BENZO[F]QUINAZOLINE INHIBITORS OF THYMIDYLATE SYNTHASE - METHYLENEAMINO-LINKED AROYLGLUTAMATE DERIVATIVES

Syntheses of several new inhibitors of thymidylate synthase (TS) struc turally related to folic acid are described in which the pterin portio n of the folate molecule is replaced by a benzo[f]quinazoline moiety, but which retain the natural methyleneamino link to the benzoylglutama te side chain. The effect on enzyme activity and cytotoxicity of vario us changes in the structure of the (p-aminobenzoyl)glutamate side chai n are reported. Replacement of the benzamide portion of the (p-aminobe nzoyl)glutamate moiety with 2-fluorobenzamido, 2-isoindolinyl, 1,2-ben zisothiazol-2-yl, and 2-thenamido moieties varied in effect from a 9-f old diminution of TS activity to a 5-fold enhancement, while cytotoxic potency on SW-480 and MCF-7 tumor lines showed increases ranging from 3.6-to 450-fold. The detrimental effect on enzyme activity and cytoto xicity of alkyl substitution on the PABA nitrogen is confirmed for the se compounds, in contrast with several series of previously reported q uinazoline antifolates (2). Substitution of a C3-methyl substituent fo r 3-amino had little effect on TS activity but was beneficial in terms of solubility and cytotoxicity. The excellent combination of TS inhib itory activity, FPGS substrate activity, and affinity for the reduced folate transport system in the most potent of these derivatives, 3e, r esulted in IC50 values of 0.2-0.8 nM against these tumor lines.