• Dabigatran etexilate (a compound of formula (I)) is the international commonly accepted non-proprietary name for ethyl 3-{[(2-{[(4-{[(hexyloxy)carbonyl]carbamimidoyl}phenyl)amino]methyl}-1-methyl-1H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino}propanoate, which has an empirical formula of C₃₄H₄₁N₇O₅ and a molecular weight of 627.73.

  
• Dabigatran etexilate is the pro-drug of the active substance, dabigatran, which has a molecular formula C₂₅H₂₅N₇O₃ and molecular mass 471.51. The mesylate salt (1:1) of dabigatran etexilate is known to be therapeutically useful and is commercially marketed as oral hard capsules in the United States and in Europe under the trade mark Pradaxa^™ for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation. 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 (see Scheme 1). Example 58 describes the condensation between ethyl 3-{[3-amino-4-(methylamino)benzoyl](pyridin-2-yl)amino}propanoate (compound II) and N-(4-cyanophenyl)glycine (compound III) in the presence of N,N‘-carbonyldiimidazole (CDI) in tetrahydrofuran to give the hydrochloride salt of ethyl 3-{[(2-{[(4-cyanophenyl)amino]methyl}-1-methyl-1H-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-1H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino}propanoate (compound V). Finally, example 113 describes the reaction between compound V and n-hexyl chloroformate (compound VI), in the presence of potassium carbonate, in a mixture of tetrahydrofuran and water, to give dabigatran etexilate after work-up and chromatographic purification. However, no information is given about the purity of the isolated dabigatran etexilate.
  

  
•  U.S. Patent No. 7,202,368 describes an alternative process for the synthesis of dabigatran etexilate (see Scheme 2). Example 3 describes the condensation between ethyl 3-{[3-amino-4-(methylamino)benzoyl](pyridin-2-yl)amino}propanoate (compound II) and 2-[4-(1,2,4-oxadiazol-5-on-3-yl)phenylamino]acetic acid (compound VII) in the presence of a coupling agent such as N,N‘-carbonyldiimidazole (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-1H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino}propanoate (compound VIII), which is subsequently hydrogenated (Example 4) in the presence of a palladium catalyst to give ethyl 3-{[(2-{[(4-carbamimidoylphenyl)amino]methyl}-1-methyl-1H-benzimidazol-5-yl)carbonyl](pyridin-2-yl)amino}propanoate (compound V). Then, Example 5 describes the acylation of compound V with n-hexyl chloroformate (compound VI) to give dabigatran etexilate. Finally, Example 6 describes the conversion of dabigatran etexilate into its mesylate salt. Although the patent describes the HPLC purities of intermediate compounds II, VII, VIII and V, no information is given neither about the purity of the isolated dabigatran etexilate nor about its mesylate salt.
  

  
•  European Patent Applications EP 1966171A and EP 1968949Adescribe similar processes for the synthesis of dabigatran etexilate to that depicted in Scheme 2, but without isolating some of the intermediate compounds. HPLC purities higher than 99% are described for both dabigatran etexilate (see Examples 6B and 6C ofEP 1966171A ) and its mesylate salt (see Example 9 ofEP 1966171A and Example 7 ofEP 1968949A). However, no information is given about the structure of the impurities present in dabigatran etexilate and / or its mesylate salt.
•  PCT Patent Application WO 2010/045900 describes the synthesis of dabigatran etexilate mesylate with 99.5% purity by HPLC (Examples 3 and 4) by following a similar synthetic process to that described in Scheme 1. However, no information is given about the structure of the impurities present in the mesylate salt of dabigatran etexilate.
•  The Committee for Medicinal Products for Human use (CHMP) assessment report for Pradaxa (i.e. dabigatran etexilate mesylate salt 1:1) reference EMEA/174363/2008, as published in the European Medicines Agency website on 23/04/2008, describes (page 8) that the proposed specifications for impurities in the active substance are for some specified impurities above the qualification threshold of the ICH guideline “Impurities in new drug substances”, i.e. above 0.15%. However, no information is given about the structure of the impurities present in the mesylate salt of dabigatran etexilate.

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Patent

http://www.google.com/patents/EP2522662A1?cl=en

There is still further provided by the present invention a process of preparing dabigatran etexilate mesylate, which process comprises the following synthetic steps:

wherein X is a leaving group, such as chloro.

Typically, intermediate (I) is prepared, preferably as a hydrochloride salt, by the following intermediate steps.

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PATENT

http://www.google.com/patents/WO2010045900A1?cl=en

One of the advanced intermediates during the production of dabigatran is the substance of formula VI.

VI

The compound of formula VI is prepared by a reaction of substance IV with reagent V as shown in Scheme 1.

Scheme 1

The procedure described in WO 9837075 produces compound VI in the form of its base or acetate. Both these products require chromatographic purification, which is very difficult to apply in the industrial scale. This purification method burdens the process economy very much and has a negative impact on the yield.

In the next stage acidic hydrolysis of the nitrile function of compound VI and a reaction with ammonium carbonate is performed to produce the substance of formula VII. The reaction is shown in Scheme 2.

Vl VII

Scheme 2 The procedure in accordance with WO 9837075 produces substance VII in the monohydro chloride form.

When reproducing the procedure of WO 9837075 we found out, in line with WO 9837075, that compound VII prepared by this method required subsequent chromatographic purification as it was an oily substance with a relatively high content of impurities. We did not manage to find a solvent that would enable purification of this substance by crystallization.

The last stage is a reaction of intermediate VII with hexyl chloroformate producing dabigatran and its transformation to a pharmaceutically acceptable salt; in the case of the above mentioned patent application it is the methanesulfonate.

Scheme 3.

EtOH

DABIGATRAN

Example 3: Preparation of dabigatran mesylate

To 9.1 g of compound VII-2HC1 (0.016 mol) 270 ml of chloroform and 9 ml (0.064 mol) of triethylamine are added. Then, a solution of 3.1 ml (0.018 mol) of hexyl chloroformate in chloroform is added dropwise at the laboratory temperature. After one hour the reaction mixture is shaken with brine and the organic layer is separated, which is dried with sodium sulfate and concentrated. The obtained evaporation residue is crystallized from ethyl acetate. Yield: 8.6 g (86%)

This product is dissolved in acetone and an equimolar amount of methanesulfonic acid is added dropwise. The separated precipitate is aspirated and dried at the laboratory temperature. Yield: 75%; content according to HPLC: 99.5%. 27

Example 4:

Preparation of dabigatran mesylate

9 g of compound VII-HCl (0.017 mol) were dissolved in 300 ml of chloroform. 6, ml of triethylamine were added to this solution and then a solution of 3.4 ml (0.02 mol) of hexyl chloroformate in chloroform was added dropwise. After one hour the reaction mixture is shaken with brine, the organic layer is separated, which is dried with sodium sulfate and concentrated. The obtained evaporation residue is crystallized from ethyl acetate. Yield: 9.6 g (90%)

This product is dissolved in acetone and an equimolar amount of methanesulfonic acid is added dropwise. The separated evaporation residue is aspirated and dried at the laboratory temperature. Yield: 73%; content according to HPLC: 99.5%.

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PATENT

http://www.google.com/patents/WO2014009966A2?cl=en

DabigatranEtexilateMesylate chemically know as N-[[2-[[[4-[[[(hexyloxy) carbonyl] amino]-iminomethyl] phenyl] amino] _. methyl]-l -methyl-lH- benzimidazol-5-yl] carbonyI]-N-2- pyridinyl-beta-Alanine ethyl ester methanesulfonate having the formula I as provided below,

Formula I

is a direct thrombin inhibitor having anti – coagulant activity when administered orally.

DabigatranEtexilate is first time reported in the US patent 6087380 (hereinafter referred as US’380) in which the process fo the preparation of DabigatranEtexilate is disclosed in the Example 49, 58a and Example 59, said process for the preparation of DabigatranEtexilate is depicted below:

Dabigatran etexilate

In accordance to the process in the Patent US’380 the substance requires complex purifying operations, such as chromatography for the production of high- quality API. Further the chromatographic purification is expensive and difficult to implement in large scale. The impurity in the Dabigatran single prodrug and Dabigatran Etexilate affects the purity of the final product DabigatranEtexilateMesylate.. Hence there is a necessity to maintain the purity level of every intermediate involved in the preparation of DabigatranEtexilateMesylate.

The patent application US201 1082299 discloses a process for the preparation Dabigatran from 3- ([2-[(4-cyanophenyl amino)-methyl]- l-methyl- l H-benzimidazole-5-carbonyl]-pyridin-2-yl-amino) ethyl propionate oxalate as one of the intermediate in order to overcome the problem of the process depicted in the product pate

The patent US81 19810 discloses the process for the preparation Dabigatran from 3- ([2-[(4-cyanophenylamino)-methyl]-l-methyl-lH- benzimidazole-5-carbonyl]-pyridin-2-yl-amino) ethyl propionate hydro bromide as one of the intermediate in order to overcome the problem of the process depicted in the product patent.

The single prodrug of Dabigatran having the formula-II,

and double

which is DabigatranEtexilate are exemplified in the examples of the patent US’380. The patent US’380 has no information about the solid state properties of the single prodrug of Dabigatran and DabigatranEtexilate. However, a similar process described in a publication of Hauel et al in Journal of Medicinal Chemistry, 2002, 45, .1757 – 1766, wherein DabigatranEtexilate is characterized by 128 – 129°C.

The PCT publication WO2006131491 discloses the anhydrous form [ of DabigatranEtexilate having the melting point 135°C, anhydrous form II of DabigatranEtexilate having the melting point 150°C, and hydrate form of DabigatranEtexilate having the melting point 90°C.

The PCT publication WO2008059029 discloses anhydrous form III of DabigatranEtexilate having melting point 128°C, anhydrous form IV of DabigatranEtexilate having the melting point 133°C, and mono hydrate form I of DabigatranEtexilate having melting point 128°C and mono hydrate form II of DabigatranEtexilate having melting point 123°C.

The different forms of the single prodrug of Dabigatran and/or the DabigatranEtexilate are disclosed in the patent applications of WO2012027543, WO2012004396 and WO 2012044595.

The patent application US2007185333 discloses the process ; for the preparation of DabigatranEtexilateMesylate from the DabigatranEtexilate by adding acetone solution of , methanesulfonic acid in an acetone solution of DabigatranEtexilate.

The patent application US 200601 83779 discloses the process for the preparation of DabigatranEtexilateMesylate from the DabigatranEtexilate by adding ethylacetate solution of methanesulfonic acid in an ethylacetate solution of DabigatranEtexilate.

Example-9: Process for the preparation of DabigatranEtexilateMesylate from DabigatranEtexilate

[0086] The DabigatranEtexilate (0.04 mol) was dissolved in acetone (250.0 ml) and added Methanesulfonic acid (0.04 mol) in Ethyl acetate (25 ml) at 25-30°C. Stirred the reaction mass for 3 hrs at the same temperature, the isolated solid was filtered and washed with acetone, dried under vacuum to get the DabigatranEtexilateMesylate. Yield: 85 %, Purity: Not less than 99.0%

Example 10: Process for the preparation of DabigatranEtexilateMesylate

[0087] To a solution of DabigatranEtexilate (0.04 mol) in Acetone (8 volumes) and Ethanol (2 volumes), Methanesulfonic acid solution [Methanesulfonic acid (0.04 mol) was dissolved in Ethyl acetate (25 ml) was added at 25-30°C and stirred for 3 hrs at the same temperature. After completion of the reaction, the resultant solid was filtered, washed with acetone and dried under vacuum. Yield: 93%

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http://www.google.com/patents/WO2013150545A2?cl=en

l-methyl-2-|Tvi-[4-(TSi-n-hexyloxycarbonylamidino)phenyl]aminomethyl]benzimidazole- 5-yl-carboxylicacid-N-(2-pyridyl)-N-(2-ethoxycarbonylethyl)amide is commonly known as Dabigatran etexilate. Dabigatran is an anticoagulant from the class of the direct thrombin inhibitors developed by Boehringer Ingelheim and is used for the treatment of thrombosis, cardiovascular diseases, and the like. Dabigatran etexilalte mesylate was approved in both US and Europe and commercially available under the brand name Pradaxa.

Dabigatran etexilate and process for its preparation was first disclosed in WO 98/37075.

The disclosed process involves the reaction of ethyl 3-(3-amino-4-(methylamino)-N-(pyridin-2- yl)benzamido)propanoate with 2-(4-cyanophenylamino) acetic acid in the presence of N,N- carbonyldiimidazole in tetrahydrofuran to provide ethyl 3-(2-((4-cyanophenylamino)methyl)-l- methyl-N-(pyridin-2-yl)-lH-benzo[d] imidazole-5-carboxamido)propanoate, which is further converted into l-methyl-2-[N-[4-amidinophenyl]aminomethyl]benzimidazol-5-ylcarboxylicacid- N-(2-pyridyl)-N-(2-ethoxycarbonylethyl)amide hydrochloride by reacting with ammonium carbonate in ethanol, followed by treating with ethanolic hydrochloric acid. The obtained compound was reacted with n-hexyl chloroformate in presence of potassium carbonate in tetrahydrofuran/water provides Dabigatran etexilate and further conversion into its mesylate salt was not disclosed. The purity of Dabigatran etexilate prepared as per the disclosed process is not satisfactory, and also the said process involves chromatographic purification which is expensive and difficult to implement in the large scale. Hence the said process is not suitable for commercial scale up.

Moreover, the said process proceeds through the l-methyl-2-[N-[4-amidinophenyl] aminomethyl]benzimidazol-5-ylcarboxylicacid-N-(2-pyridyl)-N-(2-ethoxycarbonylethyl)amide hydrochloride (herein after referred as “Dabigatran hydrochloride”), which degrades to form impurities and resulting in the formation of Dabigatran etexilate with low purity. In view of intrinsic fragility of Dabigatran hydrochloride, there is a need in the art to develop a novel salt form of 1 -methyl-2-[N-[4-amidinophenyl]aminomethyl]benzimidazol-5-ylcarboxylicacid-N-(2- pyridyl)-N-(2-ethoxycarbonyl ethyl)amide, which enhances the purity of the final compound.

The prior reported processes disclosed in WO2012004396 and WO2008095928 Al involves the usage of inorganic salts like hydrochloride and hydrobromide salts of ethyl 3-(2-((4- cyanophenylamino)methyl)- 1 -methyl -N-(pyridin-2-yl)- 1 H-benzo[d]imidazole-5-carboxamido) propanoate (herein after referred as “cyano intermediate”) and ethyl 3-(2-((4-carbamimidoyl phenylamino)methyl)- 1 -methyl -N-(pyridin-2-yl)- 1 H-benzo[d]imidazole-5-carboxamido) propanoate (herein after referred as “amidino intermediate”). The inorganic acid addition salts are less stable when compared to the organic acid addition salts and also the process for the preparation of organic acid addition salts is very much easy when compared to inorganic acid addition salt. Inorganic acid addition salts of amidine intermediate seem to be hygroscopic in nature. Therefore, organic acid addition salts are always preferable to synthesize stable salts which in-turn enhances the purity of the final compound.

The oxalate salt of cyano intermediate was disclosed in WO2009111997. However as on date, there is no other organic acid addition salts of cyano intermediate were reported in the prior art for preparing pure Dabigatran etexilate. Henceforth, there is a need to develop a novel organic acid addition salt of cyano intermediate compound which is very much efficient when compared to its corresponding oxalate salt and that result in the formation of final compound with high purity and yield.

The process disclosed in WO 98/37075 also involves the reduction of, ethyl 3-(4- (methylamino)-3-nitro-N-(pyridin-2-yl)benzamido)propanoate (herein after referred as “nitro compound”) using Pd-C in a mixture of dichloromethane and methanol under hydrogen pressure to provide ethyl 3-(3-amino-4-(methylamino)-N-(pyridin-2-yl)benzamido)propanoate (herein after referred as “diamine compound”).

The reduction of nitro compound through catalytic hydrogenation in the presence of tertiary amine under hydrogen pressure was also disclosed in WO2009153214; and in presence of inorganic base under hydrogen pressure was also disclosed in WO2012004397.

However, most of the prior art processes proceed through catalytic hydrogenation which involves the pressure reactions. Handlings of these pressure reactions are not suitable for the large scale process. Therefore, there is a significant need in the art to provide a simple reduction process which avoids the difficulties associated with catalytic hydrogenation.

JMC, 2002, 45(9), 1757-1766 disclosed a process for the preparation of ethyl 3-(3-amino- 4-(methylamino)-N-(pyridin-2-yl)benzamido)propanoate starting from 4-(methylamino)-3- nitrobenzoic acid. The disclosed process involves the conversion of 4-(methylamino)-3- nitrobenzoic acid into its acid chloride using thionyl chloride and the obtained compound was reacted with ethyl 3-(pyridin-2-ylamino)propanoate to provide nitro compound, followed by catalytic reduction using Pd-C to provide diamine compound.

However, particularly in large scale synthesis the reduction reaction occasionally stops due to catalyst poisoning which leads to incomplete reaction and requires additional catalyst to complete the reaction. Moreover the sulfur impurities which are present in nitro compound formed due to the reaction with thionyl chloride in the previous stages of the synthesis of diamine compound are strongly influence the reaction time, quality and catalyst consumption in the manufacturing process.

Surprisingly, the problem associated with the catalytic hydrogenation and catalyst poisoning is solved by the present invention by adopting a suitable reducing agent such as Fe- acetic acid and Fe-hydrochloric acid.

The crystalline forms-I, II, V and VI of Dabigatran etexilate oxalate were disclosed in WO2008043759 and WO2011110876.

The crystalline forms-Ill, IV and V of Dabigatran etexilate fumarate were disclosed in WO2008043759 and WO2011110876.

Various different salts for Dabigatran etexilate and their polymorphs were reported in WO98/37075, WO03074056, WO2005028468, WO2006114415, WO2008043759, WO2011110876, WO2012027543 and WO2012044595.

The process for the preparation of crystalline form-I of Dabigatran etexilate mesylate was described in WO2005028468 and WO2012027543.

HPLC analysis of Innovator Tablet

The present inventors has also analyzed the Pradaxa 110 mg tablet having Lot no: 808809 and compared with dabigatran etexilate mesylate obtained from the present invention and found that, the impurity profile of both the products are similar to each other i.e., amide impurity, despyridyl ethyl ester etc. are well present even in Pradaxa tablet. Henceforth, we can presume that these impurities are known from the art.

Amide Impurity: 0.31%; Despyridyl ethyl ester: 0.10%; Deshexyl Impurity: 0.08%. HPLC Method of Analysis:

a) Dabigatran etexilate (Formula-1) and Dabigatran etexilate mesylate (Formula-la):

Apparatus: A liquid chromatographic system is to be equipped with variable wavelength

UV-detector; Column: Zorbax Eclipse XDB CI 8, 100 X 4.6mm, 3.5 μιη θΓ Equivalent; Flow Rate: 1.0 mL/min; Wavelength : 300 nm; Column temperature: 25°C; Injection volume: 5 μΐ,; Run time: 50 minutes; Auto sampler temperature: 5°C; Buffer: Dissolve 0.63gm of Ammonium formate in lOOOmL of Milli-Q- Water and mix well. Adjust its pH to 8.2 with Ammonia and filtered through 0.22 μιη nylon membrane and degas it. Mobile phase-A: Buffer; Mobile phase- B: Acetonitrile: Water (80:20) v/v; Diluent: N,N-Dimethylformamide; Needle wash: Diluent; Elution: Gradient. b) Ethyl 3-(2-((4-cyanophenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-lH-benzo[d] imidazole-5-carboxamido)propanoate methanesulfonate (Formula-10)

Apparatus : A liquid chromatograph is equipped with variable wavelength UV- Detector; Column: Zorbax SB CN 150 x 4.6mm, 5μπι (or) Equivalent (Make: Agilent and PNo: 883975- 905); Flow Rate: 1.0 mL / min; Column temperature: 25°C; Wave length: 290 nm; Injection volume: 5 μΐ-.; Run time: 60 minutes; Elution: Gradient; Diluent: Water: Acetonitrile (70:30) v/v; Needle wash: Diluent; Buffer: Weigh accurately about 2 g of 1 -Octane sulphonic acid sodium salt anhydrous and add 5 mL of Ortho phosphoric acid in 1000 mL of Milli-Q- Water and mix well, filter this solution through 0.22 μηι^ΐοη membrane and sonicate to degas; Mobile Phase- A: Buffer(100%);Mobile Phase- B: Acetonitrile: Methanol (90: 10) v/v. c) Ethyl 3-(2-((4-carbamimidoylphenylamino)methyl)-l-methyl-N-(pyridin-2-yl)-lH- benzo[d] imidazole-5-carboxamido)propanoate methanesulfonate (Formula-11)

Apparatus : A liquid chromatographic system is to be equipped with variable wavelength UV- Detector and Integrator; Column : Zodiac CI 8 250 X 4.6 mm, 5 μηι (or) equivalent (Make: Zodiac and PNo. ZLS.C18.46.250.0510 ); Flow Rate: 1.0 mL/min; Wavelength: 290 nm; Column temperature: 25°C; Injection Volume: 5μί; Run time: 55 min; Elution: Gradient;

Buffer: Take 5 mL of Ortho phosphoric acid(85%) and 2 g of 1 -Octane sulfonic acid sodium salt anhydrous in 1000 mL of Milli-Q-water and adjust its pH to 2.5 with Triethyl amine filter, through 0.22 μπι Nylon membrane filter paper and sonicate to degas it; Mobile Phase-A: Buffer(l 00%) Mobile Phase-B: Acetonitrile: Water (90: 10) v/v; Diluent : Water: Acetonitrile (80:20) v/v.

Morphology: Method of analysis: Samples were mounted on aluminium stubs using double adhesive tape, coated with gold using HUS-5GB vacuum evaporation and observed in Hitachi S-3000 N SEM at an acceleration voltage of 10KV.

Following are the impurities observed during the preparation of Dabigatran etexilate mesylate.

Deshexyl Impurity Despyridyl Ethyl Ester

Methyl Carbamate Ethyl Carbamate

The present invention is schematically represented as follows:

Formula-2 ene

Formula-6

Fe-AcOH

Formula-7

Dabigatran etexilate Dabigatran etexilate Mesylate The process described in the present invention was demonstrated in examples illustrated below.

Example-13: Preparation of Dabigatran etexilate (Formula-1)

n-hexanol (30.8 g) was added to a solution of N, N-carbonyldiimidazole (61.15 g) and dichloromethane (360 ml) at 15-25°C and stirred for 3 hours. The organic layer was washed with water followed by sodium chloride solution. Distilled off the solvent from the organic layer completely under reduced pressure to get amide compound. Acetonitrile (157.5 ml) was added to the obtained amide compound. This was added to a mixture of ethyl 3-(2-((4- carbamimidoylphenylamino)methyl)-l-methyl-N-( yridin-2-yl)-lH-benzo[d]imidazole-5- carboxamido)propanoate mesylate compound of formula- 11 (90 g), potassium carbonate (62.5 g), acetonitrile (378 ml) and water (252 ml) at 25-35°C. The reaction mixture was heated to 40- 50°C and stirred for 8 hours. After completion of the reaction, both the organic and aqueous layers were separated; the organic layer was cooled to -5 to +5°C and stirred for 2 hours. Filtered the precipitated solid washed with acetonitrile and water. The obtained compound was dissolved in a mixture of acetone (270 ml) and acetonitrile (270 ml) at 45-50°C. Cooled the reaction mixture to 25-30°C and water (360 ml) was added to it. Filtered the obtained solid and dissolved in the mixture of dichloromethane and sodium chloride solution at 35-40°C. Both the organic and aqueous layers were separated; the organic layer was distilled under reduced pressure and then co-distilled with ethyl acetate. The obtained crude compound was dissolved in ethyl acetate (540 ml) by heating it to 70-80°C and stirred for 30 minutes. Filtered the reaction mixture, the filtrate was cooled to 35-45°C and ethanol (8 ml) was added to the reaction mixture. The reaction mixture was again cooled to 25-35°C and stirred for 3 hours. Filtered the precipitated solid and then dried to get pure title compound.

Yield: 44 g; MR: 128-131 °C. Purity by HPLC: 99.63%.

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http://www.google.com/patents/WO2014020555A2?cl=en

EXAMPLE 6

Preparation of dabigatran etexilate mesylate: l-methyl-2-[N-[4-( -n-hexyloxycarbonylamidino)phenyl] amino methyl]benzimidazol-5- yl-carboxylicacid-N-(2-pyridyl)-N-(2-ethoxycarbonyl ethyl) amide (100 gm) was dissolved acetone (1000 ml) under heating at 25-35 °C. A solution of methane sulfonic acid (13.77 gm) in acetone (100 ml) was added to the reaction mixture. The solution is filtered and after the addition of acetone cooled to approximately 20° C. The precipitated product was filtered and washed with acetone then dried at 50° C under reduced pressure.

Wet weight : 0.120-0.140 kg

Dry weight : 0.90-1.0 kg

Yield (W/W) : 0.90-1.0

Theoretical Yield (w/w) : 1.15

Percentage Yield : 78.2-86.9%

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WO2015124764

ERREGIERRE S.P.A. [IT/IT]; Via Francesco Baracca, 19 I-24060 San Paolo D’argon (IT)

Erregierre SpA

DABIGATRAN ETEXILATE MESYLATE, INTERMEDIATES OF THE PROCESS AND NOVEL POLYMORPH OF DABIGATRAN ETEXILATE”

Abstract

A novel process is described for the production of Dabigatran etexilate mesylate, a 5 compound having the following structural formula: and two novel intermediates of said process.

(WO2015124764) SYNTHESIS PROCESS OF DABIGATRAN ETEXILATE MESYLATE, INTERMEDIATES OF THE PROCESS AND NOVEL POLYMORPH OF DABIGATRAN ETEXILATE click herefor patent

Dabigatran etexilate mesylate is an active substance developed by Boehringer

Ingelheim and marketed under the name Pradaxa^® in the form of tablets for oral administration; Dabigatran etexilate mesylate acts as direct inhibitor of thrombin (Factor I la) and is used as an anticoagulant, for example, for preventing strokes in patients with atrial fibrillation or blood clots in the veins (deep vein thrombosis) that could form following surgery.

Dabigatran etexilate mesylate is the INN name of the compound 3-({2-[(4-{Amino-[(E)-hexyloxycarbonylimino]-methyl}-phenylamino)-methyl]-1 -methyl-1 H-benzimidazol-5-carbonyl}-pyridin-2-yl-amino)-ethyl propanoate methanesulphonate, having the following structural formula:

The family of compounds to which Dabigatran etexilate belongs was described for the first time in patent US 6,087,380, which also reports possible synthesis pathways.

The preparation of polymorphs of Dabigatran etexilate or Dabigatran etexilate mesylate is described in patent applications US 2006/0276513 A1 , WO 2012/027543 A1 , WO 2008/059029 A2, WO 2013/124385 A2, WO 2013/124749 A1 , WO 2013/1 1 1 163 A2 and WO 2013/144903 A1 , while patent applications WO 2012/044595 A1 , US 2006/0247278 A1 , US 2009/0042948 A2, US 2010/0087488 A1 and WO 2012/077136 A2 describe salts of these compounds.

One of the objects of the invention is to provide an alternative process for the preparation of Dabigatran etexilate mesylate and two novel intermediates of the process.

These objects are achieved with the present invention, which, in a first aspect thereof, relates to a process for the production of Dabigatran etexilate mesylate, comprising the following steps:

a) reacting 4-methylamino-3-nitrobenzoic acid (I) with thionyl chloride to give 4- methylamino-3-nitrobenzoyl chloride hydrochloride (II):

(I) (ID

b) reacting compound (II) with 3-(2-pyridylamino) ethyl propanoate (III) to give the compound 3-[(4-methylamino-3-nitro-benzoyl)-pyridyn-2-yl-amino]-ethyl propanoate (IV):

(II) (IV)

reducing compound (IV) with hydrogen to 3-[(3-amino-4-methyl benzoyl)-pyridin-2-yl-amino]ethyl propanoate (V):

(IV) (V)

d) reacting N-(4-cyanophenyl)glycine (VI) with 1 ,1 -carbonyldiimidazole (CDI) to give 4-(2-imidazol-1 -yl-2-oxo-ethylamino)-benzonitrile (VII):

(VI) (VII)

e) reacting compound (VII) with compound (V) obtained in step c) to give one of compounds 3-({3-[2-(4-cyano-phenylamino)-acetylamino]-4-methylamino- benzoyl}-pyridin-2-yl-amino)-ethyl propanoate (VIII) and 3-[(3-amino-4-{[(2- (4-cyano-phenylamino)-acetyl]-methylamino}-benzoyl)-pyridin-2-yl- amino]ethyl propanoate (IX), or a mixture of the two compounds (VIII) and (IX):

f) transforming, through treatment with acetic acid, compounds (VIII) or (IX) or the mixture thereof into the compound 3-({2-[(4-cyano-phenylamino)-methyl]- 1 -methyl-1 H-benzimidazol-5-carbonyl}-pyridin-2-yl-amino)-ethyl propanoate (X), and then treating compound (X) with hydrochloric or nitric acid to form the corresponding salt (XI):

CHsCOOH

[(VIII) ; (IX)]

wherein A is a chlorine or nitrate anion;

liberating in solution compound (X) from salt (XI), and reacting compound (X) in solution with ethyl alcohol in the presence of hydrochloric acid and 2,2,2-trifluoroethanol to give the compound 3-({2-[(4-ethoxycarbonimidoyl-phenylamino)-methyl]-1 -methyl-1 H-benzimidazol-5-carbonyl}-pyridin-2-yl-amino)-ethyl propanoate hydrochloride (XII):

reacting compound (XII) with ammonium carbonate to form compound Dabigatran ethyl ester (XIII):

reacting compound (XIII) with maleic acid to produce the maleate salt thereof (XI 11 ‘) and isolating the latter:

j) reacting maleate salt (XI 11 ‘) with hexyl chloroformate to give compound Dabigatran etexilate (XIV :

hexyl chloroformate

k) reacting compound (XIV) with methanesulfonic acid to give the salt Dabigatran etexilate mesylate:

a gatran etex ate mesy ate

EXAMPLE 12

Preparation of Dabigatran etexilate mesylate (step k).

All the Dabigatran etexilate obtained in Example 1 1 (4.7 kg; 7.49 moles) is loaded into a reactor along with 28.2 kg of acetone and the mass is heated at 50-60 °C until a complete solution is obtained; it is then filtered to remove suspended impurities. The filtered solution is brought to 28-32 °C. Separately, a second solution is prepared by dissolving 0.705 kg (7.34 moles) of methanesulfonic acid in 4.7 kg of acetone; the second solution is cooled down to 0-10 °C. The second solution is poured into the Dabigatran etexilate solution during 30 minutes, while maintaining the temperature of the resulting solution at 28-32 °C with cooling. The salt of the title is formed. The mass is maintained at 28-32 °C for 2 hours, then cooled to 18-23 °C to complete precipitation and the system is maintained at this temperature for 2 hours; lastly, centrifugation takes place, washing the precipitate with 5 kg of acetone. The precipitate is dried at 60 °C.

4.88 kg of Dabigatran etexilate mesylate, equal to 6.74 moles of compound, are obtained, with a yield in this step of 90%.

EXAMPLE 13

0.5 g of the crystalline compound (XIV) obtained in Example 1 1 are ground thoroughly and loaded into the sample holder of a Rigaku Miniflex diffractometer with copper anode.

The diffractogram shown in Figure 1 is obtained; a comparison with the XRPD data of the known Dabigatran etexilate polymorphs allows to verify that the polymorph of Example 1 1 is novel.

EXAMPLE 14

0.7 g of the crystalline compound (XIV) obtained in Example 1 1 are loaded into

the sample holder of a Perkin-Elmer DSC 6 calorimeter, performing a scan from ambient T to 350 °C at a rate of 10 °C/min in nitrogen atmosphere. The graph of the test is shown in Figure 2, and shows three endothermic phenomena with peaks at 83.0-85.0 °C, 104.0-104.2 °C and 129.9 °C; events linked to the thermal decomposition of the compound are evident at about 200 °C.

Figure 1 is an XRPD spectrum of the novel polymorph of Dabigatran etexilate of the invention;

Figure 2 is the graph of a DSC test on the novel polymorph of Dabigatran etexilate of the invention.

1H NMR OF

Dabigatran etexilate mesylate 872728-81-9

.

…

PATENT

http://www.google.com/patents/WO2012044595A1?cl=en

Examples

Reference examples:

Preparation of starting material: Dabigatran etexilate mesylate form I according to US 2005/0234104 example 1:

Ethyl 3 – [(2- { [4-(hexyloxycarbonylarninoimmomemyl)phenylammo]methyl } –

1 – methyl- lH-benzimidazole-5-carbonyl)pyridm-2-ylamino]propionate base (52.6 kg) (which has preferably been purified beforehand by recrystallization from ethyl acetate) is placed in an agitator apparatus which has been rendered inert and then 293 kg of acetone is added. The contents of the apparatus are heated to 40° C to 46° C with stirring. After a clear solution has formed, the contents of the apparatus is filtered into a second agitator apparatus through a lens filter and then cooled to 30° C to 36° C. 33 kg of acetone precooled to 0° C to 5° C, 7.9 kg of 99.5% methanesulfonic acid, and for rinsing another 9 kg of acetone are placed in the suspended container of the second apparatus. The contents of the suspended container are added in metered amounts to the solution of ethyl 3-[(2-{[4-(hexyloxycarbonylamino- iminomethyl)phenylamino]methyl} – 1 -methyl- 1 H-benzimidazole-5-carbonyl)pyridin-

2- ylamino]propionate base at 26° C to 36° C within 15 to 40 minutes. Then the mixture is stirred for 40 to 60 minutes at 26° C to 33° C. It is then cooled to 17° C to 23° C and stirred for a further 40 to 80 minutes. The crystal suspension is filtered through a filter dryer and washed with a total of 270 L of acetone. The product is dried in vacuum at a maximum of 50° C for at least 4 hours. Yield: 54.5-59.4 kg;

90%-98% of theory based on ethyl 3-[(2-{[4-(hexyloxycarbonyl- ammoiminomethyl)phenylamino]methyl} – 1 -methyl- 1 H-benzimidazole-5-carbonyl)- pyridm-2-ylamino]propionate base.

Preparation of starting material: Dabigatran Etexilate free base

Dabigatran Etexilate free base can be prepared according to the procedures disclosed in US 6087380 – example 113 or US 7202368 – example 5 Example 1

2.08 g of dabigatran etexilate free base was dissolved in 14.7 ml of acetone at 30 – 36 °C. 0.210 ml of methanesulfonic acid diluted in 2.20 ml of acetone was added within 15 – 40 min. at 26 – 36 °C. The resulting mixture was first steered for 40 – 60 min. at 26 – 36 °C and then for 40 – 80 min at 17 – 23 °C.

The resulting crystalline product was filtered off, washed with 17.87 ml of acetone and dried at 50 °C for 18 hours at 540 mbar.

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PAPER

4-Methylamino-3-nitrobenzoic acid(3) was prepared from 3-nitro-4-chlorobenzoic acid by methylamination. 3-[(Pyridin-2-yl)amino]propinoic acid ethyl ester(5) was prepared from 2-aminopyridine and ethyl acrylate by Michael addition. Dabigatran etexilate was synthesized from compounds 3 and 5 via condensation, catalytic hydrogenation, acylation with N-(4-cyanophenyl)glycine(9), cyclization, Pinner reaction, followed by reaction with n-hexyl chlorofomate. The overall yield is about 40% and the structure of the product was determined by IR, 1H NMR and MS.

ＥＳＩＭＳ（ｍ／ｚ）：６２８［Ｍ＋Ｈ］＋；１ ＨＮＭＲ（５００ＭＨｚ，ＤＭＳＯｄ６）， δ：０９１（ｔ，３Ｈ，Ｊ＝９０Ｈｚ，ＣＨ３），１１６（ｔ，３Ｈ，Ｊ＝８５Ｈｚ，ＣＨ３），１２５～１６９（ｍ，８Ｈ，４×ＣＨ２），２７４（ｔ， ２Ｈ，Ｊ＝１４５Ｈｚ，ＣＨ２ＣＯ），３７９（ｓ，３Ｈ，ＣＨ３Ｎ），３９５～４０３（ｍ，４Ｈ，２ＣＨ２Ｏ），４２８（ｔ，２Ｈ，Ｊ＝１４０Ｈｚ， ＣＨ２），４５１（ｄ，２Ｈ，Ｊ＝５５Ｈｚ，ＣＨ２Ｎ），６７６（ｄ，Ｊ＝８５Ｈｚ，２Ｈ，Ａｒ—Ｈ），６８８（ｄ，Ｊ＝７５Ｈｚ，１Ｈ，Ａｒ— Ｈ）， ７０２（ｓ，１Ｈ，Ｎ—Ｈ），７１３～７２１（ｍ，２Ｈ，Ｐｙ—Ｈ），７４０（ｄ，Ｊ＝８５Ｈｚ，１Ｈ，Ａｒ—Ｈ），７４７（ｄ，Ｊ＝１５Ｈｚ， １Ｈ，Ａｒ—Ｈ），７５５～７５９（ｍ，１Ｈ，Ｐｙ—Ｈ），７８６（ｄ，Ｊ＝８５Ｈｚ，２Ｈ，Ａｒ—Ｈ），８３６～８４３（ｍ，１Ｈ，Ｐｙ—Ｈ）， ９０２（ｂｒｓ，２Ｈ，ＮＨ２）；ＩＲ（ＫＢｒ），σ／ｃｍ－１ ：３３７４，２９５３，２９２９，１７３０，１６４０，１６１０，１４７０，１３８９，１３２６，１２５６，１１９２， １１４５，１１２７，１０２１，９４５，８３５，８１１，７６８，７４７。

…………

PAPER

Identification, Synthesis, and Strategy for the Reduction of Potential Impurities Observed in Dabigatran Etexilate Mesylate Processes

Synthetic impurities that are present in dabigatran etexilate mesylate were studied, and possible pathways by which these impurities are formed during the manufacturing process were examined. The impurities were monitored by high-performance liquid chromatography, and their structures were determined by mass spectrometry and ¹H and ¹³C NMR. Potential causes for the formation of these impurities are discussed, and strategies to minimize their formation are also described.

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1H NMR PREDICT

13 C NMR PREDICT ABOVE

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