6-SUBSTITUTED 2,4-DIAMINO-5-METHYLPYRIDO[2,3-D]PYRIMIDINES AS INHIBITORS OF DIHYDROFOLATE REDUCTASES FROM PNEUMOCYSTIS-CARINII AND TOXOPLASMA-GONDII AND AS ANTITUMOR AGENTS

The synthesis and biological activity of 15 6-substituted 2,4-diamino- 5-methylpyrido[2,3-d]pyrimidines are reported. These compounds were sy nthesized in improved yields by modifications of procedures previously reported by us. Specifically, dimethoxyphenyl-substituted compounds w ith H and CH3 at the N-10 position and trimethoxyphenyl-substituted co mpounds with N-10 ethyl, isopropyl, and propargyl moieties were synthe sized. These compounds were evaluated as inhibitors of dihydrofolate r eductases (DHFR) from Pneumocystis carinii, Toxoplasma gondii, and rat liver, and selected analogues were evaluated as inhibitors of the gro wth of T. gondii and tumor cells in culture. Ah the compounds showed i ncreased selectivity (vs rat liver DHFR) for T. gondii DHFR compared t o trimetrexate. In general, for the trimethoxy-substituted analogues, increasing the size of the N-10 substituent from a methyl group to lar ger groups resulted in a decrease in selectivity and potency for both P. carinii and T. gondii DHFR. For the dimethoxy-substituted analogues , N-10 methylation in general decreased potency but increased selectiv ity for T. gondii DHFR. In an attempt to improve the cell penetration of these analogues, the N-10 naphthyl-substituted analogues were also synthesized. These analogues displayed excellent cell penetration and inhibition of T. gondii cells in culture. Further, these analogues wer e potent inhibitors of the growth of tumor cells in the preclinical in -vitro screening program of the National Cancer Institute with IC(50)s in the nanomolar range.