The synthesis and biological activities of 14 6-substituted 2,4-diaminoquinazolines are reported. These compounds were designed to improve the cell penetration of a previously reported series of 2,4-diamino-6-substituted-pyrido[2,3-d]pyrimidines which had shown significant potency and remarkable selectivity for Toxoplasma gondii dihydrofolate reductase (DHFR), but had much lower inhibitory effects on the growth of T. gondii cells in culture. The target N9-H analogues were obtained via regiospecific reductive amination of the appropriate benzaldehydes with 2,4,6-triaminoquinazoline, which, in turn, was synthesized from 2,4-diamino-6-nitroquinazoline. The N9-CH3 analogues were synthesized via a regiospecific reductive methylation of the corresponding N9-H precursors. The compounds were evaluated as inhibitors of DHFR from human, Pneumocystis carinii, T. gondii, rat liver, Lactobacillus casei, and Escherichia coli, and selected analogues were evaluated as inhibitors of the growth of tumor cells in culture. These analogues displayed potent T. gondii DHFR inhibition as well as inhibition of the growth of T. gondii cells in culture. Further, selected analogues were potent inhibitors of the growth of tumor cells in culture in the in vitro screening program of the National Cancer Institute with GI50s in the nanomolar and subnanomolar range. Crystallographic data for the ternary complex of hDHFR-NADPH and 2,4-diamino-6-[N-(2', 5'-dimethoxybenzyl)-N-methylamino]pyrido[2,3-d]pyrimidine, 1c, reveal the first structural details for a reversed N9-C10 folate bridge geometry as well as the first conformational details of a hybrid piritrexim-trimetrexate analogue.

We disclose a novel series of indenopyrazole-based cyclin-dependent kinase (CDK) inhibitors. Kinetic experiments confirmed our initial molecular modeling studies that the compounds are competitive with respect to adenosine 5'-triphosphate (ATP) and bind in the kinase ATP pocket. A unique combination of active pharmacophores led us to a series of semicarbazide-based inhibitors that are highly potent against CDK2 and CDK4 while maintaining selectivity against other relevant serine/threonine kinases. These compounds were active against a transformed human colon cancer cell line (HCT116) while maintaining an acceptable margin of activity against a normal fibroblast cell line. The compounds were found to be highly protein bound in our cell-based assay with the exception of 11k, which maintained a reasonable level of activity in the presence of human plasma proteins.