HYDROLYTIC DETHIOPHOSPHORYLATION AND DESULFURIZATION OF THE MONOTHIOATE ANALOGS OF URIDINE MONOPHOSPHATES UNDER ACIDIC CONDITIONS

The hydrolytic reactions of uridine 2'-, 3'- and 5'-phosphoromonothioa tes (2'-, 3'- and 5'-UMPS) under acidic and neutral conditions have be en followed by HPLC. Under slightly acidic conditions (pH 2-5), only p a-independent dethiophosphorylation to uridine takes place. This react ion is 200- to 300-fold as fast as dephosphorylation of the correspond ing uridine monophosphates (UMP), presumably due to higher stability o f the thiometaphosphate monoanion compared to metaphosphate anion. At pH > 5, i.e. at pH > pK(a2) of the thiophosphate moiety, the dethiopho sphorylation is retarded with increasing basicity of the solution. At pH < 1, acid-catalysed desulfurization of 2'- and 3'-UMPS to an isomer ic mixture of 2'/3'-UMP competes with their dethiophosphorylation. Thi s reaction is suggested to proceed by a nucleophilic attack of the nei ghbouring hydroxy group on phosphorus. No such reaction occurs with 5' -UMPS. In contrast to 2'- and 3'-UMP, no sign of interconversion of 2' - and 3'-UMPS is detected.