Brominated 1,4-dihydropyridine derivatives as potential insecticides against the cotton aphid (Aphis gossypii): synthesis, characterization, biological evaluation, and molecular docking studies

A new series of brominated 1,4-dihydropyridine derivatives bearing various aryl and heteroaryl substituents was successfully synthesized through a microwave-assisted multicomponent Hantzsch reaction followed by bromination under solar irradiation. The synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR spectroscopy and elemental analyses. Their insecticidal activities were evaluated against adult and nymphal stages of the cotton aphid, Aphis gossypii, using the leaf-dipping bioassay technique. Biological evaluation demonstrated that all synthesized derivatives exhibited significant insecticidal activity, with nymphs showing greater susceptibility than adults. Among the tested compounds, derivative 5e displayed the highest activity, with LC₅₀ values of 0.18 and 3.03 mg L^-1 against nymphs and adults, respectively. To investigate the potential mode of action, molecular docking studies were performed against acetylcholinesterase (AChE). All compounds showed favorable binding affinities toward the enzyme, ranging from -8.3 to -9.0 kcal mol^-1. Compound 5d exhibited the strongest predicted binding affinity (-9.0 kcal mol^-1), while the biologically most active derivative, 5e, showed a docking score of -8.7 kcal mol^-1. The combined biological and computational results indicate that brominated 1,4-dihydropyridine derivatives represent promising lead structures for the development of new insecticidal agents against A. gossypii.