Design,Synthesis And Activity Study Of New Antimicrobial Peptides Analogs Of MPI And Anoplin By Intramolecular Cyclization And Side-Chain Link Strategy

Now with the emergence of many resistant bacteria in clinical and a dramatic increase in death rate in hospital,thus making the search for new drugs to replace antibiotic has become a serious problem.Antimicrobial peptides are small molecular peptides that arouse a great concern of the researchers.Therefore,in this thesis,a new intramolecular cyclization method(that is 1,3-dipolar cycloaddition)was used to design and synthesis new antimicrobial peptides.Structure modification contained two aspects.For the first,in order to improve enzyme stability of the new antimicrobial peptides,intramolecular cyclization method was used at different sites of the antimicrobial peptides of Anoplin and MPI,achieving their corresponding cyclic analogues.On the other hand,click chemistry(1,3-dipolar cycloaddition)was used to obtain a structure as triazole.Then we used the triazole structure to link the side chain of two different antimicrobial peptides.Three new combinatiorial analogs J-AR,J-MR,J-RR were synthesized by linking Trp-rich hexapeptide RW with Anoplin,MPI or itself.In four intramolecular cyclization analogs,C-MPI-I remained antimicrobial activity of the MPI,and the enzyme stability of C-MPI-1 was improved in comparing with MPI,but the hemolytic activity was slightly increased,which was in safe extent,too.The bacterial mechanism of C-MPI-I was the same to MPI.They all destroyed the integrity of bacterial cell membrane.What’s more,CD spectrum showned that the cyclization on i,i+6 C-MPI-2 may fully destroy the second structure of peptides such as a helical structure.However,cyclization on i,i+4 C-MPI-1 may increase the helicity of MPI.In three new combinatorial analogs,the antimicrobial activity was obviously improved.At the same time,the minimum inhibitory concentration values were reduced against the resistant bacterial.Three combinatorial peptides showed dose-dependent in 24 hours time-kill kinetics against standard Staphylococcus aureus(ATCC 25923)and resistant Staphylococcus aureus(725).When combined with the traditional antibiotics,the FIC value suggested that the relationship between antimicrobial peptides and antibiotics was synergic or synergetic.The enzyme stability of three analogs was the same in comparing with Anoplin and RW.Though their hemolytic activity was slightly increased,which was due to the higher hydrophobicity in three analogs,they were at a safe extent.Scanning electron microscopy,PI uptake and Outer and Inner membrane permeability assay showned that the bacterial mechanism of the three new analogs didn’t change in compared with three parental peptides.CD spectrum assay showed that the secondary structure of three new combinatorial peptides didn’t change.The research paper shows that click chemistry has a great potent in structure reformation.Whereas the recent research doesn’t cover all aspects,the following works should be applied to design high quality analogs.It may lay the foundation for the development of antimicrobial peptides in clinical.