The Antibacterial Structure-Activity Relationship Of Phloretin

Phloretin is a kind of flavonoid compound with dihydrochalcone structure.It is widely distributed in different parts of plants at different stages mainly in the form of glycosides(phlorizin),especially in the young fruit of apple.It was found that phloretin has a strong inhibitory effect on some common food-borne pathogens bacteria and pathogenic fungi,and it is a plant-derived natural product with low toxicity and other biological activities,which has great potential to be developed and produced as a natural bacteriostatic agent.At present,domestic and foreign research on the antibacterial properties of phloretin mainly focuses on the antibacterial activity of its antibacterial spectrum,but the understanding of the key sites that affect its antibacterial activity and the way in which each one is related is not clear.In view of this,this study investigated the synthesis of 8 phloretin derivatives and tested the antibacterial activity of phloretin and the obtained derivatives.The Free-Wilson method was used to calculate the contribution of each active group in the parent structure of phloretin to its bacteriostasis,and a multivariate linear regression model was used to establish a bacteriostatic structure-activity relationship model of phloretin.The purpose is to find out the key groups in the parent structure of phloretin that affect its bacteriostatic activity,and to identify the forms of association between each group and its bacteriostasis,so as to provide guidance for the development of phloretin as a new natural bacteriostatic agent and the targeted synthesis of specific phloretin derivatives.The main research methods and results are as follows:(1)With phloretin as the parent,different groups were introduced through reduction,condensation,substitution and other reactions,respectiveiy to obtain aminoethyl-phloretin,7-butoxy-phloretin,4'-nitro-phloretin,4'-cl-phloretin,5-butoxy-phloretin,5,7-dibutoxy-phloretin,phloretin isonicotinyl hydrazine and carbonyl reduction phloretin.All compounds were characterized and confirmed by 1H NMR and MS.(2)The antibacterial activities of the synthesized phloretin derivatives and phloretin on Listeria monocytogenes,Staphylococcus aureus,Escherichia coli and Pseudomonas fluorescent were detected by the Oxford Cup method.The test results showed that phloretin and phloretin derivatives all have inhibitory effects on the four strains,and the inhibitory effect on gram-positive bacteria(L.monocytogenes and S.aureus)is more obvious.At the same time,it was found that the antibacterial activity of the derivatives derived from phloretin was not as strong as that of phloretin itself.In addition,the MIC of phloretin,phlorizin and derivatives of phloretin on the four test bacteria were also detected,the results showed that the MIC of phloretin on four pathogenic bacteria were:31± 0.75ppm,40±0.45ppm,218±0.25 ppm and 312±0.55ppm,which were all smaller than the MIC of their derivatives.(3)Using the classic Free-Wilson method,respectively by the compound of four kinds of experimental fungus log 1/MIC as the dependent variable,the active functional groups of phloretin and the substituents introduced by derivatization were used as independent variables.Using the Matlab software and multivariate linear regression methods to calculate the regression coefficient of each variable,which is the contribution value of each substituent to the antibacterial activity of four common pathogenic bacteria.The results show that 4-C=0,5-OH and 7-OH in the structure of phloretin has a significant effect on its bacteriostatic performance,while the bacteriostatic activity contribution of 4'-OH was significantly weaker.(4)Establishment of quantitative structure-activity relationship of phloretin:through experimental studies in the previous parts,we can clearly see that the antibacterial property of phloretin is closely related to the 4-C=O,5-OH,7-OH and 4'-OH in its parent structure.In order to further investigate the relationship between its bacteriostatic and its structure,this part of study selected 4-C=O,5-OH,7-OH and 4'-OH active groups in the structure of phloretin as the the structural parameters,the MIC of the four test bacteria as the activity parameters,with SPSS software,using multiple linear regression method to establish the phloretin bacteriostatic quantitative structure-activity relationship model for gram-positive and negative pathogenic bacteria respectively.In summary,this study determined that 4-C=O,5-OH,7-OH in the parent structure of phloretin is the main structural parameter affecting its antibacterial activity,while 4'-OH had relatively weak effect on its antibacterial activity.And it was found that the effect of active groups in the phloretin on the bacteriostatic performance of gram-negative bacteria and gram-positive bacteria was different,mainly show is:4-C=O group in the phloretin has the most significant contribution to the bacteriostatic activity of gram-positive bacteria,and for gram-negative bacteria,the effect of 5-OH groups in the phlorizin parent body on its inhibitory ability is more superior.The quantitative structure-activity relationship model of the phlorizin antibacterial activity was analyzed,and the results showed that the model has a strong degree of fit and stability,which could provide guidance for future research of phloretin antibacterial activity.