ABSTRACT
Acetohydroxyacid synthase (AHAS) catalyzes the first essential biosynthetic step of branched-chain amino acids and is a biologically safe target against Mycobacterium tuberculosis (MTB). In our previous research, we used virtual screening to identify some novel AHAS inhibitors as potent antituberculosis agents. In this study, we synthesized twenty-four additional quinazolinone benzoates and explored their antitubercular activity. Five of these compounds displayed significant MTB-AHAS inhibition and their IC50 values were determined to be in the range of 6.50 µM-12.08 µM. Importantly, these compounds also exhibited strong in vitro activity (MICs in the range of 2.5-10 mg/L) and intracellular activity against clinically isolated extensively drug-resistant strains of M. tuberculosis. Taken together, these results indicated that the quinazolinone benzoate compounds should be regarded as promising lead compounds for the development of potent antituberculosis drugs with a novel mode of action.
Subject(s)
Acetolactate Synthase/antagonists & inhibitors , Antitubercular Agents/pharmacology , Benzoates/pharmacology , Enzyme Inhibitors/pharmacology , Mycobacterium tuberculosis/drug effects , Quinazolinones/pharmacology , Acetolactate Synthase/metabolism , Antitubercular Agents/chemical synthesis , Antitubercular Agents/chemistry , Benzoates/chemical synthesis , Benzoates/chemistry , Crystallography, X-Ray , Dose-Response Relationship, Drug , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/chemistry , Microbial Sensitivity Tests , Models, Molecular , Molecular Structure , Quinazolinones/chemical synthesis , Quinazolinones/chemistry , Structure-Activity RelationshipABSTRACT
The sulfonylurea herbicides exert their activity by inhibiting plant acetohydroxyacid synthase (AHAS), the first enzyme in the branched-chain amino acid biosynthesis pathway. It has previously been shown that if the gene for AHAS is deleted in Candida albicans , attenuation of virulence is achieved, suggesting AHAS as an antifungal drug target. Herein, we have cloned, expressed, and purified C. albicans AHAS and shown that several sulfonylureas are inhibitors of this enzyme and possess antifungal activity. The most potent of these compounds is ethyl 2-(N-((4-iodo-6-methoxypyrimidin-2-yl)carbamoyl)sulfamoyl)benzoate (10c), which has a K(i) value of 3.8 nM for C. albicans AHAS and an MIC90 of 0.7 µg/mL for this fungus in cell-based assays. For the sulfonylureas tested there was a strong correlation between inhibitory activity toward C. albicans AHAS and fungicidal activity, supporting the hypothesis that AHAS is the target for their inhibitory activity within the cell.
