2,4-DIAMINO-5-CHLOROQUINAZOLINE ANALOGS OF TRIMETREXATE AND PIRITREXIM - SYNTHESIS AND ANTIFOLATE ACTIVITY

Ten heretofore undescribed 2,4-diamino-5-chloroquinazoline analogues o f trimetrexate (TMQ) and piritrexim (PTX) were synthesized and tested as inhibitors of dihydrofolate reductase (DHFR) from rat liver, Pneumo cystis carinii, and Toxoplasma gondii. The most active quinazolines ag ainst both the P. carinii and the T. gondii enzyme were those with an ArCH2-NH or ArNHCH2 side chain. Among ArNH(CH2)(n) compounds with n = 1-3 and either 2',5'-dimethoxyphenyl or 3',4',5'-trimethoxyphenyl as t he Ar moiety, activity decreased in the order n = 1 > n = 2 > n = 3. T he best inhibitor of P. carinii DHFR, oro-6-[(N-methyl-3',4',5'-trimet hoxyanilino)methyl (10) had an IC50 of 0.012 mu M and was slightly mor e potent than TMQ and PTX Compound 10 was also the best inhibitor of T . gondii DHFR, with an IC50 of 0.0064 mu M corresponding again to a mi nor increase in activity over TMQ and PTX. However, as with these stan dard agents, 10 showed no appreciable selectivity for either the P. ca rinii or T. gondii enzyme relative to the rat liver enzyme. The highes t selectivity achieved in this limited series was with ,4',5'-trimetho xybenzyl)-N-methylamino]quinazoline (17) against T. gondii DHFR. While 17 (IC50 = 0.016 mu M) was somewhat less potent than 10, its selectiv ity, as defined by the ratio IC50(rat liver)/IC50(T. gondii) was ca. 3 0-fold higher than that of TMQ or PTX. Two compounds, -6-[(3',4',5'-tr imethoxyanilino)methyl]quinazoline (9) and -6-[N-(3',4',5'-trimethoxyb enzyl)amino]quinazoline (15), were also tested against human DHFR and were found to have an IC50/[E] of 0.5, indicating that their binding w as near-stoichiometric.