Proteinases from polymorphonuclear leukocytes and macrophages, especially elastases, for example human leukocyte elastase and cathepsin G, appear to be responsible for the chronic tissue destruction associated with inflammation, arthritis and emphysema. During infection or inflammation, the normal lung is protected from proteolytic digestion by the protease inhibitor, .alpha.1-antitrypsin. The protective mechanism appears to be nonoperative in individuals with an .alpha.1-antitrypsin deficiency due to genetic or other causes. Synthetic elastase inhibitors capable of replacing .alpha.1-antitrypsin may therefore be useful in the treatment of pulmonary emphysema and related diseases.
Several types of elastase inhibitors have been reported in the literature. These include peptide chloromethyl ketones as described by P. M. Tuhy and J. C. Powers, "Inhibition of Human Leukocyte Elastase by Peptide Chloromethyl Ketones", FEBS Letters, 50, 359-61 (1975); J. C. Powers, B. F. Gupton, A. D. Harley, N. Nishino and R. J. Whitley, "Specificity of Porcine Pancreatic Elastase, Human Leukocyte Elastase and Cathepsin G. Inhibition with Peptide Chloromethyl Ketones", Biochem. Biophys. Acta. 485, 156-66 (1977); azapeptides, C. P. Dorn, M. Zimmerman, S. S. Yang, E. C. Yurewicz, B. M. Ashe, R. Frankshun and H. Jones, "Proteinase Inhibitors. 1. Inhibitors of Elastase", J. med. Chem., 20, 1464-68 (1977); J. C. Powers and B. F. Gupton, "Reaction of Serine Proteases with Aza-amino Acid and Aza-peptide Derivatives", Meth. Enzymol., 46,208-16 (1977); sulfonyl fluorides, T. Yoshimura, L. N. Barker and J. C. Powers, "Specificity and. Reactivity of Human Leukocyte Elastase, Porcine Pancreatic Elastase, Human Granulocyte Cathepsin G, and Bovine Pancreatic Elastase, Human Granulocyte Cathepsin G, and Bovine pancreatic Chymotrypsin with Arylsulfonyl Fluorides. Discovery of a new series of potent and specific irreversible Elastase Inhibitors", J. Biol. Chem. 257, 5077-84 (1982); heterocyclic acylating agents, M. Zimmerman, H. Morman, D. Mulvey, H. Jones, R. Frankshum and B. M. Ashe, "Inhibition of Elastase and Other Serine Proteases by Heterocyclic Acylating Agents", J. Biol. Chem. 25, 9848-51 (1980); B. M. Ashe, R. L. Clark, H. Jones and M. Zimmerman, "Selective Inhibition of Human Leukocyte Elastase and Bovine a.sub.1 -Chymotrypsin by Novel Heterocycles", J. Biol. Chem. 256: 11603-6(1981); imidazole N-carboxamides, W. C. Groutas, R. C. Badger, T. D. Ocain, D. Felder, J. Frankson and M. Theodorakis, Biochem. Biophys. Res. Commun., 95, 1890 (1980); and p-nitrophenyl-N alkyl carbamates, R. E. Scofield, R. P. Werner and F. Wold, "p-Nitrophenyl Carbamates as Active-Site-Specific Reagents for Serine Proteases", Biochemistry, 16, 2492 (1977).
Some peptide chloromethyl ketones have been shownto be effective in preventing elastase induced emphysema in animal models, A. Jaoff and R. Dearing, "Prevention of Elastase Induced Experimental Emphysema by Oral Administration of Synthetic Elastase Inhibitor", Am. J. Respir. Dis. 121, 1025-3 (1980). However, there is considerable question whether such reactive agents can be used for treating emphysema in humans. This is not surprising since the alkylating moieties in these inhibitors might render them toxic when used on a continuous basis.
U.S. Pat. No. 4,643,991, Tsuji K. et al, B.B.R.C. 122(2):571 (1984) and Digenis, G. A. et al, J. Med. Chem. 29:1468 (1986) describe peptide elastase inhibitors which are specific and active-site directed.
Human Leucocyte Elastase (HLE) is a serine-dependent protease, which degrades elastin found in all elastic tissues. A growing body of experimental evidence indicates that this enzyme may be involved in tissue destruction associated with such disease states as arthritis, bronchitis, inflammation, acute respiratory distress syndrome (ARDS), cystic fibrosis, and pulmonary emphysema. In a healthy tissue a balance exists between elastase and the natural occurring antiprotease a.sub.1 -antitrypsin. Emphysema and other related diseases has been postulated to result from an imbalance between proteases such as HLE and their naturally occurring inhibitors (antiproteases) in the lung and other related tissues. Severe genetic deficiency in a.sub.1 -antitrypsin is frequently associated with development of pulmonary emphysema.
During the last 10 years potent oligopeptidyl carbamate esters like (PC1) (see formula 2) (U.S. Pat. No. 5,162,307) and (PC5) (see formula 2) (U.S. Pat. No. 4,643,991) have been shown to specifically inhibit HLE without inhibiting other similar enzymes in the body. The disadvantages of the oligopeptide inhibitors are first their multistep painstaking synthesis and purification which may render them expensive and difficult to manufacture, and second their questionable bioavailability especially oral due to their instability (chemical or enzymatic) in the G.I. tract.
To be suitable for human use, an enzyme inhibitor has to show a high degree of selectivity and must have minimal toxic side effects. As a result, most drugs are molecules that reversibly bind to specific enzymes or receptor sites. Examples are the carbamate esters physostigmine and neostigmine which have been clinically used as inhibitors of acetyl choline esterases (A. G. Gilman, L. S. Goodman, and A. Gilman, "The pharmacological Basis of Therapeutics", p. 101, MacMillan Publishing Co. (1980)).
There is a need in the art for simple carbamate esters which are elastase inhibitors which have increased stability, activity and oral bioavailability.
The present invention overcomes the deficiencies of the prior art by providing for the design and synthesis of inhibitors of elastase which are simple carbamate esters with increased stability and oral bioavailability. The present invention elucidates the mechanism by which these carbamate esters inhibit elastase in vitro. The bioavailability and pharmacologic activity of the compounds of the invention, the most potent inhibitors of elastase, is shown in experimental animals in vivo. The compounds of the invention, unexpectedly and advantageously are more potent than known elastase inhibitors PC-1 and PC-5. In addition the compounds of the present invention unexpectedly and advantageously have increased absorption and bioavailability over the compounds PC-1 and PC-5.