50% |
|
To a solution of Lambda^-acetylcytidine (65.0 g, 0.228 mol) in anhydrous pyridine (60OmL) cooled in an ice bath, DMTrCl (84.7 g, 0.251 mol) was added. The reaction mixture was stirred at room temperature overnight. To the reaction mixture cooled with an ice bath, THF (600 ml) and AgNO3 (58.1 g, 0.342 mmol) were added. Then TBSCl (51.5 g, 0.342 mmol) was added, and the reaction mixture was stirred at room temperature overnight. The reaction mixture was filtered, solvent was removed under vacuum to give a residue which was diluted with EtOAc (500 mL) and washed with water (200 ml) and brine (200 ml). The organic layer was separated and dried over anhydrous Na2SO4 and the filtrate was concentrated to a syrup which was purified by chromatography on silica gel (eluted with PE : EA = 5:1 to 3 : 1) to give N4-acetyl-2'-O-(t-butyldimethylsilyl)-5'-O- (4,4'-dimethoxytrityl)cytidine as yellow solid (80 g, 50percent). 1H NMR (CDCl3) delta 8.39 (d, J = 7.6 Hz, IH), 7.34 (dd, Jl = 1.6 Hz, J2 = 8.4 Hz, 2H), 7.21 - 7.27 (m, 6H), 7.02 (d, J = 7.2 Hz, IH), 6.80 (dd, Jl = 2.0 Hz, J2 = 6.8 Hz, 4H), 5.82 (d, J = 1.2 Hz, IH), 4.26 - 4.32 (m, IH), 4.20 (dd, Jl = 1.2 Hz, J2 = 4.4 Hz, IH), 4.00 - 4.02 (m, IH), 3.74 (d, J = 1.6 Hz, 6 H), 3.43 - 3.53 (m, 2H), 2.32 (d, J = 9.6 Hz, IH), 2.18 (s, 3H), 0.86 (s, 9H), 0.22 (s, 3H), 0.11 (s, 3H). |