Devoloping Methods For Diversification Of Peptides And Proteins Based On Dehydroalanine

Protein is one of the most important materials of lives,and bears almost all physiological activities.Because the study of native proteins has not been able to meet the needs of modern biological research and technological development,researchers have gradually focused on the study of modified proteins.However,since the specifically modified protein is difficult to be obtained by conventional gene expression techniques or enzyme catalysis,it is very important to develop effective chemical methods to synthesize proteins with site-specific post-translational modifications,or to specifically modify the proteins.At present,researchers have developed many methods to chemically modify proteins based on different strategies and chemical reactions,but it is still not easy to achieve sitespecific chemical modifications.Dehydroalanine(Dha),as a biocompatible non-natural amino acid,can be easily introduced into native proteins.More importantly,due to the special chemical properties of Dha,a variety of bioorthogonal reactions can be utilized to install site-specific protein modifications.Therefore,Dha-based protein chemical modification methods have received increasing attention in recent years.In this thesis,we developed two different methods for chemically modifying peptides and proteins based on Dha residue,and designed a novel strategy for the synthesis of lanthipeptides:(1)We developed a chemical modification method that is highly specific for Dha on peptides and proteins by utilizing the phospha-Michael addition reaction between Dha and phosphine compounds.The phospha-Michael addition reaction can be used to introduce monovalent or multivalent functional groups to Dha-containing peptides and proteins.We also developed a novel strategy for peptide stapling by this method,which could significantly improve the cell penetrating property of the peptides.(2)Bifunctionalization of olefins is a very efficient and common method for introducing functional groups to target compounds.We have developed a method for bifunctionalization of Dha on peptides mediated by cerium(IV)ammonium nitrate.The reactions undergo a free radical process,and under different reaction conditions,diazidation and hydroxyazidation of the olefin on the Dha residue can be achieved respectively.After the introduction of the azide group,the peptide can be further diversification with click chemistry.(3)Based on the structural characteristics of lanthipeptides,we designed a new strategy for the synthesis of lanthipeptides by using the cascade chemical reactions of Dha and cysteine,including cysteine disalkylation elimination,intramolecular thiaMichael addition and native chemical ligation.This strategy has the potential to achieve the total synthesis of the lanthipeptides.We successfully synthesized the lanthipeptide SapB using this strategy,which is the first report of the total synthesis of SapB.