Development of 1,2,4-oxadiazole-containing isoxazoline insecticides with improved honeybee compatibility

Spodoptera frugiperda (S. frugiperda) and Plutella xylostella (P. xylostella) are major constraints to staple and cruciferous crops, respectively, and have evolved widespread resistance to anthranilic amide insecticides. Isoxazolines, acting as γ-aminobutyric acid (GABA) receptor modulators, are promising alternatives for controlling resistant populations. However, many members of this class exhibit high toxicity toward ecologically important pollinators. Here, we report a series of new isoxazoline analogues featuring a 1,2,4-oxadiazole motif designed by a ring-closure strategy to the fluxametamide scaffold, and we systematically assess their insecticidal efficacy, honeybee toxicity, and interaction with receptors.

Incorporation of a 1,2,4-oxadiazole moiety enabled the design, synthesis, and bioevaluation of 34 novel derivatives. Compound L1 displayed potent activity against P. xylostella, with a median lethal concentration (LC₅₀) of 0.89 mg L^-1. After chiral resolution, S-(+)-L1 showed markedly enhanced potency (LC₅₀ = 0.69 mg L^-1), being 159.36-fold more active than R-(-)-L1 (LC₅₀ = 109.96 mg L^-1) and comparable to fluxametamide (LC₅₀ = 0.51 mg L^-1). Notably, S-(+)-L1 exhibited substantially reduced acute contact toxicity to honeybees (LD₅₀ = 4.58 μg a.i./bee) relative to fluxametamide (LD₅₀ = 0.25 μg a.i./bee). Enzyme-linked immunosorbent assay (ELISA)-based assays and molecular docking suggested that S-(+)-L1 binds more favorably to the pest GABA receptor than its enantiomer, while the 1,2,4-oxadiazole unit specifically weakens hydrogen-bond interactions with the bee GABA receptor, thereby mitigating toxicity.

S-(+)-L1 is identified as a selective lead combining high pesticidal potency with improved pollinator safety, suggesting ring-closure-enabled scaffold hopping as a viable strategy to retain on-target engagement while enhancing non-target compatibility. © 2026 Society of Chemical Industry.