Isoniazid‐Dihydropyrimidinone Molecular Hybrids: Design, Synthesis, Antitubercular Activity, and Cytotoxicity Investigations with Computational Validation

A new series of isoniazid-dihydropyrimidinone molecular hybrids (8a-8n) were designed, synthesized and structurally characterized using different spectroscopic techniques viz., Fourier transform infrared spectroscopy, nuclear magnetic resonance (NMR), and high-resolution mass spectrometry followed by their antitubercular evaluation including their precursors (4a-4n), and a standard antitubercular drug (isoniazid; INH). The molecular hybrids particularly 8g (minimum inhibitory concentration (MIC) = 6.25 μg mL^-1), 8h (MIC = 1.56 μg mL^-1), 8k (MIC = 0.78 μg mL^-1), 8l (MIC = 6.25 μg mL^-1), and 8n (MIC = 0.39 μg mL^-1) demonstrated the most potent inhibitory activity against wild-type M. tuberculosis mc²6230, disclosing 8n as the most potent compound in the series. However, the potent compounds lost their activity against three INH-resistant M. tuberculosis strains mutated in katG. The more efficient compounds (8h, 8k, and 8n) were subsequently evaluated for their cytotoxicity against the THP-1 human monocytic cell line. Furthermore, the stability studies of the most potent compound carried out using ¹H NMR, UV-visible, and liquid chromatography-mass spectrometry revealed their structural integrity. Finally, in silico molecular docking simulations were conducted to explore the binding orientations of the potent compounds in the active site of the target protein InhA while ADME/T (absorption, distribution, metabolism, excretion, and toxicity) and global reactivity parameters were explored to determine their drug-likeness and stability profiles, respectively.