Field of the Invention:
The present invention provides amorphous solid dispersion of (S)-isopropyl 2-((S)-(((2RJ3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyl tetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate represented by the following structural formula-1 and process for its preparation.
Background of the Invention:
(S)-Isopropyl 2-((S)-(((2RJ3Rs4Rs5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino) propanoate, commonly known as Sofosbuvir is used for hepatitis C virus (HCV) infection. Sofosbuvir is a prodrug that is metabolized to the active antiviral agent 2'-deoxy-2'-a-fluoro-P-C-methyluridine-5'-triphosphate. It was discovered at Pharmasset and developed by Gilead Sciences. Sofosbuvir got approval both in US and Europe and currently marketed under the brand name Sovaldi.
US7964580B2 discloses nucleoside phosphoramidate prodrugs such as (S)-isopropyl 2-((S)-(((2Rs3R,4R,5R)-5-(2J4-dioxo-3s4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate and process for their preparation.
US8618076B2 assigned to Gilead Pharmasset has described six crystalline polymorphs namely crystalline form-1, form-2, form-3, form-4, form-5 & form-6 and also amorphous form of (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2}4-dioxo-3,4-dihydro pyrimidin-1 (2H)-yl)-4-fluoro-3 -hydroxy-4-methyltetrahydrofuran-2-y l)methoxy)-(phenoxy) phosphorylamino)propanoate.
Still, there is a significant need in the art to develop novel polymorphic form of the said compound which is stable and having advantageous physical properties such as free flowability, greater stability and greater bioavailability.

Brief description of the invention:
The first aspect of the present invention is to provide amorphous solid dispersion comprising (S)-isopropyl 2-((S)-(((2R,3R,4R55R)-5-(2,4-dioxo yl)-4-fluoro-3-hydroxy-4-methyltetrahydro propanoate compound of formula-1 and at least one pharmaceutically acceptable excipient.
The second aspect of the present invention is to provide process for the preparation of amorphous solid dispersion comprising compound of formula-1 and at least one excipient.
Brief description of the Drawings:
Figure-1: Illustrates the PXRD pattern of amorphous solid dispersion comprising compound
of formula-1 and Eudragit L 100-55 prepared in accordance with example-1.
Figure-2: Illustrates the PXRD pattern of amorphous solid dispersion comprising compound
of formula-1 and hydroxypropyl cellulose (HPC) prepared in accordance with example-2.
Figure-3: Illustrates the PXRD pattern of amorphous solid dispersion comprising compound
of formula-1 and hydroxypropyl methylcellulose acetate succinate (HPMCAS) prepared in
accordance with example-3.
Figure-4: Illustrates the PXRD pattern of amorphous solid dispersion comprising compound
of formula-1 and hydroxypropyl methylcellulose (HPMC) prepared in accordance with
example-4.
Figure-5: Illustrates the PXRD pattern of amorphous solid dispersion comprising, compound
of formula-1 and PVP K-30 prepared in accordance with example-5.
Detailed description of the Invention:
The "suitable solvent" used in the present invention can be selected from but not limited to "hydrocarbon solvents" such as n-pentane, n-hexane, n^heptane, cyclohexane, pet ether, benzene, toluene, xylene and the like; "ether solvents" such as dimethyl ether, diethyl ether, diisopropyl ether, methyl tert-butyl ether, dimethoxyethane, diethoxyethane, dibutoxyethane, tetrahydrofuran, 1,4-dioxane and the like; "ester solvents" such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate and the like; "polar-aprotic solvents" such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone (NMP) and the like; "chloro

solvents" such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride and the like; "ketone solvents" such as acetone, methyl ethyl ketone, methyl isobutyl ketone and the like; "nitrile solvents" such as acetonitrile, propionitrile, isobutyronitrile and the like; "alcohol solvents" such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, n-pentanol, ethane-1,2-diol, propane-1,2-diol, alkyl ethers of ethylene glycol or propylene glycol selected from but not limited to ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether and the like; "polar solvents" such as water; formic acid, acetic acid or mixtures thereof.
The term "suitable base" used in the present invention refers to "inorganic bases"
selected from "alkali metal carbonates" such as sodium carbonate, potassium carbonate,
lithium carbonate, cesium carbonate and the like; "alkali metal bicarbonates" such as sodium
bicarbonate, potassium bicarbonate, lithium bicarbonate, cesium bicarbonate and the like;
"alkali metal hydroxides" such as sodium hydroxide, potassium hydroxide, lithium hydroxide
and the like; "alkali metal alkoxides" such as sodium methoxide, sodium ethoxide, potassium
methoxide, potassium ethoxide, sodium tert.butoxide, potassium tert.butoxide, lithium
tert.butoxide and the like; "alkali metal hydrides" such as sodium hydride, potassium
hydride, lithium hydride and the like; "alkali metal amides" such as sodium amide, potassium
amide, lithium amide and the like; alkali metal and alkali earth metal salts of acetic acid such
as sodium acetate, potassium acetate, magnesium acetate, calcium acetate and the like;
ammonia; "organic bases" like dimethylamine, diethylamine, diisopropyl mine,
diisopropylethylamine, diisobutylamine, triethylamine, triisopropyl amine, tributylamine,
tert.butyl amine, pyridine, 4-dimethylaminopyridine, imidazole, N-methylimidazole, 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU), l,5-diazabicyclo[4.3.0]non-5-ene (DBN),
N-methylmorpholine, l,4-diazabicyclo[2.2.2]octane (DABCO), 2,6-lutidine and the like; "organolithium bases" such as methyl lithium, n-butyl lithium, lithium diisopropylamide and the like; "organosilicon bases" such as lithium hexamethyldisilazide, sodium hexamethyldisilazide, potassium hexamethyldisilazide and the like or their mixtures.

As used herein, the term "solid dispersion" means any solid composition having at least two components. In certain embodiments, a solid dispersion as disclosed herein includes an active ingredient (compound of formula-1) dispersed among at least one other component, for example an excipient.
The first aspect of the present invention provides amorphous solid dispersion comprising (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino) propanoate and at least one pharmaceutically acceptable excipient.
In general, the excipient is selected from but not limited to polyvinylpyrrolidone (povidone or PVP; PVP of different grades like K-15, K-30, K-60, K-9Q and K-120 may be used), polyvinylpolypyrrolidone, polysorbate, cross linked polyvinyl pyrrolidone (crospovidone), Eudragit, polyethylene glycol (macrogol or PEG), polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, propylene glycol, cellulose, cellulose acetate phthalate (CAP), methyl cellulose, carboxymethyl cellulose (CMC, its sodium and calcium salts), carboxymethylethyl cellulose (CMEC), ethyl cellulose, hydroxymethyl cellulose, ethyl hydroxyethyl cellulose, hydroxyethylcellulose, hydroxypropyl cellulose (HPC), hydroxypropyl cellulose acetate succinate, hydroxypropyl methyl cellulose (hypromellose or HPMC), hydroxypropyl methylcellulose acetate succinate (HPMCAS), hydroxyethyl methyl cellulose succinate (HEMCS), hydroxypropyl cellulose acetate succinate (HPCAS), hydroxypropyl methylcellulose phthalate (HPMC-P), hydroxypropyl methylcellulose acetate phthalate, microcrystalline cellulose (MCC), cross linked sodium carboxymethyl cellulose (croscarmellose sodium), cross linked calcium carboxymethyl cellulose, magnesium stearate, aluminium stearate, calcium stearate, magnesium carbonate, talc, iron oxide (red, yellow, black), stearic acid, dextrates, dextrin, dextrose, sucrose, glucose, xylitol, lactitol, sorbitol, mannitol, maltitol, maltose, raffinose, fructose, maltodextrin, anhydrous lactose, lactose monohydrate, starches such as maize starch or corn starch, sodium starch glycolate, sodium carboxymethyl starch, pregelatinized starch, gelatin, sodium dodecyl sulfate, edetate disodium, sodium phosphate, sodium lauryl sulfate, triacetin, sucralose, calcium phosphate, polydextrose, a-, p-, y-cyclodextrins, sulfobutylether beta-cyclodextrin, sodium stearyl

fumarate, fumade acid, alginic acid, sodium alginate, propylene glycol alginate, citric acid, succinic acid, carbomer, docusate sodium, glyceryl behenate, glyceryl stearate, meglumine, arginine, polyethylene oxide, polyvinyl acetate phthalates and the like.
The amorphous solid dispersion of compound of formula-1 of the present invention is having purity of greater than 98%, preferably greater than 99% by HPLC and is useful for the preparation of various pharmaceutical compositions formulated in a manner suitable for the route of administration to be used where at least a portion of compound of formula-1 is present in the composition in particular polymorphic form mentioned. Such pharmaceutical compositions may comprise compound of formula-1 present in the composition in a range of between 0.005% and 100% (wt/wt), with the balance of the pharmaceutical composition comprising additional substances such as excipients, diluents, lubricants, binders, wetting agents, disintegrating agents, glidants, sweetening agents, flavoring agents, emulsifying agents, solubilizing agents, pH buffering agents, perfuming agents, surface stabilizing agents, suspending agents and other conventional pharmaceutically inactive agents.
The amorphous solid dispersion of the present invention is stable at room temperature under normal stability conditions and does not convert to any other solid state form.
The second aspect of the present invention provides a process for the preparation of amorphous solid dispersion comprising (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-yl)-4-fluoro-3 -hydroxy-4-methyltetrahydrofuran-2-yl) methoxy)-(phenoxy)phosphorylamino)propanoate compound of formula-1 and at least one excipient, which comprising of;
a) Dissolving the compound of formula-1 and at least one excipient in a suitable solvent or mixture of solvents at a suitable temperature,
b) removing the solvent from the reaction mixture and drying the material to provide amorphous solid dispersion comprising compound of formula-1 and excipient.
Wherein, in step-a) the suitable excipient is same as defined above in the first aspect;

the suitable solvent is selected from hydrocarbon solvents, ether solvents, ester solvents, polar-aprotic solvents, chloro solvents, ketone solvents, nitrile solvents, alcohol solvents, polar solvents, formic acid, acetic acid, alkyl ethers of ethylene glycol or propylene glycol or their mixtures; the suitable temperature ranges from 0°C to 150°C;
After dissolving the compound of formula-1 and excipient in the solvent system, the solution may optionally be treated with charcoal 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 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.
In step-b) suitable techniques which may be used for the removal of solvent from the reaction mixture includes but not limited to evaporation, evaporation under reduced pressure, flash evaporation, vacuum drying, concentrating the reaction mixture, atmospheric distillation, vacuum distillation, distillation by using a rotational distillation device such as a Buchi Rotavapor, agitated thin film drying, melt extrusion, spray drying, freeze drying (lyophilization), spray-freeze drying, addition of suitable anti-solvent to the reaction mixture followed by filtration of the precipitated solid, cooling the clear solution to lower temperatures to precipitate the solid followed by filtration of the reaction or by any other suitable techniques known in the art.
The solvent may be removed optionally under reduced pressures, at temperatures less than about 130°C, less than about 60°C, less than about 40°C, less than about 20°C, less than about 0°C, less than about -20°C, less than about -40°C or less than about -60°C.
In the above process, any physical form of compound of formula-1 can be utilized as input for the preparation of amorphous solid dispersion.

The amorphous solid dispersion of compound of formula-1 of the present invention can be further micronized or milled to achieve desired particle size distribution in order to make suitable formulation.
In the present invention, the ratio of the amount by weight of (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyl tetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate within the solid dispersion to the amount by weight of the excipient therein ranges from but not limited to about 1:0.05 to about 1:5.
One embodiment of the present invention provides a process for the preparation of amorphous solid dispersion comprising (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-y l)-4-fluoro-3 -hy droxy-4-methyltetrahydrofuran-2-yl) methoxy)-(phenoxy)phosphorylamino)propanoate compound of formula-1 and Eudragit, comprising of;
a) Dissolving the compound of formula-1 and Eudragit in a suitable solvent or mixture of solvents,
b) removing the solvent from the reaction mixture and drying the material to provide amorphous solid dispersion comprising compound of formula-1 and Eudragit.
Wherein, the suitable solvent is same as defined in step-a) of the second aspect of the present invention.
A preferred embodiment of the present invention provides a process for the preparation of amorphous solid dispersion comprising (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate compound of formula-1 and Eudragit, comprising of;
a) Dissolving the compound of formula-1 and Eudragit in methanol,
b) optionally filtering the reaction mixture,
c) distilling off solvent completely from the reaction mixture and drying the material to provide amorphous solid dispersion comprising compound of formula-1 and Eudragit.

In one embodiment, the compound of formula-1 utilized in the present invention is prepared by reacting compound of general formula-2
with l-((2R,3R)4R)5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine-2,4(lH,3H)-dione compound of formula-3 in presence of alkali metal halide/alkaline earth metal halide in a suitable solvent optionally in presence of suitable base to provide compound of formula-1.
Wherein, the alkali metal halide is selected from but not limited to LiCl, LiBr, Lil, NaBr, Nal, KBr, KI, CsCl, CsBr, Csl and the like; alkaline earth metal halide is selected from but not limited to BeCl2, BeBr2, MgCl2, MgBr2, Mgl2, CaCl2, CaBr2, Cal2, BaCl2, BaBr2, Bal2 and the like; the suitable base and the suitable solvent are same as defined above in the
specification.
'R' is a leaving group that can be selected from but not limited to halogens, aliphatic groups such as alkylsulfonyloxy; substituted/unsubstituted arylsulfonyloxy such as benzenesulfonyloxy, p-toluenesulfonyloxy and the like, camphorsulfonyloxy; aromatic groups selected from but not limited to unsubstituted or mono, di or trisubstituted aryloxy/aralkyloxy having substituents selected from hydroxy, halogens, N02, NH2, alkylamino, arylamino, alkoxy, aryloxy, cyano, sulfonic acid, SCH3, S02CH3, S02NH2 and the like; substituted/unsubstituted 1-naphthyloxy, 2-naphthyloxy, 7-azabenzotriazole-l-yloxy, 1-benzotriazolyloxy, 2,5-pyrrolidinedione-l-yloxy and the like.
The above coupling reaction can also be carried out in the presence of metal halides selected from but not limited to Zinc chloride, Zinc bromide, Zinc iodide, Copper chloride, Copper bromide, Copper iodide; Cu(OTf)2, Cu(OAc)2, Copper sulfate; metal salts of Fe, La, Yb and the like in a suitable solvent optionally in presence of a suitable base. Metal salts include halides, OTf salts and acetates.

A preferred embodiment of the present invention provides a process for the preparation of compound of formula-1, comprising of reacting the (S)-isopropyl 2-((S)-(4-nitrophenoxy)(phenoxy)phosphorylamino)propanoate compound of formula-2a
^y HO 'F
Formula-2a Formula-3
with compound of formula-3 in presence of Zinc chloride and diisopropylethyl amine in tetrahydrofuran to provide compound of formula-1.
By developing the above process for the preparation of compound of formula-1 by coupling of compound of general formula-2 with compound of formula-3 in presence of alkali metal halide/alkaline earth metal halide/metal halide or metal salts, the present inventors were able to achieve the compound of formula-1 with excellent yield and purity when compared to the prior-known processes for the preparation of compound of formula-1. This signifies that the present process is economic especially on industrial scale and hence highly advantageous.
The compound of formula-1, compound of general formula-2 and compound of formula-3 utilized in the present invention can be synthesized by any of the known processes.
PXRD analysis of compounds produced by the present invention were carried out using BRUKER/AXS X-Ray diffractometer using Cu Ka radiation of wavelength 1.5406 A° and continuous scan speed of 0.03°/min.
The best mode of carrying out the present invention is illustrated by the below mentioned examples. These examples are provided as illustration only and hence should not be construed as limitation to the scope of the invention.

Examples:
Example-1: Preparation of amorphous solid dispersion comprising (S)-isopropyl 2-((S)-
(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-
methyltetrahydrofuran-2-yI)methoxy)-(phenoxy)phosphorylamino)propanoate
compound of formula-1 and Eudragit L 100-55
a) By using 1:0.5 w/w of compound of formula-1 and Eudragit L 100-55:
A mixture of compound of formula-1 (500 mg), Eudragit L 100-55 (250 mg) and methanol (50 ml) was stirred for 10 min at 25-30°C to get clear solution. Distilled off the solvent completely from the reaction mixture under reduced pressure and then dried the obtained material to get the title compound. The PXRD pattern of the obtained compound is shown in figure-1. Yield: 580.0 mg.
b) By using 1:1 w/w of compound of formula-1 and Eudragit L 100-55:
A mixture of compound of formula-1 (500 mg), Eudragit L 100-55 (500 mg) and methanol (50 ml) was stirred for 10 min at 25-30°C to get clear solution. Filtered the reaction mixture and distilled off the solvent completely from the filtrate under reduced pressure and then dried the obtained material to get the title compound. The PXRD pattern of the obtained compound is shown in figure-1. Yield: 680.0 mg.
Example-2: Preparation of amorphous solid dispersion comprising compound of formula-1 and hydroxypropyl cellulose (HPC)
A mixture of compound of formula-1 (500 mg), hydroxypropyl cellulose (500 mg) and methanol (50 ml) was stirred for 10 min at 25-30°C to get clear solution. Distilled off the solvent completely from the reaction mixture under reduced pressure and then dried the obtained material to get the title compound. The PXRD pattern of the obtained compound is shown in figure-2. Yield: 380.0 mg.

Example-3: Preparation of amorphous solid dispersion comprising compound of formula-1 and hydroxypropyl methylcellulose acetate succinate
a) By using 1:0.5 w/w of compound of formula-1 and HPMCAS:
A mixture of compound of formula-1 (500 mg), hydroxypropyl methylcellulose acetate succinate (250 mg) and methanol (50 ml) was stirred for 10 min at 25-30°C to get clear solution. Distilled off the solvent completely from the reaction mixture under reduced pressure and then dried the obtained material to get the title compound. The PXRD pattern of the obtained compound is shown in figure-3. Yield: 380.0 mg.
b) By using 1:1 w/w of compound of formula-1 and HPMCAS:
A mixture of compound of formula-1 (500 mg), hydroxypropyl methylcellulose acetate succinate (500 mg) and methanol (50 ml) was stirred for 10 min at 25-30°C to get clear solution. Filtered the reaction mixture and distilled off the solvent completely from the filtrate under reduced pressure and then dried the obtained material to get the title compound. The PXRD pattern of the obtained compound is shown in figure-3. Yield: 450.0 mg.
Example-4: Preparation of amorphous solid dispersion comprising compound of formula-1 and hydroxypropyl methylcellulose (HPMQ
A mixture of compound of formula-1 (500 mg), hydroxypropyl methylcellulose (500 mg) and methanol (50 ml) was stirred for 20 min at 25-30°C to get clear solution. Filtered the reaction mixture and distilled off the solvent completely from the filtrate under reduced pressure and then dried the obtained material to get the title compound. The PXRD pattern of the obtained compound is shown in figure-4. Yield: 400.0 mg.
Example-5: Preparation of amorphous solid dispersion comprising compound of
formula-1 and PVP K-30
a) By using 1:0.5 w/w of compound of formula-1 and PVP K-30:
A mixture of compound of formula-1 (500 mg), PVP K-30 (250 mg) and methanol (50 ml) was stirred for 15 min at 25-30°C to get clear solution. Distilled off the solvent

completely from the reaction mixture under reduced pressure and then dried the obtained
material to get the title compound.
The PXRD pattern of the obtained compound is shown in figure-5.
Yield: 480.0 mg.
b) By using 1:1 w/w of compound of formula-1 and PVP K-30:
A mixture of compound of formula-1 (500 mg), PVP K-30 (500 mg) and methanol (50 ml) was stirred for 15 min at 25-30°C to get clear solution. Distilled off the solvent completely from the reaction mixture under reduced pressure and then dried the obtained material to get the title compound.
The PXRD pattern of the obtained compound is shown in figure-5. Yield: 680.0 mg.
Example-6: Preparation of compound of formula-1 using MgCh
Diisopropylethyl amine (9.9 gm) was slowly added to a mixture of (S)-isopropyl 2-((S)-(4-nitrophenoxy)(phenoxy)phosphorylamino)propanoate compound of formula-2a (42 gm), l-((2R,3R,4RJ5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine-2,4(lH,3H)-dione compound of formula-3 (20 gm), anhydrous magnesium chloride (8.8 gm) and tetrahydrofuran (180 ml) at 25-30°C under nitrogen atmosphere and stirred the reaction mixture for 15 hrs at the same temperature. Slowly quenched the reaction mixture with aqueous ammonium chloride solution and stirred for 10 min. Isopropyl acetate was added to the reaction mixture and stirred for 10 min. Both the organic and aqueous layers were separated and washed the organic layer with aqueous HC1 solution followed by with aqueous NaHCC>3 solution and then finally with aqueous NaCl solution. Distilled off the solvent completely from the organic layer and co-distilled with dichloromethane. Dichloromethane (100 ml) was added to the obtained compound at 25-30°C and stirred the reaction mixture for 10 min. Diisopropyl ether (20 ml) was slowly added to the reaction mixture at 25-3 0°C and stirred the reaction mixture for 4 hrs at the same temperature. Filtered the precipitated solid, washed with mixture of dichloromethane and diisopropyl ether and then dried to get title compound. Yield: 19.0 gm

Example-7: Preparation of compound of formula-1 using ZnCh
A mixture of Zinc chloride (15.7 gm) and toluene (50 ml) was heated to reflux temperature. Collected the water completely through Dean stark apparatus. Distilled off the solvent completely through azeotropic distillation. Cooled the Zinc chloride to 25-30°C under nitrogen atmosphere. Tetrahydrofuran (375 ml), l-((2Rs3R,4R,5R)-3-fluoro-4-hydroxy-5-(hydroxymethyl)-3-methyltetrahydrofuran-2-yl)pyrimidine-2,4(lH,3H)-dione compound of formula-3 (25 gm) followed by (S)-isopropyl 2-((S)-(4-nitrophenoxy)(phenoxy)phosphorylamino)propanoate compound of formula-2a (24 gm) were added to the Zinc chloride at 25-30°C under nitrogen atmosphere. Diisopropylethylamine (24.5 gm) was slowly added to the reaction mixture at 25-30°C and stirred the reaction mixture for 2 hrs at the same temperature. (S)-isopropyl 2-((S)-(4-nitrophenoxy)(phenoxy) phosphorylamino)propanoate compound of formula-2a (30 gm) was slowly added lot wise to the reaction mixture at 25-30°C and stirred the reaction mixture for 24 hrs at the same temperature. Distilled off the solvent completely from the reaction mixture under reduced pressure. Ethyl acetate was added to the obtained compound at 25-30°C and stirred the reaction mixture for 15 min at the same temperature. Aqueous HC1 solution was slowly added to the reaction mixture at 25-30°C and stirred the reaction mixture for 5 min at the same temperature. Both the organic and aqueous layers were separated and washed the organic layer with aqueous HC1 solution and then subsequently with water, aqueous sodium bicarbonate solution followed by finally with aqueous sodium chloride solution. Charcoal (2.5 gm) was added to the organic layer and stirred for 45 min. Filtered the reaction mixture through hyflow bed and washed the hyflow bed with ethyl acetate. Distilled off the solvent completely from the filtrate under reduced pressure and co-distilled with dichloromethane. Dichloromethane (100 ml) was added to the obtained compound at 25-30°C and stirred the reaction mixture for 10 min at the same temperature. Diisopropyl ether (250 ml) was slowly added to the reaction mixture at 25-30°C and stirred the reaction mixture for 4 hrs at the same temperature. Filtered the precipitated solid, washed with a mixture of dichloromethane and diisopropyl ether and then dried the material. Yield: 44.0 gm.

Example-8: Purification of compound of formula-1
A mixture of (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-y l)-4-fluoro-3 -hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate compound of formula-1 (100 gm) and dichloromethane (400 ml) was heated to reflux temperature and stirred the reaction mixture for 1 hr at the same temperature. Cooled the reaction mixture to 25-30°C and stirred for 3 hrs at the same temperature. Filtered the solid, washed with dichloromethane and spin dried the material. The obtained compound was added to ethyl acetate (400 ml) at 25-30°C and stirred the reaction mixture for 30 min at the same temperature. Filtered the reaction mixture to make it particle free and washed with ethyl acetate. Distilled off the solvent completely from the filtrate under reduced pressure and co-distilled with isopropyl alcohol. Water (2000 ml) was added to the obtained compound at 25-30°C and stirred the reaction mixture for 5 min at the same temperature. Isopropyl alcohol (100 ml) was added to the reaction mixture at 25-30°C and stirred for 5 min at the same temperature. Heated the reaction mixture to 50-5 5°C and stirred for 1 hr at the same temperature. Cooled the reaction mixture to 25-30°C and stirred for 18 hrs at the same temperature. Filtered the precipitated solid, washed with water and dried the material to provide pure compound. Yield: 79.2 gm.