DESC:FIDAXOMICIN POLYMORPHS AND PROCESSES FOR THEIR PREPARATION

INTRODUCTION
Aspects of the present application relate to crystalline forms of Fidaxomicin, and processes for their preparation. Further aspects relate to pharmaceutical compositions comprising these polymorphic forms of fidaxomicin.

Fidaxomicin (also known as OPT-80 and PAR-101) is a novel antibiotic agent and the first representative of a new class of antibacterials called macrocycles. Fidaxomicin is a member of the tiacumicin family, which are complexes of 18-membered macrocyclic antibiotics naturally produced by a strain of Dactylosporangium aurantiacum isolated from a soil sample collected in Connecticut, USA. The major component of the tiacumicin complex is tiacumicin B. Optically pure R-tiacumicin B is the most active component of Fidaxomicin. The chiral center at C(19) of tiacumicinB affects biological activity, and R-tiacumicin B has an R-hydroxyl group attached at this position. The isomer displayed significantly higher activity than other tiacumicin B-related compounds and longer post-antibiotic activity.

As per WIPO publication number 2006085838, Fidaxomicin is an isomeric mixture of the configurationally distinct stereoisomers of tiacumicin B, composed of 70 to 100% of R-tiacumicin B and small quantities of related compounds, such as S-tiacumicin B and lipiarmycin A4. Fidaxomicin was produced by fermentation of the D aurantiacum subspecies hamdenensis (strain 718C-41). It has a narrow spectrum antibacterial profile mainly directed against Clostridium difficile and exerts a moderate activity against some other gram-positive species. Fidaxomicin is bactericidal and acts via inhibition of RNA synthesis by bacterial RNA polymerase at a distinct site from that of rifamycins. The drug product is poorly absorbed and exerts its activity in the gastrointestinal (GI) tract, which is an advantage when used in the applied indication, treatment of C. difficile infection (CDI) (also known as C. difficile-associated disease or diarrhoea [CDAD]). Fidaxomicin is available as DIFICID oral tablet in US market. Its CAS chemical name is Oxacyclooctadeca-3,5,9,13,15-pentaen-2-one, 3-[[[6-deoxy-4-O-(3,5dichloro-2-ethyl-4,6-dihydroxybenzoyl)-2-O-methyl-ß-D-manno pyranosyl]oxy]methyl]-12[[6-deoxy-5-C-methyl-4-O-(2-methyl-1-oxopropyl)-ß-D-lyxo-hexo pyranosyl]oxy]-11-ethyl-8-hydroxy-18-[(1R)-1-hydroxyethyl] -9,13,15-trimethyl-, (3E,5E, 8S,9E,11S,12R,13E, 15E,18S)-. Structural formula (I) describes the absolute stereochemistry of fidaxomicin as determined by x-ray.

(I)
WIPO publication number 2004014295 discloses a process for preparation of Tiacumicins that comprises fermentation of Dactylosporangium aurantiacum NRRL18085 in suitable culture medium. It also provides process for isolation of tiacumicin from fermentation broth using techniques selected from the group consisting of: sieving and removing undesired material by eluting with at least one solvent or a solvent mixture; extraction with at least one solvent or a solvent mixture; Crystallization; chromatographic separation; High-Performance Liquid Chromatography (HPLC); MPLC; trituration; and extraction with saturated brine with at least one solvent or a solvent mixture. The product was isolated from iso-propyl alcohol (IPA) having a melting point of 166-169 ºC.

U.S. Patent No. 7378508 discloses polymorphic forms A and B of fidaxomicin, solid dosage forms of the two forms and composition thereof. As per the ‘508 patent form A is obtained from methanol water mixture and Form B is obtained from ethyl acetate.

J. Antibiotics, vol. 40(5), 575-588 (1987) discloses purification of Tiacumicins using suitable solvents wherein tiacumicin B exhibited a melting point of 143-145 ºC.

The occurrence of different crystal forms, i.e., polymorphism, is a property of some compounds. A single molecule may give rise to a variety of polymorphs having distinct crystal structures and physical properties, such as PXRD patterns, IR absorption spectra, melting points (MP), TGA curves, DSC curves, and solubilities.

Polymorphs are different solids having the same molecular structure, yet having distinct physical properties when compared to other polymorphs of the same structure. The discovery of new polymorphs and solvates of a pharmaceutical active compound provides an opportunity to improve the performance of a drug product in terms of its bioavailability or release profile in vivo, or it may have improved stability or advantageous handling properties. Polymorphism is an unpredictable property of any given compound. This subject has been reviewed in recent articles, including A. Goho, “Tricky Business,” Science News, August 21, 2004. In general, one cannot predict whether there will be more than one form for a compound, how many forms will eventually be discovered, or how to prepare any previously unidentified form.

There remains a need for additional polymorphic forms of fidaxomicin and for processes to prepare polymorphic forms in an environmentally-friendly, cost-effective, and industrially applicable manner.

SUMMARY
In an aspect, the application provides a crystalline Form I of fidaxomicin, characterized by a PXRD pattern having peaks at 7.32, 8.13, 9.92, 10.55, 12.02, 15.66 and 18.71 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form I of fidaxomicin wherein the process comprises:
a) dissolving fidaxomicin in acetic acid to obtain a solution,
b) adding an anti solvent into the solution,
c) isolating crystalline form I of fidaxomicin

In another aspect, the application provides a crystalline Form Ia of fidaxomicin, characterized by a PXRD pattern having peaks at 7.31, 15.33, 18.77 and 22.24 ±0.2° 2?.

In another aspect, the application provides a crystalline Form IIa of fidaxomicin, characterized by a PXRD pattern having peaks at 6.94, 14.66 and 18.77 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form IIa of fidaxomicin wherein the process comprises:
a) adding fidaxomicin to a mixture of solvents to obtain a slurry,
b) heating the slurry,
c) isolating crystalline form IIa of fidaxomicin.

In another aspect, the application provides a crystalline Form II of fidaxomicin, characterized by a PXRD pattern having peaks at 7.36, 8.37, 15.43, 18.68 and 22.72 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form II of fidaxomicin wherein the process comprises drying form IIa of fidaxomicin.

In another aspect, the application provides a crystalline Form IIIa of fidaxomicin, characterized by a PXRD pattern having peaks at 3.96, 7.66, 11.93, 15.50 and 18.60 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form IIIa of fidaxomicin wherein the process comprises:
a) adding fidaxomicin to a mixture of an organic solvent and water to obtain a slurry,
b) stirring the slurry,
c) isolating crystalline form IIIa of fidaxomicin.

In another aspect, the application provides a crystalline Form III of fidaxomicin, characterized by a PXRD pattern having peaks at 4.31, 8.26, 15.57 and 18.59 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form III of fidaxomicin wherein the process comprises drying form IIIa of fidaxomicin.

In another aspect, the application provides a process for preparation of amorphous fidaxomicin wherein the process comprises:
a) dissolving fidaxomicin in methanol to obtain a solution,
b) evaporating the solvent,
c) isolating amorphous fidaxomicin.

In another aspect, the application provides a process for preparation of amorphous fidaxomicin wherein the process comprises:
a) dissolving fidaxomicin in an organic solvent to obtain a solution,
b) adding an antisolvent into the solution,
c) isolating amorphous fidaxomicin.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 depicts a PXRD pattern of fidaxomicin Form I, obtained by the procedure of Example 1.
Fig. 2 depicts a PXRD pattern of fidaxomicin Form Ia, obtained by the procedure of Example 2.
Fig. 3 depicts a PXRD pattern of fidaxomicin Form IIa, obtained by the procedure of Example 3.
Fig. 4 depicts a PXRD pattern of fidaxomicin Form II, obtained by the procedure of Example 4.
Fig. 5 depicts a PXRD pattern of fidaxomicin Form IIIa, obtained by the procedure of Example 5.
Fig. 6 depicts a PXRD pattern of fidaxomicin Form III, obtained by the procedure of Example 10.
Fig. 7 depicts a PXRD pattern of amorphous fidaxomicin, obtained by the procedure of Example 11.

DETAILED DESCRIPTION
In an aspect, the application provides a crystalline Form I of fidaxomicin, characterized by a PXRD pattern having peaks at 7.32, 8.13, 9.92, 10.55, 12.02, 15.66 and 18.71 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form I of fidaxomicin wherein the process comprises:
a) dissolving fidaxomicin in acetic acid to obtain a solution,
b) adding an anti solvent into the solution,
c) isolating crystalline form I of fidaxomicin

Step a) involves preparation of a solution of fidaxomicin by dissolving it in acetic acid. In embodiments, the solution of fidaxomicin can be prepared at any suitable temperatures, such as 20°C to the reflux temperature of the solvent used. Stirring and heating can be used to reduce the time required for the dissolution process.

In embodiments, the solution of fidaxomicin may be filtered to make it clear, free of unwanted particles. The obtained solution may be optionally treated with an adsorbent material, such as carbon and/or hydrose, to remove colored components, etc., before filtration.

In embodiments of step b), anti-solvent is added to the solution obtained in step a). The anti-solvent can be added to the solution drop-wise, lot wise in one lot or more lots or rapidly. The anti-solvent suitable for the purpose is a mixture of organic ethers like methyl tert-butyl ether (MTBE), diethyl ether, diisopropyl ether, 1,4-dioxane with saturated hydrocarbons such as hexane or n-heptane. The ratio of ether and n-heptane or hexane in the mixture may be from 1:2 to 2:1(v/v). In embodiments, the anti-solvent may be added to the solution at suitable temperatures such as 20 °C to 40 ºC.

Optionally the seed of crystalline form I of fidaxomicin may be added to the solution obtained in step a). The seed can be added before or after the addition of anti-solvent to the solution obtained in step-a). Preferably the seed can be added after the addition of the anti-solvent to the solution obtained in step a). The seed can be added as a solid or by making a slurry or suspension in anti-solvent used.

In embodiments, the slurry obtained by the precipitation comprising crystalline form I of fidaxomicin and solvent can be maintained at any suitable temperatures, such as 20 °C to 40 °C. In embodiments, the slurry comprising crystalline form I of fidaxomicin can be maintained for 30 minutes to 24 hours, or longer. The slurry may be stirred during the maintenance period.

Step c) involves the isolation of crystalline form I of fidaxomicin obtained in step b). In embodiments, crystalline form I of fidaxomicin can be isolated using any techniques, such as decantation, filtration by gravity or suction, centrifugation, or the solvent can be evaporated from the mass to obtain the desired product, and optionally the obtained solid can be washed with a solvent to reduce the amount of entrained impurities.

In embodiments, the isolated crystalline form I of fidaxomicin can be dried at suitable temperatures like 30-40 ºC, and atmospheric or reduced pressures, for 1-3 hours, or longer, using any types of drying equipment, such as a tray dryer, vacuum oven, air oven, fluidized bed dryer, spin flash dryer, flash dryer, and the like. Drying temperatures and times will be sufficient to achieve desired product purity.

In another aspect, the application provides a crystalline Form Ia of fidaxomicin, characterized by a PXRD pattern having peaks at 7.31, 15.33, 18.77 and 22.24 ±0.2° 2?.

As embodiment of the aspect, the crystalline Form Ia of fidaxomicin is further characterized by a PXRD pattern having peaks at 8.01 and 9.89 ±0.2° 2?.

Form Ia of fidaxomicin is formed by conversion of form I of fidaxomicin when stored for 20 days or longer at temperature of 25 ºC to 30 ºC.

In another aspect, the application provides a crystalline Form IIa of fidaxomicin, characterized by a PXRD pattern having peaks at 6.94, 14.66 and 18.77 ±0.2° 2?. As embodiment of the aspect, the crystalline Form IIa of fidaxomicin is further characterized by a PXRD pattern having peaks at 8.27, 10.73, 20.00 and 20.69 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form IIa of fidaxomicin wherein the process comprises:
a) adding fidaxomicin to a mixture of solvents to obtain a slurry,
b) heating the slurry,
c) isolating crystalline form IIa of fidaxomicin.

Step a) involves addition of fidaxomicin to a mixture of solvents. Input fidaxomicin is crystalline fidaxomicin form A as described in US patent number 7378508. As an embodiment, the mixture contains two solvent in varying proportion. The proportion of two solvents may be from 1:2 to 2:1. As another embodiment of step a) the solvents are xylene and water. Ratio of xylene:water in the mixture is 1:1. The slurry obtained may be stirred to confer uniformity.

As embodiment of step b) the slurry may be heated to a temperature of 65 ºC to 75 ºC. The heating and stirring is maintained for suitable time like 30 minutes to 7 hours. Optionally, the seed of crystalline form IIa of fidaxomicin may be added to the slurry obtained in step a). The seed can be added as a solid or by making a slurry or suspension in the mixture of solvents used.

Step c) involves the isolation of crystalline form IIa of fidaxomicin obtained in step b). In embodiments, crystalline form IIa of fidaxomicin can be isolated using any techniques, such as decantation, filtration by gravity or suction, centrifugation, or the solvent can be evaporated from the mass to obtain the desired product, and optionally the obtained solid can be washed with a solvent to reduce the amount of entrained impurities.

In another aspect, the application provides a crystalline Form II of fidaxomicin, characterized by a PXRD pattern having peaks at 7.36, 8.37, 15.43, 18.68 and 22.72 ±0.2° 2?. As embodiment of the aspect, the crystalline Form II of fidaxomicin is further characterized by a PXRD pattern having peaks at 14.39, 22.04 and 23.79 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form II of fidaxomicin wherein the process comprises drying form IIa of fidaxomicin. As embodiment the crystalline form IIa of fidaxomicin may be dried at 20-45 ºC in vacuum tray drier for 1-3 hour.

In another aspect, the application provides a crystalline Form IIIa of fidaxomicin, characterized by a PXRD pattern having peaks at 3.96, 7.66, 11.93, 15.50 and 18.60 ±0.2° 2?.

As embodiment of the aspect, the crystalline Form IIIa of fidaxomicin is further characterized by a PXRD pattern having peaks at 9.59, 11.63, 13.38 and 20.88 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form IIIa of fidaxomicin wherein the process comprises:
a) adding fidaxomicin to a mixture of an organic solvent and water to obtain a slurry,
b) stirring the slurry,
c) isolating crystalline form IIIa of fidaxomicin.

Step a) involves addition fidaxomicin to a mixture of an organic solvent and water to obtain slurry. Input fidaxomicin is crystalline fidaxomicin form A as described in US patent number 7378508. As an embodiment, the organic solvent may be selected from group comprising of acetonitrile, propionitrile, acetone or mixtures thereof. The ratio of water in the system may be from 0.5 times to 2 times of the organic solvent used.

Optionally, the seed of crystalline form IIIa of fidaxomicin may be added to the slurry obtained in step a). The seed can be added as a solid or by making a slurry or suspension in the organic solvent used. As embodiment of step b) the slurry obtained may be stirred for 30 minutes to 36 hours. As per step c) fidaxomicin form IIIa can be isolated as per the techniques provided in above embodiments.

Form IIIa can also be prepared by subjecting fidaxomicin to temperature cycling. Temperature cycling mentioned here means subjecting the material to different set of temperature conditions for particular time periods. As embodiment slurry of fidaxomicin in solvent system comprising of an organic solvent and water is made at 25 ºC temperature is raised to 60 ºC over a period of two hours. Temperature was then slowly brought down to 5 ºC over period of 8 hours. Temperature is then raised to 25-30 ºC over a period of 2-3 hours and maintained for 2-40 hours. Fidaxomicin form IIIa is isolated using techniques described in earlier embodiments. The solvent system suitable for temperature cycling comprises an organic solvent and water. Organic solvent suitable for the purpose may be selected from group comprising of nitromethane, acetonitrile, propionitrile and acetone. The ratio of water to organic solvent in the solvent system may be 2:1 to 1:2.

In another aspect, the application provides a crystalline Form III of fidaxomicin, characterized by a PXRD pattern having peaks at 4.31, 8.26, 15.57 and 18.59 ±0.2° 2?.

As embodiment of the aspect, the crystalline Form III of fidaxomicin is further characterized by a PXRD pattern having peaks at 9.69, 12.97, 16.34 and 23.28 ±0.2° 2?.

In another aspect, the application provides a process for preparation of Form III of fidaxomicin wherein the process comprises drying form IIIa of fidaxomicin.

As embodiment of the aspect, form IIIa can be dried at temperature of 40 ºC to 110 ºC for a period of 1-5 hours. Drying may be performed in drying equipment, such as a tray dryer, vacuum oven, air oven, fluidized bed dryer, spin flash dryer, flash dryer, and the like.

In another aspect, the application provides a process for preparation of amorphous fidaxomicin wherein the process comprises:
a) dissolving fidaxomicin in methanol to obtain a solution,
b) evaporating the solvent,
c) isolating amorphous fidaxomicin.

Step a) involves preparation of a solution of fidaxomicin by dissolving it in methanol. In embodiments, the solution of fidaxomicin can be prepared at any suitable temperatures, such as 20 °C to the reflux temperature of the solvent used. Stirring and heating can be used to reduce the time required for the dissolution process.

In embodiments, the solution of fidaxomicin may be filtered to make it clear, free of unwanted particles. The obtained solution may be optionally treated with an adsorbent material, such as carbon and/or hydrose, to remove colored components, etc., before filtration. The solution obtained is subjected to evaporation by heating under reduced pressure. In embodiment of step b) the solution may be heated to 40 ºC to 60 ºC. Heating is continued till all the solvent has evaporated.

Step c) involves the isolation of amorphous fidaxomicin obtained in step b). In embodiments, amorphous fidaxomicin can be isolated using any techniques, such as decantation, filtration by gravity or suction, centrifugation, or the solvent can be evaporated from the mass to obtain the desired product, and optionally the obtained solid can be washed with a solvent to reduce the amount of entrained impurities.

In another aspect, the application provides a process for preparation of amorphous fidaxomicin wherein the process comprises:
a) dissolving fidaxomicin in an organic solvent to obtain a solution,
b) adding an antisolvent into the solution,
c) isolating amorphous fidaxomicin.

Step a) involves preparation of a solution of fidaxomicin by dissolving it in an organic solvent. In embodiments the organic solvent may be selected from the group comprising of methanol, DMSO, DMF or mixtures thereof. In embodiments, the solution of fidaxomicin can be prepared at any suitable temperatures, such as 20°C to the reflux temperature of the solvent used. Stirring and heating can be used to reduce the time required for the dissolution process. The solution of fidaxomicin may be filtered to make it clear, free of unwanted particles. The obtained solution may be optionally treated with an adsorbent material, such as carbon and/or hydrose, to remove colored components, etc., before filtration.

In embodiments of step b) anti-solvent is added to the solution obtained in step a). The anti-solvent can be added to the solution drop-wise, lot wise in one lot or more lots or rapidly. The anti-solvent suitable for the purpose is water. In embodiments, the anti-solvent may be added to the solution at suitable temperatures such as 25 °C to 40 ºC. The slurry obtained can be maintained at any suitable temperatures, such as 25 °C to 40 °C. In embodiments, the slurry can be maintained for 10 minutes to 2 hours, or longer. The slurry may be stirred during the maintenance period.

Step c) involves the isolation amorphous fidaxomicin obtained in step b). In embodiments, amorphous fidaxomicin can be isolated using any techniques, such as decantation, filtration by gravity or suction, centrifugation, or the solvent can be evaporated from the mass to obtain the desired product, and optionally the obtained solid can be washed with a solvent to reduce the amount of entrained impurities.

In embodiments, the isolated amorphous fidaxomicin can be dried at suitable temperatures like 40-100 ºC, and atmospheric or reduced pressures, for 1-50 hours, or longer, using any types of drying equipment, such as a tray dryer, vacuum oven, air oven, fluidized bed dryer, spin flash dryer, flash dryer, and the like. Drying temperatures and times will be sufficient to achieve desired product purity.

In embodiments, crystalline forms of fidaxomicin according to the present application can be substantially pure having a chemical purity greater than about 99%, or greater than about 99.5%, or greater than about 99.9%, by weight, as determined using High Performance Liquid Chromatography (HPLC). Crystalline forms of fidaxomicin according to the present application can be chemically pure having purity greater than about 99.5% and containing no single impurity in amounts greater than about 0.15%, by HPLC. Crystalline forms of fidaxomicin according to the present application can be chemically pure fidaxomicin having purity greater than about 99.8% and containing no single impurity in amounts greater than about 0.1%, by HPLC.

The pharmaceutical compositions comprising fidaxomicin of the invention together with one or more pharmaceutically acceptable excipients may be formulated as: solid oral dosage forms, such as, but not limited to: powders, granules, pellets, tablets, and capsules; liquid oral dosage forms such as but not limited to syrups, suspensions, dispersions, and emulsions; and injectable preparations such as, but not limited to, solutions, dispersions, and freeze-dried compositions. Formulations may be in the form of immediate release, delayed release or modified release. Further, immediate release compositions may be conventional, dispersible, chewable, mouth dissolving, or flash melt preparations, and modified release compositions may comprise hydrophilic or hydrophobic, or combinations of hydrophilic and hydrophobic, release rate-controlling substances to form matrix or reservoir systems, or combinations of matrix and reservoir systems. The compositions may be prepared using any one or more of techniques such as direct blending, dry granulation, wet granulation, and extrusion and spheronization. Compositions may be presented as uncoated, film coated, sugar coated powder coated, enteric coated, or modified release coated.

Pharmaceutically acceptable excipients that are useful in the present application include, but are not limited to, any one or more of: diluents such as starches, pregelatinized starches, powdered cellulose, microcrystalline cellulose, dicalcium phosphate, tricalcium phosphate, mannitol, sorbitol, sugar, and the like; binders such as acacia, guar gum, tragacanth, gelatin, polyvinylpyrrolidones, hydroxypropyl celluloses, hydroxypropyl methylcelluloses, pregelatinized starches, and the like; disintegrants such as starches, sodium starch glycolate, pregelatinized starches, crospovidones, croscarmellose sodium, colloidal silicon dioxide, and the like; lubricants such as stearic acid, magnesium stearate, zinc stearate, and the like; glidants such as colloidal silicon dioxide and the like; solubility or wetting enhancers such as anionic, cationic, and neutral surfactants; complex forming agents such as various grades of cyclodextrins and resins; and release rate controlling agents such as hydroxypropyl celluloses, hydroxymethyl celluloses, hydroxypropyl methylcelluloses, ethylcelluloses, methylcelluloses, various grades of methyl methacrylates, waxes, and the like. Other pharmaceutically acceptable excipients that are useful include, but are not limited to, film-formers, plasticizers, colorants, flavoring agents, sweeteners, viscosity enhancers, preservatives, antioxidants, and the like.

The polymorphic forms disclosed in instant application may exhibit advantageous properties selected from at least one of the following: chemical purity, flowability, solubility, morphology or crystal habit, specific surface and pycnometric density, bulk/tap density, stability - such as storage stability, stability to dehydration, stability to polymorphic conversion, low hygroscopicity, and low content of residual solvents. These powder characteristics can greatly affect the efficiency, productivity and quality of formulation processes.

Certain specific aspects and embodiments of the present application will be explained in greater detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the application in any manner. Variations of the described procedures, as will be apparent to those skilled in the art, are intended to be within the scope of the present application.

EXAMPLES
Example 1: Preparation of fidaxomicin Form I: Fidaxomicin (200 mg) and acetic acid (10 mL) were charged in a 250 mL round bottom flask (RBF) and the mixture was heated to 60 ºC. The clear solution obtained was filtered to get a clear solution. The solution was cooled to 26 ºC. A mixture of MTBE and n-heptane (100 mL; 1:1) was added to the solution. The mixture was stirred for 5 hours. Solid formed was filtered and dried at 40 ºC in a vacuum tray drier for 2 hours to obtain fidaxomicin form I. Yield- 160 mg

Example 2: Preparation of fidaxomicin Form Ia: Fidaxomicin form I obtained in example 1 was stored at 26-30 ºC for 27 days to afford fidaxomicin form Ia.

Example 3: Preparation of fidaxomicin Form IIa: Fidaxomicin (1.0 g) and a mixture of xylene (20 mL) and water (20 mL) were charged in a 100 mL RBF. The mixture was heated to 70 ºC and maintained for 5Hrs and cooled to 26 ºC. The solid formed was filtered under reduced pressure and dried under suction to afford fidaxomicin form IIa. Yield-0.85 g

Example 4: Preparation of fidaxomicin Form II: Fidaxomicin form IIa as obtained in example 3 was dried at 40 ºC in a vacuum tray drier for 2 hours to afford fidaxomicin form II.

Example 5: Preparation of fidaxomicin Form IIIa: Fidaxomicin (0.5 g) and a mixture of acetonitrile (10 mL) and water (10mL) were charged in Easy max reactor (Mettler Toledo). The reactor was set to temperature cycle with following parameters:
Starting temperature - 25 ºC
Temperature raised to 60 ºC over a period of 2 hours
Cooled to 5 ºC over a period of 8 hours
Temperature raised to 25 ºC over a period of 2 hours
Temperature maintained at 25 ºC for 30 hours.
The mixture was stirred at 500 RPM throughout the temperature cycling process.
After completion of temperature cycling process, the slurry was filtered under suction to afford fidaxomicin form IIIa.

Example 6: Preparation of fidaxomicin Form IIIa: Fidaxomicin (1.0 g) and a mixture of nitromethane (20 mL) and water (20 mL) were charged in Easy max reactor (Mettler Toledo). Rest of the process was same as mentioned in example 5. Yield – 0.83 g

Example 7: Preparation of fidaxomicin Form IIIa: Fidaxomicin (0.5 g) and 25 mL of a 1:2 mixture of propionitrile in water were charged in a 100 mL RBF. The slurry was stirred for 29 hours at 26 ºC and solid obtained was filtered and dried under suction to afford fidaxomicin form IIIa.

Example 8: Preparation of fidaxomicin Form IIIa: Fidaxomicin (0.5 g) and 20 mL of a 1:1 mixture of acetone in water were charged in a 100 mL RBF. The slurry was stirred for 22 hours at 25 ºC and solid obtained was filtered and dried under suction to afford fidaxomicin form IIIa.

Example 9: Preparation of fidaxomicin Form IIIa: Fidaxomicin (0.5 g) and 20 mL of a 1:1 mixture of acetonitrile in water were charged in a 100 mL RBF. The slurry was stirred for 16 hours at 25 ºC and solid obtained was filtered and dried under suction to afford fidaxomicin form IIIa.

Example 10: Preparation of fidaxomicin Form III: Fidaxomicin form IIIa as obtained in examples 5-9 was dried at 95 ºC in a vacuum tray drier for 2 to 5 hours to afford fidaxomicin form III.

Example 11: Preparation of amorphous fidaxomicin: Fidaxomicin (200 mg) and methanol (10 mL) were charged in a 100 mL RBF and the mixture was stirred to get solution which was filtered to get a clear solution. Water (50 mL) was added to the solution. The mixture was stirred for 30 minutes. Solid formed was filtered and dried at 40 ºC in a vacuum tray drier for 2 hours to obtain amorphous fidaxomicin. Yield- 170 mg

Example 12: Preparation of amorphous fidaxomicin: Fidaxomicin (200 mg) and DMSO (5 mL) were charged in a 100 mL RBF and the mixture was stirred and filtered to get a clear solution. Water (50 mL) was added to the solution. The mixture was stirred for 30 minutes. Solid formed was filtered and dried at 40 ºC in a vacuum tray drier for 2 hours to obtain amorphous fidaxomicin. Yield- 168 mg

Example 13: Preparation of amorphous fidaxomicin: Fidaxomicin (200 mg) and DMF (5 mL) were charged in a 100 mL RBF and the mixture was stirred and filtered to get a clear solution. Water (50 mL) was added to the solution. The mixture was stirred for 30 miutes. Solid formed was filtered and dried at 40 ºC in a vacuum tray drier for 2 hours to obtain amorphous fidaxomicin. Yield- 160 mg

Example 14: Preparation of amorphous fidaxomicin: Fidaxomicin (500 mg) and methanol (20 mL) were charged in a 100 mL RBF and the mixture was stirred and filtered to get a clear solution. The solution was heated to 60 ºC under reduced pressure to remove complete solvent to afford amorphous fidaxomicin. Yield- 432 mg
,CLAIMS:We Claim:

1. A crystalline Form III of fidaxomicin, characterized by a PXRD pattern having peaks at 4.31, 8.26, 15.57 and 18.59 ±0.2° 2?.
2. The crystalline Form III of fidaxomicin as claimed in claim 1, further characterized by a PXRD pattern having peaks at 9.69, 12.97, 16.34 and 23.28 ±0.2° 2?.
3. A crystalline Form IIIa of fidaxomicin, characterized by a PXRD pattern having peaks at 3.96, 7.66, 11.93, 15.50 and 18.60 ±0.2° 2?.
4. The crystalline Form IIIa of fidaxomicin as claimed in claim 3, further characterized by a PXRD pattern having peaks at 9.59, 11.63, 13.38 and 20.88 ±0.2° 2?.
5. A process for preparation of Form IIIa of fidaxomicin as claimed in claims 3 and 4 comprising:
a) adding fidaxomicin to a mixture of an organic solvent and water to obtain a slurry,
b) stirring the slurry, and
c) isolating crystalline form IIIa of fidaxomicin.
6. A process according to claim 5 wherein the solvent is selected from acetonitrile, propionitrile, acetone or mixtures thereof.
7. A process for preparation of Form IIIa of fidaxomicin as claimed in claims 3 and 4 comprising subjecting the fidaxomicin in an organic solvent and water to temperature cycling.
8. A process for preparation of Form III of fidaxomicin as claimed in claims 1 and 2 comprising drying of Form IIIa of fidaxomicin.
9. A process for preparation of amorphous form of fidaxomicin comprising
a) dissolving fidaxomicin in methanol to obtain a solution,
b) evaporating the solvent, and
c) isolating amorphous fidaxomicin
(or)
i) dissolving fidaxomicin in an organic solvent to obtain a solution,
ii) adding an antisolvent into the solution, and
iii) isolating amorphous fidaxomicin
10. A pharmaceutical composition comprising the crystalline forms III, IIIa of fidaxomicin as claimed in claim 1 to 4 and one or more pharmaceutically acceptable carrier.