DESC:Field of the invention
The present invention is directed towards process for preparing stable amorphous form of Sofosbuvir of Formula-I.

Formula-I

Background of the invention
Globally, 130-150 million people have CHC infection. The prevalence of hepatitis C virus (HCV) is highest in Egypt at >10% of the general population; China has the most people overall with HCV (29.8 million); approximately 3.2 million are infected in the US. Of those with CHC, =20% develop serious morbidities ± mortality, that is, cirrhosis, end stage liver disease (ESLD), hepatocellular carcinoma (HCC). CHC infection leads to approximately 10,000 deaths per year in the US and has surpassed human immunodeficiency virus (HIV) as a cause of death.

In 2011, two new HCV non structural protein 3/4A (NS3/4A) protease inhibitors, telaprevir (TPV) and boceprevir (BOC) were approved for treatment of CHC Genotype 1. The rationale was the improvement in sustained virologic response (SVR) rates to 63% and 79% when these drugs were combined with pegylated interferon alfa + ribavirin. These regimens also allow treatment options for patients previously failing to achieve SVRs, with SVR approximately 70-86% for prior relapsers, 40-59% for partial responders, and 32% for null responders (TPV only). Despite the efficacy of these combined regimens, downsides are additional toxicities: anaemia for BOC and rash for TPV. In addition, BOC and TPV are approved only for Genotype (GT) -1, leaving pegylated interferon alfa (PEG) + ribavirin (RBV) as the treatment for Genotype -2, 3, 4, 6.
Sofosbuvir is a novel nucleotide prodrug inhibitor of the HCV non structural protein 5B (NS5B) RNA dependent RNA polymerase, essential for HCV replication; as such, it is a direct-acting antiviral agent (DAA). Sofosbuvir is a component of the first all oral, interferon (IFN) free regimen approved for treating CHC infection. IFN free therapy for treatment of hepatitis C reduces the side effects associated with use of IFN. Sofosbuvir treatment regimens last 12 weeks for GT-1, 2 and 4, and 24 weeks for treatment of GT-3, in combination with PEG+RBV, or with RBV alone. This is typically half the time as with prior treatments
Sofosbuvir having the chemical name (S)-Isopropyl 2-((S)-(((2R, 3R, 4R, 5R)-5-(2, 4-dioxo3,4-dihydropyrimidin-1(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2yl) methoxy)-(phenoxy) phosphorylamino) propanoate and its diastereomeric mixture is disclosed in US7964580B2. Diastereomeric mixtures of sofosbuvir, is subjected to crystallization, chromatography, or extraction in order to obtain purified compound of formula-I.
US8618076B2 discloses diastereomeric mixture, compound of formula-I and its enantiomer in its solvates and hydrates thereof is crystalline, crystal-like, or amorphous form and process for preparation of the same.
Present invention describes process of preparation of stable amorphous form of Sofosbuvir, which is stable and not contaminated with any crystalline form, pharmaceutical compositions containing them, and to method of treatment using the same.

Object of the invention:
In one aspect, the present invention relates to a process for preparing stable amorphous form which is not contaminated with any crystalline form of Sofosbuvir, comprising the steps of
a) reacting Sofosbuvir in a suitable solvent(s) preferably selected from alcohols, acetates, ethers, ketones, amides, halogenated or mixture thereof;
b) further treating the obtained product from step (a) with suitable solvent(s) preferably selected from hydrocarbons or mixture thereof and;
c) isolating an amorphous Sofosbuvir by conventional techniques.

In another aspect, the present invention is to provide process for the preparation of an amorphous form of sofosbuvir by melting sofosbuvir followed by cooling to obtain amorphous form of Sofosbuvir.
In another aspect, the stable amorphous form of Sofosbuvir has the powder X-ray diffraction as shown in Figure-1.

Brief description of the Drawings

Figure 1 is an illustration of a PXRD pattern of an amorphous sofosbuvir

Detailed description of the invention:
Present invention relates to a process for preparing a stable amorphous form which is not contaminated with any crystalline form of sofosbuvir, comprising the steps of
a) reacting Sofosbuvir in a suitable solvent(s) or mixture thereof at suitable temperature and heating the reaction mixture at suitable temperature to obtain clear solution and further stirring the reaction mixture at suitable temperature for suitable time and isolating the compound using suitable conventional techniques at suitable temperature;
b) further treating the obtained product from step (a) with suitable solvent(s) or mixture thereof at suitable temperature for suitable time and;
c) isolating the desired product Sofosbuvir by using conventional techniques at suitable temperature for suitable time period using inert gas condition.

In one aspect the term suitable solvent(s) include one or more of alcohols, acetates, ethers, ketones, amides, hydrocarbons, halogenated solvent and mixture thereof.
In another aspect the suitable alcohols are selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, n-hexanol, n-pentanol and like.
In another aspect the suitable acetates are selected from ethylacetate, methyl acetate, isopropyl acetate, n-butyl acetate, Isobutyl actetate, amyl acetate, isoamyl acetate and like.
In another aspect the suitable ethers are selected from tetrahydrofuran, 2-methyl tetrahydrofuran, cyclopentylmethyl ether, diisopropylether, methyl tert-butyl ether and like.
In another aspect the suitable ketone solvents are selected from acetone, Methylisobutyl ketone, methylethyl ketone and like.
In another aspect the suitable amide solvents are selected from Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetramethylurea and like.
In another aspect the suitable halogenated solvents are selected from dichloromethane, chlorobenzene, ethylenedichloride, chloroform, benzotrifluoride carbon tetrachloride and like.
In another aspect the suitable hydrocarbons are selected from hexane, pentane, heptane, benzene, cyclohexane, toluene, xylene and like.
In yet another aspect the suitable temperature as used herein includes but not limited to ranges from 10-150oC, preferably selected from 15-100oC and more preferable selected from 20-80oC.
In further aspect the suitable time as used herein includes but not limited to ranges from 30 minutes to 24 hrs.
The term "conventional techniques" as used herein includes but not limited to distillation, distillation under reduced pressure or vacuum, filtration, evaporation, solvent-anti solvent, spray drying, lyophilization or freeze drying.
In another aspect of the present invention is to provide process for the preparation of an amorphous form sofosbuvir by melting Sofosbuvir followed by cooling to obtain amorphous form of sofosbuvir.
Amorphous sofosbuvir obtained by present invention is stable and not contaminated with any crystalline form.
As used herein, the term “stable amorphous form of Sofosbuvir” includes amorphous Sofosbuvir that does not convert to any other solid form when stored at a temperature of up to about 40oC and at a relative humidity of about 25% to about 75% for about three months or more.
Sofosbuvir which is used as starting material for present invention is prepared by the process disclosed in US7964580B2.
The following examples are provided to enable one skilled in the art to practice the invention and merely illustrate the process of this invention. However, it is not intended in any way to limit the scope of the present invention.

Preparation of stable amorphous sofosbuvir

Example-1:
Sofosbuvir (100.0 g) was dissolved in Methanol (500 ml) at ambient temperature, and suspension mixture was heated to 50-55°C to obtain a clear solution. The solution was then stirred for 30 minutes at same temperature. The solvent was evaporated through distillation under vacuum at about 50-55°C. The reaction mass was degassed for 2 hrs at 50-55oC under vacuum. Subsequently the vacuum was released in presence of nitrogen. n-heptane (200 mL) was added to residual mass at 20-25°C.The reaction mixture was stirred for 1 hour at 20-25oC. precipitated product was filtered. The isolated wet cake was washed with n-heptane (100 ml) at same temperature and dried in vacuum tray drier for 8-10 hrs at 40-45oC. Further the vacuum was released in presence of nitrogen to obtain the desired stable amorphous form of compound of formula-I. The powder X-ray diffractogram of the solid (FIG. 1) showed that the resulting substance was in amorphous form.
Yield: 85.0 g (85.0%); Purity: 99.9%

Example-2:
Sofosbuvir (100.0 g) was dissolved in tetrahydrofuran (600 ml) at ambient temperature, and suspension mixture was heated to 50-55°C. to obtain a clear solution. The solution was then stirred for 30 minutes at same temperature. The solvent was evaporated through distillation under vacuum at about 60-65°C. The reaction mass was degassed for 2 hrs at 60-65oC under vacuum. Subsequently the vacuum was released in presence of nitrogen. The residual mass was then allowed to cool at 20-25oC, n-heptane (300 mL) was added and stirred for 1 hr at same temperature and filtered off the solid. The isolated wet cake was washed with n-heptane (200 ml) at same temperature and dried in vacuum tray drier for 8-10 hrs at 40-45oC. Further the vacuum was released in presence of nitrogen to obtain the desired stable amorphous form of compound of formula-I.
Yield: 75.0 g (75.0%); Purity: 99.9%

Example-3:
Sofosbuvir (100.0 g) was dissolved in dichloromethane (2200 ml) at ambient temperature, and suspension mixture was heated to 40-42°C to obtain a clear solution. The solution was then stirred for 30 minutes at same temperature. The solvent was evaporated through distillation under vacuum at about 40-42°C. The reaction mass was degassed for 2 hrs at 40-42oC under vacuum. Subsequently the vacuum was released in presence of nitrogen. Charged n-heptane (200 mL) to residual mass at 20-25°C.The reaction mass was stirred for 1 hour at 20-25oC. the wet product was Filtered off . The isolated wet cake was washed with n-heptane (100 ml) at same temperature and dried in vacuum tray drier for 8-10 hrs at 40-45oC. Further the vacuum was released in presence of nitrogen to obtain the desired stable amorphous form of compound of formula-I.
Yield: 90.0 g (90.0%); Purity: 99.8%

Example-4:
Sofosbuvir (100.0 g) was suspended in ethylacetate (600 ml) at ambient temperature. Added 10% aqueous sodium bicarbonate solution (500 mL) to reaction mixture at 25-30°C. Stirred for 1 hour at 25-30C. Separated the upper organic layer then organic layer washed with DM water (500 mL) at 25-30°C. Distilled off ethylacetate completely under vacuum at 55-60°C. Degassed for 2 hours at 55-60°C under vacuum. Subsequently the vacuum was released in presence of nitrogen. n-heptane (200 mL) was added to residual mass at 20-25°C.The reaction mass was stirred for 1 hour at 20-25oC. The wet product was filtered off. The isolated wet cake was washed with n-heptane (100 ml) at same temperature and dried in vacuum tray drier for 8-10 hrs at 40-45oC. Further the vacuum was released in presence of nitrogen to obtain the desired stable amorphous form of compound of formula-I.
Yield: 88.0 g (88.0%); Purity: 99.8%
,CLAIMS:1. A process for preparing stable amorphous form of Sofosbuvir comprising of following steps:

a) reacting Sofosbuvir in presence of suitable solvent(s) preferably selected from alcohols; acetates; ethers; ketones; halogenated; amides or mixtures thereof;
b) further treating the product obtained in step (a) with suitable solvent(s) preferably selected from hydrocarbons and mixtures thereof;
c) isolating the stable amorphous form of Sofosbuvir.

2. The process as claimed in claim 1, wherein the suitable alcohols are selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, n-hexanol, n-pentanol and like.
3. The process as claimed in claim 1, wherein the suitable acetates are selected from Ethylacetate, methyl acetate, isopropyl acetate, n-Butyl acetate, Isobutyl actetate, amyl acetate, isoamyl acetate and like.
4. The process as claimed in claim 1, wherein the suitable ethers are selected from tetrahydrofuran, 2-methyl tetrahydrofuran, cyclopentylmethyl ether, Diisopropylether, methyl tert-butyl ether and like.
5. The process as claimed in claim 1, wherein the suitable ketone solvents are selected from acetone, Methylisobutyl ketone, methylethyl ketone and like.
6. The process as claimed in claim 1, wherein the suitable amide solvents are selected from Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetramethylurea and like.
7. The process as claimed in claim 1, wherein the suitable halogenated solvents are selected from dichloromethane, chlorobenzene, ethylenedichloride, chloroform, benzotrifluoride, carbon tetrachloride and like.
8. The process as claimed in claim 1, wherein the suitable hydrocarbons are selected from hexane, heptane, pentane benzene, cyclohexane, toluene, xylene and like.
9. Amorphous form of Sofosbuvir as claimed in claim 1, which is stable and do not convert to any other form when stored at temperature of up to about 40oC and at a relative humidity conditions of about 25% to about 75% for about three months or more.
10. Amorphous form of Sofosbuvir as claimed in claim 1, which is free from any crystalline form.