WaltherioneF Derivatives Synthesis And Biological Activity Studies Of Garden Plant Pathogenic Bacteria

The Garden plants are the main composition of urban green space,with economic value,cultural functions and ecological benefits.In the process of its growth and development,the prevention and control of garden plant diseases has always attracted much attention.There are many preventive measures,but they all have certain limitations.Therefore,it is inevitable to develop new efficient and low-toxic green fungicides based on natural product structure optimization.According to previous reports,Waltheriones alkaloids have antibacterial,antiviral and other biological activities.However,there are few studies on the development of new fungicides with such alkaloids as leading compounds.Taking WaltherioneF alkaloids as the leading structure,33 new compounds were designed and synthesized through structure optimization,and the structural characterization of ¹H NMR,¹³C NMR and HRMS was completed,and the fluorescence properties of the compounds were studied.Chinese rose black rot pathogen（Alternaria sp.）,lily grey mould of pathogenic bacteria（Botrytis elliptica（Berk.）Cooke）,hitom ring spot pathogen（Physalospora piricola Nose.）,peach leaf spot pathogens（Cercospora circumscissa Sacc.）and pear black rot pathogen（Alternaria kikuchiana Tanaka.）were selected as test objects,the relationship between the structural modification and biological activity of the compounds was systematically studied,and the mechanism of action was explored.Taking zinnia（Zinnia elegans Jacq.）,cosmos（Cosmos bipinnata Cav.）and ryegrass（Lolium perenne L.）as test objects,the effects of highly active compounds on seed germination and seedling growth of three herbaceous plants were measured,and the safety of compounds on garden plants was observed.The results were as follows:1.A total of 33 target compounds with novel structures were synthesized by the structural modification methods of cyclization and amidation,including intermediate4-quinolone（QD）derivatives quinoline QD-1-QD-5、quinoline esters（I）compounds I-1-I-6、4-quinolone amide（II）compounds II-A-1-II-A-13 and II-B-1-II-B-9.The synthetic compounds are the biological activity determination,studies have shown that compounds QD-4 and I-5 to haitang ring spot pathogen hyphal growth toxicity effect.The lower EC₅₀value of QD-4 was 38.9μg·m L^-1,and the EC₅₀ value of compound I-5 was 50.0μg·m L^-1.Among them,compound I-5 had the best control effect on the pathogenic bacteria of Begonia ring disease in vivo among the synthesized compounds,and its inhibitory effect was even close to that of the two commercial drugs.However,compounds II-A-1-II-A-13and II-B-1-II-B-9 affected their antibacterial activity due to their strong polarity,and their inhibitory effects on pathogenic bacteria were weak.The structure-activity relationship study showed that structure modification had different effects on the antibacterial activity of compounds against different pathogenic bacteria.The inhibitory effect of QD-4synthesized by introducing a bromine group into the 3-position of QD-3 was significantly improved on the pathogenic bacteria of Begonia ringworm.However,QD-4 was significantly weakened compared with QD-3 in the virulence effect on the pathogen of rose black spot.2.The fluorescence performance test showed that the 33 target compounds synthesized had fluorescence,among which quinolinate compound I-3 and quinolone amide compound II-B-6 have strong fluorescence and are prone to energy level transitions.The total energy,HOMO orbital energy and LUMO orbital energy of the two compounds are all high,and the large energy gap is conducive to absorbing more energy and emitting more fluorescence;I-3 was dissolved in nine solvents of different polarities,and its dichloromethane solution had the strongest fluorescence intensity,and its absolute fluorescence quantum yield value was 99.4%.The fluorescence properties of compounds are helpful to the study of the mechanism of action of highly active compounds.3.In the study of the mechanism of action of highly active compounds,the fluorescence properties of compounds are used,through a fluorescence microscope observation,I found quinolin ester compound I-5 can enter the hyphae cell,in bright light after 10 min immediately with blue excitation light,the hyphae produced obvious fluorescence phenomenon,and the compound I-5 with a concentration of 200μg·m L^-1 had a good virulence effect on the pathogenic bacteria of Begonia ringworm,which could cause hyphae to break and affects the hyphal morphology of pathogenic bacteria.The mechanism of action study showed that compound I-5 at the concentration of 200μg·m L^-1achieved the inhibitory effect on the pathogenic bacteria by destroying the cell membrane,nucleus and vacuole of Begonia rotundus.4.The research on the relevant indexes of herb seed germination showed that although quinolin ester compound I-5 exhibited inhibitory effect on the germination potential and germination rate of zinnia,it had little effect on the germination index of zinnia,and was basically nontoxic.The research on the relevant indexes of herb seed germination showed that although compound I-5 an exhibited inhibitory effect on the germination potential and germination rate of zinnia,it had little effect on the germination index of zinnia,and was basically nontoxic.In the determination of the effect on seedling growth,there was no significant difference in the relevant indexes of the seedlings treated with compound I-5 and two commercial drugs compared with the control group,and the seedlings could grow normally.