Reaction Steps
To a stirred solution of the anomeric mixture 33 (736 mg, 1.51 mmol) and thymine (381 mg, 3.03 mmol) in anhydrous acetonitrile (14.5 cm3) was added N,O-bis(trimethylsilyl)-acetamide (2.61 cm3, 10.6 mmol). The reaction mixture was stirred at reflux for 1 h, then cooled to 0° C. Trimethylsilyl triflate (0.47 cm3, 2.56 mmol) was added dropwise under stirring and the solution was stirred at 65° C. for 2 h. The reaction was quenched with a cold saturated aqueous solution of sodium hydrogen carbonate (15 cm3) and extraction was performed with dichloromethane (3×10 cm3). The combined organic phase was washed with saturated aqueous solutions of sodium hydrogencarbonate (2×10 cm3) and brine (2×10 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 (98:2, v/v) as eluent to give nucleoside 34 as a white solid material (639 mg, 76%). δH (CDCl3) 8.98 (1 H, br s, NH), 7.39-7.26 (11 H, m, Bn, 6-H), 6.22 (1 H, d, J 5.3, 1′-H), 5.42 (1 H, t, J 5.4, 2′-H), 4.63-4.43 (5H, m, 3′-H, Bn), 4.41 (1 H, d, J 12.2, 5′-Ha), 4.17 (1 H, d, J 12.1, 5′-Hb), 3.76 (1 H, d, J 10.2, 1″-Ha), 3.51 (1 H, d, J 10.4, 1″-Hb), 2.09 (3 H, s, COCH3), 2.03 (3 H, s, COCH3), 1.53 (3 H, d, J 0.9, CH3). δC (CDCl3) 170.8, 170.4 (C═O), 163.9 (C-4), 150.6 (C-2), 137.4 (C-6) 137.4, 136.1, 128.9, 128.8, 128.4, 128.2, 127.9 (Bn), 111.7 (C-5), 87.2, 87.2, 86.1 (C-1′, C-3′, C-4′), 77.6 (C-2′), 74.8, 73.9, 71.1, 63.8 (Bn, C-1″, C-5′), 20.9, 20.8 (COCH3), 12.0 (CH3). FAB-MS m/z 553 [M+H]+. Found: C, 62.7; H, 5.9; N, 4.7; C29H32N2O9 requires C, 63.0; H, 5.8; N, 5.1%.
