Design of Novel Benzothiazole-Based Succinate Dehydrogenase Inhibitors Inspired by <i>Polyrhachis dives</i>: Structural Optimization, Potential Fungicidal Activity, and Mechanistic Insights

Inspired by benzothiazole derivatives with bioactivity from <i>Polyrhachis dives</i>, 33 benzothiazole-based acetamide derivatives were designed and synthesized via structural optimization, incorporating aryl sulfide fragments and saturated six-membered aza-heterocycles. Among them, compounds <b>JSZ16</b> and <b>JSZ28</b> exhibited potent broad-spectrum fungicidal activity <i>in vitro</i>, with median effective concentration (EC₅₀) values of 4.4 and 8.5 mg/L against <i>Sclerotinia sclerotiorum</i>, respectively, comparable to boscalid (EC₅₀ = 2.4 mg/L). <i>In vivo</i> assays further demonstrated the protective efficacy of <b>JSZ16</b> (77.6% at 200 mg/L) on rape leaves, albeit with limited curative effects. Mechanistic studies confirmed that <b>JSZ16</b> influences the cell membrane permeability of pathogenic fungi. Besides, the enzymatic activity assay demonstrated that <b>JSZ16</b> (IC₅₀ = 30.3 μM) effectively inhibited succinate dehydrogenase (SDH) activity, with its activity level being comparable to that of boscalid (IC₅₀ = 24.8 μM). Molecular docking analysis revealed that <b>JSZ16</b> and <b>JSZ28</b> shared a conserved binding mode with SDH, displaying a similar interaction pattern observed for the boscalid. Acute toxicity tests in mice revealed no significant adverse effects, underscoring the safety profile of <b>JSZ16</b>. This work presents benzothiazole-based SDH inhibitors as promising candidates for combating fungal pathogens with considerable efficacy and low toxicity.