DESC:Field of the invention
The present invention is directed to a process for preparing a stable amorphous form of Ledipasvir of Formula-I, its pharmaceutical compositions and method of treatment using the same.

Formula-I

Background of the invention
Ledipasvir is an inhibitor of the hepatitis C virus NS5A protein. Ledipasvir, a drug developed by Gilead Science that is used to treat hepatitis C. Ledipasvir/Sofosbuvir fixed dose combination tablet for genotype I hepatitis C was approved recently by the USFDA under brand name Harvoni. The combination is direct acting antiviral agent that interferes with HCV replication and can be used to treat patients with genotype Ia or Ib without PEG-interferon or ribavirin.
Ledipasvir chemically known as Methyl [(2S)-1-{(6S)-6-[5-(9,9-difluoro-7¬ {2-[(1R,3S,4S)-2-{(2S)-2-[(methoxycarbonyl)amino]-3-methylbutanoyl}-2¬ azabicyclo[2.2.1]hept-3-yl]-1H-benzimidazol-6-yl}-9H-fluoren-2-yl)-1H-imidazol-2-yl]-5¬ azaspiro[2.4]hept-5-yl}-3-methyl-1-oxobutan-2-yl]carbamate.
Ledipasvir is also known as (1-{3-[6-(9,9-difluoro-7-{2-[5-(2-methoxycarbonylamino-3-methyl-butyryl)-5-aza-bicyclo[2.2.1]heptane-2-carbonyl}-2-methyl-propyl)-carbamic acid methyl ester known to be an effective anti-HCV agent, as described in WO 2010/132601. It has the following structural formula:

Formula-I

Ledipasvir and its pharmaceutical acceptable salts were first disclosed in US 8088368. However the compound was not heretofore known in any of the solid forms. US 9,056,860 disclose the process for the preparation of Ledipasvir.
Further WO 2013/184698 discloses amorphous form and various crystalline forms of Ledipasvir and its salts or solvates thereof. This disclosure also provides process for the preparation of amorphous form and crystalline forms and methods for using them in the treatment of HCV. The major disadvantage with the above prior art process was using catalysts and solvents which are very highly expensive and lowers the yield due to the amount of by-products and impurities, the said prior art process for preparing Ledipasvir is not optimal for industrial scale production.
Further crystalline solids normally require a significant amount of energy for dissolution due to their highly organized, lattice like structures. For example, the energy required for a drug molecule to escape from a crystal is more than from an amorphous or a non-crystalline form. It is known that the amorphous forms in a number of drugs exhibit different dissolution characteristics and in some cases different bioavailability patterns compared to the crystalline form (Econno T., Chem. Pharm. Bull., 1990; 38: 2003-2007). For some therapeutic indications, one bioavailability pattern may be favored over another. An amorphous form of few of the known drugs exhibit much higher bioavailability than the crystalline forms, which leads to the selection of the amorphous form as the final drug substance for pharmaceutical dosage form development. Additionally, the aqueous solubility of crystalline form is lower than its amorphous form, which may result in the difference in their in vivo bioavailability. Therefore, it is desirable to have amorphous form of drug with high purity to meet the needs of regulatory agencies and also highly reproducible process for its preparation.

Object of the invention:
In one aspect, the present invention relates to a process for preparing stable amorphous form of Ledipasvir which is not contaminated with any of the crystalline form of Ledipasvir, comprising of following steps:
i) dissolving Ledipasvir in one or more of suitable solvent(s) to obtain solution;
ii) optionally adding to the solution of step (i) with one or more suitable anti-solvent(s) at suitable temperature;
iii) isolating amorphous form of Ledipasvir.
In another general aspect, the present invention provides process for the preparation of an amorphous form of Ledipasvir by melting Ledipasvir followed by cooling to obtain amorphous form of Ledipasvir.
In another general aspect, there is provided an amorphous solid dispersion of Ledipasvir free base.
In another general aspect, there is provided a stable amorphous Ledipasvir which is at least stable during storage and drying.
In another general aspect, the present invention uses distillation, distillation under reduced pressure or vacuum, evaporation, solvent-anti-solvent, spray drying, lyophilization or freeze drying techniques for obtaining amorphous form of Ledipasvir.
In another general aspect, the present invention provides a process for preparation of an amorphous Ledipasvir premix having enhanced stability and dissolution properties.
In another general aspect, the present invention provides pharmaceutical compositions comprising the aforementioned amorphous Ledipasvir premix.

Brief description of the Drawings
Figure 1 is an illustration of a PXRD pattern of amorphous form of Ledipasvir

Detailed description of the invention:
Present invention relates to a process for preparing a stable amorphous form of Ledipasvir which is not contaminated with any crystalline form of Ledipasvir, comprising of following steps:
i) dissolving Ledipasvir in one or more of suitable solvent(s) to obtain solution;
ii) optionally adding to the solution of step (i) with one or more suitable anti-solvent(s) at suitable temperature;
iii) isolating amorphous form of Ledipasvir.
The term "conventional techniques" as used herein includes but not limited to distillation, distillation under reduced pressure or vacuum, evaporation, solvent-antisolvent, spray drying, lyophilization or freeze drying.
The term “suitable solvents” and “suitable anti-solvents” as used herein includes but not limited to polar and non-polar solvents such as water, hydrocarbons, ketones, alcohols, ethers, esters, halogenated solvents, DMSO, DMF, pyridine, phenol, DMA, carbon disulphide, acetic acid, acetonitrile and mixtures thereof.
Hydrocarbons include but not limited to such as benzene, toluene, xylene, pentane, hexane, heptane, cyclo hexane and tetraline.
Ketones include but not limited to such as acetone, methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone.
Alcohols include but not limited to such as methanol, ethanol, propanol, butanol, octanol, ethanediol, 1, 2-propane diol and S (+)-1, 2-propane diol.
Ethers include but not limited to such as diethyl ether, di isopropyl ether, di butyl ether, methyl tert-butyl ether, 1,4-dioxane, tetrahydrofuran and cyclo pentyl methyl ether.
Halogenated solvents include but not limited to such as chloroform, carbon tetrachloride, methylene chloride and 1, 2-dichloro ethane.
Esters include but not limited to such as methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate and n-propyl acetate.
In another aspect of the present invention provides a process for the preparation of stable amorphous form Ledipasvir by melting Ledipasvir followed by cooling to obtain amorphous form of Ledipasvir.
Amorphous Ledipasvir obtained by present invention is stable and not contaminated with any of crystalline form.
Amorphous Ledipasvir obtained by present invention is stable up to 180 days or more.
Another embodiment of present invention provides an amorphous Ledipasvir premix having enhanced stability and dissolution properties and process for preparation thereof.
In another aspect, the amorphous product obtained may be dried, sieved and milled to obtain suitable particle size range.
Premixes are characterized by a variety of associated properties such as stability, flow, and solubility. Typical premixes represent inclusion of the above properties, as for example, an increase in stability and dissolution properties of the premix. Although there are a variety of premixes, there is a continuous search in this field of art for premixes that exhibit improved properties. Thus, the instant invention provides a premix in which Ledipasvir exists in stable amorphous form and process of manufacture of the premix and pharmaceutical compositions comprising said amorphous Ledipasvir premix.
One of the embodiments of the present invention provides a process for the preparation of solid premix of Ledipasvir comprising:
(a) providing an intimate mixture comprising organic solvent(s), amorphous Ledipasvir and premixing agents, and optionally water;
(b) optionally removing solvent(s) from the mixture;
(c) optionally dissolving in secondary solvent(s);
(d) isolating premix of amorphous Ledipasvir.
As used herein, the term "intimate mixture" can denote a solution, suspension, emulsion, colloid, dispersion or the like. Generally, the term "intimate mixture" as used herein denotes a solution.
Suitable premixing agents are pharmaceutically acceptable carrier or excipients include but not limited to fillers, bulking agents, binders, wetting agents, disintegrating agents, surface active agents, and lubricants. Various modes of administration of the pharmaceutical compositions of the invention can be selected depending on the therapeutic purpose, for example tablets, pills, powders, liquids, suspensions, emulsions, granules, capsules, suppositories, or injection preparations.
While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

Example: 1

Ledipasvir (2.0g), S-(+)-1, 2-propane diol (0.24 g) and methylene dichloride (10mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours, diisopropyl ether (30.0 mL) added to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with diisopropyl ether (10.0 mL).The material was dried at 50-55°C under reduced pressure to get 0.83 g of Ledipasvir Amorphous.

Example: 2

Ledipasvir (2.0 g), n-butyl acetate (10 mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours reaction mass, n-Heptane (30 mL) added to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with n-Heptane (10 mL).The material was dried at 50-55°C under reduced pressure to get 1.7 g of Ledipasvir Amorphous.

Example: 3

Ledipasvir (2.0 g), Tetraline (24 mL) was charged at 20-30°C followed by heated at 75-80°C to get the clear solution. After maintaining for 2 hours reaction mass, cooled it to 20-30°C. Filtered out the material and washed with Tetraline (10 mL).The material was dried at 50-55°C under reduced pressure to get 1.2 g of Ledipasvir Amorphous.

Example: 4

Ledipasvir (2.0 g), cyclo pentyl methyl ether (8.0 mL) was charged at 20-30°C followed by heated at 45-50°C to get the clear solution. After maintaining for 2 hours reaction mass, cooled it to 20-30°C followed by addition of n-Heptane (30 mL) to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with n-Heptane (10 mL).The material was dried at 50-55°C under reduced pressure to get 0.90 g of Ledipasvir Amorphous.

Example: 5

Ledipasvir (2.0 g), S-(+)-1,2-propane diol (0.24 g) and Isopropyl acetate (10 mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours reaction mass, Cyclohexane (30 mL) added to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with Cyclohexane (10 mL).The material was dried at 50-55°C under reduced pressure to get 0.75 g of Ledipasvir Amorphous.

Example: 6

Ledipasvir (2.0 g), Methyl isobutyl ketone (4.0 mL) was charged at 50-55°C to get the clear solution. After maintaining for 2 hours reaction mass, cooled it to 20-30°C followed by addition of n-Heptane (30 mL) to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with n-Heptane (10 mL).The material was dried at 50-55°C under reduced pressure to get 1.54 g of Ledipasvir Amorphous.

Example: 7

Ledipasvir (2.0 g), ethyl acetate (5.0 mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours reaction mass, Cyclopentyl methyl ether (28 mL) added to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with Cyclopentyl methyl ether (10.0 mL).The material was dried at 50-55°C under reduced pressure to get 1.25 g of Ledipasvir Amorphous.

Example: 8

Ledipasvir (5.0 g), S(+)-1,2-propane diol (12.5mL) was charged at 20-30°C followed by heated at 160-180°C to get the clear solution. After maintaining for 2 hours reaction mass, cooled it to 20-30°C. Filtered out the material and washed with S (+)-1, 2-propane diol (5.0mL).The material was dried at 50-55°C under reduced pressure to get 3.2 g of Ledipasvir Amorphous.

Example: 9

Ledipasvir (2.0 g), ethyl acetate (5.0 mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours reaction mass, dimethyl formamide (28 mL) added to the reaction mixture and stirred it for 15 hours at 20-30°C. Separate the lower oily layer and added water (50 mL). Stir the reaction mass for 1 hour. Filter out the material and wash with water (10 mL). The material was dried at 50-55°C under reduced pressure to get 1.21 g of Ledipasvir Amorphous.

Example: 10

Ledipasvir (5.0 g), dimethyl formamide (12.50 mL) was charged at 20-30°C. Heat the reaction mass at 170-180°C to get clear solution. After maintaining for 15-30 minute reaction mass, cool the reaction mass at 25-30°C. Water (50 mL) was added to the reaction mixture and stirred it for 30 minute at 20-30°C. Filter out the material and wash with water (10 mL). The material was dried at 50-55°C under reduced pressure to get 4.61 g of Ledipasvir Amorphous.

Example: 11

Ledipasvir (2.0 g), n-propyl acetate (10 mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours reaction mass, n-Heptane (30 mL) added to the reaction mixture and stirred it for 1 hour at 20-30°C. Filtered out the material and washed with n-Heptane (10 mL).The material was dried at 50-55°C under reduced pressure to get 1.7 g of Ledipasvir Amorphous.

Example: 12

Ledipasvir (2.0 g), ethyl acetate (7.5 mL) was charged at 20-30°C to get the clear solution. After maintaining for 2 hours reaction mass, Anisole (42 mL) added to the reaction mixture and stirred it for 1 hour at 20-30°C. Material was not isolated so cyclohexane (150 mL) added to the reaction mixture and stirred for 1 hour at 20-30°C. Filtered out the material and washed with cyclohexane (10.0 mL). The material was dried at 50-55°C under reduced pressure to get 2.2 g of Ledipasvir Amorphous.

Date this 25nd day of September 2017

,CLAIMS:1. A process for preparing stable amorphous form of Ledipasvir of formula-I comprising of:

i) dissolving Ledipasvir in one or more of suitable solvent(s) to obtain
solution;
ii) optionally adding anti-solvents to the solution of step (i) at suitable temperature;
iii) isolating amorphous form of Ledipasvir.
2. The process according to claim 1, wherein suitable solvent(s) and anti-solvent(s) are selected from polar and non-polar solvent(s).
3. The process according to claim 2, wherein suitable polar and non-polar solvent(s) are selected from water, hydrocarbons, ketones, alcohols, ethers, esters, halogenated solvents, DMSO, DMF, pyridine, phenol, DMA, carbon disulphide, acetic acid, acetonitrile, anisole and mixtures thereof.
4. The process according to claim 1, wherein suitable polar and non-polar anti-solvent(s) are selected from water, hydrocarbons, ketones, alcohols, ethers, esters, halogenated solvents, DMSO, DMF, pyridine, phenol, DMA, carbon disulphide, acetic acid, acetonitrile, anisole and mixtures thereof.
5. The process according to claim 3 or 4, wherein suitable hydrocarbons are selected from pentane, n-hexane, cyclohexane, n-heptane, benzene, toluene, xylene and tetraline; halogenated solvents selected from methylene chloride, 1, 2-dichloro ethane, chloroform, carbon tetrachloride and chlorobenzene; alcohols are selected from methanol, ethanol, propanol, butanol, octanol, ethanediol, 1, 2-propane diol and S (+)-1, 2-propane diol; esters are selected from ethyl acetate, n-propyl acetate, iso-propyl acetate and n-butyl acetate; ethers are selected from diethyl ether, di isopropyl ether, di butyl ether, methyl tert-butyl ether, 1,4-dioxane, tetrahydrofuran and cyclo pentyl methyl ether; ketones are selected from acetone, methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone.
6. The process according to claim 1 , wherein amorphous form of Ledipasivir is isolated using techniques selected from distillation, distillation under reduced pressure or vacuum, filtration, evaporation, solvent-anti-solvent, spray drying, lyophilization or freeze drying.
7. Stable amorphous form of Ledipasivir according to claim 1, wherein amorphous form of is stable up to 180 days or more.
8. A process for the preparation of solid premix of Ledipasvir of formula-I comprising of:
i) providing an intimate mixture comprising organic solvent(s), amorphous Ledipasvir and premixing agents, and optionally water;
ii) optionally removing solvent(s) from the mixture;
iii) optionally dissolving in secondary solvent(s);
iv) isolating premix of amorphous Ledipasvir.

9. The process according to claim 9, wherein suitable solvent(s) are as defined in previous claims.
10. A pharmaceutical composition comprising the amorphous form of Ledipasvir of claim 1 and a pharmaceutically acceptable carrier.

Date this 25nd day of September 2017