FIELD OF THE INVENTION

The present invention relates to an improved process for the purification of Ursodeoxycholic acid (Ursodiol) of Formula (I).

BACKGROUND OF THE INVENTION

Ursodeoxycholic acid is a bile acid, and is chemically known as 3a,7p-dihydroxy-5P-cholan-24-oic acid (I). Ursodeoxycholic acid is an anticholelithogenic, which suppresses hepatic synthesis and secretion of cholesterol and also inhibits intestinal absorption of cholesterol. Ursodeoxycholic acid is marketed under the trade name Actigall®. It has been approved for the treatment of prevention of gallstone formation and primary biliary cirrhosis.

Ursodeoxycholic acid is disclosed in Journal of Biochemistry (1927), 7, 505-517. In this referenced article, Ursodeoxycholic acid is prepared by reacting Chenodeoxycholic acid (II) with barium salt to produce Chenodeoxycholic acid barium salt (III), which on hydrolysis to produce Chenodeoxycholic acid hemihydrate (IV), which is further reacted with acid to produce crude Ursodeoxycholic acid. Crystallization of crude Ursodeoxycholic acid from dilute alcohol or acetone to produce Ursodeoxycholic acid (I).
The process as shown below:

US 4,282,161 discloses a process for the purification of Ursodeoxycholic acid (I), by treating crude Ursodeoxycholic acid with methanol to produce Ursodeoxycholic acid methyl ester, which is crystallized by ethyl acetate, followed by saponification using alkali base to produce Ursodeoxycholic acid alkali metal salt (V). Further, the compound (V) is treated with an acid in the presence of chloroform to produce crystalline Ursodeoxycholic acid (I). The process as shown below:

The above purification processes involve esterification, saponification and hydrolysis steps. The number of steps is more in a chemical process means the lowering of the overall yield and the time cycle of the production is more. This does not make the suitable chemical process. Further, the use of huge volume of chloroform is not suitable on commercial scale.

Lipids (1981), 16(11), 863-865 reported the purification of crude Ursodeoxycholic acid by crystallizing from ethyl acetate to produce pure Ursodeoxycholic acid (I).
The disadvantage with the above purification process is that it does not eliminate Chenodeoxycholic acid impurity, which is formed during reduction of 3a-hydroxy-7-oxo cholanic acid (VII).

JP 58-146597 A discloses a process for the purification of Ursodeoxycholic acid, by treating crude Ursodeoxycholic acid with N-alkylmorpholines to produce corresponding N-alkylmorpholine salt, which is further hydrolyzed to produce Ursodeoxycholic acid.

Further, JP 3810610 B2 discloses the purification of Ursodeoxycholic acid by treating crude Ursodeoxycholic acid with triethylamine or 4-dimethylaminopyridine to produce corresponding triethylamine and 4-dimethylaminopyridine salts of Ursodeoxycholic acid which are further hydrolyzed to produce Ursodeoxycholic acid.

The major disadvantage with the above processes is that achieving pharmaceutically acceptable limits of triethylamine and DMAP are difficult.

Hence, there is a need to develop a purification process, which provides isolation of pure Ursodeoxycholic acid, which reduces the un-required impurities with less no of steps as I well as with higher yield.

The present invention directed to a process, wherein purification of Ursodeoxycholic acid via its secondary amine salt.

Further, the present invention also directed to a crystallization of Ursodeoxycholic acid from a solvent selected from ketone, ester and a mixture thereof to produce pure pharmaceutically acceptable grade Ursodeoxycholic acid.

OBJECTIVE OF THE INVENTION

The main objective the present invention is to provide a simple and effective process for the purification of Ursodeoxycholic acid (I) with high purity and good yields on a commercial scale.

SUMMARY OF THE INVENTION

The present invention provides an improved process for the purification of Ursodeoxycholic acid of Formula I, which comprises:

(i) treating crude Ursodeoxycholic acid with a secondary amine base in a solvent to produce an amine salt of Ursodeoxycholic acid (VI),
Wherein, M is a secondary amine, selected from dimethylamine, diethylamine, N,N- diisopropylamine and mixture thereof;
(ii) optionally purifying the amine salt of formula (VI) from a solvent;
(iii) treating the amine salt of step (i) or step (ii) with an inorganic base, followed by treating with an acid to produce Ursodeoxycholic acid, (iv) optionally crystallizing Ursodeoxycholic acid to produce pure Ursodeoxycholic acid (I).

In another embodiment, the present invention provides a process for the crystallization of Ursodeoxycholic acid (I), which comprises:

(i) providing a solution of Ursodeoxycholic acid in a solvent selected from ester, ketone and mixture thereof;
(ii) crystallizing Ursodeoxycholic acid to produce pure Ursodeoxycholic acid (I).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for the purification of Ursodeoxycholic acid of formula (I).

The process comprises, treating crude Ursodeoxycholic acid with a secondary amine base in a solvent to produce an amine salt of Ursodeoxycholic acid (VI).
The secondary amine used is selected from dimethylamine, diethylamine, N,N-diisopropylamine and the mixture thereof; The solvent used is selected from ethers such as diethyl ether, tetrahydrofuran, dioxane; halogenated hydrocarbon solvents such as methylene chloride, dichloro ethane, chloroform, esters such as ethyl acetate, butyl acetate, isopropyl acetate or mixture thereof. The reaction is performed at a temperature ranging from 0°C to about 70°C based on the solvent used for the reaction. The sufficient -period of time necessary for obtaining compound (VI) will depend on the parameters of the reaction. Preferably, maintaining the reaction mixture for 1 to 3 hours.

The amine salt of Ursodeoxycholic acid (VI) obtained by the above process is treated with a aqueous inorganic base in a solvent and pH of the resulting reaction mass is adjusted to 12 to 12.5. The resulting reaction mass is washed with a solvent, followed by treating the aqueous layer containing Ursodeoxycholic acid with an acid to adjust the pH of the reaction mass to 2-3, then cooled the reaction mass to 5 to 30°C. Pure Ursodeoxycholic acid precipitated is isolated by filtration, followed by drying the product. The inorganic base used is selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate; The solvent used for washing is selected from acetonitrile, cyclic or acyclic alkanes such as hexane, heptane, methylcyclohexane, aromatic solvents such as toluene, halogenated solvents such as dichloromethane (MDC), dichloroethane, chloroform, esters such as ethyl acetate, butyl acetate, isopropyl acetate or ethers such as diethyl ether, tetrahydrofuran or tert-butyl methyl ether and/or mixture thereof; The acid used is selected from hydrochloric acid, hydrobromic acid, acetic acid etc.

In another embodiment, the present invention provides a process for the crystallization of Ursodeoxycholic acid (I), which comprises, providing a solution of Ursodeoxycholic acid in ester solvent; adding ketone solvent to the above solution; crystallizing Ursodeoxycholic acid to produce pure Ursodeoxycholic acid (I).

The ester solvent used is selected from ethyl acetate, butyl acetate, isopropyl acetate, and mixture thereof; ketone solvent used is selected from acetone, ethyl methyl ketone and methyl isobutyl ketone and mixture thereof.

Crude Ursodeoxycholic acid used in the present invention is prepared by reacting Chenodeoxycholic acid (II) with alkali halide in the presence of a solvent and phase transfer catalyst to produce 3a-hydroxy-7-oxo cholanic acid (VII), which is further reduced in the presence of hydrogen and catalyst in a solvent to produce crude Ursodiol.

The alkali metal halide used is selected from sodium chloride, sodium bromide, potassium chloride, potassium bromide or mixture thereof; the solvent used is selected from methanol, ethanol, isopropanol, butanol or mixture thereof; The phase transfer catalyst (PTC) used is selected from tetrabutylammonium bromide, tetrabutylammonium iodide, tetrapropylammonium trifluoromethane sulfonate, tetraphenylphosphonium hexafluoroantimonate, acetylpyridinium bromide, triphenylmethyl triphenylphosponium chloride or mixture thereof. Hydrogenation catalyst used is selected from Raney nickel, Pd/C, Pd(OH)2/C.

The following examples illustrate the nature of the invention and are provided for illustrative purposes only and should not be construed to limit the scope of the invention.

EXAMPLES

EXAMPLE - 1A

PREPARATION OF CRUDE 3o>HYDROXY-7-OXO-5P-CHOLAN-24-OIC ACID

(7-KCA): Stage-I

Chenodeoxycholic acid (200 g; CDC A) was dissolved in a mixture of ethyl acetate (1.0 It), methanol (640 ml), DM water (52 ml), sodium bromide (2.6 g) and tetrabutyl ammonium bromide (0.5 g) and cooled to -20°C. Acetic acid (400 ml) followed by aqueous sodium hypochlorite solution (5.25% w/w, 795 g) were added to the solution at -20°C to -10°C . The reaction mass was stirred at -10°C for 2h and treated with 5% w/v aqueous sodium metabisulfite solution (200 ml). Mixture of ethyl acetate and methanol were distilled under reduced pressure at below 35°C. To the concentrated reaction mass, DM water (2.0 It) was added and pH was adjusted to 1.7 ± 0.1 with dilute hydrochloric acid at 0-5°C. The solid was filtered, washed with DM water and dried at 50-60°C to yield 188 g of crude 3a-hydroxy-7-oxo-5p-cholan-24-oic acid (HPLC Purity: 92.58%).

EXAMPLE - IB:

PURIFICATION OF CRUDE 3a-HYDROXY-7-OXO-5p-CHOLAN-24-OIC ACID

(7-KCA):Stage-I

3a-Hydroxy-7-oxo-5p-cholan-24-oic acid (175 g), obtained in Example - 1A, was suspended in a mixture of ethyl acetate (525 ml), methanol (52.5 ml) and DM water (52.5 ml) and heated to 70°C. The slurry was stirred for 1 h at 70°C and then cooled to 0-5°C. The solid was filtered, washed with ethyl acetate and dried at 55-60°C to Yield 146.5 g of 3a-hydroxy-7-oxo-5p-cholan-24-oic acid (HPLC Purity: 98.67%).

EXAMPLE - 2;

PREPARATION OF CRUDE URSODIOL (UDCA): Stage -II

Raney Nickel (20 ml) suspension in isopropanol was added to a mixture of 3a-hydroxy-7-oxo-5p-cholan-24-oic acid (40 g), isopropyl alcohol (1.2 It) and potassium tertiary butoxide (25.19 g) and hydrogenated at 3-5 kg / cm2 hydrogen pressure at 50°C for 18 h. The reaction mass was cooled to 25°C, filtered and concentrated under reduced pressure at below 50°C. The concentrated mass was dissolved in DM water (400 ml) and pH was adjusted to 2-2.2 with dilute hydrochloric acid at 20-25°C. The solid was filtered, washed with DM water and dried at 55-60°C to yield 38 g of crude Ursodeoxycholic acid (UDCA). HPLC purity: UDCA: 95.65%; CDCA: 3.44%; 7-KCA: 0.10%.

EXAMPLE - 3:

PREPARATION OF URSODEOXYCHOLIC ACID N,N-DIISOPROPYL AMINE

SALT: Stage-Ill

Crude Ursodeoxycholic acid (105 g) having HPLC purity of 95.7% of Ursodeoxycholic acid, 3.39% of chenodeoxycholic acid was suspended in tetrahydrofuran (1.05 It) and heated to 55°C. N,N-diisopropyl amine (13.5 g) was added to the solution and stirred for 1 h at 65°C. The resulting slurry was cooled to 0-5°C, filtered and washed with tetrahydrofuran to yield wet Ursodeoxycholic acid N,N-diisopropyl amine salt.

The wet Ursodeoxycholic acid N,N-diisopropyl amine salt was suspended in tetrahydrofuran (892 ml) and stirred for lh at 65°C. The slurry was cooled to 0-5°C, filtered, washed with tetrahydrofuran and dried at 55-60°C to yield 93 g of pure Ursodeoxycholic acid (UDCA) as N,N-diisopropyl amine salt. HPLC Purity as UDCA: UDCA: 99.87%; CDCA: 0.13; 7-KCA: nil.

EXAMPLE - 4:

PREPARTION OF URSODEOXYCHOLIC ACID N,N-DIISOPROPYL AMINE
SALT: Stage-Ill

Crude Ursodeoxycholic acid (60 g) having HPLC purity of 86.84% of Ursodeoxycholic acid, 12.3%) of chenodeoxycholic acid was suspended in tetrahydrofuran (600 ml) and heated to 65°C. N,N-diisopropyl amine (7.72 g) was added to the suspension and stirred for 1 h at 65°C. The resulting slurry was cooled to 0-5°C, filtered and washed with tetrahydrofuran to yield wet Ursodeoxycholic acid N,N-diisopropyl amine salt.

The wet Ursodeoxycholic acid N,N-Diisopropyl amine salt was suspended in tetrahydrofuran (530 ml) and stirred for lh at 65°C. The slurry was cooled to 0-5°C, filtered, washed with tetrahydrofuran and dried at 55-60°C to yield 46.7 g of pure Ursodeoxycholic acid (UDCA) as N,N-diisopropyl amine salt. HPLC Purity as UDCA: UDCA: 99.5%; CDCA: 0.39%; 7-KCA: 0.06%.
EXAMPLE - 5:

PREPARATION OF URSODEOXYCHOLIC ACID: (Stage-IV)

Ursodeoxycholic acid N,N-diisopropylamine salt (70 g) was suspended in DM water (1.4 It) and pH was adjusted to 12-12.5 with 20% v//w aqueous sodium hydroxide solution at 25-30°C. The solution was washed with methylene chloride (2 x 140 ml) and acidified with dilute hydrochloric acid to pH 2-2.5 at 45-50°C. The slurry was cooled to 20-25°C, filtered, washed with DM water and dried at 55-60°C under reduced pressure to yield 58.4 g of pure Ursodeoxycholic acid.

HPLC Purity of Ursodiol (UDCA): UDCA: 99.84%; CDCA: 0.11 %; 7-KCA: nil%.

WE CLAIM:

1. A process for the purification of Ursodeoxycholic acid of Formula I, which comprises:

(i) treating crude Ursodeoxycholic acid with a secondary amine base in a solvent to produce an amine salt of Ursodeoxycholic acid (VI),
Wherein, M is a secondary amine, selected from dimethylamine, diethylamine, N,N-diisopropylamine and mixture thereof;
(ii) optionally purifying the amine salt of formula (VI) from a solvent;
(iii) treating the amine salt of step (i) or step (ii) with an inorganic base, followed by treating with an acid to produce Ursodeoxycholic acid, (iv) optionally crystallizing Ursodeoxycholic acid to produce pure Ursodeoxycholic acid (I).

2. A process according to claim 1 wherein the solvent used in step (i) is selected from ethers such as diethyl ether, tetrahydrofuran, dioxane; halogenated hydrocarbon solvents such as methylene chloride, dichloro ethane, chloroform, esters such as ethyl acetate, butyl acetate, isopropyl acetate or mixture thereof.

3. A process according to claim 1 wherein the solvent used in step (ii) is selected from acetonitrile, cyclic or acyclic alkanes such as hexane, heptane, methylcyclohexane, aromatic solvents such as toluene, halogenated solvents such as dichloromethane (MDC), dichloroethane, chloroform, esters such as ethyl acetate, butyl acetate, isopropyl acetate or ethers such as diethyl ether, tetrahydrofuran or tert-butyl methyl ether and/or mixture thereof.

4. A process according to claim 1 wherein the inorganic base used in step (iii) is selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate.

5. A process according to claim 1 wherein acid used in step (iii) is selected from hydrochloric acid, hydrobromic acid, acetic acid or mixture thereof.

6. A process for the crystallization of Ursodeoxycholic acid (I), which comprises: (i) providing a solution of Ursodeoxycholic acid in a solvent;
(ii) crystallizing Ursodeoxycholic acid to produce pure Ursodeoxycholic acid
(I).

7. A process according to claim 6 wherein the solvent is selected from ester, ketone and mixture thereof.

8. A process according to claim 7, wherein ester solvent used is selected from ethyl acetate, butyl acetate, isopropyl acetate, and mixture thereof.

9. A process according to claim 7, wherein ketone solvent used is selected from acetone, ethyl methyl ketone, methyl isobutyl ketone and mixture thereof.