Design and synthesis of potent non-polyglutamatable quinazoline antifolate thymidylate synthase inhibitors

The synthesis is described of a series of analogues of the potent thymidylate synthase (TS) inhibitor, N-[4-[N-[(3,4-dihydro-2,7-dimethyl-4-oxo-6-quinazolinyl)methyl]-N-prop-2-ynylamino]- 2-fluorobenzoyl]-L-glutamic acid (4, ZM214888), in which the glutamic acid moiety is replaced by homologous amino acids and cl-amino acids where the omega-carboxylate is replaced by acylsulfonamides and acidic heterocycles. In general these modifications when compared to 4 gave compounds with increased potency as inhibitors of isolated TS and as cytotoxic agents against murine tumor cell lines. The new compounds require transport by the reduced folate carrier for entry into cells but are not converted intracellularly into polyglutamated species. Agents with this profile are expected-to show activity against tumors that are resistant to classical antifolates due to low expression of folylpolyglutamate synthetase. The analogue (S)-2-[4-[N-[(3,4-dihydro-2,7-dimethyl-4-oxo-6-quinazolinyl)methyl] -N-prop-2-ynylamino]2-fluorobenzamido]-4-(1H-1,2,3,4-tetrazol-5-yl)butyric acid (35, ZD9331) has been selected as a clinical development candidate and is currently undergoing phase I studies.