Field of the Invention

The present invention provides racemic dapoxetine solid, process for its preparation and pharmaceutical compositions comprising it. The present invention also provides S-enantiomer of dapoxetine solid, process for its preparation and pharmaceutical compositions comprising it.

Background of the Invention

Dapoxetine and its enantiomers are important medicament as selective serotonine reuptake inhibitors. It is useful agent for the treatment of variety of diseases such as premature ejaculation, which is most common in men and other disorders like depression, which is common psychiatric disorder in people of all gender, ages and backgrounds or anxiety. The generic name dapoxetine is marketed by Johnson & Johnson under the brand PRILIGY. Dapoxetine, chemically (S)-N,N- dimethyl-3-(naphthalen-l-yloxy)-l-phenylpropan-l-amine, is represented by the following structure:

EP Patent No. 0,288,188 Bl disclosed a process for the preparation of enantiomerically pure S-(+)-dapoxetine as oil and addition salts by treating with inorganic acids such as hydrochloric acid etc as well as organic acids such as oxalic acid, tartaric acid and p-toluene sulfonic acid.

US Patent No. 5,292,962 disclosed a process for the preparation of dapoxetine and its salts. Process for the preparation of S-(+)-dapoxetine as colorless oil was decribed in Tetrahydron: Asymmetry 17 (2006) 860-866 and Tetrahydron: Asymmetry 18 (2007) 2099-2103.

Resolution of racemic (±)-dapoxetine with (+)-di-p-toluyl tartaric acid to obtain (+)-dapoxetine and its salts was disclosed in PCT Publication No. WO 2008/035358.

The racemic dapoxetme solid and S-enantiomer of dapoxetine solid is not disclosed in the prior art. We have discovered novel racemic dapoxetine solid and novel S-enantiomer of dapoxetme solid. Since the racemic dapoxetine solid and S- enantiomer of dapoxetine solid is obtained with high purity and so, suitable for pharmaceutical preparations. The said solids can also be used to obtain pharmaceutically acceptable salts of dapoxetine in high purity.

One object of the present invention is to provide racemic dapoxetine solid, process for their preparation and pharmaceutical compositions comprising it.

Another object of the present invention is to provide S-enantiomer of dapoxetine solid, process for their preparation and pharmaceutical compositions comprising it.

Detailed Description of the Invention

According to one aspect of the present invention, there is provided racemic dapoxetine solid.

According to another aspect of the present invention, there is provided a process for preparing racemic dapoxetine solid, which comprises:

a) preparation of a solution of dapoxetine in n-hexane or cyclohexane;

b) maintaining the solution obtained in step (a) at below about 30°C; and c) collecting racemic dapoxetine solid from the contents of step (b).

The solution is prepared by dissolving oily residue in n-hexane or cyclohexane or the salts of racemic dapoxetine sulrried in water, basified and extracted with n-hexane or cyclohexane.

Preferably the solution is maintained for at least 30 minutes at below 30°C, more preferably for 1 hour to 4 hours at 0 to 5°C. The racemic dapoxetine solid may be collected by filtration or centrifugation.

It has been surprisingly found that once the solid is obtained by the process of the invention, the solid can be recrystallized from a solvent or a mixture of solvents such as ethyl acetate, butyl acetate, and alcohols such as methanol, ethanol and isopropanol to obtain racemic dapoxetine solid. Alcohols may alone or in combination with water may be used.

According to another aspect of the present invention, there is provided S- enantiomer of dapoxetine solid.

According to another aspect of the present invention there is provided a process for preparing S-enantiomer of dapoxetine solid, which comprises:

a) preparation of a solution of S-enantiomer of dapoxetine in n-hexane or cyclohexane;

b) maintaining the solution obtained in step (a) at below about 30°C; and c) collecting S-enantiomer of dapoxetine solid from the contents of step (b).

The solution is prepared by dissolving oily residue in n-hexane or cyclohexane or the salts of racemic dapoxetine sulrried in water, basified and extracted with n-hexane or cyclohexane.

Preferably the solution is maintained for at least 30 minutes at below 30°C, more preferably for 1 hour to 4 hours at 0 to 5°C.

The S-enantiomer of dapoxetine solid may be collected by filtration or centrifugation.

It has been surprisingly found that once the solid is obtained by the process of the invention, the solid can be recrystallized from a solvent or a mixture of solvents such as ethyl acetate, butyl acetate, and alcohols such as methanol, ethanol and isopropanol to obtain S-enantiomer of dapoxetine solid. Alcohols may alone or in combination with water may be used.

The compounds of the present inventions are useful drugs as selective serotonine reuptake inhibitors.

The said solids of the present invention are useful intermediates for obtaining salts of racemic dapoxetine solid and S-enantiomer of dapoxetine solid. According to another aspect of the present invention there is provided a pharmaceutical composition comprising racemic dapoxetine solid and S-enantiomer of dapoxetine solid, and a pharmaceutically acceptable excipient.

Preferable pharmaceutical composition is used in an oral dosage form.

Brief Description of the Drawing

Figure 1 is X-ray powder diffraction spectrum of racemic dapoxetine solid. Figure 2 is Differential scanning calorimetry (DSC) thermogram of racemic dapoxetine solid.

Figure 3 is X-ray powder diffraction spectrum of S-enantiomer of dapoxetine solid.

Figure 4 is Differential scanning calorimetry (DSC) thermogram of S- enantiomer of dapoxetine solid.

X-ray powder diffraction spectrum was measured on a bruker axs D8 advance X-ray powder diffractometer having a copper-Κα radiation. Approximately lgm of sample was gently flattered on a sample holder and scanned from 2 to 50 degrees two-theta, at 0.03 degrees to theta per step and a step time of 38 seconds. The sample was simply placed on the sample holder. The sample was rotated at 30 rpm at a voltage 40 KV and current 35 mA.

DSC (Differential Scanning Calorimetry) measurements were performed with a DSC Q200 (TA Instruments, Inc.). About 1 to 1.3 mg of the powder was placed in an open aluminum pan and it was crimped with an aluminum lid. The crimped sample was then placed in the DSC cell opposite to empty aluminum pan (as reference) and the sample was scanned at 10 deg C/min from 40 deg C to 100 deg C.

The invention will now be further described by the following examples, which are illustrative rather than limiting.

Reference examples

Reference example 1 :

A mixture of l-phenyl,3-napthyloxy 1-propanol (50 gm), tetrahydrofuran

(375 ml), dimethylamino pyridine (5 mg) and triethyl amine (60 ml) at room temperature. The contents were cooled to -5 to 0 C and added a mixture of methane sulfonyl chloride (33 gm) and tetrahydrofuran (125 ml). The reaction mass was maintained at 6 hours at 0 to 5°C and dimethylamine gas was passed into the reaction mass. The reaction mass raised to room temperature and stirred for 40 hours. The reaction mass poured into chilled water (500 ml) slowly and the pH was adjusted 0.5 to 1 with concentrated hydrochloric acid. Added toluene (250 ml) to the reaction mass and stirred for 30 minutes. The layers were separated and the aqueous layer pH was adjusted to 9 to 10 with 5% sodium hydroxide solution. The aqueous layer extracted with four times methylene dichloride (4 X 300 ml) and distilled off completely to obtain a residue. Ethyl acetate (100 ml) was added into the residue and the mixture was stirred for 30 minutes, filtered through hyflo bed and washed with ethyl acetate. The filtrate was distilled off completely to obtain 47 gm of racemic dapoxetine as a residual oil. Reference example 2:

To a mixture of (+)-dapoxetine tartrate (50 gm), methylene dichloride (250 ml) and water (250 ml) at room temperature and was added 10% sodium hydroxide solution (100 ml) under strring. The organic layer separated and the aqueous layer extracted with methylene dichloride (250 ml). The combined organic layer was washed with water (250 ml) and distilled off completely to obtain 29 gm of S- enantiomer of dapoxetme as a residual oil.

Examples

Example 1 :

Preparation of racemic dapoxetine solid

The residue of dapoxetine (10 gm) as obtained in reference example 1 was dissolved in n-hexane (25 ml) at reflux. The solution was cooled to 0 to 5°C, stirred for 1 hour and the precipitated solid racemic dapoxetine was filtered. The solid was washed with chilled n-hexane and dried the solid under reduced pressure to obtain 7 gm of racemic dapoxetine solid. The P-XRD spectrum and DSC of racemic dapoxetine solid are shown in figure 1 and 2 respectively (Purity by HPLC: 99.5%). Example 2:

Preparation of racemic dapoxetine solid

The residue of dapoxetine (10 gm) was dissolved in cyclohexane (20 ml) at reflux. The solution was cooled to 0 to 5°C, stirred for 2 hours and the precipitated solid racemic dapoxetine was filtered. The solid was washed with chilled cyclohexane and dried the solid under reduced pressure to obtain 6.5 gm of racemic dapoxetine solid (Purity by HPLC: 99.5%). Example 3:

Preparation of S-enantiomer of dapoxetine solid

The S-enantiomer of dapoxetine (10 gm) as obtained in reference example 2 was dissolved in n-hexane (25 ml) at reflux. The solution was cooled to 0 to 5°C, stirred for 1 hour and the precipitated solid S-enantiomer dapoxetine was filtered. The solid was washed with chilled n-hexane and dried the solid under reduced pressure to obtain 8.5 gm of S-enantiomer of dapoxetine solid. The P-XRD spectrum and DSC of S-enantiomer of dapoxetine solid are shown in figure 3 and 4 respectively (Chiral purity by HPLC : 99.9%, Purity by HPLC : 99.4%). Example 4:

Preparation of S-enantiomer of dapoxetine solid

The S-enantiomer of dapoxetine (10 gm) was dissolved in cyclohexane (20 ml) at reflux. The solution was cooled to 0 to 5°C, stirred for 2 hours and the precipitated solid S-enantiomer dapoxetine was filtered. The solid was washed with chilled cyclohexane and dried the solid under reduced pressure to obtain 7 gm of S- enantiomer of dapoxetine solid (Chiral purity by HPLC: 99.8%, Purity by HPLC: 99.2%).