Design,Synthesis And Activity Evaluation Of Cyclic Dinucleotide Analogues With A Triazole-containing And Cyclic Tetrapeptide Backbone

Cyclic dinucleotide(CDN)is the second messenger of human native immune signal pathway.CDN binds with stimulator of interferon genes(STING)and induces the production of IFN I and related cytokines,which lead to the initiation of native immune response.The presence of the ribose-phosphate backbone in the 2',3'-cyclic guanosine adenosine monophosphate(cGAMP)affect the transmembrane absorption and stability of the molecules,also the synthesis of this structure is difficult.The 2',3'-cGAMP analogues without the ribose-phosphate backbone will overcome these difficulties.In this paper,azido-functionalized peptide backbones will be designed and prepared based on the crystal structure of CDN/STING complex and molecular docking results.The azido-functionalized backbones will be used as general intermediates to react with virtually selected alkyne derivatives through click chemistry to give triazole-containing CDN analogues.In the first part,we used aspartic acid as a starting material and link it to trityl resin by solid-phase peptide synthesis,followed by a 4-azidopyrrolidine-2-carboxylic acid,aspartic acid and a4-azidopyrrolidine-2-carboxylic acid.After that,we screened different condensation systems to form cyclopeptides in a dilute solution,and finally determined the HATU/DIPEA system.A suitable acetylene derivative is determined by a virtual screening to perform a click reaction to obtain a novel CDN analogues containing a 1,2,3-triazole module.Biological experiments showed that at normal concentrations,the cyclic dinucleotide analogs we obtained were not cytotoxic in THP-1,RAW cells.Unfortunately,the compounds we synthesized did not stimulate the STING-TBK1-IRF3 signaling pathway.However,it still provides a new idea for the design and synthesis of novel CDN analogues in the future.In the second part,we designed to synthesis the peptides with the backbone of serine-proline-serine-proline.The molecular docking results showed that the aspartic acid-forming products had a better docking score than the serine-forming ring products.We used serine as the starting material,and connected the serine to the trityl resin by solid-phase peptide synthesis,followed by the4-azidopyrrolidine-2-carboxylic acid,serine and the 4-azidopyrrolidine-2-carboxylic acid completes thepeptide chain synthesis and then we use the HATU/DIPEA system to obtain a cyclic tetrapeptide.A triazole-containing CDN analogues are formed with different alkyne derivatives under the catalysis of copper(I)iodide.Cell experiments in this section are still in progress.