Studies on trypsin inhibitors. Part VI. Synthesis of the protected nonapeptide (sequence 44-52) of porcine pancreatic secretory trypsin inhibitor II (Kazal).

Synthesis is described of the partially protected nonapeptide tert-butyloxycarbonyl-valylleucylisoleucylglutaminyl-N-trifluoroacetyllsylserylglycylprolyl-S-acetamido-methylcysteine corresponding to positions 44-52 of the amino acid sequence of porcine pancreatic secretory trypsin inhibitor II. The hexapeptide free base glutaminyl-N-trifluoroacetyllsylserylglycylprolyl-S-acetamidomethylcysteine, prepared by two alternative routes, was acylated by the azide procedure, with the tripeptide tert-butyloxycarbonylvalylleucylisoleucine hydrazide. The stereochemical homogeneity of the resulting nonapeptide was assessed, after partial deprotection by treatment with aqueous 90% trifluoroacetic acid, by digestion with papain and aminopeptidase M followed by quantitative amino acid analysis.