SYNTHESIS OF S-2-ALKYL-2-THIOURIDINES

5-Substituted S-2-alkyl-2-thiouracils 1a-i were treated with 1,1,1,3,3 ,3-hexamethyldisilazane and ammonium sulfate at reflux temperature and condensed with 1,2,3,5-tetra-O-acetyl-beta-D-ribofuranose in acetonit rile using trimethylsilyl trifluoromethanesulfonate as a catalyst to a fford the corresponding protected nucleosides 2a-i which were deprotec ted with saturated ammonia in methanol. When the nucleobase was substi tuted with ethoxycarbonyl or cyano groups in the 5-position or was uns ubstituted, the deprotection reaction of the nucleoside also resulted in replacement of the methylthio group. This was not observed with 5-a lkyl and 5-methoxy substituents.