AMINOPYRIDOPYRAZINONE DERIVATIVES FOR TREATING NEURODEGENERATIVE DISEASES

Field of the Invention

[0001] The present invention relates to aminopyridopyrazinone derivatives useful in treating disorders that are mediated by adenosine receptor function, including neurodegenerative diseases and inflammation. Background of the Invention

[0002] Adenosine is a modulator of multiple physiological functions, including cardiovascular, neurological, respiratory and renal functions. Adenosine mediates its effects through specific G-protein coupled receptors. Four adenosine receptors have been identified, Ai, A _2a , A _2b and A ₃ receptors.

[0003] Adenosine A _2a receptor antagonists useful in the treatment of Parkinson's disease have been disclosed in US 6,875,772 and US 6,787,541. These disclosures ^• are incorporated herein by reference as they relate to utility.

SUMMARY OF THE INVENTION

[0004] There are provided, in accordance with embodiments of the invention, compounds of the following formula I and pharmaceutically acceptable salts thereof, which are useful as adenosine 2a receptor antagonists

wherein R ³ is selected from optionally substituted alkyl, optionally substituted aryl, and optionally substituted heteroaryl; R ² is selected from H, alkyl, halo-substituted alkyl, hydroxyalkyl and alkoxyalkyl; and R ⁴ is selected from H, halo, alkyl, alkenyl, alkynyl, aryl, and optionally substituted (C ₁ -Io hydrocarbon)amino; provided that the total number of atoms selected from the group consisting of C, N, O and S in R ³ and R ⁴ together is least five; further provided that when R ² is cyclopropyl and R ⁴ is H, R ³ is not 4-cyanophenyl.

[0005] In some embodiments, R ⁴ is H. In other embodiments, R ⁴ is selected from halo, alkyl, alkenyl, alkynyl, aryl, and optionally substituted (Ci _-10 hydrocarbon)amino. In some embodiments, R ⁴ is selected from 2,6-difluorophenylmethylamino, 2- methylpropylamino (isobutylamino), propylamino, phenyl, 2,2-dimethylpropylamino (neopentylamino), cyclopentylamino, 2-phenylethylamino, 2-methoxyethylamino, n- butylamino, 1 -methylpropylamino (sec-butylamino), ethylamino, chloro, methylamino, 4- phenylpiperazin-1-yl, n-butyl, 2-(morpholin-4-yl)-ethylamino, methyl, 2-(4-phenylpiperazin- l-yl)-ethylamino, 3,3,3-trifluoropropylamino, prop-1-ynyl, and 2-hydroxyethylamino.

[0006] In some embodiments, R ² is H. In some embodiments, R ² is selected from cyclopropylmethyl, 2,2,2-trifluoroethyl, cyclopropyl, cyclobutyl, propyl, n-butyl, ethyl, 3- hydroxypropyl, isopropyl, 3,3,3-trifluoropropyl, 4-hydroxybutyl, methyl, 2-methoxyethyl, and 3-methoxy-propyl.

[0007] In some embodiments, R ³ is selected from thiazol-2-yl, 3-cyanophenyl, furan-2-yl, 3 -fluorophenyl, 3-chlorophenyl, 5-methylfuran-2-yl, thiazol-4-yl, 3- aminocarbonylphenyl, isoxazol-5-yl, 4-methylphenyl, furan-3-yl, 4-methylthiazol-2-yl, 4- chlorophenyl, pyridin-3-yl, 5-methylthiazol-2-yl, thiazol-5-yl, pyridin-2-yl, oxazol-2-yl, pyridin-4-yl, CF ₃ , and 3-bromophenyl.

[0008] In some embodiments, the compound is selected from:

-5- thereof.

[0009] There are also provided, in accordance with embodiments of the invention, pharmaceutical compositions comprising a therapeutically effective amount of at least one compound of formula I, or a pharmaceutically acceptable salt thereof; and a pharmaceutically acceptable carrier.

[0010] The compounds and pharmaceutical compositions described herein are useful in methods for preventing and treating a condition for which an antagonist of adenosine A _2a receptor is indicated.

[0011] Thus there are also provided, in accordance with embodiments of the invention, a method for treating a disease by antagonizing a response mediated by adenosine 2a receptors, which comprises bringing into contact with adenosine receptor at least one compound of formula I or a pharmaceutically acceptable salt thereof. There are also provided a use of a compound, as described herein, for neuroprotection, of for treating, preventing or amelioriating a disease condition which is mediated by adenosine receptor function. There are also provided uses of a compound, as described herein, in the manufacture of a medicament for providing neuroprotection, or for treating, preventing or amelioriating a disease condition which is mediated by adenosine receptor function.

[0012] Thus there are also provided, in accordance with embodiments of the invention, a method of treating disease mediated by adenosine receptors in a subject in need thereof comprising administering to the subject a therapeutically effective amount of at least one compound of general formula I or a pharmaceutically acceptable salt thereof. Treating a disorder associated with adenosine receptor function includes treating disorders associated with A _2a receptors and one or more additional adenosine receptors, such as Ai, A _2b or A ₃ receptors.

[0013] The compounds in accordance with embodiments of the present invention are useful in effecting neuroprotection and as such the present invention provides a method of neuroprotection in a subject in need thereof comprising administering to the subject a therapeutically effective amount of at least one compound of formula I or a pharmaceutically acceptable salt thereof.

[0014] Other indications in which the adenosine antagonists are useful include central nervous system (CNS) disorders, neurodegenerative diseases, cardiovascular diseases and disorders, central nervous system (CNS) and peripheral nervous system (PNS) diseases, cognitive disorders, CNS injury, renal ischemia; acute and chronic pain, affective disorders, central nervous system (CNS) injury, cerebral ischemia; myocardial ischemia, muscle ischemia, sleep disorders, eye disorders, diabetic neuropathy, neural ischemia, and diabetes.

[0015] In some embodiments, the CNS and PNS diseases are movement disorder. In some embodiments, the movement disorder is selected from the group consisting of a disorder of the basal ganglia which results in dyskinesias Huntington's disease, multiple system atrophy, progressive supernuclear palsy, essential tremor, myoclonus, corticobasal degeneration, Wilson's disease, progressive pallidal atrophy, Dopa-responsive dystoma- Parkinsonism, spasticity, Alzheimer's disease and Parkinson's disease. In some embodiments, the Parkinson's disease is selected from the group consisting of early-onset Parkinson's disease, drug-induced Parkinsonism, post-encephalitic Parkinsonism, Parkinsonism induced by poisoning and post-traumatic Parkinson's disease. [0016] The compounds of formula I are useful in combination with one or more of (1) an agent useful in the treatment of Parkinson's disease, (2) an agent useful in the treatment of movement disorders, (3) an agent useful in the treatment of depression.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0017] Throughout this specification the substituents are defined when introduced and retain their definitions.

[0018] It has now been found that compounds of formula I are potent antagonists of the adenosine receptor. Compounds of formula I are useful in preventing and treating diseases and disorders mediated by adenosine receptors, including neurological diseases and disorders. Although these compounds are selective A _2a antagonists, some of them may exhibit sufficient residual affinity for other classes of adenosine receptors to be useful to treat conditions associated with additional adenosine receptors. As a result, there is also provided in accordance with embodiments of the present invention a method of treating a disorder associated with the A _2a receptor and one or more of Ai, A _2t ,or A ₃ receptors. Definitions

[0019] For convenience and clarity certain terms employed in the specification, examples and claims are described herein.

[0020] Alkyl is intended to include linear, branched, or cyclic hydrocarbon structures and combinations thereof. Lower alkyl refers to alkyl groups of from 1 to 6 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s-and t-butyl and the like. Preferred alkyl groups are those of C ₂₀ or below. Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groups of from 3 to 8 carbon atoms. Examples of cycloalkyl groups include c-propyl, c-butyl, c-pentyl, norbornyl and the like.

[0021] Ci to C ₂₀ hydrocarbon includes alkyl, cycloalkyl, alkenyl, alkynyl, aryl and combinations thereof. Examples include phenethyl, benzyl, cyclohexylmethyl, camphoryl and naphthylethyl.

[0022] Alkoxy or alkoxyl refers to groups of from 1 to 8 carbon atoms of a straight, branched, cyclic configuration and combinations thereof attached to the parent structure through oxygen. Examples include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, cyclohexyloxy and the like. Lower-alkoxy refers to groups containing one to four carbons.

[0023] Oxaalkyl refers to alkyl residues in which one or more carbons (and their associated hydrogens) have been replaced by oxygen. Examples include methoxypropoxy, 3,6,9-trioxadecyl and the like. The term oxaalkyl is intended as it is understood in the art [see Naming and Indexing of Chemical Substances for Chemical Abstracts, published by the American Chemical Society, 196, but without the restriction of 127(a)], i.e. it refers to compounds in which the oxygen is bonded via a single bond to its adjacent atoms (forming ether bonds). Similarly, thiaalkyl and azaalkyl refer to alkyl residues in which one or more carbons have been replaced by sulfur or nitrogen, respectively. Examples include ethylaminoethyl and methylthiopropyl.

[0024] Alkoxyalkyl refers to ether groups of from 3 to 8 atoms of a straight, branched, cyclic configuration and combinations thereof attached to the parent structure through alkyl. Examples include methoxymethyl, methoxyethyl, ethoxypropyl, and the like.

[0025] Acyl refers to groups of from 1 to 8 carbon atoms of a straight, branched, cyclic configuration, saturated, unsaturated and aromatic and combinations thereof, attached to the parent structure through a carbonyl functionality. One or more carbons in the acyl residue may be replaced by nitrogen, oxygen or sulfur as long as the point of attachment to the parent remains at the carbonyl. Examples include acetyl, benzoyl, propionyl, isobutyryl, t-butoxy carbonyl, benzyloxycarbonyl and the like. Lower-acyl refers to groups containing one to four carbons.

[0026] Aryl and heteroaryl mean a 5- or 6-membered aromatic or heteroaromatic ring containing 0-3 heteroatoms selected from O, N, or S; a bicyclic 9- or 10-membered aromatic or heteroaromatic ring system containing 0-3 heteroatoms selected from O, N, or S; or a tricyclic 13- or 14-membered aromatic or heteroaromatic ring system containing 0-3 heteroatoms selected from O, N, or S. The aromatic 6- to 14-membered carbocyclic rings include, e.g., benzene and naphthalene, and for the purposes of the present invention, fused moieties such as tetrahydronaphthalene (tetralin), and indane in which one or more rings are aromatic, but not all need be. The 5- to 10-membered aromatic heterocyclic rings include, e.g., imidazole, pyridine, indole, thiophene, benzopyranone, thiazole, furan, benzimidazole, quinoline, isoquinoline, quinoxaline, pyrimidine, pyrazine, tetrazole and pyrazole. [0027] Arylalkyl refers to a substituent in which an aryl residue is attached to the parent structure through alkyl. Examples are benzyl, phenethyl and the like. Heteroarylalkyl refers to a substituent in which a heteroaryl residue is attached to the parent structure through alkyl. Examples include, e.g., pyridinylmethyl, thienylethyl and the like.

[0028] Heterocycle means a cycloalkyl or aryl residue in which from one to three carbons is replaced by a heteroatom selected from the group consisting of N, O and S. The nitrogen and sulfur heteroatoms may optionally be oxidized, and the nitrogen heteroatom may optionally be quaternized. Examples of heterocycles include pyrrolidine, pyrazole, pyrrole, indole, quinoline, isoquinoline, tetrahydroisoquinoline, benzofuran, benzodioxan, benzodioxole (commonly referred to as methylenedioxyphenyl, when occurring as a substituent), tetrazole, morpholine, thiazole, pyridine, pyridazine, pyrimidine, thiophene, furan, oxazole, oxazoline, isoxazole, dioxane, tetrahydrofuran and the like. It is to be noted that heteroaryl is a subset of heterocycle in which the heterocycle is aromatic. Examples of heterocyclyl residues additionally include piperazinyl, 2-oxopiperazinyl, 2-oxopiperidinyl, 2- oxo-pyrrolidinyl, 2-oxoazepinyl, azepinyl, 4-piperidinyl, pyrazolidinyl, imidazolyl, imidazolinyl, imidazolidinyl, pyrazinyl, oxazolidinyl, isoxazolidinyl, thiazolidinyl, isothiazolyl, quinuclidinyl, isothiazolidinyl, benzimidazolyl, thiadiazolyl, benzopyranyl, benzothiazolyl, tetrahydrofuryl, tetrahydropyranyl, thienyl, benzothienyl, thiamorpholinyl, thiamoφholinylsulfoxide, thiamoφholinylsulfone, oxadiazolyl, triazolyl and tetrahydroquinolinyl. A nitrogenous heterocycle is a heterocycle containing at least one nitrogen in the ring; it may contain additional nitrogens, as well as other heteroatoms.

[0029] Substituted alkyl, aryl, cycloalkyl, heterocyclyl etc. refer to alkyl, aryl, cycloalkyl, or heterocyclyl wherein up to three H atoms in each residue are replaced with alkyl, halogen, haloalkyl, hydroxy, loweralkoxy, haloloweralkyloxy, methylenedioxy (replacing two adjacent H atoms), carboxy, carboalkoxy (also referred to as alkoxycarbonyl), carboxamido (also referred to as alkylaminocarbonyl), alkylcarbonyloxy, cyano, carboπyl, nitro, amino, alkylamino, dialkylamino, mercapto, alkylthio, sulfoxide, sulfone, acylamino, amidino, phenyl, benzyl, heterocyclyl, phenoxy, benzyloxy, or heteroaryloxy. Substituents from the foregoing group commonly found in the compounds of the invention include halogen, cyano, methyl, trifluoromethyl, trifluoromethoxy, methoxy, dialkylamino and acylamino. [0030J The terms "halogen" and "halo" refer to fluorine, chlorine, bromine or iodine.

[0031] Some of the compounds described herein may contain one or more asymmetric centers and may thus give rise to enantiomers, diastereomers, and other stereoisomeric forms that may be defined, in terms of absolute stereochemistry, as (R)- or (S)-. The present invention is meant to include all such possible isomers, as well as, their racemic and optically pure forms. Optically active (R)- and (S)- isomers may be prepared using chiral synthons or chiral reagents, or resolved using conventional techniques. When the compounds described herein contain olefinic double bonds or other centers of geometric asymmetry, and unless specified otherwise, it is intended that the compounds include both E and Z geometric isomers. Likewise, all tautomeric forms are also intended to be included. The configuration of any carbon-carbon double bond appearing herein is selected for convenience only and is not intended to designate a particular configuration; thus a carbon- carbon double bond depicted arbitrarily herein as trans may be Z, E or a mixture of the two in any proportion.

[0032] The graphic representations of racemic, ambiscalemic and scalemic or enantiomerically pure compounds used herein are taken from Maehr J. Chem. Ed. 62, 1 14- 120 (1985): solid and broken wedges are used to denote the absolute configuration of a chiral element; wavy lines indicate disavowal of any stereochemical implication which the bond it represents could generate; solid and broken bold lines are geometric descriptors indicating the relative configuration shown but denoting racemic character; and wedge outlines and dotted or broken lines denote enantiomerically pure compounds of indeterminate absolute configuration.

[0033] It will be recognized that the compounds of this invention can exist in radiolabeled form, i.e., the compounds may contain one or more atoms containing an atomic mass or mass number different from the atomic mass or mass number usually found in nature. Radioisotopes of hydrogen, carbon, phosphorous, fluorine, chlorine and iodine include ³ H, ¹⁴ C, ³⁵ S, ¹⁸ F, ³⁶ Cl and ¹²⁵ I, respectively. Compounds that contain those radioisotopes and/or other radioisotopes of other atoms are within the scope of this invention. Tritiated, i.e. ³ H, and carbon- 14, i.e., ¹⁴ C, radioisotopes are particularly preferred for their ease in preparation and detectability. Radiolabeled compounds of this invention can generally be prepared by methods well known to those skilled in the art. Conveniently, such radiolabeled compounds can be prepared by carrying out the procedures disclosed in the Examples by substituting a readily available radiolabeled reagent for a non-radiolabeled reagent. Because of the high affinity for the A _2a receptor, radiolabeled compounds of the invention are useful for A _2a receptor assays.

[0034] Terminology related to "protecting", "deprotecting" and "protected" functionalities occurs throughout this application. Such terminology is well understood by persons of skill in the art and is used in the context of processes that involve sequential treatment with a series of reagents. In that context, a protecting group refers to a group which is used to mask a functionality during a process step in which it would otherwise react, but in which reaction is undesirable. The protecting group prevents reaction at that step, but may be subsequently removed to expose the original functionality. The removal or "deprotection" occurs after the completion of the reaction or reactions in which the functionality would interfere. Thus, when a sequence of reagents is specified, as it is in the processes of the invention, the person of ordinary skill can readily envision those groups that would be suitable as "protecting groups". Suitable groups for that purpose are discussed in standard textbooks in the field of chemistry, such as Protective Groups in Organic Synthesis by T. W. Greene [John Wiley & Sons, New York, 1991], which is incorporated herein by reference.

[0035] A comprehensive list of abbreviations utilized by organic chemists appears in the first issue of each volume of the Journal of Organic Chemistry. The list, which is typically presented in a table entitled "Standard List of Abbreviations", is incorporated herein by reference.

[0036] In general, the compounds in accordance with embodiments of the present invention may be prepared by the methods illustrated in the general reaction schemes as, for example, described below, or by modifications thereof, using readily available starting materials, reagents and conventional synthesis procedures. In these reactions, it is also possible to make use of variants that are in themselves known, but are not mentioned here. The starting materials are either commercially available, synthesized as described in the examples or may be obtained by the methods well known to persons of skill in the art. [0037] Provided in accordance with embodiments of the invention are pharmaceutical compositions comprising as active agents compounds of formula I as described herein.

[0038] As used herein a "pharmaceutical composition" refers to a preparation of one or more of the compounds described herein, or physiologically acceptable salts or solvents thereof, with other chemical components such as physiologically suitable carriers and excipients.

[0039] Pharmaceutical compositions for use in accordance with embodiments of the present invention thus may be formulated in conventional manner or in a manner developed in the future using one or more physiologically acceptable carriers comprising excipients and auxiliaries, which facilitate processing of the active compounds into preparations which can be used pharmaceutically. Proper formulation is dependent upon the route of administration chosen.

[0040] Compounds that antagonize the adenosine receptor can be formulated as pharmaceutical compositions and administered to a mammalian subject, such as a human patient in a variety of forms adapted to the chosen route of administration, i.e., orally or parenterally, by intravenous, intramuscular, topical, transdermal or subcutaneous routes.

[0041] For oral administration, the compounds can be formulated readily by combining the active compounds with pharmaceutically acceptable carriers well known in the art. Such carriers enable the compounds of the invention to be formulated as tablets, pills, dragees, capsules, liquids, gels, syrups, slurries, suspensions, and the like, for oral ingestion by a patient. Pharmacological preparations for oral use can be made using a solid excipient, optionally grinding the resulting mixture, and processing the mixture of granules, after adding suitable auxiliaries if desired, to obtain tablets or dragee cores. Suitable excipients are, in particular, fillers such as sugars, including lactose, sucrose, mannitol, or sorbitol; cellulose preparations such as, for example, maize starch, wheat starch, rice starch, potato starch, gelatin, gum tragacanth, methyl cellulose, hydroxypropylmethyl-cellulose, sodium carbomethylcellulose; and/or physiologically acceptable polymers such as polyvinylpyrrolidone (PVP). If desired, disintegrating agents may be added, such as cross- linked polyvinyl pyrrolidone, agar or alginic acid or a salt thereof such as sodium alginate. [0042] In addition, enteric coating may be useful as it is may be desirable to prevent exposure of the compounds of the invention to the gastric environment.

[0043] Pharmaceutical compositions, which can be used orally, include push-fit capsules made of gelatin as well as soft, sealed capsules made of gelatin and a plasticizer, such as glycerol or sorbitol. The push-fit capsules may contain the active ingredients in admixture with filler such as lactose, binders such as starches, lubricants such as talc or magnesium stearate and, optionally, stabilizers.

[0044] In soft capsules, the active compounds may be dissolved or suspended in suitable liquids, such as fatty oils, liquid paraffin, or liquid polyethylene glycols. In addition, stabilizers may be added. All formulations for oral administration should be in dosages suitable for the chosen route of administration.

[0045] For injection, the compounds of formula I may be formulated in aqueous solutions, preferably in physiologically compatible buffers such as Hank's or Ringer's solution or physiological saline buffer. For transmucosal and transdermal administration, penetrants appropriate to the barrier to be permeated may be used in the composition. Such penetrants, including for example DMSO or polyethylene glycol, are known in the art.

[0046] For administration by inhalation, the compounds of formula I are conveniently delivered in the form of an aerosol spray presentation from a pressurized pack or a nebulizer with the use of a suitable propellant, e. g., dichlorodifluoromethane, trichlorofluoromethane, dichloro-tetrafiuoroethane or carbon dioxide. In the case of a pressurized aerosol, the dosage unit may be determined by providing a valve to deliver a metered amount. Capsules and cartridges of, e. g., gelatin for use in an inhaler or insufflator may be formulated containing a powder mix of the compound and a suitable powder base such as lactose or starch.

[0047] Pharmaceutical compositions for parenteral administration include aqueous solutions of the active ingredients in water-soluble form. Additionally, suspensions of the active compounds may be prepared as appropriate oily injection suspensions. Suitable lipophilic solvents or vehicles include fatty oils such as sesame oil, or synthetic fatty acids esters such as ethyl oleate, triglycerides or liposomes. Aqueous injection suspensions may contain substances, which increase the viscosity of the suspension, such as sodium carboxymethyl cellulose, sorbitol or dextran. Optionally, the suspension may also contain suitable stabilizers or agents, which increase the solubility of the compounds, to allow for the preparation of highly concentrated solutions.

[0048] Compounds of formula I may also be formulated in rectal compositions such as suppositories or retention enemas, using, e.g., conventional suppository bases such as cocoa butter or other glycerides.

[0049] Depending on the severity and responsiveness of the condition to be treated, dosing can also be a single administration of a slow release composition, with course of treatment lasting from several days to several weeks or until cure is effected or diminution of the disease state is achieved. The amount of a composition to be administered will, of course, be dependent on many factors including the subject being treated, the severity of the affliction, the manner of administration, the judgment of the prescribing physician. The compounds of the invention may be administered orally or via injection at a dose from 0.001 to 2500 mg/kg per day. The dose range for adult humans is generally from 0.005 mg to 10 g/day. Tablets or other forms of presentation provided in discrete units may conveniently contain an amount of compound of the invention which is effective at such dosage or as a multiple of the same, for instance, units containing 5 mg to 500 mg, usually around 10 mg to 200 mg. The precise amount of compound administered to a patient will be the responsibility of the attendant physician. However, the dose employed will depend on a number of factors, including the age and sex of the patient, the precise disorder being treated, and its severity. Also, the route of administration may vary depending on the condition and its severity.

[0050] As used herein, and as would be understood by the person of skill in the art, the recitation of "a compound" is intended to include salts, solvates and inclusion complexes of that compound. The term "solvate" refers to a compound of formula I in the solid state, wherein molecules of a suitable solvent are incorporated in the crystal lattice. A suitable solvent for therapeutic administration is physiologically tolerable at the dosage administered. Examples of suitable solvents for therapeutic administration are ethanol and water. When water is the solvent, the solvate is referred to as a hydrate. In general, solvates are formed by dissolving the compound in the appropriate solvent and isolating the solvate by cooling or using an antisolvent. The solvate is typically dried or azeotroped under ambient conditions. Inclusion complexes are described in Remington: The Science and Practice of Pharmacy 19th Ed. (1995) volume 1, page 176-177, which is incorporated herein by reference. The most commonly employed inclusion complexes are those with cyclodextrins, and all cyclodextrin complexes, natural and synthetic, are specifically encompassed within the claims.

[0051] The term "pharmaceutically acceptable salt" refers to salts prepared from pharmaceutically acceptable non-toxic acids or bases including inorganic acids and bases and organic acids and bases. When the compounds of the present invention are basic, salts may be prepared from pharmaceutically acceptable non-toxic acids including inorganic and organic acids. Suitable pharmaceutically acceptable acid addition salts for the compounds of the present invention include acetic, benzenesulfonic (besylate), benzoic, camphorsulfonic, citric, ethenesulfonic, fumaric, gluconic, glutamic, hydrobromic, hydrochloric, isethionic, lactic, maleic, malic, mandelic, methanesulfonic, mucic, nitric, pamoic, pantothenic, phosphoric, succinic, sulfuric, tartaric acid, p-toluenesulfonic, and the like. When the compounds contain an acidic side chain, suitable pharmaceutically acceptable base addition salts for the compounds of the present invention include metallic salts made from aluminum, calcium, lithium, magnesium, potassium, sodium and zinc or organic salts made from lysine, N,N'-dibenzylethylenediamine, chloroprocaine, choline, diethanolamine, ethylenediamine, meglumine (N-methylglucamine) and procaine. Furthermore, notwithstanding the statement in paragraph 49 above regarding the term "compound" including salts thereof as well, so that independent claims reciting "a compound" will be understood as referring to salts thereof as well, if in an independent claim reference is made to a compound or a pharmaceutically acceptable salt thereof, it will be understood that claims which depend from that independent claim which refer to such a compound also include pharmaceutically acceptable salts of the compound, even if explicit reference is not made to the salts in the dependent claim.

[0052] The term "preventing" as used herein refers to administering a medicament beforehand to forestall or obtund an attack. The person of ordinary skill in the medical art (to which the present method claims are directed) recognizes that the term "prevent" is not an absolute term. In the medical art it is understood to refer to the prophylactic administration of a drug to substantially diminish the likelihood or seriousness of a condition, and this is the sense intended herein.

[0053] It should be understood that in addition to the ingredients particularly mentioned above, formulations in accordance with embodiments of this invention may include other agents conventional in the art having regard to the type of formulation in question, for example those suitable for oral administration may include flavoring agents.

[0054] The compositions may be presented in a packaging device or dispenser, which may contain one or more unit dosage forms containing the active ingredient. Examples of a packaging device include metal or plastic foil, such as a blister pack and a nebulizer for inhalation. The packaging device or dispenser may be accompanied by instructions for administration. Compositions comprising a compound of the present invention formulated in a compatible pharmaceutical carrier may also be placed in an appropriate container and labeled for treatment of an indicated condition.

[0055] In accordance with embodiments of the present invention, the A _2a receptor antagonists may be administered prophylactically, for example prior to onset of an acute condition, or they may be administered after onset of the condition, or at both times.

[0056] The following examples will further describe embodiments of the invention, and are used for the purposes of illustration only, and should not be considered as limiting the invention being disclosed.

EXAMPLES

[0057] The following abbreviations and terms have the indicated meaning throughout: Ac = acetyl AcOH = acetic acid Bu = butyl Bn = benzyl DCM = dichloromethane = methylene chloride = CH ₂ Cl ₂ DEAD = diethyl azodicarboxylate DIC = diisopropylcarbodiimide DIEA = iV,iV-diisopropylethyl amine DMF = N,N-dimethylformamide DMSO = dimethyl sulfoxide DPCPX = 8-Cyclopentyl-l,3-dipropylxanthine EA (EtOAc)= ethyl acetate Et ₂ O = diethyl ether EtOH = ethanol

GC = gas chromatography h = hours

HOAc = acetic acid

HOBt = hydroxybenzotriazole

Hz = Hertz

/- = iso

M = molar

Me = methyl

MeOH = methanol min = minutes

MS = mass spectrometry

NMM = iV-methylmorpholine

NMP = jV-methylpyrrolidone

NMR = nuclear magnetic resonance

Ph = phenyl

PhOH = phenol pr = propyl

RT = rt = room temperature sat. = saturated s- = secondary t- = tertiary

TBDMS = t-butyldimethylsilyl

TFA = trifluoroacetic acid

THF = tetrahydrofuran

TMOF = trimethyl orthoformate

TMS = trimethylsilyl tosyl = p-toluenesulfonyl

Trt = triphenylmethyl Synthesis of pyridopyrazinones

[0058] Compounds of formula I can be synthesized by means of conventional organic synthesis executable by those skilled in the art. The illustration of examples, but not the limitation, of the synthesis of compounds of formula I is detailed in Schemes 1- 3.

[0059] Compounds of formula I whereby the C-6 substituent of the pyridopyrazinone is hydrogen can be synthesized in six steps from commercially available 2,4-dihydroxy-3-nitropyridine. Generation of 2,4-dichloro-3-nitropyridine (V) is achieved through reaction of 2,4-dihydroxy-3-nitropyridine with POCl ₃ (J Med. Chem. 2000, 43, 4288). Reaction of 2,4-dichloro-3-nitropyridine (V) with tert-butyl amine under microwave assisted conditions provides N-tert-butyl-2-chloro-3-nitropyridin-4-amine (VI), which is further reacted with a primary amine (R ² -NH ₂ ) to provide VII. Reduction of the nitro group followed by reaction with a ketoester provides IX, which is deprotected with trifluoroacetic acid to provide compounds of formula I where the C-6 substituent of the pyridopyrazinone is hydrogen (I-A) (Scheme 1).

[0060] Scheme 1.

3-n [0061] Procedure A: 2,4-Dichloro-3 -nitropyridine : V

A suspension of 15.0 g (96.2 mmol, 1.0 eq.) of 2,4-dihydroxy-3-nitropyridine in 200 mL of phosphorus oxychloride was heated at 90 ⁰ C for 20 h. The mixture was allowed to cool to room temperature and the volume reduced to approx. 50 mL in vacuo. The residue was carefully poured onto - 300 mL of ice, and the mixture extracted with 3 x 150 mL of EtOAc. The combined organic extracts were dried (Na ₂ SO ₄ ) and the solvent removed in vacuo. The residue was redissolved in 30 mL of EtOAc and 30 niL of hexanes added. The product was isolated by filtration through a plug of silica, eluting with 50% EtOAc/hexanes to provide 17.4 g (90.2 mmol, 94%) of 2,4-dichloro-3-nitropyridine (V) as a colourless crystalline solid. [0062] Procedure B: N-/ert-Butyl-2-chloro-3-nitropyridin-4-amine (VI):

V VI

To a solution of 1.30 g (6.74 mmol, 1.0 eq.) of 2,4-dichloro-3-nitropyridine (2) in 10 mL of THF in a microwave vial was added 1.5 mL (8.46 mmol, 1.25 eq.) of N,N- diisopropylethylamine and 0.81 mL (7.55 mmol, 1.1 eq.) of tert-butylamine. The mixture was subjected to microwave irradiation, maintaining an internal reaction temperature of 180 ⁰ C for 4 h. The mixture was diluted with 100 mL of CH ₂ Cl ₂ and washed with 50 mL of water. The aqueous phase was extracted with 50 mL of CH ₂ Cl ₂ and the combined organic extracts dried (Na ₂ SO ₄ ). The solvent was removed in vacuo and the residue purified by flash chromatography (eluting with a linear gradient of 10-60% EtOAc/hexanes) to provide 0.41 g (1.79 mmol, 27%) of iV-tert-butyl-2-chloro-3-nitropyridin-4-amine (VI) as a yellow solid and 0.29 g (1.52 mmol, 23%) of recovered starting material (V). ¹ H-NMR (δ _H , 300 MHz, CDCl ₃ ) 1.48 (s, 9H), 6.41 (bs, IH), 6.84 (d, IH), 7.95 (d, IH).

[0063] Procedure C: iV^-tert-Butylpyridine-S^-diamine (Via) - Proof of regiochemistry for VI.

VI ^VIa

To a solution of 5.6 mg of N-rert-butyl-2-chloro-3-nitropyridin-4-amine (VI) in 2 mL of MeOH was added 20 mg of 10% palladium on charcoal and the mixture stirred under a hydrogen atmosphere (1 atm) for 1 h. The mixture was filtered through Celite ^® and the pad washed with 2 mL of MeOH. The solvent was removed in vacuo and the residue dried under high vacuum to provide Λ^-te^butylpyridine-3,4-diamine (Via) as a white solid. ¹ H-NMR (δ _H , 300 MHz, CD ₃ OD) 7.08 (d, IH, J= 6.8 Hz), 7.62 (d, IH, J= 0.9 Hz), 7.76 (dd, IH, J = 6.8 Hz, J= 0.9 Hz).

[0064] Procedure D: N ⁴ -/ert-Butyl-N ² -cyclopropyl-3-nitropyridine-2,4-diamine (VII, R ² = cPr)

To a solution of 0.41 g (1.79 mmol, 1.0 eq.) of N-ter/-butyl-2-chloro-3-nitropyridin-4-amine (VI) in 5 mL of THF in a microwave vial was added 0.62 mL (8.95 mmol, 5.0 eq.) of cyclopropylamine. The mixture was subjected to microwave irradiation, maintaining an internal reaction temperature of 150 ⁰ C for 30 min. The mixture was diluted with 50 mL of CH ₂ Cl ₂ and washed with 50 mL of water. The aqueous phase was extracted with 2 x 25 mL of CH ₂ Cl ₂ and the combined organic extracts dried (Na ₂ SO ₄ ). The solvent was removed in vacuo and the residue dried under high vacuum to provide 0.43 g (1.72 mmol, 96%) of N ⁴ - tert-butyl-iV ² -cyclopropyl-3-nitropyridine-2,4-diamme (VII) as a yellow solid. ¹ H-NMR (5 _H , 300 MHz, CDCl ₃ ) 0.58 (m, 2H), 0.89 (m, 2H), 2.99 (m, IH), 6.19 (d, IH), 7.85 (d, IH), 9.09 (bs, IH), 9.60 (bs, IH).

[0065] Procedure E: 3-(8-(ter/-Butylamino)-4-cyclopropyl-3-oxo-3,4- dihydropyrido[3,2-b]pyrazin-2-yl)benzonitrile (IX, R ² = cPr, R ³ = 3-cyanophenyl)

To a so yridine- 2,4-diamine (VII) in 15 mL of EtOH was added 150 mg of 10% palladium on charcoal and the mixture stirred under a hydrogen atmosphere (1 atm) for 3 h. The mixture was filtered through Celite ^® under a blanket of argon and the ethanolic solution of I^-tert-butyl-N ² - cyclopropylpyridine-2,3,4-triamine (VIII) added to 0.65 g (3.2 mmol, 1.9 eq.) of ethyl 2-(3- cyanophenyl)-2-oxoacetate. A portion of 0.15 mL of AcOH was added and the mixture heated at 78 ⁰ C for 16 h. The mixture was allowed to cool to room temperature and the solvent was removed in vacuo. The residue was purified by flash chromatography (eluting with a linear gradient of 25 - 100% EtOAc/hexanes) to provide 0.40 g (1.1 mmol, 65%) of 3- (8-(tert-butylamino)-4-cyclopropyl-3-oxo-3,4-dihydropyrido[3 ,2-b]pyrazin-2-yl)benzonitrile (IX, R ² = cPr, R ³ = 3-cyanophenyl) as a bright yellow solid.

[0066] Procedure F: 3-(8-Amino-4-cyclopropyl-3-oxo-3,4-dihydropyrido[3,2- b]pyrazin-2-yl)benzonitrile (Example 1) (Compound Numerals also refer to the compounds as described in Table 1.)

A solution of 0.30 g (0.84 mmol, 1.0 eq.) of 3-(8-(tert-butylamino)-4-cyclopropyl-3-oxo-3,4- dihydropyrido[3,2-b]pyrazin-2-yl)benzonitrile (IX) in 3 mL of trifluoroacetic acid in a microwave vial was subjected to microwave irradiation, maintaining an internal reaction temperature of 120 ⁰ C for 10 min. The solvent was removed in vacuo and the residue purified by reverse-phase chromatography (C 18 column) to provide 0.19 g (0.46 mmol, 55%) of 3-(8- amino-4-cyclopropyl-3 -oxo-3 ,4-dihydropyrido [3 ,2-b]pyrazin-2-yl)benzonitrile (Example 1 ) as a yellow solid. ¹ H-NMR (δ _H , 300 MHz ₅ CD ₃ OD), 1.09 (m, 2H), 1.47 (m, 2H), 3.11 (m, IH), 6.87 (d, IH), 7.70 (dd, IH), 7.89 (dd, IH), 7.99 (d, IH), 8.77 (dd, IH), 8.86 (d, IH); m/z found, 304.1 [M+H] ⁺ .

[0067] Examples 2-12 incorporating a 3-cyanophenyl group at the R ³ position were synthesized using similar experimental protocols.

[0068] Procedure G: 8-Amino-4-cyclopropyl-2-(thiazol-2-yl)pyrido[3,2- b]pyrazin-3(4H)-one (Example 13)

Compound IX (R = cPr, R ³ = 2-thiazole) was synthesised using similar procedures to those described above from VIII and ethyl 2-oxo-2-(thiazol-2-yl)acetate. Compound IX (R ² = cPr, R ³ = 2-thiazole) was deprotected as described below: A solution of 19 mg (56 μmol, 1.0 eq.) of 8-(tert-butylamino)-4-cyclopropyl-2-(thiazol-2-yl)pyrido[3,2 -b]pyrazin-3(4H)-one (IX) in 2 mL of trifluoroacetic acid in a microwave vial was subjected to microwave irradiation, maintaining an internal reaction temperature of 120 ⁰ C for 30 min. The solvent was removed in vacuo and the residue purified by semi-prep. HPLC to provide 17 mg (42 μmol, 76%) of 8-amino-4-cyclopropyl-2-(thiazol-2-yl)pyrido[3,2-b]pyrazin-3 (4/7)-one (Example 13) as a yellow solid. ¹ H-NMR (δ _H , 300 MHz, d ₆ DMSO), 0.91 (m, 2H), 1.28 (m, 2H), 3.07 (m, IH), 6.71 (d, IH), 7.74 (bs, 2H), 8.06 (m, 2H), 8.18 (d, IH); m/z found, 286.2 [M+H] ⁺ .

[0069] Examples 14 - 40, incorporating non-(3-cyanophenyl) groups at the R position were synthesised using similar experimental protocols, utilizing a 30 minute trifluoroacetic acid mediated deprotection of the exocyclic tert-bvAyl amino group as described above.

[0070] Deprotection of IX where R ² = 2,4-dimethoxybenzyl was conducted in a similar manner to procedure G for 30 min to provide 8-amino-2-(thiazol-2-yl)pyrido[3,2- b]pyrazin-3(4H)-one (Example 41). Deprotection of IX where R ² = 3-hydroxy propyl and R ³ = 3-cyanophenyl was conducted in a similar manner to procedure G for 30 min, and the resulting products stirred in MeOH for 16 h. Purification of the components by semi-prep. HPLC provided 3-(8-amino-4-(3-hydroxypropyl)-3-oxo-3,4-dihydropyrido[3,2-Î ´]pyrazin-2- yl)benzonitrile (Example 42) and 3-(8-amino-4-(3-hydroxypropyl)-3-oxo-3,4- dihydropyrido[3,2-ÏŒ]pyrazin-2-yl)benzamide (Example 43). Examples 44 (3-(8-amino-4-(4- hydroxybutyl)-3-oxo-3,4-dihydropyrido[3,2-ά]pyrazin-2-yl)be nzonitrile), 45 (8-amino-2-(3- fluorophenyl)-4-(4-hydroxybutyl)pyrido[3,2-b]pyrazin-3(4H)-o ne) and 46 8-amino-4-(3- hydroxypropyl)-2-(thiazol-2-yl)pyrido[3,2-b]pyrazin-3(4Η)-o ne were synthesised in a similar manner.

[0071] Analogous compounds of formula I can be synthesized using similar experimental procedures to those described above.

[0072] Compounds of formula I whereby the C-6 substituent of the pyridopyrazinone is substituted amino can be synthesised in seven steps from commercially available 2,6-dichloropyridin-4-amine. Nitration of 2,6-dichloropyridin-4-amine to provide 2,6-dichloro-3-nitropyridin-4-amine (X) followed by benzyl protection with benzyl bromide provides N,jV-dibenzyl-2,6-dichloro-3-nitropyridin-4-amine (XI). Chlorine displacement followed by nitro group reduction allows formation of the protected chloro pyridopyrazinone (XIV) via reaction with a keto ester. Triflic acid mediated debenzylation followed by amination with a primary or a secondary amine (incorporating R ⁴ ) provides compounds of formula I where the C-6 substituent of the pyridopyrazinone is substituted amino (I-B) (Scheme 2).

[0073] Scheme 2.

MI££: ^A

[0074] Procedure Gl : 2,6-Dichloro-3-nitropyridin-4-amine (X). X

To 40 mL of concentrated H ₂ SO ₄ in a round bottom flask at -5 °C (NaCl/ice bath) was added 3.0 g (18.5 mmol, 1.0 eq.) of 2,6-dichloropyridin-4-amine. The mixture was stirred at -5 °C until a homogenous solution was obtained. A solution of 2.0 g (22.2 mmol, 1.2 eq.) of 70% HNO ₃ in 2 mL of concentrated H ₂ SO ₄ was slowly added such that the internal reaction temperature was kept below 10 °C. The mixture was stirred at 0 - 10 °C for 30 min. The mixture was allowed to warm to room temperature and stirred for 30 min. The mixture was then heated to 80 °C and stirred for an additional 1 hr. The mixture was allowed to cool to room temperature and poured onto 200 g of ice with stirring. The yellow suspension was neutralized by the slow addition of concentrated aqueous NH ₃ to pH~4 while cooling with a dry ice/acetone bath. The yellow solid was collected by filtration, washed with ice cold water and dried under high vacuum to provide 3.6 g (94%) of 2,6-dichloro-3-nitropyridin-4- amine (X) as a yellow solid; ¹ H-NMR (δ _H , 300 MHz, CDCl ₃ ), 5.77 (bs, 2H), 6.71 (s, IH). [0075] Procedure H: N,N-Dibenzyl-2,6-dichloro-3-nitropyridin-4-amine (XI).

X XI

To a solution of 2.07 g (10 mmol, 1.0 eq.) of 2,6-dichloro-3-nitropyridin-4-amine (X) in 100 mL of anhydrous DMF was added 3.6 mL (30 mmol, 3.0 eq.) of benzyl bromide and 6.9 g (50 mmol, 5.0 eq.) Of K ₂ CO ₃ . The mixture was heated at 80 °C for 4 hrs. On cooling to room temperature, the mixture was filtered and the solvent was removed in vacuo. The residue was redissolved in 300 mL of EtOAc and washed with 3x H ₂ O, Ix brine, and dried (Na ₂ SO ₄ ). Purification by flash chromatograph (EtOAc/Hexanes 1 :5) yielded 2.4 g (60%) of N, N- dibenzyl-2,6-dichloro-3-nitropyridin-4-amine (XI) as a yellow solid, m/z found 388.0 [M+H] ⁺

[0076] Procedure I: N ⁴ ,N ⁴ -Dibenzyl-6-chloro-N ² -cyclopropyl-3-nitropyridine-2,4- diamine (XIIa).

To a solution of 240 mg (0.62 mmol) N^-dibenzyl-2,6-dichloro-3-nitropyridin-4-amine in 5 mL of THF was added 39 mg (0.68 mmol, 1.1 eq.) of cyclopropylamine and 0.17 mL (1.2 mmol, 2 eq.) of triethylamine. The solution was heated at 45 °C for 16 hrs. The solvent was removed in vacuo and the residue was redissolved in 50 mL of EtOAc. The organic solution was washed with 2 x water, 1 x brine, and dried (Na ₂ SO ₄ ). Purification by flash chromatograph (25% EtOAc/Hexanes) provided 195 mg (77%) of iV^-dibenzyl-ÏŒ-chloro- N ² -cyclopropyl-3-nitropyridine-2,4-diamine (XIIa) as a yellow oil; ¹ H-NMR (5 _H , 300 MHz, CDCl ₃ ), 0.48 (m, 2H), 0.82 (m, 2H), 3.00 (m, IH), 4.25 (s, 4H), 6.28 (s, IH), 7.1-7.4 (m, 1 OH); m/z found, 409.0 [M+H] ⁺ .

[0077] Procedure J: N ⁴ ,iV ⁴ -dibenzyl-6-chloro-N ² -cyclopropylpyridine-2,3,4- triamine (XIIIa).

XIIa XIIIa

To a solution of 500 mg (1.22 mmol) of Λ^Λ^-dibenzyl-ÏŒ-chloro-Λ^-cyclopropyl-S- nitropyridine-2,4-diamine in 100 mL of THF and 100 mL of water was added 1.0 g (12.2 mmol, 10 eq.) OfNaHCO ₃ followed by 2.1 g (12.2 mmol, 10 eq.) Of Na ₂ S ₂ O ₄ . The mixture was stirred at room temperature for 16 hrs. The THF was removed in vacuo and the remaining mixture was extracted with EtOAc three times. The combined organic extracts were washed with Ix sat. NaHCO ₃ solution, 1 x brine and dried (Na ₂ SO ₄ ). The solvent was removed in vacuo to provide 415 mg (90%) of iV^A^-dibenzyl-ÏŒ-chloro-N ² - cyclopropylpyridine-2,3,4-triamine as a brown oil (XIIIa); ¹ H-NMR (δ _H , 300 MHz, CDCl ₃ ), 0.43 (m, 2H), 0.77 (m, 2H), 2.82 (m, IH), 4.05 (s, 4H), 6.40 (s, IH), 7.20 (m, 10H); m/z found, 379.5 [M+H] ⁺ .

[0078] Procedure K: 6-Chloro-4-cyclopropyl-8-(dibenzyiamino)-2-

(trifluoromethyl)pyrido[3,2-b]pyrazin-3(4H)-one (XIVa).

A solution of 1.0 g (2. -cyclopropylpyridine- 2,3,4-triamine (XIIIa) in 20 mL of ethanol in a pressure tube was degassed with argon for 5 min. A portion of 0.2 mL of trifluoroacetic acid (1% v/v final) was added to the solution followed by 495 mg (2.91 mmol, 1.1 eq.) of ethyl 3,3,3-trifluoro-2-oxopropanoate. The reaction vessel was filled with argon, sealed, and heated at 90 °C for 16 hrs. The reaction mixture was cooled to 0 °C and the yellow solid was collected by filtration to provide 1.1 g (83%) of 6-chloro-4-cyclopropyl-8-(dibenzylamino)-2-(trifluoromethyl) pyrido[3,2- b]pyrazin-3(4H)-one (XIVa). m/z found 485.2 [M+Η] ⁺

[0079] Procedure L: 8-Amino-6-chloro-4-cyclopropyl-2-

(trifluoromethyl)pyrido[3,2-b]pyrazin-3(4H)-one (XV).

To a solution of 65 mg (0.13 mmol) of 6-chloro-4-cyclopropyl-8-(dibenzylamino)-2- (trifluoromethyl)pyrido[3,2-b]pyrazin-3(4H)-one (XIVa) in 3 mL of anhydrous CH ₂ Cl ₂ in a pressure vessel at 0 °C was added 0.15 mL of trifluoromethanesulfonic acid (5% v/v final). The bath was removed and the sealed reaction vessel was heated at 40 °C for 16 hrs. On cooling to room temperature, the mixture was poured into 20 g of ice water and neutralised to pH 9 with 2 M NaOH. The mixture was extracted with 3 x 50 mL of CH ₂ Cl ₂ and the combined organic extracts washed with brine and dried (Na ₂ SO ₄ ). The solvent was removed in vacuo to provide 36 mg (87%) of 8-amino-6-chloro-4-cyclopropyl-2- (trifluoromethyl)pyrido[3,2-b]pyrazin-3(4//)-one (XVa) as a yellow solid, m/z found, 305.0 [M+H] ⁺ .

[0080] Procedure M: 6-(2,6-Difluorobenzylamino)-8-amino-4-cyclopropyl-2- (trifluoromethyl)pyrido[3,2-b]pyrazin-3(4H)-one (Example 47)

X ^v » Example 47

To a solution of 50 μmol of 8-amino-6-chloro-4-cyclopropyl-2-(trifluoromethyl)pyrido[3,2 - b]pyrazin-3(4H)-one (XVa) in 2 ml of NMP was added 5 eq. (0.25 mmol) of 2,6- difluorobenzyl amine followed by 5 eq. (0.25 mmol) of jV,./V-diisopropylethylamine. The mixture was subjected to microwave irradiation, maintaining an internal reaction temperature of 200 °C for 1 hr. The mixture was diluted with EtOAc and washed with 2x sat. NaHCO ₃ , Ix brine, and dried (Na ₂ SO ₄ ). The product was isolated by semi-preparative HPLC to provide 6-(2,6-difluorobenzylamino)-8-amino-4-cyclopropyl-2-(trifluo romethyl)pyrido[3,2- b]pyrazin-3(4H)-one (Example 47). ¹ H-NMR (δ _H , 300 MHz, CD ₃ OD/CDC1 ₃ ), 0.96 (m, 2H), 1.42 (m, 2H), 3.07 (m, IH), 4.66 (s, 2H), 6.93 (m, 2H), 7.32 (m, IH); m/z found, 412.2 [M+H] ⁺ . [0081] Examples 48-73 were synthesised using similar experimental protocols as described above.

[0082] Analogous compounds of formula I can be synthesized using similar experimental procedures to those described above.

[0083] Compounds of formula I whereby the R ⁴ substituent of the pyridopyrazinone is a carbon based substituent can be synthesised from XIV via coupling with the corresponding boronic acid followed by triflic acid mediated debenzylation (Scheme 3).

[0084] Scheme 3.

xiv _XVI i-c

[0085] Procedure N: 4-Cyclopropyl-8-(dibenzylamino)-6-phenyl-2-(thiazol-2- yl)pyrido[3,2-b]pyrazin-3(4H)-one (XVIb).

XIVb XVIb

To a solution of 20 mg (0.04 mmol) of 6-chloro-4-cyclopropyl-8-(dibenzylamino)-2-(thiazol- 2-yl)pyrido[3,2-b]pyrazin-3(4H)-one (XIVb) in 2 mL of DMF in a microwave vial was added 28 mg (0.2 mmol, 5 eq.) of potassium carbonate and 10 mg (0.08 mmol, 2 eq.) of phenyl boronic acid. A portion of 6 mg (0.2 eq.) of Pd(PPh ₃ ) ₂ C1 ₂ was added and the mixture subjected to microwave irradiation, maintaining an internal reaction temperature of 140 C for 15 min. The mixture was diluted with 10 mL of EtOAc and washed with 2 x 10 mL of sat. NaHCO ₃ . The organic phase was dried (Na2SO4) and the solvent evaporated to provide 10 mg of 4-cyclopropyl-8-(dibenzylamino)-6-phenyl-2-(thiazol-2-yl)pyr ido[3,2-b]pyrazin- 3(4H)-one (XVIb) as a yellow solid, m/z found 542.4 [M+H] ⁺

[0086] Procedure O: 8-amino-4-cyclopropyl-6-phenyl-2-(thiazol-2-yl)pyrido[3,2- b]pyrazin-3(4H)-one (Example 74).

To a solution of 10 mg of 4-cyclopropyl-8-(dibenzylamino)-6-phenyl-2-(thiazol-2- yl)pyrido[3,2-b]pyrazin-3(4H)-one (XVIb) in 3 mL of CH ₂ Cl ₂ in a pressure vessel at 0 ⁰ C was added 0.15 mL of trifluoromethanesulfonic acid (5% v/v final) and the mixture was heated at 40 °C for 16 h. On cooling to room temperature, the mixture was poured into 10 mL of ice water and neutralised to pH 9 with 2 M NaOH. The mixture was extracted with 3 x 50 mL of CH ₂ Cl ₂ and the combined organic extracts washed with brine and dried (Na ₂ SO ₄ ). The solvent was removed in vacuo to provide 4.5 mg of 8-amino-4-cyclopropyl-6-phenyl-2- (thiazol-2-yl)pyrido[3,2-b]pyrazin-3(4H)-one (Example 74) as a yellow solid; ¹ H-NMR (δ _H , 300 MHz, CD ₃ OD/CDC1 ₃ ), 1.16 (m, 2H), 1.47 (m, 2H), 3.26 (m, IH), 7.07 (s, IH), 7.49 (m, 3H), 7.68 (m, IH), 8.13 (m, 3H); m/z found, 362.0 [M+H] ⁺ .

[0087] Analogous compounds of formula I can be synthesized using similar experimental procedures to those described above.

[0088] Examples 75-78 were synthesised using similar experimental protocols as described above.

[0089] Keto esters were either commercially available, synthesized according to Tetrahedron Lett. 1983, 24, 2901, Tetrahedron Lett. 2003, 44, 5137, Chemistry of Heterocyclic Compounds 2004, 40, 759, Tetrahedron Lett. 2005, 46, 3927, J. Org. Chem. 2005, 70, 2616, Tetrahedron 2005, 61, 2897, J Med. Chem. 2002, 45, 1064, or synthesized according to the procedures detailed below.

[0090] Procedure P: Ethyl 2-oxo-2-(thiazol-2-yl)acetate

To a solution of 5.0 mL (31.3 mmol, 1.0 eq.) of 2-trimethylsilylthiazole in 250 mL Of CH ₂ Cl ₂ was added 7.0 mL (62.6 mmol, 2 eq.) of ethyl 2-chloro-2-oxoacetate. The reaction mixture was stirred at room temperature for 1 h and the solvent removed in vacuo. The residue was purified by flash chromatography (10% ethyl acetate/hexanes) to provide 3.9 g (21 mmol, 67 %) of ethyl 2-oxo-2-(thiazol-2-yl)acetate as a pale yellow oil. δ _H , 300 MHz, CDCl ₃ : 1.42 (t, 3H), 4.48 (q, 2H), 7.83 (d, IH), 8.16 (d, IH).

[0091] Procedure Q: Methyl 2-(furan-2-yl)-2-oxoacetate

To a suspension of 10.0 g (71 mmol, 1.0 eq.) of 2-(furan-2-yl)-2-oxoacetic acid in 150 mL of THF at 0 ⁰ C, was slowly added a solution of 36 mL (2 M, 72 mmol, 1.0 eq.) of (trimethylsilyl)diazomethane in diethyl ether. The reaction mixture was allowed to warm to room temperature and stirred for 1 h. The solvent removed in vacuo and the residue was purified by flash chromatography (0 - 30% ethyl acetate/hexanes) to provide 5.0 g (32 mmol, 46 %) of methyl 2-(furan-2-yl)-2-oxoacetate as an off-white solid. δ _H , 300 MHz, CDCl ₃ : 3.93 (s, 3H), 6.61 (dd, IH), 7.74 (m, 2H).

[0092] Procedure R: Ethyl 2-oxo-2-(thiazol-4-yl)acetate

A solution of 1.35 ml (10 mmol, 2.0 eq.) of isoamyl nitrite in 10 mL of THF was added dropwise to a solution of 1.0 g (5 mmol, 1.0 eq.) of 2-amino-4-thiazoleglyoxylate in 6 mL of THF and the reaction mixture was heated at 60 °C for 18 hr. The mixture was allowed to cool to room temperature and the solvent removed in vacuo. The residue was partitioned between extracted between 25 mL of EtOAc and 25 mL of sat. NaHCO ₃ and the layers separated. The organic phase was washed with sat. brine, dried (Na ₂ SO ₄ ) and the solvent removed in vacuo. The residue was purified by flash chromatography (30%-50% EtOAc/hexanes) to provide 0.57 g (2.66 mmol, 53%) of ethyl 2-oxo-2-(thiazol-4-yl)acetate. δ _H (300MHz, CDCl ₃ ) 1.40 (t, 3H), 4.44 (q, 2 H), 8.66 (d, IH), 8.95 (d, IH). [0093] Procedure S: Ethyl 2-(isoxazol-5-yl)-2-oxoacetate in) HBr, AcOH

To a solution of 4.7 g (40.7 mmol, 1.0 eq.) of isoxazole-5-carboxylic acid in 70 mL of anhydrous THF at -78 °C under an argon atmosphere was added 4.5 mL (40.7 mmol, 1.0 eq.) of iV-methylmorpholine followed by 5.3 mL (43 mmol, 1.05 eq.) of isobutyl chloroformate. The mixture stirred at -78 °C for 20 min. The mixture was filtered and the filtrate was allowed to warm to 0 °C and excess diazomethane added slowly. The mixture was allowed to warm to room temperature and stirred for 16 h. A solution of 25 mL of 33% HBr in acetic acid was added and the mixture stirred at room temperature for 10 min. The mixture was diluted with 400 mL of EtOAc and washed with 10% citric acid followed by sat. NaHCO ₃ and sat. brine. The organic phase was dried (Na ₂ SO ₄ ) and the solvent removed in vacuo. The residue was purified by flash chromatography to provide 5.2 g of 2-bromo-l-(isoxazol-5- yl)ethanone as a white solid. The 2-bromo-l-(isoxazol-5-yl)ethanone was redissolved in 300 mL of ethanol and 3.3 g (30 mmol) of selenium dioxide added. The mixture heated at 100 °C for 16 h. The mixture was allowed to cool to room temperature and filtered. The solvent was removed in vacuo and the residue partitioned between EtOAc and sat. NaHCO ₃ . The layers were separated and the aqueous phase extracted with EtOAc. The combined organic extracts were washed with sat. brine, dried (Na ₂ SO ₄ ) and the solvent removed in vacuo. The residue was purified by flash chromatography to provide 1.8 g of ethyl 2-(isoxazol-5-yl)-2- oxoacetate. δ _H (300 MHz, CDCl ₃ ) 1.43 (t, 3H), 4.47 (q, 2H), 7.40 (d, IH), 8.45 (d, IH).

[0094] Procedure T: Ethyl 2-(oxazol-2-yl)-2-oxoacetate

A solution of 0.5 g (1.4 mmol, 1.0 eq,) of 2-(tributylstannyl)oxazole in 10 mL Of CH ₂ Cl ₂ in a pressure tube was heated at 50 °C for 16 h. The mixture was allowed to cool to room temperature and the solvent removed in vacuo. The residue was purified by flash chromatography (0 - 20% EtOAc/ CH ₂ Cl ₂ ) to provide 0.22 g (1.3 mmol, 93%) of Ethyl 2- (oxazol-2-yl)-2-oxoacetate.

[0095] Procedure U: Ethyl 2-oxo-2-(pyridin-3-yl)acetate

To a solution of 12 g (100 mmol, 1.0 eq.) of 3-acetylpyridine in HBr/AcOH (35%) at 5 °C was added 1.08 eq. of bromine dropwise. On complete addition, the reaction mixture was warmed to 40 ⁰ C and stirred for 1.5 h. The solution was then warmed to 70 ⁰ C and the mixture stirred for an additional 1 h. The solution was then cooled to 0 °C and ether was added. The mixture was filtered and the filter cake was washed with cold ether and dried under vacuum to afford crude 2-bromo-l-(pyridin-3-yl)ethanone. The crude 2-bromo-l- (pyridin-3-yl)ethanone was redissolved in EtOH at and leq. of selenium dioxide was added. The mixture was heated at reflux for 16 h. The solution was allowed to cool to room temperature and poured into water. The aqueous phase was extracted with EtOAc. The organic layer was washed with water, brine, dried (MgSO ₄ ) and the solvent removed in vacuo. The residue was purified by flash chromatography to provide 8 g (45 mmol, 45%) of ethyl 2-oxo-2-(pyridin-3-yl)acetate. ¹ H NMR: δ _H (300 MHz, CDCl ₃ ) 1.44 (t, 3H), 4.46 (q, 2H), 7.47 (m, IH), 8.35 (m, IH), 8.85 (dd, IH), 9.25 (d, IH).

[0096] Analogous ketoesters can be synthesized using similar experimental procedures to those described above.

[00971 Analytical HPLC analysis:

Method A: Waters Millenium 2690/996PDA separations system employing a Phenomonex Luna 3μ C8 50 x 4.6 mm analytical column. The aqueous acetonitrile based solvent gradient involves:

0 - 1 min - Isocratic 10% of (0.1% TFA/acetonitrile); 1 min - 7 min - Linear gradient of 10 - 90% of (0.1% TFA/acetonitrile): 7 min - 9 min - Isocratic 90% of (0.1% TFA/acetonitrile); 9 min - 10 min - Linear gradient of 90 - 10% of (0.1% TFA/acetonitrile); 10 min - 12 min - Isocratic 10% of (0.1% TFA/acetonitrile). Flow rate = 1 mL/min;

Method B: Waters Millenium 2690/996PDA separations system employing a Phenomenex Columbus 5μ Cl 8 column 50 x 4.60 mm analytical column. The aqueous acetonitrile based solvent gradient involves:

0 - 0.5 min - Isocratic 10% of (0.05% TFA/ acetonitrile); 0.5 min - 5.5 min - Linear gradient of 10 - 90% of (0.05% TFA/acetonitrile): 5.5 min - 7.5 min - Isocratic 90% of (0.05% TFA/acetonitrile); 7.5 min - 8 min - Linear gradient of 90 - 10% of (0.05% TFA/acetonitrile); 8 min - 10 min - Isocratic 10% of (0.05% TFA/acetonitrile). Flow rate = 0.4 mL/min; Method C: Waters Millenium Micromass ZQ/2996PDA separations system employing a Phenomenex Columbus 5μ Cl 8 column 50 x 4.60 mm analytical column. The aqueous acetonitrile based solvent gradient involves:

0 - 0.5 min - Isocratic 10% of (0.05% TFA/ acetonitrile); 0.5 min - 5.5 min - Linear gradient of 10 - 90% of (0.05% TFA/acetonitrile): 5.5 min - 7.5 min - Isocratic 90% of (0.05% TFA/acetonitrile); 7.5 min - 8 min - Linear gradient of 90 - 10% of (0.05% TFA/acetonitrile); 8 min - 10 min - Isocratic 10% of (0.05% TFA/acetonitrile). Flow rate = 0.3 mL/min. Method D: Waters Millenium 600S/996PDA separations system employing a Sunfire Cl 8 3.5 uM 100 x 4.6 mm analytical column. The aqueous acetonitrile based solvent gradient involves:

0 - 5.5 min - Linear gradient of 20 - 90% of (0.1% TFA/acetonitrile): 5.5 min - 7.5 min - Isocratic 90% of (0.1% TFA/acetonitrile); 7.5 min - 8 min - Linear gradient of 90 - 20% of (0.1% TFA/acetonitrile); 8 min - 10 min - Isocratic 20% of (0.1% TFA/acetonitrile). Flow rate = 1 mL/min;

[0098] Mass Spectrometric Analysis

Mass Spectrometry was conducted using a Thermo-electron LCQ classic, an Applied Biosciences PE Sciex API150ex or a Waters Millenium Micromass ZQ. Liquid Chromatography Mass Spectrometry was conducted using a Waters Millenium 2690/996PDA linked Thermo-electron LCQ classic.

[0099] NMR Spectroscopy 1H NMR spectroscopy was conducted using a Varian 300 MHz Gemini 2000 FTNMR.

Membranes prepared from HEK-293 cells that express human A _2a (0.04 mg/mL final, PerkinElmer Life and Analytical Sciences, Boston, MA) were mixed with yttrium oxide wheat germ-agglutinin (WGA)-coated SPA beads (4 mg/mL final, Amersham Biosciences, Piscataway, NJ) and adenosine deaminase (0.01 mg/mL final) in assay buffer (Dulbecco's phosphate-buffered saline containing 10 mM MgCl ₂ ) for 15 minutes at 4 ⁰ C. This mixture (10 mL) was added with continuous stirring to the test compounds (10 mL) prepared in 2.5% DMSO or to 2.5% DMSO (1% final) in 384-well assay plates (Corning #3710).

[0101] Binding was initiated with the addition of 5 mL of [ ³ H]-SCH 58261 (2 nM final, Amersham Biosciences) immediately followed by centrifugation at 1000 rpm for 2 min. The assay plates were incubated in the dark, overnight at room temperature and the signal was detected using a ViewLux CCD Imager (PerkinElmer). Compounds were tested at 11 different concentrations ranging from 0.1 nM to 10 μM. Nonspecific binding was determined in the presence of 10 μM CGS 15943. Assays were performed in duplicate and compounds were tested at least twice. The data were fit to a one-site competition binding model for IC ₅₀ determination using the program GraphPad Prism (GraphPad Software, Inc., San Diego, CA) and Kj values were calculated using the Cheng-Prusoff equation (Cheng, Y, Prusoff, W.H. Biochem. Pharmacol. 1973, 22, 3099).

[0102] Ajjrinding assay:

As described in Matasi et al. (Bioorg. Med. Chem. Lett. 2005, 75, 1333), membranes (10 mg) prepared from CHO (Chinese Hamster Ovary) cells that express human Al were mixed with 1 nM (final) [ ³ H]-DPCPX in 200 mL assay buffer (2.7 mM KCl, 1.I mM KH ₂ PO ₄ , 137 mM NaCl, 7.6 mM Na ₂ HPO ₄ , 10 mM MgCl ₂ , 0.04% methyl cellulose, 20 ug/mL adenosine deaminase) containing 4% DMSO with or without test compounds. Reactions were carried out for 60 min at room temperature and were terminated by rapid filtration over GF/B filters. Filters were washed seven times with 1 mL cold distilled water, air dried, and radioactivity retained on filters were counted in a Packard TopCount ^® NXT microplate scintillation counter (Global Medical Instrumentation, Inc., Ramsey, MN). Compounds were tested at 10 different concentrations ranging from 0.1 nM to 10 mM. Nonspecific binding was determined in the presence of 10 μM NECA (5'-(iV-ethylcarboxamido)adenosine). Assays were performed in duplicate and compounds were tested two times. Data were fit to a one- site competition binding model for IC ₅₀ determination using the program GraphPad Prism (GraphPad Software, Inc., San Diego, CA) and Kj values were calculated using the Cheng- Prusoff equation (Cheng, Y, Prusoff, W.H. Biochem. Pharmacol. 1973, 22, 3099).

[0103] Compounds in Table 1 exhibited Kj for the A _2a receptor below 5 μM.

Table 1

[0104] Table 2 lists H-NMR data for the listed compounds

Table 2

1.09 6.87 7.99

3.65 7.69 8.91

0.98 (m, (t, 8.63

2.72 (m, (bs, (d, 0.94 6.58 7.93 8.96

3.40 (s, (bs, (d,

1.54 7.27 IH).

0.44 6.58 7.92 (s,

(q, (dd, (d,

1.25 7.37 IH).

1.93 4.45 7.71 8.91

1.83 3.17 7.24 8.02

0.91 6.71 8.18

0.92 4.36

1.09 6.84

1.91 3.26 7.20

0.94 6.59 8.03

2.74 (m, (bs, (d,

0.47 6.64 8.09

5.22 7.60

0.96 6.69 8.54

0.95 6.67 8.71

1.07 6.83 8.15

1.07 6.88

3.34 (s, (d, (d,

3.66 IH).

1.93 4.47 8.01

1.08 H), 6.81 8.66 1.25 8.41

0.97 6.69 8.04 9.61

1.49 4.37 7.69 8.88

(m, IH), IH).

8-Amino-4-cyclopropyl A-6-(phenethyl /CDCl ₃ ), 0.99 3.02 7.91

Cl ₆ acetone), 1.06 4.81 7.14 d ₆ DMSO), 1.2- IH), IH),

2H), IH),

0.90 1.58

(m, (m,

2H), 2H),

(m, 1.41(t, (d,

0.90 2H), 2.89 6.55 IH).

CDCI ₃ /CD ₃ OD), 2H), 2),

(m, (m, (m, (d,

2H), IH).

0.89 IH), 4.62 7.38 8.69

CD ₃ OD/CDC1 ₃ ), 2H), IH),

1.08 (m, (m, (bs,

d ₆ DMSO), 0.94 2H), IH).

1.06 (m, (m,

3H), IH),

0.92 2.92

[0105] Although the foregoing invention has been described in some detail for purposes of illustration, it will be readily apparent to one skilled in the art that changes and modifications may be made without departing from the scope of the invention described herein.