Design, synthesis and biological evaluation of 2,4‐diamino‐6‐methyl‐5‐substitutedpyrrolo[2,3‐d]pyrimidines as dihydrofolate reductase inhibitors

Nine novel nonclassical 2,4-diamino-6-methyl-5-mioarylsubstituted-7H-pyrrolo[2,3-d]pyrimidines 2-10 were synthesized as potential inhibitors of dihydrofolate reductase and as antitumor agents. The analogues contain various electron donating and electron withdrawing substituents on the phenylsulfanyl ring of the side chains and were synthesized from the key intermediate 2,6-diamino-6-methyl-7H-pyrrolo[2,3-d]-pyrimidine, 14. Compound 14, was in turn obtained by chlorination of 4-position of 2-amino-6-methylpyrrolo[2,3-d]pyrimidin-4(3H)-one, 16 followed by displacement with ammonia. Appropriately substituted phenyl thiols were appended to the 5-position of 14 via an oxidative addition reaction using iodine, ethanol and water. The compounds were evaluated against rat liver, rat-derived Pneumocystis, Mycobacterium avium and Toxoplasma gondii dihydrofolate reductase. The most potent and selective inhibitor, (2) has a 1-naphthyl side chain. In this series of compounds electron-withdrawing and bulky substituents in the side chain afford marginally active dihydrofolate reductase inhibitors. The single atom sulfur bridge in the side chain of these compounds is not conducive to potent dihydrofolate reductase inhibition.