1- [(4-Morpholinyl) alkyl] -1H-indoles useful as analgesics and preparation thereof

Abstract: 4-Arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-­ indoles, useful as analgesic agents, are prepared by reaction of a 3-arylcarbonyl-2-methylnitrobenzene with DMF dimethyl acetal; reductive cyclization of the product with hydrogen over a catalyst; and N-alkylation of the resulting 4-­ arylcarbonylindole with an appropriate 4-(halo-lower-­ alkyl)morpholine in the presence of a strong base.

Description: This invention relates to 1-[(4-morpholinyl)-lower-alkyl]-1H-indoles which are useful as analgesics. Our patent application No. 85109689.1 filed August 1, 1985 (EP-A-171037) discloses 3-arylcarbonyl-1-(amino-lower-alkyl)-1H-indoles useful as analgesic, anti-rheumatic and anti-inflammatory agents. Said indoles can be optionally substituted at the 4-, 5-, 6- or 7-positions by lower-alkyl, hydroxy, lower-alkoxy or halo. US-A-3,946,029 discloses 1-(amino-lower-alkyl)-2-lower-alkyl-3-(2-, 3- and 4-pyridylcarbonyl)-1H-indoles which are stated to possess fibrinolytic and anti-inflammatory activities. Croce, Ann. di Chim. 63 , 29-35 (1973) discloses 1-(3-aminopropyl)-3-benzoyl-2-methyl-1H-indole for which no utility is disclosed. US-A-3 489 770 and DE-A-2 329 430 disclose similar indole derivatives. We have found that certain 4-arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-indoles, which may be considered analogous to substituted benzophenone derivatives, have analgesic activity and are thus useful as analgesics. More specifically, this invention relates to 4-arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-indoles, useful as analgesics, and having the structural formula I where Ar is alkoxyphenyl having one to four carbon atoms in the alkoxy radical or 1-naphthyl and Alk is alkylene containing from two to four carbon atoms. Preferred compounds within the ambit of formula I as defined above are those where Ar is 4-C₁-C₄-alkoxyphenyl or 1-naphthyl and Alk is 1,2-ethylene or 1,3-propylene. As used herein the term C₁-C₄-alkoxy includes methoxy, ethoxy, propoxy and isopropoxy, and the term C₂-C₄ alkylene includes straight or branched C₂-C₄-alkylene, i.e. 1,2-ethylene, 1-methyl-1,2-ethylene, 2-methyl-1,2-ethylene, 1,3-propylene, 2-methyl-1,3-propylene, 3-methyl-1,3-propylene and 1,4-butylene. The compounds of the invention are prepared by reaction of a 4-arylcarbonylindole of formula II hereinbelow with an appropriate 4-(halo-C₂-C₄-alkyl)morpholine in the presence of a strong base, such as an alkali metal hydride or an alkali metal amide. The reaction is preferably carried out in an organic solvent inert under the conditions of the reaction, such as dimethylformamide (hereinafter DMF), toluene or xylene, and at temperatures from around ambient up to the boiling point of the solvent. A preferred base is sodium hydride, a preferred solvent is DMF, and it is preferred to carry out the reaction at the boiling point of the solvent. The 4-arylcarbonylindoles of formula II in turn are prepared by reaction of a 2-methyl-3-nitrobenzoyl halide with a C₁-C₄-alkoxybenzene or naphthalene under Friedel-Crafts reaction conditions in the presence of aluminum chloride; reaction of the resulting 3-aryl-carbonyl-2-methylnitrobenzene with DMF dimethyl acetal; and cyclization of the resulting 3-arylcarbonyl-2-(2-dimethylaminoethenyl)nitrobenzene by catalytic reduction. The Friedel-Crafts reaction of a 2-methyl-3-nitrobenzyl halide with a C₁-C₄-alkoxybenzene or naphthalene is carried out in an organic solvent inert under the conditions of the reaction, such as methylene dichloride, ethylene dichloride, 1,1,2,2-tetrachloroethane or benzene. It is preferred to bring the reactants together at ambient temperature and then to heat the mixture at the boiling point of the solvent. A preferred solvent is methylene dichloride. The reaction of the 3-arylcarbonyl-2-methyl-nitrobenzene with DMF dimethyl acetal is carried out by heating under reflux a solution of the former with a two to four molar excess of the latter in an organic solvent inert under the conditions of the reaction. Preferred solvents are DMF and dioxane. The reductive cyclization of the 3-arylcarbonyl-2-(2-dimethylaminoethenyl)nitrobenzene is carried out in an organic solvent inert under the conditions of the reaction, for example ethyl acetate or a lower-alkanol, such as methanol, ethanol or isopropanol, at ambient temperature and at hydrogen pressures in the range from 50 to 100 p.s.i.g. Ethyl acetate or ethanol are preferred solvents, and it is preferred to carry out the reduction under a hydrogen pressure around 50 p.s.i.g. Preferred catalysts are palladium-on-charcoal or Raney nickel. The overall synthetic sequence described above is represented by the reaction scheme: where X represents halogen and Ar and Alk have the meanings given above. The compounds of the invention in free base form can be converted to the acid-addition salt forms by interaction of the bases with an acid. In like manner, the free bases can be regenerated from the acid-addition salt forms in conventional manner, that is by treating the salts with cold, weak aqueous bases, for example alkali metal carbonates and alkali metal bicarbonates. The bases thus regenerated can be interacted with the same or a different acid to give back the same or a different acid-addition salt. Thus the novel bases and all of their acid-addition salts are readily interconvertible. It will thus be appreciated that formula I not only represents the structural configuration of the bases of formula I but is also representative of the structural entity which is common to all the compounds of formula I, whether in the form of the free bases or in the form of the acid-addition salts of the bases. It has been found that, by virtue of this common structural entity the bases of formula I and their acid-addition salts have inherent pharmacological activity of a type to be more fully described hereinbelow. This inherent pharmacological activity can be enjoyed in useful form for pharmaceutical purposes by employing the free bases themselves or the acid-addition salts formed from pharmaceutically acceptable acids, that is, acids whose anions are innocuous to the animal organism in effective doses of the salts so that beneficial properties inherent in the common structural entity represented by the free bases are not vitiated by side effects ascribable to the anions. In utilizing this pharmacological activity of the salts of the invention, it is preferred, of course, to use pharmaceutically acceptable salts. Although water-insolubility, high toxicity or lack of crystalline character may make some particular salt species unsuitable or less desirable for use as such in a given pharmaceutical application, the water-insoluble or toxic salts can be converted to the corresponding pharmaceutically acceptable bases by decomposition of the salts with aqueous base as explained above, or alternatively they can be converted to any desired pharmaceutically acceptable acid-addition salt by double decomposition reactions involving the anion, for example by ion-exchange procedures. Moreover, apart from their usefulness in pharmaceutical applications, the salts are useful as characterizing or identifying derivatives of the free bases or in isolation or purification procedures. Like all of the acid-addition salts, such characterizing or purification salt derivatives can, if desired, be used to regenerate the pharmaceutically acceptable free bases by reaction of the salts with aqueous base, or alternatively they can be converted to a pharmaceutically acceptable acid-addition salt by, for example, ion-exchange procedures. Thus appropriate acid-addition salts are those derived from such diverse acids as formic acid, acetic acid, isobutyric acid, alpha-mercaptopropionic acid, malic acid, fumaric acid, succinic acid, succinamic acid, tartaric acid, citric acid, lactic acid, benzoic acid, 4-methoxybenzoic acid, phthalic acid, anthranilic acid, 1-naphthalenecarboxylic acid, cinnamic acid, cyclohexanecarboxylic acid, mandelic acid, tropic acid, crotonic acid, acetylenedicarboxylic acid, sorbic acid, 2-furancarboxylic acid, cholic acid, pyrenecarboxylic acid, 2-pyridinecarboxylic acid, 3-indoleacetic acid, quinic acid, sulfamic acid, methanesulfonic acid, isethionic acid, benzenesulfonic acid, p-toluenesulfonic acid, benzenesulfinic acid, butylarsonic acid, diethylphosphonic acid, p-aminophenylarsinic acid, phenylstibnic acid, phenylphosphinous acid, methylphosphinic acid, phenylphosphinic acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydriodic acid, perchloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrocyanic acid, phosphotungstic acid, molybdic acid, phosphomolybdic acid, pyrophosphoric acid, arsenic acid, picric acid, picrolonic acid, barbituric acid, boron trifluoride and the like. The acid-addition salts are prepared by reacting the free base and the acid in an organic solvent and isolating the salt directly or by concentration of the solution. In standard pharmacological test procedures the 4-arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-indoles of formula I have been found to possess analgesic activity and are thus useful as analgesics. The test procedures used to determine the analgesic activity of the compounds have been described in detail in the prior art and are as follows: The acetylcholine-induced abdominal construction test, which is a primary analgesic screening test designed to measure the ability of a test agent to suppress acetylcholine-induced abdominal constriction in mice, description by Collier et al., Brit. J. Pharmacol. Chemotherap. 32 , 295 (1968) and the rotorod performance test, which is a test designed to measure neurotoxicity of a test compound, described by Dunham et al., J. Pharm. Sci. 46 , 206-209 (1957). The 4-arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-indoles of the invention can be prepared for pharmaceutical use by incorporation of the compounds in unit dosage form as tablets or capsules for oral or parenteral administration either alone or in combination with suitable adjuvants such as calcium carbonate, starch, lactose, talc, magnesium stearate, gum acacia and the like. Still further, the compounds can be formulated for oral or parenteral administration either in aqueous solutions of the water soluble salts or in aqueous alcohol, glycol or oil solutions or oil-water emulsions in the same manner as conventional medicinal substances are prepared. The percentages of active component in such compositions may be varied so that a suitable dosage is obtained. The dosage administered to a particular patient is variable, depending upon the clinician's judgment using as criteria: the route of administration, the duration of treatment, the size and physical condition of the patient, the potency of the active component and the patient's response thereto. An effective dosage amount of the active component can thus only be determined by the clinician after a consideration of all criteria and using his best judgment on the patient's behalf. The molecular structures of the 4-arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-indoles of the invention were assigned on the basis of their infrared, ultraviolet and NMR spectra. The structures were confirmed by the correspondence between calculated and found values for elementary analyses for the elements. The following examples will further illustrate the invention. All melting points are uncorrected. EXEMPLARY DISCLOSURE Preparation of Intermediates Preparation 1A To a suspension of 95.6 g (0.716 mole) of aluminum chloride in 500 ml of methylene dichloride was added, rapidly and with stirring, a solution of 110.1 g (0.551 mole) of 2-methyl-3-nitrobenzoyl chloride in 400 ml of methylene dichloride. The mixture was then transferred to an additional funnel, added with stirring to a solution of 59.8 g (0.551 mole) of anisole over a thirty minute period, and the reaction mixture then heated under reflux for two hours. The mixture was decomposed by the careful addition, with stirring, of 1 liter of water and then filtered. The organic layer was separated from the aqueous layer, dried and taken to dryness, and the residue recrystallized from ethyl acetate to give 102.9 g of 3-(4-methoxybenzoyl)-2-methylnitrobenzene , m.p. 110-113°C. Anal ., Calcd. for C₁₅H₁₃NO₄: C, 66.41; H, 4.83; N, 5.16. Found: C, 66.33; H, 4.95; N, 4.98. Preparation 1B Following a procedure similar to that described in Preparation 1A above, 71.1 g (0.554 mole) of naphthalene in 500 ml of methylene dichloride was treated, over a thirty minute period with stirring, with a mixture of 110.5 g (0.554 mole) of 2-methyl-3-nitrobenzoyl chloride and 96.0 g (0.72 mole) of aluminum chloride in 900 ml of methylene dichloride. The crude product isolated from the reaction mixture crystallized from ethyl acetate/hexane. The crystals so-obtained were recrystallized again from ethanol to give material having m.p. 100-102°C which, from its nmr spectrum and analyses for the elements, was identified as 2-methyl-3-(2-naphthylcarbonyl)nitrobenzene (45% yield). The combined mother liquors from the isolation of the 2-naphthyl isomer were taken to dryness and the resulting oil crystallized from toluene/hexane to give material which, from its nmr spectrum, was identified as 2-methyl-3-(1-naphthylcarbonyl)nitrobenzene in about 30% yield. Preparation 2A A solution of 97.9 g (0.36 mole) of 3-(4-methoxybenzoyl)-2-methylnitrobenzene and 191 ml (1.45 mole) of DMF dimethyl acetal in 400 ml of DMF was heated under reflux for about nineteen hours and the reaction mixture then taken to dryness in vacuo to give 108 g of 2-(2-dimethylaminoethenyl)-3-(4-methoxybenzoyl)nitrobenzene as a red oil. Preparation 2B Following a procedure similar to that described in Preparation 2A above, 57 g (0.195 mole) of 2-methyl-3-(1-naphthylcarbonyl)nitrobenzene and 103 ml (0.784 mole) of DMF dimethyl acetal in 300 ml of DMF was heated under reflux for seventeen hours and then taken to dryness to give 2-(2-dimethylaminoethenyl)-3-(1-naphthylcarbonyl)nitrobenzene as an oil. Preparation 3A A solution of 32 g. (0.098 mole) of 2-(2-dimethylaminoethenyl)-3-(4-methoxybenzoyl)nitrobenzene in 200 ml of ethyl acetate was treated with 5 g of 10% palladium-on-charcoal, and the starting material reduced with hydrogen under 50 p.s.i.g. The mixture was then filtered, the filtrate taken to dryness, and the residue recrystallized from etyl acetate to give 18.1 g of 4-(4-methoxybenzoyl)indole . Another sample, similarly prepared by reduction of the starting material with Raney nickel in ethanol, afforded material having m.p. 148-152°C. Anal ., Calc. for C₁₅H₁₁NO: C, 76.48; H, 5.21; N, 5.57. Found: C, 76.73; H, 5.27; N, 5.58. Preparation 3B Following a procedure similar to that described in Preparation 3A above, 72 g (0.21 mole) of 2-(2-dimethylaminoethenyl)-3-(1-naphthylcarbonyl)nitrobenzene was reduced with hydrogen over 13.5 g of 10% palladium-on-charcoal in ethyl acetate under 40 p.s.i.g. Removal of the catalyst by filtration and evaporation of the filtrate to dryness afforded 45 g of 4-(1-naphthylcarbonyl)indole as an oil, which was used as such in Example 1C without further purification. Preparation of the Final Products Example 1A To a stirred mixture of 3.5 g (0.0887 mole) of a 60% suspension of sodium hydride in hexane in 50 ml of DMF was added 18.1 g (0.0721 mole) of 4-(4-methoxybenzoyl)indole. The mixture was then treated with a solution containing 0.18 mole of 4-(2-chloroethyl)morpholine in t-butyl methyl ether (prepared by extraction of the free base from a suspension of 35.5 g of the corresponding hydrochloride in saturated sodium bicarbonate). When addition was complete, the reaction mixture was heated under reflux for about twelve hours, treated with 1500 ml of water and extracted with 500 ml of ethyl acetate. The combined organic extracts, on drying and evaporation to dryness, afforded an oil which was dissolved in 250 ml of ethyl acetate and treated with 50 ml of ethereal hydrogen chloride. The material which separated was collected and recrystallized from ethanol to give 20.3 g of 4-(4-methoxybenzoyl)-1-[2-(4-morpholinyl)ethyl]-1H-indole hydrochloride , m.p. 177-180°C. Anal ., Calc. for C₂₂H₂₄N₂O₃.HCl: C, 65.91; H, 6.29; N, 6.99; Cl, 8.84. Found: C, 66.23, H, 6.32; N, 7.18; Cl, 8.91. Example 1B Following a procedure similar to that described in Example 1A above, 10 g (0.0398 mole) of 4-(4-methoxybenzoyl) indole in 200 ml of DMF was alkylated with 16.3 g of 4-(3-chloropropyl) morpholine in the presence of 1.9 g (0.0478 mole) of a 60% suspension of sodium hydride in hexane. The product was isolated in the form of the hydrochloride salt to give 11.2 g of 4-(4-methoxybenzoyl)-1-[3-(4-morpholinyl)propyl]-1H-indole hydrochloride , m.p. 168-171°C. Anal ., Calc. for C₂₃H₂₆N₂O₃.HLC: C, 66.58; H, 6.56; N, 6.75; Cl, 8.54. Found: C, 66.30; H, 6.61; N, 6.65; Cl, 8.73. Example 1C Following a procedure similar to that described in Example 1A above, 45 g (0.17 mole) of 4-(1-naphthylcarbonyl)indole in 500 ml of DMF was alkylated with about 0.425 mole of 4-(2-chloroethyl)morpholine (prepared by extraction of the free base into 200 ml of t-butyl methyl ether from a suspension of about 79 g of the corresponding hydrochloride in sodium bicarbonate) in the presence of about 10 g of a 60% dispersion of sodium hydride in hexane. The product was isolated in the form of the p-toluenesulfonate which was crystallized from ethyl acetate to give 5.3 g of 1-[2-(4-morpholinyl)ethyl]-4-(1-naphthylcarbonyl)-1H-indole p-toluenesulfonate hydrate 3:1 , m.p. 86-88°C. Anal ., Calc. for C₃₂H₃₂N₂O₅S.1/3 H₂O: C, 68.31; H, 5.85; N, 4.98; S, 5.76. Found: C, 66.66; H, 5.15; N, 4.86; S, 5.67. BIOLOGICAL TEST RESULTS The 4-arylcarbonyl-1-[(4-morpholinyl)-lower-alkyl]-1H-indoles of the invention were tested in the acetylcholine-induced abdominal constriction test (Ach), which gives a measure of antinociceptive activity, and the rotorod assay (R.R.), which gives a measure of neurotoxicity and CNS impairment. The results, expressed in terms of the ED₅₀'s obtained on oral administration in the acetylcholine test and as the ratio of the rotorod (R.R.):Ach ED₅₀'s, are given in the following table: Compound Ach R.R,:Ach Ratio Ex. 1A 46 3.1 93%/100(s.c.) Ex. 1B 63 2.8 Ex. 1C 16 -

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, NL, SE A compound having the formula I where Ar is alkoxyphenyl having one to four carbon atoms in the alkoxy radical or 1-naphthyl, and Alk is alkylene containing from two to four carbon atoms; or a pharmaceutically acceptable acid-addition salt thereof. A compound according to claim 1, where Ar is 4-C₁-C₄-alkoxyphenyl or 1-naphthyl and Alk is 1,2-ethylene or 1,3-propylene. 4-(4-Methoxybenzoyl)-1-[2-(4-morpholinyl)ethyl]-1H-indole or a pharmaceutically acceptable acid-addition salt thereof according to claim 2. 4-(4-Methoxybenzoyl)-1-[3-(4-morpholinyl)propyl]-1H-indole or a pharmaceutically acceptable acid-addition salt thereof according to claim 2. 1-[2-(4-Morpholinyl)ethyl]-4-(1-naphthylcarbonyl)-1H-indole or a pharmaceutically acceptable acid-addition salt thereof according to claim 2. A process for preparing a compound according to claim 1, which comprises reacting a corresponding compound having the formula II with a compound of the Formula 4-(X-Alk) morpholine where X is halo and Ar and Alk are as above in the presence of a strong base, and, if desired, converting a free base obtained into a pharmaceutically acceptable acid-addition salt thereof. A process according to claim 6, in which the compound of Formula II is prepared by reacting a corresponding 3-arylcarbonyl-2-methylnitrobenzene with DMF dimethyl acetal and reductive cyclization of the resulting 3-arylcarbonyl-2-(2-dimethylaminoethenyl)nitrobenzene with hydrogen over a catalyst. An analgesic composition for the relief of pain which comprises a pharmaceutical carrier and, as the active component thereof, an analgesically effective amount of a compound according to any one of claims 1-5. A compound for use in preparing a medicament for the relief of pain in a patient requiring such treatment which comprises a compound according to any one of claims 1-5. Claims for the following Contracting States : ES, GR A process for preparing a compound having the formula I where Ar is alkoxyphenyl having one to four carbon atoms in the alkoxy radical or 1-naphthyl, and Alk is alkylene containing from two to four carbon atoms; or a pharmaceutically acceptable acid-addition salt thereof, which comprises reacting a corresponding compound having the formula II with a compound of the Formula 4-(X-Alk) morpholine where X is halo and Ar and Alk are as above in the presence of a strong base, and, if desired, converting a free base obtained into a pharmaceutically acceptable acid-addition salt thereof. A process according to claim 1, where Ar is 4-C₁-C₄-alkoxyphenyl or 1-naphthyl and Alk is 1,2-ethylene or 1,3-propylene. A process according to claim 2, in which 4-(4-methoxybenzoyl)-1-[2-(4-morpholinyl)ethyl]-1H-indole or a pharmaceutically acceptable acid-addition salt thereof is prepared. A process according to claim 2, in which 4-(4-methoxybenzoyl)-1-[3-(4-morpholinyl)propyl]-1H-indole or a pharmaceutically acceptable acid-addition salt thereof is prepared. A process according to claim 2, in which 1-[2-(4-morpholinyl)ethyl]-4-(1-naphthylcarbonyl)-1H-indole or a pharmaceutically acceptable acid-addition salt thereof is prepared. A process according to any one of the preceding claims, in which the compound of Formula II is prepared by reacting a corresponding 3-arylcarbonyl-2-methylnitrobenzene with DMF dimethyl acetal and reductive cyclization of the resulting 3-arylcarbonyl-2-(2-dimethylaminoethenyl)nitrobenzene with hydrogen over a catalyst.

Inventors: BELL, MALCOLM RICE, D'AMBRA, THOMAS EDWARD
Applicants: STERLING WINTHROP INC.
Application year: 1988
Main classification: C07D209
IPC codes: A61K31, A61P25, C07D209