Discovery of Coumarin-7-N/O-Acethydrazide Derivatives as Novel Antifungal and Herbicidal Agents

Natural products (NPs) have attracted increasing attention due to their structural diversity, abundance, and low environmental impact, making them valuable for novel fungicide development. In this study, a series of coumarin-7-N/O acethydrazide derivatives were synthesized by incorporating acetic acid moieties into the coumarin scaffold. The in vitro antifungal activities of these compounds were evaluated against six common plant pathogenic fungi. Compound B13 demonstrated significant antifungal effects, with EC₅₀ values of 3.24, 1.89, 1.70, 0.36, 4.27, and 1.50 μg/mL against Botrytis cinerea, Alternaria solani, Fusarium graminearum, Rhizoctonia solani, Colletotrichum orbiculare and Alternaria alternata, respectively. Notably, the antifungal activity against R. solani was comparable to the commercial fungicide boscalid (EC₅₀ values = 0.31 μg/mL), while the activity against A. solani and A. alternata was significantly higher than that of boscalid (EC₅₀ values = 13.60 and 2.55 μg/mL, respectively), respectively. Furthermore, in vivo assays demonstrated that the protective efficacy of B13 against R. solani at 200 μg/mL (86.9%) was comparable to that of Validamycin (92.1%). The inhibitory effects of B13 against R. solani were further confirmed through scanning electron microscopy and fluorescence microscopy. The influence of the charge distribution of the compound on its antifungal activity was investigated using Density Functional Theory (DFT). Meanwhile, some of the compounds exhibited herbicidal activity against four common field weeds. These results indicate that B13 is a promising candidate for crop protection, exhibiting high efficacy and low toxicity.