QUINAZOLINE ANTIFOLATE THYMIDYLATE SYNTHASE INHIBITORS - GAMMA-LINKEDL-D, D-D, AND D-L DIPEPTIDE ANALOGS OF -DESAMINO-2-METHYL-N-10-PROPARGYL-5,8-DIDEAZAFOLIC ACID (ICI-198583)

The syntheses of gamma-linked L-D, D-D, and D-L dipeptide analogues of -desamino-2-methyl-N-10-propargyl-5,8-dideazafolic acid (ICI 198583) are described. The general methodology for the synthesis of these mole cules involved the preparation of the dipeptide derivatives employing solution phase peptide synthesis followed by condensation of the dipep tide free bases with the appropriate pteroic acid analogue via diethyl cyanophosphoridate (DEPC) activation. In the final step, tert-butyl e sters were removed by trifluoroacetic acid (TFA) hydrolysis. Z-L-Glu-O Bu(t)-gamma-D-Ala-OBu(t), for example, was prepared from alpha-tert-bu tyl N-(benzyloxycarbonyl)-L-glutamate and tert-butyl D-alaninate via i sobutyl-mixed anhydride coupling. The Z-group was removed by catalytic hydrogenolysis and the resulting dipeptide free base condensed with d esamino-2-methyl-N-10-propargyl-5,8-didezapteroic acid via DEPC coupli ng. Finally, tert-butyl esters were removed by TFA hydrolysis to give ICI 198583-gamma-D-Ala. The compounds were tested as inhibitors of thy midylate synthase and L1210 cell growth. Good enzyme and growth inhibi tory activity were found with gamma-linked L-D dipeptides, the best ex amples being the Glu-gamma-D-Glu derivative 35 (K-i = 0.19 nM, L1210 I C50 = 0.20 +/- 0.017 mu M) and the Glu-gamma-D-alpha-aminoadipate deri vative 39 (K-i = 0.12 nM, L1210 IC50 = 0.13 +/- 0.063 mu M). In additi on, ICI 198583 L-gamma-D-linked dipeptides were resistant to enzymatic degradation in mice.