Project Summary Mycobacterium tuberculosis, the causative agent of tuberculosis, is a major health problem globally. The World Health Organization reports that billions of people are latently infected with the organism, the number of new cases continues to rise (>10 million in 2019) and >1 million died from tuberculosis in 2019. Current anti-tubercular drugs are mainly effective against metabolically active and replicating bacteria. In addition to the need for new antibiotics that are effective against both drug sensitive and drug resistant strains, there is an urgent need for new therapeutics that can shorten therapy. We have identified the triazolopyrimidines as anti-tubercular agents. The series has attractive biological properties with potent anti-tubercular activity, activity against non-replicating (persistent/tolerant) bacteria, a narrow spectrum of activity, and low cytotoxicity. Our preliminary data suggests that these molecules target a key step in bacterial respiration. We have made analogs of the series which show potential for further development. Our long-term goal is to develop the triazolopyrimidines series as new anti-tubercular agents with excellent physicochemical and biological properties. In this 3-year proposal we will complete sufficient exploration of the series to generate proof of concept that the molecules work in an animal model of infection. We will also conduct studies to identify the target and/or mode of action and to determine which other drugs (or drug candidates) would be the best partners for a novel combination regimen. The outcomes of this project would be (i) confirmation that the triazolopyrimidine series is a tractable series for further development as a novel anti-tubercular drug; (ii) confirmation of the mode of action; and (iii) identification of the best combination partners. Demonstration of in vivo activity and tractability of the series would lead to a full drug discovery and development project in the future.