Solution Phase Synthesis of Dithymidine Phosphorothioate by a Phosphotriester Method Using New S-Protecting Groups

Abstract

ABSTRACT A phosphotriester method for the synthesis of dithymidine phosphorothioates with eight S-protecting groups has been investigated. Three of the S-protecting groups possesed catalytic activity, however side reactions occurred under deprotection. The best S-protecting group was 4-chloro-2-nitrobenzyl which could be removed with a minimum of side reactions (0.3 %). The coupling reagent PyFNOP (11) gave protected dithymidine phosphorothioate in 96% yield after 15 min coupling.