Serine/threonine ligation for the chemical synthesis of proteins

• Serine/threonine ligation has been developed for the chemical synthesis of proteins.
• Ser/Thr ligation-mediated cyclization can be used for cyclic peptides synthesis.
• Ser/Thr ligation is chemoselective with side chain unprotected peptides.
• Ser/Thr ligation features a simple operational strategy with accessible materials.

Advances in the development of efficient peptide ligation methods have enabled the total synthesis of complex proteins to be successfully undertaken. Recently, a Ser/Thr ligation has emerged as a new tool in synthetic protein chemistry. The chemoselective reaction between an N-terminal serine or threonine of an unprotected peptide segment and a C-terminal salicylaldehyde ester of another unprotected peptide segment gives rise to an N,O-benzylidene acetal linked product, which upon acidolysis produces a native peptide bond at the site of ligation. Ser/Thr ligation has been used for the synthesis of the human erythrocyte acylphosphatase protein and MUC1 glycopeptide segments, semisynthesis of peptoid/PEG-RNase S protein hybrids, and cyclic peptide synthesis including cyclic tetrapeptides, cyclomontanin B, yunnanin C, mahafacyclin B, and daptomycin.

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