Nucleoside phosphorothioates

Abstract

The nucleoside-thiophosphorylating properties of the two phosphorus-thioxy anions, thiophosphate and dithiophosphate, were investigated. The heating of monoanionic thiophosphate with the nucleosides thymidine and 2 ':3'-O-ethoxymethyleneadenosine in anhydrous dimethyl formamide results in the formation thymidine 3' (5')-0-phosphorothioates and adenosine 5 '-0-phosphorothioate, respectively. From a detailed study of the thymidine reaction evidence is presented to support a two step thiophosphorylation process, involving initial condensation of thiophosphate to thiopyrophosphate followed by reaction of the nucleoside with the thiopyrophosphate leading to the formation of the 0-phosphorothioates. The formed (^-phosphorothioates undergo further reaction to thymidine 3'(5') -monophosphates. Dithiophosphate reacts smoothly at room temperature w ith the nucleosides, thymidine and 2 '-deoxycytidine to yield the corresponding 3 '- and 5'-0-phosphorothioate esters in a 2:3 ratio and an overall 50-65:1 yield. Thiophosphorylation of 0²:2'-anhydro-l-[beta]-D-arabinosylcytosine with dithiophosphate or thiophosphate gives three products; 0²:2 '-anhydro-l-[beta]-arabinosylcytosine 5'-0-phosphorothioate (36a), 0²:2'-anhydro-l-[beta]-D-arabinosylcytosine 3'-0-phosphorothioate (36b) and 2'-thio -2'-deoxy- cytidine 2':3'-phosphorothioate (39).