Quinazoline antifolate thymidylate synthase inhibitors: benzoyl ring modifications in the C2-methyl series

The synthesis of nine new 2-methyl-10-propargylquinazoline antifolates with substituents in the p-aminobenzoyl ring is described. In general the synthetic route involved the coupling of the appropriate ring-substituted diethyl N-[4-(prop-2-ynylamino)benzoyl]-L-glutamate with 6-(bromomethyl)-3,4-dihydro-2-methyl-4-oxoquinazoline followed by deprotection using mild alkali. The compounds were tested as inhibitors of partially purified L1210 thymidylate synthase (TS). They were also examined for their inhibition of the growth L1210 cells in culture. Compared to the parent compound 1a the 2'-fluoro analogue 2a exhibited enhanced potency in both systems whereas the 3'-fluoro analogue 3a showed enhanced growth inhibitory properties against L1210 cells despite being a poorer inhibitor of the isolated enzyme. Chloro, hydroxy, methoxy, and nitro substituents in the 2'-position were also well tolerated by the enzyme but failed to give enhanced growth inhibition. The series was extended to cover analogues of the 2'-fluoro, 3'-fluoro, 2'-chloro, 2'-methyl, 2'-amino, 2'-methoxy, and 2'-nitro derivatives with modified alkyl substituents at N10.