Design of a New Substituted 2,4-Diamino-5-benzylpyrimidine as Inhibitor of Bacterial Dihydrofolate Reductase Assisted by Molecular Graphics

Partial resistance of E. coli mutants against 2, 4-diamino-5-benzylpyrimidines by interactions with bacterial membrane lipopolysaccharides. Derivation of quantitative structure-binding relationships

A series of previously synthesized 2,4-diamino-5-benzylpyrimidines, inhibitors of bacterial dihydrofolate reductase (DHFR) showed decreased inhibition of E. coli cultures, despite increased inhibitory activity against DHFR. Preliminary studies using E. coli mutants with different degrees of outer membrane deficiencies suggested that the decrease in activity was partly due to inactivation because of binding to outer membrane constituents. In the present study antibacterial activities of the benzylpyrimidines have been systematically determined as a function of cell membrane defects in E. coli using bacterial growth kinetic techniques. It has been shown that the observed differences in activity were not due to different binding affinities to the target enzyme of the mutants. Lipopolysaccharides have been extracted from the mutants and used in binding studies by ultrafiltration, photometric and NMR techniques. The observed differences in binding affinity to the lipopolysaccharides have been related to the differences in the lipophilic properties and molecular weight of the substituents. Quantitative structure-activity relationships have been derived. The results of the study show the importance of drug-membrane interactions for the rational development of antibacterials.

New antifolate 4,4'-diaminodiphenyl sulfone substituted 2,4-diamino-5-benzylpyrimidines. Proof of their dual mode of action and autosynergism

New 4,4'-diaminodiphenylsulfone substituted 2,4-diamino-5-benzylpyrimidines were synthesized. These compounds are highly active inhibitors of both bacterial dihydrofolate reductase (DHFR) and dihydropteroic acid synthase (SYN). The simultaneous inhibition of both enzymes leads to autosynergism in whole cells in the same way as known for combinations of sulfonamides with trimethoprim. The inhibitory activity is demonstrated in cell-free systems of DHFR and SYN derived from various species (M. lufu, E. coli, C. albicans) and in whole cell systems of the mycobacterial strain M. lufu. The compounds are rare examples for the combination of two mechanisms of action in one molecule.