Process for preparing tiotropium bromide

1. A process for preparing tiotropium bromide comprising:

i) reacting scopine oxalate (X) with diethylamine in an inert solvent to form scopine (II)

ii) reacting scopine and methyl di-(2-dithienyl)glycolate (MDTG) in the presence of an inorganic base, and in an inert solvent to form N-demethyltiotropium;

iii) reacting N-demethyltiotropium with bromomethane in an inert solvent to form tiotropium bromide (I)

iv) crystallizing tiotropium bromide in a mixture of methanol and acetone, and optionally thereafter,

v) micronizing the tiotropium bromide so formed.

2. A process according to claim 1 further comprising:

i) removing by filtration the diethylammonium salt formed by the reaction between scopine oxalate and diethylamine in step i); and

ii) exchanging the reaction solvent.

3. A process according to claim 1 further comprising:

i) removing by filtration the inorganic salts formed during the transesterification reaction between scopine and MDTG in step ii); and

ii) washing the N-demethyltiotropium-containing solution with water or brine; and

iii) concentrating the resulting organic solution to crystallize the product, and thereafter filtering and drying the product to give N-demethyltiotrpium with a purity greater than 99.0% by HPLC.

4. A process according to claim 1 wherein:

i) tiotropium bromide formed by reaction between N-demethyltiotropium and bromomethane precipitates from the reaction mixture and thereafter more product is precipitated by addition of an anti-solvent; and optionally

ii) the tiotropium bromide so formed is re-slurried in a mixture of an inert solvent and anti-solvent; and

iii) tiotropium bromide is filtered and dried to isolate the product with a purity equal to, or greater than, 99.4% by HPLC.

5. A process according to claim 1 characterized in that the tiotropium bromide obtained from the crystallization of methanol and acetone has a purity greater than 99.5% by HPLC and is a single anhydrous crystalline form.

6. A process according to claim 1 , wherein the inert solvent from step i) is selected from the group consisting of halogenated hydrocarbons, such as dichloromethane, and ketones, such as acetone.

7. A process according to claim 6 , wherein the solvent is acetone.

8. A process according to claim 1 , wherein the reaction of step i) is carried out at a temperature of between about 30° C. and about 45° C., preferably between about 40° C. and about 45° C.

9. A process according to claim 1 , wherein the solvent of step ii) for the transesterification reaction is selected from the group consisting of mixtures of hydrocarbons, such as n-heptane, and amides, such as dimethylformamide.

10. A process according to claim 9 , wherein the solvent is a mixture of n-heptane and dimethylformamide.

11. A process according to claim 10 , wherein the solvent for the transesterification reaction is a mixture of 10 volumes of n-heptane with 1 volume of dimethylformamide.

12. A process according to claim 1 , wherein the inorganic base in step ii) is anhydrous potassium carbonate, anhydrous cesium carbonate or potassium tert-butoxyde, preferably anhydrous potassium carbonate.

13. A process according to claim 1 , wherein the transesterification reaction of step ii) is carried out at a temperature of between about 80° C. and about 110° C., preferably between about 85° C. and about 100° C., more preferably between about 90° C. and about 95° C.

14. A process according to claim 3 , wherein the organic solution obtained after the water or brine washes in step ii) is treated with activated charcoal to remove color.

15. A process according to claim 1 , wherein the solvent for the methylation reaction of step iii) is selected from the group consisting of amides, such as dimethylformamide, cyclic ethers, such as tetrahydrofuran or 2-methyltetrahydrofuran, nitriles, such as acetonitrile, and mixtures of acetone with tetrahydrofuran and of ethyl acetate with tetrahydrofuran.

16. A process according to claim 15 , wherein the solvent is dimethylformamide.

17. A process according to claim 1 , wherein the methylation reaction of step iii) is carried out at a temperature of between about 0° C. and about 5° C., followed by a temperature of between about 10° C. and about 15° C., followed by a temperature of between about 20° C. and 25° C.

18. A process according to claim 1 , wherein the crystallization of tiotropium bromide in step iv) is carried out by dissolving the product in methanol and acetone at a temperature of between about 45° C. and about 60° C., followed by cooling to a temperature of between about 0° C. and about −5° C., followed by isolation by filtration and drying of the product.

19. A process according to claim 18 , wherein the wet tiotropium bromide isolated from the methanol/acetone crystallization is dried under vacuum, at a first temperature of between about 45° C. and about 55° C., followed by drying at a second temperature of between about 100° C. and about 125° C.

20. A process according to claim 18 , wherein the crystallization of tiotropium bromide is carried out by (i) dissolving the product in methanol at ambient (room) temperature; (ii) concentrating the methanol solution under vacuum, (iii) adding acetone whilst maintaining the temperature of the solution between about 35° C. and about 60° C., (iv) cooling the solution to a temperature of between about 0° C. and about −5° C., and (v) isolating the product by filtration and drying.

21. A process according to claim 1 , wherein before the micronization of step v), tiotropium bromide is suspended in a solvent in which it is not soluble.

22. A process according to claim 21 , wherein the solvent is a hydrocarbon, such as heptane, or ethyl acetate, or acetone, or a mixture of two or more such solvents.

23. A process according to claim 1 , wherein the micronization in step v) is effected by cavitation and/or particle to particle collision and/or shear stress in the milling apparatus.

24. A process according to claim 23 , wherein cavitation and/or particle to particle collision and/or shear stress is promoted by the passage of the suspension through small channels characterized by a geometry selected from the group consisting of: (i) a “Z” type single or multi slot geometry and/or (ii) a “Y” type single or multi slot geometry.

25. A process according to claim 23 , wherein pressure is increased up to 2000 bar followed by a pressure drop.

26. A process according to claim 1 , further comprising the step of isolating tiotropium bromide in the form of powder.

27. A process according to claim 26 , wherein the isolation step comprises filtration and drying in an oven or spray drying.

28. A process according to claim 27 , wherein the spray drying step is conducted with a drying temperature above about 90° C.

29. A process according to claim 1 , wherein the crystalline form of tiotropium bromide obtained from the crystallization in step iv) is maintained during the micronization step v).

30. A process according to claim 29 , wherein the crystalline form of tiotropium bromide is anhydrous.

31. A process according to claim 29 , wherein the crystalline form obtained from the micronization step v) is maintained during the isolation step.