Multiple consecutive chemical ligation reactions can be used to make proteins of the typical size found in Nature, i.e. with polypeptide chains containing 200–300 amino acids, produced by total synthesis.
The most practical and robust method for the chemoselective reaction of unprotected peptides is native chemical ligation.
Native chemical ligation overcomes the limitations of the classical synthetic organic chemistry approach to the total synthesis of proteins, and enabled the routine total or semi- synthesis of protein molecules.
By exploiting naturally occurring inteins it is possible to prepare a recombinant polypeptide C-terminal thioester.
The recombinant thioester can be ligated to a synthetic peptide bearing an N-terminal cysteine.