Abstract
Three previously undescribed dihydrofolate reductase (DHFR) inhibitors, N^α^‐[4‐[N‐[(2,4‐diaminopyrrolo[2,3‐d]pyrimidin‐5‐yl)methyl]amino]benzoyl]‐N^δ^‐hemiphthaloyl‐L‐ornithine (7), N^α^‐ [4‐ [N‐[(2,4‐diaminothieno[2,3‐d]pyrimidin‐5‐yl)methyl]amino]benzoyl]‐ N^δ^‐hemiphthaloyl‐L‐ornithine (8), and N‐[4‐[N‐[(2,4‐diaminothieno[2,3‐d]pyrimidin‐5‐yl)methyl]amino]benzoyl]‐L‐glutamic acid (12), were synthesized and their antifolate activity was assessed. The ability of 7 and 8 to bind to DHFR and inhibit the growth of CCRF‐CEM human lymphoblastic leukemia cells in culture were dramatically reduced in comparison with the corresponding pteridine analogue, N^α^‐(4‐amino‐4‐deoxypteroyl)‐N^δ^‐hemiphmaloyl‐L‐ornithine (1, PT523). In a similar manner, the antifolate activity of 12 was markedly reduced in comparison with that of the corresponding glutamate analogue, aminopterin (5, AMT). In contrast, 7, 8, and 12 all displayed excellent affinity for the reduced folate carrier (RFC) of CCRF‐CEM cells as measured by a standard competitive influx assay. Lack of a consistent correlation between the results of the growth inhibition assays and those of the DHFR and RFC binding assays results suggest that additional factors also play a role in the antifolate activity of these compounds.