WO1992000978A1

WO1992000978A1 - Imidazopyridine paf antagonists

Info

Publication number: WO1992000978A1
Application number: PCT/EP1991/001256
Authority: WO
Inventors: Kelvin Cooper; Michael Jonathan Fray; John Steele
Original assignee: Pfizer Limited; Pfizer Inc.
Priority date: 1990-07-13
Filing date: 1991-07-04
Publication date: 1992-01-23
Also published as: GB9015524D0; EP0539418A1; CA2083056A1; IE912432A1; PT98285A; FI930108A; FI930108A0; JPH05507932A

Abstract

Compounds of formula (I), wherein R?1, R2 and R3¿ are each H or methyl, R4 is hydrogen, halo, C¿1?-C4 alkyl, or C1-C4 alkoxy and n is an integer of from 1 to 3 are PAF antagonists of utility in the treatment of allergic and inflammatory conditions.

Description

Imidazopyridine PAF Antagonists

This invention relates to imidazopyridine, specifically to certain 4-substituted-1-(2-methaylinidazo[4,5-c]pyrid-1-yl)-benzene derivatives. The compounds are potent and selective antagonists of platelet activating factor having clinical utility in the treatmant of allergic and inflammatory conditions in humans and animals.

Platelet activating factor (PAF, 1-0-alkyl-2-acetyl-snglyceryl-3-phosphorylcholine) is an ether phopholipid whose structure was first elucidated in 1979. It is produced by, released frαn and interacts with many pro-inflamaatory cells, platelets and the kidney. In addition to potent platelet aggregating activity, PAF exhibits a wide spectrum of biological activities elicited either directly or via ths release of othsr powerful mediators such as thromboxane A₂ or the leukotrienes, which make PAF inhibitors of potential value in the treatment of a variety of conditions including allergic, inflammatory and hypersecretory conditions such as asthma, arthritis, rhinitis, bronchitis and urticaria, the treatment of circulatory shock, gastric ulceration, psoriasis and cardiovascular conditions, including angina, thrombosis and stroke.

In our European patent application no 0258033 we disclose a series of 2-substituted 1,4-dihydropyridine derivatives as PAF antagonists. In our later European patent application no 0310386 we disclose a further series of dihydropyridirie PAF antagonistswherein the 2-position substituent includes in particular a

2-methyl-imidazo[4,5-c]pyrid-1-yl-phenyl group. The present invention provides further PAF antagonists having the formula:

and their pharmaceutically acceptable salts, wherein R¹, R² and

R³ are each H or methyl, R⁴ is hydrogen, halo, C₁-C₄ alkyl or

C₁-C₄ alkoxy and n is an integer of from 1 to 3.

In the above definition, the term halo means fluoro, chloro, bromo or iodo. Alkyl and alkoxy groups of 3 or more carbon atoms may be straight or branched-chain.

In preferred embodiments of the invention R¹, R² and R³ are

H, R⁴ is preferably chlorine and n is 1 or 2.

When R⁴ is a branched alkyl or alkoxy group having 4 carbon atoms, the compounds of the formula (I) may contain at least one asymmetric centre and exist as a pair of enantiomers. Such isomers may be separable by physical methods, e.g. by fractional crystallisation or chromatography of the parent compounds or of a suitable salt or derivatives thereof. The invention includes all the enantiomers whether separated or not.

The pharmaceutically acceptable acid addition salts of the compounds of the formula (I) which form such salts are those farmed from acids which form non-toxic acid addition salts, for example the hydrochloride, hydrobronide, sulphate or bisulphate, phosphate or acid phosphate, acetate, citrate, fumerate,

gluconate, lactate, maleate, succinate and tartrate salts.

The compound of formula I may be obtained by cyclisation of a compound of the formula:

wherein R¹, R², R³, R⁴ and n are as previously defined.

In a typical procedure the compound of formula II is simply heated in a high-boiling organic solvent (for example toluene or xylene) at a temperature above 100°C for a period of several hours. The solvent is evaporated and the product recovered and purified by conventional procedures. The intermediates of formula II are prepared by reaction of an amine of formula-:

with a benzoic acid or anhydride derivative of formula-:

This reaction is achieved by either reacting the anhydride with the amine (III) in water or an aqueous organic solvent in the presence of a base (e.g. sodiτxn carbonate), or by reacting the benzoic acid with the amine using a diimide coupling reagent such as 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

Appropriate reagents and conditions for these steps may be readily established by reference to standard text books and to the examples provided hereafter.

The activity of the compounds of the invention is shown by their ability to inhibit the platelet aggregating activity of PAF in vitro. Testing is performed as follows:

Blood samples are taken from either rabbit or man into 0.1 vol disodium ethylenediamine tetraacetic acid buffer and the saπples centrifuged for 15 minutes to obtain platelet rich plasma. The plasma is further centrifuged to give a platelet pellet which is washed with a buffer solution (4 mM KH₂PO₄, 6mM Na₂HPO₄, 100 mM NaCl, 0.1% glucose and 0.1% bovine serum albumin, pH 7.25) and finally resuspended in buffer solution to a concentration of 2 ×

10⁸ platelets/ml. A sample (0.5 ml) is pre-incubated with stirring for two minutes at 37ºC in a Paton aggregometer, either with vehicle alone, or with vehicle containing the particular compound under test. PAF is added at a sufficient concentration to give a maximum aggregating response in the absence of test coπpound (10^-8 to 10^-9 molar), and the platelet aggregation is measured by following the increase in light transmission of the solution. The experiment is repeated in the presence of test compound at a range of concentrations and the concentration of compound required to reduce the response to 50% of its maximm value in recorded as the IC₅₀ value.

The activity of the compounds of formula (I) is also demonstrated in vivo by their ability to protect mice from the lethal effect of an injection of PAF. A mixture of PAF (50μg/kg) and DL-propranolol (5 mg/kg) in 0.9% w/v sodium chloride is injected (0.2 ml) via a tail vein into mice. The compounds under test are either injected into the tail vein immediately prior to the PAF/propranolol injection or administered orally by gavage two hours earlier. The compounds are tested at several doses in groups of 5 mice and the dose which reduces mortality to 50% is recorded as the PD₅₀ value. For therapeutic use the compounds of the formula (I) will generally be administered in admixture with a pharmaceutical carrier selected with regard to the intended route of

administration and standard pharmaceutical practice. For example, they may be administered orally in the form of tablets containing such excipients as starch or lactose, or in capsules or ovules either alone or in admixture with excipients, or in the form of elixirs or suspensions containing flavouring or colouring agents. They may be injected parenterally, far example, intravenously, intramuscularly or subcutaneously. For parenteral administration, they are best used in the form of a sterile aqueouu solution which may contain other substances, for example, enough salts or glucose to make the solution isotonic with blood.

For administration to man in the curative or prophylactic treatment of allergic bronchial conditions and arthritis, oral dosages of the compounds will generally be in the range of from 2-1000 mg daily for an average adult patient (70 kg). Thus for a typical adult patient, individual tablets or capsules will contain from 1 to 500 mg of active compound, in a suitable

pharmaceutically acceptable vehicle or carrier. Dosages for intravenous administration would typically be within the range 1 to 10 mg per single dose as required. For the treatment of allergic and bronchial, hyper-reactive conditions, inhalation via a nebuliser or aerosol may be the preferred route of drug

administration. Dose levels by this route would be within the range 0.1 to 50 mg per single dose as required. In practice the physician will determine the actual dosage which will be most suitable for an individual patient and it will vary with the age. weight and response of the particular patient. The above dosages are exemplary of the average case but there can, of course, be individual instances where higher or lower dosage ranges are merited, and such are within the scope of this invention.

Thus in a further aspect the invention provides a

pharmaceutical composition comprising a compound of the formula (I), or a pharmaceutically acceptable salt thereof, together with a pharmaceutically acceptable diluent or carrier.

The invention also includes a compound of the formula (I), or a pharmaceutically acceptable salt thereof, for use in medicine, in particular in the treatment of allergic, inflammatory and hypersecretory conditions in a human being.

The preparation of the intermediates of formula (II) and the compounds of formula (I) will now be more particularly illustrated by reference to the following experimental Examples. The purity of compounds was routinely monitored by thin layer chromatography using Merck Kieselgel 60 F₂₅₄ plates. ¹H-Nuclear magnetic reasonance spectra were recorded using either a Nicolet QE-300 or a Bruker AC-300 spectrometer and were in all cases consistent with the proposed structures. Chemical shifts are given in parts-perntillion downfield from tetramethylsilane using conventional abbreviations for designation of major peaks: s, singlet; d, doublet; t, triplet; m, multiplet and br, broad. EXAMPLE 1

7-Chloro-3,4-dihydro-2-[4'-(2-methylimidazo[4,5-c]pyrid-1-yl)- phenyl]-5H-1,4-benzodiazepin-5-one

a) 4-Chloroisatoic anhydride (0.32 g, 1.6 mmol) was added to a solution of 2-amino-4'-(2-methylimidazo[4,5-c]pryrid-1-yl)-acetophenone (0.57 g, 1.45 mmol) in water (6 ml). After stirring to uniform consistency, a solution of sodium carbonate (0.19 g, 1.8 mmol) was added. After 1 hour, dichloromethane (12 ml) was added and two phase stirring was resulted for 66 hours. The mixture was partitioned between saturated aqueous sodium hydrogen carbonate and dichloronethane. The organic phase was separated, dried (MgSO₄) and evaporated to an amorphous solid. Flash chromatography on silica, eluting with 15 then 25% methanol in ethyl acetate afforded 2-amino-5-chloro-N-{2-[4-(2-methylimidazo- [4,5-c]pyrid-1-yl)phenyl]-2-oxoethyl}benzamide as a solid (0.14 g, 23%), m.p. H6-118°C. ¹ H NMR (CD₃SOCD₃): 2.52(3H,s), 4.79(2H,d,J 5.4Hz), 6.58hr exch (2H,s), 6.76(1H,d,J 8.9Hz), 7.21(1H,dd,J 8.9,2.2Hz), 7.28(1H,d,J 5.4Hz), 7.67(1H,d,J 2.2Hz), 7.82 and 8.28 (each 2H,d,J 8.4Hz), 8.35(1H,d,J 5.5Hz), 8.85 hr exch (1H,t,J 5.4Hz) and 8.94(1H,s).

b) A suspension of the benzamide from part (a) (0.11 g, 0.26 mmol) in xylene (5 ml, containing 2-3 drops ethanol to aid solubility) was heated to 140ºC for 5 hours. The solvent was evaporated and the residue purified by flash chromatography on silica, eluting with 10 then 20% methanol in ethyl acetate to afford the title product as a pale-yellow amorphous solid (0.041 g, 40%), m.p. 225-227°C. Found: C,63.52; H,4.14; N,16.61.

C₂₂H₁₆ClN₅O, 0.75 H₂O requires C,63.62; H,4.25; N,16.86%. EXAMPLE 2

7,8-Dichloro-3,4-dihydro-2-[4'-(2-methylimidazo[4,5-c]pyrid-c-yl)-phenyl]-5H-1,4-benzodiazepin-5-one

a) The procedure of Exanple 1 part (a) was followed but starting with 4,5-dichloroisatoic anhydride to yield 2-amino-4,5-dichloroN-{2-[4-(2-methylimidazo[4,5-c]pyrid-a-yl)phenyl]-2-oxoethyl}-benzamide.

1H NMR (CDCl₃): 2.63(3H,s), 5.00(2H,d,J 4.2Hz) , 5.69br exch. (2H,s), 6.83(1H,s), 7.18(2H,m), 7.62(3H,m), 8.33(2H,d,J 8.4Hz), 8.42(1H,d,J 5.5Hz), 9.11(1H,s).

b) The above product was cyclised following the procedure of Exanple 1(b) to give the title product in 58% yield, m.p.

174-177°C. Found: C,58.08; H,3.41; N,14.94. C₂₂H₁₅Cl₂N₅O .H₂O requires C,58.16; H,3.77; N,15.40%.

EXAMPLE 3

7,9-Dichloro-3,4-dihydro-2-[4'-(2-methylimidazo[4,5-c]pyrid-c-yl)-phenyl]-5H-1,4-benzodiazepin-5-one

a) A solution of 2-amino-4'-(2-methylimidazo[4,5-c]pyrid-1-yl)-acetophencaie hydrochloride (0.7 g, 1.8 mmol), 3,5-dichloro-2-amdnobenzoic acid (0.48 g, 2.3 mmol), N-hydroxybenzotriazole (0.34 g, 2.4 nmol), HHaethylmorphnline (1.61 ml, 16 mmol) and 1-(3-dimethylaminopropyl)-3-ethylcarhodiimide hydrochloride (0.89 g, 4.7 πmole) in dichloromethane (25 ml) was stirred at 25ºC for 3 hours. All volatiles were evaporated and the residue was partitioned between ethyl acetate and water buffered to pH 5. The organic layer was separated, dried (MgSO₄) and evaporated. Flash chromatography of the residue on silica, eluting with 10% methanol in ethyl acetate afforded 2-amino-3,5-dichloro-N-{2-[4 -(2-methylimidazo[4,5-c]pyrid-1-yl)phenyl]-2-oxoethyl}benzamide as a pale-yellow gum (0.21 g, 26%). ¹H NMR (CDCl₃): 2.62(3H,s), 4.98(2H,d,J 5.7Hz), 6.10 br exch. (3H,m), 7.13(1H,d,J 5.7Hz), 7.39(1H,d,J 2Hz), 7.48(1H,d,J 2Hz), 7.57 and 8.30 (each 2H,d,J 8.4Hz), 8.43(1H,d,J 5.7Hz) and 9.07(1H,s).

b) p-Toluenesulphonic acid hydrate (0.1 g, 0.5 nmol) was added to a refluxing solution of the ketoamine from part (a) (0.21 g, 0.47 nmol) in dichloromethane (14 ml). After 6 hours, the mixture was partitioned between dichloromethane and saturated aqueous sodium hydrogen carbonate. The organic layer was dried (MgSO₄) and evaporated to a yellow foam. Flash chromatography on silica, eluting with 5% methanol in ethyl acetate afforded the title product as an off white solid (0.065 g, 33%), m.p. 165-7°C.

Found: C,58.92; H,3.85; N,14.57. C₂₂H₁₅Cl₂N₅O, 0.5 H₂O, 0.5 EtOAc requires C,58.91; H,4.12; N,14.31%.

PREPARATION

2-Amino-4'-(2-methylimidazo[4.5-c]pyrid-1-yl) acetophenone hydrochloride

(a) 4-(4-Acetylphenyl)amino-3-nitropyridive hydrochloride

A solution of 4-chlaro-3-nitropyridine hydrochloride (9.75 g, 50 nmol) in ethanol (40 ml) was added to a slurry of p-aminoacetophenone (6.76 g, 50 nmol) in ethanol (25 ml), and the mixture was stirred at room temperature overnight. The mixture was chilled in ice, and the yellow solid filtered off and dried (10.1 g, 69%). m.p. 197-200°C.

(b) 4-(4-Acetylphenyl)amino-3-aminopyridine

4-(4-acetylphenyl) nitropyridine hydrochloride (2.0 g,

78.8 nmol) was partitioned between aqueous sodium hydroxide and dichloromethane ( 3 × 20 ml). The combined organic phases were washed with water (20 ml) and concentrated under reduced pressure to give a solid. Ethanol (20 ml) was added, and the solution was hydrogenated over 5% palladitm on carbon (0.2 g) at 50 p.s.i. (3.4 bar) for 3.5 hours. The catalyst was filtered off, and the solvent removed under reduced pressure to give a brown solid, (1.8 g, ca 100%) which was used directly for the next stage without purification.

(c) 4-2-(Methyl_imidazo[4,5-clpyrid-1-yl)acetophenone

A solution of 4-(4-acetylphenyl)amino-3-aminopyridine (68.0 g, 0.3 nmol) in acetic acid (204 ml) and acetic anhydride (204 ml) was heated at 95ºC for 1.5 hours then cooled and concentrated under reduced pressure. The residue was dissolved in water (500 ml) and rendered basic by the addition of saturated aqueous aπmonia. The product was filtered off, washed with water (2 × 100 ml) and dried under vacuum to give the title compound, (61.0 g, 81%) as a brown solid, m.p. 155-156°C (from water).

(d) Ethyl 4'-(2-methylimidazo[4,5-c]pyrid-1-yl)benzoylacetate A solution of 4-(2-methylimidazo[4,5-c]pyrid--1-yl-acetophenone (17.5 g, 69.7 nmol) in dry tetxahydrofuran (175 ml) was added to a slurry of sodium hydride (3.68 g, 153 nmol) in a mixture of dry tetrahydrofuran (35 ml) and diethyl carbonate (24.7 g, 209 nmol) at reflux with stirring over 45 minutes. After a further 1 hour, the mixture was cooled, hexane (200 ml) was added, and the resulting precipitate was filtered off and washed with hexane (2 × 100 ml). The solid was suspended in ethyl acetate (200 ml) and acetic acid (10.2 g) was added. After stirring far 15 minutes, water (200 ml) was added, and the organic layer was separated. The aqueous phase was extracted with ethyl acetate (100 ml) and the combined organic solutions were washed with water (200 ml), dried (MgSO₄) and concentrated to give the title product as a gun (17.3 g, 77%). Further purification by flash

chromatography (eluting with ethyl acetate/methanol (7:1) gave the title compound as a white solid. m.p. 111-112ºC.

(e) Ethyl 4'-(2-Methylimidazopyrid-1-yl)-2-oximinobenzoylacetate

A solution of sodiim nitrite (3.3 g, 47 nmol) in water (40 ml) was added in drops to a solution of ethyl 4'-(2-methylimidazo[4,5-c]pyrid-1-yl)benzoylacetate (12.6 g, 39 nmol) in glacial acetic acid (45 ml) at 5°C. After 1.5 hours the mixture was partitioned between dichloromethane and brine. The organic layer was washed again with brine and then with saturated aqueous sodiim bicarbonate, dried (MgSO.) and evaporated to an oil which rapidly crystallised on addition of ether (9.61 g, 70%), (2:1 mixture of syn/anti isomers). M.p. 168-170°C

(f) Ethyl 2-acetamido-4'-(2-methylimidazo[4,5-c]pyrid-c-yl]-benzoylacetate

A solution of the product from e) above (6 g, 17 nmol) in acetic acid (33 ml) and acetic anhydride (9 ml) was hydrogenated over 5% palladium an carbon (1 g) at 50 p.s.i. (3.45 bar) at 30ºC for 5 hours. The mixture was filtered through a filter pad, washing the cake with methanol and the filtrate was evaporated. The residue was chromatographed eluting with methanol and then 10% methanol in ethyl acetate to afford a colourless foam (6.1 g, 94%). M.p. 71-73°C.

(g) 2-Amino-4'-(2-methylimidazo[4,5-c]pyrid-1-yl)acetophenone dihydrochloride

A solution of the product from f) above (1.2 g, 3.2 nmol) in 2M hydrochloric acid (30 ml) was heated at reflux for 3 hours. The solution was evaporated to dryness to yield the amine hydrochloride salt as a colourless foam (1.35 g), which was stored under vacuum.

Claims

A conpound of the formal a:-

or a pharmaceuticalllyy acceptable salt thereof, wherein R¹, R² and

R³ are each H or methyl, R⁴ is hydrogen, halo, C₁-C₄ alkyl, or

C₁-C₄ alkoxy and n is an integer of from 1 to 3.

2. A ccmpound as claimed in claim 1 wherein R¹, R² and R³ are H,

R⁴ is chlorine and n is 1 or 2.

3. A conpound as claimed in claim 2 wherein said compound is: 7-chloro-3,4-dihydro-2-[4'-(2-methylimidazo[4,5-c]pyrid-1-yl)-phenyl]-5H-1,4-benzodiazepin-5-one,

7,8-dichloro-3,4-dihydro-2-[4'-(2-methylimidazo[4,5-c]pyrid-1-yl)- phenyl]-5H-1,4 -benzodiazepin-5-one or

7,9-dichloro-3,4-dihydro-2-[4^,-(2-methylimidazo[4 ,5-c]pyrid-1-yl )-phenyl]-5H-1,4-benzodiazepin-5-one.

4. A process for preparing a compound of the formula (I) as claimed in claim 1 which comprises cyclising a compound of the formula:

5. A pharmaceutical composition comprising a compound of the formula (I) or a pharmaceutically acceptable salt thereof as claimed in any one of claims 1 to 3, together with a

pharmaceutically acceptable diluent or carrier.

6. A compound of the formula (I) or a pharmaceutically

acceptable salt thereof as claimed in any one of claims 1 to 3 for use in medicine, in particular for use in the treatment of allergic, inflammatory and hypersecretory conditions in humans.

PROCESS CLAIMS

7. A process for preparing a compound of the formula:

or a pharmaceutically acceptable salt thereof, wherein R¹, R² and

R³ are each H or methyl, R⁴ is hydrogen, halo, C₁-C₄ alkyl, or

C₁-C₄ alkoxy and n is an integer of from 1 to 3, which comprises cyclising a compound of the formula:

8. A process as claimed in claim 7 wherein R¹, R² and R³ are H, R⁴ is chlorine and n is 1 or 2.

9. A process as claimed in claim 8 wherein said compound of formula (I) produced is: 7-chloro-3,4-dihydro-2-[4 '-(2-methylimidazo[4,5-c]pyrid-1-yl)-phenyl]-5H-1,4-benzodiazepin-5-one,

7,8-dichloro-3,4-dihydro-2-[4 ' -(2-methylimidazo[4,5-c]pyrid-1-yl)-phenyl]-5H-1,4-benzodiazepin-5-one or

7,9-dichloro-3,4-dihydro-2-[4'-(2-methylimidazo[4,5-c]pyrid-1-yl)phenyl]-5H-1,4-benzodiazepin-5-one.