SUBSTITUTED TROPYL AND PSEUDOTROPYL BENZOATES AND THEIR USE IN MIGRAINE TREATMENT

Abstract: Migraine is treated with a pseudotropyl or tropyl benzo­ ate derivative of the following general Formula I:- wherein:- n represents 0 or an integer from 1 to 4 R₁ represents C₁-C₄ alkoxy or chlorine; R₂ represents C₁-C₄ alkyl, C₁-C₄ alkoxy or halogen provided that R₂ is the same as R₁ when n is 2, 3 or 4; or a pharmaceuticaliy acceptable salt thereof. With the exception of tropyl-2-chlorobenzoate and tropyl-2,4-,-2,5-,-2,6-dichlorobenzoates, the derivatives of Formula I are novel compounds.

Description: SUBSTITUTED THOPYL AND PSEUDOTHOPYL BENZOATES AND THEIR USE IN MIGRAINE TREATMENT The invention relates to the treatment of migraine with certain substituted tropyl and pseudotropyl benzoates and provides pharmaceutical compositions comprising said compounds and methods of treating migraine using said compounds. Further, the invention also provides said compounds for use in treating migraine and, when said compounds are novel, it provides said novel compounds per se. Acute attacks of migraine are usually treated with a peripheral vasoonstrictor, such as ergotamine, which may be co-edinistered with caffeine, and dihydroergotarAne; an antipyretic analgesic, such as acetylsalicylic acid or p-acetylaminophenol; and/or an anti-emetic such as cyclizine, metoclopramide and thiethylperazine. It has also beenreported (JIB. Hughes; ed. J. Aust 2, No. 17, 580, 1977) that immediate relief of acute migraine attack can be obtained by slow ntravenous injection of metoclopramide (10 mg). It is believed that 5-hydroxytryptamine (5-HT) is the naturally occurring substance most likely to play a role in the pathophysiology of migraine. Increased amounts of 5-HT and its metabolite 5-hydroxyindoleacetic acid are excreted in the urine during most attacks. Further plasma and platelet 5-HT concentrations fall rapidly at the onset of an attack and remain low whilst the headache persists. Moreover, attacks of migraine have been clearly associated with periods of thrombocytopaenia in certain patients. It has been proposed that compounds which block the activity of 5-HT would be of use in the treatment of migraine (J.R. Fozard, International Headache Congress 1980) reported in Advances in Neurology, Vol 33, Raven Press, New York 1982). The known migraine prophylactic drugs methysergide, propranolol, amitriptyline, and chlorpromazine have widely different pharmacological activities but are all 5-HT D-receptor antagonists at the doses used clinically for the treatment of migraine. Metoclopramide is a potent 5-HT M-receptor antagonist and it has been proposed (J.R. Fozard supra) that blockade of the M-receptor present on afferent sensory neurones affords symptomatic relief in an acute migraine attack. The potency as 5-HT M-receptor antagonists of (-) cocaine and some related compounds, including benzoyl pseudotropine (i.e. pseudotropyl benzoate) and benzoyl tropine (i.e. tropyl benzoate), has been reported (J.R. Fozard et al, Eur. J. Pharmacol., 59(1979), 195-210) but, with the exceptions of nor(-)cocaine and benzoyl tropine, none are as potent as metoclopramide. The pA2 values reported for nor(-)cocaine, benzoyl tropine, and benzoyl pseudotropine are 7.7, 7.2 and 7.0 respectively whilst the pA2 5-HT value determined for metoclopramide by the same procedure is 7.2 (J.R. Fozard et al. Eur. J. Pharmacol., 49(1978), 109-112). It has been reported in UK Patent Patent Application No. 8215452 (as yet unpublished) that substitution of tropyl benzoate with alkyl, alkoxy or halogen in the 3,4 and 5, or 3,4, and 5 positions of the benzene ring surprisingly enhances its potency as a 5-HT M-receptor antagonist. Tests conducted with tropyl-4-chlorobenzoate (pA2 7.0), tropyl-4-methylbenzoate (pA2 7.8), tropyl-3,4-dichlorobenzoate (PA2 7.8) and tropyl-3,4-dimethoxybenzoate (pA2 7.2), indicated that corresponding substitutions elsewhere in the benzene ring would not provide the same order of increase in potency. Further, tests conducted with pseudotropyl-3,5-dimethoxybenzoate (PA2 6.6), and pseudotropyl-3,4,5-trimethoxybenzoate (PA2 5.7) indicated that corresponding substitutions in the benzene ring of pseudotropyl benzoate actually would reduce its potency as a 5-HT M-receptor antagonist. However, it has now surprisingly been found that substitution by C1 -C4 alkoxy or chlorine in at least the 2 position of the benzene ring of tropyl benzoate and pseudotropyl benzoate does substantially enhance potency as a 5-HT M-receptor antagonist. With the exceptions of tropyl 2-chlorobenzoate and tropyl 2,4-,2,5- and 2,6-dichlorobenzoate, the tropyl benzoate derivatives of Formula I are believed to be novel compounds. All the pseudotropyl benzoates -of Formula I are believed to be novel compounds. The said tropyl 2-chlorobenzoate and tropyl-dichlorobenzoates are disclosed in Schultz et al (Pharm. Zig. 1972, 117 (40), 1455-6) and stated to exhibit spasmolytic- inducing activity on isolated guinea pig ileum but no pharmacological use has been reported for the compounds. According to a first aspect of the invention, there are provided for use in the treatment of migraine and other vascular headaches a tropyl or pseudotropyl benzoate derivative of the following general Formula I: EMI5.1 wherein: - n represents 0 or an integer from 1 to 4; R1 represents C1-C4 alkoxy or chlorine; and R2 represents C1-C4 alkyl, halogen or C1-C4 alkoxy, provided that R2 is the same as R1 when n is 2, 3 or 4; or a pharmaceutically acceptable salt thereof. According to a second aspect of the invention there are provided pharmaceutical compositions in unit dose form for the effective relief of migraine comprising a compound of general Formula I in admixture or otherwise associated with a pharmaceutically acceptable diluent or carrier and containing 0.5 to 100 mg per unit dose. Usually, said compositions will contain 1 to 50 mg, especially 3 to 30 mg, per unit dose. According to a third aspect of the invention, there are provided per se all novel compounds of Formula I. According to a fourth aspect of the invention, there is provided a method of treating migraine which comprises administering to a patient suffering migraine, an effective migraine relieving amount of a compound of Formula I. Said amount usually will be in the range 0.01 mg/kg to 10 mg/kg, especially 0.03 mg/kg to 3.0 mg/kg. It is also contemplated that the compounds of Formula I can be used in the prophylaxis of migraine by administering to a patient at risk of migraine an effective migraine-prophylatic amount of the compound. When the bicylic ring of a compound of Formula I is in the endo configuration, the compound is a tropyl benzoate and, when it is in the exo configuration, the compound is a pseudotropyl benzoate. Presently, the tropyl benzoates are preferred over the pseudotropyl benzoates. The compounds of general Formula I have the benzoyloxy moiety substituted by C1 -C4 alkoxy or chlorine in at least the 2 position and optionally in other positions. In particular R1 represents C1-C4 alkoxy or chlorine; R2 represents Cl-C4 alkyl, C1-C4 alkoxy or halogen but is the same as R1 when there are two or three substituents represented by R2; and n is 0 or an integer up to 4 preferably 0, 1 or 2. In general Formula I, the phenyl ring can be substituted as shown in the following Table I: TABLE I Position 2 3 4 5 6 R1 H H H H R1 R2 H H H R1 H R2 H H R1 H H R2 H R1 H H H R2 R1 R1 R1 H H R1 R1 H R1 H R1 R1 H H R1 R1 H R1 R1 H R1 H R1 H R1 R1 R1 R1 R1 H R1 R1 R1 H R1 R1 R1 H R1 R1 R1 H1 R1 R1 R1 In the table above, R1 and R2 are as defined in connection with Formula I. Examples of C1-C4 alkoxy groups which can be represented by R1 and R2 are methoxy, ethoxy, n-propoxy, n-butoxy and iso-propoxy, with ethoxy and especially, methoxy being preferred. Examples of C1-C4 alkyl groups which can be represented by R2 are methyl, ethyl, n-propyl, n-butyl and iso-propyl with ethyl and especially methyl being preferred. The halogens which can be represented by R1 and R2 are bromine, chlorine, fluorine and iodine with bromine, fluorine and, especially, chlorine being preferred. One preferred class of compounds of the invention are those pseudotropyl benzoates and tropyl benzoates of Formula I in which n is O or an integer from 1 to 4, R1 represents chlorine and R2 represents C1-C4 alkyl or chlorine provided that R2 is chlorine when n is 2, 3 or 4. In a presently particularly preferred embodiment of the invention, the compounds are those pseudotropyl benzoates and, especially, tropyl benzoates of Formula I in which R1 and, if present, R2 represent chlorine especially at the 2; 2, 3; 2, 4;or 2, 5; positions. The said especially preferred chlorine substituted compounds are the following: tropyl-2-chlorobenzoate, tropyl-2,3-dichlorobenzoate, tropyl-2,4-dichlorobenzoate, tropyl-2,5-dichlorobenzoate, pseudotropyl-2-chlorobenzoate, pseudotropyl-2 ,3-dichlorobenzoate, pseudotropyl-2 , 4-dichlorobenzoate, pseudotropyl-2 , 5-dichlorobenzoate, In addition to the preferred compounds specified above, the following are illustrative compounds of Formula I: : tropyl 2-chloro-3-methylbenzoate; tropyl 2-chloro-4-methylbenzoate; tropyl 2-chloro-5-methylbenzoate; tropyl 2,3,5-trichlorobenzoate; tropyl 2,3,4,5-tetrachlorobenzoate; tropyl 2,3,4,5, 6-pentachlorobenzoate; tropyl 2-methoxybenzoate; tropyl 2 , 5-dimethoxybenzoate; tropyl 2-chloro-5-methoxybenzoate; pseudotropyl 2,3,5-trichlorobenzoate; pseudotropyl 2-chloro-4-methylbenzoate; The compounds of Formula I block the M-receptors for 5-hydroxytryptamine (5-HT) on afferent sensory neurones, certain of which subserve the transmission of pain. As explained above, the blocking of such M-receptors is believed to be a mechanism by which the symptoms of migraine can be relieved. Accordingly, the compounds of Formula I are useful in the treatment of migraine when administered in amounts sufficient to effectively block the said M-receptors. The activity of the compounds against 5-HT can be assessed by determining their pA2 values in the isolated rabbit heart as described by Fozard et at Europ. J. Pharmacol. 59, 195-210 (1979). In the method described the molar concentration of antagonist which reduces the effects of twice the ED50 of 5-HT to that of the ED50 in the absence of antagonist is determined. The pA2 value is the negative logarithm of said molar concentrations. In general terms, the higher the pA2 value the more potent is the compound. It is believed that the compounds of Formula I show in this test a potency as 5-HT M-receptor antagonists at least an order greater than that of tropylbenzoate or pseudotropyl benzoate. The activity of the compounds against 5-HT can be assessed in vivo by measurement of the effect of the compound on the Von Bezold-Jarisch Reflex induced by 5-HT injected intravenously into the rat (see Paintal A.S., Physiol. Rev. 53 159-227, 1973). The transient cardiac slowing arises from an increased efferent vagus activity arising from stimulation by 5-HT of sensory afferent fibres in and around the heart. The compounds of Formula I are believed to be highly selective in their action against 5-HT M-receptor. Their potency against other 5-HT receptors and other spasmogens, in particular oxytocin, acetylcholine, histamine and calcium, is believed to be at least two orders lower than that against 5-HT M-receptors. Accordingly, their use in the treatment of migraine should be without any side effects. The compounds of Formula I can be administered in various manners to achieve the desired effect. The compounds can be administered alone or in the form of pharmaceutical preparations to the patient being treated either orally or parenterally, for example, subcutaneously or intravenously. The amount of compound administered will vary and can be any effective migraine-relieving amount. Depending upon the patient and the mode of administration, the quantity of compound administered may vary over a wide range to provide from about 0.01 mg/kg to about 10 mg/kg, usually 0.03 to 3.0 mg/kg, of body weight of the patient per dose. Unit doses of these compounds can contain, for example, from about 0.5 mg to 100. mg, usually 1 to 50 mg and preferably 3 to 30 mg, of the compound and may be administered, for example, from 1 to 4 times daily. The term "unit dosage form" is used herein to mean a single or multiple dose form containing a quantity of the active ingredient in admixture with or otherwise in association with the diluent or carrier, s id quantity being such that one or more predetermined units are normally required for a single therapeutic administration. In the case of multiple dose forms such as liquids or scored tablets, said predetermined unit will be one fraction, such as a 5 ml (teaspoon) quantity of a liquid or a half or quarter of a scored tablet, of the multiple dose form. In the composition aspect of the invention there are provided pharmaceutical formulations in which form the active compounds of the invention will normally be utilized. Such formulations are prepared in a manner well knon per se in the pharmaceutical art and usually comprise at least one active compound of the invention in admixture or otherwise in association with a pharmaceutically acceptable carrier or diluent therefor. For making those formulations the active ingredient will usually be mixed with a carrier, or diluted by a diluent, or enclosed or encapsulated in a capsule, sachet, cachet, paper or other container. A carrier or diluent may be solid, semi-solid or liquid material which serves as a vehicle, excipient or medium for the active ingredient. Suitable carriers or diluents are well known per se. The formulations of the invention may be adapted for enteral or parenteral use and may be admini-stered to the patient in the form of tablets, capsules, suppositories, solutions, suspensions or the like. In the specific examples included hereinbelow illustrative examples of suitable pharmaceutical formulations are described. The derivatives of Formula I can be used in migraine therapy with antimigraine drugs having different modes of action. Such drugs include those used prophylactically, such as barbiturates, diazepam, chlorpromazine, amitriptyline, propranolol, methysergide, pizotifen, cyproheptadine, dihydroergotamine, and clonidine, and those used in the acute attack, such as vasoconstrictor agents, e.g. ergotamine and dihydroergotamine, analgaesic/ antiinflammatory agents, e.g. aspirin, paracetamol and indomethacin, or anti-nauseants, e.g. cyclizine, metoclopramide, and triethylperazine (see Fozard, J.R. J. Pharm. Pharmacol. 27, 297-321 (1975); Saper, J.R., J. Amer. Med. Assoc. 239, 480-484 (1978); Fozard, J.R., supra.) As an example, compounds of general Formula 1 would be beneficial in combination with aspirin 300-1200 mg or methysergide, 2-6 mg given daily. The compounds of general Formula I can be prepared in manner known per se from tropine or pseudotropine and an acid halide of the following general Formula IV: EMI14.1 Formula IV wherein R1 and R2 are as defined in connection with Formula I, and X represents halogen, especially chlorine. When preparing tropyl benzoate derivatives, the reaction usually will be carried out in the absence of a solvent by heating, at for example a temperature in the range 140 to 160'C, the acid halide with a hydrohalide salt of tropine whilst stirring. Hydrogen halide is evolved and the mixture first becomes liquid but subsequently becomes solid. Heating is continued for about 15 mins after solidification and the mixture is then cooled and added to water. The product is the hydrohalide of the compound of Formula I and the free base can be obtained by addition of aqueous base, such as sodium or potassium carbonate, which does not hydrolyse the ester, to render the aqueous product solution alkaline and subsequent extraction of the free base with a suitable organic solvent such as, for example, diethylether, ethylacetate and methylene chloride. The organic solution is subsequently evaporated and the residue recrystallized from, for example, aqueous methanol. When preparing pseudotropyl benzoate derivatives, the reaction usually will be carried out by stirring the acid halide and pseudotropine in an aprotic solvent, preferably methylene chloride or acetonitrile, at ambient temperature. The solvent is evaporated off, usually under reduced pressure, after about 2 to 16 hours and water added to the residue, followed by aqueous base, such as sodium or potassium carbonate, which does not hydrolyse the ester, to render the aqueous product solution alkaline. Subsequently desired free base is extracted with a suitable organic solvent such as, for example, diethyl ether, ethylacetate and methylene chloride. The organic solution is then washed with water to remove excess pseudotropine and dried. The organic solvent is evaporated off and the free base recrystallized from, for example, aqueous methanol. Alternatively, the crude free base can be converted into an acid addition salt, preferably hydrochloride, by addition of an ethereal solution of the acid. The acid salt is recrystallized from, for example ethanol or isopropanol. As mentioned previously, the compounds of Formula I can be used in the form of their pharmaceutically acceptable acid addition salts. The pharmaceutically acceptable acid addition salts can be non-toxic addition salts with suitable acids, such as those with inorganic acids, for example hydrochloric, hydrobromic, nitric, sulfuric or phosphoric acids, or with organic acids, such as organic carboxylic acids, for example, glycollic, maleic, hydroxymaleic, malic, tartaric, citric, salicylic, o-acetyloxybenzoic, nicotinic or isonicotinic, or organic sulphonic acids, for example methane sulphonic, ethane sulphonic, 2-hydroxyethane sulphonic, toluene-p-sulphonic, or naphthalene-2sulphonic acids. Apart from pharmaceutically acceptable acid addition salts, other acid addition salts, such as for example, those with picric or oxalic acid, may be serve as intermediates in the purification of the compounds or in the preparation of other, for example, pharmaceutically acceptable, acid addition salts, or are useful for identification or characterisation of the bases. An acid addition salt may be converted into the free compound according to known methods, for example, by treating it with a base, such as with a metal hydroxide or alkoxide, for example an alkali or alkaline earth metal hydroxide, for example, lithium hydroxide, sodium hydroxide, potassium hydroxide or calcium hydroxide; with a metal carbonate, such as an alkali metal or an alkaline earth metal carbonate or hydrogen carbonate, for example, sodium, potassium or calcium carbonate or hydrogen carbonate; with trialkylamine; or with an anion exchange resin. An acid addition salt may also be converted into another acid addition salt according to known methods; for example, a salt with an inorganic acid may be treated with a metal salt, for example a sodium, barium or silver salt, or an acid in a suitable diluent, in which a resulting inorganic salt is insoluble and is thus removed from the reaction medium. Acid addition salt may also be converted into another acid addition salt by treatment with an anion exchange preparation. The invention is illustrated in the following non-limiting Examples. EXAMPLE 1 TKOPYL-2,4-DICHLOROBEZOATE (i.e. 2,4-DICHLOROBENZOIC ACID END0-8-METHYL-8-AZABICYCL0[3, 2,1 )CCT-3-YL ESTER) (FORMULA I, ENDO, n = 1, H1 = R2 = chlorine) A stirred mixture of tropine hydrochloride (1.76 g) and 2,4-dichlorobenzoyl chloride (2.05 g) is heated at 130-140'C for 30 minutes during which time the mixture liquifies, evolves hydrogen chloride gas and resolidifies. A solution of the cooled solid in water is basified with a solution of potassium carbonate and the base extracted with ethyl acetate. The ethyl acetate solution is washed several times with water, dried over magnesium sulphate, and evaporated to give the free base which is converted to the hydrochloride by the addition of ethereal hydrogen chloride. Recrystallization of the precipitated solid from ethanol gives tropyl 2,4-dichlorobenzoate hydrochloride. EXAMPLE 2 PSEUDOTROPYL 2, 4-DICHLOROBENZOATE (i.e. 2,4-DICHLORO- BENZOIC ACID RX0-8-METHYL-8-AZABICYCLO[3,2,130CT-3-YL ESTER) (FORMULA I, EXO, n = 1, R1 = R2 = chlorine Pseudotropine (1.41 g) and 2,4 dichlorobenzoylchloride (2.05 g) in methylene chloride (50 ml) is stirred at ambient temperature for 3 hours. The solvent is evaporated off under reduced pressure and the residue treated with water (50 ml) and saturated aqueous potassium carbonate solution (5 ml) is added. The liberated oil is extracted into diethylether, the ethereal solution washed several times with water and then dried over anhydrous magnesium sulfate. Distillation of the dried ethereal solution gives a residue which is treated with anhydrous diethyl ether and ethereal hydrogen chloride. Crystallization of the precipitate from ethanol affords pseudotropyl-2,4dichlorobenzoate hydrochloride. In the following Examples relating to pharmaceutical compositions, the term "active compound" is used to indicate the compound tropyl-2,4-dichlorobenzoate. This compound may be replaced in these compositions by any other compound of Formula I, for example by pseudotropyl-2 , 4-dichlorobenzoate. Adjustments in the amount of medicament may be necessary or desirable depending upon the degree of activity of the medicament as is well known in the art. EXAMPLE 3 An illustrative composition for hard gelatin capsules is as follows: (a) active compound 5 mg (b) talc 5 mg (c) lactose U m The formulation is prepared by passing the dry powders of (a) and (b) through a fine mesh screen and mixing them well. The powder is then filled into hard gelatin capsules at a net fill of 100 mg per capsule. EXAMPLE 4 An illustrative composition for tablets is as follows: (a) active compound 5 mg (b) starch 43 mg (c) lactose 50 mg (d) magnesium stearate 2 mg The granulation obtained upon mixing the lactose with the compound (a) and part of the starch and granulating with starch paste is dried, screened, and mixed with the magnesium stearate. The mixture is compressed into tables weighing 100 mg each. EXAMPLE 5 An illustrative composition for an injectable suspension is the following 1 ml ampule for an intramuscular injection: Weight per cent (a) active compound 0.01 (b) polyvinylpyrrolidone 0.5 (c) lecithin 0.25 (d) water for injection to make 100.0 The material (a) - (d) are mixed, homogenized, and filled into 1 ml ampules which are sealed and autoclaved 20 minutes at 121 C. Each ampule contains 1.0 mg per ml of compound (a). EXAMPLE 6 mg/suppository Active Compound 5 Oil of Theobroma (cocoa butter) 995 The medicament is powdered and passed through a B.S. No. 100 Sieve and triturated with molten oil of theobroma at 45 C to form a smooth suspension. The mixture is well stirred and poured into moulds each of nominal 1G capacity, to produce suppositories.

Claims: CLAIMS: 1. A pharmaceutical composition comprising an amount of 0.5 to 100 mg per unit dose of a tropyl or pseudotropyl benzoate derivative having the formula EMI22.1 wherein n represents 0 or an integer from 1 to 4; R1 represents C1-C4 alkoxy or chlorine; and R2 represents C1-C4 alkyl, C1-C4 alkoxy or halogen, with the proviso that R1 and R2 are the same when n is 2, 3, or 4; or a pharmaceutically acceptable salt thereof, in admixture or otherwise associated with a pharmaceutically acceptable diluent or carrier. 2. A composition according to Claim 1 containing from 3 to 30 mg of said compound per unit dose. 3. A composition according to Claim 1 wherein R1 is methoxy or chlorine and R2 is methyl, methoxy or chlorine. 4. A composition according to Claim 1 wherein R1 and R2 are chlorine. 5. A composition according to Claim 1 wherein n is 1 and the phenyl group is substituted in the 2,3; 2,4 or 2,5 position. 6. A tropyl or pseudotropyl benzoate derivative having the following general formula EMI23.1 wherein: n represents 0 or an integer from 1 to 4; R1 represents C1 -C4 alkoxy or chlorine provided that R1 is not chlorine when n is O; R2 represents C1-C4 alkyl, C1-C4 alkoxy or halogen, provided that R2 is not chlorine in the 4, 5 or 6 position when R1 is chlorine and n is 1, and that R2 is the same as R1 when n is 2, 3 or 4; or a pharmaceutically acceptable salt thereof. 7. A compound according to Claim 6 wherein R1 is methoxy or chlorine and R2 represents methyl, methoxy or chlorine. 8. A compound according to Claim 6 wherein R1 and R2 are both chlorine. 9. A compound according to Claim 6 wherein n is 1 and the phenyl group is substituted in the 2,3; 2,4 or 2,5 positions. 10. A process for preparing a compound of Claim 6 which comprises reacting tropine or pseudotropine with an acid halide having the formula EMI23.2 wherein R1, R2 and n are as defined in Claim 6 and X represents halogen. 11. A process according to Claim 10 wherein the hydrohalide salt of tropine is heated with the acid halide in the absence of a solvent. 12. A process according to Claim 10 wherein pseudotropine is stirred with the acid halide in an aprotic solvent at ambient temperature. 13. A tropyl benzoate derivative having the following general formula EMI24.1 wherein: n represents 0 or an integer from 1 to 4; R1 represents C1-C4 alkoxy or chlorine; R2 represents C1-C4 alkyl, C1-C4 alkoxy or halogen provided that R2 is the same as R1 when n is 2, 3 or 4; or a pharmaceutically acceptable salt thereof, for use in the treatment of migraine.

Inventors: FOZARD, JOHN R., GITTOS, MAURICE W.
Applicants: MERRELL DOW FRANCE ET CIE
Application year: 1983
Main classification: C07D451
IPC codes: C07D451, A61K31, A61P25