Synthesis, insecticidal activity and toxicity to bees of phenylpyrazoles

Objective  To obtain phenylpyrazoles which have insecticidal activities and are eco-friendly based on fipronil framework.

Method  Using anilines with different substituents as materials, phenylpyrazole compounds 1−21 with different substituents were synthesized in two steps. The product structures were confirmed by ¹H NMR, ¹³C NMR and ESI-MS analysis. The biological activities of target products against Plutella xylostella were determined by leaf immersion method. Acute oral toxicities of compounds 1, 5, 12, and 16 to Apis cerana were determined.

Result  After 24 h treatment, LC₅₀ of compounds 1, 5, 12, 16 against P. xylostella were 0.26, 0.95, 0.33 and 1.10 mg·L⁻¹ respectively. The activities of compounds 1 and 12 against P. xylostella were higher than that of fipronil. Compounds 5, 12 and 16 showed lower acute oral toxicities to A. cerana compared with fipronil(0.05 mg·L⁻¹), but still were highly toxic with LC₅₀ of 0.21, 0.22 and 0.09 mg·L⁻¹ respectively. The structure-activity relationship indicated that the substituent of the phenyl-ring had a great influence on the activity of the phenylpyrazole compound. When the ortho position of the benzene ring was —Cl or —Br, the para position was —Cl, —CF₃ or —OCF₃, the compound had excellent activity against P. xylostella.

Conclusion  Replacement of substituents on the phenyl-ring of fipronil can improve the biological activity against P. xylostella, and reduce the toxicity to A. cerana, which has certain guiding significance for the development and structural optimization of arylpyrazole insecticides in the future.