New Method Toward Total Chemical Synthesis And Modification Of Proteins-Protection Of Thiol And Mild Release

Proteins are important biological macromolecules that carry out most of the biochemical functions in chemical biology. The use of modified proteins can reveal more detailed biological mechanism. However, these molecules can't be readily obtained through biological expression. The total chemical synthesis of proteins from unprotected peptide fragments has enabled the introduction of unnatural amino acids, site-specific isotopic labeling, and attachment of affinity tags or labels for imaging, and has great potential of increasing our understanding of the molecular basis of protein function.Chemoselective ligation methods have increased the efficiency of protein synthesis. In particular, currently native chemical ligation is most widely used, has led to higher reaction rates, higer reaction yields, and greater biocompatility. It can efficiently condense peptide segments in aqueous solutions under mild conditions to generate natural as well as non-natural proteins. While, the abundance of cysteine in natural proteins is only 1.7% and it is hard to prepare the thiol esters.In just few sho(?) years, various methods were developde to break through the limitations of cystein and thiol ester. For chemical synthesis of proteins without suitable Xaa-Cys ligation site(s), there is a need to use the recently developed "ligation-desulfurization" approach in which the desulfurization step is conducted in the presence of side chain protected Cys. Another challenge is the synthesis of multiple Cys-containing proteins, where an often encountered difficulty is unambiguous formation of several disulfide bridges. To solve this difficulty it often needs to conduct orthogonal protection of Cys residues for the stepwise formation of disulfide bonds. Finally, peptide-protein bioconjugation may also need selective protection and deprotection of active Cys side chains under biologically benign conditions.The popular thiol protecting groups reported before cannot meet the needs of the protein chemical synthesis, because of harsh deprotecting conditions compatibility. Thus, thiolprotecting groups which can be removed under mild conditions and compatible with the peptide and protein chemistry must be developed.In this paper, we designed and synthesis a new Cys side-chain protecting group which is compatible to the solid-phase peptide synthesis. They are readily deprotected by using aqueous hydrazine. To illustrate the method's utility, trifolitoxin and human neutrophil defensin hNP2 were manually synthesized by using Hgm and Hqm. That shows they were suited for peptide and protein synthesis as useful protecting groups.