ChemInform Abstract: Brominated Trimetrexate Analogues as Inhibitors of Pneumocystis carinii and Toxoplasma gondii Dihydrofolate Reductase

Five previously undescribed trimetrexate analogues with bulky 2′-bromo substitution on the phenyl ring were synthesized in order to assess the effect of this structure modification on dihydrofolate reductase inhibition. Condensation of 2-[2-(2-bromo-3,4,5-trimethoxyphenyl)ethyl]-1,l-dicyanopropene with sulfur in the presence of N,N-diethylamine afforded 2-amino-5-(2′-bromo-3′,4′,5′-trimethoxybenzyl)-4-methyl-thiophene-3-carbonitrile (15) and 2-amino-4-[2-(2′-bromo-3′,4′,5′-trimethoxyphenyl)ethyl]thiophene-3-car-bonitrile (16). Further reaction with chloroformamidine hydrochloride converted 15 and 16 into 2,4-diamino-5-(2′-bromo-3′,4′,5′-trimethoxybenzyl)-4-methylthieno[2,3-d]pyrimidine (8a) and 2,4-diamino-4-[2-(2′-bromo-3′,4′,5′-trimethoxyphenyl)ethylthieno[2,3-d]pyrimidine (12) respectively. Other analogues, obtained by reductive coupling of the appropriate 2,4-diaminoquinazoline-6(or 5)-carbonitriles with 2-bromo-3,4,5-trimethoxyaniline, were 2,4-diamino-6-(2′-bromo-3′,4′,5′-trimethoxyanilinomethyl)-5-chloro-quinazoline (9a), 2,4-diamino-5-(2′-bromo-3′,4′,5′-trimethoxyanilinomethyl)quinazoline (10), and 2,4-diamino-6-(2′-bromo-3′,4′,5′-trimethoxyanilinomethyl)quinazoline (11). Enzyme inhibition assays revealed that space-filling 2′-bromo substitution in this limited series of dicyclic 2,4-diaminopyrimidines with a 3′,4′,5′-trimethoxyphenyl side chain and a CH2, CH2CH2, or CH2NH bridge failed to improve species selectivity against either P. carinii or T. gondii dihydrofolate reductase relative to rat liver dihydrofolate reductase.