Structure-Based Design of New Dihydrofolate Reductase Antibacterial Agents: 7-(Benzimidazol-1-yl)-2,4-diaminoquinazolines

A new series of dihydrofolate reductase (DHFR) inhibitors, the 7-(benzimidazol-1-yl)-2,4-diaminoquinazolines, were designed and optimized for antibacterial potency and enzyme selectivity. The most potent inhibitors in this series contained a five-membered heterocycle at the 2-position of, the benzimidazole, leading to highly potent and selective compounds that exploit the differences in the size of a binding pocket adjacent to the NADPH cofactor between the bacterial and human DHFR enzymes. Typical of these compounds is 74(2-thiazol-2-yObenzimidazol-1-yl)-2,4 diaminoquinazoline, which is a potent inhibitor of S. aureus DHFR (K-i = 0.002 nM) with 46700-fold selectivity over human DHFR. This compound also has high antibacterial potency on Gram-positive bacteria with an MIC versus wild type S. aureus of 0.0125 mu g/mL and a MIC versus trimethoprim-resistant S. aureus of 0.25 mu g/mL. In vivo efficacy versus a S. aureus septicemia was demonstrated, highlighting the potential of this new series.