S. K. Das et al. / Carbohydrate Research 340 (2005) 1387–1392
Table 2. Comparative study of acetylation under microwave irradiation
1391
Substrate
Method
Ac2O (equiv)
Solvent
Yield (%)
(microwave)
Ratio (a/b)
Yield reported (%)
(non-microwave)
Glucose
Ac2O/py1
7.5
9.5
5.1
5.1
10
CH3CN
—
—
33
90
3.7/1
8.5/1
3.7/1
4.7/1
—
951
>986
988
—
6
Ac2O/I2
Ac2O/Cu(OTf)2
Ac2O/Cu(OTf)2
8
71
81
CH3CN
CH3CN
CH3CN
957
—
7
Ac2O/CoCl2
Ac2O/InCl3
No reaction
94
7.5
4/1
Galactose
Ac2O/py1
7.5
9.5
5.1
5.1
10
CH3CN
—
—
No pentaacetate
86
—
6/1
981
>986
908
—
6
Ac2O/I2
Ac2O/Cu(OTf)2
Ac2O/Cu(OTf)2
8
12
79
>95%a
4.7/1
—
CH3CN
CH3CN
CH3CN
7
Ac2O/CoCl2
Ac2O/InCl3
No reaction
99
—
—
7.5
9/1
before use. Silica gel (100–200 mesh, SRL, India) was
used for column chromatography.
16C(O)CH3), 3.82–3.97 (m, 3H, H-5, H-40 (2)), 4.01–
4.12 (m, 7H, H-4 (2), H-6 (4), H-60), 4.20–4.27 (m, 4H,
H-5, H-50 (2), H-60), 4.46 (dd, 2H, J = 12.3 and 2.5
Hz, H-60 (2)), 4.84–4.9 (m, 2H, H-10), 4.95–5.00 (m,
2H, H-2), 5.04 and 5.09 (2d, 2H, J = 10.7 Hz, H-30),
5.29 (t, 1H, J = 8.9 Hz, H-3), 5.33–5.44 (m, 2H, H-20),
5.51 (dd, 1H, J = 10.2 and 8.6 Hz, H-3), 5.74 (d, 1H,
J = 8.3 Hz, H-1a), 6.24 (d, 1H, J = 2.8 Hz, H-1b). IR
(KBr): 1754, 1373, 1225, 1035 cmꢀ1. Anal Calcd for
C28H38O19: C, 49.56; H, 5.64. Found: C, 49.90; H, 5.35.
1.2. General procedure for acetylation
To a solution of the carbohydrate (100 mg) and Ac2O
(1.5 equiv per OH) in acetonitrile (1 mL) InCl3
(0.1 equiv) was added and the mixture was irradiated
at 720 W in a microwave oven (LG model: MC-
804AAR) for the appropriate time (see Table 1). The
reaction mixture was then diluted with ethyl acetate
and washed with sodium bicarbonate and water, dried
(Na2SO4) and evaporated to dryness. The residue was
purified on silica gel to afford the desired products
in the yields listed in Table 1. All the products were
characterized by 1D 1H NMRspectroscopy, 2D
1H–1H correlation spectroscopy, IRspectroscopy, and
mass spectrometry. Spectroscopic data and combustion
analysis data are presented only for previously
unreported compounds.
Acknowledgements
We are thankful to Professor J. Iqbal and Dr. R. Raja-
gopalan for their continuous encouragement to this
work. We also thank the members of the Analytical Re-
search Department of Discovery Research for their ser-
vices. We extend our gratitude to the referees for their
comments to improve the quality of this manuscript.
1.3. p-Methoxyphenyl 3,4,6-tri-O-acetyl-2-deoxy-2-
phthalimido-b-D-glucopyranoside (8b)
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1.99, 2.00, 2.014, 2.018, 2.024, 2.027, 2.031, 2.051,
2.075, 2.10, 2.102, 2.139, 2.144, 2.17, 2.225 (15s, 48H,