Synthesis, Larvicidal Activity, and In Silico Mechanistic Insights of Novel Polyfunctionalized Pyridine Derivatives Against Culex pipiens L.

Abstract

A strategically engineered, eco-conscious synthetic platform was developed to access a novel library of eighteen polyfunctionalized pyridine-based heterocycles through high-efficiency multicomponent and annulation strategies, using 2-amino-4-(4-chlorophenyl)-6-(p-tolyl)nicotinonitrile (M) as a privileged core. Structural diversity was maximized by integrating potent pharmacophores, including pyrido[2,3-d]pyrimidines, naphthyridines, triazines, and fused pyrrolo/tetrazolo motifs, via both conventional and accelerated (microwave/ultrasound-assisted) routes, affording excellent yields with high structural fidelity as confirmed by IR, ¹H/¹³C NMR, and mass spectrometry. Biological evaluation revealed that all synthesized compounds had excellent larvicidal efficacy against Culex pipiens larvae, especially 15 and 9, emerging as lead candidates that exhibited exceptional LC₅₀ values of 0.118 and 0.137 μg/mL, respectively. Biochemical assays of the most effective compounds demonstrated pronounced inhibition of key detoxification enzymes, acetylcholinesterase, cytochrome P450 monooxygenase, and carboxylesterase. Advanced in silico analyses, encompassing molecular docking, molecular dynamics (200 ns), MM/GBSA binding free energy, and ADMET predictions, elucidated binding stability, mechanistic pathways, and favorable eco-safety profiles, including low predicted environmental persistence. Collectively, these results position the synthesized derivatives, particularly compound 15, as a promising generation of larvicidal agents with dual action targets one or more modes of action to reduce the development of resistance.