Studies on trypsin inhbitors. Part II. Synthesis of the protected tetrapeptide (sequence 11-14) of porcine pancreatic secretory trypsin inhibitor II (Kazal).

Synthesis is described of the protected tetrapeptide corresponding to positions 11-14 of the primary structure of the porcine pancreatic secretory trypsin inhibitor II (Kazal), in the form of free acid as well as protected hydrazide. The tetrapeptide tert-butyloxycarbonylglycyl-S-acetamidomethylcysteinylprolyl-Nepsilon-trifluoroacetyl-lysine was prepared by stepwise elongation from the C-terminal Nepsilon-trifluoroacetyllysine using successively 1-succinimidyl benzyloxycarbonylprolinate, p-nitrophenyl N-tert-butyloxycarbonyl-S-acetamidomethylcysteinate and 1-phenyl-3-methyl-4-(tert-butyloxycarbonylglycyl)-oximinyl-5-(benzyloxycarbonylglycyl)-imino-2-pyrazoline as acylating agents. Alternately, the dipeptide benzyloxycarbonylprolyl-Nepsilon-trifluoroacetyllsine was transformed into the corresponding tert-butyloxycarbonylhydrazide which was reacted, after catalytic hydrogenolysis, with tritylglycyl-S-acetamido-methylcysteine to give the tetrapeptide tritylglycyl-S-acetamidomethylcysteinylprolyl-Nepsilon-trifluoroacetyllsine tert-butyloxycarbonylhydrazide. The stereochemical homogeneity of the final products was assessed, after partial deprotection with aqueous 90% trifluoroacetic acid, by digestion with papain and aminopeptidase M, followed by quantitative amino acid analysis.