Study On Structural Modification And Anti-bacterial Activity Based On Pleuromutilin And Myricetin

Natural products are derived from the metabolites of bacteria,fungi,animals,plants and marine organisms with good biological activity and structural diversity.They are often used as lead compounds for drug discovery and have always been a hot spot in the field of medicinal chemistry and drug design.Many early marketed antibiotic drugs are derived from penicillin and macrolide natural products.With the deepening of research on natural products,more and more antibacterial active ingredients have been discovered,including antibacterial peptides,terpenes,flavonoids,phenols,and active ingredients with new structures.Based on the extensive research of natural products in the field of anti-bacteria.The research content of this paper includes two parts:（1）Design,synthesis and evaluation of biological activity of novel pleuromutilin compounds;（2）Synthesis of myricetin glycosides and evaluation of antibacterial activity.Objective:Antibiotic resistance poses a serious threat to global health,while the number of new antibiotics approved for marketing is declining.Therefore,the search for more new antibacterial drugs has become imminent.In order to discover antibacterial drugs with good activity,we base our research on pleuromutilin and myricetin in order to obtain lead compounds with development value.Methods:The first part:A series of new pleuromutilin compounds were designed,and the synthetic route of their target compounds was determined,which using pleuromutilin as starting material,through sulfonic acid esterification,substitution reaction,reductive amination and nucleophilic addition reaction,a series of pleuromutilin compounds were prepared.In vitro antibacterial activity,in vitro-kill curves and cytotoxic activity were evaluated,and molecular docking simulations and ADMET predictions were performed on selected target compounds.The second part:the synthetic method designed in the previous stage was improved to prepare a large number of myricetin glycoside derivatives II-4.The antibacterial activity of 17myricetin glycosides and flavonoids was evaluated by broth dilution method.A preliminary study on the structure-activity relationship of its antibacterial activity.Results:The first part:Using pleuromutilin as starting material,32 pleuromutilin compounds were designed and synthesized,and their chemical structures were confirmed by ¹H-NMR,¹³C-NMR and HRMS.The results of in vitro antibacterial activity showed that most of the targeted compounds exhibit good potency in inhibiting the growth of pathogens including Methicillin-susceptible S.aureus（MSSA,ATCC29213,MIC:0.0625-16μg/m L）,Methicillin-resistant S.aureus（MRSA,ATCC43300,MIC:0.125-16μg/m L）and M.pneumoniae（ATCC15531 MIC:0.125-1μg/m L,ATCC29342 MIC:0.0625-0.25μg/m L and drug resistant strain MIC:0.5-2μg/m L）.In particular,the compounds I-57 and I-58 containing phenyl-urea group showed excellent activity with the MIC value less than 0.0625μg/m L against S.aureus ATCC29213.At 4 x MIC,the time-dependent killing assay indicated that I-58possessed more rapid bactericidal kinetics against MRSA than tiamulin.The binding free energy of compound I-58 was calculated to be-10.6 kcal/mol by molecular docking simulation,which was very similar to the interaction of tiamulin with ribosomes.The second part:through the improved synthesis method,we could be able to prepare a large number of myricetin glycoside derivatives II-4 and intermediates in the laboratory,and their structures were characterized by NMR and ESI-MS.The results of in vitro antibacterial activity showed that 8 myricetin derivatives had stronger antibacterial activity than myricetin.Conclusion:The first part:In this paper,the effective combination of urea/thiourea functional groups with pleuromutilin not only enriched the structural diversity of this class of compounds,but also helped to provide design ideas for this class of antibiotics.Based on the research on these compounds,it provided a valuable theoretical basis for improving the biological activity and druggability of pleuromutilin compounds in the next step.The second part:the modification of flavonol 3-hydroxygalactose can significantly increase the antibacterial activity of myricetin,which provides new clues for the further study.