Synthesis of paeonol hydrazone derivatives and their anti‐oomycete, anti‐fungal, and nematicidal activities

Abstract BACKGROUND The natural product paeonol is a rich and sustainable natural bioresource, and its derivatives have various unique biological efficacy. As is well known, Schiff bases are a class of organic compounds with a wide range of biological activities, including anti‐fungal, insecticidal, anti‐viral, and nematicidal. RESULTS To discover biorational natural product‐based pesticides, nine intermediates (2–10), 12 sulfonylhydrazones (11a–11c, 12a–12c, 13a–13c, and 14a–14c) and 20 benzylidene hydrazones (18a–18r, 19a, and 20a) were synthesized by structural modification of paeonol, and their structures were characterized by proton nuclear magnetic resonance ( 1 H NMR), carbon‐13 ( 13 C) NMR, and high‐resolution mass spectrometry (HRMS). The stereochemical configurations of compounds 14a, 18d, and 18r were unambiguously confirmed by single‐crystal X‐ray diffraction. Furthermore, bioactivities of these compounds as anti‐oomycete, anti‐fungal, and nematicidal agents against three serious agricultural pests, Phytophthora capsici , Fusarium graminearum , and Heterodera glycines were evaluated. Among all tested compounds: (i) compound 7 exhibited promising anti‐oomycete against Phytophthora capsici , with a half maximal effective concentration (EC 50 ) value of 15.81 mg L −1 ; (ii) compounds 2, 7, 10, and 19a displayed promising anti‐fungal against F. graminearum , with EC 50 values of 12.22, 14.72, 23.39, and 33.10 mg L −1 , respectively; (iii) ten compounds (12a–12c, 14c, 18g–18j, 18m, and 19a) showed significant nematicidal activity against H. glycines , with median lethal concentration (LC 50 ) values all less than 30.00 mg L −1 . Especially for compound 18g, its LC 50 value is the smallest, at 12.65 mg L −1 . CONCLUSION The research results indicate that introducing nitro groups at the C5 position of paeonol, or introducing halogens at both C5 and C3 positions, can significantly enhance its biological activity against Phytophthora capsici , F. graminearum , and H. glycines . © 2024 Society of Chemical Industry.