SUBSTITUTED DIBENZOCYCLOHEPTENIMINES

Abstract: The present invention provides a compound of formula (I): or a pharmaceutically acceptable salt thereof, wherein one of R¹, R², R³ and R⁴ represents a hydrocarbon or hydrocarbyloxycarbonyl group and the remaining groups R¹, R², R³ and R⁴ independently represent hydrogen, hydrocarbon, hydrocarbyloxycarbonyl, halogen, hydroxy or C₁₋₆ alkoxy, or R¹ and R² or R³ and R⁴ may together represent the residue of a carbocyclic ring; R⁵ and R⁶ independently represent hydrogen, hydrocarbon, hydroxy or fluoro; R⁷ represents hydrogen or C₁₋₃ alkyl; and R⁸ represents methyl or ethyl; which compounds are useful as anticonvulsant agents and in the treatment of neurodegenerative diseases.

Description: This invention relates to a class of dibenzocycloheptenimines, and in particular to derivatives of 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine substituted with a hydrocarbon or hydrocarbyloxycarbonyl group. The compounds are useful as anticonvulsant agents and in the treatment of neurodegenerative diseases. British Patent No. 2,004,872 (and US Patent No. 4,399,141) describes 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine and derivatives thereof as anticonvulsant agents. The use of those compounds as non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, and therefore their value in the treatment of neurodegenerative diseases, is disclosed in European patent application, publication No. 230370. It has now been found that derivatives substituted with a hydrocarbon or hydrocarbyloxycarbonyl group on the benzo ring are also good anticonvulsants and NMDA receptor antagonists. None of the prior documents discloses or suggests hydrocarbon or hydrocarbyloxycarbonyl substituents at that position. The compounds of this invention are useful in the prevention and/or treatment of neurodegeneration in pathological conditions such as stroke, hypoglycaemia, cerebral palsy, transient cerebral ischaemic attack, cerebral ischaemia during cardiac pulmonary surgery or cardiac arrest, perinatal asphyxia, epilepsy, Huntington's chorea, Alzheimer's disease, Olivo-pontocerebellar atrophy, anoxia such as from drowning, spinal cord injury and poisoning by exogeneous NMDA poisons (e.g. some forms of lathyrism). The present invention provides a compound of formula (I): or a pharmaceutically acceptable salt thereof, wherein one of R¹, R², R³ and R⁴ represents a group of formula -R or -CO₂R, and the remaining groups R¹, R², R³ and R⁴ independently represent hydrogen, halogen, hydroxy, C₁₋₆ alkoxy or a group of formula -R or -CO₂R, in which R represents a hydrocarbon group having up to 18 carbon atoms, which group may be substituted with a group selected from halogen, C₁₋₆ alkyl, phenyl, C₁₋₆ alkoxy, halo(C₁₋₆)alkyl, hydroxy, amino, nitro, cyano, carboxy, c₁₋₆ alkoxycarbonyl, C₁₋₆ alkoxycarbonyl(C₁₋₆)alkyl, C₁₋₆ alkylcarbonyloxy and C₁₋₆ alkylcarbonyl, and groups of formula -CONR a R b and -NR a .COR b in which R a and R b independently represent hydrogen or C₁₋₆ alkyl, or R¹ and R² or R³ and R⁴ together represent the residue of a saturated or unsaturated carbocyclic ring, the R¹/R² or R³/R⁴ carbon chain of which comprises from 2 to 6 carbon atoms; R⁵ and R⁶ independently represent hydrogen, hydroxy, fluoro or a group of formula -R as defined above; R⁷ represents hydrogen or C₁₋₃ alkyl; and R⁸ represents methyl or ethyl. The term 'hydrocarbon' as used herein with reference to the moiety -R refers to groups having up to 18 carbon atoms. Suitably, the group -R contains up to 10 carbon atoms, conveniently up to 6 carbon atoms. Suitable hydrocarbon groups of formula -R include C₁₋₆ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl, C₃₋₇ cycloalkyl, C₃₋₇ cycloalkyl(C₁₋₆)alkyl, aryl, and aryl(C₁₋₆)alkyl. Suitable alkyl groups include straight and branched chain alkyl groups containing from 1 to 6 carbon atoms, such as methyl, ethyl, propyl and butyl. A particular alkyl group is methyl. When used herein the term 'aryl' includes phenyl and naphthyl. Preferred substituent groups on the hydrocarbon moiety -R include halogen, hydroxy, C₁₋₆ alkyl, C₁₋₆ alkoxy and C₁₋₆ alkoxycarbonyl. Suitable aryl groups include phenyl and chlorophenyl. Suitable aryl(C₁₋₆)alkyl groups are benzyl and chlorobenzyl. Preferably R⁷ represents hydrogen and R⁸ represents methyl. When R¹ and R² or R³ and R⁴ together represent the residue of a saturated or unsaturated carbocyclic ring, the R¹/R² or R³/R⁴ carbon chain preferably comprises 3 or 4 carbon atoms, i.e. forming a fused 5- or 6-membered ring, such as benzo. In a preferred subgroup of compounds of formula (I), one of R¹ to R⁴ represents C₁₋₆ alkyl, hydroxy(C₁₋₆)alkyl, phenyl or C₁₋₆ alkoxycarbonyl, and the remaining groups R¹ to R⁴ represent hydrogen or halogen, in particular chloro or bromo. It is also preferred that R⁵ represents hydrogen, hydroxy or methyl and R⁶ represents hydrogen or hydroxy, in particular exo -hydroxy. The substituent of formula -R or -CO₂R represented by R¹ to R⁴ may be present at any position of the benzo rings, suitably at positions 2, 3, 4, 6, 7 or 8, in particular at positions 2, 3, 7 or 8. Substitution by the group of formula -R or -CO₂R at positions 3 and 7 leads to preferred compounds. Particular compounds of this invention include: 5,7-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine; 5,9-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine; 3,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine; 1,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine; 5-methyl-3-phenyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine; 7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine; 7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,13-imine; 2,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine; 5,8-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 3-methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 3-hydroxymethyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; and salts thereof. Suitable acid addition salts of compounds of this invention include pharmaceutically acceptable inorganic salts such as the sulphate, nitrate, phosphate, borate, hydrochloride and hydrobromide and pharmaceutically acceptable organic acid addition salts such as acetate, tartrate, maleate, citrate, succinate, benzoate, ascorbate, methanesulphonate, α-ketoglutarate, α-glycerophosphate, and glucose-1-phosphate. Preferably the acid addition salt is a hemisuccinate, hydrochloride, α-ketoglutarate, α-glycerophosphate or glucose-1-phosphate, in particular the hydrochloride salt. Also included within the scope of the present invention are pharmaceutical compositions comprising the imines of this invention. Preferably these compositions are in unit dosage forms such as tablets, pills, capsules, powders, granules, sterile parenteral solutions or suspensions, or suppositories for oral, parenteral or rectal administration. For preparing solid compositions such as tablets, the principal active ingredient is mixed with a pharmaceutical carrier, e.g. conventional tableting ingredients such as corn starch, lactose, sucrose, sorbitol, talc, stearic acid, magnesium stearate, dicalcium phosphate or gums, and other pharmaceutical diluents, e.g. water, to form a solid preformulation composition containing a homogeneous mixture of an imine of the present invention, or a non-toxic pharmaceutically acceptable salt thereof. When referring to these preformulation compositions as homogeneous, it is meant that the active ingredient is dispersed evenly throughout the composition so that the composition may be readily subdivided into equally effective unit dosage forms such as tablets, pills and capsules. This solid preformulation composition is then subdivided into unit dosage forms of the type described above containing from 0.1 to about 500 mg of the active ingredient of the present invention. The tablets or pills of the novel composition can be coated or otherwise compounded to provide a dosage form affording the advantage of prolonged action. For example, the tablet or pill can comprise an inner dosage and an outer dosage component, the latter being in the form of an envelope over the former. The two components can be separated by an enteric layer which serves to resist disintegration in the stomach and permits the inner component to pass intact into the duodenum or to be delayed in release. A variety of materials can be used for such enteric layers or coatings, such materials including a number of polymeric acids and mixtures of polymeric acids with such materials as shellac, cetyl alcohol and cellulose acetate. The liquid forms in which the novel compositions of the present invention may be incorporated for administration orally or by injection include aqueous solutions, suitably flavoured syrups, aqueous or oil suspensions, and flavoured emulsions with edible oils such as cottonseed oil, sesame oil, coconut oil and peanut oil, as well as elixirs and similar pharmaceutical vehicles. Suitable dispersing or suspending agents for aqueous suspensions include synthetic and natural gums such as tragacanth, acacia, alginate, dextran, sodium carboxymethylcellulose, methylcellulose, polyvinylpyrrolidone, and gelatine. The novel imines of this invention are useful as anticonvulsants at a dosage level of from about 0.01 to about 20 mg per kilogram of body weight, preferably about 0.05 to 2 mg/kg of body weight, on a regimen of 1 to 4 times a day. In the treatment of neurodegeneration, a suitable dosage level is about 0.01 to 50 mg/kg, preferably about 0.05 to 10 mg/kg and especially about 0.05 to 0.5 mg/kg/day. The compounds may be administered on a regimen of 1 to 4 times per day. The compounds of this invention wherein R⁵ is hydrogen or a group -R and R⁶ is hydrogen may be prepared by a process which comprises reducing the N-hydroxy compound of formula (II): wherein R¹ to R⁴ and R⁸ are as defined with respect to formula (I) above and R¹⁵ represents hydrogen or a group of formula -R as defined above; and, when R⁷ is other than hydrogen, alkylation of the product. The preferred reducing agent is nascent hydrogen generated by the action of a metal, preferably zinc, with an acid, such as acetic acid. Suitable conditions for the process are a temperature of from 40°C to 100°C for 1 to about 10 hours. The intermediate compounds of formula (II) may be prepared by the cyclisation of a compound of formula (III): wherein R¹ to R⁴ and R⁸ are as defined with respect to formula (I) above and R¹⁵ is as defined with respect to formula (II) above. The conditions for this reaction are elevated temperature or the presence of a base and are generally as described in US Patent No. 4477668. Both compounds (II) and (III) are novel compounds and represent further aspects of this invention. The compound (II) may also be prepared by processes analogous to those described in U.S. Patents Nos. 4399141 and 4232158. The novel compounds of this invention wherein R⁸ represents a group of formula -CH₂R⁹, in which R⁹ is hydrogen or methyl, may also be prepared by ring closure of a 10-NHX-5-(=CHR⁹)- 10,11-dihydro-5H-dibenzo[a,d]cycloheptene (where X is the group R⁷ or a protecting group, such as acetyl) by treatment with a strong base such as an organometallic reagent, for example n-butyllithium, in an ethereal solvent such as tetrahydrofuran or 1,2-dimethoxyethane, at about 0°C to about 30°C for about 5 minutes to about 1 hour, followed if necessary by removal of the protecting group. The compounds of formula (I) in which at least one of R¹ to R⁴ represents a group -R may be prepared, where appropriate, by alkylation or arylation, i.e. by reaction of a compound of formula (IV): wherein R⁵ to R⁸ are as defined with respect to formula (I) above, one of R¹¹, R¹², R¹³ and R¹⁴ represents halogen, and the remaining groups R¹¹, R¹², R¹³ and R¹⁴ independently represent hydrogen, halogen, hydroxy, C₁₋₆ alkoxy or a group of formula -R as defined above; with a reagent which replaces halogen by the group -R. For example, a Grignard reagent such as an alkyl- or arylmagnesium bromide may be employed in the presence of a catalyst such as 1,3-bis(diphenylphosphino)propane nickel(II) chloride. If the substituent -R is phenyl, a suitable reagent is PhB(OH)₂/(PPh₃)₄Pd [phenyl boronic acid/tetrakis(triphenylphosphine)palladium]. The compounds of formula (I) in which at least one of R¹ to R⁴ represents a group of formula -CO₂R may conveniently be prepared by metalation of a compound of formula (IV) as defined above with, for example, n-butyllithium; treatment of the resulting anion in situ with carbon dioxide; and subsequent esterification of the resulting carboxylic acid by standard means, such as by treatment with boron trifluoride etherate in the presence of a suitable alcohol. Where appropriate, a compound of formula (I) initially obtained may subsequently be elaborated into a further compound of formula (I) as defined above. For example, a compound of formula (I) wherein one or more of R¹ to R⁴ is/are hydroxymethyl may conveniently be obtained from the corresponding compound of formula (I) wherein one or more of R¹ to R⁴ is/are a group of formula -CO₂R by treatment of the latter with a suitable reducing agent, e.g. lithium aluminium hydride. The compounds of formula (I) in which R⁵ represents hydroxy may be prepared by methods analogous to those described in EP-A-0264183. A further method is to treat the N-hydroxy compound of formula (II) above, in which R¹⁵ is hydrogen, with manganese acetate, and subsequently to reduce the product thereby obtained with, for example, zinc in acetic acid. This method may be illustrated by the following scheme: When it is desired that R⁷ should be other than hydrogen, the resulting product can subsequently be alkylated. The compounds of formula (I) in which R⁶ represents hydroxy may be prepared by reducing an 11-oxo compound, in which the nitrogen atom may be protected. The reduction may be effected by treatment with, for example, diisobutylaluminium hydride (Dibal-H) in an ethereal solvent such as ether, tetrahydrofuran or 1,2-dimethoxyethane at about -90 to -60°C, preferably about -78°C, for about 1 to 3 hours. This process produces a mixture of endo and exo hydroxy derivatives which, after deprotection, may be separated by conventional techniques such as preparative chromatography. Alternatively, in order to obtain the 11-hydroxy compound selectively as its desired exo or endo isomer, the 11-oxo compound may be reduced with a chiral reducing agent such as D - or L -Selectride. Thus, it will be appreciated that a mixture of the exo and endo isomers can be converted into a single desired exo or endo isomer by oxidation to the 11-oxo compound and subsequent application of the foregoing selective reduction technique. This approach can equally be adopted for the conversion of a single exo or endo isomer into the opposite isomer. Further illustrative methods of preparing the exo and endo isomers of the 11-hydroxy compound selectively are described in EP-A-0264183. The 10-fluoro derivative of compound (I) may be prepared by treating the corresponding 10-hydroxy compound with diethylaminosulphur trifluoride (DAST) in an inert organic solvent such as a chlorinated hydrocarbon such as chloroform or methylene dichloride at about 15 to 30°C for about 30 minutes to 2 hours. The isomeric 11-fluoro compound may be prepared by treating the aziridine of formula (V): wherein R¹ to R⁵ and R⁸ are as defined with respect to formula (I) above; with hydrogen fluoride-pyridine (HF-70%; pyridine-30%) at about -90 to -60°C, preferably about -78°C, followed by spontaneous warming to ambient temperature (15 to 30°C) for about 12 to 36 hours. During any of the above reactions it may be necessary to protect any reactive groups on any of the molecules concerned with conventional protecting groups which may subsequently be removed using methods known from the art. The compounds useful in this invention bind with a high affinity and in a reversible and saturable manner to membranes from rat brain cortex. In addition these compounds potently and selectively block responses to NMDA in a brain slice from rat cortex, and antagonise NMDA-induced seizures in the mouse. Binding Studies The compounds of the invention were tested for their ability to displace a standard compound from rat brain. The standard compound employed is 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine, hereinafter referred to as MK-801. Binding of [³H]-MK-801 to rat brain in vitro was conducted in a crude synaptosomal membrane fraction (P₂) prepared from rat cerebral cortex according to a modified method of Hulme et al ., Molecular Pharmacology , 1978, 14 , 737-750. Compounds of the invention displaced the [³H]-MK-801 binding in a concentration-dependent manner. The concentrations of the compounds of accompanying Examples 1 to 12 required to displace 50% of specific [³H]-MK-801 binding (IC₅₀) were below 10 µM in each case. Cortical Slice Studies The effects of compounds of the invention on responses to NMDA were assessed using the rat cortical slice as described by Wong et al, Proc . Natl . Acad . Sci . USA , 1986, 83 , 7104. The apparent equilibrium constant (Kb) was calculated from the righthand shift in the NMDA concentration-response curve produced by the compound under test. The compounds of accompanying Examples 1 to 6, 8 to 10 and 12 were tested and their K b values were found to be below 5 µM in each case. Antagonism of NMDLA-induced seizures Compounds of the invention were examined for their ability to antagonise tonic seizures induced by N-methyl-DL-aspartic acid (NMDLA). Groups of 8 male Swiss-Webster mice (25-30 g) were injected intravenously with the test compound at various doses, 15 min before s.c. administration of NMDLA (500 mg/kg). Animals were observed for the following 30 min and the number of mice protected from tonic extension of the forelimbs noted. ED₅₀ values for the antagonism of the NMDLA induced tonic seizures were determined using probit analysis. The compounds of accompanying Examples 1, 2, 5, 6 and 12 were tested and their ED₅₀ values were found to be below 10 mg/kg in each case. The following Examples illustrate the preparation of compounds of this invention: EXAMPLE 1 5,7-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine. Step A: Preparation of 2-(2-(4-methylphenyl)ethyl) benzoic acid. 1,5-Diazabicyclo[4.3.0]non-5-ene (29.1g) was added to a solution of 2-(carbomethoxy)benzyl triphenylphosphonium bromide (100g) and p-tolualdehyde (26.7g) in acetonitrile (250ml). The mixture was refluxed for 10 minutes, the solvents removed in vacuo and the residue dissolved in chloroform (200ml), washed with 1N aqueous hydrochloric acid (100ml) and water (100ml), then dried over sodium sulphate, filtered and evaporated. The residue was refluxed overnight in water (250ml) and methanol (100ml) containing potassium hydroxide (56g), then cooled, diluted with water (250ml) and washed with chloroform (3 x 250ml). The aqueous solution was acidified to pH 2 with conc. hydrochloric acid, and extracted with chloroform (3 x 200ml). The extract was washed, dried and evaporated to afford 2-carboxy-4'-methyl stilbene (44.2g) as a cis- trans mixture. This mixture was hydrogenated in dimethylformamide (50ml) at 50 psi (344765 Nm⁻²) in the presence of 10% palladium on charcoal catalyst (2g). The catalyst was removed by filtration and solvent evaporated. The residue was dissolved in ether. washed with water, dried and filtered to afford, after evaporation and hexane trituration, 2-(2-(4-methylphenyl)ethyl)benzoic acid (40.0g), m.p. 80-2°C. Step B: Preparation of 3-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-one. The acid from Step A (37.5g) in sulfolane (200ml) was heated to 110°C and polyphosphoric acid (150ml) added. After 1.5hr at 110°C the mixture was poured into water (500ml), extracted with hexane (3 x 200ml) and the extract washed, dried, diluted with an equal volume of ether and percolated through silica (200g). The eluate was evaporated to afford 3-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-one (30.5g) as an oil. 60MHz NMR in deuterochloroform 2.35 (CH₃), 3.20 ppm [(CH₂)₂]. Steps C: Preparation of 3-methyl-5H-dibenzo[a-d] cyclohepten-5-one. The ketone from Step B (30.25g) and N-bromosuccinimide (29.1g) were refluxed in carbon tetrachloride (300ml) for 5 hrs. The solution was cooled, filtered and evaporated and the residue dissolved in dimethylformamide (100ml) and 1,5-diazabicyclo[4.3.0]non-5-ene (22g) added. The solution was heated to 80° for 20 mins, then poured into water (300ml) and extracted with ether (3 x 300ml). The extract was washed with dilute aqueous hydrochloric acid and water, then dried and evaporated. Crystallisation from acetone/hexane gave pure 3-methyl-5H-dibenzo[a,d]cyclohepten-5-one (22.2g). m.p. 81-83°C. Step D: Preparation of 3,5-dimethyl-5H-dibenzo [a,d]cyclohepten-5-ol. To a solution of the ketone from Step C (22g) in dry tetrahydrofuran (400ml) at 0°C under nitrogen was added a solution of methyl lithium in diethyl ether (100ml of 1.4M). The solution was stirred for 1 hr at 0°C, then water was cautiously added and solvents evaporated to give an aqueous mixture which was extracted with ether (2 x 150ml). The combined extracts were washed with water, dried and evaporated. Crystallisation from ether/hexane gave 3,5-dimethyl-5H-dibenzo[a,d]cyclohepten-5-ol (20.18g), m.p. 102-3°C. Step E: Preparation of 3,5-dimethyl-5H-dibenzocyclohepten-5-hydroxylamine. To a refluxing, vigorously stirred suspension of the carbinol from step D (5g), anhydrous sodium acetate (17.37g) and hydroxylamine hydrochloride (14.6g) in dichloromethane (50ml) was added dropwise, dichloroacetic acid (15ml in 50ml dichloromethane). The reaction was followed by TLC on silica in 1:1 ethyl acetate/hexane. The mixture was cooled, washed with 2N aqueous sodium hydroxide, (2 x 50ml), water (50ml), then dried and evaporated. Trituration with 1:1 ether/hexane gave 3,5-dimethyl-5H-dibenzo[a,d] cyclohepten-5-hydroxylamine (4.92g), m.p. 142-4°C. Step F: Preparation of a mixture of 3- and 7-methyl-5-methyl-12-hydroxy-10,11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imines. To xylene (50ml) at reflux was added. over a 20 minute period, a solution of the hydroxylamine from Step E (1g) in xylene (100ml) under nitrogen. The solution was refluxed a further 10 minutes, then cooled, evaporated on silica using 2 : 3 ethyl acetate/hexane eluant to give the product mixture (520mg), as a buff solid, m.p. 125-30°C. Two pairs of atropisomers in the ratio 2:1 were evident in the 360 MHz ¹H nmr spectrum. Step G: Preparation of a mixture of 3- and 7-methyl-5-methyl-10,11-dihydro-(5H)-dibenzo[a,d] cycloheptenimines. To a solution of the mixture from Step F (500mg) in glacial acetic acid (5ml) was added zinc powder (600mg) and the mixture stirred at 65°C for 3 hrs. A further 200mg zinc was added and the mixture heated a further 1 hr. The mixture was filtered, the cake washed with acetic acid and solvents evaporated. The residue was partitioned between 2N aqueous sodium hydroxide and other, the organic layer separated, washed with water, dried and evaporated then chromatographed on silica using chloroform eluant to afford a mixture of 3- and 7- methyl compounds as an oil (270mg). Rf 0.31 on silica in 5% methanol/chloroform. Step H: Preparation and separation of a mixture of 3- and 7-methyl-5-methyl-12-tert-butoxycarbonyl-10,11-dihydro-(5H)-dibenzo[a,d]cyclohepten-5,10-imines. To a solution of the mixture of 3- and 7-methyl compounds from Step G (250mg) in dichloromethane (2ml) was added t-butylpyrocarbonate (327mg) and triethylamine (152mg), and the solution stirred at room temperature for 0.5hr. The solution was evaporated to dryness, and the residue partitioned between ether and water. The water was discarded and the ether layer dried and evaporated to give an oil which was chromatographed on a Lobar silica column using 1% ethyl acetate/hexane as eluent. Fractions were analysed by HPLC using 2% ethyl acetate/hexane. Isomers A (20mg) and B (90mg) were collected. Step I: Preparation of 5,7-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrochloride. To a solution of isomer B (90mg) from step G, in dry ethyl acetate (1ml) was added hydrogen chloride gas in ethyl acetate (5.5M, 1ml) and the solution stirred for 0.5hr. Evaporation and crystallisation from methanol/ether gave 5,7-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrochloride (32mg), mp 275-80°C. Contamination with 3-isomer < 5% by HPLC. The structure was confirmed as the 7-methyl isomer by ¹H nmr spectroscopy. EXAMPLE 2 3,5-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine . To a solution of isomer A (20mg) from Example 1 (H) above, in dry ethyl acetate (0.5ml) was added hydrogen chloride gas in ethyl acetate (5.5M, 0.5ml) and the solution stirred for 0.5hr. Evaporation and crystallisation from methanol/diethylether gave 3,5-dimethyl-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrochloride (9.2mg) . Contamination with 7-isomer < 5% by HPLC. The structure was confirmed as the 3 isomer by ¹H nmr spectroscopy. EXAMPLE 3 5,9-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine. Step A: Preparation of 2-[2-(2-methylphenyl)ethyl] benzoic acid. Prepared from o-tolualdehyde as described in Example 1A (61% yield), m.p. 122-3°C (from ether/hexane). Step B: Preparation of 1-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-one. Prepared from the above compound as described in Example 1B (65% yield), νmax (Nujol) 1660cm⁻¹ (c=o). Step C: Preparation of 1-methyl-5H-dibenzo[a,d]cyclohepten-5-one. Prepared from the above compound as described in Example 1C (20% yield), mp. 77-80°C (from acetone/hexane). Step D: Preparation of 1,5-dimethyl-5H-dibenzo[a,d]cyclohepten-5-ol. Prepared from the above compound as described in example 1D (60% yield), m.p. 107-9° (from ethyl acetate/hexane). Step E: Preparation of 1,5-dimethyl-5-hydroxylamino-5H-dibenzo[a,d]cycloheptene. Prepared from the above carbinol as in Example 1E. Yield 76%, m.p. 127-30°C. Step F: Preparation of a mixture of 1,5-dimethyl-12-hydroxy-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine and 5,9-dimethyl-12-hydroxy-10,11-dihydro-5Hdibenzo[a,d]cyclohepten-5,10-imine. Prepared from the above hydroxylamine as in Example 1F. to give an orange solid in 50% yield. Two atropisomers of each compound were present as adjudged by 360MHZ nmr: δ (CDCl₃) 2.40 (0.3H), 2.55 (0.3H), 2.68 (0.15H), and 2.85 (0.15H) (CH of CH₂, J=18Hz). Step G: Preparation of a mixture of 1,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine and 5,9-dimethyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine. To the mixture from step F (800mg) in glacial acetic acid (6ml) was added powdered zinc (800mg) and the mixture heated at 60° for 2hr, cooled, filtered and the cake washed with ether and water. Aqueous sodium hydroxide was added to the washings to pH 14, the ether layer separated, washed with brine, dried and evaporated. The residue was purified by column chromatography to give the product mixture as an oil (200mg), which was used as such for step H. Step H: Preparation of 1,5-dimethyl-10,11-dihydro-12-tert-butoxycarbonyl-5H-dibenzo[a,d]cyclohepten-5,10, imine and 5,9-dimethyl-10,11-dihydro 12-tert-butoxy carbonyl-5H-dibenzo[a,d]cyclohepten 5,10 imine. The mixture from step G was treated with tert-butyl pyrocarbonate and the products separated as described in Example 1(H), to give the isomeric products A (105mg) and B (27mg) as oils. Isomer A: nmr δ(CDCl₃) 2.59 (1H, d, J=14.4 Hz, C H A H B ); 3.61 (1H, dd CH A H B ); 5.38 (1H, dd CH). Isomer B: nmr δ(CDCl₃) 2.40 (1H, d, J=18Hz, C H A H B ); 3.25 (1H, dd, CH A H B ); 5.39 (1H, d, J=8.6Hz, CH). Step I: Preparation of 1,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrochloride. Isomer A from step H above (105mg) was treated with dry HCl as in Example 1(I) to give 1,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]-cycloheptene-5,10-imine hydrochloride (80mg, 88%), m.p. 275-278°C. EXAMPLE 4 1,5-Dimethyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine. Prepared from isomer B (Example (3H))as described in Example 1(I).m.p. > 325°C (dec). EXAMPLE 5 3,5-Dimethyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine hydrochloride. A solution of 412 mg (1.37 mmol) 3-bromo-10,11-dihydro-5-methyl-5H-dibenzo[a,d]-cyclohepten-5, 10-imine in 40 ml of ethyl ether was treated with 350 mg (0.64 mmol) of 1,3-bis(diphenylphosphino)propane nickel (II) chloride under an inert atomosphere. To the mixture was added a solution of methyl magnesium bromide in ether (3.0 M, 1.4 ml) and after the initial exothermic reaction had subsided, the mixture was heated at 40° for 18 hours. TLC indicated incomplete reaction and an additional 3.0 ml of the Grignard reagent (3.0 M) was added portionwise and the mixture heated at reflux for 6 hours. Thereafter the reaction was cooled and quenched by the addition of 100 ml each of water and ether, the mixture transferred to a separatory funnel with an additional 300 ml of water and 200 ml of ammonium hydroxide. The mixture was shaken with 600 ml more ether and the layers allowed to separate. The ether layer was removed and dried (sodium sulfate), then concentrated under vacuum to afford 159 mg of a mixture which was partially purified by flash chromatography (ethyl acetate). Additional purification of the 3-methyl compound was achieved by preparative HPLC using a Waters PrepPak C-18 column. Homogeneous fractions were combined and concentrated to dryness, the material was flashed once more (chloroform, up to 5% methanol) and the hydrochloride salt of the title compound was prepared using ethanolic HCl: C₁₇H₁₇N.HCl.0.4 H₂O, 99.1% by HPLC. Anal. Calcd.: N, 5.02; C, 73.18; H, 6.60 Found : N, 5.03; C, 73.48; H, 6.63 EXAMPLE 6 5-dimethyl-3-phenyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine hydrochloride. A mixture of 100 mg (0.33 mmol) of 3-bromo -10,11-dihydro-5-methyl-5H-dibenzo[a,d]-cyclohepten-5,10-imine,20 mg (0.017 mmol) of tetrakis(triphenylphosphine)palladium (0), 0.14 mL of triethylamine, 60 mg (0.5 mmol) of phenylboronic acid and 3 mL of N,N-dimethylformamide was warmed to 100°C under nitrogen atmosphere for 12 h. The mixture was concentrated by short path distillation under reduced pressure (0.05 mm, bath temp 35°C) to dryness. The nearly black residue was taken up in 10 mL of dilute aqueous ammonia (50 mL)) and extracted with three 50 mL portions of ethyl acetate. The combined extracts were washed with 10 mL of dilute aqueous ammonia, dried over magnesium sulfate, and concentrated to dryness. The residue was partially purified by flash chromatography with ethyl acetate as eluant, then appropriate fractions combined and further purified by preparative HPLC using a Whatman ODS-3 preparative column, eluting with 3% methanol, 57% water and 40% acetonitrile (isochratic). The homogeneous fractions (by HPLC) were combined, concentrated to dryness and the residue partitioned between 50 mL of 0.5 N sodium hydroxide and 50 mL of chloroform. The residue from concentration of the chloroform extracts was dissolved in ether and acidified with 1 mL of 5.12 N ethanolic hydrochloric acid. The white precipitate (56 mg) was collected and dried to give the title compound. C₂₂H₁₉N.HCl.0.5H₂O; 99.95% by HPLC Anal. Calcd.: N, 4.09: C, 77.06; H, 6.17 Found: N, 4.38: C, 76.88: H, 6.21 EXAMPLE 7 7-Methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine Step A: Preparation of 7-hydroxy-7-methyl-7H-benzo[4,5]cyclohepta[1,2-a]naphthalene. To a solution of 7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7-one (1.75g, prepared by the method of Bergmann et al, J. Org. Chem ., 1963, 28 , 3341) in dry tetrahydrofuran (40ml) at 0°C under nitrogen was added a solution of methyl lithium in diethyl ether (8ml of 1.4M). After 90 minutes at 0°C the reaction was quenched by the dropwise addition of water (20ml) and the reaction mixture extracted into diethyl ether (2 x 75ml), dried (Na₂SO₄), filtered and the solvents removed under reduced pressure to give a light brown oil (1.9g). Step B: Preparation of 7-hydroxylamino-7-methyl-7H-benzo[4,5]cyclohepta[1,2-a]naphthalene Sodium acetate (5.7g) and dichloroacetic acid (8.5ml) were stirred together in dichloromethane (8.5ml) at 0°C for 5 minutes then hydroxylamine hydrochloride (4.8g) added. After 1h at room temperature more dichloromethane (17ml) was added and after a further 30 minutes, the product from Example 7, Step A (1.9g) was added. After 1 h at room temperature the reaction mixture was poured into ice-water (200ml) and washed with ammonia solution (70ml). The organic layer was dried (Na₂SO₄), filtered and concentrated in vacuo to give the required product (2.04g) as a colourless form. Spectral data were consistent with the proposed structure. Step C: Preparation of 12-hydroxy-7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine and 12-hydroxy-7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7-13-imine. To xylene (100ml) at reflux was added, over a 20 minute period, the hydroxylamine product from Example 7B (1.9g) in xylene (100ml) under nitrogen. After 30 minutes at reflux the reaction mixture was allowed to cool and the solvent removed under high vacuum to leave a brown residue. Trituration with ethyl acetate and filtration gave a white solid which was washed with methanol and dried in the vacuum oven to give, as a mixture of atropisomers, 12-hydroxy-7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine (0.72g, 40%). The filtrate was concentrated in vacuo and the residue obtained, purified by chromatography on silica gel with 25% ethyl acetate in hexane as eluent to give, as a white solid, 12-hydroxy-7-methyl-12,13-dihydro-7H-benzo[4,5] cyclohepta[1,2-a]naphthalen-7,13-imine (0.41g. 26%). Step D: Preparation of 7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine hydrochloride. 12-Hydroxy-7-methyl-12,13-dihydro-7H-benzo[4,5] cyclohepta[1,2-a]naphthalen-7,12-imine (0.25g) and zinc dust (0.3g) were heated together at 65°C in glacial acetic acid (3ml) for 14h under an atmosphere of nitrogen. After this time the reaction mixture was filtered and the solvent removed in vacuo to leave a light brown oil. This was dissolved in ether (40ml) and washed with 1N sodium hydroxide solution (2 x 25ml) then water (1 x 25ml), dried (Na₂SO₄), filtered and concentrated under reduced pressure. The residue was dissolved in a 5 molar solution of hydrogen chloride in ethyl acetate then reconcentrated and dried under high vacuum to give 7-Methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine hydrochloride (130mg). m.p. > 250°C (dec.). p.m.r. (free base) (360MHz, DMSO-d₆) δ 2.03 (3H, s, CH₃), 3.09 (1H, d, J = 16.9Hz, H-11 endo ), 3.77 (1H, dd, J = 16.9 and 5.6Hz, H-11 exo ), 4.91 (1H, d. J = 5.6Hz, H-10), 7.08 (3H, m, aromatics), 7.30-7.45 (3H, m, aromatics), 7.50 (1H, d, J = 8.6Hz), 7.63 (1H, d, J = 8.6Hz). 7.72 (1H, d, J = 7.9Hz) and 7.81 (1H, d, J = 7.9Hz). COSY spectra showed that H-6, H-7 and H-8 are in the 3 proton multiplet centred at δ 7.08, H-9 is at δ 7.33 and H-4 is at δ 7.50. Irradiation of the methyl group (δ 2.03) produced a n.O.e. to H-4 (δ 7.50) and H-6 (δ 7.08) while irradiation of H-10 gave a n.O.e. to H-9 (δ 7.33). Found: C, 73.81; H, 5.78; N, 4.19. C₂₀H₁₇N.HCl.H₂O requires: C, 73.72; H, 6.9; N, 4.30%. EXAMPLE 8 7-Methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,13-imine hydrochloride. 12-Hydroxy-7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,13-imine (Example 7, Step C, 300mg) and zinc dust (370mg) were heated together in glacial acetic acid (4ml) at 65°C for 14h under an atmosphere of nitrogen. After this time the reaction mixture was filtered and the solvent removed in vacuo to leave a residue which was dissolved in ether (50ml) and washed with IM sodium hydroxide solution (1 x 25ml), water (1 x 25ml) then dried (Na₂SO₄), filtered and concentrated under vacuum. The white foam obtained was dissolved in a 5M solution of hydrogen chloride in ethyl acetate and the solvent removed in vacuo to leave as a white foam 7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,13-imine hydrochloride (0.195g), mp 208-210°C. p.m.r. (free base) (360MHz, DMSO-d₆) δ 2.02 (3H, s, CH₃), 2.85 (1H, d, J = 16.8Hz, H-11 endo ), 3.54 (1H, dd, J = 16.8 and 5.4Hz, H-11 exo ), 5.28 (1H, d, J = 5.4Hz, CH), 6.88 (1H, m), 7.05 (2H, m), 7.28 (2H, m), 7.40 (1H, dd, J = 8.2, 8.0Hz), 7.64 (1H, dd, J = 8.3, 8.OHz), 7.81 (1H, d, J = 8.2Hz) and 7.86 (1H, d, J = 8.3Hz). COSY spectra showed H-1 to be at δ 6.88 and H-16 to be at δ 7.86. Irradiation of H-10 (δ 5.28) gave a n.O.e. to H-16 (δ 7.86). EXAMPLE 9 2,5-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine 2-Methyl-5H-dibenzo[a,d]cyclohepten-5-one (prepared by the method of Dunn et al, J. Med. Chem. , 1977, 20 , 1557) was converted as described in Example 1, Steps D-H, to a mixture of 2- and 8-methyl-5-methyl-12-tert-butoxycarbonyl-10,11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imines. Separation of the regioisomers was performed by reverse phase chromatography, using a C-18 column, eluting with CH₃CN/H₂O (65:35). The 2-methyl regioisomer was deprotected as described in Example II to give 2,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrochloride , m.p. 185-195°C. δ (360MHz, CDCl₃) 2.29 (3H, s, CH₃), 2.33 (3H, s, CH₃), 2.88 (1H, d, C H A H B ), 3,99 (1H, dd, CH A H B ), 5.25 (1H, d, CH) and 6.94-7.26 (7H, m, ArH). Found: C, 66.55; H, 6.16; N, 4.49. C₁₇H₁₇N.2HCl requires: C, 66.24; H, 6.21; N, 4.54%. m/e 235 (M⁺). The assigned regiochemistry was confirmed by n.O.e. studies. EXAMPLE 10 5,8-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine 5,8-Dimethyl-12-tert-butoxycarbonyl-10,11-dihydro-5H-dibenzo[a.d]cyclohepten-5,10-imine (separated from the 2-methyl regioisomer as described in Example 9) was deprotected as described in Example 1H to give 5,8-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine , m.p. 190-195°C. δ (360MHz, CDCl₃) 2.20 (3H, s, CH₃), 2.31 (3H, s, CH₃), 2.85 (1H, d, C H A H B ), 3.94 (1H, dd, CH A H B ), 5.28 (1H, d, CH) and 6.81-7.36 (7H, m, ArH). m/e 235 (M⁺). The assigned regiochemistry was confirmed by n.O.e. studies. EXAMPLE 11 3-methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine Step A: Preparation of 3-carboxy-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine In a 3 neck flask fitted with a thermometer, magnetic stirrer, rubber septum and a gas inlet tube connected to a bubbler was dissolved 500 mg (1.66 mmole) of 3-bromo-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine in 10 ml of THF, previously distilled over sodium benzophenone ketyl. The solution, stirred at -78°C under nitrogen atmosphere, was treated with 2.45 ml (4.15 meqs) of a 1.7M solution of tert -butyllithium in pentane. After stirring at -78°C for 30 minutes, the nitrogen was replaced by carbon dioxide generated from dry ice and sublimed, passing through a Drierite column en route to the reaction vessel. After a few minutes a copious white precipitate had formed and the cooling bath was removed. Stirring under CO₂ was continued at ambient temperature for two hours, then 1 ml of water was added and the THF removed in vacuo . The residue was slurried in water (20 ml) until nearly a clear solution, filtered, and any undissolved solids washed with a small amount of water. The pH of the clear filtrate was carefully adjusted to 6.5 by addition of glacial acetic acid. The white solid which precipitated was washed with water, then with ether/acetonitrile mixtures to give the title compound, 280 mg (64%). PMR (d₆-DMSO) δ 1.87 (s, 3H, CH₃), 2.66 (d, 1H, J = 17Hz, C-11 exo H), 3.39 (dd, 1H, J = 17 and 5.6Hz, C-11 endo H), 4.61 (d, 1H, J = 5.3 Hz, C-10 H), 7.00-7.17 (m, 4H, aryl), 7.33 (d. 1H, J = 6Hz, H1), 7.64 (dd, 1H, J = 7.8 and 1.5Hz, H-2) and 7.83 (s, 1H, H-4). Step B: Preparation of 3-methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine. The 3-carboxy compound from Step A (265 mg, 1 mmole) was suspended in 25 ml abs. CH₃OH, the mixture treated with 0.6 ml (5 mmol) boron trifluoride etherate and the resulting solution was stirred at reflux for 18 hours. Removal of the solvent left a residue which was extracted with ether-saturated sodium bicarbonate. The combined ether extracts were washed (H₂O, brine) and dried (Na₂SO₄) to afford 240 mg of 3-methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine . PMR (CDCl₃) δ 1.99 (s, 3H, CH₃), 2.63 (broad s,1H, NH), 2.80 (d, 1H, J = 17Hz, C-11- exo H), 3.50 (dd, 1H, J = 17, 5.4Hz, C-11 endo -H), 3.90 (s, 3Gm ICH₃), 4. 72 (d, 1H, J = 5.4Hz, C-10 H), 7.01-7.33 (m, 5H, aryl). 7.77 (dd, 1H, J = 8 and 1.6Hz, H-2) and 7.95 (d, 1H, J = 1.7Hz, H-4). EXAMPLE 12 3-Hydroxymethyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine A solution of 3-methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (279mg, 1.0mmol) in a mixture of ether (20 ml) and dry THF (10 ml) was added dropwise with stirring, under nitrogen, to a suspension containing 87 mg (2.3mmole) of lithium aluminium hydride in 25 ml dry ether at 40°C. When the addition was complete the mixture was heated at 55°C for 2 hours, then stirred at 25°C for 18 hours. TLC (SiO₂, CHCl₃ : CH₃OH:NH₄OH 90:10:1) indicated the reaction was complete. The mixture was chilled in an ice-bath and quenched by the dropwise addition of 10ml of saturated aqueous sodium potassium tartrate. After stirring for several hours the mixture was filtered and the while solid washed with water, then ether to give 3-hydroxymethyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (195 mg, 74%), mp 215-217°C. Additional product could be obtained from the ether wash. The title compound had satisfactory PMR and high resolution spectra; for C₁₇H₁₇NO.0.5H₂O. Anal. Calc'd: N, 5.38; C, 78.43; H, 6.97 Found: N, 5.28; C, 78.53; H, 6.87 EXAMPLE 13 Tablet Preparation Tablets containing 1.0, 2.0, 25.0, 26.0, 50.0 and 100.0 mg, respectively. of the following compounds are prepared as illustrated below: 5,7-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine 3,5-Dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine 3-Hydroxymethyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine 3-Methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine TABLE FOR DOSES CONTAINING FROM 1-25 MG OF THE ACTIVE COMPOUND Amount-mg Active Compound 1.0 2.0 25.0 Microcrystalline cellulose 49.25 48.75 37.25 Modified food corn starch 49.25 48.75 37.25 Magnesium stearate 0.50 0.50 0.50 TABLE FOR DOSES CONTAINING FROM 26-100 MG OF THE ACTIVE COMPOUND Amount-mg Active Compound 26.0 50.0 100.0 Microcrystalline cellulose 52.0 100.0 200.0 Modified food corn starch 2.21 4.25 8.5 Magnesium stearate 0.39 0.75 1.5 All of the active compound, cellulose, and a portion of the corn starch are mixed and granulated to a 10% corn starch paste. The resulting granulation is sieved, dried and blended with the remainder of the corn starch and the magnesium stearate. The resulting granulation is then compressed into tablets containing 1.0 mg. 2.0 mg, 25.0 mg, 26.0 mg, 50.0 mg and 100.0 mg of active ingredient per tablet.

Claims: A compound of formula (I): or a pharmaceutically acceptable salt thereof, wherein one of R¹, R², R³ and R⁴ represents a group of formula -R or -CO₂R, and the remaining groups R¹, R², R³ and R⁴ independently represent hydrogen, halogen, hydroxy, C₁₋₆ alkoxy or a group of formula -R or -CO₂R, in which R represents a hydrocarbon group having up to 18 carbon atoms, which group may be substituted with a group selected from halogen, C₁₋₆ alkyl, phenyl, C₁₋₆ alkoxy, halo(C₁₋₆)alkyl, hydroxy, amino, nitro, cyano, carboxy, C₁₋₆ alkoxycarbonyl, C₁₋₆ alkoxycarbonyl(C₁₋₆)alkyl, C₁₋₆ alkylcarbonyloxy and C₁₋₆ alkylcarbonyl, and groups of formula -CONR a R b and -NR a .COR b in which R a and R b independently represent hydrogen or C₁₋₆ alkyl, or R¹ and R² or R³ and R⁴ together represent the residue of a saturated or unsaturated carbocyclic ring, the R¹/R² or R³/R⁴ carbon chain of which comprises from 2 to 6 carbon atoms; R⁵ and R⁶ independently represent hydrogen, hydroxy, fluoro or a group of formula -R as defined above; R⁷ represents hydrogen or C₁₋₃ alkyl; and R⁸ represents methyl or ethyl. A compound as claimed in claim 1 wherein one of R¹ to R⁴ represents C₁₋₆ alkyl, hydroxy(C₁₋₆)alkyl, phenyl or C₁₋₆ alkoxycarbonyl, and the remaining groups R¹ to R⁴ represent hydrogen or halogen. A compound as claimed in claim 1 wherein R¹ and R² or R³ and R⁴ together represent the residue of a saturated or unsaturated carbocyclic ring, the R¹/R² or R³/R⁴ carbon chain of which comprises 3 or 4 carbon atoms. A compound as claimed in any one of the preceding claims wherein R⁵ represents hydrogen, hydroxy or methyl and R⁶ represents hydrogen or hydroxy. A compound as claimed in any one of the preceding claims wherein R⁷ represents hydrogen and R⁸ represents methyl. A compound as claimed in any one of the preceding claims wherein the substituent R¹ to R⁴, of formula -R or -CO₂R, is present at position 3 or 7 of the benzo rings. A compound as claimed in claim 1 selected from: 5,7-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 5,9-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 3,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 1,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 5-methyl-3-phenyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,12-imine; 7-methyl-12,13-dihydro-7H-benzo[4,5]cyclohepta[1,2-a]naphthalen-7,13-imine; 2,5-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 5,8-dimethyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imine; 3-methoxycarbonyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; 3-hydroxymethyl-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; and salts thereof. A pharmaceutical composition comprising a compound as claimed in any one of the preceding claims in association with a pharmaceutically acceptable carrier or excipient. A compound as claimed in any one of claims 1 to 7 for use as a therapeutic agent. The use of a compound as claimed in any one of claims 1 to 7 for the preparation of a medicament for the treatment of convulsions and/or of neurodegenerative diseases. A process for the preparation of a compound as claimed in any one of claims 1 to 7 which comprises: (A) for the preparation of a compound of formula (I) wherein R⁵ is hydrogen or a group -R and R⁶ is hydrogen: reduction of an N-hydroxy compound of formula (II): wherein R¹ to R⁴ and R⁸ are as defined in claim 1 and R¹⁵ represents hydrogen or a group of formula -R as defined in claim 1; followed, when R⁷ is other than hydrogen, by alkylation of the product thereby obtained; or (B) for the preparation of a compound of formula (I) wherein R⁸ represents a group of formula -CH₂R⁹ in which R⁹ is hydrogen or methyl: ring closure of a 10-NHX-5-(=CHR⁹)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene (where X is the group R⁷ as defined in claim 1 or a protecting group) by treatment with a strong base; followed, if necessary, by removal of the protecting group; or (C) for the preparation of a compound of formula (I) wherein at least one of R¹ to R⁴ represents a group -R: reaction of a compound of formula (IV): wherein R⁵ to R⁸ are as defined in claim 1, one of R¹¹, R¹², R¹³ and R¹⁴ represents halogen, and the remaining groups R¹¹, R¹², R¹³ and R¹⁴ independently represent hydrogen, halogen, hydroxy, C₁₋₆ alkoxy or a group of formula -R as defined in claim 1; with a reagent which replaces halogen by the group -R; (D) for the preparation of a compound of formula (I) wherein at least one of R¹ to R⁴ represents a group of formula -CO₂R: metalation of a compound of formula (IV) as defined above; treatment of the resulting anion in situ with carbon dioxide; and subsequent esterification of the resulting carboxylic acid by standard means; or (E) for the preparation of a compound of formula (I) wherein R⁵ represents hydroxy: treatment of the N-hydroxy compound of formula (II) as defined above, in which R¹⁵ is hydrogen, with manganese acetate; reduction of the product thereby obtained; and, when R⁷ is other than hydrogen, alkylation of the resulting product; or (F) for the preparation of a compound of formula (I) wherein R⁶ represents hydroxy: reduction of the corresponding 11-oxo compound, in which the nitrogen atom is protected; deprotection of the nitrogen atom; and, if desired, separation of the product thereby obtained into its individual endo and exo isomers by conventional techniques; or (G) for the preparation of a compound of formula (I) wherein R⁵ is fluoro: treatment of the corresponding 10-hydroxy compound with diethylaminosulphur trifluoride; or (H) for the preparation of a compound of formula (I) wherein R⁶ is fluoro: treatment of the aziridine of formula (V): wherein R¹ to R⁵ and R⁸ are as defined in claim 1, with hydrogen fluoride in the presence of pyridine; any of the above processes being followed, if desired, by conversion, where appropriate, of a compound of formula (I) initially obtained into a further compound of formula (I) as defined in claim 1 using methods known per se ; any of the above processes being followed, if desired, by conversion of a compound of formula (I) initially obtained into a salt thereof or by conversion of a salt of a compound of formula (I) initially obtained into a compound of formula (I) or into a further salt thereof; and any reactive groups on any of the molecules concerned in the above reactions being protected throughout the duration of said reactions with conventional protecting groups, said protecting groups being subsequently removed using methods known per se . A compound of formula (II): or a salt thereof; wherein R¹ to R⁴ and R⁸ are as defined in claim 1 and R¹⁵ is as defined in claim 11. A process for the preparation of a compound as claimed in claim 12 which comprises cyclising a compound of formula (III): wherein R¹ to R⁴ and R⁸ are as defined in claim 1 and R¹⁵ is as defined in claim 11. A compound of formula (III): or a salt thereof; wherein R¹ to R⁴ and R⁸ are as defined in claim 1 and R¹⁵ is as defined in claim 11.

Inventors: BAKER, RAYMOND, BRITCHER, SUSAN F., LEESON, PAUL D.
Applicants: MERCK SHARP & DOHME LTD.
Application year: 1988
Main classification: C07D451
IPC codes: C07C67, A61P3, A61K31, A61P9, C07C239, C07D451, A61P25