Excellent inhibitory activity of aromatic selenocyanates against phytopathogenic bacterium and structure-activity...

Selenium-containing organic compounds have gained attention for their diverse biological activities. Aromatic selenocyanates, in particular, show promise in medicinal chemistry, but their potential in agriculture - especially against plant pathogenic bacteria - remains unexplored. With the rise of bacterial resistance and limited effective bactericides, new agrochemicals with strong, broad-spectrum activity are urgently needed.

Twenty-three aromatic selenocyanates were synthesized and tested against three major phytopathogenic bacteria: Xanthomonas citri subsp. citri (citrus canker), X. oryzae pv. oryzae (rice blight), and X. oryzae pv. oryzicola (rice leaf streak). Compounds 3, 7, 8, 12, 15, and 16 exhibited exceptional antibacterial activity, with half-maximal effective concentration (EC₅₀) values generally below 1 μg mL^-1; significantly lower than commercial controls (thiodiazole-copper and tebuconazole, EC₅₀ > 63 μg mL^-1). Structure-activity relationship (SAR) analysis showed that para-fluoro, ortho-cyano, and 3,4-dichloro substitutions enhanced activity; pyridine-based analogs outperformed others; and α-selenocyanato acetophenones were less active than benzyl-type derivatives. Converting -SeCN to diselenide or thiocyanate (-SCN) greatly reduced potency. Molecular docking revealed that the -SeCN group binds strongly to the ParE subunit of topoisomerase IV, confirmed its role as a key pharmacophore. In vivo tests showed compound 12 achieved 85.19% disease control efficiency at 200 ppm, effectively suppressing bacterial growth in citrus plants.

This study is the first to systematically demonstrate the potential antibacterial activity of aromatic selenocyanates against phytopathogens, both in vitro and in vivo, highlighting the -SeCN group as a critical motif for agrochemical design. These findings open new avenues for developing selenium-based antibacterial agents in agriculture. © 2026 Society of Chemical Industry.