Reaction Steps
Nucleoside 24 (2.57 g, 5.53 mmol) was dissolved in anhydrous pyridine (18 cm3) and cooled to 0° C. Methanesulfonyl chloride (1.28 cm3, 16.6 mmol) was added dropwise and the mixture was stirred at room temperature for 30 min. The reaction was quenched with water (5 cm3) and the resulting mixture was extracted with dichtoromethane (3×80 cm3). The combined extract was washed with saturated aqueous sodium hydrogencarbonate (3×120 cm3) and dried (Na2SO4). The solvent was evaporated under reduced pressure and the residue was purified by silica gel column chromatography using dichloromethane/methanol (99:1, v/v) as eluent to give nucleoside 25 as a yellow foam (2.53 g, 84%). δH (CDCl3) 8.92 (1H, br s, NH), 7.71 (1H, d, J 1.4, 6-H), 7.41-7.28 (10H, m, Bn), 6.57 (1H, d, J 7.8, 1′-H), 5.99-5.61 (4H, m, 2′-H, 1″-H and 2″-Ha, 2″-Hb), 4.86-4.50 (4H, m, Bn), 4.37 (1H, dd, J 1.5, 2.4, 4′-H), 8.82 (1H, dd, J 2.6, 11.0, 5′-Ha), 3.55 (1H, dd, J 1.2, 11.0, 5′-Hb), 3.02 (3H, s, CH3), 1.47 (3H, d, J 1.1, CH3). δC (CDCl3) 163.7 (C-4), 151.5 (C-2), 138.7, 136.7 (Bn), 135.7 (C-6), 130.9 (C-1″), 128.8, 128.5, 128.4, 127.6, 127.0 (Bn), 121.8 (C-2″), 111.9 (C-5), 85.1 (C-1′), 84.5 (C-3′), 84.0 (C-4′), 80.7 (C-2′), 73.7 (C-5′), 69.2, 67.7 (Bn), 38.9 (CH3), 11.8 (CH3).
