Proteinases participate in an enormous range of biological processes and constitute approximately 2% of all the gene products identified following analysis of several completed genome sequencing programmes. Proteinases mediate their effect by cleavage of peptide amide bonds within the myriad of proteins found in nature.
This hydrolytic action involves recognising, and then binding to, specific three-dimensional electronic surfaces of a protein, which aligns the bond for cleavage precisely within the proteinase catalytic site. Catalytic hydrolysis then commences through nucleophilic attack of the amide bond to be cleaved either via an amino acid side-chain of the proteinase itself, or through the action of a water molecule that is bound to and activated by the proteinase.
Proteinases in which the attacking nucleophile is the thiol side-chain of a Cys residue are known as cysteine proteinases. The general classification of “cysteine proteinase” contains many members found across a wide range of organisms from viruses, bacteria, protozoa, plants and fungi to mammals.
Cysteine proteinases are classified into “clans” based upon similarity of their three-dimensional structure or a conserved arrangement of catalytic residues within the proteinase primary sequence. Additionally, “clans” may be further classified into “families” in which each proteinase shares a statistically significant relationship with other members when comparing the portions of amino acid sequence which constitute the parts responsible for the proteinase activity (see Barrett, A. J et al, in ‘Handbook of Proteolytic Enzymes’, Eds. Barrett, A. J., Rawlings, N. D., and Woessner, J. F. Publ. Academic Press, 1998, for a thorough discussion).
To date, cysteine proteinases have been classified into five clans, CA, CB, CC, CD and CE (Barrett, A. J. et al, 1998). A proteinase from the tropical papaya fruit ‘papain’ forms the foundation of clan CA, which currently contains over eighty distinct entries in various sequence databases, with many more expected from the current genome sequencing efforts.
Over recent years, cysteinyl proteinases have been shown to exhibit a wide range of disease-related biological functions. In particular, proteinases of the clan CA/family C1 (CAC1) have been implicated in a multitude of disease processes [a) Lecaille, F. et al, Chem. Rev. 2002, 102, 4459; (b) Chapman, H. A. et al, Annu. Rev. Physiol. 1997, 59, 63; Barrett, A. J. et al, Handbook of Proteolytic Enzymes; Academic: New York, 1998]. Examples include human proteinases such as cathepsin K (osteoporosis), cathepsins S and F (autoimmune disorders), cathepsin B (tumour invasion/metastases) and cathepsin L (metastases/autoimmune disorders), as well as parasitic proteinases such as falcipain (malaria parasite Plasmodium falciparum), cruzipain (Trypanosoma cruzi infection) and the CPB proteinases associated with Leishmaniasis [Lecaille, F. et al, ibid, Kaleta, J., ibid].
The inhibition of cysteinyl proteinase activity has evolved into an area of intense current interest [(a) Otto, H.-H. et al, Chem. Rev. 1997, 97, 133; (b) Heranandez, A. A. et al, Curr. Opin. Chem. Biol. 2002, 6, 459; (c) Veber, D. F. et al, Cur. Opin. Drug Disc. Dev. 2000, 3, 362-369; (d) Leung-Toung, R. et al, Curr. Med. Chem. 2002, 9, 979]. Selective inhibition of any of these CAC1 proteinases offers enormous therapeutic potential and consequently there has been a concerted drive within the pharmaceutical industry towards the development of compounds suitable for human administration [for example, see (a) Bromme, D. et al, Curr. Pharm. Des. 2002, 8, 1639-1658; (b) Kim, W. et al, Expert Opin. Ther. Patents 2002, 12(3), 419]. To date, these efforts have primarily focused on low molecular weight substrate based peptidomimetic inhibitors, the most advanced of which are in early clinical assessment.
Cysteinyl proteinase inhibitors investigated to date include peptide and peptidomimetic nitriles (e.g. see WO 03/041649), linear and cyclic peptide and peptidomimetic ketones, ketoheterocycles (e.g. see Veber, D. F. et al, Curr. Opin. Drug Discovery Dev., 3(4), 362-369, 2000), monobactams (e.g. see WO 00/59881, WO 99/48911, WO 01/09169), α-ketoamides (e.g. see WO 03/013518), cyanoamides (WO 01/077073, WO 01/068645), dihydropyrimidines (e.g. see WO 02/032879) and cyano-aminopyrimidines (e.g. see WO 03/020278, WO 03/020721).
