5-(3,5-Dinitrophenyl)-1,3,4-oxadiazol-2-amine derivatives, their precursors, and analogues: Synthesis and evaluation of novel highly potent antitubercular agent.

Drug resistance is a growing problem for many pathogens, including mycobacteria. Small heterocyclic molecules are among the leading scaffolds for developing potential antimycobacterial agents. Therefore, based on the molecular hybridization approach, we have prepared an extensive series of N-substituted 5-(3,5-dinitrophenyl)-1,3,4-oxadiazol-2-amine derivatives. We also investigated their isosteres and acyclic synthetic precursors. The compounds were evaluated for their in vitro activity against Mycobacterium tuberculosis (Mtb) H37Rv, a panel of multidrug- and extensively drug-resistant Mtb isolates and two nontuberculous mycobacterial strains (NTM; M. avium and M. kansasii). The ability to inhibit mycobacterial growth was quantified using minimum inhibitory concentration (MIC) values. Many compounds achieved MIC values ≤ 0.03 µM for NTM and Mtb, regardless of their resistance profile. The highest activity was associated with oxadiazole and thiadiazole scaffolds with benzylamino or C5-C9 alkylamino substitution. The experimentally confirmed mechanism of action of these compounds consists of disruption of mycobacterial cell wall biosynthesis via inhibition of decaprenylphosphoryl-β-D-ribose 2'-epimerase (DprE1). In vitro toxicity evaluation was performed in a hepatocyte model (HepG2), while in vivo toxicity was evaluated using Danio rerio embryos. These findings identify a promising new chemotype with potent, broad-spectrum and selective antimycobacterial activity, including efficacy against resistant strains, and support its further development as a potential therapeutic candidate.