Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PROCESS FOR THE PREPARATION OF PURE SOFOSBUVIR
Document Type and Number:
WIPO Patent Application WO/2017/093973
Kind Code:
A1
Abstract:
The present invention provides pure sofosbuvir and a process for the preparation of pure sofosbuvir and its intermediates.

Inventors:
MATTA HARI BABU (IN)
SHARMA ATUL (IN)
SHAIKH SHAKIR SHABBIR (IN)
SHARMA KAPIL (IN)
SAINI ANIL (IN)
KHANNA MAHAVIR SINGH (IN)
PRASAD MOHAN (IN)
Application Number:
PCT/IB2016/057325
Publication Date:
June 08, 2017
Filing Date:
December 02, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SUN PHARMACEUTICAL IND LTD (IN)
International Classes:
C07H19/073; C07H1/00
Domestic Patent References:
WO2015158317A12015-10-22
Foreign References:
CN104558079A2015-04-29
US20130281686A12013-10-24
US20150231166A12015-08-20
Download PDF:
Claims:
We Claim:

1. Pure sofosbuvir of Formula I

Formula I having content of reduced sofosbuvir of Formula II

Formula II which is not more than 0.01%.

2. Pure sofosbuvir of Formula I

Formula I having content of bromo-sofosbuvir of Formula III

Formula III

which is not more than 0.3%.

3. Pure sofosbuvir of Formula I

Formula I

produced by a process comprising hydrogenation of the bromo-sofosbuvir of Formula III.

Formula III

4. A process for the preparation of pure sofosbuvir of Formula I

Formula I

comprising hydrogenation of bromo-sofosbuvir of Formula III.

Formula III

5. A process according to claim 3 or 4, wherein hydrogenation is carried out in the presence of an organic base.

6. A process for the preparation of pure sofosbuvir of Formula I

Formula I

comprising the steps of: i) reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl to obtain L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester;

ii) condensing L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester of step i) with 2'-deoxy-2'-fluoro-2'-C-methyluridine to obtain bromo-sofosbuvir; and

iii) hydrogenating bromo-sofosbuvir of step ii) to obtain pure sofosbuvir.

7. A process for the preparation of bromo-sofosbuvir of Formula III

Formula III

comprising the steps of:

i) reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl to obtain L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester; and

ii) condensing L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester of step i) with 2'-deoxy-2'-fluoro-2'-C-methyluridine to obtain bromo-sofosbuvir.

8. A process for the preparation of pure L-alanine, N-[(<S)-(4- bromophenoxy)(LG)phosphinyl]-, 1 -methylethyl ester, comprising a step of reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl.

9. The process according to claim 8, wherein pure L-alanine, N-[(<S)-(4- bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester is prepared in the presence of an organic base in a solvent.

10. The process according to claim 3, 4, or 6, wherein bromo-sofosbuvir is hydrogenated using hydrogen gas in the presence of a catalyst, and an organic base in a solvent.

11. The process according to claim 10, wherein the catalyst is Pd/C.

12. The process according to claim 3, 4, or 6, wherein the hydrogenation of bromo- sofosbuvir is carried at a hydrogen pressure of about 0.5 bar to about 3.0 bar.

13. The process according to claim 6 or 7, wherein L-alanine, N-[(<S)-(4- bromophenoxy)(LG) phosphinyl]-, 1-methylethyl ester is condensed with 2'-deoxy- 2'-fluoro-2'-C-methyluridine in the presence of a Lewis acid and an organic base in a solvent.

14. The process according to claim 13, wherein the Lewis acid is selected from the

group consisting of zinc chloride, zinc bromide, magnesium chloride, magnesium bromide, copper (II) chloride, and copper (II) bromide.

15. The process according to claim 5, 9, 10, or 13, wherein the organic base is selected from the group consisting of pyridine, trimethylamine, triethylamine, diethylamine, diisopropylethylamine, imidazoles, triethanolamine, morpholine, and N-methyl morpholine.

16. The process according to claim 9, 10, or 13, wherein the solvent is selected from the group consisting of tetrahydrofuran, tetrahydropyran, dichloromethane, ethyl acetate, diethyl ether, diisopropyl ether, methyl tert-butyl ether, and 1,4-dioxane.

17. The process according to claim 6, 7, or 8, wherein LG is a leaving group.

18. The process according to claim 6, 7, or 8, wherein H-LG is a hydrogen-protected leaving group.

19. The process according to claim 17 or 18, wherein the leaving group is selected from the group consisting of tosylate, mesylate, trifluoroacetate, pentafluorophenoxide, 4- nitrophenoxide, 2,4-dinitrophenoxide, lH-benzotriazol-l-olate, 2,5-dioxopyrrolidin- 1-olate, tetrazol-l-ide, 5-methoxy-lH-benzimidazole-2-thiolate, and 1H- benzimidazole-2-thiolate.

20. The process according to claim 6, 7, or 8, wherein 4-bromophenyl

phosphorodichloridate is prepared by reacting 4-bromophenol with phosphoryl trichloride.

21. The process according to claim 8, wherein pure L-alanine, N-[(<S)-(4- bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester has a purity of more than 99.7%.

22. A pharmaceutical composition comprising pure sofosbuvir and one or more pharmaceutically acceptable carriers, diluents, or excipients.

23. A method of treating hepatitis C infection in a patient in need thereof comprising administering pure sofosbuvir.

Description:
PROCESS FOR THE PREPARATION OF PURE SOFOSBUVIR

Field of the Invention

The present invention provides pure sofosbuvir and a process for the preparation of pure sofosbuvir and its intermediates.

Background of the Invention

Sofosbuvir is chemically designated as (<S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5- (2,4-dioxo-3 ,4-dihydropyrimidin- 1 (2H)-yl)-4-fluoro-3 -hydroxy-4-methyltetrahydrofuran- 2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate depicted by Formula I.

Formula I

Sofosbuvir is indicated for the treatment of chronic hepatitis C infection.

U.S. Patent Nos. 7,964,580, 8,334,270, 8,580,765, and 9,085,573 disclose sofosbuvir and processes for the preparation of sofosbuvir analogs.

U.S. Patent No. 8,642,756 discloses a process for the preparation of sofosbuvir comprising reacting isopropyl-alanate, di-halo-phenylphosphate, 2'-deoxy-2'-fluoro-2'-C- methyluridine and a base.

U.S. Patent No. 8,629,263 discloses a diastereomerically pure isopropyl-alanyl- phosphoramidate, an intermediate used for the preparation of sofosbuvir.

U.S. Patent No. 9,090,642 discloses a process for the separation of

diastereomerically pure phosphoramidates. The process comprises dissolving racemic phosphorus atom containing phosphoramidate in a suitable solvent and inducing crystallization by addition of acyclic/cyclic hydrocarbons. U.S. Publication No. 2014/0205566 discloses L-alanine, N-[(5)-(4- chlorophenoxy)(2,3,4,5,6-pentafluorophenoxy)phosphinyl]-, 1-methylethyl ester.

U.S. Publication No. 2015/0232501 discloses L-alanine, N-[(4- halophenoxy)(2,3,4,5,6-pentafluorophenoxy)phosphinyl]-, 1-methylethyl ester.

There is a need for an alternate and improved process for the preparation of pure sofosbuvir. The present invention provides an efficient and industrially feasible process for the preparation of pure sofosbuvir. The present invention also provides a process for the preparation of pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester and its use for the preparation of pure sofosbuvir.

Summary of the Invention

The present invention provides pure sofosbuvir.

The present invention also provides pure sofosbuvir produced by a process comprising hydrogenation of bromo-sofosbuvir in the presence of an organic base.

The present invention also provides a process for the preparation of pure sofosbuvir comprising hydrogenation of bromo-sofosbuvir in the presence of an organic base.

The present invention also provides a process for the preparation of pure sofosbuvir, comprising the steps of:

i) reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl to obtain L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester;

ii) condensing L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester of step i) with 2'-deoxy-2'-fluoro-2'-C-methyluridine to obtain bromo-sofosbuvir; and

iii) hydrogenating bromo-sofosbuvir of step ii) to obtain pure sofosbuvir.

The present invention also provides a process for the preparation of bromo- sofosbuvir, comprising the steps of:

i) reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl to obtain L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester; and ii) condensing L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester of step i) with 2'-deoxy-2'-fluoro-2'-C-methyluridine to obtain bromo-sofosbuvir.

The present invention also provides a process for the preparation of pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester comprising a step of reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl.

The present invention also provides a pharmaceutical composition comprising pure sofosbuvir and one or more pharmaceutically acceptable carriers, diluents, or excipients.

The present invention also provides a method of treating hepatitis C infection in a patient in need thereof comprising administering pure sofosbuvir.

Detailed Description of the Invention

Various embodiments and variants of the present invention are described hereinafter.

The term "about," as used herein, refers to any value which lies within the range defined by a variation of up to ±10% of the value.

The term "reduced sofosbuvir," as used herein, refers to (<S)-isopropyl 2-((<S)- (((2i?,3i?,4i?,5i?)-5-(2,4-dioxotetrahydropyrimidin-l(2H)-yl )-4-fluoro-3-hydroxy-4- methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino )propanoate depicted by Formula II.

Formula II

The term "bromo-sofosbuvir," as used herein, refers to (<S)-isopropyl 2-((5)- (((2i?,3i?,4i?,5i?)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)- yl)-4-fluoro-3-hydroxy-4- methyltetrahydrofuran-2-yl)methoxy)-(4-bromo-phenoxy)phospho rylamino)propanoate depicted by Formula III.

Formula III

The term "LG," as used herein, refers to a leaving group selected from the group consisting of tosylate, mesylate, trifluoroacetate, pentafluorophenoxide, 4-nitrophenoxide, 2,4-dinitrophenoxide, lH-benzotriazol-l-olate, 2,5-dioxopyrrolidin-l-olate, tetrazol-l-ide, 5-methoxy- lH-benzimidazole-2-thiolate, and lH-benzimidazole-2-thiolate.

The term "H-LG," as used herein, refers to a hydrogen-protected leaving group

(LG).

The term "base," as used herein, refers to organic bases and inorganic bases.

Examples of organic bases include pyridine, trimethylamine, triethylamine, diethylamine, diisopropylethylamine, imidazoles, triethanolamine, morpholine, and N-methyl morpholine. Examples of inorganic bases include sodium hydride, ammonium hydroxide, sodium carbonate, sodium hydroxide, potassium hydroxide, magnesium hydroxide, dipotassium hydrogen orthophosphate, magnesium carbonate, sodium carbonate, and potassium carbonate.

The term "treating," as used herein, includes adding, dissolving, slurrying, stirring, and combinations thereof.

The term "hydrogenation," as used herein, refers to treatment with hydrogen.

Pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester refers to L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester having chromatographic (HPLC) purity of more than 99.7%.

The term "pure sofosbuvir," as used herein, refers to sofosbuvir having a content of "reduced sofosbuvir" which is not more than 0.01% and/or a content of "bromo- sofosbuvir" which is not more than 0.3%. The term "isolating," as used herein, includes precipitation, cooling, filtration, concentration, centrifugation, or combinations thereof.

A first aspect of the present invention provides pure sofosbuvir of Formula I

Formula I

having a content of "reduced sofosbuvir" of Formula II, which is not more than 0.01% and/or that of "bromo-sofosbuvir" of Formula III, which is not more than 0.3%.

Formula II

Formula III

A second aspect of the present invention provides pure sofosbuvir of Formula I

Formula I

produced by a process comprising hydrogenation of bromo-sofosbuvir of Formula III.

Formula III

According to one embodiment of this aspect, the process of hydrogenating bromo- sofosbuvir is carried out in the presence of an organic base.

A third aspect of the present invention provides a process for the preparation of pure sofosbuvir of Formula I

Formula I

comprising hydrogenation of bromo-sofosbuvir of Formula III in the presence of an organic base.

Formula III

A fourth aspect of the present invention provides a process for the preparation of pure sofosbuvir of Formula I,

Formula I

comprising the steps of:

i) reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl to obtain L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester;

ii) condensing L-alanine, N-[(5)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester of step i) with 2'-deoxy-2'-fluoro-2'-C-methyluridine to obtain bromo-sofosbuvir; and

iii) hydrogenating bromo-sofosbuvir of step ii) to obtain pure sofosbuvir.

A fifth aspect of the present invention provides a process for the preparation of bromo-sofosbuvir of Formula III,

Formula III

comprising the steps of:

i) reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl to obtain L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester; and

ii) condensing L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester of step i) with 2'-deoxy-2'-fluoro-2'-C-methyluridine to obtain bromo-sofosbuvir.

A sixth aspect of the present invention provides a process for the preparation of pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester, comprising a step of reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl.

L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester is prepared by reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-Z- alanine ester.HCl.

The preparation of 4-bromophenyl phosphorodichloridate is carried out by reacting 4-bromophenol with phosphoryl trichloride in the presence of diethylamine.HCl or triethylamine.HCl. The reaction mixture is maintained at a temperature of about 90°C to about 125°C, for a period of about 5 hours to about 7 hours.

4-Bromophenyl phosphorodichloridate is isolated by filtration, decantation, extraction, distillation, evaporation, chromatography, precipitation, concentration, crystallization, centrifugation, or recrystallization, and dried under reduced pressure, by air drying, or vacuum tray drying. The preparation of L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester is carried out by reacting 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L-alanine ester.HCl in the presence of an organic base in a solvent.

The solvent is selected from the group consisting of tetrahydrofuran,

dichloromethane, ethyl acetate, diethyl ether, diisopropyl ether, methyl tert-butyl ether, and 1,4-dioxane.

The addition of 4-bromophenyl phosphorodichloridate, H-LG, and isopropyl-L- alanine ester.HCl is carried out at a temperature of about -40°C and below.

L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester is isolated by treating with an organic solvent.

The organic solvent is selected from the group comprised of ethers, acyclic/cyclic hydrocarbons, and mixtures thereof.

Examples of ethers include methyl tert-butyl ether, diisopropyl ether, cyclopropyl methyl ether and diethyl ether. Examples of acyclic/cyclic hydrocarbons include pentane, hexane, heptane, cyclopentane, cyclohexane and cycloheptane.

The reaction mixture of L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester and an organic solvent is heated at a temperature of about 50°C to about 70°C, followed by cooling to a temperature of about 20°C to about 25°C.

The isolation of pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1- methylethyl ester is carried out by heating Z-alanine, N-[(<S)-(4- bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester in diisopropyl ether (DIPE) at a temperature of about 50°C to about 70°C, followed by cooling to a temperature of about 20°C to about 25 °C.

The isolation of pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG) phosphinyl]-, 1- methylethyl ester is further carried out by filtration, followed by washing, and then drying under vacuum at a temperature less than 40°C for about 6 hours.

Pure L-alanine, N-[(<S)-(4-bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester wherein LG is 2,3,4,5,6-pentafluorophenoxy group, has a purity of more than 99.7%.

Bromo-sofosbuvir is prepared by condensing L-alanine, N-[(<S)-(4- bromophenoxy)(LG)phosphinyl]-, 1-methylethyl ester with 2'-deoxy-2'-fluoro-2'-C- methyluridine in the presence of a Lewis acid and an organic base in a solvent. The Lewis acid is selected from the group consisting of zinc chloride, zinc bromide, magnesium chloride, magnesium bromide, copper (II) chloride, and copper (II) bromide. More preferably, the Lewis acid is magnesium chloride.

The solvent is selected from the group consisting of tetrahydrofuran,

tetrahydropyran, dichloromethane, ethyl acetate, diethyl ether, diisopropyl ether, methyl tert-butyl ether, and 1,4-dioxane.

The preparation of bromo-sofosbuvir is carried out at a temperature of about 25 °C to about 50°C, for example, at about 35°C to about 40°C.

The preparation of bromo-sofosbuvir is carried out for about 2 hours to about 7 hours, for example, for about 3 hours to about 5 hours.

Bromo-sofosbuvir is isolated by filtration, decantation, extraction, distillation, evaporation, chromatography, precipitation, concentration, crystallization, centrifugation, or recrystallization, and dried under reduced pressure, by air drying, or vacuum tray drying.

The hydrogenation of bromo-sofosbuvir to obtain pure sofosbuvir is carried out in the presence of hydrogen gas, an organic base, and a catalyst in a solvent.

The catalyst is a metal catalyst, for example, platinum, palladium, nickel, or rhodium. More preferably, the catalyst is palladium/carbon (Pd/C). The preferable concentration ratio of the Pd/C catalyst with respect to bromo-sofosbuvir is about 3% to about 10%. The Pd/C catalyst is optionally mixed with water and then added into the reaction mixture.

The solvent is selected from the group consisting of tetrahydrofuran,

tetrahydropyran, dichloromethane, ethyl acetate, diethyl ether, diisopropyl ether, methyl tert-butyl ether, and 1,4-dioxane.

The hydrogenation of bromo-sofosbuvir is carried out at a hydrogen pressure of about 0.5 bar to about 3.0 bar.

The hydrogenation of bromo-sofosbuvir is carried out at a temperature of about 15°C to about 35°C, for example, at about 20°C to about 25°C.

The hydrogenation of bromo-sofosbuvir is carried out for about 5 hours to about 10 hours, for example, for about 6 hours to about 7 hours. The pure sofosbuvir is isolated by filtration, decantation, extraction, distillation, evaporation, chromatography, precipitation, concentration, crystallization, centrifugation, or recrystallization, and dried under reduced pressure, by air drying, or vacuum tray drying.

A seventh aspect of the present invention provides a pharmaceutical composition comprising pure sofosbuvir and one or more pharmaceutically acceptable carriers, diluents, or excipients.

An eighth aspect of the present invention provides a method of treating hepatitis C infection in a patient in need thereof comprising administering pure sofosbuvir.

While the present invention has been described in terms of its specific aspects and embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended within the scope of the present invention.

Method:

The High Performance Liquid Chromatography (HPLC) instrument used for detecting chromatographic purity of L-alanine, N-[(<S)-(4-bromophenoxy)(2,3,4,5,6- pentafluorophenoxy)phosphinyl]-, 1-methylethyl ester is a Waters ® Alliance ® HPLC with a Waters ® 2996 PDA detector. The HPLC column is a Daicel ® Chiralpak ® IA ® (250x4.6 mm), 5μπι.

The HPLC instrument used for detecting chromatographic purity of sofosbuvir is a Waters ® Alliance ® HPLC with a Waters ® 2996 PDA detector. The HPLC column is an ACE ® C18 PFP (250x4.6 mm) or a YMC-Triart C18 (250x4.6 mm), 5μιη.

The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention in any way.

EXAMPLES

Example 1 : Preparation of pure sofosbuvir

Stage 1: Preparation of 4-bromophenyl phosphorodichloridate:

Phosphoryl trichloride (POCb, 619.2 g) and diethylamine.HCl (EtiNH.HCl, 15.8 g) were charged into a flask at 20°C to 25°C to obtain a reaction mass. The reaction mass was heated to 105°C to 110°C, followed by the slow addition of a 4-bromophenol solution (prepared by dissolving 500 g of 4-bromophenol in 1000 mL of toluene at 40°C to 45°C) over a period of 6 hours to 7 hours at 105°C to 110°C. The reaction mixture was maintained at 105°C to 110°C for 5 hours while stirring. Toluene and excess POCb were distilled out under vacuum at a temperature of less than 60°C. The title product was distilled out under high vacuum (-10 mm/Hg) at a temperature of 100°C to 110°C.

Yield: 440.1 g

Stage 2: Preparation of L-alanine, N-[( )-(4-bromophenoxy)(2,3,4,5,6- pentafluorophenoxy) phosphinyl]-, 1-methylethyl ester:

This reaction stage was performed in the presence of a nitrogen atmosphere. Dichloromethane (600 mL) and 4-bromophenyl phosphorodichloridate (30 g, obtained from stage 1) were charged into a flask at 20°C to 25 °C to obtain a reaction mass. The reaction mass was cooled to -60°C to -50°C, and then isopropyl-L-alanine ester.HCl (17.33 g) was added while stirring. A triethylamine solution (prepared by dissolving 20.94 g of triethylamine in 60 mL of dichloromethane) was slowly added to the reaction mixture over a period of 1 hour at -60°C to -50°C, and the mixture was maintained at this temperature for 2 hours while stirring. A pentafluorophenol solution (prepared by dissolving 17.13 g of pentafluorophenol in 60 mL of dichloromethane) was added to the reaction mixture at -60°C to -50°C over a period of 15 minutes while stirring. A triethylamine solution (prepared by dissolving 10.45 g of triethylamine in 60 mL of dichloromethane) was slowly added to the reaction mixture over a period of 1 hour at -60°C to -50°C, and the reaction mixture was maintained at -60°C to -50°C for 1 hour while stirring. The temperature of the reaction mixture was raised to 20°C to 25 °C, and the mixture was maintained at this temperature for 1 hour while stirring. The reaction mixture was washed with deionized water (3 x300 mL), followed by washing with a 3% aqueous NaHCCb solution (2x 150 mL), and then with deionized water (300 mL).

Dichloromethane was distilled out from the reaction mixture at a temperature of less than 30°C under vacuum to obtain a residue. Diisopropyl ether (DIPE, 60 mL) was charged to the residue at 20°C to 25°C, and then the mixture was heated to 50°C to 55°C, and maintained at 50°C to 55°C for 30 minutes to obtain a clear solution. The clear solution was cooled to 20°C to 25 °C and maintained at this temperature for 1 hour. The solid obtained was filtered, and the wet solid (22.9 g) was then washed with DIPE (30 mL).

DIPE (45 mL) and above -obtained solid (22.5 g) were charged into a flask at 20°C to 25°C, and the mixture was heated to 50°C to 55°C. The mixture was maintained at 50°C to 55°C for 30 minutes. The mixture was cooled to 20°C to 25 °C, and was then stirred at this temperature for 2 hours to obtain a solid. The solid was filtered, then washed with DIPE (22.5 mL), and then dried under vacuum at a temperature less than 40°C for 6 hours to obtain the title product.

Yield: 9.1 g

Chromatographic purity (HPLC): 99.90 %

Stage 3: Preparation of bromo-sofosbuvir

Tetrahydrofuran (THF, 80 mL), 2'-deoxy-2'-fluoro-2'-C-methyluridine (4 g), anhydrous magnesium chloride (4.38 g), and L-alanine, N-[(<S)-(4- bromophenoxy)(2,3,4,5,6-pentafluorophenoxy) phosphinyl]-, 1-methylethyl ester (8.59 g, obtained from stage 2) were charged into a flask at 20°C to 25°C while stirring to obtain a reaction mass. The reaction mass was heated to 35°C to 40°C. A diisopropyl ethyl amine (DIPEA) solution (1.99 g DIPEA dissolved in 20 mL of THF) was slowly added to the reaction mass over a period of 1 hour to 2 hours at 35°C to 40°C while stirring. The reaction mass was maintained at 35°C to 40°C for 3 hours, followed by the addition of deionized water (12 mL), and then stirring for 10 minutes. THF was distilled out under vacuum at a temperature of less than 35°C. Dichloromethane (DCM, 100 mL) was charged into the reaction mass at 20°C to 25°C. The reaction mass was washed with a 0.5N HQ solution (3 x40 mL), and then washed with a 2.5N aqueous NaiCC solution (3 x40 mL), followed by deionized water (3 χ 40 mL). Dichloromethane was distilled out under vacuum at a temperature of less than 30°C. DIPE (40 mL) was charged to the residue at 20°C to 25°C, and the mixture was stirred at this temperature for 2 hours. The solid was filtered, and then washed with DIPE (8 mL). The wet solid was dried under vacuum at a temperature less than 35 °C for 3 hours to obtain the title product.

Yield: 4.1 g

Chromatographic Purity (HPLC): 86.86%

Stage 4: Preparation of sofosbuvir from bromo-sofosbuvir:

Isopropyl alcohol (IPA, 70 mL), bromo-sofosbuvir (3.5 g, obtained from stage 3), and dry Pd/C (5% Pd/C, 0.35 g) were charged into a Parr ® Shaker cylinder at 20°C to 25 °C. The reaction mixture was maintained under hydrogen gas pressure (3 kg/cm 2 ) at 20°C to 25 °C for 10 hours. The reaction mass was filtered through a Hyflo ® , and then the bed was washed with IPA (10 mL). IPA was distilled out from the filtrate under vacuum at a temperature of less than 35°C. Dichloromethane (105 mL) was added to the residue at 20°C to 25 °C, and was then washed with deionized water (3 x35 mL). Dichloromethane was distilled out under vacuum at a temperature of less than 30°C. Dichloromethane (35 mL) was again charged to the residue at 20°C to 25 °C, and then the mixture was heated to reflux at 35°C to 40°C. The reaction mixture was maintained under reflux for 30 minutes, and was then cooled to 20°C to 25 °C, followed by stirring for 30 minutes. DIPE (14 mL) was charged to the reaction mixture at 20°C to 25 °C, and the mixture was stirred at this temperature for 16 hours. The solid obtained was filtered, and the wet solid was washed with a mixture of dichloromethane and DIPE (1 : 1 mixture ratio, 7 mL), and then dried under vacuum at a temperature less than 35°C for 2 hours to obtain the title product.

Yield: 1.8 g

Chromatographic purity (HPLC): 98.54 %

Bromo-sofosbuvir: 0.22%

Stage 5: Purification of sofosbuvir:

Dichloromethane (45 mL) and sofosbuvir (1.5 g, as obtained from stage 4) were charged into a flask at 20°C to 25 °C to obtain a reaction mixture. The reaction mixture was heated to reflux at 40°C, and then stirred under reflux for 30 minutes to obtain a clear solution. The clear solution was filtered through a Hyflo ® , and then the bed was washed with dichloromethane (7.5 mL). Dichloromethane was distilled out from the filtrate (15 mL to 18 mL), and stirred at 20°C to 25 °C for 3 hours. The solid was filtered, and then washed with dichloromethane (3 mL). The wet solid obtained was dried under vacuum at a temperature less than 35°C for 2 hours to obtain the title product.

Yield: 0.86 g

Chromatographic purity (HPLC): 99.64 %

Bromo-sofosbuvir: 0.16%

Example 2: Preparation of sofosbuvir

Bromo-sofosbuvir (50 g, obtained by following Example 1, stage 3) was charged into tetrahydrofuran (THF, 500 mL) followed by the addition of sodium bicarbonate (20.7 g). The resulting reaction mixture was stirred at 25 °C for about 10 minutes. Dry Pd/C (10 g, 2.5% Pd/C) was added into the reaction mixture under a nitrogen atmosphere at 25°C. The reaction vessel was flushed with THF (500 mL), and then stirred for 10 minutes at 25°C. The temperature of the reaction mixture was raised to 28°C to 30°C with stirring, and then hydrogen gas was flushed twice into the reaction mixture.

The reaction mixture was hydrogenated with a hydrogen pressure of 3.0 bar to 3.5 bar [about 50 pounds per square inch (PSI)] at 28°C to 30°C for 10 hours. The progress of the reaction was monitored by high performance liquid chromatography (HPLC). After 10 hours, the reaction mixture was cooled to 25°C and filtered through a Hyflo ® bed. The filtrate was concentrated under reduced pressure at 38°C to 40°C to obtain a residual foamy solid residue (42.5 g).

The solid residue (42.5 g) was dissolved in IPA (150 mL) at 40°C to 45°C to obtain a clear solution. The clear solution was filtered through a 0.45 micron filter, and then the filtrate was transferred to a round-bottom flask, and then flushed with IPA (100 mL). The solution was stirred at 40°C to 45°C for 10 minutes to 15 minutes. N-Heptane (500 mL) was slowly added to the stirred solution at 40°C to 45°C over a period of 60 minutes to 90 minutes, and then the mixture was gradually cooled to 25 °C with stirring for 4 hours to 5 hours. The thick slurry so obtained was filtered under vacuum. The filter cake was washed with a mixture of IPA and n-heptane (1:2, 100 mL). The wet solid obtained was dried under suction for 20 minutes to 30 minutes, and then dried under vacuum at 35°C to 40°C for 1 hour to 2 hours to obtain a white solid compound (24.2 g, sofosbuvir).

Sofosbuvir (24 g) was dissolved in IPA (96 mL) at 40°C to 45°C to obtain a clear solution. The clear solution was filtered through a 0.45 micron filter, and then the filtrate was transferred to a round-bottom flask, and then flushed with IPA (24 mL). The solution was stirred at 40°C to 45 °C for 15 minutes to 20 minutes. N-Heptane (240 mL) was slowly added to the stirred solution at 40°C to 45°C over a period of 60 minutes to 90 minutes, and then the mixture was gradually cooled to 25°C with stirring for 2 hours to 3 hours. The thick slurry so obtained was filtered under vacuum. The filter cake was washed with a mixture of IPA and n-heptane (1 :2, 48 mL). The wet solid obtained was dried under suction for 15 minutes to 20 minutes, and then dried under vacuum at 35°C to 40°C for 6 hours to 8 hours to afford the title compound as a white solid.

Yield: 18.6 g

Chromatographic purity: 97.95% Reduced sofosbuvir: 2.01%

Example 3 : Preparation of pure sofosbuvir

Bromo-sofosbuvir (15 g, obtained by following Example 1, stage 3) was charged into THF (100 mL) at 25°C to obtain a reaction mixture. Dry Pd/C (0.75 g, 2.5% Pd/C) mixed in water (0.75 mL) was added into the reaction mixture under a nitrogen atmosphere at 20°C to 25°C. The reaction vessel was flushed with THF (50 mL), and then diisopropyl ethylamine (4.8 g) was added into the reaction mixture at 20°C to 25 °C with stirring. Hydrogen gas was flushed twice into the reaction mixture. The reaction mixture was hydrogenated with a hydrogen pressure of 1.0 bar to 1.5 bar (about 15 PSI to 22 PSI) at 20°C to 25 °C for 7 hours. The reaction mixture was cooled to 25 °C, and then the mixture was filtered through a Hyflo ® bed, followed by washing with THF (50 mL). The combined filtrate was concentrated under reduced pressure to afford a foamy solid residue (14.5 g).

The foamy solid residue (14.5 g) was dissolved in IPA (75 mL) at 35°C to 40°C to obtain a clear solution. The temperature of the solution was raised to 40°C to 45°C, and then the solution was stirred at 40°C to 45°C for 10 minutes to 15 minutes. N-Heptane (150 mL) was slowly added to the stirred solution at 40°C to 45°C over a period of 60 minutes to 90 minutes. The mixture was gradually cooled to 25°C, and then stirred for 15 hours to 16 hours. The thick slurry obtained was filtered under vacuum. The filter cake was washed with a mixture of IPA and n-heptane (1 :2, 30 mL). The obtained solid was dried under vacuum at 35°C to 40°C for 8 hours to afford the title compound as a white solid.

Yield: 8.0 g

Chromatographic purity: 99.81%

Reduced sofosbuvir: 0.01%