Aminoacyl Derivatives of 4-Thiothymidine, Cytosine, and Cytidine

5\u27-0-Triphenylmerthyl-4-thiothymidine (III) was coupled to N-benzyloxycarbonyl-D,L-alanine or N-t-butyloxycarbonyl-L-phenylalanine by the N,N-dicyclohexylcarbodiimide method, yielding 3\u27-nucleos1de esters V and VII. The removal of the protectilng triphenylmethyl and t-butyloxycarbonyl groups of compound VII afforded 3\u27-0-(L-phenylalanyl)-4-thiothymidine (IX). Appropriately blocked glycylglycine and L-phenyla1anine were also coupled to cytosine and 2\u27,3\u27-0-isopropylidene-cytidine by the active ester or dicyclohexylcarbodiimide method, yie1ding N-4- acylated cytosi1ne X and cytidine XIII. It was establi,shed that the catalytic hydrogenation of 4-N-(glycylglycyl)-cytosine (XI) over 5°/o rhodium on carbon afforded 4-N-(glycylglycyl)-5,6-dihydrocytosine (XII) in a quantitative yield