Semisynthesis, pesticidal properties, and toxicological study of osthole ether derivatives containing isoxazoline/isoxazole fragments at the C‐7 position

BACKGROUND Agricultural pests such as Mythimna separata Walker, Hyalopterus arundimis Fabricius, and Plutella xylostella Linnaeus pose significant threats to crops and trees. Due to overuse of chemical pesticides resulting in pest resistance and safety concerns, nowadays development of new pesticides is highly desirable. Therefore, new osthole ether derivatives containing isoxazoline/isoxazole fragments at the C‐7 position were studied as pesticidal agents. RESULTS Against M. separata , compounds 4d (R = 4‐ClPh), 5f (R = 2‐BrPh), 5 g (R = 4‐BrPh) and 5o (R = 1,3‐diphenylpyrazol‐4‐yl) showed 2.2 to 2.5 folds insecticidal activity compared to osthole; they showed delayed insecticidal activity and most of M. separata treated with them all died at the larval period. Against H. arundimis , compound 4d exhibited 4.4 times aphicidal activity compared to osthole. Against P. xylostella , an intermediate 3b showed 1.8‐fold effective insecticidal activity compared to osthole. Moreover, according to the toxicological study of 3b ‐treated P. xylostella , the changes in activities of three insect detoxification enzymes such as carboxylesterase (CarE), mixed function oxidase (MFO), and glutathione S ‐transferase (GST) over time were observed. CONCLUSION Compounds 3b and 4d can be further studied as leads for controlling P. xylostella , and M. separata and H. arundimis , respectively.