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

Abstract BACKGROUND 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. RESULTS 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 (LC 50 ) of 0.89 mg L −1 . After chiral resolution, S ‐(+)‐L1 showed markedly enhanced potency (LC 50 = 0.69 mg L −1 ), being 159.36‐fold more active than R ‐(−)‐L1 (LC 50 = 109.96 mg L −1 ) and comparable to fluxametamide (LC 50 = 0.51 mg L −1 ). Notably, S ‐(+)‐L1 exhibited substantially reduced acute contact toxicity to honeybees (LD 50 = 4.58 μg a.i./bee) relative to fluxametamide (LD 50 = 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. CONCLUSION 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.