Synthesis And Antimicrobial Activity Of Coumarins

Coumarin is the most family among the found 1-benzopyran derivatives so far,which are widely distributed in the higher plants.Their diverse structure,more species,rich pharmacological action and extensive biological activity always acctract the great attention of the experts on chemistry,pharmacology and plant extraction at home and abroad.Although significant progress has been made in extraction,structural modification and biological activity of various coumarins in last decades,the development of their biosynthesis is relatively less.Therefore,a series of benzene ring substituted coumarin compounds with simple structure were designed and synthesized in this research.The activities of the target componds against phytopathogenic fungi and bacteria were systematically screened as well as their structure-activity relationships were preliminarily analyzed.The main contens and results of this study are as follows:1.Using substituted salicylic aldehyde and diethyl malonate as starting materials,20 kinds of ethyl coumarin-3-formates and 19 classes of coumarin-3-formic acid were synthesized by Knoevenagel consendation reation.Picked substituted resorcinol and ethyl acetoacetate as starting materials,four types of 7-hydroxy coumarins were generated via Pechmann condensation reaction of catalyzed by concentrated sulfuric acid;then 7-hydroxy coumarins and halogenated hydrocarbon carried out Williamson reaction to afford seven species of substituted coumarins.The structural characterization of all compounds was determined by the spectra of ¹H NMR and ¹³C NMR,and ESI-MS.2.The in vitro antifungal activity of 50 kinds of coumarins against 12 strains of plant pathogenic fungi was tested at 50?g/m L by the mycelium linear growth rate method,with kresoxim-methyl and carbendazim as positive controls.Furthermore,the compounds with higher initial activities were further assayed for median effective concentrations(EC₅₀). The results of antifungal tests disclosed that most of the compounds displayed the antifungal activity in varying degrees at 50?g/mL.The EC₅₀ values of 13 kinds of coumarins against Valsa mali(EC₅₀=4.6-73.1?g/m L)were lower than that of kresoxim-methyl(EC₅₀=98.5?g/m L),which was the most sensitive strain for tested compounds.Among of them,B19exhibited the highest activity with the EC₅₀ value of 4.6?g/m L.Furthermore,the activity of B6 and B19 against Fusarium solani,which EC₅₀ values were 11.5 and 11.1?g/m L,were higher than that of positive control(EC₅₀=14.2?g/mL).As far as Valsa mali,Colletotrichum gloeosporioides,Fusarium solani,and Fusarium oxysporum sp.Niveum were concerned,the EC₅₀0 values of B19 against them were 4.6,6.2,11.1,and 4.7?g/m L,respectively,which showed the highest inhibitory activity and wide antimicrobial spectrum.The EC₅₀0 value of B3against Curvularia lunata(EC₅₀=46.8?g/m L)was obviously lower than that of kresoxim-methyl(EC₅₀=89.6?g/mL).3.The study on the preliminary structure-activity relationship showed that:?1?For most of tested plant pathogenic fungi,the introduction of electron-withdrawing groups or the electron-donating groups to the phenyl ring improved their antifungal activity at different degrees.?2?The introduction of electron-donating groups greatly improved the antifungal activity of the corresponding compounds,while the introduction of electron-withdrawing groups enhanced the activity a little.For example,the activity of coumarins with 7-OCH₃,7-OEt or 7-OPr is generally higher,while that of 6-NO₂ substituted products is generally lower.?3?The sequence of the antifungal activity for the the same substituent at different positions is C-7>C-6>C-8,which documents that the alkoxy group at C7 is the key to maintain the antifungal activity.4.According to the filtering paper method,all compounds were screened for antibacterial activity in vitro at 2 mg/mL against 4 strains of bacteria.The results proved that most of the compounds displayed the antibacterial activity in varying degrees.In summary,this study not only synthesized a series of three series of coumarins via a simple and efficient protocol,but also achieved three leading compounds with good activity against plant pathogenic fungi.This provides a theoretical basis for the subsequent structural optimization of coumarins,as well as lays a firm foundation for the research and development of coumarin antimicrobial agents.The continued research will synthesize novel coumarins,complete the in vivo antimicrobial experiments and safety experiments,and explore the activities of anticancer,insecticidal and antioxidant activities.