Reaction Steps
To a stirred solution of 1-(3,5-di-O-benzyl-4-C-hydroxymethyl-(3-D-ribofuranosyl)uracil 41 (3.55 g, 7.81 mmol) in dichloromethane (50 cm3) were added DMAP (3.82 g) and p-toluenesulphonyl chloride (4.47 g, 23.5 mmol) at room temperature. Stirring was continued for 2 h, and dichloromethane (100 cm3) was added. The reaction mixture was washed with a saturated aqueous solution of sodium hydrogen carbonate (2×75 cm3) and dried (Na2SO4). The organic phase was evaporated under reduced pressure and the residue was purified by silica gel column chromatography using dichloromethane/methanol (99.5:0.5, v/v) as eluent to give nucleoside 75 (4.65 g, 78%) as a white solid material. δH (CDCl3) 8.49 (1H, br s, NH), 7.67 (1H, d, J 8.3, 6-H), 7.51-7.03 (18H, m, Bn, Ts), 6.0 (1H, d, J 7.6, 1′-H), 5.05 (1H, m, 2′-H), 4.91 (2H, m, 5-H, Bn), 4.56 (2H, m, Bn), 4.42 (1H, d, J 10.4, Bn), 4.31 (1H, d, J 4.9, 3′-H), 4.05 (2H, m, 1″-H), 3.75-3.64 (2H, m, 5′-H), 2.41 (3H, s, CH3), 2.34 (3H, s, CH3). δC (CDCl3) 162.2 (C-4), 149.5 (C-2), 146.0, 145.3 (Ts), 139.0 (C-6), 136.7, 131.9, 130.0, 129.9, 128.9, 128.7, 128.5, 128.4, 128.3, 128.2, 128.0, 127.6 (Bn, Ts) 102.7 (C-5), 85.5 (1′-C), 84.4 (4′-C), 79.2, 78.3, 75.1, 74.3, 72.4, 69.1 (Bn, 3′-C, 2′-C, 5′-C, 1″-C), 21.7, 21.6 (Ts). FAB-MS m/z 763. Found: C, 61.2; H, 4.4; N, 3.3; C38H38N2O11S2 requires C, 59.8; H, 5.0; N, 3.6.
