The approval of bedaquiline has placed energy metabolism in the limelight as an attractive target space for tuberculosis antibiotic development. While bedaquiline inhibits the mycobacterial F 1 F 0 ATP synthase, small molecules targeting other components of the oxidative phosphorylation pathway have been identified. Of particular interest is Telacebec (Q203), a phase 2 drug candidate inhibitor of the cytochrome bcc:aa 3 terminal oxidase. A functional redundancy between the cytochrome bcc:aa 3 and the cytochrome bd oxidase protects M. tuberculosis from Q203-induced death, highlighting the attractiveness of the bd-type terminal oxidase for drug development. Here, we employed a facile whole-cell screen approach to identify the cytochrome bd inhibitor ND-011992. Although ND-011992 is ineffective on its own, it inhibits respiration and ATP homeostasis in combination with Q203. The drug combination was bactericidal against replicating and antibiotictolerant, non-replicating mycobacteria, and increased efficacy relative to that of a single drug in a mouse model. These findings suggest that a cytochrome bd oxidase inhibitor will add value to a drug combination targeting oxidative phosphorylation for tuberculosis treatment.

Mycobacteria have shown enormous resilience to survive and persist by remodeling and altering metabolic requirements. Under stringent conditions or exposure to drugs, mycobacteria have adapted to rescue themselves by shutting down their major metabolic activity and elevate certain survival factor levels and efflux pathways to survive and evade the effects of drug treatments. A fundamental feature in this adaptation is the ability of mycobacteria to vary the enzyme composition of the electron transport chain (ETC), which generates the proton motive force for the synthesis of adenosine triphosphate via oxidative phosphorylation. Mycobacteria harbor dehydrogenases to fuel the ETC, and two terminal respiratory oxidases, an aa3-type cytochrome c oxidase (cyt-bcc-aa3) and a bacterial specific cytochrome bd-type menaquinol oxidase (cyt-bd). In this study, we employed homology modeling and structure based virtual screening studies to target mycobacteria specific residues anchoring the b558 menaquinol binding region of Mycobacterium tuberculosis cyt-bd oxidase to obtain a focused library. Furthermore, ATP synthesis inhibition assays were carried out. One of the ligands MQL-H2 inhibited both NADH2-, and succinate driven ATP synthesis inhibition of M. smegmatis inside-out vesicles in micromolar potency. Similarly, MQL-H2 also inhibited NADH2-driven ATP synthesis in inside-out vesicles of the cytochrome-bcc oxidase deficient M. smegmatis strain. Since neither varying the electron donor substrates nor deletion of the cyt-bcc oxidase, a major source of protons, hindered the inhibitory effects of the MQL-H2, reflecting that MQL-H2 targets the terminal oxidase cytochrome bd oxidase, which was consistent with molecular docking studies.

A synthesis of the proposed structure of afzeliindanone was achieved by using an alkyne [2+2+2]-cyclotrimerization as a key step. The data for the synthetic material were found not to match those for the natural material, indicating a structural misassignment.

My heart is filled with gratitude to everyone who have accompanied me through my PhD journey. The completion of this research would not have been possible without the contribution of many individuals.First and foremost, I would like to extend my sincerest gratitude to my main supervisor, Prof.Gerhard Grüber. His valuable advice, encouragement, and insightful comments have provided a rewarding learning experience. I appreciate the life lessons, many of which will be carried with me throughout my whole life. I am extremely grateful to Prof. Roderick Wayland Bates. Prof. Bates first sparked my interest in research during my first year of my undergraduate studies. His patience, immense knowledge, and unwavering support have played a big role to where I am today.I would like to thank my mentor, Prof. Thomas Dick, and Prof. Kevin Pethe, for their valuable suggestions and advice. Special thanks to their students, Mr. Jickky Palmae Sarathy, Ms. Lee Bei Shi, and Ms. Ekaterina Sviriaeva, for the enjoyable moments where we exchanged ideas and experiences.