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[摘要]：A facile and selective N- or O-alkylation of 4-beta-D-ribofuranosyl[1,2,5]thiadiazolo[3,4-d] pyrmidine-5,7(4H,6H)-dione as well as uridines was accomplished via bimolecular base alkylation or bimolecular nucleophilic substitution reaction controlled by the reagents. In the presence of 18-crown-6 and anhydrous K2CO3, the highly chemoselective O-methylation was performed using dimethyl carbonate (DMC) in DMF at 22-25 degrees C, i.e. the 2',3'-O-isopropylidene derivatives of 4-beta-D-ribofurnosyl[1,2,5]thiadiazolo[3,4-d]pyrmidine-5,7(4H,6H)-dion e, uridine, and 5-bromouridine underwent only the primary alcoholic O-methylation reaction without affecting the NH group of the pyrimidne ring. The novel N-alkylated derivatives of 4-beta-D-ribofurnosyl[1,2,5]thiadiazolo[3,4-d]pyrmidine-5,7(4H,6H)-dion e were also prepared using the appropriate alkylhalides with a base. |
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