The Derivative Study On The L-lysine-bis-lactam Peptide [i,i+4]-stapling

To develop approaches to efficiently modulating protein–protein interactions(PPIs)has been an active area in modern chemical biology and drug discovery efforts.The primary type of the PPIs targeted are those mediated by α-helix.The stapled peptides have become a significant type of the PPI blockers since they are able to reproduce the pharmacophore of the parent linear peptide bound to a biological target and have various superior properties.Professor Weiping Zheng’s research group(our research group)and Professor Zhenghe Wang’s research group found a unique PPI in colon cancer cells and proved that this PPI can become a new target for the development of colon cancer drugs.It was also found in the study that an all-hydrocarbon [i,i+4]-stapled peptide with 18 amino acids built upon the amino acids 541-558 segment of the oncogenic E545 K variant of the catalytic subunit p110α of phosphatidylinositol 3-kinase α(PI3Kα)(i.e.p110α[E545K])was able to effectively inhibit the interaction of p110α[E545K]with insulin receptor substrate 1(IRS1)in colon cancer cells,but this stapled peptide(i.e.lead compound 1)was found to exhibit low % α-helicity and proteolytic stability.In the subsequent work in our research group,based on the all-hydrocarbon [i,i+4]-and [i,i+7]-stapling modes,the effects of the staple length and structural characteristics of the corresponding bis-lactam stapled peptides on % α-helicity were investigated and a bis-lactam stapling mode was found to be superior to that of the afore-mentioned lead compound 1 and to also represent the best bis-lactam [i,i+4]-stapling mode by then,i.e.that stapled with 1,4-phenylenediacetic acid on two L-lysine side chains.In order to explore if the afore-mentioned then best L-lysine bis-lactam [i,i+4]stapling mode could be further improved,in the current thesis work,we started out with evaluating a derivative mode,i.e.the L-lysine bis-thiourea [i,i+4]-stapling.However,the corresponding stapled peptide built upon the afore-mentioned p110 α [E545K](541-558)sequence(i.e.2)was found to exhibit a much lower %α-helicity than that of the corresponding L-lysine bis-lactam [i,i+4]-stapled peptide(i.e.lead compound 1).In view of this finding,we turned our attention to evaluate the outcome of replacing L-α-methyl-lysine for L-lysine in the afore-mentioned then best bis-lactam[i,i+4]-stapling mode.For this,L-α-methyl-lysine would be a direct replacement for L-lysine,however,for the sake of synthetic accessibility and our interest in examining the impact of different stereochemistry at the stapling site,we decided to employ the afore-mentioned p110α[E545K](541-558)sequence as the template to prepare the D/L-α-methyl-thialysine-stapled peptides 3-6 together with the L-thialysine-stapled peptide 7.The % α-helicity values calculated from the circular dichroism(CD)measurements on the stapled peptides 3-6 indicated that,while their % α-helicity values were largely comparable to each other,they were all greater than that of the stapled peptide 7.In addition,the stapled peptide 6 was also found to be proteolytically more stable than the stapled peptide 7.In the current thesis work,another pair of the bis-lactam [i,i+4]-stapled peptides(i.e.8 and 9)were also prepared,i.e.those modeled on a sequence derived from ribonuclease A(RNase A).The CD measurement and the proteolytic stability assessment indicated that the L-α-methyl-thialysine-stapled peptide 8 exhibited greater % α-helicity and proteolytic stability than the L-thialysine-stapled peptide 9.Moreover,the stapled peptides 7 and9 were found to exhibit greater % α-helicity and proteolytic stability than their respective linear counterparts,i.e.peptides 10 and 11.These findings suggested that similar results may also be obtained when other model peptide sequences are employed.The findings of this thesis work,especially the finding with two model peptide sequences employed for the stapling with L-α-methylthialysine or L-thialysine that the introduction of α-methyl into two stapling sites could enhance the % α-helicity and proteolytic stability of the L-lysine bis-lactam [i,i+4]-stapling,which will promote the application of bis-lactam peptide [i,i+4]-stapling in biomedical fields,especially for the development of superior PPI inhibitors,such as the inhibitors for the PPIs involving p110α[E545K],they have a positive impact.