2-Iodoethyl (methyl α-d-glucopyranosid)uronate and 2-iodoethyl (methyl β-d-glucopyranosid)thiouronate were prepared in five steps by an efficient synthetic route starting from -d-glucuronic. Both compounds were used to alkylate dithymidine phosphorothioate and phosphorodithioate diesters, leading to the corresponding phosphotriesters 12 to 15. Hydrolytic stability of 12-15 was studied in different biological media. The enzymatic hydrolysis of 12-15 was accompanied by another reaction resulting in formation of the dithymidine phosphodiesters. Several possible mechanisms for these reactions are proposed.