Design, synthesis, and anti-oomycete, antifungal and nematicidal activities of novel paeonol ether derivatives containing isoxazoline/isoxazole moiety

BACKGROUND Paeonol is the main active ingredient in root bark of Paeonia suffruticosa , with broad-spectrum bioactivity. Additionally, isoxazoline/isoxazole is becoming the core skeleton for creating efficient and green pesticides today owing to its unique structural advantages and bioactivity potential. RESULTS In order to discover biorational natural product-based pesticides, 26 novel paeonol ether derivatives ( 3a–q and 5a , c , d , f–j , m ) were synthesized by ingeniously introducing an isoxazoline/isoxazole ring, and their structures were well-characterized by proton and carbon nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS). The stereochemical configurations of five target compounds 3a , 3g , 3j , 5a and 5h were unambiguously subjected to single-crystal X-ray diffraction (XRD) analysis. Furthermore, we screened the bioactivities of these compounds as anti-oomycete, antifungal and nematicidal agents. Amongst evaluated derivatives, (1) compounds 2 and 4 displayed promising anti-oomycete against the plant pathogen Phytophthora capsici , with median effective concentration (EC 50 )values of 28.51 and 42.52 mg L –1 , respectively. (2) Compounds 2 and 4 also exhibited excellent antifungal activity against the plant pathogen Fusarium graminearum , with EC 50 values of 29.11 and 31.23 mg L –1 , respectively. (3) Nine compounds ( 3f–h , j , o–q and 5f , g ) showed significant nematicidal activity against Heterodera glycines , with LC 50 values all <30.00 mg L –1 . Especially for compound 3g , its LC 50 value is the smallest, at 21.78 mg L –1 . CONCLUSION The research results indicate that, on the one hand, introducing an allyl or propargyl group at the hydroxyl position of paeonol can effectively enhance its anti-oomycete and antifungal activities. On the other hand, further introduction of an isoxazoline/isoxazole ring into the structural skeleton of paeonol can significantly enhance its nematicidal activity. © 2026 Society of Chemical Industry.