EP0609278A1 - Imidazopyridines and indolizines as 5-ht 4 antagonists - Google Patents

Abstract

Compounds represented by formula (I) wherein R1 represents hydrogen, halogen, CF3, alkyl, alkoxy, alkylthio, alkylsulphonyl, alkylsulphinyl, acyl, cyano, alkoxy-carbonyl, acylamino, hydroxy, nitro or amino, amino-carbonyl or aminosulphonyl, phenyl or an optionally substituted phenyl alkyl group in the cyclic phenyl compound; one of X1 and X2 represents N and the other represents C; X3 represents N or CR where R represents hydrogen, alkoxy, halo, alkyl or cyano; Ra represents hydrogen, halo, alkyl, amino, nitro or alkyl; Rb represents hydrogen, halo, alkyl or alkoxy; Y represents O or NH; Z is part of the sub-formula (a), (b) or (c) in which n1 is 1, 2, 3 or 4; n2 is 0, 1, 2, 3 or 4; n3 is 2, 3, 4 or 5; q is 0, 1, 2 or 3; p is 0, 1 or 2; m is 0, 1 or 2; use of said compounds in the treatment of gastrointestinal, cardiovascular diseases and diseases of the central nervous system.

Description

IMIDAZOPYRIDINES AND INDOLIZINES AS 5-HT4 ANTAGONISTS

This invention relates to novel compounds having pharmacological activity, to a process for their preparation and to their use as pharmaceuticals.

European Journal of Pharmacology 146 (1988), 187-188, and Naunyn- Schmiedeberg's Arch. Pharmacol. (1989) 340:403-410, describe a non classical 5-hydroxytryptamine receptor, now designated the 5-HT4 receptor, and that ICS 205-930, which is also a 5-HT3 receptor antagonist, acts as an antagonist at this receptor.

Some 5-HT3 receptor antagonists have been disclosed as of potential use in the treatment of certain aspects of irritable bowel syndrome (see

EP-A- 189002 (Sandoz Limited) and EP-A-201165 (Beecham Group p.l.c)).

5-HT3 receptor interactions which are of potential use in the treatment of IBS are those associated either with the visceral pain and abnormal perception of sensation aspects of this disease, or they are related to the ability of some 5-ΗT3 receptor antagonists to cause constipation in volunteers.

Some 5-HT3 receptor antagonists have been disclosed as of potential use in the treatment of gastrointestinal disorders associated with upper gut motility [see EP-A-226266 (Glaxo Group Ltd.) and EP-A- 189002 (Sandoz Limited)]. 5-HT3 receptor antagonists are also well known antiemetics, such as ondansetron, granisetron and tropisetron (see Drugs of the Future 1989, 14 (9) p.875 - F.D. King and G.J. Sanger).

WO 91/16045 (SmithKline and French Laboratories Limited) describes the use of cardiac 5-HT4 receptor antagonists in the treatment of atrial arrhythmias and stroke.

EP-A-501322 (Glaxo Group Limited) describes indole derivatives having 5-HT4 antagonist activity.

EP-A-289170 and EP-A-254584 (Beecham Group p.l.c.) describes inter alia indolizine derivatives with a bridged piperidyl moiety having 5-HT3 receptor antagonist activity.

A class of novel, structurally distinct compounds has now been discovered, which compounds are indolizine derivatives with an azacyclic, fused azabicyclic or aminoalkyl moiety. These compounds have 5-HT4 receptor antagonist activity and are therefore of potential use in the treatment of IBS or atrial aιτh thmias and stroke.

The compounds of the present invention also have a potential use in the treatment of CNS disorders such as anxiety and/or migraine, in the treatment of upper gut motility disorders and as antiemetics.

When used herein, 'treatment' includes prophylaxis as appropriate.

Accordingly, the present invention provides a compound of formula (I), or a pharmaceutically acceptable salt thereof

(I)

wherein

Rx is hydrogen, halogen, CF3, Cχ_g alkyl, Cχ_g alkoxy, Cχ_g alkylthio, Cχ_g alkylsulphonyl, Cχ_g alkylsulphinyl, Cχ_7 acyl, cyano, Cχ_g alkoxycarbonyl, Cχ.7 acylamino, hydroxy, nitro or amino, aminocarbonyl, or aminosulphonyl, optionally N-substituted by one or two groups selected from Cχ_g alkyl, C3.3 cycloalkyl, and C3-8 cycloalkyl Cχ.4 alkyl or disubstituted by C4 or C5 polymethylene; phenyl or phenyl Cχ.4 alkyl group optionally substituted in the phenyl ring by one or two of halogen, Cχ.g alkoxy or Cχ.g alkyl groups; one of x and X2 is N and the other is C;

X3 is N or CR wherein R is hydrogen, Cχ.g alkoxy, halo, Cχ.g alkyl or cyano; R_a is hydrogen, halo, Cχ.g alkyl, amino, nitro or Cχ.g alkyl; Rb is hydrogen, halo, Cχ.g alkyl or Cχ.g alkoxy;

Yis O or NH;

Z is of sub-formula (a), (b) or (c):

(a)

(b)

(c)

wherein n¹ is 1, 2, 3 or 4; n² is 0, 1, 2, 3 or 4; n³ is 2, 3, 4 or 5; q is 0, 1, 2 or 3; p is 0, 1 or 2; m is 0, 1 or 2;

R5 is hydrogen, Cχ.χ2 alkyl, aralkyl or R5 is (CH2 10 wherein r is 2 or 3 and Rχo is selected from cyano, hydroxyl, Cχ.g alkoxy, phenoxy, C(0)Cχ_g alkyl, COCgH₅, -CONRχχRχ2, NRχχCOR₁₂, Sθ2NRχ Rχ2 or N χ S02Rχ2 wherein xx and Rχ2 are hydrogen or Cχ.g alkyl; and

Rg, R7 and Rs are independently hydrogen or Cχ.g alkyl; and R9 is hydrogen or Cχ_χo alkyl; or a compound of formula (I) wherein the CO-Y linkage is replaced by a heterocyclic bioisostere; having 5-HT4 receptor antagonist activity.

Examples of alkyl or alkyl containing groups include Cχ_> C2, C3, C4, C5, Cg, C7, Cg, Cg_f Cχo, Cx or Cχ2 branched, straight chained or cychc alkyl, as appropriate. Cχ.4 alkyl groups include methyl, ethyl n- and iso-propyl, n-, iso-, sec- and teri-butyl. Cyclic alkyl includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

Aryl includes phenyl and naphthyl optionally substituted by one or more substituents selected from halo, Cχ.g alkyl and Cχ.g alkoxy.

Halo includes fluoro, chloro, bromo and iodo.

A suitable bioisostere for the amide or ester linkage containing Y in formula (I), is of formula (d):

(d)

wherein the dotted circle represents one or two double bonds in any position in the 5-membered ring; H, J and I independently represent oxygen, sulphur, nitrogen or carbon, provided that at least one of H, J and I is other than carbon; U represents nitrogen or carbon.

Suitable examples of (d) are as described for X, Y and Z in EP-A-328200 (Merck Sharp & Dohme Ltd.), such as an oxadiazole moiety.

Rx is preferably CF3 or an ethyl group.

X3 is preferably N, C-H or C-OCH3;

R_a is preferably hydrogen.

b is preferably hydrogen or halo, such as iodo.

Y is preferably O or NH.

When Z is of sub-formula (a), n^ is preferably 2, 3 or 4 when the azacycle is attached at the nitrogen atom and n^ is preferably 1 when the azacycle is attached at a carbon atom, such as the 4-position when q is 2.

Values of R5 include C3 or larger alkyl or optionally substituted benzyl and those values described for (CH2) ^ in formula (I), in relation to (la), preferred classes therein and the specific examples of EP-A-501322. When Z is of sub-formula (b), n² is preferably such that the number of carbon atoms between the ester or amide linkage is from 2 to 4 carbon atoms.

Suitable values for p and m include p = m = 1; p = 0, m = 1, p = 1, m = 2.

When Z is of sub-formula (c), n³ is preferably 2, 3 or 4.

s and Rg are preferably both alkyl, especially one of Rg and R9 is C4 or larger alkyl.

Specific values of Z of particular interest are as follows:

,NMe Bu (iv)

The invention also provides novel compounds within formula (I) with side chains (i), (ii), (iϋ), (iv), (v), (vi) or (vii). In a further aspect, the piperidine ring in (i), (ii) or (iϋ) may be replaced by pyrrolidinyl or azetidinyl, and/or the N-substituent in (i) or (ii) may be replaced by C3 or larger alkyl or optionally substituted benzyl.

In an alternative aspect, the N-substituent in formula (i) or (ii) may be replaced by (CH2)_nR^, as defined in formula(I) and in relation to the specific examples of EP-A-501322.

The pharmaceutically acceptable salts of the compounds of the formula (I) include acid addition salts with conventional acids such as hydrochloric, hydrobromic, boric, phosphoric, sulphuric acids and pharmaceutically acceptable organic acids such as acetic, tartaric, maleic, citric, succinic, benzoic, ascorbic, methanesulphonic, α-keto glutaric, α-glycerophosphoric, and glucose-1-phosphoric acids.

Examples of pharmaceutically acceptable salts include quaternary derivatives of the compounds of formula (I) such as the compounds quatemised by compounds Rχ-T wherein Rx is Cχ.g alkyl, phenyl-Cχ_g alkyl or C5.7 cycloalkyl, and T is a radical corresponding to an anion of an acid. Suitable examples of Rx include methyl, ethyl and n- and iso-propyl; and benzyl and phenethyl. Suitable examples of T include halide such as chloride, bromide and iodide.

Examples of pharmaceutically acceptable salts also include internal salts such as N-oxides.

The compounds of the formula (I), their pharmaceutically acceptable salts, (including quaternary derivatives and N-oxides) may also form pharmaceutically acceptable solvates, such as hydrates, which are included wherever a compound of formula (I) or a salt thereof is herein referred to.

It will also be reahsed that the (CH2)n moiety in compounds of formula (I) wherein Z is (b), may adopt an α or β or configuration with respect to the fused azabicyclic moiety. The compounds of formula (I) are prepared by conventional coupling of the indolizine moiety with Z. Suitable methods are as described in GB

2125398A (Sandoz Limited), GB 1593146A, EP-A-36269 and EP-A-289170

(Beecham Group p.l.c. When CO-Y is replaced by a heterocyclic bioisostere, suitable methods are described in EP-A-328200 (Merck Sharp

& Dohme Limited). Reference is also made to EP-A-501322 (Glaxo Group

Limited).

Azabicyclic side chain intermediates are known compounds or may be prepared from the ketones of formula (II):

(ID according to conventional methods.

The compounds of the present invention are 5-HT4 receptor antagonists and it is thus believed may generally be used in the treatment or prophylaxis of gastrointestinal disorders, cardiovascular disorders and CNS disorders.

They are of potential interest in the treatment of irritable bowel syndrome (IBS), in particular the diarrhoea aspects of IBS, i.e., these compounds block the ability of 5-HT to stimulate gut motility via activation of enteric neurones. In animal models of IBS, this can be conveniently measured as a reduction of the rate of defaecation. They are also of potential use in the treatment of urinary incontinence which is often associated with IBS.

They may also be of potential use in other gastrointestinal disorders, such as those associated with upper gut motility, and as antiemetics. In particular, they are of potential use in the treatment of the nausea and gastric symptoms of gastro-oesophageal reflux disease and dyspepsia. Antiemetic activity is determined in known animal models of cytotoxic-agent radiation induced emesis.

Specific cardiac 5-HT4 receptor antagonists which prevent atrial fibrillation and other atrial arrhythmias associated with 5-HT, would also be expected to reduce occurrence of stroke (see A.J. Kaumann 1990,

Naumyn-Schmiedeberg's Arch. Pharmacol. 342, 619-622, for appropriate animal test method).

It is beHeved that platelet-derived 5-HT induces atrial arrhythmias which encourage atrial fibrillation and atrial disorders are associated with symptomatic cerebral and sytemic embolism. Cerebral embolism is the most common cause of ischaemic stroke and the heart the most common source of embolic material. Of particular concern is the frequency of embolism associated with atrial fibrillation.

Anxiolytic activity is likely to be effected via the hippocampus (Dumuis et al 1988, Mol Pharmacol., 34, 880-887). Activity may be demonstrated in standard animal models, the social interaction test and the X-maze test.

Migraine sufferers often undergo situations of anxiety and emotional stress that precede the appearance of headache (Sachs, 1985, Migraine, Pan Books, London). It has also been observed that during and within 48 hours of a migraine attack, cyclic AMP levels are considerably increased in the cerebrospinal fluid (Welch et al., 1976, Headache 16, 160-167). It is believed that a migraine, including the prodomal phase and the associated increased levels of cyclic AMP are related to stimulation of 5-HT4 receptors, and hence that administration of a 5-HT4 antagonist is of potential benefit in relieving a migraine attack.

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

Such compositions are prepared by admixture and are usually adapted for enteral such as oral, nasal or rectal, or parenteral administration, and as such may be in the form of tablets, capsules, oral liquid preparations, powders, granules, lozenges, reconstitutable powders, nasal sprays, suppositories, injectable and infusable solutions or suspensions. Sublingual or transdermal administration is also envisaged. Orally administrable compositions are preferred, since they are more convenient for general use. Tablets and capsules for oral administration are usually presented in a unit dose, and contain conventional excipients such as binding agents, fillers, diluents, tabletting agents, lubricants, disintegrants, colourants, flavourings, and wetting agents. The tablets may be coated according to well known methods in the art, for example with an enteric coating.

Suitable fillers for use include cellulose, mannitol, lactose and other similar agents. Suitable disintegrants include starch, polyvinylpolypyrrolidone and starch derivatives such as sodium starch glycollate. Suitable lubricants include, for example, magnesium stearate.

Suitable pharmaceutically acceptable wetting agents include sodium lauryl sulphate. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups, or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, gelatin, hydroxyethylcellulose, carboxymethylcellulose, aluminium stearate gel or h drogenated edible fats, emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example, almond oil, fractionated coconut oil, oily esters such as esters of glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents.

Oral liquid preparations are usually in the form of aqueous or oily suspensions, solutions, emulsions, syrups, or elixirs or are presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles (which may include edible oils), preservatives, and flavouring or colouring agents.

The oral compositions may be prepared by conventional methods of blending, filling or tabletting. Repeated blending operations may be used to distribute the active agent throughout those compositions employing large quantities of fillers. Such operations are, of course, conventional in the art. For parenteral administration, fluid unit dose forms are prepared containing a compound of the present invention and a sterile vehicle. The compound, depending on the vehicle and the concentration, can be either suspended or dissolved. Parenteral solutions are normally prepared by dissolving the compound in a vehicle and filter sterilising before filling into a suitable vial or ampoule and sealing. Advantageously, adjuvants such as a local anaesthetic, preservatives and buffering agents are also dissolved in the vehicle. To enhance the stability, the composition can be frozen after filling into the vial and the water removed under vacuum.

Parenteral suspensions are prepared in substantially the same manner except that the compound is suspended in the vehicle instead of being dissolved and sterilised by exposure of ethylene oxide before suspending in the sterile vehicle. Advantageously, a surfactant or wetting agent is included in the composition to facilitate uniform distribution of the compound of the invention.

The invention further provides a method of treatment of irritable bowel syndrome, gastro-oesophagal reflux disease, dyspepsia, atrial arrhythmias and stroke, anxiety and/or migraine in mammals, such as humans, which comprises the administration of an effective amount of a compound of the formula (I) or a pharmaceutically acceptable salt thereof. In particular, the method comprises treatment of IBS or atrial arrhythmias and stroke.

An amount effective to treat the disorders hereinbefore described depends on the relative efficacies of the compounds of the invention, the nature and severity of the disorder being treated and the weight of the mammal. However, a unit dose for a 70 kg adult will normally contain 0.05 to 1000 mg for example 0.5 to 500 mg, of the compound of the invention. Unit doses maybe administered once or more than once a day, for example, 2, 3 or 4 times a day, more usually 1 to 3 times a day, that is in the range of approximately 0.0001 to 50 mg/kg/day, more usually 0.0002 to 25 mg/kg/day.

No adverse toxicological effects are indicated within the aforementioned dosage ranges. The invention also provides a compound of formula (I) or a pharmaceutically acceptable salt thereof for use as an active therapeutic substance, in particular for use in the treatment of irritable bowel syndrome, gastro-oesophagal reflux disease, dyspepsia, atrial arrhythmias and stroke, anxiety and/or migraine, in particular IBS or atrial arrhythmias and stroke.

The invention also provides the use of a compound of formula (I) in the manufacture of a medicament for use as a 5-HT4 receptor antagonist in the treatment of irritable bowel syndrome, gastro-oesophagal reflux disease, dyspepsia, atrial arrhythmias and stroke, anxiety and/or migraine, in particular, IBS or atrial arrhythmias and stroke.

The following Examples illustrate the preparation of compounds of formula (I); the following Descriptions illustrate the preparation of intermediates.

■12-

E4 Me N CH CH O (i)

E5 H N CH C-OCH3 O (i)

E6 Et C-H N C-H O Cvi)

E7 Et C-H N C-H ox -CH₂ - (hi)

E8 Et C-H N C-H O (i)

E9 N C-H C-OCH3 O ⁽iii)

E10 H N C-H C-OCH3 O

Ell Et N C-H C-OCH3 O

E12 Et N C-H C-OCH3 O

ox = wherein CO-Y is replaced by 5,3 substituted 1,2,4-oxadiazole Example 1

l-(l-Butyl-4-piperidyl)methyl-3- ethylimidazo(l,5-a)pyridinecarboxylate (El)

A solution of 3-ethylimidazo(l,5-a)pyridine-l-carboxyhc acid (326 mg, 0.0017 mole) in acetonitrile (20 ml) was treated with bis- carbonyldiimidazole (275 mg, 0.0017 mole) and the mixture was stirred at room temperature for one and a half hours. The solvent was removed in υacuo to leave the crude imidazolide.

A solution of l-butyl-4-piperidinemethanol (290 mg, 0.0017 mole) in dry THF (10 ml) was cooled in an ice bath. n-Butyllithium (1.06 ml of a 1.6M solution in hexane) was added dropwise and the resulting solution was stirred at 0°C for 15 minutes.

The imidazolide was dissolved in dry THF (20 ml) and the resulting solution added dropwise to the solution of the lithium alkoxide at 0°C. The reaction mixture was allowed to warm to room temperature and was stirred for 3 hours. The solvent was removed in υacuo and the residue was partitioned between EtOAc and H2O. The EtOAc layer was separated, washed several times with H2O, dried and concentrated to give a pale yellow gum.

lH NMR (250 MHz)) CDCI3

δ: 8.12 (d, 1H), 7.88 (d, 1H), 7.10 (dt, 1H), 6.8 (dt, 1H), 4.29 (d, 2H), 2.90- 3.10 (m, 4H), 2.3-2.41 (m, 2H), 1.20-2.10 (m, 14H), 0.90 (t, 3H).

Example 2

l-(2-(l-Piperidyl))ethyl-3- trifluoromethylimidazo(l,5-a)pyridinecarboxylate (E2)

The title compound was prepared from 3-trifluoromethyl- imidazo(l,5-a)pyridine-l-carboxylic acid and l-(2-hydroxyethyl)piperidine by the method described for Example 1. The product was isolated as the hydrochloride salt, mp 213-14°C.

!H NMR (250 MHz) CDCI3 (free base)

δ: 8.40 (d, IH), 8.22 (d, IH), 7.32 (dt, IH), 7.03 (dt, IH), 4.55 (t, 2H), 2.70 (t, 2H), 2.5 (bt, 4H), 1.40-1.68 (m, 6H).

Example 3

3-EthyI-l-(2-(l-piperidyI))ethylindolizine carboxylate (E3)

The title compound was prepared from 3-ethyhndohzinecarboxy-ic acid and l-(2-hydroxyethyl)piperidine by the method described for Example 1. The product was isolated as the hydrochloride salt, mp 198-9°C.

!H NMR (250 MHz) CDCI3 (free base)

δ: 8.20 (d, IH), 7.72 (d, IH), 7.02 (dt, 2H), 6.75 (dt, IH), 4.45 (t, 2H), 2.50- 2.85 (m, 8H), 1.35-1.68 (m, 9H).

Example 4

3-(l-Butyl-4-piperidylnιethyl)-l-m.ethylindoliziιι-3-ylcarboxylate hydrochloride (E4)

To l-methylindoHzine-3-carbonyl chloride (Dl) (250 mg) in dry dichloromethane (20 ml) was added dropwise, a mixture of N- Butylpiperidin-4-ylmethanol (220 mg) and triethylamine (0.2 ml) in dry dichloromethane (20 ml). The reaction mixture was stirred at ambient temperature overnight, and then washed with water. The organic phase was dried (Na2Sθ4), the solvent was evaporated under reduced pressure and the residue passes through a short silica (flash) column, eluting with methanol/chloroform (1%, 2%). The product was isolated as the hydrochloride salt, from iso-propylalcohol and diethylether to give the title compound (80 mg, 21%) mp 183-5°C. iH NMR ^DCls) 250 MHz (free base)

δ: 9.36 (d, IH), 7.42 (d, IH), 7.35 (s, IH), 6.98 (t, IH), 6.78 (t, IH), 4.18 (d, 2H), 3.05 (br d, 2H), 2.5-2.28 (m, 5H), 2.05 (t, 2H), 1.95-1.7 (m, 3H), 1.68- 1.43 (m, 4H), 1.43-1.2 (m, 2H), 0.94 (t, 3H).

Example 5

3-(l-Butyl-4-piperidylmethyl)-2-methoxyindolizin-3-ylcarboxylate hydrochloride (E5)

Following the procedure outlined in Example 1, 2-methoxyindolizine-3- carbonyl chloride (D2) (250 mg) was converted to the title compound (140 mg, 31%). mp 205-7°C.

*H NMR (CDC1₃) 250 MHz (free-base)

δ: 9.40, (d, IH), 7.32 (d, IH), 7.02 (t, IH), 6.75 (t, IH), 6.05 (s, IH), 4.21 (s, IH), 3.95 (s, 3H), 3.00 (br d, 2H), 2.4-2.3 (m, 2H), 2.05-1.7 (m, 5H), 1.6-1.2 (m, 6H), 0.92 (t, 3H).

Example 6

l-(eqr-Quinolizidin-2-yl)methyl-3-ethylindolizine-l-carboxylate (E6)

eg-2-Hydroxymethylquinolizidine (N.J. Leonard et al, J. Org. Chem., 1957, 22, 1445) was reacted with the imidazolide of 3-ethylindolizine-l- carboxyhc acid (F.D. King et al, J. Med. Chem., 1990, 33, 1924) using the method of Example 1. The product was chromatographed on silica gel eluting with ethyl acetate to afford the title compound as a colourless oil. This was converted to its hydrochloride salt mp 181-182°C (acetone/ether).

H NMR (HC1 salt) (d⁶DMSO)

δ: 10.45 (br.s,lH), 8.26 (d,lH), 8.06 (d,lH), 7.21 (dd,lH), 7.00 (s,lH), 6.92 (dd,lH), 4.10 (d,2H), 3.23-3.43 (m,2H), 2.83 (q,2H), 2.74-3.15 (m,3H),

2.00-2.15 (m,lH), 1.35-1.95 (m,8H), 1.30 (t,3H).

MS (El) M+ 340.

Example 7

5-(3-(Piperidino)propyl)-3-(3-ethylindoliz-l-yl)-l^,4-oxadiazole (E7)

3-EthylindoHzine-l-carboxamide oxime was dissolved in dry THF (8 ml) and treated with ground 4A° molecular sieves (lg). The mixture was stirred at room temperature for ¥&., sodium hydride (80% disp in mineral oil) (0.049g, 1.62 mmol) was then added and the mixture heated to reflux. After Sh, ethyl 4-piperidinobutyrate in dry THF (3 ml) was added. Reflux was then continued for a further 1.5h. The reaction mixture was then allowed to cool and was filtered. The filter pad was then washed with THF (~15 ml), and the filtrate was evaporated under reduced pressure to give a brown oil. The oil was purified by silica-gel chromatography using Pentane : EtOAc 3:2 - 1:1 as eluant to give the title compound (0.165g, 32%) as a colourless oil, which was converted to the hydrochloride salt, mp 168-169⁰C (HC1 salt)

lH NMR (270 MHz, CDC1₃) (HC1 salt)

δ: 12.35 br (s, IH), 8.18 (d, IH), 7.82 (d, IH), 7.12 (s, IH), 6.98 (t, IH), 6.72 (t, IH), 3.58 (m, 2H), 2.98-3.20 (m, 4H), 2.82 (q, 2H), 2.43-2.75 (m, 4H), 2.14-2.44 (m, 2H), 1.69-2.03 (m, 4H), 1.42 (t, 3H).

Example 8

l-(l-Butyl-4-piperidyl)methyl-3-ethylindolizine-l-carboxylate (E8)

The title compound was prepared from 3-ethyhndoHzinecarboxylic acid (F.D. King et al, J. Med. Chem., 1990, 33, 1924) and l-butyl-4- hydroxymethylpiperidine using the method described in Example 1. The product was converted to its hydrochloride salt mp 198-200°C (acetone).

*H NMR (HC1 salt) (d^βDMSO)

δ: 10.45 (br.s,lH), 8.25 (d,lH), 8.07 (d,lH), 7.19 (dd,lH), 7.00 (s,lH), 6.88- 6.96 (m,lH), 4.11 (d,2H), 3.43-3.52 (m,2H), 2.80-3.05 (m,6H), 1.60-2.10 (m,7H), 1.30 (t,3H), 1.20-1.40 (m,2H), 0.90 (t,3H).

MS (CI) MH+ 343.

Example 9

3- ( 1-Piperidyl)ethyl- l-iodo-2-methoxyindolizin-3-ylcarboxylate oxalate (E9)

A solution of (l-piperidylethyl)-2-methoxyindolizin-3-yl carboxylate (0.45g) in glacial acetic acid (10 mL) was stirred with N-iodosuccinimide (0.36g) overnight at room temperature. The HOAc was removed by rotary evaporation and the residue treated with NaHC03 solution to basic and the product extracted into EtOAc (2x50mL). The combined organic extracts were dried (K2CO3), separated and concentrated. The residue was purified by column chromatography on silica, eluting with CHCI3 to give the title compound free base (0.33g). Treatment in MeOH with 1 equivalent of oxalic acid, and precipitation with Et2θ afforded the title compound (280 mg).

mp 143- 144⁰C

NMR (d^-DMSO) 250 MHz

δ: 9.32(d,lH), 7.48(d,lH), 7.32(t,lH), 7.05(t,lH), 4.60(brs, 2H), 3.92(s,3H), 3.47(brs,2H), 3.16(brs, 4H), 1.80-1.65(m,4H), 1.60-1.45(m,2H) Example 10

1-Piperidylethyl 2-methoxyindolizidin-3-ylcarboxylate oxalate

(E10)

The title compound was prepared in an analogous manner to the compound of Example 9, mp 120-130°C

NMR (d6-DMSO) 250 MHz

δ: 9.32(d,lH), 7.55(d,lH), 7.20(t,lH), 6.94(t,lH), 6.32(s,lH), 4.55(brs,2H), 3.90(s,3H), 3.38(brs, 2H), 3.25(brs, 4H), 1.85-1.65(m,4H), 1.60-1.42(m,2H).

Example 11

3-(l-Butyl-4-piperidyl)methyl-l-ethyl-2- methoxyindolizinylcarboxylate hydrochloride (Ell)

The title compound was prepared in an analogous manner to the compound of Example 4 from l-ethyl-2-methoxyindolizine-3- carbonylchloride (D4), mp 176-8°C

iHNMR (CDCI3) 250 MHz (free base)

δ: 9.4 (d, IH), 7.39 (d, IH), 7.0 (t, IH), 4.22 (d, 2H), 3.95 (s, 3H), 2.99 (brd, 2H), 2.72 (q,2H), 2.4-2.27 (m, 2H), 2.05-1.7 (m, 5H), 1.6-1.15 (m, 9H), 0.92 (t, 3H).

Example 12

(l-Ethyl-2-methoxy-3-(2-(l-piperidyl)ethylindolizine carboxylate hydrochloride (E12)

The title compound was prepared in an analogous manner to Example 11, mp 168-90°C iHNMR (CDCI3) 250 MHz (free base)

δ: 9.42 (d, IH), 7.38 (d, IH), 7.0 (t, IH) 6.75 (t, IH) 4.50 (t, IH), 3.98 (s, 3H), 2.87 - 2.65 (m, 4H), 2.55 (brs, 4H), 1.7 - 1.35 (m, 6H) 1.24 (t, 3H)

Descriptions

Description 1 (intermediate for Example 4)

a) 4-Dimethylaminobutan-2-one

Following the procedure outlined by E.C. du Feu et al., J.O.C. 1937, 53, a mixture of acetone (30 ml), dimethylamine hydrochloride (15.6g), paraformaldehyde (8.4g) and methanol (5 ml) was converted to the title compound (9.59g, 44%) b.p. 40-42°C, 9.5 mm.

iH NMR CDCls) 250 MHz

δ: 2.65-2.55 (m, 4H), 2.23 (s, 6H), 2.19 (s, 3H).

b) NJ^-Dimethyl-3-hydroxy-3- (2-pyridyl)butylamine

Following the procedure outlined by P.A. Barrett and K.A. Chambers, J.C.S., 338, 1958, 4-dimethylaminobutan-2-one (9.59g) was converted to the title compound (14.69g, 91%).

lH NMR (CDCI3) 250 MHz

δ: 8.55 (d, IH), 7.8-7.6 (m, 2H), 7.18-7.08 (m, IH), 2.3-1.94 (m, 11H), 1.5 (t, 3H).

c) 3-Acetyl-l-methylindolizine

Following the procedure outlined by P.A. Barrett and K.A. Chambers, J.C.S., 338, 1985, N,N-dimethyl-3-hydroxy-3-(2-pyridyl)butylamine (lg) was converted to the title compound (D3) (0.31g, 35%). lH NMR (CDCI3) 250 MHz

δ: 9.84 (d, IH), 7.48 (d, IH), 7.31 (s, IH), 7.11 (t, IH), 6.85 (t, IH), 2.55 (s, 3H), 2.35 (s, 3H).

d) 1-Methylindolizine

Following the procedure outlined by P.A. Barrett and KA. Chambers, J.C.S., 338, 1958, 3-acetyl-l-methylindohzine (3.1g) was converted to the title compound (2.12g, 90%).

lH NMR (CDCI3) 250 MHz

δ: 7.82 (d, IH), 7.29 (d, IH), 7.22 (d, IH), 6.6 (d, IH), 6.56 (t, IH), 6.38 (t, IH), 2.35 (s, 3H).

e) l-Methylindolizine-3-carbonylchloride

iHNMR ODDC ) 250 MHz

δ: 9.26 (d, IH), 7.6-7.48 (m, 2H), 7.28 (t, IH), 6.98 (t, IH), 2.35 (s, 3H).

Description 2 (intermediate for Example 5)

a) 2-Methoxyindolizine

Following the procedure outlined by A.Kakelis et al., J.Org. Chem. 1980, 45, 5100-4, ethyl(2-methylpyridinium-l-acetate) bromide (A. Kakelis et al., ChemXett. 1979, 297) (5g) was converted to the title compound (0.8g, 28%).

iHNMR (CDCI3 (250 MHz)

δ: 7.8 (d, IH), 7.2 (d, IH), 6.98 (s, IH), 6.65 (t, IH), 6.4 (t, IH), 6.06 (s, IH), 3.84 (s, 3H). b) 2-Methoxyindolizine-3-carbonylchloride

Following the procedure outlined by G.Jones and J. Stanyer, J.Chem.Soc (c), 1969, 901, 2-methoxyindohzine (0.8g) was converted to the title compound (D2) (520 mg, 46%).

IH NMR (CHC1₃) (250 MHz)

δ: 9.35 (d, IH), 7.39 (d, IH), 7.27 (t, IH), 6.39 (t, IH), 6.06 (s, IH), 4.0 (s, 3H).

Description 3 (intermediate for Example 7)

a) l-Cyano-3-ethylindolizine

A solution of 2-pyridylacetonitrile (3.12 ml, 0.028 mmol), 2,6, lutidine (3.75 ml, 0.032 mol) and 2-bromobutyraldehyde (J. Riehl, Compt. Rend 1957, 245, 1321-1322) (3.50g, 0.023 mol) in xylene (120 ml) was heated under reflux for 22h, with removal of water using a Dean-Stark apparatus. The reaction mixture was then allowed to cool and the resulting black solution was washed with 10% citric acid (2x), dried (Na2Sθ4) and evaporated to give a black oil. The oil was purified by Siθ2 chromatography using pentane : Et2θ, 2:1, as eluant, to give the title compound (D3) as a pale brown solid (1.18g, 30%).

IH NMR (250 MHz, CDCI3)

δ: 7.88 (d, IH), 7.62 (d, IH), 7.04 (t, IH), 6.80 (m, 2H), 2.80 (q, 2H), 1.40 (t, J=6Hz, 3H).

b) 3-Ethylindolizine-l-carboxamide oxime

Sodium (0.306g, 0.013 mol) was dissolved in methanol (10 ml).

Hydroxylamine hydrochloride (0.924g, 0.013 mol) in methanol (8 ml) was then added dropwsie. The solution was then stirred at room temperature for V_ ι, before being filtered, the filter pad was then washed with methanol (~2 ml). The filtrate was then treated with the nitrile (1.13g,

0.0067 mol) in methanol (5 ml). The mixture was then heated to reflux under N2. After 32h, the reaction mixture was allowed to cool. The material that crystallised out of the reaction mixture was then filtered off, washed with cold methanol and dried in vacuo to yield the title compound

(1.18g, 87%) as a pale yellow solid. m.p. 157-159°C (decomp.)

IH NMR (250 MHz, CD3SOCD3)

δ: 9.10 (s, IH), 8.00 (t, IH), 6.95 (s, IH), 6.78 (t, IH), 6.58 (t, IH), 5.60 (s, 2H), 2.82 (q, 2H), 1.32 (t, 3H).

Description 4

a) l-Ethyl-2-methoxyindolizine

Following the procedure outlined by A. Kakelii et al., J. Org. Chem. 1980, 45. 5100, ethyl (2-propylpyridinium-l-acetate) bromide (A. Kakelii et al. Chem. Lett. 1979, 297) (l)g) was converted to the title compound (2g, 33%)

iHNMR (CDCI3) 250 MHz

δ: 7.75 (d, IH), 7.18 (d, IH), 6.9 (s, IH), 6.59 (t, IH), 6.3 (t, IH), 3.82 (s, 3H), 2.69 (q. 2H), 1.2 (t, 3H)

b) l-Ethyl-2-methoxyindolizine3-carbonylchloride

Following the procedure outlined by Jones and Stanyer, J. Chem. Soc. (C), 1969, 901, l-ethyl-2-methoxyindolizine (2g) was converted to the title compound (D4) (1.65g, 64%)

δ: 9.35 (d, IH), 7.48 (d, IH), 7.28 (t, IH), 6.994 (t, IH), 4.02 (s, 3H), 2.75 (q, 2H), 1.28 (t, 3H). 5-HT4 RECEPTOR ANTAGONIST ACTIVITY

4 5 1) Guinea pig colon

' Male guinea-pigs, weighing 250-400g are used. Longitudinal muscle- myenteric plexus preparations, approximately 3cm long, are obtained from the distal colon region. These are suspended under a 0.5g load in isolated 10 tissue baths containing Krebs solution bubbled with 5% CO2 in O2 and maintained at 37°C. In all experiments, the Krebs solution also contains methiothepin 10"^M and granisetron lO'^M to block effects at 5-HTχ, 5-HT2 and 5-HT3 receptors.

15 After construction of a simple concentration-response curve with 5-HT, using 30s contact times and a lδmin dosing cycle, a concentration of 5-HT is selected so as to obtain a contraction of the muscle approximately 40- 70% maximum (10'^M approx). The tissue is then alternately dosed every lδmin with this concentration of 5-HT and then with an approximately

20 equi-effective concentration of the nicotine receptor stimulant, dimethylphenylpiperazinium (DMPP). After obtaining consistent responses to both 5-HT and DMPP, increasing concentrations of a putative 5-HT4 receptor antagonist are then added to the bathing solution. The effects of this compound are then determined as a percentage reduction of

25 the contractions evoked by 5-HT or by DMPP. From this data, PIC50 values are determined, being defined as the -log concentration of antagonist which reduces the contraction by 50%. A compound which reduces the response to 5-HT but not to DMPP is believed to act as a 5-HT4 receptor antagonist.

30

The compounds of the Examples had a PIC50 value of of 8 or below, E8 having particularly good activity.

2) Piglet Atria

35

Compounds are tested in the piglet spontaneous beating screen (Naunyn- Schmiedeberg's Arch. Pharmacol 342, 619-622). E8 had a pKB of 9.4. 3) Rat oesophagus

Rat oesophageal tunica muscularis mucosae is set up according to Baxter et al. Naunyn-Schmiedeberg's Arch. Pharmacol., 343, 439-446 (1991). The inner smooth muscle tube of the muscularis mucosae is isolated and mounted for isometric tension recording in oxygenated (95% 02/5% CO2) Tyrodes solution at 37°C. All experiments are performed in pargyline pre- treated preparations (lOOmM for 15 min followed by washout) and in the presence of cocaine (30mM). Relaxant responses to 5-HT are obtained after pre-contracting the oesophagus tissue with carbachol (3mM).

4) 5-HT-induced motility in dog gastric pouch

Compounds are tested for inhibition in the in vivo method described in "Stimulation of canine motihty by BRL 24924, a new gastric prokinetic agent", Bermudez et al, J. Gastrointestinal Motility, 1990, 2(4), 281-286.

Claims

Claims

1. A compound of formula (I), or a pharmaceutically acceptable salt thereof

(I)

wherein Rx is hydrogen, halogen, CF3, Cχ.g alkyl, Cχ.g alkoxy, Cχ.g alkylthio, Cχ.g alkylsulphonyl, Cχ.g alkylsulphinyl, Cχ.7 acyl, cyano, Cχ.g alkoxycarbonyl, Cχ.7 acylamino, hydroxy, nitro or amino, aminocarbonyl, or aminosulphonyl, optionally N-substituted by one or two groups selected from Cχ.g alkyl, 03.3 cycloalkyl, and C3.8 cycloalkyl Cχ.4 alkyl or disubstituted by C4 or C5 polymethylene; phenyl or phenyl Cχ.4 alkyl group optionally substituted in the phenyl ring by one or two of halogen, Cχ.g alkoxy or Cχ.g alkyl groups; one of Xx and X2 is N and the other is C; X3 is N or CR wherein R is hydrogen, Cχ.g alkoxy, halo, Cχ.g alkyl or cyano; R_a is hydrogen, halo, Cχ.g alkyl, amino, nitro or Cχ.g alkyl; Rb is hydrogen, halo, Cχ.g alkyl or Cχ.g alkoxy; Y is O or NH; Z is of sub-formula (a), (b) or (c):

(a)

(b)

(0

wherein i is 1, 2, 3 or 4; n² is 0, 1, 2, 3 or 4; n³ is 2, 3, 4 or 5; qis 0, 1, 2 or 3; p is 0, 1 or 2; mis 0, 1 or 2; 5 is hydrogen, Cχ_χ2 alkyl, aralkyl or R5 is (CH^ RlO wherein r is 2 or 3 and Rχo is selected from cyano, hydroxyl, Cχ.g alkoxy, phenoxy, C(0)Cχ.g alkyl, COC₆H₅, -CONRχχRχ₂, NRχχCORχ₂,

Sθ2NRχχRχ2 or NRχχS02Rχ2 wherein Rxx and Rχ2 are hydrogen or Cχ.g alkyl; and Rg, R7 and R3 are independently hydrogen or Cχ.g alkyl; and Rg is hydrogen or Cχ.χo alkyl; or a compound of formula (I) wherein the CO-Y linkage is replaced by a heterocyclic bioisostere; having 5-HT4 receptor antagonist activity.

2. A compound according to claim 1 wherein Rx is CF3 or an ethyl group.

3. A compound according to claim 1 wherein X3 is N, C-H or C-OCH3.

4. A compound according to claim 1 wherein R_a is hydrogen.

5. A compound according to claim 1 wherein fo is hydrogen or halo.

6. A compound according to any one of claims 1 to 5 wherein Y is O or NH.

7. A compound according to any one of claims 1 to 6 wherein Z is of sub-formula (a) and CH2)nl is attached at a carbon atom of the azacycle.

8. A compound according to claim 7 wherein Z is N-substituted 4-piperidylmethyl.

9. A compound according to claim 8 wherein the N-substituent is C2 or greater alkyl, or optionally substituted benzyl.

10. A compound according to claim 1 selected from the compounds El to E12 inclusive, as described herein, including pharmaceutically acceptable salts thereof.

11. A process for preparing the ester or amide compounds according to claim 6, which comprises reacting an appropriate benzoic acid derivative with an appropriate alcohol or amine.

12. A pharmaceutical composition comprising a compound according to any one of claims 1 to 10, and a pharmaceutically acceptable carrier.

13. A compound according to claim 1 for use as an active therapeutic substance.

14. The use of a compound according to claim 1 in the manufacture of a medicament for use as a 5-HT4 receptor antagonist.

15. The use according to claim 14 for use as a 5-HT4 antagonist in the treatment or prophylaxis of gastrointestinal disorders, cardiovascular disorders and CNS disorders.

16. The use according to claim 15 for use in the treatment of IBS.

17. The use according to claim 16 for use in the treatment of atrial arrhythmias and stroke.

18. A method of treatment of IBS in mammals which comprises the administration of an effective amount of a compound according to claim 1.

19. A method of treatment of atrial arrhythmias and stroke in mammals which comprises the administration of an effective amount of a compound according to claim 1.