Reaction Steps
A solution of compound 27 (2.26 g, 4.83 mmol) in anhydrous pyridine (20 cm3) was stirred at −40° C. and a solution of methanesulphonyl chloride (0.482 cm3, 4.83 mmol) in anhydrous pyridine (10 cm3) was added. The reaction mixture was stirred at room temperature for 17 h, water (5o cm3) was added, and the mixture was extracted with dichloromethane (2×100 cm3). The combined organic phase was washed with saturated aqueous sodium hydrogencarbonate (3×100 cm3), dried (Na2SO4) and evaporated under reduced pressure. The residue was purified by silica gel column chromatography using dichloromethane/methanol (99:1, v/v) as eluent to give an intermediate which after evaporation of the solvents was dissolved in anhydrous DMF (15 cm3). This solution was added dropwise to a suspension of 60% sodium hydride (461 mg, 11.5 mmol) in anhydrous DMF (15 cm3) at 0° C. The reaction was stirred at room temperature for 30 min, then quenched with water (60 cm3). After neutralisation using dilute aqueous hydrochloric acid, the mixture was dissolved in dichloromethane (150 cm3), washed with saturated aqueous sodium hydrogencarbonate (3×100 cm3) and dried (Na2SO4). The solvents were evaporated and the residue was purified by silica gel column chromatography using dichloromethane/methanol (99:1, v/v) as eluent to give nucleoside 28 as a white foam (2.00 g, 93%). δH (CDCl3) 9.13 (1H, br s, NH), 7.55 (1H, d, J 1.4, 6-H), 7.40-7.26 (Bn), 5.99 (1H, d, J 2.5, 1′-H), 5.30 (1H, d, J 2.7, 2′-H), 4.88-4.57 (6H, m, 1″-Ha, 1″-Hb, Bn), 4.22-4.19 (1H, m, 4′-H), 3.92 (1H, dd, J 6.2, 10.8, 5′-Ha), 3.82 (1H, dd, J 3.7, 10.8, 5′-Hb), 1.91 (3H, d, J 1.3, CH3). δC (CDCl3) 163.8 (C-4), 150.3 (C-2), 137.6 (C-6), 137.5, 137.0 (Bn), 128.7, 128.6, 128.2, 128.0, 127.8, 127.3 (Bn), 109.8 (C-5), 85.7 (C-3′), 84.1 (C-1′), 83.5 (C-4′), 79.7 (C-1″), 73.9 (C-2′), 73.6 (C-5′), 68.6, 67.8 (Bn), 12.4 (CH3). FAB m/z 451 [M+H]+, 473 [M+Na]+. Found: C, 66.3; H, 5.9; N, 6.1; C25H26N2O6 requires C, 66.7; H, 5.8; N, 6.2%.
