Design and Synthesis of Metabolically Stable Tricyclic-SpiroLactams Inhibitors of Mycobacterium tuberculosis Type-II NADH Dehydrogenase: Structure−Activity and Structure−Property Relationship Studies

Tuberculosis (TB) remains a major global health threat, intensified by rising drug resistance. Tricyclic spirolactam (TriSLa) inhibitors targeting mycobacterial type II NADH dehydrogenases (Ndh/NdhA) represent a promising antibiotic class but previously suffered from poor metabolic stability. Through extensive structure−activity and structure−property optimization, we identified BDM91465, a potent and metabolically stable TriSLa analog. Cryo-EM analysis revealed its binding mode within the menaquinone pocket of Ndh, consistent with observed SAR trends. BDM91465 displayed favorable pharmacokinetics, including good bioavailability and low clearance, resulting in sustained exposure above its MIC. In vivo, BDM91465 significantly reduced Mycobacterium tuberculosis burden in mice, mirroring the phenotype of Ndh-2 genetic inactivation. These findings provide the first demonstration of Ndh-2 inhibition efficacy in a murine model, validating Ndh-2 as a druggable target and supporting further development of TriSLa-based regimen.