NO309814B1 - Zwitterion Forms of Trovafloxacin, Methods of Preparation and Preparations Containing These - Google Patents

Description

Background for the invention

The present invention relates to the naphthyridone antibiotic trovafloxacin. More particularly, it relates to polymorphs and the pentahydrate of the zwitterionic form thereof having formula I, below and methods of their preparation. The invention further relates to pharmaceutical preparations comprising the compounds according to the present invention for the treatment of bacterial infections in mammals.

The antibacterial activity of the above-mentioned naphthyridone antibiotic is described in US Patents 5,164,402 [the '402 patent] and 5,229,396 granted November 17, 1992 and July 20, 1993, respectively, the contents of which are incorporated herein in their entirety by reference. The above patents have been transferred as the present application.

The zwitterion forms of trovafloxacin are useful for administering the drug as a suspension.

Summary of the invention

According to a first embodiment of the invention, there is provided a zwitterionic crystal form of trovafloxacin having the formula

which is selected from the group consisting of

a) a non-hygroscopic first polymorph Pl having the following characteristic X-ray powder diffraction pattern

b) a hygroscopic second polymorph PH having the characteristic X-ray powder diffraction pattern

and

c) a pentahydrate, trovafloxacin zwitterion pentahydrate, which has the characteristic X-ray powder diffraction pattern

A second embodiment of the invention relates to a process for the preparation of a zwitterion of trovafloxacin of formula I which is selected from the group consisting of a non-hygroscopic polymorph P1, a hygroscopic polymorph P1 and a pentahydrate thereof, as described above, comprising A. treatment of an aqueous suspension of a metastable form of the compound of formula I 1) with a non-polar solvent, followed by azeotropic removal of residual water and vacuum drying to form said hygroscopic polymorph Pli having the characteristic X-ray powder diffraction pattern set forth in claim 1 ; 2) with a polar solvent, followed by azeotropic removal of residual water and vacuum drying; or 3) with water and air drying the residue at elevated temperature, removing the mother liquor and air drying the residue at room temperature to constant weight to form the pentahydrate; or B) treating the hygroscopic second polymorph P1 with a polar solvent under reflux to form the non-hygroscopic first polymorph P1. The metastable form of the zwitterion of trovafloxacin of formula I is prepared by a) treating an acid salt of trovafloxacin with a base to raise the pH of the mixture to between 7.5 and 8.5 at an elevated temperature, removing the mother liquor,

washing the crystals with water and drying the crystals under vacuum at approx. 35 to approx. 40 °C; or

b) treatment of a compound of the formula

where A is hydrogen or an amine protecting group such as t-butyloxycarbonyl,

benzyloxycarbonyl, (C 1 -C 6 )alkylcarbonyl and benzyl; and

B is hydrogen or a carboxylic acid protecting group selected from benzyl, t-butyl and (C 1 -C 6 ) alkyl; with respectively an amine and/or carboxylic acid deprotecting agent.

According to a final embodiment of the invention, there is provided a preparation for the treatment of a bacterial infection in a mammal comprising an amount of a compound of formula I which is effective for the treatment of a bacterial infection, and a pharmaceutically acceptable carrier.

Detailed description of the present invention

The present invention relates to a compound comprising a stable zwitterionic form of the antibiotic trovafloxacin with the formula

More particularly, it relates to a compound of formula I selected from

a) a non-hygroscopic first polymorph P1 having the characteristic X-ray powder diffraction pattern described above; b) a hygroscopic second polymorph Pil having the characteristic X-ray powder diffraction pattern described above; -

and c) a pentahydrate, trovafloxacin zwitterion pentahydrate, which has the characteristic X-ray powder diffraction pattern described above.

The invention also relates to methods for preparing the compounds of formula I as illustrated in the following schemes.

As shown in Scheme 1, a trovafloxacin salt becomes 1, where X is an anion selected from those formed from mineral acids such as hydrochloric, sulfuric, nitric and phosphoric; organic acids such as sulphonic acids, e.g. benzenesulfonic acid (benzylic), p-toluenesulfonic acid (PTSA, tosyl), methanesulfonic acid (MSA, mesyl) and trifluoromethanesulfonic acid (triflin); and carboxylic acids e.g. acetic acid, propionic acid, benzoic acid, citric acid, tartaric acid, maleic acid, fumaric acid, succinic acid and malic acid, is converted to a metastable zwitterionic form 2 by raising the pH of a slurry comprising compound 1 to a pH of between approx. 7.5 and 8.5 at a temperature in the range approx. 45 to approx. 55°C when using an aqueous basic solution. A preferred salt is the mesylate. Bases useful for this embodiment of the present invention include inorganic bases such as alkali or alkaline earth hydroxides, carbonates and bicarbonates and organic bases such as tri(C 1 -C 6 )alkyl amines, pyridine and morpholine. A preferred aqueous base is saturated sodium bicarbonate. The wet product is then dried to constant weight, in vacuum at a temperature from approx. 35 to approx. 40°C.

Alternatively, as shown in Scheme 2, compound 2 can be prepared directly from protected precursors 6, for trovafloxacin salts 1, with the formula

where A is hydrogen or an amine protecting group such as t-butyloxycarbonyl, benzyloxycarbonyl, (C 1 -C 6 )alkylcarbonyl and benzyl; and

B is hydrogen or a carboxylic acid protecting group selected from benzyl, t-butyl and (C 1 -C 6 ) alkyl; with respectively an amine and/or carboxylic acid deprotecting agent.

A preferred compound 6, where A is hydrogen and B is ethyl, is converted to compound 2 by treatment with a solution of NaOH in a polar solvent at an elevated temperature. A preferred solvent is methanol and the temperature is the reflux temperature of the solvent. The pH of the solution was then regulated to between approx. 6.5 and 8.0 with dilute HCl, and saturated aqueous NaHCO 3 was then added to adjust the pH to between ca. 7.5 and 8.5. The product was recovered as indicated above.

Metastable trovafloxacin zwitterion 2 is converted to hygroscopic polymorph Pli, 4, by treatment with a non-polar solvent such as a hydrocarbon. Preferred hydrocarbons are hexanes. Remaining water is removed azeotropically, and the product is dried at approx. 35 to approx. 40°C under vacuum. Solvents useful for azeotropic removal of trace water include non-polar aliphatic hydrocarbons such as hexanes and octanes and aromatic hydrocarbons such as benzene and toluene. Preferred solvents are aliphatic hydrocarbons, most preferably hexanes.

A non-hygroscopic polymorph Pl 3 can be prepared from compound 2 by treatment with a polar solvent followed by azeotropic removal of water and vacuum drying at ca. 30 to approx. 40°C. Polar solvents useful for this conversion include (C 1 -C 6 )alkyl esters of (C 2 -C 6 )alkyl carboxylic acids and (C 1 -C 6 )alkanols. A preferred solvent is ethyl acetate.

Alternatively, compound 3 can be prepared from compound 4 by treating compound 4 with a polar solvent under reflux, as described above. A preferred solvent is ethyl acetate.

Compound 5, the pentahydrate of the compound of formula I, is prepared by air drying the wet crystals of compound 1, at room temperature, until constant weight is obtained. Alternatively, compound 5 can be prepared from compound 4 by treatment with water until constant water uptake is achieved. Compound 3 is not converted to compound 5 upon exposure to water.

The antibacterial compounds according to the present invention, i.e. polymorph P1, polymorph PH and the pentahydrate (hereinafter "the active compounds") are useful in the treatment of animals and humans who have a wide spectrum of bacterial infections. They are particularly useful for treating Gram-positive bacterial strains.

The active compounds may be administered alone, but will generally be administered together with a pharmaceutical carrier selected with regard to the intended method of administration and standard pharmaceutical practice. For example, they may be administered orally or in the form of tablets containing additives such as starch or lactose or in capsules either alone, in a mixture with additives or in the form of elixirs or suspensions containing flavoring agents or coloring agents. For animals, they are advantageously added to animal feed or drinking water in a concentration of approx. 5 to approx. 5000 ppm, preferably approx. 25 to approx. 500 ppm. They can be injected parenterally, for example intramuscularly, intravenously or subcutaneously. For parenteral administration, they are best used in the form of a sterile aqueous solution which may contain other soluble substances, for example sufficient salt or glucose to make the solution isotonic. For animals, the compounds of formula I can be administered intramuscularly or subcutaneously at dose levels of about 0.1 to approx. 50 mg/kg/day, advantageous approx. 0.2 to approx. 10 mg/kg/day given as a single daily dose or up to 3 divided doses.

The active compounds can be administered to humans for the treatment of bacterial diseases either orally or parenterally. They can be administered orally in dose levels of approx. 0.1 to 500 mg/kg/day, advantageously 0.5-50 mg/kg/day given in a single dose or up to 3 divided doses. For intramuscular or intravenous administration, the dose levels are approx. 0.1-200 mg/kg/day, advantageously 0.5-50 mg/kg/day. While intramuscular administration can be a single dose or up to 3 divided doses, intravenous administration can involve a continuous drip. Variations will necessarily occur depending on the weight and condition of the individual being treated and the particular route of administration chosen, as will be known to those skilled in the art.

The active compound may be administered alone, but will normally be administered mixed with a pharmaceutical carrier selected with regard to the particular route of administration and standard pharmaceutical practice. For example, it may be administered orally or in the form of tablets containing such additives as starch or lactose or in capsules either alone or mixed with additives or in the form of elixirs or suspensions containing flavoring or coloring agents. For animals, they are advantageously added to the animal feed or drinking water in a concentration of approx. 5 to approx. 5000 ppm, preferably approx. 25 to approx. 500 ppm. They can be injected parenterally, for example intramuscularly, intravenously or subcutaneously. For parenteral administration, they are best used in the form of a sterile aqueous solution which may contain other soluble substances, for example sufficient salt or glucose to make the solution isotonic. To animals, the compounds of formula I can be administered intramuscularly or subcutaneously at dose levels of about 0.1 to approx. 50 mg/kg/day, advantageous approx. 0.2 to approx. 10 mg/kg/day given as a single daily dose or up to 3 divided doses. The active compounds can be administered to humans either orally or parenterally and can be administered orally at dose levels of about 0.1 to 500 mg/kg/day, advantageously 0.5-50 mg/kg/day given in a single dose or up to 3 divided doses. For intramuscular or intravenous administration, the dose level is approx. 0.1-200 mg/kg/day, advantageously 0.5-50 mg/kg/day. While intramuscular administration can be a single dose or up to 3 divided doses, intravenous administration involves a continuous drip. Variations will necessarily occur depending on the weight and condition of the subject being treated and the particular route of administration chosen, as is known to those skilled in the art.

The antibacterial activity of the compounds of the present invention has been demonstrated by testing according to Steer's replicator technique which is a standard in vitro bacterial test method described by E. Steers et al., Antibiotics and Chemotherapy, 9, 307 (1959).

The following examples illustrate the methods and compounds of the present invention. However, it should be understood that the invention is not limited to the specific examples.

Example 1

Trovafloxacin zwitterion. metastable form

A. Trovafloxacin mesylate (prepared according to Example 13B of the '402 patent) (20 g) was stirred with demineralized water (100 mL). The crystal slurry was heated to approx. 50 °C and the slurry was regulated to a pH of approx. 8.0 when adding saturated sodium bicarbonate solution. The slurry was kept at approx. 50 °C for 30 minutes, allowed to cool to approx. 25 °C and was stirred at this temperature for 30 minutes. The crystals were isolated by filtration

and washed with demineralized water (27 ml). The wet crystals were suspended in demineralized water (100 ml) and stirred for approx. 1 hour at approx. 50 °C, then cooled to approx. 20°C and stirred at this temperature for approx. 1 hour. The crystals were filtered from the mother liquor, washed with demineralized water (approx. 27 ml) and dried to constant weight under vacuum at approx. 40 °C which gave the title product containing 2.5% residual water by analysis. Yield 16.25 g, 97%.

B. The ethyl ester of trovafloxacin (prepared according to the method of concurrent US Patent Application No. 08/490827, filed June 15, 1995, the disclosure of which is incorporated herein by reference in its entirety. The application is assigned in the same manner as the present application.) (10 g) was stirred with methanol (75 ml), water (25 ml) and sodium hydroxide pellet (1.8 g). The resulting mixture was heated to reflux at ca. 72 °C to form a solution. The solution was cooled to approx. 25°C and the pH was regulated to approx. 7.5, by adding 6N hydrochloric acid to form a slurry. Saturated sodium bicarbonate solution (50 ml) was added and the slurry was stirred for 30 minutes at approx. 25 °C. The title product was isolated and washed with water (20 ml) and dried under vacuum at approx. 45 °C. Yield 7.72 g, 82.5%.

Example 2

Trovafloxacin zwitterionic polymorph P1 (non-hydroscopic form) Trovafloxacin mesylate, (75 g) was stirred with demineralized water (375 ml). The crystal slurry was heated to approx. 50 °C and the slurry was regulated to a pH of approx. 8.0 when adding saturated sodium bicarbonate solution. The slurry was kept at approx. 50 °C for 30 minutes, allowed to cool to approx. 25 °C and was stirred at this temperature for 30 minutes. The crystals were isolated by filtration and washed with demineralized water (100 mL). The wet crystals were suspended in demineralized water (375 ml) and stirred for 1 hour at approx. 50 °C, and was then cooled to approx. 20 °C and stirred at this temperature for approx. 1 hour. The crystalline product was filtered from the mother liquor and washed with demineralized water (about 100 ml). The wet crystals were stirred with ethyl acetate (1125 mL), the resulting slurry was heated to reflux and water was removed azeotropically. The essentially water-free slurry was cooled to approx. 25 °C, the crystals were isolated by filtration and dried under vacuum at 40 °C until all solvent was removed, yielding the title product. Yield 60.9 g, 94%.

The product is characterized by the X-ray powder diffraction pattern described above.

Example 3

Trovafloxacin- zwitterion hvgroscopic polymorph PH

The title product from Example 1, Section A, (5 g) was mixed with hexanes (150 mL) to form a slurry. The slurry was heated to reflux and traces of residual water were removed azeotropically. After 4 hours at reflux, the crystal slurry was cooled to approx. 25 °C, isolated by filtration and dried to constant weight under vacuum at approx. 40 °C.

Yield 4.7 g, 94%. The title product is characterized by the X-ray powder diffraction pattern described above.

Example 4

Trovafloxacin zwitterion pentahdrate

Trovafloxacin mesylate (50 g) was stirred with demineralized water (250 ml). The crystal slurry was heated to 50 °C and the slurry was adjusted to a pH of approx. 8.0 when adding saturated sodium bicarbonate solution. The slurry was kept at approx. 50 °C for 30 minutes, allowed to cool to approx. 25 °C and was stirred at this temperature for 30 minutes. The crystals were isolated by filtration and washed with demineralized water (70 mL). The wet crystals were suspended in demineralized water (250 ml) and stirred for 1 hour at approx. 50 °C, then cooled to approx. 20°C and stirred at this temperature for approx. 1 hour. The crystalline product was filtered from the mother liquor and washed with demineralized water (about 70 ml). The wet crystals were air dried to constant weight at room temperature to give the title product containing 17.6% water by analysis. Yield 48.4 g, 84%

The title product is characterized by the X-ray powder diffraction pattern described above.

Claims (8)

I f \ I ^ 1 ^ I I XI X/X v 1. Trovafloxacin zwitterion crystal form, characterized by the formula selected from the group consisting of a) a non-hygroscopic first polymorph Pl having the characteristic X-ray powder diffraction pattern b) a hygroscopic second polymorph Pli having the characteristic X-ray powder diffraction pattern and c) a pentahydrate, trovafloxacin zwitterion pentahydrate, having it characteristic X-ray powder diffraction patterns 2. Procedure for preparing a compound of the formula selected from the group consisting of a non-hygroscopic polymorph Pl, a hygroscopic polymorph PH and a pentahydrate thereof, characterized byA. treatment of an aqueous suspension of a metastable form of the compound of formula I 1) with a non-polar solvent followed by azeotropic removal of residual water and vacuum drying, yielding said hygroscopic polymorph PM having the characteristic X-ray powder diffraction pattern described in claim 1; 2) with a polar solvent followed by azeotropic removal of residual water and vacuum drying; or 3) with water and air-drying the residue at elevated temperature, removing the mother liquor and air-drying the residue at room temperature to constant weight, yielding the pentahydrate; or B. by treating the hygroscopic second polymorph PH with a polar solvent under reflux, yielding the non-hygroscopic first polymorph Pl. 3. Method according to claim 2, characterized in that the metastable form of the compound with formula I is produced by a) treating an acid salt of trovafloxacin with a base to raise the pH of the mixture to between 7.5 and 8.5 at elevated temperature; or b) treating a compound of the formula where A is hydrogen or an amine protecting group such as t-butyloxycarbonyl, benzyloxycarbonyl, (C 1 -C 6 )alkylcarbonyl and benzyl; and B is hydrogen or a carboxylic acid protecting group selected from benzyl, t-butyl and (C 1 -C 6 )alkyl; with respectively an amine and/or carboxylic acid protecting agent. 4. Method according to claim 2, characterized in that in step a) the solvent is hexanes, and in step b), the polar solvent is ethyl acetate. 5. Method according to claim 3, characterized in that A is hydrogen or an amine protecting group such as t-butyloxycarbonyl, benzyloxycarbonyl, (d-Ce)alkylcarbonyl and benzyl. 6. Method according to claim 3, characterized in that in said compound B is hydrogen and A is selected from benzyl, t-butyl and (Ci-Ce)alkyl. 7. Preparation for treating bacterial infections in a mammal, characterized in that it comprises an amount of a compound according to claim 1 which is effective in treating a bacterial infection and a pharmaceutically acceptable carrier. 8. Preparation according to claim 7, characterized in that said preparation is a suspension.