The rising development of resistance to conventional fungicides is driving the search for new alternative candidates to control plant diseases. In this study, a series of new fluorine-containing stilbene derivatives was synthesized on the basis of our previous quantitative structure-activity relationship analysis results. Bioassays in vivo revealed that the title compounds exhibited potent fungicidal activities against phytopathogenic fungi (Colletotrichum lagenarium and Pseudoperonospora cubensis) from cucumber plants. In comparison to the previous results, the introduction of a fluorine moiety showed improved activities of some compounds against those fungi. Notably, compound 9 exhibited a control efficacy against C. lagenarium (83.4 ± 1.3%) comparable to that of commercial fungicide (82.7 ± 1.7%). For further understanding the possible mode of action of the stilbene against C. lagenarium, the effects on hyphal morphology, electrolyte leakage, and respiration of mycelial cell suspension were studied. Microscopic observation showed considerably deformed mycelial morphology. The conductivity of mycelial suspension increased in the presence of compound 9, whereas no significantly inhibitory effect on respiration was observed. Taken together, the fungicidal mechanism of this stilbene is associated with its membrane disruption effect, resulting in increased membrane permeability. These results provide important clues for mechanistic study and derivatization of stilbenes as alternative sources of fungicidal agents for plant disease control.
A total of 22 novel stilbene derivatives containing the 1,3,4-oxadiazole moiety and trimethoxybenzene were designed and synthesized. Their chemical structures were characterized by (1)H and (13)C nuclear magnetic resonance, infrared, and high-resolution mass spectrometry. Bioassay results revealed that some of the title compounds showed potent in vivo fungicidal activities against three phytopathogenic fungi (Pseudoperonospora cubensis, Colletotrichum lagenarium, and Septoria cucurbitacearum) from cucurbits at 600 μg/mL. Notably, compounds 4b, 4d, 4i, 4k, and 4l exhibited a broad spectrum and remarkably high activities against those fungi, some of which even showed a comparable control efficacy to that of the commercial fungicides. Three-dimensional quantitative structure-activity relationship based on comparative molecular field analysis with good predictive ability (q(2) = 0.516; r(2) = 0.920) was reasonably discussed. For the first time, the present work suggested that the stilbene derivatives containing the 1,3,4-oxadiazole moiety could be developed as potential fungicides for crop protection.
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