Development of a Facile Method for Polypeptide Synthesis. Synthesis of Bovine Pancreatic Trypsin Inhibitor (BPTI)

A new method for the preparation of pure polypeptides based on the minimun-protection strategy is described. Its effectiveness was demonstrated by a synthesis of bovine pancreatic trypsin inhibitor (BPTI). Protected peptide segments of Z-[Arg(Tos)1, Asp(OcHex)3, Cys(Acm)5, Glu(OcHex)7]-BPTI(1–13), Boc-[Cys(Acm)14,30, Lys(Z)15,26]-BPTI(14–36), and [Cys(Acm)38,51,55, Lys(Z)41,46]-BPTI(37–58) were prepared by modifying the products obtained by solid-phase peptide syntheses. The protected peptides corresponding to BPTI(14–36) and BPTI(37–58) were coupled by an active ester method to give protected BPTI(14–58). Next, protected BPTI(1–13) was coupled to the BPTI(14–58) by an active ester method after removing the Boc group from the protected BPTI(14–58). All of the protecting groups on BPTI(1–58) were removed, and the resulting peptide was oxidized to give the native form of BPTI in a very pure form. The synthetic BPTI was shown to be identical with the native BPTI in an elution experiment on ion-exchange chromatography and in its inhibitory activity. The new method proved to be very effective for a rapid preparation of pure polypeptide.