Based on the previously described antimicrobial activity of salicylanilide derivatives, we designed and synthesized novel 2-(phenylcarbamoyl)phenyl 4-substituted benzoates. The most active salicylanilides were selected for esterification by various 4-substituted benzoic acids. These compounds were evaluated in vitro against Mycobacterium tuberculosis, including multidrug-resistant strains, nontuberculous mycobacteria (Mycobacterium avium and Mycobacterium kansasii), and eight bacterial and fungal strains. We also investigated the cytostatic and cytotoxic actions of the esters. The minimum inhibitory concentrations (MICs) against mycobacteria ranged from 0.125 to 8μM. Interestingly, the drug-resistant strains exhibited the highest susceptibility without any cross-resistance with established drugs. 4-Bromo-2-[4-(trifluoromethyl)phenylcarbamoyl]phenyl 4-nitrobenzoate showed the most potent inhibition with MIC values ranging from 0.25 to 2μM. Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, were inhibited by two derivatives with MIC values of at least 0.49μM, whereas Gram-negative bacteria and most of the tested fungi did not display any marked susceptibility. Benzoates exhibited no cytotoxicity at concentrations up to 50μM but most caused significant cytostasis with IC50 values lower than 10μM. Some cytotoxicity-based selectivity indexes for drug-susceptible and drug-resistant M. tuberculosis as well as Staphylococci were higher than 100. These values indicate that some of these derivatives are promising candidates for future research.
Keywords: Antimicrobial activity; Benzoate; Cytostasis; Cytotoxicity; Ester; In vitro activity; Multidrug-resistant tuberculosis; Mycobacterium tuberculosis; Nontuberculous mycobacteria; Salicylanilide.
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