Photoinduced Synthesis Of Natural Small Molecule Cyclic Peptide Analogues And Biological Activity

In recent years,cyclic peptide compounds have attracted extensive attention of medical researchers because of their unique structural characteristics.Small cyclic peptides have moderate molecular size,diverse functional groups,high selectivity and affinity for targets,and their restricted conformation can effectively resist the degradation of proteases in blood,thus improving the metabolic stability in serum.This paper aims to synthesize analogues of small molecule antitumor natural cyclic peptide analogs by photoinduced single electron transfer cycination method,study the stereo-structure,screen high activity antitumor compounds,and preliminarily explore the mechanism of the antitumor action.Galaxamide is a cyclopentapeptide isolated from seaweed and contains three leucine and two N-methylleucine in its structure,which has significant inhibitory effect on liver cancer cells.In this paper,Galaxamide was used as the lead compound to conduct structural modification and biological activity study.Eight linear peptide analogs and their ring peptide analogs were designed and synthesized by intramolecular photoinduced single electron transfer method.Isoindolinone fragment was introduced into the ring peptide structure,the number and configuration of n-methyl amino acids were also changed.At the same time,the stereoscopic chiral configurations of eight c-3compounds were determined as S,S,S,R,R,R,R,R by electron circular dichroism combined with theoretical calculation.In biological experiments,MTT assay was used to study the antitumor activity of eight cyclic peptides,and the compound 8 was found with superior antitumor activity against HEPG-2 cells.Then,the effects of compound 8on apoptosis,cell cycle,mitochondrial membrane potential and intracellular Ca2+concentration of tumor cells were studied by flow cytometry.Meanwhile,the changes of intracellular lactate dehydrogenase activity were also studied after drug treatment.In addition,Galaxmaide is a hydrophobic cyclic peptide,which may interact with oncoprotein MDM2 to enhance the intracellular level of tumor suppressor protein P53.In this paper,western bloting was used to study the expression levels of MDM2,p53 and cytochrome c in tumor cells treated with different concentrations of compound8 for 48 hours.It was found that with the increase of drug concentration,the content of MDM2 decreased significantly,along with increased p53 level and gradually increased cytochrome c.The results showed that the synthesized cyclic peptide did have an important inhibitory effect on oncoprotein.In order to explore the binding characteristics of cyclic peptide to MDM2,eight compounds were docked with the hydrophobic cavities of MDM2 protein by molecular docking method.It was found that compound 8 with the best activity had the strongest binding force to the target,which proved that MDM2 might be a potential drug target of the prepared cyclic peptides.In view of the activity differences of different cyclic peptides,we carried out a preliminary structure-activity relationship discussion,and found that dimethyl substitution was not conducive to the bioactivity of Galaxamide analogizes,indicating that the methylation of small cyclic peptides is uncertain to improve the bioactivity.