Synthesis, nematicidal activity, fungicidal activity, and safety evaluation of tralopyril‐triphenylphosphonium derivatives

BACKGROUND: Plant-parasitic nematodes and phytopathogenic fungi severely threaten agricultural production, requiring highly efficient and safe novel pesticides. Herein, two series of tralopyril-triphenylphosphonium derivatives were synthesized, and their nematicidal/fungicidal activities and biological safety were systematically evaluated against Caenorhabditis elegans, Meloidogyne incognita, and phytopathogenic fungi. RESULTS: All target compounds showed nematicidal activity against C. elegans, with 7 g (LC₅₀ = 29.52 mg/L) exhibiting a significantly lower LC₅₀ than fosthiazate (LC₅₀ = 72.37 mg/L). In M. incognita pot assays under root-drenching conditions, 5f at 50/100 mg/L achieved 63.33%/76.67% control efficacy, outperforming cyclobutrifluram (61.11%/72.22%). At 100 mg/L, 5f showed protective efficacy against rapeseed Sclerotinia stem rot in a semi-in vivo assay with a protection rate of 77.98%, which was comparable to that of fludioxonil (80.01%) at the same concentration; meanwhile, 5a showed a protective efficacy of 72.00% against rice sheath blight in pot assays, demonstrating efficacy comparable to that of fludioxonil (75.11%). Seed safety assays detected that these high-activity compounds caused no significant phytotoxicity in rice, rapeseed, and wheat seeds. CONCLUSIONS: The tralopyril-triphenylphosphonium derivatives synthesized in this study exhibit high nematicidal and fungicidal activities, holding potential for further development as novel agrochemicals. © 2026 Society of Chemical Industry.