Brominated trimetrexate analogues as inhibitors of pneumocystis carinii and toxoplasma gondii dihydrofolate reductase

Abstract

AbstractFive 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.