FIELD OF THE INVENTION
The present invention relates to purification process of Obeticholic acid (I). The present invention further relates to crystalline forms of Obeticholic acid, which are useful to produce highly pure amorphous Obeticholic acid.
BACKGROUND OF THE INVENTION
Obeticholic acid (OCA) is chemically known as 3a,7a-dihydroxy-6a-ethyl-5P-cholan-24-oic acid and it was first approved by the U.S. Food and Drug Administration (FDA) on May 27, 2016 and then approved by European Medicine Agency (EMA) on Dec 12, 2016. It was developed and marketed as Ocaliva® by Intercept Pharms Inc, in the U.S. Obeticholic acid is available as Tablet for oral use, containing 5 mg and 10 mg strength.
OCA is being developed for the treatment of various liver diseases such as non-alcoholic steatohepatitis (NASH) and primary biliary cirrhosis (PBC), also known as primary biliary cholangitis. NASH is the most extreme form of non-alcoholic fatty liver disease (NAFLD) occurring when fat is deposited (steatosis) in the liver due to causes other than excessive alcohol use. PBC is a rare liver disease that primarily results from autoimmune destruction of the bile ducts that transport bile acids out of the liver, resulting in cholestasis which can cause scarring, fibrosis and cirrhosis. As cirrhosis progresses, and the amount of scar tissue in the liver increases, the liver loses its ability to function.
Obeticholic acid is a semi-synthetic bile acid analogue, which is used as a drug to treat primary biliary cholangitis (PBC), and is undergoing development for several other liver diseases and related disorders. It is an analog of the naturally occurring bile acid chenodeoxycholic acid (CDCA) and agonist of the farnesoid X receptor and it's represented by formula (I).

The compound OCA is known in the art (e.g. from WO 02/072598). The OCA currently being developed as an active pharmaceutical ingredient is a non-crystalline solid, as the many attempts made in the art to find a crystalline form thereof suitable for commercial purposes have failed so far.
WO 2013/192097 (Example 1, step 6) discloses or explained that crystalline Obeticholic acid could readily be isolated on large scale when n-butyl acetate was used as the crystallization solvent. This crystalline Obeticholic acid was determined to be consistent with Form C from the initial crystallization and polymorph study; Form C being characterized by an X-ray diffraction pattern including characteristic peaks at about 4.2, 6.4, 9.5, 12.5, and 16.7 degrees 2-Theta. This patent suggests that in a subsequent step, said Form C can be readily converted to amorphous Obeticholic acid.
However, the use of n-butyl acetate as crystallization solvent bears significant disadvantages. For example, in the course of a multistep synthesis it may not be possible to perform each and every reaction in n-butyl-acetate. Solvent changes are then required from one step to the next. Ideally, in the course of a multistep synthesis, organic solvents are changed as rarely as possible, especially on an industrial scale, since each solvent change is connected with additional steps such as extractions, distillations, vessel changes, which render an industrial process time-consuming and uneconomical. In addition, n-butyl acetate possesses a rather high boiling temperature of about 127°C, which requires high energy input in process steps such as distillations and drying.
WO 2013/192097 discloses or explained in order to identify as many relevant crystalline forms as possible, exposing OCA to a large range of solvents are used for crystallization process. Five different solid forms of Obeticholic acid are observed, i.e., Three forms A, C, and D of

Obeticholic acid were mixed hydrates/solvates containing 0.25 mole equivalents of water and varying amounts of a range of organic solvents. However, these solvated forms were not suitable for further development as a pharmaceutical ingredient due to their low melting temperatures and high solvent content. The two remaining forms G and F had higher melting temperatures, but Form G could not be reproduced on scale-up, nor repeated despite many attempts. The non-solvated Form F required extensive recrystallization procedures and the use of nitromethane, which is a toxic solvent and may detonate if sensitized by amines, alkalis, strong acids, or high temperatures or adiabatic compression. Therefore, Forms G and F are also unsuitable for development of this drug on a commercial scale.
EP 3293196 A discloses process for the purification of crystalline Obeticholic acid by using ethyl acetate, isopropyl acetate, isobutyl acetate, ethyl propionate as a solvent.
The main drawbacks of the prior art process are low yields and purity as a n-butyl acetate and isopropyl acetate are used as a solvent, which has an extremely high boiling point. Therefore, its handling in a larger scale represents a certain risk. Hence, it is not recommendable for industrial process.
Hence, there is an unmet need for an economical process of preparing crystalline OCA, which is useful to produce highly pure amorphous OCA. Accordingly, it is an object of the present invention to provide a process for preparing crystalline OCA, in particular a process which employs organic solvents having a lower boiling temperature than n-butyl acetate and isopropyl acetate.
In view of the foregoing, the present inventors have result of extensive studies and found that the dichloromethane as a purification solvent, which is not carried in prior arts. Hence, the present inventors are concluded that the usage of dichloromethane reduces the reaction time and simultaneously it produces high yield and purity for the preparation of Crystalline Obtecholic acid, further it converts into amorphous Obtecholic acid with high purity.
SUMMARY OF THE INVENTION
The present invention relates to a purification process of Obeticholic acid

In one aspect of the present invention, provides a purification process of Obeticholic acid (I), comprising the steps of:
a) dissolving crude obeticholic acid in a dichloromethane;
b) stir the obtained suspension a), heating at about 40-45°C for 30-45 minutes,
c) cooling the solution obtained in step b) at 0-5°C, and
d) crystallizing obeticholic acid from the solution obtained in step (c).
In another aspect of the present invention provides process for the preparation pure amorphous Obeticholic acid from crystalline Obeticholic acid.
In yet another aspect of the present invention provides process for the preparation of amorphous Obeticholic acid, which is comprising the steps of;
a) dissolving crystalline Obeticholic acid in a sodium hydroxide solution,
b) stir the solution to obtain sodium salt of Obeticholic acid,
c) adding the aqueous solution of orthophosphoric acid to step b), and
d) isolating an amorphous form of Obeticholic acid.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the XRPD diffractogram of crystalline obeticholic acid Figure 2 shows the XRPD diffractogram of amorphous obeticholic acid.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to purification process of Obeticholic acid (I). The present invention further relates to crystalline forms of Obeticholic acid, which are useful to produce highly pure amorphous Obeticholic acid.
In one embodiment of the present invention, provides a purification process of Obeticholic acid (I), comprising the steps of:

a) dissolving crude obeticholic acid in a dichloromethane;
b) stir the obtained suspension a), heating at about 40-45°C for 30-45 minutes,
c) cooling the solution obtained in step b) at 0-5°C, and
d) crystallizing obeticholic acid from the solution obtained in step (c).
According to the embodiment of present invention, wherein the crude Obeticholic acid in dichloromethane, stir for 30 minutes. The obtained solution was allow to heat at 40-60°C for 20 to 50 minutes. Preferably 40 to 45°C for 30-45 minutes. The reaction mixture is cool at 0-5°C and stir for 1-2 hours. The reaction mixture was filter and dried to obtained pure crystalline Obeticholic acid.
According to an embodiment of the present invention, the crystalline form of Obeticholic acid is characterized by it XRPD having peaks at 6.43, 8.30, 9.55, 11.19, 12.55, 14.23, 15.84, 16.83, 18.64, 20.94 and 44.0, degrees of two theta as illustrated in fig.l.
In another embodiment of the present invention provides process for the preparation pure amorphous Obeticholic acid from crystalline Obeticholic acid.
In yet embodiment of the present invention provides process for the preparation of amorphous Obeticholic acid, which is comprising the steps of;
a) dissolving crystalline Obeticholic acid in a sodium hydroxide solution,
b) stir the solution to obtain sodium salt of Obeticholic acid,
c) adding the aqueous solution of orthophosphoric acid to step b), and
d) isolating an amorphous form of Obeticholic acid.
According to the embodiment of present invention, wherein the crystalline Obeticholic acid in a freshly prepared sodium hydroxide solution, stir for 30-45 minutes to obtained sodium salt of Obeticholic acid. Adding the solution of orthophosphoric acid in water to the obtained solution sodium salt of Obeticholic acid at 25-30°C and stir for 60-90 minutes. The obtained reaction mixture was filtered and washed with water and dried at 40-45°C for 12-16 hours to get 99.9% pure Amorphous Obeticholic acid.

According to the embodiment of present invention, provides process for the preparation pure amorphous Obeticholic acid from crystalline Obeticholic acid. The amorphous form of Obeticholic acid is characterized by it XRPD as illustrated in fig.2. Advantages of the present invention:
i) filtration is easy, there is no frothing was observed (less time required),
ii) filtrate is clear solution, and
iii) residue on ignition (ROI) is less than 0.1% (as per ICH guidelines).
The process details of the invention are provided in the examples given below, which are provided by way of illustration only and therefore should not be construed to limit the scope of the invention.
EXAMPLES
Purification of Crystalline Obeticholic acid:
Example 1:
To a solution of crude 100 g Obeticholic acid (HPLC purity- 94.08%) in dichloromethane (1000 mL), stir for 30 minutes and filter through micron filter. The mixture was heat at 40-45°C for 30-45 minutes and distilled the dichloromethane half volume, cool the mixture at 0-5°C and stir for 1-2 hours. The resultant solid was filtered,washed with dichloromethane (100 mL) and dried at 40-50°C for 8-10 hours to obtain pure crystalline Obeticholic acid.
Yield: 80 g
HPLC purity: 99.06%
Example-2:
To a solution of crude 250 g Obeticholic acid (HPLC purity 94.08%) in dichloromethane (5625 mL), stir for 30 minutes and filter through micron filter. The mixture was heat at 40-45°C for 30-45 minutes and distilled the dichloromethane -60%, cool the mixture at 25-30°C and stir for 30 minutes, further cooled to 0-5°C. The solid precipitation was observed and stir for 1-2 hours,

the resultant solid was filtered and washed with dichloromethane (900 mL) and dried at 40-50°C for 6-8 hours to obtain pure crystalline Obeticholic acid.
Yield: 75 g
HPLC purity: 99.34%
Example-3:
To a solution of crude Obeticholic acid (100 g) in dichloromethane (2250 mL), stir for 30 minutes and filter through micron filter. The reaction mixture was heat at 40-45°C for 30-45 minutes and distilled the dichloromethane -60%, cool the mixture at 25-30°C, stir for 30 minutes and further cooled to 0-5°C. The solid precipitation was observed and stir for 1-2 hours, filter the solid,wash with dichloromethane (180 mL) and dried under vacuum for 1-2 hours. The unloaded material was transfer into RBF, add dichloromethane (630 mL), reflux for 30-45 min, cool the mixture at 20-25°C and stir for 1-2 hours. The resultant solid was filtered,washed with dichloromethane (70 mL) and dried under vacuum oven at 40-45°C for 6-8 hours to give the pure crystalline form of Obeticholic acid.
Yield: 70 g
HPLC purity: 99.92%
^NMRinCDCb: 5= 11.955 (s, 1H), 4.292 (s, 1H), 4.035-4.047 (d,j = 4.8 Hz, 1H), 3.482 (s, 1H), 3.114 (s, 1H), 0.793-2.254 (m, 36 H), 0.592 (s, 3H). 13C NMR in CDC13: 174.89, 70.64, 68.44, 55.54, 50.10, 45.33, 42.03, 41.32, 39.08, 38.80, 35.56, 35.19, 34.98, 33.54, 32.65, 30.75, 30.44, 27.87, 23.09, 22.20, 20.44, 18.16, 11.71.Mass m/z: C26H44O4 Calculated mass m/z = 420.32 Observed mass 419.49 [M-H]~
Preparation of amorphous Obeticholic acid
Example-1:
Crystalline Obeticholic acid (250 g) was dissolved in freshly prepared sodium hydroxide solution (26.15 g of sodium hydroxide in 2000 mL of water) at 25-30°C and stir for 30-45 min to get clear solution), filter the solution through micron filter and wash with water (250 mL) to obtain sodium salt of Obeticholic acid solution. The resultant Obeticholic acid solution was slowly

added to aqueous orthophosphoric acid {orthophosphoric acid in 3750 mL water) at 25-30°C and stir for 60-90 minutes. The obtain solid was filtered and washed with water (2500 mL), suck dry the material under vacuum for 2 hours and further dried under oven at 40-45°C for 12-16 hours to give pure Obeticholic acid amorphous.
Yield: 95 g
HPLC purity: 99.90%
Example-2:
Crystalline Obeticholic acid (100 g) was dissolved in freshly prepared sodium hydroxide solution (10.46 g of sodium hydroxide in 800 mL of water) at 25-30°C and stir for 30-45 min (Till clear solution), filter the solution through micron filter and wash with water (100 mL), transfer the filtrate in RBF, followed by addition of aqueous orthophosphoric acid solution till the reaction mixture pH 1-2 and stir for 60-90 minutes. The resultant solid was filtered, washed with water (1000 mL) and dried under vacuum at 40-45°C for 10-12 hours to give a high purity of title compound.
Yield: 90 g
HPLC purity: 99.89%
Example-3:
Crystalline Obeticholic acid (100 g) was dissolved in freshly prepared sodium hydroxide solution (10.46 g of sodium hydroxide in 800 mL of water) at 25-30°C and stir for 30-45 min (Till clear solution), filter the solution through micron filter and wash with water (100 mL), transfer the filtrate in RBF and add IN hydrochloride solution till pH 1-3 and stir for 60-90 minutes. The resultant solid was filtered,washed with water (1000 mL), suck dry for 2 hours and further dried under vacuum at 40-45°C for 10-12 hours to get title compound.
Yield: 80 g
HPLC purity: 99.85%

1. A purification process for the preparation of crystalline Obeticholic acid (I) which is
comprising the steps of;
a) dissolving crude Obeticholic acid in a dichloromethane;
b) stir the obtained suspension a), heating at about 40-45°C for 30-45 minutes,
c) cooling the solution obtained in step b) at 0-5°C, and
d) crystallizing obeticholic acid from the solution obtained in step (c).

2. The process as claimed in claim 1, crystalline form of Obeticholic acid is characterized by it XRPD having peaks at 6.43, 8.30, 9.55, 11.19, 12.55, 14.23, 15.84, 16.83, 18.64, 20.94 and 44.0, degrees of two theta as illustrated in fig.l.
3. A process for the preparation of amorphous Obeticholic acid, which is comprising the steps of;

a) dissolving crystalline Obeticholic acid in a sodium hydroxide solution,
b) stir the solution to obtain sodium salt of Obeticholic acid,
c) adding the aqueous solution of orthophosphoric acid to step b), and
d) isolating an amorphous form of Obeticholic acid.

4. The process as claimed in claim 3, Amorphous form of Obeticholic acid is characterized by it XRPD as illustrated in fig. 2.
5. The process as claimed in claim 1 and 3, purity of Obeticholic acid is 99.9%