Synthesis, biological evaluation, molecular docking studies, ADME toxicity, enzymatic target prediction, and FMO analysis of aryl thiosemicarbazone analogues

A series of fifteen aryl thiosemicarbazone analogues ( 3a – o ) were synthesized and characterized using FT-IR, 1 H NMR, and mass spectrometry. Their antibacterial activity was evaluated against a panel of Gram-positive and Gram-negative bacterial strains using the disc diffusion method, with several compounds displaying broad-spectrum efficacy e.g. 3a , 3b , 3c , 3d , 3e , and 3h . Specifically the following compounds showed the lowest MIC value such as 3n and 3o against S. aureus (50 μg mL −1 ), 3d and 3h against C. freundii (100 μg mL −1 ), 3a against C. sakazakii (50 μg mL −1 ), 3o against S. enteritidis (50 μg mL −1 ) , 3m against E. coli (50 μg mL −1 ) , 3b against Y. pestis (50 μg mL −1 ) . Compound 3n exhibited the highest antioxidant activity (IC₅₀ = 0.33 μg mL −1 ) in the DPPH assays, outperforming ascorbic acid (IC 50 = 1.15 μg mL −1 ), followed by compounds 3k (IC 50 = 4.66 μg mL −1 ), 3o (IC 50 = 3.052 μg mL −1 ), and 3m (IC 50 = 10.6 μg mL −1 ). Molecular docking studies with S. aureus DNA gyrase (PDB ID: 2XCT ) revealed strong binding affinities for compounds 3b and 3h , indicating potential as antibacterial agents. Furthermore, molecular docking of compound 3n with the human antioxidant enzyme receptor (PDB ID: 3MNG ) elucidated the antioxidant mechanism of aryl thiosemicarbazones. Drug-likeness and ADME/toxicity profiles were assessed via Molinspiration and Osiris Cheminformatics, indicated favorable pharmacokinetic and safety characteristics, with most compounds adhering to Lipinski's rule of five and exhibiting minimal toxicity. Enzymatic target prediction suggested activity against kinases, enzymes and proteases, supporting their potential as multi-target therapeutics. Finally, DFT calculations at the B3LYP/6-311G(d,p) level were employed to analyze frontier molecular orbital (FMO) energies, offering valuable insights into the electronic structure, reactivity, and potential biological activity of the thiosemicarbazone analogues. FMO analysis highlighted 3h as more reactive and polar, while 3b showed greater stability. These findings suggest that aryl thiosemicarbazones are promising candidates for the development of new antimicrobial and antioxidant agents.