Design,Synthesis And Antibacterial Study Of Novel Stapled Antibacterial Peptide Mimics

Diseases caused by bacterial infections often endanger people’s health.Before antibiotics were found,humans were often helpless to the diseases caused by infections.The discovery of penicillin opened the prelude for humans to fight bacterial infections.With the further development of antibiotics,humans benefit from the convenience brought by antibiotics,but also suffer from a series of problems caused by antibiotic resistance.Several important drug-resistant bacteria strains have been reported to cause great harm to human health:for example,vancomycin and methicillin resistant Staphylococcus aureus,carbapenems resistant P.aeruginosa,E.coli,and multi-drug resistant tubercle bacillus.Therefore,it is of great significance to develop new antibiotic drugs.However,in recent years,the development of antibacterial drugs has been declined,and bacteria could evolve resistance to the antibiotic drugs on the market in short time.Therefore,we urgently need to find new treatments to deal with infectious diseases caused by these drug-resistant bacteria.Cationic antimicrobial peptides are an important class of antimicrobial peptide normally with amphiphilic structure.Since the antimicrobial peptide was first found in the silkworm of North America,many peptides with antibacterial activity had been successively discovered and isolated from bacteria,fungi,plants,insects,amphibians,mammals,etc.Through the study of these antimicrobial peptides obtained,it was found that the antimicrobial peptides have diverse antibacterial mechanism(eg,destruction of bacterial cell membranes,interference with bacterial DNA or RNA and protein synthesis,and inhibition of mitochondrial function,etc).At the same time,most antibacterial peptides not only have good antibacterial activity but also have many other functions:such as promoting the expression of chemical factors;neutralizing the activity of endotoxin(LPS);promoting the apoptosis of macrophages and activated lymphocytes;Immune response to specific antigens;promotion of new blood vessel formation,etc.These excellent effects of antimicrobial peptides make them an important part of research in the development of anti-infectious drugs,and are also considered to be a good alternative to traditional antibiotics for drug-resistant bacterial infections.However,the inherent peptide properties of antimicrobial peptides,such as poor metabolic stability and susceptibility to protease hydrolysis,have limited the clinical application of most antimicrobial peptides.OH-CATH30 is an antimicrobial peptide isolated from the venom of King Cobra by the team of Professor Zhang Yun.Through further optimization of OH-CATH30,OH-CM6 was obtainedwith good antibacterial activity and immunomodulatory activity.With OH-CM6 as a template,our laboratory previously obtained a series of stapled OH-CM6 analogues with improved antibacterial activity,increased serum/plasma stability,and low hemolytic activity through the introduction of cationic bridge on its hydrophilic surface.In this study,we used the OH-CM6 as a template to synthesize(1)stapled analogues with an all-hydrocarbon bridgeon its hydrophobic surface and(2)bicyclic stapled analogues with one all-hydrocarbon bridge on the hydrophobic surface and another cationic bridge on the hydrophilic surface.The effects of the introduction of stapled structure on either hydrophilic surface or hydrophobic surface on the antibacterial activity was studied.Furthermore,the single or duble-brideged analogues were evaluated to find stapled antimicrobial with improved antimicrobial activity and increased protease stability.By introduction of an all-hydrocarbon bridge,on the hydrophobic surface at i and i+4 position of peptide sequence,we synthesized a series stapled analoues of OH-CM6.Furthurmore,a series of doule stapled analogues were synthesized with an additional cationic bridge on the hydrophilic surface.By screening of the antibacterial activity it was found that most of the stapled analogues of OH-CM6 had a broad antibacterial spectrum and good antibacterial activity against G~+and G~-bacteria.Compared with OH-CM6,most of the analogues of OH-CM6 can maintain their antibacterial activity,and some of the analogues had improved antibacterial activity.Initial study of the double-stapled analouges showed that they had comparable antibacterial activity as the the single-stapled analogues.In summary,in this study,we successfully synthesized a series of all-hydrocarbon stapled antimicrobial peptides and a series of double stapled antimicrobial peptides with an additional cationic bridge on the hydrophilic surface of OH-CM6.Through the study of their antimicrobial activity,some stapled peptide analogues with good antibacterial activity were found,which laid the foundation for our further research.