Lipophilic Antifolates as Agents against Opportunistic Infections. 1. Agents Superior to Trimetrexate and Piritrexim against Toxoplasma gondii and Pneumocystis carinii in in Vitro Evaluations

Abstract

2,4-Diaminopteridines (21 compounds) and 2,4-diamino-5-methyl-5-deazapteridines (34 compounds) along with three 2,4-diamino-5-unsubstituted-5-deazapteridines and four 2,4-diaminoquinazolines, each with an aryl groups attached to the 6-position of the heterocyclic moiety through a two-atom bridge (either CH2NH, CH2N(CH3),CH2S, or CH2CH2), were synthesized and evaluated as inhibitors of the growth of Toxoplasma gondii in culture and as inhibitors of dihydrofolate reductase enzymes from T. gondii, Pneumocystis carinii, and rat liver. Exceptionally high levels of combined potency and selectivity as growth inhibitors of T. gondii and as inhibitors of the microbial enzymes relative to the mammalian enzyme were found among the 5-methyl-5-deazapteridines but not for the other heterocyclic types. Thirty of the 34 5-methyl-5-deaza compounds gave growth inhibition IC50 values lower than that of pyrimethamine (0.4 microM) with 14 compounds below 0.1 microM, values that compare favorably with those for piritrexim and trimetrexate (both near 0.02 microM). 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 those of piritrexim (0.017 microM) and trimetrexate (0.010 microM), and 17 compounds of this group gave IC50 values versus P. carinii DHFR similarly comparable with those of piritrexim (0.031 microM) and trimetrexate (0.042 microM). Thirteen of these congeners gave both T. gondii growth inhibition and DHFR inhibition IC50 values of 0.10 microM or less, thus indicating facile penetration of the cell membrane. Eleven of these inhibitors of both T. gondii growth and DHFR have selectivity ratios (IC50 rat liver divided by IC50 T. gondii) of 5 or greater for the parasite DHFR. The highest selectivity ratio of nearly 100 belongs to the 5-methyl-5-deaza compound whose 6-substituent is CH2CH2C6H3(OCH3)2-2,5. This compound is over 10(3)-fold more selective for T. gondii DHFR than bridge homologue piritrexim (selectivity ratio 0.088), a compound now in clinical trials. The candidate with CH2NHC6H3(CH3)2-2,5 in the 6-position gave the highest P. carinii DHFR selectivity ratio of 4.0, which is about 60-fold more selective than trimetrexate (0.071) and 80-fold more selective than piritrexim (0.048) toward this enzyme. The 10 best compounds with respect to potency and selectivity includes six compounds 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-tetrahydro-1-naphthyl groups. Bridge groups represented in the 10 choice compounds are CH2NH, CH2N(CH3), CH2CH2, and CH2S. The high levels of both potency and selectivity among these agents suggest that in vivo studies now underway may lead to agents that could replace trimetrexate and piritrexim in treatment of toxoplasmosis and P. carinii pneumonia.

Antimycobacterial Activities of 2,4-Diamino-5-Deazapteridine Derivatives and Effects on Mycobacterial Dihydrofolate Reductase

“…The structures of the compounds used in the present study are presented below (see Tables 2 through 5) and are numbered consecutively as 1 through 78. The compounds were synthesized according to the method of Piper et al (22). The synthesis of each particular class of analogs was carried out by the exact procedures that are well described by Piper et al (22), and these descriptions need not be duplicated here.…”

“…The compounds were synthesized according to the method of Piper et al (22). The synthesis of each particular class of analogs was carried out by the exact procedures that are well described by Piper et al (22), and these descriptions need not be duplicated here. In general, the appropriate 5-substituted 5-deaza-6-bromomethylpteridine was reacted with the desired, commercially available thiophenol or aniline to obtain the S-or N-linked analogs, respectively.…”

“…In general, the appropriate 5-substituted 5-deaza-6-bromomethylpteridine was reacted with the desired, commercially available thiophenol or aniline to obtain the S-or N-linked analogs, respectively. The 10-CH 2 -linked analogs were prepared by Wittig coupling of the reaction product of triphenylphosphine and 5-methyl-5-deaza-6-bromomethylpteridine with the appropriately substituted and commercially available benzaldehyde derivative followed by catalytic hydrogenation (22). All compound structures were verified by mass and 1 H-labeled nuclear magnetic resonance (NMR) spectroscopy.…”

“…It is notable that these compounds do not have defined melting points, but generally decompose above 300°C. The full experimental details of these compounds are available in the reference of Piper et al (22) or will be reported elsewhere (unpublished data). As examples of these preparations, both compound 1 (SRI-8686) and compound 78 (SRI-20094) are presented.…”

“…Although DHFR does not represent a new target, there is still enthusiasm for the development of improved derivatives of this class of inhibitor (1,5,18,22,25,26), particularly with regard to mycobacteria (7,15,16,17,19,28,29; W. J. Suling, R. C. Reynolds, J. R. Piper, V. Pathak, E. W. Barrow, L. E. Gundy, S. Z. V. Ginkel, L. Westbrook, and W. W. Barrow, Abstr. 39th Intersci.…”