New drugs against Mycobacterium tuberculosis are urgently needed to deal with the current global TB pandemic. We report here on the discovery of a series of arylvinylpiperazine amides (AX-35 to AX-39) that represent a promising new family of compounds with potent in vitro and in vivo activities against M. tuberculosis. AX compounds target the QcrB subunit of the cytochrome bc1 terminal oxidase with a different mode of interaction compared to those of known QcrB inhibitors. This study provides the first multifaceted validation of QcrB inhibition by recombineering-mediated allelic exchange, gene expression profiling, and bioenergetic flux studies. It also provides further evidence for the compensatory role of cytochrome bd oxidase upon QcrB inhibition. In the absence of cytochrome bd oxidase, AX compounds are bactericidal, an encouraging property for future antimycobacterial drug development.

A series of derivatives of the antimycobacterial natural product pyridomycin have been prepared with the C2 side chain attached to the macrocyclic core structure by a C–C single bond, in place of the synthetically more demanding enol ester double bond found in the natural product. Hydrophobic C2 substituents of sufficient size generally provide for potent anti-Mtb activity of these dihydropyridomycins (minimum inhibitory concentration (MIC) values around 2.5 μM), with several analogs thus approaching the activity of natural pyridomycin. Surprisingly, some of these compounds, in contrast to pyridomycin, are insensitive to overexpression of InhA in Mycobacterium tuberculosis (Mtb). This indicates that their anti-Mtb activity does not critically depend on the inhibition of InhA and that their overall mode of action may differ from that of the original natural product lead.

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