We designed and synthesized a classical analog N- [4-[(2-amino-6-ethyl-3,4-dihydro-4-oxo-7H-pyrrolo

A novel classical antifolate N-{4- [(2,4-diamino-5-methyl-furo[2,3-d]pyrimidin-6-yl)thio]-benzoyl}-L-glutamic acid 5 and 11 nonclassical antifolates 6-16 were designed, synthesized, and evaluated as inhibitors of dihydrofolate reductase (DHFR) and thymidylate synthase (TS). The nonclassical compounds 6-16 were synthesized from 20 via oxidative addition of substituted thiophenols using iodine. Peptide coupling of the intermediate acid 21 followed by saponification gave the classical analog 5. Compound 5 is the first example, to our knowledge, of a 2,4-diamino furo[2,3-d]pyrimidine classical antifolate that has inhibitory activity against both human DHFR and human TS. The classical analog 5 was a nanomolar inhibitor and remarkably selective inhibitor of P. carinii DHFR and M. avium DHFR at 263-fold and 2107-fold respectively compared to mammalian DHFR. The nonclassical analogs 6-16 were moderately potent against pathogen DHFR or TS. This study shows that the furo [2,3-d]pyrimidine scaffold is conducive to dual human DHFR-TS inhibitory activity and to high potency and selectivity for pathogen DHFR.

A series of ten novel 2-amino-4-oxo-5-[(substitutedbenzyl)thio]pyrrolo [2,3-d]pyrimidines 2-11 were synthesized as potential inhibitors of thymidylate synthase and as antitumor agents. The analogues contain various electron withdrawing and electron donating substituents on the benzylsulfanyl ring of the side chains and were synthesized from the key intermediate 2-amino-4-oxo-6-methylpyrrolo[2,3-d]pyrimidine, 14. Appropriately substituted benzyl mercaptans were appended to the 5-position of 14 via an oxidative addition reaction using iodine, ethanol and water. The compounds were evaluated against human, Escherichia coli and Toxoplasma gondii thymidylate synthase and against human, Escherichia coli and Toxoplasma gondii dihydrofolate reductase. The most potent inhibitor, (6) which has a 4'-methoxy substituent on the side chain, has an IC 50 =25 µM against human thymidylate synthase. Contrary to analogues of general structure 1, electron donating or electron withdrawing substituents on the side chain of 2-11 had little or no influence on the human thymidylate synthase inhibitory activity.