WO1999006400A1

WO1999006400A1 - Pyrazoloquinolinone derivatives as gaba alpha 5 receptor inverse agonists

Info

Publication number: WO1999006400A1
Application number: PCT/GB1998/002289
Authority: WO
Inventors: Sylvie Bourrain; Angus Murray Macleod; Graham Andrew Showell
Original assignee: Merck Sharp & Dohme Limited
Priority date: 1997-08-01
Filing date: 1998-07-30
Publication date: 1999-02-11
Also published as: GB9716345D0; AU8552098A

Abstract

2-(3-fluorophenyl)- and 2-(2-fluorophenyl)-7-methoxy-2,5-dihydro-pyrazolo[4,3-c]quinolin-3-one of formula (I) are disclosed. The compounds are inverse agonists at GABAα5 receptors, and are useful in enhancing cognition, particularly in subjects suffering from Alzheimer's Disease.

Description

PYRAZOLOQUINOLINONE DERIVATIVES AS GABA ALPHA 5 RECEPTOR INVERSE AGONISTS

The present invention relates to pyrazoloquinolinone derivatives and their use in enhancing cognition, particularly in subjects suffering from Alzheimer's Disease. Processes for their preparation are also disclosed.

A number of dementing illnesses and cognition deficit states are characterised by poor and often a progressive deterioration in the cognition of the sufferer. It would clearly be desirable to enhance cognition in subjects desirous of such treatments. International Patent Application No. PCT/GB 96/00377 discloses that certain GABAα₅ receptor inverse agonists ("α5 inverse agonists") may be used to enhance cognition without producing convulsions. Also by choosing an as inverse agonist that does not have significant α₁₍ α₂, or α₃ agonism it is possible to avoid benzodiazepine receptor activity such as that associated with marked anxiolytic, sedative or anti-depressive effects.

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 α subunits, three β subunits, three γ subunits and one δ 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 α subunit, a β subunit and a γ subunit constitute the minimum requirement for forming a fully - ^ -

functional GABAA receptor expressed by transiently transfecting cDNAs into cells. As indicated above, a δ 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 α, one β and one γ 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 αlβ2γ2, α2β2/3γ2, α3βγ2/3, α2βγl, α5β3γ2/3, α6βγ2, α6βδ and 4βδ. Subtype assemblies containing an αl subunit are present in most areas of the brain and account for over 40% of GABAA receptors in the rat. Subtype assemblies containing α2 and α3 subunits respectively account for about 25% and 17% of GABAA receptors in the rat. Subtype assemblies containing an α5 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 αl subunit in combination with β2 and γ2. This is the most abundant GABAA receptor subtype, representing almost half of all GABAA receptors in the brain. 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. We have now discovered that it is possible to obtain medicaments which have cognition enhancing effects which may be employed with less risk of proconvulsant and/or sedating effects previously described with benzodiazepine receptor partial or full inverse agonists.

It has now been discovered that use of an α5 receptor partial or full inverse agonist which is relatively free of activity at αl and/or α2 and/or α3 receptor binding sites can be used to provide a medicament which is useful for enhancing cognition but in which proconvulsant activity is reduced or eliminated. Inverse agonists at α5 which are not free of activity at αl and/or α2 and/or α3 but which are functionally selective for α5 can also be used. Inverse agonists which are both selective for α5 and are relatively free of activity at αl , α2 and α3 receptor binding sites are preferred.

A compound similar to those of the present invention, in which the fluorine atom is in the para-position, is disclosed in EP-A-214092. There is no suggestion there as to whether this compound would enhance cognition. There is no specific disclosure in the art of the compounds of the present invention.

The present invention provides a compound of formula I:

(I) wherein: one of R¹ and R² is hydrogen and the other is fluorine; or a pharmaceutically acceptable salt thereof. Suitable pharmaceutically acceptable salts include acid addition salts with mineral or organic acids such as the salts with hydrochloric, sulphuric, hydrobromic, phosphoric, methane sulfonic, ethane sulfonic, camphor sulfonic, acetic, lactic, citric, tartaric, maleic, benzoic, propionic, succinic, fumaric, gluconic or malic acid.

The compounds of the present invention may be used in the form of the free base.

Specific compounds of the present invention are: 2-(3-fluoro-phenyl)-7-methoxy-2,5-dihydro-pyrazolo[4,3-c]quinolin-3-one; and 2-(2-fluoro-phenyl)-7-methoxy-2,5-dihydro-pyrazolo[4,3-c]quinolin-3- one.

The present compounds can be prepared as described in the Examples. The aniline starting material is commercially available. The hydrazine starting materials are commercially available or can be prepared by analogy with the compounds disclosed in Arzneim-forsch, 1972, 22(12), 2099 by methods known to the skilled artisan.

The aniline and diethyl ethoxymethylenemalonate are generally reacted at about 150°C for about four hours and then added to an inert oil such as Dowtherm A at about 250°C for about two hours to produce an oxoquinoline carboxylic acid ester. This compound is converted to its chlorinated analogue by reaction with a chlorinating agent such as POCI3 generally at reflux for about two hours.

The compound produced is reacted with the hydrazine starting material and a base, such as Hunig's base, generally at about 140°C in a solvent such as xylene for about two hours.

The compounds of the present invention can be freely interconverted between salt and base forms by methods known in the art.

The present invention also provides a pharmaceutical composition comprising a compound of formula (I) or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable excipient.

The compositions are most aptly adapted for oral administration to humans although parenteral modes of administration are also envisaged, for example by intravenous, intramuscular or subcutaneous administration or topically or rectally.

For oral use of the cognition enhancer the selected compound may be administered for example in the form of a tablet or a pharmaceutically acceptable carriers or diluents, optionally with known adjuvants, such as alum, in a pharmaceutical composition, according to standard pharmaceutical practice. The compounds can be administered orally, parenterally, including by intravenous, intramuscular, intraperitoneal or subcutaneous administration, or topically.

For oral use the cognition enhancer may be administered, for example, in the form of tablets or capsules, or as an aqueous solution or suspension. In the case of tablets for oral use, carriers which are commonly used include lactose, macrocrystalline cellulose, carboxymethyl cellulose and corn starch, and lubricating agents, such as magnesium stearate, are commonly added. For oral administration in capsule form, useful diluents include lactose and dried corn starch. When aqueous suspensions are required for oral use, the active ingredient is combined with emulsifying and suspending agents. If desired, certain sweetening and/or flavouring agents may be added.

For intramuscular, intraperitoneal, subcutaneous and intravenous use, sterile solutions of the active ingredient are usually prepared, and the pH of the solutions should be suitably adjusted and buffered. For intravenous use, the total concentration of solutes should be controlled in order to render the preparation isotonic.

For topical administration, the cognition enhancer may be formulated as, for example, a suspension, lotion, cream or ointment employing a pharmaceutically acceptable carrier such as, for example, water, mixtures of water and water-miscible solvents such as lower alkanes, vegetable oils, polyalkylene glycols and the like.

The pharmaceutical preparation may also contain non-toxic auxiliary substances such as emulsifying, preserving, wetting agents, bodying agents and the like, as for example, polyethylene glycols 200, 300, 400 and 600, carbowaxes 1,000, 1,500, 4,000, 6,000 and 10,000, antibacterial components such as quaternary ammonium compounds, phenylmercuric salts known to have cold sterilizing properties and which are non-injurious in use, thimerosal, methyl and propyl paraben, benzyl alcohol, phenyl ethanol, buffering ingredients such as sodium chloride, sodium borate, sodium acetates, gluconate buffers, and other conventional ingredients such as sorbitan monolaurate, triethanolamine, oleate, polyoxyethylene sorbitan monopalmitylate, dioctyl sodium sulfosuccinate, monothioglycerol, thiosorbitol, ethylenediamine tetraacetic acid, and the like.

When a cognition enhancer is used in a human subject, the daily dosage will normally be determined by the prescribing physician with the dosage generally varying according to the age, weight, and response of the individual patient, as well as the severity of the patient's symptoms. However, in most instances, an effective daily dosage will be in the range from about 0.005mg/kg to about lOOmg kg of body weight, and preferably, of from 0.05mg/kg to about 50mg kg, such as from about 0.5mg/kg to about 20mg/kg of body weight, administered in single or divided doses. In some cases, however, dosage outside these limits may be used. Generally the daily dose will be administered as in from 1 to 6 times a day, generally 1 to 3 times per day.

In a further aspect the present invention 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 use in the enhancement of cognition. 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 α5 subunit. In particular, they are desirably inverse agonists of the α5 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.

Also, the present invention provides the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof for the manufacture of a medicament for use in the enhancement of cognition.

There is also disclosed a method of treatment of a subject suffering from a neurocognitive disorder, such as Alzheimer's Disease, which method comprises administering to that subject a therapeutically effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof.

The compounds of formula (I) were tested for functional efficacy in the following assay and were shown to be inverse agonists at the α5 receptor subtype.

The functional efficacy of compounds was assessed using transiently expressed receptors and two electrode voltage clamp recording from Xenopus oocytes using the following methods.

Oocytes were isolated from female Xenopus laevis in an isolation medium (IM) and were then transferred into modified Barth's saline (MBS) where they were defollicated using forceps. Oocytes were then treated with collagenase (0.5 mg/ml of MBS for 5 to 10 minutes) to remove adherent somatic cells. The IM contained (in mM) NaCl (108), KC1 (2), EDTA (0.1), HEPES (1), and the pH was adjusted to 7.9 with NaOH. The MBS contained (in mM) NaCl (88), KC1 (1), HEPES (10), MgSO4 (0.82), Ca(NO3)2 (0.33), CaC12 (0.91), NaHCO3 (2.4) and the pH was adjusted to 7.5 with NaOH.

Oocytes were injected with a combination of human GABAA receptor α, β and γ subunit cDNA constructs using a Drummond microinjector. The efficacy of compounds on human α5 containing receptors was determined using cells injected with a combination of α5 + β3 + γ2(short) subunit cDNA. Their functional selectivity was determined using cells injected with αl, α2, or α3 subunit cDNA in place of α5 cDNA. cDNA mixtures were prepared in sterile water (injection buffer) containing NaCl (0.514 g / 100 mis), KC1 0.0075 (g / 100 mis), Hepes (0.357 g / 100 mis) at pH 7.0 adjusted with 1 M NaOH. After injection cells were placed in an incubation medium for 1 to 4 days at 22 °C before recording. The incubation medium consisted of 1 litre of MBS containing penicillin

(10,000 units), streptomycin (10 mg), gentamycin (50 mg), theophylline (90 mg), and Na+pyruvate (2 M).

Transfected oocytes were placed in a recording chamber (volume = 500 μL) and were perfused with MBS at a rate of 1 to 2 mis / min. Cells were voltage clamped using conventional two electrode voltage-clamp recording methodology. Cells were held at -60 mV and the whole cell current was monitored on a chart recorder. The expression of GABAA receptors in each cell was confirmed by the activation of an inward current upon application of a high concentration of γ-aminobutyric acid (GABA; 100 μM to 1 mM) to the perfusate. After perfusion with MBS for a further 10-15 minutes to allow recovery from GABA-mediated receptor desensitization a concentration effect curve to GABA was then constructed on each oocyte to determine the concentration of GABA required to activate an inward current that was 20% of the maximum (GABA EC20). GABA was typically applied for 2 minutes until a maximum inward current was activated and then oocytes were washed in MBS for 3 minutes before the next agonist application. The EC20 concentration of GABA was then repeatedly applied using this 2 minutes application plus 3 minute wash cycle until a stable response was obtained (<5% variation from the previous response). Test compounds were dissolved in 100% dimethylsulfoxide (DMSO) and were applied to each oocyte in MBS at a concentration approximately 100 times their binding affinity (final bath concentration of DMSO = 0.1%). Compounds were allowed to equilibrate with the oocyte for approximately 2 minutes before application of a GABA EC20 dose in the continuing presence of the test compound. The ability of compounds to modulate the peak chloride current activated by the GABA EC20 (ID) was quantified and expressed as the percentage change from of the peak current activated under control conditions (Ic), where efficacy (%) = (100 * ID / IC) - 100. Efficacy values are the mean ± standard error of the mean of data obtained from at least 3 separate cells. The following Examples illustrate the present invention.

EXAMPLE 1

2-(3-Fluorophenyl)-7-methoxy-2,5-dihvdro-pyrazolof4,3-c1quinolin-3-one

Step 1: 7-Methoxy-4-oxo-l,4-dihvdro-quinoline-3-carboxylic acid ethyl ester

3-Anisidine (43g, 350mmol) and diethyl ethoxymethylene malonate (75.7g, 350mmol) were combined and heated at 150°C for 4 hours. The resulting oil was added to hot (250°C) stirring Dowtherm A (500ml) and the mixture maintained at reflux for 1 hour. The mixture was cooled to room temperature and the solid filtered and washed with hexane to give the title compound as a beige solid (29g, 35%). mp 282-284°C. δ Η NMR (250MHz, d_G-DMSO) 1.27 (3H, t, J=7Hz), 3.86 (3H, s), 4.20 (2H, q, J=7Hz), 6.97-7.05 (2H, m), 7.28 (IH, d, J=7Hz), 8.72 (IH, s), 12.5 (IH, br s). MS CI⁺ m/z=248 for (M+H)⁺.

Step 2: 4-Chloro-7-methoxy-quinoline-3-carboxylic acid ethyl ester

The foregoing dihydro-quinoline (15g, 61mmol) was heated at reflux for 2 hours in phosphorus oxychloride (250ml). After evaporating the excess phosphorus oxychloride the residue was cooled, diluted carefully with ice (200ml), basified with ammonia and extracted with dichloromethane (3x200ml). The combined organics were washed with water (600ml), dried (sodium sulfate) and evaporated. The residue was purified by plug column chromatography on silica eluting with methanol/dichloromethane (99/1) to give the title compound as a colourless solid (9.2g, 57%). mp 133-134°C. δ Η NMR (360MHz, CDC1₃) 1.46 (3H, t, J=7Hz), 3.99 (3H, s), 4.48 (2H, q, J=7Hz), 7.32 (IH, dd, J=2 and 9Hz), 7.44 (IH, d, J=2Hz), 8.30 (IH, d, J=8Hz), 9.17 (lH,s ). MS, CI⁺ m/z=266 and 268 for (M+H)⁺. Found C, 58.81; H, 4.44; N, 5.38. C₁₃H₁₂ClNO₃ requires C, 58.77; H, 4.55; N, 5.27%.

Step 3: 2-(3-Fluorophenyl)-7-methoxy-2,5-dihydro-pyrazolof4,3-c]quinolin- 3-one

A mixture of 3-fluorophenyl hydrazine hydrochloride (65mg, 0.4mmol), Hunig's Base (142μl, 0.82mmol) and the foregoing chloroquinoline (112mg, 0.42mmol) were heated at 140°C in xylene (3ml) for 2 hours. After cooling the xylene was decanted and the oil crystallised from methanol. The solid was filtered, washed with diethyl ether, water (2x) and diethyl ether to afford the title compound (75mg, 60%). δ ^XH NMR (360MHz, d₆-DMSO) 3.89 (3H, s), 6.98 (IH, t, J=8Hz), 7.20 (2H, dd, J=2 and 7Hz), 7.43-7.50 (IH, m), 8.06-8.12 (2H, m), 8.15 (IH, d, J=8Hz), 8.72 (IH, s), 12.70 (IH, br s). MS, CI⁺ m/z=310 for (M+H)⁺.

EXAMPLE 2

2-(2-Fluorophenyl)-7-methoxy-2,5-dihydro-pyrazolor4,3-c1quinolin-3-one The title compound was obtained using the procedure described in Example 1 Step 3 using 2-fluorophenyl hydrazine hydrochloride instead of 3-fluorophenyl hydrazine hydrochloride. δ Η NMR (360MHz, d_G-DMSO) 3.88 (3H, s), 7.13-7.21 (2H, m), 7.28-7.49 (3H, m), 7.55-7.61 (IH, m), 8.04 (IH, d, J=9Hz), 8.67 (IH, s), 12.60 (IH, br s). MS CI⁺ m/z=310 for (M+H)⁺.

Claims

A compound of Formula I:

wherein: one of R¹ and R² is hydrogen and the other is fluorine; or a pharmaceutically acceptable salt thereof.

2. A compound selected from: 2-(3-fluoro-phenyl)-7-methoxy-2,5-dihydro-pyrazolo[4,3-c]quinolin-3-one; and 2-(2-fluoro-phenyl)-7-methoxy-2,5-dihydro-pyrazolo[4,3-c]quinolin-3- one; and pharmaceutically acceptable salts thereof.

3. A pharmaceutical composition comprising a compound according to claim 1 or claim 2 and a pharmaceutically acceptable excipient.

4. A compound according to claim 1 or claim 2 for use in a method of treatment of the human or animal body.

5. The use of a compound according to claim 1 or claim 2 for the manufacture of a medicament for use in the enhancement of cognition.

6. A method of treatment of a subject suffering from a neurocognitive disorder, which method comprises administering to that subject a therapeutically effective amount of a compound according to claim 1 or claim 2.

7. A method of preparing a compound according to claim 1 or claim 2 comprising the steps of:

(1) reacting 3-anisidine with diethyl ethoxymethylene malonate at elevated temperature to form 7-methoxy-4-oxo-l,4-dihydro- quinoline-3-carboxylic acid ethyl ester;

(2) reacting the product of step (1) with a chlorinating agent; and

(3) reacting the product of step (2) with either 3-fluorophenyl hydrazine hydrochloride or 2-fluorophenyl hydrazine hydrochloride in the presence of base.