Description:FIELD OF THE INVENTION:
The present invention relates to an efficient and industrially advantageous process for the preparation of Daprodustat.
The present invention also relates to a process for the preparation of Daprodustat intermediates and their use for the preparation of Daprodustat.
BACKGROUND OF THE INVENTION:
Daprodustat is chemically known as N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycine, having the structure of Formula I,

[Formula I]
Daprodustat has been developed by GlaxoSmithKline (GSK) and approved by PMDA (Pharmaceuticals and Medical Devices Agency), Japan on Jun. 29, 2020, under the proprietary name Duvroq®. Daprodustat is used for the treatment of anemia in patients with chronic kidney disease.
U.S. patent number US8324208 (herein after referred as US’208) first disclosed Daprodustat. US’208 also discloses a process of preparation of Daprodustat which involves series of reactions. Initially, N,N-dicyclohexylcarbodiimide is reacted with malonic acid in presence of anhydrous tetrahydrofuran to obtain 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione. Resulting compound is then reacted with ethyl isocyanatoacetate in presence of diisopropylethylamine and dichloromethane at room temperature overnight to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate. Resulting ester was then hydrolysed using aqueous sodium hydroxide in presence of ethanol at room temperature to obtain a crude Daprodustat. Finally, crude Daprodustat was recrystallized using glacial acetic acid to obtain Daprodustat.
US’208 process has a drawback such as lower yield and purity of intermediates at various stages, tedious isolation process of intermediates, requiring higher volumes of solvent for purification of Daprodustat and thus causing lower overall yield. Daprodustat intermediate, 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione obtained by US’208 process using tetrahydrofuran as a solvent results into only 72% yield. Further, preparation of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate involves tedious work up process and uses multiple solvents. Also, the process is not efficient to remove inorganic salt and require high volume of acetic acid. Therefore, the process disclosed in US’208 is not an attractive option to use for industrial scale.
“Journal of the American Chemical Society, Volume: 84, Pages 1310-11” discloses a process for the preparation of 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione comprising reacting malonic acid with N,N'-dicyclohexylcarbodiimide in presence of tetrahydrofuran.
The main drawback of this article is it results into lower yield of obtained 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione. Also, the article is silent on the purity of obtained 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione. Therefore, the process is industrially non-economic.
“Journal of Medicinal Chemistry, Volume 54, Issue 7, Pages 2409-2421” also discloses a process for the preparation of pyrimidine-2,4,6-triones (PYT) compounds including 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione, starting from S,S-dimethyl carbonodithioate and amines.
The process disclosed in above article is significantly lengthy and results into lower yield of 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione. Also, the exact purity of obtained 1,3-dicyclohexylpyrimidine-2,4,6(1H,3H,5H)-trione is not mentioned in the said article. Therefore, the said process is not an attractive option to use for industrial scale.
“Journal of Organic Chemistry, Volume 84, Issue 8, Pages 4948-4952” discloses a process for the preparation of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate using 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione and ethyl isocyanatoacetate in continuous flow reactor in presence of triethylamine and tetrahydrofuran as a solvent.
The process disclosed in above article is not commercially suitable since it requires specific set-up which have their own limitations like high pressure drops, a limited flow capacity and a tendency to block, difficulties in cleaning and dismantling. The shortcomings of this process are that it is a flow process involving a typically arranged model of micro and batch reactors. The process disclosed not only requires a capital investment for flow reactors but also demands a special operational expertise making its commercial implementation difficult.
Like any synthetic compound, drug intermediates too can contain extraneous compounds or impurities that can come from many sources which may get carried forward to final active pharmaceutical ingredient (API) i.e. Daprodustat or alternatively the impurities may react to form other new products. These extraneous compounds in the intermediate may be unreacted starting materials, by products of the reactions, products of side reactions, or degradation products. Impurities generated due to any reason in any active pharmaceutical ingredient (API) like Daprodustat are undesirable and as they may be harmful to a patient being treated with a dosage form containing the API.
The American Food and Drug Administration (FDA) as well as European medicament control offices require, following of Q7A ICH (International Conference on Harmonization) guidelines, according to which Active Pharmaceutical Ingredient (API) should be free of impurities to the maximum extent possible. This would result in achieving maximum safety of the drug in the clinical practice. National inspection and control offices usually require that the content of an individual impurity in an API should not exceed the limit of 0.1%. All the substances (generally referred to as impurities) contained in an API over the limit of 0.1% should be isolated and characterized in accordance with the ICH recommendations. Q7A ICH guidance for manufacturers also states that level of process impurities must be maintained below set limits by specifying the quality of raw materials, controlling process parameters, such as temperature, pressure, time and stoichiometric ratio of the raw materials, and including purification steps, such as crystallization, distillation, and liquid-liquid extraction, in the manufacturing process. It is always advantageous to use intermediates of high purity which is free from the undesired impurities, or such impurities should be present in acceptable amounts. The purity of the chemical compounds can be tested by chromatographic techniques such as high-pressure liquid chromatography (HPLC). The control of impurities at intermediate step is always important, since impurities present in the intermediate stage may carry forward and may react further with reagents and which could result in formation of new impurities along with main product.
Prior art references involve tedious work up process, use of costly solvent(s), requires specific set-up. Also, the prior art processes results into lower yield or purity of the intermediates of Daprodustat, ultimately leading to the overall yield at a lower side and increased production cost. Additionally, most of the prior arts are silent on the purity of Daprodustat and its intermediates prepared by the said methods. Therefore, there exists a need for the process for the preparation of Daprodustat of Formula I and its intermediates which overcomes the drawbacks of prior arts processes and provide product at a lower cost having higher yield and higher purity.
The present inventors have developed an improved and cost-effective process for the preparation of Daprodustat of Formula I and its intermediates which gives advantages over the prior art processes in terms of higher yield, higher purity, simple work up process and industrially economical.
OBJECT OF THE INVENTION:
The main object of the present invention is to provide an efficient and industrially advantageous process for the preparation of Daprodustat having higher yield and purity.
Another object of the present invention is to provide an industrially advantageous process for the preparation of Daprodustat intermediates, namely 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,

[Formula IV]
and ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI,

[Formula VI]
and their use for the preparation of Daprodustat.
Yet another object of the present invention is to provide a process for the purification of Daprodustat of Formula I.
SUMMARY OF INVENTION:
First aspect of the present invention is to provide a process for the preparation of Daprodustat of Formula I,

[Formula I]
comprising the steps of:
i. reacting N,N'-dicyclohexylcarbodiimide of Formula II,

[Formula II]
with malonic acid of Formula III,

[Formula III]
in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV;

[Formula IV]
ii. reacting 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV with ethyl isocyanatoacetate of Formula V,

[Formula V]
in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;

[Formula VI]
and
iii. hydrolysing N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI using base in absence of organic solvent to obtain Daprodustat of Formula I,
“wherein solvent in step (i) and step (ii) is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
Second aspect of the present invention is to provide a process for the preparation of 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,

[Formula IV]
comprising reacting N,N'-dicyclohexylcarbodiimide of Formula II,

[Formula II]
with malonic acid of Formula III,

[Formula III]
in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,
“wherein solvent is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
Third aspect of the present invention is to provide a process for the preparation of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;

[Formula VI]
comprising reacting 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,

[Formula IV]
with ethyl isocyanatoacetate of Formula V,

[Formula V]
in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;
“wherein the solvent is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
Fourth aspect of the present invention is to provide a process for the preparation of Daprodustat of Formula I,

[Formula I]
comprising hydrolysing N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI,

[Formula VI]
using base in absence of organic solvent to obtain Daprodustat of Formula I.

Fifth aspect of the present invention is to provide a process for the purification of Daprodustat of Formula I,

[Formula I]
comprising treating Daprodustat of Formula I with an organic acid and aromatic hydrocarbon solvent to obtain pure Daprodustat of Formula I.
Sixth aspect of the present invention is to provide a process for the purification of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI,

[Formula VI]
comprising treating ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI with an alcohol solvent.
DETAILED DESCRIPTION OF INVENTION:
In order to provide a clear and consistent understanding of the terms used in the present specification, a number of definitions are provided below. Moreover, unless defined otherwise, all technical and scientific terms as used herein have the same meaning as understood by the person skilled in the art.
The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may not only mean “one”, but also encompasses the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more.
As used in this specification the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “consisting” (and any form of consisting, such as “consists”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.
The invention will now be described in detail in connection with certain preferred embodiments, so that various aspects thereof may be fully understood and appreciated.
Accordingly, in first embodiment, the present invention provides the process for the preparation of Daprodustat of Formula I,

[Formula I]
comprising the steps of:
i. reacting N,N'-dicyclohexylcarbodiimide of Formula II,

[Formula II]
with malonic acid of Formula III,

[Formula III]
in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV;

[Formula IV]
ii. reacting 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV with ethyl isocyanatoacetate of Formula V,

[Formula V]
in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;

[Formula VI]
and
iii. hydrolysing N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI using base in absence of organic solvent to obtain Daprodustat of Formula I,
“wherein solvent in step (i) and step (ii) is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
In accordance with step (i) of the first embodiment, N,N'-dicyclohexylcarbodiimide of Formula II can be reacted with malonic acid of Formula III in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV;

[Formula IV]
In accordance with step (i) of the first embodiment, solvent can be selected from the group consisting of dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof, preferably the solvent is dichloromethane.
The volume of the solvent used during the reaction can be in the range of 10.0 volume to 25.0 volume, preferably 15.0 volume to 25.0 volume, more preferably 20.0 volume to 23.0 volume.
In accordance with step (i) of the first embodiment, solution of N,N'-dicyclohexylcarbodiimide Formula II in solvent can be added to mixture of malonic acid of Formula III in solvent at temperature -10°C to 10°C, preferably at -5°C to 5°C. The said mode of addition controls the possible side products.
In accordance with step (i) of the first embodiment, solution of N,N'-dicyclohexylcarbodiimide Formula II in solvent can be added to mixture of malonic acid of Formula III in solvent in 3 hours to 7 hours, preferably 4 hours to 5 hours. After completion of addition, the temperature of mixture can be raised up to 25°C to 30°C and resulting mixture can be stirred for 2 hours.
After completion of reaction, resulting mixture can be filtered, washed with solvent used during the reaction to obtain a filtrate and wet cake. The resulting wet cake contains byproduct formed in the reaction. The solvent can be distilled from the resulting filtrate followed by stripping using alcohol which can be selected from methanol, ethanol, n-propanol or isopropanol to obtain a concentrated mass. Alcohol can be added to the resulting concentrated mass and the mixture can be refluxed for 2 hours to 3 hours. Resulting mixture can be cooled to 10°C to 20°C and can be stirred for 2 hours. Resulting solid can be filtered, washed with alcohol to obtain wet cake. Resulting wet cake can be dried in Air Tray Dryer (ATD) or Vacuum Tray Dryer (VTD) for 6 hours to 8 hours to obtain a pure 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV.
The resulting 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV may have purity greater than 98% by High-performance liquid chromatography (HPLC), preferably greater than 98.5% by HPLC.
The resulting 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV may have yield greater than 85%, preferably greater than 90%.
In accordance with step (ii) of the first embodiment, 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV can be reacted with ethyl isocyanatoacetate of Formula V in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI;

[Formula VI].
In accordance with step (ii) of the first embodiment, solvent can be selected from the group consisting of dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof, preferably the solvent is dichloromethane.
The volume of the solvent used during the reaction can be in the range of 3.0 volume to 8.0 volume, preferably 4.5 volume to 5.5 volume.
In accordance with step (ii) of the first embodiment, triethylamine can be used in the proportion of 2.0 to 3.0 molar equivalents with respect to 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV.

In accordance with step (ii) of the first embodiment, the reaction of 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV with ethyl isocyanatoacetate of Formula V can be carried out at temperature of 30? to 50?, preferably at 35? to 40?.
After completion of reaction, purified water can be added to the reaction mixture at 20? to 30?. pH of the resulting mixture can be adjusted to not more than 2 at same temperature using concentrated hydrochloric acid. Resulting mixture is allowed to settle and resulting layers can be separated to obtain organic and aqueous layer. Resulting organic layer can be washed with water and can be treated with carbon. Finally, solvent can be distilled from the organic layer and further stripped with alcohol which can be selected from methanol, ethanol, n-propanol or isopropanol, to obtain a concentrated mass. Alcohol can be added to the resulting concentrated mass and the mixture can be refluxed for 2 hours to 3 hours. Resulting mixture can be cooled to 0°C to 5°C and can be stirred for 2 hours. Resulting solids can be filtered, washed with alcohol to obtain wet cake. Resulting wet cake can be dried in Air Tray Dryer (ATD) or Vacuum Tray Dryer (VTD) to obtain an ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI.
The resulting ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI may have purity greater than 99.5% by HPLC, preferably greater than 99.8% by HPLC.
The resulting ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI may have yield greater than 90%, preferably greater than 95%.
In accordance with step (iii) of the first embodiment, ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI can be hydrolyzed using base in absence of organic solvent to obtain Daprodustat of Formula I,

[Formula I].
In accordance with step (iii) of the first embodiment, hydrolysis of N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI can be carried out using a base selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate or lithium hydroxide; preferably the base is sodium hydroxide.
The base can be used in the proportion of 4.0 to 6.0 molar equivalents with respect to N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI.
In accordance with step (iii) of the first embodiment, hydrolysis of N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI can be carried out at temperature of 70? to 100?, preferably at 85°C to 95°C.
After completion of reaction, the reaction mixture can be cooled to 20°C to 30°C and solvent selected from toluene, xylene, mesitylene can be added to the resulting mixture, preferably the solvent is toluene. Resulting mixture can be allowed to settle and organic and aqueous layers can be separated. Resulting aqueous layer can be extracted with solvent. Resulting aqueous layer can be filtered on hyflow bed, washed with purified water. Resulting filtrate can be acidified using an acid, such as concentrated hydrochloric acid, concentrated sulfuric acid, acetic acid, citric acid; preferably by using concentrated hydrochloric acid to adjust the pH not more than 2.0 and stirred for an hour. The solid obtained can be filtered, washed with purified water to remove the inorganics. The resulting wet cake can be further treated with toluene and water to obtain a Daprodustat of Formula I. Addition of toluene at this stage helps in reducing the size of the wet cake. This makes the work up process easier and efficient. Additionally, it also helps to control the impurity level in Daprodustat of Formula I thus obtained.
The resulting Daprodustat of Formula I may have purity greater than 99.5% by HPLC, preferably greater than 99.8% by HPLC.
The resulting Daprodustat of Formula I may have yield greater than 85%, preferably greater than 90%.
In second embodiment, N,N'-dicyclohexylcarbodiimide of Formula II, can be reacted with malonic acid of Formula III in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV;

[Formula IV]
In accordance with second embodiment, solvent can be selected from the group consisting of dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof, preferably the solvent is dichloromethane.
The volume of the solvent used during the reaction can be in the range of 10. 0 volume to 25.0 volume, preferably 15.0 volume to 25.0 volume, more preferably 20.0 volume to 23.0 volume.
In accordance with second embodiment, solution of N,N'-dicyclohexylcarbodiimide Formula II in solvent can be added to mixture of malonic acid of Formula III in solvent at temperature -10°C to 10°C, preferably at -5°C to 5°C. The said mode of addition controls the possible side products.
In accordance with second embodiment, solution of N,N'-dicyclohexylcarbodiimide Formula II in solvent can be added to mixture of malonic acid of Formula III in solvent in 3 hours to 7 hours, preferably 4 hours to 5 hours. After completion of addition, the temperature of mixture can be raised up to 25°C to 30°C and resulting mixture can be stirred for 2 hours.
After completion of reaction, resulting mixture can be filtered, washed with solvent used during the reaction to obtain a filtrate and wet cake. The resulting wet cake contains byproduct formed in the reaction. The solvent can be distilled from the resulting filtrate followed by stripping using alcohol which can be selected from methanol, ethanol, n-propanol or isopropanol to obtain a concentrated mass. Alcohol can be added to the resulting concentrated mass and the mixture can be refluxed for 2 hours to 3 hours. Resulting mixture can be cooled to 10°C to 20°C and can be stirred for 2 hours. Resulting solid can be filtered, washed with alcohol to obtain wet cake. Resulting wet cake can be dried in Air Tray Dryer (ATD) or Vacuum Tray Dryer (VTD) for 6 hours to 8 hours to obtain a pure 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV.
The resulting 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV may have purity greater than 98% by High-performance liquid chromatography (HPLC), preferably greater than 98.5% by HPLC.
The resulting 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV may have yield greater than 85%, preferably greater than 90%.
In third embodiment, 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV can be reacted with ethyl isocyanatoacetate of Formula V, in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI;

[Formula VI]
In accordance with third embodiment, solvent can be selected from the group consisting of dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, methyl tert-butyl or mixture(s) thereof, preferably the solvent is dichloromethane.
The volume of the solvent used during the reaction can be in the range of 3.0 volume to 8.0 volume, preferably 4.5 volume to 5.5 volume.
In accordance with third embodiment, triethylamine can be used in the proportion of 2.0 to 3.0 molar equivalents with respect to 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV.
In accordance with third embodiment, the reaction of 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV with ethyl isocyanatoacetate of Formula V can be carried out at temperature of 30? to 50?, preferably at 35? to 40?.
After completion of reaction, purified water can be added to the reaction mixture at 20? to 30?. pH of the resulting mixture can be adjusted to not more than 2 at same temperature using concentrated hydrochloric acid. Resulting mixture is allowed to settle and resulting layers can be separated to obtain organic and aqueous layer. Resulting organic layer can be washed with water and can be treated with carbon. Finally, solvent can be distilled from the organic layer and further stripped with alcohol which can be selected from methanol, ethanol, n-propanol or isopropanol to obtain a concentrated mass. Alcohol can be added to the resulting concentrated mass and the mixture can be refluxed for 2 hours to 3 hours. Resulting mixture can be cooled to 0°C to 5°C and can be stirred for 2 hours. Resulting solids can be filtered, washed with alcohol to obtain wet cake. Resulting wet cake can be dried in Air Tray Dryer (ATD) or Vacuum Tray Dryer (VTD) to obtain an ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI.
The resulting ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI may have purity greater than 99.5% by HPLC, preferably greater than 99.8% by HPLC.
The resulting ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI may have yield greater than 90%, preferably greater than 95%.
In fourth embodiment, ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI can be hydrolyzed using base in absence of organic solvent to obtain Daprodustat of Formula I,

[Formula I]
In accordance with fourth embodiment, hydrolysis of N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI can be carried out using a base selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate or lithium hydroxide; preferably the base is sodium hydroxide.
The base can be used in the proportion of 4.0 to 6.0 molar equivalents with respect to N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI.
In accordance with fourth embodiment, hydrolysis of N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI can be carried out at temperature of 70? to 100?, preferably at 85°C to 95°C.
After completion of reaction, the reaction mixture can be cooled to 20°C to 30°C and solvent selected from toluene, xylene, mesitylene can be added to the resulting mixture, preferably the solvent is toluene. Resulting mixture can be allowed to settle and organic and aqueous layers can be separated. Resulting aqueous layer can be extracted with solvent. Resulting aqueous layer can be filtered on hyflow bed, washed with purified water. Resulting filtrate can be acidified using an acid, such as concentrated hydrochloric acid, concentrated sulphuric acid, acetic acid, citric acid; preferably by using concentrated hydrochloric acid to adjust the pH not more than 2.0 and stirred for an hour. The solid obtained can be filtered, washed with purified water to remove the inorganics. The resulting wet cake can be further treated with toluene and water to obtain a Daprodustat of Formula I. Addition of toluene at this stage helps in reducing the size of the wet cake. This makes the work up process easier and efficient. Additionally, it also helps to control the impurity level in Daprodustat of Formula I, thus obtained.
The resulting Daprodustat of Formula I may have purity greater than 99.5% by HPLC, preferably greater than 99.8% by HPLC.
The resulting Daprodustat of Formula I may have yield greater than 85%, preferably greater than 90%.
In Fifth embodiment, Daprodustat of Formula I,

[Formula I]
can be purified by treating Daprodustat of Formula I with an organic acid and aromatic hydrocarbon as a solvent to obtain pure Daprodustat of Formula I.
In accordance with fifth embodiment, Daprodustat of Formula I can be treated using an organic acid and aromatic hydrocarbon solvent by purification methods such as recrystallization method or slurry wash to obtain highly pure Daprodustat of Formula I.
In accordance with fifth embodiment, organic acid can be selected from formic acid, acetic acid, propionic acid or butyric acid. Preferably the organic acid is acetic acid.
In accordance with fifth embodiment, aromatic hydrocarbon solvent can be selected from toluene, xylene or mesitylene. Preferably the aromatic hydrocarbon solvent is toluene.
In accordance with fifth embodiment recrystallization can be carried out using mixture of an organic acid and aromatic hydrocarbon by heating up to the reflux temperature of the solvent followed by cooling at 10°C to 20°C.
The volume of the solvent mixture of organic acid and aromatic hydrocarbon can be in the range of 8 volume to 15 volume, preferably 10 volumes to 12 volumes. The ratio of organic acid and aromatic hydrocarbon used for the purification can be in the ratio having the range of 90:10, 80:20, 60:40; preferably 60:40.
In accordance with the fifth embodiment, Daprodustat of Formula I can be added in the mixture of organic acid and aromatic hydrocarbon solvent. The mixture can be heated up to reflux temperature of solvent used as to make a clear solution and maintained for 30 minutes at the same temperature. Resulting clear solution can be hot filtered on hyflow bed. Solvent from the resulting filtrate can be distilled out partly under reduced pressure at 70°C to 90°C to keep 7 to 9 volume of solvent mixture in the system. Resulting mixture can be cooled to 10°C to 20°C and can be stirred for 3 hours at the same temperature. The precipitated solid can be filtered and washed with organic acid to obtain a wet cake. Resulting wet cake can be slurried in water, filtered and suck dried. Finally, the wet cake can be dried in Air Tray Dryer (ATD) or Vacuum Tray Dryer (VTD) for 12 hours to 14 hours at 85°C to 95°C.
The resulting Daprodustat of Formula I may have purity greater than 99.90% by HPLC, preferably greater than 99.95% by HPLC.
The aforesaid purification process is efficient to remove inorganic materials and thus results into highly pure Daprodustat of Formula I in terms of assay. The aforesaid process is efficient in terms of handling as well and thus makes it industrially viable.
The resulting Daprodustat of Formula I may have yield greater than 85%, preferably greater than 90%.
In sixth embodiment, ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI;

[Formula VI]
can be purified by treating ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI with an alcohol.
In accordance with sixth embodiment, ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate can be treated using an alcohol by purification methods such as recrystallization method or slurry wash.
In accordance with sixth embodiment, an alcohol can be selected from methanol, ethanol, n-propanol, isopropanol or n-butanol. Preferably the alcohol is methanol.
In accordance with sixth embodiment, recrystallization can be carried out using alcohol by heating crude ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate up to the reflux temperature of the solvent.
The volume of the alcohol can be in the range of 5 volume to 10 volume, 7 volume to 9 volume preferably 6 volumes to 8 volumes.
After refluxing the mixture for 2 hours to 3 hours, resulting mixture can be cooled to 0°C to 5°C and can be stirred for 2 hours at the same temperature. Resulting solid can be filtered, washed with alcohol to obtain wet cake. Resulting wet cake can be dried in Air Tray Dryer (ATD) or Vacuum Tray Dryer (VTD) for 6 hours to 8 hours to obtain a pure ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI.
The resulting ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI may have purity greater than 99.5 % by High-performance liquid chromatography (HPLC), preferably greater than 99.8 % by HPLC.
EXAMPLES:
Following examples are given by way of illustration. It may be understood for the person skilled in the art that these examples are only typical embodiments of the invention and are not therefore considered to be limiting the scope of the present invention.
Example 01: Preparation of 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV
To a stirred mixture of malonic Acid (180 g) in dichloromethane (3240 mL), separately prepared solution of N,N-dicyclohexyl carbodiimide (720 g) in dichloromethane (720 mL) was added slowly at temperature -5°C to 5 °C in 5 hours. The temperature of the reaction mixture was then raised up to 25°C to 30°C and maintained for 2 hours. After completion of reaction, resulting mixture was filtered and cake was slurry washed with dichloromethane (3 x 600 mL). The obtained filtrate was filtered through hyflow bed and washed with dichloromethane. Resulting filtrate was distilled and stripped out with methanol to obtain concentrated mass. Methanol (1080 mL) was added to resulting mass and mixture was refluxed for 2 hours. The obtained mixture was cooled to 10°C to 20°C and stirred for 2 hours to precipitate the solid. Resulting solid was filtered and washed with methanol (3 x180 mL) to obtain wet cake. Resulting wet cake was dried in air tray dryer for 12 hours at 85°C to 95°C to obtain title compound (458.7 g) having HPLC purity of 98.7%.
Example 02: Preparation of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI
To stirred solution of 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione (400 g) of Formula IV obtained in example 1 in dichloromethane (2000 mL), triethylamine (280 g) was added slowly at 10°C to 20°C. Resulting mixture was stirred for 25 minutes at same temperature. Ethyl isocyanatoacetate (240 g) was added slowly to resulting mixture at 10°C to 20°C in 3 hours. Resulting mixture was then heated to 33°C to 38°C and maintained for 2 hours. After completion of reaction (monitored by HPLC), purified water (40 mL) followed by concentrated hydrochloric acid (336 g) was added to the mixture. Resulting mixture was stirred at 20°C to 30°C for 30 minutes. Resulting mixture was allowed to settle the organic and aqueous layer. The obtained layers were separated and resulting organic layer was washed with purified water (2 x 200mL). Resulting organic layer was treated with activated carbon and filtered through hyflow bed and washed with dichloromethane (1200 mL). Resulting filtrate was distilled and stripped out with methanol (3 x 800 mL) to obtain concentrated mass.
Methanol (2400 ml) was added to concentrated mass and refluxed for 2 hours. Resulting mixture was cooled to 0°C to 5°C and stirred for 2 hours. resulting solid was filtered, washed with methanol (2 x 200mL) to obtain a wet cake. Resulting wet cake was dried in air tray dryer for 8 hours at 65°C to 70°C to obtain a title compound (558 g) having HPLC purity of 99.86 %
Example 03: Preparation of Daprodustat
To stirred solution of sodium hydroxide (190 g) in purified water (2500 mL), ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl]glycinate of Formula VI (500 gm) obtained in example 2 was added at 20°C to 95°C. Resulting mixture was stirred for 4 hours at 85°C to 95°C. After completion of reaction (monitored by HPLC), the reaction mixture was cooled to 30°C to 60°C and extracted with toluene (3 x 125 mL). Finally, obtained aqueous layer was filtered through hyflow bed and washed with purified water (2 x 500 mL). Resulting filtrate was added slowly to aqueous hydrochloric acid solution [concentrated hydrochloric acid (580 g) + purified water (2500 mL)] at 25°C to 35°C to adjust the pH not more than 3. Resulting mixture was then stirred for 1 hour at same temperature. Resulting solid was then filtered, washed with purified water (2 x 500 mL) to obtain a wet cake. The obtained wet cake was slurried with purified water (2500 mL) and stirred for 1 hour at 25°C to 35°C. Resulting solid was filtered, washed with purified water (2 x 500 mL) to obtain a wet cake.
To a stirred solution of toluene (4000 mL) and purified water (1500 mL), above obtained wet cake was added. Resulting mixture was heated to 80°C to 90°C and stirred for 1 hour. Resulting mixture was then cooled to 25°C to 35°C and further stirred for 1 hour. The solid obtained was filtered, washed with toluene (2 x 250 mL) and dried in air tray dryer for 6 hours at 85°C to 95°C to obtain a title compound (442.7 g) having HPLC purity of 99.97%.
Example 04: Purification of Daprodustat
To a stirred solution of acetic acid (1420 mL) and toluene (945 mL), Daprodustat (215 g) was added. Resulting mixture was heated to 90°C to 100°C. Resulting mixture was hot filtered through hyflow bed, washed with mixture of acetic acid and toluene. Resulting filtrate was distilled up to approximately 1180 mL of solvent mixture. Resulting partly concentrated mixture was cooled to 10°C to 15°C temperature and stirred for 3 hours at 10°C to 15°C. The obtained solid was filtered, washed with acetic acid (2 x 110 mL) to obtain a wet cake. Resulting wet cake was added in purified water (1720 mL) and stirred 1 hour. Resulting solid was filtered, washed with purified water (2 x 215 mL) and dried in vacuum tray dryer for 12 hours at 85°C to 95°C to obtain a highly pure Daprodustat (198.8 g) having HPLC purity of 99.97 %.
Advantages of the present invention:
1. Process provides highly pure Daprodustat.
2. Process provides highly pure intermediate compounds with substantially improved yield.
3. Simple work up process to isolate the intermediate compounds.
4. Purification of Daprodustat requires less amount of solvent, minimizing the solvent cost of the process.
5. Hydrolysis of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate is done in absence of any organic solvent, making the process green as well as economic.
, Claims:I / We Claim:
1. A process for preparation of Daprodustat of Formula I,

[Formula I]
comprising the steps of:
i. reacting N,N'-dicyclohexylcarbodiimide of Formula II,

[Formula II]
with malonic acid of Formula III,

[Formula III]
in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6 (1H,3H,5H)-pyrimidinetrione of Formula IV;

[Formula IV]
ii. reacting 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV with ethyl isocyanatoacetate of Formula V,

[Formula V]
in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;

[Formula VI]
and
iii. hydrolysing N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI using base in absence of organic solvent to obtain Daprodustat of Formula I,
“wherein the solvent in step (i) and step (ii) is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
2. The process as claimed in claim 1, wherein solution of N,N'-dicyclohexylcarbodiimide Formula II in solvent is added to a mixture of malonic acid of Formula III in solvent at temperature -10°C to 10°C.
3. A process for preparation of 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,

[Formula IV]
comprising reacting N,N'-dicyclohexylcarbodiimide of Formula II,

[Formula II]
with malonic acid of Formula III,

[Formula III]
in presence of solvent to obtain 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,
“wherein the solvent is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
4. The process as claimed in claim 3, wherein solution of N,N'-dicyclohexylcarbodiimide Formula II in solvent is added to a mixture of malonic acid of Formula III in solvent at temperature -10°C to 10°C.
5. A process for preparation of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;

[Formula VI]
comprising reacting 1,3-dicyclohexyl-2,4,6(1H,3H,5H)-pyrimidinetrione of Formula IV,

[Formula IV]

with ethyl isocyanatoacetate of Formula V,

[Formula V]
in presence of triethylamine and solvent to obtain ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI;
“wherein the solvent is selected from dichloromethane, dichloroethane, chloroform, ethyl acetate, toluene, monoglyme, acetone or mixture(s) thereof”.
6. A process for preparation of Daprodustat of Formula I,

[Formula I]
comprising hydrolysing N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl)carbonyl]glycinate of Formula VI using base in absence of organic solvent.
7. The process as claimed in claim 6, wherein the base is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate or lithium hydroxide.
8. A process for the purification of Daprodustat of Formula I,

[Formula I]
comprising treating Daprodustat of Formula I with an organic acid and aromatic hydrocarbon solvent.
9. The process as claimed in claim 8, wherein the organic acid is selected from formic acid, acetic acid, propionic acid or butyric acid and aromatic hydrocarbon solvent is selected from, toluene, xylene and mesitylene.

10. A process for the purification of ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI,

[Formula VI]
comprising treating ethyl N-[(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydro-5-pyrimidinyl) carbonyl] glycinate of Formula VI with alcohol solvent.
11. The process as claimed in claim 10, wherein the alcohol is selected from methanol, ethanol, n-propanol, isopropanol or n-butanol.

Dated this 2nd day of February 2023

Dr. Virendra Thakrar,
Sr. Vice- President R&D,
Ami Lifesciences Pvt. Ltd.