Patent ID: 7566697

Claim:
A method of chemically ligating two oligopeptides, wherein a first oligopeptide thioester having an acidic C-terminal amino acid, said acidic C-terminal amino acid having a thioester moiety, a side chain, and a side chain protecting group selected from the group consisting of: 9-fluorenylmethyl ester, (phenylsulfonyl)ethyl ester, 2,2,2-trichloroethyl ester, and a phenacyl ester, such that said side chain protecting group substantially prevents rearrangements between atoms of said side chain and atoms of said thioester moiety, is contacted with a second oligopeptide having an N-terminal amino acid under chemical ligation conditions such that said thioester moiety of said first oligopeptide thioester ligates to said N-terminus of said second oligopeptide to form an oligopeptide or polypeptide product.