DIHYDROPYRIDINE DERIVATIVES, THEIR PREPARATION AND THEIR USE

Abstract: Compounds of formula (I): in which: Ar represents a phenyl group having at least one substituent selected from nitro, C₁ - C₄ haloalkyl, C₁ - C₄ haloalkoxy and cyano groups and halogen atoms; R represents a C₁ - C₁₆ alkyl g roup, a C₃ - C₆ cycloalkyl group, a C₁ - C₄ alkyl group having a C₃ - C₆ cycloalkyl substituent, a C₂ - C₄ alkenyl group, a cinnamyl group or a C₁ - C₁₆ alkyl group having at least one substituent selected from hydroxy, C₁ - C₄ alkoxy and C₁ - C₄ alkylthio groups; R¹ represents a hydrogen atom or a C₁ - C₃ alkyl group; R 2a and R 2b are the same or different and each represents an unsubstituted phenyl group or a substituted phenyl group having at least one substituent selected from C₁ - C₄ alkyl, C₁ - C₄ alkoxy and C₁ - C₄ haloalkyl groups and halogen atoms; one of R³ and R⁴ represents a methyl group and the other represents an amino group; and n is an integer from 1 to 3; These compounds have a variety of valuable activities, including antihypertensive and Ca⁺⁺-blocking activities, leading to their use for the treatment of circulatory and coronary disorders. They may be prepared by condensation of appropriate substituted benzylideneacetoacetic acid esters with appropriate amidinoacetic acid esters.

Description: The present invention relates to a new dihydropyridine derivative, and provides a process for preparing it as well as compositions for its pharmaceutical use. Circulatory and coronary disorders are amongst the major causes of death in the industrialized world and, even where they do not result in death, some disablement or a severe curtailment of lifestyle may result. Notwithstanding this, the full etiology of such disorders has not been resolved, even though certain factors, notably genetic and dietary factors, have been implicated. There is, therefore, a substantial need for medicines to treat this major problem. In attempting to treat circulatory and coronary disorders, attention has been focused on a variety of different pharmacodynamic activities, and the drugs used in such treatment have a variety of different structures, depending upon the particular pharmacodynamic activity which it is desired to influence. Of the many classes of drug proposed for use in such treatment, some compounds have a 4-(substituted phenyl)-1,4-dihydropyridine basic structure and included within such general classes of drug are nifedipine (which is included amongst the compounds disclosed in British Patent Specification No. 1 173 862) and nicardipine (which is included amongst the compounds disclosed in British Patent Specification No. 1 455 502). All of these compounds have in common a 4-(nitrophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid ester structure. However, it is believed that the closest prior art to the compound of the present invention is disclosed in European Patent Publication No. 125 803. This discloses compounds which are said to have cardiovascular activity, in much the same way as does the compound of the present invention. This prior art, although disclosing compounds some of which have an ester grouping resembling that of the present invention, differ in the overall structure of the compounds and notably in the nature of the groups at the 2- and 6-positions of the dihydropyridine ring, whereby the specific nature and arrangement of these groups, as contained in the compound of the present invention, is neither disclosed nor suggested. Other related compounds are disclosed in European Patent Publication No. 207 674, available under Art 54(3) EPC only, but these differ from the compound of the present invention in that the prior compounds contain a nitrooxy group in their molecular structure, which is not possesed by the compounds of the present invention. Yet further related compounds are disclosed in Japanese Patent Publication 61-158962 (see Chem Abs 106 32851 b ), GB Patent Specification 2014134, EP 63365, and EP 106276. All of these patent specifications disclose 2,6-dimethyl-4-(substituted phenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-aralklheterocyclic 5-alkyl esters. The compound of the invention is the dihydropyridine derivative of formula (I): in which: Ar represents a phenyl group having one nitro substituent at the 3-position; R represents an isopropyl group; R¹ represents a hydrogen atom; R 2a and R 2b are the same and each represents an unsubstituted phenyl group; R³ is a methyl group; R⁴ represents an amino group and n is the integer 1; and pharmaceutically acceptable acid addition salts thereof. The invention also provides a pharmaceutical composition for the treatment of cardiovascular disorders, which composition comprises a dihydropyridine derivative in admixture with a pharmaceutically acceptable carrier or diluent, wherein said dihydropyridine derivative is the compound of formula (I) or a pharmaceutically acceptable salt thereof. The invention still further provides the use for the manufacture of a medicament, especially for the treatment of cardiovascular disorders, of the compound of formula (I) or a pharmaceutically acceptable salt thereof. The invention also provides processes for preparing the compound of the invention, which are described in more detail hereafter. The compound of the present invention has been found to have various valuable pharmacological activities such as calcium antagonism, antihypertensive and vasodilator activity as well as low toxicity and is thus useful as a medicine for the treatment of cardiovascular dysfunctions such as hypertension and angina pectoris. The compound of the invention can form acid addition salts. The nature of such salts is not critical to the present invention, except that, where the salts are to be used for therapeutic purposes, they must be pharmaceutically acceptable, which, as is well understood in the art, means that the salts should not have reduced activity (or unacceptably reduced activity) and should not have increased toxicity (or unacceptably increased toxicity) as compared with the free compound. However, where the salt is to be employed for other purposes, for example as an intermediate in the preparation of other compounds, even this criterion does not apply. A wide variety of acids may be employed to form such salts and representative examples of such acids include: mineral acids, such as hydrochloric acid, hydrobromic acid, hydroiodic acid, phosphoric acid, metaphosphoric acid, nitric acid or sulphuric acid; organic carboxylic acids, such as acetic acid, oxalic acid, tartaric acid, citric acid, benzoic acid, glycolic acid, gluconic acid, glucuronic acid, succinic acid, maleic acid or fumaric acid; and organic sulphonic acids, such as methanesulphonic acid, ethanesulphonic acid, benzenesulphonic acid or p -toluenesulphonic acid. Such acid addition salts may be prepared by conventional methods well known to those skilled in the art. The compound of formula (I) may contain several asymmetric carbon atoms, and thus can form a variety of optical isomers. The present invention includes both the individual isolated isomers and mixtures thereof. 1-11. 3-(1-Benzhydryl-3-azetidinyl) 5-isopropyl 2-amino-6-methyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate and salts thereof, especially its dihydrochloride; The compound of formula (I) in accordance with the present invention can be prepared, for example, by the following reaction, specifically, it can be prepared by reacting an α-benzylideneacetoacetic acid ester of formula (II): with an amidinoacetic acid ester of formula (III): In the above formulae, Ar is as defined above and one of R⁵ and R⁶ represents a group of formula (IV): (in which n , R¹, R 2a and R 2b are as defined above) and R⁵ represents the group defined above in respect of R. More specifically, the reaction involved in the preparation of the compounds of the invention may be as illustrated below in order to prepare the compounds of formula (I): In the above formulae, Ar, n , R, R¹, R 2a and R 2b are as defined above. In order to carry out this reaction, the compound of formula (II), (IIa) is mixed with the compound of formula (III) or (IIIa), preferably in equimolar amounts, although a greater than equimolar amount of either of the reagents may be employed, if desired. However, this tends to be wasteful of reagents and so equimolar proportions are preferred. The reaction is preferably carried out in the presence of a solvent, more preferably an organic solvent, for example: an alcohol, such as ethanol, isopropanol or t-butanol; an ether, such as dioxane; a fatty acid amide, such as dimethylformamide; a sulphoxide, such as dimethyl sulphoxide; or a nitrile, such as acetonitrile; or in the presence of water; or a mixture of any two or more thereof. Alternatively, the reaction may be effected in the absence of a solvent. The reaction will take place over a wide range of temperatures, and the precise temperature chosen is not critical to the present invention. However, we generally find it convenient to carry out the reaction at about room temperature or with heating, preferably at or about the reflux temperature of the reaction mixture, and normally at or about the reflux temperature of the solvent if a solvent is employed. Normally, we prefer to carry out the reaction under atmospheric pressure or under superatmospheric pressure. Most conveniently, the reaction is carried out in the presence of one or more of the above solvents under atmospheric pressure and at around the boiling point of the solvent employed. The reaction time will vary depending upon many factors, notably the reaction temperature, and is not critical to the practice of the present invention. However, at the temperatures suggested above, a period of from 30 minutes to five hours will usually suffice. In this reaction, the compound of formula (III), (IIIa) is preferably used in the form of an acid addition salt, such as the hydrochloride, hydrobromide or acetate and, in that case, the reaction is preferably carried out in the presence of a base, preferably an equimolar amount of a base, and preferably an alkali metal (e.g. sodium or potassium) alkoxide, such as sodium methoxide or sodium ethoxide. After completion of the reaction, the desired compound of formula (I) may be recovered from the reaction mixture by conventional means, and, if necessary, it may be further purified by such conventional purification techniques as recrystallization or the various chromatography techniques, notably column chromatography. Of the starting materials employed in the reactions described above, the compound of formula (IIa) may be prepared by the dehydrating condensation of an aldehyde of formula Ar-CHO with an acetoacetic acid ester of formula CH₃COCH₂COOR according to a known method [e.g., G. Jones, "Knoevenagel Condensation", Org. Reactions, Volume 15, 204 (1967)]. The acetoacetic ester employed in this reaction may be prepared from diketene and an alcohol of formula R-OH according to a known method [e.g., A. B. Boese, Jr., Industrial and Engineering Chemistry, 32 , 16 (1940)]. In the above formulae, Ar and R are as defined above. The compound of formula (IIIa) can easily be prepared by reacting a cyanoacetic acid ester of formula (V): (in which n R¹, R 2a and R 2b are as defined above) with ammonia or with an ammonium salt according to a known method [S. A. Glickman and A. C. Cope, J. Amer. Chem. Soc., 67 , 1017 (1945); S. M. McElvain and B. E. Tate, J. Amer. Chem. Soc., 73 , 2760 (1951)]. The compound of formula (V) can be prepared by a conventional esterification between cyanoacetic acid and an alcohol of formula (VI): (in which n , R¹, R 2a and R 2b are as defined above), e.g. a dehydration reaction catalyzed with an acid or in the presence of a carbodiimide, such as 1,3-dicyclohexylcarbodiimide. The alcohol of formula (VI) can easily be prepared by reacting a cyclic amine of formula (VII): (in which n and R¹ are as defined above) with an optionally substituted benzhydryl halide of formula (VIII): (in which R 2a and R 2b are as defined above and X represents a halogen atom). The alcohol of formula (VI) in which n is 1 can be prepared from epichlorohydrin and benzhydrylamine according to a known method [e.g. A. G. Anderson, Jr. and R. Lok., J. Org. Chem., 37 , 3953(1972)]. Compounds of formula (I) synthesized according to the reactions described above can form a number of stereoisomers, for example optical isomers, because of the presence in their molecules of a number of asymmetric carbon atoms, e.g. at the 4-position of the dihydropyridine ring or in the alcohol moiety which forms the ester group. Geometric isomers ( cis or trans ) may also be formed in some cases as a result of the same alcohol moiety. The individual isolated isomers may, in some cases, be prepared by stereospecific synthesis techniques or they may be isolated by methods known per se from mixtures of isomers. The present invention embraces both the individual isolated isomers and mixtures of isomers. BIOLOGICAL ACTIVITY The dihydropyridine derivative of the present invention exhibits significant calcium antagonism and antihypertensive activity as shown below. 1. Calcium Antagonism An isolated rat aorta was suspended in a calcium-free and high potassium Krebs-Henseleit solution maintained at a temperature of 37°C. The contractile response of the aorta to calcium chloride in concentrations ranging from 10⁻⁵ to 10⁻²M was recorded by means of an isometric transducer. The dose-response curve of the aorta was obtained before and after addition of a test compound at a concentration of 5nM. Addition of the test compound shifted the dose-response curve to the right, the magnitude of the shift depending upon the potency of the Ca⁺⁺-blocking activity. The test compound showed a significant rightwards movement and was comparable with that of nifedipine, and had excellent duration of activity. 2. Antihypertensive activity The test animals were spontaneously hypertensive rats of the SHR strain, each aged about 15 weeks. The antihypertensive activities of the test compound was determined in these rats as follows. Each animal was anaesthetized with sodium pentobarbital (50 mg/kg, intraperitoneally) and a polyethylene cannula was inserted into the abdominal aorta by the method of Weeks and Jones [J.R. Weeks and J.A. Jones, Proc. Soc. Exptl. Biol. Med., 104 , 646 - 648 (1960)]. The other end of the cannula left the animal's body at, and was fixed to, the neck. About 1 week after this surgery, when the animal had completely recovered from surgical stress, the free end of the aortic cannula was connected to a sphygmomanometer to measure blood pressure and heart rate of the animal directly in the conscious, aparalytic and unrestrained state. The blood pressure and heart rate were monitored, and, when these had stabilized, which was after about 1 hour, the stable values were recorded as control values. At this time, the test compound suspended in a 0.3% w/v aqueous carboxymethylcellulose solution was administered orally in the dose shown in the following Table 8. The blood pressure and heart rate were then recorded every 15 minutes during the 24 hours after administration of the test compound. The experiment was carried out with Compound No. 1-11, as well as with nifedipine and nicardipine, and the results are recorded in the following Table 8. Cpd. No. Ex. No. Dose (mg/kg, po) 12 Hour Area T max (hours) T 0.5 max (hours) 1-11 1 1 -184 6.0 10.4 1-11 1 3 -334 5.0 12.7 nifedipine - 3 -237 0.3 7.0 nicardipine - 3 -175 0.5 5.3 In the above Table, the results are reported as follows: T max : the time in hours after administration of the compound under test before the maximum change in blood pressure was recorded; T 0.5 max : the time in hours after administration of the compound under test which is required for the blood pressure to return to one half of its maximum value; 12 hour area: the integrated value of the area above the graph of blood pressure change against time after administration of the compound under test over a period of 12 hours after administration to show the potency of the blood pressure lowering action. Although the maximum levels of hypotension produced by the compound of the invention tested were found to be comparable with those produced by nifedipine and nicardipine, there was a considerable difference in the time of onset of activity and in the duration of activity between the compounds of the present invention and the prior art compounds used for comparison. As is obvious from the results reported in Table 8, Compound 1-11 lowered blood pressure much more slowly than did nifedipine or nicardipine, which was an unexpected advantage of Compound 1-11. Also the duration of the antihypertensive activity produced by Compound 1-11 was much longer than that produced by nifedipine and nicardipine. In addition, nifedipine (but not Compound 1-11) increased heart rate, which was most probably caused by a baroreceptor reflex due to the abrupt reduction in blood pressure. Accordingly, the compound of the invention and pharmaceutically acceptable acid addition salts thereof can be used for the treatment of cardiovascular diseases, such as hypertension, angina pectoris miocardial infarction, arrhythmia, arteriosclerosis and cerebrovascular disorders, such as cerebral ischaemia. The compound may be administered in any suitable form, depending upon the nature and condition of the patient, the nature of the disorder and the desired route of administration. For example, the compound may be administered orally in the form of tablets, capsules, granules, powders or syrups. Alternatively, the compound may be administered non-orally by, for example, subcutaneous injection, intravenous injection or suppository. The compound may, if desired, be mixed with carriers, excipients or other auxiliary substances commonly employed in the formulation of pharmaceutical preparations, for example diluents, binders, disintegrating agents, lubricants, flavours, solubilizers and suspending agents. The dose will vary, depending upon the symptoms, age and body weight of the patient, as well as the nature and severity of the disease or disorder to be treated; however, a dose of from 3 to 300 mg per day will normally be appropriate for an adult human patient, and this may be administered in a single dose or in divided doses. The invention is further illustrated with reference to the following Example. Preparation of certain of the starting materials employed in this Example is also illustrated in the subsequent Preparations. EXAMPLE 1 3-(1-Benzhydryl-3-azetidinyl) 5-isopropyl 2-amino-6-methyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate and its dihydrochloride Preparation of free base 0.27 g (0.005 mole) of sodium methoxide was added to a solution of 1.39 g (0.005 mole) of isopropyl 2-(3-nitrobenzylidene)acetoacetate and 1.62 g (0.005 mole) of the acetic acid salt of 1-benzhydryl-3-azetidinyl amidinoacetate (prepared as described in Preparation 2) dissolved in 80 ml of isopropanol, and the mixture was heated under reflux for 4 hours. At the end of this time, the mixture was cooled, insoluble materials were filtered off and the filtrate was concentrated by evaporation under reduced pressure. The residue was dissolved in ethyl acetate and washed with water, after which it was dried over anhydrous sodium sulphate. The solvent was then removed by distillation under reduced pressure, and the residue was subjected to column chromatography through silica gel, using a 3 : 1 by volume mixture of toluene and ethyl acetate as eluent, to give 2.17 g (yield 74%) of the title compound (a free base) as pale yellow crystals, melting at 95 - 98°C. Infrared Absorption Spectrum (KBr) ν max cm⁻¹: 3450, 3310 (NH) and 1675 (-CO₂-). Mass Spectrum (CI) m/e : 583 (M⁺ + 1), 344 (M⁺ - benzhydrylazetidinyloxy) and 167 [⁺CH(phenyl)₂]. Nuclear Magnetic Resonance Spectrum: (CDCl₃) δ ppm: 1.08, 1.26 (6H, 2 x doublet, J=6Hz); 2.35 (3H, singlet); 2.63, 3.06, 3.50, 3.62 (4H, 4 x triplet, J=8Hz); 4.26 (1H, singlet); 4.87-5.04 (3H, multiplet); 6.04 (1H, broad singlet); 6.11 (2H, broad singlet); 7.1-8.17 (14H, multiplet). The resulting free base was recrystallized from a mixture of benzene and hexane to afford pale yellow crystals, melting at 120 - 124°C. The free base was also recrystallized from a mixture of 1,2-dimethoxyethane and hexane to afford pale yellow crystals melting at 162.5 - 164.5°C. The crystals contained an equimolar amount of 1,2-dimethoxyethane (determined by NMR spectrum). These crystals were dried above 100°C under reduced pressure, giving the desired compound as yellow crystals melting at 158 - 160°C. Both kinds of crystals described above melting at 120 - 124°C and at 158 - 160°C were identified with the free base by NMR spectroscopy. Elemental analysis: Calculated for C₃₃H₃₄N₄O₆: C, 68.03%; H, 5.88%; N, 9.62% Found : C, 68.36%; H, 5.94%; N, 9.20%. (free base) C, 68.49%; H, 5.71%; N, 9.62%. (after recrystallization from a mixture of benzene and hexane) C, 67.94%; H, 5.91%; N, 9.63 (after recrystallization from a mixture of 1,2-dimethoxyethane and hexane and drying at about 100°C under reduced pressure). Preparation of dihydrochloride Hydrogen chloride was bubbled into a solution of 0.87 g of the free base in 20 ml of chloroform for 5 minutes. At the end of this time, the solvent was removed by evaporation under reduced pressure, giving 0.95 g of the title compound dihydrochloride as pale yellow crystals, melting at 118 - 120°C. Infrared Absorption Spectrum: (KBr) ν max cm⁻¹: 3400, 3280 (NH) and 1685 (-CO₂-). Mass Spectrum: m/e : 583 (M⁺ + 1), 539 [M⁺ - CH(CH₃)₂], and 167 [⁺CH(phenyl)₂]. Elemental analysis: Calculated for C₃₃H₃₆N₄O₆Cl₂: C, 60.46%; H, 5.53%; N, 8.55%. Found: C, 60.59%; H, 5.81%; N, 8.44%. PREPARATION 1 1-Benzhydryl-3-azetidinyl cyanoacetate 4.25 g (0.05 mole) of cyanoacetic acid and 11.95 g (0.05 mole) of 1-benzhydryl-3-hydroxyazetidine were dissolved in 400 ml of tetrahydrofuran. 12.38 g (0.06 mole) of 1,3-dicyclohexylcarbodiimide were then added to the solution, whilst stirring, after which the mixture was stirred at 55°C for a further 11 hours. At the end of this time, the mixture was cooled, precipitated crystals were removed and the solvent was removed by distillation under reduced pressure. The residue was dissolved in ethyl acetate and the resulting solution was washed with water and then dried over anhydrous sodium sulphate. The solution was then concentrated by evaporation under reduced pressure, and the residue was subjected to column chromatography through silica gel, using a 19 : 1 by volume mixture of toluene and ethyl acetate as eluent, to give 14.25 g (93%) of the title compound as a pale yellow oil. Infrared Absorption Spectrum (capillary) ν max cm⁻¹: 2250 (CN) and 1745 (-CO₂-). Mass Spectrum m/e: 306 (M⁺) and 167 [⁺CH(phenyl)₂]. Nuclear Magnetic Resonance Spectrum: (CDCl₃) δ ppm: 3.1 (2H, multiplet); 3.46 (2H, singlet); 3.6 (2H, multiplet); 4.37 (1H, singlet); 5.16 (1H, quartet, J=6 Hz); 7.1-7.5 (10H, multiplet). PREPARATION 2 Acetic acid salt of 1-benzhydryl-3-azetidinyl amidinoacetate A solution of 7.0 g (0.0229 mole) of 1-benzhydryl-3-azetidinyl cyanoacetate (prepared as described in Preparation 1) and 1.26 g (0.0275 mole) of ethanol dissolved in 300 ml of chloroform was cooled with a mixture of salt and ice. Hydrogen chloride was then bubbled into the solution for 30 minutes, whilst cooling, and the mixture was allowed to stand overnight, also whilst cooling. At the end of this time, the temperature of the mixture was allowed to rise to room temperature, and then the mixture was freed from the solvent by evaporation under reduced pressure. The residue was dissolved in 300 ml of chloroform and ammonia was bubbled into the solution for 1 hour, whilst ice-cooling. The precipitated salt was removed by filtration, and the solvent was distilled off under reduced pressure. The residue was dissolved in 50 ml of acetonitrile, and 1.76 g (0.0229 mole) of ammonium acetate was then added to the solution. The mixture was stirred at 55°C for 1 hour. At the end of this time, unreacted ammonium acetate was removed from the still hot reaction mixture by filtration, and the solvent was distilled off under reduced pressure. The residue was crystallized by adding diethyl ether, and the resulting crystals were collected by filtration and then dried under reduced pressure to afford 7.6 g (yield 87% based on the cyanoacetate) of the title compound as colourless crystals, melting at 100 - 103°C. Mass Spectrum m/e: 324 (M⁺ + 1) and 167 [⁺CH(phenyl)₂].

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LU, NL, SE Compound of formula (I): in which: Ar represents a phenyl group having one 3-position nitro substituent; R represents an isopropyl group; R¹ represents a hydrogen atom; R 2a and R 2b are the same and each represents an unsubstituted phenyl group; R³ represents a methyl group; R⁴ represents an amino group; and n is the integer 1; and pharmaceutically acceptable acid addition salts thereof. A pharmaceutical composition comprising an active compound in admixture with a pharmaceutically acceptable carrier or diluent, in which said active compound is the compound according to Claim 1. A process for preparing a compound according to Claim 1, which process comprises reacting an α-benzylideneacetoacetic acid ester of formula (II): with an amidinoacetic acid ester of formula (III): [in the above formulae: Ar is as defined in Claim 1; and R⁶ represents a group of formula (IV): (in which n , R¹, R 2a and R 2b are as defined in Claim 1) and R⁵ represents an isopropyl group, and optionally salifying and/or desalifying the resulting product to give said compound of formula (I) or said pharmaceutically acceptable acid addition salt thereof. The use for the manufacture of a medicament, especially for the treatment of cardiovascular disorders, of a compound of formula (I) or a pharmaceutically acceptable salt thereof, as claimed in Claim 1. Claims for the following Contracting States : AT, ES, GR A process for preparing a compound of formula (I): [in which: Ar represents a phenyl group having one 3-position nitro substituent; R represents an isopropyl group; R¹ represents a hydrogen atom; R 2a and R 2b are the same and each represents an unsubstituted phenyl group; R³ represents a methyl group; R⁴ represents an amino group; and n is the integer 1]; and pharmaceutically acceptable acid addition salts thereof, which process comprises: reacting an α-benzylideneacetoacetic acid ester of formula (II): with an amidinoacetic acid ester of formula (III): [in the above formulae: Ar is as defined above; and R⁶ represents a group of formula (IV): (in which n , R¹, R 2a and R 2b are as defined above) and R⁵ represents an isopropyl group; and optionally salifying and/or desalifying the resulting product to give said compound of formula (I) or said pharmaceutically acceptable acid addition salt thereof. The use for the manufacture of a medicament, especially for the treatment of cardiovascular disorders, of a compound of formula (I): or a pharmaceutically acceptable salt thereof, as defined in Claim 1.

Inventors: KOIKE, HIROYUKI SANKYO COMPANY LTD., NISHINO, HIROSHI SANKYO COMPANY LTD., YOSHIMOTO, MASAFUMI SANKYO COMPANY LTD.
Applicants: SANKYO COMPANY LIMITED, UBE INDUSTRIES LIMITED
Application year: 1987
Main classification: C07D211
IPC codes: A61K31, C07D211, C07D413, A61P9, A61P3, C07D401, A61P7, C07D205