Benzopyran-type compounds

Abstract: Compounds of formula (I), and pharmaceutically acceptable salts thereof: wherein a and b together form an -O- linkage or a bond or (when R₂ is hydrogen), CH₂; either Y is N and R₂ is hydrogen; or Y is C-R₁ wherein either one of R₁ and R₂ is hydrogen and the other is nitro, cyano, halo, CF₃, C₂F₅, formyl, aldoxime, CF₃O, NO₂-CH=CH-, NC-CH=CH-; a group R x X- wherein R x is C₁₋₆ alkyl, aryl or heteroaryl either of which may be optionally substituted by one, two or three of C₁₋₄ alkyl, C₁₋₄ alkoxy, nitro, halo, CF₃ and cyano; and X is C=O, O.C=O C=O.O, CHOH, SO, SO₂, O.SO, O.SO₂, CONH, O.CONH, O.SO₂NH, CO-CH=CH, C=NHOH, C=NNH₂; or a group R y R z NZ- wherein R y and R z are independently hydrogen or C₁₋₆ alkyl and Z is C=O, SO or SO₂; or a group (R w O)₂P(O)W wherein R w is hydrogen or C₁₋₆ alkyl and W is O or a bond; or R₁ is a C₃₋₈ cycloalkyl group or a C₁₋₆ alkyl group optionally substituted by a group which is hydroxy, C₁₋₆ alkoxy, amino optionally substituted by one or two C₁₋₆ alkyl groups, C₁₋₇ alkanoylamino, C₃₋₈ cycloalkyloxy or C₃₋₈ cycloalkylamino; and R₂ is hydrogen; or one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl and the other is a different group selected from nitro, cyano, halo, C₁₋₃ alkylcarbonyl, methoxy or amino optionally substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl; or R₁ and R₂ together with the carbon atoms to which they are attached, form 2,1,3-oxadiazole; either one of R₃ and R₄ is hydrogen or C₁₋₄ alkyl and the other is C₁₋₄ alkyl; or R₅ is hydrogen, hydroxy, amino, C₁₋₆ alkoxy or C₁₋₇ acyloxy; and E is hydrogen; or R₅ and E together form a bond; either R₆ is hydrogen or C₁₋₆ alkyl; and R₇ is hydrogen, C₃₋₈ cycloalkyl, C₂₋₆ alkenyl, C₁₋₆ alkyl optionally substituted by hydroxy, C₁₋₆ alkoxy, C₁₋₆ alkoxycarbonyl, carboxy, halogen or amino optionally substituted by one or two C₁₋₆ alkyl groups; aryl or heteroaryl either being optionally substituted by one or more groups or atoms selected from the class of C₁₋₆ alkyl, C₁₋₆ alkoxy, hydroxy, halogen, trifluoromethyl, nitro, cyano, C₁₋₁₂ carboxylic acyl, or R₇ is amino or aminocarbonyl optionally substituted by one or two C₁₋₆ alkyl groups or substituted by C₃₋₈ cycloalkyl, or a group OR₉ wherein R₉ is C₁₋₆ alkyl or benzyl optionally substituted as defined for R₇; or R₆ and R₇ are joined together to form C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond(s); and X is oxygen or sulphur; which are potassium channel activators, useful in the treatment of disorders associated with smooth muscle contraction, a process for their preparation and their use as pharmaceuticals.

Description: The present invention relates to novel compounds having pharmacological activity, to a process and intermediates for their preparation and their use as pharmaceuticals. EP-A-76075, 91748, 95316, 120426, 120427, 126367, 126350, 126311, 138134, 139992, 168619, 205292, 214818, 250077 and 321165 (all in the name of Beecham Group p.l.c.) describe classes of compounds which are benzopyran, tetrahydronaphthalene, pyranopyridine or indane derivative potassium channel activators. EP-A-277611 and 277612 (Hoechst Aktiengesellschaft), EP-A-314446 (American Home Products Corporation) and WO 89/07103 (Nissan Chemical Industries Limited), describe further classes of benzopyran derivatives. A novel class of compounds has now been discovered, which are also believed to be potassium channel activators, useful in the treatment of disorders associated with smooth muscle contraction. Such disorders include hypertension, including pulmonary hypertension, and cardiovascular disorders other than hypertension, such as congestive heart failure, angina, peripheral vascular disease and cerebral vascular disease. Other disorders include those of the gastrointestinal tract, respiratory system, uterus and urinary tract. Such disorders include irritable bowel syndrome and diverticular disease; reversible airways obstruction and asthma; premature labour; incontinence and kidney stones. They may also be of potential use in the treatment of epilepsy. Accordingly, the present invention provides a compound of formula (I), or a pharmaceutically acceptable salt thereof: wherein a and b together form an -O- linkage or a bond or (when R₂ is hydrogen), CH₂; either Y is N and R₂ is hydrogen; or Y is C-R₁ wherein either one of R₁ and R₂ is hydrogen and the other is nitro, cyano, halo, CF₃, C₂F₅, formyl, aldoxime, CF₃O, NO₂-CH=CH-, NC-CH=CH-; a group R x X-wherein R x is C₁₋₆ alkyl, aryl or heteroaryl either of which may be optionally substituted by one, two or three of C₁₋₄ alkyl, C₁₋₄ alkoxy, nitro, halo, CF₃ and cyano; and X is C=O, O.C=O, C=O.O, CHOH, SO, SO₂, O.SO, O.SO₂, CONH, O.CONH, O.SO₂NH, CO-CH=CH, C=NHOH, C=NNH₂; or a group R y R z NZ- wherein R y and R z are independently hydrogen or C₁₋₆ alkyl and Z is C=O, SO or SO₂; or a group (R w O)₂P(O)W wherein R w is hydrogen or C₁₋₆ alkyl and W is O or a bond; or R₁ is a C₃₋₈ cycloalkyl group or a C₁₋₆ alkyl group optionally substituted by a group which is hydroxy, C₁₋₆ alkoxy, amino optionally substituted by one or two C₁₋₆ alkyl groups, C₁₋₇ alkanoylamino, C₃₋₈ cycloalkyloxy or C₃₋₈ cycloalkylamino; and R₂ is hydrogen; or one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl and the other is a different group selected from nitro, cyano, halo, C₁₋₃ alkylcarbonyl, methoxy or amino optionally substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl; or R₁ and R₂ together with the carbon atoms to which they are attached, form 2,1,3-oxadiazole; either one of R₃ and R₄ is hydrogen or C₁₋₄ alkyl and the other is C₁₋₄ alkyl; or R₃ and R₄ together are C₂₋₅ polymethylene. R₅ is hydrogen, hydroxy, amino, C₁₋₆ alkoxy or C₁₋₇ acyloxy; and E is hydrogen; or R₅ and E together form a bond; either R₆ is hydrogen or C₁₋₆ alkyl; and R₇ is hydrogen, C₃₋₈ cycloalkyl, C₂₋₆ alkenyl, C₁₋₆ alkyl optionally substituted by hydroxy, C₁₋₆ alkoxy, C₁₋₆ alkoxycarbonyl, carboxy, halogen or amino optionally substituted by one or two C₁₋₆ alkyl groups; aryl or heteroaryl either being optionally substituted by one or more groups or atoms selected from the class of C₁₋₆ alkyl, C₁₋₆ alkoxy, hydroxy, halogen, trifluoromethyl, nitro, cyano, C₁₋₁₂ carboxylic acyl, or R₇ is amino or aminocarbonyl optionally substituted by one or two C₁₋₆ alkyl groups or substituted by C₃₋₈ cycloalkyl, or a group OR₉ wherein R₉ is C₁₋₆ alkyl or benzyl optionally substituted as defined for R₇; or R₆ and R₇ are joined together to form C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond(s); and X is oxygen or sulphur. a and b are preferably an -O- linkage and Y is preferably C-R₁ as defined. When either one of R₁ and R₂ is hydrogen, the other is preferably selected from halo, CF₃, C₂F₅, C₁₋₆ alkylcarbonyl, C₁₋₆ alkoxycarbonyl, nitro or cyano. When one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl the other is, favourably, amino optionally substituted by one or two C₁₋₆ alkyl groups or by C₂₋₇ alkanoyl. In particular, when one of R₁ and R₂ is nitro, cyano or acetyl, the other is amino, methylamino, dimethylamino or acetylamino. Preferably, when one or R₁ and R₂ is nitro or cyano, especially cyano, the other is amino. Halo substituents in R₁ and/or R₂ are usually chloro or bromo. Values for R x when alkyl in R₁/R₂ are usually selected from methyl, ethyl, n - and iso -propyl, n -, iso -, sec -and tert -butyl, preferably methyl or ethyl. Suitable examples of other alkyl or alkyl containing groups in R₁ and in R₃ to R₇ when alkyl include those listed for R₁ and R₂ alkyl groups. Cycloalkyl groups include C₃, C₄, C₅, C₆, C₇ and C₈ cycloalkyl. When R₂ is hydrogen, a preferred value for R₁ is C₁₋₆ alkyl, such as methyl, ethyl, iso -propyl or t -butyl. A sub-group of R x or R₇ heteroaryl is 5- or 6-membered monocyclic or 9- or 10-membered bicyclic heteroaryl of which 5- or 6-membered monocyclic heteroaryl is preferred. In addition, 5- or 6-membered monocyclic or 9- or 10-membered bicyclic heteroaryl preferably contains one, two or three heteroatoms which are selected from the class of oxygen, nitrogen and sulphur and which, in the case of there being more than one heteroatom, are the same or different. Examples of 5- or 6-membered monocyclic heteroaryl containing one, two or three heteroatoms which are selected from the class of oxygen, nitrogen and sulphur include furyl, thienyl, pyrryl, oxazolyl, thiazolyl, imidazolyl and thiadiazolyl, and pyridyl, pyridazyl, pyrimidyl, pyrazyl and triazyl. Preferred examples of such groups include furyl, thienyl, pyrryl and pyridyl, in particular 2- and 3-furyl, 2- and 3-pyrryl, 2- and 3-thienyl, and 2-, 3- and 4-pyridyl. Examples of 9- or 10-membered bicyclic heteroaryl containing one, two or three heteroatoms which are selected from the class of oxygen, nitrogen and sulphur include benzofuranyl, benzothienyl, indolyl and indazolyl, quinolyl and isoquinolyl, and quinazonyl. Preferred examples of such groups include 2- and 3-benzofuryl, 2- and 3-benzothienyl, and 2- and 3-indolyl, and 2- and 3-quinolyl. R x or R₇ when aryl is usually phenyl or naphthyl. Examples of the groups or atoms for optional substitution of R x or R₆ when aryl or heteroaryl include methyl, methoxy, hydroxy, fluoro, chloro, nitro or cyano. R₁ is preferably nitro, cyano, acetyl, CF₃, C₂F₅ or C₁₋₄ alkyl. Preferably R₃ and R₄ are both methyl groups. Suitable examples of R₅ when alkoxy include methoxy, ethoxy, n - and iso -propoxy, of which methoxy is preferred. When R₅ is C₁₋₇ acyloxy it is usually C₁₋₇ carboxylic acyloxy, such as C₁₋₇ alkanoyloxy wherein the alkyl moiety is usually as listed for alkyl in R₁ and R₂ above. R₅ is preferably hydroxy. Preferably R₆ and R₇ are not joined, and R₆ is hydrogen and R₇ is optionally substituted phenyl, preferably 4-fluorophenyl, or branched C₁₋₆ alkyl, such as t-butyl; OR₉ wherein R₉ is C₁₋₆ alkyl or benzyl, or R₇ is optionally substituted amino as defined, most preferably t-butylamino. Examples of pharmaceutically acceptable salts include acid addition salts with acids such as hydrochloric, hydrobromic, phosphoric, sulphuric, citric, tartaric, lactic or acetic acid. The compounds of formula (I) have at least one asymmetric centre and therefore exist in more than stereoisomeric form. The invention extends to each of these forms individually and to mixtures thereof, such as racemates. The R₆NCXR₇ moiety may be cis or trans to the R₅ group when R₅ is hydroxy, amino, C₁₋₆ alkoxy or C₁₋₇ acyloxy. The trans configuration is preferred. The compounds of formula (I) and their salts may form solvates, such as hydrates, and these are included as an aspect of the invention, wherever a compound of formula (I) or a salt thereof is herein referred to. The invention also provides a process for the preparation of a compound of formula (I), or a pharmaceutically acceptable salt thereof, which process comprises acylating a compound of formula (II): wherein Y′ and R₂′ are Y and R₂ respectively or groups or atoms convertible thereto, R₅¹ is hydroxy, C₁₋₆ alkoxy, C₁₋₇ acyloxy or azide, R₆¹ is hydrogen or C₁₋₆ alkyl and the R₆¹NH group is trans to the R₅¹ group (when R₅¹ is other than than azide), with a) an acylating agent of formula (III): R₇¹COQ (III) wherein Q is a leaving group and R₇¹ is R₇ as defined or a group convertible thereto, when not joined to R₆ or, (when R₆¹ is hydrogen), R₇¹ is a group R₁₀ which is C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond(s), terminally substituted by a leaving group, L; and thereafter, when R₇¹ is R₁₀, cyclising the resulting compound; or b) (when R₇ is NHR₁₁ wherein R₁₁ is hydrogen or C₁₋₆ alkyl), with a compound of formula (IV): X = C = NR₁₁ (IV) wherein X and R₁₁ are as hereinbefore defined; and thereafter, as desired or necessary, converting R₅¹ to R₅, converting Y′ and/or R₂′ to Y and/or R₂, optionally thiating X when oxygen to X is sulphur and/or dehydrating a compound wherein R₅¹ is hydroxy to form a compound of formula (I) wherein R₅ and E form a bond or converting a compound of formula (I) wherein the R₆NCXR₇ moiety is trans to R₅ when hydroxy, to a corresponding cis isomer; and optionally forming a pharmaceutically acceptable salt thereof. In the process variant a) acylation of a compound of formula (II) with an acylating agent of formula (III), the leaving group Q is a group that is displaceable by a primary or secondary amino nucleophile. Examples of such a group include C₁₋₄ alkanoyloxy, and halogen, such as chloro and bromo. When the leaving group Q is either of these examples, the acylating agent of formula (III) is either an acid anhydride or an acid halide. When it is an acid anhydride, it may be a mixed or simple anhydride. If it is a mixed anhydride, it may be prepared in situ from a carboxylic acid and an acid halide, although this is less preferred than using the halide itself. In process variant a), when R₇ in the desired compound of formula (I) is an R₇ optionally substituted amino-substituted alkyl group as hereinbefore defined, it is preferred that R₇¹ is a group convertible to the R₇ substituted alkyl group as hereinbefore defined, in particular that it is C₁₋₆ alkyl substituted by halo, especially bromo. The R₇¹ halo substituent in the resultant compound of process variant a) may be converted to an R₇ substituent which is amino optionally substituted as hereinbefore defined, by a conventional amination reaction with ammonia or a corresponding alkyl- or dialkylamine. Less favourably R₇¹ may be C₁₋₆ alkyl substituted by protected amino, protected C₁₋₆ alkylamino or amino substituted by two independent C₁₋₆ alkyl groups, it being necessary to protect the R₇ amino function in process variant a). When the acylating agent of formula (III) is an acid anhydride, the acylation of the compound of formula (II) may be carried out in the presence of an acid acceptor, such as sodium acetate, optionally using the anhydride as the solvent. When the acylating agent of formula (III) is an acid halide, the acylation of the compound of formula (II) is, preferably, carried out in a non-aqueous medium, such as dichloromethane, in the presence of an acid acceptor, such as triethylamine, trimethylamine, pyridine, picoline or calcium, potassium or sodium carbonate. When R₅ in a compound of formula (II) is hydroxy, there is a risk of a side-reaction between the hydroxy group and the acylating agent of formula (III). However, the reaction may be carried out under controlled conditions such that only the R₆¹NH- is acylated, for example, by using a C₂₋₉ acyloxy group as the leaving group Q, in the acylating agent of formula (III) in the manner as previously described for an acid anhydride, and/or effecting the reaction at relatively low temperature, e.g. at below 10 o C. Alternatively R₅ may be C₁₋₇ acyloxy in a compound of formula (II), although less preferably if R₅ in the resultant compound of formula (I) is to be hydroxy, and, after reaction with the acylating agent of formula (III), be converted into hydroxy, as described hereinafter. When R₇¹ is R₁₀ as hereinbefore defined, the leaving group L is a group that is displaceable by a secondary amino nucleophile adjacent to a carbonyl function. A preferred example is chloro. The cyclisation reaction when R₇¹ is R₁₀ where the variables are as hereinbefore defined is preferably carried out in an inert solvent such as tetrahydrofuran or dimethylformamide. In process variant b), the reaction is preferably carried out in an inert solvent, such as dichloromethane, at temperatures at ambient or below, such as below 10 o C. When R₁₁ is hydrogen in formula (IV), the reaction is preferably carried out using a corresponding alkali metal cyanate or thiocyanate, for example, that of sodium or potassium in an optionally methanolic aqueous medium acidified with a mineral acid, such as dilute hydrochloric acid, at an elevated temperature 50 to 90 o C. Examples of a conversion of R₅¹ into R₅ are generally known in the art. For example, when R₅¹ is hydroxy, it may be alkylated using an alkyl iodide in an inert solvent, such as toluene, in the presence of a base, such as potassium hydroxide, or it may be acylated using a carboxylic acid chloride or anhydride in a non-hydroxylic solvent in the presence of an acid acceptor. Alternatively, when R₅¹ is C₁₋₇ acyloxy or C₁₋₆ alkoxy, it may be converted into hydroxy by conventional hydrolysis with, for example, dilute mineral acid. When R₅¹ is azide, it may be converted to R₅ is amino by reduction, preferably using propane-1,3-dithiol, as described in Example 26 hereinafter. Suitable conversions of Y′/R₂′ are as described in aforementioned European Patent Publications. The optional thiation of the R₆-N-CO-R₇ group in a compound of formula (I) to give another compound of formula I, wherein X is sulphur, is, preferably, carried out with conventional thiation agents, such as hydrogen sulphide, phosporous pentasulphide and Lawesson's reagent (p-methoxyphenylthiophosphine sulphide dimer). The use of hydrogen sulphide and phosporous pentasulphide may lead to side-reactions and, therefore, the use of Lawesson's reagent is preferred. The thiation reaction conditions are conventional for the thiation agent employed. For example, the use of hydrogen sulphide is, preferably, acid catalysed by, for example, hydrogen chloride in a polar solvent, such as acetic acid or ethanol. The preferred use of Lawesson's reagent is, preferably, carried out under reflux in a dry solvent, such as toluene or dichloromethane. The dehydration of a resulting compound of formula (I) wherein R₅ is hydroxy and E is hydrogen may be carried out under conventional dehydration conditions, using a dehydrating agent such as sodium hydride, in an inert solvent, such as dry tetrahydrofuran, at reflux temperature. Conversion of a compound of formula (I) wherein the R₆NCXR₇ moiety is trans to R₅ when hydroxy, to a corresponding cis isomer, may be achieved according to the method described by C.S.V. Houge Frydrych and I.L. Pinto, Tetrahedron Letters 30 , 1989, p3349. The optional formation of a pharmaceutically acceptable salt, when the resulting compound of formula (I) contains a salifiable group, may be carried out conventionally. The intermediates of formula (II) wherein R₆¹ is hydrogen and R₅ is OH, are prepared by hydrolysis of an aziridine intermediate of formula (V): wherein R c is an amino protecting group and the remaining variables are as hereinbefore defined; followed by deprotection, if necessary. Examples of the group R c include t -butyloxycarbonyl, ethoxycarbonyl, methoxycarbonyl and benzyloxycarbonyl, removed by conventional methods. The t -butyloxycarbonyl group is preferred, in which case, the deprotection preferably takes place under acidic conditions, using trifluoroacetic acid, in an inert solvent, such as dichloromethane at a temperature of around 0 o C. The trans intermediates of formula (II) wherein R₆¹ is hydrogen and R₅ is azide, are prepared by reacting an intermediate of formula (V) as hereinbefore defined, with sodium azide, as described in Description 15 hereinafter. The cis intermediates of formula (II) wherein R₆¹ is hydrogen and R₅ is azide may be prepared from the intermediates of formula (VI), as hereinafter defined, by reaction with sodium azide. When R₆¹ is other than hydrogen, the intermediates of formula (II) are prepared from the corresponding intermediate wherein R₆¹ is hydrogen, by conventional methods of forming secondary amines, i.e. by alkylation or reductive amination. Compounds of the formula (V) are prepared by reacting a compound of formula (VI): wherein the chloro substituent is trans to the NHR c substituent, with a base, such as potassium carbonate, as described in Description 2 hereinafter; or (when a and b together are a bond), with sodium hydride/DMF/40 o C. Compounds of the formula (VI) are prepared by reacting a compound of formula (VII): with, when R c is t-butyloxycarbonyl, t -butyl-N,N-dichlorocarbamate, in a similar manner to that described in Description 1 hereinafter. Another suitable solvent is carbon tetrachloride and it will be appreciated that the choice of solvent will be influenced by the value of Y′ and/or a and b. Compounds of the formula (VII) are described in the aforementioned Patent Publications, prepared by the process depicted below (when a and b together form an -O- linkage): (a) Reflux; acetone; K₂CO₃/KI; or a phase transfer catalytic method with optional sonification; (b) Heat in 1,2-dichlorobenzene or N,N-diethylaniline; When R c is t-butyloxycarbonyl, the intermediates of formula (II) wherein R₆¹ is hydrogen and R₅ is hydrogen are prepared from the intermediates of formula (VII) by reaction with t -butyl-N,N-dichlorocarbamate, followed by ammonium acetate/zinc dust in ethanolic dioxan, as described in Example 4 hereinafter. It will be appreciated that, when R₆ is hydrogen and R₇ in the desired compound of formula (I) is C₁₋₆ alkoxycarbonyl, R c may be identical to R₇ and therefore deprotection and subsequent acylation of the compound of formula (II) is not necessary (see Examples 1 and 4 hereinafter). As mentioned previously, some of the compounds of formula (I) may exist in optically active forms, in particular it will be appreciated that the carbon atoms to which E and R₅ are attached are asymmetric when R₅ and E together do not form a bond. The individual enantiomers may be resolved by conventional methods; or they may be prepared from resolved intermediates of formula (II). It is preferred that the compounds of formula (I) are isolated in substantially pure pharmaceutically acceptable form. The intermediates of formulae (II), (V) and (VI) are novel and represent an aspect of the present invention. As mentioned previously, the compounds of formula (I) have been found to have blood-pressure lowering activity and/or bronchodilator activity. They are therefore useful in the treatment of hypertension. They are also believed to be of potential use in the treatment of other disorders hereinbefore referred to. The present invention accordingly provides a pharmaceutical composition which comprises a compound of formula (I) or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier. In particular, the present invention provides an anti-hypertensive or bronchodilator pharmaceutical composition which comprises an effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier. The compositions are preferably adapted for oral administration. However, they may be adapted for other modes of administration, for example parenteral administration for patients suffering from heart failure. Other alternative modes of administration include sublingual or transdermal administration. A composition may be in the form of spray, aerosol or other conventional method of inhalation, for treating respiratory tract disorders. The compositions may be in the form of tablets, capsules, powders, granules, lozenges, suppositories, reconstitutable powders, or liquid preparations, such as oral or sterile parenteral solutions or suspensions. In order to obtain consistency of administration it is preferred that a composition of the invention is in the form of a unit dose. Unit dose presentation forms for oral administration may be tablets and capsules and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinylpyrrolidone; fillers, for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricants, for example magnesium stearate; disintegrants, for example starch, polyvinylpyrrolidone, sodium starch glycollate or microcrystalline cellulose; or pharmaceutically acceptable wetting agents such as sodium lauryl sulphate. The solid 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. The tablets may be coated according to methods well known in normal pharmaceutical practice, in particular with an enteric coating. Oral liquid preparations may be in the form of, for example, 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,hydrogenated 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. For parenteral administration, fluid unit dosage forms are prepared utilizing the compound and a sterile vehicle, and, depending on the concentration used, can be either suspended or dissolved in the vehicle. In preparing solutions the compound can be dissolved in water for injection and filter sterilized before filling into a suitable vial or ampoule and sealing. Advantageously, adjuvants such as a local anaesthetic, a preservative and buffering agents can be 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 sterilization cannot be accomplished by filtration. The compound can be sterilized by exposure to 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. The compositions may contain from 0.1% to 99% by weight, preferably from 10-60% by weight, of the active material, depending on the method of administration. The present invention further provides a method of prophylaxis or treatment of hypertension or respiratory tract disorders in mammals including man, which comprises administering to the suffering mammal an anti-hypertensive or bronchodilator effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof. An effective amount will depend on the relative efficacy of the compounds of the present invention, the severity of the disorder being treated and the weight of the sufferer. However, a unit dose form of a composition of the invention may contain from 0.05 to 500 mg of a compound of the invention and more usually from 0.1 to 50 mg, for example 0.5 to 25 mg such as 0.5, 1, 2, 5, 10, 15 or 20 mg. Such compositions may be administered from 1 to 6 times a day, more usually from 1 to 4 times a day, in a manner such that the daily dose is from 0.01 to 25 mg per kg body weight and more particularly from 0.1 to 10 mg/kg. No toxicological effects are indicated at the aforementioned dosage ranges. It will be appreciated that the compounds of the invention may be administered in combination with other antihypertensives, especially ACE inhibitors or β-blockers, or with diuretics. The present invention further provides a compound of formula (I) or a pharmaceutically acceptable salt thereof for use as an active therapeutic substance, in particular, in the treatment or prophylaxis of hypertension and/or respiratory tract disorders. The invention also provides the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof in the manufacture of a medicament for use in the treatment or prophylaxis of hypertension and/or respiratory tract disorders. Tables 1, 2, 3 and 4 show the intermediates and compounds of the invention prepared. The following descriptions relate to the preparation of intermediates and the following examples relate to the preparation of compounds of formula (I). Description 1 Trans-6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonylamino)-4-chloro-2H-1-benzopyran (D1) A solution of t-butyl-N,N-dichlorocarbamate (2.19 g, prepared by the method of R.E. White and P. Kovacic, J.A.C.S., 97 , 1180(1975)) in dry toluene (10 ml) was added dropwise to a solution of 2,2-dimethyl-6-cyano-2H-1-benzopyran (2.0 g) in dry toluene (20 ml) at 35-40 o C. The solution was then stirred at 45-50 o C for 6 h, cooled to 0 o C, and a 20% solution of sodium metabisulphite (20 ml) added. The mixture was stirred vigorously for 18 h and the layers were separated. The organic layer was washed with water, saturated sodium bicarbonate solution, brine, then dried over sodium sulphate. Removal of solvents in vacuo and trituration of the residue with pentane:ethyl acetate (95:5) gave the title compound as a colourless solid (2.1 g, 58%). A sample recrystallised from ethyl acetate:60-80 o C petrol had m.pt. 164-166 o C; ¹H n.m.r (CDCl₃) δ 1.30 (s, 3H); 1.46 (s, 9H); 1.53 (s, 3H); 4.17 (t, J=8, 8Hz, 1H); 4.63 (d, J=8Hz, 1H); 4.88 (d, J=8Hz, 1H); 6.92 (d, J=9Hz, 1H); 7.48 (dd, J=9, 2Hz, 1H); 7.82 (d, J=2Hz, 1H). Anal . Found: C,60.71%, H,6.46%, N,8.33%. C₁₇H₂₁N₂O₃Cl requires: C,60.62%, H,6.28%, N,8.32%. Description 2 6-Cyano-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D2) A solution of trans-6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonylamino)-4-chloro-2H-1-benzopyran (1.57 g) and potassium carbonate (1.0 g) in ethanol (100 ml) and water (5 ml) was stirred for 18 h. Solvents were removed in vacuo ; and the residue extracted with ethyl acetate. The extracts were dried over magnesium sulphate and evaporated in vacuo to give the title compound (1.38 g, 98% as a colourless solid having m.pt. 116-118 o C; ¹H n.m.r. (CDCl₃) δ 1.25 (s, 3H); 1.46 (s, 9H); 1.65 (s, 3H); 3.05 (d, J=6Hz, 1H); 3.50 (d, J=6Hz, 1H); 6.86 (d, J=9Hz, 1H); 7.49 (dd, J=9, 2Hz, 1H); 7.65 (d, J=2Hz, 1H). Description 3 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D3) A solution of trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol (2.0g) (E1), and trifluoroacetic acid (18 ml) in dry dichloromethane (50 ml) was stirred at 0 o C for 8h. Solvents were removed in vacuo , and the residue dissolved in ethyl acetate and washed with saturated sodium bicarbonate solution, then dried (MgSO₄) and evaporated to give the title compound (1.0g) as a solid which was used without further purification. ¹H n.m.r. (CDCl₃) δ: 1.30 (s, 3H); 1.50 (s, 3H); 3.15 (d, J=9, 1H); 4.40 (brs, 3H); 4.65 (d, J=9, 1H); 6.72 (d, J=9, 1H); 7.36 (dd, J=9,2, 1H); 7.68 (d, J=2, 1H). Description 4 trans-6-Chloro-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-chloro-2H-1-benzopyran (D4) The compound of this description was prepared from 6-chloro-2,2-dimethyl-2H-1-benzopyran [J.Med.Chem., 1983, 26 , 1582], in a similar manner to the compound of description 1, to give the title compound (D4), as a colourless solid having m.pt. 140-1 o C. ¹H n.m.r. (CDCl₃) δ 1.30 (s,3H), 1.45 (s,9H), 1.62 (s,3H), 4.16 (m,1H), 4.68 (d,J=8Hz,1H), 4.87 (d,J=6Hz,1H), 6.78 (d,J=9Hz,1H), 7.18 (J=9,2,Hz,1H), 7.45 (d,J=2Hz,1H). Description 5 6-Chloro-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D5) The compound of this description was prepared from trans -6-chloro-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonylamino)-4-chloro-2H-1-benzopyran (D4), in a similar manner to the compound of description 2, to give the title compound (D5) as a solid, which was used without further purification. ¹H n.m.r. (CDCl₃) δ 1.20 (s,3H), 1.45 (s,9H), 1.62 (s,3H), 3.00 (d,J=6Hz,1H), 3.44 (d,J=6Hz,1H), 6.75 (d,J=9Hz,1H), 7.15 (dd,J=9,2Hz,1H), 7.32 (d,J=2Hz,1H). Description 6 trans-6-Chloro-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol (D6) The compound of this description was prepared from 6-chloro-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D5), in a similar manner to the compound of example 1, to give the title compound as a colourless solid having m.pt. 132-3 o C. ¹H n.m.r. (CDCl₃) δ 1.25 (s,3H), 1.42 (s,3H), 1.46 (s,9H), 3.83 (m,1H), 4.48 (d,J=6Hz,1H), 4.66 (m,1H), 4.80-5.20 (brs,1H), 6.74 (d,J=9Hz,1H), 7.14 (dd,J=9,2Hz,1H), 7.46 (d,J=2Hz,1H). Description 7 trans-6-Chloro-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D7) The compound of this description was prepared from trans -6-chloro-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol (D6), in a similar manner to the compound of description 3, to give the title compound (D7) as a gum. ¹H n.m.r. (CDCl₃) δ 1.32 (s,3H), 1.55 (s,3H), 3.26 (d,J=9Hz,1H), 4.82 (d,J=9Hz,1H), 5.10-6.00 (brs,3H), 6.72 (d,J=9Hz,1H), 7.13 (dd,J=9,2Hz,1H), 7.49 (d,J=2Hz,1H). Description 8 trans-6-Trifluoromethyl-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-chloro-2H-1-benzopyran (D8) The compound of this description was prepared from 6-trifluoromethyl-2,2-dimethyl-2H-1-benzopyran, in a similar manner to the compound of description 1, to give the title compound (D8) which recrystallised from ethyl acetate: 60-80 o C petrol as colourless needles having m.pt. 220-3 o C (decomp.). ¹H n.m.r. (CDCl₃) δ 1.30 (s,3H), 1.46 (s,9H), 1.54 (s,3H), 4.19 (dd,J=9,6Hz,1H), 4.67 (d,J=9Hz,1H), 4.92 (d,J=6Hz,1H), 6.92 (d,J=9Hz,1H), 7.46 (dd,J=9,2Hz,1H), 7.75 (d,J=2Hz,1H). Description 9 6-Trifluoromethyl-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D9) The compound of this description was prepared from trans -6-trifluoromethyl-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-chloro-2H-1-benzopyran (D8), in a similar manner to the compound of description 2, to give the title compound (D9) as a solid, which was used without further purification. ¹H n.m.r. (CDCl₃) δ 1.25 (s,3H), 1.45 (s,9H), 1.60 (s,3H), 3.02 (d,J=6Hz,1H), 3.50 (d,J=6Hz,1H), 6.85 (d,J=9Hz,1H), 7.40-7.65 (m,2H). Description 10 trans-6-Trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol (D10) The compound of this description was prepared from 6-trifluoromethyl-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D9), in a similar manner to the compound of example 1, to give the title compound (D10) as colourless microcrystals having m.pt. 147-8 o C. ¹H n.m.r. (CDCl₃) δ 1.27 (s,3H), 1.44 (s,9H), 1.48 (s,3H), 2.80-3.30 (brs,1H), 3.88 (m,1H), 4.54 (d,J=8Hz,1H), 4.65 (m,1H), 6.89 (d,J=9Hz,1H), 7.44 (dd,J=9,2Hz,1H), 7.28 (d,J=2Hz,1H). Description 11 trans-6-Trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D11) The compound of this description was prepared from trans -6-trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol (D10),in a similar manner to the compound of description 3, to give the title compound (D11) as a crude solid, which was used without further purification. ¹H n.m.r. (CDCl₃) δ 1.20 (s,3H), 1.48 (s,3H), 2.20-2.30 (brs,3H), 2.87 (d,J=10Hz,1H), 4.40 (d,J=10Hz,1H), 6.85 (d,J=9Hz,1H), 7.43 (dd,J=9,2Hz,1H), 7.78 (d,J=2Hz,1H). Description 12 Benzyl-N,N-dichlorocarbamate (D12) Hydrochloric acid (54 mL, 5N) was added dropwise to a stirred suspension of benzylcarbamate (9.6g) and calcium hypochlorite (18.3g) in dichloromethane (80 mL) at 0 o C. The mixture was stirred whilst allowing to warm to room temperature over 1h, separated and the organic layer washed with water, then dried (MgSO₄). Evaporation of solvent in vacuo gave the title compound (D13) as a gum (13.0g) which was used without further purification. ¹H n.m.r. (CDCl₃) δ 5.24 (s,2H), 7.35 (s,5H). Description 13 trans-6-Cyano-3,4-dihydro-2,2-dimethyl-3-(benzyloxycarbonylamino)-4-chloro-2H-1-benzopyran (D13) The compound of this description was prepared from 2,2-dimethyl-6-cyano-2H-1-benzopyran in a similar manner to the compound of description 1, but using benzyl-N,N-dichlorocarbamate (D13). Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (D13) as colourless needles having m.pt. 125-6 o C. ¹H n.m.r. (CDCl₃) δ 1.30 (s,3H), 1.53 (s,3H), 4.25 (m,1H), 4.80-5.00 (m,1H) overlapping 4.90 (d,J=6Hz,1H), 5.18 (s,2H), 6.90 (d,J=9Hz,1H), 7.36 (s,5H), 7.48 (dd,J=9,2Hz,1H), 7.80 (d,J=2Hz,1H). Description 14 6-Cyano-3,4-[(N-benzyloxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D14) A mixture of trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(benzyloxycarbonyl)amino-4-chloro-2H-1-benzopyran (D13) (0.5g), potassium bicarbonate (0.25g), and potassium carbonate (50 mg) in ethanol (20 mL) and water (0.5 mL) was stirred vigorously for 4 days. Solvents were removed in vacuo , and the residue extracted with ethyl acetate. The extracts were dried (MgSO₄) and evaporated in vacuo to give the title compound (D14) (0.35g) as a solid which was used without further purification. ¹H n.m.r. (CDCl₃) δ 1.25 (s,3H), 1.55 (s,3H), 3.15 (d,J=6Hz,1H), 3.60 (d,J=6Hz,1H), 5.15 (s,2H), 6.82 (d,J=9Hz,1H), 7.30 (s,5H), 7.45-7.80 (m,2H). Description 15 trans-6-Cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-azido-2H-1-benzopyran (D15) Sodium azide (0.79g) was added to a stirred mixture of 6-cyano-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (D2) (3.32g), and ammonium chloride (0.64g) in dry N,N-dimethylformamide (30mL). The reaction mixture was heated at 60-65 o C for 5h, then cooled and partitioned between ethyl acetate and water. The organic layer was washed with water, brine and then dried (HgSO₄) and evaporated in vacuo to give the title compound (D15) (2.9g). A sample recrystallised from ethyl acetate: 60-80 o C petrol having mpt 167-8 o C. Example 1 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol (E1) A solution of 6-cyano-3,4-[N-t-butoxycarbonyl)-aziridino]-2,2-dimethyl-2H-1-benzopyran (D2) (0.5g) in dioxan (20 ml) and water (20 ml) was treated with dil. H₂SO₄ (0.25 ml) and the solution stirred at room temperature for 18h. Solvents were evaporated in vacuo and the residue partitioned between ethyl acetate and water. The organic extracts were dried (MgSO₄) and evaporated to give a solid which recrystallised from 60-80 o C petrol:ethyl acetate as microcrystals (0.2g) having m.pt. 150-2 o C. ¹H n.m.r. (CDCl₃) δ: 1.25 (s, 3H); 1.42 (s, 9H); 1.46 (s, 3H); 3.50 (br s, O H ); 3.85 (m, 1H); 4.52 (d, J=9, 1H); 4.70 (d, N H ); 6.87 (d, J=9, 1H); 7.46 (dd, J=9,2, 1H); 7.82 (d, J=2, 1H). Found: C, 64.30; H, 7.14; N, 8.79%; C₁₇H₂₂N₂O₄ requires C, 64.13; H, 6.97; N, 8.80%. Example 2 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(2-oxo-1-piperidinyl)-2H-1-benzopyran-4-ol (E2) To a solution of trans-6-cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D3) (1.0g) and triethylamine (1 ml) in dichloromethane (30 ml) at 0 o C was added 5-chlorovalerylchloride (0.71g). The solution was stirred at room temperature for 24h, then water was added, and the mixture extracted with ethyl acetate. The combined organic layers were washed with dil. HCl, water, brine, and dried (MgSO₄). Removal of solvents in vacuo gave the crude amide (1.2g) which was dissolved in dry tetrahydrofuran (100 ml) and sodium hydride (0.116g, 80% dispersion in oil) added. The solution was stirred at room temperature for 6 days, then water was added, and the mixture extracted with ethyl acetate. The combined organic layers were dried (MgSO₄) and evaporated in vacuo . The residue was chromatographed on a silica gel column eluted with ethyl acetate to give the title compound (0.2g) which recrystallised from ethyl acetate:pentane as needles having m.pt. 222-5 o C. ¹H n.m.r. (DMSO-d₆) δ: 1.32 (s, 3H); 1.42 (s, 3H); 1.80 (m, 4H); 2.45 (m, 2H); 3.28 (m, 2H); 3.50 (brs, 1H); 4.78 (d, J=8, 1H); 5.10 (d, J=8, 1H); 6.86 (d, J=9, 1H); 7.46 (dd, J=9,2, 1H); 7.85 (d, J=2, 1H). Example 3 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(4-fluorobenzoylamino)-2H-1-benzopyran-4-ol (E3) To a solution of trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D3) (0.576g) and triethylamine (1 ml) in dichloromethane (40 ml) at 0 o C, was added 4-fluorobenzoyl chloride (0.835g). The reaction mixture was stirred at room temperature for 3 days, then water was added, and the mixture separated. The organic layer was washed with dil. HCl, sodium bicarbonate solution, water, brine, and then dried. Solvent removed in vacuo , and the residue dissolved in methanol (20 ml) and sodium hydroxide solution (0.4 ml, 10%) added. The solution was stirred at room temperature for 18h, then water was added and the mixture extracted with ethyl acetate. The combined organic extracts were washed with water, and dried (MgSO₄). Evaporation of solvent in vacuo gave a solid which recrystallised from ethyl acetate: 60-80 o C petrol as colourless microcrystals (0.2g) having m.pt. 212-5 o C. ¹H n.m.r. (CDCl₃) δ: 1.34 (s, 3H); 1.50 (s, 3H); 3.35 (brs, 1H); 3.90 (brs, 1H); 4.40 (d, J=9, 1H); 4.70 (d, J=9, 1H); 6.90 (d, J=9, 1H); 7.15 (m, 2H); 7.50 (m, 1H); 7.90 (m, 3H). Example 4 2,2-Dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-6-cyano-2H-1-benzopyran (E4) A solution of 6-cyano-2,2-dimethyl-2H-1-benzopyran (1.0g) and N,N-dichloro-t-butylurethane (1.1g) in toluene (20 ml) was heated at 50 o C for 5 h. The solution was cooled, and solvent removed in vacuo . The residue was dissolved in dioxan (20 ml) at 0 o C, a solution of ammonium acetate (2.08g) in water (20 ml) added, and zinc dust (1.76g) added portionwise. The mixture was stirred for 18 h at room temperature, decanted, and diluted with water and extracted with ethyl acetate. The organic extracts were washed with brine, dried (MgSO₄) and evaporated in vacuo . The residue was chromatographed on a silica gel column eluted with ethyl acetate:pentane (1:9) to give the title compound as a solid (1.17g, 72%) which recrystallised from 60-80 o petrol as needles having m.pt. 141-2 o C. ¹H n.m.r. (CDCl₃) δ 1.32 (s, 3H); 1.38 (s, 3H); 1.45 (s, 9H); 2.70 (dd, J=15, 4, 1H); 3.13 (dd, J=15, 4, 1H); 3.97 (m, 1H); 4.58 (d, J=9, N H ); 6.87 (d, J=9, 1H); 7.40 (m, 2H). Example 5 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol (E5) A solution of t-butylisocyanate (0.14g) in dichloromethane (10ml) was added to a stirred solution of trans-6-cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (0.303g) (D3) in dichloromethane (30ml) at 0 o C. The solution was allowed to warm to room temperature, and then stirred for a further 1 hr. The precipitate was collected by filtration to give the required compound (0.2g, 46%) as a colourless solid having m.pt. 129-132 o C. ¹H n.m.r. (DMSO-d⁶) δ: 1.27 (s,3H), 1.32 (s,9H), 1.42 (s,3H), 3.88 (m,1H), 4.40 (apparent t, J=9, 1H), 5.82 (br s, N H ), 5.88 (d, J=6, O H ), 5.95 (d,J=9,N H ), 7.04 (d,J=9,1H), 7.70 (dd, J=9,2,1H), 7.89 (d,J=2,1H). Example 6 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(3,4-difluorobenzoylamino)-2H-1-benzopyran-4-ol (E6) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using 3,4-difluorobenzoyl chloride. Recrystallisation from ethyl acetate: 60-80 o C petrol gave the title compound (E6) as colourless microcrystals having m.pt. 220-222 o C. Anal . Found: C,63.64, H,4.53, N,7.70%; C₁₉H₁₆N₂O₃F₂ requires C,63.68, H,4.50, N,7.82%. Example 7 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(methylureido)-2H-1-benzopyran-4-ol (E7) The compound of this example was prepared from D3 in a similar manner to the compound of Example 5, but using methylisocyanate to give the title compound (E7) as a colourless solid, having m.pt. 217 o C (decomp.). ¹H n.m.r. (DMSO-d₆) δ 1.25 (s,3H), 1.47 (s,3H), 2.74 (s,3H), 3.30-3.60 (brs,2H), 3.95 (m,1H), 4.45 (d,J=9Hz,1H), 5.90 (d,J=8Hz,1H), 6.85 (d,J=9Hz,1H), 7.43 (dd,J=9,2Hz,1H), 7.82 (d,J=2Hz,1H). Example 8 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-acetylamino-2H-1-benzopyran-4-ol (E8) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using acetyl chloride. Recrystallisation from ethyl acetate: 60-80 o C petrol gave the title compound (E8) as a colourless solid having m.pt. 179-181 o C. Anal. Found: C,64.60, H,6.24, N,10.54%; C₁₄H₁₆N₂O₃ requires C,64.60, H,6.20, N,10.76%. Example 9 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(2-pyridine-carbonylamino)-2H-1-benzopyran-4-ol (E9) Ethyl chloroformate (0.6g) in dichloromethane (10 mL) was added dropwise to a solution of picolinic acid (0.68g) in dichloromethane (50 mL) and triethylamine (0.77 mL), and the solution stirred at room temperature for 2h. A solution of trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (1.0g) (D3) in dichloromethane (30 mL) was then added, and the reaction mixture stirred at room temperature for 48h. Water was then added, the layers separated, and the organic layer washed with water, brine, then dried (MgSO₄) and evaporated in vacuo . The residue was triturated with ethyl acetate:pentane (1:1) and recrystallised from ethyl acetate:methanol:60-80 o C petrol to give the title compound (E9) (300 mg) as a colourless solid having m.pt. 216-9 o C. ¹H n.m.r. (DMSO-d₆) δ 1.35 (s,3H), 1.47 (s,3H), 4.33 (t,J=9Hz,1H), 4.96 (dd,J=9,7Hz,1H), 5.90 (d,J=7Hz,1H), 7.08 (d,J=9Hz,1H), 7.75 (m,2H), 7.92 (m,1H), 8.10-8.20 (m,2H), 8.80 (m,2H). Example 10 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(t-butylacetylamino)-2H-1-benzopyran-4-ol (E10) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using t-butylacetyl chloride. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E10) as a colourless solid having m.pt. 174-6 o C. Anal . Found: C,68.23, H,7.65, N,8.68%; C₁₈H₂₄N₂O₃ requires C,68.33, H,7.65, N,8.85%. Example 11 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(cyclohexane-carbonylamino)-2H-1-benzopyran-4-ol (E11) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using cyclohexanecarbonyl chloride. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E11) as a colourless solid having m.pt. 208-10 o C. ¹H n.m.r. (CDCl₃) δ 1.10-1.40 (m,4H), overlapping 1.30 (s,3H), 1.44 (s,3H), 1.60-1.85 (m,6H), 2.10 (m,1H), 3.30-3.70 (brs,1H), 4.21 (dd,J=10,8Hz,1H), 4.50 (d,J=8Hz,1H), 5.53 (d,J=10Hz,1H), 6.89 (d,J=9Hz,1H), 7.47 (dd,J=9,2Hz,1H), 7.83 (d,J=2Hz,1H). Example 12 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(cyclohexylureido)-2H-1-benzopyran-4-ol) (E12) The compound of this example was prepared from D3 in a similar manner to the compound of Example 5, but using cyclohexylisocyanate, to give the title compound (E12) as a colourless solid having m.pt. 182-3 o C. Anal . Found: C,66.46, H,7.45, N,12.35%; C₁₉H₂₅N₃O₃ requires C,66.65, H,7.07, N,12.27%. Example 13 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-benzoylamino-2H-1-benzopyran-4-ol (E13) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using benzoyl chloride. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E13) as colourless plates having m.pt. 183-5 o C. ¹H n.m.r. (DMSO-d₆) δ 1.25 (s,3H), 1.38 (s,3H), 4.27 (t,J=8Hz,1H), 4.75 (dd,J=8,6Hz,1H), 5.79 (d,J=6Hz,1H), 6.95 (d,J=9Hz,1H), 7.45-7.65 (m,4H), 7.85-7.95 (m,3H), 8.42 (d,J=8Hz,1H). Example 14 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(isopropylureido)-2H-1-benzopyran-4-ol (E14) The compound of this example was prepared from D3 in a similar manner to the compound of Example 5, but using isopropylisocyanate. Recrystallisation from methanol:ethyl acetate:60-80 o C petrol gave the title compound (E14) as a colourless solid having m.pt. 198-200 o C. ¹H n.m.r. (DMSO-d₆) δ 1.12 (s,3H), 1.15 (s,3H), 1.36 (s,3H), 1.43 (s,3H), 3.77 (m,1H), 3.90 (m,1H), 4.43 (m,1H), 5.80 (d,J=6Hz,1H), 5.86 (d,J=6Hz,1H), 5.97 (d,J=10Hz,1H), 7.02 (d,J=9Hz,1H), 7.70 (dd,J=9,2Hz,1H), 7.90 (d,J=2Hz,1H). Example 15 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(ethylureido)-2H-1-benzopyran-4-ol (E15) The compound of this example was prepared from D3 in a similar manner to the compound of Example 5, but using ethylisocyanate. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E15) as a colourless solid having m.pt. 173-5 o C. Example 16 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(n-propylureido)-2H-1-benzopyran-4-ol) (E16) The compound of this example was prepared from D3 in a similar manner to the compound of Example 5, but using n-propylisocyanate. Recrystallisation from methanol:ethyl acetate:60-80 o C petrol gave the title compound (E16) as a colourless solid having m.pt. 190-2 o C. Example 17 trans-6-Chloro-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol (E17) The compound of this example was prepared from trans -6-chloro-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D7), in a similar manner to the compound of Example 5. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E17) as colourless crystals having m.pt. 190-3 o C. Example 18 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(dimethylaminocarbonylamino)-2H-1-benzopyran-4-ol (E18) A solution of trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (500 mg) (D3), triethylamine (1 mL), and N,N-dimethylcarbamyl chloride (247 mg) in dichloromethane (30 mL) was stirred at room temperature for 42 days. Dilute hydrochloric acid (50 mL, 2N) was then added, and the layers separated. The organic layer was washed with sodium bicarbonate solution, brine, then dried (Na₂SO₄) and evaporated in vacuo . The residue was chromatographed (Si gel, eluant EtOAc:pentane) to give the crude product which was recrystallised from ethyl acetate:methanol as colourless plates (200 mg) having m.pt. 210-212 o C. Anal . Found: C,62.35, H,6.63, N,14.50%; C₁₅H₁₉N₃O₃ requires C,62.28, H,6.57, N,14.53%. Example 19 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-(isopropylthioureido)-2H-1-benzopyran-4-ol (E19) The compound of this example was prepared from D3 in a similar manner to the compound of Example 5, but using isopropylthioisocyanate, to give the title compound as a colourless solid having m.pt. 100-102 o C (decomp.). ¹H n.m.r. (CDCl₃) δ 1.21 (s,3H), 1.25 (s,3H), 1.35 (s,3H), 1.51 (s,3H), 2.60-3.30 (brs,1H), 4.20 (m,1H), 4.60 (m,1H), 4.77 (d,J=6Hz,1H), 6.04 (brs,1H), 6.25 (brs,1H), 6.90 (d,J=9Hz,1H), 7.47 (dd,J=9,2Hz,1H), 7.75 (d,J=2Hz,1H). Example 20 trans-6-Trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol (E20) The compound of this example was prepared from trans -6-trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol (D11), in a similar manner to the compound of Example 5. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E20) as colourless microcrystals having m.pt. 193-5 o C (decomp.). Example 21 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-trimethylacetylamino-2H-1-benzopyran-4-ol (E21) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using trimethylacetyl chloride. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E21) as a colourless solid having m.pt. 186-8 o C. ¹H n.m.r. (CDCl₃) δ 1.16 (s,9H), 1.30 (s,3H), 1.42 (s,3H), 4.23 (dd,J=9,8Hz,1H), 4.50 (d,J=8Hz,1H), 5.70 (d,J=9Hz,1H), 6.89 (d,J=9Hz,1H), 7.48 (dd,J=9,2Hz,1H), 7.84 (d,J=2Hz,1H). Example 22 trans-6-Cyano-2,2-dimethyl-3,4-dihydro-3-isobutyrylamino-2H-1-benzopyran-4-ol (E22) The compound of this example was prepared from D3 in a similar manner to the compound of Example 3, but using isobutyryl chloride. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E24) as a colourless solid having m.pt.176-8 o C. Example 23 trans-6-Cyano-3,4-dihydro-2,2-dimethyl-3-(benzyloxycarbonyl)amino-2H-1-benzopyran-4-ol (E23) The compound of this example was prepared in a similar manner, from 6-cyano-3,4-[(N-benzyloxycarbonyl)-aziridino]-2,2-dimethyl-2H-1-benzopyran (D14) in a similar manner to the compound of Example 1. Recrystallisation from ethyl acetate:60-80 o C petrol gave the title compound (E23) as a colourless solid having m.pt. 174-7 o C. Example 24 2,2-Dimethyl-3,4-dihydro-3-(t-butylureido)-6-cyano-2H-1-benzopyran (E24) A solution of 2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-6-cyano-2H-1-benzopyran (E4) (0.5g) and trifluoroacetic acid (5 mL) in dry dichloromethane (30 mL) was stirred at 0 o C for 5h. Solvents were removed in vacuo , and the residue dissolved in ethyl acetate and washed with sodium bicarbonate solution, water, brine and then dried (MgSO₄). Removal of drying agent and solvent gave a gum (0.24 g) which was dissolved in dry dichloromethane (30 mL), cooled to 0 o C, under nitrogen, and t-butylisocyanate (0.13g) added. The reaction mixture was stirred at room temperature for 48h, solvent evaporated in vacuo , and the residue chromatographed on silica gel, eluting with 50% ethyl acetate:pentane, to give the title compound (E24) as a solid (0.17g). ¹H n.m.r. (CDCl₃) δ 1.29 (s,9H), 1.31 (s,3H), 1.39 (s,3H), 2.70 (d,J=15Hz,1H), 3.12 (dd,J=15,4Hz,1H), 4.10-4.20 (m,2H), 6.87 (d,J=9Hz,1H), 7.30 (s,1H), 7.40 (m,2H). Example 25 trans-6-Cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-methoxy-2H-1-benzopyran (E25) To a stirred solution of 6-cyano-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran (300 mg) (D2) in dry methanol (30 mL) was added boron trifluoride etherate (0.1 mL) and the solution stirred at room temperature for 18h. Solvents were evaporated in vacuo , and the residue chromatographed on a silica gel column, eluting with 30% ethyl acetate:pentane, to give the crude product which was triturated with pentane:ethyl acetate (9:1) to give the title compound as a colourless solid (90 mg) having m.pt. 121-3 o C. Example 26 trans-6-Cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-amino-2H-1-benzopyran (E26) Propane-1,3-dithiol (1.38g) was added to a stirred solution of trans -6-cyano-3,5-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-azido-2H-1-benzopyran (D15) (2.36g) in methanol (40mL) and triethylamine (1.9mL). The reaction mixture was filtered and solvents removed in vacuo . The residue was dissolved in ether and extracted with 2N HCl (3 x 100mL). The acid extracts were basified with NaOH, and extracted with ethyl acetate (2 x 100mL). The organic extracts were dried (MgSo₄) and evaporated in vacuo to give the title compound (E26) as a solid having m.pt. 123-6 o C. PHARMACOLOGICAL DATA 1. Antihypertensive Activity Systolic blood pressures were recorded by a modification of the tail cuff method described by I.M. Claxton, M.G. Palfreyman, R.H. Poyser, R.L. Whiting, European Journal of Pharmacology, 37, 179 (1976). A W+W BP recorder, model 8005 was used to display pulses. Prior to all measurements rats were placed in a heated environment (33.5 ± 0.5 o C) before transfer to a restraining cage. Each determination of blood pressure was the mean of at least 5 readings. Spontaneously hypertensive rats (ages 12-18 weeks) with systolic blood pressures >180 mmHg were considered hypertensive. The results were as follows: Compound Dose (mg/kg) % b.p. fall E1 3.0 30 E3 3.0 42 E5 0.3 ≧40 E14 0.3 22 E21 1.0 36 2. Bronchodilator Activity Male guinea pigs (300-600g) were stunned by a blow to the head and bled from the carotid artery. The trachea was exposed, dissected free of connective tissue, and transferred to oxygenated Krebs solution at 37 o C. Next, spirals (2 per trachea) were prepared by cutting the whole trachea spirally along its longitudinal axis and then dividing this spiral lengthwise. Each preparation was mounted, using silk thread, in a 10ml organ bath filled with krebs solution at 37 o C and bubbled with 5% CO₂ with O₂. The resting tension of the preparations was set at 2g and changes in muscle tension were monitored isometrically by means of a UFI (2oz) force and displacement transducer (Ormed Ltd) connected to a Linseis pen recorder. All preparations were allowed to equilibrate for 60 minutes. During this equilibration period the preparations were washed by upward displacement at 15 minute intervals and, if necessary, the resting tension was readjusted to 2g using a mechanical micromanipulator system. Once a steady resting tension had been obtained, the preparations were dosed simultaneously with the test compound (10⁻⁸-2x10⁻⁵M), and finally a maximum relaxation achieved by addition of 10⁻³M isoprenaline. The fall in tension evoked by the test compound was expressed as a percentage of the total relaxation evoked in the presence of 10⁻³ isoprenaline. Appropriate concentration-relaxation curves were then constructed and values for potency (IC₅₀) were obtained. [The composition of Krebs solution is: sodium chloride 118.07mM, sodium hydrogen carbonate 26.19mM, potassium chloride 4.68mM, potassium orthophosphate 1.18mM, magnesium sulphate septahydrate 1.8mM and calcium chloride 2.52mM;pH ca . 7.45.] The compound of Example 5 gave an IC₅₀ value of 2.8µm.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, GR, IT, LI, LU, NL, SE A compound of formula (I), or a pharmaceutically acceptable salt thereof: wherein a and b together form an -O- linkage or a bond or (when R₂ is hydrogen), CH₂; either Y is N and R₂ is hydrogen; or Y is C-R₁ wherein either one of R₁ and R₂ is hydrogen and the other is nitro, cyano, halo, CF₃, C₂F₅, formyl, aldoxime, CF₃O, NO₂-CH=CH-, NC-CH=CH-; a group R x X-wherein R x is C₁₋₆ alkyl, aryl or heteroaryl either of which may be optionally substituted by one, two or three of C₁₋₄ alkyl, C₁₋₄ alkoxy, nitro, halo, CF₃ and cyano; and X is C=O, O.C=O, C=O.O, CHOH, SO, SO₂, O.SO, O.SO₂, CONH, O.CONH, O.SO₂NH, CO-CH=CH, C=NHOH, C=NNH₂; or a group R y R z NZ- wherein R y and R z are independently hydrogen or C₁₋₆ alkyl and Z is C=O, SO or SO₂; or a group (R w O)₂P(O)W wherein R w is hydrogen or C₁₋₆ alkyl and W is O or a bond; or R₁ is a C₃₋₈ cycloalkyl group or a C₁₋₆ alkyl group optionally substituted by a group which is hydroxy, C₁₋₆ alkoxy, amino optionally substituted by one or two C₁₋₆ alkyl groups, C₁₋₇ alkanoylamino, C₃₋₈ cycloalkyloxy or C₃₋₈ cycloalkylamino; and R₂ is hydrogen; or one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl and the other is a different group selected from nitro, cyano, halo, C₁₋₃ alkylcarbonyl, methoxy or amino optionally substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl; or R₁ and R₂ together with the carbon atoms to which they are attached, form 2,1,3-oxadiazole; either one of R₃ and R₄ is hydrogen or C₁₋₄ alkyl and the other is C₁₋₄ alkyl; or R₃ and R₄ together are C₂₋₅ polymethylene R₅ is hydrogen, hydroxy, amino, C₁₋₆ alkoxy or C₁₋₇ acyloxy; and E is hydrogen; or R₅ and E together form a bond; either R₆ is hydrogen or C₁₋₆ alkyl; and R₇ is hydrogen, C₃₋₈ cycloalkyl, C₂₋₆ alkenyl, C₁₋₆ alkyl optionally substituted by hydroxy, C₁₋₆ alkoxy, C₁₋₆ alkoxycarbonyl, carboxy, halogen or amino optionally substituted by one or two C₁₋₆ alkyl groups; aryl or heteroaryl either being optionally substituted by one or more groups or atoms selected from the class of C₁₋₆ alkyl, C₁₋₆ alkoxy, hydroxy, halogen, trifluoromethyl, nitro, cyano, C₁₋₁₂ carboxylic acyl, or R₇ is amino or aminocarbonyl optionally substituted by one or two C₁₋₆ alkyl groups or substituted by C₃₋₈ cycloalkyl, or a group OR₉ wherein R₉ is C₁₋₆ alkyl or benzyl optionally substituted as defined for R₇; or R₆ and R₇ are joined together to form C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond( s); and x is oxygen or sulphur. A compound according to claim 1 wherein Y is C-R₁ and a and b together are an -O- linkage. A compound according to claim 1 or 2 wherein R₁ is nitro, cyano, acetyl, CF₃, C₂F₅ or C₁₋₄ alkyl, and R₂ is hydrogen. A compound according to claim 3 wherein R₁ is cyano. A compound according to any one of claims 1 to 4 wherein R₃ and R₄ are both methyl groups. A compound according to any one of claims 1 to 5 wherein R₅ is hydroxy and E is hydrogen and the R₆NCXR₇ moiety is trans to R₅. A compound according to any one of claims 1 to 6 wherein R₆ is hydrogen and R₇ is optionally substituted phenyl, branched C₁₋₆ alkyl, C₁₋₆alkoxy, benzyloxy or optionally substituted amino. A compound according to claim 7 wherein R₇ is t-butylamino. A compound selected from the group consisting of: trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(2-oxo-1-piperidinyl)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(4-fluorobenzoylamino-2H-1-benzopyran-4-ol, 2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-6-cyano-2H-1-benzopyran, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(3,4-difluorobenzoylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(methylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-acetylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(2-pyridine-carbonylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butylacetylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(cyclohexane-carbonylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(cyclohexylureido)-2H-1-benzopyran-4-ol), trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-benzoylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(isopropylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(ethylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(n-propylureido)-2H-1-benzopyran-4-ol), trans -6-chloro-2,2-dimethyl-3,4-dihydro-3-(t-butylureido-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(dimethylaminocarbonylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-isopropylthioureido-2H-1-benzopyran-4-ol, trans -6-trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-(t-butylureido-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-trimethylacetylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-isobutyrylamino-2H-1-benzopyran-4-ol, trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(benzyloxycarbonyl)amino-2H-1-benzopyran-4-ol, 2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-6-cyano-2H-1-benzopyran, trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-methoxy-2H-1-benzopyran and trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-amino-2H-1-benzopyran. A process for the preparation of a compound according to claim 1, which process comprises acylating a compound of formula (II): wherein Y′ and R₂′, are Y and R₂ respectively or groups or atoms convertible thereto, R₅¹ is hydroxy, C₁₋₆ alkoxy, C₁₋₇ acyloxy or azide, R₆¹ is hydrogen or C₁₋₆ alkyl and the R₆¹NH group is trans to the R₅¹ group (when R₅¹ is other than than azide), with a) an acylating agent of formula (III): R₇¹COQ (III) wherein Q is a leaving group and R₇¹ is R₇ as defined in claim 1, or a group convertible thereto, when not joined to R₆ or, (when R₆¹ is hydrogen), R₇¹ is a group R₁₀ which is C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond(s), terminally substituted by a leaving group, L; and thereafter, when R₇¹ is R₁₀, cyclising the resulting compound; or b) (when R₇ is NHR₁₁ wherein R₁₁ is hydrogen or C₁₋₆ alkyl), with a compound of formula (IV): X = C = NR₁₁ (IV) wherein X and R₁₁ are as hereinbefore defined; and thereafter, as desired or necessary, converting R₅¹ to R₅, converting Y′ and/or R₂′ to Y and/or R₂, optionally thiating X when oxygen to X is sulphur and/or dehydrating a compound wherein R₅¹ is hydroxy to form a compound of formula (I) wherein R₅ and E form a bond or converting a compound of formula (I) wherein the R₆NCXR₇ moiety is trans to R₅ when hydroxy, to a corresponding cis isomer; and optionally forming a pharmaceutically acceptable salt thereof. A compound of formula (II), (V) or (VI): wherein R c is an amino protecting group and the other variable groups are defined in claim 10. A compound selected from the group consisting of: trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol, trans -6-chloro-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol, trans -6-trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-amino-2H-1-benzopyran-4-ol, 6-cyano-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran, 6-chloro-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran, 6-trifluoromethyl-3,4-[(N-t-butoxycarbonyl)aziridino]-2,2-dimethyl-2H-1-benzopyran, 6-cyano-3,4-[(N-benzyloxycarbonyl)aziridino]- 2,2-dimethyl-2H-1-benzopyran, trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonylamino)-4-chloro-2H-1-benzopyran, trans -6-chloro-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-chloro-2H-1-benzopyran, trans -6-trifluoromethyl-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-chloro-2H-1-benzopyran and trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(benzyloxycarbonylamino)-4-chloro-2H-1-benzopyran. A pharmaceutical composition comprising a compound according to any one of claims 1 to 9, and a pharmaceutically acceptable carrier. A compound according to any one of claims 1 to 9 for use as an active therapeutic substance. A compound according to any one of claims 1 to 9 for use in the treatment of hypertension and/or respiratory tract disorders. Use of a compound according to any one of claims 1 to 9 in the manufacture of a medicament for use in the treatment of hypertension and/or respiratory tract disorders. Claims for the following Contracting State : ES A process for the preparation of a compound of formula (I), or a pharmaceutically acceptable salt thereof: wherein a and b together form an -O- linkage or a bond or (when R₂ is hydrogen), CH₂; either Y is N and R₂ is hydrogen; or Y is C-R₁ wherein either one of R₁ and R₂ is hydrogen and the other is nitro, cyano, halo, CF₃, C₂F₅, formyl, aldoxime, CF₃O, NO₂-CH=CH-, NC-CH=CH-; a group R x X-wherein R x is C₁₋₆ alkyl, aryl or heteroaryl either of which may be optionally substituted by one, two or three of C₁₋₄ alkyl, C₁₋₄ alkoxy, nitro, halo, CF₃ and cyano; and X is C=O, O.C=O, C=O.O., CHOH, SO, SO₂, O.SO, O.SO₂, CONH, O.CONH, O.SO₂NH, CO-CH=CH, C=NHOH, C=NNH₂; or a group R y R z NZ- wherein R y and R z are independently hydrogen or C₁₋₆ alkyl and Z is C=O, SO or SO₂; or a group (R w O)₂P(O)W wherein R w is hydrogen or C₁₋₆ alkyl and W is O or a bond; or R₁ is a C₃₋₈ cycloalkyl group or a C₁₋₆ alkyl group optionally substituted by a group which is hydroxy, C₁₋₆ alkoxy, amino optionally substituted by one or two C₁₋₆ alkyl groups, C₁₋₇ alkanoylamino, C₃₋₈ cycloalkyloxy or C₃₋₈ cycloalkylamino; and R₂ is hydrogen; or one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl and the other is a different group selected from nitro, cyano, halo, C₁₋₃ alkylcarbonyl, methoxy or amino optionally substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl; or R₁ and R₂ together with the carbon atoms to which they are attached, form 2,1,3-oxadiazole; either one of R₃ and R₄ is hydrogen or C₁₋₄ alkyl and the other is C₁₋₄ alkyl; or R₃ and R₄ together are C₂₋₅ polymethylene R₅ is hydrogen, hydroxy, amino, C₁₋₆ alkoxy or C₁₋₇ acyloxy; and E is hydrogen; or R₅ and E together form a bond; either R₆ is hydrogen or C₁₋₆ alkyl; and R₇ is hydrogen, C₃₋₈ cycloalkyl, C₂₋₆ alkenyl, C₁₋₆ alkyl optionally substituted by hydroxy, C₁₋₆ alkoxy, C₁₋₆ alkoxycarbonyl, carboxy, halogen or amino optionally substituted by one or two C₁₋₆ alkyl groups; aryl or heteroaryl either being optionally substituted by one or more groups or atoms selected from the class of C₁₋₆ alkyl, C₁₋₆ alkoxy, hydroxy, halogen, trifluoromethyl, nitro, cyano, C₁₋₁₂ carboxylic acyl, or R₇ is amino or aminocarbonyl optionally substituted by one or two C₁₋₆ alkyl groups or substituted by C₃₋₈ cycloalkyl, or a group OR₉ wherein R₉ is C₁₋₆ alkyl or benzyl optionally substituted as defined for R₇; or R₆ and R₇ are joined together to form C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond(s); and X is oxygen or sulphur; which process comprises acylating a compound of formula (II): wherein Y′ and R₂′, are Y and R₂ respectively or groups or atoms convertible thereto, R₅¹ is hydroxy, C₁₋₆ alkoxy, C₁₋₇ acyloxy or azide, R₆¹ is hydrogen or C₁₋₆ alkyl and the R₆¹NH group is trans to the R₅¹ group (when R₅¹ is other than than azide), with a) an acylating agent of formula (III): R₇¹COQ (III) wherein Q is a leaving group and R₇¹ is R₇ as defined, or a group convertible thereto, when not joined to R₆ or, (when R₆¹ is hydrogen), R₇¹ is a group R₁₀ which is C₃₋₄ polymethylene optionally substituted by one or two C₁₋₆ alkyl groups and optionally containing one or, (when C₄ polymethylene), two, C=C double bond(s), terminally substituted by a leaving group, L; and thereafter, when R₇¹ is R₁₀, cyclising the resulting compound; or b) (when R₇ is NHR₁₁ wherein R₁₁ is hydrogen or C₁₋₆ alkyl), with a compound of formula (IV): X = C = NR₁₁ (IV) wherein X and R₁₁ are as hereinbefore defined; and thereafter, as desired or necessary, converting R₅¹ to R₅, converting Y′ and/or R₂′, to Y and/or R₂, optionally thiating X when oxygen to X is sulphur and/or dehydrating a compound wherein R₅¹ is hydroxy to form a compound of formula (I) wherein R₅ and E form a bond or converting a compound of formula (I) wherein the R₆NCXR₇ moiety is trans to R₅ when hydroxy, to a corresponding cis isomer; and optionally forming a pharmaceutically acceptable salt thereof. A process according to claim 1 wherein Y is C-R₁ and a and b together are an -O- linkage. A process according to claim 1 or 2 wherein R₁ is nitro, cyano, acetyl, CF₃, C₂F₅ or C₁₋₄ alkyl, and R₂ is hydrogen. A process according to claim 3 wherein R₁ is cyano. A process according to any one of claims 1 to 4 wherein R₃ and R₄ are both methyl groups. A process according to any one of claims 1 to 5 wherein R₅ is hydroxy and E is hydrogen and the R₆NCXR₇ moiety is trans to R₅. A process according to any one of claims 1 to 6 wherein R₆ is hydrogen and R₇ is optionally substituted phenyl, branched C₁₋₆ alkyl, C₁₋₆alkoxy, benzyloxy or optionally substituted amino. A process according to claim 7 wherein R₇ is t-butylamino. A process according to claim 1 for the preparation of a compound selected from the group consisting of: trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(2-oxo-1-piperidinyl)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(4-fluorobenzoylamino)-2H-1-benzopyran-4-ol, 2,2-dimethyl-3,4-dihydro-3-(t-butoxycarbonyl)amino-6-cyano-2H-1-benzopyran, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(3,4-difluorobenzoylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(methylureido-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-acetylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(2-pyridine-carbonylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(t-butylacetylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(cyclohexane-carbonylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(cyclohexylureido)-2H-1-benzopyran-4-ol), trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-benzoylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(isopropylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(ethylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(n-propylureido)-2H-1-benzopyran-4-ol), trans -6-chloro-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(dimethylaminocarbonylamino)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-(isopropylthioureido)-2H-1-benzopyran-4-ol, trans -6-trifluoromethyl-2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-trimethylacetylamino-2H-1-benzopyran-4-ol, trans -6-cyano-2,2-dimethyl-3,4-dihydro-3-isobutyrylamino-2H-1-benzopyran-4-ol, trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(benzyloxycarbonyl)amino-2H-1-benzopyran-4-ol, 2,2-dimethyl-3,4-dihydro-3-(t-butylureido)-6-cyano-2H-1-benzopyran, trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-methoxy-2H-1-benzopyran and trans -6-cyano-3,4-dihydro-2,2-dimethyl-3-(t-butoxycarbonyl)amino-4-amino-2H-1-benzopyran. Use of a compound of formula (I) as defined in any one of claims 1 to 9, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for use in the treatment of hypertension and/or respiratory tract disorders.

Inventors: STEMP GEOFFREY BEECHAM PHARMAC, STEMP, GEOFFREY BEECHAM PHARMACEUTICALS
Applicants: BEECHAM GROUP PLC
Application year: 1989
Main classification: C07D311
IPC codes: C07D407, A61K31, A61P9, C07D417, C07D405, C07D311, C07D413, A61P11, C07D491, C07D409