PROCESS FOR THE PREPARATION OF CRYSTALLINEFORM I OF
METHANESULFONATE SALT OF DABIGATRAN ETEXILATE
Field of the Invention
The present invention relates to a process for the preparation of crystalline Form I
of the methanesulfonate salt of dabigatran etexilate. The present invention does not
require the isolation of a dabigatran etexilate intermediate.
Background of the Invention
The drug substance used in the commercial drug product formulation of Pradaxa®
is the methanesulfonate salt of dabigatran etexilate, which is chemically designated as b-
Alanine, N-[[2-[[[4-[[[(hexyloxy)carbonyl]amino]iminomethyl]phenyl]amino]methyl]-lmethyl-
lH-benzimidazol-5-yl]carbonyl]-N-2-pyridinyl-,ethyl ester, methanesulfonate salt
of Formula I .
FORMULA I
Dabigatran etexilate of Formula II
FORMULA II
is a prodrug of dabigatran of Formula III
FORMULA III
which is a direct thrombin inhibitor. Dabigatran etexilate is indicated to reduce the risk of
stroke and systemic embolism in patients with non-valvular atrial fibrillation. It may be
used alone or in combination with other therapeutic agents.
U.S. Publication No. 2005/0234104 describes processes for the preparation of
crystalline Forms I and II of the methanesulfonate salt of dabigatran etexilate. The
crystalline Form I of the methanesulfonate salt of dabigatran etexilate is prepared by
dissolving dabigatran etexilate in acetone followed by the addition of a solution of
methane sulfonate in acetone.
PCT Publication No. WO 2012/077136 describes a process for the preparation of
crystalline Form I of the methanesulfonate salt of dabigatran etexilate using an ester and
alcohol solvent system, and specifically using ethyl acetate and ethanol solvents.
Processes for the preparation of dabigatran etexilate and its methanesulfonate salt
are also described in U.S. Patent No. 6,087,380 and PCT Publication Nos. WO
2012/027543, WO 2008/059029, WO 201 1/1 10478, and WO 2006/131491.
Summary of the Invention
The present inventors have developed a process for the preparation of crystalline
Form I of a methanesulfonate salt of dabigatran etexilate. The present process involves
the direct addition of a methane sulfonic acid solution to the reaction mixture without
isolating a dabigatran etexilate intermediate. The present process is simple and capable of
preparing crystalline Form I of a methanesulfonate salt of dabigatran etexilate in a
reproducible manner on an industrial scale.
Brief Description of the Drawings
Figure 1 depicts the X-ray powder diffraction (XRPD) pattern of crystalline Form I
of the methanesulfonate salt of dabigatran etexilate.
Table 1 provides the values of XRPD pattern depicted in Figure 1.
Detailed Description of the Invention
An aspect of the present invention provides a process for the preparation of
crystalline Form I of a methanesulfonate salt of dabigatran etexilate, wherein the process
comprises
a) contacting ethyl N-[(2-{[(4-carbamimidoylphenyl)amino]methyl}-l-methyl-
3a,7a-dihydro-l H-benzimidazol-5-yl)carbonyl ]-N-pyridin-2-yl -P-alaninate of
Formula IV
FORMULA IV
or its salt with n-hexyl chloroformate;
b) treating the reaction mixture obtained in step a) with methane sulfonic acid;
and
c) isolating crystalline Form I of the methanesulfonate salt of dabigatran
etexilate from the mixture thereof.
The ethyl N- [(2- {[(4-carbamimidoylphenyl)amino]methyl} - 1-methyl-3a,7adihydro-
l H-benzimidazol-5-yl)carbonyl ]-N-pyridin-2-yl -P-alaninate of Formula IV or its
salt may be prepared according to methods described in the literature, for example, U.S.
Patent No. 6,087,380.
The salts of ethyl N-[(2-{[(4-carbamimidoylphenyl)amino]methyl}-l-methyl-
3a,7a-dihydro- lH-benzimidazol-5-yl)carbonyl ]-N-pyridin-2-yl -P-alaninate of Formula IV
may be selected from hydrochloride, hydrobromide, or acetate salt. The salt of compound
of Formula IV is preferably the acetate salt.
The compound of Formula IV is contacted with n-hexyl chloroformate in the
presence of a solvent selected from the group consisting of water, ethers, halogenated
hydrocarbons, esters, or mixtures thereof. The ether solvent may be selected from the
group comprising tetrahydrofuran, diisopropyl ether, or methyl t-butyl ether. The
halogenated hydrocarbon solvent may be dichloromethane. The ester solvent may be, for
example, ethyl acetate. The solvent is preferably tetrahydrofuran, either alone or in
combination with water. Hexyl chloroformate may be used either as a solid or in solution
form with tetrahydrofuran.
The compound of Formula IV is contacted with n-hexyl chloroformate in the
presence of an organic or inorganic base. The organic base may be selected from the
group comprising ethylamine or diisopropyl ethyl amine. The inorganic base may be
selected from the group comprising sodium carbonate or potassium carbonate. Preferably,
the base is potassium carbonate.
The compound of Formula IV is contacted with n-hexyl chloroformate at a
temperature of about 10°C to about 40°C, for example, about 15°C to about 25°C. The
compound of Formula IV is contacted with n-hexyl chloroformate for about 3 hours to
about 6 hours, for example, about 4 hours to about 6 hours.
The reaction mixture may be subjected to carbon treatment. The reaction mixture
may optionally be treated with butylated hydroxytoluene. The solvent may be recovered
from the reaction mixture and the reaction mixture used as such for the next step.
The present invention does not require the isolation of the dabigatran etexilate
intermediate in step a). The reaction mixture obtained in step a) may be treated with
methane sulfonic acid in the presence of a solvent selected from the group comprising of
ketones, esters, alcohols, or mixtures thereof. The ketone solvent selected from the group
comprising acetone, methyl butyl ketone, or methyl isopropyl ketone. The ester solvent
may be selected from the group comprising ethyl acetate, isopropyl acetate, or butyl
acetate. The alcohol solvent may be selected from the group comprising ethanol,
methanol, n-propanol, or butanol. Preferably, the solvent is acetone. The methane
sulfonic acid may be used as a solid or as a solution with acetone.
The reaction mixture obtained in step a) is treated with methane sulfonic acid at a
temperature of about 10°C to about 40°C, for example, about 15°C to about 25°C. The
reaction mixture obtained in step a) is treated with methane sulfonic acid for about 3 hours
to about 6 hours, for example, about 4 hours to about 6 hours.
The crystalline Form I of methanesulfonate salt of dabigatran etexilate may be
isolated from the reaction mixture by filtration, decantation, evaporation, distillation, or
combinations thereof. The crystalline Form I of methanesulfonate salt of dabigatran
etexilate has substantially the same XRPD pattern as depicted in Figure 1, and can further
be characterized by differential scanning calorimetry (DSC).
The XRPD of the sample was determined using a Panalytical X'Pert Pro X-Ray
Powder Diffractometer in the range 3-40 degree 2 theta and under tube voltage and current
of 45 Kv and 40 mA respectively. Copper radiation of wavelength 1.54 angstrom and
Xceletor detector was used.
While the present invention has been described in terms of its specific
embodiments, certain modifications and equivalents will be apparent to those skilled in the
art and are intended to be included within the scope of the present invention.
EXAMPLE
Preparation of Crystalline Form I of methane sulfonate salt of dabigatran etexilate
The acetate salt of ethyl N-[(2-{[(4-carbamimidoylphenyl)amino]methyl}-lmethyl-
3a,7a-dihydro- lH-benzimidazol-5-yl)carbonyl ]-N-pyridin-2-yl -P-alaninate (50 g)
was added to tetrahydrofuran (750 mL) and deionized water (250 mL) and the mixture
was stirred for 20 minutes. Potassium carbonate (37.08 g) was added to the reaction
mixture and the mixture was stirred for 30 minutes. A solution of n-hexyl chloroformate
(16.19 g) in tetrahydrofuran (250 mL) was added to the reaction mixture at 18°C to 20°C.
The reaction mixture was stirred for 2 hours at 20°C to 22°C. The reaction mixture was
taken in a separating funnel and the tetrahydrofuran layer was collected. Potassium
carbonate (40 g) was added to the reaction mixture and the mixture was stirred for 30
minutes.
The layers obtained were separated and the tetrahydrofuran layer was taken.
Carbon (5 g) was added to the tetrahydrofuran layer and it was stirred for 20 minutes. The
reaction mixture was filtered through celite. The tetrahydrofuran layer was collected and
butylated hydroxytoluene (0.5 g) was added to the reaction mixture. The solvents were
recovered under vacuum. Acetone (150 mL) was added to the reaction mixture and the
mixture was stirred for 20 minutes. The acetone (130 mL) was recovered under vacuum.
The solid obtained was dissolved in acetone (392 mL). A solution of methane sulfonic
acid (8.14 g) in acetone (56 mL) was added to the reaction mixture at 18°C to 20°C. The
reaction mixture was stirred at 20°C to 22°C for 2 hours, filtered, and dried under suction.
The reaction mixture was further dried under vacuum at 55°C for 15 hours to get the title
compound having an XRPD pattern as depicted in Figure 1.
Yield: 52 g
Percentage Yield: 80.6%

We claim:
1. A process for the preparation of crystalline Form I of a methanesulfonate salt of
dabigatran etexilate, wherein the process comprises
a) contacting ethyl N-[(2-{[(4-carbamimidoylphenyl)amino]methyl}-l-methyl-
3a,7a-dihydro- lH-benzimidazol-5-yl)carbonyl ]-N-pyridin-2-yl -P-alaninate of
Formula IV
FORMULA IV
or salts thereof with n-hexyl chloroformate;
b) treating the reaction mixture obtained in step a) with methane sulfonic acid;
and
c) isolating the crystalline Form I of the methanesulfonate salt of dabigatran
etexilate from the mixture thereof.
2. The process according to claim 1, wherein the salt of the compound Formula IV is
selected from hydrochloride, hydrobromide, or acetate salts.
3. The process according to claim 2, wherein the salt of the compound of Formula IV
is an acetate salt.
4. The process according to claim 1, wherein the compound of Formula IV is
contacted with n-hexyl chloroformate in the presence of a solvent selected from the group
consisting of water, ethers, halogenated hydrocarbons, esters, or mixtures thereof.
5. The process according to claim 4, wherein the solvent is tetrahydrofuran, or
tetrahydrofuran in combination with water.
6. The process according to claim 1, wherein n-hexyl chloroformate is used either as
a solid or in a solution with tetrahydrofuran.
7. The process according to claim 1, wherein the compound of Formula IV is
contacted with n-hexyl chloroformate in the presence of a base.
8. The process according to claim 7, wherein the base is potassium carbonate.
9. The process according to claim 1, wherein the product prepared in step a) is not
isolated.
10. The process according to claim 1, wherein the reaction mixture obtained in step a)
is treated with methane sulfonic acid in a solvent selected from the group consisting of
ketones, esters, alcohols, or mixtures thereof.
11. The process according to claim 10, wherein the solvent is acetone.
12. The process according to claim 1, wherein methane sulfonic acid is used as a solid
or in solution with acetone.
13. The process according to claim 1, wherein the crystalline Form I of the
methanesulfonate salt of dabigatran etexilate has substantially the same XRPD pattern as
depicted in Figure 1.