5-Cyano-2'-deoxyuridine 5'-phosphate: a potent competitive inhibitor of thymidylate synthetase.

The 5'-phosphate (1) of the antiviral nucleoside 5-cyano-2'-deoxyuridine was synthesized and evaluated for inhibition of thymidylate synthetase purified from methotrexate-resistant Lactobacillus casei. Compound 1 was a potent competitive inhibitor with a K1 of 0.55 microns. Irreversible enzyme inhibition by this compound could not be detected.