, 66.7, 55.6
(C6H6OCH3), 20.9, 20.8, 20.7, 20.6, 20.5, 20.4 (6 ꢂ COCH3), 17.2,
17.1 (2 ꢂ C–CH3). HRMS calcd for C51H62O21Na (M+Na)+:
1033.3681, found: 1033.3678.
4.6. p-Methoxyphenyl 6-O-benzoyl-3,4-O-isopropylidene-b-
D
-
0
0
00 00
galactopyranoside (10)
To a suspension of compound 9 (4.1 g, 12.5 mmol) in dry CH3CN
(30 mL), BzCN (1.5 mL, 12.5 mmol) was added followed by Et3N
(20 lL) and allowed to stir at 0 °C. The solution became clear with-
in 15 min and the TLC (n-hexane–EtOAc; 2:1) showed complete
consumption of the starting material. MeOH (2 mL) was added to
quench the reaction. Solvents were evaporated in vacuo and the
residue was purified by flash chromatography using 2:1 n-hex-
ane–EtOAc to afford pure p-methoxyphenyl-6-O-benzoyl-3,4-O-
isopropylidene-b-
D
-galactopyranoside 10 (4.8 g, 88%). ½a D25
ꢁ
+79 (c
1.0, CHCl3). 1H NMR (500 MHz, CDCl3) d: 8.08–6.67 (m, 9H, ArH),
4.72 (dd, 1H, J6a,6b 11.5 Hz, J5,6a 3.0 Hz, H-6a), 4.67 (d, 1H, J1,2
8.5 Hz, H-1), 4.62 (m, 1H, H-6b), 4.24 (m, 2H, H-3, H-4), 3.89 (t,
1H, J1,2, J2,3 8.5 Hz, H-2), 3.73 (s, 3H, C6H4–OCH3), 3.72 (m, 1H, H-
5), 1.59, 1.43 (2s, 6H, 2 ꢂ isopropylidene-CH3). 13C NMR
(125 MHz, CDCl3) d: 166.2 (COPh), 155.4, 151.0, 133.1, 129.8,
Compound 8: 1H NMR (500 MHz, CDCl3) d: 7.34–7.26 (m, 10H,
ArH), 6.97 (d, 2H, J 9.0 Hz, C6H4OMe), 6.82 (d, 2H, J 9.0 Hz,

2346
P. Verma et al. / Carbohydrate Research 346 (2011) 2342–2347
129.7 (2 ꢂ C), 128.4 (2 ꢂ C), 118.6 (2 ꢂ C), 114.4 (2 ꢂ C) (ArC),
110.8 [C(CH3)2], 101.6 (C-1), 78.9, 73.3, 73.2, 71.4, 63.6, 55.5
(C6H4–OCH3), 26.3, 22.6 (2 ꢂ isopropylidene CH3). HRMS calcd for
(C–CH3). HRMS calcd for C32H38O15Na [M+Na]+: 685.2108, found:
685.2106.
C
23H26O8Na (M+Na)+: 453.1525, found: 453.1521.
4.9. p-Methoxyphenyl 2,3,4-tri-O-acetyl-a-L-rhamnopyranosyl-
(1?2)-4-O-acetyl-6-O-benzoyl-b- -galactopyranoside (13)
D
4.7. p-Methoxyphenyl 2,3,4-tri-O-acetyl-
(1?2)-6-O-benzoyl-3,4-O-isopropylidene-b-
a
-
L
-rhamnopyranosyl-
-galacto-
D
To a solution of 12 (2.4 g, 3.6 mmol) in dry CH3CN (2.5 mL), tri-
methyl orthoacetate (803 L, 4.68 mmol) was added followed by
pyranoside (11)
l
CSA (50 mg) and the mixture was allowed to stir at room temper-
ature until complete conversion of the starting material was
evident by TLC (2:1 n-hexane–EtOAc). After 45 min, the solution
was neutralised by Et3N and evaporated in vacuo. The resulting
syrupy mass was dissolved in CH2Cl2 (30 mL) and washed succes-
sively with 1 N HCl (3 ꢂ 50 mL) to rearrange the orthoester to
corresponding 4-O-acetate, followed by wash with aq. NaHCO3
(2 ꢂ 50 mL) and brine (50 mL). Organic layer was separated, dried
(Na2SO4) and evaporated to syrup. The crude product was purified
by flash chromatography (4:1 n-hexane–EtOAc) to give pure disac-
A mixture of compound 10 (2 g, 4.65 mmol), compound 6 (2.2 g,
0
5.5 mmol) and MS 4 ÅA (2 g) in dry CH2Cl2 (25 mL) was stirred under
nitrogen for 1 h. NIS (1.6 g, 7.4 mmol) was added and the mixture
was cooled to 0 °C followed by addition of La(OTf)3 (100 mg). The
mixture was allowed to stir at 0 °C for 30 min. when TLC showed
complete consumption of the acceptor 10. The mixture was filtered
through a pad of Celite. The filtrate was diluted with CH2Cl2
(20 mL) and washed successively with Na2S2O3 (2 ꢂ 50 mL), NaH-
CO3 (2 ꢂ 50 mL) and brine (50 mL). The organic layer was col-
lected, dried (Na2SO4) and evaporated in vacuo. The residue was
purified by flash chromatography using n-hexane–EtOAc (2:1) to
charide acceptor 13 (2.2 g, 87%) as colourless foam. ½a D25
ꢁ
+93 (c 1.1,
CHCl3). 1H NMR (500 MHz, CDCl3) d: 8.04–7.44 (m, 5H, ArH), 6.97
(d, 2H, J 9.0 Hz, C6H4OMe), 6.70 (d, 2H, J 9.0 Hz, C6H4OMe), 5.38
afford pure compound 11 (2.6 g, 83%) as white foam. ½a D25
ꢁ
+113
(c 1.1, CHCl3). 1H NMR (500 MHz, CDCl3) d: 8.06–7.44 (m, 5H,
ArH), 6.97 (d, 2H, J 9.5 Hz, C6H4OMe), 6.66 (d, 2H, J 9.5 Hz,
(br d, 1H, J3,4 1.5 Hz, H-4), 5.35 (dd, 1H, J1 ,2 2.0 Hz, J2 ,3 3.5 Hz,
0
0
0
0
H-20), 5.30 (d, 1H, J1 ,2 2.0 Hz, H-10), 5.23 (dd, 1H, J2 ,3 3.5 Hz, J3 ,4
0
0
0
0
0
0
C6H4OMe), 5.33 (dd, 1H, J1 ,2 2.0 Hz, J2 ,3 3.5 Hz, H-20), 5.26 (d,
10.0 Hz, H-30), 5.09 (t, 1H, J3 ,4 , J4 ,5 10.0 Hz, H-40), 4.88 (d, 1H, J1,2
7.0 Hz, H-1), 4.45 (dd, 1H, J5,6a 11.5 Hz, J6a,6b12.5 Hz, H-6a), 4.39
(dd, 1H, J5,6b 5.5 Hz, J6a,6b12.5 Hz, H-6b), 4.35 (m, 1H, H-50), 4.08–
4.03 (m, 3H, H-2, H-3, H-5), 3.73 (s, 3H, C6H4OCH3), 3.03 (br s,
1H, OH), 2.19, 2.12, 2.02, 1.97 (4s, 12H, 4 ꢂ COCH3), 1.25 (d, 3H, J
6.0 Hz, C–CH3). 13C NMR (125 MHz, CDCl3) d: 171.4, 170.3
(2 ꢂ C), 170.0 (4 ꢂ COCH3), 166.0 (COPh), 155.4, 151.0, 133.3,
129.7 (2 ꢂ C), 129.5, 128.5 (2 ꢂ C), 118.2 (2 ꢂ C), 114.5 (2 ꢂ C)
(ArC), 100.5 (C-1), 98.1 (C-10), 75.3, 73.3, 71.1, 70.9, 70.2, 69.6,
69.3, 66.6, 62.4, 55.6 (C6H4OCH3), 20.9, 20.8 (2 ꢂ C), 20.7
(4 ꢂ COCH3), 17.3 (C–CH3). HRMS calcd for C34H40O16Na (M+Na)+:
727.2214, found: 727.2211.
0
0
0
0
0
0
0
0
1H, J1 ,2 2.0 Hz, H-10), 5.24 (dd, 1H, J2 ,3 3.5 Hz, J3 ,4 10.0 Hz, H-30),
0
0
0
0
0
0
5.10 (t, 1H, J3 ,4 , J4 ,5 10.0 Hz, H-40), 4.74 (d, 1H, J1,2 8.0 Hz, H-1),
4.69 (dd, 1H, J5,6a 4.0 Hz, J6a,6b12.5 Hz, H-6a), 4.62 (dd, 1H, J5,6b
11.5 Hz, J6a,6b12.5 Hz, H-6b), 4.35 (m, 1H, H-50), 4.31 (dd, 1H, J2,3
7.0 Hz, J3,4 2.0 Hz, H-3), 4.25 (br d, 1H, J3,4 2.0 Hz, H-4), 4.21 (m,
1H, H-5), 4.00 (dd, 1H, J1,2 8.0 Hz, J2,3 7.0 Hz, H-2), 3.71 (s, 3H,
C6H4OCH3), 2.16, 2.03, 1.96 (3s, 9H, 3 ꢂ COCH3), 1.57, 1.35 (2s,
6H, 2 ꢂ isopropylidene-CH3), 1.24 (d, 3H, J 6.0 Hz, C–CH3). 13C
NMR (125 MHz, CDCl3) d: 170.1, 170.0, 169.9 (3 ꢂ COCH3), 166.1
(COPh), 155.5, 151.2, 133.2, 129.8, 129.7 (2 ꢂ C), 128.4 (2 ꢂ C),
118.6 (2 ꢂ C), 114.4 (2 ꢂ C) (ArC), 111.0 [C(CH3)2], 100.2 (C-1),
95.9 (C-10), 79.8, 75.0, 73.5, 71.2, 71.0, 69.5, 69.2, 66.4, 63.6, 55.5
(C6H4OCH3), 27.8, 26.3 (2 ꢂ isopropylidene CH3), 20.9, 20.8, 20.7
(3 ꢂ COCH3), 17.3 (C–CH3). HRMS calcd for C35H42O15Na [M+Na]+:
725.2421, found: 725.2423.
0
0
0
0
4.10. p-Methoxyphenyl 2,3,4-tri-O-acetyl-
syl-(1?2)-3-O-(2,3,4,6-tetra-O-acetyl-b- -glucopyranosyl)-
(1?3)-4-O-acetyl-6-O-benzoyl-b- -galactopyranoside (15)
a-L-rhamnopyrano-
D
D
A mixture of compound 13 (2 g, 2.8 mmol), compound 14 (2.2 g,
0
4.8. p-Methoxyphenyl 2,3,4-tri-O-acetyl-
a-L-rhamnopyranosyl-
4.5 mmol) and MS 4 ÅA (2 g) in dry CH2Cl2 (25 mL) was stirred under
nitrogen for 1 h. The reaction mixture was cooled to ꢃ10 °C fol-
lowed by addition of H2SO4-silica (40 mg). The mixture was al-
lowed to stir at 0 °C for 30 min. when TLC showed complete
consumption of the acceptor 13. The mixture was filtered through
a pad of Celite and neutralised with Et3N. The filtrate was diluted
with CH2Cl2 (20 mL) and washed with H2O. The organic layer
was collected, dried (Na2SO4) and evaporated in vacuo. The residue
was purified by flash chromatography using n-hexane–EtOAc (2:1)
(1?2)-6-O-benzoyl-b- -galactopyranoside (12)
D
A solution of compound 11 (2.8 g, 3.9 mmol) in 80% AcOH
(30 mL) was stirred at 80 °C for 2 h when TLC (n-hexane–EtOAc;
1:1) showed complete conversion of the starting material to a
slower moving spot. Solvents were evaporated in vacuo and the
residue thus obtained was purified by flash chromatography using
gradient mixture of n-hexane and EtOAc (2:1 to 1:1) to afford pure
compound 12 (2.4 g, 92%) as white foam. ½a D25
ꢁ
+76 (c 1.0, CHCl3). 1H
to afford pure compound 15 (2.3 g, 81%). ½a D25
ꢁ
+81 (c 1.0, CHCl3). 1H
NMR (500 MHz, CDCl3) d: 8.06–7.45 (m, 5H, ArH), 6.96 (d, 2H, J
NMR (500 MHz, CDCl3) d: 8.04–7.44 (m, 5H, ArH), 6.97 (d, 2H, J
9.0 Hz, C6H4OMe), 6.68 (d, 2H, J 9.0 Hz, C6H4OMe), 5.38 (dd, 1H,
9.0 Hz, C6H4OMe), 6.66 (d, 2H, J 9.0 Hz, C6H4OMe), 5.43 (br d, 1H,
J1 ,2 1.5 Hz, J2 ,3 3.0 Hz, H-20), 5.34 (d, 1H, J1 ,2 1.5 Hz, H-10), 5.23
J3,4 1.5 Hz, H-4), 5.32 (dd, 1H, J1 ,2 1.5 Hz, J2 ,3 3.5 Hz, H-20), 5.26
0
0
0
0
0
0
0
0
0
0
(dd, 1H, J2 ,3 3.0 Hz, J3 ,4 10.0 Hz, H-30), 5.09 (t, 1H, J3 ,4 , J4 ,5
(t, 1H, J2 ,3 , J3 ,4 9.5 Hz, H-300), 5.23 (dd, 1H, J2 ,3 3.5 Hz, J3 ,4
0
0
0
0
0
0
0
0
00 00
00 00
0
0
0
0
10.0 Hz, H-40), 4.82 (d, 1H, J1,2 8.0 Hz, H-1), 4.63 (dd, 1H, J5,6a
5.0 Hz, J6a,6b12.5 Hz, H-6a), 4.55 (dd, 1H, J5,6b 7.5 Hz, J6a,6b12.5 Hz,
H-6b), 4.31 (m, 1H, H-50), 4.01 (dd, 1H, J1,2 8.0 Hz, J2,3 9.5 Hz, H-
2), 3.96 (br s, 1H, H-4), 3.89 (dd, 1H, J2,3 9.5 Hz, J3,4 1.0 Hz, H-3),
3.87 (m, 1H, H-5), 3.72 (s, 3H, C6H4OCH3), 3.51 (br s, 1H, OH),
3.21 (br s, 1H, OH), 2.13, 2.02, 1.98 (3s, 9H, 3 ꢂ COCH3), 1.21 (d,
3H, J 6.0 Hz, C–CH3). 13C NMR (125 MHz, CDCl3) d: 170.5 (2 ꢂ C),
170.0 (3 ꢂ COCH3), 166.5 (COPh), 155.3, 151.1, 133.3, 129.8
(2 ꢂ C), 129.6, 128.5 (2 ꢂ C), 118.3 (2 ꢂ C), 114.4 (2 ꢂ C) (ArC),
100.6 (C-1), 97.9 (C-10), 75.9, 74.2, 72.5, 70.9, 69.7, 69.4, 69.1,
66.7, 63.1, 55.6 (C6H4OCH3), 20.9, 20.8, 20.7 (3 ꢂ COCH3), 17.3
10.0 Hz, H-30), 5.16 (d, 1H, J1 ,2 1.5 Hz, H-10), 5.13 (t, 1H, J3 ,4 , J4 ,5
0
0
0
0
0
0
10.0 Hz, H-40), 5.10 (t, 1H, J3 ,4 , J4 ,5 9.5 Hz, H-400), 4.89 (t, 1H,
00 00
00 00
J1 ,2 7.5 Hz, J2 ,3 9.5 Hz, H-200), 4.84 (d, 1H, J1,2 7.5 Hz, H-1), 4.78
00 00
00 00
(d, 1H, J1 ,2 7.5 Hz, H-100), 4.41 (m, 2H, H-6a, H-6b), 4.37 (dd, 1H,
00 00
00
0
00
00
00
00
J5 ,6a 2.5 Hz, J6a ,6b 12.0 Hz, H-6a ), 4.34 (m, 1H, H-5 ), 4.12–4.06
(m, 4H, H-2, H-4, H-5, H-6b00), 3.72 (m, 1H, H-500), 3.71 (s, 3H,
C6H4OCH3), 2.19, 2.15, 2.09, 2.04, 2.02, 2.01, 2.00, 1.97 (8s, 24H,
8 ꢂ COCH3), 1.18 (d, 3H, J 6.5 Hz, C–CH3). 13C NMR (125 MHz,
CDCl3) d: 170.8, 170.3 (2 ꢂ C), 170.1, 170.0 (2 ꢂ C), 169.4, 168.9
(8 ꢂ COCH3), 155.5, 151.0, 133.2, 129.8 (2 ꢂ C), 129.7, 128.5
(2 ꢂ C), 118.2 (2 ꢂ C), 114.5 (2 ꢂ C) (ArC), 100.6 (C-1), 99.4 (C-

P. Verma et al. / Carbohydrate Research 346 (2011) 2342–2347
2347
100), 97.5 (C-10), 77.8, 74.1, 72.3, 72.1, 71.8, 71.5, 70.7, 69.6, 69.3,
Supplementary data
68.9, 68.3, 67.0, 62.7, 61.0, 55.6 (C6H6OCH3), 20.8 (2 ꢂ C), 20.7
(2 ꢂ C), 20.6, 20.5 (2 ꢂ C), 20.4 (8 ꢂ COCH3), 17.2 (C–CH3). HRMS
calcd for C48H58O25Na (M+Na)+: 1057.3165, found: 1057.3163.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2011.08.004.
4.11. p-Methoxyphenyl
a-
L
-rhamnopyranosyl-(1?2)-3-O-b-
D-
References
glucopyranosyl-(1?3)-b-
D
-galactopyranoside (2)
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(475 mg, 83%). ½a D25
ꢁ
+91 (c 0.9, H2O). 1H NMR (500 MHz, D2O) d:
6.95 (d, 2H, J 9.0 Hz, C6H4OMe), 6.84 (d, 2H, J 9.0 Hz, C6H4OMe),
5.05 (d, 1H, J1,2 7.5 Hz, H-1), 5.04 (d, 1H, J1 ,2 1.5 Hz, H-10), 4.52
0
0
(d, 1H, J1 ,2 8.0 Hz, H-100), 4.11 (br d, 1H, J3,4 3.0 Hz, H-4), 3.96
00 00
(m, 1H, H-50), 3.93 (dd, 1H, J1 ,2 1.5 Hz, J2 ,3 3.0 Hz, H-20), 3.88
(dd, 1H, J2,3 9.5 Hz, J3,4 3.0 Hz, H-3), 3.86–3.74 (m, 3H, H-2, H-30,
H-40), 3.65 (s 3H, C6H4OCH3), 3.64–3.55 (m, 4H, H-5, H-6a, H-6b,
H-6a00), 3.39–3.21 (m, 5H, H-200, H-300, H-400, H-500, H-6b0), 1.05 (d,
3H, J 6.0 Hz, C–CH3). 13C NMR (125 MHz, D2O) d: 154.6, 150.4,
117.6 (2 ꢂ C), 115.1 (2 ꢂ C) (ArC), 104.1 (C-100), 101.2 (C-1), 99.3
(C-10), 82.9, 75.9, 75.8, 75.7, 74.8, 73.1, 71.9, 70.2 (2 ꢂ C), 69.4,
68.9, 68.6, 60.6, 60.5, 55.8 (C6H6OCH3), 16.6 (C–CH3). HRMS calcd
for C25H38O16Na (M+Na)+: 617.2058, found: 617.2061.
0
0
0
0
19. Chang, C.-W. T.; Hui, Y.; Elchert, B.; Wang, J.; Li, J.; Rai, R. Org. Lett. 2002, 26,
4603–4606.
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Acknowledgements
P.V. is thankful to University Grants Commission, New Delhi for
Senior Research Fellowship and V.K.K. is thankful to Indian Insti-
tute of Science Education and Research-Kolkata (IISER-K) for the
fellowship. The work is funded by Department of Science and Tech-
nology, New Delhi, India through Grant SR/S1/OC-67/2009.