Design, synthesis and insecticidal activity of novel Isoxazoline Acylhydrazone compounds

Nowadays, the diamondback moth has ascended to become one of the most formidable pests plaguing cruciferous vegetables. Consequently, the exigency for the development of efficacious pesticide candidates for crop protection has never been more paramount. In response to this pressing need, this study presents a compendium of novel isoxazoline derivatives, incorporating acylhydrazone moieties, synthesized with the express purpose of serving as potential insecticides.

The structures of these derivatives were confirmed using Proton nuclear magnetic resonance (¹ H NMR), Carbon-13 nuclear magnetic resonance (¹³ C NMR), and high-resolution mass spectrometry (HR-MS). Most of these derivatives demonstrated effective insecticidal activities against Plutella xylostella. Notably, compound E3 exhibited exceptional insecticidal activity against Plutella xylostella (LC₅₀  = 0.19 mg L^-1 ), surpassing the effectiveness of ethiprole (LC₅₀  = 3.28 mg L^-1 ), and comparable to that of fluxametamide (LC₅₀  = 0.22 mg L^-1 ). Interestingly, compound E3 also displayed potent insecticidal activity against Pyrausta nubilalis (LC₅₀  = 0.182 mg L^-1 ) and Chilo suppressalis (LC₅₀  = 0.64 mg L^-1 ), and the LC₅₀ values of fluxametamide were 0.23 mg L^-1 (P. nubilalis) and 2.26 mg L^-1 (C. suppressalis), respectively. The molecular docking results revealed that the compound E3 can form a hydrogen bond and two Pi-Pi bonds with the active sites of GABA receptors. In addition, the DFT calculations were also performed to study the relationship between insecticidal activities. The structure-activity relationships suggested that the identity of the R substituent was crucial for their pesticidal activities.

The results of the present study suggest that isoxazoline acylhydrazone derivatives could be promising candidates against P. xylostella and other Lepidopteran pests. © 2023 Society of Chemical Industry.