8-cyanobenzothiazinone analogs with potent antitubercular activity

Abstract

8-Nitrobenzothiazinones (BTZs) exemplified by macozinone are a new class of antitubercular agents with exceptionally potent activity. The aryl nitro group has been considered indispensable for activity since this is bioactivated within mycobacteria by the flavoenzyme DprE1 to a reactive nitroso metabolite that covalently labels Cys387. However, the aryl nitro group is a potential liability with regards to safety, stability, and resistance. In this paper, we introduced a nitrile as a bioisosteric replacement of the nitro group, which we hypothesize can maintain a similar covalent mechanism of inhibition, but mitigate against the aforementioned concerns. 8-cyanobenzothiazinone 1d displayed potent antitubercular activity with an MIC of 130 nM and had an improved volume of distribution in mice that increased the intrinsic half-life by twofold compared to macozinone. Analysis of the C-2 substituent of 1d revealed similar structure–activity relationships as observed for macozinone. Overall, the results confirm the 8-nitro group of benzothiazinones can be successfully replaced with a nitrile to retain useful activity and favorable pharmacokinetic properties. [Figure not available: see fulltext.].