Reaction Steps
To a stirred solution of nucleoside 54 (3.4 g, 5.3 mmol) in methanol (20 cm3) was added sodium methoxide (0.663 g, 11.66 mmol). The reaction mixture was stirred at room temperature for 10 min and then neutralised with 20% aqueous hydrochloric acid. The solvent was partly evaporated and the residue was extracted with dichloromethane (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 compound 55 as a white solid material (1.6 g, 54%). δH (CDCl3) 9.95 (1H, br s, NH), 8.33 (1H, d, J 7.4, 6-H), 7.98 (2H, m, Bz), 7.60-7.12 (14H, m, Bn, Bz, 5-H), 6.17 (1H, d, J 1.6, 1′-H), 4.78 (1H, d, J 11.8, Bn), 4.48-4.27 (5H, m, Bn, 2′-H, 3′-H), 3.85 (1H, d, J 11.8, 5′-H,), 3.66-3.61 (2H, m, 5′-Hb, 1″-H), 3.47 (1H, d, J 10.4, 1″-Hb). δC (CDCl3) 167.5, 162.31 (C-4, C═O), 155.36 (C-2), 145.34 (C-6), 137.49, 137.08, 133.09, 133.01, 128.94, 128.67, 128.48, 128.30, 128.01, 127.90, 127.80 (Bn, Bz), 96.53 (C-5), 93.97, 89.35 (C-1′, C-4′), 76.06, 75.28, 73.70, 72.76, 70.26, 62.44 (C-2′, C-3′, Bn, C-5′, C-1″). FAB-MS m/z 558 [M+H]+.
