| Currently the most important method in the field of chemical synthesis of protein is native chemical ligation, which can efficiently condense peptide segments in aqueous solutions under mild conditions to generate natural as well as non-natural proteins. Comparing with other ligation methods, native chemical ligation has several advantages, such as, more efficiency, high chemoselectivity and without protection strategy. Scientific research workers think that the alkyl thioester is an indispensable part in native chemical ligation. The mainly reason is that the alkyl thioester is relatively stable, and the aminolysis reaction will not happen at a low concentration. However, there are many shortcomings with thioester. For example, thioester mediated ligation proceeded slowly with a variety of hindered C-terminal amino acid residues, including Val, Ile, and Pro ,and can't be masked.By the systematic study of thioester derivatives, we found a new class of molecule that can be used in native chemical liagtion - phenol peptide esters. At the same time, we develop a new type of catalyst (imidazole) which is different from the thiol additives .To some extent, we solve the difficult ligation between the hindered C-terminal amino acid residues and Cys.In this paper, we develop a new peptide fragment ligation methods through the synthesis of thioester derivatives and the establishment of a new catalytic system .The work discussed in this dissertation into three parts:1. Design and synthesize different thioester derivatives, then test their ligations efficiency with Cys, with the purpose of optimization of the molecules.2. Compare the efficiency of catalytic system between thiol and imidazole in more sterical site ligation, propose a possible mechanism for the imidazole catalyst system.3. Exploration and development of solid-phase peptide synthesis of phenol ester technology, chemical total synthesis of the protein- Hadrurin,by the new method we developed.
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