WO2022195541A1

WO2022195541A1 - A crystalline salt of edaravone, processes for the preparation and use thereof

Info

Publication number: WO2022195541A1
Application number: PCT/IB2022/052455
Authority: WO
Inventors: Thierry Bonnaud; Alan Chorlton; Jonathan HARRHY
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2021-03-18
Filing date: 2022-03-17
Publication date: 2022-09-22
Anticipated expiration: 2023-09-18
Also published as: GB202103807D0

Abstract

A crystalline salt of edaravone, namely edaravone hemi edisylate is disclosed. In addition, processes for the preparation of the crystalline form and pharmaceutical compositions containing the crystalline form are disclosed herein.

Description

A Crystalline Salt of Edaravone. Processes for the Preparation and Use Thereof

The present invention relates to a crystalline salt of edaravone, namely edaravone hemi edisylate, to processes for the preparation of the crystalline form, and to pharmaceutical compositions containing the crystalline form.

Background

Edaravone has the IUPAC name of 5-methyl-2-phenyl-4/-/-pyrazol-3-one and has the chemical structure illustrated below:

Edaravone may be prepared using the Knorr pyrazole synthesis (see Comprehensive Organic Chemistry Experiments for the Laboratory Classroom, The Royal Society of Chemistry, 2017, Supplementary Information, pages 1-8).

Edaravone is a tautomeric molecule and three major tautomers have been proposed for the keto, enol and amino forms. In an acidic or basic environment, the enol form equilibrates to an anionic form. The keto form appears to be the most thermodynamically stable form both as a crystalline solid and in polar and non-polar solutions (Gonzalez and Galano, J. Phys. Chem. B 2011, 115, 5, 1306-1314). The anionic and tautomeric forms of edaravone are illustrated in Gonzalez and Galano, and are shown below:

The pKa of edaravone is accepted to be approx. 7.0 and as such it exists in an equilibrium mixture between the enol and anion forms in a solution at pH 7. The equimolar concentration of enol and anion forms of edaravone result in poor aqueous stability as it readily forms a serious of stable radicals which further react to form a trimer compound (Tanaka et al, J. Clin. Biochem. Nutr. 2017, 61, 3, 159-163).

W02019/073052 (to Treeway TW001 B.V.) describes napadisylate salts of edaravone.

CN104257603A (to Nanjing Baite Bioengineering Co Ltd) describes edaravone/ cyclodextrin inclusion compounds.

US2020/0268712 (to Hayama et al) describes an edaravone suspension for oral administration including edaravone particles, a dispersant, and water.

Parikh et al (Drug Delivery, 24: 1, 962-978) describes a lipid-based nanosystem of edaravone.

In the EU, an orphan designation has been granted to edaravone for the treatment of amyotropic lateral sclerosis (ALS).

Definitions

The term "about" or "approximately" means an acceptable error for a particular value as determined by a person of ordinary skill in the art, which depends in part on how the value is measured or determined. In certain embodiments, the term "about" or "approximately" means within 1, 2, 3 or 4 standard deviations. In certain embodiments, the term "about" or "approximately" means within 30%, 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or 0.5% of a given value or range. In certain embodiments and with reference to X- ray powder diffraction two-theta peaks, the terms "about" or "approximately" means within ± 0.2 ⁰ 2Q.

The term "ambient temperature" means one or more room temperatures between about 15 °C to about 30 °C, such as about 15 °C to about 25 °C.

The term "consisting" is closed and excludes additional, unrecited elements or method steps in the claimed invention.

The term "consisting essentially of" is semi-closed and occupies a middle ground between "consisting" and "comprising". "Consisting essentially of" does not exclude additional, unrecited elements or method steps which do not materially affect the essential characteristic(s) of the claimed invention. The term "comprising" is inclusive or open-ended and does not exclude additional, unrecited elements or method steps in the claimed invention. The term is synonymous with "including but not limited to". The term "comprising" encompasses three alternatives, namely (i) "comprising", (ii) "consisting", and (iii) "consisting essentially of".

The term "crystalline" and related terms used herein, when used to describe a compound, substance, modification, material, component or product, unless otherwise specified, means that the compound, substance, modification, material, component or product is substantially crystalline as determined by X-ray diffraction. See, e.g., Remington: The Science and Practice of Pharmacy, 21st edition, Lippincott, Williams and Wilkins, Baltimore, Md. (2005); The United States Pharmacopeia, 23rd ed., 1843-1844 (1995).

The term "pharmaceutical composition" is intended to encompass a pharmaceutically effective amount of edaravone hemi edisylate of the invention and a pharmaceutically acceptable excipient. As used herein, the term "pharmaceutical compositions" includes pharmaceutical compositions such as tablets, pills, powders, liquids, suspensions, emulsions, granules, capsules, suppositories, or injection preparations.

The term "excipient" refers to a pharmaceutically acceptable organic or inorganic carrier substance. Excipients may be natural or synthetic substances formulated alongside the active ingredient of a medication, included for the purpose of bulking-up formulations that contain potent active ingredients (thus often referred to as "bulking agents," "fillers," or "diluents"), or to confer a therapeutic enhancement on the active ingredient in the final dosage form, such as facilitating drug absorption or solubility. Excipients can also be useful in the manufacturing process, to aid in the handling of the active substance, such as by facilitating powder flowability or non-stick properties, in addition to aiding in vitro stability such as prevention of denaturation over the expected shelf life.

The term "patient" refers to an animal, preferably a human, who has been the object of treatment, observation or experiment. Preferably, the patient has experienced and/or exhibited at least one symptom of the disease or disorder to be treated and/or prevented. Further, a patient may not have exhibited any symptoms of the disorder, disease or condition to be treated and/prevented, but has been deemed by a physician, clinician or other medical professional to be at risk for developing said disorder, disease or condition.

The terms "treat", "treating" and "treatment" refer to the eradication or amelioration of a disease or disorder, or of one or more symptoms associated with the disease or disorder. In certain embodiments, the terms refer to minimizing the spread or worsening of the disease or disorder resulting from the administration of one or more therapeutic agents to a patient with such a disease or disorder. In some embodiments, the terms refer to the administration of the crystalline salt provided herein, with or without other additional active agents, after the onset of symptoms of a disease.

Certain aspects of the embodiments described herein may be more clearly understood by reference to the drawings, which are intended to illustrate but not limit, the invention, and wherein:

Figure 1 shows the asymmetric unit of the crystalline edaravone hemi edisylate salt.

Figure 2 is a representative XRPD pattern of edaravone hemi edisylate.

Figure 3 is a representative TGA thermogram and a DSC thermogram of edaravone hemi edisylate.

Figure 4 is a representative XRPD pattern of edaravone hemi napadisylate (not according to the invention).

Figure 5 is a representative TGA thermogram and a DSC thermogram of edaravone hemi napadisylate (not according to the invention).

Figure 6 is a representative XRPD pattern of edaravone cyclodextrin clathrate (not according to the invention).

Figure 7 illustrates the dissolution profiles of edaravone hemi edisylate, edaravone, edaravone hemi napadisylate, and edaravone cyclodextrin clathrate. Edaravone, edaravone hemi napadisylate, and edaravone cyclodextrin clathrate are not according to the invention.

Figure 8 illustrates how centrifugal forces are applied to particles in the Speedmixer™. Figure 8A is a view from above showing the base plate and basket. The base plate rotates in a clockwise direction.

Figure 8B is a side view of the base plate and basket.

Figure 8C is a view from above along line A in Figure 8B. The basket rotates in an anti-clockwise direction.

It was discovered that edaravone can be prepared in a well-defined and consistently reproducible hemi edisylate salt form. In certain embodiments and depending on time, temperature and humidity, the crystalline salt form was stable.

The crystalline form described herein was characterised using a number of methods known to the skilled person in the art, including single crystal X-ray diffraction, X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy (including solution and solid-state NMR). The chemical purity was determined by standard analytical methods, such as thin layer chromatography (TLC), gas chromatography, high performance liquid chromatography (HPLC), and mass spectrometry (MS).

The edaravone hemi edisylate salt provided by the present invention may be useful as an active ingredient in pharmaceutical formulations.

Edaravone free base is sparingly soluble in water and poorly soluble in weakly acidic media. Poor oral bioavailability (ca. 5%) means that intraveneous administration is currently only available, which increases the burden on patients, along with patient compliance.

The known forms of edaravone enhance solubility in neutral aqueous or mildly acidic media e.g. in simulated intestinal fluid.

Edaravone hemi edisylate of the present invention was demonstrated to have significantly enhanced solubility in very acidic media, such as simulated gastric fluid, compared with edaravone, and other known forms of edaravone. In this respect, edaravone hemi edisylate is approximately 7-9.5 times more soluble than edaravone free form in highly acidic media. This difference is even more pronounced for other known salts and complexes (see Example 6 and Figure 7).

In one aspect, the present invention provides crystalline edaravone hemi edisylate salt. The molar ratio of edaravone to 1,2-ethanedisulfonic acid may be about 2 : about 1.

Single crystal X-ray diffraction shows that the edaravone hemi edisylate salt is present as a salt of the enol tautomer (see Figure 1).

Crystalline edaravone hemi edisylate has an X-ray powder diffraction pattern comprising one or more peaks (for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 peaks) selected from the group consisting of about 10.4, 12.2, 17.4, 20.9, 21.5, 22.0, 23.4, 25.2, 26.2, and 28.4 degrees two- theta ± 0.2 degrees two-theta. In one embodiment, the crystalline salt has the X-ray powder diffraction pattern substantially as shown in Figure 2.

The hemi edisylate salt exihibited a DSC thermogram comprising an endothermal event with an onset temperature at about 42.1 °C. The DSC thermogram further comprises one or more endothermal events in the range of about 165 °C to about 215 °C. In certain embodiments, the DSC thermogram comprised an endothermal event with a peak temperature at about 202.9 °C. In one embodiment, the crystalline salt exihibited a DSC thermogram substantially as shown in Figure 3.

The hemi edisylate salt exhibited a TGA thermogram comprising a mass loss of about 4.1% when heated from about ambient temperature to about 150 °C. In one embodiment, the crystalline salt exhibited a TGA thermogram substantially as shown in Figure 3.

A reliable and scalable method for producing the edaravone hemi edisylate salt was developed, which is suitable for the commercial scale manufacture of the salt. In certain embodiments, the crystalline salt form was purifiable. In certain embodiments, the crystalline salt form was easy to isolate and handle. In certain embodiments, the process was high yielding.

Crystalline edaravone hemi edisylate as described above was prepared by a process comprising the step of reacting edaravone and 1,2-ethanedisulfonic acid using low energy ball milling or low energy grinding to form the crystalline salt.

The edaravone may be present as the free form.

The 1,2-ethanedisulfonic acid is a solid under typical laboratory conditions, and the dihydrate has a melting point of about 109 °C to about 113 °C. The 1,2-ethanedisulfonic acid used may be anhydrous or a hydrate (e.g. the dihydrate).

The molar ratio of edaravone to 1,2-ethanedisulfonic acid was in the range of about 2.5 : about 1 moles to about 1 : about 2.5 moles, for example about 2 moles of edaravone : about 1 mole of acid.

When low energy ball milling was utilised, the milling process was controlled by various parameters including the speed at which the milling takes place, the length of milling time and/or the level to which the milling container was filled.

The speed at which the milling takes place was from about 50 rpm to about 1000 rpm. In one embodiment, the speed was from about 75 rpm to about 750 rpm. In another embodiment, the speed was from about 80 rpm to about 650 rpm. In one embodiment, the speed was about 500 rpm.

Low energy grinding involved shaking the materials within a grinding container. The grinding occurred via the impact and friction of the materials within the container. The process was controlled by various parameters including the frequency at which the grinding takes place, the length of grinding time and/or the level to which the container was filled.

The frequency at which the grinding takes place was from about 1 Hz to about 100 Hz. In one embodiment, the frequency was from about 10 Hz to about 70 Hz. In another embodiment, the frequency was from about 20 Hz to about 50 Hz. In one embodiment, the frequency was about 30 Hz.

Regardless of whether milling or grinding is used, milling or grinding media was used to assist the reaction. In this instance, the incorporation of hard, non-contaminating media can additionally assist in the breakdown of particles where agglomeration has occurred, for example, as a result of the manufacturing process or during transit. Such breakdown of the agglomerates further enhanced the reaction of edaravone and 1,2-ethanedisulfonic acid. The use of milling/grinding media is well-known within the field of powder processing and materials such as stabilised zirconia and other ceramics are suitable provided they are sufficiently hard or ball bearings e.g. stainless steel ball bearings.

Regardless of whether milling or grinding is used, an improvement in the process can be made by controlling the particle ratio, the size of the milling/grinding media and other parameters as are familiar to the skilled person.

The length of milling or grinding time was from about 1 minute to about 2 days, for example, about 10 minutes to about 5 hours, such as about 20 minutes to 3 hours.

The process was carried out in the presence of a solvent. The solvent may act to minimise particle welding. The addition of the solvent may be helpful if the edaravone and/or 1,2- ethanedisulfonic acid being reacted has agglomerated prior to use, in which case the solvent can assist with breaking down the agglomerates.

The solvent (e.g. methanol, ethanol, or a mixture thereof) may be anhydrous (e.g. absolute methanol, absolute ethanol, or a mixture thereof) or may contain a proportion of water. The process may tolerate a certain quantity of water provided it does not significantly adversely impact the formation of the crystalline salt. Water may be introduced into the reaction when the 1,2-ethanedisulfonic acid used is a hydrate. The quantity of solvent is not particularly limiting provided there is enough solvent to dissolve the edaravone and/or 1,2-ethanedisulfonic acid and form a solution, or suspend the edaravone and/or 1,2-ethanedisulfonic acid. The w/v ratio of edaravone to solvent was in the range of about 1 mg edaravone : about 0.25 pi to about 10 pi of solvent, for example, about 1 pg edaravone : about 0.3 pi to about 5 pi of solvent, such as about 1 mg edaravone : about 0.4 pi of solvent.

The edaravone and 1,2-ethanedisulfonic acid was contacted with the solvent at ambient temperature or less. Alternatively, the edaravone was contacted with the solvent at a temperature greater than ambient i.e. greater than 30 °C and below the boiling point of the reaction mixture. The boiling point of the reaction mixture may vary depending on the pressure under which the contacting step is conducted. In one embodiment, the contacting step was carried out at atmospheric pressure (i.e. 1.0135 x 10⁵ Pa).

The edaravone hemi edisylate salt was recovered as a crystalline solid. The crystalline salt was recovered by directly by filtering, decanting or centrifuging if solvent remained within the reaction vessel. If desired and if a suspension is obtained, the suspension may be triturated and/or mobilised with additional portions of the solvent prior to recovery of the crystalline solid. Alternatively, a proportion of the solvent may be evaporated prior to recovery of the crystalline solid. Alternatively, if the crystalline salt in the reaction vessel has no visible solvent present, the salt may be removed by any suitable means, e.g. by mechanical means such as scaping the solid out of the vessel.

Howsoever the crystalline salt was recovered, the separated salt was washed with solvent (e.g. as described above) and dried. Drying was performed using known methods, for example, at temperatures in the range of about 10 °C to about 60 °C, such as about 20 °C to about 40 °C, for example, ambient temperature under vacuum (for example about 1 mbar to about 30 mbar, such as about 25 mbar) for about 1 hour to about 24 hours, such as about 6 hours. Alternatively or in combination with another drying method, the crystalline salt was left to dry under ambient temperature naturally i.e. without the active application of vacuum. It is preferred that the drying conditions are maintained below the point at which the salt decomposes and so when the salt is known to decompose within the temperature or pressure ranges given above, the drying conditions should be maintained below the decomposition temperature or vacuum pressure.

Alternatively, the crystalline edaravone hemi edisylate salt as described above was prepared by a process comprising the step of applying dual asymmetric centrifugal forces to a mixture of edaravone and 1,2-ethanedisulfonic acid to form the crystalline salt.

The edaravone may be present as the free form. The 1,2-ethanedisulfonic acid is a solid under typical laboratory conditions, and the dihydrate has a melting point of about 109 °C to about 113 °C. The 1,2-ethanedisulfonic acid used may be anhydrous or a hydrate (e.g. the dihydrate).

The molar ratio of edaravone to 1,2-ethanedisulfonic acid was in the range of about2.5 : about 1 moles to about 1 : about 2.5 moles, for example about 2 moles of edaravone : about 1 mole of acid.

The crystalline edaravone hemi edisylate salt was formed using dual asymmetric centrifugal forces. By "dual asymmetric centrifugal forces" we mean that two centrifugal forces, at an angle to each other, are simultaneously applied to the particles. In order to create an efficient mixing environment, the centrifugal forces preferably rotate in opposite directions. The Speed mixer™ by Hauschild (http://www.speedmixer.co.uk/index.php) utilises this dual rotation method whereby the motor of the Speedmixer™ rotates the base plate of the mixing unit in a clockwise direction (see Figure 8A) and the basket is spun in an anti-clockwise direction (see Figures 8B and 8C).

The process may be controlled by various parameters including the rotation speed at which the process takes place, the length of processing time, the level to which the mixing container is filled, the use of milling media and/or the control of the temperature of the components within the milling pot.

The dual asymmetric centrifugal forces was applied for a continuous period of time. By "continuous" we mean a period of time without interruption. The period of time was from about 1 second to about 10 minutes, such as about 5 seconds to about 5 minutes, for example, about 10 seconds to about 200 seconds e.g. 2 minutes.

Alternatively, the dual asymmetric centrifugal forces may be applied for an aggregate period of time. By "aggregate" we mean the sum or total of more than one periods of time (e.g. 2, 3, 4, 5 or more times). The advantage of applying the centrifugal forces in a stepwise manner is that excessive heating of the particles can be avoided. The dual asymmetric centrifugal forces was applied for an aggregate period of about 1 second to about 20 minutes, for example about 30 seconds to about 15 minutes and such as about 10 seconds to about 10 minutes e.g. 6 minutes. In one embodiment, the dual asymmetric centrifugal forces was applied in a stepwise manner with periods of cooling therebetween. In another embodiment, the dual asymmetric centrifugal forces was applied in a stepwise manner at one or more different speeds. The speed of the dual asymmetric centrifugal forces was from about 200 rpm to about 4000 rpm. In one embodiment, the speed was from about 300 rpm to about 3750 rpm, for example about 500 rpm to about 3500 rpm. In one embodiment, the speed was about 3500 rpm. In another embodiment, the speed was about 2300 rpm.

The level to which the mixing container is filled was determined by various factors which will be apparent to the skilled person. These factors include the apparent density of the edaravone and 1,2-ethanedisulfonic acid, the volume of the mixing container and the weight restrictions imposed on the mixer itself.

Milling media as described above may be used to assist the reaction. In certain embodiments, the dual asymmetric centrifugal forces was applied in a stepwise manner in which milling media was used for some, but not all, periods of time.

The process was carried out in the presence of a solvent. The solvent may act to minimise particle welding. The addition of the solvent was helpful if the edaravone and/or 1,2- ethanedisulfonic acid being reacted has agglomerated prior to use, in which case the solvent can assist with breaking down the agglomerates.

The solvent (e.g. methanol, ethanol, or a mixture thereof) may be anhydrous (e.g. absolute methanol, absolute ethanol, or a mixture thereof) or may contain a proportion of water. The process may tolerate a certain quantity of water provided it does not significantly adversely impact the formation of the crystalline salt. Water may be introduced into the reaction when the 1,2-ethanedisulfonic acid used is a hydrate.

When the dual asymmetric centrifugal forces are applied for an aggregate period of time, the presence or absence of solvent was changed for each period of time. For example, the process comprised a first period of time in which the environment is dry (i.e. edaravone and 1,2- ethanedisulfonic acid are reacted together optionally with milling media in the absence of solvent), and a second period of time in which the environment was "wet" after the addition of solvent.

The edaravone hemi edisylate salt was recovered as a crystalline solid. The crystalline salt was recovered by directly by filtering, decanting or centrifuging if solvent remains within the reaction vessel. If a suspension was obtained, the suspension may be triturated and/or mobilised with additional portions of the solvent prior to recovery of the crystalline solid. Alternatively, a proportion of the solvent may be evaporated prior to recovery of the crystalline solid. Alternatively, if the crystalline salt in the reaction vessel had no visible solvent present, the salt was removed by any suitable means, e.g. by mechanical means such as scaping the solid out of the vessel. Howsoever the crystalline salt was recovered, the separated salt was washed with solvent (e.g. as described above) and dried. Drying was performed using known methods, for example, at temperatures in the range of about 10 °C to about 60 °C, such as about 20 °C to about 40 °C, for example, ambient temperature under vacuum (for example about 1 mbar to about 30 mbar, such as about 25 mbar) for about 1 hour to about 24 hours, such as about 6 hours. Alternatively or in combination with another drying method, the crystalline salt was left to dry under ambient temperature naturally i.e. without the active application of vacuum. It is preferred that the drying conditions are maintained below the point at which the salt decomposes and so when the salt is known to decompose within the temperature or pressure ranges given above, the drying conditions should be maintained below the decomposition temperature or vacuum pressure.

Alternatively, the crystalline edaravone hemi edisylate salt as described above was prepared by a process comprising the steps of:

(a) contacting edaravone with a solvent comprising methanol, ethanol, or a mixture thereof, to form a solution;

(b) adding 1,2-ethanedisulfonic acid to the solution of edaravone; and

(c) recovering the edaravone hemi edisylate as a crystalline solid.

Crystalline edaravone hemi edisylate is as described above.

The edaravone may be present as the free form.

In one embodiment, the solvent consists essentially of or consists of ethanol.

The quantity of the solvent is not particularly limiting provided there was enough solvent to dissolve the edaravone and form a solution. The w/v ratio of edaravone to the solvent was in the range of about 1 mg of edaravone: about 1 to about 1000 pi of solvent, such as about 1 mg of edaravone : about 1 to about 500 pi of solvent, for example about 1 mg of edaravone : about 1 to about 150 pi of solvent, e.g. about 1 mg of edaravone : about 1 to about 50 pi of solvent. In one embodiment, the w/v ratio of edaravone to the solvent was about 1 mg of edaravone : about 5 pi of solvent. The edaravone may be contacted with the solvent at ambient temperature or less. In one embodiment, the contacting step may be carried out at one or more temperatures in the range of > about 0 °C to about < 25 °C. In some embodiments, the contacting step is carried out at one or more temperatures > about 1 °C. In some embodiments, the contacting step is carried out at one or more temperatures > about 2 °C. In some embodiments, the contacting step is carried out at one or more temperatures > about 3 °C. In some embodiments, the contacting step is carried out at one or more temperatures > about 4 °C. In some embodiments, the contacting step is carried out at one or more temperatures > about 5 °C. In some embodiments, the contacting step is carried out at one or more temperatures < about 20 °C. In some embodiments, the contacting step is carried out at one or more temperatures < about 15 °C. In some embodiments, the contacting step is carried out at one or more temperatures < about 10 °C. In one embodiment, the contacting step is carried out at one or more temperatures in the range of > about 0 °C to < about 10 °C, for example, about 5 °C. In one embodiment, the contacting step may be carried out at about ambient temperature e.g. about 25 °C.

Alternatively, the edaravone may be contacted with the solvent at a temperature greater than ambient i.e. greater than 30 °C and below the boiling point of the reaction mixture. The boiling point of the reaction mixture may vary depending on the pressure under which the contacting step is conducted. In one embodiment, the contacting step was carried out at atmospheric pressure (i.e. 1.0135 x 10⁵ Pa). In one embodiment, the contacting step was carried out at one or more temperatures in the range of > about 40 °C to about < 70 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 41 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 42 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 43 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 44 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 45 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 46 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 47 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 48 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 49 °C. In some embodiments, the contacting step was carried out at one or more temperatures > about 50 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 69 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 68 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 67 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 66 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 65 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 64 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 63 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 62 °C. In some embodiments, the contacting step was carried out at one or more temperatures < about 61 °C. In one embodiment, the contacting step was carried out at one or more temperatures in the range of > about 45 °C to < about 65 °C. In one embodiment, the contacting step was carried out at a temperature of about 50 °C. In another embodiment, the contacting step was carried out at a temperature of about 60 °C.

The dissolution of edaravone may be encouraged through the use of an aid such as stirring (e.g. at about 400 to about 500 rpm), shaking and/or sonication. Additional solvent may be added to aid the dissolution of the edaravone.

The period of time for which the mixture of edaravone and solvent is treated at the desired temperature is not particularly limiting. In one embodiment, the period of time may be from about 1 minute to about 24 hours.

In step (b), 1,2-ethanedisulfonic acid is added to the reaction mixture, optionally with stirring. The quantity of 1,2-ethanedisulfonic acid is not particularly limiting. In one embodiment, the molar ratio of edaravone to 1,2-ethanedisulfonic acid may be in the range from about 1 mole of edaravone : about 0.9 to about 2 mole of 1,2-ethanedisulfonic acid, such as about 1 mole of edaravone : about 1 to about 1.5 mole of 1,2-ethanedisulfonic acid, for example about 1 mole of edaravone : 1 mole of 1,2-ethanedisulfonic acid. These molar ratios have been calculated using the moles of edaravone initially dissolved in the solvent i.e. the quantity of edaravone inputted into the process. As the molar ratio of edaravone : 1,2-ethanedisulfonic acid is about 2 : about 1, an initial molar ratio of about 1 mol of edaravone : 1 mol of 1,2- ethanedisulfonic acid means that excess acid is inputted into the reaction.

The 1,2-ethanedisulfonic acid is a solid under typical laboratory conditions, and the dihydrate has a melting point of about 109 °C to about 113 °C. The 1,2-ethanedisulfonic acid used may be anhydrous or a hydrate (e.g. the dihydrate). In the latter instance, a proportion of water is also added to the reaction mixture.

The acid may be added to the reaction as solid. Alternatively, the acid may be added to the reaction mixture as a solution in a solvent as described above, for example ethanol. The quantity of the solvent is not particularly limiting provided there is enough solvent to dissolve the acid and form a solution. The w/v ratio of acid to the solvent may be in the range of about 1 mg of acid : about 1 to about 1000 pi of solvent, such as about 1 mg of acid : about 1 to about 500 pi of solvent, for example about 1 mg of acid : about 1 to about 150 pi of solvent, e.g. about 1 mg of acid : about 1 to about 50 pi of solvent. In one embodiment, the w/v ratio of acid to the solvent may be about 1 g of acid : about 1 mI of solvent. In one embodiment, the w/v ratio of acid to the solvent may be about 1 mg of acid : about 4 to about 5 mI of solvent.

The dissolution of the acid may be encouraged through the use of an aid such as stirring (e.g. at about 400 to about 500 rpm), shaking and/or sonication. Additional solvent may be added to aid the dissolution of the acid.

The acidic solution may have a temperature of ambient temperature or less when it is added to the reaction mixture. In one embodiment, the acidic solution may have a temperature in the range of > about 0 °C to about < 25 °C. In some embodiments, the acidic solution may have a temperature of > about 1 °C. In some embodiments, the acidic solution may have a temperature of > about 2 °C. In some embodiments, the acidic solution may have a temperature one or more temperatures of > about 3 °C. In some embodiments, the acidic solution may have a temperature of > about 4 °C. In some embodiments, the acidic solution may have a temperature of > about 5 °C. In some embodiments, the acidic solution may have a temperature of < about 20 °C. In some embodiments, the acidic solution may have a temperature of < about 15 °C. In some embodiments, the acidic solution may have a temperature of < about 10 °C. In one embodiment, the acidic solution may have a temperature in the range of > about 0 °C to < about 10 °C, for example, about 5 °C. In one embodiment, the acidic solution may have a temperature of about ambient temperature e.g. about 25 °C.

Alternatively, the acidic solution may have a temperature greater than ambient i.e. greater than 30 °C and below the boiling point of the reaction mixture, when it is added to the reaction mixture. The boiling point of the reaction mixture may vary depending on the pressure under which the contacting step is conducted. In one embodiment, the contacting step is carried out at atmospheric pressure (i.e. 1.0135 x 10⁵ Pa). In one embodiment, the acidic solution may have a temperature of in the range of > about 40 °C to about < 70 °C. In some embodiments, the acidic solution may have a temperature of > about 41 °C. In some embodiments, the acidic solution may have a temperature of > about 42 °C. In some embodimentsthe acidic solution may have a temperature of > about 43 °C. In some embodiments, the acidic solution may have a temperature of > about 44 °C. In some embodiments, the acidic solution may have a temperature of > about 45 °C. In some embodiments, the acidic solution may have a temperature of > about 46 °C. In some embodiments, the acidic solution may have a temperature of > about 47 °C. In some embodiments, the acidic solution may have a temperature of > about 48 °C. In some embodiments, the acidic solution may have a temperature of > about 49 °C. In some embodiments, the acidic solution may have a temperature of > about 50 °C. In some embodiments, the acidic solution may have a temperature of < about 69 °C. In some embodiments, the acidic solution may have a temperature of < about 68 °C. In some embodiments, the acidic solution may have a temperature of < about 67 °C. In some embodiments, the acidic solution may have a temperature of < about 66 °C. In some embodiments, the acidic solution may have a temperature of < about 65 °C. In some embodiments, the acidic solution may have a temperature of < about 64 °C. In some embodiments, the acidic solution may have a temperature of < about 63 °C. In some embodiments, the acidic solution may have a temperature of < about 62 °C. In some embodiments, the acidic solution may have a temperature of < about 61 °C. In one embodiment, the acidic solution may have a temperature of in the range of > about 45 °C to < about 65 °C. In one embodiment, the acidic solution may have a temperature of about 50 °C. In another embodiment, the acidic solution may have a temperature of about 60 °C.

The acid (as a solid or acidic solution) may be added to the reaction mixture in a single portion. Alternatively, the acid may be added portionwise (e.g. dropwise if an acidic solution is utilised). The period of time over which the acid is added to the reaction mixture is not particularly limiting and may be from about 1 minute to about 60 minutes.

The period of time for which the mixture of acid and solvent is treated at the desired temperature before addition to the edaravone solution is not particularly limiting. In one embodiment, the period of time may be from about 1 minute to about 24 hours.

When the acid is added to the reaction mixture as a solution, the total quantity of solvent used in the process will be the combined volumes used to dissolve the edaravone, as well as that used to dissolve the acid.

After the addition of the acid, the reaction mixture may be treated for a period of time at ambient temperature or less as described above in connection with step (a). The reaction mixture may be stirred.

Alternatively, the reaction mixture may be treated for a period of time at one or more temperatures greater than ambient i.e. greater than 30 °C and below the boiling point of the reaction mixture as described above in connection with step (a). The reaction mixture may be stirred.

Additional solvent may be added to aid the dissolution or suspension of the reaction mixture.

The reaction mixture may be left for a further period of time, e.g. about 1 minute to about 24 hours.

The solution or suspension may then be cooled such that the resulting solution or suspension has a temperature below that of the solution or suspension of step (b), optionally with stirring. The rate of cooling may be from about 0.05 °C/minute to about 2 °C/minute, such as about 0. 1 °C/minute to about 1.5 °C/minute, for example about 0.1 °C/rminute or 0.5 °C/rminute. When a solution of edaravone and 1,2-ethanedisulfonic acid is cooled, a suspension may eventually be observed.

The solution or suspension may be cooled to ambient temperature or a temperature of less than ambient temperature. In one embodiment, the solution or suspension may be cooled to one or more temperatures in the range of > about 0 °C to about < 20 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures > about 1 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures > about 2 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures > about 3 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures > about 4 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures > about 5 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures < about 15 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures < about 14 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures < about 13 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures < about 12 °C. In some embodiments, the solution or suspension may be cooled to one or more temperatures < about 11 °C. In some embodiments, the solution or suspension is cooled to one or more temperatures < about 10 °C. In one embodiment, the solution or suspension is cooled to one or more temperatures in the range of about 5°C to about 10 °C.

In one embodiment, the solution or suspension may be cooled to one temperature at a particular rate, further cooled to a second temperature at the same or different rate, and then further cooled to a third temperature at the same or different rate. For example, the solution or suspension may be cooled to ambient temperature (e.g. about 25 °C) at a rate of about 0.5 °C/minute, further cooled to about 20 °C at a rate of about 0.5 °C/minute, and then further cooled to about 5 °C at a rate of about 0.1 °C/minute.

The solution or suspension may be held for a period of time between each period of cooling. The holding period not particularly limiting. In one embodiment, each period of time at which the solution or suspension is held may be from about 1 minute to about 72 hours, and may be same or different to each of the other holding periods. In one embodiment, a holding period may be about 30 minutes. In another embodiment, a holding period may be about 16 hours. In another embodiment, a holding period may be about 48 hours.

In step (c), edaravone hemi edisylate is recovered as a crystalline solid. The crystalline solid may be recovered by directly by filtering, decanting or centrifuging. If a suspension is obtained, the suspension may be mobilised with additional portions of the solvent prior to recovery of the crystalline solid. Alternatively, a proportion or substantially all of the solvent may be evaporated prior to recovery of the crystalline solid. The solvent may be as described above.

Howsoever the crystalline salt is recovered, the separated salt may be washed with solvent (e.g. as described above) and dried. Drying may be performed using known methods, for example, at temperatures in the range of about 10 °C to about 60 °C, such as about 20 °C to about 40 °C, for example, ambient temperature under vacuum (for example about 1 mbar to about 30 mbar, such as about 25 mbar) for about 1 hour to about 24 hours, such as about 6 hours. Alternatively or in combination with another drying method, the crystalline salt may be left to dry under ambient temperature naturally i.e. without the active application of vacuum. It is preferred that the drying conditions are maintained below the point at which the salt decomposes and so when the salt is known to decompose within the temperature or pressure ranges given above, the drying conditions should be maintained below the decomposition temperature or vacuum pressure.

Steps (a) to (c) may be carried out one or more times (e.g. 1, 2, 3, 4 or 5 times). When steps (a) to (c) are carried out more than once (e.g. 2, 3, 4 or 5 times), step (a) may be optionally seeded with crystalline salt (which was previously prepared and isolated by a method described herein).

Alternatively or in addition, when steps (a) to (c) are carried out more than once (e.g. 2, 3, 4 or 5 times), the solution or suspension formed in step (b) may be optionally seeded with crystalline salt (which was previously prepared and isolated by a method described herein).

The crystalline salt may be optionally recrystallised from a solvent as described above in connection with step (a). The crystalline salt may be dissolved in the solvent and treated for a period of time at one or more temperatures greater than ambient i.e. greater than 30 °C and below the boiling point of the reaction mixture as described above in connection with step (a) (e.g. at about 50 to about 60 °C). The solution may then be cooled (e.g. to about 5 °C) and the recrystallised salt may be recovered, optionally washed and dried as described above.

Pharmaceutical compositions comprising crystalline edaravone hemi edisylate salt, methods of treatment comprising the salt, and uses thereof In another aspect, the present invention provides a pharmaceutical composition comprising crystalline edaravone hemi edisylate salt as described herein and a pharmaceutically acceptable excipient. In one embodiment, the pharmaceutical composition is an oral dosage form, such as a tablet, capsule, syrup, or dissolution film which may dissolve when placed e.g. under the tongue. In another aspect, the present invention provides a method for treating amyotropic lateral sclerosis (ALS) in a patient comprising administering a therapeutically effective amount of crystalline edaravone hemi edisylate salt as described herein to the patient.

In another aspect, the present invention provides crystalline hemi edisylate salt as described herein for use in treating ALS.

Embodiments and/or optional features of the invention have been described above. Any aspect of the invention may be combined with any other aspect of the invention, unless the context demands otherwise. Any of the embodiments or optional features of any aspect may be combined, singly or in combination, with any aspect of the invention, unless the context demands otherwise.

The invention will now be described further by reference to the following examples, which are intended to illustrate but not limit, the scope of the invention.

Abbreviations

API active pharmaceutical ingredient

EtOH ethanol rprm revolutions per minute

RH relative humidity

RT room temperature

SCXRD single crystal X-ray diffraction

1 Instrument and Methodology Details

1.1 XRPD

1.1.1 Bruker AXS D8 Advance

XRPD diffractograms were collected on a Bruker D8 diffractometer using Cu Ka radiation (40 kV, 40 mA) and a Q-2Q goniometer fitted with a Ge monochromator. The incident beam passes through a 2.0 mm divergence slit followed by a 0.2 mm anti-scatter slit and knife edge. The diffracted beam passes through an 8.0 mm receiving slit with 2.5° Soller slits followed by the Lynxeye Detector. The software used for data collection and analysis was Diffrac Plus XRD Commander and Diffrac Plus EVA respectively.

Samples were run under ambient conditions as flat plate specimens using powder as received. The sample was prepared on a polished, zero-background (510) silicon wafer by gently pressing onto the flat surface or packed into a cut cavity. The sample was rotated in its own plane. The details of the standard data collection method are:

• Angular range: 2 to 42° 2Q

• Step size: 0.05° 2Q

• Collection time: 0.5 s/step (total collection time: 6.40 min)

The instrument is performance checked weekly using NIST1976 corundum to the peak position of 35.149 ± 0.01° 2Q.

1.1.2 Panalytical Empyrean

XRPD diffractograms were collected on a PANalytical Empyrean diffractometer using Cu Ka radiation (45 kV, 40 mA) in transmission geometry. A 0.5° slit, 4 mm mask and 0.04 rad Soller slits with a focusing mirror were used on the incident beam. A PIXcel³⁰ detector, placed on the diffracted beam, was fitted with a receiving slit and 0.04 rad Soller slits. The software used for data collection was X'Pert Data Collector using X'Pert Operator Interface. The data were analysed and presented using Diffrac Plus EVA or HighScore Plus.

Samples were prepared and analysed in either a metal or Millipore 96 well-plate in transmission mode. X-ray transparent film was used between the metal sheets on the metal well-plate and powders (approximately 1 - 2 mg) were used as received. The Millipore plate was used to isolate and analyse solids from suspensions by adding a small amount of suspension directly to the plate before filtration under a light vacuum.

The scan mode for the metal plate used the gonio scan axis, whereas a 2Q scan was utilised for the Millipore plate.

The details of the standard screening data collection method are:

• Angular range: 2.5 to 32.0° 2Q

• Step size: 0.0130° 2Q

• Collection time: 12.75 s/step (total collection time of 2.07 min)

The instrument is performance checked weekly using a silicon powder reference to the peak position of 28.441 ± 0.2° 2Q.

1.2 Differential Scanning Calorimetry (DSC)

DSC data were collected on a TA Instruments Q2000 equipped with a 50 position auto-sampler. Typically, 0.5 - 3 mg of each sample, in a pin-holed aluminium pan.

The sample was heated at 10 °C/min from 25 °C to 250 °C. A purge of dry nitrogen at 50 ml/min was maintained over the sample. The instrument control software was Advantage for Q Series and Thermal Advantage and the data were analysed using Universal Analysis or TRIOS.

1.3 Thermo-Gravimetric Analysis (TGA)

TGA data were collected on a TA Instruments Discovery TGA, equipped with a 25 position autosampler. Typically, 5 - 10 mg of each sample was loaded onto a pre-tared aluminium DSC pan and heated at 10 °C min ¹ from ambient temperature to 350 °C. A nitrogen purge at 25 mL min ¹ was maintained over the sample.

The instrument control software was TRIOS and the data were analysed using TRIOS or Universal Analysis.

1.4 Dissolution Rate Studies

Media : Simulated gastric fluid (SGF) buffer pH 1.2 was prepared as follows: Sodium chloride (2.0 g) and concentrated hydrochloric acid (37 wt. % solution, 7 mL) were added to a 1000 mL volumetric flask and made up to volume with deionised water.

Experiments were conducted in 25 mL glass reaction vessels (Cambridge Reactor Design) equipped with overhead stirring and side sampling port. The solid API sample (ca. 10 - 15 mg) was compressed in a 3 mm disc recess (larger 8 mm disc recess was used for cyclodextrin sample), under 100 kg for 2 minutes, with greaseproof paper on the compression base, to form non-disintegrating discs. The discs were then plugged with a bung so that only one surface was exposed to the media during analysis. The formed discs were then added to the reaction media (20 mL) and, carried out at 37.5 °C and the dissolution media (SGF) was agitated at 400 rpm via overhead stirring for 1 h. Aliquots (0.2 mL) were withdrawn at 2, 5, 10, 20, 40 and 60 minute timepoints, filtered with a syringe filter (Acrodisc 0.2 pm) and diluted with HPLC grade ACN : H20 (1 : 1 v/v) solvent (0.5 mL). Samples were analysed via HPLC to determine the cumulative amount of API dissolved. HPLC quantification was performed using a calibration plot covering the appropriate concentration range (R² = 0.9974) in the same solvent system. A dissolution profile was obtained by plotting the cumulative amount of sample dissolved per unit area of the disc (7.1 mm² - 50.3 mm²) against unit time. All dissolution rate experiments were performed in duplicate and error was calculated via standard error of the mean values.

Table 1 HPLC method for dissolution rate measurements

1.5 Thermodynamic Aqueous Solubility

Sufficient sample was suspended in 1.0 ml media for a maximum anticipated concentration of 11-16 mg/ml of the free form of the compound. The resulting suspensions were then shaken at 25 °C/ 750 rpm for 4 hours. After equilibration, the appearance was noted, and the pH of the saturated solution was measured. Samples were then filtered through a glass 'C' fibre filter (Particle retention 1.2 pm), before dilution with buffer as appropriate.

Quantitation was by HPLC with reference to a standard solution of approximately 0.15 mg/ml. Different volumes of the standard and diluted sample solutions were injected. The solubility was calculated using the peak areas determined by integration of the peak found at the same retention time as the principal peak in the standard injection.

Table 2 Media Details for solubility measurements

Table 3 HPLC method for solubility measurements

Analysis was performed on an Agilent HP1100/ Infinity II 1260 series system equipped with a diode array detector and using OpenLAB software.

Edaravone salt screening process (not according to the invention)

Example 1

An edaravone salt screening process was performed using a mechanochemical methodology. Several acids with a pKa range of -9.0 - 1.3 were chosen as potential suitable salt formers:

Edaravone (50 mg, 0.3 mmols) and 1 molar equivalent of the requisite acid were added to a series of 1.5 mL glass HPLC vials. Ethanol solvent (0.02 mL) and two 3mm stainless steel ball bearings were added to each of the vials. The solid mixtures were then milled in a planetary mill at 500 rpm for 2 hours. The resultant solid was dried in a vacuum oven (25 mbar) at 25 °C for 6 hours and the obtained powder products were analysed by XRPD (Panalytical Empyrean), the results of which are displayed below in Table 4: Table 4: Edaravone solvent drop grinding salt screening with sulfonic acids.

* according to the invention

* not according to the invention Edaravone hemi edisylate (according to the invention)

Example 2

Edaravone (200 mg, 1.2 mmols) was dissolved in EtOH (1.0 mL) at 60 °C in a glass vial with constant magnetic stirring (400 rpm). A separate solution was prepared by dissolving 1,2- ethanedisulfonic acid dihydrate (300 mg, 1.2 mmols) in EtOH (1.3 mL) at 60 °C in a glass vial with constant magnetic stirring (400 rpm). The 1,2-ethanedisulfonic acid solution was added in one portion to the edaravone solution and the mixture was cooled to 25 °C at a rate of 0.5 °C min ¹ held for 30 minutes and cooled further to 20 °C at the same rate with constant magnetic stirring (400 rpm). The turbid yellow mixture was subsequently cooled to 5 °C at a rate of 0.1 °C min ¹ and held at this temperature for 16 hours. A thick white precipitate formed which was isolated by filtration using a 3 mL plastic syringe and frit under compressed air. The isolated powder was dried in a vacuum oven (25 mbar) at 25 °C for 4 hours to yield the final product as a white powder.

Example 3 Edaravone (1.0 g, 5.7 mmols) was dissolved in EtOH (5 mL) at 50 °C in a glass vial with constant magnetic stirring (500 rpm). A separate solution was prepared by dissolving 1,2- ethanedisulfonic acid dihydrate (1.3 g, 5.7 mmols) in EtOH (1.3 mL) at 50 °C in a glass vial with constant magnetic stirring (400 rpm). The 1,2-ethanedisulfonic acid solution was added to the edaravone solution in a dropwise manner at which point the yellow solution turned turbid. The mixture was cooled to 5 °C at a rate of 0.1 °C min ¹ and held at this temperature for 48 hours. A thick white precipitate formed which was isolated via filtration using a 3 mL plastic syringe and frit under compressed air. The isolated powder was dried in a vacuum oven (25 mbar) at 25 °C for 1 hour to yield the final product as a white powder.

Yield : 86.6% Edaravone Hemi Edisylate Characterisation

Single crystals of edaravone hemi edisylate were grown from the mother liquors of Example 2. The single crystal parameters for the salt as determined by SCXRD are shown below in Table 7 Table 5: Crystal data for edaravone hemi edisylate prepared according to Example 2

Table 6: Data collection and structure refinement for edaravone hemi edisylate prepared according to Example 2 _

Diffractometer XtaLAB Synergy-S, Dualflex, HyPix-6000HE

Radiation source PhotonJet (Cu) X-ray Source, CuKoc

Data collection method omega scans

Theta range for data collection 5.225 to 76.832° Index ranges -17 < h 9, -12 £ k 12, -21 < / 21

Reflections collected 11980 Independent reflections 2452 [R(int) = 0.0336] Coverage of independent reflections 100.0 % Absorption correction Multi-Scan Max. and min. transmission 1.00000 and 0.53568 Structure solution technique Direct Methods Structure solution program SHELXTL (Sheldrick, 2013) Refinement technique Full-matrix least-squares on F² Refinement program SHELXL-2014/6 (Sheldrick, 2014) Function minimised å w(F₀ ² - F_c ²)² Data / restraints / parameters 2452 / 0 / 172 Goodness-of-fit on F² 1.066

^^Gmax 0.001 Final R indices

2333 data; I>2s(I) R1 = 0.0371, wR2 = 0.1045 all data R1 = 0.0385, wR2 = 0.1057 Weighting scheme w = 1 / [s² (Fo²) + 0.0662P P)²+ 1.1148P] where

P = ( Fo ² + 2Fc²)/3

Extinction coefficient n/a Largest diff. peak and hole 0.547 and -0.506e A ³

Figure 1 shows the ORTEP single crystal structure of edaravone hemi edisylate. The figure illustrates that the salt has an asymmetric unit , and that the molecular ratio of edaravone : 1,2-ethanedisulfonic acid is 2 : 1. Figure 2 shows a representative XRPD pattern of edaravone hemi edisylate obtained according to Example 2. The following table provides an XRPD peak list for the salt.

Table 7: Peak list for XRPD pattern of edaravone hemi edisylate prepared according to

Example 2

Edaravone hemi edisylate was also characterised by TGA and DSC analysis (see Figure 3).

Edaravone hemi edisylate was stable (as determined by XRPD) in an accelerated stability test where it was stored at 40 °C and 75% relative humidity (RH) for 7 days.

Edaravone Hemi Naoadisylate (not according to the invention)

Example 4

Edaravone hemi napadisylate was used as a reference compound for dissolution rate investigations and was prepared in accordance with Example 1 of patent application W02019073052A1 :

Edaravone (508 mg) was dissolved in acetonitrile (10.8 mL) at 25 °C under constant stirring. To the resultant solution was added an aqueous solution of 1,5-naphthalenedisulfonic acid (0.7 eq., 548 mg), a white solid precipitated immediately upon addition of the aqueous solution. The mixture was thermocycled between 20 °C and 50 °C and the solid product was obtained as a crystalline white powder by filtration and subsequent drying under compressed air using a 5 mL plastic syringe and frit. Edaravone Hemi Naoadisylate Characterisation

Figure 4 shows a representative XRPD pattern of edaravone hemi napadisylate obtained according to Example 4. The following table provides an XRPD peak list for the salt.

Table 8: Peak list for XRPD pattern of edaravone hemi napadisylate prepared according to Example 4

Edaravone hemi napadisylate was also characterised by TGA and DSC analysis (see Figure 5).

Edaravone Cvclodextrin Clathrate (not according to the invention)

Example 5

Edaravone cyclodextrin clathrate was used as a comparative compound for dissolution rate investigations and was prepared in accordance with the method detailed in patent application CN104257603A:

2-Hydroxypropyl-3-cyclodextrin (3.36 g) was dissolved in HPLC grade water (15.8 mL) in a 100 mL round bottom flask under constant stirring (500 rpm). To the solution was added a solution of edaravone (0.14 g) in ethanol (7.1 mL) in a dropwise manner. The mixture was left to stir at 25 °C for 24 h under constant stirring (500 rpm). The solution was then filtered using a sintered glass funnel under vacuum and ethanol was removed from the filtrate by rotary evaporation at 45 °C under reduced pressure (50 mbar). A clear residue/oil remained which was redispersed in HPLC grade water (20 mL) and placed in a freezer for 72 hours. The frozen solution was transferred to a freeze dryer to remove water and was held at -80 °C under reduced pressure (0.4 mbar) for 24 h. The final product was obtained as a glassy solid.

Edaravone Cvclodextrin Clathrate Characterisation

Figure 6 shows a representative XRPD pattern of edaravone cyclodextrin clathrate obtained according to Example 5. The cyclodextrin clathrate spectrum did not exhibit any characteristic peaks.

Dissolution Studies

Example 6

The dissolution profiles of edaravone, edaravone hemi edisylate (prepared according to Example 2), edaravone heminapadisylate (prepared according to Example 4), and edaravone cyclodextrin clathrate (prepared according to Example 5) were obtained using the method described in section 1.4 above. Figure 7 shows that edaravone hemi edisylate according to the present invention is significantly more soluble in simulated gastric fluid (SGF) buffer than edaravone, edaravone heminapadisylate, and edaravone cyclodextrin clathrate.

Table 9: The quantities of the free form equivalent of edaravone dissolved after 20 minutes

* according to the invention

* not according to the invention; average of two runs

Table 9 evidences that edaravone hermi edisylate according to the present invention is approximately 7-9.5 times more soluble than edaravone free form in highly acidic media. This difference is even more pronounced for other known salts and complexes.

Thermodynamic Solubility

Example 7

The thermodynamic solubility of edaravone, and edaravone hemi edisylate (prepared according to Example 2) were obtained using the method described in section 1.6 above.

Table 10: Thermodynamic solubility results for edaravone hemi edisylate prepared according to Example 2 and edaravone

* according to the invention

* not according to the invention

Table 10 evidences that edaravone hemi edisylate according to the present invention is significantly more soluble in acidic media over a testing period of four hours than edaravone.

Claims

1. A crystalline salt which is crystalline edaravone hermi edisylate salt.

2. A crystalline salt according to claim 1, wherein the molar ratio of edaravone to 1,2- ethanedisulfonic acid is about 2 : about 1.

3. A crystalline salt according to claim 1 or claim 2, wherein the crystalline edaravone hemi edisylate salt has an X-ray powder diffraction pattern comprising one or more peaks selected from the group consisting of about 10.4, 12.2, 17.4, 20.9, 21.5, 22.0, 23.4, 25.2, 26.2, and 28.4 degrees two-theta ± 0.2 degrees two-theta.

4. A crystalline salt according to claim 4, wherein the crystalline edaravone hemi edisylate salt has a X-ray powder diffraction pattern substantially as shown in Figure 2

5. A crystalline salt according to any one of claims 1 to 4, wherein the crystalline edaravone hemi edisylate salt has a DSC thermogram comprising an endothermal event with an onset temperatures at about 42.1 °C.

6. A crystalline salt according to claim 5, wherein the crystalline edaravone hemi edisylate salt has a DSC thermogram substantially as shown in Figure 3.

7. A crystalline salt according to any one of claims 1 to 6, wherein the crystalline edaravone hemi edisylate salt has a TGA thermogram comprising a mass loss of about 4.1% when heated from about ambient temperature to about 150 °C.

8. A crystalline salt according to claim 7, wherein the crystalline edaravone hemi edisylate salt has a TGA thermogram substantially as shown in Figure 3.

9. A process for the preparation of crystalline edaravone hemi edisylate salt comprising the step of reacting edaravone and 1,2-ethanedisulfonic acid using low energy ball milling or low energy grinding to form the crystalline salt.

10. A process for the preparation of crystalline edaravone hemi edisylate salt comprising the step of applying dual asymmetric centrifugal forces to a mixture of edaravone and 1,2-ethanedisulfonic acid to form the crystalline salt.

11. A process for the preparation of crystalline edaravone hemi edisylate salt comprising the steps of: (a) contacting edaravone with a solvent comprising methanol, ethanol, or a mixture thereof, to form a solution;

(b) adding 1,2-ethanedisulfonic acid to the solution of edaravone; and

(c) recovering the edaravone hemi edisylate as a crystalline solid.