Semicarbazide-sensitive amine oxidase (SSAO) activity is an enzyme activity expressed by Vascular Adhesion Protein-1 (VAP-1) or Amine Oxidase, Copper Containing 3 (AOC3), belongs to the copper-containing amine oxidase family of enzymes (EC.1.4.3.6). Therefore inhibitors of the SSAO enzyme may also modulate the biological functions of the VAP-1 protein. Members of this enzyme family are sensitive to inhibition by semicarbazide and utilize cupric ion and protein-derived topa quinone (TPQ) cofactor in the oxidative deamination of primary amines to aldehydes, hydrogen peroxide, and ammonia according to the following reaction:R—CH2—NH2+O2→R—CHO+H2O2+NH3 
Known substrates for human SSAO include endogenous methylamine and aminoacetone as well as some xenobiotic amines such as benzylamine [Lyles, Int. J. Biochem. Cell Biol. 1996, 28, 259-274; Klinman, Biochim. Biophys. Acta 2003, 1647(1-2), 131-137; Matyus et al., Curr. Med. Chem. 2004, 11(10), 1285-1298; O'Sullivan et al., Neurotoxicology 2004, 25(1-2), 303-315]. In analogy with other copper-containing amine oxidases, DNA-sequence analysis and structure determination suggest that the tissue-bound human SSAO is a homodimeric glycoprotein consisting of two 90-100 kDa subunits anchored to the plasma membrane by a single N-terminal membrane spanning domain [Morris et al., J. Biol. Chem. 1997, 272, 9388-9392; Smith et al., J. Exp. Med. 1998, 188, 17-27; Airenne et al., Protein Science 2005, 14, 1964-1974; Jakobsson et al., Acta Crystallogr. D Biol. Crystallogr. 2005, 61(Pt 11), 1550-1562]. SSAO activity has been found in a variety of tissues including vascular and non-vascular smooth muscle tissue, endothelium, and adipose tissue [Lewinsohn, Braz. J. Med. Biol. Res. 1984, 17, 223-256; Nakos & Gossrau, Folia Histochem. Cytobiol. 1994, 32, 3-10; Yu et al., Biochem. Pharmacol. 1994, 47, 1055-1059; Castillo et al., Neurochem. Int. 1998, 33, 415-423; Lyles & Pino, J. Neural. Transm. Suppl. 1998, 52, 239-250; Jaakkola et al., Am. J. Pathol. 1999, 155, 1953-1965; Morin et al., J. Pharmacol. Exp. Ther. 2001, 297, 563-572; Salmi & Jalkanen, Trends Immunol. 2001, 22, 211-216]. In addition, SSAO protein is found in blood plasma and this soluble form appears to have similar properties as the tissue-bound form [Yu et al., Biochem. Pharmacol. 1994, 47, 1055-1059; Kurkijarvi et al., J. Immunol. 1998, 161, 1549-1557]. It has recently been shown that circulating human and rodent SSAO originates from the tissue-bound form [Gökürk et al., Am. J. Pathol. 2003, 163(5), 1921-1928; Abella et al., Diabetologia 2004, 47(3), 429-438; Stolen et al., Circ. Res. 2004, 95(1), 50-57], whereas in other mammals the plasma/serum SSAO is also encoded by a separate gene called AOC4 [Schwelberger, J. Neural. Transm. 2007, 114(6), 757-762].
The precise physiological role of this abundant enzyme has yet to be fully determined, but it appears that SSAO and its reaction products may have several functions in cell signalling and regulation. For example, recent findings suggest that SSAO plays a role in both GLUT4-mediated glucose uptake [Enrique-Tarancon et al., J. Biol. Chem. 1998, 273, 8025-8032; Morin et al., J. Pharmacol. Exp. Ther. 2001, 297, 563-572] and adipocyte differentiation [Fontana et al., Biochem. J. 2001, 356, 769-777; Mercier et al., Biochem. J. 2001, 358, 335-342]. In addition, SSAO has been shown to be involved in inflammatory processes where it acts as an adhesion protein for leukocytes [Salmi & Jalkanen, Trends Immunol. 2001, 22, 211-216; Salmi & Jalkanen, in “Adhesion Molecules: Functions and Inhibition” K. Ley (Ed.), 2007, pp. 237-251], and might also play a role in connective tissue matrix development and maintenance [Langford et al., Cardiovasc. Toxicol. 2002, 2(2), 141-150; Goktark et al., Am. J. Pathol. 2003, 163(5), 1921-1928]. Moreover, a link between SSAO and angiogenesis has recently been discovered [Noda et al., FASEB J. 2008, 22(8), 2928-2935], and based on this link it is expected that inhibitors of SSAO have an anti-angiogenic effect.
Several studies in humans have demonstrated that SSAO activity in blood plasma is elevated in conditions such as congestive heart failure, diabetes mellitus, Alzheimer's disease, and inflammation [Lewinsohn, Braz. J. Med. Biol. Res. 1984, 17, 223-256; Boomsma et al., Cardiovasc. Res. 1997, 33, 387-391; Ekblom, Pharmacol. Res. 1998, 37, 87-92; Kurkijarvi et al., J. Immunol. 1998, 161, 1549-1557; Boomsma et al., Diabetologia 1999, 42, 233-237; Meszaros et al., Eur. J. Drug Metab. Pharmacokinet. 1999, 24, 299-302; Yu et al., Biochim. Biophys. Acta 2003, 1647(1-2), 193-199; Mntyus et al., Curr. Med. Chem. 2004, 11(10), 1285-1298; O'Sullivan et al., Neurotoxicology 2004, 25(1-2), 303-315; del Mar Hernandez et al., Neurosci. Lett. 2005, 384(1-2), 183-187]. The mechanisms underlying these alterations of enzyme activity are not clear. It has been suggested that reactive aldehydes and hydrogen peroxide produced by endogenous amine oxidases contribute to the progression of cardiovascular diseases, diabetic complications and Alzheimer's disease [Callingham et al., Prog. Brain Res. 1995, 106, 305-321; Ekblom, Pharmacol. Res. 1998, 37, 87-92; Yu et al., Biochim. Biophys. Acta 2003, 1647(1-2), 193-199; Jiang et al., Neuropathol Appl Neurobiol. 2008, 34(2), 194-204]. Furthermore, the enzymatic activity of SSAO is involved in the leukocyte extravasation process at sites of inflammation where SSAO has been shown to be strongly expressed on the vascular endothelium [Salmi et al., Immunity 2001, 14(3), 265-276; Salmi & Jalkanen, in “Adhesion Molecules: Functions and Inhibition” K. Ley (Ed.), 2007, pp. 237-251]. Accordingly, inhibition of SSAO has been suggested to have a therapeutic value in the prevention of diabetic complications and in inflammatory diseases [Ekblom, Pharmacol. Res. 1998, 37, 87-92; Salmi et al., Immunity 2001, 14(3), 265-276; Salter-Cid et al., J. Pharmacol. Exp. Ther. 2005, 315(2), 553-562].
SSAO knockout animals are phenotypically overtly normal but exhibit a marked decrease in the inflammatory responses evoked in response to various inflammatory stimuli [Stolen et al., Immunity 2005, 22(1), 105-115]. In addition, antagonism of its function in wild type animals in multiple animal models of human disease (e.g. carrageenan-induced paw inflammation, oxazolone-induced colitis, lipopolysaccharide-induced lung inflammation, collagen-induced arthritis, endotoxin-induced uveitis) by the use of antibodies and/or small molecules has been shown to be protective in decreasing the leukocyte infiltration, reducing the severity of the disease phenotype and reducing levels of inflammatory cytokines and chemokines [Kirton et al., Eur. J. Immunol. 2005, 35(11), 3119-3130; Salter-Cid et al., J. Pharmacol. Exp. Ther. 2005, 315(2), 553-562; McDonald et al., Annual Reports in Medicinal Chemistry 2007, 42, 229-243; Salmi & Jalkanen, in “Adhesion Molecules: Functions and Inhibition” K. Ley (Ed.), 2007, pp. 237-251; Noda et al., FASEB J. 2008 22(4), 1094-1103; Noda et al., FASEB J. 2008, 22(8), 2928-2935]. This anti-inflammatory protection seems to be afforded across a wide range of inflammatory models all with independent causative mechanisms, rather than being restricted to one particular disease or disease model. This would suggest that SSAO may be a key nodal point for the regulation of the inflammatory response, and it is therefore likely that SSAO inhibitors will be effective anti-inflammatory drugs in a wide range of human diseases. SSAO (VAP-1) is up regulated in gastric cancer and has been identified in the tumour vasculature of human melanoma, hepatoma and head and neck tumours (Yoong K F, McNab G, Hubscher S G, Adams D H. (1998), J Immunol 160, 3978-88; Irjala H, Salmi M, Alanen K, Gre'nman R, Jalkanen S (2001), Immunol. 166, 6937-6943; Forster-Horvath C, Dome B, Paku S, et al. (2004), Melanoma Res. 14, 135-40.). One report (Marttila-Ichihara F, Castermans K, Auvinen K, Oude Egbrink M G, Jalkanen S, Griffioen A W, Salmi M. (2010), J Immunol. 184, 3164-3173.) has shown that mice bearing enzymically inactive VAP-1 grow melanomas more slowly, and have reduced tumour blood vessel number and diameter. The reduced growth of ic) these tumours was also reflected in the reduced (by 60-70%) infiltration of myeloid suppressor cells. Encouragingly VAP-1 deficiency had no effect on vessel or lymph formation in normal tissue.
Small molecules of different structural classes have previously been disclosed as SSAO inhibitors, for example in WO 02/38153 (tetrahydroimidazo[4,5-c]pyridine derivatives), in WO 03/006003 (2-indanylhydrazine derivatives), in WO 2005/014530 (allylhydrazine and hydroxylamine (aminooxy) compounds) and in WO 2007/120528 (allylamino compounds). Additional SSAO inhibitors are disclosed in PCT/EP2009/062011 and PCT/EP2009/062018.
Our co-pending International Patent Application No.: PCT/EP2011/053818 relates to SSAO inhibitors of formula (I) or a pharmaceutically acceptable salt, or N-oxide thereof:
whereinR1 is phenyl or 6-membered heteroaryl, optionally substituted with one or more substituents selected from halogen, cyano, C1-4-alkyl, halo-C1-4-alkyl, C1-4alkoxy-C1-4alkyl, hydroxy-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)amino-C1-4-alkyl, —NR4AR4B, —NR6C(O)OR5, —NR6C(O)R5, —NR6C(O)NR4AR4B, —C(O)NR4AR4B, —C(O)R5, —C(O)OR5, and —NR6S(O)2R5;A is a bond;R2 is —B-Q-[R3]n or —B—R3;wherein n=1, 2, 3, or 4B is a bond, O, NR4, —C(O)— or C1-3-alkylene;Q is saturated or partially unsaturated monocyclic 3-7 membered heterocyclic or C3-7-cycloalkyl ring;when R2 is —B-Q-[R3]n, R3 is selected from hydrogen, halogen, cyano, amino, hydroxyl, oxo, C1-4-alkyl, halo-C1-4-alkyl, C1-4-alkoxy, C1-4alkoxy-C1-4alkyl, hydroxy-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)amino-C1-4-alkyl, —NR4AR4B, —NR6C(O)OR5, —NR6C(O)R5, —NR6C(O)NR4AR4B, —C(O)NR4AR4B, —C(O)R5, —C(O)OR5, —NR6S(O)2R5, —S(O)2R5, phenyl-C1-4-alkyl and heteroaryl-C1-4-alkyl, and wherein any phenyl or heteroaryl residue is optionally substituted with one or more substituents selected from halogen, cyano, C1-4-alkyl, halo-C1-4-alkyl, C1-4-alkoxy, C1-4alkoxy-C1-4alkyl, hydroxy-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)amino-C1-4-alkyl, —NR4AR4B, —NR6C(O)OR5, —NR6C(O)R5, —NR6C(O)NR4AR4B, —C(O)NR4AR4B, —C(O)R5, —C(O)OR5, —NR6S(O)2R5;when R2 is —B—R3, R3 is selected from amino, C1-4-alkoxy, C1-4alkoxy-C1-4alkyl, hydroxy-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)amino-C1-4-alkyl, —NR4AR4B, —NR6C(O)OR5, —NR6C(O)R5, —NR6C(O)NR4AR4B, —C(O)NR4AR4B, —C(O)R5, —NR6S(O)2R5, phenyl-C1-4-alkyl and heteroaryl-C1-4-alkyl, and wherein any phenyl or heteroaryl residue is optionally substituted with one or more substituents selected from halogen, cyano, C1-4-alkyl, halo-C1-4-alkyl, C1-4-alkoxy, C1-4alkoxy-C1-4alkyl, hydroxy-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)amino-C1-4-alkyl, —NR4AR4B, —NR6C(O)OR5, —NR6C(O)R5, —NR6C(O)NR4AR4B, —C(O)NR4AR4B, —C(O)R5, —C(O)OR5, —NR6S(O)2R5, provided that when R2 is —B—R3, and B is a bond and R3 is —C(O)R5, then R5 is not hydrogen;R4A, R4B and R5 are each independently selected from hydrogen, C1-4-alkyl, hydroxy-C1-4-alkyl, halo-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)-amino-C1-4-alkyl or C1-4alkoxy-C1-4alkyl; or R4A and R4B together with the nitrogen to which they are attached form a cyclic amino group such as a piperidinyl, piperazinyl, N-substituted piperazinyl, morpholinyl or homopiperidinyl group;R4A1 is selected from C1-4-alkyl, hydroxy-C1-4-alkyl, halo-C1-4-alkyl, cyano-C1-4-alkyl, amino-C1-4-alkyl, C1-4-alkylamino-C1-4-alkyl, di(C1-4-alkyl)amino-C1-4-alkyl or C1-4alkoxy-C1-4alkyl; or R4A1 and R4B together with the nitrogen to which they are attached form a cyclic amino group such as a piperidinyl, piperazinyl, N-substituted piperazinyl, morpholinyl or homopiperidinyl group;R6 is hydrogen or C1-4-alkyl; andX is selected from the radicals of formulae (1-16) wherein the bond marked * is attached to R1A- and the bond marked ** is attached to —R2:
wherein Y is selected from hydrogen, hydroxyl, amino, —NHR6, —OCH3;Z is selected from hydrogen, fluorine, hydroxyl, C1-4-alkoxy, halo-C1-4-alkyl, CONH2, cyano, SO2NH2, amino, —NHR6;W is selected from H, C1-4-alkyl, halo-C1-4-alkyl;