Oligosaccharides through reactivity tuning: convergent synthesis of the trisaccharides of the steroid glycoside Sokodoside B isolated from marine sponge Erylus placenta

Article abstract of DOI:10.1016/j.tet.2007.09.072

Chemical synthesis of the trisaccharide of the steroid glycoside Sokodoside B isolated from Erylus placenta is reported. Stereoselective, high-yielding glycosylation strategies through thioglycoside activation using H₂SO₄ immobilized

Full text of DOI:10.1016/j.tet.2007.09.072

Tetrahedron 63 (2007) 12310–12316
Oligosaccharides through reactivity tuning: convergent synthesis
of the trisaccharides of the steroid glycoside Sokodoside B
isolated from marine sponge Erylus placenta*
Somnath Dasgupta,a Kausikisankar Pramanikb and Balaram Mukhopadhyaya,
*
aMedicinal and Process Chemistry Division, Central Drug Research Institute, Chattar Manzil Palace,
Lucknow 226001, Uttar Pradesh, India
bDepartment of Chemistry, Inorganic Chemistry Section, Jadavpur University, Jadavpur, Kolkata 700032, West Bengal, India
Received 10 July 2007; revised 11 September 2007; accepted 27 September 2007
Available online 29 September 2007
Dedicated to Professor Yashwant D. Vankar, Chemistry Department, Indian Institute of Technology, Kanpur, India
Abstract—Chemical synthesis of the trisaccharide of the steroid glycoside Sokodoside B isolated from Erylus placenta is reported. Stereo-
selective, high-yielding glycosylation strategies through thioglycoside activation using H2SO4 immobilized on silica in conjunction with
N-iodosuccinimide are used for better results. A late stage TEMPO-mediated oxidation was performed for the formation of required uronic
acid moiety. An analog of the target trisaccharide is also prepared by using a bis-glycosylation approach.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Sokodoside B, from the marine sponge Erylus placenta
collected off Hachijo Island. Sokodoside B exhibited a broad
spectrum of growth inhibitory activities against several
strains of yeasts and fungus. In continuation to our effort
toward the syntheses of biodynamic oligosaccharides, here
we report a convergent route for the synthesis of the
trisaccharide (1, Fig. 1) of Sokodoside B involving a
TEMPO-mediated oxidation at a late stage8 of the total syn-
thesis. Once the target trisaccharide has been made through
one-to-one glycosylation approach, we then achieved the
same target using reactivity tuning approach by exploiting
the reactivity difference between 2- and 3-positions of
arabinose moiety. Synthesis of an analog (2, Fig. 1) of the
target structure is also reported by using a bis-glycosylation
approach.
Marine sponge derived triterpene glycosides have earned
a great deal of interest in past years for their biological activ-
ities that include antimicrobial, cytotoxic, and growth inhib-
itory. Thus, considerable effort has been paid to the isolation
and characterization of this unique class of secondary
metabolites. As a result various steroid glycosides with
different biodynamic characters have been reported from
taxonomically diverse marine sponges such as Niphatidae,1
Pachastrellidae,2 Ancorinidae,3,4 Mycalidae,5 and Raspali-
dae.6 Similar to that of saponins, the glycosides attached to
the steroid aglycon are highly important for the biological
activities they exert. It is believed that the glycosylation
occurs at a late stage of the biosynthetic pathway of these
natural products. However, exact order of events and the
involvement of characteristic glycosyl transferases responsi-
ble are still ambiguous. Therefore, chemical synthesis of the
oligosaccharide fragments related to marine sponge derived
steroid glycosides will be highly relevant when detailed
elucidation of the biosynthetic pathway of the total structure
is concerned.
HO
O
HO
O
HO
HO
HO
OH
O
O
O
O
O
CO2H
O
OMP
OMP
HO
OH
OH
OH
OH
HO
HO
O
O
OH
OH
HO
HO
During the course of their screening for growth inhibitory
activities against genetically modified yeasts, Fusetani et al.7
have found and characterized a novel steroid glycoside,
1
2
Trisaccharide of
Sokodoside B
The analog
MP =p-Methoxyphenyl
*
CDRI communication no. 7270.
* Corresponding author. E-mail: sugarnet73@hotmail.com
Figure 1. Target structure of the trisaccharide of Sokodoside B isolated from
marine sponge Erylus placenta and its analog.
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.09.072

S. Dasgupta et al. / Tetrahedron 63 (2007) 12310–12316
12311
OAc
O
AcO
AcO
2. Results and discussion
STol
HO
HO
O
2.1. Synthesis of the trisaccharide (1) of Sokodoside B
OAc
a
5
O
O
OMP
OMP
O
b
OH
OH
Synthesis of the trisaccharide commenced with known
p-methoxyphenyl a-L-arabinopyranoside (3). p-Methoxy-
phenyl group at the reducing end was chosen since selective
deprotection at the target trisaccharide stage is possible to
prepare glycoconjugates for biological screening. Arabino-
side 3 was converted to its 3,4-O-isopropylidene derivative
4 using 2,2-dimethoxy propane and acetone in the presence
of 10-camphorsulfonic acid.9 Then compound 4 was coupled
with known p-tolyl 2,3,4,6-tetra-O-acetyl-1-thio-b-D-galac-
topyranoside (5) using N-iodosuccinimide in the presence
of H2SO4–silica10 to afford disaccharide 6 in 89% yield.
Use of H2SO4–silica as the catalyst for NIS promoted thio-
glycoside activation instead of using corrosive TfOH or
TMSOTf was proved to be a better choice as it is much easier
to handle. Removal ofisopropylidene acetal by80% AcOH at
80 ꢀC11 followed by orthoesterification and rearrangement
furnished the disaccharide acceptor 8 in 85% yield. In a sep-
arate experiment, known thiogalactoside 9 was treated with
TBDMS-Cl in pyridine12 followed by Ac2O to afford p-tolyl
2,3,4-tri-O-acetyl-6-O-(tert-butyl dimethylsilyl)-1-thio-b-D-
galactopyranoside (10) in 81% yield. Glycosylation between
disaccharide acceptor 8 and donor 10 using NIS in the pres-
ence of H2SO4–silica furnished the protected trisaccharide
11 in 83% yield. The TBDMS group was then removed selec-
tively using 1 M Bu4NF in THF13 using equimolar amount of
AcOH in the reaction media to prevent the migration of the 4-
O-acetyl group to 6-position. Extraction and purification of
the crude material afforded the trisaccharide 12 in 78% yield.
Oxidation of the primary OH group to obtain the required
uronic acid moiety, TEMPO-mediated phase-transfer oxida-
tion process, has been used as reported by Huang et al.14
Among other methods available in the literature,15 this proto-
col was particularly ofinterest as the phase-transfer condition
is favorable for a blocked oligosaccharide. The reaction was
satisfactory and afforded the corresponding uronic acid
derivative 13 in 75% yield. Global deprotection of the acetyl
3
4
O
OH
AcO
O
O
O
O
O
OMP
OMP
OMP
O
HO
HO
c
d
OAc
OAc
OAc
O
AcO
AcO
AcO
STol
O
O
AcO
O
OAc
6
OAc
7
OAc
8
AcO
AcO
OH
O
HO
HO
OTBDMS
O
AcO
AcO
e
STol
OH
OAc
10
9
AcO
AcO
AcO
OTBDMS
OH
O
AcO
AcO
AcO
AcO
O
O
O
O
O
b
f
OMP
OMP
O
8 +10
O
AcO
OAc
OAc
AcO
O
AcO
AcO
O
OAc
OAc
AcO
11
12
OR
COOH
O
RO
OR
O
OMP
g
O
RO
OR
O
RO
O
OR
RO
13 R = Ac
h
1
R = H
Scheme 1. Synthesis of trisaccharide 1 through conventional one-to-one
glycosylation approach. Reagents and conditions: (a) 2,2-DMP, acetone,
ꢀ
˚
CSA, rt, 30 min; (b) NIS, H2SO4–silica, MS 4 A, CH2Cl2, ꢁ40 C, 1 h;
(c) 80% AcOH, 80 ꢀC, 2 h; (d) (i) trimethyl orthoacetate, CSA, CH3CN,
1 h; (ii) 80% AcOH, rt, 45 min; (e) (i) TBDMS-Cl, Py, 4 h; (ii) Ac2O,
2 h; (f) Bu4NF–THF, AcOH, 0 ꢀC–rt, 16 h; (g) TEMPO, NaOCl, NaOCl2,
CH2Cl2; (h) NaOMe, MeOH, rt, 3 h.
ready for oxidation. Similar to the previous approach, the
primary OH group was oxidized using Huang’s condition
and global deprotection furnished the target trisaccharide 1
(Scheme 2).
ꢀ
groups using Zemplen conditions furnished the target trisac-
charide 1 in 87% yield (Scheme 1).
During the course of the glycosylation steps for the synthesis
of trisaccharide 1, we observed that low temperature (ꢁ30
to ꢁ40 ꢀC) is necessary for clean conversion. At higher tem-
perature (greater than ꢁ10 ꢀC) partial loss of TBDMS group
was observed. Taking the advantage of this observation and
anticipating the reactivity difference among 2- and 3-posi-
tions of arabinose moiety, we have targeted one-pot sequential
glycosylation approach. Thus, p-methoxyphenyl 4-O-
acetyl-a-L-arabinopyranoside (14) was prepared from 3 by
making the corresponding 3,4-orthoester derivative using
trimethyl orthoacetate and then rearrangement by 80%
AcOH at room temperature. The acceptor diol (14) was first
coupled with donor 10 followed by addition of the second
donor 5. The sequential glycosylations were performed at
ꢁ40 ꢀC using NIS and H2SO4–silica and afforded the
same trisaccharide as obtained from the previous approach.
After complete glycosylation, the temperature of the reac-
tion mixture was raised to room temperature during 1 h.
To our satisfaction, the required removal of the TBDMS
group was achieved cleanly to afford the trisaccharide 12
HO
HO
OAc
a
10
c
5
O
O
OMP
OMP
RO
HO
b
b
one-pot
OH
OH
14
3
OR
COOH
O
AcO
OH
O
OR
AcO
AcO
O
O
OMP
d
O
O
O
OR
O
RO
OMP
O
AcO
RO
OAc
AcO
O
OR
RO
13 R = Ac
OAc
AcO
12
e
1
R = H
Scheme 2. Synthesis of trisaccharide 1 through sequential one-pot glycosyl-
ation approach using reactivity tuning. Reagents and conditions: (a) (i) tri-
methyl orthoacetate, CSA, CH3CN, 1 h;ꢀ(ii) 80% AcOH, rt, 45 min; (b) NIS,
˚
H2SO4–silica, MS 4 A, CH2Cl2, ꢁ40 C, 1 h; (c) temperature raised to
10 ꢀC in 1 h; (d) TEMPO, NaOCl, NaOCl2, CH2Cl2; (e) NaOMe, MeOH,
rt, 3 h.

12312
S. Dasgupta et al. / Tetrahedron 63 (2007) 12310–12316
2.2. Synthesis of the trisaccharide analog (2) of
Sokodoside B
acid. An orcinol dip, prepared by careful addition of concen-
trated 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 230–400 mesh (Qualigens, India). Optical rotations
were measured at the sodium D-line at ambient temperature
For the analog of Sokodoside B trisaccharide, compound 3
was reacted with trimethyl orthoacetate in the presence of
CSA to get the corresponding 3,4-orthoester, which was
subsequently rearranged using 80% AcOH at room temper-
ature to afford the diol acceptor 14 in 86% yield. Acceptor
diol (14) was coupled with two galactose moieties by using
2.5 equiv of the donor 5. Same NIS promoted activation
of thioglycoside donor in the presence of H2SO4–silica
afforded the bis-glycosylated product 15 in 84% yield.
1
with a Perkin–Elmer 141 polarimeter. H NMR and 13C
NMR spectra were recorded on a Bruker Avance spectro-
meter at 300 and 75 MHz, respectively, using Me4Si or
CH3OH as internal standard, as appropriate.
ꢀ
De-O-acetylation using Zemplen condition afforded the
target analog 2 in 89% yield as amorphous white powder
(Scheme 3).
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.
AcO
OAc
AcO
AcO
O
OAc
O
O
OMP
4.1.1. p-Methoxyphenyl 3,4-O-isopropylidene-a-L-arabi-
nopyranoside (4). To a slurry of compound 3 (3 g,
11.7 mmol) in dry acetone (20 mL) was added 2,2-DMP
(1.7 mL, 14 mmol) followed by CSA (15 mg). The mixture
was allowed to stir at room temperature for 30 min when the
solution became clear and the starting material was com-
pletely converted to a faster running spot (Rf 0.6, n-hex-
ane–EtOAc; 1:1). The solution was neutralized with Et3N
and the solvents were evaporated in vacuo. The light brown
syrupy mass was purified by flash chromatography using 3:1
n-hexane–EtOAc as eluent to afford pure compound 4
(3.15 g, 91%) as colorless glass. [a]2D5 +102 (c 1.0,
5
O
AcO
AcO
a
O
OAc
OMP
HO
3
HO
b
O
OH
14
OAc
AcO
15
OH
O
HO
HO
O
O
OMP
O
HO
c
OH
HO
O
OH
HO
2
CHCl3). IR (neat): 2360, 1598, 1373, 1226, 1075 cmꢁ1
;
Scheme 3. Synthesis of trisaccharide 2 using bis-glycosylation approach.
Reagents and conditions: (a) (i) trimethyl orthoacetate, CSA, CH3CN, rt,
1H NMR (300 MHz, CDCl3) d: 6.93 (d, 2H, J 9.0 Hz,
C6H4OCH3), 6.77 (d, 2H, J 9.0 Hz, C6H4OCH3), 4.73 (d,
1H, J 7.2 Hz, H-1), 4.29–4.26 (m, 1H, H-4), 4.10 (t, 1H, J
7.2 Hz, H-2), 4.08 (dd, 1H, J 4.5, 7.2 Hz, H-3), 3.86 (dd,
1H, J 2.1, 12.9 Hz, H-5a), 3.82 (dd, 1H, J 4.2, 12.9 Hz, H-
5b), 3.75 (s, 3H, C6H4OCH3), 2.94 (br s, 1H, OH), 1.54 (s,
3H, isopropylidene-CH3), 1.36 (s, 3H, isopropylidene-
CH3). 13C NMR (75 MHz, CDCl3) d: 148.8, 136.7, 118.7,
114.7 (ArC), 110.2 (isopropylidene-C), 101.5 (C-1), 77.9,
72.9, 72.4, 62.7 (C-5), 55.5 (C6H4OCH3), 27.8, 25.8
(2ꢂisopropylidene-C). HRMS Calcd for C15H24O6N
(M+NH4): 314.1604; found 314.1601.
˚
1 h; (ii) 80% AcOH, rt, 45 min; (b) NIS, H2SO4–silica, MS 4 A, CH2Cl2,
10 ꢀC, 1 h; (c) NaOMe, MeOH, rt, 3 h.
3. Conclusion
In conclusion, we have successfully prepared the tri-
saccharide of the steroid glycoside Sokodoside B using
conventional one-to-one approach and also through one-
pot sequential glycosylation using reactivity tuning strategy.
TEMPO-mediated phase-transfer oxidation was performed
efficiently at a late stage of the total synthesis. An analog
of the concerned trisaccharide has also been synthesized
in very good yield using a bis-glycosylation approach. The
choice of the p-methoxyphenyl group as reducing end
glycoside in all cases offers further glycoconjugate for-
mation for future biological evaluation of the synthesized
oligosaccharides.
4.1.2. p-Methoxyphenyl 2,3,4,6-tetra-O-acetyl-b-D-galac-
topyranosyl-(1/2)-3,4-O-isopropylidene-a-L-arabino-
pyranoside (6). A mixture of compound 4 (1 g, 3.4 mmol),
˚
compound 5 (2 g, 4.8 mmol), and MS 4 A (2 g) in dry
CH2Cl2 (25 mL) was stirred under nitrogen for 1 h. After
addition of NIS (1.4 g, 6.2 mmol), the mixture was cooled
to ꢁ40 ꢀC followed by addition of H2SO4–silica (30 mg)
and the mixture was allowed to stir at the same temperature
for 1 h when the acceptor 4 was completely consumed (Rf
0.3, n-hexane–EtOAc; 2:1). The mixture was filtered
through a pad of Celite and the filtrate was washed succes-
sively with Na2S2O3 (2ꢂ30 mL), NaHCO3 (2ꢂ30 mL),
and brine (30 mL). The organic layer was collected, dried
(Na2SO4), and concentrated in vacuo. The crude product
was purified by flash chromatography using 2:1 n-hexane–
EtOAc as eluent to afford the disaccharide 6 (1.9 g, 89%)
as colorless foam. [a]D25 +106 (c 1.1, CHCl3). IR (KBr):
1753, 1725, 1637, 1605, 1367, 1229, 1045 cmꢁ1; 1H NMR
4. Experimental
4.1. General methods
All reagents and solvents were dried prior to use according
to standard methods.16 Commercial reagents were used
without further purification unless otherwise stated. Analyt-
ical TLC was performed on silica gel 60-F254 (Merck or
Whatman) with detection by fluorescence and/or by charring
following immersion in a 10% ethanolic solution of sulfuric

S. Dasgupta et al. / Tetrahedron 63 (2007) 12310–12316
12313
(300 MHz, CDCl3) d: 6.94 (d, 2H, J 9.0 Hz, C6H4OCH3),
6.78 (d, 2H, J 9.0 Hz, C6H4OCH3), 5.32 (m, 1H, H-40),
5.20 (dd, 1H, J 8.1, 10.5 Hz, H-20), 5.04 (d, 1H, J 7.8 Hz,
H-1), 5.01 (dd, 1H, J 4.2, 10.5 Hz, H-30), 4.75 (d, 1H,
J 8.1 Hz, H-10), 4.32 (m, 1H, H-4), 4.11 (t, 1H, J 7.8 Hz,
H-2), 4.02–3.80 (m, 5H, H-5a, H-5b, H-50, H-6a0, H-6b0),
3.73 (s, 3H, C6H4OCH3), 3.67 (dd, 1H, J 3.3, 7.8 Hz,
H-3), 2.10, 2.07, 1.96, 1.88 (4s, 12H, 4ꢂCOCH3), 1.51 (s,
3H, isopropylidene-CH3), 1.23 (s, 3H, isopropylidene-
CH3). 13C NMR (75 MHz, CDCl3) d: 170.4, 170.2 (2),
169.7 (4ꢂCOCH3), 155.6, 151.2, 118.5, 114.9 (ArC),
102.9 (C-10), 100.4 (C-1), 83.2, 76.7, 72.2, 71.1 (2C),
69.5, 67.1, 62.4, 61.0, 55.9 (C6H4OCH3), 28.1, 26.0
(2ꢂisopropylidene-C), 21.2, 21.0, 20.9, 20.8 (4ꢂCOCH3).
HRMS Calcd for C29H42O15N (M+NH4): 644.2554; found
644.2551.
J 2.1, 8.1 Hz, H-3), 3.41, 2.98 (br s, H, OH), 2.10 (2),
2.08, 1.96, 1.89 (5s, 15H, 5ꢂCOCH3). 13C NMR
(75 MHz, CDCl3) d: 170.8 (2C), 170.6, 170.5, 169.8
(5ꢂCOCH3), 155.8, 150.6, 118.1 (2C), 115.0 (2C) (ArC),
102.2 (C-10), 100.4 (C-1), 79.8, 71.3, 71.1, 69.8, 69.6,
69.3, 67.2, 61.8, 61.2, 56.0 (C6H4OCH3), 21.4, 21.2, 21.0,
20.9 (2C) (5ꢂCOCH3). HRMS Calcd for C28H40O16N
(M+NH4): 646.2347; found 646.2345.
4.1.5. p-Tolyl 2,3,4-tri-O-acetyl-6-O-tert-butyldimethyl-
silyl-1-thio-b-D-galactopyranoside (10). To a solution of
compound 9 (1.5 g, 5.2 mmol) in dry pyridine (20 mL)
was added TBDMS-Cl (1.1 g, 6.8 mmol) and the solution
was allowed to stir for 4 h at room temperature. After that,
Ac2O (5 mL) was added and the solution was stirred for an
additional 2 h. The solvents were evaporated in vacuo and
co-evaporated with toluene to remove traces of pyridine.
The residue was purified by flash chromatography using
n-hexane–EtOAc (5:1) to afford compound 10 (2.2 g,
81%) as colorless glass. [a]2D5 +68 (c 1.1, CHCl3). IR
4.1.3. p-Methoxyphenyl 2,3,4,6-tetra-O-acetyl-b-D-galac-
topyranosyl-(1/2)-a-L-arabinopyranoside (7). A solu-
tion of compound 6 (1.8 g, 5.4 mmol) in AcOH–H2O (9:1,
20 mL) was stirred at 80 ꢀC for 2 h when the starting mate-
rial was completely converted to a slower moving compo-
nent (TLC). The solvents were evaporated, co-evaporated
with toluene, and the crude product was purified by flash
chromatography using n-hexane–EtOAc (1:1) as eluent to
afford pure compound 7 (1.6 g, 96%) as white amorphous
powder. [a]2D5 +98 (c 1.0, CHCl3). IR (KBr): 2933, 2365,
(neat): 1753, 1375, 1232, 1067, 778 cmꢁ1 1H NMR
;
(300 MHz, CDCl3) d: 7.38 (d, 2H, SC6H4CH3), 7.10 (d,
2H, SC6H4CH3), 5.46 (d, 1H, J 3.0 Hz, H-4), 5.20 (t, 1H,
J 9.9 Hz, H-2), 5.03 (dd, 1H, J 3.0, 9.9 Hz, H-3), 4.64 (d,
1H, J 9.9 Hz, H-1), 3.71 (m, 2H, H-6a, H-6b), 3.58 (m,
1H, H-5), 2.31 (s, 3H, SC6H4CH3), 2.08, 2.06, 1.84 (3s,
9H, 3ꢂCOCH3), 0.84 [s, 9H, C(CH3)3], ꢁ0.21, ꢁ0.22 [2s,
6H, Si(CH3)2C(CH3)3]. 13C NMR (75 MHz, CDCl3) d:
169.0, 168.9, 168.3 (3ꢂCOCH3), 137.2, 132.4 (2C),
129.04 (2C), 128.7 (ArC), 86.2 (C-1), 76.6, 71.8, 67.1,
66.8, 60.4 (C-6), 25.3 (3) [C(CH3)3], 20.6, 20.2, 20.0
(3ꢂCOCH3), 17.6 [C(CH3)3], ꢁ5.6, ꢁ6.0 [Si(CH3)2].
HRMS Calcd for C25H42O8NSSi (M+NH4): 544.2400;
found 544.2402.
1
1753, 1594, 1375, 1224, 1047 cmꢁ1; H NMR (300 MHz,
CDCl3) d: 6.98 (d, 2H, J 9.0 Hz, C6H4OCH3), 6.78 (d, 2H,
J 9.0 Hz, C6H4OCH3), 5.44 (m, 1H, H-40), 5.17 (dd, 1H, J
8.1, 9.6 Hz, H-20), 5.04 (dd, 1H, J 3.3, 9.6 Hz, H-30), 5.02
(d, 1H, J 7.8 Hz, H-1), 4.82 (d, 1H, J 8.1 Hz, H-10), 4.13–
3.86 (m, 5H, H-50, H-5a, H-5b, H-6a0, H-6b0), 3.82–3.75
(m, 2H, H-2, H-4), 3.74 (s, 3H, C6H4OCH3), 3.58 (dd, 1H,
J 3.3, 7.8 Hz, H-3), 3.41 (br s, 1H, OH), 3.24 (br s, 1H,
OH), 2.12, 2.07, 1.98, 1.90 (4s, 12H, 4ꢂCOCH3). 13C
NMR (75 MHz, CDCl3) d: 170.0, 169.9 (2C), 169.7
(4ꢂCOCH3), 155.2, 150.4, 117.7, 114.5 (ArC), 101.8 (C-
10), 100.0 (C-1), 79.7, 77.2, 70.9, 70.6 (2C), 69.3, 66.9,
66.6, 63.4, 60.6, 55.4 (C6H4OCH3), 20.7, 20.6 (2C), 20.5
(4ꢂCOCH3). HRMS Calcd for C26H38O15N (M+NH4):
604.2241; found 604.2243.
4.1.6. p-Methoxyphenyl 2,3,4-tri-O-acetyl-6-O-tert-butyl-
dimethylsilyl-b-D-galactopyranosyl-(1/3)-4-O-acetyl-
2-O-(2,3,4,6-tetra-O-acetyl-b-D-galactopyranosyl)-a-L-
arabinopyranoside (11). A mixture of compound 8 (1.3 g,
˚
2.1 mmol), compound 10 (1.4 g, 2.7 mmol), and MS 4 A
(2 g) in dry CH2Cl2 (25 mL) was stirred under nitrogen for
1 h. NIS (800 mg, 3.5 mmol) was added and the mixture
was cooled to ꢁ40 ꢀC followed by addition of H2SO4–silica
(20 mg), and the mixture was allowed stir at the same
temperature for 1 h when all acceptor disaccharide 8 was
consumed (Rf 0.4, n-hexane–EtOAc; 1:1). 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). The organic layer
was separated, dried (Na2SO4), and concentrated. The crude
product thus obtained was purified by flash chromatography
using n-hexane–EtOAc (2:1) to get the pure trisaccharide 11
(1.8 g, 83%) as white foam. [a]2D5 +91 (c 1.0, CHCl3). IR
4.1.4. p-Methoxyphenyl 2,3,4,6-tetra-O-acetyl-b-D-galac-
topyranosyl-(1/2)-4-O-acetyl-a-L-arabinopyranoside
(8). To a solution of compound 7 (1.5 g, 2.6 mmol) in dry
CH3CN (20 mL) were added trimethyl orthoacetate
(0.5 mL, 3.9 mmol) and CSA (15 mg), and the solution
was stirred at room temperature for 1 h. Then the solution
was neutralized with Et3N and the solvents were evaporated
in vacuo. The residue was dissolved in AcOH (80% aq) and
stirred at room temperature for 45 min. Solvents were evap-
orated and co-evaporated with toluene and the resulting
crude product was purified by flash chromatography using
n-hexane–EtOAc (2:1) to furnish the disaccharide acceptor
8 (1.4 g, 85%) as white foam. [a]2D5 +101 (c 1.1, CHCl3).
IR (KBr): 2941, 2372, 1760, 1603, 1383, 1231,
(KBr): 1745, 1387, 1225, 1076, 768 cmꢁ1 1H NMR
;
(300 MHz, CDCl3) d: 6.93 (d, 2H, J 9.0 Hz, C6H4OCH3),
6.80 (d, 2H, J 9.0 Hz, C6H4OCH3), 5.43 (d, 1H, J 3.0 Hz,
H-40), 5.32 (d, 1H, J 3.3 Hz, H-400), 5.23 (d, 1H, J 3.3 Hz, H-
4), 5.15 (t, 2H, J 9.0 Hz, H-20, H-200), 5.11–5.03 (m, 3H, H-1,
H-30, H-300), 4.76 (d, 1H, J 7.8 Hz, H-10), 4.65 (d, 1H, J
7.8 Hz, H-100), 4.16 (m, 1H, H-3), 3.98 (m, 2H, H-6a0,
H-6a00), 3.86–3.74 (m, 3H, H-2, H-5a, H-6b0), 3.79 (s, 3H,
C6H4OCH3), 3.72–3.55 (m, 3H, H-50, H-500, H-6b00), 3.48
(dd, 1H, J 3.3, 11.4 Hz, H-5b), 2.19, 2.15, 2.11, 2.03, 2.02,
1
1057 cmꢁ1; H NMR (300 MHz, CDCl3) d: 6.95 (d, 2H, J
9.0 Hz, C6H4OCH3), 6.80 (d, 2H, J 9.0 Hz, C6H4OCH3),
5.34 (m, 1H, H-40), 5.19 (dd, 1H, J 8.1, 10.5 Hz, H-20),
5.08–4.96 (m, 3H, H-1, H-30, H-4), 4.81 (d, 1H, J 8.1 Hz,
H-10), 4.03–3.85 (m, 5H, H-50, H-5a, H-5b, H-6a0, H-6b0),
3.79 (m, 1H, H-2), 3.73 (s, 3H, C6H4OCH3), 3.59 (dd, 1H,

12314
S. Dasgupta et al. / Tetrahedron 63 (2007) 12310–12316
1.98, 1.96, 1.94 (8s, 24H, 8ꢂCOCH3), 0.85 [s, 9H, C(CH3)3],
ꢁ0.11, ꢁ0.12 [2s, 6H, Si(CH3)2C(CH3)3]. 13C NMR (75 MHz,
CDCl3) d: 170.1 (2C), 170.0 (2C), 169.4 (2C), 168.9, 168.8
(8ꢂCOCH3), 155.1, 149.8, 117.9 (2C), 114.5 (2C) (ArC),
100.7 (C-10), 100.3 (C-100), 96.1 (C-1), 78.6, 76.3, 75.7, 73.2,
70.9, 69.4, 68.7, 67.3, 66.8, 66.3, 66.0, 60.2, 60.00, 59.2,
55.3 (C6H4OCH3), 25.7 (3) [C(CH3)3], 20.9 (2C), 20.7, 20.6
(2C), 20.5 (2C), 20.4 (8ꢂCOCH3), 18.1 [C(CH3)3], ꢁ5.6,
ꢁ5.7 [Si(CH3)2]. HRMS Calcd for C46H70O24NSi (M+NH4):
1048.4057; found 1048.4055.
conversion. The mixture was diluted with saturated
NaH2PO4 (45 mL) and the product was extracted with
EtOAc (3ꢂ30 mL). The combined organic 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 13
(610 mg, 75%) as light yellow gel. [a]2D5 +86 (c 1.1,
CHCl3). IR (neat): 2368, 1759, 1603, 1387, 1232, 1049,
1
738 cmꢁ1; H NMR (300 MHz, CDCl3) d: 6.95 (d, 2H, J
9.0 Hz, C6H4OCH3), 6.79 (d, 2H, J 9.0 Hz, C6H4OCH3),
5.40 (d, 1H, J 3.0 Hz, H-40), 5.34 (d, 2H, J 3.3 Hz, H-4, H-
400), 5.32–5.19 (m, 3H, H-1, H-20, H-200), 5.06 (m, 2H, J
2.1, 9.3 Hz, H-30, H-300), 4.91 (d, 1H, J 7.8 Hz, H-10), 4.85
(d, 1H, J 7.8 Hz, H-100), 4.38 (m, 1H, H-3), 4.09–4.00 (m,
5H, H-2, H-50, H-500, H-6a0, H-6a00), 3.86 (m, 1H, H-5a),
3.75 (s, 3H, C6H4OCH3), 3.55 (m, 1H, H-5b), 2.14, 2.13,
2.12, 2.10, 2.03, 2.01, 1.98, 1.94 (8s, 24H, 8ꢂCOCH3).
13C NMR (75 MHz, CDCl3) d: 170.9 (COOH), 170.4,
170.0, 169.7 (2C), 169.0 (2C), 169.1, 168.9 (8ꢂCOCH3),
155.0, 150.1, 117.8 (2C), 114.5 (2C) (ArC), 100.2 (C-10),
100.0 (C-100), 97.7 (C-1), 78.1, 76.6, 76.5, 75.8, 74.7, 73.6,
73.1, 70.9, 68.7, 68.5, 67.0, 66.4, 62.5, 55.4 (C6H4OCH3),
20.7 (2C), 20.6 (2C), 20.4 (2C), 20.2 (2C) (8ꢂCOCH3).
HRMS Calcd for C40H50O25Na (M+Na): 953.2539; found
953.2541.
4.1.7. p-Methoxyphenyl 2,3,4-tri-O-acetyl-b-D-galacto-
pyranosyl-(1/3)-4-O-acetyl-2-O-(2,3,4,6-tetra-O-acetyl-
b-D-galactopyranosyl)-a-L-arabinopyranoside (12). To a
stirred solution of compound 11 (1.5 g, 1.45 mmol) in dry
THF (20 mL) at 0 ꢀC was added AcOH (93 mL, 1.6 mmol)
followed by Bu4NF (1 N in THF, 7.4 mL) and the solution
was allowed to stir at room temperature for 12 h when the
starting material was completely converted to a slower mov-
ing spot (Rf 0.1, n-hexane–EtOAc; 1:2). The solvents were
evaporated 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
12 (1.0 g, 78%). [a]2D5 +107 (c 1.0, CHCl3). IR (neat): 2939,
2373, 1758, 1605, 1386, 1237, 1053 cmꢁ1 1H NMR
;
(300 MHz, CDCl3) d: 6.96 (d, 2H, J 9.0 Hz, C6H4OCH3),
6.81 (d, 2H, J 9.0 Hz, C6H4OCH3), 5.43 (d, 1H, J 3.0 Hz,
H-40), 5.36 (d, 1H, J 3.3 Hz, H-400), 5.26 (d, 1H, J
3.3 Hz, H-4), 5.23–5.11 (m, 2H, H-20, H-200), 5.05 (dd, 1H,
J 2.1, 9.3 Hz, H-30), 5.03 (m, 2H, H-1, H-300), 4.95 (d,
1H, J 7.8 Hz, H-10), 4.67 (d, 1H, J 7.8 Hz, H-100), 4.29 (m,
1H, H-3), 4.09–3.91 (m, 5H, H-2, H-5a, H-6a0, H-6a00,
H-6b0), 3.76 (s, 3H, C6H4OCH3), 3.57–3.48 (m, 4H, H-50,
H-500, H-5b, H-6b00), 3.18 (br s, 1H, OH), 2.21, 2.20,
2.16, 2.11, 2.10, 2.03, 1.98, 1.96 (8s, 24H, 8ꢂCOCH3).
13C NMR (75 MHz, CDCl3) d: 169.8, 169.7 (2C), 169.5
(2C), 169.1 (2C), 168.9 (8ꢂCOCH3), 154.8, 149.5, 118.2
(2C), 114.1 (2C) (ArC), 100.3 (C-10), 100.1 (C-100),
97.9 (C-1), 78.0, 76.8, 76.4, 75.7, 74.5, 73.8, 73.2, 70.7,
68.8, 68.4, 66.9, 66.4, 62.5, 60.6, 55.0 (C6H4OCH3),
20.9 (2C), 20.4 (2C), 20.2 (2C), 20.1 (2C) (8ꢂCOCH3).
HRMS Calcd for C40H56O24N (M+NH4): 934.3192; found
934.3193.
4.1.9. p-Methoxyphenyl b-D-galactopyranosyl-(1/3)-2-
O-(b-D-galactopyranosyl)-a-L-arabinopyranosiduronic
acid (1). To a solution of compound 13 (550 mg, mmol) in
MeOH (10 mL) was added NaOMe (0.5 M in MeOH,
1 mL) and the solution was allowed to stir at room temper-
ature for 6 h. Then the solution was neutralized with
DOWEX 50W H+ and filtered. The filtrate was evaporated
to afford pure compound 1 (305 mg, 87%) as amorphous
white solid. [a]2D5 +72 (c 1.0, H2O). IR (KBr): 2373, 1758,
1
1608, 1389, 1229, 1049, 741 cmꢁ1; H NMR (300 MHz,
D2O) d: 6.91 (d, 2H, J 9.0 Hz, C6H4OCH3), 6.79 (d, 2H, J
9.0 Hz, C6H4OCH3), 4.99 (d, 1H, J 6.9 Hz, H-1), 4.57 (d,
1H, J 7.8 Hz, H-10), 4.54 (d, 1H, J 7.8 Hz, H-100), 3.62 (s,
3H, C6H5CH3). 13C NMR (75 MHz, D2O) d: 170.8
(COOH), 153.3, 148.9, 116.4 (2C), 113.7 (2C) (ArC),
102.1 (C-10), 102.0 (C-100), 98.5 (C-1), 79.2, 76.2, 73.6,
72.7, 71.2, 70.9, 70.2, 69.1, 68.3, 67.0, 66.1, 63.7, 58.8,
54.5 (C6H4OCH3). HRMS Calcd for C24H34O17Na
(M+Na): 617.1694; found 617.1696.
4.1.8. p-Methoxyphenyl 2,3,4-tri-O-acetyl-b-D-galacto-
pyranosyl-(1/3)-4-O-acetyl-2-O-(2,3,4,6-tetra-O-acetyl-
b-D-galactopyranosyl)-a-L-arabinopyranosiduronic acid
(13). To a solution of compound 12 (800 mg, 0.9 mmol) in
CH2Cl2 (21 mL) and H2O (4.5 mL) were added aq NaBr
(1 M, 480 mL, 0.5 mmol), aq tetrabutylammonium bromide
(1 M, 960 mL, 1 mmol), TEMPO (45 mg, 0.3 mmol), and
saturated aq NaHCO3 (2.4 mL) at 0 ꢀC. To the resulting mix-
ture, aq NaOCl (2.9 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 conversion of the starting material to a faster mov-
ing spot, presumably the corresponding aldehyde derivative.
The mixture was neutralized with 1 N HCl (w250 mL) to
keep the pH of the mixture at 6–7. Then tert-butanol
(13 mL), 2-methyl-but-2-ene (2 M in THF, 27 mL), NaOCl2
(960 mg, 8.8 mmol), and NaH2PO4 (765 mg, 6.4 mmol)
were added and the mixture was allowed to stir at room
temperature for another 4 h when TLC showed complete
4.1.10. p-Methoxyphenyl 4-O-acetyl-a-L-arabinopyrano-
side (14). To a slurry of compound 3 (2 g, 7.8 mmol) in dry
CH3CN (25 mL) was added trimethyl orthoacetate (1.5 mL,
11.7 mmol) followed by CSA (20 mg) and the slurry was
allowed to stir at room temperature for 1 h when the starting
material was converted completely to a faster moving
component (Rf 0.7, n-hexane–EtOAc; 1:1). The solution
was neutralized with Et3N and the solvents were evaporated.
The residue was dissolved in 80% aq AcOH (30 mL) and
the solution was allowed to stir at room temperature for
45 min. After evaporating the solvents in vacuo and
co-evaporating with toluene, the residue was purified by
flash chromatography using 1:1–2:1 EtOAc–n-hexane to
afford pure compound 14 (2 g, 86%) as white foam. [a]D25
+49 (c 1.1, MeOH). IR (KBr): 2953, 2377, 1701, 1593,
1271, 1089, 1017, 719 cmꢁ1
;
1H NMR (300 MHz,
CDCl3+DMSO-d6) d: 7.02 (d, 2H, J 9.0 Hz, C6H4OCH3),

S. Dasgupta et al. / Tetrahedron 63 (2007) 12310–12316
12315
6.80 (d, 2H, J 9.0 Hz, C6H4OCH3), 5.13 (br s, 1H, OH),
4.93 (m, 1H, H-4), 4.76 (d, 1H, J 6.8 Hz, H-1), 4.60 (br
s, 1H, OH), 3.94 (d, 1H, J 13.2 Hz, H-5a), 3.85–3.78 (m,
2H, H-2, H-3), 3.76 (s, 3H, C6H4OCH3), 3.64 (d, 1H,
J 13.2 Hz, H-5b), 2.14 (s, 3H, COCH3). 13C NMR
(75 MHz, CDCl3+DMSO-d6) d: 170.4 (COCH3), 154.7,
150.7, 118.9 (2C), 114.0 (2C) (ArC), 102.1 (C-1), 70.9,
70.7, 70.0, 63.4 (C-5), 55.1 (C6H4OCH3), 20.4 (COCH3).
HRMS Calcd for C14H22O7N (M+NH4): 316.1396; found
316.1395.
100.0 (C-1), 79.1, 76.9, 75.5, 74.9, 73.4 (2C), 70.9, 70.4,
68.3, 67.9, 64.4, 60.6 (2C), 59.9, 55.4 (C6H4OCH3).
HRMS Calcd for C24H36O16Na (M+Na): 603.1901; found
603.1903.
Acknowledgements
S.D. is thankful to CSIR, New Delhi for providing fellow-
ship. Instrumentation facilities from SAIF, CDRI are grate-
fully acknowledged. The work is funded by Department of
Science and Technology, New Delhi, India by SERC Fast-
Track Grant SR/FTP/CS-110/2005.
4.1.11. p-Methoxyphenyl 2,3,4,6-tetra-O-acetyl-b-D-gal-
actopyranosyl-(1/3)-4-O-acetyl-2-O-(2,3,4,6-tetra-O-
acetyl-b-D-galactopyranosyl)-a-L-arabinopyranoside
(15). A mixture of compound 14 (1.0 g, 3.4 mmol), com-
˚
References and notes
pound 5 (3.8 g, 8.4 mmol), and MS 4 A (3 g) in dry
CH2Cl2 (40 mL) was stirred under nitrogen for 1 h. NIS
(2.5 mg, 10.9 mmol) was added and the mixture was cooled
to 10 ꢀC followed by addition of H2SO4–silica (30 mg), and
the mixture was allowed to stir at the same temperature for
1 h when all acceptor 14 was consumed (TLC). The mixture
was immediately filtered through a pad of Celite and the fil-
trate was washed successively with Na2S2O3 (2ꢂ30 mL),
NaHCO3 (2ꢂ30 mL), and brine (30 mL). The organic layer
was separated, dried (Na2SO4), and evaporated. The crude
product thus obtained was purified by flash chromatography
using n-hexane–EtOAc (1:1–1:2) to get the pure trisaccha-
ride 15 (2.7 g, 84%) as white foam. [a]2D5 +99 (c 1.0,
CHCl3). IR (KBr): 2944, 2372, 1771, 1587, 1386, 1253,
1. Yeung, B. K. S.; Hamann, M. T.; Scheuer, P. J.; Kellyborges, M.
Tetrahedron 1994, 50, 12593–12598.
2. Ryu, G.; Choi, B. W.; Lee, B. H.; Hwang, K. H.; Lee, U. C.;
Jeong, D. S.; Lee, N. H. Tetrahedron 1999, 55, 13171–
13178.
3. Dai, H. F.; Edrada, R. A.; Ebel, R.; Nimtz, M.; Wray, V.;
Proksch, P. J. Nat. Prod. 2005, 68, 1231–1237.
4. Sandler, J. S.; Forsburg, S. L.; Faulkner, D. J. Tetrahedron
2005, 61, 1199–1206 and references therein.
5. Antonov, A. S.; Afiyatullov, S. S.; Kalinovsky, A. I.;
Ponomarenko, L. P.; Dmitrenok, P. S.; Aminin, D. L.;
Agafonova, I. G.; Stonik, V. A. J. Nat. Prod. 2003, 66, 1082–
1088.
1
1051 cmꢁ1; H NMR (300 MHz, CDCl3) d: 6.97 (d, 2H,
J 9.0 Hz, C6H4OCH3), 6.83 (d, 2H, J 9.0 Hz, C6H4OCH3),
5.39 (br d, 2H, J 3.0 Hz, H-40, H-400), 5.30 (br d, 1H,
J 3.0 Hz, H-4), 5.27 (m, 2H, H-1, H-30), 5.08 (t, 1H,
J 10.2 Hz, H-20), 5.07 (t, 1H, J 10.2 Hz, H-200), 5.00 (dd,
1H, J 3.0, 10.2 Hz, H-300), 4.78 (d, 1H, J 8.1 Hz, H-10),
4.67 (d, 1H, J 8.1 Hz, H-100), 4.22–3.85 (m, 9H, H-2, H-3,
H-5a, H-50, H-500, H-6a0, H-6a00, H-6b0, H-6b00), 3.76 (s, 3H,
C6H4OCH3), 3.49 (dd, 1H, J 3.3, 11.4 Hz, H-5b), 2.17,
2.15, 2.09, 2.07, 2.05, 2.00, 1.98, 1.97, 1.93 (9s, 27H,
9ꢂCOCH3). 13C NMR (75 MHz, CDCl3) d: 170.2 (2C),
170.0 (2C), 169.8 (3C), 169.7, 169.6 (2C), 169.1
(9ꢂCOCH3), 155.1, 149.7, 118.0 (2C), 114.5 (2C) (ArC),
100.7 (C-10 or C-100), 100.6 (C-10 or C-100), 98.1 (C-1),
76.1, 74.6, 70.9, 70.7 (2C), 68.9, 68.7 (2C), 67.0, 66.7
(2C), 61.2, 60.8, 55.5 (C6H4OCH3), 20.8 (2C), 20.7 (3C),
20.6 (2C), 20.5 (2C) (9ꢂCOCH3). HRMS Calcd for
C42H58O25N (M+NH4): 976.3298; found 976.3300.
6. Campagnuolo, C.; Fattorusso, E.; Taglialatela-Scafati, O.
Tetrahedron 2001, 57, 4049–4055.
7. Okada, Y.; Matsunaga, S.; van Soest, R. W. M.; Fusetani, N.
J. Org. Chem. 2006, 71, 4884–4888.
8. Chauvin, A.-L.; Nepogodiev, S. A.; Field, R. A. J. Org. Chem.
2005, 70, 960–966.
ꢀ
ꢀ ꢀ
9. Liptak, A.; Imre, J.; Nanasi, P. Carbohydr. Res. 1981, 92,
154–156.
10. For the use of H2SO4–silica in carbohydrate synthesis see: (a)
Mukhopadhyay, B. Tetrahedron Lett. 2006, 47, 4337–4341; (b)
Rajput, V. K.; Mukhopadhyay, B. Tetrahedron Lett. 2006, 47,
5939–5941; (c) Rajput, V. K.; Roy, B.; Mukhopadhyay, B.
Tetrahedron Lett. 2006, 47, 6987–6991; (d) Dasgupta, S.;
Roy, B.; Mukhopadhyay, B. Carbohydr. Res. 2006, 341,
2708–2713; (e) Roy, B.; Mukhopadhyay, B. Tetrahedron Lett.
2007, 48, 3783–3787; For the use of H2SO4–silica in
organic synthesis, see: (f) Zolfigol, M. A.; Bamoniri, A.
Synlett 2002, 1621–1623; (g) Zolfigol, M. A. Tetrahedron
2001, 57, 9509–9511; (h) Zolfigol, M. A.; Shirini, F.;
Ghorbani Choghamarani, A.; Mohammadpoor-Baltork, I.
Green Chem. 2002, 4, 562–564; (i) Shirini, F.; Zolfigol,
M. A.; Mohammadi, K. Bull. Korean Chem. Soc. 2004, 25,
325–327; For similar type of glycosylations using HClO4–
silica, see: (j) Mukhopadhyay, B.; Maurer, S. V.; Rudolph,
N.; van Well, R.; Russell, D. A.; Field, R. A. J. Org. Chem.
2005, 70, 9059–9062; (k) Mukhopadhya, B.; Collet, B.;
Field, R. A. Tetrahedron Lett. 2005, 46, 5923–5925; (l)
Mukhopadhyay, B.; Field, R. A. Carbohydr. Res. 2006, 341,
1697–1701; (m) Du, Y.; Wei, G.; Cheng, S.; Hua, Y.;
Linhardt, R. J. Tetrahedron Lett. 2006, 47, 307–310.
4.1.12. p-Methoxyphenyl b-D-galactopyranosyl-(1/3)-
2-O-(b-D-galactopyranosyl)-a-L-arabinopyranoside (2).
To a solution of compound 15 (1 g, 1.0 mmol) in MeOH
(20 mL) was added NaOMe (0.5 M in MeOH, 2 mL) and
the solution was stirred at room temperature for 6 h. After
neutralizing the solution with DOWEX 50W H+, the mixture
was filtered and the filtrate was evaporated in vacuo to afford
pure compound 2 (540 mg, 89%) as white powder. [a]2D5 +38
1
(c 0.8, H2O). IR (KBr): 2367, 1693, 1203, 778 cmꢁ1; H
NMR (300 MHz, D2O) d: 6.95 (d, 2H, J 9.0 Hz,
C6H4OCH3), 6.83 (d, 2H, J 9.0 Hz, C6H4OCH3), 4.97 (d,
1H, J 7.2 Hz, H-1), 4.61 (d, 1H, J 7.8 Hz, H-10), 4.57 (d,
1H, J 7.8 Hz, H-100), 3.69 (s, 3H, C6H5CH3). 13C NMR
(100 MHz, DMSO-d6) d: 154.4, 150.8, 117.9 (2C), 114.5
(2C) (ArC), 104.1 (C-10 or C-100), 103.9 (C-10 or C-100),
11. Gent, P. A.; Gigg, R. J. Chem. Soc., Perkin Trans. 1 1974,
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12. Limberg, G.; Thiem, J. Carbohydr. Res. 1995, 275, 107–115.

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S. Dasgupta et al. / Tetrahedron 63 (2007) 12310–12316
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