Synthesis, Antitubercular Activity, and Computational Characterization of Novel Phenylpyrazole-Isoniazid Derivatives

Six new phenyl-1H-pyrazole-carbaldehyde isonicotinylhydrazone derivatives 1-10 were synthesized and characterized by spectroscopic (FT-IR, 1H NMR, and 13C NMR) techniques and electrospray ionization–mass spectrometry (ESI–MS). Homonuclear data from 2D-NMR (¹H-¹H NOESY) revealed that 3 and 5 adopt the transE isomeric form. The in vitro antitubercular activity of all the synthesized compounds was determined against Mycobacterium tuberculosis (sensitive H37RV and resistant TB DM97). With respect to the isoniazid (INH) standard drug (MIC = 0.91 μM), all the prepared compounds showed greater antitubercular activity with MIC values in the range of 0.38–0.82 μM against Mtb H37Rv-sensitive strain. However, the preliminary results indicated that Compounds 1–10 tested against the TB DM97-resistant strain showed low bioactivity. The optimized geometry of Compounds 1–10 has been determined by density functional theory (DFT) calculations. For Compounds 1–6, the most stable isomers (in DMSO) exhibited an E geometrical configuration, while Compounds 7–10 exhibited a Z configuration. The global reactivity values indicate that Compounds 1–10 are slightly more reactive and less stable than the standard (INH). Additionally, they exhibit a strong binding capacity to biomolecules, comparable to INH. The MEP map reveals that the negative and positive potential sites are predominantly located on the C=O and HN–NH groups, respectively, similar to those observed for INH. Drug-likeness and ADME properties were evaluated. All compounds showed adequate ADME properties and are drug-like. Molecular docking studies (Compounds 1–10) into the active site of mycobacterial InhA showed an acceptable dissociation constant with improved binding energy (from −6.7 to −8.1 kcal mol⁻¹) compared to isoniazid (−5.6 kcal mol⁻¹). Molecular dynamics simulations revealed that the molecules cmp3 (3) and cmp5 (5) form stable ternary complexes with InhA through persistent hydrogen bonding and hydrophobic interactions. These compounds showed reduced active-site fluctuations and superior binding free energies compared to INH. The findings represent a significant advancement in the discovery of potential antitubercular agents.