HRP20040546A2 - Methods for the purification of levofloxacin - Google Patents

Description

References of related applications

This application is a continuation application in part of patent application serial number 10/262,965, filed 10/3/2002, which refers to provisional applications serial number 60/326,958, filed 10/3/2001, 60/334,316, filed 11/29/2001. and 60/354,939, filed on February 11, 2002, and patent application serial number 10/263,192, filed on October 3, 2002. The entire contents of each of these applications are incorporated herein by reference.

Field of invention

The present invention relates to methods for the purification of levofloxacin. In a preferred embodiment, levofloxacin is prepared with antioxidants.

Background of the invention

Levofloxacin is a broad-spectrum synthetic antibiotic. Levofloxacin is the S-enantiomer of the racemate ofloxacin, a fluoroquinolone antimicrobial agent. The antibacterial activity of ofloxacin is present primarily in the S-enantiomer. The mechanism of action of levofloxacin and other fluoroquinolone antimicrobials involves inhibition of DNA gyrase (bacterial topoisomerase II), an enzyme required for DNA replication, transcription error correction, and recombination. Levofloxacin is available as LEVAQUIN® which can be given orally or can be given intravenously.

Levofloxacin is a chiral fluorinated carboxyquinolone. Its chemical name is (S)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de] -1,4-benzoxazine-6-carboxylic acid hemihydrate (CAS Registry No. 100986-85-4). The chemical structure of levofloxacin is shown as formula I.

[image]

LOUSE. Patent No. 4,382,892 is directed to pyrido[1,2,3-de][1,4]benzoxazine derivatives and processes for their preparation.

LOUSE. Patent No. 5,053,407 is directed to optically active pyridobenzoxazine derivatives, processes for their preparation, and intermediates useful in processes for the preparation of such derivatives.

LOUSE. Patent No. 5,051,505 is directed to processes for the preparation of piperazinyl quinolone derivatives. The procedure involves the reaction of dihaloquinolones with piperazine derivatives and tetraalkyl ammonium halides in the presence of a polar solvent such as acetonitrile, dimethyl formamide, pyridine, sulfolane, and dimethyl sulfoxide.

LOUSE. Patent No. 5,155,223 is directed to the preparation of quinolinecarboxylic acids.

LOUSE. Patent No. 5,545,737 discloses the selective production of levofloxacin hemihydrate or monohydrate by controlling the water content of the aqueous solvent in which levofloxacin is dissolved during crystallization. Arutla et al., Arzneimittelforschung (October 1998) 48(10): 1024-7, claims that a racemic mixture of loxacin has antioxidant properties.

One drawback of levofloxacin purification procedures in previous works is that they often do not achieve satisfactory recovery. For example, typical yields are 45-65%. There remains a need for new procedures for the purification of levofloxacin, especially purified preparations with reduced impurities, such as anti-levofloxacin, desmethyl levofloxacin, N-oxide levofloxacin, des fluoro-levofloxacin and/or decarboxy-levofloxacin.

Summary of the invention

The present invention provides new processes for the purification of levofloxacin. Levofloxacin is dissolved in a polar solvent, preferably selected from the group consisting of DMSO, methyl ethyl ketone, acetonitrile, alcohol (preferably butanol), ketone, mixtures thereof and aqueous mixtures thereof, at elevated temperature and crystallizes to form levofloxacin. In one embodiment, the solvent is anhydrous. In another embodiment, an antioxidant is added, resulting in a purer levofloxacin product.

Detailed description of the invention

Raw and semi-raw preparations of levofloxacin can be prepared by methods known in the art.

Alternatively, crude levofloxacin can be prepared, for example, as follows: A 1 liter reaction vessel equipped with a mechanical stirrer, condenser and thermometer, heated to 80°C, is charged with 87.5 g (0.31 mol) (S)-(-) -9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acid, 61.3 mL DMSO and 86.3 mL (0.77 mol) N-methylpiperazine. The emulsified mixture is stirred at a speed of 250 rpm (revolutions per minute) in a nitrogen atmosphere at 80°C until complete reaction (monitoring by HPLC). Then the emulsified mixture is cooled to 75°C, a mixture of isopropanol (675 mL) and water (25 mL) is added dropwise at this temperature over 2 hours. The emulsified mixture is then cooled to 5°C over 4 hours, maintained at this temperature for 2 hours and filtered under vacuum at this temperature. The solid is then washed with 175 mL of isopropanol (2 washes) and dried in vacuo to give crude levofloxacin.

In one embodiment of the present invention, crude levofloxacin is purified. As used herein, "purified levofloxacin" is a relative term meaning more pure. As used herein, "crude levofloxacin" refers to levofloxacin that has not undergone a purification crystallization step. The crude preparation of levofloxacin is mixed with a suitable solvent to form a mixture which is typically a suspension. The temperature of the mixture is then raised to enhance the dissolution of levofloxacin in the solvent. Typically, the elevated temperature ranges from about 80°C to about 110°C. Preferably, the mixture is heated to reflux. Preferably, when the levofloxacin is dissolved in the solvent, the mixture is filtered while hot. The purified levofloxacin is then precipitated, preferably by slow cooling, and preferably collected. Purified levofloxacin preferably has a purity of about 99% or more, more preferably about 99.5% or more.

Polar solvents are generally suitable. Preferably, the solvent is DMSO, methyl ethyl ketone, butanol, acetonitrile, mixtures thereof or aqueous mixtures thereof. As used herein, the term "polar solvent" is intended as a relative term to mean relatively more polar than another solvent.

The solvent may be anhydrous or may contain a small amount of water. The solvent preferably contains water when a water-soluble antioxidant such as sodium metabisulfite is used. The amount of water should be less than about 20% (v/v) and preferably about 10% (v/v) or less. Larger amounts of water tend to reduce yield. n-BuOH : H 2 O (9:1) and acetonitrile : H 2 O (99:1) are examples of suitable solvents containing water. Acetonitrile and acetonitrile : H2O (99:1) are the most preferred solvents for levofloxacin purification.

In another embodiment, the antioxidant is added to the mixture prior to deposition. The antioxidant can be any one that prevents the formation of levofloxacin N-oxide, especially during crystallization. Examples include ascorbic acid, sodium ascorbate, calcium ascorbate, ascorbic palmitate, butylated hydroxyanisole, butylated hydroxytoluene, 2,4,5-trihydroxybutyrophenone, 4-hydroxymethyl-2,6-di-tert-butyl phenol, erythorbic acid, guaiac gum ), propyl gallate, thiodipropionic acid, dilauryl thiodipropionate, and t-butylhydroquinone, tocopherols (such as vitamin E) and their pharmaceutically acceptable salts and mixtures thereof. Preferably, the antioxidant includes sodium metabisulfite or ascorbic acid.

Antioxidant, if used, can be added at various points in the purification process. For example, in one embodiment, the antioxidant is mixed with levofloxacin before or during the crystallization step or before the dissolution step. In another embodiment, the antioxidant is mixed with (S)-(-)-9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1 ,4]benzoxazine-6-carboxylic acid, the precursor of levofloxacin, before its conversion to levofloxacin at elevated temperature.

The amount of antioxidant, when present, is preferably about 0.2% to about 5% by weight, more preferably about 0.2% to about 1%.

The function and advantages of these and other embodiments of the present invention will be more fully understood from the examples given below. The following examples are intended to illustrate the advantages of the present invention, but do not exemplify the entire scope of the invention.

EXAMPLES

The following Table 1 summarizes the results of the experiments described below in the Examples section. The percentage of each component in Table 1 was determined by HPLC using a procedure based on the European Pharmacopoeia procedure for loxacin-related substances.

Table 1: Purification during crystallization

[image] [image] ND = Not observed.

Example 1

n-BuOH

1 g of crude levofloxacin was suspended in 7 ml of n-BuOH. The mixture is heated to the reflux temperature until the substance is completely dissolved. Then the solution was cooled to RT over a period of 2.5 hours. The precipitate was vacuum filtered, washed with n-BuOH and dried at 60°C in a vacuum oven to give 810 mg (81%) of purified levofloxacin hemihydrate.

Example 2

n-BuOH/ascorbic acid

1.5 g of crude levofloxacin and 36 mg of ascorbic acid were suspended in 9.5 ml of n-BuOH under an inert atmosphere. The mixture was heated to reflux temperature and hot filtration was carried out. The solution was then evaporated to dryness and n-BuOH (10 ml) was added. The mixture was heated to reflux until complete dissolution and then cooled to RT over a period of 1.5 hours. The precipitate was filtered in vacuo, washed with n-BuOH (4 ml) and dried at 60°C in a vacuum oven to give 840 mg (56%) of purified levofloxacin hemihydrate.

Example 3

n-BuOH:H2O (9:1)/metabisulfite

1.5 g of crude levofloxacin and 10 mg of sodium metabisulfite were suspended in 6 ml of a mixture of n-BuOH:H2O (9:1) under a nitrogen atmosphere. The mixture is heated to the reflux temperature until the substance is completely dissolved. Then the solution was cooled to RT over a period of 1.5 hours. The precipitate was filtered under vacuum, washed with a mixture of n-BuOH:H2O (9:1) (4 ml) and dried at 60°C in a vacuum oven to obtain 1.2 g (81 %) of purified levofloxacin hemihydrate. Purified levofloxacin hemihydrate contained almost no levofloxacin N-oxide.

Example 4

ACN

1.5 g of crude levofloxacin was suspended in 10.5 ml of ACN. The mixture was heated to the reflux temperature until the substance completely dissolved. Then the solution was cooled to 0°C over a period of 20 minutes. The precipitate was filtered in vacuo, washed with ACN (1.5 ml) and dried at 30 °C in a vacuum oven to give 1.15 g (77%) of purified levofloxacin (hemihydrate/monohydrate mixture). The purified levofloxacin contained approximately half the amount of desmethyl levofloxacin compared to the crude sample.

Example 5

ACN:H2O (99:1)

25 g of wet raw levofloxacin (about 22.17 g of dry levofloxacin) was suspended in 225 mL of ACN:H2O (99:1) mixture under a nitrogen atmosphere. The mixture was heated to reflux temperature for 1 hour and then vacuum filtered through Hyflow while still hot. Then the solution was reheated to reflux and cooled to 0°C over a period of 1 hour. The precipitate was filtered under vacuum, washed with ACN : H2O (2×12 mL) and dried in a vacuum oven to give 18.6 g (84%) of purified levofloxacin hemihydrate. The purified levofloxacin hemihydrate contained approximately one-third less desmethyl levofloxacin than the crude sample.

Example 6

ACN:H2O (99:1)/metabisulfite

8 g of moist crude levofloxacin (about 5.6 g of dry levofloxacin) and 14 mg of sodium metabisulfite were suspended in 39 ml of a mixture of ACN:H2O (99:1) under a nitrogen atmosphere. The mixture was heated to reflux temperature for 1 hour, 0.65 g of Hyflo was added and heating under reflux was continued for an additional half hour. The mixture was vacuum filtered while still hot. Then the solution is cooled to 3°C over a period of 30 minutes. The precipitate was filtered under vacuum, washed with ACN:H2O (99:1) (5 ml) and dried at 60°C in a vacuum oven to give 1.77 g (31%) of purified levofloxacin. Technical problems during hot filtering reduced the yield.

Example 7

ACN / metabisulfate

1.5 g of crude levofloxacin and 8 mg of sodium metabisulfite were suspended in 10.5 ml of ACN under a nitrogen atmosphere. The mixture was heated to reflux and hot filtered. Then the solution is heated again to the reflux temperature until the substance completely dissolves. The solution is then cooled to 0°C over a period of 30 minutes. The precipitate was vacuum filtered and dried at 60°C in a vacuum oven to give 1.04 g (69%) of purified levofloxacin. Purified levofloxacin contained approximately half the amount of levofloxacin N-oxide compared to the crude sample.

Example 8

DMSO / H2O

1 g of crude levofloxacin was suspended in 1.5 ml of DMSO. The mixture was heated to 108°C until the substance completely dissolved. Then H2O (7.5 ml) was added over 10 minutes and the mixture was cooled to RT. The precipitate was filtered in vacuo, washed with 1 ml of DMSO:H2O 1:5 and dried at 60°C in a forced air oven to give 840 mg (84%) of purified levofloxacin hemihydrate.

Example 9

SOFT

1.5 g of crude levofloxacin was suspended in 15 ml of MEK. The mixture is heated to the reflux temperature until the substance is completely dissolved. Then the solution was cooled to -5°C over a period of 3 hours. The precipitate was vacuum filtered, washed with 1.5 ml of MEK and dried at 30°C in a vacuum oven to give 840 mg (84%) of purified levofloxacin hemihydrate.

Example 10

ACN:H2O (9:1) / metabisulfite

1.5 g of crude levofloxacin and 8 mg of sodium metabisulfite were suspended in 10.5 ml of ACN:H2O 9:1 mixture under a nitrogen atmosphere. The mixture is heated to the reflux temperature until the substance is completely dissolved. Then the solution was cooled to RT over a period of 30 minutes. The precipitate was vacuum filtered, washed with ACN:H2O 9:1 (4 ml) and dried at 60°C in a vacuum oven to give 1.16 g (77%) of pure levofloxacin.

Example 11

ACN:H2O (95:5) / metabisulfite (8 mg)

1.5 g of crude levofloxacin and 8 mg of sodium metabisulfite were suspended in 10.5 ml of ACN:H2O 95:5 mixture under a nitrogen atmosphere. The mixture was heated to reflux and hot filtered. The solution was again heated to the reflux temperature and then cooled to 3°C over 30 minutes. The precipitate was vacuum filtered and dried at 60°C in a vacuum oven to give 500 mg (33%) of pure levofloxacin.

Example 12

ACN:H2O (95:5) / metabisulfite (4 mg)

1.5 g of crude levofloxacin and 4 mg of sodium metabisulfite were suspended in 15 ml of ACN:H2O 95:5 mixture under a nitrogen atmosphere. The mixture is heated to the reflux temperature until the substance is completely dissolved. Then the solution was cooled to 3°C over a period of 2 hours. The precipitate was filtered under vacuum and dried at 60°C in a vacuum oven to obtain 1.3 g (86.7%) of pure levofloxacin.

Example 13

DMSO / ascorbic acid

5g (17.8 mmol) (S)-(-)-9,10-difluoro-3-methyl-7-oxo was placed in a three-necked flask equipped with a condenser, in suspension in 3.5 ml of DMSO at 80°C in a nitrogen atmosphere. -2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acid, 4.46 g (44.6 mmol), 31 mg (0.17 mmol) ascorbic acid. The reaction mixture was heated at this temperature (4 h 30) until the complete completion of the reaction. Then the solution was cooled to 70°C and IPA (40 ml) was added. The mixture was cooled to 0°C over 1 hour and then stirred at this temperature for 30 minutes. The precipitate was filtered under vacuum, washed with IPA (1Gml) and dried at 60°C in a vacuum oven to give 5.63 g (87.6%) of pure levofloxacin.

Example 14

DMSO / metabisulfite

10 g (35.5 mmol) (S)-(-)-9,10-difluoro-3-methyl- 7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acid, 9.0 g (90 mmol), 34 mg (0.17 mmol) sodium metabisulfite. The reaction mixture was heated at this temperature (5h 30) until the complete completion of the reaction. Then the solution was cooled to 70°C and IPA (40 ml) was added. The mixture was cooled to 0°C over 1 hour and then stirred at this temperature for 30 minutes. The precipitate was vacuum filtered, washed with IPA (10 ml) and dried at 60°C in a vacuum oven to give 11.8 g (92.4%) of pure levofloxacin.

Claims (42)

1. A process for the preparation of levofloxacin with a purity of about 99% or more, characterized by the fact that it includes: dissolution of levofloxacin in a polar solvent at elevated temperature; and crystallization of purified levofloxacin. 2. The method according to patent claim 1 characterized in that the purity of the purified levofloxacin is about 99.5% by weight or more. 3. The method according to patent claim 1 characterized in that the elevated temperature is in the range of about 80°C to about 110°C. 4. The method according to patent claim 1 characterized in that the elevated temperature is the reflux temperature of the solution. 5. The method according to patent claim 1 characterized in that the polar solvent is selected from the group consisting of a series of dimethyl sulfoxide, methylethyl ketone, acetonitrile, butanol, their mixture and their aqueous mixture. 6. The method according to patent claim 1 characterized in that the solvent is acetonitrile. 7. The method according to patent claim 1 characterized in that the solvent is a mixture of acetonitrile and water where the amount of water in the solvent is about 10% or less. 8. The method according to patent claim 1 characterized in that the amount of desmethyl levofloxacin in the purified levofloxacin is at least one third less than the amount in the starting levofloxacin. 9. The method according to patent claim 1 characterized in that it further comprises the addition of antioxidants before the crystallization step. 10. The method according to patent claim 9 characterized in that the antioxidant is selected from the group consisting of ascorbic acid, sodium ascorbate, calcium ascorbate, ascorbic palmitate, butylated hydroxyanisole, butylated hydroxytoluene, 2,4,5-trihydroxybutyrophenone, 4-hydroxymethyl- 2,6-di-tert-butylphenol, erythorbic acid, guaiac gum, propyl gallate, thiodipropionic acid, dilauryl thiodipropionate, tert-butylhydroquinone, tocopherols and their pharmaceutically acceptable salts and mixtures. 11. The method according to patent claim 9 characterized in that the antioxidant is sodium metabisulfite. 12. The method according to claim 9, characterized in that the antioxidant is ascorbic acid. 13. The method according to patent claim 9 characterized in that the amount of N-oxide levofloxacin in the purified levofloxacin is at least one third less than the amount in the starting levofloxacin. 14. The method according to patent claim 9 characterized in that the amount of levofloxacin N-oxide to purified levofloxacin is about 0.1% or less. 15. The method according to patent claim 9 characterized in that the purity of the purified levofloxacin is about 99.5% by weight or more. 16. The method according to patent claim 9 characterized in that it further includes the step of determining whether the starting levofloxacin contains an amount of N-oxide levofloxacin that cannot be detected by HPLC. 17. The method according to patent claim 9 characterized in that the solvent is acetonitrile and where the purified levofloxacin is fundamentally pure levofloxacin hemihydrate. 18. The method according to patent claim 1 characterized in that and where the purified levofloxacin is fundamentally pure levofloxacin hemihydrate. 19. A process for the preparation of levofloxacin hemihydrate with a purity of about 99% or more characterized by including: dissolution of levofloxacin in a polar solvent at elevated temperature; and crystallization of levofloxacin hemihydrate. 20. The method according to patent claim 19 characterized in that the elevated temperature is in the range from 80°C to about 110°C. 21. The method according to patent claim 19 characterized in that the elevated temperature is the reflux temperature of the solution. 22. The method according to claim 19 characterized in that the solvent is selected from the group consisting of acetonitrile, dimethylsulfoxide:H2O, methylethyl ketone, butanol and their mixtures. 23. The method according to patent claim 19 characterized in that the solvent is dimethyl sulfoxide: H2O in a ratio of about 1:5. 24. The method according to claim 19, characterized in that the solvent is methyl ethyl ketone. 25. The method according to patent claim 19 characterized in that the solvent is n-butanol. 26. The method according to claim 19, characterized in that the solvent is acetonitrile. 27. Product characterized by the fact that it was obtained by the process according to patent claim 1. 28. Product characterized by the fact that it was obtained by the process according to patent claim 9. 29. Product characterized by the fact that it was obtained by the process according to patent claim 19. 30. A process for the preparation of levofloxacin with a purity of about 99% or more characterized by including: dissolution of levofloxacin in a polar solvent; addition of antioxidants; and crystallization of purified levofloxacin, where the addition step takes place before or after the dissolution step and before the crystallization step. 31. The method according to patent claim 9 characterized in that the antioxidant is in the range of about 0.2% to about 5% by weight of levofloxacin. 32. The method according to patent claim 9 characterized in that the antioxidant is added to levofloxacin before the dissolution step. 33. The method according to claim 1 characterized in that it further comprises the addition of antioxidants during the crystallization step. 34. A process for the preparation of levofloxacin with a purity of about 99% or more characterized in that it comprises the translation of (S)-(-)-9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[1 ,2,3-de][1,4]benzoxazine-6-carboxylic acid to levofloxacin at elevated temperature in the presence of antioxidants. 35. The method according to patent claim 34 characterized in that the purity of levofloxacin is about 99.5% by weight or more. 36. The method according to patent claim 34 characterized in that the amount of levofloxacin N-oxide in levofloxacin is about 0.1% or less. 37. Process for the preparation of levofloxacin hemihydrate characterized by the fact that it includes: dissolving levofloxacin in a solvent selected from the group consisting of acetonitrile, acetonitrile:H2O, dimethyl sulfoxide:H2O, methyl ethyl ketone, butanol, butanol:H2O and mixtures thereof; and crystallization of levofloxacin hemihydrate, 38. The method according to patent claim 37 characterized in that the solvent essentially consists of a mixture of butanol:H2O in a ratio of about 9:1 or acetonitrile:H2O in a ratio of about 99:1. 39. The method according to patent claim 38 characterized in that the solvent essentially consists of a mixture of acetonitrile:H2O in a ratio of about 99:1. 40. The method according to patent claim 37 characterized in that the temperature of the solvent is raised to a temperature of more than 80°C and less than 110°C. 41. The method according to patent claim 37 characterized in that the dissolving step includes heating the solvent with reflux. 42. The method according to patent claim 36 characterized in that it comprises drying crystallized levofloxacin hemihydrate at about 60°C.