Rational design of hybrid benzilmonoxime-thiocarbohydrazide Schiff bases as emerging anti-tubercular chemotypes:...

The continued emergence of multidrug-resistant tuberculosis (TB) necessitates the development of structurally novel anti-tubercular agents with improved efficacy, favorable safety profiles, and the potential to overcome existing resistance mechanisms. In the present study, three Benzilmonoxime-thiocarbohydrazide Schiff base derivatives (HBMT2,4-DMB, HBMT2,5-DMB, and HBMT3,4-DMB) incorporating dimethoxy-substituted aromatic motifs were rationally designed, synthesized, and comprehensively characterized using FT-IR, ¹H/¹³C NMR, HRMS, CHNS elemental analysis, and HPLC purity assessment. Their antimycobacterial activity was evaluated against Mycobacterium tuberculosis H37Rv, while cytocompatibility was assessed in HEK293 cells to determine selectivity and preliminary safety characteristics. Among the investigated derivatives, HBMT2,4-DMB exhibited the most favorable biological profile, demonstrating potent antimycobacterial activity (MIC = 1.25 ± 0.08 μg/mL), low cytotoxicity, and the highest selectivity index. To gain molecular-level insights into the observed biological activity, an integrated computational approach involving density functional theory (DFT) calculations, molecular docking, molecular dynamics (MD) simulations, MM/GBSA binding free-energy analysis, and in silico ADMET prediction was employed. Computational investigations revealed favorable electronic characteristics, stable protein-ligand interactions, and strong binding affinity toward the M. tuberculosis Polyketide Synthase 13 (Pks13) thioesterase domain, a validated target involved in mycolic-acid biosynthesis and cell-wall assembly. Notably, HBMT2,4-DMB consistently displayed the most favorable overall profile across biological evaluation, docking, and simulation studies, suggesting that the 2,4-dimethoxy substitution pattern contributes positively to target engagement and antimycobacterial activity. Furthermore, ADMET analyses predicted favorable drug-likeness, oral absorption potential, and acceptable safety characteristics for the investigated compounds. Collectively, these findings identify Benzilmonoxime-thiocarbohydrazide Schiff bases as a promising and previously underexplored class of anti-tubercular chemotypes. In particular, HBMT2,4-DMB emerged as the most promising lead-like scaffold, providing a valuable foundation for future structure-activity relationship studies, mechanistic investigations, and evaluation against drug-resistant M. tuberculosis strains.