Quinoxaline and quinoxaline-1,4-di-N-oxides: An emerging class of antimycobacterials.

Tuberculosis (TB) is a highly dreaded, infectious, chronic, airborne disease affecting more than two million people all around the world, with more than eight million cases every calendar year. TB is the second leading infectious cause of death after HIV/AIDS. Over the past few decades, numerous efforts have been undertaken to develop new anti-TB agents. The current frontline therapy for TB consists of administering three or more different drugs (usually isoniazid, rifampin, pyrazinamide, and ethambutol) over an extended period of time. But these drugs will take 6-12 months to cure TB, along with many side effects; hence, there is an urgent need to explore new anti-TB agents. Quinoxaline derivatives are a class of compounds that show a spectrum of biological properties and the interest in these compounds is exponentially growing within the field of medicinal chemistry. Quinoxaline-1,4-di-N-oxide derivatives have shown to improve the biological results and are endowed with anti-viral, anti-cancer, anti-bacterial, and anti-protozoal activities with application in many other therapeutic areas. Since quinoxaline derivatives are regarded as a new class of effective anti-TB candidates, their 1,4-di-N-oxide analogues may show promising in vitro and in vivo anti-TB activities and might be able to prevent the drug resistance to a certain extent. Therefore, the main aim of this review is to focus on important quinoxaline and quinoxaline-1,4-di-N-oxide analogues that have shown anti-TB activities, and their structure-activity relationships for designing anti-TB agents with better efficacies. The present review will be helpful in providing insights for rational designs of more active and less toxic quinoxaline-based anti-TB prodrugs.