WO 2016027077, Cipla Ltd, New patent, Dabigatran

(WO2016027077) PROCESSES FOR THE PREPARATION OF DABIGATRAN ETEXILATE AND INTERMEDIATES THEREOF

WO 2016027077, Cipla Ltd, New patent, Dabigatran

CIPLA LIMITED [IN/IN]; Cipla House Peninsula Business Park Ganpatrao Kadam Marg Lower Parel Mumbai 400 013 (IN).

RAO, Dharmaraj Ramachandra; (IN).
MALHOTRA, Geena; (IN).
PULLELA, Venkata Srinivas; (IN).
ACHARYA, Vinod Parameshwaran; (IN).
SINARE, Sudam Nanabhau; (IN)

Dabigatran etexilate (a compound of Formula I) is the international commonly accepted nonproprietary name for ethyl 3-{[(2-{[(4-{(hexyloxy)carbonyl]carbamimidoyl}phenyl)amino]methyl}-1 -methyl-1 H- benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino}propanoate,

 

(I)

Dabigatran etexilate is the pro-drug of the active substance, dabigatran. The mesylate salt (1 : 1 ) of dabigatran etexilate is known to be therapeutically useful as an oral anticoagulant from the class of the direct thrombin inhibitors and is commercially marketed as oral hard capsules as Pradaxa™ in Australia, Europe and in the United States; as Pradax™ in Canada and as Prazaxa™ in Japan. Additionally, it is also marketed in Europe under the same trade mark for the primary prevention of venous thromboembolic events in adult patients who have undergone elective total hip replacement surgery or total knee replacement surgery.

Dabigatran etexilate was first described in U.S. Patent No. 6,087,380, according to which the synthesis of dabigatran etexilate was carried out in three synthetic steps as depicted in Scheme 1.

Scheme 1

 

1. HCL , EtOH

2. (NH4)2C03, EtOH

 

Dabigatran etexilate

II. HCI

The process involves the condensation between ethyl 3-{[3-amino-4-(methylamino)benzoyl] (pyridin-2-yl)amino}propanoate (compound VI) and N-(4-cyanophenyl)glycine (compound VIII) in the presence of Ν,Ν'-carbonyldiimidazole (CDI) in tetrahydrofuran (THF) to give the hydrochloride salt of ethyl 3-{[(2-{[(4-cyanophenyl)amino]methyl}-1-methyl-1 H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino} propanoate (compound IV), which is subsequently reacted with ethanolic hydrochloric acid, ethanol and ammonium carbonate to give the hydrochloride salt of ethyl 3-{[(2-[{(4-carbamimidoylphenyl)amino]methyl}-1-methyl-1 H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino} propanoate (compound II). Finally, the reaction between compound II and n-hexyl chloroformate (compound IX), in the presence of potassium carbonate, in a mixture of THF and water, affords dabigatran etexilate of Formula (I) after work- up and chromatographic purification. However, no information is given about the purity of the isolated dabigatran etexilate (I) product. Further, the process is not viable industrially as it requires chromatographic purification in several of its steps, thus making it very difficult and costly to implement on an industrial scale.

In order to simplify the process for obtaining dabigatran etexilate described in U.S. Patent No. 6,087,380, several alternative processes have been developed and reported in the art.

EP2118090B discloses a process for the preparation of the intermediate compound of Formula (II) by crystallization from a salt with p-toluenesulfonic acid. The amidine salt (ll-pTsOH) is obtained from a compound of formula (IV), which is also isolated in the form of a hydrobromide salt, (IV-HBr).

EP2262771A discloses a process for the preparation of the intermediate compound of Formula (IV), which is obtained in the form of a salt with oxalic acid. This document indicates that the oxalate intermediate of the compound (IV) crystallizes easily and is a good synthesis intermediate to obtain the amidine hydrochloride salt (ll-HCI) with high purity on an industrial scale. The compound (IV) in oxalate salt form is transformed in dabigatran following the process disclosed in WO 98/37075.

WO 2006/000353 describes an alternative process for the synthesis of dabigatran etexilate as depicted in Scheme 2.

 

Dabigatran etexilate

The process involves condensation between ethyl 3-{[3-amino-4-(methylamino)benzoyl](pyridin-2-yl)amino}propanoate (compound VI) and 2-[4-(1 ,2,4-oxadiazol-5-on-3-yl)phenylamino]acetic acid (compound Villa) in the presence of a coupling agent such as CDI, propanephosphonic anhydride (PPA), or pivaloyl chloride, to give ethyl 3-{[(2-{[(4-{1 ,2,4-oxadiazol-5-on-3-yl}phenyl)amino]methyl}-1 -methyl-1 H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino}propanoate (compound IVa), which is subsequently hydrogenated in the presence of a palladium catalyst to give ethyl 3-{[(2-{[(4-carbamimidoylphenyl)amino]methyl}-1-methyl-1 H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino} propanoate (compound II). The compound II is acylated with n-hexyl chloroformate (compound I) to give dabigatran etexilate. Finally, dabigatran etexilate is converted into its mesylate salt. Although the patent describes the HPLC purities of intermediate compounds II, IVa, Villa and VI, no information is given concerning the purity of the isolated dabigatran etexilate or the mesylate salt thereof.

WO 2010/045900 discloses a process to prepare the intermediate amidine hydrochloride compound (ll-HCI) from the oxalate salt of the compound (IV) by reacting with hydrogen chloride in ethanol, followed by reaction with ammonium carbonate to avoid chromatography which is not feasible on an industrial scale.

WO 2014/012880 discloses a process to prepare an intermediate of dabigatran etexilate (compound IV) by reacting carboxylic acid (compound VIII) with diamaine (compound VI) in the presence of the coupling agent CDI, followed by reaction with 6 equivalents of acetic acid at 130°C to obtain compound IV in acetate salt form, having a purity of 94%. The isolated solid is further recrystallized from ethanol to obtain a purity of 99%. The purified (compound IV. acetate) is reacted with hydrogen chloride in the presence of an alcohol, and then with ammonia in an aqueous medium to form the amidine hydrochloride salt (compound ll-HCI) in the presence of water.

The synthesis of intermediate compound II has been reported in the patent literature and known methods require either chromatographic purification or a lengthy purification procedure, such as converting the compound into the HCI salt followed by recrystallization, to obtain 97% pure intermediate compound II. In previously reported methods, the product yield is undesirably less than 50 %.

Similarly, the intermediate compound IV prepared by CDI mediated coupling with glycine derivatives followed by acetic acid mediated cyclization according to known methods results in the formation of highly impure products, which require purification by either column chromatography or by converting the crude reaction mixture to suitable salts. Previously reported methods afford low product yields and purity, which mean that such processes are not suitable for the commercial scale production of dabigatran.

In view of the foregoing, it is of great interest to continue investigating and develop other alternative simplified processes for the large scale industrial production of the active pharmaceutical ingredient dabigatran etexilate or salts thereof, which avoid complicated and costly purification steps in the synthesis of intermediates, while maintaining a high quality of synthesis intermediates and improving the yields of each step of reaction.

SCHEME 3

SCHEME4

Examples:

Example 1. Preparation of DAB Glycin-CDI complex of Formula (VII)

71.02 g (0.438 mol) of CDI was dissolved in 700 ml dichloromethane under nitrogen atmosphere. Added 66.89 g (0.379 mol) of 2-(4-cyanophenylamino)acetic acid of Formula (VIII), under stirring at 20-25°C and stirred for 90-100 minutes. Solid was isolated by filtration under nitrogen atmosphere and washed with 100 ml dichloromethane to yield DAB Glycin-CDI complex.

Example 2. Preparation of ethyl 3-(2-((4-cyanophenylamino)methyl)- l-methyl-N- (pyridin-2-yl)-IH-benzo[d]- imidazole-5-carboxamido) propanoate of Formula (IV)

DAB Glycin-CDI Complex obtained in Example 1 was stirred in 650 ml toluene. Added 100 g (0.292 mol) of ethyl 3-(3-amino-4-(methyl amino)-N-(pyridin-2-yl)benzamido)propanoate of Formula (VI) to the reaction mass and stirred for 3 hours at -45-50°C. The reaction mass was further refluxed for 3 hours. The reaction mass was cooled to 75-80°C, added 50 ml ethanol, further cooled to 20-25°C and stirred for 6 hours. The solid was isolated by filtration and washed with 100 ml toluene.

The wet cake was stirred in 500 ml water at 20-25°C for about 1 hour. The solid was isolated by filtration, washed with 100 ml water and dried in vacuum below 60 °C.

Yield: 120 g

Efficiency: 85%

Example 3. Preparation of ethyl 3-(2-((4-carbamimidoylphenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-IH-benzo[d]imidazole-5-carboxamido) propanoate of Formula (II)

100 g (0.207 mol) of ethyl 3-(2-((4-cyanophenylamino)methyl)- l-methyl-N- (pyridin-2-yl)-IH-benzo[d]- imidazole-5-carboxamido) propanoate of Formula (IV) was added to 1000 ml EtOH.HCI (32-35%w/w) at 5-10°C under nitrogen atmosphere and stirred for 24 hours at 15-20°C. The solvent was distilled off in vacuum below 40°C. Added 500 ml ethanol and cooled to 0-5°C. The pH of the reaction mass was adjusted to 9.5-10.0 by addition of 400 ml EtOH.NH₃ (10-13%w/w). The temperature of the reaction mass was raised to 20-25°C and stirred for 12 hours. The reaction mass was filtered and the clear filtrate was partially distilled to the half volume below 40°C. The temperature of the reaction mass was raised to 55-60°C. Added 600 ml ethyl acetate at reflux. The reaction mass was cooled to 20-25°C and stirred further for 5 hours. The solid was isolated by filtration and washed with 100 ml-ethyl acetate. The solid was dried in vacuum below 45 °C.

Yield: 72.5 g

Efficiency: 70%

Example 4. Preparation of DAB etexilate of Formula (I)

120 ml acetone, 60 ml water, 16.6 g (0.120 mol) potassium carbonate and 20g (0.040 mol) of ethyl 3-(2-((4-carbamimidoylphenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-IH-benzo[d]imidazole-5-carboxamido) propanoate of Formula (II) were stirred at 20-25°C. A solution of 9.88 g (0.060 mol) of hexyl chloroformate of Formula (IX) in 50 ml acetone was added to the reaction mass at 15-20°C in 1 .5 hours. The reaction mass was further stirred for 2 hours at 15-20°C. The precipitated solid was filtered and washed with 40 ml water.

The wet cake was dissolved in 160 ml acetone at 20-25°C. The insoluble were removed by filtration. Added 160 ml water to the clear filtrate at 20-25°C in 2 hours and the reaction mass was further stirred for 2 hours. The solid was isolated by filtration, washed with mixture of acetone : water (1 : 1), and dried under vacuum below 45°C to obtain dabigatran etexilate.

Yield: 18.85 g

Efficiency: 75%

Purification:

18 g of Dabigatran etaxilate was stirred in mixture of acetone: ethanol: ethyl acetate (1.5:0.5:6 volumes) at 50-55°C and stirred for 20 minutes. The reaction mass was cooled to 20-25°C and further chilled to 15-20 °C for 3 hours. The solid was isolated by filtration, washed with ethyl acetate and dried under vacuum below 45°C to obtain dabigatran etexilate.

Yield: 13.5 g

Efficiency: 75%

Example 5. Preparation of DAB etexilate mesylate

10 g (0.02 mol) of dabigatran etexilate was dissolved in 200 ml acetone under nitrogen atmosphere. The temperature of the reaction mass was raised to 50-55°C and treated with a solution of 1.86 g (0.0193 mol) of methane sulfonic acid in 50 ml acetone. The reaction mixture was stirred for 45 minutes, then cooled to 20-25 °C and further stirred for 45 minutes. The solid was isolated by filtration, washed with acetone and dried under vacuum below 45°C to obtain dabigatran etexilate mesylate.

Yield: 10 g

Efficiency: 86%

Example 6. Preparation of ethyl 3-(2-((4-carbamimidoylphenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-IH-benzo[d]imidazole-5-carboxamido) propanoate of Formula (ll)using N-acetyl cysteine

10 g (0.020 mol) of ethyl 3-(2-((4-cyanophenylamino)methyl)- l-methyl-N- (pyridin-2-yl)-IH-benzo[d]- imidazole-5-carboxamido) propanoate of Formula (IV) was dissolved in 600 ml EtOH.NH₃ (15-18%w/w) and stirred at 25°C. Added 3.38 g (0.020 mol) of N-acetyl cysteine to the reaction mass and stirred for 24 hours at 70-75°C under 2.0-2.3 kg of pressure. The ethanol was distilled under vacuum and residue was purified by column.

Yield: 5.5 g

Efficiency: 53%

Example 7. Preparation of DAB Amidine of Formula (II) using N-acetyl cysteine

10 g (0.020 mol) of ethyl 3-(2-((4-cyanophenylamino)methyl)- l-methyl-N- (pyridin-2-yl)-IH-benzo[d]- imidazole-5-carboxamido) propanoate of Formula (IV) with 3.5 g (0.021 mol) of N-acetyl-(S)cysteine were initially charged in 10 ml of ethanol. The reaction mixture was heated to 60-65°C, and saturated with ammonia. After 4 hours, ethanol was distilled under vacuum to obtain titled compound as a solid.

Yield: 7.0 g

Efficiency: 67%

Example 8. Preparation of 2-pyridyl impurity B

Part I: 12.0g (0.016 mol) of dabigatran etexilate was added to the solution of 2.8 g (0.07 mol) sodium hydroxide (in 300 ml water and 150 ml ethanol. The reaction mass was stirred for 5 hours. The solution was concentrated under vacuum and neutralized with aq. solution of citric acid (10%v/v). The solid was separated by filtration and washed with cold water and dried under vacuum to afford the acid as a white crystal.

Yield: 8.50 g

Part 11:10 g ( 0.0166 mol) of DAB-Acid obtained in part I was stirred with 25 ml thionyl chloride under nitrogen The temperature of the reaction mass was raised to 40-45°C and maintained for 1 hour. Thionyl chloride was distilled under vacuum completely The residue was stirred in solution of 100 ml toluene and 10 ml triethyl amine at 5-10°C. Added 3.1 g (0.0329 mol) 2-amino pyridine to the reaction mass at 5-10°C under nitrogen atmosphere. Temperature of the reaction mass was raised to 50-55°C and stirred. Toluene was distilled under vacuum and the residue was dissolved in 150 ml DCM. The organic layer was washed with water, dried on sodium sulfate. The organic layer was distilled under vacuum to obtain t crude 2-Pyridyl impurity which was purified by column chromatography.

Yield: 4.0 g

Example 9. Preparation of ethyl 3-(2-((4-cyanophenylamino)methyl)- l-methyl-N- (pyridin-2-yl)-IH-benzo[d]- imidazole-5-carboxamido) propanoate of Formula (IV)

To a solution of N, N-Carbonyldiimidazole (1.17kg, 7.21 mol) and dichloromethane (1 1.25 L), added 2-(4-cyanophenylamino)acetic acid of Formula (VIII), (1.15Kg,6.52 mol) at 30°C under nitrogen atmosphere. The reaction mixture was stirred for 90-100 min and the resulting solid was filtered under nitrogen atmosphere to obtain form Dab glycine CDI complex of Formula (VII).

Dab glycine CDI complex of Formula (VII) was stirred in toluene (9.0L). Added ethyl 3-(3-amino-4-(methyl amino)-N-(pyridin-2-yl)benzamido)propanoate of Formula (VI) (1.5Kg, 4.38 mol) and maintained the reaction at 45-55°C for 3.0 hrs to form DAB coupling intermediate of Formula (V), which further heated to 90-100°C for 3.0 hrs. The reaction mixture was cooled to 25-30°C and the solid precipitated out was isolated by filtration. The wet cake was stirred in water (9.0L), filtered and dried in vacuum below 60 °C to obtain titled compound.

Yield: 1.80kg

Efficiency: 85 %

Example 10. Preparation of ethyl 3-(2-((4-carbamimidoylphenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-IH-benzo[d]imidazole-5-carboxamido) propanoate of Formula (II)

A mixture of ethyl 3-(2-((4-cyanophenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-IH-benzo[d]-imidazole-5-carboxamido) propanoate of Formula (IV) (1.73 kg,3.58mol) was stirred in ethanol denatured with toluene HCI (32-35 % w/w) (20.76 L) at 15- 20°C for 24 hrs. Reaction mass was distilled out completely and the residue was treated with ethanol denatured with toluene. NH₃ (at 10-15% w/w) was added to get the pH 9.0-9.5. The reaction mixture was stirred further for 12.0 hrs. The inorganic was separated by filtration and the filtrate was distilled out and the residue was stirred in ethyl acetate (10 L) . The solid was isolated by filtration and washed with ethyl acetate. The solid was dried in vacuum below 45°C to obtain titled compound.

Yield: 1.70kg

Efficiency: 95 %

Example 11. Preparation of DAB etexilate of Formula (I)

To a solution of ethyl 3-(2-((4-carbamimidoylphenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-IH-benzo[d]imidazole-5-carboxamido) propanoate of Formula (II) (1.61 kg, 3.22mol ), acetone (19.32 L), water( 9.66 L) and potassium carbonate (1.34Kg, 9.69moles ) was added hexyl chloroformate (0.795 kg, 83 moles) slowly at 20-25°C in 2-3 hrs. The reaction mixture was stirred further for 90 min. The solid was filtered and stirred in 7.5 volumes of acetone at 35-40°C. To the clear solution was added dropwise, 7.5 volumes of purified water. The reaction mixture was stirred further for 2 hours at 20-25°C, solid was isolated by filtration and dried at 45°C. The solid was stirred in a mixture of ethanol: ethyl acetate (1 : 10 volume) at 35-40°C to get clear solution, then gradually cooled to 10-15°C and further stirred for 6.0 hours. The solid was isolated by filtration, washed with ethyl acetate and dried under vacuum below 45°C to obtain dabigatran etexilate.

Yield: 1.10 kg

Efficiency: 65%

Example 12. Preparation of DAB etexilate mesylate

Dabigatran etexilate (1.0Kg, 1.59mol) was dissolved in acetone (20.0L) at 50-55°C under nitrogen atmosphere and treated with a solution of methane sulfonic acid (0.15Kg, 1 .56mol) in acetone (1 .5L). The reaction mixture was stirred for 45 minutes, then cooled to 20-25 °C and further stirred for 45 minutes. The solid was isolated by filtration, washed with acetone and dried under vacuum below 45°C to obtain dabigatran etexilate mesylate.

Yield: 1.10kg Efficiency: 95 %

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