NIS/H2SO4-Silica: a mild and efficient reagent system for the hydrolysis of thioglycosides

Article abstract of DOI:10.1016/j.carres.2006.09.005

Chemoselective hydrolysis of a variety of thioglycosides in the presence of a wide range of protecting groups has been achieved by using N-iodosuccinimide and H₂SO₄ immobilized on silica in good to excellent yields.

Full text of DOI:10.1016/j.carres.2006.09.005

Carbohydrate Research 341 (2006) 2708–2713
Note
NIS/H2SO4–Silica: a mild and efficient reagent system
for the hydrolysis of thioglycosidesI
Somnath Dasgupta, Bimalendu Roy and Balaram Mukhopadhyay*
Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226 001, India
Received 16 June 2006; received in revised form 26 August 2006; accepted 4 September 2006
Available online 2 October 2006
Dedicated to Professor David A. Russell, University of East Anglia, Norwich, UK
Abstract—Chemoselective hydrolysis of a variety of thioglycosides in the presence of a wide range of protecting groups has been
achieved by using N-iodosuccinimide and H2SO4 immobilized on silica in good to excellent yields.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Thioglycoside; Hydrolysis; H2SO4–Silica
Thioglycosides are perhaps the most widely used
building blocks in synthetic carbohydrate chemistry ow-
ing to their stability under various reaction conditions
and the ease of preparation.1–3 Compatibility of thiogly-
cosides with many protecting groups allows the protect-
ing group manipulations that are required during
oligosaccharide synthesis.3,4 Hence they are often used
as glycosyl donors for the synthesis of oligosaccharides
and glycoconjugates.5 Furthermore, they can be used
in chemoselective glycosylation strategies due to their
inertness towards activating agents other than those tar-
geting anomeric thio functionality.6
Apart from the obvious requirement of stability to-
wards the reaction conditions employed, it is desirable
that the anomeric protecting group be removed to afford
the respective hemiacetal or that it can be transformed
into other glycosyl donors for further glycosylation.
Suitably protected hemiacetals are also useful substrates
for Wittig or Horner–Emmons reactions in the synthesis
of enantiomerically pure natural products. Therefore,
hydrolysis of thioglycosides to the corresponding hemi-
acetals has become an important requirement in syn-
thetic carbohydrate chemistry.
Considering the excellent glycosylation properties of
thioglycosides under mild conditions, one would antici-
pate that thioglycosides should be easily hydrolysable by
using standard thioglycoside activation procedure in the
presence of H2O as acceptor. Unfortunately this conver-
sion is not so trivial. Numerous procedures have been
reported in the literature for the hydrolysis of thioglyco-
sides including thiophilic heavy metal salts, NBS or NIS
in wet acetone,7–9 AgNO3 in wet acetone,10,11 NBS in
combination with aqueous NaHCO3 or aqueous CaCO3
in THF,5 Bu4NIO4 and triflic acid,12 Bu4NIO4
with TrB(C6H5)4,12 Bu4NIO4/HClO4,12 NBS/HCl,13
(NH4)6Mo7O24Æ4H2O–H2O2 with HClO4/NH4Br,14
V2O5–H2O2/NH4Br,15 NIS/TfOH,16 Chloramin-T17
and, very recently, NIS/TFA.18 Despite their potential
use under specific reaction conditions, many of these
methods suffer from use of toxic materials, harsh reac-
tion conditions, low yields and incompatibility with var-
ious protecting groups. Therefore, a mild procedure for
the hydrolysis of thioglycosides, compatible with a range
of protecting groups, would be useful. Noting the recent
reports on the use of H2SO4–silica in various organic
reactions,19 we felt that sulfuric acid immobilized on sil-
ica (H2SO4–silica) could act as a good protic acid source
under mild and safer conditions than other silica-
supported reagents such as HClO4–silica.20 This com-
munication describes the successful use of H2SO4–silica
q CDRI Communication No. 7044.
*
Corresponding author. Fax: +91 522 2623405; e-mail: sugarnet73@
hotmail.com
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.09.005

S. Dasgupta et al. / Carbohydrate Research 341 (2006) 2708–2713
2709
application of H2SO4–silica as
a
promoter for
Ph
O
Ph
O
NIS/H2SO4-silica
O
O
O
O
OH
OBn
STol
various trichloroacetimidate donors are underway in
our laboratory and the results will be reported in due
course.
BnO
BnO
CH2Cl2-H2O 10:1
0 oC
OBn
93%
Scheme 1. NIS/H2SO4-promoted hydrolysis of thioglycosides.
in conjunction with NIS for the hydrolysis of
thioglycosides in good to excellent yields (75–95%) with-
out affecting a diverse range of protecting groups
(Scheme 1).
1. Experimental
1.1. General methods
Our initial experiment with p-tolyl 2,3-di-O-benzyl-
4,6-O-benzylidene-1-thio-b-D-glucopyranoside (1) using
1.1 equiv of NIS and H2SO4–silica in wet CH2Cl2 at
0 ꢁC afforded the corresponding hemiacetal (2) in 93%
yield after chromatographic purification (Table 1, entry
1). No deprotection of the acid labile benzylidene pro-
tecting group was observed on TLC, thus affirming the
mildness of the reaction condition. Successful execution
of this reaction prompted us to evaluate its utility on a
diverse range of carbohydrate derivatives.
Commercial reagents were used without further purifica-
tion unless otherwise stated. Analytical TLC was per-
formed on silica gel 60-F254 (Merck) with detection by
fluorescence and/or by charring following immersion
in a 10% ethanolic solution of sulfuric acid. Flash chro-
matography was performed with Silica Gel 60 (Fluka).
1H NMR and 13C NMR spectra were recorded on a
Varian Unity plus spectrometer at 300 and 75 MHz,
respectively, using (CH3)4Si as internal standards.
Table 1 represents the experimental results of the
NIS/H2SO4–silica-mediated hydrolysis of a diverse set
of thioglycosides. These results clearly show that the
reaction is effective irrespective of the substitution pat-
tern and the nature of the protecting groups in the
starting thioglycoside. Most of the reactions went to
completion within 30 min at 0 ꢁC as monitored by
TLC. It is worth noting that both alkyl and aryl thio-
glycosides are equally reactive under these conditions
and the reaction is compatible with acid labile benzyl-
idene, isopropylidene, p-methoxybenzyl (PMB), chloro-
acetyl (CA) and silyl ether groups as well as the
phthaloyl protecting group. Moreover, the nature of
the parent glycoside (gluco-, galacto-, manno- or
rhamnopyranosyl or arabinofuranosyl or di- and trisac-
charide) appears to have no influence on the outcome
of the hydrolysis. A scale-up reaction using 20 mmol
of compound 1 showed no considerable change in the
yield, proving the applicability of the reagent system
in large-scale preparations.
To justify the utility of the current protocol, the
hemiacetal 4 obtained from the per-O-acetylated p-tolyl
thioglucoside (3) was converted to the trichloroacetimi-
date derivative using trichloroacetonitrile and DBU.
The per-O-acetylated glucosyltrichloroacetimidate thus
obtained was glycosylated with ethyl 2,3-O-isopropylid-
ene-1-thio-L-rhamnopyranoside in the presence of
H2SO4–silica to obtain a novel disaccharide thioglyco-
side that can act as a glycosyl donor for further glycosyl-
ation (Scheme 2).
1.2. Preparation of H2SO4 immobilized on silica
To a slurry of silica gel (5 g, mesh 60–120, Spectrochem,
India) in diethyl ether (20 mL) was added commercially
available concd H2SO4 (250 lL) and the solvent was
evaporated under vacuum. The free flowing silica thus
obtained was heated at 110 ꢁC for 2 h and kept in a des-
iccator over P2O5 for further use.
1.3. General procedure for the hydrolysis of thioglycosides
To a stirred mixture of the thioglycoside (1 mmol) in
CH2Cl2–H2O (10:1, 5 mL) was added NIS (1.2 mmol)
followed by H2SO4–silica (100 mg) at 0 ꢁC. The mixture
was allowed to stir at that temperature until TLC
showed complete conversion of the starting material
(Table 1). The mixture was diluted with CH2Cl2 and
was washed successively with aq Na2S2O3, aq NaHCO3
and brine. The organic layer was collected, dried
(Na2SO4) and evaporated. The crude residue was puri-
fied by column chromatography using an appropriate
mixture of n-hexane and EtOAc to afford a pure hydro-
lyzed product.
1.4. 2,3-Di-O-benzyl-4,6-O-benzylidene-D-glucopyranose
(2)
The reaction was quenched after 30 min. Column chro-
matography using n-hexane–EtOAc (3:1) yielded com-
pound 2 (417 mg, 93%) as colourless oil. 1H NMR
(CDCl3) d: 7.55–7.28 (m, 15H, aromatic protons), 5.60
(s, 1H, PhCH), 5.21 (d, 1H, J1,2 = 3.0 Hz, H-1), 5.00–
4.73 (4d, 4H, J = 11.4 Hz, 2 · CH2Ph), 4.06 (t, 1H,
In conclusion, we have introduced a new reagent sys-
tem for the hydrolysis of thioglycosides. A wide range
of commonly used protecting groups remain unaffected
under these conditions. Furthermore, we have demon-
strated the synthetic utility of the hydrolyzed product
in oligosaccharide synthesis. Further studies on the
J2,3 = J3,4 = 8.7 Hz, H-3), 3.78 (t, 1H, J3,4 = J4,5
8.7 Hz, H-4), 3.73–3.61 (m, 3H, H-2, H-6a, H-6b),
=

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S. Dasgupta et al. / Carbohydrate Research 341 (2006) 2708–2713
Table 1. Results of the hydrolysis of thioglycosides using NIS–H2SO4–silicaa
Entry
1
Starting material
Product
Time
(min)
Yield
(%)b
Ref.
(if known)
Ph
Ph
O
O
O
O
30
93
O
O
OH
STol
BnO
BnO
OBn
OBn
1
2
OAc
O
OAc
O
AcO
AcO
OH
STol
2
3
4
5
6
30
30
30
30
30
90
87
91
78
89
21
14
8
AcO
AcO
OAc
OAc
3
4
OBz
O
OBz
O
BzO
BzO
BzO
BzO
STol
SEt
OH
OBz
OBz
5
6
OBn
O
OBn
O
BnO
BnO
BnO
BnO
OH
OBn
OBn
7
8
Ph
Ph
O
O
O
O
O
O
OH
STol
BzO
BzO
OBz
OBz
9
10
OBz
O
OBz
O
BzO
BzO
BzO
BzO
OH
STol
22
15
OBz
OBz
11
12
OBn
O
OBn
O
BnO
BnO
BnO
OH
7
8
SMe
30
30
86
75
BnO
OBn
13
OBn
14
OTBDPS
O
OTBDPS
O
AcO
AcO
AcO
AcO
STol
OH
AcO
AcO
15
16
OAc
O
OAc
O
AcO
AcO
AcO
AcO
9
10
11
30
45
30
90
88
95
17
AcO
AcO
OH
SPh
17
18
OAc
O
OAc
O
AcO
AcO
AcO
AcO
OH
SPh
NHPhTh
19
NHPhTh
20
OH
Me
O
STol
OBn
Me
O
OBn
17
OBn
21
BnO
OBn
22
BnO

S. Dasgupta et al. / Carbohydrate Research 341 (2006) 2708–2713
2711
Table 1 (continued)
Entry
Starting material
Product
Time
(min)
Yield
(%)b
Ref.
(if known)
OH
STol
Me
BnO
O
Me
BnO
O
12
30
93
BnO
OBn
BnO
OBn
24
23
STol
OH
Me
Me
O
O
PMBO
PMBO
13
14
15
30
30
45
90
86
82
O
O
O
O
26
25
STol
OH
Me
Me
O
O
BnO
BnO
CAO
CAO
OAc
OAc
28
27
OAc
O
OAc
O
AcO
AcO
AcO
AcO
OAc
O
OAc
O
O
O
AcO
17
17
OH
OH
STol
STol
AcO
AcO
AcO
AcO
AcO
29
30
OAc
OAc
O
O
AcO
AcO
AcO
AcO
OAc
O
OAc
O
16
45
85
AcO
AcO
O
O
AcO
AcO
OAc
OAc
31
32
OAc
O
OAc
O
AcO
AcO
AcO
AcO
OAc
O
OAc
O
AcO
AcO
17
45
82
23
O
O
OAc
OAc
O
AcO
AcO
AcO
AcO
O
O
O
OH
STol
AcO
AcO
33
34
OAc
OAc
a All compounds were characterized by NMR spectroscopy and mass spectrometry, data for the known compounds are in agreement with those
reported in the literature.
b Yields reported are those obtained after chromatographic purification.
SEt
Me
HO
O
O
O
SEt
OAc
O
OAc
O
OAc
O
36
Me
O
AcO
AcO
AcO
AcO
a, b
O
AcO
AcO
STol
c
O
AcO
OAc
37
O
O
CCl3
OAc
3
35
NH
Scheme 2. Reagents and conditions: (a) NIS/H2SO4–silica, CH2Cl2–H2O (10:1), 0 ꢁC; (b) CCl3CN, DBU, CH2Cl2; (c) H2SO4–silica, CH2Cl2, 0 ꢁC.

2712
S. Dasgupta et al. / Carbohydrate Research 341 (2006) 2708–2713
3.45 (m, 1H, H-5); 13C NMR d: 138.1, 137.3, 128.9,
128.5, 128.3, 128.2, 128.1, 128.0, 127.8, 127.7, 127.6,
126.0 (aromatic carbons), 101.2 (CHPh), 92.1 (C-1),
82.9, 79.3 (CH2Ph), 78.3, 75.7, 73.7, 68.6, 62.4. ESIMS:
m/z calcd for ½C27H28O6ꢀNH4þ: 466.2230. Found:
466.2232.
170.8, 170.1, 169.9 (3 · COCH3), 169.6, 167.8 (Phth
C@O), 134.7, 134.4, 131.3, 131.0, 123.9, 123.6 (aro-
matic carbons), 92.6 (C-1), 71.9, 70.6, 67.9, 62.1, 55.9
(C-2), 20.9, 20.7, 20.4 (3 · COCH3). ESIMS: m/z
þ
calcd for ½C20H21O10NꢀNH4
:
453.1509. Found:
453.1508.
1.8. 2,3,4-Tri-O-benzyl-L-rhamnopyranose (24)
1.5. 4,6-O-Benzylidene-2,3-di-O-benzoyl-D-glucopyranose
(10)
The reaction was quenched after 30 min. Column chro-
matography using n-hexane–EtOAc (3:1) yielded com-
pound 24 (404 mg, 93%) as colourless oil. 1H NMR
(CDCl3) d: 7.44–7.28 (m, 15H, aromatic protons), 5.20
(s, 1H, H-1), 5.03 (d, 1H, J = 11.4 Hz, CH2Ph), 4.85–
4.69 (m, 5H, CH2Ph), 4.00 (br d, 1H, J3,4 = 7.8 Hz, H-
3), 3.87 (m, 1H, H-2), 3.72 (t, 1H, J3,4 = J4,5 = 7.8 Hz,
H-4), 3.44 (m, 1H, H-5), 1.40 (d, 3H, J5,6 = 6.3 Hz, H-
6). 13C NMR d: 138.5, 138.3, 138.2, 128.5, 128.4,
128.2, 128.1, 127.9, 127.8, 127.7, 127.5, 127.4 (aromatic
carbons), 92.7 (C-1), 82.9, 80.4, 75.3, 75.2, 72.7, 72.1,
The reaction was quenched after 30 min. Column chro-
matography using n-hexane–EtOAc (3:1) yielded com-
1
pound 10 (372 mg, 78%) as foam. H NMR (CDCl3)
d: 8.12–7.28 (m, 15H, aromatic protons), 6.14 (t, 1H,
J3,4 = J4,5 = 9.3 Hz, H-4), 5.87 (t, 1H, J2,3 = J3,4
=
9.3 Hz, H-3), 5.70 (br s, 1H, H-1), 5.57 (s, 1H, CHPh),
5.31 (dd, 1H, J1,2 = 4.8 Hz, J2,3 = 9.3 Hz, H-2), 4.39
(m, 1H, H-6a), 3.97–3.85 (m, 3H, H-4, H-5, H-6b),
3.45 (br s, 1H, OH); 13C NMR d: 165.7, 165.6
(2 · COPh), 136.8, 136.6, 133.9, 133.4, 133.0, 128.8,
128.7, 128.6, 128.2, 128.0, 126.1, 126.0 (aromatic
carbons), 101.6 (CHPh), 91.2 (C-1), 74.8, 72.7, 69.þ8,
68.0,
17.8
(C-6).
ESIMS:
m/z
calcd
for
½C27H30O5ꢀNH4þ: 452.2437. Found: 452.2436.
66.8, 63.2. ESIMS: m/z calcd for ½C27H24O8ꢀNH4
:
1.9. 2,3-O-Isopropylidene-4-O-p-methoxylbenzyl-L-
rhamnopyranose (26)
494.1815. Found: 494.1813.
The reaction was quenched after 30 min. Column chro-
1.6. 2,3,4-Tri-O-acetyl-6-O-tert-butyldiphenylsilyl-D-
galactopyranose (16)
matography using n-hexane–EtOAc (3:1) yielded com-
1
pound 26 (292 mg, 90%) as foam. H NMR (CDCl3)
d: 7.29–7.27 (2d, 4H, aromatic protons), 5.33 (s, 1H,
H-1), 4.82, 4.56 (2d, J = 11.4 Hz, CH2–C6H4–OCH3),
The reaction was quenched after 30 min. Column chro-
matography using n-hexane–EtOAc (3:1) yielded com-
pound 16 (408 mg, 75%) as colourless oil. 1H NMR
(CDCl3) d: 7.68–7.35 (m, 10H, aromatic carbons), 6.30
4.30 (t, 1H, J3,4 = J4,5 = 7.8 Hz, H-4), 4.16 (d, J2,3
=
3.6 Hz, H-2), 3.94 (dd, 1H, J2,3 = 3.6 Hz, J3,4 = 7.8 Hz,
H-3), 3.80 (s, 3H, C6H4–OCH3), 3.26 (dq, 1H,
J4,5 = 7.8 Hz, J5,6 = 6.3 Hz, H-5), 1.52, 1.38 (2s, 6H,
isopropylidene–CH3), 1.25 (d, 1H, J5,6 = 6.3 Hz, H-6).
13C NMR d: 159.1, 130.2, 129.5, 113.6 (aromatic
carbons), 109.0, 91.7 (C-1), 80.2, 78.4, 76.5, 72.5, 64.8,
(d, 1H, J1,2 = 3.0 Hz, H-1), 5.28 (dd, 1H, J1,2
=
3.0 Hz, J2,3 = 7.8 Hz, H-2), 5.25 (m, 1H, H-4), 5.20
(dd, 1H, J = 2.7, 7.8 Hz, H-3), 3.91 (m, 1H, H-5), 3.72
(m, 2H, H-6a, H-6b), 3.16 (br s, 1H, OH), 2.15, 2.08,
1.93 (3s, 9H, 3 · COCH3), 1.06 (s, 9H, C(CH3)3). 13C
NMR d: 171.4, 169.3, 169.2 (3 · COCH3), 135.5,
133.0, 129.6, 127.6 (aromatic carbons), 91.4 (C-1),
73.5, 72.3, 69.6, 67.8, 62.4, 26.6, 20.7, 20.6, 19.8
(3 · COCH3). ESIMS: m/z calcd for ½C28H36-
O9SiꢀNH4þ: 562.2472. Found: 562.2474.
55.1 (C6H4–OCH3), 29.6, 27.8 (isopropylidene–CH3),
þ
17.9 (C-6). ESIMS: m/z calcd for ½C17H24O6ꢀNH4
:
342.1917. Found: 342.1915.
1.10. 2-O-Acetyl-4-O-benzyl-3-O-chloroacetyl-L-rhamno-
pyranose (28)
1.7. 3,4,6-Tri-O-acetyl-2-deoxy-2-phthalimido-D-gluco-
pyranose (20)
The reaction was quenched after 30 min. Column chro-
matography using n-hexane–EtOAc (3:1) yielded com-
1
pound 28 (320 mg, 86%) as foam. H NMR (CDCl3) d:
The reaction was quenched after 45 min. Column
chromatography using n-hexane–EtOAc (3:1) yielded
compound 20 (540 mg, 88%) as colourless oil. 1H
NMR (CDCl3) d: 7.87–7.71 (m, 4H, aromatic protons),
5.83 (dd, 1H, J1,2 = 8.4 Hz, J2,3 = 9.3 Hz, H-2), 5.63 (d,
1H, J1,2 = 8.4 Hz, H-1), 5.17 (m, 2H, H-3, H-4), 4.33–
4.17 (m, 2H, H-6a, H-6b), 3.93 (m, 1H, H-5), 2.14,
2.05, 1.87 (3s, 9H, 3 · COCH3); 13C NMR d:
7.35–7.27 (m, 5H, aromatic protons), 5.38 (dd, 1H,
J2,3 = 3.3 Hz, J3,4 = 8.1 Hz, H-3), 5.24 (br d, 1H,
J2,3 = 3.3 Hz, H-2), 5.10 (s, 1H, H-1), 4.66 (s, 2H,
CH2Ph), 4.08 (m, 1H, H-5), 3.87 (d, 2H, OCOCH2Cl),
3.52 (t, 1H, J = 8.1 Hz, H-4), 2.10 (s, 3H, COCH3), 1.28
(d, 3H, J5,6 = 6.3 Hz, H-6); 13C NMR d: 170.9 (COCH3),
166.3 (COCH2Cl), 137.8, 128.3, 127.7 (aromatic carbons),
91.7 (C-1), 78.6, 74.9, 73.5, 70.6, 67.4, 40.5 (COCH2Cl),

S. Dasgupta et al. / Carbohydrate Research 341 (2006) 2708–2713
2713
20.8 (COCH3), 17.8 (C-6). ESIMS: m/z calcd for
Supplementary data
½C17H21O7ClꢀNH4þ: 390.1320. Found: 390.1315.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2006.09.005.
1.11. Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-b-D-glucopyr-
anosyl-(1!4)-2,3-O-isopropylidene-1-thio-a-L-rhamno-
pyranoside (37)
References
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side (1) (1.0 g, 2.2 mmol) was converted to the corre-
sponding hemiacetal 2 using the general procedure. To
a solution of compound 2 (700 mg, 2 mmol) in CH2Cl2
(10 mL) was added CCl3CN (600 lL, 6 mmol) followed
by DBU (catalytic amount). After 30 min when the
starting material was completely converted to a faster
moving spot (TLC), the solution was diluted with
CH2Cl2 (10 mL), and washed with cold water
(2 · 20 mL). The organic layer was collected, dried
(Na2SO4) and evaporated. The crude residue was puri-
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(2:1) to afford pure per-O-acetylated glucopyranosyl tri-
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chloroacetimidate (35, 800 mg, 1.6 mmol) and ethyl 2,3-
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O-isopropylidene-1-thio-a-L-rhamnopyranoside
(36,
˚
323 mg, 1.3 mmol) and MS 4 A (500 mg) in dry CH2Cl2
(15 mL) was added H2SO4–silica (50 mg) at 0 ꢁC under
argon. The mixture was stirred at 0 ꢁC for 1 h when
the consumption of the starting material was found to
be complete (TLC). The mixture was then filtered
through Celite, the organic layer was washed with aq
NaHCO3 and brine, dried (Na2SO4) and evaporated.
The crude mixture was purified by column chromato-
graphy using n-hexane–EtOAc (3:1) to afford the desired
25
disaccharide (37, 640 mg, 85%); ½aꢀD +35; 1H NMR
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(CDCl3) d: 5.24 (t, 1H, J3 ,4 = J4 ,5 = 9.3 Hz, H-40),
0
0
0
0
5.05 (t, 1H, J2 ,3 = J3 ,4 = 9.3 Hz, H-30), 4.98 (s, 1H,
0
0
0
0
0
0
0
0
H-1), 4.94 (dd, 1H, J1 ,2 = 7.8 Hz, J2 ,3 = 9.3 Hz, H-
15. Bujar Barua, P. M.; Saho, P. R.; Mondal, E.; Bose, G.;
Khan, A. T. Synlett 2002, 1, 81–84.
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2623–2632.
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(b) Zolfigol, M. A. Tetrahedron 2001, 57, 9509; (c)
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2), 4.23–4.07 (m, 4H, H-10, H-6a0 , H-6b0 , H-2), 4.03 (t,
1H, J3,4 = J4,5 = 6.3 Hz, H-4), 3.95 (dd, 1H, J2,3
=
3.9 Hz, J3,4 = 6.3 Hz, H-3), 3.70 (m, 1H, H-50), 3.60
(dd, 1H, J4,5 = 6.3 Hz, J5,6 = 6.0 Hz, H-5), 2.55 (m,
2H, S–CH2–CH3), 2.08, 2.07, 2.03, 2.01 (4s, 12H,
4 · COCH3), 1.53, 1.34 (2s, 6H, isopropylidene CH3),
1.25 (d, J5,6 = 6.0 Hz, H-6); 13C NMR (CDCl3) d:
171.0, 170.6, 169.8, 169.4 (4 · COCH3), 109.6
(C(CH3)2), 100.0 (C-10), 87.9 (C-1), 79.9, 76.9, 73.7,
70.3, 69.2, 68.7, 67.4, 64.9, 63.4, 28.4, 26.8 (isopropylid-
ene CH3), 21.1 (4 COCH3), 18.4 (C-6), 15.0 (S–CH2–
CH3); HRMS: m/z calcd. for [C25H38O13S+NH4]+:
596.2377. Found: 596.2378.
Acknowledgements
S.D. and B.R. are thankful to CSIR, New Delhi, for
providing fellowship. The instrumentation facility of
SAIF, CDRI, is gratefully acknowledged.
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