The enzyme stability of dehydropeptides

A pentapeptide, Z-Gly-Gly-Phe-Phe-Ala · OH $\text{(1b)}$ and the corresponding unsaturated pentapeptide, Z-Gly-Gly-Phe-Δ^ZPhe-Ala · OH $\text{(1a)}$, have been synthesized. The saturated compound $\text{(1b)}$ was rapidly hydrolyzed by both chymotrypsin and thermolysin to the expected products, but the dehydropeptide was completely unhydrolyzed by either enzyme even after thirty hours. A new method of peptide stabilization to enzymolysis is made available.