DE UT ET RABE NAZINE

FIELD OF INVENTION

The present invention provides novel process for preparation of tetrabenazine and deutetrabenazine.

BACKGROUND OF THE INVENTION

Tetrabenazine (I) is a benzoqui nol i ne compound and a vesicular monoamine transporter 2 (VMAT2) inhibitor commonly prescribed for the treatment of Huntington's disease. Deutetrabenazine (II) is a deuterated analog of tetrabenazine (I) which has improved pharmacokinetic properties when compared to the non- deuterated drug. Currently the New Drug Application (NDA) for deutetrabenazine has been accepted by the U.S. Food and Drug Administration (FDA) for the treatment of chorea associated with Huntington disease.

The carbon- hydrogen bonds of tetrabenazine (I) contain a naturally occurring distribution of hydrogen isotopes however increased levels of deuterium incorporation may produce a detectable Deuterium Kinetic Isotope Effect (DKIE) that could affect the pharmacokinetic, pharmacologic and/or toxicologic profiles of tetrabenazine in comparison with tetrabenazine having naturally occurring levels of deuterium.

The patent US 3,045, 021 discloses process for preparation of tetrabenazine (I) and patent US 8,524,733 discloses deutetrabenazine (II).

The patent US 3,045, 021, provides process for preparation of tetrabenazi ne (I) which comprises condensation of 6,7-dimethoxy-3,4-dihydroisoquinoline with 3-methylene-5- methyl-2-hexanone (VI) in an alkaline medium.

Another patent G B 999095 described process for preparation of tetrabenazi ne which involves reaction of 3,4-dihydro-6,7-dimethoxyisoqui noline and (2-acetyl-4-methyl- pentyl)-tri methyl -ammonium iodide (V) in alcohol.

The patent US 8,524,733, provides process for preparation of deutetrabenazine by reaction of d6-6,7-Dimethoxy-3,4-dihydroisoquinoline and (2-acetyl-4-methyl-pentyl)- tri methyl -ammonium iodide (V) in ethanol. The product is isolated by column chromatography in yield of 35%. The intermediate d6-6,7-Dimethoxy-3,4- dihydroisoqui noline is prepared by series of reaction wherein (E)-4-(2- nitrovinyl)benzene-1,2-diol is reacted with d3-Iodomethane to produce d6-(E)-1,2- Dimethoxy-4-(2-nitrovinyl)benzene which undergoes reduction in presence of lithium aluminum hydride to give 2-(3,4-d6-Di methoxyphenyl)ethanamine which further reacts with hexamethylenetetramine in presence of acetic acid/trifluoroacetic acid to give the intermediate d6-6,7-Dimethoxy-3,4-dihydroisoquinoline. The process utilizes expensive reagents like d3-Iodomethane, tedious technique of column chromatography resulting in low yields hence is not industrially feasible.

Another patent application US 20150152099 describes process for preparation of deutetrabenazine by reaction of d6-6,7-Di methoxy-3,4-dihydroisoquinoline and (2-acetyl- 4-methyl-pentyl)-tri methyl -ammonium iodide (V) in various solvents. The i ntermediate d6-6,7-Dimethoxy-3,4-dihydroisoquinoline is prepared by series of reaction wherein dopamine hydrochloride reacts with ethyl formate to give N-(2-(3,4-di hydroxy-phenyl)- ethyl)-formamide which reacts further with d3-Iodomethane to produce deuteriated compound which is cyclized in presence of phosphoryl chloride to give d6-6,7- Dimethoxy-3, -dihydroisoquinoline hydrochloride. The process utilizes expensive reagents like d3-Iodomethane.

The present invention provides novel process for preparation of tetrabenazine (I) and deutetrabenazine (II) which is efficient, industrially viable and cost effective. The present invention provides novel process for preparation of deutetrabenazine (II) that does not involve tedious technique of column chromatography or expensive and non-commercial ly available d3-Iodomethane.

SU M MA RY OF T H E INV E NTIO N

The present invention provides novel process for preparation of tetrabenazine (I) comprising reacting di hydroxy isoquinoline compound (IV) or a salt thereof with (2- acetyl- -methyl-pentyl)-trimethyl-ammonium iodide (V) or 3-methylene-5-methyl-2- hexanone (VI) to obtain di hydroxy benzoquinoli ne compound (III) followed by treatment with source of methyl. The present invention further provides novel process for preparation of deutetrabenazine (II) comprising reacting dihydroxy isoquinoline compound (IV ) or a salt thereof with (2-acetyl-4-methyl-pentyl)-trimethyl-ammonium iodide (V) or 3-methylene-5-methyl-2-hexanone (VI) to obtain dihydroxy benzoquinol ine compound (III) followed by treatment with source of deuteriated methyl.

DE TAIL E D DE SC R IPT ION O F T H E I NV E NT IO N

In the first embodiment the present invention provides process for preparation of dihydroxy benzoquinoline compound (III) which includes the step of:

(III) reacting dihydroxy isoquinoline compound (IV) or a salt thereof

(IV) with (2-acetyl-4-methyl-pentyl)-tri methyl-ammonium iodide (V).

Salt of dihydroxy isoquinoline compound (IV) can be selected from inorganic salts such as hydrochloric, hydrobromic, sulfuric, phosphoric and the like.

In the second embodiment the present invention provides process for preparation of dihydroxy benzoquinoline compound (III) comprising reacting dihydroxy isoquinoline compound (IV) or a salt thereof with 3- methyl ene-5- methyl -2- hexanone (VI).

(VI)

In the third embodiment the present invention provides process for preparation of tetrabenazine (I), comprising treating di hydroxy benzoquinoline compound (III) with source of methyl.

In the fourth embodiment the present invention provides process for preparation of deutetrabenazine (II), comprising treating di hydroxy benzoquinoline compound (III) with source of deuteriated methyl.

In the fifth embodiment the present invention provides process for preparation of tetrabenazine (I) comprising: i) obtaining di hydroxy benzoquinol ine compound (III) by reacting di hydroxy isoquinol ine compound (IV) or a salt thereof with (2-acetyl-4-methyl-pentyl)- tri methyl -ammonium iodide (V) or 3-methylene-5-methyl-2-hexanone (VI) ii) treating di hydroxy benzoquinoli ne compound (III) with source of methyl.

In the sixth embodiment the present invention provides process for preparation of deutetrabenazine (II) comprising: i) obtaining di hydroxy benzoquinol ine compound (III) by reacting di hydroxy isoquinol ine compound (IV) or a salt thereof with (2-acetyl-4-methyl-pentyl)- tri methyl -ammonium iodide (V) or 3-methylene-5-methyl-2-hexanone (VI) ii) treating dihydroxy benzoquinoline compound (III) with source of deuteriated methyl.

The reaction of dihydroxy isoquinoline compound (IV) or a salt thereof with (2-acetyl-4- methyl-pentyl)-tri methyl -ammonium iodide (V) can be carried out in presence of solvent and a base. The solvent can be selected from polar solvents like alcohols; alcohol can be selected from methanol, ethanol, propanol, butanol etc.; nitriles selected from acetonitri I e, propionitrile etc.; acetone, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, glycol, dioxane, propanediol, butanediol, water or mixture thereof. The base can be selected from organic or inorganic base; organic base can be selected from alky I amines like tri ethyl amine or tri butyl amine etc. inorganic bases include hydroxide, al koxides or carbonates, bi carbonates of alkali or alkaline earth metal like sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium carbonate, potassium carbonate, sodium bicarbonate etc. The reaction can be carried out at a temperature of 20 to 60eC.

The reaction of di hydroxy isoquinoline compound (IV) or a salt thereof with 3- methylene-5-methyl-2-hexanone (VI) can be carried out in presence of solvent and a base. The solvent can be selected from polar solvents like alcohols; alcohol can be selected from methanol, ethanol, propanol, butanol etc.; nitriles selected from acetonitrile, propionitrile etc.; acetone, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, glycol, dioxane, propanediol, butanediol, water or mixture thereof. The base can be selected form organic or inorganic base; organic base can be selected form alky I amines like tri ethyl amine or tri butyl amine etc. inorganic bases include hydroxide, al koxides or carbonates, bi carbonates of alkali or alkaline earth metal like sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium carbonate, potassium carbonate, sodium bicarbonate etc. The reaction can be carried out at a temperature of 20 to 60eC.

The di hydroxy benzoquinoline compound (III) can be isolated by techniques known in art like filtration, evaporation, concentration etc. The di hydroxy benzoquinoline compound (III) is obtained in a HPLC purity of greater than 98.0%, preferably greater than 98.5 %.

In the process of step (ii) for preparation of tetrabenazine (I), di hydroxy benzoquinoline compound (III) is treated with a source of methyl, selected form methanol, methoxy (diphenyl) phosphine, trimethoxy phosphine, trimethyl sulfonium hydroxide, dimethyl sulfate, dimethyl carbonate, methyl iodide, methyl bromide, methyl 2,2,2-trichloroacetate, morphoiine, 4- methyl etc. The reaction can be carried out in solvents selected from nitriles like acetonitrile, propionitrile etc.; acetone, tetrahydrofuran, di methyl formamide, dimethyl sulfoxide, glycol, dioxane, propanediol, butanediol, or mixture thereof. In the process of step (ii) for preparation of tetrabenazine (I), wherein methanol is used as source of methyl, the reaction can be optionally carried out in presence catalyst selected from azodicarboxylate such as diethyl azodicarboxylate (DEA D) or diisopropyl azodicarboxylate (DIA D) and tri phenyl phosphine. The reaction can be carried out at an ambient temperature of 5 to 30eC.

Tetrabenazine (I) can be isolated by techniques known in art like filtration, evaporation, concentration etc. Tetrabenazine (I) obtained by this process is free from triphenyl phosphine and triphenyl phosphine oxide impurities.

In the process of step (ii) for preparation of deutetrabenazine (II), dihydroxy benzoquinoline compound (III) is treated with a source of deuteriated methyl selected from deuteriated methanol, deuteriated methoxy (di phenyl) phosphine, deuteriated trimethoxy phosphine, deuteriated trimethyl sulfonium hydroxide, deuteriated dimethyl sulfate, deuteriated dimethyl carbonate, deuteriated methyl iodide, deuteriated methyl bromide, deuteriated methyl 2,2,2-trichloroacetate, deuteriated morphoiine, 4-methy! etc. In the process of step (ii) for preparation of deutetrabenazine (II), wherein deuteriated methanol is used as source of deuterated methyl, the reaction can be optionally carried out in presence of catalyst selected from azodicarboxylate such as diethyl azodicarboxylate (DEA D) or diisopropyl azodicarboxylate (DIA D) and tri phenyl phosphine. In the reaction the mole ratio of source of deuterated methyl plays an important role. The mole ratio of source of deuterated methyl with respect to dihydroxy benzoquinoline compound (III) is greater than 2.5 moles. The reaction can be carried out in solvents selected from nitriles like acetonitri le, propionitrile; chlorinated hydrocarbon solvents like dichloromethane, ethylene dichloride, carbon tetrachloride, chloroform and other solvents selected from acetone, tetrahydrofuran, dimethyl formamide, dimethyl sulfoxide, glycol, dioxane, propanediol, butanediol, or mixture thereof. The reaction can be carried out at an ambient temperature of 5 to 30eC. Deutetrabenazine (II) can be isolated by techniques known in art like filtration, evaporation, concentration etc. Isolated deutetrabenazine (II) was obtained in a H PLC purity of greater than 98.0%.

Deutetrabenazine (II) can be further recrystallized from solvents selected from esters like ethyl acetate, butyl acetate etc.; alcohols selected from methanol, ethanol, n-propanol, isopropanol, butanol etc.; nitriles selected from acetonitrile, propionitrile etc.; ketones selected from acetone, methyl isobutyl ketone etc., tetrahydrofuran, di methyl formamide, dimethyl sulfoxide, glycol, dioxane, propanediol, butanediol, water ; non-polar solvents like toluene, hexane, heptane etc. or mixture thereof. Deutetrabenazine (II) obtained by this process is free from triphenyl phosphine and triphenyl phosphine oxide impurities and is highly pure. Deutetrabenazine (II) obtained by the present method has a H PLC purity of greater than 99.0 %, preferably greater than 99.5%.

The present invention is further illustrated by the following representative examples and does not I i mi t the scope of the i nventi on.

EXAM PL E S

E xample 1 : preparation of dihydroxy benzoquinoline compound (III)

A mixture of methanol (675 ml), dihydroxy isoquinoline compound (IV) hydrochloride (150 g) and water (225 ml) was stirred and (2-acetyl-4-methyl-pentyl)-tri methyl- ammonium iodide (V) (285 g) was added to it The reaction mass was stirred at 25-30eC and potassium carbonate (34.5 g) was added. The reaction mass was heated to 45-50eC and was stirred for 30 hours. The reaction mass was cooled to 25-30eC and water (450 ml) was added to it and stirred for 4 hours. The solid was filtered, washed with water and dried under vacuum Y ield: 138 g.

E xample 2: preparation of dihydroxy benzoquinoline compound (III)

A mixture of methanol (12 L), dihydroxy isoquinoline compound (IV ) hydrochloride (4.0 kg) and water (12 L) was stirred and (2-acetyl-4-methyl-pentyl)-trimethyl-ammonium iodide (V) (6.60 kg) was added to it The reaction mass was stirred at 25-30eC and potassium carbonate (2.8 kg) was added. The reaction mass was heated to 65-70 eC and was stirred for 30 hours. The reaction mass was cooled to 25-30eC and water (12 L) was added to it and stirred for 4 hours. The solid was filtered and washed with water. The solid was taken up in isopropanol (10 L) and the mixture was heated to 75-80e for 15-30 minutes. The reaction mass was cooled, the solid was filtered and washed with isopropanol and dried undervacuum Y ield: 4.0 kg. H PLC purity: 98.6%.

E xample 3: preparation of tetrabenazine (I):

To a mixture of tetrahydrofuran (2000 ml), di hydroxy benzoqui nol i ne compound (III) (250 g), methanol (276.8 g) and tri phenyl phosphine (679.9 g) was added a solution of diisopropylazodicraboxylate (DIA D) (524.1 g) in tetrahydrofuran (500 ml) at 25-30eC. The reaction mass was stirred for 3-6 hours at 25-30eC. The reaction mass was concentrated under vacuum A mixture of water (2500 ml) and toluene (7500 ml) was added to the concentrated mass and the mixture was stirred. The aqueous layer was separated and the organic layer was washed with 5% aqueous sodium hydrogen sulphate solution (2500 ml, 3 times). The aqueous layers were col lected together and the pH was adj usted to 9-11 using aqueous ammonia solution (750 ml). Dichloromethane (2500 ml) was added to it and the organic layer was separated and concentrated under vacuum. Water (1250 ml) was added to the concentrated mass and the mass was stirred for at 25- 30eC for 2 hours. The solid was filtered, washed with water and dried under vacuum Y ield: 262.3g.

E xample 4: purification of tetrabenazine (I):

A mixture of tetrabenazine (I) (10 g) and ethyl acetate (30 ml) was heated to 65-70eC. The mixture was stirred for 60-90 minutes and filtered through micron filter. T he filtrate was cooled to 25-30eC and n- heptane (100 ml) was added to it The mixture was stirred for about 4 hours at 25-30eC. The solid was filtered, washed with n-heptane and dried under vacuum Y ield: 9.6 g.

E xample 5: preparation of deutetrabenazine (II):

To a mixture of tetrahydrofuran (224 ml), di hydroxy benzoqui nol ine compound (III) (28 g), deuteriated methanol (34.9 g) and tri phenyl phosphi ne (76.1 g) was added a solution of diisopropylazodicraboxylate (DIAD) (58.7 g) in tetrahydrofuran (56 ml) at 25-30eC. The reaction mass was stirred for 3-6 hours at 25-30eC. The reaction mass was concentrated under vacuum A mixture of water (280 ml) and toluene (840 ml) was added to the concentrated mass and the mixture was stirred. The aqueous layer was separated and the organic layer was washed with 5% aqueous sodium hydrogen sulphate solution (280 ml, 3 times). The aqueous layers were collected together and the pH was adjusted to 9-11 using aqueous ammonia solution. Dichloromethane (280 ml) was added to it and the organic layer was separated and concentrated under vacuum Water (140 ml) was added to the concentrated mass and the mass was stirred for at 25-30eC for 2 hours. The solid was filtered, washed with water and dried under vacuum. Y ield: 29.4 g.

E xample 6: preparation of deutetrabenazine (II):

To a mixture of dichloromethane (24 L), dihydroxy benzoquinoline compound (III) (3.0 kg), deuteriated methanol (3.75 kg) and tri phenyl phosphine (8.16 kg) was added a solution of diisopropylazodicraboxylate (DIAD) (6.30 kg) in dichloromethane (6 L) at 25- 30eC. The reaction mass was stirred for 2 hours at 25-30eC. T he reaction mass was washed with water and the organic layer was concentrated under vacuum. Toluene was added to the residue and the mixture was stirred. T he mixture was filtered and the filtrate was washed with 5% aqueous sodium hydrogen sulphate solution (15 L, 3 times). The aqueous layers were collected together and the pH was adjusted to 9-11 using aqueous ammonia solution. Dichloromethane (30 L) was added to it and the organic layer was separated and concentrated under vacuum Ethyl acetate (30 L) was added to the residue, carbon treatment was given and ethyl acetate was removed under vacuum Isopropanol (6 L) was added to the residue and the mixture was heated to 75-80eC for 15-30 minutes. The reaction mass was cooled, the solid was filtered and washed with isopropanol and dried undervacuum Y ield: 1.75 kg. H PLC purity: 98.5%.

E xample 7: purification of deutetrabenazine (II):

A mixture of deutetrabenazine (II) (10 g) and ethyl acetate (30 ml) was heated to 65- 70eC. The mixture was stirred for 60-90 minutes and filtered through micron filter. The filtrate was cooled to 25-30eC and n- heptane (100 ml) was added to it The mixture was stirred for about 4 hours at 25-30eC. The solid was filtered, washed with n-heptane and dried under vacuum. Y ield: 9.6 g.

E xample 8: purification of deutetrabenazine (II):

A mixture of deutetrabenazine (II) (1.70 kg) and ethyl acetate (13.6 L) was heated to 60- 65eC. The mixture was stirred for 60-90 minutes and filtered through micron filter. The filtrate was concentrated under vacuum and isopropanol (1.7 L) was added to the residue. T he mixture was heated to 75-80e for 15-30 mi nutes and then was cool ed to 25-30eC . T he solid was filtered, washed with isopropanol and dried under vacuum Y ield: 1.53 kg. H PLC purity: 99.7%.