Synthesis and kinetic evaluation of peptide alpha-keto-beta-aldehyde-based inhibitors of trypsin-like serine proteases.

New, synthetic peptide analogues bearing a C-terminal basic alpha-keto-beta-aldehyde moiety were prepared as novel inhibitors of the trypsin-like serine proteases. The compounds, Ac-Leu-Leu-Arg-COCHO, Ac-Arg-Gln-Arg-COCHO and Boc-Val-Leu-Lys-COCHO were evaluated kinetically against trypsin and three other trypsin-like serine proteases, tryptase, plasmin and thrombin, all of which are implicated as mediators of important disease processes. Results illustrate that alpha-keto-beta-aldehydes are potent inhibitors, with similar potency to comparable peptide aldehydes, and intriguingly, appearto act, in some instances, by a novel mechanism of action. Ac-Leu-Leu-Arg-COCHO, an analogue of the natural product leupeptin, is a potent, tight-binding inhibitor of trypsin (Ki(final) = 1.9 microM), plasmin (Ki(final) = 4.9 microM) and tryptase (Ki(final) = 1.2 microM) and an irreversible inactivator of thrombin (k2nd 4,500 M(-1).min(-1)). Boc-Val-Leu-Lys-COCHO was found to be a tight-binding inhibitor of its target protease plasmin (Ki(final) = 3.1 microM) and was inactive against thrombin. Ac-Arg-Gln-Arg-COCHO was a slow-binding inhibitor of tryptase (Ki(final) = 1.6 microM) and also irreversibly inactivated trypsin (k2nd = 8,920 M(-1) min(-1)). Peptides or peptidomimetics with a C-terminal basic alpha-keto-beta-aldehyde function thus provide a useful new molecular template for the development of new therapeutic agents against a wide range of disorders, such as coagulopathies and asthma, which may be mediated by the aberrant activity of trypsin-like serine proteases.