Radical deoxygenation of tert-alcohols in 2'-branched-chain sugar pyrimidine nucleosides: Synthesis and antileukemic activity of 2'-deoxy-2'(S)-methylcytidine.

We have synthesized 2'-deoxy-2' (S) -methylcytidine (7), a new antileukemic nucleoside. The carbonyl methylation of 2'-ketonucleoside (1) with MeLi, Me3Al and MeMgX was examined. Only in the reaction with MeMgX, did the more hindered β-attack afford the 2'-methyl-t-alcohol (2b). Compound 2b was converted into the methyl oxalate (4), which was subjected to radical deoxygenation to give the 2'-deoxy-2' (S) -methyl derivative (5). The deprotection of 5 followed by substitution with NH3 furnished 7. The structure-activity relationships of 7 and some other 2'-branched-chain sugar cytidines against L1210 cells are also described.