Patent ID: 7674881

Claim:
A method of synthesizing a polypeptide comprising: obtaining a first C-activated peptide, having (1) an N-terminal-protected cysteinyl residue or an N-terminal non-cysteinyl residue and (2) a good C-terminal thiol-based leaving group; a first N-deprotected peptide, having an N-terminal unprotected cysteinyl residue and a weak C-terminal thiol-based leaving group; a second C-activated peptide, having an N-terminal-protected cysteinyl residue and a good C-terminal thiol-based leaving group, wherein the good C-terminal thiol-based leaving groups are the same or different; a second N-deprotected peptide, having (1) an N-terminal unprotected cysteinyl residue and (2) a C-terminal α-carboxylate, α-carboxamide, or a weak C-terminal thiol-based leaving group, wherein the weak C-terminal thiol-based leaving groups are the same or different; combining the first C-activated peptide with the first N-deprotected peptide to form a first ligation product having an amide bond between the α-carbon of the C-terminal residue of the first C-activated peptide and the α-carbon of the N-terminal of the first N-deprotected peptide; combining the second C-activated peptide with the second N-deprotected peptide to form a second ligation product having an amide bond between the α-carbon of the C-terminal residue of the second C-activated peptide and the α-carbon of the N-terminal of the second N-deprotected peptide; replacing the weak C-terminal thiol-based leaving group of the first ligation product or the second ligation product with a good C-terminal thiol-based leaving group to form a C-activated ligation product, and deprotecting the N-terminal-protected cysteinyl residue of the first ligation product or the second ligation product to form a N-deprotected ligation product; combining the C-activated ligation product with the N-deprotected ligation product to form a third ligation product having an amide bond between the α-carbon of the C-terminal residue of the C-activated ligation product and the α-carbon of the N-terminal of the N-deprotected ligation product; whereby the third ligation product is a polypeptide.