Synthesis and insecticidal/acaricidal activities of osthole derivatives containing the 1,3,4-oxadiazol-2-ylsulfenyl fragment

To further enhance the utility of osthole, we designed and synthesized 26 novel osthole derivatives containing the 1,3,4-oxadiazol-2-ylsulfenyl fragment, and measured their insecticidal and acaricidal activities. Meanwhile, through scanning electron microscope (SEM), the effects of compound 6h on the cuticle layer of Tetranychus cinnabarinus Boisduval were observed. The results shown that compound 6h (R=3-OCH₃Ph) exhibited the highest acaricidal activity against female adults of T. cinnabarinus with a 72 h LC₅₀ value of 0.466 mg/mL, which was 2.6-fold activity of osthole (LC₅₀ value 1.200 mg/mL); compounds 6u (R=4-CF₃Ph) and 6v (R=3-CNPh) displayed the most potent insecticidal activity against the 3rd instar larvae of Plutella xyllostella Linnaeus with 48 h LC₅₀ values of 0.617 and 0.853 mg/mL, respectively; compound 6u showed 2.4-fold insecticidal activity of osthole (LC₅₀ value 1.503 mg/mL). The SEM results showed that the cuticle layer of female adults of T. cinnabarinus was folded and collapsed within 24 h after treatment with compound 6h , and this distinct symptom persisted over time. Overall, this study establishes a framework for the application of osthole derivatives as acaricidal and insecticidal agents.