Synthesis and biological characterization of metarylpicoxamid: a fungicide for control of soybean diseases

BACKGROUND: Various fungal diseases inflict significant damage to soybean production globally, with Asian soybean rust (ASR) caused by Phakopsora pachyrhizi of a major concern in South America. Metarylpicoxamid, the third fungicide in the picolinamide chemical class following fenpicoxamid and florylpicoxamid, was discovered and characterized for control of key soybean diseases. RESULTS: Potent inhibition of fungal mitochondrial electron transport in Parastagonospora nodorum and cross-resistance with the natural product UK-2A in three yeast isolates carrying specific Qi target site mutations (L198F, G37C and N31K) confirmed metarylpicoxamid binds to the Qi site of fungal cytochrome b (cyt b) protein. A homology model with a preferred binding pose to cyt b of P. parachizi was developed, with the likely effect of the three amino acid exchanges on target site binding proposed. Metarylpicoxamid demonstrated strong protectant and curative activity against ASR. The fungicide exerts its protectant activity by preventing the appressoria formation on germinating spores and delivers curative potency by arresting the growth and development of infecting fungal mycelia. Effective foliar redistribution and long-distance xylem transport in soybean plants, as well as translaminar movement were detected. Additionally, metarylpicoxamid was highly active against soybean powdery mildew and potent against additional soybean pathogens including Cercospora kikuchii, Septoria glycines, Corynespora cassiicola, Colletotrichum truncatum and Sclerotinia sclerotiorum. CONCLUSIONS: With a novel Qi target site of action for soybean markets, metarylpicoxamid provides a new solution to growers to manage ASR and other major soybean diseases. The fungicide also represents a much-needed sustainable alternative to implement practical strategies for fungicide resistance management. © 2026 Society of Chemical Industry.