Design, synthesis, and biological activities of classical N-{4-[2-(2-amino-4-ethylpyrrolo[2,3-d]pyrimidin-5-yl)ethylbenzoyl}-L-glutamic acid and its 6-methyl derivative as potential dual inhibitors of thymidylate synthase and dihydrofolate reductase and as potential antitumor agents

Two novel analogues, N-{2-amino-4-ethyl[(pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl}-L-glutamic acid (2) and N-{2-amino-4-ethyl-6-methyl[(pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl}-L-glutamic acid (4), were designed and synthesized as potent dual inhibitors of thymidylate synthase (TS) and dihydrofolate reductase (DHFR) and as antitumor agents. Compound 2 had inhibitory potency against human DHFR similar to N-{4-[2-(amino-3,4-dihydro-4-oxo-7H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl}-L-glutamic acid (LY231514) and 1, whereas 4 was inactive against human DHFR. Both 2 and 4 were more potent than LY231514 against E. coli TS. Against human TS, 2 was 7-fold less potent than LY231514 and 4 showed similar inhibitory activity as LY231514. In contrast to 2, which was an efficient substrate of human folypoly-glutamate synthetase (FPGS), 4 was a poor substrate of FPGS. Compound 2 showed GI(50) values in the nanomolar range against more than 18 human tumor cell lines in the standard NCI preclinical in vitro screen.