Integrated Experimental and Computational Investigation of Salicylaldehyde-Derived Imine/Amine Derivatives as Antioxidant and Cytotoxic Agents.

Imines, commonly known as Schiff bases, are widely investigated compounds because of their structural versatility and biological properties. In this study, we aimed to evaluate the antioxidant potential of salicylaldehyde-derived imines and to determine how their reduction to the corresponding secondary amines affects their radical-scavenging activity and mechanism of action. Two series of phenolic derivatives, imines I1-I6 and amines A1-A6, were synthesized and assessed using an integrated experimental and theoretical strategy combining five in vitro antioxidant assays with density functional theory calculations. Antioxidant evaluation by DPPH, ABTS, FRAP, phenanthroline, and CUPRAC assays revealed distinct activity profiles for the two series. The imine derivatives were more effective in electron-transfer-based assays, whereas the reduced amines showed stronger DPPH radical-scavenging activity. Compound A6 exhibited the highest overall antioxidant activity, with IC50 values (e.g., DPPH IC50 = 26.7 ± 0.97 µM; ABTS IC50 = 11.69 ± 0.43 µM) lower than BHT (DPPH IC50 = 85.85 ± 3.69 µM) and BHA (DPPH IC50 = 59.39 ± 1.9 µM) in most assays. DFT calculations in aqueous medium indicated that the phenolic OH groups govern antioxidant reactivity and identified SPLET as the dominant mechanism for A6, supported by a remarkably high rate constant (k = 1.40 × 105 M-1s-1) and a 100% branching ratio (G), completely outcompeting the HAT mechanism (k = 2.28 × 10-2 M-1s-1). In addition to the antioxidant investigation, cytotoxicity was assessed in MDA-MB-231 breast cancer cells and Vero normal cells, revealing that the chlorinated derivatives such as I5 combine moderate anticancer activity (MDA-MB-231 IC50 = 122.6 ± 2.23 µM) with lower toxicity toward non-tumor cells (Vero IC50 > 400 µM). Molecular docking studies were conducted to elucidate the binding modes of the active derivatives within the active sites of EGFR, Tubulin, and Topoisomerase IIβ, while subsequent 100 ns molecular dynamics simulations validated the structural stability and sustained interaction energies of these predicted complexes.