This application claims the benefit of Indian Provisional Patent Application No. 3299/CHE/2012, filed on August 10, 2012, which is incorporated herein by reference.

Filed of the Invention

The present invention provides a novel amorphous Form of doxercalciferol, process for its preparation and pharmaceutical compositions comprising it. The present invention also provides a solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier, process for its preparation and pharmaceutical compositions comprising it. The present invention further provides a novel crystalline Form of doxercalciferol, process for its preparation and pharmaceutical compositions comprising it.

Background of the Invention

Doxercalciferol is chemically, (lS,3i?,5Z,7£,22£)-9,10-Secoergosta-5,7,10,22- tetraene-l ,3-diol and has the structural formula:

Doxercalciferol (trade name Hectorol) is drug for secondary hyperparathyroidism and metabolic bone disease. It is a synthetic analog of ergocalciferol (vitamin D ₂ ). It suppresses parathyroid synthesis and secretion. Doxercalciferol and its process were disclosed in U.S. patent no. 3,907,843.

Polymorphism is defined as "the ability of a substance to exist as two or more crystalline phases that have different arrangement and/or conformations of the molecules in the crystal Lattice. Thus, in the strict sense, polymorphs are different crystalline structures of the same pure substance in which the molecules have different arrangements and/or different configurations of the molecules". Different polymorphs may differ in their physical properties such as melting point, solubility, X-ray diffraction patterns, etc. Although those differences disappear once the compound is dissolved, they can appreciably influence pharmaceutically relevant properties of the solid form, such as handling properties, dissolution rate and stability. Such properties can significantly influence the processing, shelf life, and commercial acceptance of a polymorph. It is therefore important to investigate all solid forms of a drug, including all polymorphic forms, and to determine the stability, dissolution and flow properties of each polymorphic form. Polymorphic forms of a compound can be distinguished in the laboratory by analytical methods such as X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC) and infrared spectrometry (IR).

Solvent medium and mode of crystallization play very important role in obtaining one polymorphic Form over the other.

Doxercalciferol can exist in different polymorphic Forms, which may differ from each other in terms of stability, physical properties, spectral data and methods of preparation.

U.S. patent application publication no. 2012/108554 disclosed crystalline Form of doxercalciferol.

We have found a novel amorphous Form of doxercalciferol. The amorphous Form of doxercalciferol is stable, reproducible and so, suitable for pharmaceutical preparations.

We have also found a solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier. The solid dispersion of doxercalciferol is stable, reproducible and so, suitable for pharmaceutical preparations.

We have also found a novel crystalline Form of doxercalciferol. The novel Form is stable, reproducible and so, suitable for pharmaceutical preparations. Thus, an object of the present invention is to provide a novel amorphous Form of doxercalciferol, process for its preparation and pharmaceutical compositions comprising it.

Another object of the present invention is to provide a solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier, process for its preparation and pharmaceutical compositions comprising it.

Another object of the present invention is to provide a novel crystalline Form of doxercalciferol, process for its preparation and pharmaceutical compositions comprising it.

Summary of the Invention

In one aspect, the present invention provides a doxercalciferol amorphous Form. In another aspect, the present invention provides a process for the preparation of doxercalciferol amorphous Form, which comprises:

a) dissolving doxercalciferol in an alcoholic solvent; and

b) subjecting the resulting solution to spray drying to obtain doxercalciferol

amorphous Form.

In another aspect, the present invention provides a pharmaceutical composition comprising amorphous Form of doxercalciferol and pharmaceutically acceptable excipients.

In another aspect, the present invention provides a solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier.

In another aspect, the present invention there is provided a process for the preparation of solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier, which comprises:

a) preparing a solution comprising a mixture of doxercalciferol and one or more pharmaceutically acceptable carriers selected from copovidone, ethyl cellulose, povidone, hydroxypropyl methylcellulose, polyethylene glycol, span-20 or soluplus in a solvent; and

b) removing the solvent to obtain a solid dispersion of doxercalciferol in

combination with a pharmaceutically acceptable carrier. In another aspect, the present invention provides pharmaceutical compositions comprising a therapeutically effective amount of solid dispersion of doxercalciferoi along with a pharmaceutically acceptable carrier, and at least one pharmaceutically acceptable excipient.

In another aspect, the present invention provides a crystalline Form of doxercalciferoi designated as Form HI characterized by peaks in the powder x-ray diffraction spectrum having 2Θ angle positions at about 3.1, 13.9, 15.8, 16.4 and 16.8 ± 0.2 degrees.

In another aspect, the present invention provides a process for the preparation of doxercalciferoi crystalline Form HI , which comprises:

a) dissolving doxercalciferoi in dimethylformamide;

b) adding water to the solution obtained in step (a);

c) maintaining the reaction mass; and

d) isolating doxercalciferoi crystalline Form HI .

Yet in another aspect, the present invention provides a pharmaceutical composition comprising crystalline Form HI of doxercalciferoi and pharmaceutically acceptable excipients.

Brief Description of the Drawings

Figure 1 is an X-ray powder diffraction spectrum of doxercalciferoi amorphous

Form.

Figure 2 is an X-ray powder diffraction spectrum of solid dispersion of doxercalciferoi in combination with a pharmaceutically acceptable carrier.

Figure 3 is an X-ray powder diffraction spectrum of doxercalciferoi crystalline Form HI.

X-ray powder diffraction spectrum was measured on a bruker axs D8 advance X- ray powder diffractometer having a copper- α radiation. Approximately 500 gm of sample was gently flattered on a sample holder and scanned from 2 to 50 degrees two- theta, at 0.020 degrees two theta per step and a step time of 1 second. 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. Detailed Description of the Invention

The term "room temperature" refers to temperature at about 25 to 35°C.

According to one aspect of the present invention, there is provided a

doxercalciferol amorphous Form. The powdered x-ray diffractogram (PXRD) of doxercalciferol amorphous Form is shown in figure 1.

According to another aspect of the present invention, there is provided a process for the preparation of doxercalciferol amorphous Form, which comprises:

a) dissolving doxercalciferol in an alcoholic solvent; and

b) subjecting the resulting solution to spray drying to obtain doxercalciferol

amorphous Form.

The alcoholic solvent used in step (a) may preferably be a solvent or mixture of solvents selected from methanol, ethanol, isopropyl alcohol, tert-butyl alcohol, n-butainol and isobutyl alcohol. More preferably the alcoholic solvent is ethanol.

The term "Spray drying" refers to is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas.

According to another aspect of the present invention, there is provided a pharmaceutical composition comprising amorphous Form of doxercalciferol and pharmaceutically acceptable excipients, and optionally other therapeutic ingredients. The amorphous Form may preferably be formulated into tablets, capsules, suspensions, dispersions, injectables or other pharmaceutical forms.

According to another aspect of the present invention, there is provided a solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier.

The powdered x-ray diffractogram (PXRD) of solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier is shown in figure 2.

Solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier is found to be stable.

Preferably, the solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier may be amorphous.

Preferably, the ratio of doxercalciferol to the pharmaceutically acceptable carrier is 1:0.5 to 1 :4.0. Preferably the pharmaceutically acceptable carriers may be one or more of copovidone, ethyl cellulose, povidone, hydroxypropyl methylcellulose, polyethylene glycol, span-20 or soluplus.

According to another aspect of the present invention, there is provided a process for the preparation of solid dispersion of doxercalciferol in combination with a pharmaceutically acceptable carrier, which comprises:

a) preparing a solution comprising a mixture of doxercalciferol and one or more pharmaceutically acceptable carriers selected from copovidone, ethyl cellulose, povidone, hydroxypropyl methylcellulose, polyethylene glycol, span-20 or soluplus in a solvent; and

b) removing the solvent to obtain a solid dispersion of doxercalciferol in

combination with a pharmaceutically acceptable carrier.

Doxercalciferol used in step (a) may preferably be doxercalciferol obtained by the known process.

The solvent used in step (a) may preferably be a solvent or a mixture of solvents selected from water, methylene chloride, ethylene chloride, chloroform, carbon tetrachloride, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methanol, ethanol, isopropanol, n-butanol and n-pentanol. More preferably the solvents are water, methylene chloride, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, ethanol and methanol.

Preferably the pharmaceutically acceptable carriers used in step (a) may be selected from copovidone, soluplus, povidone or hydroxypropyl methylcellulose.

The solvent may be removed from the solution in step (b) by known methods, for example, distillation, freeze drying or spray drying.

The distillation of the solvent may be carried out at atmospheric pressure or at reduced pressure. The distillation may preferably be carried out until the solvent is almost completely distilled off.

As used herein, "reduced pressure" refers to a pressure of less than 100 mmHg.

The term "Freeze drying" refers to a sublimation process that removes free water in the form of solid. According to another aspect of the present invention, there is provided pharmaceutical compositions comprising a therapeutically effective amount of solid dispersion of doxercalciferol along with a pharmaceutically acceptable carrier, and at least one pharmaceutically acceptable excipient. The solid dispersion of doxercalciferol may preferably be formulated into tablets, capsules, suspensions, dispersions, injectables or other pharmaceutical forms.

According to another aspect of the present invention* there is provided a crystalline Form of doxercalciferol designated as Form HI characterized by peaks in the powder x-ray diffraction spectrum having 2Θ angle positions at about 3.1, 13.9, 15.8, 16.4 and 16.8 ± 0.2 degrees. The powdered x-ray diffractogram (PXRD) of doxercalciferol crystalline Form HI is shown in figure 3.

According to another aspect of the present invention, there is provided a process for the preparation of doxercalciferol crystalline Form HI, which comprises:

a) dissolving doxercalciferol in dimethylformamide;

b) adding water to the solution obtained in step (a);

c) maintaining the reaction mass; and

d) isolating doxercalciferol crystalline Form HI .

Doxercalciferol used in step (a) may preferably be doxercalciferol obtained by the known process.

The step (c) may conveniently be carried out at room temperature.

The doxercalciferol crystalline Form HI may be isolated in step (d) by methods known such as filtration or centrifugation.

According to another aspect of the present invention, there is provided a pharmaceutical composition comprising crystalline Form HI of doxercalciferol and pharmaceutically acceptable excipients, and optionally other therapeutic ingredients. The crystalline Form HI may preferably be formulated into tablets, capsules, suspensions, dispersions, injectables or other pharmaceutical forms.

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

Examples

Example 1 : Preparation of doxercalciferol

(lR,3S,5Z)-5-((8E)-2-((lR,3aS,7aR)-hexahydro-7a-methyl-l-((E ,2R,5R)-5,6- dimethylhept-3-en-2-yl)-lH-inden-4-(7aH)-ylidene)ethylidene) -4- methylenecyclohexane-l,3-diol (16 gm), ethyl acetate (96 ml) and maleic anhydride (2.3 gm) were added and then maintained for 5 hours at room temperature. The solvent was distilled off under vacuum at below 35°C to obtain residual mass and then added methylene chloride (2800 ml). The residual mass was purified by flash chromatography on silica gel using 30% ethyl acetate in hexane (1500 ml) for the elution. There were obtained 4 gm of doxercalciferol.

Example 2:

Preparation of doxercalciferol amorphous Form

Doxercalciferol (10 gm) was dissolved in ethanol (100 ml) under stirring and filtered. The resulting filtrate was subjected to spray drying at 85 to 90°C to provide 7.5 gm of doxercalciferol amorphous Form.

Example 3:

Preparation of doxercalciferol amorphous Form

Doxercalciferol (5 gm) was dissolved in methanol (40 ml) under stirring and filtered. The resulting filtrate was subjected to spray drying at 85 to 90°C to provide 3.5 gm of doxercalciferol amorphous Form.

Example 4:

Preparation of doxercalciferol solid dispersion with povidone

A mixture of doxercalciferol (10 gm) and povidone (10 gm) was dissolved in methanol (300 ml) at room temperature. The contents were heated to 50°C and maintained for 2 hours. The solution was then cooled to room temperature and filtered through celite bed. The solvent was distilled off under reduced pressure at below 55°C and then dried to provide 19.5 gm of doxercalciferol solid dispersion with povidone.

Example 5: Preparation of doxercalciferol solid dispersion with povidone

A mixture of doxercalciferol (5 gm) and povidone (5 gm) was dissolved in ethanol (100 ml) at room temperature. The contents were heated to 50°C and maintained for 2 hours. The solution was then cooled to room temperature and filtered through celite bed. The solvent was distilled off under reduced pressure at below 55°C and then dried to provide 9 gm of doxercalciferol solid dispersion with povidone.

Example 6:

Preparation of doxercalciferol solid dispersion with povidone

Example 4 was repeated using dimethylformamide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with povidone.

Example 7:

Preparation of doxercalciferol solid dispersion with povidone

Example 4 was repeated using dimethylacetamide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with povidone.

Example 8:

Preparation of doxercalciferol solid dispersion with povidone

Example 4 was repeated using dimethyl sulfoxide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with povidone.

Example 9:

Preparation of doxercalciferol solid dispersion with povidone

Example 4 was repeated using methylene chloride solvent instead of methanol solvent to provide doxercalciferol solid dispersion with povidone.

Example 10:

Preparation of doxercalciferol solid dispersion with hydroxypropyl methylcellulose A mixture of doxercalciferol (5 gm) and hydroxypropyl methylcellulose (5 gm) was dissolved in methanol (150 ml) at room temperature. The contents were heated to 45 to 50 C and maintained for 2 hours to obtain a clear solution. The solution was then cooled to room temperature and filtered through celite bed. The solvent was distilled off under reduced pressure at below 55°C and then dried to provide 9 gm of doxercalciferol solid dispersion with hydroxypropyl methylcellulose.

Example 1 1 :

Preparation of doxercalciferol solid dispersion with hydroxypropyl methylcellulose

Example 10 was repeated using dimethylformamide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with hydroxypropyl methylcellulose.

Example 12:

Preparation of doxercalciferol solid dispersion with hydroxypropyl methylcellulose

Example 10 was repeated using dimethylacetamide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with hydroxypropyl methylcellulose.

Example 13:

Preparation of doxercalciferol solid dispersion with hydroxypropyl methylcellulose

Example 10 was repeated using dimethyl sulfoxide e solvent instead of methanol solvent to provide doxercalciferol solid dispersion with hydroxypropyl methylcellulose.

Example 14:

Preparation of doxercalciferol solid dispersion with hydroxypropyl methylcellulose

Example 10 was repeated using methylene chloride solvent instead of methanol solvent to provide doxercalciferol solid dispersion with hydroxypropyl methylcellulose.

Example 15:

Preparation of doxercalciferol solid dispersion with hydroxypropyl methylcellulose

Example 10 was repeated using ethanol solvent instead of methanol solvent to provide doxercalciferol solid dispersion with hydroxypropyl methylcellulose. Example 16:

Preparation of doxercalciferol solid dispersion with copovidone

A mixture of doxercalciferol (5 gm) and copovidone (5 gm) was dissolved in methanol (150 ml) at room temperature. The contents were heated to 45 to 50°C and maintained for 2 hours to obtain a clear solution. The solution was then cooled to room temperature and filtered through celite bed. The solvent was distilled off under reduced pressure at below 55°C and then dried to provide 9 gm of doxercalciferol solid dispersion with copovidone. Example 17:

Preparation of doxercalciferol solid dispersion with copovidone

Example 16 was repeated using ethanol solvent instead of methanol solvent to provide doxercalciferol solid dispersion with copovidone. Example 18:

Preparation of doxercalciferol solid dispersion with copovidone

Example 16 was repeated using dimethyl formamide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with copovidone. Example 19:

Preparation of doxercalciferol solid dispersion with copovidone

Example 16 was repeated using dimethylacetamide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with copovidone. Example 20:

Preparation of doxercalciferol solid dispersion with copovidone

Example 16 was repeated using dimethyl sulfoxide solvent instead of methanol solvent to provide doxercalciferol solid dispersion with copovidone. Example 21 :

Preparation of doxercalciferol solid dispersion with copovidone Example 16 was repeated using ethanol solvent instead of methanol solvent to provide doxercalciferol solid dispersion with copovidone.

Example 22:

Preparation of doxercalciferol solid dispersion with soluplus

A mixture of doxercalciferol (5 gm) and soluplus (5 gm) was dissolved in methanol (150 ml) at room temperature. The contents were heated to 45 to 50°C and maintained for 2 hours to obtain a clear solution. The solution was then cooled to room temperature and filtered through celite bed. The solvent was distilled off under reduced pressure at below 55°C and then dried to provide 9 gm of doxercalciferol solid dispersion with soluplus.

Example 23:

Preparation of doxercalciferol solid dispersion with polyethylene glycol

A mixture of doxercalciferol (5 gm) and polyethylene glycol (5 gm) was dissolved in methanol (150 ml) at room temperature. The contents were heated to 45 to 50°C and maintained for 2 hours to obtain a clear solution. The solution was then cooled to room temperature and filtered through celite bed. The solvent was distilled off under reduced pressure at below 55°C and then dried to provide 9 gm of doxercalciferol solid dispersion with polyethylene glycol.

Example 24:

Preparation of doxercalciferol crystalline Form HI

Doxercalciferol (10 gm) was dissolved in dimethylformamide (40 ml) under stirring to provide a clear solution. To the solution was added water (400 ml) slowly for 20 minutes and maintained for 6 hours at room temperature. The separated solid was filtered and then dried to provide 9 gm of doxercalciferol crystalline Form HI.

Example 25:

Preparation of doxercalciferol crystalline Form HI Doxercalciferol (10 Kg) was dissolved in dimethylformamide (35 L) under stirring to provide a clear solution. To the solution was added water (300 L) slowly for 20 minutes and maintained for 6 hours at room temperature. The separated solid was filtered and then dried to provide 8.9 Kg of doxercalciferol crystalline Form HI .