tokens: Recent preclinical and clinical studies with the thymidylate synthase inhibitor N10-propargyl-5,8-dideazafolic acid ( CB 3717 ). CB 3717 , N10-propargyl-5,8-dideazafolic acid , is a tight - binding inhibitor of thymidylate synthase ( TS ) whose cytotoxicity is mediated solely through the inhibition of this enzyme .