Design, Synthesis, Biological Evaluation, and Computational Studies of Pyrazine-1,3,4-Oxadiazole Analogs as Potential Antitubercular Agents

Tuberculosis (TB) remains a major global health threat, with Mycobacterium tuberculosis (Mtb) causing high morbidity and mortality. The rise of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) necessitates novel therapeutics with improved efficacy and safety. Among heterocyclic frameworks, pyrazine and oxadiazole derivatives have shown promising antimycobacterial activity. Pyrazinamide is a key pyrazine-based drug, whereas 1,3,4-oxadiazoles exhibit strong enzyme inhibition. In this study, a series of pyrazine-1,3,4-oxadiazole derivatives were synthesized and characterized using infrared (IR), mass spectrometry, nuclear magnetic resonance (NMR), and elemental analysis. Their antitubercular activity was evaluated against the Mtb H 37 Rv strain using the microplate alamar blue assay (MABA). The compounds exhibited minimum inhibitory concentration (MIC) values ranging from 3.13 to 12.5 µg/mL (9.39-55.75 µM). Notably, compounds 2e, 2f, and 2n exhibited the highest potency, attributed to halogen substitutions that enhanced lipophilicity and target interactions. Molecular docking studies reinforced these results, with compound 2f demonstrating a strong binding affinity (-9.0 kcal/mol) for the DprE1 enzyme, surpassing standard anti-TB drugs, isoniazid (-5.3 kcal/mol) and rifampicin (-7.9 kcal/mol). In addition, molecular dynamics (MD) simulation results revealed that compound 2f exhibits superior structural stability, compactness, and consistent binding interactions with DprE1. These findings highlight the potential of pyrazine-oxadiazole hybrids as promising scaffolds for developing novel antitubercular agents.