Enantiomerically pure carbocyclic 2'-deoxy-3'-azidothymidine monophosphate (AZTMP) and carba-2'deoxy-3'-thiocyanatothymidine monophosphate were synthesized to study their behavior toward their phosphorylation by thymidylate kinase. The nucleotides were synthesized starting from the parent nucleosides by an alkaline hydrolysis of the corresponding cycloSal-phosphate triesters.