To a stirred solution of nucleoside 40 (2.0 g, 3.7 mmol) in methanol (25 cm3) was added sodium methoxide (0.864 g, 95%, 16.0 mmol). The reaction mixture was stirred at room temperature for 10 min and neutralised with 20% aqueous hydrochloric acid. The solvent was partly evaporated and the residue was extracted with ethyl acetate (3×50 cm3). The combined organic phase was washed with a saturated aqueous solution of sodium hydrogencarbonate (3×20 cm3) and was dried (Na2SO4). The solvent was removed under reduced pressure and the residue was purified by silica gel column chromatography using dichloromethane/methanol (98.5:1.5, v/v) as eluent to give 41 as a white solid material (1.58 g, 95%). δH (CDCl3) 9.95 (1H, br s, NH), 7.69 (d, J 8.1, 6-H), 7.35-7.17 (10H, m, Bn), 6.02 (1H, d, J 2.3, 1′-H), 5.26 (1H, d, J 8.1, 5-H), 4.80 (1H, d, J 11.7, Bn), 4.47 (1H, d, J 11.7, Bn), 4.45-4.24 (4H, m, Bn, 2′-H, 3′-H), 3.81 (1H, d, J 11.9, 1″-Ha), 3.69 (2H, br s, 2′-OH, 1″-OH), 3.67 (2H, m, 5′-Ha, 1″-Hb), 3.48 (1H, d, J 10.3, 5′-Hb). δC (CDCl3) 163.78 (C-4), 150.94 (C-2), 140.61 (C-6), 137.33, 137.22, 128.59, 128.18, 128.01 (Bn), 102.16 (C-5), 91.46, 88.36 (C-1′, C-4′), 76.73, 74.66, 73.71, 73.29, 70.81, 62.81 (C-2′, C-3′, C-5′, C-1″, Bn). FAB-MS m/z 455 [M+H]+.
