FIELD OF THE INVENTION

The present invention relates to an improved process for the preparation of sofosbuvir. The present invention involves use of reagents that are less expensive, easier to handle and environmental friendly process.

BACKGROUND OF THE INVENTION

Sofosbuvir (formerly PSI-7977 or GS-7977) is an approved drug for the treatment of hepatitis C. It was discovered at Pharmasset and then acquired for development by Gilead Sciences. Sofosbuvir is a prodrug that is metabolized to the active antiviral agent 2'-deoxy-2'-a-fluoro-B-C- methyluridine-5'-monophosphate. It is a nucleotide analogue inhibitor of the hepatitis C virus (HCV) polymerase.

Nucleoside phosphoramidate are inhibitors of RNA-dependent, RNA viral replication and are useful as inhibitors of HCV NS5B polymerase, as inhibitors of HCV replication and for treatment of hepatitis C infection in mammals. Sofosbuvir is chemically known as Isopropyl (2S)-2-[[[(2R, 3R, 4R, 5R)-5-(2, 4-dioxopyrimidin- 1 -yl)-4-fluoro-3-hydroxy-4-methyl-tetrahydrofuran-2-yl] methoxy-phenoxy-phosphoryl] amino] propanoate of Formula (I-Sp).

(I)

Sofosbuvir was first described in Example 25 of U.S. Patent No. 7,964,580 B2, which corresponds to WO 2008/121634 A2 and also discloses other novel nucleoside phosphoramidates and their preparations and use as agents for treating viral diseases. wherein the process is disclosed, Compound of formula VI protected with benzoyl group in presence of benzoylchloride and pyridine base to obtained compound of formula V. followed by this on deprotected in presence of 80% AcOH under reflux conditions and Ammonia / methanol as a solvent to get a compound of formula III. Compound of formula III reacts with compound of formula Ila in presence of base and a solvent to get Diastereomeric mixture at "P" of (Sp & Rp Sofosbuvir this on chiral resolution by Supercritical Fluid Chromatography (SFC) using 20% MeOH in C0 ₂ as a solvent to get Sofosbuvir (I).

The process described herein leads to the production of nucleoside phosphoramidate prodrugs with less than 50% of the desired isomer, which requires additional purifications to get the desired isomer, which enhances the number of steps and cost. This reference does not provide a particular combination of solvents and bases which provides or increases the stereo selectivity during the reaction for the production of required Sp isomer.

The above process is schematically shown as below:

PCT publication no. WO 2011/123645 A2 discloses various crystalline forms and process for the preparation of (S)-isopropyl 2-(S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l-(2 H)- yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl) methoxy)(phenoxy) phosphoryl)amino)propanoate (Sofosbuvir) . Deprotection of compound of formula (V) in presence of 70% AcOH followed by hydrolyzing to obtained compound of formula III. This on reacted with compound of formula (II) in presence of Grignard reagent to get a Sofosbuvir.

Sofosbuvir (I)

According to the above prior art processes which involves the condensation reaction of compound of formula (III) with compound of formula (II) in presence of Grignard reagent causes low yield and high impurity profile.

Hence, the use of Grignard reagent may not feasible and it is not economical for industrial scale production for the preparation of Sofosbuvir (I).

PCT publication no. WO 2006/012440 A2, WO 2008/045419 Al, WO 2006/031725 A2 and US patent nos. 7,601,820 B2 and 8,492,539 B2, disclose process for the preparation of intermediates, which can be used for the preparation of sofosbuvir.

PCT publication no. WO 2010/135569 Al discloses various processes for the preparation of sofosbuvir and its intermediates. PCT publication no. WO 2014/08236 Al discloses process for the preparation of diastereomerically enriched phosphoramidate derivatives and WO 2014/047117 Al, CN103804446A and WO2014/056442 Al disclose various process for the preparation of intermediates and nucleoside phosphoramidates compounds.

In view of the foregoing, the present inventors have result of extensive studies, the efficiency is extremely only the condensation reaction of compound of formula (III) with the compound of formula (II) is carried out in presence of metallic salts, it was found that the corresponding Sofosbuvir can be produced in high yield and purity and it is desirable to provide a simple, efficient more economical and eco-friendly process for the preparation of sofosbuvir. The process of the present invention is simple, cost-effective, eco-friendly and commercially viable.

ADVANTAGES:

01) We can avoid Grignard reagents

02) We can avoid commercially non suitable temperatures -20°C to - 15°C

03) Reaction has been performed at room temp which is very easy in the commercial aspects.

04) Organic bases was used in the reaction. SUMMARY OF THE INVENTION

The present invention relates to an improved, commercially viable and industrially advantageous process for the preparation of Sofosbuvir.

In aspect of the present invention, provides an improved process for the preparation of Sofosbuvir (I), comprising the steps of: a) The compound of formula (V) is deprotected in presence of acidic conditions to obtain compound of formula (IV).

(V) (IV)

b) The product of step a) is hydrolyzing in presence of base and solvent to obtain compound of formula (III).

(III) c) The product of step b) is reacted with compound of formula (II) in presence of metallic salt, base and solvent to obtain compound of formula (I).

(II)

In yet another aspect of the present invention provides the process for the preparation of Sofosbuvir by condensing compound of formula (III) with compound of formula (II) in presence of metallic salt.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improved, commercially viable and industrially advantageous process for the preparation of Sofosbuvir. In an embodiment of the present invention relates to an improved process for the preparation of Sofosbuvir comprising the steps of: a) The compound of formula (V) is deprotected in presence of acidic conditions to obtain compound of formula (IV), b) The product of step a) is hydrolyzing in presence of base and solvent to obtain compound of formula (III). c) The product of step b) is reacted with compound of formula (II) in presence of metallic salt, base and solvent, and d) To obtain compound of formula (I).

In an embodiment of the present invention, wherein the compound of formula (V) is deprotected in presence of acidic conditions, under reflux conditions over night till completion of reaction, further it was cooled to 15°C and allow to stir and then raise the temperature to obtain compound of formula (IV);The obtain precipitated compound of formula(IV) was filtered, washed with solvent and dried to get desired product of formula(IV) and followed by hydrolysis in presence of base and solvent, allow to stir at 0°C for 30 min, warmed to room temperature slowly and it was stirred at same temperature for another 18-24 hours to obtain compound formula (III). The compound of formula (III) is reacted with compound of formula (II) in presence of metallic salt, base and solvent at room temperature under nitrogen atmosphere at 25-30°C and allow to stir for 2 - 6 hrs. at same temperature. The resultant solvent in reaction mixture was distilled out at suitable temperature and further it was purified with suitable solvents to isolate the Sofosbuvir of formula (I). According to the embodiment of the present invention, the deprotection is taken place in presence of suitable acids like trifluoroacetic acid, hydrochloric acid, sulphuric acid, methane sulphonic acid and acetic acid; most preferably acetic acid.

In an embodiment of the present invention, the bases are selected from bases like triethyl amine, diisopropylethylamine, diisopropylamine, pyridine and ammonia. Preferably triethyl amine (or) diisopropylethylamine In an embodiment of the present invention, the metallic salts are selected from magnesium chloride, magnesium bromide, magnesium iodide, lithium chloride, lithium bromide, lithium iodide, copper chloride, copper bromide, copper iodide etc., Preferably magnesium chloride,

According to preceding embodiments, the solvent which are used in the reactions is selected from acetone, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile and ethyl acetate, dichloromethane, methyl tertiary butyl ether, acetic acid, methanol, ethanol, isopropanol, water or mixtures thereof.

In an embodiment of the present invention is also provides purification process, which is done by using techniques like anti-solvent, recrystallization, filtration and evaporation. The solvent is used in the purification process is selected from diethyl ether, diisoprorpyl ether, MTBE (Methyl tertiary butyl ether), preferably MTBE.

Hence, the present inventors are concluded that condensation reaction of compound of formula (III) with compound of formula (II) is carried out in presence of metallic salts is industrial feasible, eco-friendly and commercially industrial applicable process for preparation of Sofosbuvir and its analogues.

The following examples illustrate the present invention, but should not be construed as limiting the scope of the invention.

EXAMPLES Example-1

Preparation of N ⁴ ,3 ' ,5 ' -dibenzoyl-2 ' -Deoxy-2 ' -fluoro-2 ' -C-meth yluridine : N ⁴ ,3',5'-tribenzoyl-2'-Deoxy-2'-fluoro-2'-C-methylcytidi ne (20 gm) was added to 80% aqueous acetic acid (1 liter) and refluxed for overnight till completion of reaction. After cooling and standing at room temperature (15°C), most of the product was precipitated and then filtered through a sintered funnel. The resultant precipitate was washed with water and co-evaporated with toluene to give a white solid of titled product. (Yield: 85-90 %) Example-2

Preparation of 2'-deoxy-2'-fluoro-2'-C-methyluridine:

To a solution of 3',5'-dibenzoyl-2'-Deoxy-2'-fluoro-2'-C-methyluridine (10 gm) in MeOH (120 mL) was added to a solution of saturated ammonia in MeOH (60 mL). The reaction mixture was stirred at 0°C for 30 min, warmed to room temperature slowly and then allow to stir for another 18 hours at same temperature. The solvent in the resultant mixture was evaporated under reduced pressure to give the residue, further it was recrystallized with methanol and water to afford pure compound of title product. (Yield: 50-60 %)

Example-3

Preparation of (S)-isoprpyl-2-(((R)-r(2, 3, 4, 5, 6-pentafluoro-phenoxy)-phenoxy-phosphoryl aminolpropanoate :

To a 2 L of three-necked round bottom flask fitted with a mechanic stirrer and low temperature thermometer were added 30 g of phenyl dichlorophosphate and 300 mL of anhydrous dichloromethane. The solution was cooled to 0°C under nitrogen atmosphere and iso-propyl alanate hydrochloride salt (23.5 g ) was added quickly as a solid. The mixture was stirred and cooled to -55°C in a dry ice-acetone bath. A solution of 31 g of triethylamine in 150 mL of dichloromethane was added through an addition funnel over 70 minutes. The white cloudy mixture was stirred at -55°C for half hour and then the temperature was raised to -5°C. slowly over 1.5 h. A pre-cooled mixture of pentafluorophenol and triethylamine in 100 mL of dichloromethane was added to the mixture via an addition funnel over 1 hour at 0° C and the resulting mixture was stirred at 0°C for 4 hours. The white precipitate (TEA.HC1) was filtered out and rinsed with dichloromethane. The filtrate was concentrated under reduced pressure and white solid residue was triturated in 880 mL of t-butyl methyl ether (TBME) at room temperature for one hour. White suspension was filtered and solid was rinsed with TBME. Solid was distributed in a mixture of ethyl acetate and water. Organic layer was separated and washed with water. Organic layer was dried over MgS0 ₄ and concentrated to afford as a white feather solid. The obtain solid was dissolved in ethyl acetate, further the solution was washed with water/ brine and dried over MgS0 ₄ . The resultant solution was concentrated under reduced pressure to obtained title compound.

(Yield: 70-80 %)

Example-4 Preparation of Sofosbuvir:

To a 4 L of four-necked round bottom flask fitted with a mechanical stirrer and low temperature thermometer were added lOOgm of uridine intermediate and 1500ml of Tetrahydrofuran (THF) and stir for 5-10 min under nitrogen atmosphere at 25-30°C, further added 54.8gm of MgC and stir for 2 hours, followed by slow addition of 261.0 gm of phosphramide intermediate and stir for 8-lOhrs at same temperature. After complies the reaction (checked by HPLC), distilled out THF completely at below 45°C and allow to cool the reaction mass at 25-30°C, added 1.0 Lit dichloromethane and 1.0 Lit of Aqueous ammonium chloride solution in to reaction mass, stirred at room temperature to separate the layers.

The obtain organic layer was distilled out completely to get a residue, followed by addition of 300 mL of MDC & 300 mL MTBE and Stir for 6 hrs. at 25-30°C and then cooled to 10-15°C and stir for 2hrs. The resultant precipitated material was filtered, washed with mixture of dichloromethane and MTBE (1: 1) and dried under vacuum for 15 min at 50- 60°C to isolate the title product (Yield: 70-80 %)

Example-5

Preparation of Sofosbuvir:

To a 4 L of four-necked round bottom flask fitted with a mechanical stirrer and low temperature thermometer were added lOOgm of uridine intermediate and 1500 mL of Tetrahydrofuran (THF) and stir for 5-10 min under nitrogen atmosphere at 25-30°C, further added 54.8gm of LiC and stir for 2 hours, followed by slow addition of 261.0 gm of phosphramide intermediate and stir for 8-10 hrs. at same temperature. After complies the reaction (checked by HPLC), distilled out THF completely at below 45°C and allow to cool the reaction mass at 25-30°C, added 1.0 Lit dichloromethane and 1.0 Lit of Aqueous ammonium chloride solution into reaction mass, stirred at room temperature to separate the layers.

The obtain organic layer was distilled out completely to get a residue, followed by addition of 300 mL of MDC & 300 mL MTBE and Stir for 6 hrs. at 25-30°C and then cooled to 10-15°C and stir for 2hrs. The resultant precipitated material was filtered, washed with mixture of dichloromethane and MTBE (1: 1) and dried under vacuum for 15 min at 50- 60°C to isolate the title product

(Yield: 60-70 %)