Abstract
Condensation of adenine (1a) with 1-O-acetyl-2, 3, 5-tri-O-benzoyl-β-D-ribofuranose (2a) in acetonitrile in the presence of stannic chloride at room temperature gave blocked nucleoside. After removal of the benzoyl group, adenosine (4a) was obtained in 78% overall yield. When 1, 2, 3, 5-tetra-O-acetyl-β-D-ribofuranose (2b) was used instead of 2a in the same reaction, 2', 3', 5'-tri-O-acetyladenosine (3b) was obtained in 77% yield. In both cases, the α-isomer or 1-, 3- or 7-riboside could not be detected in the reaction. In an application of this reaction, 6-chloropurine (1b) and purin-6-yl benzyl disulfide (1c) were coupled with 2a or 2b followed by reaction with thiourea or β-mercaptoethanol to give 2', 3', 5'-tri-O-acyl-6-thioinosine (3c). Coupling of 6-methylthiopurine (1d) with 3a after deblocking of the acyl group yielded 9-β-D-ribofuranosyl-6-methylthiopurine in 75% yield. In addition, 2, 6-dichloropurine (1e) coupled with 2b under the same conditions to give 9-β-D-ribofuranosyl-2, 6-dichlororopurine tri-O-acetate in 81% yield.
