Synthesis, Antibacterial Activity, and Mechanisms of Novel 6-Sulfonyl-1,2,4-triazolo[3,4-<i>b</i>][1,3,4]thiadiazole Derivatives

Abstract

A series of novel 6-sulfonyl-1,2,4-triazolo[3,4-<i>b</i>][1,3,4]thiadiazole derivatives were designed and synthesized. CoMFA models were established to analyze the quantitative structure-activity relationships on the basis of the EC₅₀ values of the compounds. The models were used to design and synthesize compounds <b>32</b> and <b>33</b> with higher activities. The EC₅₀ values of compound <b>33</b> against <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) and <i>Xanthomonas oryzae</i> pv. <i>oryzicola</i> (<i>Xoc</i>) were 0.59 and 1.63 mg/L, respectively, which were higher than those of thiodiazole copper (90.43 and 97.93 mg/L) and bismerthiazol (68.37 and 75.59 mg/L). Moreover, protective activities of compound <b>33</b> against bacterial leaf streak (BLS) and bacterial leaf blight (BLB) were 49.65% and 49.42%, respectively, which were superior to those of thiodiazole copper (44.28% and 41.51%) and bismerthiazol (38.89% and 40.09%). Protective activity of compound <b>33</b> against BLS was closely related to the improvement of defense-related enzyme activities, chlorophyll content, and photosynthesis activation. This is consistent with the upregulated expression of defense responses and photosynthesis-related proteins.