WO2016035006A1

WO2016035006A1 - Novel nucleotide analogs, process for the preparation of sofosbuvir and its analogs, novel forms of sofosbuvir and solid dispersion of sofosbuvir

Info

Publication number: WO2016035006A1
Application number: PCT/IB2015/056629
Authority: WO
Inventors: Pallavi Rao; Srinivas ORUGANTI; Vilas Hareshwar Dahanukar; Ramesh Chakka; Rakeshwar Bandichhor; Abhishek Sud; Pramod Sambhaji CHAUDHARI; Venkata Krishna Rao Badarla; Kiran Kumar Doniparthi; Ramanaiah CHENNURU; Vishweshwar Peddy; Sunitha Vyala
Original assignee: Dr. Reddy’S Laboratories Limited
Priority date: 2014-09-01
Filing date: 2015-09-01
Publication date: 2016-03-10

Abstract

Aspects of the present application relate to novel nucleotide analogs, their use in the preparation of nucleoside phosphoramidates, (2R)-2-deoxy-2-fluoro-2-C- methyl-D-ribofuranose compounds, their use in the preparation of nucleoside phosphoramidates, stereoselective preparation of sofosbuvir, crystalline polymorph, cocrystal of sofosbuvir, processes for their preparation, amorphous solid dispersion of sofosbuvir and processes for the preparation of amorphous sofosbuvir.

Description

NOVEL NUCLEOTIDE ANALOGS, PROCESS FOR THE PREPARATION OF SOFOSBUVIR AND ITS ANALOGS, NOVEL FORMS OF SOFOSBUVIR AND

SOLID DISPERSION OF SOFOSBUVIR

INTRODUCTION

Sofosbuvir is one of the nucleoside phosphoramidate prodrugs which chemically described as (S)-lsopropyl 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. It has the structure of Formula A.

Formula A

Sofosbuvir is an orally administrable, direct-acting antiviral agent against the hepatitis C virus which is approved in USA for the treatment of subjects with HCV genotype 1 , 2, 3 or 4 infections. U.S. Patent No. 7, 964, 580 B2 discloses sofosbuvir and process for its preparation. The process described in this patent involves reaction of suitably substituted phophochloridate (racemic at phosphorous) with a nucleoside analog in the presence of anhydrous aprotic solvent such as tetrahydrofuran, dioxane in presence of a base such as N-methylimidazole, collidine, pyridine, 2,6-lutidine, 2,6-tBu-pyridine, etc. or a tertiary amine base, such as trimethylamine, diisoproylethyl amine etc. 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 the required Sp isomer.

U.S. Patent No. 8,642,756 B2 describes the preparation of sofosbuvir by reacting a mixture of isopropyl-alanate, di-LG-phenylphosphate and 2-deoxy-2- fluoro-2-C-methyluridine. The same patent describes another process wherein isopropyl-alanyl-phosphoramidate is reacted with 3'-0- protected or unprotected 2- deoxy-2-fluoro-2-C-methyluridine to produce sofosbuvir. Further, it describes a process for preparation of deuterated sofosbuvir from phosphorochloridate and deuterated nucleoside in THF by using N-methylimidazole as a base. The obtained product is having 1 :1 ratio of diastereomers.

WO2014008236A1 describe processes for preparing diastereomerically enriched nucleoside phosphoramidate compounds wherein 1 -(3-fluoro-4-hydroxy-5- (hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione allowed to react with (2S)-isopropyl 2-(hydroxy(phenoxy)phosphorylamino)propanoate or its salt in the presence of an activator, a base, and an optional additive to give sofosbuvir. In the similar way many other compounds were prepared.

U.S. Patent No. 7,429,572 B2 describes (2R)-2-Deoxy-2-Fluoro-2-C-Methyl- D-Ribofuranose compounds, (2R)-2-Deoxy-2-Fluoro-2-C-Methyl-D-Ribofuranose nucleosides, processes for preparation, compositions and their use in treating a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection in a host, including animals, and especially in humans.

U.S. Patent No. 8,618,076 B2 describes six polymorphic forms of sofosbuvir. This patent describes Form 1 , Form 2, Form 3, Form 4, Form 5, Form 6 and amorphous form and their processes for preparation by using different solvents. CN104277088A, CN1 04130302A & CN104447924A also describe different crystalline forms of sofosbuvir.

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.

Polymorphs are different solids having the same molecular structure, yet having distinct physical properties when compared to other polymorphs of the same molecular 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.

On the other hand, the formation of pharmaceutically acceptable co-crystals of active pharmaceutical ingredients provides an alternative approach to the generation of new solid forms of the active substance. In this context a co-crystal, or alternatively co-crystal, is understood to be a binary molecular crystal containing the molecules of the API together with another molecular species in a defined stoichiometric ratio where both components are in their neutral state.

A widely accepted definition of a pharmaceutical cocrystal is a crystalline system containing an active pharmaceutical molecule and a cocrystal former that is a solid at ambient temperature and pressure in a defined stoichiometric ratio, although a cocrystal is not limited to containing only two components. The components of the cocrystal are linked by hydrogen bonding and other non-covalent and non-ionic interactions. This definition differentiates cocrystals from crystalline solvates, in which case one of the components is a liquid at ambient temperature and pressure.

Also, there remains a need for additional polymorphic form, cocrystal of sofosbuvir and for processes to prepare polymorphic and cocrystal forms in an environmentally-friendly, cost-effective, and industrially applicable manner. Further, there remains a need for the simple and cost effective process for the preparation of amorphous form of Sofosbuvir.

The present application describes novel polymorphic forms of sofosbuvir, solid dispersion of sofosbuvir and their process for preparation. It also describes process for preparation of amorphous sofosbuvir.

The prior art processes suffer from one or more drawbacks such as low purity, less yield and lengthy workup which does not result an industrially feasible process. Hence, there is a need to provide simple, environment friendly, cost effective, industrially feasible processes for the preparation of sofosbuvir and its intermediates.

Hence, there is a need to provide simple, environment friendly, cost effective, industrially feasible processes for the preparation of sofosbuvir. SUMMARY

In a first aspect, the application provides novel nucleotide analogs having a Formula I, its salts, stereo isomers polymorphs and solvates thereof.

Formula I

wherein, base is a substituted or unsubstituted purine or pyrimidine attached to the furanose ring through a carbon or nitrogen atom.

R and Ri are independently selected from the group consisting of H, alkyl, halo;

X is H, OH, any leaving group;

R₂ is OH or protected hydroxyl group;

R₃ is substituted or unsubstituted aryl;

In a second aspect, the application provides processes for the preparation of novel nucleotide analogs having a Formula I.

In a third aspect, the application provides processes for the preparation of nucleoside phosphoramidate compounds such as sofosbuvir involving the use of novel nucleotide analogs.

In a fourth aspect, the application provides (2R)-2-Deoxy-2-Fluoro-2-C- Methyl-D-Ribofuranose having a Formula I, their salts, stereo isomers, polymorphs and solvates thereof.

Formula VIII

wherein, R_u R₂ are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyl, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl; and L is F, OMs or -OC(HN)CCI₃.

In a fifth aspect, the application provides processes for preparation of (2R)-2- Deoxy-2-Fluoro-2-C-Methyl-D-Ribofuranose having a Formula VIII.

In a sixth aspect, the application provides use of novel (2R)-2-Deoxy-2- Fluoro-2-C-Methyl-D-Ribofuranose compounds in preparation of nucleoside phosphoramidate prodrugs such as sofosbuvir.

In a seventh aspect, the application provides a stereoselective process for preparation of sofosbuvir having Formula A.

Formula A

In an eighth aspect, the application provides a crystalline Form A of sofosbuvir, characterized by a PXRD pattern comprising peaks at about 4.55, 8.53, 9.10, 12.78 and 13.68 ±0.2° 2Θ. Crystalline Form A of sofosbuvir further characterized by PXRD pattern having peaks selected from the following: about 4.91 , 7.15, 15.91 , 17.91 and 25.04 ±0.2°2Θ.

In a ninth aspect, the application provides a process for preparation of Form A comprising peaks at about 4.55, 8.53, 9.10, 12.78 and 13.68 ±0.2° 2Θ; comprising: a) contacting sofosbuvir and a solvent or a mixture of solvents wherein the solubility of sofosbuvir is low;

b) mixing the slurry obtained in step (a);

c) isolating crystalline Form A of sofosbuvir.

In a tenth aspect, the application provides a cocrystal of sofosbuvir with caffeine, characterized by a PXRD pattern comprising peaks at about 3.70, 4.42, 5.32, 14.82, 16.36, 17.21 and 21.04 ± 0.2° 2Θ. Cocrystal of sofosbuvir with caffeine, further characterized by PXRD pattern having peaks selected from the following: about 7.41 , 10.03 and 19.36 ± 0.2° 2Θ.

In an eleventh aspect, the application provides a process for preparation of cocrystal of sofosbuvir with caffeine comprising peaks at about 3.70, 4.42, 5.32, 14.82, 16.36, 17.21 and 21.04 ± 0.2° 2Θ; comprising: a) contacting sofosbuvir and caffeine to a solvent or a mixture of solvents wherein the solubility of sofosbuvir and caffeine is low;

b) contacting slurry obtained in step (a) with a solvent or a mixture of solvents; c) mixing the slurry obtained in step (b);

d) isolating the cocrystal of sofosbuvir with caffeine.

In a twelfth aspect, the present application provides a process for the preparation of amorphous form of Sofosbuvir, comprising the steps of;

a) providing a solution of Sofosbuvir in a solvent;

b) removing solvent from the solution obtained in step a), and

c) isolating the amorphous form of Sofosbuvir.

In a thirteenth aspect, the present invention provides a process for the preparation of amorphous Sofosbuvir comprising:

a) providing a solution of Sofosbuvir in a solvent selected from Acetone, Methanol or Ethyl acetate or mixtures thereof;

b) removing solvent from the solution obtained in step a), and

c) isolating amorphous Sofosbuvir.

In a fourteenth aspect, the present invention also provides pharmaceutical formulations comprising amorphous Sofosbuvir together with one or more pharmaceutically acceptable excipients.

In a fifteenth aspect, the present application provides an amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers.

In a sixteenth aspect, the present invention provides a process for preparing an amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers, comprising:

a) providing a solution or suspension of Sofosbuvir in combination with one or more pharmaceutically acceptable carriers in a solvent or mixture of solvents;

b) removing solvent from the solution obtained in step a), and

c) isolating amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carrier.

In a seventeenth aspect, the present invention provides a process for the preparation of amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers, comprising: a) providing a solution of Sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from Polyvinylpyrrolidone, Copovidone, Hydroxypropyl cellulose (HPC) and Hydroxypropy methyl cellulose (HPMC) in a solvent;

b) removing solvent from the solution obtained in step a), and

c) isolating amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carrier selected from Polyvinylpyrrolidone, Copovidone, Hydroxypropyl cellulose (HPC) and Hydroxypropy methyl cellulose (HPMC).

In an eighteenth aspect, the present invention also provides pharmaceutical formulations comprising amorphous solid dispersions of Sofosbuvir together with one or more pharmaceutically acceptable excipients.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 depicts a PXRD pattern of sofosbuvir Form A, obtained by the procedure of Example 22.

Fig. 2 depicts a PXRD pattern of a cocrystal of sofosbuvir with caffeine, obtained by the procedure of Example 24, after vacuum filtration.

Fig. 3 depicts a PXRD pattern of a cocrystal of sofosbuvir with caffeine, obtained by the procedure of Example 24, after vacuum filtration followed by drying at 40°C in Air tray dryer for about 1 hour.

Fig. 4 depicts a PXRD pattern of amorphous Sofosbuvir, obtained according to the procedure of example 26.

Fig. 5 depicts a PXRD pattern of amorphous Sofosbuvir, obtained according to the procedure of example 28.

Fig. 6 depicts a PXRD pattern of amorphous solid dispersion of Sofosbuvir, obtained according to the procedure of example 30.

DETAILED DESCRIPTION

In a first aspect of the application provides nucleotide analog compounds having a Formula I, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula I

wherein, base is a naturally occurring or modified purine or pyrimidine base and is attached to the furanose ring though a carbon or nitrogen atom.

X is H, OH or any leaving group;

R₂ is OH or protected hydroxyl group;

R₃ is substituted or unsubstituted aryl.

In an embodiment of the first aspect, the application provides nucleotide analog compounds having a Formula I, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula I

wherein, base is selected from

Y is N or CH; R₄, R₅ and R₆ are independently H, halogen (including F, CI, Br, I), OH, OR', SH, SR', NH₂, NHR', NR'₂, lower alkyl of C C₆, halogenated (F, CI, Br, I) lower alkyl of CrC₆ such as CF₃ and CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH=CH₂, halogenated (F, CI, Br, I) lower alkenyl of C₂-C₆ such as CH=CHCI, CH=CHBr and CH=CHI, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, CI, Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C C₆ such as CH₂OH and CH₂CH₂OH, halogenated (F, CI, Br, I) lower alkoxy of C C₆, C0₂H, C0₂R', CONH₂, CONHR', CONR'₂, CH=CHC0₂H, CH=CHC0₂R'; R' is an optionally substituted alkyl of Ci-Ci₂ (particularly when the alkyl is an amino acid residue), cycloalkyl, optionally substituted alkynyl of C₂-C₆, optionally substituted lower alkenyl of C₂-C₆, or optionally substituted acyl.

and wherein R, Ri , X, R₂, R₃ is defined as above.

In another embodiment of the first aspect, the application provides nucleotide analog compounds having a Formula I, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula I

wherein, base is selected from

R₄ and R5 are independently H, halogen (including F, CI, Br, I), OH, OR', SH, SR', NH₂, NHR', NR'₂, lower alkyl of C C₆, halogenated (F, CI, Br, I) lower alkyl of C C₆ such as CF₃ and CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH=CH₂, halogenated (F, CI, Br, I) lower alkenyl of C₂-C₆ such as CH=CHCI, CH=CHBr and CH=CHI, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, CI, Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C C₆ such as CH₂OH and CH₂CH₂OH, halogenated (F, CI, Br, I) lower alkoxy of C C₆, C0₂H, C0₂R', CONH₂, CONHR', CONR'₂, CH=CHC0₂H, CH=CHC0₂R'; R' is an optionally substituted alkyl of C Ci₂ (particularly when the alkyl is an amino acid residue), cycloalkyl, optionally substituted alkynyl of C₂-C6, optionally substituted lower alkenyl of C₂-C6, or optionally substituted acyl.

and wherein R, R_{1 ;} X, R_2, R₃ is defined as above.

Formula I

wherein, base is selected from

R₄ and R₅ are independently H, OH, OR', NH₂, NHR', R' is an optionally substituted alkyl of Ci-Ci₂ (particularly when the alkyl is an amino acid residue), cycloalkyl, optionally substituted alkynyl of C₂-C₆, optionally substituted lower alkenyl of C₂-C₆, or optionally substituted acyl.

and wherein R, R_{1 ;} X, R_2, R₃ is defined as above.

Formula I

wherein, base is selected from

R₄ and R₅ are independently H, OH or NH₂

and wherein one of R, Ri are methyl and other one is fluoro. X is H, OH or any leaving group, R₂ is selected from OH or protected hydroxyl group. R₃ is substituted or unsubstituted aryl.

R

Formula I

wherein, base is selected from

R₄ and R₅ are independently H, OH or NH₂

and wherein one of R, Ri are methyl and other one is fluoro. X is H, OH or any leaving group, R₂ is selected from OH or protected hydroxyl group. R₃ is phenyl or substituted phenyl.

In another embodiment of the first aspect, the application provides nucleotide analog compounds having a Formula II, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula II

wherein X is H, OH or any leaving group and R₂ is OH or protected hydroxyl group.

In another embodiment of the first aspect, the application provides specific nucleotide analog compounds having a Formula II, its stereo isomers, salts, polymorphs, and solvates thereof.

wherein X and R₂ are as defined in the below table 1 .

H OLev

CI OLev

Br OLev

1 OLev

OH OLev wherein above Lev is levulinyl group.

In another embodiment of the first aspect, the application provides the following specific nucleotide analog compounds, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula g

In an embodiment of the second aspect, the application provides a process for preparation of novel nucleotide analogs having a Formula I

Formula I wherein, all the substituent same as defined above in Formula I of the first embodiment.

which comprising contacting a com ound of Formula III

Formula III

wherein, R3 is substituted or unsubstituted aryl, X and X1 are independently selected from H, OH or any leaving group. Provided when X or is H, then the other one is a leaving group.

with a compound of Formula IV or a salt there of.

Formula IV

wherein, Base, R, Ri and R₂ are same as defined in Formula I.

The reaction is performed in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited to anhydrous aromatic solvents. The reaction is initiated at a temperature ranging from -50°C to 40°C. The reaction is then allowed to stir within the range of temperature between -50°C to 40°C for a period of about 30 minutes to 3 hours or longer.

Salts of above compounds can be prepared from bases including organic bases such as pyridine, triethylamine, methyl amine, imidazole, benzimidazole, histidine or inorganic bases such as NaOH, KOH, Mg(OH)2, Ca(OH)2, Na2CO3, K2CO3, NH4OH.

In another embodiment of the second aspect, the application more preferably provides a process for preparation of analog compounds having a Formula II which comprises one or more of the following steps;

Formula II

wherein, X and R₂ are same as defined in the first embodiment;

Contacting a compound of Form salt thereof

Formula V

with a compound of Formula VI or salts thereof,

Formula VI

wherein, X, and R₂ are same as defined in the previous embodiment;

The reaction is performed in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited an anhydrous aromatic solvents. The reaction is initiated at a temperature ranging from -50°C to 40°C. The reaction is then allowed to stir within the range of temperature between -50°C to 40°C for a period of about 30 minutes to 3 hours or longer. The reaction can be conducted in pyridine solvent at a temperature range between -50°C to 40°C for about 1 to 2 hours or longer.

In another embodiment of the second aspect, the application provides a process for preparation of nucleoside phosphoramidate compounds having a Formula VII, which comprises one or more of the following steps;

Formula VII

wherein, A is a substituted or unsubstituted aminoacid;

base, R, Ri , R₂ and R₃ are same as defined in compound of Formula I in the first embodiment of the second aspect.

a) Contacting a compound of Formula III or a salt thereof

o I I

x-p-R₃

Formula III

wherein, R₃, X and Xi are same as defined in the previous embodiment;

with a compound of Formula IV or a salt thereof.

Formula IV

where in base, R, Ri and R₂ are same as defined above to produce a compound of Formula I.

Formula I

wherein,base, R, Ri ,R₂ and R₃ are same as defined above.

b) If X is H or OH, then converting them into any leaving group.

c) Contacting compound of Formula I or salts thereof, wherein X is a leaving group, with a substituted or unsubstituted amino acid.

wherein step a), the reaction is performed in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited an anhydrous aromatic solvents. The reaction is initiated at a temperature ranging from -50°C to 40°C. The reaction is then allowed to stir within the range of temperature between -50°C to 40°C for a period of about 30 minutes to 3 hours or longer

wherein step b), the reaction can be conducted in a polar aprotic solvent, preferably acetonitrile, acetone, Ν,Ν-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and their combinations. The compounds of the Formula I obtained in step a) when X=H or -OH can be converted to any leaving group before the next step. For example, the compounds of Formula I having X= H or -OH can treated in presence of a halogen containing organic agent such as CCI₄, CH₃CI, CH₂CI₂, CHCI₃, CF₄, CFCI₃, CF2CI2, CF3CI, CBr₄, CBrCIa, CBr₂CI₂, CBr₃CI, Cl₃, I2, CCI3CN and an organic or inorganic base to place appropriate halo derivatives. The reaction can be conducted at a preferred reaction temperature range between from -50°C to 40°C.

The reaction is conducted in presence of a halogen containing organic solvent such as CCI₄, CHCI₃, CH₂CI₂, CH₃CI, CCI₃CN or their combinations to produce halogen leaving group. The same reagents can also be used as solvents in the same reaction. Any suitable solvents other than the solvents mentioned can be used in the reaction if they do not involve any reaction with the reagents.

The intermediates of the compound of Formula I can be converted to salts or polymorphs or solvates or stereoisomers specifically at chiral phosphorous atom before proceeding to the next reaction.

The intermediates of compound of Formula I obtained after step b) can be in situ treated with amino acids such as isopropyl L-alaninate to produce the compounds of Formula VII.

The obtained compounds of Formula VII, intermediates of Formula VII may be racemic or enantiomerically enriched compounds specifically at chiral phosphorous atom depending on the intermediates used or procedures followed.

The compounds of Formula I and Formula VII wherein R₂ is protecting group can be hydrolyzed to produce the hydroxyl derivative at any stage of the process before proceeding to the next step or at the final stage.

In an embodiment of the third aspect, the application provides a process for preparation of sofosbuvir having a Formula A, which comprises one or more of the following steps; a) Contacting a compound of Formula II or a salt thereof

Formula II

wherein, X and Xi are same as defined in the previous embodiment. Provided when X or Xi is H, then the other one is a leaving group,

with a compound of Formula III or a salt thereof.

Formula III

wherein base, R₂ is same as defined in the previous embodiment.

Formula I

wherein, base, R₂ is same as defined above.

b) If X is H or OH then displacing them with a leaving group. Preferably with a halogen.

c) contacting compound of Formula I or salts thereof obtained from step c) with isopropyl L-alaninate or its salts provides sofosbuvir of Formula A or 3-O-protected Sofosbuvir.

d) If R₂ is a protecting group, then hydrolyzing the 3-O-protected compound provides Sofosbuvir of Formula A.

Different halogenating agents such as CCI₄, CH₃CI, CH₂CI₂, CHCI₃, CCI₃CN, CF₄, CFCI3, CF₂CI₂, CF3CI, CBr₄, CBrCI₃, CBr₂CI₂, CBr₃CI, Cl₃, l₂, N-Chloro succinimide, CuCI₂, Trityl chloride, 2-Chlorotriphenyl methylchloride, 1 ,3 Dibromo 5,5-Dimethyl Hydantoin, Bromo succinimide, Bromo phthalimide can be used in halogenation reaction.

wherein step b), the reaction can be conducted in a polar aprotic solvent, preferably acetonitrile, acetone, Ν,Ν-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and their combinations. The compounds of the Formula I obtained in step as when X=H or -OH can be converted to any leaving group before the next step. For example, the compounds of Formula I having X= H or -OH can treated in presence of a halogen containing organic solvent such as CCI₄, CH₃CI, CH₂CI₂, CHC , CF₄, CFCI3, CF2CI2, CF3CI, CBr₄, CBrCIa, CBr₂CI₂, CCI3CN, CBr₃CI, Cl₃, I2 and an organic or inorganic base to place appropriate halo derivatives. The reaction can be conducted at a preferred reaction temperature range between from -10°C to 30°C.

The reaction is conducted in presence of a halogen containing organic solvent such as CCI₄, CHCI₃, CH₂CI₂, CH₃CI, CCI₃CN or their combinations to produce halogen leaving group. The same reagents can also be used as solvents in the same reaction. Any suitable solvents other than the solvents mentioned can be used in the reaction if they do not involve any reaction with the reagents. The intermediates of the compound of Formula A can be converted to salts or polymorphs or solvates or stereoisomers specifically at chiral phosphorous atom before proceeding to the next reaction.

The intermediates of compound of Formula I obtained after step b) can be in situ treated with amino acids such as isopropyl L-alaninate to produce the compounds of Formula A.

The obtained compounds of Formula A, intermediates of Formula A may be racemic or enantiomerically enriched compoundsspecifically at chiral phosphorous atom depending on the intermediates used or procedures followed.

The compounds of Formula I and Formula A wherein R₂ is protecting group can be hydrolyzed to produce the hydroxyl derivative at any stage of the process before proceeding to the next step or at the final stage.

In another embodiment of the third aspect, the application provides a process for preparation of sofosbuvir having a Formula A, which comprises one or more of the following steps;

a) Contacting a compound of F a salt thereof

Formula V wherein, R₃ is defined same as in the previous embodiment. X and Xi are independently selected from H or OH. Provided when X or is H, then the other one is a leaving group.

with a compound of Formula VI or a salt thereof.

Formula VI

wherein R₂ is same as defined above to produce a compound of Formula II.

Formula II

wherein, X and R₂ are same as defined above.

b) displacing H or OH of Formula II or its salt with a leaving group. Preferably with a halogen.

c) contacting compound of Formula II or salts thereof obtained from step b) with isopropyl L-alaninate or its salts provides sofosbuvir of Formula A or 3-O-protected Sofosbuvir.

wherein step b), if X is OH then the reaction can be conducted in organic solvents such as dichloromethane, acetonitrile, chloroform.

wherein step b), if X is H then the reaction can be conducted inanhydrous aromatic solvents, in the presence of organic bases such as triethyl amine, pyridine, collidine, Diisopropylamine (DIPEA).

Steps a), c) and d) can be performed as per the procedures described in the previous embodiments.

The product of step b), wherein if X is OH, then it can be converted to salts. Preferably with organic or inorganic bases to produce respective salts. These salts can be used to purify the compound of formula II and/ or also to improve the chiral purity at phosphorous atom. The halogenation reaction can be conducted in presence of inorganic or organic base. The inorganic bases are alkali metal hydroxides or alkali metal carbonates such as Sodium hydroxyl (NaOH) or Sodium carbonate (Na₂C0₃) and the organic bases are amines such as triethyl amine, pyridine, collidine, Diisopropylamine (DIPEA).

The halogenation reaction may be carried out in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited totetrachloromethane, dichloromethane, chloroform, diethyl ether, THF, acetonitrile, DMF and toluene, aqueous organic solvents such as water/ethanol, water/DMF, methanol or ethanol, Iso-propanol or Iso-propanaol and water.

Phase transfer catalyst can be optionally used in halogenation reaction as per the requirement to initiate and accelerate the rate of the reaction.

In another embodiment of the third aspect, the application provides processes for separation racemic mixture of nucleotide analog compounds and nucleoside phospharamidate compounds into specific diasteriomers by different methods such as crystallization, crystal picking, preferential crystallization in the presence of additives, assymetric transformation of racemates, enzymatic separation and chemical resolution processes. The chemical resolution can be done by using chiral resolving agents or chiral chromatography. In chiral resolution process the racemate is treated with chiral resolving agents such as tartaric acid, a-methyl-β- phenylethylamine, C6H5CH2CH(NH2)CH3, amino acids including but not limited to substituted or unsubstituted glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline, serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginine and histidine. In a preferred embodiment, the amino acid is in the L-configuration. Alternatively, the amino acid can be a derivative of alanyl, valinyl, leucinyl, isoleucinyl, prolinyl phenylalaninyl, tryptophanyl, methioninyl, glycinyl, serinyl, threoninyl, cysteinyl, tyrosinyl, asparaginyl, glutaminyl, aspartoyl, glutaroyl, lysinyl, argininyl, histidinyl, .beta.-alanyl, .beta.-valinyl, .beta.-leucinyl, .beta.-isoleucinyl .beta.-prolinyl, .beta.-phenylalaninyl, .beta.-tryptophanyl, .beta.-methioninyl, .beta.-glycinyl, .beta.-serinyl, .beta.- threoninyl, .beta.-cysteinyl, .beta.-tyrosinyl, .beta.-asparaginyl, .beta.-glutaminyl, .beta.-aspartoyl, .beta.-glutaroyl, .beta.-lysinyl, .beta.-argininyl or .beta.-histidinyl. When the term amino acid is used, it is considered to be a specific and independent disclosure of each of the esters of .alpha., .beta, .gamma, or .delta, glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline, serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginine and histidine, isopropyl alaninate in the D and L-configurations.

The obtained compounds of Formula I, Formula VII and Formula A may be racemic compounds at due to the chiral phosphorous atom which may be further separated into pure enantiomers by following known methods in the art. Preferably, the compounds are (S) isomers.

The pure chiral (S) isomers of Formula I, Formula VII and Formula A can be produced by general methods known in the art such as crystallization, chromatography, use of enzymes etc.

In a fourth aspect, the present application provides (2R)-2-Deoxy-2-Fluoro-2- C-Methyl-D-Ribofuranose having a Formula VIII, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula VIII

Wherein, R1 , R2 are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyl, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl; and

L is F, OMs or -OC(HN)CCI3.

In an embodiment of the fourth aspect, the application provides (2R)-2-Deoxy- 2-Fluoro-2-C-Methyl-D-Ribofuranose compound having a Formula IX, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula IX

Wherein, R1 , R2 are same as they described in the previous embodiment. In another embodiment of the fourth aspect, the application provides (2R)-2- Deoxy-2-Fluoro-2-C-Methyl-D-Ribofuranose compound having a Formula X, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula X

wherein, R1 , R2 are same as they described in the previous embodiment.

In another embodiment of the fourth aspect, the application provides (2R)-2- Deoxy-2-Fluoro-2-C-Methyl-D-Ribofuranose compound having a Formula XI, its stereo isomers, salts, polymorphs, and solvates thereof.

Formula XI

wherein, R1 , R2 are same as they described in the previous embodiment.

In another embodiment of the fourth aspect, the application provides the following specific nucleotide analog compounds of Formula h, Formula i, Formula j, their stereo isomers salts ol mor hs and solvates thereof.

Formula h Formula i Formula j

In an embodiment of the fifth aspect, the application provides the application provides a process for preparation of (2R)-2-Deoxy-2-Fluoro-2-C-Methyl-D- Ribofuranose having a Formula VIII, their stereo isomers, salts, polymorphs, and solvates thereof, which comprises one or more of the following steps:

Formula VIII

wherein, R1 , R2 and L are same as they defined in the previous embodiment; which comprising contacting a com ound of Formula XII

Formula XII

wherein, R1 , R2 are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyl, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl;

with suitable reagents to substitute fluorine, mesyl or trichloroacetonitrile groups at C1 position of (2R)-2-Deoxy-2-Fluoro-2-C-Methyl-D-Ribofuranose.

The reaction can be performed in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited to polar organic solvents such as dichloromethane, chlorobenzene, dichloroethane, chloroform, toluene, acetonitrile and terahydrofuran. The reaction is initiated at a temperature ranging from -100°C to 50°C. The reaction is then allowed to stir within the range of temperature between - 100°C to 50°C for a period of about 10 minutes to 5 hours or longer.

In another embodiment of the fifth aspect, the application provides a process for preparation of (2R)-2-Deoxy-2-Fluoro-2-C-Methyl-D-Ribofuranose compound having a Formula IX, its stereo isomers, salts, polymorphs, and solvates thereof, which comprises one or more of the followin steps:

Formula IX

wherein, all the substituent same as defined above in Formula IX of the previous embodiment; which comprising contacting a compound of Formula XII;

Formula XII

wherein, R1 , R2 are same as they described in the previous embodiment. with fluorinating agents comprising but not limited to Bis(2- methoxyethyl)aminosulfur Trifluoride (Deoxo-Fluor®), Diethylaminosulfur trifluoride (DAST), HF-Pyridine, 3HF.Et3N, 1 ,1 ,2,2-Tetrafluoroethyl-N,N-dimethylamine (TFEDMA), XtalFluor-E®, XtalFluor-M.

The reaction can be performed in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited to polar organic solvents such as dichloromethane, acetonitrile, tetrahydrofuran, toluene and chloroform. The reaction is initiated at a temperature ranging from -100°C to 50°C. The reaction is then allowed to stir within the range of temperature between -100°C to 50°C for a period of about 10 minutes to 5 hours or longer.

In another embodiment of the fifth aspect, the application more preferably provides a process for preparation of (2R)-2-Deoxy-2-Fluoro-2-C-Methyl-D- Ribofuranose compound having a Formula X, its stereo isomers, salts, polymorphs, and solvates thereof, which com rises one or more of the following steps:

Formula X

Wherein, R1 , R2 are same as they described in the previous embodiment; which comprising contacting a compound of Formula XII;

Formula XII

Wherein, R1 , R2 are same as they described in the previous embodiment. with methanesulfonyl chloride.

The reaction can be conducted in presence of bases including organic bases such as pyridine, triethylamine, methyl amine, imidazole, benzimidazole, histidine or inorganic bases such as NaOH, KOH, Mg(OH)2, Ca(OH)2, Na2C03, K2C03, NH40H, optionally in presence phase transfer catalysts.

In another embodiment of the fifth aspect, the application more preferably provides a process for preparation of (2R)-2-Deoxy-2-Fluoro-2-C-Methyl-D- Ribofuranose compound having a Formula XI, its stereo isomers, salts, polymorphs, and solvates thereof, which com rises one or more of the following steps:

Formula XI

wherein, all the substituent same as defined above in Formula XI of the previous embodiment; which comprisin contacting a compound of Formula XII;

Formula XII

Wherein, R1 , R2 are same as they described in the previous embodiment, with 2,2,2 trichloroacetonitrile.

The reaction can be conducted in presence of a bases including organic bases such as 1 ,8-Diazabicycloundec-7-ene (DBU), triethylamine, pyridine, diisopropylamine and diethylamine.

If R1 is other than H, then it can be optionally converted to H by using the procedures known in the art.

In another embodiment of the fifth aspect, the application more preferably provides a process for preparation of nucleoside analog compound having a Formula XIII which comprises one or more of the followin steps;

Formula XIII

wherein, R1 and R2 are defined same as in the previous embodiment; and B is a base, which is selected from

Y is N or CH; R4, R5 and R6 are independently H, halogen (including F, CI, Br, I), OH, OR', SH, SR\ NH2, NHR', NR'2, lower alkyl of C1 -C6, halogenated (F, CI, Br, I) lower alkyl of C1 -C6 such as CF3 and CH2CH2F, lower alkenyl of C2-C6 such as CH=CH2, halogenated (F, CI, Br, I) lower alkenyl of C2-C6 such as CH=CHCI, CH=CHBr and CH=CHI, lower alkynyl of C2-C6 such as C≡CH, halogenated (F, CI, Br, I) lower alkynyl of C2-C6, lower alkoxy of C1 -C6 such as CH20H and CH2CH20H, halogenated (F, CI, Br, I) lower alkoxy of C1 -C6, C02H, C02R', CONH2, CONHFt', CONFt'2, CH=CHC02H, CH=CHC02Ft'; Ft' is an optionally substituted alkyl of C1 -C12 (particularly when the alkyl is an amino acid residue), cycloalkyi, aryl, optionally substituted alkynyl of C2-C6, optionally substituted lower alkenyl of C2-C6, or optionally substituted acyl.

which comprising contactin a compound of Formula VIII;

Formula VIII

wherein, R1 , R2 and L are same as they described in the previous embodiment.

wherein solvents, reagents used and conditions followed are same as in previous embodiment.

In another embodiment of the fifth aspect, the application more preferably provides a process for preparation of nucleoside analog compounds having a Formula XIV, their stereo isomers, salts, polymorphs, and solvates thereof, which comprises one or mor f the following steps:

Formula XIV

XlVa xivb

alpha isomer beta isomer wherein, all the substituent same as defined above in Formula XIV of the previous embodiment; which comprising contacting a compound of Formula IX, Formula X and Formula XI

Formula IX Formula X Formula XI wherein, all the substituent same as defined above in Formula IX, Formula X and Formula XI of the previous embodiment.

If Ri is other than H, then it can be optionally converted to H by using the procedures known in the art.

In an embodiment of sixth aspect, the present application provides a process for preparation of nucleoside phosphoramidate compounds having Formula XV, their stereo isomers, salts, polymorphs, and solvates thereof, which comprises one or more of the following steps;

a) Contacting a compound of Form or a salt thereof

Formula XV

wherein, R3 is a leaving group. X' and X" are independently selected from H or OH. Provided when one of X' or X" is H, then the other one is a leaving group,

with a compound of Formula XIII or a salt thereof.

Formula XIII wherein, R1 is H and R2 is same as defined in the previous embodiment, to produce a compound of Formula XVI.

Formula XVI

wherein, R2, B are same as defined in the previous embodiment, R3 and X" are same as defined above in the present embodiment.

b) If X" is H or OH then displacing them with a leaving group. Preferably with a halogen.

c) Contacting compound of Formula XVI or salts thereof obtained from step with substituted or unsubstituted aminoacids or their salts provides nucleoside phosphoramidate compounds of Formula XVII or 3-O-protected nucleoside phosphoramidate compounds.

Formula XVII

wherein, R2, R3 and B are same as defined in the previous embodiment; A is substituted or unsubstituted amino acid,

d) If R2 is a protecting group, optionally deprotecting the 3-O-protected compound provides nucleoside phosphoramidate compounds,

wherein step a), the reaction is performed in a suitable inert solvent. Suitable solvent can be any solvent which has no adverse effect on the reaction or on the reagents involved and that it can dissolve the reagents, at least to some extent. Examples of such solvents include but are not limited an anhydrous aromatic solvents. The reaction is initiated at a temperature ranging from -50°C to 40°C. The reaction is then allowed to stir within the range of temperature between -50°C to 40°C for a period of about 30 minutes to 3 hours or longer wherein step b), the reaction can be conducted in a polar aprotic solvent, preferably acetonitrile, acetone, Ν,Ν-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and their combinations. The reaction can be conducted at a preferred reaction temperature range between from -50°C to 40°C.

The reaction is conducted in presence of a halogen containing organic solvent such as CCI4, CHCI3, CH2CI2, CH3CI, CCI3CN or their combinations to produce halogen leaving group. The same reagents can also be used as solvents in the same reaction. Any suitable solvents other than the solvents mentioned can be used in the reaction if they do not involve any reaction with the reagents.

In another embodiment of sixth aspect, the application provides a process for preparation of sofosbuvir having Formula A, their stereo isomers, salts, polymorphs, and solvates thereof,

Formula A

which comprises one or more of the following steps;

Contacting a compound of a salt thereof

Formula XVIII

Wherein, L is a leaving group.

with a compound of Formula XIX or a salt thereof.

Formula XIX In an embodiment of the sixth aspect, the application provides a compound of Formula XIX used in the reaction can be a racemic mixture or the chirally pure at phosphorous atom. In other embodiment of the present invention, if compound of formula XIX is racemic mixture, then it can be converted enatiomerically pure R and S isomers. In another embodiment of the present invention, compound of Formula XIX can be prepared by the following procedures known in the art.

The obtained compounds from Formula VIII to Formula XVII may be further separated into pure enantiomers by following general methods known in the art such as crystallization, chromatography, use of enzymes etc.

In a seventh aspect, the application provides a stereoselective process for preparation of sofosbuvir having a Formula A.

Formula A

In an embodiment of the seventh aspect, the application provides a process for preparing the compound of Formula A, which comprises reacting a chlorophosphoramidate compound of Formula XX with a nucleoside compound of Formula XXI, in the presence of anhydrous solvents and bases, wherein the solvents can be selected from dichloromethane, 2-methyl tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine, tributylamine and their combinations, or any functional equivalent thereof and bases can be selected from tripropyl amine, tributyl amine, diisopropyl ethyl amine, and their combinations, or any functional equivalent thereof.

Formula XX

Formula XXI

In another embodiment of the seventh aspect, the application provides a process wherein the chlorophosphoramidate compound of Formula XX is dissolved in a solvent and added to the mixture of the nucleoside compound of Formula XXI and base.

In another embodiment of the seventh aspect, the application provides the reaction can be performed in anhydrous solvents such as dichloromethane, 2-methyl tetrahydrofuran, tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, 1 ,4-dioxane, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine, tributylamine and their combinations, or any functional equivalent thereof.

In another embodiment of the seventh aspect, the application provides the base can be selected from tripropyl amine, tributyl amine, diisopropyl ethyl amine, and their combinations, or any functional equivalent thereof.

In another embodiment of the seventh aspect, the application provides the reaction can be typically initiated and conducted at a temperature range from -78°C to 40°C. The reaction can be performed for a period of 30 minutes to 24 hours. The reaction can be allowed to stir over a period of time at a temperature between about -78°C and 40°C. The solvent is removed from the reaction mixture and the product is purified by chromatography on silica gel, crystallization or other methods known in the art.

In another embodiment of the seventh aspect, the application provides use of tripropylamine, tributylamine, diisopropylethylamine or any functional equivalent bases in combination with appropriate solvents like dichloromethane, 2-methyl tetrahydrofuran, tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, 1 ,4-dioxane, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine give the desired the S-isomer at phosphorous atom as the major product.

The selection of solvent and base is very much crucial as some of the combinations may lead to the formation of undesired isomer (R-isomer) in excess level. For example, use of bases such as K₂C0₃ and Cs₂C0₃ in tetrahydrofuran produced only the ratio of isomers (Sp : Rp) 1 :3.4 and 1 :6 respectively. Further, as indicated above, the literature referred bases and solvents lead to the formation of about 1 :1 ratio of isomers (Sp : Rp) .

In another embodiment of the seventh aspect, the application provides stereoselectivity of desired compound such as sofosbuvir of Formula A, at phosphorous atom range starting from about 2.5:1 to 7:1 .

In another embodiment of the seventh aspect, the application provides the compound such as sofosbuvir of Formula A can be prepared by using combinations of specific solvents and specific bases as described above.

In another embodiment of the seventh aspect, the application provides the obtained compounds from Formula A may be further purified by separating the undesired enantiomers by the known techniques such as crystallization, chromatography, use of enzymes, simulated moving bed chromatography etc.

In another embodiment of the seventh aspect, the application provides the obtained compound of Formula A can be recrystallized by solvent & anti-solvent process wherein the solvents can be selected from dichloromethane, ethyl acetate, methanol, toluene and their functionally equivalents thereof and the anti-solvents can be selected from isopropyl ethyl ether, diisopropyl ether, heptane and methyl tertiarybutyl ether and functional equivalents thereof.

In another embodiment of the seventh aspect, the application provides a process for preparation of nucleoside phosphoramidate compound of Formula XXII, which comprises reacting a phosphoramidate compound of Formula XXIII with a nucleoside compound of Formula XXIV, in the presence of anhydrous solvents and bases, wherein the solvents can be selected from dichloromethane, 2-methyl tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine, tributylamine and their combinations, or any functional equivalent thereof and bases can be selected from tripropyl amine, tributyl amine, diisopropyl ethyl amine, and their combinations, or any functional equivalent thereof.

Formula XXII

Formula XXIII

Formula XXIV

wherein,

(a) Ri is hydrogen, n-alkyl; branched alkyl, cycloalkyi; or aryl, which includes, but is not limited to, phenyl or naphthyl, where phenyl or naphthyl are optionally substituted with at least one of Ci-₆ alkyl, C₂-₆ alkenyl, C₂-₆ alkynyl, Ci-₆ alkoxy, F, CI, Br, I, nitro, cyano, Ci_-6 haloalkyl, — N(R₁ ')₂, Ci-₆ acylamino, — NHS0₂Ci-₆ alkyl, — S0₂N(R₁')₂, COR1", and —S0₂Ci_-6 alkyl; (Ri' is independently hydrogen or alkyl, which includes, but is not limited to, d-₂₀ alkyl, C_{1 -10} alkyl, or Ci_-6 alkyl, Rr is— OR'

(b) R₂ is hydrogen, Ci-i₀ alkyl, R^3a or R^3b and R₂ together are (CH₂)n so as to form a cyclic ring that includes the adjoining N and C atoms, C(0)CR^3aR^3bNHR₁ , where n is 2 to 4 and Ri , R^3a, and R^3b;

(c) R^3a and R^3b are (i) independently selected from hydrogen, C1-1₀ alkyl, cycloalkyi, — (CH₂)c(NR₃')₂, Ci_-6 hydroxyalkyl, — CH₂SH, — (CH₂)₂S(0)_dMe, — (CH₂)₃NHC(=NH)NH₂, (1 H-indol-3-yl)methyl, (1 H-imidazol-4-yl)methyl, — (CH₂)cCOR₃", aryl and aryl Ci_₃ alkyl, said aryl groups optionally substituted with a group selected from hydroxyl, C1-1₀ alkyl, Ci-₆ alkoxy, halogen, nitro and cyano; (ii) R^3a and R^3b both are d-₆ alkyl; (iii) R^3a and R^3b together are (CH₂)r so as to form a spiro ring; (iv) R^3a is hydrogen and R^3b and R₂ together are (CH₂)n so as to form a cyclic ring that includes the adjoining N and C atoms (v) R^3b is hydrogen and R₃a and R₂ together are (CH₂)n so as to form a cyclic ring that includes the adjoining N and C atoms, where c is 1 to 6, d is 0 to 2, e is 0 to 3, f is 2 to 5, n is 2 to 4, and where R₃' is independently hydrogen or d-₆ alkyl and R₃" is— OR' or— N(R₃')₂); (vi) R^3a is H and R₃b is H, CH₃, CH₂CH₃, CH(CH₃)₂, CH₂CH(CH₃)₂, CH(CH₃)CH₂CH₃, CH₂Ph, CH₂-indol-3-yl, — CH₂CH₂SCH₃, CH₂C0₂H, CH₂C(0)NH₂, CH₂CH₂COOH, CH₂CH₂C(0)NH₂, CH₂CH₂CH₂CH₂NH₂,— CH₂CH₂CH₂NHC(NH)NH₂, C₂-imidazol-4- yl, CH₂OH, CH(OH)CH₃, CH₂((4'-OH)-Ph), CH₂SH, or lower cycloalkyi; or (viii) R^3a is CH₃,— CH₂CH₃, CH(CH₃)₂, CH₂CH(CH₃)₂, CH(CH₃)CH₂CH₃, CH₂Ph, CH₂-indol-3-yl, — CH₂CH₂SCH₃, CH₂C0₂H, CH₂C(0)NH₂, CH₂CH₂COOH, CH₂CH₂C(0)NH₂, CH₂CH₂CH₂CH₂NH₂, — CH₂CH₂CH₂NHC(NH)NH₂, CH₂-imidazol-4-yl, CH₂OH, CH(OH)CH₃, CH₂((4'-OH)-Ph), CH₂SH, or lower cycloalkyi and R^3b is H, where R₃' is independently hydrogen or alkyl, which includes, but is not limited to, Ci-₂₀ alkyl, Ci_ io alkyl, or Ci-₆ alkyl, R₃" is—OR' or— N(R₃')₂);

(d) R₄ is hydrogen, Ci_i₀ alkyl, Ci_i₀ alkyl optionally substituted with a lower alkyl, alkoxy, di(lower alkyl)-amino, or halogen, Ci_i₀ haloalkyl, C₃-i₀ cycloalkyi, cycloalkyi alkyl, cycloheteroalkyi, aminoacyl, aryl, such as phenyl, heteroaryl, such as, pyridinyl, substituted aryl, or substituted heteroaryl;

(e) R₅ is H, a lower alkyl, CN, vinyl, 0-(lower alkyl), hydroxyl lower alkyl, i.e., — (CH₂)pOH, where p is 1 -6, including hydroxyl methyl (CH₂OH), CH₂F, N₃, CH₂CN, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or halogen, including F, CI, Br, or I, with the provisos that when X is OH, base is cytosine and R₆ is H, R₅ cannot be N₃ and when X is OH, R₆ is CH₃ or CH₂F and B is a purine base, R₅ cannot be H;

(f) R₆ is H, CH₃, CH₂F, CHF₂, CF₃, F, or CN;

(g) X is H, OH, F, OMe, halogen, NH₂, or N₃;

(h) Y is OH, H, Ci-₄ alkyl, C₂-₄ alkenyl, C₂-₄ alkynyl, vinyl, N₃, CN, CI, Br, F, I, N0₂, OC(0)0(Ci-₄ alkyl), OC(0)0(Ci-₄ alkyl), OC(0)0(C₂-₄ alkynyl), OC(0)0(C₂- 4 alkenyl), OCM O haloalkyl, O(aminoacyl), O(Ci-i₀ acyl), 0(Ci_-4 alkyl), 0(C2-4alkenyl), S(Ci-₄ acyl), S(Ci-₄ alkyl), S(C₂-₄ alkynyl), S(C₂-₄ alkenyl), SO(Ci-₄ acyl), SO(Ci- 4 alkyl), SO(C₂-₄ alkynyl), SO(C₂-₄ alkenyl), S0₂(d-₄ acyl), S0₂(Ci-4 alkyl), S0₂(C₂. ₄ alkynyl), S₀₂(C₂-₄ alkenyl), OS(0)₂(Ci-₄ acyl), OS(0)₂(C1 -4alkyl), OS(0)₂(C₂. 4 alkenyl), NH₂, NH(Ci_-4 alkyl), NH(C₂-₄ alkenyl), NH(C₂-₄ alkynyl), NH(Ci-₄ acyl), N(Ci- 4 alkyl)₂, N(Ci-is acyl)₂, wherein alkyl, alkynyl, alkenyl and vinyl are optionally substituted by N₂, CN, one to three halogen (CI, Br, F, I), N0₂, C(0)0(Ci-4 alkyl), C(0)0(Ci-4 alkyi), C(0)0(C₂-₄ alkynyl), C(0)0(C₂-₄ alkenyl), 0(Ci-₄ acyl), 0(Ci-₄ alkyi), 0(C₂-₄alkenyl), S(Ci_₄ acyl), S(_Ci- alkyi), S(C2 -4 alkynyl), S(C2-4 alkenyl), S0(C1 - 4 acyl), S0(C1 -4 alkyi), SO(C₂-₄ alkynyl), SO(C₂.₄ alkenyl), S02(C1 -4 acyl), S02(C1 - 4 alkyi), S02(C2-4 alkynyl), S02(C2-4 alkenyl), OS(0)2(Ci-₄ acyl), OS(0)₂(Ci-₄alkyl), OS(0)₂(C₂-₄ alkenyl), NH₂, NH(Ci-₄ alkyi), NH(C₂-₄ alkenyl), NH(C₂-₄ alkynyl), NH(Ci- ₄ acyl), N(Ci-₄ alkyl)₂, N(Ci-₄ acyl)₂;

The base is a naturally occurring or modified purine or pyrimidine base represented by the following structures:

wherein

R₇, R₈,R₉, Rio, and Rn are independently H, F, CI, Br, I, OH, OR', SH, SR', NH₂, NHR', NR'₂, lower alkyi of C C₆halogenated (F, CI, Br, I) lower alkyi of C C₆, lower alkenyl of C₂-C₆, halogenated (F, CI, Br, I) lower alkenyl of C₂-C₆, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, CI, Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C C₆, halogenated (F, CI, Br, I) lower alkoxy of C C₆, C0₂H, C0₂R', CONH₂, CONHR', CONR'₂, CH=CHC0₂H, or CH=CHC0₂R', wherein FT is an optionally substituted alkyl, which includes, but is not limited to, an optionally substituted Ci_₂o alkyl, an optionally substituted Ci-i₀ alkyl, an optionally substituted lower alkyl; an optionally substituted cycloalkyl; an optionally substituted alkynyl of C₂-C₆, an optionally substituted lower alkenyl of C₂-C₆, or optionally substituted acyl, which includes but is not limited to C(O) alkyl, C(0)(Ci- ₂₀ alkyl), C(O)(Ci-i₀ alkyl), or C(0)(lower alkyl) or alternatively, in the instance of NR'₂, each R' comprise at least one C atom that are joined to form a heterocycle comprising at least two carbon atoms; and

Ri2 is H, halogen (including F, CI, Br, I), OH, OR', SH, SR\ NH2, NHR', NR'₂, N0₂ lower alkyl of CrC₆, halogenated (F, CI, Br, I) lower alkyl of CrC₆, lower alkenyl of C₂-C₆, halogenated (F, CI, Br, I) lower alkenyl of C₂-C₆, lower alkynyl of C₂-C₆, halogenated (F, CI, Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C C₆, halogenated (F, CI, Br, I) lower alkoxy of C C₆, C0₂H, C0₂R', CONH₂, CONHR', CONR'₂, CH=CHC0₂H, or CH=CHC0₂R'; with the proviso that when base is represented by the structure c with Rn being hydrogen, Ri₂ is not a: (i)— C≡C— H, (ii)— C=CH₂, or (iii)— N0₂.

X' is a suitable leaving group.

In another embodiment of the seventh aspect, the application provides the reaction can be performed in anhydrous solvents such as dichloromethane, 2-methyl tetrahydrofuran, tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, acetone, methyl ethyl ketone, 1 ,4-dioxane, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine and their combinations, or any functional equivalent thereof.

In another embodiment of the seventh aspect, the application provides the reaction can be typically initiated and conducted at a temperature range from -78°C to 40°C. The reaction can be performed for a period of 30 minutes to 24 hours. The reaction can be allowed to stir over a period of time at a temperature between about -78°C and 40°C. The solvent is removed from the reaction mixture and the product is purified by chromatography on silica gel, crystallization, or other methods known in the art. In another embodiment of the seventh aspect, the application provides the obtained nucleoside phosphoramidate compounds of Formula XXII can be recrystallized by solvent & anti-solvent process wherein the solvents can be selected from dichloromethane, ethyl acetate, methanol, toluene and their functionally equivalents thereof and the anti-solvents can be selected from isopropyl ethyl ether, diisopropyl ether, heptane and methyl tertiarybutyl ether and functional equivalents thereof.

In another embodiment of the seventh aspect, the application provides use of tripropylamine, tributylamine, diisopropylethylamine or any functional equivalent bases in combination with appropriate solvents like dichloromethane, 2-methyl tetrahydrofuran, tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine give the desired the S-isomer at phosphorous atom as the major product.

The product obtained according to the present invention can be useful for the preparation of desired polymorphic forms known in the art or for the preparation of novel crystalline forms.

The product obtained according to the present invention can be useful for the preparation of novel pharmaceutically acceptable salts.

In an eighth aspect, the application provides a crystalline Form A of sofosbuvir, characterized by a PXRD pattern comprising peaks at about 4.55, 8.53, 9.10, 12.78 and 13.68 ±0.2° 2Θ. Crystalline Form A sofosbuvir further characterized by PXRD pattern comprising peaks at about 4.91 , 7.15, 15.91 , 17.91 and 25.04 ±0.2° 2Θ.

In a ninth aspect, the application provides a process for preparation of Form A comprising peaks at about 4.55, 8.53, 9.10, 12.78 and 13.68 ±0.2° 2Θ; embodiments comprising:

a) contacting sofosbuvir with a solvent or a mixture of solvents wherein the solubility of sofosbuvir is low;

b) mixing the slurry obtained in step (a);

c) isolating crystalline Form A of sofosbuvir.

In an embodiment of the ninth aspect, the application provides a process for preparation of Form A of sofosbuvir, wherein step a) involves contacting sofosbuvir to a solvent or a mixture of solvents wherein the solubility of sofosbuvir is low. In embodiments, sofosbuvir added into a solvent or a mixture of such solvents wherein sofosbuvir has low solubility. In embodiments, a solvent a mixture of solvents which would least dissolve sofosbuvir is added to sofosbuvir. In embodiments, the ratio of sofosbuvir to a solvent or a mixture of such solvents, wherein sofosbuvir has low solubility, used is about 1 : 20 to about 20: 1 .

In another embodiment of the ninth aspect, the application provides the solvents or a mixture of solvents used are those wherein the sofosbuvir has low solubility. In embodiment, the solvents or mixture of solvents used are anti-solvents or mixture of anti-solvents. In embodiments, slurry of sofosbuvir is prepared by contacting sofosbuvir to anti-solvent or mixture of anti-solvents or vice versa. The anti-solvents used in the process can be alkanes or cycloalkanes or aromatic hydrocarbons or ethers and their mixtures comprising but not limited to n-heptane, n- hexane, cyclohexane, n-pentane, xylenes, toluene, MTBE, DIPE and their combinations. In embodiments, the ratio of sofosbuvir to anti-solvent or mixture of anti-solvents used is about 1 : 20 to about 20: 1 .

In another embodiment of the ninth aspect, the application a process for preparation of Form A of sofosbuvir, wherein step b) involves, mixing the slurry obtained in step (a). In embodiments, sofosbuvir and anti-solvent or mixture of anti- solvents is allowed to physical mixing. In embodiments, sofosbuvir and anti-solvent or mixture of anti-solvents is allowed to mechanical stirring. In embodiments, sofosbuvir and anti-solvent or mixture of anti-solvents is allowed to slurrying. Mixing may be used to reduce the time required for the making slurry.

In another embodiment of the ninth aspect, the application provides slurry of sofosbuvir can be prepared at any suitable temperatures, such as from about room temperature to about the reflux temperature based on the anti-solvent or mixture of anti-solvents selected. In embodiment, the slurrying comprises suspending sofosbuvir. The slurry of sofosbuvir can be maintained at any suitable temperatures, such as from about -5°C to 80°C. Optionally, the slurry of sofosbuvir and anti-solvent or mixture of anti-solvents is heated once after formation of slurry. Slurrying at above room temperature may reduce the required time for the formation Form A of sofosbuvir.

In another embodiment of the ninth aspect, the application provides optionally solvents wherein sofosbuvir is soluble can be added to the slurry of sofosbuvir and anti-solvents or mixture of anti-solvents. The solvent or mixture of solvents can be added at any suitable temperatures, such as from about room temperature to about the reflux temperature based on the solvent or mixture of solvents added to the slurry. The solvents can be used this process preferably comprising but not limited to alcohols such as propanol, ethanol and methanol or their combination.

In another embodiment of the ninth aspect, the application the temperature at which the slurry is maintained plays a role with respect to time for which the desired formation of Form A of sofosbuvir.

In another embodiment of the ninth aspect, the application provides optionally slurry of sofosbuvir and anti-solvent or mixture of anti-solvents is cooled. In embodiments, optionally slurry of sofosbuvir, anti-solvent or mixture of anti-solvents and solvent or mixture of solvents can be cooled. Slurry of sofosbuvir can be cooled to a temperature ranging from 28°C to -5°C or lower.

In another embodiment of the ninth aspect, the application provides in general, yields of the crystalline product will be improved by maintaining the reaction mass at lower temperatures that are above the freezing point of the solvent or anti- solvent, and/or by increasing the solute content of the solution.

In another embodiment of the ninth aspect, the application provides a process for preparation of Form A of sofosbuvir, wherein step c) involves, isolating crystalline Form A of sofosbuvir. In embodiments, crystalline Form A of sofosbuvir 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 solid can be washed with a solvent, such as the solvent used for the crystallization to reduce the amount of entrained impurities in the product. In embodiments, crystalline Form A of sofosbuvir can be isolated by filtration and optionally washing the wet cake with the same solvent.

In another embodiment of the ninth aspect, the application provides crystalline Form A of sofosbuvir that is isolated can be dried at suitable temperatures such as room temperature to about 50°C reduced pressures, for about 10 minutes to about 10 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, or the like. Drying temperatures and times will be sufficient to achieve desired product purity.

In tenth aspect, the present application provides a cocrystal of sofosbuvir with caffeine, characterized by a PXRD pattern comprising peaks at about 3.70, 4.42, 5.32, 14.82, 16.36, 17.21 and 21.04 ± 0.2° 2Θ. Cocrystal of sofosbuvir with caffeine, further characterized by PXRD pattern having peaks selected from the following: about 7.41 , 10.03 and 19.36 ± 0.2° 2Θ.

The cocrystal of sofosbuvir with caffeine described herein in the present application is consistently reproducible and cocrystal of sofosbuvir with caffeine which may be used in the preparation of pharmaceutical formulations for the treatment of HCV genotype 1 , 2, 3 or 4 infections.

In eleventh aspect, the application provides a process for preparation of cocrystal of sofosbuvir with caffeine comprising peaks at about 3.70, 4.42, 5.32, 14.82, 16.36, 17.21 and 21 .04 ± 0.2° 2Θ; comprising:

a) contacting sofosbuvir and caffeine to a solvent or a mixture of solvents wherein the solubility of sofosbuvir and caffeine is low;

d) isolating the cocrystal of sofosbuvir with caffeine.

In an embodiment of the eleventh aspect, the application provides a process for preparation of cocrystal of sofosbuvir with caffeine, wherein step a) involves contacting sofosbuvir and caffeine to a solvent or a mixture of solvents wherein the solubility of sofosbuvir and caffeine is low. In embodiments, sofosbuvir added into a solvent or a mixture of such solvents wherein sofosbuvir caffeine have low solubility. In embodiments, a solvent a mixture of solvents which would least dissolve sofosbuvir and caffeine is added to sofosbuvir and caffeine. In embodiments, the ratio of sofosbuvir and caffeine mixture to a solvent or a mixture of such solvents, wherein sofosbuvir and caffeine have low solubility, used is about 1 : 20 to about 20: 1 .

In another embodiment of the eleventh aspect, the application provides provides the molar ratio of sofosbuvir and caffeine can be used in the range of about 5:1 to about 1 :5. Caffeine can be initially added to sofosbuvir before contacting sofosbuvir with the solvent or a mixture of solvents (or) after contacting it with the solvent or mixture of solvents. Caffeine can be contacted with sofosbuvir or a solution of sofosbuvir in one lot or many lots.

In another embodiment of the eleventh aspect, the application provides the solvents or a mixture of solvents used are those wherein the sofosbuvir and caffeine have low solubility. In embodiment, the solvents or mixture of solvents used are anti- solvents or mixture of anti-solvents. In embodiments, slurry of sofosbuvir is prepared by contacting sofosbuvir to anti-solvent or mixture of anti-solvents or vice versa. The anti-solvents used in the process can be alkanes or cycloalkanes comprising but not limited to n-heptane, n-hexane, cyclohexane, n-pentane and their combinations. In embodiments, the ratio of sofosbuvir to anti-solvent or mixture of anti-solvents used is about 1 : 20 to about 20: 1 .

In another embodiment of the eleventh aspect, the application provides slurry of cocrystal of sofosbuvir with caffeine can be prepared at any suitable temperatures, such as from about room temperature to about the reflux temperature based on the anti-solvent or mixture of anti-solvents selected. In embodiment, the slurrying comprises suspending sofosbuvir and caffeine. The slurry of sofosbuvir and caffeine can be maintained at any suitable temperatures, such as from about -5°C to 80°C. Optionally, the slurry of sofosbuvir and caffeine & anti-solvent or mixture of anti- solvents can be heated once after formation of slurry. Slurrying at above room temperature may reduce the required time for the formation cocrystal of sofosbuvir with caffeine. In embodiment, sofosbuvir, caffeine, solvents or a mixture of solvents used are those wherein the sofosbuvir and caffeine have low solubility can be added into a reactor in any order at a temperature ranging from about 10 to about 50°C, or longer.

In another embodiment of the eleventh aspect, the application provides a cocrystal of sofosbuvir with caffeine, wherein step b) involves contacting slurry obtained in step a) with a solvent or a mixture of solvents. The solvents or mixture of solvents are those wherein sofosbuvir and caffeine are soluble. The solvent or mixture of solvents can be added at any suitable temperatures, such as from about room temperature to about the reflux temperature based on the solvent or mixture of solvents added to the slurry. The solvents can be used this step preferably comprising but not limited to alcohols such as propanol, ethanol and methanol or their combination.

In another embodiment of the eleventh aspect, the application provides a process for preparation of cocrystal of sofosbuvir with caffeine, wherein step c) involves mixing the slurry obtained in step b). In embodiments, the slurry obtained in step b) is allowed to physical mixing. In embodiments, the slurry obtained in step b) is allowed to mechanical stirring. In embodiments, the slurry obtained in step b) is allowed to slurrying. Mixing may be used to reduce the time required for the making slurry. In another embodiment of the eleventh aspect, the application provides optionally the slurry obtained in step c) is cooled. In embodiments, optionally slurry of sofosbuvir, caffeine, anti-solvent or mixture of anti-solvents and solvent or mixture of solvents can be cooled. Slurry of sofosbuvir and caffeine can be cooled to a temperature ranging from 28°C to -5°C or lower.

In another embodiment of the eleventh aspect, the application provides in general, yields of the cocrystalline product will be improved by maintaining the reaction mass at lower temperatures that are above the freezing point of the solvent or anti-solvent, and/or by increasing the solute content of the solution.

In another embodiment of the eleventh aspect, the application provides a process for preparation of cocrystal of sofosbuvir with caffeine, wherein step d) involves, isolating cocrystal of sofosbuvir with caffeine. In embodiments, cocrystal of sofosbuvir with caffeine 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 solid can be washed with a solvent, such as the solvent used for the crystallization to reduce the amount of entrained impurities in the product. In embodiments, cocrystal of sofosbuvir with caffeine can be isolated by filtration and optionally washing the wet cake with the same solvent.

In another embodiment of the eleventh aspect, the application cocrystal of sofosbuvir with caffeine that is isolated can be dried at suitable temperatures such as room temperature to about 50°C under atmospheric or reduced pressures, for about 10 minutes to about 10 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, or the like. Drying temperatures and times will be sufficient to achieve desired product purity.

In another embodiment of the eleventh aspect, the application provides sofosbuvir which is used as the starting material may be prepared by any method, including methods known in art. Optionally, sofosbuvir which is used as the starting material may be purified by using any methods known in art to enhance chemical purity.

In another embodiment of the eleventh aspect, the application the staring material, i.e.: sofosbuvir used for the preparation of Form A and caffeine cocrystal may be any crystalline form or amorphous form, preferably Form 1 of sofosbuvir. In another embodiment of the eleventh aspect, the application provides isolated crystalline Form A or cocrystal of sofosbuvir with caffeine according to the present invention can have a degree of crystallinity of at least about 80%, about 90%, about 95%, about 98%, about 99%, or above.

In another embodiment of the eleventh aspect, the application provides isolated crystalline Form A or cocrystal of sofosbuvir with caffeine according to the present invention can have isomeric purity of sofosbuvir at least about 90% of 'S' configuration at phosphorous position, about 98%, about 99%, or about 100%.

In another embodiment of the eleventh aspect, the application provides crystalline Form A or cocrystal of sofosbuvir with caffeine according to the present application can be substantially pure having a chemical purity greater than about 98% purity or greater than 99% purity, 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 sofosbuvir according to the present application can be chemically pure having purity greater than about 99% and containing no single known impurity in amounts greater than about 0.15%, by HPLC. In embodiment, crystalline forms of sofosbuvir according to the present application can be chemically pure having purity greater than about 99% and containing no single unknown impurity in amounts greater than about 0.1%, by HPLC.

The pharmaceutical compositions comprising crystalline Form A or cocrystal of sofosbuvir with caffeine 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.

The pharmaceutical compositions comprising crystalline Form A or cocrystal of sofosbuvir with caffeine of the invention together with one or more other active pharmaceutically ingredients, such as pan-genotypic NS5B/NS5A inhibitors, NS3 protease inhibitors, non-nucleoside NS5B site 2 polymerase inhibitors, pan- genotypic NS3 protease inhibitors, nucleotide reverse transcriptase inhibitors, Tarmogen T cell immunity stimulators, TLR-7 agonists, monoclonal antibodies etc., and 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 and cocrystal 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.

In thirteenth aspect, the application provides a process for the preparation of amorphous form of Sofosbuvir, comprising the steps of;

a) providing a solution of Sofosbuvir in a solvent;

b) removing solvent from the solution obtained in step a), and

c) isolating the amorphous form of Sofosbuvir.

Providing a solution of Sofosbuvir in step a) includes: i) direct use of a reaction mixture containing Sofosbuvir that is obtained in the course of its synthesis; or ii) dissolving Sofosbuvir in a solvent.

Any physical form of Sofosbuvir may be utilized for providing the solution of Sofosbuvir in step a). Sofosbuvir that may be used as the input for the process of the present invention may be obtained by any process including the processes described in the art.

Suitable solvents that may be used in step a) include, but are not limited to, alcohol solvents; ester solvents; ketone solvents; or mixtures thereof.

The dissolution temperatures may range from about 10°C to about the reflux temperature of the solvent, depending on the solvent used for dissolution, as long as a clear solution of Sofosbuvir is obtained without affecting its quality. The solution may optionally be treated with carbon, flux-calcined diatomaceous earth (Hyflow), or any other suitable material to remove color and/or to clarify the solution. Optionally, the solution obtained above may be filtered to remove any insoluble particles. The insoluble particles may be removed suitably by filtration, centrifugation, decantation, or any other suitable techniques. The solution may be filtered by passing through paper, glass fiber, or other membrane material, or a bed of a clarifying agent such as Celite® or Hyflow. Depending upon the equipment used and the concentration and temperature of the solution, the filtration apparatus may need to be preheated to avoid premature crystallization.

Step b) involves the removal of solvents from the solution obtained from step a). Suitable techniques which may be used for the removal of the solvent include using a rotational distillation device such as a rotavapor, spray drying, agitated thin film drying, freeze drying (lyophilization), hot melt extrusion (HME) and the like, or any other suitable technique.

The solvent may be removed, optionally under reduced pressures, at temperatures less than about 100°C, less than about 60°C, less than about 40°C, less than about 20°C, less than about 0°C or any other suitable temperatures.

Step c) involves isolation of an amorphous form of Sofosbuvir from the solution of step b). The compound obtained from step b) may be collected using techniques such as by scraping, or by shaking the container, or adding solvent to make slurry followed by filtration, or other techniques specific to the equipment used.

Step c), the amorphous obtained from step b) may be optionally dried. Drying may be suitably carried out in a tray dryer, vacuum oven, rotavapor, air oven, fluidized bed dryer, spin flash dryer, flash dryer, or the like. The drying may be carried out at atmospheric pressure or under reduced pressures at temperatures of less than about 1 00°C, less than about 60°C, less than about 40°C, or any other suitable temperatures. The drying may be carried out for any time period required for obtaining a desired quality, such as from about 15 minutes to 10 hours or longer.

In an embodiment of the thirteenth aspect, the application provides a process for the preparation of amorphous form of Sofosbuvir comprising:

b) removing solvent from the solution obtained in step a), and

c) isolating the amorphous form of Sofosbuvir.

Providing a solution of Sofosbuvir in step a) includes: i) direct use of a reaction mixture containing Sofosbuvir that is obtained in the course of its synthesis; or ii) dissolving Sofosbuvir in a solvent selected from methanol, ethyl acetate, dichloromethane, acetonitrile or mixtures thereof;

The dissolution temperatures may range from about 10°C to about the reflux temperature of the solvent, depending on the solvent used for dissolution, as long as a clear solution of Sofosbuvir is obtained without affecting its quality. The solution may optionally be treated with carbon, flux-calcined diatomaceous earth (Hyflow), or any other suitable material to remove color and/or to clarify the solution.

Optionally, the solution obtained above may be filtered to remove any insoluble particles. The insoluble particles may be removed suitably by filtration, centrifugation, decantation, or any other suitable techniques. The solution may be filtered by passing through paper, glass fiber, or other membrane material, or a bed of a clarifying agent such as Celite® or Hyflow. Depending upon the equipment used and the concentration and temperature of the solution, the filtration apparatus may need to be preheated to avoid premature crystallization.

The dried product may be optionally milled to get desired particle sizes. Milling or micronization may be performed before drying, or after the completion of drying of the product. Techniques that may be used for particle size reduction include, without limitation, ball, roller and hammer mills, and jet mills.

Examples of amorphous Sofosbuvir obtained using the above process is characterized by powder X-ray diffraction ("PXRD") pattern substantially as illustrated by Figs. 1 and 2.

In another embodiment of the thirteenth aspect, the application provides the amorphous form of Sofosbuvir obtained according to the present invention can be used as an intermediate for making any crystalline form of Sofosbuvir or solid dispersion of Sofosbuvir along with the other pharmaceutically acceptable excipients.

In another embodiment of the thirteenth aspect, the application provides pharmaceutical formulations comprising amorphous form of Sofosbuvir, together with one or more pharmaceutically acceptable excipients. Amorphous form of Sofosbuvir together with one or more pharmaceutically acceptable excipients of the present application may be formulated as: solid oral dosage forms such as, but not limited to, powders, granules, pellets, tablets, or capsules; liquid oral dosage forms such as, but not limited to, syrups, suspensions, dispersions, or emulsions; or injectable preparations such as, but not limited to, solutions, dispersions, or freeze dried compositions. Formulations may be in the forms of immediate release, delayed release, or modified release. Further, immediate release compositions may be conventional, dispersible, chewable, mouth dissolving, or flash melt preparations, or modified release compositions that may comprise hydrophilic or hydrophobic, or combinations of hydrophilic and hydrophobic, release rate controlling substances to form matrix or reservoir or combination of matrix and reservoir systems. The compositions may be prepared using techniques such as direct blending, dry granulation, wet granulation, or extrusion and spheronization. Compositions may be presented as uncoated, film coated, sugar coated, powder coated, enteric coated, or modified release coated. Compositions of the present application may further comprise one or more pharmaceutically acceptable excipients. Pharmaceutically acceptable excipients that are useful in the present application include, but are not limited to: diluents such as starches, pregelatinized starches, lactose, powdered celluloses, microcrystalline celluloses, dicalcium phosphate, tricalcium phosphate, mannitol, sorbitol, sugar, or the like; binders such as acacia, guar gum, tragacanth, gelatin, polyvinylpyrrolidones, hydroxypropyl celluloses, hydroxypropyl methyl celluloses, pregelatinized starches, or the like; disintegrants such as starches, sodium starch glycolate, pregelatinized starches, crospovidones, croscarmellose sodium, colloidal silicon dioxide, or the like; lubricants such as stearic acid, magnesium stearate, zinc stearate, or the like; glidants such as colloidal silicon dioxide or the like; solubility or wetting enhancers such as anionic or cationic or neutral surfactants; complex forming agents such as various grades of cyclodextrins or resins; release rate controlling agents such as hydroxypropyl celluloses, hydroxymethyl celluloses, hydroxypropyl methylcelluloses, ethylcelluloses, methylcelluloses, various grades of methyl methacrylates, waxes, or the like. Other pharmaceutically acceptable excipients that are of use include, but are not limited to, film formers, plasticizers, colorants, flavoring agents, sweeteners, viscosity enhancers, preservatives, antioxidants, or the like.

In a fifteenth aspect, the present application provides amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers.

In a sixteenth aspect, the present application provides a process for preparing an amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers, comprising:

b) removing solvent from the solution obtained in step a), and

Providing the solution in step a) includes:

(i) direct use of a reaction mixture containing Sofosbuvir that is obtained in the course of its manufacture, if desired, after addition of one or more pharmaceutically acceptable carriers; or

(ii) dissolution of Sofosbuvir in a suitable solvent, either alone or in combination with one or more pharmaceutically acceptable carriers. Any physical form of Sofosbuvir may be utilized for providing a solution in step a).

Pharmaceutically acceptable carriers that may be used for the preparation of amorphous solid dispersions of Sofosbuvir of the present invention include, but are not limited to: pharmaceutical hydrophilic carriers such as polyvinylpyrrolidones (homopolymers or copolymers of N-vinyl pyrrolidone), gums, cellulose derivatives (including hydroxypropyl methylcelluloses, hydroxypropyl celluloses, hydroxypropyl methylcellulose acetate succinate, microcrystalline celluloses and others), polymers of carboxymethyl celluloses, cyclodextrins, gelatins, hypromellose phthalates, sugars, polyhydric alcohols, polyethylene glycols, polyethylene oxides, polyoxyethylene derivatives, polyvinyl alcohols, propylene glycol derivatives, or the like; water soluble sugar derivatives including any pharmaceutically acceptable water soluble sugar excipients, preferably having low hygroscopicity, which include, but are not limited to, mannitol, lactose, fructose, sorbitol, xylitol, maltodextrin, dextrates, dextrins, lactitol, or the like; or organic amines such as alkyl amines (primary, secondary, and tertiary), aromatic amines, alicyclic amines, cyclic amines, aralkyl amines, hydroxylamine or its derivatives, hydrazine or its derivatives, and guanidine or its derivatives. The use of mixtures of more than one of the pharmaceutical excipients to provide desired release profiles or for the enhancement of stability is within the scope of this invention. Also, all viscosity grades, molecular weights, commercially available products, their copolymers, and mixtures are all within the scope of this invention without limitation. The preferable pharmaceutically acceptable carriers include but not limited to Polyvinylpyrrolidone (PVP K-30), Copovidone, Hydroxypropyl cellulose (HPC) and Hydroxypropy methyl cellulose (HPMC).

When the solution or suspension of Sofosbuvir is prepared together with a pharmaceutically acceptable carrier, the order of charging different materials to the solution is not critical for obtaining the desired solid dispersion. A specific order may be preferred with respect to the equipment being used and will be easily determined by a person skilled in the art. Sofosbuvir or pharmaceutically acceptable carrier may be completely soluble in the solvent or they may form a suspension.

In an embodiment of the sixteenth aspect, the application provides sofosbuvir and the pharmaceutically acceptable carrier dissolved either in the same solvent or in different solvents, and then combined to form a mixture.

Suitable solvents that may be used in step a) include, but are not limited to, alcohol solvents; or mixtures thereof. The dissolution temperatures may range from about 10°C to about the reflux temperature of the solvent, depending on the solvent used for dissolution, as long as a clear solution of Sofosbuvir is obtained without affecting its quality. The solution may optionally be treated with carbon, flux-calcined diatomaceous earth (Hyflow), or any other suitable material to remove color and/or to clarify the solution.

Step c) involves isolation of amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers from the solution of step b).

The compound obtained from step b), may be collected using techniques such as by scraping, or by shaking the container, or adding solvent to make slurry followed by filtration, or other techniques specific to the equipment used. The product thus isolated may be optionally further dried to afford an amorphous form of Sofosbuvir together with a pharmaceutically acceptable excipients. Drying may be suitably carried out in a tray dryer, vacuum oven, rotavapor, air oven, fluidized bed dryer, spin flash dryer, flash dryer, or the like.

The drying may be carried out at atmospheric pressure or under reduced pressures at temperatures of less than about 100°C, less than about 60°C, less than about 40°C, or any other suitable temperatures. The drying may be carried out for any time period required for obtaining a desired quality, such as from about 15 minutes to 10 hours or longer.

Examples of amorphous solid dispersion of Sofosbuvir together with a pharmaceutically acceptable carrier obtained using the above process is characterized by powder X-ray diffraction ("PXRD") pattern substantially as illustrated by Fig. 3.

In seventeenth aspect, the present application provides a process for the preparation of amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers, comprising:

a) providing a solution of Sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from The carriers include but not limited to Polyvinylpyrrolidone, Copovidone, Hydroxypropyl cellulose (HPC) and Hydroxypropy methyl cellulose (HPMC) in a solvent;

b) removing solvent from the solution obtained in step a), and

In an embodiment seventeenth aspect, the application provides step a) wherein the solution of Sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from polyvinylpyrrolidones, copovidone, hydroxypropyl methylcelluloses, hydroxypropyl celluloses or hydroxypropyl methylcellulose acetate succinate can be obtained by dissolving Sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from polyvinylpyrrolidones, copovidone, hydroxypropyl methylcelluloses, hydroxypropyl celluloses or hydroxypropyl methylcellulose acetate succinate in a solvent selected. Stirring and heating may be used to reduce the time required for the dissolution process.

In another embodiment seventeenth aspect, the application provides a solution of sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from polyvinylpyrrolidones, copovidone, hydroxypropyl methylcelluloses, hydroxypropyl celluloses or hydroxypropyl methylcellulose acetate succinate may be filtered to make it clear, free of unwanted particles. In embodiments, the obtained solution may be optionally treated with an adsorbent material, such as carbon and/or hydrose, to remove colored components, etc., before filtration.

Step c) involves isolation of amorphous solid dispersion of Sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from polyvinylpyrrolidones, copovidone, hydroxypropyl methylcelluloses, hydroxypropyl celluloses or hydroxypropyl methylcellulose acetate succinate from the solution of step b).

The compound obtained from step b) may be collected using techniques such as by scraping, or by shaking the container, or adding solvent to make slurry followed by filtration, or other techniques specific to the equipment used. The product thus isolated may be optionally further dried to afford an amorphous form of Sofosbuvir in combination with one or more pharmaceutically acceptable carriers selected from polyvinylpyrrolidones, copovidone, hydroxypropyl methylcelluloses, hydroxypropyl celluloses or hydroxypropyl methylcellulose acetate succinate. Drying may be suitably carried out in a tray dryer, vacuum oven, rotavapor, air oven, fluidized bed dryer, spin flash dryer, flash dryer, or the like.

In eighteenth aspect, the application provides pharmaceutical formulations comprising amorphous solid dispersions of Sofosbuvir together with one or more pharmaceutically acceptable excipients.

In an embodiment of the eighteenth embodiment, the application provides optionally adding carriers to the amorphous solid dispersion of Sofosbuvir. Addition of carriers to the amorphous solid dispersion of Sofosbuvir may also be necessary when the formulation contains a hygroscopic ingredient, especially when absorption of moisture produces a cohesive powder that will not feed properly to the tablet press. In such instances use of an carrier or absorbent such as syloid, methyl cellulose, colloidal silicon dioxide, Eudragit, amorphous silica, micro crystalline cellulose, and the like, in the formulation has been found to be of particular value.

A solid dispersion of sofosbuvir together with one or more pharmaceutically acceptable excipients of the present invention may be further 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 forms 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 that may comprise hydrophilic or hydrophobic, or combinations of hydrophilic and hydrophobic, release rate controlling substances to form matrix or reservoir or combination of matrix and reservoir systems. The compositions may be prepared using 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, and modified release coated. Compositions of the present invention may further comprise one or more pharmaceutically acceptable excipients.

Form A of sofosbuvir, cocrystal of sofosbuvir with caffeine, solid dispersion of sofosbuvir and amorphous sofosbuvir produced according to the present invention can be used as intermediates in preparation of other polymorphic forms of sofosbuvir. Pharmaceutically acceptable excipients that are useful in the present invention include, but are not limited to: diluents such as starches, pregelatinized starches, lactose, powdered celluloses, microcrystalline celluloses, dicalcium phosphate, tricalcium phosphate, mannitol, sorbitol, sugar or the like; binders such as acacia, guar gum, tragacanth, gelatin, pregelatinized starches or the like; disintegrants such as starches, sodium starch glycolate, pregelatinized starches, crospovidones, croscarmellose sodium, colloidal silicon dioxide or the like; lubricants such as stearic acid, magnesium stearate, zinc stearate or the like; glidants such as colloidal silicon dioxide or the like; solubility or wetting enhancers such as anionic or cationic or neutral surfactants; complex forming agents such as various grades of cyclodextrins and resins; release rate controlling agents such as hydroxypropyl celluloses, hydroxymethyl celluloses, hydroxypropyl methylcelluloses, ethylcelluloses, methylcelluloses, various grades of methyl methacrylates, waxes or the like. Other pharmaceutically acceptable excipients that are of use include but are not limited to film formers, plasticizers, colorants, flavoring agents, sweeteners, viscosity enhancers, preservatives, antioxidants, or the like.

Different solid forms are characterized by scattering techniques, e.g., x-ray powder diffraction pattern, by spectroscopic methods, e.g., infra-red, ¹³C nuclear magnetic resonance spectroscopy, and by thermal techniques, e.g., differential scanning calorimetry or differential thermal analysis. The compound of this application is best characterized by the X-ray powder diffraction pattern determined in accordance with procedures that are known in the art. For a discussion of these techniques see J. Haleblian, J. Pharm. Sci. 1 975 64:1269-1288, and J. Haleblian and W. McCrone, J. Pharm. Sci. 1969 58:91 1 -929. Amorphous form of the application can be further processed to modulate particle size. For example, the amorphous form of the application can be milled to reduce average crystal size and/or to prepare a sample suitable for manipulation or formulation.

In another embodiment of the eighteenth embodiment, the application provides amorphous Sofosbuvir or amorphous solid dispersions of sofosbuvir prepared according to the processes of 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). Amorphous Sofosbuvir or amorphous solid dispersions of Sofosbuvir produced by the method of present invention 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.

The pharmaceutical compositions comprising amorphous Sofosbuvir of the invention together with one or more other active pharmaceutically ingredients, such as pan-genotypic NS5B/NS5A inhibitors, NS3 protease inhibitors, non-nucleoside NS5B site 2 polymerase inhibitors, pan-genotypic NS3 protease inhibitors, nucleotide reverse transcriptase inhibitors, Tarmogen T cell immunity stimulators, TLR-7 agonists, monoclonal antibodies etc., and 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.

Amorphous sofosbuvir or amorphous solid dispersions of sofosbuvir 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. DEFINITIONS

As used herein, the term "alkyl" refers to a straight or branched saturated monovalent cyclic or acyclic hydrocarbon radical, having the number of carbon atoms vary from CMO.

The term "aryl," as used herein, and unless otherwise specified, refers to substituted or unsubstituted phenyl (Ph), biphenyl, or naphthyl, preferably the term aryl refers to substituted or unsubstituted phenyl. The aryl group can be substituted with one or more moieties selected from among hydroxyl, F, CI, Br, I, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, and phosphonate, either unprotected, or protected as necessary, as known to those skilled in the art, for example, as taught in T. W. Greene and P. G. M. Wuts, "Protective Groups in Organic Synthesis," 3rd ed., John Wiley & Sons, 1999. Preferably the aryl can be substituted or unsbustituted phenyl.

The term "halo," as used herein, includes chloro, bromo, iodo and fluoro.

The term "protecting group", as used herein and unless otherwise defined, refers to a group that is added to an oxygen, nitrogen, or phosphorus atom to prevent its further reaction or for other purposes. A wide variety of oxygen and nitrogen protecting groups are known to those skilled in the art of organic synthesis. Non-limiting examples include: C(0)-alkyl, C(0)Ph, C(0)aryl, CH₃, CH₂-alkyl, CH₂- alkenyl, CH₂Ph, CH₂-aryl, CH₂0-alkyl, CH₂0-aryl, S0₂-alkyl, S0₂-aryl, tert- butyldimethylsilyl, tert-butyldiphenylsilyl, and 1 ,3-(1 ,1 ,3,3-tetraisopropyl disiloxanylidene).

The term "amino acid" includes naturally occurring and synthetic .alpha, beta, gamma or delta amino acids, and includes but is not limited to, amino acids found in proteins, i.e. glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline, serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginine and histidine. In a preferred embodiment, the amino acid is in the L-configuration. Alternatively, the amino acid can be a derivative of alanyl, valinyl, leucinyl, isoleucinyl, prolinyl phenylalaninyl, tryptophanyl, methioninyl, glycinyl, serinyl, threoninyl, cysteinyl, tyrosinyl, asparaginyl, glutaminyl, aspartoyl, glutaroyl, lysinyl, argininyl, histidinyl, .beta.-alanyl, .beta.-valinyl, .beta.- leucinyl, .beta.-isoleucinyl .beta.-prolinyl, .beta.-phenylalaninyl, .beta.-tryptophanyl, .beta.-methioninyl, .beta.-glycinyl, .beta.-serinyl, .beta.-threoninyl, .beta.-cysteinyl, .beta.-tyrosinyl, .beta.-asparaginyl, .beta.-glutaminyl, .beta.-aspartoyl, .beta.- glutaroyl, .beta.-lysinyl, .beta.-argininyl or .beta.-histidinyl. When the term amino acid is used, it is considered to be a specific and independent disclosure of each of the esters of .alpha., .beta, .gamma, or .delta, glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline, serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginine and histidine in the D and L-configurations.

The term is a leaving group, such as CI, Br, I, sulfate, acetate, tosylate, mesylate, trifluoroacetate, trifluorosulfonate, phenoxide, pentafluorophenoxide, p- N02-phenoxide, tert-butyldimethylsilyl and levulinyl group or other commonly used leaving groups as disclosed in Advanced Organic Chemistry by March, Fourth Edition.

The term "about" when used in the present invention preceding a number and referring to it, is meant to designate any value which lies within the range of ±10%, preferably within a range of ±5%, more preferably within a range of ±2%, still more preferably within a range of ±1 % of its value. For example "about 1 0" should be construed as meaning within the range of 9 to 1 1 , preferably within the range of 9.5 to 10.5, more preferably within the range of 9.8 to 10.2, and still more preferably within the range of 9.9 to 10.1 .

A "pharmaceutically acceptable salt" form of an active ingredient may also initially confer a desirable pharmacokinetic property on the active ingredient which were absent in the non-salt form, and may even positively affect the pharmacodynamics of the active ingredient with respect to its therapeutic activity in the body. The phrase "pharmaceutically acceptable salt" of a compound as used herein means a salt that is pharmaceutically acceptable and that possesses the desired pharmacological activity of the parent compound. Such salts include: (1 ) acid addition salts, formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like; or formed with organic acids such as glycolic acid, pyruvic acid, lactic acid, malonic acid, malic acid, inaleic acid, fumaric acid, tartaric acid, citric acid, 3-(4-hydroxybenzoyl)benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, 1 ,2-ethane- disulfonic acid, 2-hydroxyethanesulfonic acid, benzenesulfonic acid, 4- chiorobenzenesulfonic acid, 2-naphthalenesulfonic acid, 4-toluenesulfonic acid, camphorsulfonic acid, lauryl sulfuric acid, gluconic acid, glutamic acid, salicylic acid, muconic acid, and the like or (2) basic addition salts formed with the conjugate bases of any of the inorganic acids listed above, wherein the conjugate bases comprise a cationic component selected from among Na⁺, K⁺, Mg²⁺andCa²⁺. It should be understood that all references to pharmaceutically acceptable salts include solvent addition forms (solvates) or crystal forms (polymorphs) as defined herein, of the same acid addition salt.

The term "purified," as described herein, refers to the purity of a given compound. For example, a compound is "purified" when the given compound is a major component of the composition, i.e., at least 50% w/w pure. Thus, "purified" embraces at least 50% w/w purity, at least 60% w/w purity, at least 70% purity, at least 80% purity, at least 85% purity, at least 90% purity, at least 92% purity, at least 94% purity, at least 96% purity, at least 97% purity, at least 98% purity, at least 99% purity, at least 99.5% purity, and at least 99.9% purity, wherein "substantially pure" embraces at least 97% purity, at least 98% purity, at least 99% purity, at least 99.5% purity, and at least 99.9% purity.

As used throughout herein, the term room temperature refers to a temperature of from about 18°C to about 28°C, preferably about 20°C to about 25°C.

The anti-solvent is a solvent in which sofosbuvir, caffeine and a mixture of sofosbuvir and caffeine have a low solubility.

The term "amorphous" refers to a solid lacking any long-range translational orientation symmetry that characterizes crystalline structures although; it may have short range molecular order similar to a crystalline solid.

The following definitions are used in connection with the present application unless the context indicates otherwise. In general, the number of carbon atoms present in a given group or compound is designated "C_x-C_y", where x and y are the lower and upper limits, respectively. For example, a group designated as "CrC₆" contains from 1 to 6 carbon atoms. The carbon number as used in the definitions herein refers to carbon backbone and carbon branching, but does not include carbon atoms of the substituents, such as alkoxy substitutions and the like.

Celite^® is flux-calcined diatomaceous earth. Celite^® is a registered trademark of World Minerals Inc.

Hyflow is flux-calcined diatomaceous earth treated with sodium carbonate. Hyflo Super Cel™ is a registered trademark of the Manville Corp. An "alcohol solvent" is an organic solvent containing a carbon bound to a hydroxyl group. "Alcoholic solvents" include, but are not limited to, methanol, ethanol, 2- nitroethanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, hexafluoroisopropyl alcohol, ethylene glycol, 1 -propanol, 2-propanol (isopropyl alcohol), 2-methoxyethanol, 1 - butanol, 2-butanol, i-butyl alcohol, t-butyl alcohol, 2-ethoxyethanol, diethylene glycol, 1 -, 2-, or 3-pentanol, neo-pentyl alcohol, t-pentyl alcohol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, cyclohexanol, benzyl alcohol, phenol, glycerol, d-₆alcohols, or the like.

An "ester solvent" is an organic solvent containing a carboxyl group -(C=0)-0- bonded to two other carbon atoms. "Ester solvents" include, but are not limited to, ethyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, ethyl formate, methyl acetate, methyl propanoate, ethyl propanoate, methyl butanoate, ethyl butanoate, C₃-6 esters, or the like.

A "ketone solvent" is an organic solvent containing a carbonyl group -(C=0)- bonded to two other carbon atoms. "Ketone solvents" include, but are not limited to, acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone, C₃-₆ketones, 4- methyl-pentane-2-one or the like.

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 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:

1 -((2R,3R,4R,5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3- methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione (100 mg), pyridine (0.6 mL) and 4 A molecular sieves (20 mg) were added into a round bottom flask and stirred at -10°C for 10 minutes. Diphenyl phosphite (0.09 mL) was added to the reaction mixture under nitrogen atmosphere and stirred at -1 0°C to 0°C for 50 minutes. The reaction mixture was analyzed to identify the presence of starting material. An additional quantity of diphenyl phosphite (0.06 mL) was added at 0°C and stirred for additional 20 minutes to complete the reaction.

A solution of hydrochloride salt of isopropyl L-Alanine ester (148 mg) in acetonitrile (2 mL) and pyridine (0.25 mL) was added to the above reaction mixture and stirred at 0°C for 5 minutes. Carbon tetrachloride (CCI₄) (1 mL) and triethylamine (0.37 mL) were added to the reaction mixture at 0°C, then the reaction mixture warmed to 30°C and stirred for 10 minutes. After completion of the reaction, the solvent was evaporated under reduced pressure.The residue was dissolved in ethyl acetate (EtOAc) (20 mL) and washed with water (5 mL), brine solution (5 mL), dried over Sodium sulfate (Na₂S0₄). Then solvent from the reaction mass was evaporated under reduced pressure to obtain the crude product which was purified by silica gel column chromatography (60-120 mesh, 3% MeOH-CH2CI2) to obtain 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 as a pale yellow solid.

Yield = 30 mg

Example-2: Preparation of 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:

1 -((2R,3R,4R,5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3- methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione (50 mg) and dimethyl formamide (DMF) (1 mL) were charged into a round bottom flask; and stirred at 27°C. Imidazole (66 mg) and tert-Butyldimethylsilyl chloride (TBDMSCI) (145 mg) were added to the reaction mixture and stirred for 24 hours at 27°C. The reaction mixture is analyzed to identify the presence of starting material. Additional quantity of imidazole (66 mg) and tert-Butyldimethylsilyl chloride (TBDMSCI) (145 mg) were added to the reaction mixture and stirred at 27°C for another 24 hours to get 1 - ((2R,3R,4R,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert- butyldimethylsilyl)oxy)methyl)-3-fluoro-3-methyltetrahydrofuran-2-yl)pyrimidine- 2,4(1 H,3H)-dione. After completion of the reaction, the reaction mixture was quenched with saturated Sodium bicarbonate (NaHC0₃) (10 mL) and stirred for 1 0 min, extracted with dichloromethane (DCM) (3 x 15 mL), washed with water (2 x 10 mL), brine (2 x 10 mL) and dried over Na₂S0₄. The solvent from the reaction mass was evaporated under reduced pressure to obtain the crude product which was purified by silica gel column chromatography (100-200 mesh, 20% EtOAc-Hexane) to obtain a colorless liquid.

Yield = 85 mg

1 -((2R,3R,4R,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert- butyldimethylsilyl)oxy)methyl)-3-fluoro-3-methyltetrahydrofuran-2-yl)pyrimidine- 2,4(1 H,3H)-dione (85 mg) and tetrahydrofuran (THF) (2 mL) were charged into a round bottom flask; and stirred at 0°C. A solution of trichloroacetic acid (455 mg) in water (0.5 mL) was added to the round bottom flask and stirred at 0°C for 18 hours to get 1 -((2R,3R,4R,5R)-4-((tert-butyldimethylsilyl)oxy)-3-fluoro-5-(hydroxymethyl)-3- methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione.The above obtained reaction mass was quenched with Sodium bicarbonate (NaHC0₃)(1 g) and water (1 mL) till the reaction mixture turned basic and extracted with dichloromethane (DCM) (3 x 10 mL) and washed with water (2 x 10 mL), brine (1 x 10 mL) and dried over Na₂S0_4. Evaporation of the solvent gave the product as a white solid.

Yield = 35 mg

1 -((2R,3R,4R,5R)-4-((tert-butyldimethylsilyl)oxy)-3-fluoro-5-(hydroxymethyl)-3- methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione (50 mg), dry pyridine (0.3 mL) and 4 A molecular sieves (20 mg) was added into a round bottom flask under nitrogen atmosphere. The reaction mixture was cooled to -10°C and diphenyl phosphite (77 μΐ) was added.The reaction mixture was stirred at -10°C to 0°C for 1 hour. After the completion of starting material as monitored by mass analysis, a solution of HCI salt of isopropyl L-Alanine ester (32.5 mg) in acetonitrile (2 mL) and pyridine (0.2 mL); followed by carbon tetrachloride (CCI₄) (1 mL), triethylamine (95 μΐ) were added to the reaction mixture at 0°C and stirred at 20°C for 30 min to get isopropyl ((((2R,3R,4R,5R)-3-((tert-butyldimethylsilyl)oxy)-5-(2,4-dioxo-3,4- dihydropyrimidin-1 (2H)-yl)-4-fluoro-4-methyltetrahydrofuran-2- yl)methoxy)(phenoxy)phosphoryl)-L-alaninate.

After completion of the reaction, the solvent was evaporated under reduced pressure. The crude product was purified by silica gel column chromatography (60- 120 mesh, 50% EtOAc-Hexane) to obtain a pale yellow liquid.

Yield = 40 mg

Isopropyl ((((2R,3R,4R,5R)-3-((tert-butyldimethylsilyl)oxy)-5-(2,4-dioxo-3,4- dihydropyrimidin-1 (2H)-yl)-4-fluoro-4-methyltetrahydrofuran-2- yl)methoxy)(phenoxy)phosphoryl)-L-alaninate(40 mg) in tetrahydrofuran(THF) (0.5 mL) added into a round bottom flask. 80% aqueous AcOH (0.5 mL) was added into the reaction mixture and stirred at 80°C for 72 hours. The reaction mixture was cooled to 25°C and the solvent was evaporated under reduced pressure. Analysis of the crude reaction mass indicated the presence of starting material along with the product 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.

Example-3: Preparation of 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:

1 -((2R,3R,4R,5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3- methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione (1 g) and pyridine (10 mL) were charged into a round bottom flask; and stirred at 32°C. The reaction mixture was cooled to 0°C. Tert-Butyldimethylsilyl chloride (TBDMSCI) (1 .27 g) was added over a period of 3 minutes and stirred the reaction mass at 25°C for 18 hours to get 1 -((2R,3R,4R,5R)-5-(((tert-butyldimethylsilyl)oxy)methyl)-3-fluoro-4-hydroxy-3- methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)-dione. After completion of the reaction, the reaction mixture was quenched with methanol (3 mL) and solvent was evaporated under reduced pressure. The crude reaction mass obtained was diluted with ethyl acetate (EtOAC) (25 mL) and water (15 mL), washed with saturated Sodium bicarbonate (NaHC0₃) (1 x 20 mL), water (1 x 10 mL), brine (1 x 10 mL) and dried over Na2S04. Evaporation of solvent gave product as a pale yellow liquid. Yield = 1 .5 gram

Levulinic acid (1 mL) in 1 ,4 dioxane ( 20 mL)were charged into a round bottom flask under nitrogen atmosphere at 31 °C. The reaction mixture was cooled to 0°C. Ν,Ν'-Dicyclohexylcarbodiimide (DCC) (1.07 g) was added over a period of 30 minutes wherein a white precipitate was formed. The reaction mixture was stirred at 31 °C for 30 minutes. A solution of 1 -((2R,3R,4R,5R)-5-(((tert- butyldimethylsilyl)oxy)methyl)-3-fluoro-4-hydroxy-3-methyltetrahydrofuran-2- yl)pyrimidine-2,4(1 H,3H)-dione (1 .5 g) and pyridine (5 mL) were charged into the above reaction mixture in 5 minutes and the reaction mass was stirred at 31 °C for 17 hours. The reaction mixture is analyzed to identify the presence of starting material. Additional quantity of Ν,Ν'-Dicyclohexylcarbodiimide (DCC) (576 mg) was added and stirred at 31 °C for 3 hours to get (2R,3R,4R,5R)-2-(((tert- butyldimethylsilyl)oxy)methyl)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-yl)-4-fluoro-4- methyltetrahydrofuran-3-yl 4-oxopentanoate.

After the completion of the reaction, the reaction mass was filtered and the solvent evaporated under reduce pressure. Then the crude product was diluted with ethyl acetate (EtOAC) (25 mL) and water (20 mL), washed with saturated sodium bicarbonate (NaHC0₃) (2 x 10 mL), brine (1 x 10 mL) and dried over sodium sulfate (Na₂S0₄). Evaporation of solvent gave the product as a pale yellow liquid.

Yield = 1 .8 gm

(2R,3R,4R,5R)-2-(((tert-butyldimethylsilyl)oxy)methyl)-5-(2,4-dioxo-3,4- dihydropyrimidin-1 (2H)-yl)-4-fluoro-4-methyltetrahydrofuran-3-yl 4-oxopentanoate (1 .8 g) in THF (36 mL) was added into a round bottom flask under nitrogen atmosphere. The reaction mass was cooled to 0°C. Acetic acid (1 0.1 1 mL) and tetra- n-butylammonium fluoride (TBAF) (1 M in THF) (7.6 mL) were sequentially added to the reaction mixture and stirred at 27°C for 16 hours.

After completion of the reaction mixture, the solvent was evaporated under reduced pressure. The reaction mass was diluted with ethyl acetate (EtOAC) (30 mL) and water (15 mL), washed with saturated sodium bicarbonate (NaHC0₃) (1 x 20 mL), brine solution (2 x 10 mL) and dried over sodium sulphate (Na₂S0₄). Then it was purified by silica gel column chromatography (60-1 20 mesh, 75-80% ethyl acetate-Hexane) to obtain (2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)- yl)-4-fluoro-2-(hydroxymethyl)-4-methyltetrahydrofuran-3-yl 4-oxopentanoate as a colorless liquid .

Yield = 500 mg

(2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-yl)-4-fluoro-2- (hydroxymethyl)-4-methyltetrahydrofuran-3-yl 4-oxopentanoate (200 mg), dry pyridine (1 .2 mL) and 4 A molecular sieves (50 mg) were added into a round bottom flask at 31 °C under nitrogen atmosphere. The reaction mixture was cooled to -10°C and diphenyl phosphite (0.32 mL) was added into the reaction mixture and stirred at -10°C to 0°C for 1 hour.

After the completion of starting material as monitored by mass analysis, a solution of hydrochloride salt of isopropyl L-Alanine ester (233 mg) in acetonitrile (4 mL) and pyridine (0.5 mL) were added into a round bottom flask under nitrogen atmosphere. The reaction mixture was charged into above solution and the reaction mass was cooled to 0°C. Carbon tetrachloride (CCI₄) (2 mL) and triethylamine (0.39 mL) were added to the reaction mixture at 0°C and stirred at 30°C for 30 min. After completion of the reaction mixture, the solvent was evaporated under reduced pressure. The reaction mass was diluted with ethyl acetate (EtOAC) (20 mL) and water (5 mL), washed with 1 N HCI (1 x 10 mL), brine solution (1 x 5 mL) and dried over sodium sulphate (Na₂S0₄). Then it was purified by silica gel column chromatography (60-120 mesh, 2% MeOH-CH2CI2) to obtain product as a colorless liquid.

Yield = 1 10 mg

The above product (50 mg) in tetrahydrofuran (THF) (1 mL) was added into a round bottom flask. A solution of sodium sulfite (25 mg dissolved in 1 mL water) was added to the reaction mass and stirred at 31 °C for 4 hours.

After completion of the reaction, solvent was evaporated under reduced pressure. The obtained crude product was diluted with ethyl acetate (EtOAC) (2 x 5 mL), washed with water (1 x 5 mL), brine solution (1 x 3 mL) and dried over sodium sulfate (Na₂S0₄). It was further purified by silica gel column chromatography (60-120 mesh, 3% MeOH-CH2CI2) to yield 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 as a colorless liquid.

Yield = 20 mg

Example-4: Preparation of phenyl dihydrogen phosphate:

Phenyl dichlorophosphate (5 gm) was charged into a round bottom flask at 27°C. The flask was cooled to 10°C. Water is added to the reaction mass in a single lot and stirred at 10°C for 30 minutes. The reaction mixture was warmed to 27°C and stirred for 16 hours.

The reaction mixture is evaporated at 50°C under reduced pressure followed by co-evaporated with toluene (2x25 mL) at 50°C. The reaction mass was triturated with n-Hexane (2x25 mL). The product was dried at 50°C under vacuum for 30 minutes.

Yield = 4 g

Example-5: Preparation of ((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin- 1 (2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methyl phenyl hydrogen phosphate: Phenyl dihydrogen phosphate (174 mg) and pyridine (4 mL) were charged into a round bottom flask at 27°C under nitrogen atmosphere. 1 -((2R,3R,4R,5R)-3- fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine- 2,4(1 H,3H)-dione (260 mg) and trichloro acetonitrile (1 mL) were added to reaction mixture and stirred at 27°C for 10 minutes. The reaction mixture was maintained to 70°C for 24 hours. The reaction mass was evaporated completely under reduced pressure at 50°C. The reaction mass was triturated with Methyl ferf-butyl ether(MTBE) (2x10 mL) and dried at 50°C.

The obtained reaction mixture was dissolved in Methanol (10 mL) and 1 N sodium hydroxide (1 mL). The reaction mass was evaporated under reduced pressure at 50°C followed by co-evaporated with Toluene (2x15 mL) and triturated with Methyl ferf-butyl ether(MTBE) (2x10 mL). The obtained reaction mass was dissolved in deionized water (15 mL) and passed through Dowex 50WX2-200 (H) ion exchange resin. The solvent was evaporated under reduced pressure at 50°C to obtain a solid which was co-evaporated with toluene (2 x 10 mL) and dried under vacuum for 1 h at 50°C.

Yield = 350 mg

Example-6: Preparation of Isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo3,4- dihydropyrimidin-1 (2H)-yl)-4-fluoro-3-hydroxy-4-m

methoxy)-(phenoxy)phosphorylamino)propanoate:

((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-yl)-4-fluoro-3- hydroxy-4-methyltetrahydrofuran-2-yl)methyl phenyl hydrogen phosphate(40 mg) and anhydrous dichloromethane (5 mL) were charged at 27°C under nitrogen atmosphere.Triphenyl phosphine (50.4 mg) was added to the reaction mixture at 27°C and stirred for 5 minutes. Trichloroacetonitrile (19.2 μΐ) was added to the reaction mixture and stirred for 20 minutes. L-Alanine isopropyl ester Hydrochloride (40.18 mg) and Et₃N (40 μΐ) were added to the above reaction mixture and stirred at 27°C for 16 hours.

The reaction mixture was diluted with dichloromethane (15 mL), washed with water (2 x 2 mL), 1 N HCI (1 x 2 mL) and brine solution (2 mL). The organic layer was dried with anhydrous sodium sulfate (Na₂S0₄) and evaporated under reduced pressure. The reaction mixture was titurated with n-hexane (10 mL) and purified by column chromatography by using S1O2, 100-200 mesh in 3% methanol - dichloro methane. Yield = 15 mg

Example-7: Preparation of ((2R,3R,4R)-3-(benzoyloxy)-4,5-difluoro-4- methyltetrahydrofuran-2-yl)methyl benzoate:

((2R,3R,4R)-3-(benzoyloxy)-4-fluoro-5-hydroxy-4-metriyltetrariydrofuran-2- yl)methyl benzoate (150 mg) and dichloromethane (3 mL) were charged into a round bottom flask under nitrogen atmosphere at 27°C. The reaction mixture was cooled to 0°C. Deoxo-fluoro (50% in THF) (0.35 mL) was added drop wise into the reaction mixture and stirred for 30 minutes at 0°C.

The obtained reaction mixture was diluted with dichloromethane (15 mL); the organic layer was washed with water (2 x 5 mL), saturated aqueous NaHC0₃ solution (1 x 5 mL), and brine solution (1 x 5 mL); the organic layer was dried with Na₂S0₄ and evaporated under reduced pressure. The obtained crude reaction mixture of ((2R,3R,4R)-3-(benzoyloxy)-4,5-difluoro-4-methyltetrahydrofuran-2- yl)methyl benzoate was co evaporated with dichloromethane (5 mL) and carried out to next step.

Example-8: Preparation of ((2R,3R,4R)-3-(benzoyloxy)-4,5-difluoro-4- methyltetrahydrofuran-2-yl)methyl benzoate:

((2R,3R,4R)-3-(benzoyloxy)-4-fluoro-5-hydroxy-4-methyltetrahydrofuran-2- yl)methyl benzoate (5 g) and dichloromethane (60 mL) were charged into a round bottom flask under nitrogen atmosphere at 27°C. The reaction mixture was cooled to -78°C. Diethylaminosulfur trifluoride (DAST) (3.53mL) was added drop wise into the reaction mixture and stirred for 1 5 minutes at the same temperature. The reaction mixture was further stirred at -78°C for 1 hour 30 minutes.

The obtained reaction mixture was diluted with dichloromethane (150 mL) and quenched with saturated aqueous NaHC0₃ solution (5 mL) at -78°C. The reaction mixture was allowed to reach 27°C and stirred for 30 minutes. The organic layer was washed with water (2 x 25 mL), brine solution (1 x 25 mL), dried with Na2S0₄ and evaporated under reduced pressure. The obtained crude reaction mixture of ((2R,3R,4R)-3-(benzoyloxy)-4,5-difluoro-4-methyltetrahydrofuran-2-yl)methyl benzoate was co evaporated with dichloromethane (50 mL) and carried out next step.

Example-9: Preparation of (2R,3R,4R,5R)-5-(4-benzamido-2-oxopyrimidin-1 (2H)- yl)-2-((benzoyloxy)methyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate: N-(2-((trimethylsilyl)oxy)pyrimidin-4-yl)benzamide (5.74 g) was charged into a round bottom flask under nitrogen atmosphere at 27°C. A solution of ((2R,3R,4R)-3- (benzoyloxy)-4,5-difluoro-4-methyltetrahydrofuran-2-yl) methyl benzoate (5 g) in chlorobenzene (80 mL) was added to N-(2-((trimethylsilyl)oxy)pyrimidin-4- yl)benzamide in one portion and stirred for 10 minutes, under nitrogen atmosphere, at 27°C. SnCI₄ (6.3 mL) was added into the reaction mixture and stirred at 27°C for 45 minutes. Then the reaction mixture was heated to 70°C and stirred at the same temperature for 2 hours.

NaHCC>3 (26.6 g), Celite (5 g) and dichloromethane (500 mL) were charged into a 1 L 2-neck round bottom flask at 27°C and cooled to 0°C. The reaction mixture was added to the cooled dichloromethane solution. The reaction mixture was quenched with water (5 mL) and stirred at 27°C for 30 minutes. The resultant reaction mixture was filtered through celite pad. The obtained residue was dissolved in dichloromethane (2 x 250 mL) and stir for 15 minutes. The combined organic layer was dried with Na₂S0₄ and evaporated under reduced pressure. HPLC analysis of the crude reaction mixture indicated formation α:β mixture in 1 :5 ratio. For purification of the desired β isomer, the crude product was suspended in 1 :1 ratio of MeOH:IPA (80 mL) and refluxed for 30 minutes. The crude reaction mixture was cooled to 0°C. The obtained (2R,3R,4R,5R)-5-(4-benzamido-2-oxopyrimidin-1 (2H)- yl)-2-((benzoyloxy)methyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate was filtered through buckner funnel, washed with hexane (50 mL) and dried under vacuum for 2hours.

Yield = 3.4 grams

Example-10: Preparation of ((2R,3R,4R)-3-(benzoyloxy)-4-fluoro-4-methyl-5- ((methylsulfonyl)oxy)tetrahydrofuran-2-yl)methyl benzoate:

((2R,3R,4R)-3-(benzoyloxy)-4-fluoro-5-hydroxy-4-methyltetrahydrofuran-2- yl)methyl benzoate (53 g) and dichloromethane (795 mL) were charged into a 2L round bottom flask under nitrogen atmosphere at 25°C. The reaction mixture was cooled to -10°C. Triethylamine (29.56 mL) and methanesulfonyl chloride (12.98 mL) were added drop wise at 0°C into the reaction mixture and stirred for 1 hour at the same temperature.

The obtained reaction mixture was diluted with dichloromethane (530 mL) and quenched with 1 N HCI solution (530 mL); the organic layer was separated, washed with water (530 mL), saturated aqueous NaHC0₃ solution (530 mL), and brine solution (530 mL); the organic layer was dried with anhy. Na₂S0₄ and evaporated under reduced pressure. The obtained crude reaction mixture of ((2R,3R,4R)-3- (benzoyloxy)-4-fluoro-4-methyl-5-((methylsulfonyl)oxy)tetrahydrofuran-2-yl)methyl benzoate was carried out to next step.

Yield: 64 grams

Example-11 : Preparation of (2R,3R,4R,5R)-5-(4-benzamido-2-oxopyrimidin-

1 (2H)-yl)-2-((benzoyloxy)methyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate:

N-(2-((trimethylsilyl)oxy)pyrimidin-4-yl)benzamide (60.95 g) was charged into a round bottom flask under nitrogen atmosphere at 25°C. A solution of ((2R,3R,4R)- 3-(benzoyloxy)-4-fluoro-4-methyl-5-((methylsulfonyl)oxy)tetrahydrofuran-2-yl)methyl benzoate (64 g) in chlorobenzene (1 .02 L) was added to N-(2- ((trimethylsilyl)oxy)pyrimidin-4-yl)benzamide in one portion and stirred for 5 minutes, under nitrogen atmosphere, at 25°C. SnCI₄ (68.26 mL) was added into the reaction mixture and stirred at 25°C for 40 minutes. Then the reaction mixture was heated to 70°C and stirred at the same temperature for 2 hours.

NaHC0₃ (284 g), Celite (32 g) and dichloromethane (1 L) were charged into a 5L 3-neck round bottom flask at 25°C and cooled to 0°C. The reaction mixture was added to the cooled dichloromethane solution slowly and stirred for 5 min. The reaction mixture was quenched with water (64 mL) and stirred at 25°C for 1 hour at RT. The resultant reaction mixture was filtered through celite pad. The solid was washed with dichloromethane (2 x 250 mL). The residue was transferred to an RB flask and stirred with dichloromethane (500 mL) for 20 minutes; filtered and washed with dichloromethane (2 x 100 mL). The combined organic layer was dried with Na₂S0₄ (20 g) and solvent was evaporated under reduced pressure. HPLC analysis of the crude reaction mixture indicated formation α:β mixture in 1 :4 ratio. For purification of the desired β isomer, the crude product was suspended in MeOH (1 L) and heated to 90°C for 2h. The crude reaction mixture was cooled to 25°C. The obtained (2R,3R,4R,5R)-5-(4-benzamido-2-oxopyrimidin-1 (2H)-yl)-2-((benzoyloxy) methyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate was filtered through buckner funnel, washed with methanol (2 x 1 00 mL), hexane (100 mL) and dried under vacuum for 1 hour 30 minutes. Yield = 28.5 grams

Example-12: Preparation of ((2R,3R,4R)-3-(benzoyloxy)-4-fluoro-4-methyl-5- (2,2,2-trichloro-1-iminoethoxy)tetrahydrofuran-2-yl)methyl benzoate:

1 ,8-Diazabicycloundec-7-ene (DBU) (8 μΙ_) was charged into the 2,2,2- trichloroacetonitrile (1 mL) under nitrogen atmosphere at 27°C. The reaction mixture was cooled to 0°C and a solution of ((2R,3R,4R)-3-(benzoyloxy)-4-fluoro-5-hydroxy- 4-methyltetrahydrofuran-2-yl)methyl benzoate (125 mg) in dichloromethane (5 mL) was slowly added drop wise into it under nitrogen atmosphere at 0°C for 5 minutes. The reaction mixture was stirred at 0°C for 30 minutes. The solvent was evaporated to obtain the crude product which was taken to next step without further purification. Example-13: Preparation of (2R,3R,4R,5R)-5-(4-benzamido-2-oxopyrimidin- 1 (2H)-yl)-2-((benzoyloxy)methyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate:

N-(2-((trimethylsilyl)oxy)pyrimidin-4-yl)benzamide (188 mg) was charged into a round bottom flask under nitrogen atmosphere at 27°C. A solution of ((2R,3R,4R)- 3-(benzoyloxy)-4-fluoro-4-methyl-5-(2,2,2-trichloro-1 -iminoethoxy)tetrahydrofuran-2- yl)methyl benzoate (170 mg) in chlorobenzene (7 mL) was added to the N-(2- ((trimethylsilyl)oxy)pyrimidin-4-yl)benzamide in one portion and stirred for 5 minutes, under nitrogen atmosphere, at 27°C. SnCI4 (0.15 mL) was added into the reaction mixture and stirred at 27°C for 30 minutes. Then the reaction mixture was heated to 70°C and stirred at the same temperature for 3 hours.

NaHC03 (661 mg), Celite (200 mg) and dichloromethane (60 mL) were charged into a 1 L 2-neck round bottom flask at 27°C. The reaction mixture was added to the dichloromethane solution. The reaction mixture was quenched with water (0.2 mL) and stirred at 27°C for 15 minutes. The resultant reaction mixture was filtered through celite pad. The obtained residue was dissolved in dichloromethane (2 x 15 mL) and stir for 1 5 minutes. The combined organic layer was washed with water (2 x 1 5 mL), brine solution (2 x 15 mL), dried with Na2S04 and evaporated to get crude (2R,3R,4R,5R)-5-(4-benzamido-2-oxopyrimidin-1 (2H)-yl)-2-((benzoyloxy) methyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate as α/β mixture.

Example-14: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo- 3,4-dihydropyrimidin-11-(2H)-yl)-4-flouro-3-hydroxy-4-methyltetrahydroxyfuran- 2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate: (2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (1.767 g) and acetone (5 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. Tripropyl amine (828 mg) was added into the reaction mass followed by the addition of 1 -((2R,3R,4R,5R)-3-fluoro-4- hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine-2,4(1 H,3H)- dione (500 mg). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 12 hours.

The reaction mixture was concentrated on rotavapour under high vacuum. The obtained crude was dissolved in 10 mL of ethyl acetate, washed with 1 N HCI, saturated sodium bicarbonate, brine solution and dried over sodium sulfate. The final reaction mass was evaporated under vacuum and placed under high vacuum.

The ratio towards desired isomer (Sp:Rp) = 4.3:1

Example-15: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo- 3,4-d i hyd ropy ri m id i n-11 -(2H)-y I )-4-fl ^

2- yl)methoxy)(phenoxy)phosphoryl)amino)propanoate:

(2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (587 mg) and Methylisobutyl ketone (5 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. Tripropyl amine (828 mg) was added into the reaction mass followed by the addition of 1 -((2R,3R,4R,5R)-

3- fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine- 2,4(1 H,3H)-dione (500 mg). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 5 hours.

The ratio towards desired isomer (Sp:Rp) = 6.6:1

Example-16: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo- 3,4-dihydropyrimidin-11-(2H)-yl)-4-flouro-3-hydroxy-4-methyltetrahydroxyfuran- 2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate:

(2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (1 .712 g) and Methyl-t-butyl ether (5 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. N,N-Diisopropylethyl amine (724 mg) was added into the reaction mass followed by the addition of 1 - ((2R,3R,4R,5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2- yl)pyrimidine-2,4(1 H,3H)-dione (500 mg). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 1 2 hours.

The reaction mixture was concentrated on rotavapour under high vacuum. The obtained crude was dissolved in 1 0 mL of ethyl acetate, washed with 10 mL of 10% aqueous HCI, 10 mL of brine solution, 10 mL of saturated sodium bicarbonate, 10 mL brine solution and dried over sodium sulfate. The final reaction mass was evaporated under vacuum and placed under high vacuum.

The ratio towards desired isomer (Sp:Rp) = 5.8:1

Example-17: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo- 3,4-d i hyd ropy ri m id i n-11 -(2H)-y I )-4-fl ^

2- yl)methoxy)(phenoxy)phosphoryl)amino)propanoate:

(2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (1.767 g) and Methyl-t-butyl ether (5 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. Tripropyl amine (828 mg) was added into the reaction mass followed by the addition of 1 -((2R,3R,4R,5R)-

3- fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine- 2,4(1 H,3H)-dione (500 mg). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 17 hours.

The reaction mixture was concentrated on rotavapour under high vacuum. The obtained crude was dissolved in 10 mL of ethyl acetate, washed with 10% aqueous HCI, 10 mL of brine solution, 10 mL of saturated sodium bicarbonate, 10 mL brine solution and dried over sodium sulfate. The final reaction mass was evaporated under vacuum and placed under high vacuum.

The ratio towards desired isomer (Sp:Rp) = 5.9:1

Example-18: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo-

3,4-dihydropyrimidin-11-(2H)-yl)-4-flouro-3-hydroxy-4-methyltetrahydroxyfuran-

2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate:

(2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (1.767 g) and ethyl acetate (5 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. Tripropyl amine (828 mg) was added into the reaction mass followed by the addition of 1 -((2R,3R,4R,5R)- 3 luoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidin

2,4(1 H,3H)-dione (500 mg). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 17 hours.

The reaction mixture was concentrated on rotavapour under high vacuum. The obtained crude was dissolved in 15 mL of ethyl acetate, washed with 10% aqueous HCI, 10 mL of brine solution, 10 mL of saturated sodium bicarbonate, 10 mL brine solution and dried over sodium sulfate. The final reaction mass was evaporated under vacuum and placed under high vacuum.

The ratio towards desired isomer (Sp:Rp) = 4.9:1

Example-19: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo- 3,4-d i hyd ropy ri m id i n-11 -(2H)-y I )-4-fl ^

2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate:

(2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (8.81 g) and tetrahydrofuran (50 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. Tributyl amine (28.5 g) was added into the reaction mass followed by the addition of 1 -((2R,3R,4R,5R)-3- fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine- 2,4(1 H,3H)-dione (5 g). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 21 hours.

The obtained crude was dissolved in 100 mL of ethyl acetate, washed with 100 mL of 10% aqueous HCI, 100 mL of saturated sodium bicarbonate for three times, and dried over 10 g of sodium sulfate. The reaction mass was evaporated under vacuum and placed under high vacuum. The reaction mass was again dissolved in 10 mL ethyl acetate, 60 mL hexane and decanted. The final reaction mass was placed under high vacuum.

The ratio towards desired isomer (Sp:Rp) = 2.8:1

Example-20: Preparation of (S)-isopropyl 2-(((S)-(((2R,3R,4R,5r)-5-(2,4-dioxo- 3,4-dihydropyrimidin-11-(2H)-yl)-4-flouro-3-hydroxy-4-methyltetrahydroxyfuran- 2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate:

(2S)-isopropyl-2-((chloro(phenoxy)phophoryl)amino)propanoate (1.712 g) and Methyl-t-butyl ether (5 mL) were charged into a round bottom flask under nitrogen atmosphere at 28°C. The reaction mass was cooled to 0°C. Tripropyl amine (724 mg) was added into the reaction mass followed by the addition of 1 -((2R,3R,4R,5R)- 3-fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidin

2,4(1 H,3H)-dione (500 mg). Temperature of the reaction mixture was raised to 28°C and allowed to maintain for 12 hours.

The reaction mixture was concentrated on rotavapour under high vacuum.

The obtained crude was dissolved in 10 mL of ethyl acetate, washed with 10% aqueous HCI, 10 mL of brine solution, 10 mL of saturated sodium bicarbonate, 10 mL brine solution and dried over sodium sulfate. The final reaction mass was evaporated under vacuum and placed under high vacuum.

The ratio towards desired isomer (Sp:Rp) = 4:1

Example-21 : Preparation of sofosbuvir Form A

Sofosbuvir (500 mg) and n-heptane (30 ml) were charged into an easy max reactor at 28°C. The obtained mixture was heated to 50°C and stirred for 30 minutes. Ethanol (200 μΐ) was added slowly into the mixture to give slurry. The slurry was stirred for at 50°C for 5 hours. Ethanol (300 μΙ_) was added to the slurry at 50°C and the slurry was cooled to 25°C and kept the material at 25°C overnight. It was filtered and dried at 30°C in air tray dryer for 1 hour.

Example-22: Preparation of sofosbuvir Form A

Sofosbuvir (500 mg), n-heptane (30 mL) and ethanol (200 μΐ) were charged in easy max reactor and the mixture was heated to 50°C. The mixture was stirred for 8 hours at the same temperature. It was cooled to 25°C filtered and dried at 30°C in vacuum tray dryer for 1 hour.

Example-23: Preparation of sofosbuvir Form A

Sofosbuvir (500 mg) and n-heptane (30 ml) were charged into an easy max reactor at 28°C. The obtained suspension was stirred and heated to 50°C for 2 hours. The hot mixture was filtered and dried at 30°C in vacuum tray dryer for 1 hour.

Example-24: Preparation of sofosbuvir Form A

Sofosbuvir (500 mg) and n-heptane (30 ml) were charged into an easy max reactor at 0°C. The mixture was stirred at the same temperature for 6 hours 30 minutes. It was filtered at 0°C and dried at 30°C in vacuum tray dryer for 1 hour.

Example-25: Preparation of cocrystal of sofosbuvir with caffeine

Sofosbuvir (500 mg), Caffeine (90 mg) and n-heptane (30 ml) were charged into an easy max reactor at 30°C. The obtained suspension was stirred for 5 minutes. Ethanol (2 mL) was charged slowly into the suspension. The obtained slurry was stirred at the same temperature for 2 hours and kept the material at 25°C overnight. It was filtered at 25°C and dried at 40°C air tray dryer for 1 hour.

Example-26: Preparation of amorphous Sofosbuvir

Sofosbuvir (500 mg) and acetone (15 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with acetone (5 ml) at 26°C. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 50°C.

Example-27: Preparation of amorphous Sofosbuvir

Sofosbuvir (8.5 g) and methanol (170 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with methanol (80 ml) at 26°C. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 57°C. The obtained reaction mass was dried under vacuum 2 hours.

Example-28: Preparation of amorphous Sofosbuvir

Sofosbuvir (3 g) and methanol (60 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The solution was allowed to evaporate by spray drying at 70°C with a flow rate at 9 ml/min.

Example-29: Preparation of amorphous Sofosbuvir

Sofosbuvir (500 mg) and ethyl acetate (20 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered at 26°C. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 60°C.

Example-30: Preparation of amorphous solid dispersion of Sofosbuvir with Polyvinylpyrrolidone

Sofosbuvir (300 mg) and methanol (15 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with methanol (10 ml) at 26°C. Polyvinylpyrrolidone (PVP K-30; 300 mg) added to the reaction mass and the reaction mass was stirred to dissolve PVP K-30 completely. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 60°C. The obtained reaction mass was dried for 30 minutes under vacuum at 60°C.

Sofosbuvir (200 mg) and methanol (5 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with methanol (5 ml) at 26°C. The solution was filtered; and the filtrate was transferred into the reaction mass of Sofosbuvir and polyvinylpyrrolidone obtained in the previous step. Polyvinylpyrrolidone (PVP K-30; 200 mg) added to the reaction mass and the reaction mass was stirred to dissolve PVP K-30 completely. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 60°C. The obtained reaction mass was dried for 30 minutes under vacuum at 60°C.

Syloid (244FP grade; 500 mg) was added to the dry Sofosbuvir with polyvinylpyrrolidone at room temperature and mixed well for the uniform distribution. Example-31 : Preparation of amorphous solid dispersion of Sofosbuvir with Copovidone

Sofosbuvir (500 mg) and methanol (15 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with methanol (5 ml) at 26°C. Copovidone NF (500 mg) added to the reaction mass and it was stirred to dissolve copovidone NF completely. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 60°C. The obtained reaction mass was dried under vacuum 30 minutes at 60°C. Syloid (244FP grade; 500 mg) was added to the dry Sofosbuvir with copovidone at room temperature and mixed well for the uniform distribution. Example-32: Preparation of amorphous solid dispersion of Sofosbuvir with Hydroxypropy methyl cellulose

Sofosbuvir (500 mg) and methanol (15 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with methanol (5 ml) at 26°C. Hydroxypropy methyl cellulose (HPMC SCPS; 500 mg) added to the reaction mass and it was stirred to dissolve HPMC completely. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 60°C. The obtained reaction mass was dried under vacuum 50 minutes at 60°C. Syloid (244FP grade; 500 mg) was added to the dry Sofosbuvir with hydroxypropy methyl cellulose at room temperature and mixed well for the uniform distribution.

Example-33: Preparation of amorphous solid dispersion of Sofosbuvir with Hydroxypropyl cellulose

Sofosbuvir (500 mg) and methanol (15 ml) were charged into a round bottom flask at 26°C. The contents were stirred to dissolve Sofosbuvir completely. The reaction mass was filtered and washed with methanol (5 ml) at 26°C. Hydroxypropyl cellulose (HPC - Klucel LF; 500 mg) added to the reaction mass and it was stirred to dissolve HPC completely. The resulting solution was evaporated completely in Buchi® Rotavapor® under vacuum at 60°C. The obtained reaction mass was dried under vacuum 90 minutes at 60°C. Syloid (500 mg) was added to the dry amorphous solid dispersion of Sofosbuvir with hydroxypropyl cellulose at room temperature and mixed well for the uniform distribution.

Claims

CLAIMS:

1 . A compound, its salts, stereo isomers, polymorphs or solvates represented by a Formula I,

Formula I wherein, base is a substituted or unsubstituted purine or pyrimidine attached to the furanose ring through a carbon or nitrogen atom; R and Ri are independently selected from the group consisting of H, alkyl, halo; X is H, OH, any leaving group; R₂ is OH or protected hydroxyl group and R₃ is substituted or unsubstituted aryl.

2. The compound according to claim 1 , its salts, stereo isomers, polymorphs or solvates represented by a Formula II,

wherein, X is H, OH or any leaving group and R₂ is OH or protected hydroxyl group.

3. The compounds according to claim 1 , its salts, stereo isomers, polymorphs or solvates represented by Formula c, Formula d, Formula e, Formula f and Formula g.

Formula g

4. A process for preparation of the compound according to claim 1 , its salts, stereo isomers, polymorphs or solvates represented by Formula I,

Formula I wherein, base is a substituted or unsubstituted purine or pyrimidine attached to the furanose ring through a carbon or nitrogen atom; R and Ri are independently selected from the group consisting of H, alkyl, halo; X is H, OH, any leaving group; R₂ is OH or protected hydroxyl group and R₃ is substituted or unsubstituted aryl; comprising: contacting a compound of Formula III,

Formula III wherein, R₃ is substituted or unsubstituted aryl, X and Xi are independently selected from H, OH or any leaving group, provided when X or is H, then the other one is a leaving group; with a compound of Formula IV or a salt,

Formula IV wherein, base is a substituted or unsubstituted purine or pyrimidine attached to the furanose ring through a carbon or nitrogen atom; R and Ri are independently selected from the group consisting of H, alkyl, halo; X is H, OH, any leaving group; R₂ is OH or protected hydroxyl group.

5. A process for preparation of sofosbuvir, its salts, stereo isomers, polymorphs, and solvates, represented by Formula A,

Formula A wherein the process comprising:

contacting a compound of Formula V or a salt,

Formula V wherein, X and Xi are independently selected from H or OH; provided when X or is H, then the other one is a leaving group; with a compound of Formula VI or a salt,

Formula VI wherein, R₂ is OH or protected hydroxyl group to produce a compound of Formula II;

Formula II wherein, X is H, OH, any leaving group; R₂ is OH or protected hydroxyl group;

a) displacing H or OH of Formula II or its salt with a leaving group;

b) contacting compound of Formula II or salts thereof obtained from step b) with isopropyl L-alaninate or its salts provides sofosbuvir of Formula A or 3-O-protected sofosbuvir; and optionally deprotecting the protecting group if R₂ is a protecting group.

6. A compound, its salts, stereo isomers, polymorphs or solvates represented by a Formula VIII,

Formula VIII wherein, R_{1 5} R₂ are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyi, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl; and L is F, OMs or -OC(HN)CCI₃.

7. The compound according to claim 6, represented by Formula h, Formula i and Formula j.

Formula h Formula i Formula j

3. A process for preparation of a compound represented by a Formula VIII, its stereo isomers, salts, polymorphs, and solvates,

Formula VIII wherein R_u R₂ are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyi, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl; and L is F, OMs or -OC(HN)CCI3; comprising: contacting a compound of Formula XII,

Formula XII wherein, R_{1 5} R₂ are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyl, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl; with fluorinating agent, mesylation agent or trichloroacetonitrilation agent.

8. A process for preparation of a compound represented by a Formula XIII,

Formula XIII wherein, R_{1 5} R₂ are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyl, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl; and B is a base, which is selected from

Y is N or CH; R₄, R₅ and R₆ are independently H, halogen (including F, CI, Br, I), OH, OR', SH, SR', NH₂, NHR', NR'₂, lower alkyl of C C₆, halogenated (F, CI, Br, I) lower alkyl of C C₆ such as CF₃ and CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH=CH₂, halogenated (F, CI, Br, I) lower alkenyl of C₂-C₆ such as CH=CHCI, CH=CHBr and CH=CHI, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, CI, Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C C₆ such as CH₂OH and CH₂CH₂OH, halogenated (F, CI, Br, I) lower alkoxy of C C₆, C0₂H, C0₂R', CONH₂, CONHR', CONR's, CH=CHC0₂H, CH=CHC0₂R'; R' is an optionally substituted alkyl of d-Ci₂ (particularly when the alkyl is an amino acid residue), cycloalkyi, aryl, optionally substituted alkynyl of C₂-C₆, optionally substituted lower alkenyl of C₂-C₆, or optionally substituted acyl; comprising: contacting a compound of Formula VIII,

Formula VIII wherein, Ri , R₂ are independently H, methyl, benzyl, trityl, triethylsilyl, t- butyldimethylsilyl, t-butyldiphenylsilyl, ethoxymethyl, methoxymethyl (MOM), methoxyethyl (MEM), benzyloxymethyl (BOM), acetyl, benzoyl, pivaloyl, 2-, 3-, or 4- nitrobenzoyl, 2-, 3-, or 4-chlorobenzoyl, or toluoyl;

with a naturally occurring or modified purine or pyrimidine base.

9. A stereoselective process for preparation of sofosbuvir represented by a Formula A, its stereo isomers, salts, polymorphs, and solvates;

Formula A comprising: contacting a compound or a salt,

Formula XVIII wherein, L is a leaving group; with a compound of Formula XIX or a salt.

Formula XIX wherein the reaction is conducted in anhydrous solvents selected from dichloromethane, 2-methyl tetrahydrofuran, tetrahydrofuran, methyl-t-butyl ether, ethyl acetate, acetonitrile, cyclopentyl methylether, 1 ,4-dioxane, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ethyl amine, tripropylamine, tributylamine and their combinations.

10. A crystalline Form A of sofosbuvir, characterized by a PXRD pattern comprising peaks at about 4.55, 8.53, 9.10, 12.78 and 13.68 ±0.2° 2Θ.

1 1 . A crystalline Form A of sofosbuvir according to claim 10, further characterized by a PXRD pattern comprising peaks at about 4.91 , 7.15, 15.91 , 1 7.91 and 25.04 ±0.2°2Θ.

12. A process for preparation of crystalline Form A of sofosbuvir, characterized by a PXRD pattern comprising peaks at about 4.55, 8.53, 9.10, 12.78 and 13.68 ±0.2° 2Θ, comprising: a) contacting sofosbuvir and a solvent or a mixture of solvents wherein the solubility of sofosbuvir is low; b) mixing the slurry obtained in step (a); and c) isolating crystalline Form A of sofosbuvir.

13. A cocrystal of sofosbuvir with caffeine, characterized by a PXRD pattern comprising peaks at about 3.70, 4.42, 5.32, 14.82, 16.36, 17.21 and 21.04 ± 0.2° 2Θ.

14. A cocrystal of sofosbuvir with caffeine according to claim 13, further characterized by PXRD pattern comprising peaks at about 7.41 , 10.03 and 19.36 ± 0.2° 2Θ.

15. A process for preparation of cocrystal of sofosbuvir with caffeine comprising peaks at about 3.70, 4.42, 5.32, 14.82, 16.36, 17.21 and 21 .04 ± 0.2° 2Θ; comprising: a) contacting sofosbuvir and caffeine to a solvent or a mixture of solvents wherein the solubility of sofosbuvir and caffeine is low;

b) contacting slurry obtained in step (a) with a solvent or a mixture of solvents;

c) mixing the slurry obtained in step (b); and

d) isolating the cocrystal of sofosbuvir with caffeine.

16. A process for preparation of amorphous form of sofosbuvir, comprising: a) providing a solution of sofosbuvir in a solvent;

b) removing solvent from the solution obtained in step a); and

c) isolating the amorphous form of sofosbuvir.

17. A process for preparation of amorphous form of sofosbuvir according to claim 16, wherein the solvent selected from acetone, methanol or ethyl acetate or their combinations.

18. An amorphous solid dispersion of sofosbuvir together with one or more pharmaceutically acceptable carriers.

19. An amorphous solid dispersion of sofosbuvir according to claim 18, wherein the pharmaceutically acceptable carriers are polyvinylpyrrolidones, gums, cellulose derivatives, polymers of carboxymethyl celluloses, cyclodextrins, gelatins, hypromellose phthalates, sugars, polyhydric alcohols, polyethylene glycols, polyethylene oxides, polyoxyethylene derivatives, polyvinyl alcohols, propylene glycol derivatives, water soluble sugar derivatives, aromatic amines, alicyclic amines, cyclic amines, aralkyl amines, hydroxylamine or its derivatives, hydrazine or its derivatives, or guanidine or its derivatives or .

20. A process for preparation of amorphous solid dispersion of sofosbuvir together with one or more pharmaceutically acceptable carriers according to claim 18, comprising: a) providing a solution or suspension of sofosbuvir in combination with one or more pharmaceutically acceptable carriers in a solvent or mixture of solvents;

b) removing solvent from the solution obtained in step a); and

c) isolating amorphous solid dispersion of Sofosbuvir together with one or more pharmaceutically acceptable carriers.

21 . A process for preparation of amorphous solid dispersion of sofosbuvir together with one or more pharmaceutically acceptable carriers according to claim 20, wherein the pharmaceutically acceptable excipients selected from Polyvinylpyrrolidone, Copovidone, Hydroxypropyl cellulose (HPC) and Hydroxypropy methyl cellulose (HPMC).

22. A pharmaceutical composition of Form A of sofosbuvir, cocrystal of sofosbuvir with caffeine, solid dispersion of sofosbuvir or amorphous sofosbuvir produced according to any of the preceding claims together with one or more pharmaceutically acceptable excipients.