Biological evaluation of potent triclosan-derived inhibitors of the enoyl-acyl carrier protein reductase InhA in drug-sensitive and drug-resistant strains of mycobacterium tuberculosis

New triclosan (TRC) analogues were evaluated for their activity against the enoyl-acyl carrier protein reductase InhA in Mycobacterium tuberculosis (Mtb). TRC is a well-known inhibitor of InhA, and specific modifications to its positions 5 and 4' afforded 27 derivatives; of these compounds, seven derivatives showed improved potency over that of TRC. These analogues were active against both drug-susceptible and drug-resistant Mtb strains. The most active compound in this series, 4-(n-butyl)-1,2,3-triazolyl TRC derivative 3, had an MIC value of 0.6 μg mL^-1 (1.5 μM) against wild-type Mtb. At a concentration equal to its MIC, this compound inhibited purified InhA by 98 %, and showed an IC₅₀ value of 90 nM. Compound 3 and the 5-methylisoxazole-modified TRC 14 were able to inhibit the biosynthesis of mycolic acids. Furthermore, mc²4914, an Mtb strain overexpressing inhA, was found to be less susceptible to compounds 3 and 14, supporting the notion that InhA is the likely molecular target of the TRC derivatives presented herein.