Imidazoquinoxaline compounds and their preparation and use

Abstract: New imidazoquinoxaline compounds having the general formula wherein R³ is or CO₂R′ wherein R′ is C₁₋₆-alkyl, which may be straight or branched, C₃₋₇-cyclo­ alkyl or phenyl; and R⁴ is hydrogen or C₁₋₆-alkyl; and 5-N-oxides thereof. The compounds are useful in psychopharmaceutical preparati­ ons as anticonvulsants, anxiolytics, hypnotics, and in improving the cognitive function of the brain of mammals.

Description: The present invention relates to imidazoquinoxaline compounds, their preparation, pharmaceutical compositions comprising them, and their therapeutic use. Squires et al , Nature (London) 266 (1977) 732-734, disclose that specific sites in the central nervous systems of vertebrates exhibit a high specific affinity for binding 1,4- and 1,5-benzodiazepines. These sites are called benzodiazepine receptors. EP-A-0225013 discloses 3-(5-substituted-1,2,4-oxadiazol-3-yl)-4,5-dihydro-4-imidazo[1,5-a]quinoxalines. It has now been found that members of a novel group of imidazoquinoxaline compounds have strong affinity for the benzodiazepine receptors which make them useful in psychopharmaceutical preparations. The imidazoquinoxaline compounds of the invention have the general formula I wherein R' is C₁₋₆ alkyl (which may be straight or branched), C₃₋₇ cycloalkyl or phenyl; and R⁴ is hydrogen or C₁₋₆ alkyl; and 5-N-oxides thereof. The invention also relates to a method of preparing the compounds of formula I, by reacting a compound of formula II wherein R⁴ is as defined above and Y is a leaving group, with a 5-(R'-substituted)-3-isocyanomethyl-1,2,4-oxadiazole. The leaving group, Y, may be any suitable leaving group and, for example, those disclosed in U.S. Patents 4,031,079 or 4,359,420, for example, halogen, alkylthio, e.g., methylthio, aralkylthio, N-nitrosoalkylamino, alkoxy, mercapto, -OP(O)(OR)₂ wherein R is lower-alkyl or -OP(O)(NR'R'') wherein R' and R'' each represents lower-alkyl or phenyl, or together with the nitrogen atom to which they are attached represent a heterocyclic radical such as morpholino, pyrrolidino, piperidino, or methylpiperazino. The reaction is preferably carried out under alkaline conditions, i.e., in the presence of a base, and among bases alkali metal, e.g., potassium or sodium, alkoxides or hydrides are preferred. The reaction is preferably conducted in the presence of an organic solvent which is nonreactive with the reactants and products of reaction under the conditions of reaction, especially an anhydrous solvent and preferably an anhydrous aprotic solvent such as dimethylformamide (DMF) or the like. The temperature range employed may be any range suitable for the reaction to proceed at a reasonable rate and without undue delay or decomposition and a range from a minus forty (-40) degrees Celsius to about room temperature is accordingly usually particularly suitable. The starting materials may be prepared from commercially available organic compounds and by using well known synthetic methods and as described in Synthesis, Vol. 10 , pp. 681-682. The pharmaceutical properties of the compounds of the invention can be illustrated by determining their capability for displacing radioactive labelled flunitrazepam from benzodiazepine receptors. The displacement activity of the compounds of the invention may be found by determining the ED₅₀ value. The ED₅₀ value represents the dose (mg/kg) of a test substance which causes the specific binding of flunitrazepam to benzodiazepine receptors in a living brain to be reduced to 50% of the control value. Such an in vivo test is carried out as follows: Principle . Twenty minutes after a dose of ³H-flunitrazepam (³H-FNM) (200 µCi/kg, i.v.) the amount of specific ³H-FNM binding to brain benzodiazepine receptors has reached its maximal value. This specific binding of ³H-FNM can be partly or completely prevented by simultaneous or prior administration of pharmacologically active benzodiazepines and by some benzodiazepine-like agents (Chang and Snyder, Eur.J. Pharmacol. 48 , 212-218 (1978)). Test procedure . Suspensions of test substances (2 mg/ml) are prepared in 5% Duphasol-X (TM Duphar, castor oil-ethylene oxide derivative for emulsifying and solubilizing oil and other water-insoluble substances) by sonification for 10 min using a Branson B15 microtip ultrasonifier (setting 7). Groups of three mice (female, NMR, 18-22 grams) are injected with the test substance at 100 mg/kg intraperitoneally. Fifteen minutes after test substance administration the mice are challenged with 4 µCi intravenously of ³H-FNM (70-90 Ci/mole) in 200 µl physiological saline. Twenty minutes after ³H-FNM administration mice are sacrificed by decapitation, the forebrains rapidly excised (within 30 sec) and homogenized in 12 ml of icecold 25 mM KH₂PO₄, pH 7.1, using an Ultra-Turrax homogenizer fitted with an N 10 shaft. Two aliquots of 1 ml are immediately filtered through Whatman GF/C glassfibre filters and washed with 2 x 5 ml of the above mentioned buffer. The amounts of radioactivity on the filters are determined by conventional scintillation counting. One group of untreated mice serves as control. One to three mice are injected with 25 µg/kg clonazepam i.p. 30 minutes before ³H-FNM to determine the amount of non-specific ³H-FNM binding, which should be between 8-15% of total binding. When doses of 100 mg/kg inhibit more than 50% of specific ³H-flunitrazepam binding; test substances are administered in doses, which are factors of 3.16 times lower than 100 mg/kg. The ED₅₀ for a test substance is defined as that dose which inhibits 50% of specific ³H-FNM binding. Specific binding is the amount of binding in controls minus the amount binding in clonazepam-treated mice. Results . The ED₅₀ value is determined from dose response curves. If only one dose of test substance is administered the ED₅₀ value is calculated as follows, provided that the inhibition of specific binding is within the range of 25-75%: where C o is specific binding in controls and C x is specific binding in mice treated with test substance. Test results obtained by testing some compounds of the invention will appear from the following table I. Compound of Example ED₅₀ (mg/kg) 1 1.8 2 1.3 The compound of the invention, together with a conventional adjuvant, carrier, or diluent, and if desired in the form of a pharmaceutically-acceptable acid addition salt thereof, may be placed into the form of pharmaceutical compositions and unit dosages thereof, and in such form may be employed as solids, such as tablets or filled capsules, or liquids, such as solutions, suspensions, emulsions, elixirs, or capsules filled with the same, all for oral use, in the form of suppositories for rectal administration; or in the form of sterile injectable solutions for parenteral (including subcutaneous) use. Such pharmaceutical compositions and unit dosage forms thereof may comprise conventional ingredients in conventional proportions, with or without additional active compounds or principles, and such unit dosage forms may contain any suitable effective central nervous system ailment alleviating amount of the active ingredient commensurate with the intended daily dosage range to be employed. Tablets containing one (1) milligram of active ingredient or, more broadly, one (1) to thirty (30) milligrams, per tablet, are accordingly suitable representative unit dosage forms. The compounds of this invention can thus be used for the formulation of pharmaceutical preparations, e.g., for oral and parenteral administration to mammals including humans, in accordance with conventional methods of galenic pharmacy. Conventional excipients are such pharmaceutically acceptable organic or inorganic carrier substances suitable for parenteral or oral application which do not deleteriously react with the active compound. Examples of such carriers are water, salt solutions, alcohols, polyethylene glycols, polyhydroxyethoxylated castor oil, gelatin, lactose, amylose, magnesium stearate, talc, silicic acid, fatty acid monoglycerides and diglycerides, pentaerythritol fatty acid esters, hydroxymethylcellulose and polyvinylpyrrolidone. The pharmaceutical preparations can be sterilized and mixed, if desired, with auxilliary agents, such as lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salt for influencing osmotic pressure, buffers and/or coloring substances and the like, which do not deleteriously react with the active compound. For parenteral application, particularly suitable are injectable solutions or suspensions, preferably aqueous solutions with the active compound dissolved in polyhydroxylated castor oil. Ampoules are convenient unit dosage forms. For oral application, particularly suitable are tablets, dragees, or capsules having talc and/or a carbohydrate carrier or binder or the like, the carrier preferably being lactose and/or corn starch and/or potato starch. A syrup, elixir or like can be used when a sweetened vehicle can be employed. Generally, as to broader ranges, the compounds of the invention are dispensed in unit dosage form comprising 0.05-100 mg in a pharmaceutically-acceptable carrier per unit dosage. A typical tablet which may be prepared by conventional tabletting techniques contains: Active compound 1.0 mg Lactosum 67.8 mg Ph.Eur. Avicel® 31.4 mg Amberlite® IRP 88 1.0 mg Magnesii stearas 0.25 mg Ph.Eur. Due to their high degree of affinity for the benzodiazepin receptors, the compounds of the invention are extremely useful in the treatment of central nervous system ailments or disorders, when administered in an amount effective for the alleviation, amelioration, or elimination thereof. The important CNS activity of the compounds of the invention includes both anticonvulsant and anxiolytic activities along with a low toxicity, together presenting a most favorable therapeutic index. The compounds of the invention may accordingly be administered to a subject, e.g., a living animal body, including a human, in need of the same for the treatment, alleviation, amelioration, or elimination of an indication, associated with the central nervous system and the socalled benzodiazepin receptors, which requires such psychopharmaceutical treatment, e.g., especially convulsion and/or anxiety states, if desired in the form of a pharmaceutically-acceptable acid addition salt thereof (such as the hydrobromide, hydrochloride, or sulfate, in any event prepared in the usual or conventional manner, e.g., evaporation to dryness of the free base in solution together with the acid), ordinarily concurrently, simultaneously, or together with a pharmaceutically-acceptable carrier or diluent, especially and preferably in the form of a pharmaceutical composition thereof, whether by oral, rectal, or parenteral (including subcutaneous) route, in an effective psychopharmaceutical central nervous system ailment alleviating amount, e.g., an anticonvulsant and/or anxiolytic amount, and in any event an amount which is effective for the alleviation of such a central nervous system ailment due to their benzodiazepine receptor affinity. Suitable dosage ranges per day are 1-200 mg, preferably 1-100 mg, and especially 1-30 mg, depending as usual upon the exact mode of administration, form in which administered, the indication toward which the administration is directed, the subject involved and the body weight of the subject involved, and the preference and experience of the physician or veterinarian in charge. The following Examples illustrate the preparation of compounds of the invention. Example 1 4-methyl-3-(5-methyl-1,2,4-oxadiazol-3-yl)-imidazo[1,5-a]quinoxaline 3-Methyl-2-quinoxalinol (2.84 g, 18 mmol) was dissolved in dry DMF (40 ml) and charged with sodium hydride (55% oil dispersion, 1.0 g, 23 mmol). The resulting solution was cooled under nitrogen to -20°C, whereafter chlorodiethylphosphate (3.3 ml, 23 mmol) was added. The reaction mixture was allowed to reach room temperature, and there was then added a -30°C cold solution of 3-isocyanomethyl-5-methyl-1,2,4-oxadiazole (23 mmol) and potassium t-butoxide (2.6 g, 23 mmol) in dry DMF (25 ml). The mixture was stirred for 45 min at ambient temperature, whereafter acetic acid (3 ml) was added. The crystalline precipitate was collected by filtration, rinsed with DMF and water and dried, yielding the title compound, mp 192-193°C. Example 2 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4-methylimidazo[1,5-a]quinoxaline In a manner similar to Example 1, the title compound, mp 165-167°C, was obtained from 3-methyl-2-quinoxalinol and 5-cyclopropyl-3-isocyanomethyl-1,2,4-oxadiazole.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, LU, NL, SE An imidazoquinoxaline compound having the formula I wherein R' is C₁₋₆ alkyl, C₃₋₇ cycloalkyl or phenyl; and R⁴ is hydrogen or C₁₋₆ alkyl; or a 5-N-oxide thereof. A compound of claim 1, which is 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4-methylimidazo[1,5-a]quinoxaline. A compound of claim 1, which is 4-methyl-3-(5-methyl-1,2,4-oxadiazol-3-yl)imidazo[1,5-a]quinoxaline. A pharmaceutical composition suitable for use in the treatment of a central nervous system ailment, comprising a compound of any of claims 1 to 3 together with a pharmaceutically-acceptable carrier or diluent. A composition according to claim 4, in the form of an oral dosage unit containing 1 to 100 mg of the compound. Use of a compound of any of claims 1 to 3, for the manufacture of a medicament for use in treating a central nervous system ailment. A method of preparing a compound of formula I as defined in claim 1, which comprises reacting a corresponding compound of formula II wherein Y is a leaving group, with a corresponding 5-(R'-substituted)-3-isocyanomethyl-1,2,4-oxadiazole. A method according to claim 7, wherein the product is 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4-methylimidazo[1,5-a]quinoxaline. A method according to claim 7, wherein the product is 4-methyl-3-(5-methyl-1,2,4-oxadiazol-3-yl)imidazo[1,5-a]-quinoxaline. A method of any of claims 7 to 9, wherein the reaction is carried out under alkaline conditions. Claims for the following Contracting State : GR An imidazoquinoxaline compound having the formula I wherein R' is C₁₋₆ alkyl, C₃₋₇ cycloalkyl or phenyl; and R⁴ is hydrogen or C₁₋₆ alkyl; or a 5-N-oxide thereof. A compound of claim 1, which is 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4-methylimidazo[1,5-a]quinoxaline. A compound of claim 1, which is 4-methyl-3-(5-methyl-1,2,4-oxadiazol-3-yl)imidazo[1,5-a]quinoxaline. Use of a compound of any of claims 1 to 3, for the manufacture of a medicament for use in treating a central nervous system ailment. A method of preparing a compound of formula I as defined in claim 1, which comprises reacting a corresponding compound of formula II wherein Y is a leaving group, with a corresponding 5-(R'-substituted)-3-isocyanomethyl-1,2,4-oxadiazole. A method according to claim 5, wherein the product is 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4-methylimidazo[1,5-a]quinoxaline. A method according to claim 5, wherein the product is 4-methyl-3-(5-methyl-1,2,4-oxadiazol-3-yl)imidazo[1,5-a]-quinoxaline. A method of any of claims 5 to 7, wherein the reaction is carried out under alkaline conditions. Claims for the following Contracting State : ES A method of preparing an imidazoquinoxaline compound having the formula I wherein R' is C₁₋₆-alkyl, C₃₋₇-cycloalkyl or phenyl; and R⁴ is hydrogen or C₁₋₆-alkyl; or a 5-N-oxide thereof; which comprises reacting a corresponding compound of formula II wherein Y is a leaving group, with a corresponding 5-(R'-substituted)-3-isocyanomethyl- 1,2,4-oxadiazole. A method of claim 1, wherein the imidazoquinoxaline compound is 3-(5-methyl-1,2,4-oxadiazol-3-yl)imidazo-[1,5-a]quinoxaline. A method of claim 1, wherein the imidazoquinoxaline compound is 4-methyl-3-(5-methyl-1,2,4-oxadiazol-3-yl)imidazo[1,5-a]quinoxaline. A method of any of claims 1, 2 and 3, wherein the reaction is carried out under alkaline conditions. Use of an imidazoquinoxaline compound as defined in any of claims 1 to 3, for the manufacture of a medicament for use in treating a central nervous ailment.

Inventors: HANSEN HOLGER CLAUS, WATJEN FRANK, HANSEN, HOLGER CLAUS, WATJEN, FRANK, Wâtjen, Frank
Applicants: NOVONORDISK AS, NOVO NORDISK A/S
Application year: 1989
Main classification: C07D487
IPC codes: A61K31, A61P25, C07D487