Development of Isoniazid–Pyrazole Hybrids as Potential Antitubercular Agents

A series of INH–pyrazole molecular hybrids (6a–o) was synthesized and evaluated for in vitro anti-tubercular activity against drug-susceptible, multidrug-resistant (MDR), and extensively drug-resistant (XDR) Mycobacterium tuberculosis strains, alongside their corresponding precursors (4a–o), using isoniazid (INH) as the reference drug. Overall, the hybrid compounds exhibited inhibitory activity comparable to or exceeding that of INH against the drug-susceptible strain. Among the series, compounds 6a, 6d–6f, and 6m demonstrated the highest potency, with a minimum inhibitory concentration (MIC) of 0.9 µM, corresponding to an approximately 4.3-fold enhancement relative to INH. Compounds 6b,c, 6g–i, and 6l,m also showed noticeable activity (MIC = 1.95 µM), representing an approximate twofold improvement over INH and significantly outperforming their respective precursors. Notably, compound 6o exhibited enhanced activity against the XDR strain (MIC = 121 µM), reflecting an approximately 2.8-fold improvement compared to precursor 4o (MIC > 341 µM), thereby highlighting the advantage of molecular hybridization. However, all compounds displayed diminished activity relative to INH against the resistant strains. Against the MDR strain, compounds 4h, 6e, and 6g displayed measurable activity, with MIC values of 76, 125, and 112 µM, respectively. Cytotoxicity assessment using THP-1 human monocytic cells revealed low toxicity, with all tested compounds maintaining acceptable cell viability at 10 µg/mL. In addition, in silico ADME analysis indicated that the hybrid molecules comply with key drug-likeness criteria. Collectively, these findings suggest that INH–pyrazole hybrids represent promising lead scaffolds for the development of next-generation anti-tubercular agents.