Preliminary Study On Structure Optimization Of Active Compound Quercetin From Polygonum Orientale And Its Antibacterial Effect On Clavibacter Michiganensis Subsp.sepedonicus

Clavibacter michiganensis subsp.sepedonicus is a serious pathogen during potato planting.At present,chemical antibacterial agents are mainly used to control the pathogen,but chemical antibacterial agents are easy to remain and pollute.Compared with them,plant-derived antibacterial agents have less toxic side effects and are easy to degrade,and have gradually become a research hotspot.Quercetin,a leading compound against C.michiganensis subsp.sepedonicu,was previously isolated from the aquatic plant Polygonum orientale by our research group.In this dissertation,its structure was optimized as a skeleton,the optimal antibacterial derivative was obtained through screening,and the mechanism of optimal antibacterial derivative was studied.The research contents and results are as follows:1.Synthesis of quercetin derivativesQuercetin,the leading compound of Polygonum orientale,was used as the skeleton.The isopentenyl group with the name of‘natural plant defense’was introduced into A-ring 7-OH of quercetin.B ring selected common antibacterial groups to replace the positions of 3’,4’and 3’4’,including electron-withdrawing group and electron-donating group.The electron-withdrawing groups are chlorine atom and bromine atom,and the electron-donating group is methoxy group.Finally,nine target compounds with 7-isopentenyloxyflavonol structure were obtained.The structures of the derivatives were characterized by ¹H NMR,¹³C NMR and ESI-MS.Nine compounds have not been reported in the literature and are synthesized for the first time.2.Screening of antibacterial activity of quercetin derivativesThe screening standard is the effect against C.michiganensis subsp.sepedonicu.Thebestantibacterialderivative7-isopentenyloxy-4’-chloroflavonol was screened by the determinations of inhibition zone diameter,minimum inhibitory concentration,in vivo prevention and treatment effect.The pot experiment was carried out with this derivative.The results showed that the incidence of potato plants decreased,the disease index decreased significantly,the physiological indexes of seedlings increased significantly,the chlorophyll content increased,and the overall quality of seedlings increased.3.Antibacterial mechanism of 7-isopentenyloxy-4’-chloroflavonolAfter treated with 7-isopentenyloxy-4’-chloroflavonol,the extracellular alkaline phosphatase activity was significantly increased,the fluorescence intensity was significantly enhanced as PI entering the cell,the membrane potential was decreased,the extracellular concentrations of Na⁺and Mg²⁺were increased,and the activities of ATP,MDH and LDH in the pathogen were significantly decreased.The results indicated that7-isopentenyloxy-4’-chloro-flavonol destroyed the cell wall of the pathogen,damaged the cell membrane of the pathogen,disordered the transport of substances inside and outside the membrane,lost the selective permeability of the cell membrane,and interfered the normal respiratory metabolism of the pathogen.The results of this study can provide a basis for the further transformation of compounds against C.michiganensis subsp.sepedonicu,and provide a new way for the control of C.michiganensis subsp.sepedonicu.