N-Thio-Beta-Lactams Targeting L,D-Transpeptidase-2, With Activity Against Drug-Resistant Strains Of Mycobacterium Tuberculosis

Effective treatment of tuberculosis is frequently hindered by the emerging antimicrobial resistance of Mycobacterium tuberculosis. The present study evaluates monocyclic beta-lactam compounds targeting the mycobacterial cell wall remodeling. Novel N-thio-beta-lactams were designed, synthesized, and characterized on the L,D-transpeptidase-2, a validated target in M. tuberculosis. The candidates were evaluated in biochemical assays identifying five compounds presenting target-specific kinetic constants equal or superior to meropenem, a carbapenem currently considered for tuberculosis therapy. Mass spectrometry in line with the crystal structures of five target-ligand complexes revealed that the N-thio-beta-lactams act via an unconventional mode of adduct formation, transferring the thio-residues from the lactam ring to the active-site cysteine of Ldt(Mt2). The resulting stable adducts lead to a long-term inactivation of the target protein. Finally, the candidates were evaluated in vitro against a drug-susceptible and multidrug-resistant clinical isolates of M. tuberculosis, confirming the antimycobacterial effect of these novel compounds.