Abstract:
The present invention relates to the use of Collismycin and derivatives thereof as inhibitors of oxidative stress in cells and their use for the preparation of medicaments for the treatment and/or prevention of oxidative stress-induced diseases or conditions, especially neurodegenerative diseases, such as Alzheimer&#39;s Disease and Parkinson&#39;s Disease.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is filed under the provisions of 35 USC §371 based on International Application No. PCT/EP06/07521 filed Jul. 28, 2006, which in turn claims the priority of European Patent Application No. 05380175.9 filed Jul. 29, 2005. The disclosures of such international application and European patent application are hereby incorporated herein by reference in their respective entireties, for all purposes. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to the use of Collismycin and derivatives thereof as inhibitors of oxidative stress in cells and their use for the preparation of medicaments for the treatment and/or prevention of oxidative stress-induced diseases or conditions, especially neurodegenerative diseases, such as Alzheimer&#39;s Disease and Parkinson&#39;s Disease.  
       BACKGROUND OF THE INVENTION  
       [0003]     Alzheimer&#39;s disease (AD) and Parkinson&#39;s disease (PD) are the most frequent progressive neurodegenerative diseases affecting millions of people in the world. Because a significant percentage of patients share common clinical and pathological features from both entities, this seems to indicate the existence of a common pathological mechanism. Based on in vitro and in situ data, an unified molecular oxidative stress model induced by dopamine (DA), 6-hydroxydopamine (6-OHDA); 5,6 &amp; 5,7-dihydrytryptamine (5,6 &amp; 5,7 DHT); amyloid beta 25-35 (Aβ25-35), and metals [e.g. iron (Fe 2+ ), copper (Cu 2+ ), zinc (Zn 2+ ), manganese (Mn 2+ )] has been widely proposed as a possible explanation of neural loss in AD/PD overlapping cases. This hypothesis might contribute to a better understanding of the pathophysiology cascades of both disorders, and also support the notion that oxidative stress generated by H 2 O 2  represent an essential molecule of intracellular signalization leading to cell death.  
         [0004]     Therefore, an interesting approach for developing new pharmaceutical compounds for treating neurodegenerative diseases may be designing compounds which inhibit cellular oxidative stress. Reactive oxygen species (ROS), such as oxygen radical superoxide (O 2 ) or hydrogen peroxide (H 2 O 2 ), are produced during normal metabolic processes and perform several useful functions (Reactive oxygen species and the central nervous system, Halliwell B., J Neurochem.; 1992, 59 859: 1609-1623). Cells are provided with several mechanisms to control levels of these oxidative agents, for instance, superoxide dismutase (SOD), glutathione or vitamin E. In normal physiological conditions, a balance between ROS and these anti-oxidative mechanisms exists. An excessive production of ROS and a loss of efficiency of the anti-oxidative defences can lead to pathological conditions in cells and provoke tissue damage. This event seems to occur more dramatically in neurons, because of their high rate of metabolic activity, and thus seems to be related to a series of degenerative processes, diseases and syndromes, for example, Alzheimer&#39;s Disease, Parkinson&#39;s Disease, amyotrophic lateral sclerosis (ALS) and schizophrenia (Glutathione, oxidative stress and neurodegeneration, Schulz et al., Eur. J. Biochem.; 2000, 267, 4904-4911). Also other diseases or pathological conditions have been related to oxidative stress, such as Huntington&#39;s Disease (Oxidative damage in Huntington&#39;s disease, Segovia J. and Pérez-Severiano F, Methods Mol. Biol; 2004; 207: 321-334), brain injuries, such as stroke and ischemia, (Oxidative Stress in the Context of Acute Cerebrovascular Stroke, El Kossi et al., Stroke; 2000; 31: 1889-1892), diabetes (Oxidative stress as a therapeutic target in diabetes: revisiting the controversy, Wiermsperger N F, Diabetes Metab.; 2003; 29, 579-85), multiple sclerosis (The role of oxidative stress in the pathogenesis of multiple sclerosis: the need for effective antioxidant therapy, Gilgun-Sherki Y. et al., J. Neurol:, 2004; 251 (3): 261-8), epilepsy (Oxidative injury in epilepsy: potential for antioxidant therapy?, Costello D. J. and Delanty N., Expert. Rev. Neurother.; 2004; 4(3): 541-553), atherosclerosis (The oxidative stress hypothesis of atherogenesis, luliano L., Lipids; 2001; 36 suppl: S41-44), Friedreich&#39;s Ataxia (Oxidative stress mitochondrial dysfuntion and cellular stress response in Friedreich&#39;s ataxia, Calabrese et al., J. Neurol. Sci.; 2005) and heart failure (Oxygen, oxidative stress, hypoxia and heart failure, Giordano F. J., J. Clinic. Invest.; 2005; 115 (3): 500-508). Treatments that lead to an enhancement of the anti-oxidative mechanisms may slow the progression of some of the mentioned diseases.  
         [0005]     Collismycins are 2,2′-bypiridine molecules which have been isolated from  Streptomyces  species. Several kinds of these molecules were firstly isolated by Gomi et al. (Novel Antibiotics SF2738A, B and C and their analogues produced by  Streptomyces  sp., Gomi et al., J. Antibiot., 1994, 47:1385-1394) from a culture of  Streptomyces  sp. SF2738, and their structure was described by spectral analyses and chemical conversion. Biological activities of different types of collismycins were also studied and, among them, specially Collismycin A was described to be endowed with antibiotic activity against some bacteria and a wide range of fungi. This antifungal activity against some species, such as,  Saccharomyces cerevisiae  and  Candida albicans , has been demonstrated by Stadler et al. (Antifungal Actinomycete Metabolites Discovered in a Differential Cell-Based Screening Using a Recombinant TOPO1 Deletion Mutant Strain, Stadler et al., Arch. Pharm. Med. Chem., 2001, 334: 143-147). Two yeast strains, a wild type (SCAL 141) and a recombinant topoisomerase 1 (TOPO1) deletion mutant (SCAL 143), were used for the screening of compounds produced by actinomycetes strains WS 1410 and BS 1465. They were also used to test the biological activities of collismycins, among other compounds, with the activity of camptothecin as a reference. Results show that the mechanism of action of collismycins is not based on the inhibition of topoisomerase 1, because collismycins are active against both wild type and mutant yeast strains.  
         [0006]     Cytotoxicity is another biological activity that has been described for some collismycins. This property was also demonstrated by Gomi et al. (see above) in a study of the cytotoxic ability of these molecules on P388 murine leukaemia cells. In JP5078322 Collismycin is related to the use of Collismycins A and B as antitumoral substances, useful as carcinostatic agents, for parenteral or oral administration. A lot of other patent publications refer to the use of Collismycins A and B in combination with other antitumoral agents. This is the case, for example, of WO02/053138, which discloses the use of incensole and/or furanogermacrens, derivatives, metabolites and precursors thereof in the treatment of neoplasia, particularly resistant neoplasia and immune dysregulatory disorders. These compounds may be administered alone or in combination with conventional chemotherapeutic, anti-viral, anti-parasite agents, radiation and/or surgery. The listed chemotherapeutic agents include Collismycins A and B.  
         [0007]     Another biological activity of collismycins was described by Shindo et al. in 1994 (Collismycins A and B, novel non-steroidal inhibitors of dexamethasone-glucocorticoid receptor binding, Shindo et al., J Antibiot., 1994, 47: 1072-1074). It was suggested that Collismycin A and its isomer B could have an anti-inflammatory activity inhibiting the dexamethasone-glucocorticoid receptor binding, although no complementary results to this study seem to have been published.  
         [0008]     A synthesis of Collismycin A has been described by Trécourt et al. in 1998 (First Synthesis of Caerulomycin E and Collismycins A and C. A New Synthesis of Caerulomycin A, Trécourt et al. J. Org. Chem., 1998, 63:2892-2897) starting from 2,2′-bipyridine N-oxide. Functionalization at C-4 and C-6 through different pathways leads to 6-bromo-4-methoxy-2,2′-bipyridines; a subsequent metalation reaction introduces a methylthio moiety at C-5. In a last step of the synthesis pathway, Br at C-6 is substituted by a formyl group which reacts with hydroxylamine to provide Collismycin A. This document is herewith incorporated by reference into the present application.  
         [0009]     In particular, Collismycin A presents the following structure:  
                         
 
 and Collismycin B:  
                         
 
         [0010]     Some other 2,2′-bipyridine compounds with structures close to that of Collismycin have been described in the literature.  
         [0011]     Some examples are: 
 
 Pyrisulfoxin-A (N. Tsuge et al., J. Antibiot. 52 (1999) 505-7)  
                         
 
 Caerulomycin-B; Cerulorycin-B  
                         
 
 Caerulomycin-C; Cerulomycin-C  
                         
 
 Caerulomycin; Caerulomycin-A; Cerulomycin  
                         
 
       SUMMARY OF THE INVENTION  
       [0012]     It has now been found that Collismycin A and close synthetic derivatives thereof exhibit a strong oxidative stress inhibition in cells.  
         [0013]     Accordingly, the present invention is related to the use of a compound of formula (I)  
                         
 
 or a pharmaceutically acceptable salt, prodrug or solvate thereof, wherein 
 
 A is selected from —C(R 3 )— and —N—, 
 
 R 1 , R 2 , R 3 , R 4 , and R 5  are independently selected from hydrogen, substituted or unsubstituted alkyl, —CN, —O—R a , —NR b R c , —NO 2 , or halogen; 
 
 R 7  is selected from halogen, preferably fluor, hydrogen and —S—R 9 ; 
 
 R 10  is selected from —CN, —CH═N—O—R 6 , and —CH 2 —O—R 6 , 
 
 R 8  is selected from hydrogen, —O—R 11 , and —S—R 9 , 
 
 with the proviso that at least one of R 7  and R 8  is different from hydrogen, 
 
 R 6  and R 11  are independently selected from hydrogen, substituted or unsubstituted alkyl, —NR b R c , —C(═O)R d ; 
 
 R 9  is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aralkyl, substituted or unsubstituted aryloxy, halogen; 
 
 R a , R b , R c  and R d  are each independently selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl, substituted or unsubstituted heterocyclyl, or halogen; 
 
 in the preparation of a medicament for the treatment and/or prevention of a oxidative-stress-induced disease or condition selected from the group formed by Alzheimer&#39;s Disease, Parkinson&#39;s Disease, Huntington&#39;s Disease, Amyotrophic Lateral Sclerosis (ALS), Multiple Sclerosis (ML), Friedreich&#39;s ataxia, tardive dyskynesia, brain injuries, such as ischemia, reperfusion injury or stroke, myocardial infarction, schizophrenia, atherosclerosis, heart failure, diabetes, specially diabetes type II, epilepsy and AIDS dementia. 
 
         [0014]     According to a preferred embodiment, R 1 , R 2 , R 3 , R 4  and R 5  are independently selected from hydrogen, substituted or unsubstituted alkyl or halogen.  
         [0015]     In another embodiment R 7  is preferably —S—R 9 .  
         [0016]     In a further preferred embodiment R 7  is —S—R 9 , R 10  is —CH═N—O—R 6 , R 8  is —O—R 11 , wherein R 6 , R 9  and R 11  are independently selected from hydrogen and substituted or unsubstituted alkyl.  
         [0017]     More preferably, in the compound of formula (I) R 7  is —S—R 9 , R 10  is —CH═N—O—R 6 , R 8  is -0-R 11  and R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 9  and R 11  are independently selected from hydrogen and unsubstituted alkyl.  
         [0018]     Even more preferably, R 7  is —S—R 9 , R 1 , R 2 , R 3 , R 4  and R 5  are hydrogen; R 8  is -0-R 11 , R 10  is —CH═N—OH; wherein R 9  and R 11  are independently selected from unsubstituted alkyl.  
         [0019]     In a preferred embodiment, the compound of formula (I) is  
                         
 
 or its pharmaceutically acceptable salts and solvates. 
 
         [0020]     The term “oxidative stress-induced disease or condition”, as used herein, means any disease or other deleterious condition induced or co-induced by oxidative stress.  
         [0021]     Preferably, the oxidative stress-induced disease or condition is a neurodegenerative disease or condition.  
         [0022]     According to a preferred embodiment of the present invention, the neurodegenerative disease is Alzheimer&#39;s Disease.  
         [0023]     According to another preferred embodiment, the neurodegenerative disease or condition is Parkinson&#39;s Disease.  
         [0024]     According to an additional embodiment, the oxidative stress-induced disease or condition is stroke or ischemia.  
         [0025]     Another aspect of this invention relates to a method of treating and/or preventing an oxidative stress-induced disease or condition selected from the group formed by Alzheimer&#39;s Disease, Parkinson&#39;s Disease, Huntington&#39;s Disease, Amyotrophic Lateral Sclerosis (ALS), Multiple Sclerosis (ML), Friedreich&#39;s ataxia, tardive dyskynesia, brain injuries, such as ischemia, reperfusion injury or stroke, myocardial infarction, schizophrenia, atherosclerosis, heart failure, diabetes, specially diabetes type II, epilepsy and AIDS dementia, with a compound as described above, which method comprises administering to a patient in need of such a treatment a therapeutically effective amount of a compound of formula (I) as defined in the claims or a pharmaceutically acceptable salt, prodrug or solvate thereof, or a pharmaceutical composition thereof. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0026]      FIG. 1 .—Results of toxicity assay in SHSY5Y human neuroblastoma cells, Lactate dehydrogenase activity is measured after incubation at different Collismycin A concentrations.  
         [0027]      FIG. 2 .—Results of neuroprotection assay on human neuroblastoma cells exposed to H 2 O 2  induced oxidative stress, previous incubation with Collismycin A.  
         [0028]      FIG. 3 .—Results of cell survival assay on human neuroblastoma cells exposed to H 2 O 2  induced oxidative stress, previous incubation with Collismycin A.  
         [0029]      FIG. 4 .—Protective effect of 2 hour preincubation with Collismycin A against toxicity caused by 6-hydroxydopa mine.  
         [0030]      FIG. 5 .—Diagram showing cell survival previous 2 hour preincubation at different concentrations of Collismycin A, compared with 6OHDA and NAC.  
         [0031]      FIG. 6 .—Neuroprotection against cellular death induced by 6OHDA, previous 1 hour preincubation with Collismycin A.  
         [0032]      FIG. 7 .—Diagram showing cell survival previous 1 hour preincubation at different concentrations of Collismycin A, compared with 6OHDA and NAC. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     The typical compounds of this invention show good properties regarding inhibition of oxidative stress caused by H 2 O 2  and cellular protection against the deleterious effects of the toxine 6-hydroxidopamine, which are similar or even better than the properties of the widely used control NAC (N-Acetylcysteine); simultaneously, the compounds show very high levels of cell survival.  
         [0034]     In the above definition of compounds of formula (I) the following terms have the meaning indicated:  
         [0035]     “Alkyl” refers to a straight or branched hydrocarbon chain radical consisting of carbon and hydrogen atoms, containing no saturation, having one to eight carbon atoms, and which is attached to the rest of the molecule by a single bond, e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, n-pentyl, etc. Alkyl radicals may be optionally substituted by one or more substituents such as halo, hydroxy, alkoxy, carboxy, cyano, carbonyl, acyl, alkoxycarbonyl, amino, nitro, mercapto and alkylthio.  
         [0036]     “Aryl” refers to a phenyl, naphthyl, indenyl, fenanthryl or anthracyl radical, preferably phenyl or naphthyl radical. The aryl radical may be optionally substituted by one or more substituents such as hydroxy, mercapto, halo, alkyl, phenyl, alkoxy, haloalkyl, nitro, cyano, dialkylamino, aminoalkyl, acyl and alkoxycarbonyl, as defined herein.  
         [0037]     “Aralkyl” refers to an aryl group linked to an alkyl group. Preferred examples include benzyl and phenethyl.  
         [0038]     “Cycloalkyl” refers to a stable 3- to 10-membered monocyclic or bicyclic radical which is saturated or partially saturated, and which consist solely of carbon and hydrogen atoms. Unless otherwise stated specifically in the specification, the term “cycloalkyl” is meant to include cycloalkyl radicals which are optionally substituted by one or more such as alkyl, halo, hydroxy, amino, cyano, nitro, alkoxy, carboxy and alkoxycarbonyl.  
         [0039]     “Halo” refers to bromo, chloro, iodo or fluoro.  
         [0040]     “Heterocycle” refers to a heterocyclyl radical. The heterocycle refers to a stable 3- to 15 membered ring which consists of carbon atoms and from one to five heteroatoms selected from the group consisting of nitrogen, oxygen, and sulfur, preferably a 4- to 8-membered ring with one or more heteroatoms, more preferably a 5- or 6-membered ring with one or more heteroatoms. For the purposes of this invention, the heterocycle may be a monocyclic, bicyclic or tricyclic ring system, which may include fused ring systems; and the nitrogen, carbon or sulfur atoms in the heterocyclyl radical may be optionally oxidised; the nitrogen atom may be optionally quaternized; and the heterocyclyl radical may be partially or fully saturated or aromatic. Examples of such heterocycles include, but are not limited to, azepines, benzimidazole, benzothiazole, furan, isothiazole, imidazole, indole, piperidine, piperazine, purine, quinoline, thiadiazole, tetrahydrofuran.  
         [0041]     References herein to substituted groups in the compounds of the present invention refer to the specified moiety that may be substituted at one or more available positions by one or more suitable groups, e.g., halogen such as fluoro, chloro, bromo and iodo; cyano; hydroxyl; nitro; azido; alkanoyl such as a C1-6 alkanoyl group such as acyl and the like; carboxamido; alkyl groups including those groups having 1 to about 12 carbon atoms or from 1 to about 6 carbon atoms and more preferably 1-3 carbon atoms; alkenyl and alkynyl groups including groups having one or more unsaturated linkages and from 2 to about 12 carbon or from 2 to about 6 carbon atoms; alkoxy groups having one or more oxygen linkages and from 1 to about 12 carbon atoms or 1 to about 6 carbon atoms; aryloxy such as phenoxy; alkylthio groups including those moieties having one or more thioether linkages and from 1 to about 12 carbon atoms or from 1 to about 6 carbon atoms; alkylsulfinyl groups including those moieties having one or more sulfinyl linkages and from 1 to about 12 carbon atoms or from 1 to about 6 carbon atoms; alkylsulfonyl groups including those moieties having one or more sulfonyl linkages and from 1 to about 12 carbon atoms or from 1 to about 6 carbon atoms; aminoalkyl groups such as groups having one or more N atoms and from 1 to about 12 carbon atoms or from 1 to about 6 carbon atoms; carbocylic aryl having 6 or more carbons, particularly phenyl or naphthyl and aralkyl such as benzyl. Unless otherwise indicated, an optionally substituted group may have a substituent at each substitutable position of the group, and each substitution is independent of the other.  
         [0042]     Unless otherwise stated, the compounds of the invention are also meant to include compounds which differ only in the presence of one or more isotopically enriched atoms. For example, compounds having the present structures except for the replacement of a hydrogen by a deuterium or tritium, or the replacement of a carbon by a  13 C- or  14 C-enriched carbon or  15 N-enriched nitrogen are within the scope of this invention.  
         [0043]     The term “pharmaceutically acceptable salts, solvates, prodrugs” refers to any pharmaceutically acceptable salt, ester, solvate, or any other compound which, upon administration to the recipient is capable of providing (directly or indirectly) a compound as described herein. However, it will be appreciated that non-pharmaceutically acceptable salts also fall within the scope of the invention since those may be useful in the preparation of pharmaceutically acceptable salts. The preparation of salts, prodrugs and derivatives can be carried out by methods known in the art.  
         [0044]     For instance, pharmaceutically acceptable salts of compounds provided herein are synthesized from the parent compound which contains a basic or acidic moiety by conventional chemical methods. Generally, such salts are, for example, prepared by reacting the free acid or base forms of these compounds with a stoichiometric amount of the appropriate base or acid in water or in an organic solvent or in a mixture of the two. Generally, nonaqueous media like ether, ethyl acetate, ethanol, isopropanol or acetonitrile are preferred. Examples of the acid addition salts include mineral acid addition salts such as, for example, hydrochloride, hydrobromide, hydroiodide, sulphate, nitrate, phosphate, and organic acid addition salts such as, for example, acetate, maleate, fumarate, citrate, oxalate, succinate, tartrate, malate, mandelate, methanesulphonate and p-toluenesulphonate. Examples of the alkali addition salts include inorganic salts such as, for example, sodium, potassium, calcium, ammonium, magnesium, aluminium and lithium salts, and organic alkali salts such as, for example, ethylenediamine, ethanolamine, N,N-dialkylenethanolamine, tπethanolamine, glucamine and basic aminoacids salts.  
         [0045]     Particularly favoured derivatives or prodrugs are those that increase the bioavailability of the compounds of this invention when such compounds are administered to a patient (e.g., by allowing an orally administered compound to be more readily absorbed into the blood) or which enhance delivery of the parent compound to a biological compartment (e.g., the brain or lymphatic system) relative to the parent species.  
         [0046]     Any compound that is a prodrug of a compound of formula (I) is within the scope of the invention. The term “prodrug” is used in its broadest sense and encompasses those derivatives that are converted in vivo to the compounds of the invention. Such derivatives would readily occur to those skilled in the art, and include, depending on the functional groups present in the molecule and without limitation, the following derivatives of the present compounds: esters, amino acid esters, phosphate esters, metal salts sulfonate esters, carbamates, and amides. Examples of well known methods of producing a prodrug of a given acting compound are known to those skilled in the art and can be found e.g. in Krogsgaard-Larsen et al. “Textbook of Drug Design and Discovery” Taylor &amp; Francis (April 2002).  
         [0047]     The compounds of formula (I) defined above can be obtained from natural sources, by synthetic modifications of the natural compound or by total synthesis using available synthetic procedures. As mentioned above, according to Trécourt et al (First Synthesis of Caerulomycin E and Collismycins A and C. A New Synthesis of Caerulomycin A, Trécourt et al. J. Org. Chem., 1998, 63: 2892-2897), a synthesis of Collismycin A starting from 2-2′-bipyridine-N-oxide can be undertaken. This document is herewith incorporated by reference into the present application.  
         [0048]     This pathway mainly involves efficiently controlled reactions such as metalation and cross-coupling:  
                         
 
         [0049]     The synthesis pathway starts from 4-methoxy-2,2′-bipyridine N-oxide (1), which can be easily prepared from 2,2′-bypiridine by a known three-step sequence (Wenkert, D., Woodward, R. B., J. Org. Chem. 1983, 48, 283). The first part of the synthesis pathway involves functionalization at carbon in position six (C-6) of compound (1). A metalation of 4-methoxy-2,2′-bipyridine N-oxide using LDA at −70° C. and BrCN as electrophile is undertaken in order to obtain a bromine N-oxide (2). This molecule is subsequently reduced with PBr 3 , rendering a good yield and leading to 6-bromo-4-methoxy-2,2′-bipyridine (3).  
         [0050]     In a second sequence of reactions, the obtained bromine-bipyridine is subjected to another metalation with the same conditions of LDA at −70° C. but using methyl disulfide as electrophile (Turner J. A., J. Org. Chem 1983, 48, 3401) to introduce a methyltio moiety at C-5, thus obtaining compound (4). Conditions have to be carefully optimised to avoid side replacement of the brome at C-6 by a methyltio moiety before hydrolysis (First Synthesis of Caerulomycin E and Collismycins A and C. A New Synthesis of Caerulomycin A, Trécourt et al. J. Org. Chem., 1998, 63:2892-2897). To reach the target molecule, Collismycin A, the functionalization of C-6 is carried out through a strategy of bromine-lithium exchange. The chelate BuLi-TMEDA performs this exchange, and the obtained lithium derivative is then quenched in presence of DMF to give an aldehyde (5). Reacting this aldehyde with hydroxylamine leads to Collismycin A (6).  
         [0051]     Other alternative procedures may be found in Org. Lett. 2002, 4(14) 2385-2388; J. Org. Chem. 2002, 67(10), 3272-3276; J. Org. Chem. 1996, 61(5), 1673-1676.  
         [0052]     Additional alternative procedures will be apparent to the person skilled in the art, using standard reactions in organic Chemistry such as those described in “March&#39;s Advanced Organic Chemistry” 5 th  Edition, 2001 Wiley-Interscience.  
         [0053]     The compounds of the invention may be in crystalline form either as free compounds or as solvates (e.g. hydrates) and it is intended that both forms are within the scope of the present invention. Methods of salvation are generally known within the art. Suitable solvates are pharmaceutically acceptable solvates. In a particular embodiment the solvate is a hydrate.  
         [0054]     The compounds of formula (I) or their salts or solvates are preferably in pharmaceutically acceptable or substantially pure form. By pharmaceutically acceptable form is meant, inter alia, having a pharmaceutically acceptable level of purity excluding normal pharmaceutical additives such as diluents and carriers, and including no material considered toxic at normal dosage levels. Purity levels for the drug substance are preferably above 50%, more preferably above 70%, most preferably above 90%. In a preferred embodiment it is above 95% of the compound of formula (I), or of its salts, solvates or prodrugs.  
         [0055]     The compounds of the present invention represented by the above described formula (I) may include enantiomers depending on the presence of chiral centres or isomers depending on the presence of multiple bonds (e.g. Z, E). The single isomers, enantiomers or diastereoisomers and mixtures thereof fall within the scope of the present invention.  
         [0056]     The compounds and compositions of this invention may be used with other drugs to provide a combination therapy. The other drugs may form part of the same composition, or be provided as a separate composition for administration at the same time or at different time.  
         [0057]     The following examples are intended to further illustrate the invention. They should not be interpreted as a limitation of the scope of the invention as defined in the claims.  
       EXAMPLES  
     Synthesis  
       [0058]     Compounds of formula (I) were prepared based on the synthesis pathway detailed above. Detailed synthesis of some of the compounds is hereinafter included:  
       Example 1  
     Preparation of Compound 1  
     4-Methylsulfanyl-[2,2′]bipyridinyl-6-carbonitrile  
       [0059]    
       
                 
         
             
             
         
       
     
       First Step: Preparation of the Intermediate  
     4-Methylsulfanyl-[2,2′]bipyridinyl-oxide  
       [0060]     4-Nitro-[2,2′]bipyridinyl 1-oxide (1.00 (g, 4.6 mmol) (D. Wenkert; R. B. Woodward, J. Org. Chem. 1983, 48, 283-289) and sodium methylthiolate (0.73 g, 10.3 mmol) were refluxed in tetrahydrofuran (30) mL) for 6 hours. The mixture was allowed to reach room temperature and the solvent was evaporated in vacuo. The oily residue obtained was redissolved in methylene chloride and washed sequentially with water and a saturated solution of sodium chloride, dried with anhidrous sodium sulfate and evaporated. Pure 4-methylsulfanyl-[2,2′]bipyridinyl 1-oxide was isolated after flash chromatography (SiO 2 , MeOH/CH 2 Cl 2  1:25) as a yellowish oil that slowly solidified (1.59 g, 59% yield).  
         [0061]      1 H NMR (400 MHz, CDCl 3 ):  
         [0062]     8.91, 8.68, 8.14, 7.95, 780, 7.32, 705, 2.53  
         [0063]      13 C NMR (100 MHz, CDCl 3 ):  
         [0064]     149.27, 149.23, 146.41, 139.92, 139.15, 136.21, 125.65, 124.34, 123.30, 121.80, 14.82  
       Second Step: Preparation of 4-Methylsulfanyl-[2,2′]bipyridinyl-6-carbonitrile  
       [0065]     4-Methylsulfanyl-[2,2′]bipyridinyl 1-oxide (480 mg, 2.20 mmol) was treated under nitrogen with diethyl phosphorocyanidate and triethylamine in dry acetonitrile following a described procedure (I. Antonioni; G. Cristalli; P. Franchetti; M. Grifantini; S. Martelli,  Il Farmaco,  1986, 41, 346-354). Crystallization in ethyl acetate afforded 4-methylsulfanyl-[2,2′]bipyridinyl-6-carbonitrile as a white solid (360 mg, 72% yield)  
         [0066]      1 H NMR (400 MHz, CDCl 3 ):  
         [0067]     8.67, 8.47, 8.44, 8.00, 7.85, 7.46, 7.37, 2.61  
         [0068]      13 C NMR (100 MHz, CDCl 3 ):  
         [0069]     156.72, 153.83, 153.59, 149.17, 137.20, 132.88, 124.79, 124.08, 121.82, 119.38, 117.30, 13.96  
       Example 2  
     Preparation of Compound 2  
     5-Fluoro-[2,2′]bipyridinyl-6-carbaldehyde oxime  
       [0070]    
       
                 
         
             
             
         
       
     
       First Step: Preparation of 5-Fluoro-[2,2′]bipyridinyl-6-carbaldehyde  
       [0071]     To obtain 5-Fluoro-[2,2′]bipyridinyl-6-carbaldehyde, a mixture of 2-Bromo-6 fluoro-6-formylpyridine (2.45 mmol, 0.5 g) and 2-tributylstannyl-pyridine (2.94 mmol; 1.08 g) and Tetrakis(triphenylphosphine)-palladium(0) (0.09 mmol, 0.103 g) in anhydrous toluene was refluxed under nitrogen for 54 h. The resulting brown mixture was evaporated in vacuo and the dark, muddy liquid was dissolved in dichloromethane. The organic phase was washed with aqueous HCl 6M (3×). To remove the product from the solution the combined aqueous layers were transferred dropwise in aqueous ammonia (10%) under cooling. The resulting oil was extracted with dichloromethane (3×). The organic phases were washed with ammonia and water, and the solvent was removed. The resulting crude was purified by column chromatography using as eluent Acetate/Hexane, 1/2, thus obtaining 5-Fluoro-[2,2′]bipyridinyl-6-carbaldehyde (Ulrich, S. Schubert; Christian Eschbaumer; Marcel Heller. Org. Lett, 2000, 2(21), 3373-3376).  
         [0072]     Yield: 200 mg (43%), yellow solid.  
         [0073]      1 H-NMR (CDCl 3 ): 10.2 (s, 1H); 8.64 (m, 2H); 8.45 (d, 1H, J=7.9 Hz); 7.81 (t, 1H, J=7.6 Hz); 7.63 (t, 1H, J=9.2 Hz); 7.33 (m, 1H)  
         [0074]      13 C-NMR (CDCl 3 ): 189.8 (CHO, J=3.3 Hz); 159.0 (C—F, J=275.5 Hz); 153.8 (py); 152.7 (J=4.5 Hz); 149.1 (py); 139.2 (J=7.5 Hz); 137.0 (py); 127.0 (J=4.5 Hz); 126.2 (J=18.8 Hz); 124.2 (py); 121.0 (py).  
       Second Step: Preparation of 5-Fluoro-[2,2′]bipyridinyl-6-carbaldehyde oxime  
       [0075]     5-Fluoro-[2,2′]bipyridinyl-6-carbaldehyde (0.36 mmol, 73 mg), hydroxylamine hydrochloride (1.8 mmol, 125 mg), pyridine (1.6 mmol, 0.12 mL) and EtOH were heated at reflux during 2 h. The solvent was evaporated under vacuum, and H 2 O was added. The filtration of the white precipitate obtained provided the final product without needing any purification (Florence Mongin; François Trécourt; Bruno Gervais; Oliver Mongin; Guy Quéquiner, J. Org. Chem., 2002, 67, 3272-3276).  
         [0076]     Yield: 47 mg (60%), white solid.  
         [0077]      1 H-NMR (DMSO): 12.0 (N—OH); 8.76 (d, 1H, J=4.4 Hz); 8.46 (dd, 1H, J 1 =8.5 Hz, J 1 =3.4 Hz); 8.40 (d, 1H, J=7.9 Hz); 8.34 (s, 1H); 8.01 (m, 2H); 7.54 (m, 1H)  
         [0078]      13 C-NMR (DMSO): 157.5 (C—F, J=270.5 Hz); 153.8 (py); 151.3 (J=4.5 Hz); 149.2 (py); 145.2 (C═N, J=6.2 Hz); 138.9 (J=7.5 Hz); 137.4 (py); 125.5 (J=18.5 Hz); 124.2 (py); 122.1 (J=5.2 Hz); 120.4 (py).  
       Example 3  
     Preparation of 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde oxime  
       [0079]    
       
                 
         
             
             
         
       
     
       First Step: Preparation of 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde  
       [0080]     To obtain 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde, a mixture of 2-Bromo-6 fluoro-6-formylpyridine (2.45 mmol, 0.5 g) and 2-tributylstannyl-pyridine or 2-tributylstannyl-pyrazine (2.94 mmol; 1.00 g) and Tetrakis(triphenylphosphine)-palladium(0) (0.09 mmol, 0.103 g) in anhydrous toluene was refluxed under nitrogen for 54 h. The resulting brown mixture was evaporated in vacuo and the dark, muddy liquid was dissolved in dichloromethane. The organic phase was washed with aqueous HCl 6M (3×). To remove the product from the solution the combined aqueous layers were transferred dropwise in aqueous ammonia (10%) under cooling. The resulting oil was extracted with dichloromethane (3×). The organic phases were washed with ammonia and water, and the solvent was removed. The resulting crude was purified by column chromatography using as eluent Acetate/Hexane, 1/1, to obtain 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde (Ulrich, S. Schubert; Christian Eschbaumer; Marcel Heller. Org. Lett, 2000, 2(21), 3373-3376).  
         [0081]     Yield: 68 mg (10%), white solid.  
         [0082]      1 H-NMR (CDCl 3 ): 10.25 (s, 1H); 9.69 (d, 1H, J=1.5 Hz); 8.64 (m, 3H); 7.7 (t, 1H, J=8.95 Hz)  
         [0083]      13 C-NMR (CDCl 3 ): 189.5 (CHO, J=3.3 Hz); 159.0 (C—F, J=275.5 Hz); 150.8 (J=4.6 Hz); 148.9; 145.0; 143.5; 143.2; 139.7 (J=7.6 Hz); 127.4 (J=6.4 Hz); 126.6 (J=18.8 Hz)  
       Second Step: Preparation of 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde oxime  
       [0084]     To obtain 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde oxime, 3-Fluoro-6-pyrazin-2-yl-pyridine-2-carbaldehyde (0.24 mmol, 48 mg), hydroxylamine hydrochloride (1.18 mmol, 82.2 mg), pyridine (1.01 mmol, 0.082 mL) and EtOH were heated at reflux for 2 h. The solvent was evaporated under vacuum, and H 2 O was added. The filtration of the white precipitate obtained provided the final product without needing any purification (Florence Mongin; François Trécourt; Bruno Gervais; Oliver Mongin; Guy Quéquiner, J. Org. Chem., 2002, 67, 3272-3276).  
         [0085]     Yield: 30 mg (58%), white solid.  
         [0086]      1 H-NMR (DMSO): 12.0 (N—OH); 9.49 (d, 1H, J=1.4 Hz); 8.75 (m, 2H); 8.35 (dd, 1H, J 1 =8.8 Hz, J 1 =3.8 Hz); 8.31 (s, 1H); 7.99 (m, 1H).  
         [0087]      13 C-NMR (DMSO): 157.5 (C—F, J=270.5 Hz); 149.5 (J=4.5 Hz); 148.9; 145.2 (C═N, J=6.2 Hz); 144.9; 143.9; 142.2; 139.4 (J=7.5 Hz); 125.9 (J=18.5 Hz); 122.7 (J=5.2 Hz)  
         [0000]     Biology  
         [0088]     The following compounds were assayed to determine their toxicity, their capacity of protecting against hydrogen peroxide-induced cell death and their capacity of protecting against 6-OHDA-induced cell death.  
                         
 
 Toxicity 
 
         [0089]     The potential effects on cell viability of the assayed compounds are assayed in SH-SY5Y human neuroblastoma cells, by quantification of Lactate dehydrogenase (LDH) activity release. SH-SY5Y human neuroblastoma cells are seeded into 96-well culture plates at 104 cells/well. The medium is then removed and the cells incubated with different concentrations of the compounds during 24 h. The compounds are tested at final concentrations of 1, 10, 100 and 1000 μM, in fresh culture medium. After 24 h, the medium is removed and cells attached to the bottom of the well are lysed by adding 50 μl of Krebs-Hepes; Triton X-100 1% during 5 minutes at room temperature. For LDH release quantification, we use the Roche cytotoxicity detection kit (Cat. No. 11 644 793 001). The LDH activity is measured by its absorbance at 492 nm with reference wavelength 620 nm.  
         [0090]     The results for Collismycin A are shown in  FIG. 1 . An effect on cell viability was only observed at 1000 μM, the highest concentration tested.  
         [0091]     Caerulomycin A, Collismycin C and Compound 2 were assayed at a maximum concentration of 1000 μM, and resulted non toxic. Compound 1 and Compound 3 were assayed at a maximum concentration of 5 and 10 μM respectively, and resulted also non toxic.  
         [0000]     Protection Against Hydrogen Peroxide-Induced Cell Death  
         [0092]     The aim of this assay is to determine the neuroprotective effect of the compounds of formula (I), when human neuroblastoma cells are exposed to oxidative stress induced by hydrogen peroxide, which is highly deleterious to the cell and its accumulation causes oxidation of cellular targets such as DNA, proteins, and lipids leading to mutagenesis and cell death.  
         [0093]     SH-SY5Y human neuroblastoma cells are seeded into 96-well culture plate at a density of 104 cells/well. Cells are exposed to the different concentrations of the compound one hour before the treatment with H 2 O 2  100 μM during 24 h. 5 mM NAC, a known anti-oxidant agent was used as a positive control, and preincubated 1 hour before the treatment with H 2 O 2 . After 24 h, the medium is removed and cells attached to the bottom of the well are lysed by adding 50 μl of Triton X-100 1% in Krebs-Hepes during 5 minutes at room temperature. For LDH release quantification, Roche cytotoxicity detection kit (Cat. No. 11 644 793 001) is used.  
         [0094]     Results for neuroprotection of Collismycin A at different concentrations, compared to the neuroprotection of NAC 5 mM, are shown in  FIG. 2 .  
         [0095]     Cell survival was determined in parallel in the same assay.  FIG. 3  shows the results obtained with different concentrations of Collismycin A, together with the comparative results for the control NAC at 5 mM and H 2 O 2  alone. As can be observed from the results, Collismycin A shows a significant neuroprotective activity at 0.05 μM.  
         [0096]     For Caerulomycin A, the lowest concentration at which neuroprotective effects were detected was 0.05 μM.  
         [0097]     For Collismycin C and Compound 3, the lowest concentration at which neuroprotective effects were detected was 10 μM.  
         [0098]     For Compound 1 and Compound 2, the lowest concentrations at which neuroprotective effects were detected were 5 μM and 0.5 μM, respectively.  
         [0000]     Protection Against 6-OHDA-Induced Cell Death  
         [0099]     The aim of this experiment is to determine the protective effect of the compounds of formula (I) against the toxicity caused by 6-hydroxydopamine (6-OHDA). This toxin induces a cell death similar to which occurs in Parkinson&#39;s disease, destroying dopaminergic neurons (“MPTP and 6-hydroxydopamine-induced neurodegeneration as models for Parkinson&#39;s disease: neuroprotective strategies”; Grunblatt E, et al.; J Neurol. 2000 April; 247 Suppl 2:1195-102).  
         [0100]     Two or three days before the experiment, the SH-SY5Y human neuroblastoma cells are seeded into 96-well culture plate at a density of 10 4  cells/well.  
         [0101]     Cells are exposed to the treatment with 6-OHDA and, finally, cell death is measured by LDH quantification. As positive control we used NAC.  
         [0102]     The assay is performed in two different experimental conditions:  
         [0103]     A) NAC and the compound of formula (I) are preincubated during 2 hours before the treatment with 6-OHDA 75 μM during 16 hours. The assay is performed in medium containing 10% Foetal bovine serum.  
         [0104]     The neuroprotective results against cellular death induced by 6-OHDA are shown in  FIG. 4 .  
         [0105]     The results relating to cell survival in this assay, at different concentrations of Collismycin A, together with the comparative results for the control NAC at 5 mM and 6-OHDA alone, are shown in  FIG. 5 .  
         [0106]     Caerulomycin A resulted neuroprotective at a minimum concentration of 1 μM.  
         [0107]     Collismycin C, Compound 2 and Compound 3 showed a neuroprotective activity at a minimum concentration of μM.  
         [0108]     B) NAC and the compound of formula (I) are preincubated during 1 hour before the treatment with 6-OHDA 50 μM during 24 hours. The assay is performed in medium without any fetal bovine serum.  
         [0109]     The neuroprotective results for Collismycin A against cellular death induced by 6-OHDA are shown in  FIG. 6 .  
         [0110]     The results relating to cell survival in this assay, at different concentrations of Collismycin A, together with the comparative results for the control NAC at 5 mM and 6-OHDA alone, are shown in  FIG. 7 .  
         [0111]     Caerulomycin A showed a neuroprotective effect at a minimum concentration of 1 μM, Collismycin C at 10 μM, and Compound 2 at 0.5 μM.