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 1H and 13C 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 (q2 = 0.516; r2 = 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.

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.

•Asymmetrical 1,3,4-oxadiazole dyes were efficiently synthesized.•Structure–optical properties relationships were investigated.•The compounds exhibit bright violet–blue emission with high fluorescence quantum yields.•The high HOMO levels (−5.17 to −5.03 eV) are beneficial for hole-transporting.Six novel asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units have been efficiently synthesized and characterized by FT-IR, 1H NMR, 13C NMR, mass spectrometry and elemental analysis. The UV–vis absorption maximum wavelength, fluorescence excitation wavelength, fluorescence emission wavelength and fluorescence quantum yield were measured in dilute tetrahydrofuran solution. The solvent effect was also studied. The HOMO and LUMO levels of these compounds were calculated by density functional theory (DFT) (B3LYP, 6-31G*) method and cyclic voltammetry. They emit bright violet to blue emission with high fluorescence quantum yields (0.23–0.94) and large Stokes shifts (53–102 nm). These compounds possess high HOMO levels (−5.03 to −5.17 eV) and suitable band gaps, indicating that they could be benefit for hole injection. The results show that they have a potential for application in optoelectronic materials.Graphical abstract

•24 components were indentified in A. guilinensi essential oils (EO) by GC and GC–MS.•The antibacterial activities of fruits EO were the strongest and the diameter of inhibition zone of leaves EO was close to that of antibiotic streptomycin.•Stems EO increased cell membrane permeability, showing difference from streptomycin.•Three essential oils demonstrated low hemolytic rates (<1%) on human red blood cells.•Considering these merits, A. guilinensis EOs may be exploited as safe presearvatives.Concerns about the use of synthetic preservatives during food processing and storage have been raised due to their potential side effects on human health and the environment. The chemical compositions, bactericidal activities and mechanism of Alpinia guilinensis essential oils (EO) hydrodistilled from fruits, leaves and stems were investigated as a potential substitute for synthetic preservatives for the first time, respectively. The diameter of inhibition zone (DIZ), minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of three EOs against four foodborne pathogenic bacteria (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas eruginosa) indicated their broad-spectrum and strong antibacterial activities. Notably, three EOs showed obvious effects on S. aureus and the DIZ of leaves essential oil (16.8 mm) against S. aureus was close to that of antibiotic streptomycin (18.3 mm). The antibacterial mechanism of A. guilinensis EOs differed from streptomycin on the basis of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. A. guilinensis EOs may increase bacterial membrane permeability and directly break cell structure, leading to bacterial shrinkage and lysis. The low hemolytic rates (below 1%) of three EOs on human red blood cells (RBC) further suggested their safety for use. Taken together, the essential oils of A. guilinensis may provide natural and safe preservatives in food processing and storage.Download full-size image