Patent ID: 8642725

Claim:
A process for producing a peptide thioester comprising the following steps (a) to (c): (a) a step of producing a first intermediate by reacting a compound A represented by the following formula (I) with a thiol group of a cysteine residue to eliminate R 2 in a peptide chain having the cysteine residue: wherein X is a sulfur atom or an oxygen atom, and R 1 and R 2 are leaving groups; (b) a step of reacting a compound B represented by the following formula (II) with said first intermediate in an organic solvent to add a —NH—C(═Y)NHR 3 group to a carboxyl group forming a peptide bond between the cysteine residue and an amino acid adjacent to an N-terminal-side of said cysteine residue, and cleaving said peptide bond, thereby obtaining a peptide fragment from the N-terminal-side closer to the N-terminal-side than the cleaved peptide bond as a second intermediate: wherein Y is an oxygen atom, a sulfur atom or an NH group and R 3 is a hydrogen atom, an acyl group or an alkoxycarbonyl group; and (c) a step of thioesterifying a C-terminal of the second intermediate by reacting thiol with the second intermediate to exchange the —NH—C(═Y)NHR 3 group at the C-terminal for the thiol group.