Design, Synthesis, and Antifungal Evaluation of Novel Pyrazole-5-sulfonamide Derivatives for Plant Protection.

To develop further novel environmentally friendly antifungal agents with high efficacy, a series of pyrazole-5-sulfonamide derivatives were designed and synthesized by using the active molecules synthesized in previous works as lead compounds. Their antifungal activities were evaluated in vitro against ten highly destructive plant pathogenic fungi. The bioassay results indicated that more than half of the target compounds displayed potent antifungal activities (inhibition rate ≥85%) against and at 20 mg/L. Among them, compound exhibited significant broad-spectrum antifungal activities against , , , , and , with EC values of 0.45, 0.49, 3.06, 0.57, and 1.43 mg/L, respectively. Moreover, compounds and exhibited remarkable protective effects on apple canker similar to (89.5%) at 50 mg/L. Preliminary antifungal mechanism investigations demonstrated that compound may have inhibited mycelial growth by inducing oxidative damage to the mycelium and compromising the integrity of the cell membrane. Meanwhile, compounds and exhibited no obvious toxicity to worker bees ( ligustica). Taken together, these pyrazole-5-sulfonamide derivatives, particularly compound , possess huge potential to be developed as novel environmentally friendly fungicides with high efficacy.