PYRIDINE DERIVATIVES

Abstract: The present ivention provides compounds of formula (1): and their pharmaceutically acceptable salts. In formula (1) R¹ and R² are the same or different and are hydrogen, C 1_6 alkyl, C₁₋₆alkoxy or halogen; R³ is optionally substituted pyridyl, where the optional sub­ stituents are one or more C₁₋₆alkyl, C₁₋₆alkoxy, or hydroxy groups or halogen atoms; b is from 2 to 4; R⁴ is hydrogen or C₁₋₆alkyl, and r is 1 or 2. The compounds are useful as histamine H₁-antagonists.

Description: PYRO DINE DERIVATIVES This invention relates to certain pyridine derivatives, a process for their preparation, compositions containing them and their use as histamine H1-antagonists. Histamine, a physiologically active compound endogenous in mammals, exerts its action by interacting with certain sites called receptors. One type of receptor is known as a histamine H1-receptor (Ash and Schild, Brit. J. Pharmac. 1966, 27, 427) and the actions of histamine at these receptors are inhibited by drugs commonly called antihistamines (histamine H1antagonists) a common example of which is mepyramine. According to the present invention there is provided compounds of formula (1) EMI1.1 and pharmaceutically acceptable salts thereof, where R1 and R2 are the same or different and are hydrogen, C16alkyl, C16alkoxy or halogen; R3 is optionally substituted pyridyl, where the optional substituents are one or more C1 6alkyl, C1 6 alkoxy, or hydroxy groups or halogen atoms; b is from 2 -to 4 R4 is hydrogen or C1-6alkyl, and r is 1 or 2. The compounds of this invention are histamine Hl antagonists and are useful for the treatment of diseases for example bronchial asthma, rhinitis, hayfever and allergic eczema whose symptoms are mediated through the action of histamine at H1-receptors. Examples of halogens for RÚ, Rê and the halogen substituent in R3 are fluorine, chlorine, bromine and iodine. Examples of C 1-6 alkyl groups for R1 and R2 and the C C1 alkyl substituent in R3 are methyl, ethyl, n-propyl, iso-propyl, n-butyl and t-butyl. Examples of C1 6alkoxy groups for R1 and R2 and the C1 alkoxy substituents in R3 are methoxy, ethoxy, n-propoxy and n-butoxy. Preferably R1 and R2 are both hydrogen. By way of example, b can be 2, 3 or 4. Preferably it is 3. Examples of optionally substituted pyridyl groups for R3 are optionally substituted 2-pyridyl, 3-pyridyl or 4-pyridyl groups. In particular R3 is 2-pyridyl, 3-pyridyl or 4-pyridyl. Preferably R3 is 2-pyridyl or 4-pyridyl. R4 is in particular, hydrogen or methyl. Preferably R4 is hydrogen. Preferably r is 1. Compounds of formula (1) also form pharmaceutically acceptable salts with pharmaceutically acceptable acid addition salt-forming acids. Accordingly, in this specification the term "pharmaceutically acceptable salts" means salts with bases or acid addition salts as the context requires. Examples of pharmaceutically acceptable acid addition salt-forming acids are hydrochloric, sulphuric, hydrobromic, phosphoric, tartaric, citric, maleic, lactic, 2-hydroxyethanesulphonic, methanesulphonic, toluene-4sulphonic, ethanedisulphonic, ethanesulphonic and camphorsulphonic acids. Compounds of formula (1) can be prepared by reacting an amine of formula (2): EMI3.1 where R1, R2, R3, and b are as defined with reference to formula (1) with a compound of formula (3): EMI4.1 where X is a group displaceable with an amine and X1 is a group displaceable with an amine or a group of formula NHR4 where R4is as previously defined, and where X1 is a group displaceable with an amine, thereafter reacting with an amine of formula (4): R4NH2 (4) where R4 is as defined with reference to formula (1). Examples of leaving groups displaceable by amines are where X and X1 are QS-, QSO-, QSO2, or QO (Q being Cl¯6alkyl, aryl or aralkyl), halogen, particularly chlorine and bromine, and nitroamino. Preferably the groups X and X1 are QO- where Q is methyl. The conditions under which the reaction is carried out depends upon the nature of the reagents. The reaction is carried out at moderate to low temperature e.g. from OOC to room temperature. The choice of solvent is affected by the solubility characteristics of the reagents. Preferably the solvent is pyridine, a picoline or mixture of picolines, a Cl¯6alkanol, preferably ethanol or l-propanol, 1,2-ethanediol, a high boiling alkoxyaryl ether for example anisole, or a polar aprotic solvent, for example dimethylformamide, dimethylacetamide, dimethylsulphoxide, hexamethylphosphoramide or sulpholane. Pharmaceutically acceptable acid-addition salts of compounds of formula (1) can be prepared by standard methods, for example by reacting a solution of the compound of formula (1) with a solution of the acid. Compounds of formula (2) can be prepared by reacting a compound of formula (5): EMI5.1 where R1 and R2 and b are as defined with reference to formula (1) or a derivative thereof where the primary amino group is protected, with a compound of formula (6): R3CH2X2 (6) where R3 is as defined with reference to formula (1) (provided that any hydroxy groups in R3 are protected) and X2 is halogen, in the presence of a strong base and thereafter removing any protecting groups. Compounds of formula (5) can be prepared in turn by reducing a compound of formula (7): EMI5.2 where R1, R2 and b are as defined with reference to formula (1). Preferably the reducing agent is lithium aluminium hydride. Compounds of formula (5) can also be prepared by reacting a compound of formula (8): EMI6.1 where R1, R2 and R3 are as defined with reference to formula (1) (provided that any hydroxy groups in R3 are protected) with a compound of formula (9): X2(CH2)bR6 (9) where b is as defined with reference to formula (1), x2 is halogen and R6 is a protected amino group, in the presence of a strong base and thereafter removing any protecting groups. Examples of hydroxy protecting groups are C1 6alkyl, for example methyl, and C1 alkanoyl, for example formyl or acetyl. These protecting groups can be removed by standard methods, in particular under basic conditions. Examples of protected amino groups for R6 include phthalimido. In formulae (6), (7) and (9), x2 can be chlorine, bromine or iodine. Examples of strong bases are alkali metal hydrides, particularly sodium hydride. The reaction is carried out in the presence of a polar solvent for example dimethylsulphoxide. The protected amino group can be converted into amino by standard methods, for example when it is phthalimido by reaction with hydrazine. The use of protecting groups is discussed in J.F. McOmie, Protective Groups in Organic Chemistry, 1973, Plenum Press, IBSN 0-306-30717-0. Compounds of formula (3) are known or can be made by known methods as described in for example British Patent Application No. 2067987A. Compounds of formulae (6) to (9) are known or can be made by known methods. The histamine H1-antagonist activity of the compounds of formula (1) can be demonstrated in vitro in the guinea pig ileum test. In this test an isolated portion of the guinea pig ileum is secured under tension (500 mg) between an anchorage and a transducer in a 10 ml tissue bath and immersed in magnesium free Tyrode solution with constant aeration at a temperature of 30 C. The output from the transducer is amplified. The amplified output is in turn fed to a flat bed recorder. Measured amounts of histamine are added to the tissue bath so that the histamine concentration increases step-wise until the force of the contraction reaches a maximum. The tissue bath is washed out and filled with fresh magnesium free Tyrode solution containing compound under test. The solution is left in contact with the tissue for 8 min. and measured amounts of histamine are added again until a maximum contraction is recorded. The assay is repeated with increasing concentrations of test compound and the dose of histamine giving 50% of maximum contraction is noted. A dose ratio (DR) was calculated by comparing the concentrations of histamine required to produce 50% maximum response in the absence and in the presence of the antagonist. A plot of Log DR-l against Log D (the concentration of compound under test) is made and the point of intersection with the Log (DR-1) ordinate is taken as the measure of the activity (Pk2 value). The compounds of the Examples have pA2 values greater than 7. The activity of compounds of formula (1) as histamine Hl-antagonists can be demonstrated in vivo by the inhibition of histamine induced bronchoconstriction. Guinea pigs of either sex are anaesthetised by intraperitoneal injection of sodium pentobarbitone, 90 mg/kg. The trachea is cannulated. The animal is respired artificially with a fixed volume of air just adequate to inflate the lungs. The pressure needed to inflate the lungs is monitored from the respiratory system using a low pressure transducer. Intravenous injection of histamine causes dose-dependent increases in the pressure to inflate the lungs reflecting the bronchoconstrictor action of histamine. Responses to histamine can be antagonised using histamine H1-receptor antagonists. Dose-response curves to histamine are established at 20, 40, 80, 160 and 320 nmols/kg. Antagonists are then administered by intravenous injection and 5 minutes later a new histamine dose-response curve is established increasing the doses of histamine as necessary. The effect of the antagonist can be quantified by the displacement, to the right, of the histamine dose-response curve, expressed as a dose-ratio. A series of doses of antagonists may be given to each animal allowing calculation of dose-ratios for each dose of antagonist. In order to use the compounds of the invention as histamine H1-antagonists, they can be formulated as pharmaceutical compositions in accordance with standard pharmaceutical procedure. The invention also includes pharmaceutical compositions comprising a compound of formula (1) or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier. Compounds of formula (1) and their pharmaceutically acceptable salts can be administered topically or systemically. Topical formulations for administration to the skin include lotions and creams. Topical formulations for administration to the respiratory tract include solutions for application via a nebulizer or as an aerosol, or a microfine insufflatable powder. The active ingredient in an insufflatable powder has a small particle size i.e. less than 50 microns and preferably less than 10 microns. The active material is co-presented with a solid carrier for example lactose which has a particle size of less than 50 microns. Systemic administration can be achieved by rectal, oral or parenteral administration. A typical suppository formulation comprises the active compound with a binding agent and/or lubricating agent for example gelatine or cocoa butter or other low melting vegetable waxes or fats. Typical parenteral compositions consist of a solution or suspension of the active material in a sterile aqueous carrier or parenterally acceptable oil. Compounds of formula (1) which are active when given orally can be formulated as syrups, tablets, capsules and lozenges. A syrup formulation generally consists of a suspension or solution of the compound in a liquid carrier for example ethanol, glycerine or water with a flavouring or colouring agent. Where the composition is in the form of a capsule, the solid in granular form optionally with a binding agent is encased in a gelatin shell. Where the composition is in the form of a tablet, any suitable pharmaceutical carrier routinely used for preparing solid formulations can be used. Examples of such carriers include magnesium stearate, starch, lactose, glucose, sucrose, and cellulose. Preferably the composition is in unit dose form for example a tablet, capsule or metered aerosol so that the patient may administer to himself a single dose. Where appropriate, small amounts of bronchodilators and anti-asthmatics for example sympathomimetic amines particularly isoprenaline, isoetharine, salbutamol, phenylephrine and ephedrine; xanthine derivatives particularly theophylline and aminophylline; and corticosteroids particularly prednisolone and adrenal stimulants particularly ACTH can be included. As in common practice, the compositions will usually be accompanied by written or printed directions for use in the medical treatment concerned, in this case as a histamine H1- antagonist for treatment of, for example, asthma, hayfever, rhinitis or allergic eczema. Each dosage unit for oral administration contains preferably from 5 to 200 mg of a compound of formula (1) or a pharmaceutically acceptable salt thereof calculated as the free base. The pharmaceutical compositions of the invention will normally be administered to a man for the treatment of rhinitis, hayfever, bronchial asthma or allergic eczema. An adult patient will receive an oral dose of between 15 mg and 400 mg and preferably between 15 mg and 200 mg or an intravenous, subcutaneous or intramuscular dose of between 1 mg and 50 mg, and preferably between 1 mg and 10 mg of a compound of formula (1) or a pharmaceutically acceptable salt thereof calculated as the free base, the composition being administered 1 to 4 times per day. The following Examples illustrate the invention. Example 1 i) A solution of 3-anilinopropionitrile (15 g) in ether (450 ml) was added to a stirred suspension of lithium aluminium hydride (12 g) in ether (450 ml) under nitrogen, over 1 hr., maintaining the temperature at ca. 200C. The mixture was stirred for 2 hr. at room temperature and then cooled to 120-150C. A mixture of water (12 ml) and tetrahydrofuran (58 ml) was added dropwise to the reaction mixture, followed by sodium hydroxide solution (4N, 12 ml) and water (35 ml). This mixture was stirred for 45 min. and then allowed to stand overnight at room temperature. The resulting solid was removed by filtration. The filtrate was dried over potassium carbonate and the solvent was evaporated to give 3-anilinopropylamine (13.7 g; 89%), which was used without further purification. ii) Sodium hydride (1.0 g) was dissolved in dimethylsulphoxide (25 ml) at 70 -75 C. under nitrogen. The solution was cooled and to it was added 3-anilinopropylamine (2.85 g) in dimethylsulphoxide (10 ml) at room temperature. A solution of 2-chloromethylpyridine hydrochloride (3.42 g) in dimethylsulphoxide (15 ml) was added dropwise maintaining the temperature of the reaction mixture in the range 250-350C. After 1.5 hr. the reaction mixture was diluted with water (70 ml) and the mixture was extracted with chloroform. The chloroform extracts were washed with 2N hydrochloric acid and the aqueous layer adjusted to pH 4 and then 6, each time extracting with chloroform. The pH was raised to 11-13 and then extracted with ether. The ether extracts were evaporated to dryness and the residue chromatographed (silica gel, chloroform/methanolic ammonia 60:1) to give 3-[N-phenyl-N-(2-pyridylmethyl)aminopropylamine as an oil (0.97 g; 218). iii) A solution of 3-[N-phenyl-N-(2-pyridylmethyl) amino]propylamine (0.92 g) in methanol (15 ml) was added dropwise over 40 minutes to a stirred suspension of 3,4-dimethoxy-1,2,5-thiadiazole-1-oxide (0.62 g) in methanol (30 ml) at 00-50C. After allowing the mixture to stand for a further 3 hr. at 10 C. the mixture was cooled to 00-50C. and methanol saturated with ammonia (15 ml) was added dropwise to it. This mixture was then allowed to stand at room temperature for 2.5 days. The solvent was evaporated and the residue was chromatographed (silica gel, chloroform/methanol 20:1). The fractions which contained the required product were collected and the solvent was evaporated. The residue was crystallised twice from ethanol to give 3-[3-(N-phenyl-N-pyrid-2-yl methylamino)propylamino)]-4-amino-1,2,5-thiadiazole-1-oxide (0.47 g; 35%) m.p. 1900-1920C. C17H20N6 S Found: C 57.19, H 5.64, N 23.36, S 9.18 Requires: C 57.28, H 5.66, N 23.58, S 9.00 Example 2 i) Substituting 4-chloromethylpyridine hydrochloride (4.91 g) for 2-chloromethylpyridine hydrochloride and using corresponding molar proportions of other reagents in the method of Example l(ii) gave, after medium pressure chromatography (silica gel, chloroform/methanolic ammonia 60:1), 3-[N-phenyl-N-(4- pyridylmethyl)amino]propylamine as an oil (0.66 g; 14z). ii) Substituting 3-[N-phenyl-N- (4-pyridylmethyl) amino]propylamine (0.63 g) for 3-[N-phenyl-N-(2-pyridyl me-thyl) amino]propylamine and using corresponding molar propprtions of other reagents in the method of Example l(iii) gave, after crystallisation from ethanol, 3-[3 (N-phenyl-N-pyrid-4-ylmethylamino)propylaminol-4-amino 1,2,5-thiadiazole-l-oxide (0.34 g; 37%) m.p. 96 -99 C. C17H20N60S Found: C 56.98, H 5.72, N 23.41, S 8.88 Requires: C 57.28, H 5.66, N 23.58, S 9.00 Example 3 i) Substituting 3-chloromethylpyr idine hydrochloride (10.49 g) for 2-chloromethylpyridine hydrochloride and using corresponding molar proportions of other reagents in the method of Example l(ii) gave, after medium pressure chromatography (silica gel, chloroform/methanolic ammonia 24:1), 3-[N-phenyl-N-(3- pyridylmethyl)amino]propylamine as an oil (6.22 g; 48%). ii) Substituting 3-[N-phenyl-N- (3-pyridylmethyl)amino]propylamine (1.30 g) for 3- [N-phenyl-N- (2-pyridyl- methyl)amino]propylamine and using corresponding molar proportions of other reagents in the method of Example l(iii) gave, after crystallisation from chloroform, 3-[3 (N-phenyl-N-pyr id-3-ylmethylamino) propylaminol -4-amino- 1,2,5-thiadiazole-l-oxide (0.60 g; 31%) m.p. 1250-1280C. (decomp.). C17H2nN,OS.1.14H2O Found: C 53.31, H 5.94, N 21.77, S 8.41 Requires: C 53.30, H 5.87, N 21.94, S 8.37 Example 4 A pharmaceutical composition for oral administration is prepared containing % by weight A EMI15.1 <SEP> <tb> 3-[3-(N-phenyl-N-pyrid-4-ylmethyl- 55 amino)propylamino]-4-amino-1,2,5-thia- diazole-l-oxide Dibasic calcium phosphate dihydrate 20 Approved coloring agent 0.5 Polyvinylpyrrolidone 4.0 B EMI15.2 Microcrystalline Cellulose 8.0 Maize Starch 8.0 Sodium glycollate 4.0 Magnesium Stearate 0.5 by mixing together the ingredients A (substituting lactose or microcrystalline cellulose for dibasic calcium phosphate dihydrate if desired), adding a concentrated solution of polyvinylpyrrolidone and granulating, drying and screening the dried granules; adding the ingredients B to the dried granules and compressing the mixture into tablets containing 5 mg, 25 mg or 50 mg of the free base. Example 5 A pharmaceutical composition for injectable administration is prepared by forming a solution of 3-[3 (N-phenyl-N-pyrid-4-ylmethylamino)propylamino]-4-amino 1,2,5-thiadiazole-l-oxide in sterile water to give a 1 to 5% w/w solution. The solution is clarified by filtration and filled into vials which are sealed and sterilised. A suitable vial contains 2 ml of the solution.

Claims: Claims: (BE, CH, DE, FR, GB, IT, LI, LU, NL and SE) 1. A compound of formula (1) EMI16.1 and pharmaceutically acceptable salts thereof, where R1 and R2 are the same or different and are hydrogen, C1-6alkyl, C16alkoxy or halogen; R3 is optionally substituted pyridyl, where the optional substituents are one or more C1-6alkyl, C16 alkoxy, or hydroxy groups or halogen atoms; b is from 2 to 4 R4 is hydrogen or C1 6alkyl, and r is 1 or 2. 2. A compound as claimed in claim 1 where R1 and R2 are both hydrogen. 3. A compound as claimed in claim 1 or claim 2 where b is 3. 4. A compound as claimed in claim 3 where R3 is 2-pyridyl or 4-pyridyl. 5. A compound as claimed in any one of claims 1 to 4 where R4 is hydrogen. 6. A compound as claimed in any one of claims 1 to 5 where r is 1. 7. A compound as claimed in any one of claims 1 to 6 which is: 3-[3-(N-phenyl-N-pyrid-2-ylmethylamino)propylamino)]- 4-amino-1,2,5-thiadiazole-1-oxide, 3-[3-(N-phenyl-N-pyrid-4-ylmethylamino)propylamino]-4 amino-1,2,5-thiadiazole-l-oxide, or 3-[3-(N-phenyl-N-pyrid-3-ylmethylamino)propylamino)]- 4-amino-1,2,5-thiadiazole-l-oxide. 8. A process for preparing a compound as claimed in any one of claims 1 to 7 which comprises reacting a compound of formula (2): EMI17.1 where R1, R2, R3 and b are as defined with reference to formula (1), with a compound of formula (3): EMI17.2 where X is a group displaceable with an amine and X1 is a group displaceable with an amine or a group of formula NHR4, where R4 is as defined with reference to formula (1), and where X1 is a group displaceable with an amine, reacting with an amine of formula (4): R4NH2 (4) where R4 is as defined with reference to formula (1); and optionally converting a compound of formula (1) so obtained into a pharmaceutically acceptable acid addition salt. 9. A pharmaceutical composition comprising a compound as claimed in any one of claims 1 to 7 and a pharmaceutically acceptable salt. 10. A compound as claimed in any one of claims I to 7 for use as a histamine H1- antagonist. Claims (AT) 1. A process for preparing a compound of formula EMI19.1 and pharmaceutically acceptable salts thereof, where R1 and R2 are the same or different and are hydrogen, C1-6alkyl, Cl¯6alkoxy or halogen; R3 is optionally substituted pyridyl, where the optional substituents are one or more Cl¯6alkyl, C16 alkoxy, or hydroxy groups or halogen atoms; b is from 2 to 4 R4 is hydrogen or C16alkyl, -and r is 1 or 2; which comprises reacting a compound of formula (2): EMI19.2 where RÚ, Rê, R and b are as defined with reference to formula (1), with a compound of formula (3): EMI20.1 where X is a group displaceable with an amine and X1 is a group displaceable with an amine or a group of formula 4. NHR4, where R4 is as defined with reference to formula (1), and where X1 is a group displaceable with an amine, reacting with an amine of formula (4): R4NH2 (4) where R4 is as defined with reference to formula (1); and optionally converting a compound of formula (1) so obtained into a pharmaceutically acceptable acid addition salt. 2. A process as claimed in claim 1 where R1 and R2 are both hydrogen. 3. A process as claimed in claim 1 or claim 2 where b is 3. 4. A process as claimed in claim 3 where R3 is 2-pyridyl or 4-pyridyl. 5. A process as claimed in any one of claims 1 to 4 where R4 is hydrogen. 6. A process as claimed in any one of claims 1 to 5 where r is 1. 7. A process as claimed in any one of claims 1 to 6 for preparing: 3-[3-(N-phenyl-N-pyrid-2-ylmethylamino)propylamino)]- 4-amino-1,2,5-thiadiazole-1-oxide, 3-[3-(N-phenyl-N-pyrid-4-ylmethylamino)propylamino]-4 amino-1,2,5-thiadiazole-l-oxide, or 3-[3-(N-phenyl-N-pyrid-3-ylmethylamino)propylamino)]- 4-amino-1,2,5-thiadiazole-l-oxide. 8. A process for preparing a pharmaceutical composition comprising a compound of formula (1) in claim 1 which comprises bringing into association a compound of formula (1) in claim 1 or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier. 9. A process according to any one of claims 1 to 7 in which X and X1 are QS-, OSO-, QSO2- or QO-, where Q is C16alkyl, aryl or aralkyl, halogen or nitroamino. 10. A process according to claim 9 in which X and xl are both methoxy.

Inventors: IFE, ROBERT JOHN
Applicants: SMITH KLINE & FRENCH LABORATORIES LIMITED
Application year: 1986
Main classification: C07D417
IPC codes: A61P37, A61P11, A61K31, C07D417, A61P43