Synthesis and Anti-Mycobacterium tuberculosis Activity of N-oxide Containing Heterocycles

Tuberculosis (TB) is an infectious disease caused by the bacterium, Mycobacterium tuberculosis (Mtb). The last surveys conducted by the World Health Organization (WHO) have described TB as the infectious disease responsible for the highest number of deaths worldwide. Furthermore, an increasing number of multidrug-resistant (MDR) and extensively-drug resistant (XDR) strains have complicated the scenario. In this regard, various N-oxide derivatives, such as furoxan, benzofuroxan, and quinoxaline 1,4-di-N-oxide, have been previously described as promising scaffolds with a potential to be explored as novel antitubercular drugs. Herein, 22 new N-oxide-containing compounds were synthesized followed by in vitro evaluation of their antitubercular potential against Mtb. Moreover, their safety and primary mechanism of action were also explored. The compounds demonstrated MIC₉₀ values ranging from 0.40 to 62 μM. Among the different heterocyclic compounds containing N-oxide, the benzofuroxan derivative 8 was found to be the most promising compound, with MIC₉₀ values of 1.10 and 6.62 μM against active and non-replicating Mtb, respectively. Cytotoxicity tests using MRC–5 cell line demonstrated an IC₅₀ value of 519.2 μM. Compound 8 was also active against monoresistant strains. Microarray-based initial studies on the mechanism of action revealed an upregulation of a number of transcripts encoding proteins belonging to both small and large subunits of the ribosome, suggesting that compound 8 blocked the process of translation. Altogether, these results indicated benzofuroxan derivative 8 to be a promising lead compound for the development of a novel chemical class of antitubercular drugs.