WO2000044729A1

WO2000044729A1 - Crystalline quinoxaline derivative

Info

Publication number: WO2000044729A1
Application number: PCT/EP2000/000612
Authority: WO
Inventors: James David Meadows; Kim Marissa Pincott; John Frederick Seager
Original assignee: Glaxo Group Limited
Priority date: 1999-01-28
Filing date: 2000-01-27
Publication date: 2000-08-03
Also published as: AU2545300A; GB9901795D0

Abstract

Crystalline forms of (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1-carboxylic acid isopropyl ester, also known as (S)-1-methylethyl 2-ethyl-7-fluoro-3,4-dihydro-3-oxo-1(2H)-quinoxaline carboxylate, the compound of formula (I), process for their preparation, pharmaceutical formulations thereof and their use in therapy.

Description

CRYSTALLINE QUINOXALINE DERIVATIVE

The present invention relates to quinoxaline derivatives and their use in medicine. More particularly the invention is concerned with particular physical forms of (S)-2- ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1-carboxylic acid isopropyl ester, also known as (S)-l-methylethyl 2-ethyl-7-fluoro-3,4-dihydro-3-oxo-1(2H)- quinoxaline carboxylate, the compound of formula (I):

process for their preparation, pharmaceutical formulations thereof and their use in therapy.

European patent application publication no. 0 509 398 discloses a class of quinoxaline compounds which has been found to show activity against the human immunodeficiency virus (HIV). This class of compounds includes the compound of formula (I), but there is no specific disclosure of the compound of formula (I). Also disclosed is an effective process for the preparation of compounds of this class. A sub-class of the compounds of EPA 0 509 398 is disclosed in European patent application publication no. 0 708 093. This application contains a specific disclosure of the compound of formula (I) at Table 2, number 39, where its melting point is given as 123-125°C.

We have now found that the compound of formula (I) exhibits polymorphism. In particular, we have identified three polymorphic forms of the compound of formula (I).

We have found that the compound of formula (I) may be obtained by crystallisation under certain conditions in the form of a mixture of columnar and plate - like crystals forming approximately spherical agglomerates having a melting point of approximately 127-129°C for pure material (herein after Form 1).

The compound of formula (I) may also be crystallised in the form of two polymorphic forms (hereinafter Form 2 and Form 3) of similar energy. Form 2 typically shows a phase transformation at 110-114°C. Form 3 typically shows a phase transformation at 115-119°C.

Form 2 is the most stable of the three polymorphs at ambient temperature. Form 2 crystals have the advantage that their isolation is robust in routine manufacture and material with good handling properties (e.g. filterability and flow properties) can be obtained. Furthermore, Form 2 is stable in suspension even after protracted periods of storage.

The polymorphs of the compound of formula (I) are further defined by their X-ray diffraction spectra. For Form 1 , the definitive peaks in the X-ray diffraction spectrum occur at the following angles: 6.630, 10.695, 15.650 and 18.525. The definitive peaks in the X-ray diffraction spectrum of Form 2 occur at the following angles: 6.895, 10.865, 14.670, 16.100, 20.710 and 22.280. The definitive peaks in the X-ray diffraction spectrum of Form 3 occur at the following angles: 6.815, 11.540, 15.020 and 16.940.

The advantageous properties of Form 2, namely its particularly good stability which gives rise to enhanced robustness of the isolation and processing stages of manufacture, makes this polymorph particularly useful for the preparation of pharmaceutical formulations.

In a first aspect the invention provides the compound of formula (I) in the form of Form 2 as herein defined substantially free of other morphic forms, in particular of Form 1 and Form 3 as herein defined.

By "substantially free" is meant containing less than 5% of the alternative morphic forms, such as less than 2%, for example less than 1 % of the alternative forms. The present invention further provides a pharmaceutical formulation comprising the compound of formula (I) as Form 2 crystals.

The good handling properties of Form 2 facilitate its use in the preparation of solid dosage forms.

Solid pharmaceutical dosage forms comprising the compound of formula (I) suitable for use in conjunction with the present invention may be prepared by conventional means. Such dosage forms include, for example, those suitable for oral, rectal, nasal, topical (including buccal and sub-lingual) or vaginal administration or in a form suitable for administration by inhalation or insufflation. The formulations may, where appropriate, be conveniently presented in discrete dosage units and may be prepared by any of the methods well known in the art of pharmacy. All methods include the step of bringing into association the active compound with liquid carriers or finely divided solid carriers or both and then, if necessary, shaping the product into the desired formulation.

Pharmaceutical formulations suitable for oral administration may conveniently be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient. Tablets and capsules for oral administration may contain conventional excipients such as binding agents, fillers, lubricants, disintegrants, or wetting agents. The tablets may be coated according to methods well known in the art.

Preferably the solid dosage forms according to the invention will comprise unit dosage forms containing from 10mg to 1000mg of the compound of formula (I), preferably from 15mg to 300mg, more preferably 20mg to 200mg of the compound of formula (I) by weight.

It will be appreciated by those skilled in the art that the solid pharmaceutical dosage forms according to the invention may optionally comprise other therapeutic agents, in particular other antiviral agents.

We have found that suspensions of Form 1 crystals stored at ambient temperature are converted over time to suspensions of Form 2 and Form 3. The stability of Form 1 in suspension is dependent upon its impurity profile and upon the solvent, for example, in n-heptane, Form 1 is converted to a mixture of Form 2 and Form 3 in about 16 hours. Suspensions of Form 3 crystals are converted to suspensions of Form 2 over time, whereas Form 2 suspensions are stable to protracted storage at ambient temperature. Form 2 is therefore particularly advantageous for formulation as pharmaceutical suspensions.

Thus according to a further aspect, the present invention provides a pharmaceutical suspension comprising the compound of formula (I) as Form 2 crystals.

Pharmaceutical suspensions according to the invention will preferably be formulated for oral administration and may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles (which may include edible oils), or preservatives.

In a particularly preferred aspect, the present invention provides an oral suspension suitable for paediatric use comprising the compound of formula (I) as Form 2 crystals.

The compound of formula (I) may be prepared in crystalline form by crystallisation from aqueous or non-aqueous solution.

We have found that each of Forms 1 , 2 and 3 may be prepared substantially free from the alternative Forms by controlling the solvent, rate and temperature at which crystallisation occurs and in particular by controlling the time for which the crystallisation mixture is aged before the crystals are isolated. Typically, the Form 1 , Form 2 or Form 3 crystals will be isolated by filtration, suitably under reduced pressure. The isolated crystals may be dried by conventional means.

In general, the compound of formula (I) may be obtained as Form 1 crystals by crystallisation of the compound from aqueous or organic solution, preferably at a temperature greater than about 50°C, more preferably 55-65°C, followed by rapid cooling to ambient temperature and rapid isolation, e.g. by filtration, and drying. Suitable solvents for the crystallisation of Form 1 include aqueous ethanol and, preferably, heptane. In order to isolate Form 1 substantially free from Form 2, the timing of the isolation step is highly dependent upon the impurity profile of Form 1 material and the solvent used. For example, for pure material using n-heptane as solvent, the isolation should be effected within about 1.6 hours of the beginning of the crystallisation.

Form 1 may also be obtained by heating Form 2 and/or Form 3 in suspension at temperatures greater than 50°C or by heating Form 2 and/or Form 3 in the solid state at approximately 90°C for at least 6 hours, such as 6-8 hours.

In general, the compound of formula (I) may be obtained as Form 2 crystals by crystallisation of the compound from an organic solvent such as for example heptane or butanone or a mixture of solvents such as heptane/ethyl acetate, wherein the crystallisation mixture is aged at a temperature below about 40°C, preferably about 20°C.

In general, the compound of formula (I) may be obtained as Form 3 crystals by crystallisation of the compound from an aqueous solution of isopropanol.

The isolation of Form 2 substantially free of Form 3 has been found to be difficult. This is believed to be because the two crystalline forms are close in energy. We have now found that Form 2 can be isolated substantially free of Form 3 by extending the ageing period of the crystallisation. We found that the ageing period required depends on the presence or absence of impurities which can inhibit the morphic form turnover. This finding enabled us to develop a practical process for the preparation of Form 2 material by reducing the required ageing time to less than 24 hours. With pure material, we have found that, under particularly favourable conditions, turnover from Form 3 to Form 2 can take place in as little as 4 hours. More typically, an ageing time of at least 8 hours such as about 12 hours to about 16 hours is required in order to isolate Form 2 substantially free from Form 3. Hence by adopting suitable procedures, such as removal of impurities by washing of reaction solutions and temperature control, the process for the preparation of the compound of formula (I) can be tailored to provide highly pure material in solution. The high purity of this material facilitates isolation as Form 2. Suitable procedures for the removal of impurities will be apparent to those skilled in the art.

The methods for the preparation of crystalline material, and in particular methods for the preparation of substantially pure Forms 1 , 2 and 3, described herein constitute further aspects of the present invention.

Forms 1 , 2 and 3 have been subjected to X-ray powder diffraction studies. Diffraction traces were obtained using a Philips X'pert MPD diffractometer (serial DY667) and CuK_α radiation. X-Ray intensities were measured at 0.02° increments for 4 second intervals using a scintillation counter, between values of 2 and 45° 2Θ. The d-spacings and line intensities obtained for Forms 1 , 2 and 3 are shown in Tables 1 , 2 and 3, respectively.

TABLE 1

Sample identification: R2821/66/1 - Form 1

Dl file name: X7624.DI Input file name: X7624

(NB θ = Theta)

Start angle [°2Θ ]: 2.010 End angle [°2Θ]: 44.990

Start d-value [Angstrom]: 43.91761 End d-value [Angstrom]: 2.01332 Maximum number of counts: 182756

Anode material: Cu Wavelength [Angstrom]: 1.54060 α₂ Wavelength [Angstrom]: 1.54439

Intensities for FIXED slit Peak positions defined by: Minimum of 2nd derivative of peak

Minimum peak tip width: 0.00

Maximum peak tip width: 1.00

Maximum peak base width: 2.00

Minimum significance: 0.75

Number of peaks: 63

DIFFRACTION LINES:

TABLE 2

Sample identification: R4289/156/2 -Form 2

Dl file name: X7625.DI Input file name: X7625

NB Θ = Theta

Start angle [°2Θ ]: 2.010 End angle [°2Θ ]: 44.990 Start d-value [Angstrom]: 43.91761 End d-value [Angstrom]: 2.01332 Maximum number of counts: 211232

Anode material: Cu α. Wavelength [Angstrom]: 1.54060 α₂ Wavelength [Angstrom]: 1.54439

Intensities for FIXED slit

Peak positions defined by: Minimum of 2nd derivative of peak Minimum peak tip width: 0.00 Maximum peak tip width: 1.00 Maximum peak base width: 2.00 Minimum significance: 0.75 Number of peaks: 67 DIFFRACTION LINES

TABLE 3

Sample identification: R4289/124/5 - Form 3

Dl file name: X7626.DI Input file name: X7626

(NB Θ = Theta)

Start angle [°2Θ ]: 2.010

End angle [°2Θ ]: 44.990

Start d-value [Angstrom]: 43.91761

End d-value [Angstrom]: 2.01332

Maximum number of counts: 199184

Anode material: Cu cq Wavelength [Angstrom]: 1.54060 ₂ Wavelength [Angstrom]: 1.54439

Intensities for FIXED slit

Peak positions defined by: Minimum of 2nd derivative of peak

Minimum peak tip width: 0.00

Maximum peak tip width: 1.00

Maximum peak base width: 2.00 Minimum significance: 0.75 Number of peaks: 60

DIFFRACTION LINES

Figure 1 shows the X-ray diffraction spectrum of Form 1 Figure 2 shows the X-ray diffraction spectrum of Form 2 Figure 3 shows the X-ray diffraction spectrum of Form 3 Figure 4 shows agglomerates of Form 1 crystals Figure 5 shows a Form 1 agglomerate Figure 6 shows Form 2 crystals Figure 7 shows Form 2 crystals Figure 8 shows Form 3 crystals.

Example 1

Preparation of Form 1

(S)-2-Ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (5g) was suspended in n-heptane (25mL) and the mixture warmed to over 70°C to give a clear solution. The stirred solution was allowed to cool. Crystallisation occurred at about 59°C and the stirred mixture was cooled to about 20°C before the solid was collected by vacuum filtration, washed with n-heptane (10mL) and dried in a vacuum oven at up to 45°C to give the Form 1 material (4.6g).

Example 2

Preparation of Form 1

(S)-2-Ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (15g) was suspended in n-heptane (75mL) and the mixture warmed to about 78°C to give a clear solution. The solution was allowed to cool to 65°C and seeded with (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (Form 1 , 0.45g). The stirred mixture was cooled to 20°C over about 80 minutes and aged at the same temperature for a further 20 minutes. The solid was collected by vacuum filtration, washed with n-heptane (30mL) and dried in a vacuum oven at 40°C to give the Form 1 material (14.24g).

Example 3

Preparation of Form 2

(S)-2-Ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (10.8g) was suspended in n-heptane (102mL) and the mixture warmed to 68°C to ensure complete dissolution. The solution was allowed to cool to 55°C and seeded with a sample of Form 1 material (0.104g). The mixture was allowed to cool to ambient temperature and stirred for 5 days. The product was harvested by vacuum filtration, washed with n-heptane (10mL) and dried in a vacuum oven at 40°C to give Form 2 material (6.48g).

Example 4

Preparation of Form 2

(S)-2-Ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (14.76 g) was suspended in n-heptane (160 mL) and the mixture warmed to 65°C to ensure complete dissolution. The solution was allowed to cool to 50°C at which point it was seeded with a sample of Form 2 material (0.15 g). The mixture was allowed to cool to ambient temperature and the resultant mixture stirred for 4 days. The product was harvested by vacuum filtration, washed with n-heptane (2 x 20 mL) and dried in a vacuum oven at 40°C to give the Form 2 material (12.78g). Example 5

Preparation of Form 3

(S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (40.07g) was suspended in a mixed solution of 2-propanol in water (1 :1 , 200 mL) and warmed to 70°C to ensure complete dissolution. The solution was then allowed to cool and at 26°C spontaneous crystallisation occurred. The suspension was stirred at room temperature and sampled periodically (to determine by X-ray powder diffraction the point at which Form 3 is present as the sole morphic form). Once the material had been confirmed as Form 3 the product was immediately harvested by vacuum filtration, washed with a 1:1 solution of 2-propanol in water (20 mL) and dried in a vacuum oven at 40°C to give the Form 3 product (19.8 g).

Example 6

Synthesis of (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester and isolation of Form 2

A mixture of L-(+)-2-aminobutyric acid (15kg), difluoronitrobenzene (25.5kg; 1.1equiv) and sodium hydrogen carbonate (26.9kg; 2.2equiv) was stirred in 5% aqueous propan-2-ol (115L) at near to reflux for about 12 hours. The reaction mixture was cooled to about 20°C, stirred for a few hours and the solid (mainly sodium fluoride) was removed by filtration and washed with 5% aqueous propan-2- ol. The combined filtrate and washes were distilled at atmospheric pressure to about 75L. Water (75L) was added and the distillation was continued to a residual volume of about 75L. The aqueous solution was extracted twice with toluene before 75%w/w phosphoric acid (20.85kg; 1.1equiv) was added to the separated aqueous layer which was extracted twice with ethyl acetate.

Acetic acid (4.35kg; O.δequiv) was added to the combined ethyl acetate extracts

(about 140L) and catalyst (10%PdO/C, 50% wet with water, 0.72kg) and charcoal

(1.5kg) were added and the resultant mixture was stirred under hydrogen for several hours, until hydrogen uptake ceased. The catalyst and charcoal were removed by filtration and the filtrate was washed sequentially with aqueous sodium hydroxide (5M and 1 M), water, dilute aqueous sodium chloride solution, 1 M aqueous hydrochloric acid, water again and finally with dilute aqueous sodium chloride solution.

The solution in ethyl acetate (about 150L) was concentrated by distillation under reduced pressure to about 85L and left under nitrogen. Potassium hydrogen carbonate (27kg; 1.85equiv) and water (21 L) were added and the temperature was adjusted to about 35°C. Isopropyl chloroformate (19.5kg; 1.1equiv) was added over 40mins and the mixture was stirred at 40 - 45°C for 20 hours. Pyridine (0.15L) was added over 10 mins at <5°C and the mixture was stirred at about 5°C for 1 hour. After warming to about 20°C, n-heptane (75L) and 2M aqueous sodium hydroxide were added with stirring. The organic layer was separated and washed sequentially with water, 1 M aqueous hydrochloric acid and finally water.

The resultant solution was concentrated by distillation at atmospheric pressure and n-heptane was added at intervals until all of the ethyl acetate has been removed and the mixture comprised a total volume of about 195L. At 66°C, the solution was seeded with Form 2 crystals (1.3kg) and the mixture was cooled to 20 to 25°C at about 0.5°/min with stirring.

The resultant suspension, a mixture of morphic forms, was stirred at 20 to 25°C for 21 hours, by which time all of the solid present was Form 2. The solid was harvested by filtration, washed with n-heptane and dried at up to 40° under vacuum to give (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-1 -carboxylic acid isopropyl ester (30.2kg).

Example 7

Tablet Formulation.

Ingredients 50mg/tablet 200mg/tablet

Compound of formula (I) 50.0 200.0

Lactose Monohydrate 28.0 112.0

Microcrystalline Cellulose 12.5 50.0

Crosscarmellose Sodium 4.0 16.0

Povidone K30 3.0 12.0

Sodium Lauryl Sulphate 1.0 4.0

Magnesium Stearate 1.5 6.0

Opadry/Opadry II (optionally) 2.0 8.0

Method Of Manufacture

Compound of formula (I), lactose monohydrate, microcrystalline cellulose and a proportion of crosscarmellose sodium are dryblended in a suitable mixer. The powders are granulated with a solution of povidone K30 and sodium lauryl sulphate in purified water. The damp granule is oven dried or fluid-bed dried and then sieved. The remaining portion of crosscarmellose sodium and magnesium stearate are added to the sieved granule and blended. The blend is suitably compressed into tablets which are optionally film-coated with Opadry/Opadry II dispersions.

Example 8

Paediatric suspension formulation.

Ingredients 100mg/5 ml dose

Compound of formula (I) 100.00

Tween 20 150.00 Sorbic Acid 50.00 Xanthan Gum 20.00 Purified Water qs to 5.00 ml

Method of Manufacture

Tween 20 is dissolved in purified water to give 3%w/v solution and the compound of formula (I) dispersed therein. Sorbic acid is added to the dispersion. Xanthan gum is added and mixed until a suitable suspension is produced.

The suspension may additionally contain flavourings, sweetener, taste masking agents, colourants and stabilising agents.

Claims

CLAIMS:

1. The compound of formula (I):

in a crystalline form which shows a phase transformation at 110-114°C.

2. The compound of formula (I) as defined in claim 1 in the form of crystals characterised in that the definitive peaks in their powder X-ray diffraction spectrum occur at the following angles [°2Θ ]: 6.895, 10.865, 14.670, 16.100, 20.710 and 22.280.

3. A pharmaceutical formulation comprising the compound of formula (I) in a form as claimed in claim 1 or claim 2.

4. A pharmaceutical formulation as claimed in claim 3 in the form of a suspension.

5. A solid pharmaceutical dosage form comprising the compound of formula (I) in a form as claimed in claim 1 or claim 2.

6. The compound of formula (I) in the form claimed in claim 1 or claim 2 substantially free of other morphic forms.

7. A method for preparing the compound of formula (I) in a form as claimed in claim 1 or claim 2 which method comprises crystallisation from organic solution wherein the crystallisation solution is aged at a temperature below about 40°C.

8. A method as claimed in claim 7 wherein the compound is substantially free of other morphic forms.

9. A method as claimed in claim 7 or claim 8 wherein the solution is aged for less than 24 hours.

10. The use of the compound of formula (I) in a form as claimed in any of claims 1 ,2 and 6 for the manufacture of a pharmaceutical formulation.