Imidazoquinoxalines and their preparation

Abstract: A novel chemical process for preparing imidazoquinoxalines bearing hydrogen substitution in the 5-position comprises dealkylation of the novel corresponding 5-tert-butyl compound (which also has vaulable pharmacological properties).

Description: This invention relates to imidazoquinoxalines and to their preparation. EP-A-0225013 discloses imidazoquinoxalines having the general formula A wherein X is wherein R' is C₁₋₆ alkyl, C₃₋₇ cycloalkyl, phenyl, thienyl, or (C₁₋₃ alkoxy)methyl; R⁶ and R⁷ are each hydrogen or halogen; and R'' is hydrogen, C₃₋₇ cycloalkyl or C₁₋₆ alkyl. The compound of Example 1 therein is 3-(3-cyclopropyl-1,2,4-oxadiazol-5-yl)-4,5-dihydro-5-methyl-4-oxoimidazo[1,5-a]quinoxaline. These compounds are disclosed as having pharmacological properties that make then useful as, for example, anticonvulsants and anxiolytics. Various processes for preparing the compounds are disclosed. EP-A-0283162 relates to fused imidazo derivatives which also possess affinity towards benzodiazepine receptors but bear a C₁₋₆ alkyl group in position 5. The preferred embodiments are derived from pyridopyrazine. EP-A-0320136 discloses imidazoquinoxalines bearing an isopropyl group in position 5. Novel compounds, according to the present invention, are of formula A wherein X is as defined above and R' is C₃₋₇ is cycloalkyl; R⁶ and R⁷ are independently hydrogen, halogen or CF₃; and R'' is tert -butyl. These compounds have anticonvulsant and anxiolytic properties. The novel compounds can be prepared by any process generally described in EP-A-0225013, and more specifically by the process claims of this specification. The following Examples illustrate the invention. EXAMPLE 1 N-tert-butyl-N-ethoxalyl-2-nitroaniline To a stirred solution of 2-nitro-N-tert-butylaniline (37 g) and triethylamine (35 ml) in tetrahydrofuran (400 ml) was added dropwise a solution of ethoxalyl chloride (25 ml) in tetrahydrofuran (50 ml). The mixture was then brought to reflux temperature for 8 h. The solvent was removed by evaporation, and the residue was partitioned between ether (300 ml) and water (500 ml). The organic phase was washed twice with water, dried over Na₂SO₄ and evaporated. This left the title compound as light yellow crystals, m.p. 73-74°C. N-tert-butyl-N-ethoxalyl-o-phenylenediamine A solution of N-tert-butyl-N-ethoxalyl-2-nitroaniline (45 g) in absolute ethanol (500 ml) was hydrogenated at standard conditions (1 atm ) using 5% Pd/C (5 g) as catalyst The catalyst was filtered off and the solvent was removed in vacuo . This left an oil, which crystallized upon standing, m.p. 64-65°C. 1-tert-butyl-1,2,3,4-tetrahydro-2,3-dioxo-quinoxaline The neat crystals of N-tert-butyl-N-ethoxalyl-o-phenylene diamine (88 g) were heated to 100°C for 4 h. The crude product hereby deposited from the melt as crystals. After cooling to ambient temperature, the solid was taken up in ether and the product was filtered off as white crystals, m.p. >300°C. 5-tert-butyl-3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4,5-dihydro-4-oxo-imidazo[1,5-a]quinoxaline To a stirred solution of 1-tert-butyl-1,2,3,4-tetrahydro-2,3-dioxo-quinoxaline (0.5 g, 2.3 mmol) in dry dimethylformamide (DMF) (30 ml) was added potassium t- butylate (0.34 g, 3 mmol). After additional stirring for 15 min. diethyl chlorophosphate was added (0.43 ml, 3 mmol). Stirring was continued at ambient temperature for further 20 min., whereafter the solution was cooled to - 30°C. 5-cyclopropyl-3-isocyanomethyl-1,2,4-oxadiazole (0.5 g, 3.5 mmol) was now added followed by the addition of a solution of potassium t-butylate (0.5 g, 3.5 mmol) in DMF (15 ml). The mixture was now allowed to attain to room temperature (45 min.) before acetic acid (1 ml) was added. After removal of the solvent in vacuo the residue was partitioned between water: ether (50 ml, 20 ml). This treatment afforded precipitation of the crude title compound as pale crystals, which could be purified by recrystallization from 2-propanol, m.p. 154-155°C. EXAMPLE 2 In a similar manner to Example 1, the following compound was prepared: Ethyl 5-tert-butyl-4,5-dihydro-4-oxo-imidazo[1,5-a]quinoxaline-3-carboxylate, m.p. 289-290°C by reaction between ethyl isocyanoacetate and 1-tert-butyl-1,2,3,4-tetrahydro-2,3-dioxo-quinoxaline 5-tert-butyl-3-(3-cyclopropyl-1,2,4-oxadiazol-5-yl)-4,5-dihydro-4-oxo-imidazo[1,5-a]quinoxaline Ethyl 5-tert-butyl-4,5-dihydro-4-oxo-imidazo[1,5-a]quinoxaline-3-carboxylate (0.5 g), cyclopropanecarboxaimidoxime and 5 g crushed mol. sieves (4Å) were added to absolute dry ethanol (30 ml) wherein sodium (30 mg) previously had been dissolved. The stirred mixture was refluxed for 1.5 h, then cooled to room temperature, and filtered through a pad of celite. The filtrate was evaporated in vacuo to ca. 5 ml and water (25 ml) was added. The precipitated product was filtered off and purified by recrystallization from 2-propanol, m.p. 182-184°C.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, GR, IT, LU, NL, SE A compound of formula A wherein X is wherein R' is C₃₋₇ cycloalkyl; and, R⁶ and R⁷ independently are hydrogen, halogen or CF₃. A compound according to claim 1, which is 3-(3-cyclopropyl-1,2,4-oxadiazol-5-yl)-4,5-dihydro-4-oxo-5- tert -butyl-imidazo[1,5-a]quinoxaline. A compound according to claim 1, which is 3-(3-cyclopropyl-1,2,4-oxadiazol-3-yl)-4,5-dihydro-4-oxo-5- tert -butyl-imidazo[1,5-a]quinoxaline. A compound according to any preceding claim, for use in the treatment of anxiety or convulsions. Claims for the following Contracting State : ES A process for preparing a compound of formula A wherein X is wherein R' is C₃₋₇ cycloalkyl; and R⁶ and R⁷ independently are hydrogen, halogen or CF₃ , which comprises reacting a compound of the formula with a compound of the formula CN-CH₂-X, wherein R⁶, R⁷ and X are as defined above and Y is a leaving group. A process for preparing a compound of formula A as defined in claim 1, wherein X is which comprises reacting a reactive derivative of a compound of the formula with a compound of the formula R'-C(NH₂)=NOH, wherein R⁶, R⁷ and R' are as defined in claim 1. A process for preparing a compound of formula A as defined in claim 1, wherein X is as defined in claim 2, which comprises reacting a compound of the formula with a compound of the formula R'-C(OCH₃)₂-N(CH₃)₂, wherein R⁶, R⁷ and R' are as defined in claim 1. A process for preparing a compound of formula A as defined in claim 1, wherein X is which comprises reacting a compound of the formula with NH₂OH, and reacting the resultant compound of the formula with R'-COCl, wherein R⁶, R⁷ and R' are defined in claim 1. A process according to any of claims 1 to 4, wherein the compound of formula A is 3-(3-cyclopropyl-1,2,4-oxadiazol-5-yl)-4,5-dihydro-4-oxo-5- tert -butyl-imidazo[1,5-a]quinoxaline. A process according to any of claims 1 to 4, wherein the compound of formula A is 3-(3-cyclopropyl-1,2,4-oxadiazol-3-yl)-4,5-dihydro-4-oxo-5- tert -butyl-imidazo[1,5-a]quinoxaline.

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