Amino acids and peptides. XLIV. Synthesis of stereoisomeric pentapeptides of thiol proteinase inhibitor.

Stereoisomers of thiol proteinase inhibitor (TPI) were synthesized by a conventional solution method. Among them, iNoc-D-Gln-Val-Val-Ala-Ala-pNA weakly inhibited the amidolytic activity of papain, although iNoc-Gln-Val-Val-Ala-Ala-pNA inhibited papain activity fairly potently. However, the other five D-amino acid-containing peptides did not show any inhibitory effects on papain. The circular dichroism (CD) spectra of the enzyme-peptides mixtures were measured in order to study the relationship between the peptide anilides-papain interaction and the inhibitory activity.