IE912432A1 - Imidazopyridine paf antagonists - Google Patents

Abstract

Compounds of formula (I), wherein R<1>, R<2> and R<3> are each H or methyl, R<4> is hydrogen, halo, C1-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

Tmidazgpyridine PAF Antagonists This invention relates to imidazopyridines, specifically to certain 4-suhstituted-l- (2^nethylimidazo[4,5-c]pyrid-l-yl) -benzene derivatives. Hie oempounds are potent and selective antagonists of platelet activating factor having clinical utility in the treatment of allergic and inflanmatary conditions in humans and animal».

Platelet activating factor (PAF, l-O-alkyl-2-aoetyl-snglyeeryl-3-phosphorylcholine) is an ether phopholipid whose structure was first elucidated in 1979. It is produced by, released from and interacts with many pro-inf lanmatory 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 the release of other powerful mediators such as thromboxane A^ or the leukotrienes, trfiich make PAF inhibitors of potential value in the treatment of a variety of conditions including allergic, inflanmatary and hypersecretary 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 cis PAF antagonists. In our later European patent application no 0310386 we disclose a further series of dihydropyridine PAF antagonists therein the 2-position substituent includes in particular a 2-methyl-imidazo[ 4,5-c] pyrid-l-yl-phenyl group. Ihe present -2invention provides further PAF antagonists having the formula: and their pharmaceutically acceptable salts, wherein R1, R^ and 3 4 R are each H or methyl, R is hydrogen, halo, C^-C^ alkyl or Cj-C^ 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. 2 3 In preferred embodiments of the invention K, R and R are 4 H, R is preferably chlorine and n is 1 or 2.

When R is a branched alkyl or alkoxy group having 4 carbon atoms, the conpounds of the formula (I) may contain at least one asymnetric centre and exist as a pair of enantiomers. Such isomers may be separable by physical methods, e.g. by fractional crystal 1 i sation or chromatography of the parent conpounds 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 conpounds of the formula (I) which form such salts are those -3farmed from acids which farm non-taxic acid addition salts, for exanple the hydrochloride, hydrobrcmide, sulphate or hi sulphate, phosphate or acid phosphate, acetate, citrate, funerate, gluconate, lactate, maleate, succinate and tartrate salts.

Hie conpound of formula I may be obtained by cyclisation of a conpound of the formula: wherein R1, R^, r\ r^ and n are as previously defined.

In a typical procedure the conpound of formula II is sinply heated in a high-boiling organic solvent (for example toluene or xylene) at a teuperature above 100°C for a period of several hours. The solvent is evaporated and the product recovered and purified by conventional procedures. _4_ Hie intermediates of formula II are prepared by reaction of an amine of formula-: This reaction is achieved hy either reacting the anhydride with the amine (III) in water or an aqueous organic solvent in the presence of a base (e.g. sodiun carbonate), or by reacting the benzoic acid with the amine using a diimide coupling reagent such as 1- (3-dimethylarainopropyl) -3-ethylcarbodiimide.

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

The activity of the ccnpounds of the invention is shown by their ahi 1 i ty 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 -5vol disodiun ethylenediamine tetraacetic acid buffer and the samples 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 KH^PO^, 6nM Na^HPO^, 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 x g platelets/ml. A sample (0.5 ml) is pre-incubated with stirring for two minutes at 37°C 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 —8 —9 compound (10 to 10 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 maximun value in recorded as the ΙΟ,-θ value.

The activity of the compounds of formula (I) is also demonstrated in vivo by their ahi 1 i ty to protect mice from the lethal effect of an injection of PAF. A mixture of PAF (50 /jg/kg) and DL-prcpranolol (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 earl ier. The compounds are tested at several doses in groups of 5 mice and the dose which reduces mortality to 50% is recorded as the PDC_ value. “6— For therapeutic use the ccnpounds of the formula (I) will generally be adni ni stered in adnixture with a pharmaceutical carrier selected with regard to the intended route of ackninistration 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 acknixture with excipients, or in the form of elixirs or suspensions containing flavouring or colouring agents. Biey may be injected parenterally, for example, intravenously, intramuscularly or subcutaneously. For parenteral administration, they are best used in the form of a sterile aqueous 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 -reqni τ-pH . 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. —7— weight and response of the particular patient. The above dosages are exenplary 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 conprising a conpound of the formula (I), or a pharmaceutically acceptable salt thereof, together with a pharmaceutically acceptable diluent or carrier.

The invention also includes a conpound of the formula (I), or a pharmaceutically acceptable salt thereof, for use in medicine, in particular in the treatment of allergic, inflamnatory and hypersecretory conditions in a hunan 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· ^H-^iuclear 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-permillian downfield from tetramethylsilane using conventional abbreviations for designation of major peaks: s, singlet; d, doublet; t, triplet; m, multiplet and hr, broad. —8EXftMPLE 1 7-Chloro-3.4-dihydro-2-r 42-methrylimidazor 4.5-clpyrid—1-yl )phenyl1-5H-1.4-benzodiazepin-5-one a) 4-Chlaroisatoic anhydride (0.32 g, 1.6 nmol) was added to a solution of 2-amino-4'-(2-methylimidazo[4,5-c]pyrid-l-yl)acetophenone (0.57 g, 1.45 nmol) in water (6 ml). After stirring to uniform consistency, a solution of sodium carbonate (0.19 g, 1.8 nmol) was added. After 1 hour, dichloromethane (12 ml) was added and two phase stirring was resumed for 66 hours. Hie mixture was partitioned between saturated agueous sodium hydrogen carbonate and dichloromethane. Hie organic phase was separated, dried (MgSO^) 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-l-yl)phenyl]-2-oxoethyl}benzamide as a solid (0.14 g, 23%), m.p. H6-118°C. NMR (CD3SOCD3): 2.52(3H,s), 4.79(2H,d,J 5.4Hz), 6.58hr exch (2H,s), 6.76(lH,d,J 8.9Hz), 7.21(lH,dd,J 8.9,2.2Hz), 7.28(lH,d,J 5.4Hz), 7.67(lH,d,J 2.2Hz), 7.82 and 8.28 (each 2H,d,J 8.4Hz}, 8.35(lH,d,J 5.5Hz), 8.85 br exch (lH,t,J 5.4Hz) and 8.94(lH,s). b) A suspension of the benzamide from part (a) (0.11 g, 0.26 nmol) in xylene (5 ml, containing 2-3 drops ethanol to aid solubility) was heated to 140°C for 5 hours. Hie 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. C22H16ClN50, 0.75 ^0 requires C,63.62; H,4.25; N,16.86%. -9— EXAMPLE 2 7.8— Dichloro—3,4—dihydro-2—Γ4'-(2-methylimidazor4,5-clpvrid-l-yl)phenyl~l-5H-l. 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-l-yl) phenyl] -2-oxoethyl }benzamide.

NMR (CDCl3): 2.63(3H,s), 5.00(2H,d,J 4.2Hz), 5.69br exch. (2H,s), 6.83(lH,s), 7.18(2H,m), 7.62(3H,m), 8.33(2H,d,J 8.4Hz), 8.42(lH,d,J 5.5Hz), 9.11(lH,s). b) The above product was cyr.1i.sed following the procedure of Example 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. .HgO requires C,58.16; H,3.77; N,15.40%.

EXAMPLE 3 7.9- Dichloro-3,4-dihvdro-2-Γ4'-(2-methvJi mi dazoΓ4,5-clpyrid-l-yl)phenyl1-5H-l.4-benzodiazepin-5-one a) A solution of 2-amino-4'-(2-methylimidazo[4,5-c]pyrid-l-yl)acetophenone hydrochloride (0.7 g, 1.8 nmol), 3,5-dichloro-2aminobenzoic acid (0.48 g, 2.3 nmol), N-hydraxybenzotriazole (0.34 g, 2.4 nmol), N-methylmorphaline (1.61 ml, 16 nmol) and 1-(3diinethylamincpropyl)-3-ethylcarbodiimide hydrochloride (0.89 g, 4.7 nmole) in dichloromethane (25 ml) was stirred at 25°C 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 (MgSO^) and evaporated. Flash chromatography of the residue on silica, eluting with 10% -10methanol in ethyl acetate afforded 2-amino-3,5-dichloro-N-{2-[4 -(2-methylimidazo[4,5-c]pyrid-l-yl)phenyl]-2-axoethyl}benzamide as a pale-yellow gun (0.21 g, 26%). ^H NMR (CDClj): 2.62(3H,s), 4.98(2H,d,J 5.7Hz), 6.10 hr exch. (3H,m), 7.13(lH,d,J 5.7Hz), 7.39(lH,d,J 2Hz), 7.48(lH,d,J 2Hz), 7.57 and 8.30 (each 2H,d,J 8.4Hz), 8.43(lH,d,J 5.7Hz) and 9.07(lH,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 dichlorcmethane and saturated aqueous sodiun hydrogen carbonate. The organic layer was dried (MgSO^) 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. ^2^5^21¾° ' 0-5 ”2°' requires C.58.91; H,4.12; N,14.31%. 0.5 EtOAc —11— PKEPARftTION 2-Amino-4'-(2-methyllmidazor4.5-clpyrid-l-yl) acetophenone hydrochloride (a) 4-(4-Acetylphenyl)amino-3-nitropyridine hydrochloride A solution of 4-chloro-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-aminopvridine 4-(4-acetylphenyl)andno-3-nitrcpyridine hydrochloride (2.0 g, 78.8 nmol) was partitioned between aqueous soditm hydroxide and dichloromethane ( 3 x 20 ml). The contained 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% palladium on carbon (0.2 g) at 50 p.s.i. (3.4 bar) for 3.5 hours. Hie 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-(Methylimi4.5-clpyrid-l-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 95°C 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 anmonia. The product was filtered off, washed with water (2 x 100 —12— ml) and dried under vacuum to give the title conpound, (61.0 g, 81%) as a brown solid, m.p. 155-156°C (from water). (d) Ethyl 4'-(2-tnethylimidazor4.5-clpyrid-l-yl)benzoylacetate A solution of 4-(2-methylimidazo[4,5-c]pyrid-l-ylacetophenone (17.5 g, 69.7 nmol) in dry tetrahydrofuran (175 ml) was added to a slurry of sodiun hydride (3.68 g, 153 mmol) in a mixture of dry tetrahydrofuran (35 ml) and diethyl carbonate (24.7 g, 209 mmol) 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 x 100 ml). The solid was suspended in ethyl acetate (200 ml) and acetic acid (10.2 g) was added. After stirring for 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 (MgSO^) 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 conpound as a white solid, m.p. ~m-112°C. (e) Ethyl 4'-(2-Methylimida7-opyrid-l-yl)-2-oodmnobenzoylacetate A solution of sodiun 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-l-yl)benzqylacetate (12.6 g, 39 mmol) 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 -13sodiun 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-aoetamido-4,-(2-methyl3midazor4.5-clpyrid-l-yl1benzoylacetate 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 on carbon (1 g) at 50 p.s.i. (3.45 bar) at 30°C for 5 hours. The mixture was filtered through a fi 1 ter 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-Απήηο-4' -( 2-methvl1 mi ΗατόΓ 4,5-clpyridr-l-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 (10)

1. R are each H or methyl, R is hydrogen, halo, C 1 ~C 4 alkyl, or C^-C 4 alkoxy and n is an integer of from 1 to 3.

2. A compound as claimed in claim 1 wherein R 1 , R 2 and R 3 are H R is chlorine and n is 1 or 2.

3. A compound as claimed in claim 2 wherein said compound is: 7-chloro-3,

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

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

6. A ccnpound 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, inf lanmatory and hypersecretory ccmditions in hunans. - 167. A process according to claim 4, substantially as hereinbefore described, with particular reference to the accompanying Examples and Preparations. 7.9- dichloro-3,4-dihydio-2-[4' -( 2-methylimidazo[4,5-c]pyrid-l-yl) phenyl ]-5H-1,4-benzodiazepin-5-one. -154. A process for preparing a compound of the formula (I) as claimed in claim 1 which ccnprises cyclising a coipound of the formula:

7.8- dichloro-3,4-dihydro-2-[4' - ( 2-methyliinidazo[ 4,5-c]pyrid-l-yl) · phenyl]-5H-l,4-benzodiazepin-5-ane or

8. A compound of the formula (I) given and defined in claim 1 or a pharmaceutically acceptable salt thereof whenever prepared by a process claimed in claim 4 or 7.

9. A pharmaceutical composition according to claim 5, substantially as hereinbefore described.

10. Use according to claim 6, substantially as hereinbefore described.