NONCLASSICAL 2,4-DIAMINO-8-DEAZAFOLATE ANALOGS AS INHIBITORS OF DIHYDROFOLATE REDUCTASES FROM RAT-LIVER, PNEUMOCYSTIS-CARINII, AND TOXOPLASMA-GONDII

The synthesis and biological activity of 42 6-substituted-2,4-diaminop yrido[3,2-d]pyrimidines (2,4-diamino-8-deazafolate analogues) are repo rted. The compounds were synthesized in improved yields compared to pr evious classical analogues using modifications of procedures reported previously by us. Specifically, the S-phenyl-; mono-, di-, and trimeth oxyphenyl-; and mono-, di-, and trichlorophenyl-substituted analogues with H or CH3 at the N10 position and methyl and trifluoromethyl pheny l ketone analogues with H, CH3, and CH2C=CH at the N10 position were s ynthesized. The S10 and N10 alpha- and beta-naphthyl analogues along w ith the N10 CH3 analogues were also synthesized. These compounds were evaluated as inhibitors of dihydrofolate reductases (DHFR) from Pneumo cystis carinii (pc) and Toxoplasma gondii (tg); selectivity ratios wer e determined against rat liver (rl) DHFR as the mammalian reference en zyme. Against pcDHFR the IC50 values ranged from 0.038 x 10(-6) M for yl-2'-naphthylamino)methyl]pyrido[3,2-d]pyrimidine (28) to 5.5 x 10(-6 ) M for 4'-dimethoxyanilino)methyl]pyrido[3,2-d]pyrimidine (15). N10 m ethylation in all instances increased potency. None of the analogues w ere selective for pcDHFR. Against tgDHFR the most potent analogue was B-[(N-methylanilino)methyl]pyrido[3,2-d]pyrimidine (5) (IC50 0.0084 x 10(-6) M) and the least potent was -[(2'-naphthylamino)methyl]pyrido[3 ,2-d]pyrimidine (37) (IC50 0.16 x 10(-6) M). N10 methylation afforded an increase in potency up to 10-fold. In contrast to pcDHFR, several o f the 8-deaza analogues were significantly selective for tgDHFR, most notably oro-N-methylanilino)methyl]pyrido[3,2-d]pyrimidine (13), '-tri methoxyanilino)methyl]pyrido[3,2-d]pyrimidine (29), and 6'-trichloroan ilino)methyl]pyrido[3,2-d]pyrimidine (32) which combined high potency at 10(-8) M along with selectivities of 8.0, 5.0, and 12.4, respective ly. The potency of these three analogues are comparable to the clinica lly used agent trimetrexate while their selectivities for tgDHFR are 1 7-43-fold better than trimetrexate.