Synthesis, characterization, and lipoxygenase inhibition of salicylaldehyde-derived schiff base metal complexes:  enzymatic and in silico evaluation using quinoa lipoxygenase

In the present study, novel Schiff base ligands were synthesized via the condensation of salicylaldehyde derivatives with o-aminophenol, and their metal complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and UO₂(VI) metal actetates were successfully prepared. The compounds were comprehensively characterized using FT-IR, ¹H-NMR, ¹³C-NMR, UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and magnetic susceptibility measurements. FT-IR spectra confirmed azomethine (C = N) coordination through characteristic bands at 1612-1630 cm^-1, while ¹H-NMR spectra exhibited diagnostic azomethine proton signals at δ 8.84-8.62 ppm. XRD analysis revealed a semi-crystalline nature with prominent reflections at 2θ = 18.02° and 20.87°, and SEM images demonstrated nanorod-like morphologies. Magnetic moment values supported the proposed coordination geometries of the paramagnetic complexes. The biological activity of the synthesized compounds was investigated through in vitro inhibition studies against lipoxygenase (LOX), a ~ 97 kDa enzyme purified from Chenopodium quinoa Willd. with 77.89% purity and 7.24% yield. All compounds exhibited competitive inhibition toward LOX, with inhibition constants (K_i) in the range of 0.014 ± 0.002 to 0.858 ± 0.194 μM, indicating remarkable inhibitory potency. Molecular docking studies further substantiated the experimental results by revealing key hydrogen-bonding and π-cation interactions between the most active compounds and essential amino acid residues within the LOX active site. Overall, the results demonstrate that these Schiff base metal complexes represent promising candidates for the development of potent LOX inhibitors.