CLIAMS:
1. A process for the purification of regadenoson, compound of formula I:

Formula I
, which comprises:
a) providing a solution of regadenoson in dimethyl sulfoxide;
b) adding a ketone into the solution of step a) ; and
c) recovering the solid from the step b) with purity greater than or equal to 99.5%.

2. The process of claim 1, wherein the solution of step a) is heated to about 45 to about 50 °C.

3. The process of claim 1, wherein the ketone is selected from acetone, methyl ethyl ketone, acetophenone, ethyl isopropyl ketone, methyl isobutyl ketone, methyl isopropyl ketone and butanone.

4. The process of claim 1, wherein the ketone is acetone.

5. The process of claim 1, wherein the pure regadenoson contains less than 0.15 of pyrazole ester impurity.

6. The process of claim 1, wherein the pure regadenoson contains less than 0.15% of pyrazole acid impurity.

7. The process of claim 1, wherein purity greater than 99.5% is 99.8 % of regadenoson by HPLC.
,TagSPECI:Field of Invention

The present invention provides a process for the purification of regadenoson using dimethyl sulfoxide and ketone solvent at a specific temperature.

Background of the invention

Regadenoson is chemically known as adenosine, 2-[4-[(methylamino)carbonyl]-1H-pyrazol-1-yl]-, monohydrate. Its structural formula is depicted as Formula I:

Formula I
Regadenoson is a selective A 2 A-adenosine receptor agonist that is a coronary vasodilator. It is currently marketed in the form of a monohydrate as a pharmacologic stress agent indicated for radionuclide myocardial perfusion imaging (MPI) in patients unable to undergo adequate exercise stress.

U.S. Patent Nos. 6,403,567 and 7,183,264 discloses Regadenoson and synthesis of regadenoson.

U.S. Patent No. 7,732,595 & PCT application No. 2008/143667’ discloses a process for the preparation of regadenoson monohydrate and purification thereof. The purification process involves dissolution of regadenoson in dimethyl sulfoxide and addition of the resultant solution into water while maintaining temperature of 83 °C to precipitate the solid. However, it has been found that the prior art process is not effective to remove the impurities completely and to provide highly pure compound.

PCT application No. 2012/149196 discloses a process for the preparation of regadenoson and its purification. The purification process involves use of tedious reverse phase chromatography with the elute of water and methanol.

PCT application No. 2013/026424 discloses a process for the preparation of regadenoson having purity 99.9% (HPLC), which involves reaction of 2-(4-methoxycarbonylpyrazol-1-yl)adenosine with 40% methylamine in presence of methanol for a period of above 18 hours, and then subjected for isolation of solid from the solution by concentration slightly followed by the addition of water. However, the inventors of the present invention found that the process of the WO ‘424 is not commercially viable and involves longer hours.

Further, impurities in any active pharmaceutical ingredient are undesirable, and, in extreme cases, might even be harmful to a patient. Furthermore, the undesired impurities may reduce the availability of the API in the pharmaceutical composition and can decrease the stability of a pharmaceutical dosage form.

Therefore, there is a need to develop a simple, industrially feasible and robust process for purification of crude regadenoson to provide highly pure compound.

Summary of the Invention

Surprisingly, the inventors has now been found certain reaction conditions, which provides desired high purity for regadenoson, for example, use of ketone solvent and a temperature of about 25 to about 60 °C.

In an aspect of the present invention provides a process for the purification of regadenoson, compound of formula I:

Formula I
, which comprises:
a) providing a solution of regadenoson in dimethyl sulfoxide;
b) adding a ketone into the solution of step a); and
c) recovering the solid from the step b) with purity greater than or equal to 99.5%.

In another aspect, the present invention is to provide regadenoson with purity greater than 99.5% and impurity each less than 0.1%. The impurity is one or more of pyrazole ester and pyrazole acid.

The resultant pure regadenoson is useful for the preparation of pharmaceutical composition in combination with at least one carrier/excipient.

Description of the Invention

The term “pure” as used herein, unless otherwise defined, refers to regadenoson or its pharmaceutically acceptable salt that has purity of about 99.5 % or above.

The starting material, crude regadenoson contains purity less than or equal to 99% or less than or equal to 98% or about 95% and single largest unknown impurity about 1.0% or less than or equal to 0.5% or less than or equal to 0.2% for purification as used herein may be free base or its salt.

The salt as used herein, unless otherwise defined, refers to inorganic or organic salt. Inorganic salt may include hydrochloride, hydrobromide and the like; organic slat may include acetate, mesylate, tosylate and the like.

In an aspect of the present invention provides a process for the purification of regadenoson, compound of formula I:

Formula I
, which comprises:
a) providing a solution of regadenoson in dimethyl sulfoxide;
b) adding a ketone into the solution of step a) ; and
c) recovering the solid from the step b) with purity greater than or equal to 99.5%.

Regadenoson (or its salt) may be obtained using any of the processes described in the art, for example, 6,403,567.

The step a) involves providing a solution of regadenoson in dimethyl sulfoxide.

The solution of regadenoson may be obtained by the dissolution of regadenoson in a dimethyl sulfoxide or it may be obtained from the reaction directly. Any form of regadenoson, such as anhydrous crystalline, amorphous, crystalline hydrate, or mixtures of amorphous and crystalline forms of regadenoson is acceptable for forming the solution.

The concentration of regadenoson in the solution is not critical, but the quantity of solvent employed is usually kept to a minimum so as to avoid excessive product losses during the crystallization of solid. The concentration of regadenoson in the solution may range from about 0.2 to about 0.4 g/ml in the solvent.

Regadenoson is mixed with sufficient amount of the solvent to provide solution at or below the reflux temperature of the solvent. Optionally, the solution obtained above can be filtered to remove the undissolved particles followed by further processes.

The solution can be filtered by passing through paper, glass fiber, or other membrane material, or a clarifying agent such as celite. Depending upon the equipment used and the concentration and temperature of the solution, the filtration apparatus may need to be preheated to avoid premature crystallization

The step b) involves adding a ketone into the solution of step a).

The resultant solution of step a) is heated to a temperature of about 25 to about 60 °C or about 45 to about 50 °C.

The solvent, ketone, is added or charged to the reaction solution while maintaining the temperature not less than 40 °C. The ketone solvent used but not limited to acetone, methyl ethyl ketone, acetophenone, ethyl isopropyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, butanone, and the like. The quantity of ketone may range from about 0.02 to about 0.1 g/ml or about 0.05 g/ml.

The reaction mixture may be stirred for about 10 minutes or more and then it may be cooled to below 25 °C or to below 15 °C to improve the quality and quantity of the precipitated solid.

The step c) involves recovering the solid from the step b) with purity greater than or equal to 99.5%.

The resultant solid of step b) may be separated / recovered by using suitable techniques such as filtration by gravity or by suction, centrifugation, decantation, and the like. After separation, the solid may optionally be washed with suitable solvent such as ketone.

The wet solid may optionally be further dried. Drying can be suitably carried out in a tray dryer, vacuum oven, air oven, fluidized bed drier, spin flash dryer, flash dryer and the like. The drying may be carried out at temperatures of about 35 °C. to about 60° C or of about 40 to about 45 °C. The drying can be carried out for any time periods necessary for obtaining a desired weight consistent, such as from about 1 to about 8 hours, or longer.

Regadenoson obtained from the present invention contains purity greater than or equal to 99.8% by HPLC.

In another aspect, the present invention is to provide regadenoson with purity greater than 99.5% and impurity each less than 0.1%. The impurity is one or more of pyrazole ester and pyrazole acid.

The present purification provides high purity Regadenoson from the crude Regadenoson and the process removes known as well as unknown impurities less than or equal to 0.1%.

The resultant regadenoson of the present invention may be used for the preparation of pharmaceutical composition in combination with one or more carriers or excipients.

The present invention is further illustrated by the following example, which does not limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present application.

EXAMPLES

Reference Example:
Purification of regadenoson according to the prior art:

Crude Regadenoson (10 gm; 98.9%) was dissolved in N,N-dimethylsulfoxide (30 ml) under stirring, and filtered through Whatman paper. To a separate RBF, 100 ml water was charged. The clear filtrate was added to water slowly under continuous stirring at ambient temperature of 25-35 °C. The suspension was stirred for 30 minutes, and then filtered under vacuum through Whatman paper. The wet cake was washed with water (200 ml) and sucked well. The wet cake was then transferred to a clean RBF containing water (150 ml), and stirred for 30 minutes. The slurry was then filtered under vacuum and washed with water (100 ml), followed by ethanol (100 ml) and sucked well. The resulting solid was dried in vacuum oven at 40-45 °C for 8 hours and submitted for HPLC purity.

HPLC purity: 99.29%, Pyrazole ester: 0.16%, Pyrazole acid impurity: 0.13%, Single Largest Unknown Impurity: 0.16%

Example-1:
Purification of regadenoson:

Crude Regadenoson (10 gm; 98.9%) was dissolved in N,N-dimethylsulfoxide (35 ml) under stirring, and filtered through Whatman paper. The filtrate was charged to a clean RBF, and heated under stirring to 45 to 50 °C under stirring. To this solution, acetone (200 ml) was charged under continuous stirring at not less than 40 °C. The resultant suspension was cooled under stirring, filtered under vacuum through Whatman paper and washed with acetone (100 ml). The wet solid was sucked well, and then dried in vacuum oven at 40-45 °C for 8 hours and submitted for HPLC purity.

HPLC purity: 99.87%, Pyrazole ester: 0.02%, Pyrazole acid impurity: 0.05%, Single Largest Unknown Impurity: 0.05%