Reaction Steps
To a stirred suspension of the anomeric mixture 33 (5.0 g, 10.3 mmol) and 6-N-benzoyladenine (3.76 g, 15.7 mmol) in anhydrous dichloromethane (200 cm3) was added N,O-bis(trimethylsilyl)acetamide (15.54 cm3, 61.8 mmol). The reaction mixture was stirred at reflux for 1 h and then cooled to room temperature. Trimethylsilyl triflate (7.0 cm3, 38.7 mmol) was added dropwise and the mixture was refluxed for 20 h. The reaction mixture was allowed to cool to room temperature and the volume of the mixture was reduced to ¼ under reduced pressure. Dichloromethane (250 cm3) was added, and the solution was washed with a saturated aqueous solution of sodium hydrogencarbonate (3×50 cm3) and water (50 cm3). The organic phase was dried (Na2SO4) and evaporated under reduced pressure. The residue was purified by silica gel column chromatography using dichloromethane/methanol (99.5:0.5, v/v) as eluent to give nucleoside 58 as white solid material (3.65 g, 52%). δH (CDCl3) 9.25 (1H, br s, NH), 8.71 (1H, s, 8-H), 8.24 (1H, s, 2-H), 8.0 (2H, d, J 7.5, Bz), 7.60-7.23 (13H, m, Bn, Bz), 6.35 (1H, d, J 4.6, 1′-H), 5.99 (1H, dd, J 4.9, 5.3, 2′-H), 4.78 (1H, d, J 5.6, 3′-H), 4.64-4.42 (5H, m, Bn, 1′-Ha), 4.25 (1H, d, J 12.1, 1″-Hb), 3.72 (1H, d, J 10.1, 5′-Ha), 3.56 (1H, d, J 10.1, 5′-Hb), 2.07 (3H, s, COCH3), 2.02 (3H, s, COCH3). δC (CDCl3) 170.42, 169.72 (COCH3), 164.60 (NHCO), 152.51 (C-6), 151.45 (C-2), 149.46 (C-4), 141.88 (C-8), 137.04, 137.00, 133.50, 132.60, 128.86, 128.66, 128.53, 128.41, 128.38, 128.18, 128.06, 127.91, 127.88, 127.79, 127.63, 123.26 (Bz, Bn, C-5), 86.38 (C-1′), 86.25 (C-4′), 77.74, 74.74, 74.44, 73.48 (C-2′, C-3′, 2×Bn), 70.11 (C-1″), 63.42 (C-5′), 20.70, 20.54 (COCH3). FAB-MS m/z 666 [M+H]+.
