EFFECT OF N-9-METHYLATION AND BRIDGE ATOM VARIATION ON THE ACTIVITY OF 5-SUBSTITUTED 2,4-DIAMINOPYRROLO[2,3-D]PYRIMIDINES AGAINST DIHYDROFOLATE REDUCTASES FROM PNEUMOCYSTIS-CARINII AND TOXOPLASMA-GONDII

The effect of N-9-methylation and bridge atom variation on inhibitory potency and selectivity of 2,4-diaminopyrrolo[2,3-d]pyrimidines agains t dihydrofolate reductases (DHFR) was studied. Specifically three nonc lassical ((N-methylanilino)methyl)pyrrolo[2,3-d]pyrimidines with 2',5' -dimethoxyphenyl (2), 3',4'-dichlorophenyl (3), 1'-naphthyl (4), one c lassical analogue with a 4'-L-glutamate substituent (10), and four non classical no-5-((phenylthio)methyl)pyrrolo[2,3-d]pyrimidines with 3',4 '-dimethoxyphenyl (5), 3',4'-dichlorophenyl (6), 1'-naphthyl (7), and 2'-naphthyl (8) substituents were synthesized. The classical and noncl assical analogues were obtained by displacement of the intermediate 2, 4-diamino-5-bromomethylpyrrolo[2,3-d]pyrimidine, 14, with appropriatel y substituted N-methylaniline, thiophenols, or 4-(N-methylamino)benzoy l-L-glutamate. Compounds 2-8 and 10 were evaluated against Pneumocysti s carinii (pc), Toxoplasma gondii (tg), and rat liver (rl) DHFRs. The N-methyl and thiomethyl analogues were more inhibitory than their corr esponding anilino-methyl analogues (previously reported) against all t hree DHFRs. The inhibitory potency of these analogues was greater agai nst rlDHFR than against tgDHFR which resulted in a loss of selectivity for tgBHFR compared to the N-9-H analogues. The classical N-9-methyl analogue 10 was more potent and about a-fold more selective against tg DHFR than its corresponding desmethyl analogue. All of the analogues, 2-8 and 10, were more selective than trimetrexate (TMQ) against pcDHFR (except 4) and significantly more selective than TMQ against tgDHFR.