Design, Synthesis, and Biological Evaluation of 1,2,3-Benzothiadiazine-1,1-dioxide Derivatives as Potential Antifungal and Herbicidal Agents with Preliminary Mechanism Study.

Plant pathogenic fungi threaten crop health and yield by disrupting plant physiological and biochemical functions. In this study, we designed and synthesized a series of N-acetylhydrazine (amine)-1,2,3-benzothiadiazine-1,1-dioxide derivatives and evaluated their antifungal activity. Compound B2 showed strong activity against Rhizoctonia solani (EC50 = 0.320 μg/mL, superior to boscalid 1.25 μg/mL) and Fusarium graminearum (EC50 = 0.830 μg/mL, comparable to carbendazim 0.880 μg/mL), surpassing or comparable to commercial fungicides. Structure-activity relationship and DFT analyses highlighted the importance of substituent selection. Mechanistic studies indicated that B2 disrupted hyphal morphology, increased ROS, and enhanced membrane permeability. Several derivatives also exhibited herbicidal activity against common field weeds, suggesting potential multifunctional agrochemical applications.