The present invention is directed to 4-oxo-tetrahydroindozole-3-carboxamide compounds according to Formula (I) or a pharmaceutically acceptable salt thereof that are GABA-A Alpha 5 ligands useful for enhancing cognition:
The,present invention relates to tetrahydroindazole derivatives, pharmaceutical compositions comprising them and to their use in therapy. More particularly, this invention is concerned with substituted derivatives which are ligands for GABAA receptors, in particular for GABAA xcex15 receptors and are therefore useful in therapy particularly where cognition enhancement is required.
Receptors for the major inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), are divided into two main classes: (1) GABAA receptors, which are members of the ligand-gated ion channel superfamily; and (2) GABAB receptors, which may be members of the G-protein linked receptor superfamily. Since the first cDNAs encoding individual GABAA receptor subunits were cloned the number of known members of the mammalian family has grown to thirteen (six xcex1 subunits, three xcex2 subunits, three xcex3 subunits and one xcex4 subunit). It may be that further subunits remain to be discovered; however, none has been reported since 1993.
Although knowledge of the diversity of the GABAA receptor gene family represents a huge step forward in our understanding of this ligand-gated ion channel, insight into the extent of subtype diversity is still at an early stage. It has been indicated that an xcex1 subunit, a xcex2 subunit and a xcex3 subunit constitute the minimum requirement for forming a fully functional GABAA receptor expressed by transiently transfecting cDNAs into cells. As indicated above, a xcex4 subunit also exists, but is apparently uncommon in the native receptor.
Studies of receptor size and visualisation by electron microscopy conclude that, like other members of the ligand-gated ion channel family, the native GABAA receptor exists in pentameric form. The selection of at least one xcex1, one xcex2 and one xcex3 subunit from a repertoire of thirteen allows for the possible existence of more than 10,000 pentameric subunit. combinations. Moreover, this calculation overlooks the additional permutations that would be possible if the arrangement of subunits around the ion channel had no constraints (i.e. there could be 120 possible variants for a receptor composed of five different subunits).
Receptor subtype assemblies which do exist include xcex11xcex22xcex32, xcex12xcex22/3xcex32, xcex13xcex2xcex32/3, xcex12xcex2xcex31, xcex15xcex23xcex32/3, xcex16xcex2xcex32, xcex16xcex2xcex4 and xcex14xcex2xcex4. Subtype assemblies containing an xcex11 subunit are present in most areas of the brain and account for over 40% of GABAA receptors in the rat. Subtype assemblies containing xcex12 and xcex13 subunits respectively account for about 25% and 17% of GABAA receptors in the rat. Subtype assemblies containing an xcex15 subunit are primarily hippocampal and represent about 4% of receptors in the rat.
A characteristic property of some GABAA receptors is the presence of a number of modulatory sites, of which the most explored is the benzodiazepine (BZ) binding site through which anxiolytic drugs such as diazepam and temazepam exert their effect. Before the cloning of the GABAA receptor gene family, the benzodiazepine binding site was historically subdivided into two subtypes, BZ1 and BZ2, on the basis of radioligand binding studies. The BZ1 subtype has been shown to be pharmacologically equivalent to a GABAA receptor comprising the xcex11 subunit in combination with xcex22 and xcex32. This is the most abundant GABAA receptor subtype, representing almost half of all GABAA receptors in the brain.
Two other major populations are the xcex12xcex2xcex32 and xcex13xcex2xcex32/3 subtypes. Together these constitute approximately a further 35% of the total GABAA receptor repertoire. Pharmacologically this combination appears to be equivalent to the BZ2 subtype as defined previously by radioligand binding, although the BZ2 subtype may also include certain xcex15-containing subtype assemblies. The physiological role of these subtypes has hitherto been unclear because no sufficiently selective agonists or antagonists were known.
It is now believed that agents acting as BZ agonists at xcex11xcex2xcex32, xcex12xcex2xcex32 or xcex13xcex2xcex32 subunits will possess desirable anxiolytic properties. The xcex11-selective GABAA receptor agonists alpidem and zolpidem are clinically prescribed as hypnotic agents, suggesting that at least some of the sedation associated with known anxiolytic drugs which act at the BZ1 binding site is mediated through GABAA receptors containing the al subunit. Accordingly, it is considered that GABAA receptor agonists which bind more effectively to the xcex12 and/or xcex13 subunit than to xcex11 will be effective in the treatment of anxiety with a reduced propensity to cause sedation. Also, agents which are antagonists or inverse agonists at xcex11 might be employed to reverse sedation or hypnosis caused by xcex11 agonists.
A number of dementing illnesses such as Alzheimer""s disease are characterised by a progressive deterioration in cognition in the sufferer. It would clearly be desirable to enhance cognition in subjects desirous of such treatment, for example for subjects suffering from a dementing illness. It is believed this can be done utilising compounds which are ligands for the GABAA xcex15 receptor subtype.
The present invention is directed to 4-oxo-tetrahydroindozole-3-carboxamide compounds according to Formula (I) or a pharmaceutically acceptable salt thereof that are GABA-A Alpha 5 ligands useful for enhancing cognition: 
The present invention provides a compound of formula (I) or a pharmaceutically acceptable salt thereof: 
wherein:
R1 and R4 are independently chosen from hydrogen, halogen, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C1-6 haloalkyl, C2-6 haloalkenyl and C2-6 haloalkynyl:
R2 is hydrogen or C1-6 alkyl; and
Ar is phenyl, a 5-membered heterocyclic group containing 1, 2, 3 or 4 heteroatoms chosen from N, O and S, no more than one of which is O or S, or a 6-membered heterocyclic group containing one or two nitrogen atoms, each of which groups Ar is unsubstituted or substituted by from one to three groups independently chosen from halogen, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C3-7 cycloalkyl, C1-6 alkoxy, C2-6 alkenyloxy, C2-6 alkynyloxy, C3-7 cycloalkoxy, C1-6 haloalkyl, C2-6 haloalkenyl, C2-6 haloalkynyl, amino, C1-6 alkylamino, di(C1-6)alkylamino, hydroxy, hydroxy C1-6 alkyl, cyano, nitro, amino C1-6 alkyl, C1-6 alkylaminoC1-6 alkyl, di(C1-6 alkyl)aminoC1-6alkyl or C1-6alkoxycarbonylaminoC1-6alkyl.
R1 is preferably hydrogen, halogen or C1-6 alkyl and is particularly hydrogen.
R2 is preferably hydrogen or methyl especially hydrogen.
R4 is preferably hydrogen.
Ar is preferably phenyl or pyridine. When Ar is pyridine it may be 2-pyridine.
Ar is preferably unsubstituted or substituted with one or two groups independently selected from methyl, fluoro, chloro, methoxy, ethoxy, aminomethyl, aminoethyl, hydroxy, methylaminoethyl, dimethylaminoethyl and t-butoxycarbonylaminomethyl, especially from methoxy, fluoro, aminoethyl, methylaminoethyl, dimethylaminoethyl and t-butoxycarbonylaminomethyl.
Specific Examples of compounds according to the present invention are:
4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carboxylic acid phenylamide;
4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carboxylic acid-2,5-difluorophenylamide;
4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carboxylic acid pyridin-2-ylamide;
4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carboxylic acid 4-methoxyphenylamide; and
4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carboxylic acid 4-(2-aminoethyl)phenylamide; and the pharmaceutically acceptable salts thereof.
Further specific examples of compounds according to the present invention are:
[N-(4-(2-methylaminoethyl)-phenyl)]-(4-oxo-4,5,6,7-tetrahydro)-1H-indazole-3-carboxamide;
[4-[(4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carbonyl)amino]benzyl]carbamic acid-tert-butyl ester;
(N-(4-aminomethyl)phenyl))-4-oxo-4,5,6,7-tetrahydro-1H-indazole-3-carboxamide; and
[N-(4-(2-dimethylaminoethyl)phenyl)]-(4-oxo-4,5,6,7-tetrahydro)-1H-indazole-3-carboxamide;
and the pharmaceutically acceptable salts thereof.
There is also provided a pharmaceutical composition comprising a compound of formula I according to the present invention, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient.
Preferably the compositions according to the present invention are in unit dosage forms such as tablets, pills, capsules, powders, granules, solutions or suspensions, or suppositories, for oral, parenteral or rectal administration, by inhalation or insufflation or administration by trans-dermal patches or by buccal cavity absorption wafers.
For preparing solid compositions such as tablets, the principal active ingredient is mixed with a pharmaceutical carrier, e.g. conventional tableting ingredients such as corn starch, lactose, sucrose, sorbitol, talc, stearic acid, magnesium stearate, dicalcium phosphate or gums, and-other pharmaceutical diluents, e.g. water, to form a solid preformulation composition containing a homogeneous mixture of a compound of the present invention, or a non-toxic pharmaceutically acceptable salt thereof. When referring to these preformulation compositions as homogeneous, it is meant that the active ingredient is dispersed evenly throughout the composition so that the composition may be readily subdivided into equally effective unit dosage forms such as tablets, pills and capsules. This solid preformulation composition is then subdivided into unit dosage forms of the type described above containing from 0.1 to about 500 mg of the active ingredient of the present invention. The tablets or pills of the novel composition can be coated or otherwise compounded to provide a dosage form affording the advantage of prolonged action. For example, the tablet or pill can comprise an inner dosage and an outer dosage component, the latter being in the form of an envelope over the former. The two components can be separated by an enteric layer which serves to resist disintegration in the stomach and permits the inner component to pass intact into the duodenum or to be delayed in release. A variety of materials can be used for such enteric layers or coatings, such materials including a number of polymeric acids and mixtures of polymeric acids with such materials as shellac, cetyl alcohol and cellulose acetate.
The liquid forms in which the novel compositions of the present invention may be incorporated for administration orally or by injection include aqueous solutions, suitably flavoured syrups, aqueous or oil suspensions, and flavoured emulsions with edible oils such as cottonseed oil, sesame oil, coconut oil, peanut oil or soybean oil, as well as elixirs and similar pharmaceutical venicies. Suitable dispersing or suspending agents for aqueous suspensions include synthetic and natural gums such as tragacanth, acacia, alginate, dextran, sodium carboxymethylcellulose, methylcellulose, polyvinyl-pyrrolidone or gelatin.
Compositions for inhalation or insufflation include solutions and suspensions in pharmaceutically acceptable, aqueous or organic solvents, or mixtures thereof, and powders. The liquid or solid compositions may contain suitable pharmaceutically acceptable excipients as set out above. Preferably the compositions are administered by the oral or nasal respiratory route for local or systemic effect. Compositions in preferably sterile pharmaceutically acceptable solvents may be nebulised by use of inert gases. Nebulised solutions may be breathed directly from the nebulising device or the nebulising device may be attached to a face mask, tent or intermittent positive pressure breathing machine. Solution, suspension or powder compositions may be administered, preferably orally or nasally, from devices which deliver the formulation in an appropriate manner.
Compositions of the present invention may also be presented for administration in the form of trans-dermal patches using conventional technology. The compositions may also be administered via the buccal cavity using, for example, absorption wafers.
In disorders associated with GABAA xcex1 receptors, a suitable dosage level is about 0.01 to 250 mg/kg per day, preferably about 0.05 to 100 mg/kg per day, and especially about 0.05 to 5 mg/kg per day. The compounds may be administered on a regimen of 1 to 4 times per day.
The present invention also provides a process for the preparation of a pharmaceutical composition which comprises adding a compound of formula (I) or a pharmaceutically acceptable salt thereof to a pharmaceutically acceptable excipient.
The present invention also provides a compound of formula (I) or a pharmaceutically acceptable salt thereof for use in a method of treatment of the human or animal body, in particular for the treatment or prevention of conditions for which the administration of a cognition enhancing agent is desirable, such as Alzheimer""s disease.
The compounds of formula (I) are of potential value in the treatment or prevention of a wide variety of clinical conditions which can be alleviated by a ligand selective for GABAA receptors containing the xcex15 subunit. In particular, they are desirably inverse agonists of the xcex15 subunit.
Thus, for example, such a ligand can be used in a variety of disorders of the central nervous system. Such disorders include delirium, dementia and amnestic and other cognitive disorders. Examples of delirium are delirium due to substance intoxication or substance withdrawal, delirium due to multiple etiologies and delirium NOS (not otherwise specified). Examples of dementia are: dementia of the Alzheimer""s type with early onset which can be uncomplicated or with delirium, delusions or depressed mood; dementia of the Alzheimer""s type, with late onset, which can be uncomplicated or with delirium, delusions or depressed mood; vascular dementia which can be uncomplicated or with delirium, delusions or depressed mood; dementia due to HIV disease; dementia due to head trauma; dementia due to Parkinson""s disease; dementia due to Huntington""s disease; dementia due to Pick""s disease; dementia due to Creutzfeld-Jakob disease; dementia which is substance-induced persisting or due to multiple etiologies; and dementia NOS. Examples of amnestic disorders are amnestic disorder due to a particular medical condition or which is substance-induced persisting or which is amnestic disorder NOS. In particular the compounds of formula (I) may be of use in conditions which require cognition enhancement.
Where the compounds of the present invention are selective ligands for GABAA xcex12 or xcex13 subtype receptors they may be used in the treatment and/or prevention of a variety of disorders of the central nervous system. Such disorders include anxiety disorders, such as panic disorder with or without agoraphobia, agoraphobia without history of panic disorder, animal and other phobias including social phobias, obsessive-compulsive disorder, stress disorders including post-traumatic and acute stress disorder, and generalized or substance-induced anxiety disorder; neuroses; convulsions; migraine; and depressive or bipolar disorders, for example single-episode or recurrent major depressive disorder, dysthymic disorder, bipolar I and bipolar II manic disorders, and cyclothymic disorder.
The present invention also provides the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof for the manufacture of a medicament for the treatment or prevention of a condition requiring the administration of a ligand selective for GABAA receptors containing the xcex15 subunit, in particular for conditions requiring cognition enhancement such as Alzheimer""s disease.
There is also disclosed a method of treatment or prevention of a condition associated with GABAA receptors containing the xcex15 subunit which comprises administering to a subject suffering from or prone to such a condition a therapeutically or prophylactically effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof. In particular there is disclosed the treatment and prevention of conditions which require the administration of a cognition enhancing agent, such as Alzheimer""s disease.
As used herein, the expression xe2x80x9cC1-6alkylxe2x80x9d includes methyl and ethyl groups, and straight-chained and branched propyl, butyl, pentyl and hexyl groups. Particular alkyl groups are methyl, ethyl, n-propyl, isopropyl and t-butyl. Derived expressions such as xe2x80x9cC2-6alkenylxe2x80x9d and xe2x80x9cC2-6alkynylxe2x80x9d are to be construed in an analogous manner.
The expression xe2x80x9cC3-7cycloalkylxe2x80x9d includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl groups.
Suitable 5- and 6-membered heteroaromatic rings include pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, furyl, thienyl, pyrrolyl, pyrazolyl, oxazolyl, isoxazolyl, isothiazolyl, imidazolyl, tetrazolyl, oxadiazolyl and thiadiazolyl groups. These rings also include thiazolyl and triazolyl groups.
The term xe2x80x9chalogenxe2x80x9d as used herein includes fluorine, chlorine, bromine and iodine, especially fluorine, chlorine and bromine.
For use in medicine, the salts of the compounds of formula (I) will be pharmaceutically acceptable salts. Other salts may, however, be useful in the preparation of the compounds according to the invention or of their pharmaceutically acceptable salts. Suitable pharmaceutically acceptable salts of the compounds of this invention include acid addition salts which may, for example, be formed by mixing a solution of the compound according to the invention with a solution of a pharmaceutically acceptable acid such as hydrochloric acid, sulphuric acid, methanesulphonic acid, fumaric acid, maleic acid, succinic acid, acetic acid, benzoic acid, oxalic acid, citric acid, tartaric acid, carbonic acid or phosphoric acid. Furthermore, where the compounds of the invention carry an acidic moiety, suitable pharmaceutically acceptable salts thereof may include alkali metal salts, e.g. sodium or potassium salts; alkaline earth metal salts, e.g. calcium or magnesium salts; and salts formed with suitable organic ligands, e.g. quaternary ammonium salts.
Where the compounds of formula (I) have at least one asymmetric centre, they may accordingly exist as enantiomers. Where the compounds of formula (I) possess two or more asymmetric centres, they may additionally exist as diastereoisomers. It is to be understood that all such isomers and mixtures thereof in any proportion are encompassed within the scope of the present invention.
The present invention also provides a process for producing a compound of formula I which comprises reacting a compound of formula II with a compound of formula III: 
wherein R1, R2, R4 and Ar are as defined above. The reaction is generally carried out in a mixture of DMF/DCM and in the presence of a coupling agent such as 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride and dimethylaminopyridine. The reaction is generally carried out for about 36 h.
If necessary any reactive portions of the moiety Ar are protected with a protecting group such as tert-butyloxycarbonyl. Such protecting groups can be removed after reaction of the compounds of formulae II and, III to yield a compound of formula I.
The compound of formula II can be made by hydrolyzing a compound of formula IV: 
wherein R1, R2 and R4 are as defined above, with a base such as NaOH generally by heating at reflux for about 3 h in a solvent such as EtOH.
The compound of formula IV wherein R2 is other than hydrogen can be made by reaction of a compound of formula IV where R2 is hydrogen with a strong base such as Na H followed by alkylation for example with the appropriate alkyl iodide.
The compound of formula IV is made by reacting a compound of formula V with a compound of formula VI: 
The compound of formula V is made by reacting a compound of formula VII with a compound of formula VIII: 
wherein R1 and R4 are as defined above and the compound of formula VII is generally pre-reacted with trimethylsilylchloride.
wherein R2 is as defined above, generally in a solvent such as DMF and in the presence of a base such at Et3N at about 50xc2x0 C. for about 3 days.
Compounds of formulae III, V, VI, VII and VIII are commercially available or can be made from commercially available compounds by methods known in the art.
The following Examples illustrate pharmaceutical compositions according to the invention.
The active ingredient(s), cellulose, lactose and a portion of the corn starch are mixed and granulated with 10% corn starch paste. The resulting granulation is sieved, dried and blended with the remainder of the corn starch and the magnesium stearate. The resulting granulation is then compressed into tablets containing 1.0 mg, 2.0 mg, 25.0 mg, 26.0 mg, 50.0 mg and 100 mg of the active compound per tablet.
The sodium phosphate, citric acid monohydrate and sodium chloride are dissolved in a portion of the water. The active ingredient(s) is (are) dissolved or suspended in the solution and made up to volume.
The white soft paraffin is heated until molten. The liquid paraffin and emulsifying wax are incorporated and stirred until dissolved. The active ingredient(s) is (are) is added and stirring continued until dispersed. The mixture is then cooled until solid.
The following Examples illustrate the compounds of the present invention.
The compounds in accordance with this invention potently inhibit the binding of [3H]-flumazenil to the benzodiazepine binding site of human GABAA receptors containing the xcex15 subunit stably expressed in Ltkxe2x88x92 cells.
Reagents
Phosphate buffered saline (PBS).
Assay buffer: 10 mM KH2PO4, 100 mM KCl, pH 7.4 at room temperature.
[3H]-Flumazenil (18 nM for xcex11xcex23xcex32 cells; 18 nM for xcex12xcex23xcex32 cells; 10 nM for xcex13xcex23xcex32 cells; 10 nM for xcex15xcex23xcex32 cells) in assay buffer.
Flunitrazepam 100 xcexcM in assay buffer.
Cells resuspended in assay buffer (1 tray to 10 ml).
Harvesting Cells
Supernatant is removed from cells. PBS (approximately 20 ml) is added. The cells are scraped and placed in a 50 ml centrifuge tube. The procedure is repeated with a further 10 ml of PBS to ensure that most of the cells are removed. The cells are pelleted by centrifuging for 20 min at 3000 rpm in a benchtop centrifuge, and then frozen if desired. The pellets are resuspended in 10 ml of buffer per tray (25 cmxc3x9725 cm) of cells.
Assay
Can be carried out in deep 96-well plates or in tubes. Each tube contains:
300 xcexcl of assay buffer.
50 xcexcl of [3H]-flumazenil (final concentration for xcex11xcex23xcex32: 1.8 nM; for xcex12xcex23xcex32: 1.8 nM; for xcex13xcex23xcex32: 1.0 nM; for xcex15xcex23xcex32: 1.0 nM).
50 xcexcl of buffer or solvent carrier (e.g. 10% DMSO) if compounds are dissolved in 10% DMSO (total); test compound or flunitrazepam (to determine non-specific binding), 10 xcexcM final concentration.
100 xcexcl of cells.
Assays are incubated for 1 hour at 40xc2x0 C., then filtered using either a Tomtec or Brandel cell harvester onto GF/B filters followed by 3xc3x973 ml washes with ice cold assay buffer. Filters are dried and counted by liquid scintillation counting. Expected values for total binding are 3000-4000 dpm for total counts and less than 200 dpm for non-specific binding if using liquid scintillation counting, or 1500-2000 dpm for total counts and less than 200 dpm for non-specific binding if counting with meltilex solid scintillate. Binding parameters are determined by non-linear least squares regression analysis, from which the inhibition constant Ki can be calculated for each test compound.
The compounds of the accompanying Examples were tested in the above assay, and all were found to possess a Ki value for displacement of [3H]Ro 15-1788 from the xcex15 subunit of the human GABAA receptor of 500 nM or less, preferably of 100 nM or less, and more particularly of 50 nM or less.
More preferably the compounds of the present invention are inverse agonists at the GABAA xcex15 subtype whilst being substantially antagonists at the xcex11, xcex12 and xcex13 subtypes. Details of how the effects at the various subtypes can be measured are given in WO-A-9625948.
Further, the present compounds preferably bind preferentially to the GABAA xcex15 subtype when compared with the xcex11, xcex12 and xcex13 subtypes. The preferential binding is preferably 5-fold, more preferably 10-fold and most preferably 20-fold.