Diphenyl Ether Hydrazone Derivatives as Novel Succinate Dehydrogenase Inhibitors for Effective Control of Rice Sheath Blight

Rice sheath blight, caused by <i>Rhizoctonia solani</i> pathogen, poses a significant threat to global food security. To address this challenge, we designed and synthesized diphenyl ether hydrazone derivatives (<b>3aa-</b><b>3bb</b>) as potential succinate dehydrogenase inhibitors. Most of these derivatives achieved 100% inhibition against <i>R. solani</i> at 50 μg/mL concentration. Notably, compound <b>3az</b> exhibited an exceptional efficacy of 95% control rate with an EC₅₀ of 0.28 μg/mL, which significantly outperformed boscalid at a concentration of 200 μg/mL, without affecting the rice growth and development. Furthermore, after treatment with <b>3az</b>, the growth morphology and intracellular changes of <i>R. solani</i> mycelia were consistent with those observed with boscalid. Additionally, the IC₅₀ values of compounds <b>3ay</b> and <b>3az</b> were 1.55 and 1.11 μM, respectively, which were better than the IC₅₀ value of boscalid (1.85 μM). The finding by molecular docking studies revealed that compound <b>3az</b> interacts with novel binding sites, offering an opportunity for the development of innovative SDH inhibitors for the efficient control of rice sheath blight disease.