Antiphytopathogenic Diphenyl Ethers from the Marine-derived Fungus Aspergillus sydowii

Background: Natural products from the marine-derived Aspergillus sp. have great potential in agricultural usage due to their broad biological activities. Objective: This study was designed to investigate the antiphytopathogenic compounds from marinederived fungus Aspergillus sydowii LW09. Methods: The compounds were isolated and purified by chromatography methods, and their structures were elucidated by analysis of the NMR and MS spectroscopic data as well as comparison with those of literature. All compounds were evaluated for antibacterial activities against phytopathogenic bacteria Pseudomonas syringae and Ralstonia solanacarum, along with spore germination inhibition of phytopathogenic fungi Fusarium oxysporum and Alternaria alternata. Results: Two diphenyl ethers violaceols I (1) and II (2), along with two alkaloids acremolin (3) and WIN 64821 (4) were isolated from the fermentation extracts of A. sydowii LW09. Compound 1 showed significant antibacterial activity against P. syringae and R. solanacarum with the same MIC values of 4 μg/mL, while compound 2 showed obvious antibacterial activity against P. syringae and R. solanacarum with MIC values of 2 and 1 μg/mL, respectively. Moreover, both 1 and 2 could inhibit the spore germination of F. oxysporum in the concentration range of 64–128 μg/mL. In addition, violaceol I (1) also inhibited the spore germination of A. alternata at 128 μg/mL. Conclusion: This study provided the potential antiphytopathogenic drug candidate for further studies.