The effect of the base in the fragmentation of nucleotide C4′ radicals

A series of 3′-O-diethylphosphoryl-4′-α-[(2-halophenylethylthio)carbonyl] substituted esters of thymidine, cytidine, adenosine and guanosine are prepared by total synthesis and used as C4′-radical precursors in a competition kinetic method using tributyltin hydride as the reductant. The pseudo-first order rate constants for the C4′-radicals so generated decrease in the order guansoine>cytidine>adenosine>thymidine with that for guanosine being too rapid for determination by the present competition kinetic method. A 119Sn NMR method is presented for estimation of the purity of tin hydride solutions.