DESC:Field of the invention
The present invention provides substantially pure tiotropium bromide or its hydrate and a process for preparation of the same.

Background and the prior art
Tiotropium bromide, (1a, 2ß, 4ß, 5a, 7ß)-7-[(Hydroxydi-2-thienylacetyl) oxy]-9, 9-dimethyl-3-oxa-9-azoniatricyclo [3.3.1.02,4]nonane bromide is represented by formula (1). It is presently approved for the treatment of respiratory disorders, such as asthma or chronic obstructive pulmonary disease (COPD), including chronic bronchitis and emphysema. This active pharmaceutical ingredient is administered by inhalation and is available commercially as SPIRIVA® HandiHaler®. It is a highly effective anticholinergic agent with specificity for muscarinic receptors.

A pharmaceutical composition of tiotropium bromide is mentioned in EP0418716 patent for treating chronic obstructive bronchitis.

EP’716 patent discloses a process for the preparation of tiotropium bromide. The method involves, in the first step, a transesterification reaction between scopine and methyl di-(2-thienyl) glycolate to form di-(2-thienyl) glycolic acid scopine ester, which is then quaternized with methyl bromide to form tiotropium bromide. However said patent does not disclose how to obtain a pure tiotropium bromide acceptable as per regulatory norms.

Other processes for the preparation of tiotropium bromide are also known in the art. However, neither of these documents describes a method for preparing substantially pure tiotropium bromide having decreased content of regioisomeric impurities and other impurities as per regulatory norms.

So there exists a scope of developing an improve process that consistently yields substantially pure tiotropium bromide or its hydrate meeting regulatory norms.

Object of the invention
Objective of the present invention is to provide a substantially pure tiotropium bromide or its hydrate.

A second objective of the present invention is to provide a substantially pure tiotropium bromide or its hydrate which having reduced content of undesired by-products or impurities.

Another objective of the present invention is to provide a purification process of methyl di-(2-thienyl) glycolate to reduce the content of regioisomeric impurity.

Another objective of the present invention is to provide an improved process for preparation of the said substantially pure tiotropium bromide or its hydrate.

Description of the invention
Accordingly, the present invention provides a process for preparation of a substantially pure tiotropium bromide or its hydrate with reduced contents of undesired by-products or impurities. The present invention provides a cost effective and industrially viable process for obtaining tiotropium bromide or its hydrate with higher purity and higher yield.

According to the present invention, tiotropium bromide or its hydrate of the present invention is substantially free of regioisomeric impurity, (1R,2R,4S,5S,7s)-7-(2-hydroxy-2-(thiophen-2-yl)-2-(thiophen-3-yl)acetoxy)-9,9-dimethyl-3-oxa-9-azatricyclo[3.3.1.02,4]nonan-9-ium bromide of formula (2).

The present invention provides a process for the purification of methyl di-(2-thienyl) glycolate to reduce the regioisomeric impurity methyl-2-(thiophene-2yl)-2-(thiophene-3-yl) glycolate (2,3-MDTG) formula (3) and converting the purified methyl di-(2-thienyl) glycolate to tiotropium bromide or its hydrate by known methods in the art or by a novel process.

The present invention further describes a process for obtaining the substantially pure tiotropium bromide or its hydrate by purifying the key starting material methyl di-(2-thienyl) glycolate and further the purified methyl di-(2-thienyl) glycolate is converted to the scopine methyl di-(2-thienyl) glycolate in the presence of an inorganic base which may be optionally purified. The scopine methyl di-(2-thienyl) glycolate is then quaternized with methyl bromide to afford tiotropium bromide substantially free of impurity of formula (2).

The present inventors have found that the regioisomer 2,3-MDTG of formula (3) in the key starting material methyl di-(2-thienyl) glycolate gives rise to the impurity of formula (2).

The present inventors have also found that the regioisomeric impurity of formula (2) is difficult to remove from tiotropium bromide or its hydrate due to the similarity in polarity of tiotropium bromide or its hydrate and the regioisomeric impurity of formula (2).

According to the present invention, methyl di-(2-thienyl) glycolate is purified in a suitable solvent at elevated temperature.

According to the present invention, the preferred suitable solvent is an organic solvent or water or combinations thereof. The preferred organic solvent of the present invention is selected from alcohols such as methanol, ethanol, isopropanol etc., ketones such as acetone etc., ethers such as tetrahydrofuran, 1,4-dioxane etc., polar aprotic solvents and mixtures thereof.

According to the present invention, the crude methyl di-(2-thienyl) glycolate is purified by dissolving into the 1,4-dioxane at 50-100 oC, preferably at 50-70 oC or more preferably at 50-55 oC.

According to the present invention, 0.5 to 2.0 volume of water is added to reaction mass gradually at elevated temperature, preferably 0.5 – 1.0 volume.

According to the present invention, the reaction mass is cooled gradually to about 0-15 oC, preferably to 8-10 oC and maintained at the same temperature for about an hour and filtered it.

According to the present invention, the wet cake obtained is slurried with water, filtered and dried under vacuum to afford the purified methyl di-(2-thienyl) glycolate having reduce content of 2,3-MDTG.

According to the present invention, the regioisomeric impurity 2,3-MDTG of formula (3) in the purified methyl di-(2-thienyl) glycolate obtained by the process of the present invention is 0.2 % or less measured as area percentage by HPLC.

A representative example of the process for purification of methyl di-(2-thienyl) glycolate is illustrated in example-1.

According to the present invention, purified methyl di-(2-thienyl) glycolate characterized by containing 0.2 or less of methyl-2-(thiophene-2yl)-2-(thiophene-3-yl) glycolate, produced by a method according to present invention.

The purified methyl di-(2-thienyl) glycolate is further reacted with scopine, (1R, 2R, 4S, 5S, 7s)-9-Methyl-3-oxa-9-azatricyclo [3.3.1.02, 4] nonan-7-ol in the presence of an inorganic base, wherein the base is selected from the metal carbonates, metal bicarbonates or metal hydroxides. Preferably the inorganic base is metal hydroxide, preferably sodium, potassium, lithium, calcium, or magnesium, more preferably lithium hydroxide and an aprotic solvent at elevated temperatures to obtain the scopine di-(2-thienyl) glycolate (scopine ester).

The preferred base of the present invention is preferably added in lots to the reaction mass, more preferably in two lots.

According to the present invention, the reaction is carried out at a temperature between about 50 and about 90 oC, preferably between about 60 oC and about 70 oC.

The scopine ester thus obtained is optionally purified. A representative example is illustrated in example-2.

According to the present invention, the scopine di-(2-thienyl) glycolate is then quaternized with methyl bromide to afford tiotropium bromide. The tiotropium bromide thus obtained is optionally purified to afford pure tiotropium bromide substantially free of the regioisomeric impurity of formula (2).

According to the present invention, the pure tiotropium bromide of the present invention is dried by the techniques known in the art, such that the residual solvents in the drug substance are within the scope of the regulatory guidelines.

Accordingly, the tiotropium bromide of the present invention is dried using drying equipment known in the art such as oven tray, rotary cone, paddle and tumble dryers or rotary evaporators wherein the drying typically is carried out at reduced pressure.

The present inventors have found that the gentle removal of solvents from the tiotropium bromide by evaporation using rotatory evaporator is beneficial in quicker drying and avoiding degradation of tiotropium bromide to its precursor, the scopine ester.

A representative example is illustrated in example-3.

In another preferred aspect, the tiotropium bromide is converted to substantially pure tiotropium bromide hydrate by known method in the art.

In another preferred aspect, the product obtained by the process of the present invention is substantially pure tiotropium bromide hydrate having purity >99% measured as area percentage by HPLC.

In another preferred aspect, the regioisomeric impurity of formula (2) in the pure tiotropium bromide hydrate obtained by the process of the present invention is 1.0% or less measured as area percentage by HPLC.

A representative example is illustrated in example-4.

In another preferred aspect, the tiotropium bromide hydrate containing 0.10 % or less of the regioisomeric impurity of formula (2), produced by a method according to present invention.

In another preferred aspect, the tiotropium bromide hydrate containing 0.08 % or less of the regioisomeric impurity of formula (2), produced by a method according to present invention.

In another preferred aspect, the tiotropium bromide hydrate containing 0.06 % or less of the regioisomeric impurity of formula (2), produced by a method according to present invention.

Measuring techniques for characterizing the methyl di-(2-thienyl) glycolate and substantially pure tiotropium bromide according to present invention:

1. Method of measuring area percentage of the regioisomeric impurity methyl-2-(thiophene-2yl)-2-(thiophene-3-yl) glycolate (2,3-MDTG) of formula (3) in methyl di-(2-thienyl) glycolate by HPLC:
· Detector : ultraviolet absorptiometer (detection wavelength: 254 nm)
· Column : Zorbax RX C-8 (4.6 × 150)mm, 5µ
· Flow rate : 2.0 mL/min
· Column oven temperature : 25 oC
· Mobile phase : (A) dissolved triethyl amine in water and adjust pH to 3.0 with perchloric acid; (B) acetonitrile

2. Method of measuring area percentage of the regioisomeric impurity of formula (2) in the tiotropium bromide hydrate by HPLC:
· Detector : ultraviolet absorptiometer (detection wavelength: 240 nm & 317 nm)
· Column : Zorbax SB C-3 (3.0 × 150)mm, 3.5µ
· Flow rate : 1.20 mL/min
· Column oven temperature : 50 oC
· Mobile phase : (A) ammonium acetate : triethyl amine : trifluoroacetic acid (100:0.2:0.1); (B) ammonium acetate : acetonitrile : isopropyl alcohol : methanol : triethyl amine : trifluoroacetic acid (50:20:20:10:0.2:0.1)

Present invention is further illustrated by the following non-limiting examples.

Example-1: Purification of methyl di-(2-thienyl) glycolate

Methyl di-(2-thienyl) glycolate (100g) (having 0.29% 2,3-MDTG) and 1,4-dioxane (180ml) were added to a clean round bottomed flask. The reaction mass was heated at 50-52 oC to dissolve methyl di-(2-thienyl) glycolate. Water (48 ml) was added in to the reaction mass at 50-52 oC within 15-20 minutes and the reaction mass was further stirred for additional 20-25 minutes at 50-52 oC. Thereafter, the reaction mass was cooled gradually to 8-10 oC and stirred for 1 hour at 8-10 oC. Precipitated solid was filtered and slurry washed with water (200ml×2). The solid was filtered, suck dried and dried under vacuum till m/c was NMT 0.5%.

Yield = 40 gm; Purity of the product = 99.84 %; Content of 2,3-MDTG = 0.15%

Table-1
Purity of methyl di-(2-thienyl) glycolate
Input material Purified material
Sample Purity (HPLC) of crude methyl di-(2-thienyl) glycolate Content of the regioisomeric impurity of formula (3) Purity (HPLC) of pure methyl di-(2-thienyl) glycolate Content of the regioisomeric impurity of formula (3)
Lab batch-1 99.71 % 0.29 % 99.84 % 0.15 %
Lab batch-2 99.71 % 0.29 % 99.87 % 0.12 %

Example-2: Preparation of Scopine ester

Scopine (100gm) and methyl di-(2-thienyl) glycolate (163.9g) were dissolved in dimethyl formamide (1300ml) in a clean round bottomed flask by heating at 55-65 oC. Anhydrous lithium hydroxide (3.8 gm) was added to the reaction mass and flushed with DMF (100ml). Thereafter vacuum was applied to reaction mass (70-80 mm of Hg) and the reaction mass was maintained under stirring for 120-135 minutes at 60-65 oC bath temperature. The vacuum was released and reaction volume was adjusted to initial volume by adding more of DMF. Second lot of lithium hydroxide (2 gm) was added to the reaction mass at 60-65 oC bath temperature. Vacuum was again applied to reaction mass (70-80 mm of Hg) and the reaction mass was maintained under stirring for 120-135 minutes at 60-65 oC bath temperature. The vacuum was released and reaction volume was adjusted to initial volume by adding more of DMF. The reaction mass was cooled to 0-5 oC and water (400ml) was added. The pH of the reaction mass was adjusted to 2 to 3 using aq. HCl at 0-5 oC. The temperature of the reaction mass was raised to 20-25 oC and washed with toluene (800ml×2). The aqueous layer was cooled to 0-5 oC and the pH was adjusted to 9.5-10 using aq. potassium carbonate solution. The reaction mass was stirred for 90-120 minutes at 0-5 oC and precipitated solid was filtered. The wet cake was taken into water, the pH was adjusted to 6-7 using aq. HCl, stirred for 30-45 min, filtered and dried under vacuum. The crude scopine ester thus obtained was purified from acetonitrile to afford pure scopine ester.

Yield: 74.0 gm.

Example-3: Preparation of Tiotropium bromide

Scopine ester (100g), dichloromethane (400ml) and acetonitrile (600ml) were added to a clean round bottomed flask. The reaction mass was heated at 38-40 oC and further stirred for 15-30 minutes at 38-40 oC. To the reaction mass, 25% methyl bromide solution in acetonitrile (502.8g) was added at 38-40 oC. The reaction mass was cooled to 25-30 oC. After completion of the reaction, the product was filtered under nitrogen atmosphere, washed with dichloromethane (200ml), suck dried and dried under vacuum till constant LOD. Thereafter the dried product was purified from a mixture of methanol and acetone (ratio of methanol: acetone is 2:3), filtered under nitrogen atmosphere, dried under vacuum on a rotatory evaporator.

Yield = 90.0 gm.

Example-4: Preparation of Tiotropium bromide hydrate

Tiotropium bromide (100 gm) and water (200ml) were added in a clean round bottomed flask. The reaction mass was heated at 80-85 oC to dissolve the tiotropium bromide and further stirred for 30 to 60 minutes at 80-85 oC. Then after, the reaction mass was cooled to 3-8 oC and stirred for 90 to 120 minutes at 3-8 oC. Precipitated solid was filtered, washed with pre-cooled water and dried under vacuum at 25-30 oC.

Yield = 85.0 gm; Purity of the product = 99.85 %; Content of the regioisomeric impurity of formula (2) = 0.06%

Table-2
Purity of tiotropium bromide hydrate
Sample Purity (HPLC) of tiotropium bromide hydrate Content of the regioisomeric impurity of formula (2)
Lab batch-1 [using purified methyl di-(2-thienyl) glycolate] 99.85 % 0.06 %
Lab batch-2 [using purified methyl di-(2-thienyl) glycolate] 99.87 % 0.09 %
Reference batch-1 [using crude methyl di-(2-thienyl) glycolate] 99.72 % 0.15 %
Reference batch-1 [using crude methyl di-(2-thienyl) glycolate] 99.81 % 0.15 %

,CLAIMS:1) A process for the preparation of substantially pure tiotropium bromide or its hydrate with reduced content of regioisomeric impurity, (1R,2R,4S,5S,7s)-7-(2-hydroxy-2-(thiophen-2-yl)-2-(thiophen-3-yl)acetoxy)-9,9-dimethyl-3-oxa-9-azatricyclo[3.3.1.02,4]nonan-9-ium bromide of formula (2), comprising:
· purifying methyl di-(2-thienyl) glycolate to reduce the regioisomeric impurity; and
· converting purified methyl di-(2-thienyl) glycolate to the tiotropium bromide or its hydrate.

2) Tiotropium bromide hydrate containing 0.10% or less of the regioisomeric impurity of formula (2), produced by method according to claim-1.

3) Tiotropium bromide hydrate containing 0.08% or less of the regioisomeric impurity of formula (2), produced by method according to claim-1.

4) Tiotropium bromide hydrate containing 0.06% or less of the regioisomeric impurity of formula (2), produced by method according to claim-1.

5) A process for purifying methyl di-(2-thienyl) glycolate comprising:
· dissolving crude methyl di-(2-thienyl) glycolate in organic solvent;
· adding water to the reaction mass; and
· filter the pure methyl di-(2-thienyl) glycolate having decreased content of methyl-2-(thiophene-2yl)-2-(thiophene-3-yl) glycolate.

6) A process according to claim-5, wherein organic solvent is water miscible organic solvents.

7) A process according to claim-5 and 6, wherein water miscible organic solvents are methanol, ethanol, isopropanol, acetone, tetrahydrofuran, 1,4-dioxane and mixture thereof.

8) Methyl di-(2-thienyl) glycolate having 0.2% or less of methyl-2-(thiophene-2yl)-2-(thiophene-3-yl) glycolate, produced by a process according to claim-5.

9) Methyl di-(2-thienyl) glycolate having 0.15% or less of methyl-2-(thiophene-2yl)-2-(thiophene-3-yl) glycolate, produced by a process according to claim-5.