CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefits of U.S. Provisional Patent Application Nos. 60/583,641, filed June 28, 2004, 60/609,716, filed September 14, 2004, 60/622,065, filed October 25, 2004, 60/652,330, filed February 11, 2005, 60/583,644, - filed June 28, 2004, 60/652,332, filed February 11, 2005, 60/583,643, filed June 28, 2004, 60/652,331, filed February 11, 2005, 60/666,666, filed March 30, 2005, 60/675,369, filed April 26, 2005, Application No. Not Yet Known (Attorney Docket No. 12670/46803), filed June 9, 2005, and Application No. Not Yet Known (Attorney Docket No. 12670/47001), filed June 14, 2005, the contents of all of which are incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates to a process for optical resolution of racemic tomoxetine. The present invention also relates to a process for recycling of (S)-(+)- tomoxetine.

BACKGROUND OF THE INVENTION Atomoxetine HCl is a selective norepinephrine reuptake inhibitor. It is marketed under the name STRATTERA® for the treatment of Attention- Deficit/Hyperactivity Disorder (ADHD) and is available in 10 mg, 18 mg, 25 mg, 40 mg, and 60 mg dosage forms. It is a white to practically white solid, which has a solubility of 27.8 mg/ml in water.

Atomoxetine, chemically known as (R)(-)-N-methyl-3-(2-methylphenoxy)-3- phenylpropylamine, has the following structure:

Atomoxetine, the (R)-(-) enantiomer of tomoxetine, is an aryloxyphenylpropylamine. It is about twice as effective as the racemic mixture and about nine times more effective than the (+)-enantiomer, as disclosed in U.S. Patent No. 4,018,895 (assigned to Eli Lilly and Co.), EP 0 052 492 (Eli Lilly and Co.), and EP 0 721 777 (Eli Lilly and Co.).

Several processes for synthesizing 3-aryloxy-3-phenylpropylamines are known in the art. For example, U.S. Patent No. 4,018,895 assigned to Eli Lilly and Co. discloses an aliphatic nucleophilic displacement of N-protected-3-halogen-3- phenylpropylamines by phenols, followed by N-deprotection. U.S. Patent No. 4,868,344 assigned to Aldrich-Boranes, Inc. relates to the Mitsunobu reaction between 3-hydroxy-3-phenylpropylhalides and phenols, followed by amination of the resulting 3-aryloxy-3-phenylpropylhalides. Tomoxetine is also synthesized by the processes disclosed in U.S. Patent No. 6,541,668, and WO 00/58262 assigned to Eli Lilly and Co. and WO 94/00416 by Richter Gedeon Vegyeszeti Gyar RT. These patents disclose an aromatic nucleophilic displacement of an aryl halide by 3- hydroxy-3-phenylpropylamines under strongly basic conditions. The nucleophilic aromatic displacement process disclosed in WO 00/58262 comprises reacting N- methyl-3-hydroxy-3-phenylpropylamine with a protected 2-fluorobenzaldehyde to produce tomoxetine after several functional group interconversion steps.

Optical resolution of racemic tomoxetine into (R)-(-)-tomoxetine (atomoxetine) and (S)-(+)-tomoxetine is known in the art. Common techniques include chiral chromatography and fractional crystallization of (S)-(+)-mandelic acid diastereoisomeric addition salts. Because the former is more costly and not optimized for large scale synthesis, the latter is preferred for commercial processes.

EP Patent No. 0 052 492 discloses a process wherein racemic tomoxetine, prepared from N-methyl-3-hydroxy-3-phenylpropylamine, is resolved with (S)-(+)- mandelic acid to obtain (R)-(— )-tomoxetine (S)-(+)-mandelate salt. This process produces a poor yield of about 18%. This process is inefficient and also requires solvents which may be harmful to the environment, such as diethyl ether and dichloromethane. US Patent No. 6,541,668, assigned to Eli Lilly and Co., discloses an improved resolution process having fewer steps. This process also yields approximately 18% (R)-(-)-tomoxetine (S)-(+)-mandelate (prepared from N-methyl- 3-hydroxy-3-phenylpropylamine). However, the optical purity of the (R)-(-)- tomoxetine product is not disclosed.

The poor yields indicate that, in the solvents used, a large amount of the racemic tomoxetine may be unrecovered as (S)-(+)-tomoxetine, the unwanted enantiomer. U.S. Patent No. 4,777,291, assigned to Eli Lilly and Co., discloses a racemization process from (S)-(+)-tomoxetine to racemic tomoxetine by means of alkyl-alkali metals or alkylamide-alkali metals in tetrahydrofuran or 1,2- dimethoxyethane, preferably butyllithium in tetrahydrofuran. This process requires hazardous solvents and bases unsuitable in a large scale commercial synthesis. Moreover, the patent discloses and one of skill in the art appreciates, that anhydrous media are required in this process.

Epimerizing bases other than alkyl-alkali metals or alkylamide-alkali metals are known in the art for 3-aryloxy-3-phenylpropylamines other than tomoxetine. For example, WO 00/64855 (Eli Lilly and Co.) discloses a racemization process of (S)- fluoxetine into racemic fluoxetine involving a base having a potassium counter-ion in an aprotic highly dipolar solvent.

There is a need in the art for additional processes for optical resolution of racemic tomoxetine in higher yields that can be utilized in large-scale commercial operations. Furthermore, there is also a need for more efficient processes for the epimerization of the unwanted (S)-(+)-enantiomer of tomoxetine.

SUMMARY OF THE INVENTION The present invention provides a process for the optical resolution of racemic tomoxetine under reaction conditions that improve reaction yields and/or optical purity. The invention also provides an epimerization process of the unwanted (S)-(+) enantiomer.

Thus, in one aspect, the present invention provides a process for the optical resolution of racemic tomoxetine comprising: a) providing a mixture of tomoxetine racemate, a C1-4 alcohol, an aromatic solvent, and (S)-(+)-mandelic acid, b) heating the mixture to a temperature of about 6O0C to about 8O0C; and c) crystallizing (R)-(— )-tomoxetine (S)-(+)-mandelate from the reaction mixture. In another aspect, the present invention provides a process for optical resolution of racemic tomoxetine comprising: a) combining, at a temperature of about 4O0C to about 600C, (S)-(+)-mandelic acid in an aqueous basic solution, tomoxetine racemate, an aromatic solvent and acetic acid, to obtain a mixture; b) maintaining the mixture for at least one hour to obtain (R)-(-)-tomoxetine (S)- (+)-mandelate; and c) recovering (R)-(-)-tomoxetine (S)-(+)-mandelate from the reaction mixture.

In yet another aspect, the present invention provides a process for recycling of (S)-(+)-tomoxetine by epimerization. This process comprises: a) providing a mixture of (S)-(+)-tomoxetine, an aprotic dipolar solvent and a base having a highly ionic counter ion, b) heating the mixture to a temperature of about 8O0C to about 15O0C, and

c) maintaining the mixture for at least 3 hours to obtain racemic tomoxetine.

The racemate may further be optically resolved into the desired (R)-(-)- tomoxetine by the process described above, or by any methods known in the art, e.g., crystallizing (R)-(-)-tomoxetine (S)-(+)-mandelate from the reaction mixture. In a further aspect, the present invention comprises the preparation of atomoxetine or a pharmaceutically acceptable salt thereof by converting the R(-)- tomoxetine S-(+)-mandelate prepared above to atomoxetine or a pharmaceutical acceptable salt thereof.

Preferably, the pharmaceutically acceptable salt is atomoxetine hydrochloride.

DETAILED DESCRIPTION OF THE INVENTION As used herein the term "aromatic solvent" refers to a C6-1O aromatic hydrocarbon, such as but not limited to, benzene, xylene, or toluene.

The present invention provides processes for the optical resolution of racemic tomoxetine, obtained, for example, according to the process described in US patent no. 6,541,668, under reaction conditions that are expected to improve reaction yields and/or optical purity from processes in the prior art.

It is believed that the processes of the present invention have several advantages over the prior art: they do not require distillation of toluene, which is necessary in the process disclosed in U.S. Patent No. 6,541,668; they avoid anhydrous media and solvents that may be harmful to the environment, which are required in the processes disclosed in EP 0 052 492 and U.S. Patent No. 4,777,291. Using more environmentally compatible materials is also believed to facilitate large-scale commercial production.

In one embodiment, the process provided by the present invention comprises combining racemic tomoxetine, a C1-4 alcohol, and an aromatic solvent. Preferably, the C1-4 alcohol is methanol. A preferred aromatic solvent is toluene. Preferably, the C1-4 alcohol is combined in an amount of about 0.1 ml per 1 g of the tomoxetine racemate. (S)-(+)-mandelic acid is then added to the racemic tomoxetine solvent mixture. The mixture is heated to a temperature of about 6O0C to about 8O0C, which induces dissolution. Preferably, the mixture is heated to a temperature of about 65°C to about 700C. After all solids have dissolved, (R)-(-)-tomoxetine (S)-(+)-mandelate is recovered, preferably by crystallization at a temperature of about -50C to about 2O0C. More preferably, (R)-(-)-tomoxetine (S)-(+)-mandelate is recovered at a temperature of about O0C.

hi another embodiment, the present invention provides a process for optical resolution of racemic tomoxetine in abiphasic system. This process comprises combining tomoxetine racemate with an aqueous solution of (S)-(+)-mandelic acid and a base, in the presence of acetic acid and an aromatic solvent, preferably toluene. The base may be any one of sodium, potassium, cesium, calcium and ammonium hydroxide. More preferably the base is sodium hydroxide. The mixture is then heated to a temperature of about 40°C to about 6O0C until dissolution occurs, then cooled to a temperature of about -50C to about 2O0C, and maintained for a sufficient time to bring about the crystallization of (R)-(-)-tomoxetine (S)-(+)-mandelate. Preferably, the mixture is cooled to a temperature of about O0C.

In another embodiment, the obtained (R)-(— )-tomoxetine (S)-(+)-mandelate salt may be recrystallized from a solution comprising an aromatic solvent and a C1-4 alcohol. Preferably, the mixture is heated to a temperature of about 600C to about 8O0C, more preferably to a temperature of about 650C to about 7O0C, until all solids dissolve. The obtained solution is then cooled to a temperature from about -5°C to about 200C, at which (R)-(-)-tomoxetine (S)-(+)-mandelate recrystallizes. More preferably, the solution is cooled to about 00C. Preferably, the C1-4 alcohol is added in an amount of about 0.6 ml per 1 g of the (R)-(-)-tomoxetine (S)-(+)-mandelate salt. Preferably, the C1-4 alcohol is methanol. A preferred aromatic solvent is toluene.

The yield of (R)-(-)-tomoxetine (S)-(+)-mandelate, prepared from N-methyl- 3-hydroxy-3-phenylpropylamine, by the process of the present invention is expected to be at least about 35%.

(R)-(— )-tomoxetine (S)-(+)-mandelate may be separated from the reaction mixture by techniques known in the art, such as filtration. The product may be washed with an organic solvent. The product may then be dried, preferably under reduced pressure.

The present invention further provides an improved process for recycling the undesired (S)-(+)-tomoxetine, which is obtained after the optical resolution of the tomoxetine racemate, into the desired (R)-(-) enantiomer. This process comprises racemization of the (S)-(+)-tomoxetine by combining it with an aprotic dipolar solvent, and a base having a highly ionic counter ion, followed by heating of the mixture. Preferably, the mixture is heated to a temperature of about 800C to about 150°C, most preferably, the mixture is heated to a temperature of about 85°C to about 90°C. Preferably, the solvent and base are each added in an amount of at least 2 moles per mole (S)-(+)-tomoxetine. Preferably, the aprotic dipolar solvent is selected from the group consisting of DMF, dimethylacetamide, l,3-dimethyl-2-imidazolinone and dimethylsulfoxide (DMSO). Most preferably, the aprotic dipolar solvent is DMSO. A preferred base is potassium hydroxide.

The reaction is followed by observing the optical rotation of the mixture. The reaction is complete when the optical rotation of the mixture decreases to 0.00. The duration of the reaction is approximately 3 hours. An organic solvent and water are then added to produce a 2-phase system, and following phase separation, racemic tomoxetine is recovered from the organic phase, preferably by concentration to a residue.

The process provided in the present invention may be depicted as follows: Racemization (+/-)-Tomoxetine ofunwanted enantiomer

Optical mother liquors resolution

(R)(-)-Tomoxetine

Atomoxetine HCI

The solvent mixture ("mother liquor") containing the (S)-(+)-tomoxetine that remains following the optical resolution of racemic tomoxetine may be concentrated, preferably under vacuum, in order to decrease reaction time. The term "vacuum," as commonly known in the art, refers to a pressure of less than one atmosphere.

The racemic tomoxetine prepared by this recycling process may then be optically resolved to yield (R)-(-)-tomoxetine (S)-(+)-mandelate, by the processes described above, or by any other methods known in the art.

By epimerizing the unwanted (S)-(+) enantiomer, the atomoxetine yield is increased, and the amount of the reagents wasted during the preparation of atomoxetine is substantially reduced.

In a further embodiment, R(-)-tomoxetine S-(+)-mandelate prepared above is converted into atomoxetine or a pharmaceutically acceptable salt thereof. Preferably, the pharmaceutically acceptable salt is a hydrochloride salt. Atomoxetine hydrochloride can be prepared by adding a base to a mixture of (R)-(-)-tomoxetine (S)-(+)-mandelate and an organic solvent, followed by adding HCl, to obtain atomoxetine HCl.

Moreover, the present invention provides a process for preparing a pharmaceutical composition comprising R(-)-tomoxetine (atomoxetine) or a pharmaceutically acceptable salt thereof, which comprises bringing R(-)-tomoxetine (atomoxetine) or a pharmaceutically acceptable salt thereof into contact with one or more pharmaceutically acceptable carriers or excipients.

EXAMPLES

Achiral HPLC analysis Instrument: HPLC Hewlett Packard VWD detector HPl 100 Column: YMC ODS-AQ 250mm x 4.6mm (i.d.) cod. AQ-303 Mobile phase: NaH2PO4 0.02M pH 3 buffer - Acetonitrile gradient Flow: 1.5 ml/min Temperature: 40°C Wavelength: 215 nm

Chiral HPLC analysis Instrument: HPLC Hewlett Packard VWD detector HPl 100 Column: CHIRACEL OD-R cellulose tris (3,5-dimethylphenylcarbamate) 250 mm x 4.60 mm x 10 mm (Daicel Chemicals cat. N° DAIC14625) Mobile phase: KPF6 100 mM / Acetonitrile - 60 / 40 Flow: 0.8 ml/min Temperature: 35°C Wavelength: UV, 215 nm

Example 1 (R,S)-N-methyl-3-(2-methylphenoxy)-3-phenylpropylamine (Tomoxetine synthesis) 1100 g (14.1 mol) of dimethylsulfoxide, 200 g (1.21 mol) of N-methyl-3- hydroxy-3-ρhenylpropylamine and 221 g (3.63 mol) of potassium hydroxide (bulk industrial grade, 92.1% assay) were heated under stirring at 110°C, then the mixture was concentrated by vacuum distillation until about 130 g of solvent were removed. The mixture was allowed to cool to 80°C, then 400 g (3.63 mol) of 2-fiuorotoluene were added. The mixture was heated to reflux (145°C - 147°C) for one hour, and then allowed to cool to about 90°C. 1000 ml of water and 1000 ml of toluene were added. The mixture was stirred for some minutes, at which time the phases were separated. The aqueous phase was extracted with 2 x 200 ml of toluene. The organic phases were collected and washed with 3 x 200 ml of water. Final organic phase weight: 1700 g. Tomoxetine content: 16.83% by weight (HPLC assay). Yield: 92.7%.

Example 2 (R)-(-)-Tomoxetine (S)-(+)-Mandelate (Tomoxetine Optical Resolution)

A solution in toluene of crude racemic tomoxetine (276.13 g, 1.081 mol, by HPLC assay) prepared as described in example 1 was concentration in vacuo to remove water. The residue was taken up with 2025 ml of toluene and 26 ml of methanol. To the obtained solution 94 g (0.618 mol) of (S)-(+)-mandelic acid were added at 250C. All solids were solubilized by heating to 65°-70°C, and then crude mandelate salt was crystallized on cooling. The solid was isolated by filtration at 5°~ 100C, washed with about 300 ml of toluene and dried in vacuo. Weight: 178 g. Tomoxetine content: 63.2% by weight (HPLC assay). Yield: 43.15%. Crude mandelate salt (R)-(— )-tomoxetine enantiomeric ratio: R/S is about 95/5 (by chiral HPLC).

163 g of the obtained crude mandelate salt was re-crystallized from 489 ml of toluene and 49 ml of methanol as follows: the salt was solubilized by heating to 65°- 70°C, then (R)-(-)-tomoxetine (S)-(+)-mandelate was crystallized on cooling, isolated by filtration at 5°-10°C, washed with about 2 x 90 ml of toluene and dried in vacuum. Weight: 153 g. Tomoxetine content: 63.97% by weight (HPLC assay). Yield: 38.7% from racemic tomoxetine. (R)-(-)-tomoxetine (atomoxetine) enantiomeric ratio: R/S > 99/1 (by chiral HPLC).

Example 3 (R)-(-)-Tomoxetine (S)-(+)-Mandelate (Tomoxetine Optical Resolution)

To 26.5 g of crude racemic Tomoxetine (0.104 mol, by HPLC assay) in toluenic solution (from example 2) 1.6 ml of methanol and 9.6 g (0.063 mol) of (S)- (+)-mandelic acid were added at 25°C. AU solids were solubilized by heating to 65°- 70°C, then crude mandelate salt was crystallized on cooling. The salt was isolated by filtration at 5°-10°C, washed with about 30 of toluene and dried in vacuum. Weight: 16.4 g. Tomoxetine content: 64.35% by weight (HPLC assay). Yield: 40% from racemic Tomoxetine. Crude mandelate salt (R)-(-)-tomoxetine enantiomeric ratio: R/S is about 97/3 (by chiral HPLC).

Example 4 (R)-(-)-Tomoxetine (S)-(+)-Mandelate (Tomoxetine Optical Resolution)

To a suspension of (S)-(+)-mandelic acid (10.72 g; 0.070 mol) in water (10 ml) 9.86 g (0.0739 mol) of 30% aqueous sodium hydroxide were added and the mixture was heated to 50-60°C until complete dissolution. The resulting clear aqueous solution was dropped over a solution of crude racemic tomoxetine acetate in toluene, obtained by addition of glacial acetic acid (7.40 g; 0.123 mol) to a solution in toluene of crude racemic tomoxetine (30 g, 0.117 mol, by HPLC assay), prepared on its turn as described in Example 1. During the addition, temperature was raised to 350C; the biphasic system was then heated under vigorous stirring to 400C and then it spontaneously cooled to 20°C. The resulting suspension was then stirred at 200C for one hour, filtered and washed twice with toluene (30 ml each). The solid was dried at 5O0C under vacuum. (R)-(-)-tomoxetme mandelate 18.24 g; enantiomeric ratio: R/S 97: 3 (by chiral HPLC). Yield: 38.1%.

Example 5 Racemization of Unwanted Enantiomer

About 310 ml of toluenic solvent mixture ("mother liquors") from optical resolution (Examples 2-4) were washed with about 50 ml of 2% aqueous sodium hydroxide, and then concentrated under vacuum. The oily residue weighed 72.6 g and contained 51.29 g (0.20 mol) of tomoxetine (HPLC assay). 550 g (7.03 mol) of DMSO and 36.7 g (0.60 mol) of potassium hydroxide (bulk industrial grade, 92.1% assay) were added to the concentrate and the mixture was heated between 850C and 90°C until optical rotation of the mixture decreased to 0.00 (3 hours). Heating was stopped, 300 ml of water and 300 ml of toluene were added. The mixture was stirred for some minutes, and then phases were separated. The aqueous phase was extracted with 50 ml of toluene. The organic phases were collected and washed with 3 x 80 ml of water, then concentrated under vacuum. Residue weight: 64.23 g. Tomoxetine content: 49.07 g (0.19 mol) (HPLC assay).

The residue was taken up with 392 ml of toluene and 2.9 ml of methanol, and then 17.15 g (0.115 mol) of (S)-(+)-mandelic acid were added to the obtained solution at 25°C. AU solids were solubilized by heating to 65°-70°C. The solution was cooled, crude mandelate salt crystallized, was isolated by filtration at 5°-10°C, washed with about 2 X 40 ml of toluene and dried in vacuo. Weight: 33.6 g. Tomoxetine content: 62.9% by weight (HPLC assay). Yield: 41.2%. Crude mandelate salt (R)-(-)- Tomoxetine enantiomeric ratio: R/S is about 95/5 (by chiral HPLC).

Example 6 (R)-(—)-N-methyl-3-(2-methylphenoxy)-3-phenylpropylamine hydrochloride (Atomoxetine Hydrochloride)

45 g (0.110 mol) of (R)-(— )-tomoxetine (S)-(+)-mandelate were mixed under stirring with 225 ml of toluene and 225 ml of water. Keeping the temperature at about 40°C by means of gentle heating, 21 g (about 0.16 mol) of 30% aqueous sodium hydroxide were added. The phases were then separated. The organic phase was washed with 100 ml of 1% aqueous sodium hydroxide, then filtered on paper and concentrated in vacuum to give 29.67 g of an oil containing 26.8 g of tomoxetine (by HPLC assay).

23.5 g of the oil were dissolved in 211 ml of ethyl acetate under stirring then, keeping temperature between 12°C and 180C by means of water-ice bath cooling; gaseous hydrogen chloride was bubbled into the solution until acid reaction of litmus paper. The hydrochloride then crystallized. The obtained suspension was stirred at about 15°C for one hour, then the solid was collected by filtration, washed with ethyl acetate and dried in vacuo. Tomoxetine hydrochloride content: > 99% by HPLC assay. Weight: 24.3 g (0.0832mol). Yield: 95%. Atomoxetine hydrochloride enantiomeric ratio: R/S > 99/1 (by chiral HPLC). Having thus described the invention with reference to particular preferred embodiments and illustrative examples, those in the art may appreciate modifications to the invention as described and illustrated that do not depart from the spirit and scope of the invention as disclosed in the specification. The Examples are set forth to aid in understanding the invention but are not intended to, and should not be construed to, limit its scope in any way. The examples do not include detailed descriptions of conventional methods. Such methods are well known to those of ordinary skill in the art and are described in numerous publications. All references mentioned herein are incorporated in their entirety.