Reaction Steps
A mixture of compound 51 (440 mg, 1.21 mmol) and 4,4′-dimethoxytrityl chloride (573 mg, 1.69 mmol) was dissolved in anhydrous pyridine (7 cm3) and was stirred at room temperature for 4 h. The mixture was evaporated under reduced pressure to give an oil. Extraction was performed in a system of dichloromethane/water (1:1, v/v, 40 cm3). The organic phase was separated and concentrated to give a solution in a minimal volume of dichloromethane containing 0.5% of pyridine (v/v) which was applied to a silica gel column equilibrated by the same solvent. The product was eluted in gradient concentrations of methanol (0.6-2%, v/v) in dichloromethane containing 0.5% of pyridine (v/v) to give compound 52 as a white solid material (695 mg, 86%). δH (CDCl3) 12.17 (1H, br s, NHCO), 10.09 (1H, br s, NH), 7.87 (1H, s, 8-H), 7.42-6.72 (13H, m, DMT), 5.69 (1H, s, 1′-H), 4.59 (1H, s, 2′-H), 4.50 (1H, s, 3′-H), 3.98 (1H, d, J 8.1, 1″-Ha), 3.69-3.39 (9H, m, DMT, 5′-H, 1″-Hb), 2.72 (1H, m, CHCO), 1.17 (6H, d, J 6.8, CH3CH). δC (CDCl3) 179.8 (COCH), 158.8, 144.5, 135.6, 135.5, 130.1, 128.1, 127.7, 126.9, 113.2 (DMT), 155.8, 147.9, 147.5, 137.0, 120.8 (guanine), 87.6, 86.4, 86.1 (C-1′, C-4′, DMT), 79.7 (C-3′), 72.6, 71.4 (C-2′, C-5′), 59.8 (C-1″), 55.2 (DMT), 36.1 (COCH), 19.1, 18.8 (CH3CH). FAB-MS m/z 668 [M+H]+.
