Synthesis of 2,4-Diaminopteridines with Bulky Lipophilic Groups at the 6-Position as Inhibitors of Pneumocystis carinii, Toxoplasma gondii, and Mammalian Dihydrofolate Reductase

SummaryTen previously undescribed 2,4-diamino-6-(2-naphthylamino )methylpteridines with lipophilic chlorine or long-chain alkyl groups on the naphthyl moiety and either hydrogen or a methyl group on N 10 were synthesized from the appropriate 2-naphthylamine or N-methyl-2-naphthylamine by reaction with 2-amino-5-chloromethylpyrazine-3-carbonitrile and ring closure with guanidine . One analogue with a methyl group at the 7 -position was also prepared. The N 10 -unsubstituted analogues were consistently less active than the N1o-methyl analogues as inhibitors of Pneumocystis carin ii, Toxoplasma gondii, and rat liver dihydrofolate reductase. However the potency of the series as a whole was relatively low against all three enzymes, with the best inhibitors giving ICoo values only in the 0.1-1.0 ~M range and several giving IC50 values in the 10-100 ~M range. Moreover, while several compounds with ICso values of Pnellmocystis carinii and/or Toxoplasma gondii enzyme relative to the rat liver enzme, the magnitude of this effect was marginal «4-fold). Assays were also performed against purified human dihydrofolate reductase and against wild-type and methotrexateresistant human leukemic lymphoblasts in culture. Activity against the enzyme was very low, the best inhibitors giving only 50-70% inhibition at 10 ~M. Although none of the compounds inhibited the growth of wild-type CEM cells by more than 20% at 1 ~M, several were more active (60-75% inhibition at 1 ~M) against the methotrexate-resistant subline CEM/MTX, which is defective in methotrexate and reduced folate transport, than they were against the methotrexate-sensitive parental CEM cells. Overall the results suggest that 2,4-diamino-6-substituted pteridines with chlorine or long-chain alkyl substituents in the 2-naphthyl moiety and hydrogen or a methyl group on NIO are not likely to be therapeutically useful agents.