FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention -Novel Reference markers of Dabigatran
2. Applicant(s)
(a) NAME: ALEMBIC PHARMACEUTICALS LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS; Alembic Campus, Alembic Road,
Vadodara-390, 003, Gujarat, India
3, PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which is to be
performed:

FIELD OF THE INVENTION
The present invention deals with a new method of obtaining chemically pure and
pharmaceutically acceptable Dabigatran or its pharmaceutical acceptable salt having purity at
least about 99 %, wherein the content of Dabigatran impurity is less than 0.03-0.15 % as
measured by HPLC. The invention also discloses a method of removing specific impurities that
are generated either due to the intrinsic instability of Dabigatran or produced in the process of its
preparation.
BACKGROUND OF THE INVENTION
Preparation of Dabigatran was first described in the document no. WO 9837075; however, this
method brings many technological problems, e.g. very complicated purifying operations,
problems with low purity of intermediate products and the resulting low yield and low purity of
the final product.
One of the advanced intermediates during the production of dabigatran is the substance of
formula (111)

Formula (111) The compound of formula (III) is prepared by a reaction of substance IV with reagent V as shown in Scheme 1.

The procedure described in WO 9837075 produces compound III 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 conversion of cyano group tp amidate using etlranolic HC1 followed by ammonium carbonate to obtain substance of formula (VI), The reaction is shown in Scheme 2.
The procedure in accordance with WO 9837075 produces substance VI in the monohydro chloride form.
When reproducing the procedure of WO 9837075 we found out, in line with WO 9837075, that compound VI 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 VI 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.
However, the method in accordance with WO 9837075 does not make it possible to prepare dabigatran with high purity, which is required in the case of a pharmaceutical substance, and in a yield acceptable in the industrial scale. The reason is mainly low purity of the intermediate products, which are moreover produced in forms requiring complicated purification with the use of chromatographic methods.
Several methods for the preparation of Dabigatran have been described like any synthetic compound, Dabigatran, or a pharmaceutically-acceptable salt thereof can contain process impurities, unreacted starting materials, chemical derivatives of impurities contained in starting materials, synthetic by-products, and degradation products. It is also known in the art that impurities present in an active pharmaceutical ingredient ("API") may arise from degradation of the API, for example, during storage or during the manufacturing process, including the chemical synthesis,

It is well known in the art that, for human administration, safety considerations require the establishment, by national and international regulatory authorities, of very low limits for identified, but lexicologically uneharacterized impurities, before an active pharmaceutical ingredient (API) product is commercialized. Typically, these limits are less than about 0.15 percent by weight of each impurity, Limits for unidentified and/or uneharacterized impurities are obviously lower, typically less than 0.1 percent by weight. Specific standards can be applied to certain drugs where a pharmacopoeia monograph has been established for that drug. Typically, for impurities that are present in an amount of greater than 0.1 percent by weight, the impurity should be fully identified and characterized.
Therefore, in the manufacture of active pharmaceutical ingredients (APIs) knowledge of the purity of the API, such as Dabigatran, is required before commercialization, as is the purity of the API in the manufactured formulated pharmaceutical product.
Impurities introduced during commercial manufacturing processes must be limited to very small amounts and are preferably substantially absent. For example, the ICH Q7A guidance for API manufacturers requires that process impurities be maintained below set limits by specifying the quality of raw materials, controlling process parameters, such as temperature, pressure, time, and stoichiometric ratios, and including purification steps, such as crystallization, distillation, and liquid-liquid extraction, in the manufacturing process.
Impurities generally found in pharmaceutically active agents and formulations containing them include residual amounts of synthetic precursors to the active agent, by-products which arise during synthesis of the active agent, residual solvent, isomers of the active agent, contaminants which were present in materials used in the synthesis of the active agent or in the preparation of the pharmaceutical formulation, and unidentified adventitious substances. Other impurities which may appear on storage include substances resulting from degradation of the active agent, for instance by oxidation or hydrolysis, the ICH Q7A guidance for API manufacturers requires that process impurities be maintained below set limits by specifying the quality of raw materials, controlling process parameters, such as temperature, pressure, time, and stoichiometric ratios, and including purification steps, such as crystallization, distillation, and liquid-liquid extraction, in the manufacturing process.
At certain stages during processing of an API, such as Dabigatran Etexilate, or a pharmaceutically-acceptable salt thereof, it must be analyzed for purity, typically, by HPLC or

GC analysis, to determine if it is suitable for continued processing and, ultimately, for use in a pharmaceutical product. The API need not be absolutely pure, as absolute purity is a theoretical ideal that is typically unattainable. Rather, purity standards are set with the intention of ensuring that an API is as free of impurities as possible, and, thus, are as safe as possible for clinical use. In the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use ("ICH") guidelines recommend that the amounts of unknown impurities be limited to less than 0,1 percent.
As is known by those skilled in the art, the management of process impurities is greatly enhanced by understanding their chemical structures and synthetic pathways, and by identifying the parameters that influence the amount of impurities in the final product.
Impurities in Dabigatran Etexilate includes, but not limited to, unreacted starting materials, byproducts of the reaction, products of side reactions, or degradation products are undesirable and, in extreme cases, might even be harmful to a patient being treated with a dosage form containing the API. Thus, there is a need in the art for a method for determining the level of impurities in Dabigatran samples and removing the impurities.
While developing a process for the preparation of Dabigatran Etexilate, present inventors serendipitously found an improved process for the preparation of highly pure Dabigatran which minimizes process impurity like
Ethyl 2-{[(4-carbamimidoylphenyl) amino]methyl}-l-methy)-H-benzimidazole-5-carboxylate hydrochloride,
Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methyl]-lH-methyl-\H- benzimidazole-5-carboxylate,
Ethyl-3-[[[2-[[(4-(ethoxycarbonyl) phenyl)amino]methyl]-l-methyl-lH-benzimidazol-5-
yl]carbonyl]pyridine-2-ylamino]propionate hydrochloride,
Ethyl 2-({[4-(ethoxycarbonyl)phenyl] amino}methyl)-l-methyI-lH-benzimidazole-5-carboxylate,
Ethyl-3-[[[2-[[(4-carbamoylphenyl) amino]rnethyl]-l-methyl-lH- benzimidazol-5-yl]
carbonyl]pyridine-2-ylamino]propionate,

Ethyl 2-{f(4-cyanopheny])amino] mgthyl}-!-methyl-lH-benzimidazole- 5-carboxylate,
Ethyl 2-{[(4-carbamoyiphenyl)amino]m6thyl}-l-methyl-3H-benzimidazole-5-carboxylate,
N-(pyridine-2-yl)-3-[[[2-[[(4-amidinophenyl)arnino] methyl]-l-methyl-lH-benzimidazol-5-yl] carbonyl]pyridine-2-ylamino] propionamide,
Methyl-3-[[[2-[[(4-[imino(ethoxy)methyl]phenyl)amino]raethyI]-l-methyl-lH- benzimidazol -5-yl] garbonyl]pyridine-2-ylamino]propionate
MethyI-3-[[[2-[[(4-amidjnophenyl)amino] methyl]-l-methyl-lH-benzimidazol- 5-yl]
carbonyl]pyridine-2-ylarnino] propionate
OBJECT OF THE INVENTION
The present object of the invention is to provide Dabigatran impurities like,

Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methyl]-l-methyl-lH- benzimidazole-5-carboxylate

Ethyl]-3-[[[2-[[(4-(ethoxycarbonyl) pheny!)amino]methyl]-l-methyl-lH-benzirnidazol-5-
yl]carbonyl]pyridine-2-ylamino]propionate hydrochloride,

Ethyl 2-{[(4-carbamimidoylphenyl) amino] methyl}-l-methyl-lH-benzimidazole-5-carboxylate
hydrochloride, having following formula,




Ethyl-3-[[[2-[[(4-amidinophenyl) amino]methyl]--l-methyl-lH-benzimidazol-5-yl]
carbonyl]pyridine-2-ylamino] propionate
Ethyl 2-{[(4-cyanopheny])amino] mgthyl}-1-methyl-lH-benzimidazole- 5-carboxylate,
Ethyl 2-{[(4-cyanopheny])amino] mgthyl}-1-methyl-lH-benzimidazole- 5-carboxylate,

Ethyl 2-{[(4-cyanopheny])amino] mgthyl}-1-methyl-lH-benzimidazole- 5-carboxylate,
Methyl-3-[[[2-[[(4-amidinophenyl) amino]methyl]-l-methyl-lH-benzimidazol-5-yl]
carbonyl]pyridine-2-ylamino] propionate

N-(pyridine-2-yl-3-[[[24[(4-amidinophenyl)amino methyl]-1 -methyl- lH-benzimidazol-5-yl] carbonyl]pyridine-2-ylamino] propionamide,

Methyl-3-[[[2-[[(4-amidinophenyl)amino] methyl]--l-methyl-lH-benzimidazol- 5-yl]
carbonyl]pyridine-2-ylamino] propionate


Yet another object of the invention is to provide Dabigatran Etexilate salt having purity at least about 99 % with the less content from any of the above mentioned impurities and its salts thereof, Moreover the above impurities having HPLC purity range from less than 0.03-0.IS % as measured by HPLC.
Further object of the invention is to provide Dabigatran impurity, ethyl 2-{[(4-earbamimidoylphenyl)amjno]methyl}-1-methyl-1H -benzimidazole-5-carboxylate hydrochloride used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further object of the invention is to provide Dabigatran impurity, Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methyI]-l-methyl-lH benzimidazole-5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt,
Further object of the invention is to provide Dabigatran impurity, Ethyl-3-[[[2-[[(4-(ethoxycarbonyl) phenyl)amino]methyl]- 1 -methyl- lH-benzimidazol-5-yl]carbonyl] pyrtdine-2-ylamino]propionate hydrochloride used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further object of the invention is to provide Dabigatran impurity, Ethyl 2-({[4-(ethoxycarbonyl)phenyl] amino}methyl)-l-methyl-lH-benzimidazole-5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further object of the invention is to provide Dabigatran impurity, Ethyl-3-[[[2-[[(4-carbamoylphenyl) amino]methyl]-l-methyl-1H- benzimidazol-5-yl] carbonyl]pyridine-2-ylaminojpropionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further object of the invention is to provide Dabigatran impurity, Ethyl 2-{[(4-cyanophenyl)amino] methyl}-1-methyl-1H-benzimidazole- 5-carboxyIate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt
Further object of the invention is to provide Dabigatran impurity, Ethyl 2-{[(4-carbamoylphenyl) amino]methyl}-l-methyl-li/-benzimidazole-5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.

Further object of the invention is to provide Dabigatran impurity, N=(pyridine-2-yl)-3-|;[[2-E[(4^ amidinophenyl)amino] methyl]-!-methyl-lH-benzimidazol-5-yl] earbonyl]pyridine-2-ylamino] propionamide used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt,
Further object of the invention is to provide Dabigatran impurity, Methyl-3-[[[2-[[(4-
[imino(ethoxy)methyi]phenyl)amino]methyl]-]-methyl-1H- benzimidazol -5-yl]
earbonyl]pyridine-2-ylamino]propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further object of the invention is to provide Dabigatran impurity, Methyl-3-[[[2-[[(4-amidinophenyl)amino] methyl]-1-methyl-lH-benzimidazol- 5-yl] carbonyl]pyridine-2-ylamino] propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
SUMMARY OF THE INVENTION
The present aspect of the invention is to provide Dabigatran impurities like,
Ethyl 2-{[(4-carbamimidoylphenyl) amino] methyl}-l-methyl-lH-benzimidazole-5-carboxylate hydrochloride, having following formula,

Ethyl 2~[({4-[imino(ethoxy) Methyl] phenyl}amino)methyl]-l-methyl-\H- benzimidazole-5-earboxylate

Ethyl-3-[[[2[[(4-ethoxyearbonyl) phenyl)amino]methyl]-l-methyl-lH-benzimidazol-5-
yl]carbonyl]pyridine-2-ylamino]propionate hydrochloride,

Ethyl 2-{[(4-cyanopheny])amino] mgthyl}-1-methyl-lH-benzimidazole- 5-carboxylate,

Ethyl-3-[[[2-[[(4-carbamoylphenyl) aminb]methyl]-l -methyl-lH- benzimidazol-5-yVj
carbonyl]pyridine-2-ylamino]propionate,

Ethyl 2-{[(4-cyanopheny])amino] mgthyl}-1-methyl-lH-benzimidazole- 5-carboxylate,

Ethyl 2-{[(4-carbamoylphenyl)amino]methyl}-l-methyI-lH-benzimidazole-5-carboxylate,

N-(pyridine-2-yl)-3-[[[2-[[(4-amidinophenyl)amino] methyl]-l-methyl-lH-benzirnidazol-5-yl] carbonyl]pyridine-2-ylamino] propionamide,

Methyl-3-[[[2-[[(4-[iminQ(ethoxy)methyl]phenyl)amino]methyl]-l-methyl-lH' benzimidazol -5-yl] carbonyl]pyridine-2-ylamino]propiQnate

Methyi-3-[[[2-[[(4-amidinophenyl)amino] methyl]-] -methyl- lH-benzimidazol- 5-yl]
carbonyl]pyridine-2-ylamino] propionate


Yet another aspect of the invention is to provide Dabigatran Etexilate salt having purity at least about 99 % with the less content from any of the above mentioned impurities and its salts thereof. Moreover the above impurities having HPLC purity range from less than 0.03-0.15 % as measured by HPLC.
Further aspect of the invention is to provide Dabigatran impurity, ethyl 2-{[(4-carbamimidoylphenyl)amino]methyl}-l-methyl-lH-benzimidazole-S-carboxylate hydrochloride used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity. Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyI}amino)methyl]-l-methyl-lH- benzimidazole-5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, Ethyl-3-[[[2-[[(4-(ethoxycarbonyl) phenyl)amino]methyl]- 1 -methyl -H-benzimidazol-5-yl]carbonyl] pyridine-2-ylaminojpropionate hydrochloride used as referent marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, Ethyl 2-({[4-(ethoxycarbonyl)phenyl] amino}methyl)-l-methyl-1H-benzimidazole-5-carboxylato used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, Ethyl-3-[[[2-[[(4-carbamoylphenyl) amino]methyl]-l-methyl-1H. benzimldarol-S-yl] carbonyl]pyridine-2-ylamino]propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, Ethyl 2-{[(4-cyanophenyl)amino] methyl}-l-methyl-lH-benzimidazole. 5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.

Further aspect of the invention is to provide Dabigatran impurity, Ethyl 2-{[(4>carbamoyIphenyl} amino]methyl}-l-methyl-lif-benzimidazole-5-earboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, N-(pyridine-2-yI)-3-[[[2-[[(4-amidinophenyl)amino] methyl]-1 -methyl- l.H-benzimidazol-5-yl] earbonyl]pyridine-2-ylamino] propionamide used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, Methyl~3-[[[2-[[(4-
[imino(ethoxy)methyl]phenyl)amino]rnethy!]-l -methyl- 1H- benzimidazol -5-yl]
carbonyl]pyridine-2-ylamino]propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further aspect of the invention is to provide Dabigatran impurity, Methyl-3-[[[2-[[{4-amidinophenyl)amino] methyl]-1-methyl-IH-benzimjdazoI- 5-yl] carbonyl]pyridine-2-ylamino] propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
DETAILS DESCRIPTION OF THE INVENTION
The present embodiment of the invention is to provide Dabigatran impurities like,
Ethyl 2-{[(4-carbamimidoylphenyl) amino] methyl}-l-methyI-l//-benzimidazole-5-carboxylate hydrochloride, having following formula,

Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methylH-methyl-liy-bgnzimidazole-5-carboxylate

Ethyl-3-[[[2-[[(4-(etboxycarbonyI) phenyl)amino]methyl]-l-me(hyl-lH-bensdmidazol-5-
yl]carbony!]pyfidine-2-ylamino]propionate hydrochloride,

Ethyl 2-{[4-ethoxycarbonyl)phenyl]amino}methy])-1-methyl-1H-benzimidaTOJe-5-.carboxyJateI

Ethyl-3-[[[2-[[(4-carbamoylphenyl) amino]methyl]-l-methyl-1H- benzimidazol-5-yl]
carbonyl]pyridine-2-ylamino]propionate,

Ethyl 2-{[(4-cyanophenyl)amino] methyl}-l-methyl-lH-benzimidazole- 5-carboxylate,

Ethyl 2-{[(4-carbamoylphenyl}amino]methyI}-l-methy-1H-benzimidazole-S-carboxylate,

N-(pyridine-2-yl)-3-[[[2-[[(4-amidinophenyl)amino] methyl]-1-methyl-lH-benzimidazol-5-yl] carbonyl]pyridine-2-ylamino] propionamide,

Methyl-3-[[[2-[[(4-[itnjno(8thoxy)methyl]phenyl)aniino]methyl]-l=methyl-lH- benzimldazol -5-yl] earbonyl]pyrldine-2-ylairiino]prepionate



Methyl-3-[[[2-[[(4-am!dinaphenyl)amina] methyl]-1 -methyMH-beflslmldwol- S-yl]
sarbonyl]pyridine-2-ylamlno] propionate
Yet another embodiment of the invention is to provide Dabigatran Etexilate salt having purity at least about 99 % with the less content from any of the above mentioned impurities and its salts thereof. Moreover the above impurities having HPLC purity range from less than 0.03-0,15 % as measured by HPLC.
Further embodiment of the invention is to provide Dabigatran impurity, ethyl 2-{[(4-carbamimidoyiphenyl)amino]methyl}-l-methyi-I/T-benzimidazole-5-carboxylate hydrochloride used as reference marker or reference standard for determining the purity of Dabigatran Etexilate
salt.
Further embodiment of the invention is to provide Dabigatran impurity, Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methyl]-l -methyl-\H- benzimidazole-5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further embodiment of the invention is to provide Dabigatran impurity, Ethyl"3-[[[2-[[(4-(ethoxycarbonyl) phenyI)amino]methyl]- I-methyl-lH-benzimidazol-5-yl]carbonyI] pyridine-2-ylamino]propionate hydrochloride used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further embodiment of the invention is to provide Dabigatran impurity, Ethyl 2-({[4-(ethoxycarbonyl)phenyl] amino} methyl)-1 -methyl- l/f-benzimidazole-5-carboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt
Further embodiment of the invention is to provide Dabigatran impurity, Ethyl-3«[[[2-[[(4-carbamoylphenyl) amino]methyl]-l-methyl-1H- benzimidazol-S-yi] carbonyl]pyridine-2-ylamino]propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.

Further embodiment of the invention is to provide Dabigatran impurity, Ethyl 2~{[(4-cyanophenyl)ammo] methyl}-l-rnethyl-lH-benzimidazpie- 5-earboxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt,
Further embodiment of the invention is to provide Dabigatran impurity, Ethyl 2-{[(4-earbamoylphenyl) amino]methyl}-l-methyl-lH-benzimidazoIe-5-carbaxylate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further embodiment of the invention is to provide Dabigatran impurity, N-(pyndine-2-yI}-3-[[[2-[[(4-amidinophenyl)aniino] methyl]-l-methyl-lH-benzimidazol»5-yl] carbonyl]pyridine-2-ylamino] propionamide used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further embodiment of the invention is to provide Dabigatran impurity, Methyl-3-[[[2-[[(4-
[imino(ethoxy)methyl]phenyl)amino]methyl]-l-methyl-lH- benzimidazol -5-yl]
carbonyl]pyridine-2-ylamino]propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt.
Further embodiment of the invention is to provide Dabigatran impurity, Methyl-3-[[[2-[[{4-amidinophenyl)amino] methyl]-1 -methyl-lH-benzimidazol- 5-yl] carbonyl]pyridine-2-ylamino] propionate used as reference marker or reference standard for determining the purity of Dabigatran Etexilate salt,
Impurities isolated by column chromatography form the process of preparation of Dabigatran process in conversion of cyano to imidiate ester:
To the previously prepared saturated solution of HC1 in Ethanol (The solution is prepared by
passing dry HC1 gas to the absolute alcohol), was added a solution of cyano compound in a
mixture of Ethanol and Dichloromethane at 1S-309C. After completion of addition, reaction
mixture was allowed to stir at 20-30OC for about 6h. After that the reaction was terminated and
taken for work up.
Isopropyl ether waS added to the above reaction mass, stirred it for 5-lQmin, decant supernatant layer, Isopropyl ether was added to it. Again decant supernatant layer, potassium carbonate solution (15%) in water was added into reaction mass and extract with ethyl acetate. Distilled out solvent under vacuum and purified by column chromatography to isolate impurities:

i) Ethyl 2"[({4-[im!no(ethoxy)MfthyI3phenyl}aminQ)metliyl]4-m©thyl4H'
bensdmidazole-S-earboxylate
ii) Ethyl-3-[[[2-[[(4-(ethoxyoarbonyl) phenyl)amino]met|iyl]-l-methyl-lH-
benzimidazol-S-yl]earbenyl]pyridine-2-yl8mino]prapienate, hydrQchloride iii) Ethyl 2-({[4-(ethoxyeat,bony])phenyI]amino}methy:l)-l-methyl-lH-benzimidazele=§' carboxylate
iv) Ethyl 2-{[(4-eyanophenyl)&mino]mgthyl}-NmethyI'lH-benziiTiidai?ole--5--c8rbpsy!afe
v) Methyl-3-[[[2-[[(4-[imino(ethoxy)methyl]phenyl)amino]methyl]-l-methyl-]H-
benzimidazol-5-yl]carbonyl]pyridine-2-ylamino]propionate
Impurities isolated by column chromatography form the process of preparation of Dabigatran process in conversion of imidiate ester to amidine:
To the previously prepared saturated solution bf HC1 in Ethanol (The solution is prepared by passing dry HCi gas to the absolute alcohol), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-30eC, After completion of addition, reaction mixture was allowed to stir at 20-30°C for about 6h. After that the reaction was terminated and taken for work up.
Isopropyl ether was added to the above reaction mass, stirred it for 5-10min. decant supernatant layer, Isopropyl ether was added to it, Again decant supernatant layer, Ethanol was added to the residue to give clear solution. To this solution, was added previously prepared ammonical ethanol (Ammonia gas passed into ethanol) at 15-30°C. The reaction mixture was allowed to stir at r. t, for about 20-24h.
The reaction mass was filtered and washed with ethanol The filtrate was distilled under vacuum and residue was purified by column chromatography to isolate impurities:
i) Ethyl 2-{[(4-carbamimidoylphenyl)amino]methyl}-l-methyl-lH-benzimidazole-5-
carboxylate hydrochloride
ii) Ethyl-3-[[[2-[[(4-carbamoylphenyl)amino]methyl]-l-methyI-lH-benzimidazol-S-
yl]carbonyl]pyridine-2-ylamino]propionate
iii) ethyl 2-{[(4-carbamoylphenyI) amino]methylH-methyl-lH-benzimidazole»S-
carboxylate
iv) N-(pyridine-2-yl)3-[[[2-[[(4-amidinophenyl)amino]methyl]-l-methyL-1H-
benzimidazol-5-yl]carbonyl]pyridine-2-ylamino]propionamide

v) Methy3-3-[[I2-[[(4-amidinophenyl)amino]methyl]'l-methyl-lH-benzimidazol-'S-
yl]carbonyl3pyridlne-2-ylamino]propionatc
According to one aspect of the present invention, there is provided a reversed-phase liquid chromatographic (RP-LC) method for quantifying, by area percent, the amounts of Dabigatran Etexilate mesylate and all impurities, preferably, KSM-I, Stage-IIA, Stage-11, Propionate ester, Methyl Ester, Amidine impurity, Amide Diester, Diester impurity and Etexilate impurity present in a sample of Dabigatran Etexilate mesylate.
According to another aspect of the present invention, there is provided a stability indicating analytical method using the samples generated from forced degradation studies.
According to another aspect of the present invention, there is provided an accurate and well-defined stability indicating HPLC method for the determination of Dabigatran Etexilate mesylate in the presence of degradation products.
Preferably, the method for determining the amount of impurities in a Dabigatran Etexilate mesylate sample comprises the steps of
a) Combining a Dabigatran Etexilate mesylate sample with eluent A and acetonitrile in the ratio of about 20:30 (v/v) to obtain a solution;
b) injecting the sample solution into a 150 mm x 4.6 mm, column with 3,5u.m u.m ZORBAX SB-Phenyl column;
c) gradient eluting the sample with a mixture of buffer and acetonitrile in the ratio of 85:15 (v/v) initial and progressively increased to 30:70(v/v) in 45 minutes.
d) Preparing eluent A by dissolving 4.14 g of Sodium dihydrogen phosphate in 1000 ml of
water, dissolve and adjust pH = 5,8 with sodium hydroxide solution, Filter it through 0,45 u
membrane filter and degas.
e) Measuring of the amounts of Dabigatran and each impurity at 225nm wavelength with a UV detector (having an appropriate recording deviee).
Preferably, the initial ratio of eluent A and acetonitrile in step-(c) may be continued at the same ratio for 5 minutes then changed linearly to 55:45 (v/v) within 35 minutes followed by same ratio for 5 minutes. Again changed linearly to 30:70 (v/v) within 45 minutes followed by same ratio for 5 minutes. After 3 minutes the initial gradient of 85:15 is for 7 minutes to be conditioned for every analysis, The column temperature may be maintained at about 50°C.

Specificity is the ability ef the method to measure the analyte response in the presence of its potential impurities and degradation products, The specificity of the LC method for Dabigatran Etexilate mesylate, Intentional degradation was attempted to stress conditions of acid hydrolysis (using 1M HCI), base hydrolysis (using 1M NaOH), and oxidative degradation (using 3.0% H2O2X to evaluate the ability of the proposed method to separate Dabigatran Etexllate mesylate from its degradation products. To check and ensure the homogeneity and purity of Dabigatran peak in the stressed sample solutions, PDA-UV detector was employed.
The present invention is described by the following Example, which is illustrative only and should not be construed so as to limit the scope of the invention in any manner.
Example 1:
Preparation of Ethyl 2-({[4-(ethoxycarbonyl)phenyl]amino}methyl)-l-methyl-lH-
benzimidazole-5-carboxylate:
To the previously prepared saturated solution of HCI in Ethanol (The solution is prepared by passing dry HCI gas to the absolute alcohol at -10-20°C), was added a solution of 1-methyl -2-[N-(4-cyanophenyl)-aminomethyl]benzimidazol-5-yl-carboxylicacid''N-(2-pyridyl)-N-(2-ethoxy carbonyl ethyl)-amide (cyano compound) in a mixture of Ethanol and Dichloromethane at 15-30°C. After completion of addition, reaction mixture was allowed to stir at 20-30aC for about 6h. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-lQmin,, decant supernatant layer. Isopropyl ether was added to it again and decant supernatant layer. Potassium carbonate solution (15%) in water was added into reaction mass and extracted with ethyl acetate. Solvent was distilled out under vacuum and purified by column chromatography. Eluent was 10% Ethyl acetate in n-Hexane and collect the fraction of Impurity. Solvent evaporate at 45°C under vacuum and characterized by mass (M+l=382.5).
Example 2:
Preparation of Ethyl-3-({[2-[[(4-(ethoxycarbonyl) phenyl)3mii)o]methylj-l-m(>thyl-lH-
benzimidazoI-S-yl]carbonyl]pyridine-2-ylamino]propionate, hydrochloride:
To the previously prepared saturated solution of HCI in Ethanol (The solution is prepared by passing dry HCI gas to the absolute alcohol at ~10-20°C), was added a solution of cyano

compound in a mixture of Ethanol and Diohloromethane at 15-30eC. After completion of addition, reaction mixture was allowed to stir at 20'30eC for about 6h. After that the reaction was terminated and taken for work up, Isopropyl ether was added to the above reaction mass, stirred it for 5-lOmin,, decant supernatant layer. Isopropyl ether was added to it again and decant supernatant layer. Potassium carbonate solution (15%) in water was added into reaction mass and extracted with ethyl acetate, Solvent was distilled out under vacuum and purified by column chromatography, Eluent was 15% Ethyl acetate in n-Hexane and collect the fraction of impurity, Solvent evaporate at 45QC under vacuum and characterized by mass (M-f 1=530.5).
Example 3;
Preparation of Ethyl 2-{[(4-cyanophenyl)amino]methy]}-l-methyl-lH-bens5imidazoIe-S-
carboxylate:
To the previously prepared saturated solution pf HCI in Ethanol (The solution is prepared by passing dry HCI gas to the absolute alcohol at ~10-2Q°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-3Q°C. After completion of addition, reaction mixture was allowed to stir at 20-3 0°C for about 6h. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-10min., decant supernatant layer. Isopropyl ether was added to it again and decant supernatant layer. Potassium carbonate solution (15%) in water was added into reaction mass and extracted with ethyl acetate. Solvent was distilled out under vacuum and purified by column chromatography. Eluent was 25% Ethyl acetate in n-Hexane and collect the fraction of impurity, Solvent evaporate at 45°C under vacuum and characterized by mass (M+1=335.4).
Example 4:
Preparation of Ethyl 2-[({4-[imino(ethoxy)Methyl]phenyl}amino)mcthyl]-l-methyHH-
benzimldazole-5-earboxylate:
To the previously prepared saturated solution of HCI in Ethanol (The solution is prepared by passing dry HCI gas to the absolute alcohol at ~10-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-30°C After completion of addition, reaction mixture was allowed to stir at 20-30oC for about 6h, After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-10min„ decant supernatant layer. Isopropyl ether was added to it again and decant supernatant layer. Potassium carbonate solution (15%) in water was added into reaction mass and

extracted with ethy] aeetate, Solvent was distilled out under vacuum and purified by column chromatography. Eluent was 40% Ethyl acetate in n-Mexane and collect the fraction of impurity, Solvent evaporate at 45oC under vacuum and characterized by mass (M+l=380.4).
Example 3;
Preparation of Methyl-3-[[[2-[[(4-[imino(ethoxy)methyljphenyI)amino]raethyl]-l-metbyl-
lH-bt'ii2lmidazol-5-yljcarbonylJpyridine-2-ylainino]propionate:
To the previously prepared saturated solution of HC1 in Ethanol (The solution is prepared by passing dry HCl gas to the absolute alcohol at ~10-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-30°C. After completion of addition, reaction mixture was allowed to stir at 20-30°C for about 6h. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-lQmin., decant supernatant layer. Isopropyl ether was added to it again and decant supernatant layer. Potassium carbonate solution (15%) in water was added into reaction mass and extracted with ethyl acetate. Solvent was distilled out under vacuum and purified by column chromatography. Eluent was neat Ethyl acetate and collect the fraction of impurity, Solvent evaporate at 45°C under vacuum and characterized by mass (M+l=514.5),
Example 6:
Preparation of Ethyl 2-{[(4-carban)imiddoylphcnyl)amino]methyl}-'l-methyI-IH-
benzimidazole-5-carboxylate hydrochloride;
To the previously prepared saturated solution of HCl in Ethanol (The solution is prepared by passing dry HCl gas to the absolute alcohol at ~10-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-3(PC After completion of addition, reaction mixture was allowed to stir at 20-30°C for about 6h. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-10min, decant supernatant layer, Isopropyl ether was added to it. Again decant supernatant layer, ethanol was added to the residue to give clear solution. To this solution, was added previously prepared ammonical ethanol (Ammonia gas passed into ethanol) at 15-30°C. The reaction mixture was allowed to stir at r. t. for about 20-24h. The reaction mass was filtered and washed with ethanol the filtrate was distilled under vacuum and residue was purified by column chromatography. Eluent was neat Ethyl acetate and collect the fraction of impurity. Solvent evaporate at 48aC under vacuum and characterized by mass (M+1=3S2.5),

Example 7;
Preparation Methyll-3-!|!2-[f(4-amidinophenyl)amino]mclhyl]-l-methyl4H-
benzimidnzol-5-yl]carbonyl]pyrldlne-2-yIamino|propionate
To the previously prepared saturated solution of HC1 in Ethane! (The solution is prepared by passing dry HC1 gas to the absolute alcohol at -0-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-30°C. After completion of addition, reaction mixture was allowed to stir at 20-30oC for about 6h. After that the reaction was terminated and taken for work up, Isopropyl ether was added to the above reaction mass, stirred it for 5-10min, decant supernatant layer, Isopropyl ether was added to it. Again decant supernatant layer, Ethanol was added to the residue to give clear solution. To this solution, was added previously prepared ammonieal ethanol (Ammonia gas passed into ethanol) at 15-308C. The reaction mixture was allowed to stir at r. t. for about 20-24h.
The reaction mass was filtered and washed with ethanol the filtrate was distilled under vacuum and residue was purified by column chromatography. Eluent was neat Ethyl acetate and collect the fraction of impurity. Solvent evaporate at 48°C under vacuum and characterized by mass (M+l-486.5).
ExampleS:
Preparation of Ethyl 2-{[(4-carbamoyIphenyl) amino]methyl}-l-methyl-lH-
bciizimidazole-5-carboxy)ate;
To the previously prepared saturated solution of HC1 in Ethanol (The solution is prepared by passing dry HC1 gas to the absolute alcohol at ~10-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 1S-30BC. After completion of addition, reaction mixture was allowed to stir at 20-30BC for about 6h. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-10min. decant supernatant layer, Isopropyl ether was added to it. Again decant supernatant layer, Ethanol (5T) was added to the residue to give clear solution, To this solution, was added previously prepared ammonieal ethanol (Ammonia gas passed into ethanol) at 15-30BC, The reaction mixture was allowed to stir at r. t. for about 20-24h. The reaction mass was filtered and washed with ethanol the filtrate was distilled under vacuum and residue was purified by column

chromatography, Eluent was 5% ethanol in ethyl acetate and collect the fraction of impurity. Solvent evaporate at 48eC under vacuum and characterized by mass (M+l=353.5),
Example 9:
Preparation of Ethyl-3-[[[2-[[(4-carbamoylphenyl)amino]methyl]-l-inethyl»lH-
benzimidazol-5-yl]earbonyIjpyridine-2-y!aminQjpropionate
To the previously prepared saturated solution of HC1 in Ethanol (The solution is prepared by passing dry HC1 gas to the absolute alcohol at ~1Q-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-30eC. After completion of addition, reaction mixture was allowed to stir at 20-30°C for about 6b. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 5-10min. decant supernatant layer, Isopropyl ether was added to it. Again decant supernatant layer, Ethanol was added to the residue to give clear solution. To this solution, was added previously prepared ammonical ethanol (Ammonia gas passed into ethanol) at 15-308C. The reaction mixture was allowed to stir at r. t. for about 20-24h. The reaction mass was filtered and washed with ethanol the filtrate was distilled under vacuum and residue was purified by column chromatography. Eluent was 10% ethanol in ethyl acetate and collect the fraction of impurity, Solvent evaporate at 4g°C under vacuum and characterized by mass (M+1=501.6),
Example 10:
Preparation of N-(pyridine-2-yl)-3-[[[2-[[(4-amidinophenyl)aminoImethyl]-l-methyl-
lH-bcnzimidazol-5-yl]carbonyl]pyridine-2-ylamino]propionamide
To the previously prepared saturated solution of HC1 in Ethanol (The solution is prepared by passing dry HCI gas to the absolute alcohol at ~10-20°C), was added a solution of cyano compound in a mixture of Ethanol and Dichloromethane at 15-30°C. After completion of addition, reaction mixture was allowed to stir at 20-30°C for about 6h. After that the reaction was terminated and taken for work up. Isopropyl ether was added to the above reaction mass, stirred it for 540min. decant supernatant layer, Isopropyl ether was added to it. Again decant supernatant layer, Ethanol was added to the residue to give clear solution. To this solution, was added previously prepared ammonical ethanol (Ammonia gas passed into ethanol) at 15-30°C. The reaction mixture was allowed to stir at r. t. for about 20-24h. The reaction mass was filtered and washed with ethanol the filtrate was distilled under vacuum and residue was purified by column

chromatography. Eluent was 20% ethanol in ethyl acetate and collect the fraction of impurity. Solvent evaporate at 48eC under vacuum and characterized by mass (M+1=548,6).

We Claim,
1, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound Ethyl 2-{[(4-cat*bamimidoyiphenyl) amino] methyl}-1-methyl-1if-benzimidazole-5-carboxylate hydrochloride.
2, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methyl]-l-methyl-\H~ benzimidazole-5-earboxylate,
3, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound Ethyl-3-[[[2-[[(4-(ethoxycarbonyl) phenyl)arnino]rnethyl]-l-methyl-lH-benzimidazol-5-yl]carbony!]pyridine-2^ylamino]propionate hydrochloride.
4, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compoundEthyl 2-({[4-(ethoxycarbony!)phenyl] am|no}methyl)-l-methyl-l#-benzimidazole-S-carboxylate.
5, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compoundEthyl-3-[[[2'[[(4"Carbamoylphenyl) amino]methyl]"l-methyl-1H-benzimidazol-S-yl] earbonyl]pyHdine-2-ylamino]propionate.
6, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound Ethyl 2-{[(4-eyanophenyl)amino] methyl}-l-methyl-l//-benzimidazole-5-carboxylate,
7, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence

of a compound Ethyl 2-{[(4-carbamoy!phenyl) amino]methyI}-l-methyl-l//-benzimidazole-5-carboxylate.
8, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound N-(pyridine-2-yl)-3-[[[2-[[(4-amidinoph0iiy!)amino] methyl]-!-methyl-lH-benzimidazol-S-yl] carbonyl]pyridine-2-ylamino] propienamide.
9, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound Methyl-3-[[[2-[[{4-[imino(ethoxy)methyl]phenyl)amino]methyl]-l-methyl-lH- benzimidazol -5-yl] carbonyl]pyridine-2-ylamino]propionate.
10, A method of testing the purity of a sample of Dabigatran Etexilate or a pharmaceutical dosage form of Dabigatran Etexilate, comprises assaying the said sample for the presence of a compound Methyl-3-[[[2-[[(4-amidlnophenyl)amino] methyl]-1-methyl-1H-benzimidazpl- S-yl] carbonyl]pyridine-2-ylamino] propionate.
Jl. A method of testing the purity of a sample of Dabigatran Etexilate or its salt or a pharmaceutical dosage form comprising Dabigatran Etexilate according to claim 1 to claim 10, which method further comprises using a sample of compound
(a) Ethyl 2-{[(4-carbamimidoylphenyl) amino] methyl}-l-methyl-l#-benzimidazole-S-carboxylate hydrochloride, or
(b) Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}amino)methyl]-l -methyl-Iff-benztmidazole-5-carboxylate, or
(c) EthyI-3-[[[2-[[(4-(ethoxycarbonyl) phenyl)amino]methyl]-l-methyl-lH-benzimidazol-5-yl]carbonyl]pyridine-2-ylamino]propionate hydrochloride, or
(d) Ethyl 2-({[4-(ethoxycarbonyl)phenyl] amino}methyl)-l"methyl4#-benzimidazole-5-carboxylate, or
(e) Ethyl-3~[[[2-[[(4-carbamoylphenyl) amino]methyl]-l-methyl-1H- benzimidazol-S-yl] carbonyl]pyridine-2-ylamino]propionate, or
(f) Ethyl 2-{[(4-cyanophenyl)amino] methyl}-!-methyl-W=benzimidazole- 5-carboxylate, or
(g) Ethyl 2-{[(4-carbamoylphenyl) amino]methyl}-l-methyl-l/f-benzimidazole-5-earboxylate, or

(h) N-(pyridine4-yl)=3-[[[24[(4-smidinephenyl)amino] methyl]-!-methyl- 1H-
benzimidmo\-5-yl] carbonyl]pyridine-2-ylamina] propionamide, or
(i) Methyl-3-[[[2-[[(4-[imino(ethoj(y)methyl]phenyl)amino]methyl]-I -methyl- 1H-benzimidazol -5-yl] carbony|]pyridine-2-ylamino]propionate, or
(j) Methyl-3-[[[2-[[(4-amidinophenyl)amino] methyl]-!-methyl-lH-benzimidazol-5-yl] carbonyl]pyridine-2-ylamino] propionate having a purity level of at least 80% as a reference marker.
12. An isolated specific impurity of dabigatran etexilate chemically, Ethyl 2-{[(4-earbamimidoylphenyl) amino] methyl}-1-methyl-lH-benzimidazole-5-carboxylate hydrochloride, having following formula,

13. An isolated specific impurity of dabigatran etexilate chemically, Ethyl 2-[({4-[imino(ethoxy) Methyl] phenyl}arnino)methyl]-l-methyl-lH- benzimidazole-5-carboxylate

14. An isolated specific impurity of dabigatran etexilate chemically, Ethyl-3-[[[2-[[(4-
(ethoxycarbonyl) phenyl)amino]methyl]-i-methyl-lH-benzimidflzel-S-
yl]carbonyl]pyridine-2-ylamino]propionate hydrochloride,

15. An isolated specific impurity of dabigatran etexilate chemically, Ethyl 2-({[4-(ethoxycarbonyl)phenyl] amino}methyl)-l-methyl-lHben:dmidazole-S-earboxylate,


16. An isolated specific impurity of dabigatran qtexilate chemically, Ethyl-3-[[[2-[[(4-carbamoylphenyl) amino]methyl]-l-methyl- 1H- benzimidazol-5-yl] carbonyl]pyridine-2-ylamino]propionate,

17. An isolated specific impurity of dabigatran etexifate chemically, Ethyl 2-{[(4-cyanophenyl)amino] methyl }4-methyl-lH-benzimidazole- 5-carboxylate,

18. An isolated specific impurity of dabigatran etesilate chemically, Ethyl 2-{[(4-carbamoy!phenyl)amino]methyl}-l-methyl-lH-benzimidazole-5-earboxylate,

19. An isolated specific impurity of dabigatran etexilate ehemtaally, N-(pyridine-2-yl)-3-[[[2-[[{4-ftmidinophenyl)amino] methyl]-1-methyl-lH-benzimidazol-5-yl] carbonyl]pyrid|ne-2-ylamino] propionamide,


20. An isolated specific impurity of dabigatran etexilate chemically, Methyl-3-[[[2-[[(4-[imino(ethoxy)methyl]phenyl)araino]methy]1 -methyl-1H- benzimidazol -5-yl] earbenyl]|jyi'idine-2-ylamino]propionatc

21, Ap isolated specific impurity of dabigatran etexilate chemically, Methyl-3-[[[2-[[(4-amidinophenyl)amino] methyl]-l-methyl-lH~benzimidazol- 5-yl] carbpnyl]pyrldine-2-ylamino] propionate

22. A Dabigatran Etexilate salt, containing 0,15 % and less of individual impurities of claim 12 to claim 21,
23. A Dabigatran Etexilate salt having purity at least about 99 % wherein impurities of claim 12 to claim 21 In individual is in the range of about 0.03 % to about 0.15 % as measured by HPLC.
24. A process for using reference marker for determining the presence of impurities of in Dabigatran Etexilate or salt comprising the steps of;

(a) dissolving a reference standard of impurities to produce a reference solution,
(b) dissolving a sample of Dabigatran Etexilate or salt in a solvent (diluent) to produce a sample solution
(c) injecting the diluent, reference solution and sample solution on to an HPLC column, and determining the area of each peak and calculating the purity of Dabigatran Etexilate or salt.
25. A method for determining the amount of impurities in a Dabigatran Etexilate mesylate
sample comprises the steps of:

(a) Combining a Dabigfttran Etexilate mesylate sample with eiuent A and aeetonitrile in the ratio of about 20:30 (v/v) to obtain a solution;
(b) injecting the sample solution into a 150 mm x 4,6 mm, column with 3.Sum um ZQRBAX SB-Phenyl column;
(e) gradient ©luting the sample with a mixture of buffer and aeetenltrile in the ratio of 85:15 (v/v) initial and progressively increased to30:70(v/v) in 45 minutes.
(d) Preparing eluent A by dissolving 4,14 g of Sodium dihydrogen phosphate in 1000 ml of water, dissolve and adjust pH = 5.8 with sodium hydroxide solution, Filter it through 0,45 |A membrane filter and degas.
(e) Measuring of the amounts of Dabigatran and each impurity at 225nm wavelength with a UV detector.