Reaction Steps
To a solution of nucleoside 26 (2.00 g, 4.31 mmol) in a mixture of THF (15 cm3) and water (15 cm3) was added sodium periodate (2.76 g, 12.9 mmol) and a 2.5% solution of osmium tetraoxide in t-butanol (w/w, 0.54 cm3, 43 μmol). The reaction was stirred at room temperature for 18 h, quenched with water (50 cm3), and the mixture was extracted with dichloromethane (2×100 cm3). The combined extract was washed with saturated aqueous sodium hydrogen carbonate (3×75 cm3), dried (Na2SO4) and evaporated under reduced pressure. The residue was redissolved in a mixture of THF (15 cm3) and water (15 cm3), and sodium borohydride (488 mg, 12.9 mmol) was added. The reaction mixture was stirred at room temperature for 1 h, water (50 cm3) was added, and the mixture was extracted with dichloromethane (2×100 cm3). The combined organic phase was washed with saturated aqueous sodium hydrogencarbonate (3×75 cm3) and dried (Na2SO4). The solvent was removed and the residue was purified by silica gel column chromatography using dichloromethane/methanol (98:2, v/v) as eluent to give nucleoside 27 as a white foam (732 mg, 36%). δH (CDCl3) 11.09 (1H, br s, NH), 7.41 (1H, d, J 1.0, 6-H), 7.38-7.26 (Bn), 6.16 (1H, d, J 2.6, 1′-H), 5.12 (1H, d, J 5.4, 2′-OH), 4.66-4.29 (6H, m, 2′-H, 4′-H, Bn), 4.02-3.96 (2H, m, 1″-Ha, 1″-Hb), 3.90 (1H, dd, J 7.2, 9.7, 5′-Ha), 3.79 (1H, dd, J 5.6, 9.7, 5′-Hb), 2.49 (1H, t, J 6.4, 1″-OH), 1.68 (3H, d, J 0.6, CH3); δC (CDCl3) 166.1 (C-4), 150.6 (C-2), 139.0, 137.9, 137.0 (C-6, Bn), 128.7, 128.6, 128.4, 128.3, 128.0 (Bn), 107.5 (C-5), 88.2 (C-1′), 88.1 (C-3′), 84.2 (C-4′), 73.7 (C-5′), 72.1 (C-2′), 69.3, 65.4 (Bn), 58.6 (C-1″), 12.3 (CH3).
