WO2012104823A2

WO2012104823A2 - Pyridopyrimidinone compounds in the treatment of neurodegenerative diseases

Info

Publication number: WO2012104823A2
Application number: PCT/IB2012/050514
Authority: WO
Inventors: Stefan Frentzel; Paolo Paganetti; Christoph WIESSNER
Original assignee: Novartis Ag
Priority date: 2011-02-04
Filing date: 2012-02-03
Publication date: 2012-08-09
Also published as: WO2012104823A3

Abstract

The present invention relates to pyridopyrimidinone compounds of formula (I) for use in the treatment of neurodegenerative diseases.

Description

Pyridopyrimidinone compounds in the treatment of neurodegenerative diseases

Field of the invention

The present invention relates to pyridopyrimidinone compounds for use in the treatment of neurodegenerative diseases.

Background of the invention

In many chronic neurodegenerative diseases, it is hypothesized that the capacity of molecular chaperones in the brain is insufficient to cope with increasing amounts of misfolded and aggregated proteins.

These diseases include Huntington's disease (HD) whereby polyQ-Huntingtin (polyQ-Htt) proteins aggregate in the brain. Huntington's disease is a progressive, fatal, autosomal- dominant neurological disorder characterized by involuntary movements, severe emotional disturbance and cognitive decline. HD usually strikes in mid-life, in the thirties or forties, although it can also attack children and the elderly. There is presently no treatment to halt the inexorable progression of such disease, which leads to death within ten to twenty years.

Pharmacological induction of heat-shock proteins is proposed to readdress the balance by promoting refolding of mutant proteins, inhibiting aggregation of misfolded proteins as well as disposing of misfolded proteins and toxic oligomeric intermediates by the proteasome or by autophagy.

Therapeutic strategies inhibiting the molecular chaperone HSP90 and increasing the activity of HSP70 in the central nervous system might slow or halt progression of a broad spectrum of neurodegenerative disorders, including Huntington's disease (Ann N Y Acad Sci. 2005 1057:206, Ann N Y Acad Sci. 2006 1086:21 , Neuropathol Appl Neurobiol 2007 33:135). A class of HSP90 inhibitors is described in WO2007/041362.

Other known HSP90 inhibitors such as geldanamycin suffer from severe drawbacks such as low selectivity, poor brain penetration and associated toxicities.

There is therefore a need for new pharmacological compounds that overcome at least some of these hurdles. Summary of the invention

It has been found that pyridopyrimidinone compounds may be useful in the treatment and prevention of neurodegenerative diseases.

Accordingly, a first aspect of the invention relates to a compound of formula (I)

in free form or in salt form, wherein

R1 is selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl;

R3 is selected from H, halogen, C1-C6 alkyl; Xi is CH or N; X₂ is CR4 or N; X₃ is CH or N, wherein at least one of Xi, X₂, or X₃ is N and not more than 2 of Xi, X₂, or X₃ are N;

R4 is selected from halogen, hydroxy, C1-C6 alkyl, C1 -C6 alkoxy;

R5 and R6 are independently selected from H, halogen, C1-C6 alkyl, C1 -C6 alkoxy, for use in the treatment or prevention of a neurodegenerative disease. Another aspect of the invention pertains to a compound of formula (I) in free form or in salt form as defined above for the treatment or prevention of a neurodegenerative disease.

A further aspect of the invention relates to the use of a compound of formula (I) in free form or in salt form as defined above for the manufacture of a medicament for the treatment or prevention of a neurodegenerative disease. A further aspect of the invention relates to a method of treatment or prevention of a neurodegenerative disease comprising administering a therapeutically effective amount of a compound of formula (I) in free form or in salt form as defined above to a subject in need thereof.

A further aspect of the invention relates to a combination comprising a therapeutically effective amount of a compound of formula (I) in free form or in salt form as defined above and one or more therapeutically active co-agents for use in the treatment or prevention of a neurodegenerative disease.

A further aspect of the invention relates to a pharmaceutical composition comprising a therapeutically effective amount of a compound of formula (I) in free form or in salt form as defined above and one or more pharmaceutically acceptable carriers for use in the treatment or prevention of a neurodegenerative disease.

A further aspect of the invention relates to an HSP90 inhibitor for use in the treatment or prevention of a neurodegenerative disease, which HSP90 inhibitor is characterised by a brain/plasma ratio of at least 5, when measured 24 hours after administration of Ι ΟμΓΤΐοΙ/kg of said HSP90 inhibitor in a mouse. Brief description of the figures

- Figure 1 shows a timeline comparison after 1 h, 4h or 24h of plasma and brain levels of compound A after i.v. (intravenous) and p.o. (oral) administration of 30 μΓΤΐοΙ/kg of said compound in a mouse.

- Figure 2.1 depicts a Western Blot detection of protein levels at varying concentrations of compound A.

- Figure 2.2 shows a densitometry quantification of Hsp70 protein normalized to tubulin for Huntington's disease fibroblast lysates treated with Compound A overnight. The quantification was performed for two independent experiments ("A" and "B").

- Figure 2.3 shows a time-resolved FRET quantification of soluble mutant huntingtin normalized to PicoGreen at varying concentrations of compound A.

- Figure 3 is a schematic representation of a 1 ^st in vivo experiment in osynucleopathic mice. Up-arrows indicate performance measurements in the Rotarod. Down-pointing arrow-heads denote p.o. (oral) treatments with compound A.

- Figure 4 compares the effects of Compound A versus a vehicle in wild-type versus Thy1-haSN(A53T) on Rotarod performance. - Figure 5 shows a dose response analysis of Compound A versus a vehicle in Thy1 - haSN(A53T) on Rotarod performance.

- Figure 6A shows the rotating beam of Thy1-haSN(A53T) treated with 5 or 12.5 mg/kg Compound A versus a vehicle. - Figure 6B shows the grip strength of Thy1 -haSN(A53T) treated with 5 mg/kg

Compound A versus a vehicle.

Detailed description of the invention

The invention therefore provides a compound of formula (I)

in free form or in salt form, wherein

R1 is selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl;

R3 is selected from H, halogen, C1-C6 alkyl; X is CH or N; X₂ is CR4 or N; X₃ is CH or N, wherein at least one of X_{1 ;} X₂, or X₃ is N and not more than 2 of X_{1 ;} X₂, or X₃ are N;

R4 is selected from halogen, hydroxy, C1-C6 alkyl, C1 -C6 alkoxy;

R5 and R6 are independently selected from H, halogen, C1-C6 alkyl, C1 -C6 alkoxy, for use in the treatment or prevention of a neurodegenerative disease.

In the present invention, the following terms have the following meanings, unless otherwise specified. Unless specified otherwise, the term "compound(s) of the present invention" refers to compound(s) of formula (I), (la), (lb), (lc), (Id), (le), prodrugs thereof, salts of the compound(s) and/or prodrugs, hydrates or solvates of the compounds, as well as all stereoisomers (including diastereoisomers and enantiomers), tautomers and isotopically labeled compounds (including deuterium substitutions), as well as inherently formed moieties (e.g., polymorphs, solvates and/or hydrates).

As used herein, the term "halogen" (or halo) refers to fluorine, bromine, chlorine or iodine, in particular fluorine or chlorine.

As used herein, the term "alkyl" refers to a fully saturated branched or unbranched hydrocarbon moiety. A C1-C6 alkyl refers to hydrocarbon moieties having 1 to 6 carbon atoms; a C1 to C3 alkyl refers to hydrocarbon moieties having 1 to 3 carbon atoms. Representative examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, iso- propyl, n-butyl, sec-butyl, /^'so-butyl, ferf-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl and the like.

As used herein, the term "alkoxy" refers to alkyl-O-, wherein alkyl is defined herein above. Representative examples of alkoxy include, but are not limited to, methoxy, ethoxy, propoxy, 2-propoxy, butoxy, ferf-butoxy, pentyloxy, hexyloxy, cyclopropyloxy-, cyclohexyloxy- and the like. Typically, alkoxy groups have 1 to 6, preferably 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms.

As used herein, the term "neurodegenerative disease" includes diseases which cause a progressive loss of function of the central nervous system, including death of neurons. These diseases include Huntington's disease, Alzheimer's disease, Parkinson's disease, spinobulbar muscular atrophy, amyotrophic lateral sclerosis, ataxia, spino-cerebellar ataxia- 2, -6, -7, machado-Joseph disease, Niemann-Pick diseases, leukodystrophies, neurodystrophies, neuropathies, Charcot-Marie-Tooth disease, Marinesco-Sjoegren disease.

As used herein, the term "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, coatings, surfactants, antioxidants, preservatives (e.g., antibacterial agents, antifungal agents), isotonic agents, absorption delaying agents, salts, preservatives, drug stabilizers, binders, excipients, disintegration agents, lubricants, sweetening agents, flavoring agents, dyes, and the like and combinations thereof, as would be known to those skilled in the art (see, for example, Remington's Pharmaceutical Sciences, 18th Ed. Mack Printing Company, 1990, pp. 1289- 1329). Except insofar as any conventional carrier is incompatible with the active ingredient, its use in the therapeutic or pharmaceutical compositions is contemplated.

The term "a therapeutically effective amount" of a compound of the present invention refers to an amount of the compound of the present invention that will elicit the biological or medical response of a subject, for example, reduction or inhibition of an enzyme or a protein activity, or ameliorate symptoms, alleviate conditions, slow or delay disease progression, or prevent a disease, etc. In one non-limiting embodiment, the term "a therapeutically effective amount" refers to the amount of the compound of the present invention that, when administered to a subject, is effective to (1 ) at least partially alleviate, inhibit, prevent and/or ameliorate a condition, or a disorder or a disease (i) mediated by HSP90, or (ii) associated with HSP90 activity, or (iii) characterized by activity (normal or abnormal) of HSP90; or (2) reducing or inhibiting the activity of HSP90; or (3) reducing or inhibiting the expression of HSP90.

In another non-limiting embodiment, the term "a therapeutically effective amount" refers to the amount of the compound of the present invention that, when administered to a cell, or a tissue, or a non-cellular biological material, or a medium, is effective to at least partially reducing or inhibiting the activity of HSP90; or at least partially reducing or inhibiting the expression of HSP90.

As used herein, the term "subject" refers to an animal. Typically the animal is a mammal. A subject also refers to for example, primates (e.g., humans, male or female), cows, sheep, goats, horses, dogs, cats, rabbits, rats, mice, fish, birds and the like. In certain embodiments, the subject is a primate. In yet other embodiments, the subject is a human.

As used herein, the term "inhibit", "inhibition" or "inhibiting" refers to the reduction or suppression of a given condition, symptom, or disorder, or disease, or a significant decrease in the baseline activity of a biological activity or process.

As used herein, the term "treat", "treating" or "treatment" of any disease or disorder refers in one embodiment, to ameliorating the disease or disorder (i.e., slowing or arresting or reducing the development of the disease or at least one of the clinical symptoms thereof). In another embodiment "treat", "treating" or "treatment" refers to alleviating or ameliorating at least one physical parameter including those which may not be discernible by the patient. In yet another embodiment, "treat", "treating" or "treatment" refers to modulating the disease or disorder, either physically, (e.g., stabilization of a discernible symptom), physiologically, (e.g., stabilization of a physical parameter), or both.

As used herein, the term "prevent", "preventing" or "prevention" of any disease or disorder refers in one embodiment to preventing or delaying the onset or development or progression of the disease or disorder.

As used herein, a subject is "in need of" a treatment if such subject would benefit biologically, medically or in quality of life from such treatment.

As used herein, the term "a," "an," "the" and similar terms used in the context of the present invention (especially in the context of the claims) are to be construed to cover both the singular and plural unless otherwise indicated herein or clearly contradicted by the context.

one embodiment, the invention relates to a compound of formula (Ic)

wherein R1 , R2, R3, R4, R5, R6, X1 , X2 and X3 are as defined hereinbefore in relation to formula (I) in free form or in salt form, for use in the treatment or prevention of a neurodegenerative disease. On account of at least one asymmetrical carbon atom which is present in the compound of formula (I) and (Ic), a corresponding compound of formula (I) and (Ic) may exist in pure optically active form or in the form of a mixture of optical isomers, e.g. in the form of a racemic mixture. All of such pure optical isomers and all of their mixtures including the racemic mixtures, are part of the present invention. In one embodiment, the invention relates to a compound of formula (la)

wherein R1 , R2, R3, R4, R5, R6, X1 , X2 and X3 are as defined hereinbefore in relation to formula (I) in free form or in salt form, for use in the treatment or prevention of a neurodegenerative disease.

In one embodiment, the invention therefore relates to a compound of formula (lb)

In one embodiment, the invention relates to a compound of formula (Id)

In one embodiment, the invention therefore relates to a compound of formula (le)

Any asymmetric atom (e.g., carbon or the like) of the compound(s) of the present invention can be present in racemic or enantiomerically enriched, for example the (/?)-, (S)- or (Reconfiguration. In certain embodiments, each asymmetric atom has at least 50 % enantiomeric excess, at least 60 % enantiomeric excess, at least 70 % enantiomeric excess, at least 80 % enantiomeric excess, at least 90 % enantiomeric excess, at least 95 % enantiomeric excess, or at least 99 % enantiomeric excess in the (R)- or (S)- configuration. Substituents at atoms with unsaturated double bonds may, if possible, be present in c/^'s- (Z)- or trans- (£)- form.

Accordingly, as used herein a compound of the present invention can be in the form of one of the possible isomers, rotamers, atropisomers, tautomers or mixtures thereof, for example, as substantially pure geometric (c/^'s or trans) isomers, diastereomers, optical isomers (antipodes), racemates or mixtures thereof.

Any resulting mixtures of isomers can be separated on the basis of the physicochemical differences of the constituents, into the pure or substantially pure geometric or optical isomers, diastereomers, racemates, for example, by chromatography and/or fractional crystallization.

Any resulting racemates of final products or intermediates can be resolved into the optical antipodes by known methods, e.g., by separation of the diastereomeric salts thereof, obtained with an optically active acid or base, and liberating the optically active acidic or basic compound. In particular, a basic moiety may thus be employed to resolve the compounds of the present invention into their optical antipodes, e.g., by fractional crystallization of a salt formed with an optically active acid, e.g., tartaric acid, dibenzoyl tartaric acid, diacetyl tartaric acid, di-0,0'-p-toluoyl tartaric acid, mandelic acid, malic acid or camphor-10-sulfonic acid. Racemic products can also be resolved by chiral chromatography, e.g., high pressure liquid chromatography (HPLC) using a chiral adsorbent. As used herein, the term "isomers" refers to different compounds that have the same molecular formula but differ in arrangement and configuration of the atoms. Also as used herein, the term "an optical isomer" or "a stereoisomer" refers to any of the various stereo isomeric configurations which may exist for a given compound of the present invention and includes geometric isomers. It is understood that a substituent may be attached at a chiral center of a carbon atom. The term "chiral" refers to molecules which have the property of non-superimposability on their mirror image partner, while the term "achiral" refers to molecules which are superimposable on their mirror image partner. Therefore, the invention includes enantiomers, diastereomers or racemates of the compound. "Enantiomers" are a pair of stereoisomers that are non-superimposable mirror images of each other. A 1 :1 mixture of a pair of enantiomers is a "racemic" mixture. The term is used to designate a racemic mixture where appropriate. "Diastereoisomers" are stereoisomers that have at least two asymmetric atoms, but which are not mirror-images of each other. The absolute stereochemistry is specified according to the Cahn-lngold-Prelog R-S system. When a compound is a pure enantiomer, the stereochemistry at each chiral carbon may be specified by either R or S. Resolved compounds whose absolute configuration is unknown can be designated (+) or (-) depending on the direction (dextro- or levorotatory) which they rotate plane polarized light at the wavelength of the sodium D line. Certain compounds described herein contain one or more asymmetric centers or axes and may thus give rise to enantiomers, diastereomers, and other stereoisomeric forms that may be defined, in terms of absolute stereochemistry, as (/?)- or (S)-.

The present invention is meant to include all such possible isomers, including racemic mixtures, diastereomeric mixtures and optically pure forms. Optically active (R)- and (S)- isomers may be prepared using chiral synthons or chiral reagents, or resolved using conventional techniques. If the compound contains a double bond, the substituent may be E or Z configuration. If the compound contains a disubstituted cycloalkyl, the cycloalkyl substituent may have a cis- or trans-configuration. All tautomeric forms are also intended to be included. A compound of formula (I), (la), (lb), (Ic), (Id), (le) may exist in free form or in salt form, for example a basic compound in acid addition salt form or an acidic compound in the form of a salt with a base. All of such free compounds and salts for use in the treatment and prevention of a neurodegenerative disease are part of the present invention.

In one embodiment, the invention relates to a compound of formula (I), (la), (lb), (Ic), (Id), (le) as defined herein, in free form, for use in the treatment and prevention of a neurodegenerative disease.

In another embodiment, the invention relates to a compound of formula (I), (la), (lb), (Ic), (Id), (le) as defined herein, in salt form, for use in the treatment and prevention of a neurodegenerative disease. In a further embodiment, the invention relates to a compound of formula (I), (la), (lb), (Ic), (Id), (le) as defined herein, in pharmaceutically acceptable salt form, for use in the treatment and prevention of a neurodegenerative disease.

In yet a further embodiment, the invention relates to a compound of formula (Id) which is (R)- 2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one in free form for use in the treatment and prevention of a neurodegenerative disease.

In yet a further embodiment, the invention relates to a compound of formula (Id) which is (R)- 2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one in free form for use in the treatment and prevention of a neurodegenerative disease.

In yet a further embodiment, the invention relates to a compound of formula (Id) which is (R)- 2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one in salt form, for use in the treatment and prevention of a neurodegenerative disease.

In yet a further embodiment, the invention relates to a compound of formula (Id) which is (R)- 2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one in salt form, for use in the treatment and prevention of a neurodegenerative disease.

In yet a further embodiment, the invention relates to a compound of formula (Id) which is (R)- 2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one in pharmaceutically acceptable salt form for use in the treatment and prevention of a neurodegenerative disease. In yet a further embodiment, the invention relates to a compound of formula (Id) which is (R)- 2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one in pharmaceutically acceptable salt form for use in the treatment and prevention of a neurodegenerative disease.

As used herein, the terms "salt" or "salts" refers to an acid addition or base addition salt of a compound of the invention. "Salts" include in particular "pharmaceutical acceptable salts". The term "pharmaceutically acceptable salts" refers to salts that retain the biological effectiveness and properties of the compounds of this invention and, which typically are not biologically or otherwise undesirable. In many cases, the compounds of the present invention are capable of forming acid and/or base salts by virtue of the presence of amino and/or carboxyl groups or groups similar thereto.

Furthermore, the compounds of the present invention, including their salts, can also be obtained in the form of their hydrates, or include other solvents used for their crystallization. The compounds of the present invention may inherently or by design form solvates with pharmaceutically acceptable solvents (including water); therefore, it is intended that the invention embrace both solvated and unsolvated forms. The term "solvate" refers to a molecular complex of a compound of the present invention (including pharmaceutically acceptable salts thereof) with one or more solvent molecules. Such solvent molecules are those commonly used in the pharmaceutical art, which are known to be innocuous to the recipient, e.g., water, ethanol, and the like. The term "hydrate" refers to the complex where the solvent molecule is water.

The compounds of the present invention, including salts, hydrates and solvates thereof, may inherently or by design form polymorphs. Pharmaceutically acceptable acid addition salts can be formed with inorganic acids and organic acids, e.g., acetate, aspartate, benzoate, besylate, bromide/hydrobromide, bicarbonate/carbonate, bisulfate/sulfate, camphorsulfonate, chloride/hydrochloride, chlortheophyllonate, citrate, ethandisulfonate, fumarate, gluceptate, gluconate, glucuronate, hippurate, hydroiodide/iodide, isethionate, lactate, lactobionate, laurylsulfate, malate, maleate, malonate, mandelate, mesylate, methylsulphate, naphthoate, napsylate, nicotinate, nitrate, octadecanoate, oleate, oxalate, palmitate, pamoate, phosphate/hydrogen phosphate/dihydrogen phosphate, polygalacturonate, propionate, stearate, succinate, subsalicylate, tartrate, tosylate and trifluoroacetate salts.

Inorganic acids from which salts can be derived include, for example, hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like.

Organic acids from which salts can be derived include, for example, acetic acid, propionic acid, glycolic acid, oxalic acid, maleic acid, malonic acid, succinic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, toluenesulfonic acid, sulfosalicylic acid, and the like. Pharmaceutically acceptable base addition salts can be formed with inorganic and organic bases.

Inorganic bases from which salts can be derived include, for example, ammonium salts and metals from columns I to XII of the periodic table. In certain embodiments, the salts are derived from sodium, potassium, ammonium, calcium, magnesium, iron, silver, zinc, and copper; particularly suitable salts include ammonium, potassium, sodium, calcium and magnesium salts.

Organic bases from which salts can be derived include, for example, primary, secondary, and tertiary amines, substituted amines including naturally occurring substituted amines, cyclic amines, basic ion exchange resins, and the like. Certain organic amines include isopropylamine, benzathine, cholinate, diethanolamine, diethylamine, lysine, meglumine, piperazine and tromethamine.

The pharmaceutically acceptable salts of the present invention can be synthesized from a basic or acidic moiety, by conventional chemical methods. Generally, such salts can be prepared by reacting free acid forms of these compounds with a stoichiometric amount of the appropriate base (such as Na, Ca, Mg, or K hydroxide, carbonate, bicarbonate or the like), or by reacting free base forms of these compounds with a stoichiometric amount of the appropriate acid. Such reactions are typically carried out in water or in an organic solvent, or in a mixture of the two. Generally, use of non-aqueous media like ether, ethyl acetate, ethanol, isopropanol, or acetonitrile is desirable, where practicable. Lists of additional suitable salts can be found, e.g., in "Remington's Pharmaceutical Sciences", 20th ed., Mack Publishing Company, Easton, Pa., (1985); and in "Handbook of Pharmaceutical Salts: Properties, Selection, and Use" by Stahl and Wermuth (Wiley-VCH, Weinheim, Germany, 2002). Any formula given herein is also intended to represent unlabeled forms as well as isotopically labeled forms of the compounds. Isotopically labeled compounds have structures depicted by the formulas given herein except that one or more atoms are replaced by an atom having a selected atomic mass or mass number. Examples of isotopes that can be incorporated into compounds of the invention include isotopes of hydrogen, carbon, nitrogen, oxygen, phosphorous, fluorine, and chlorine, such as ²H, ³H, ¹¹C, ¹³C, ¹⁴C, ¹⁵N, ¹⁸F ³¹ P, ³²P, ³⁵S, ³⁶CI, ¹²⁵l respectively. The invention includes various isotopically labeled compounds as defined herein, for example those into which radioactive isotopes, such as ³H and ¹⁴C, or those into which non-radioactive isotopes, such as ²H and ¹³C are present. Such isotopically labelled compounds are useful in metabolic studies (with ¹⁴C), reaction kinetic studies (with, for example ²H or ³H), detection or imaging techniques, such as positron emission tomography (PET) or single-photon emission computed tomography (SPECT) including drug or substrate tissue distribution assays, or in radioactive treatment of patients. In particular, an ¹⁸F or labeled compound may be particularly desirable for PET or SPECT studies. Isotopically- labeled compounds of formula (I) can generally be prepared by conventional techniques known to those skilled in the art or by processes analogous to those described in WO2007/041362 using an appropriate isotopically-labeled reagent in place of the non- labeled reagent previously employed.

Further, substitution with heavier isotopes, particularly deuterium (i.e., ²H or D) may afford certain therapeutic advantages resulting from greater metabolic stability, for example increased in vivo half-life or reduced dosage requirements or an improvement in therapeutic index. It is understood that deuterium in this context is regarded as a substituent of a compound of the formula (I). The concentration of such a heavier isotope, specifically deuterium, may be defined by the isotopic enrichment factor. The term "isotopic enrichment factor" as used herein means the ratio between the isotopic abundance and the natural abundance of a specified isotope. If a substituent in a compound of this invention is denoted deuterium, such compound has an isotopic enrichment factor for each designated deuterium atom of at least 3500 (52.5% deuterium incorporation at each designated deuterium atom), at least 4000 (60% deuterium incorporation), at least 4500 (67.5% deuterium incorporation), at least 5000 (75% deuterium incorporation), at least 5500 (82.5% deuterium incorporation), at least 6000 (90% deuterium incorporation), at least 6333.3 (95% deuterium incorporation), at least 6466.7 (97% deuterium incorporation), at least 6600 (99% deuterium incorporation), or at least 6633.3 (99.5% deuterium incorporation).

Pharmaceutically acceptable solvates in accordance with the invention include those wherein the solvent of crystallization may be isotopically substituted, e.g. D₂0, d₆-acetone, d₆-DMSO.

Compounds of the invention, i.e. compounds of formula (I) that contain groups capable of acting as donors and/or acceptors for hydrogen bonds may be capable of forming co-crystals with suitable co-crystal formers. These co-crystals may be prepared from compounds of formula (I) by known co-crystal forming procedures. Such procedures include grinding, heating, co-subliming, co-melting, or contacting in solution compounds of formula (I) with the co-crystal former under crystallization conditions and isolating co-crystals thereby formed. Suitable co-crystal formers include those described in WO 2004/078163. Hence the invention further provides co-crystals comprising a compound of formula (I), (la), (lb), (Ic), (Id), (le) for use in the treatment or prevention of a neurodegenerative disease.

Various embodiments of the invention are described herein. It will be recognized that features specified in each embodiment may be combined with other specified features to provide further embodiments. For example, the skilled person will appreciate that one or more of paragraphs (1 ) to (40) below can be combined in any combination or subcombination to limit the broadest definitions of formulae (I), (la), (lb), (Ic), (Id) or (le).

In certain embodiments, the invention relates to a compound of the formula (I), (la), (lb), (Ic), (Id), (le) in free form or in salt form, in which: (1 ) R1 is H, halogen, C1 -C6 alkyl, C1-C6 alkoxy;

(2) R1 is hydrogen or C1-C3alkyl;

(3) R1 is methyl;

(4) R2 is independently hydrogen or C1 -C6alkyl; (5) R2 is independently hydrogen or C1 -C3alkyl;

(6) R2 is hydrogen (7) R2 is C1 -C3alkyl;

(8) R2 is methyl;

(9) R3 is hydrogen, halogen or C1 -C6alkyl;

(10) R3 is hydrogen, halogen or C1-C3 alkyl;

(1 1 ) R3 is fluoro, bromo, chloro or iodo;

(12) R3 is fluoro;

(13) R3 is C1-C3alkyl; (14) R4 is halogen, hydroxy, C1-C6alkyl or C1-C6alkoxy;

(15) R4 is fluoro, bromo, chloro or iodo;

(16) R4 is fluoro;

(17) R4 is hydroxy;

(18) R4 is C1-C3alkoxy;

(19) R4 is methoxy;

(20) R4 is ethoxy;

(21 ) R4 is C1-C3 alkyl;

(22) R5 is hydrogen, halogen, C1-C6 alkyl or C1-C6 alkoxy; (23) R5 is hydrogen

(24) R5 is C1-C6 alkoxy;

(25) R5 is C1-C3 alkoxy;

(26) R5 is methoxy;

(27) R5 is ethoxy; (28) R6 is hydrogen, halogen, C1-C6 alkyl or C1-C6 alkoxy;

(29) R6 is hydrogen

(30) R6 is C1-C6 alkoxy; (31 ) R6 is C1-C3 alkoxy;

(32) R6 is methoxy;

(33) R6 is ethoxy;

(34) R5 is hydrogen and R6 is C1-C6 alkoxy; (35) R5 is C1-C6 alkoxy and R6 is hydrogen;

(36) R5 is hydrogen and R6 is hydrogen;

(37) X1 is CH, X2 is CR4 and X3 is N;

(38) X1 is N, X2 is N and X3 is CH; (39) X1 is N, X2 is CR4 and X3 is N;

(40) X1 is CH, X2 is N and X3 is CH.

In another embodiment, the invention relates to a compound of the invention in free form or in salt form which is selected from: 2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one; and

2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one, for use in the treatment or prevention of a neurodegenerative disease. In a preferred embodiment, the invention relates to a compound of the invention in free form or in salt form which is selected from:

(R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one (herein referred to as compound A); and (R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one, for use in the treatment or prevention of a neurodegenerative disease.

In another embodiment, the invention relates to a compound of the invention in free form or in salt form which is selected from:

(S)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one; and

(S)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one, for use in the treatment or prevention of a neurodegenerative disease.

In a further aspect, the invention relates to a compound of the invention for the treatment or prevention of neurodegenerative diseases wherein the disease is selected from Huntington's disease, Alzheimer's disease, Parkinson's disease, spinobulbar muscular atrophy, amyotrophic lateral sclerosis, ataxia, spino-cerebellar ataxia-2, -6, -7, machado-Joseph disease, Niemann-Pick diseases, leukodystrophies, neurodystrophies, neuropathies, Charcot-Marie-Tooth disease, Marinesco-Sjoegren disease.

In another aspect, the invention relates to a compound of the invention for use in the treatment or prevention of Huntington's disease. In another aspect, the invention relates to a compound of the invention for use in the treatment or prevention of Parkinson's disease.

In another aspect, the invention relates to a compound of the invention for use in the treatment or prevention of spinobulbar muscular atrophy (SBMA).

In another aspect, the invention relates to the use of a compound of the invention in free from or in salt form for the treatment or prevention of a neurodegenerative disease. In another aspect, the invention relates to the use of a compound of the invention in free form or in salt form for the manufacture of a medicament for the treatment or prevention of a neurodegenerative disease.

In a further aspect, the invention relates to the use of a compound of the invention in free form or in salt form for the manufacture of a medicament for the treatment or prevention of Huntington's disease.

In a further aspect, the invention relates to the use of a compound of the invention in free form or in salt form for the manufacture of a medicament for the treatment or prevention of Parkinson's disease. In a further aspect, the invention relates to the use of a compound of the invention in free form or in salt form for the manufacture of a medicament for the treatment or prevention of spinobulbar muscular atrophy (SBMA).

In another aspect, the invention relates to a method of treatment or prevention of a neurodegenerative disease comprising administering a therapeutically effective amount of a compound of the invention in free form or in salt form to a subject in need thereof.

In one embodiment, the invention relates to a combination comprising a therapeutically effective amount of a compound of the invention in free form or in salt form and one or more therapeutically active co-agents for use in the treatment or prevention of a neurodegenerative disease. The compound of the present invention may be administered either simultaneously with, or before or after, one or more other therapeutic agent. The compound of the present invention may be administered separately, by the same or different route of administration, or together in the same pharmaceutical composition as the other agents.

In one embodiment, the invention provides a product comprising a compound of formula (I) and at least one other therapeutic agent as a combined preparation for simultaneous, separate or sequential use in therapy. In one embodiment, the therapy is the treatment of a disease or condition mediated by HSP90. Products provided as a combined preparation include a composition comprising the compound of formula (I) and the other therapeutic agent(s) together in the same pharmaceutical composition, or the compound of formula (I) and the other therapeutic agent(s) in separate form, e.g. in the form of a kit.

In another aspect, the present invention provides a pharmaceutical composition comprising a compound of the present invention and a pharmaceutically acceptable carrier for use in the treatment or prevention of a neurodegenerative disease. The pharmaceutical composition can be formulated for particular routes of administration such as oral administration, parenteral administration, and rectal administration, etc. In addition, the pharmaceutical compositions of the present invention can be made up in a solid form (including without limitation capsules, tablets, pills, granules, powders or suppositories), or in a liquid form (including without limitation solutions, suspensions or emulsions). The pharmaceutical compositions can be subjected to conventional pharmaceutical operations such as sterilization and/or can contain conventional inert diluents, lubricating agents, or buffering agents, as well as adjuvants, such as preservatives, stabilizers, wetting agents, emulsifiers and buffers, etc. Typically, the pharmaceutical compositions are tablets or gelatin capsules comprising the active ingredient together with a) diluents, e.g., lactose, dextrose, sucrose, mannitol, sorbitol, cellulose and/or glycine; b) lubricants, e.g., silica, talcum, stearic acid, its magnesium or calcium salt and/or polyethyleneglycol; for tablets also c) binders, e.g., magnesium aluminum silicate, starch paste, gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose and/or polyvinylpyrrolidone; if desired d) disintegrants, e.g., starches, agar, alginic acid or its sodium salt, or effervescent mixtures; and/or e) absorbents, colorants, flavors and sweeteners.

Tablets may be either film coated or enteric coated according to methods known in the art.

Suitable compositions for oral administration include an effective amount of a compound of the invention in the form of tablets, lozenges, aqueous or oily suspensions, dispersible powders or granules, emulsion, hard or soft capsules, or syrups or elixirs. Compositions intended for oral use are prepared according to any method known in the art for the manufacture of pharmaceutical compositions and such compositions can contain one or more agents selected from the group consisting of sweetening agents, flavoring agents, coloring agents and preserving agents in order to provide pharmaceutically elegant and palatable preparations. Tablets may contain the active ingredient in admixture with nontoxic pharmaceutically acceptable excipients which are suitable for the manufacture of tablets. These excipients are, for example, inert diluents, such as calcium carbonate, sodium carbonate, lactose, calcium phosphate or sodium phosphate; granulating and disintegrating agents, for example, corn starch, or alginic acid; binding agents, for example, starch, gelatin or acacia; and lubricating agents, for example magnesium stearate, stearic acid or talc. The tablets are uncoated or coated by known techniques to delay disintegration and absorption in the gastrointestinal tract and thereby provide a sustained action over a longer period. For example, a time delay material such as glyceryl monostearate or glyceryl distearate can be employed. Formulations for oral use can be presented as hard gelatin capsules wherein the active ingredient is mixed with an inert solid diluent, for example, calcium carbonate, calcium phosphate or kaolin, or as soft gelatin capsules wherein the active ingredient is mixed with water or an oil medium, for example, peanut oil, liquid paraffin or olive oil. An oral formulation of a compound of the invention is described in WO2010/088336.

Certain injectable compositions are aqueous isotonic solutions or suspensions, and suppositories are advantageously prepared from fatty emulsions or suspensions. Said compositions may be sterilized and/or contain adjuvants, such as preserving, stabilizing, wetting or emulsifying agents, solution promoters, salts for regulating the osmotic pressure and/or buffers. In addition, they may also contain other therapeutically valuable substances. Said compositions are prepared according to conventional mixing, granulating or coating methods, respectively, and contain about 0.1-75%, or contain about 1-50%, of the active ingredient.

Suitable compositions for transdermal application include an effective amount of a compound of the invention with a suitable carrier. Carriers suitable for transdermal delivery include absorbable pharmacologically acceptable solvents to assist passage through the skin of the host. For example, transdermal devices are in the form of a bandage comprising a backing member, a reservoir containing the compound optionally with carriers, optionally a rate controlling barrier to deliver the compound of the skin of the host at a controlled and predetermined rate over a prolonged period of time, and means to secure the device to the skin.

Suitable compositions for topical application, e.g., to the skin and eyes, include aqueous solutions, suspensions, ointments, creams, gels or sprayable formulations, e.g., for delivery by aerosol or the like. Such topical delivery systems will in particular be appropriate for dermal application, e.g., for the treatment of skin cancer, e.g., for prophylactic use in sun creams, lotions, sprays and the like. They are thus particularly suited for use in topical, including cosmetic, formulations well-known in the art. Such may contain solubilizers, stabilizers, tonicity enhancing agents, buffers and preservatives. As used herein a topical application may also pertain to an inhalation or to an intranasal application. They may be conveniently delivered in the form of a dry powder (either alone, as a mixture, for example a dry blend with lactose, or a mixed component particle, for example with phospholipids) from a dry powder inhaler or an aerosol spray presentation from a pressurised container, pump, spray, atomizer or nebuliser, with or without the use of a suitable propellant.

The present invention further provides anhydrous pharmaceutical compositions and dosage forms comprising the compounds of the present invention as active ingredients, since water may facilitate the degradation of certain compounds. Anhydrous pharmaceutical compositions and dosage forms of the invention can be prepared using anhydrous or low moisture containing ingredients and low moisture or low humidity conditions. An anhydrous pharmaceutical composition may be prepared and stored such that its anhydrous nature is maintained. Accordingly, anhydrous compositions are packaged using materials known to prevent exposure to water such that they can be included in suitable formulary kits. Examples of suitable packaging include, but are not limited to, hermetically sealed foils, plastics, unit dose containers (e. g., vials), blister packs, and strip packs.

The invention further provides pharmaceutical compositions and dosage forms that comprise one or more agents that reduce the rate by which the compound of the present invention as an active ingredient will decompose. Such agents, which are referred to herein as "stabilizers," include, but are not limited to, antioxidants such as ascorbic acid, pH buffers, or salt buffers, etc.

The pharmaceutical composition or combination of the present invention can be in unit dosage of about 1-1000 mg of active ingredient(s) for a subject of about 50-70 kg, or about 1-500 mg or about 1-250 mg or about 1 -150 mg or about 0.5-100 mg, or about 1 -50 mg of active ingredients. The therapeutically effective dosage of a compound, the pharmaceutical composition, or the combinations thereof, is dependent on the species of the subject, the body weight, age and individual condition, the disorder or disease or the severity thereof being treated. A physician, clinician or veterinarian of ordinary skill can readily determine the effective amount of each of the active ingredients necessary to prevent, treat or inhibit the progress of the disorder or disease.

The above-cited dosage properties are demonstrable in vitro and in vivo tests using advantageously mammals, e.g., mice, rats, dogs, monkeys or isolated organs, tissues and preparations thereof. The compounds of the present invention can be applied in vitro in the form of solutions, e.g., aqueous solutions, and in vivo either enterally, parenterally, advantageously intravenously, e.g., as a suspension or in aqueous solution. The dosage in vitro may range between about 10^"3 molar and 10^"9 molar concentrations. A therapeutically effective amount in vivo may range depending on the route of administration, between about 0.1-500 mg/kg, or between about 1-100 mg/kg.

The activity of a compound according to the present invention can be assessed by the following in vitro & in vivo methods, as described in the examples.

In one embodiment, the invention provides a pharmaceutical composition comprising a compound of formula (I) and another therapeutic agent(s) for use in the treatment or prevention of a neurodegenerative disease. Optionally, the pharmaceutical composition may comprise a pharmaceutically acceptable excipient, as described above.

In one embodiment, the invention provides a kit comprising two or more separate pharmaceutical compositions, at least one of which contains a compound of the present invention, for use in the treatment or prevention of a neurodegenerative disease. In one embodiment, the kit comprises means for separately retaining said compositions, such as a container, divided bottle, or divided foil packet. An example of such a kit is a blister pack, as typically used for the packaging of tablets, capsules and the like.

In one embodiment, the invention provides a kit comprising a compound of the present invention in free form or in salt form and instructions for using said compound in the treatment or prevention of a neurodegenerative disease.

The kit of the invention may be used for administering different dosage forms, for example, oral and parenteral, for administering the separate compositions at different dosage intervals, or for titrating the separate compositions against one another. To assist compliance, the kit of the invention typically comprises directions for administration. In the combination therapies of the invention, the compound of the invention and the other therapeutic agent may be manufactured and/or formulated by the same or different manufacturers. Moreover, the compound of the invention and the other therapeutic may be brought together into a combination therapy: (i) prior to release of the combination product to physicians (e.g. in the case of a kit comprising the compound of the invention and the other therapeutic agent); (ii) by the physician themselves (or under the guidance of the physician) shortly before administration; (iii) in the patient themselves, e.g. during sequential administration of the compound of the invention and the other therapeutic agent. Accordingly, the invention provides the use of a compound of formula (I) for treating a disease or condition mediated by HSP90, wherein the medicament is prepared for administration with another therapeutic agent. The invention also provides the use of another therapeutic agent for treating a disease or condition mediated by HSP90, wherein the medicament is administered with a compound of formula (I).

The invention also provides a compound of formula (I) for use in a method of treating a disease or condition mediated by HSP90, wherein the compound of formula (I) is prepared for administration with another therapeutic agent. The invention also provides another therapeutic agent for use in a method of treating a disease or condition mediated by HSP90, wherein the other therapeutic agent is prepared for administration with a compound of formula (I). The invention also provides a compound of formula (I) for use in a method of treating a disease or condition mediated by HSP90, wherein the compound of formula (I) is administered with another therapeutic agent. The invention also provides another therapeutic agent for use in a method of treating a disease or condition mediated by HSP90, wherein the other therapeutic agent is administered with a compound of formula (I).

The invention also provides the use of a compound of formula (I) for treating a disease or condition mediated by HSP90, wherein the patient has previously (e.g. within 24 hours) been treated with another therapeutic agent. The invention also provides the use of another therapeutic agent for treating a disease or condition mediated by HSP90, wherein the patient has previously (e.g. within 24 hours) been treated with a compound of formula (I).

In an embodiment, the present invention relates to an HSP90 inhibitor for use in the treatment or prevention of a neurodegenerative disease, which HSP90 inhibitor is characterised by a brain/plasma ratio of at least 5, when measured 24 hours after administration of Ι ΟμΓΤΐοΙ/kg of said HSP90 inhibitor in a mouse. A preferred HSP90 inhibitor according to the invention has a brain/plasma ratio of at least 10, preferably 10 to 20.

The HSP90 inhibitor used in the present invention therefore shows good brain penetration.

By "HSP90 inhibitor" is meant a compound that binds directly to HSP90 receptor in vitro and is inhibiting the receptor to perform its physiological function.

Binding can be measured by the method described in example 2a, i.e. a biochemical assay using purified HSP90 in a binding buffer with biotinylated radicicol and progressively higher concentrations of the HSP90 inhibitor. The HSP90 inhibitor used in the present invention has a binding potency (IC50 value) typically of less than 1 μΜ, preferably less than 500nM, more preferably less than 100nM, even more preferably less than 20nM.

Inhibition can be assessed by a measure of the depletion of client proteins and upregulation of co-chaperone HSP70, e.g. as described in example 2b.

In one embodiment, the HSP90 inhibitor used in the present invention has an EC50 value for HSP70 upregulation, e.g. when measured in the assay described in example 2b, of less than 1 μΜ, preferably less than 500nM, more preferably less than 100nM, even more preferably less than 30nM. In one embodiment, the HSP90 inhibitor used in the present invention has an IC50 value for c-Met degradation, e.g. when measured in the assay described in example 2b, of less than 1 μΜ, preferably less than 500nM, more preferably less than 100nM, even more preferably less than 30nM.

In one embodiment, the HSP90 inhibitor of the invention is selective for HSP90, in particular for Hsp90a and Ηβρθθβ. The selectivity can be measured by an AlphaScreen biochemical assay which was developed to determine the binding potency and selectivity of Hsp90 inhibitors against the three Hsp90 family members Hsp90a, Hsp903 and Grp94 (see example 4). This assay measures the ability of Hsp90 inhibitors to compete with biotinylated geldanamycin (GA) in the ATP-binding pocket of full length Hsp90 isoforms. The AlphaScreen assays are more sensitive than the TRF binding assay, and the concentrations of Hsp90 proteins used in the reaction are much lower (0.5, 1 and 3 nM for Hsp90a, Hsp903 and Grp94, respectively). As such, the IC50 values of Hsp90 inhibitors for full length Hsp90a determined in the AlphaScreen assay are in general -10 fold lower than those for Hsp90a N- terminal domain determined by the TRF binding assay.

A preferred HSP90 inhibitor of the invention has an IC50 at least 2 fold higher for Grp94 than for Hsp90a and Hsp903 when measured in the AlphaScreen assay described herein.

A more preferred HSP90 inhibitor of the invention has an IC50 at least 5 fold higher for Grp94 than for Hsp90a and Hsp903 when measured in the AlphaScreen assay described herein.

An even more preferred HSP90 inhibitor of the invention has an IC50 at least 6 to 12 fold higher for Grp94 than for Hsp90a and Hsp903 when measured in the AlphaScreen assay described herein. In one embodiment, the HSP90 inhibitor is a low molecular weight compound.

In one embodiment, the HSP90 inhibitor has a maximum molecular weight of 1500 daltons.

In one embodiment, the HSP90 inhibitor has a maximum molecular weight of 1000 daltons.

In one embodiment, the HSP90 inhibitor has a maximum molecular weight of 800 daltons. In one embodiment, the HSP90 inhibitor has a maximum molecular weight of 500 daltons.

In one embodiment, the HSP90 inhibitor is a compound of formula (I) as defined herein.

In one embodiment, the HSP90 inhibitor is (R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2- yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3-d]pyrimidin-5-one in free form or in salt form.

The following examples are intended to illustrate the invention and are not to be construed as being limitations thereon.

The following are abbreviations used in the examples and in the figures: 2B7-Tb: 2B7 Terbium cryptate Akt: serine/threonine protein kinase AKT aSN: alpha-synuclein

ATP: adenosine triphosphate BSA: bovine serum albumin cm: centimeter c-Met: MNNG HOS Transforming gene EC50: half maximal effective concentration

FRET: fluorescence resonance energy transfer g: gram h: hour

HEPES: (4-(2-hydroxyethyl)-1 -piperazineethanesulfonic acid) His: histidine HSF: heat-shock factor

HSP: heat-shock protein

HSP70: heat-shock protein 70

HSP90: heat-shock protein 90

IC50: concentration of an inhibitor that causes a 50% reduction in a measured activity i.v.: intravenous

KCI: potassium chloride

MgCI₂: magnesium chloride

min: minute

mM: millimolar

Mo: monday

mRNA: messenger Ribonucleic acid

MW1-Alexa488: MW1-Alexa Fluor 488

NaCI: sodium chloride

NaH₂P0₄: sodium phosphate

NaF: sodium fluoride

ng: nanogram

nm: nanometer

nM: nanomolar

P-Akt: phosphrylated Akt

PBS: phosphate buffered saline

p.o.: oral administration

rpm: rounds per minute

sec: second Th: Thursday

TRF : time-resolved fluorescence TSE: Tris/Sucrose/EDTA Tub: tubulin Tween: polysorbate wt: wild-type

Examples

Example 1 : compounds for use in the present invention A method for synthesizing compounds of the invention is known from WO2007/041362.

Example 1 a: (R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8- dihydro-6H-pyrido[4,3-d]pyrimidin-5-one (herein referred to as compound A)

Example 1 b: (R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8- dihydro-6H-pyrido[4,3-d]pyrimidin-5-one

Example 2: In vitro properties of compound A

Example 2a: TRF (Time-resolved fluorescence) Binding Assay

In this example, the binding potency of Compound A as measured by a TRF binding assay is described.

TRF competition binding assays were performed to determine the binding potency (IC50 values) of Compound A. Purified His-tagged N-terminal ATP binding domain (amino acid residues 9-236) of HSP90a (HSP90a GenelD: 3320; mRNA Sequence NM_005348) was incubated for two hours at room temperature in binding buffer (50 mM HEPES, 6 mM MgCI2, 20 mM KCI and 0.1 % BSA) with biotinylated radicicol and progressively higher concentrations of the competing compounds. A fraction of the mixture was transferred to capture plates (coated with streptavidin) and incubated for one hour at room temperature. After washing with DELFIA wash buffer, europium-labeled anti-his antibody was added and incubated for two hours at room temperature, followed by washing with DELFIA buffer. DELFIA enhancement solution was then added. After gentle shaking for 10 minutes, the plates were read in VICTOR for europium counts.

Note: IC50 values can also be determined using published methods in the following references:

- Carreras, C. W., A. Schirmer, et al. (2003). "Filter binding assay for the geldanamycin-heat shock protein 90 interaction." Anal Biochem 317(1 ): 40-6;

- Kim, J., S. Felts, et al. (2004). "Development of a fluorescence polarization assay for the molecular chaperone HSP90." J Biomol Screen 9(5): 375-81 ;

- Zhou, V., S. Han, et al. (2004). "A time-resolved fluorescence resonance energy transfer- based HTS assay and a surface plasmon resonance-based binding assay for heat shock protein 90 inhibitors." Anal Biochem 331 (2): 349-57.

Example 2b: In -eel I Western Assay

The classical way to confirm the molecular mechanism of action of Hsp90 inhibitors is to assess the depletion of client proteins and upregulation of co-chaperone Hsp70, a molecular signature of Hsp90 inhibition. On the other hand, Hsp90 inhibition also causes increased activity of heat shock factor (HSF), which induces production of Hsp70.

In-cell Western assays using TRF technology were developed to quantitatively determine the cellular level of c-Met and Hsp70 following treatment of GTL-16 with compound A.

GTL-16 gastric tumor cells were treated with various concentrations of compound A for 24h. Cells were fixed w/ 4% paraformaldehyde, and IC50 or EC50 values for compound A were measured by c-Met degradation or upregulation of Hsp70 determined by in-cell Western analysis.

The results of TRF binding and In-cell Western assays are shown in table 1 below.

EC50 (†Hsp70) 20nM

IC50 (jc-Met) 28nM

Table 1

Example 3: pharmacokinetic data of compound A in mice

An acute single treatment of Compound A in two independent doses (10 or 30 μΓΤΐοΙ/kg) was administered to wild-type mice either per intravenous (i.v.) or oral (p.o.) administration. Plasma and brain levels of Compound A were quantified 1 , 4 or 24 hours after administration (see table 2 and Figure 1 ). Both doses allow to reach brain concentrations of Compound A of 350 nM, a concentration approximately 10x higher than the IC50 of the compound (30 nM). Pharmacological study doses can be administered at < 10 μΓτιοΙ/kg per oral administration as administration at 30 μΓΤΐοΙ/kg does not result in higher brain concentration of the compound.

Table 2

Example 4: selectivity of compound A as HSP90 inhibitor AlphaScreen biochemical assays were developed to determine the binding potency and selectivity of Hsp90 inhibitors against the three Hsp90 family members Hsp90a, Hsp903 and Grp94. This assay measures the ability of Hsp90 inhibitors to compete with biotinylated geldanamycin (GA) in the ATP-binding pocket of full length Hsp90 isoforms. The AlphaScreen assays are more sensitive than the TRF binding assay, and the concentrations of Hsp90 proteins used in the reaction are much lower (0.5, 1 and 3 nM for Hsp90a, Hsp903 and Grp94, respectively). As such, the IC50 values of Hsp90 inhibitors for full length Hsp90a determined in the AlphaScreen assay are in general -10 fold lower than those for Hsp90a N- terminal domain determined by the TRF binding assay.

Table 3 summarizes the biochemical potency of 17AAG (17-(Allylamino)-17- demethoxygeldanamycin), and compound A. Interestingly, whereas 17-AAG binds to all three Hsp90 isoforms equipotently (< 2 fold difference), the IC50 values of compound A for Grp94 are approximately 6-12 fold higher than those for Hsp90a and Ηβρθθβ.

Table 3

Final conditions were 0.25 nM Hsp90a, 1 nM Hsp903 and 3 nM Grp94, combined with 10 nM biotinylated GA for Hsp90a and Hsp903, and 30 nM biotinylated GA for Grp94. Assays were read 4.5 hours post bead additions. IC50 curves and values were generated using Excel fit one site dose response model. IC50 results were expressed as nM values and were an average of N=4.

Example 5: treatment of Huntington's disease fibroblasts with compound A

Material and Methods

Huntington's disease patient-derived fibroblasts with endogenous expression of full-length mutant huntingtin carrying 67Q were seeded in a concentration of 30000 cells per well. 24 hours after plating, cells were incubated over night with Compound A in a serial dilutions series of 0.3 to 1000 nM. Cells were lysed in PBS + 1 % TritonXl OO + Complete Protease Inhibitor. Lysates were analysed for Hsp70, tubulin, AKT and phospho-AKT levels by Western Blotting (see Figure 2.1 ). Densitometry quantification of protein band intensities was performed with Gel Doc™ XR+ System. The Hsp70 protein levels normalized to tubulin protein of two independent experiments ("A" and "B") were blotted against Compound A treatment concentration (see Figure 2.2).

Soluble mutant huntingtin levels were quantified by time-resolved TR-FRET by pipetting 5μΙ sample (Sigma-Aldrich, USA) and 1 μΙ detection buffer (50mM NaH2P04, 400mM NaF, 0.1 % BSA and 0.05% Tween + detection reagents) per low-volume white 384-well so that final amounts of detection reagents per well were 0.3ng 2B7-Tb, 3ng MW1-Alexa488 and 1 :200 stock dilution of PicoGreen (Invitrogen, USA). Plates were incubated for 30 min at room temperature. After excitation of the Terbium donor at 320 nm and a time-delay of Ι ΟΟμβ, emission signals of D2 were detected at 665 nm respectively with an Envision reader (PerkinElmer, Switzerland). PicoGreen was detected at 535 nm after excitation at 485 nm (see Figure 2.3).

The results show that in a Huntington's disease patient's cell line, Compound A can successfully inhibit Hsp90 at doses as low as 10 nM and induce the expected cellular responses (increase in Hsp70 expression; decrease in Akt and pAkt). In addition, Hsp90 inhibition by Compound A in a patient's cell line leads to a reduction of mutant huntingtin protein at higher doses as quantified by time-resolved FRET. Together this data indicates that Hsp90 inhibition by Compound A is a viable option for reducing mutant huntingtin protein levels in Huntington's disease patients.

Example 6: effect of compound A in a mouse model of alpha-synucleopathy

HSP90 inhibitors are known inducers of heat-shock proteins (HSPs), a cellular defense mechanism against proteotoxic conditions, which transcriptional control by heat-shock factor 1 (Moromoto et al. 2005). HSPs elicit neuroprotective properties in vitro by refolding of misfolded proteins as well as genetics have shown beneficial effects of HSPs in animal models of neurodegenerative diseases (Muchowski et al., 2005; Bonini et al., 2002). Mutant osynuclein transgenic mice (Thy1-haSN(A53T)) mice develop a neuronal osynucleopathy, similar to human Lewy body pathology, with axonal degeneration and motor deficits (van der Putten et al., 2000). Motor coordination and exploratory activity are strongly impaired, and forelimb muscle weakness is already apparent at five weeks of age. Concomitantly, high molecular weight and truncated osynuclein (aSN) species as well as hyperphosphorylated aSN are seen in neurons of Thy1-haSN(A53T). To test whether HSP90 inhibitors and induction of HSPs have an effect on abberrant osynuclein and thereby on the phenotype, compound A was administered twice weekly 5 or 12.5 mg/kg, for several weeks by p.o. gavage. This dosing regimen was found to be tolerated by Thy1-haSN(A53T). These experiments were carried out to analyse potential improvement in motor coordination of Thy1-haSN(A53T). 1 Methods

1.1 Animals

Table 1 -1 Animal characteristics

Species Strain Category Vendor Gender Weight Age

Mouse (Mus C57BL/6 wild-type Charles River Male ca. 20g 10w musculus)

Mouse (Mus B6-Thy1 - transgenic Novartis, Male ca. 20g 8- musculus) haSN(A53T) CHBS, LAS 16w

(Thy1 -9813)

1.2 Maintenance Conditions

The animals were housed in a temperature-controlled room that was maintained on a 12 hr light/dark cycle. Food and water were available ad libitum. All experiments were carried out in accordance with authorization guidelines for the care and use of laboratory animals. Studies described in this report were performed according to Novartis animal licence number 2063. 1.3 Study designs and motor coordination tests

Compound formulation for compound A was carried out as described below:

Compound A was resuspended by sonification in Neoral placebo formulation solution (1/10 final volume) until obtaining a clear solution (about 10 sec). After this, NaCI 0.9% (9/10 final volume) was gently added, while maintaining constant sonification. This stock solution was kept at room temperature for 1 week. Before injection, the solution was resuspended by stirring. Treatments were done in male or female C57/BI6 mice and Thy1-haSN(A53T) - twice weekly (every 3.5 days, i.e. Monday and Thursday) and sacrifice 24h after the last dosing.

1^st trial (Table 2-1 ): Single dose treatment. Gender used according to analysis, for behavioral (male) and biochemical analysis (female) respectively (Figure 3). Note, there is a pretraining for the animals before onset of treatment. Experiments were abandoned at week 17 (yellow star), due to mortality.

2^nd trial (Table 2-2): Two dose treatment in male animals. This trial also includes analysis of the animals in Rotating Beam as well as forelimb grip strength. Performance in motor coordination (Rotarod and Rotating Beam) and muscle strength (forelimb grip strength) was measured as described in the following:

1.3.1 Rotating Beam

The rotating beam was build in-house and is connected to a rotarod apparatus (Lugo Basile, Italy). It consists of a metal beam (0 1 cm, length 122 cm) coated with rubber attached to a rotarod apparatus (gradient angle upwards of 10°) which controls the constant rotating speed (4 rpm and 8 rpm). The beam is divided into four equal sections which are used for scoring the performance of the mice (scores 1-5). The mouse is placed at the beginning on the already rotating beam facing upwards.

Score 1 (best): mouse reaches the end of the beam without falling down or hanging on the beam head-down,

Score 2: mouse falls down or is hanging head-down in the section 4 of beam

Score 3: mouse falls down or is hanging head-down in the section 3 of beam

Score 4: mouse falls down or is hanging head-down in the section 2 of beam

Score 5: mouse falls down or is hanging head-down in the section 1 of beam

Trials are finished if a mouse reaches the end of the beam, hangs at the beam head-down, or falls down completely. One session consist out of two trials of 4 rpm and two trials of 8 rpm, whereas the sequence is one trial of 4 rpm followed by on trial of 8 rpm in the morning and in the afternoon. 1.3.2 Rotarod

To measure motor coordination mice were placed on a computerized treadmill (TSE rotarod system, Germany) and the latency to fall-off the rotating rod is determined. The rotarod program consists of three different running speeds (12 rpm, 24 rpm and 36 rpm) each for 30 sec with intervals of acceleration lasting for 10 sec. Starting speed is 4 rpm. Rotarod performance was assessed by evaluating the two best trials out of three performed in one day.

1.3.3 Forelimb grip strength

To measure forelimb grip strength, mice are allowed to grasp a handle connected to a force- measuring device (San Diego Instruments, USA) and then pulled back with their tails until they release the handle. The best out of four consecutive trials is evaluated in N. Table 2-1 Treatment groups, 1^st trial:

Name Duration Nr of animal / qroup qenotvoe

Vehicle po 26 weeks (2x/week-Mo/Th) 14 male A53T

Vehicle po 2 weeks (2x/week-Mo/Th) 7 female A53T Vehicle po 12 weeks (2x/week-Mo/Th) 7 female A53T

Vehicle po 26 weeks (2x/week-Mo/Th) 14 male wt littermate

Vehicle po 2 weeks (2x/week-Mo/Th) 7 female wt littermate

Vehicle po 12 weeks (2x/week-Mo/Th) 7 female wt littermate Compound A 12,5 mg/kg po 26 weeks (2x/week-Mo/Th) 14 male A53T

Compound A 12,5 mg/kg po 2 weeks (2x/week-Mo/Th) 7 female A53T

Compound A 12,5 mg/kg po 12 weeks (2x/week-Mo/Th) 7 female A53T

Compound A 12,5 mg/kg 26 weeks (2x/week-Mo/Th) 14 male wt littermate Compound A 12,5 mg/kg 2 weeks (2x/week-Mo/Th) 7 female wt littermate Compound A 12,5 mg/kg 12 weeks (2x/week-Mo/Th) 7 female wt littermate

Table 2-2 Treatment groups, 2^na trial:

Name Duration Nr of animal / qroup genotype

Vehicle 8-26 weeks (2x/week-Mo/Th) 25 male A53T Vehicle 8-26 weeks (2x/week-Mo/Th) 25 male wt littermate

Compound A 5 mg/kg po 8-26 weeks (2x/week-Mo/Th) 25 male A53T Compound A 5 mg/kg po 8-26 weeks (2x/week-Mo/Th) 25 male wt littermate Compound A 12,5 mg/kg po 8-26 weeks (2x/week-Mo/Th) 25 male A53T Compound A 12,5 mg/kg po 8-26 weeks (2x/week-Mo/Th) 25 male wt littermate

Treatment groups from two consecutive in vivo experiments: Thy1 -haSN(A53T) = A53T

2 Results

2.1 Improved motor coordination of Thy1 -haSN(A53T) after chronic treatment with compound A

Thy1-haSN(A53T) show a decreased latency to fall off on the Rotarod, compared to wild- type control mice (Fig. 4), presumably as consequence of impaired synaptic transmission in the brain. In our first trial using compound A, a twice weekly treatment with 12.5 mg/kg evoked a clear trend towards an improvement in this task, which became highly significant at the end of the in vivo experiment (Fig. 4). In fact, the performance of the transgenic animals approached wild-type level after seven weeks of treatment. Interestingly, compound A had no effect in wild-type animals, as no significant difference to vehicle-treated control animals could be observed.

These results were confirmed in a second experiment with animals of the same genotype, including also a lower dose cohort of 5 mg/kg (Fig. 5). As before, after onset of treatment, Thy1-haSN(A53T) significantly improved in the Rotarod performance over time (Fig. 5).

In addition to Rotarod, in Rotating Beam coordination tests (Fig. 6A), compound A treated Thy1-haSN(A53T) had a superior outcome, corroborating the initial findings of better motor coordination induced by HSP90 inhibitor treatment. Furthermore, muscle weakness of Thy1- haSN(A53T) significantly decreased at the lower dose of 5 mg/kg (Fig. 6B).

Taken together, efficacy of compound A was demonstrated in a model for osynucleopathies on the behavioral level. Importantly, a therapeutic index could be achieved with 5 mg/kg of compound A. The data therefore suggests that compound A can be used for diseases related to osynucleopathies such as Alzheimer's disease or Parkinson's disease.

- Bonini NM (2002) Chaperoning brain degeneration. PNAS 99:16407-1641 1

- Klucken J, Shin Y, Masliah E, Hyman BT, McLean PJ (2004) Hsp70 Reduces a-Synuclein Aggregation and Toxicity. JBC 279:25497-25502 - Muchowski PJ, Wacker JL. (2005) Modulation of neurodegeneration by molecular chaperones. Nat Rev Neurosci 6:1 1-22

- van der Putten H, Wiederhold KH, Probst A, Barbieri S, Mistl C, Danner S, Kauffmann S, Hofele K, Spooren WPJM, Ruegg MA, Lin S, Caroni P, Sommer P, Tolnay M, Bilbe G (2000) Neuropathology in Mice Expressing Human a-Synuclein, J Neurosc. 20:6021 -6029.

The following are further embodiments of the invention: Embodiment 1 : A compound of formula (I)

in free form or in salt form, wherein

R1 is selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy; R2 independently is selected from H, C1 -C6 alkyl; R3 is selected from H, halogen, C1-C6 alkyl;

Xi is CH or N; X₂ is CR4 or N; X₃ is CH or N, wherein at least one of Xi, X₂, or X₃ is N and not more than 2 of X_{1 ;} X₂, or X₃ are N;

R4 is selected from halogen, hydroxy, C1-C6 alkyl, C1 -C6 alkoxy;

Embodiment 2: A compound of formula (la) according to embodiment 1 ,

in free form or in salt form, wherein

R1 is selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl;

Xi is CH or N; X₂ is CR4 or N; X₃ is CH or N, wherein at least one of Xi, X₂, or X₃ is N and not more than 2 of Xi, X₂, or X₃ are N;

R4 is selected from halogen, hydroxy, C1-C6 alkyl, C1 -C6 alkoxy;

Embodiment 3: A compound of formula (lb) according to embodiment 1 ,

in free form or in salt form, wherein

R1 is selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl; X_! is CH or N; X₂ is CR4 or N; X₃ is CH or N, wherein at least one of Xi, X₂, or X₃ is N and not more than 2 of Xi, X₂, or X₃ are N;

R4 is selected from halogen, hydroxy, C1 -C6 alkyl, C1 -C6 alkoxy;

R5 and R6 are independently selected from H, halogen, C1 -C6 alkyl, C1 -C6 alkoxy, for use in the treatment or prevention of a neurodegenerative disease

Embodiment 4: A compound of formula (lc)

in free form or in salt form, wherein

R1 is selected from H, halogen, C1 -C6 alkyl, C1 -C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl;

R3 is selected from H, halogen, C1 -C6 alkyl;

R4 is selected from halogen, hydroxy, C1 -C6 alkyl, C1 -C6 alkoxy;

R5 and R6 are independently selected from H, halogen, C1 -C6 alkyl, C1 -C6 alkoxy, for use in the treatment or prevention of a neurodegenerative disease.

Embodiment 5: A compound of formula (Id) according to embodiment 2,

in free form or in salt form, wherein

R1 is selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl;

R3 is selected from H, halogen, C1-C6 alkyl and

R4 is selected from halogen, hydroxy, C1-C6 alkyl, C1 -C6 alkoxy;

Embodiment 6: A compound of formula (le) according to embodiment 4,

in free form or in salt form, wherein

selected from H, halogen, C1-C6 alkyl, C1-C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl; R3 is selected from H, halogen, C1-C6 alkyl and

R4 is selected from halogen, hydroxy, C1-C6 alkyl, C1 -C6 alkoxy; R5 and R6 are independently selected from H, halogen, C1-C6 alkyl, C1 -C6 alkoxy, for use in the treatment or prevention of a neurodegenerative disease.

Embodiment 7: A compound of formula (I), (la), (lb), (lc), (Id) or (le) in free from or in salt form for use in the treatment or prevention of a neurodegenerative disease according to any of embodiments 1 to 6, wherein R1 is C1-C3 alkyl,

R2 independently is H or C1 -C3 alkyl,

R3 is halogen

X^ is CH, X₂ is CR4, X₃ is N, R4 is C1 -C6 alkoxy, R5 and R6 are independently H or C1 -C6 alkoxy or Xi is N, X₂ is N, X₃ is CH, R5 and R6 are independently H or C1 -C6 alkoxy.

Embodiment 8: A compound of formula (lc) according to embodiment 4 in free form or in salt form for use in the treatment or prevention of a neurodegenerative disease, which is selected from:

2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one and

2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H-pyrido[4,3- d]pyrimidin-5-one.

Embodiment 9: A compound of formula (Id) according to embodiment 5 in free form or in salt form for use in the treatment or prevention of a neurodegenerative disease, which is selected from:

(R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one and

(R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one. Embodiment 10: A compound of formula (le) according to embodiment 6 in free form or in salt form for use in the treatment or prevention of a neurodegenerative disease, which is selected from:

(S)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyridin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one and

(S)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one.

Embodiment 1 1 : A compound according to any of embodiments 1 to 10 for use in the treatment or prevention of a neurodegenerative disease, wherein the neurodegenerative disease is selected from Huntington's disease, Alzheimer's, Parkinson's, spinobulbar muscular atrophy, amyotrophic lateral sclerosis, ataxia, spino-cerebellar ataxia-2, -6, -7, machado-Joseph disease, Niemann-Pick diseases, leukodystrophies, neurodystrophies, neuropathies, Charcot-Marie-Tooth disease, Marinesco-Sjoegren disease.

Embodiment 12: A compound according to any of embodiments 1 to 10 for use in the treatment or prevention of a neurodegenerative disease, wherein the neurodegenerative disease is Huntington's disease.

Embodiment 13: A compound according to any of embodiments 1 to 10 for use in the treatment or prevention of a neurodegenerative disease, wherein the neurodegenerative disease is Parkinson's disease.

Embodiment 14: A compound of formula (I), (la) or (Id) in free form or in salt form as defined in any of embodiments 1 , 2 or 5 for the treatment or prevention of a neurodegenerative disease.

Embodiment 15: A compound according to any of embodiments 1 to 10 in free form or in salt form for the treatment or prevention of a neurodegenerative disease.

Embodiment 16: Use of a compound of formula (I), (la) or (Id) in free form or in salt form as defined in any of embodiments 1 , 2 or 5 for the manufacture of a medicament for the treatment or prevention of a neurodegenerative disease.

Embodiment 17: Use according to embodiment 16, wherein the neurodegenerative disease is Huntington's disease.

Embodiment 18: Use according to embodiment 16, wherein the neurodegenerative disease is Parkinson's disease. Embodiment 19: Method of treatment or prevention of a neurodegenerative disease comprising administering a therapeutically effective amount of a compound of formula (I), (la) or (Id) in free form or in salt form as defined in any of embodiments 1 , 2 or 5 to a subject in need thereof. Embodiment 20: A combination comprising a therapeutically effective amount of a compound of formula (I), (la) or (Id) in free form or in salt form as defined in any of embodiments 1 , 2 or 5 and one or more therapeutically active co-agents for use in the treatment or prevention of a neurodegenerative disease.

Embodiment 21 : A pharmaceutical composition comprising a therapeutically effective amount of a compound of formula (I), (la) or (Id) in free form or in salt form as defined in any of embodiments 1 , 2 or 5 and one or more pharmaceutically acceptable carriers for use in the treatment or prevention of a neurodegenerative disease.

Embodiment 22: An HSP90 inhibitor for use in the treatment or prevention of a neurodegenerative disease, which HSP90 inhibitor is characterised by a brain/plasma ratio of at least 5, when measured 24 hours after administration of Ι ΟμΓΤΐοΙ/kg of said HSP90 inhibitor in a mouse.

Embodiment 23: An HSP90 inhibitor for use in the treatment or prevention of a neurodegenerative disease according to embodiment 22, which HSP90 inhibitor is characterised by a brain/plasma ratio of at least 10, when measured 24 hours after administration of Ι ΟμΓΤΐοΙ/kg of said HSP90 inhibitor in a mouse.

While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

Claims

1 . A compound of formula (I)

in free form or in salt form, wherein

R1 is selected from H, halogen, C1 -C6 alkyl, C1 -C6 alkoxy;

R2 independently is selected from H, C1 -C6 alkyl;

R3 is selected from H, halogen, C1 -C6 alkyl;

Xi is CH or N; X₂ is CR4 or N; X₃ is CH or N, wherein at least one of X_{1 ;} X₂, or X₃ is N and not more than 2 of Xi, X₂, or X₃ are N;

R4 is selected from halogen, hydroxy, C1 -C6 alkyl, C1 -C6 alkoxy;

2. A compound according to claim 1 of formula (la),

in free form or in salt form, wherein R1 is selected from H, halogen, C1 -C6 alkyl, C1 -C6 alkoxy; R2 independently is selected from H, C1 -C6 alkyl;

R4 is selected from halogen, hydroxy, C1 -C6 alkyl, C1 -C6 alkoxy;

3. A compound according to claim 2 of formula (Id),

in free form or in salt form, wherein

R1 is selected from H, halogen, C1 -C6 alkyl, C1 -C6 alkoxy; R2 independently is selected from H, C1 -C6 alkyl; R3 is selected from H, halogen, C1 -C6 alkyl and

R4 is selected from halogen, hydroxy, C1 -C6 alkyl, C1 -C6 alkoxy;

4. A compound in free from or in salt form for use in the treatment or prevention of a neurodegenerative disease according to any of claims 1 to 3, wherein R1 is C1-C3 alkyl,

R2 independently is H or C1 -C3 alkyl, R3 is halogen

Xi is CH, X₂ is CR4, X₃ is N, R4 is C1-C6 alkoxy, R5 and R6 are independently H or C1-C6 alkoxy or

Xi is N, X₂ is N, X₃ is CH, R5 and R6 are independently H or C1 -C6 alkoxy.

5. A compound of formula (Id) according to claim 3 in free form or in salt form for use in the treatment or prevention of a neurodegenerative disease, which is selected from

(R)-2-Amino-7-[4-fluoro-2-(6-methoxy-pyrazin-2-yl)-phenyl]-4-methyl-7,8-dihydro-6H- pyrido[4,3-d]pyrimidin-5-one.

6. A compound according to any of claims 1 to 5 for use in the treatment or prevention of a neurodegenerative disease, wherein the neurodegenerative disease is selected from Huntington's disease and Parkinson's disease.

7. A compound according to any of claims 1 to 5 for use in the treatment or prevention of a neurodegenerative disease, wherein the neurodegenerative disease is Huntington's disease.

8. A compound according to any of claims 1 to 5 for use in the treatment or prevention of a neurodegenerative disease, wherein the neurodegenerative disease is Parkinson's disease.

9. A compound in free form or in salt form as defined in any of claims 1 to 5 for the treatment or prevention of a neurodegenerative disease.

10. Use of a compound in free form or in salt form as defined in any of claims 1 to 5 for the manufacture of a medicament for the treatment or prevention of a neurodegenerative disease.

1 1. Use according to claim 10, wherein the neurodegenerative disease is Huntington's disease.

12. Use according to claim 10, wherein the neurodegenerative disease is Parkinson's disease.

13. A method of treatment or prevention of a neurodegenerative disease comprising administering a therapeutically effective amount of a compound in free form or in salt form as defined in any of claims 1 to 5 to a subject in need thereof.

14. A combination comprising a therapeutically effective amount of a compound in free form or in salt form as defined in any of claims 1 to 5 and one or more therapeutically active co-agents for use in the treatment or prevention of a neurodegenerative disease.

15. A pharmaceutical composition comprising a therapeutically effective amount of a compound in free form or in salt form as defined in any of claims 1 to 5 and one or more pharmaceutically acceptable carriers for use in the treatment or prevention of a neurodegenerative disease.