A PROCESS FOR THE PREPARATION OF 10-OXO-10,11-DIHYDRO-5H-DIBENZ(b,f)AZEPIN-5-CARBOXAMIDE

Abstract: The present invention relates to a novel process for the preparation of 10-oxo-10,11-dihydro-5H-dibenz(b,f)azepin-5-carboxamide (VI) starting from 10-methoxy-5H-dibenz(b,f)azepine (IV) by means of direct carbamoylation with isocyanic acid generated in situ from cyanates and acids and subsequent acid hydrolysis of the enol ether. The invention also relates to an alternative process to obtain VI starting from IV, effecting the hydrolysis reaction before the carbamoylation one. In this case the carbamoylating agent is chlorosulfonyl isocyanate.

Description: A PROCESS FOR THE PREPARATION OF 10-OXO-lO .11-DIHYDRO- 5H-DIBENZ. b . f .AZEPIN-5-CARBOXAMIDE The present invention relates to a process for the preparation of 10-oxo-lO , ll-dihydro-5H-dibenz( b, f )aze- pin-5-carboxamide (IV), also known under the non- proprietary name of oxcarbazepine , a substitute for carbamazepine , starting from 10-methoxy-5H- dibenz ( b, f )azepine IV by means of direct carbamoylation with isocyanic acid generated in situ from cyanates and acids and subsequent acid hydrolysis of the enol ether, according to scheme A: SCHEME A (V) (IV) CVT) Alternatively, according to a further object of the invention, the hydrolysis reaction can be carried out before the carbamoylation, according to scheme B: SCHEME B C IV) (V bi s) (VT ) The chemical synthesis of oxcarbazepme is not immediate, in fact a number of alternative routes, very different from each other, are known at present. The main ones are summarized in the following schemes. SCHEME C: oxidation of the carbamazepine VII to 10,11- oxiran derivative VIII and rearrangement of the latter to oxcarbazepme VI (German Patent 2,246,842 and Swiss Patent 633,271) ( VI I ) (VI I I ) (VI ) The ma drawbacks of this process resides in the use, as a reagent, of the carbamazepine which is expensive, being itself a final product; moreover, the epoxidation reaction gives poor yields, due to the substrate sensitivity, when using conventional epoxidizers such as peracetic acid, or it requires remarkable excesses of expensive reagents such as 3- chloroperben oic acid. Moreover, dangerous side-products form during the epoxidation process. The rearrangement reaction epoxide > ketone takes place with important amounts of expensive catalysts, is delicate since a variety of side-products are formed, and it yields a crude which requires thorough purifications giving low yields . SCHEME D: nitration of 5-cyano-5H-dιbenz(b, f )azepιne (IX, N-cyanoιmιnostιlbene ) at the position 10 (X), followed by reduction of the nitro group to ammo group and simultaneous hydrolysis of the enamme to ketone, to obtain 10-oxo-lO ,ll-dιhydro-5-cyano-5H-dιbenz(b, f )aze- pme (IX) which is hydrolyzed to oxcarbazepme VI ( EP-A- 0 028 028) . (XI) (VI) The drawbacks of this process consist above all the starting product IX which can be obtained, according to EP-A-0029409 , either from carbamazepine VII which is an expensive product, or from 5H-dιbenz-(b, f )azepme ( lmmostilbene I) by reaction with cyanogen chloride, which is a toxic gas difficult to handle: SCHEME E ( I ) ( IX ) Moreover, the nitration gives acceptable yields only if carried out with nitrating agents such as N O3 or 2 0 4 , which are difficult to use. Finally the hydrolysis of the cyano group requires preferably the use of BF complexes, which are expensive and must be handled carefully since they are very aggressive. The total yield of the process is low. SCHEME F: hydrolysis of the 10 chloro-5H- dibenz ( b, f )azepιn carboxamide with concentrated sulfuric acid, to give directly oxcarbazepme (Swiss Patent 642,950). (XII) (VI) Actually, the hydrolysis reaction is very slow and widely incomplete at the indicated temperature, whereas an even slight raising of the temperature yields a degradation. Moreover the preparation of XII requires either the reaction of phosgene, a toxic gas, with 10-chloro-5H- dibenz(b,f Jazepine (XIII) or the carbamazepine VII according to the Scheme G and G' as the starting reagent : SCHEME G' (VII) (XV) Whereas scheme G involves a great number of steps, the drawback of scheme G' resides in the high cost of the starting material VII. SCHEME H Carbamoylation reaction of 10-methoxyminostilbene IV by treatment with phosgene followed by ammonolysis of the chlorocarbonyl derivative XVI and hydrolysis of the vinyl ether V (German Patent 2,011,087) ( IV ) ( XVI ) ( V ) The most important problem with this process is the use of phosgene, a toxic gas which is subjected to very severe regulations. Now it has surprisingly been found that the carbamoylation reaction of 10-methoxyminostilbene IV takes place in very good yields and in a single step from IV to V (scheme A), by means of isocyanic acid generated i sϋu from metal cyanates and acids. Moreover the carbamoyi derivative V can be hydrolyzed with aqueous mineral acids, without recovery, directly in the reaction environment to give a crude oxcarbazepme which, upon a single crystallization, yields a product of excellent purity. This is even more surprising since this type of carbamoylation does not occur on all kind of substrates; in fact it was tried first on 10-ketoιmmodιbenzyl V bis, obtained by hydrolysis from the enol ether IV, with no results, not even traces. Subsequently V bis was found to be barely reactive in tnese conditions, in fact it reacts only with chlorosulfonyl isocyanate, the most reactive of the known isocyanates (scheme B). The process is remarkably interesting due to the easiness of availability and handling of the reagents used as well as since 10-methoxymιnostιlbene IV can be obtained in nearly quantitative yields starting from lminostilbene I, according to the process shown m scheme K. SCHEME K (I) (II) X = C l Br ( IV ) This process is disclosed in Belgian Patent 597,793 and in USA Patent Re 27622. Contrary to what stated in EP-A-0 028 028, the process is simple and easily reproducible and, when correctly applied, it gives excellent yields. According to the invention, 10-methoxyminostilbene IV is reacted in the presence of an alkali or alkaline- earth (preferably sodium or potassium) cyanate, in an equimolar amount or in a slight excess, in an aprotic organic solvent such as an aromatic hydrocarbon, or in a chlorinated solvent such as toluene, benzene, chlorobenzene, dichloromethane, chloroform, 1,2- dichloroethane, 1 ,1 ,1-trichloroethane, trichloro- ethylene, at temperatures from 20 to 60°C. A mineral acid such as 98% sulfuric acid 98%, anhydrous hydrochloric or hydrobromic acids or the solutions thereof in acetic acid, or acetic, formic, monochloroacetic , monobromoacetic, dichloroacetic, trichioroacetic, propionic, 2-chloropropιonιc acids are added to the mixture, in an amount equimolar to the cyanate. Catalytic amounts of water or alcohols can increase the reaction rate. The mixture is stirred quickly for some hours, until completion of the carbamoylation reaction, diluted with water, the phases are separated and the organic phase is concentrated; the residue is hydrolyzed with a diluted mineral acid, such as hydrochloric, hydrobromic or sulfuric acid, under reflux. The crude solid product is pump-filtered or centπfuged, washed and recrystallized from solvents such as acetone, methanol, dioxane, dimethylformamide, dimethylacetamide , cycloexanone, methylcellosolve, ethylcellosolve , butylcellosolve, also in mixture with water. Alternatively, 10-oxo-lO , ll-dιhydro-5H- dιbenz(b, f )azepm-5-carboxamιde VI can be obtained starting from 10-methoxy-5H-dιbenz(b,f (azepine according to the scheme B. The enol ether group of compound IV is hydrolyzed to ketone with diluted mineral acids such as hydrochloric, hydrobromic or 10% sulfuric acid. The 10- oxo-10 ,ll-dιhydro-5H-dιbenz(b,f )azepιne V bis is then carbamoylated with chlorosulfonyl isocyanate in anhydrous chlorinated solvents such as chloroform or dichloromethane or other. After hydrolyzmg the chlorosulfonyl group with water and ice and recrystallizing from one of the solvents mentioned above for scheme A, product VI m a good purity degree is obtained. The invention is further illustrated in the following examples. EXAMPLE 1 10-oxo-lO ,ll-dιhydro-5H-dιbenz(b,f )azepin-5-carboxamide 22.3 g (0.1 moles) of 10-methoxy-5H- dιbenz(b,f )azepme prepared according to US Pat. Re 27622 are dissolved m 150 ml of toluene. 8.92 g (0.11 moles) of potassium cyanate and 10.8 g (0.11 moles) of 96% sulfuric acid are added. The mixture is heated between 40° and 50° C stirring vigorously for 24 hours. When the analytical control detects a starting product content < 2%, 50 ml of water are dropped into the mixture, which is stirred and the phases are separated. The organic phase is evaporated to dryness under vacuum and taken up into 100 ml of 10% sulfuric acid. The mixture is refluxed for 2 - 3 hours, cooled at room temperature and pump-filtered, washing with water; then it is recrystallized from dimethylacetamide (50 ml), filtered through charcoal washing the precipitate on the filter with acetone, and dried under vacuum. The product is identified by IR, NMR and mass spectroscopies. Yield g 15.5 m.p. 222" C EXAMPLE 2 The procedure of example 1 is repeated, using equimolar amounts of trichloroacetic acid instead of sulfuric acid; the reaction lasts 48 hours. The product is recrystallized from cycloexanone. Yield g 14.3 m.p. 222° C EXAMPLE 3 The procedure of example 2 is repeated, using dichloromethane under reflux instead of toluene. Yield g 14.8 m.p. 221° C EXAMPLE 4 The procedure of example 1 is repeated, replacing sulfuric acid with an equimolar amount of anhydrous hydrochloric acid dissolved in acetic acid and using chloroform as the solvent. Yield g 16.2 m.p. 222° C EXAMPLE 5 The procedure of example 2 is repeated, using chloroform as the solvent and recrystallizmg from ethylcellosolve. Yield g 15 m.p. 222° C EXAMPLE v The procedure of example 1 is repeated, using an equimolar amount of sodium cyanate instead of potassium cyanate. Yield g 16.5 m.p. 221° C EXAMPLE 7 The procedure of example 6 is repeated, using equimolar amounts of monochloroacetic acid instead of sulfuric acid, and hydrolyzing with 2N hydrochloric acid. Yield g 11.5 m.p. 223° C EXAMPLE 8 The procedure of example 7 is repeated, using chloroform and recrystallizmg from ethylcellosolve. Yield g 12.7 m.p. 222° C EXAMPLE 9 The procedure of example 6 is repeated, using equimolar amounts of trichloroacetic acid instead of sulfuric acid, chloroform as the solvent and adding 0.5 ml of water. The reaction lasts 4 hours. The product is recrystallized from dimethylformamide and water 2 ÷ 1. Yield g 13.5 m.p. 223 * C EXAMPLE IQ The procedure of example 9 is repeated, using dichloroacetic acid equimolar to trichloroacetic acid and recrystallizmg from methanol. Yield g 14.8 m.p. 224° C EXAMPLE 11 10-oxo-lO,ll-dιhydro-5H-dιbenz(b,f )azepine 22.3 g of 10-methoxy-5H-dιbenz(b, f Jazep e are heated under reflux with 100 ml of 2N hydrochloric acid for 2 hours. The gummy residue is extracted with chloroform (50 + 50 ml), the combined extracts are washed with water and evaporated to dryness under vacuum. The residue is taken up into 200 ml of ethanol, treated with charcoal (2 g) for 1 h under reflux, filtered, evaporated to dryness under vacuum, finally taken up into 50 + 50 ml of toluene, stripping thoroughly. The residue is kept for further working-up. Yield g 20 EXAMPLE 12 10-oxo-lO,ll-dιhydro-5H-dιbenz(b,f )azepιn-5-carboxamιde The residue of the example 11 is taken up into 200 ml of chloroform and m this solution, always maintained below 25 * C, 15.8 g of chlorosulfonyl isocyanate (0.11 moles) dissolved in 50 ml of chloroform are dropped therein, shielding from room humidity. The mixture is stirred at room temperature overnight and triturated ice (200 g) is poured therein, stirring thoroughly for a further 24 hours. The phases are separated, the aqueous phase is extracted with chloroform (20 + 20 ml) and the combined extracts are evaporated to dryness under vacuum The residue is taken up into hot acetone, obtaining a crude product which is recrystallized from dioxane, to yield 8.5 of a good quality product. m.p. 220° - 222° C.

Claims: CLAIMS 1. A process for the preparation of lO-oxo-10 ,11- dihydro-5H-dibenz(b, f )azepin-5-carboxamide of formula VI VT) which comprises: a) the reaction of 10-methoxy-5H-dibenz(b,f )azepine of formula IV (IV) with alkali or alkaline-earth cyanates, in the presence of acids; b) the acid hydrolysis of the intermediate V obtained in a) (V) 2. A process according to claim 1, wherein the acids used in step a) are selected from 98% sulfuric acid, anhydrous hydrochloric or hydrobromic acids, optionally in solution with glacial acetic acid, formic, acetic, mono-, di-, or trichloroacetic, monobromoacetic , propionic or 2-chloropropionic acid. 3. A process according to claim 1 or 2 , wherein the reaction a) is carried out in a solvent selected from aromatic and/or chlorinated hydrocarbons. 4. A process according to claim 3, wherein the solvent is selected from benzene, toluene, chlorobenzene, dichloromethane, chloroform, 1 ,2-dιchloroethane, 1,1,1- trichloroethane, trichloroethylene . 5. A process according to claim 4, wherein the reaction is carried out in the presence of catalytic amounts of water or alcohols. 6. A process according to any one of the above claims, wherein the final hydrolysis is carried out with diluted mineral acids. 7. A process according to claim 6, wherein the acids are hydrochloric, hydrobromic or 10% sulfuric acid. 8. A process according to claim 1, wherein the final product is crystallized from solvents selected from acetone, methanol, dioxane, dimethylformamide , dimethylacetamide, cycloexanone, methylcellosolve , ethylcellosolve, butylcellosolve, also in mixture with water. 9. A process according to any one of the above claims, wherein the intermediate V is subjected directly to the acid hydrolysis without being isolated. 10. A process for the preparation of oxcarbazepme, which process comprises : a) the acid hydrolysis of 10-methoxy-5H- dιbenz(b, f )azepιne IV; b) the reaction of the intermediate obtained in a) with chlorosulfonyl isocyanate in chlorinated solvents, followed by hydrolysis in an aqueous medium. 11. A process according to claim 10, wherein the acid hydrolysis of step a) is carried out by heating in the presence of hydrochloric, hydrobromic or 10% (by weight) sulfuric acid. 12. A process according to claim 10 or 11, wherein the reaction with chlorosulfonyl isocyanate is carried out in a solvent selected from dichloromethane, chloroform, 1,2-dιchloroethane, 1 ,1,1-trιchloroethane. 13. A process according to any one of claims 10 to 12, wherein the final product is crystallized from the same solvents as in claim 8.

Inventors: MILANESE ALBERTO, MILANESE, ALBERTO
Applicants: MILANESE ALBERTO, TRIFARMA SRL, MILANESE, ALBERTO, TRIFARMA, S.R.L.
Application year: 1996
Main classification: C07D223
IPC codes: C07D223