The synthesis of 5, 10-methylene-5-deazatetrahydrofolic acid (2), a stable, rigid analogue of 5, lO-methylenetetrahydrofolate (l), is reported as a potential inhibitor of thymidylate synthase. The target compound was obtained by a Fisher-indole type cyclization of the hydrazone 16 from 2-amino-6-hydrazino-4-oxopyrimidine (10) and diethylN-[4-(3-formyl-l- pyrrolyl) benzoyll-~-glutamate (15) followed by catalytic reduction of the product 17. ...