Polypeptide synthesis using an expressed peptide as a building block via the thioester method

An expressed peptide was proven to be useful as a building block in the synthesis of a polypeptide via the thioester method. A partially protected peptide segment, [Lys(Boc)15,25,31,48,57,68,80,95]-Max(14–101), was prepared via transamination of an N-terminal amino group from p21Max(13–101), which was obtained by expression using Escherichia coli. This peptide was utilized in the synthesis of [Ser(PO3H2)2,11]-p21Max(1–101) via condensation with the peptide thioester, Boc-[Ser(PO3H2)2,11]-p21Max(1–13)-SCH2CH2CO-Leu-OH.