THE IN-VIVO METABOLIC STABILITY OF DIPEPTIDE ANALOGS OF THE QUINAZOLINE ANTIFOLATE, ICI-198583, IN MICE

In the search for quinazoline thymidylate synthase inhibitors that are not subject to intracellular polyglutamation, a class of dipeptide an alogues of the diglutamate of -desamino-2-methyl-N-10-propargyl-5,8-di deazofolic acid (ICI 198583-gamma-L-glu) has been evaluated for their stability to in vivo hydrolysis. Replacement of the second glutamate w ith another amino acid, e.g. alanine, prevented polyglutamation in vit ro but such compounds were subject to hydrolysis when injected into mi ce. The extent of hydrolysis was measured in pl;asma, liver and kidney by HPLC analysis of tissue removed from mice 1 hr after i.p. injectio n. The enzyme responsible for this hydrolysis is thought to be a gamma -glutamyl hydrolase which hydrolyses the amide bond, releasing ICI 198 583 which may then be polyglutamated. Development of stable dipeptide compounds was achieved by structural modification in two principal way s: either by replacement of the second amino acid (e.g. glutamate or a lanine) with its D-enantiomer or removal of the carboxyl on the alpha- carbon of the second amino acid (alpha(1)-COOH). In this second approa ch two series of compounds were investigated. Monocarboxylate-derived dipeptides, e.g. ICI 198583-gamma-L-phenylalanine or ICI 198583-gamma- phenylglycine, resulted in stable compounds after removal of the alpha (1)-COOH (to give -ethylamide and -benzylamide derivatives, respective ly). However, for the dicarboxytic amino acids a less clear picture em erged. Although removal of the alpha(1)-COOH from ICI198583-gamma-L-gl utamate to give ICI 198583-gamma-gamma-aminobutyric acid resulted in a stable compound, the corresponding aspartate analogue (-beta-alanine) was subject to hydrolysis.