Reaction Steps
To a stirred solution of compound 61B (0.50 g) in anhydrous pyridine (20 cm3) was added 4,4′-dimethoxytrityl chloride (0.71 g, 2.09 mmol) and 4-N,N-dimethylaminopyridine (DMAP) (0.1 g). After stirring for 2 h at room temperature and for 1 h at 50° C., the reaction mixture was cooled to 0° C. and a saturated aqueous solution of sodium hydrogencarbonate (100 cm3) was added. After extraction using dichloromethane (3×50 cm3), the combined organic phase was dried (Na2SO4) and evaporated under reduced pressure. The residue was purified by silica gel column chromatography eluting with dichloromethane/methanol/pyridine (98.0:1.5:0.5) to give nucleoside 61C as a white solid material (0.36 g, ˜50% from 61A). δH (C5D5N) 12.52 (NHCO), 9.10 (2H, d, J 7.7, Bz), 8.88 (1H, s, 8-H), 8.50-7.11 (17H, m, DMT, Bz, 2-H), 6.65 (1H, s, H-1′), 5.25 (2H, s, H-2′, H-3′), 4.71 (1H, d, J 7.8, 1″-Ha), 4.56 (1H, d, J 7.8, 1″-Hb), 4.20 (1H, d, J 10.8, 5′-Ha), 4.07 (1H, d, J 10.8, 5′-Hb), 3.82, 3.81 (2×3H, 2×s, 2×OCH3). δC (C5D5N) 167.56 (NHCO), 159.24 (C-6), 152.50, 152.08, 151.81, 145.84, 141.45, 136.52, 136.28, 132.55, 130.76, 130.70, 129.32, 128.85, 128.76, 128.46, 127.38, 126.33 (DMT, Bz, C-2, C-4, C-8), 113.84 (C-5), 88.64, 87.20, 86.85, 80.52, 73.13, 72.16, 60.86 (C-1′, C-4′, DMT, C-2′, C-3′, C-1″, C-5′), 55.24 (OCH3). FAB-MS m/z 686 [M+H]+. Found: C, 68.3; H, 5.0; N, 9.7; C39H35N5O7 requires C, 68.3; H, 5.1; N, 10.2%).
