LIPOPHILIC ANTIFOLATES AS AGENTS AGAINST OPPORTUNISTIC INFECTIONS .1.AGENTS SUPERIOR TO TRIMETREXATE AND PIRITREXIM AGAINST TOXOPLASMA-GONDII AND PNEUMOCYSTIS-CARINII IN IN-VITRO EVALUATIONS

2,4-Diaminopteridines (21 compounds) arid 2,4-diamino-5-methyl-5-deaza pteridines (34 compounds) along with three 2,4-diamino-5-unsubstituted -5-dieazapteridines and four 2,4-diaminoquinazolines, each with an ary l group attached to the 6-position of the heterocyclic moiety through a two-atom bridge (either CH2NH, CH2N(CH3), CH2S, or CH2CH2), were syn thesized and evaluated as inhibitors of the growth of Toxoplasma gondi i in culture and as inhibitors of dihydrofolate reductase enzymes from T. gondii, Pneumocystis carinii, and rat liver. Exceptionally high le vels of combined potency and selectivity as growth inhibitors of T. go ndii and as inhibitors of the microbial enzymes relative to the mammal ian enzyme were found among the 5-methyl-5-deazapteridines but not for the other heterocyclic types. Thirty of the 34 5-methyl-5-deaza compo unds gave growth inhibition IC50 values lower than that of pyrimethami ne (0.4 mu M) with 14 compounds below 0.1 mu M, values that compare fa vorably with those for piritrexim and trimetrexate (both near 0.02 mu M). As inhibitors of T. gondii DHFR, all but three of the 34 5-methyl- 5-deaza compounds gave IC50 values in the order of magnitude with thos e of piritrexim (0.017 mu M) and trimetrexate (0.010 mu M), and 17 com pounds of this group gave IC50 values versus P. carinii DHFR similarly comparable with those of piritrexim (0.031 mu M) and trimetrexate (0. 042 mu M). Thirteen of these congeners gave both T. gondii growth inhi bition and DHFR inhibition IC50 values of 0.10 mu M or less, thus indi cating facile penetration of the cell membrane. Eleven of these inhibi tors of both T. gondii growth and DHFR have selectivity ratios (IC50 r at liver divided by IC50 T gondii) of 5 or greater for the parasite DH FR. The highest selectivity ratio of nearly 100 belongs to the 5-methy l-5-deaza compound whose B-substituent is CH2CH2C6H3(OCH3)(2)-2,5. Thi s compound is over 10(3)-fold more selective for T. gondii DHFR than b ridge homologue piritrexim (selectivity ratio 0.088), a compound now i n clinical trials. The candidate with CH2NHC6H3(CH3)(2)-2,5 in the 6-p osition gave the highest P. carinii DHFR selectivity ratio of 4.0, whi ch is about 60-fold more selective than trimetrexate (0.071) and 80-fo ld more selective than piritrexim (0.048) toward this enzyme. The 10 b est compounds with respect to potency and selectivity includes six com pounds bearing 2,5-disubstituted phenyl groups in the side chain (with little, if any, difference in effects of methyl, methoxy, or ethoxy), two side chains bearing 1-naphthyl groups, and two with 5,6,7,8-tetra hydro-1-naphthyl groups. Bridge groups represented in the 10 choice co mpounds are CH2NH, CH2N(CH3), CH2CH2, and CH2S. The high levels of bot h potency and selectivity among these agents suggest that in vivo stud ies now underway may lead to agents that could replace trimetrexate an d piritrexim in treatment of toxoplasmosis and P. carinii pneumonia.