2-Aryl-Benzoimidazoles as Type II NADH Dehydrogenase Inhibitors of <i>Mycobacterium tuberculosis</i>

The nonproton pumping type II NADH dehydrogenase in <i>Mycobacterium tuberculosis</i> is essential for meeting the energy needs in terms of ATP under normal aerobic and stressful hypoxic environmental states. Type II NADH dehydrogenase conduits electrons into the electron transport chain in <i>Mycobacterium tuberculosis</i>, which results in ATP synthesis. Therefore, the inhibition of NDH-2 ensures the abolishment of the entire ATP synthesis machinery. Also, type II NADH dehydrogenase is absent in the mammalian genome, thus making it a potential target for antituberculosis drug discovery. Herein, we have screened a commercially available library of drug-like molecules and have identified a hit having a benzimidazole core moiety (<b>6</b>, H37Rv mc²6230; minimum inhibitory concentration (MIC) = 16 μg/mL and ATP IC₅₀ = 0.23 μg/mL) interfering with the oxidative phosphorylation pathway. Extensive medicinal chemistry optimization resulted in analogue <b>8,</b> with MIC = 4 μg/mL and ATP IC₅₀ = 0.05 μg/mL against the H37Rv mc²6230 strain of <i>Mycobacterium tuberculosis</i>. Compounds <b>6</b> and <b>8</b> were found to be active against mono- and multidrug-resistant mycobacterium strains and demonstrated a bactericidal response. The Peredox-mCherry experiment and identification of single-nucleotide polymorphisms in mutants of <b>CBR-5992</b> (a known type II NADH dehydrogenase inhibitor) were used to confirm the molecules as inhibitors of the type II NADH dehydrogenase enzyme. The safety index >10 for the test active molecules revealed the safety of test molecules.