Synthesis of reaper, a cysteine-containing polypeptide, using a peptide thioester in the presence of silver chloride as an activator

Abstract Reaper was synthesized by condensing two peptide segments, one of which was a partially protected peptide thioester, Boc-[Lys(Boc) 20 ]-reaper(1–32)-SCH 2 CH 2 CO-β-Ala-NH 2 , and the other a peptide which contained an Cys(Acm) residue, H-[Cys(Acm) 49 , Lys(Boc) 52,56,59,62 ]-reaper(33–65)-OH. The condensation proceeded without loss of the Acm group when silver chloride was used as an activator of thioester moiety. This result indicates that silver chloride is a generally applicable activating reagent to the preparation of polypeptides which contain Cys(Acm) residues.