Exploration of New Dihydroindazole Derivatives as Promising Anti-TB Agents: Design, Synthesis, In Silico, and Biological Evaluation

The escalating threat of drug-resistant Mycobacterium tuberculosis (Mtb) necessitates the discovery of novel chemotherapeutic agents. In this study, a series of dihydroindazole-based derivatives were designed, synthesized, and evaluated for their antimycobacterial potential. Among the synthesized compounds, 8u exhibited the most potent in vitro activity against Mtb H₃₇Rv with a minimum inhibitory concentration (MIC) of 2 µg/mL, while 8i and 8q showed moderate activity (MIC = 8 µg/mL). Several analogs demonstrated MICs in the range of 16–32 µg/mL. 8u also displayed enhanced activity against single-drug-resistant Mtb strains, outperforming ethambutol and rifampicin. Structure–activity relationship analysis indicated that both the hydrazide linker and heteroaryl substitutions significantly influenced antimycobacterial activity. 8u was non-cytotoxic to Vero cells (CC₅₀ > 100 µg/mL), yielding a selectivity index (SI) > 50. Time–kill kinetics confirmed its bactericidal nature. Mechanistic investigations using molecular docking and 100-ns molecular dynamics simulations identified InhA as the probable molecular target. In silico ADMET predictions (QikProp and ProTox-3.0) supported favorable pharmacokinetic and toxicity profiles. Collectively, these findings highlight 8u as a promising lead for the development of next-generation anti-TB agents.