Elastase is an enzyme known to facilitate the digestion of elastin, collagen, and other elastic tissue by covalent catalysis. The enzyme combines with its substrate to form a highly reactive transitional compound. At the active sight of the enzyme, the hydroxyl group of a specific serine residue joins with an acyl group in the substrate to form an acyl-enzyme intermediate, thus rendering the substrate protein more vulnerable to decomposition. Inhibitors are known to suppress enzymatic catalysis by combining with the free enzyme, with the enzyme-substrate complex, or with both. Elastase is of pharmacological interest because of its presumed role in the pathology of certain diseases, such as pancreatitis, pulmonary emphysema, arthritis, and atheriosclerosis. Inhibitors of elastase are likewise of interest for their potential therapeutic value in the treatment of these diseases.
Alkylamides of dipeptides are known to be effective inhibitors of elastase (See Belgian Pat. Nos. 855,851 and 856,064). These dipeptides mimic the characteristics of amino acid compositions known to be preferred by elastase. Optimum substrate studies for pancreatic elastase have revealed the presence of a specific electrostatic bond between the enzyme and its substrate at a position toward the substrate's N-terminal. This bond is believed to be related to a primary interaction between substrate and enzyme. Synthetic elastolytic substances designed to induce this or a similar interaction are potential elastase inhibitors. See I. Schechter et al., Biochem. Biophys. Res. Commun. 32, 898 (1968); Eur. J. Biochem. 69, 1 (1976); FEBS Lett. 40, 353 (1974).
The earlier work revealed that the elastolytic hydrolysis of these synthetic substances could be enhanced by the presence of a carboxyl group in the N-terminal part of the inhibitor. The carboxyl group, as opposed to a hydrophobic residue (such as an acetyl) increased elastase inhibition in the same manner.
It is also known that the properties of an elastase inhibitor vary with the length of the peptide chain: tripeptides are more effective inhibitors than dipeptides. See U.S. patent application, Ser. No. 406,168 (Czechoslovakian Pat. No. PV 5977-81); Eur. J. Biochem. 69,1 (1976).
U.S. patent application Ser. No. 406,168 discloses certain carboxyalkanoylpeptide alkylamides that show significant elastase inhibiting properties and are physiologically tolerated. These synthetic peptides were observed to interact with the enzyme electrostatically, within their respective N-terminal regions. See Eur. J. Biochem. 69, 1 ( 1976); FEBS Lett. 40, 353 (1974). As previously known in the art, electrostatic coupling is induced by residues of dicarboxylic acids, e.g. succinic or glutaric acid.
In the present invention, the incorporation of aspartic or glutamic acid residues into the N-terminal region of the synthetic polypeptide inhibitor molecule, combined with appropriate N-acyl substitution, has been shown to induce similar electrostatic interactions. Thus, a new species of elastase inhibitors, and their method of preparation, is revealed.