DESC:FORM 2

THE PATENTS ACT 1970
(SECTION 39 OF 1970)

&

THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(Section 10 and Rule 13)

AN IMPROVED PROCESS FOR THE PREPARATION OF NUCLEOSIDE DERIVATIVE

We, GRANULES INDIA LIMITED,
a company incorporated under the companies act, 1956 having address at
My Home Hub; 2nd Floor; 3rd Block; Madhapur; Hyderabad – 500081, India

The following specification particularly describes the invention and the manner in which it is to be performed:

Field of the Invention
The present invention relates to an improved process for the preparation of nucleoside derivative which are used as agents in the treatment of viral diseases. In particular, the present invention relates to process for the preparation of a nucleotide analog inhibitor of HCV NS5B polymerase.
Background of the Invention
Sofosbuvir is sold under the brand name SOVALDI® and is a Hepatitis C virus (HCV) nucleotide analog NS5B polymerase inhibitor indicated for the treatment of chronic hepatitis C (CHC) infection as a component of a combination antiviral treatment regimen. The chemical name of Sofosbuvir is (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo3,4-dihydropyrimidin-1(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2yl)methoxy)-(phenoxy)phosphorylamino)propanoate and the molecular formula is C22H29FN3O9P with a molecular weight of 529.4. The structural formula of Sofosbuvir is:

Formula I
Sofosbuvir is disclosed for the first time in US 7,964,580 B2. This patent also discloses process for preparing Sofosbuvir by reacting phosphorochloridate compound with nucleoside analog to give Sofosbuvir. The process is shown in the scheme given below:

Scheme I

The product has several chiral centres and it is desirable to have diastereomeric purity. Hence, It is of considerable importance to employ an efficient method for the preparation of Sofosbuvir which is simple, economical and industrially viable.

The inventors have now surprisingly found a new process of preparing Sofosbuvir which results in greater efficiency than the prior art processes and higher product purity.

Objective of the Invention
The main objective of the present invention is to provide a simple and effective process for the preparation of Sofosbuvir of Formula I on a commercial scale.

Another objective of the present invention is to provide a process for novel intermediates that are used in the preparation of Sofosbuvir.

Summary of the Invention
Accordingly, the present invention provides an improved process for the preparation of Sofosbuvir of Formula I which comprises:
i) reacting the compound of Formula II

Formula II
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I);with a compound of Formula III

Formula III
wherein L represents a suitable leaving group; in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IV,

Formula IV
ii) optionally isolating compound of formula IV,
iii) reacting the compound of Formula IV with alanine isopropyl ester in a solvent in the presence of a base and optionally in the presence of a catalyst to give compound of Formula V,

Formula V
wherein Pg and Nu are as defined above.
iv) deprotecting the compound of Formula V in a suitable solvent and reagent to give compound of Formula I and
v) optionally converting the compound of Formula I when Nu is other than F to compound of Formula I where Nu is F.

In another aspect, the present invention provides an improved process for the preparation of intermediate compound of Formula V which comprises:
i) reacting the compound of Formula II

Formula II
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I); with a compound of Formula III

Formula III
wherein L represents a suitable leaving group; in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IV and

Formula IV
ii) optionally isolating compound of formula IV, and
iii) reacting the compound of Formula IV with alanine isopropyl ester in a solvent in the presence of a base and optionally in the presence of a catalyst to give compound of Formula V,

Formula V
wherein Pg and Nu are as defined above.

In another aspect, the present invention provides an improved process for the preparation of intermediate compound of Formula IV which comprises:
i) reacting the compound of Formula II

Formula II
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I); with a compound of Formula III

Formula III
wherein L represents a suitable leaving group; in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IV

Formula IV
wherein Pg and Nu are as defined above.

Detailed Description of the Invention
The present invention relates to an improved process for the preparation (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo3,4-dihydropyrimidin-1(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2yl)methoxy)-(phenoxy)phosphorylamino)propanoate (Sofosbuvir) of Formula I.

According to the present invention suitable protecting group Pg is selected from methyl, t-butyl, formyl, acetyl, benzyl, 4-methoxybenzyl, tetrahydropyranyl, methoxymethyl, 2-methoxyethoxymethyl, or R"C(O)-; wherein R" is a straight or branched alkyl, or cycloalkyl, amino acid, aryl, alkylaryl, aralkyl, alkoxyalkyl, aryloxyalkyl or substituted alkyl, substituted aryl, wherein the substitution may comprise at least one selected from chloro, bromo, fluoro, iodo, nitro, C=O, substituted or unsubstituted C1 to C4 alkyl or C1 to C4 alkoxy, sulfonate esters, mono, di, or triphosphate ester, trityl or monomethoxy-trityl, substituted alkaryl, aralkyl, alkoxyalkyl, or aryloxyalkyl;trityl, trialkylsilyl, isopropyldialkylsilyl, alkyldiisopropylsilyl, triisopropylsilyl, tetraisopropyldisilyl, t-butyldialkylsilyl or t-butyldiphenylsilyl.

In another embodiment of the present invention suitable Leaving groups used is selected from amino acid, substituted or unsubstitutedaryloxy, alkoxyalkyloxy, aryloxyalkyloxy, C1 to C4alkoxy, sulfonate esters, mono, di, or triphosphate ester, trityl, monomethoxy-trityl, trialkylsilyl, isopropyldialkylsilyl, alkyldiisopropylsilyl, triisopropylsilyltetraisopropyldisilyl, t-butyldialkylsilyl or t-butyldiphenylsilyl or halogens such as chlorine, bromine, iodine or trifluoroacetate or alkylsulfonyloxy group such as methanesulfonyloxy and the like or trifluoroalkylsulfonyloxy such as a trifluoromethanesulfonyloxy and the like or arylsulfonyloxy group such as benzenesulfonyloxy, p-toluenesulfonyloxy, p-nitrobenzenesulfonyloxy, o-nitrobenzenesulfonyloxy, fluorosulfonyl, camphorsulfonyl and the like or phenoxides such as pentafluorophenoxide, p-NO2-phenoxide and the like or thio phenyls and the like or 2,2-dimethyl-3-(3-(trifluoromethyl)phenyl)propanoyl chloride and the like; bicyclic compounds such as indole,benzotriazoles or tricyclic compounds such as Fmoc or menthol or compounds represented by the Formula

In yet another embodiment suitable base used in the present invention is selected from either inorganic base like alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide; alkali metal carbonates such as sodium carbonate, potassium carbonate, cesium carbonate and lithium carbonate; Alkali metal bicarbonates such as sodium bicarbonate and potassium bicarbonate; alkali metal alkoxides such as sodium methoxide, potassium methoxide, sodium tertiary butoxide, potassium tertiary butoxide or mixtures thereof or organic bases such as triethylamine, triethanolaminetributylamine, N-methylmorpholine, N,N-diisopropylethylamine,di-n-propylamine, N-methylpyrrolidine, pyridine, 4-(N,N-dimethylamino)pyridine, morpholine, imidazole, 2-methylimidazole, 4-methylimidazole, 1,4-diazabicyclo[2,2,2]octan and the like.

In yet another embodiment suitable solvents used in the present invention are selected from aprotic solvents such as pentane, hexane, heptane, benzene, toluene, xylene, diethyl ether, diisopropyl ether, tert-butyl methyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, dioxane, diglyme, triglyme, N,N-dimethylformamide, N,N-dimethylacetamide, DMSO, acetonitrile, chloroform, dichloromethane, dichloroethane, carbon tetrachloride and the like.

In yet another embodiment the catalyst in the present invention include chiral crown ethers such as 8-crown-6 or 15-crown-5 18-crown-6 or dibenzo-18-crown-ether and the like or cinchona alkaloids such as N-(acridin-9-ylmethyl)quininium bromide or N-(anthracenylmethyl)quininium bromide, N-(anthracenylmethyl)cinchonidinium chloride, O(9)-allyl-N-9-anthracenylmethylcinchonidium bromide, (8S,9R)-(-)-N-benzyl cinchonidium chloride.

In another embodiment of the present invention, suitable solvent used for deprotection is selected from THF : water, methanolic ammonia, ammonium hydroxide: methanol, lithiumhydroxide : THF : water and the like.

According to the present invention, one or more sequential steps are carried out with or without isolating intermediate compounds.

In a preferred embodiment, the present invention provides an improved process for the preparation of Sofosbuvir of Formula I which comprises:
i) reacting the compound of Formula IIa

Formula IIa
with a compound of Formula IIIa

Formula IIIa
in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IVa,

Formula IVa
ii) reacting the compound of Formula IVa with alanine isopropyl ester in a solvent in the presence of a base and a catalyst to give compound of Formula Va and

Formula Va
iii) deprotecting the compound of Formula Va in a suitable solvent and reagent to give compound of Formula I.

In a most preferred embodiment, the present invention provides an improved process for the preparation of Sofosbuvir of Formula I which comprises:
i) reacting the compound of Formula IIa

Formula IIa
with a compound of Formula IIIa

Formula IIIa
in anhydrous pyridine in the presence of molecular sieves to give compound of Formula IVa,

Formula IVa
ii) reacting the compound of Formula IVa with alanine isopropyl ester in acetonitrile in the presence of triethylamine to give compound of Formula Va and

Formula Va
iii) deprotecting the compound of Formula Va using mixture of THF and water to give compound of Formula I.

In yet another preferred embodiment, the present invention provides an improved process for the preparation of intermediate compound of Formula Va which comprises:
i) reacting the compound of Formula IIa

Formula IIa
with a compound of Formula IIIa

Formula IIIa
in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IVa and

Formula IVa
ii) reacting the compound of Formula IVa with alanine isopropyl ester in a solvent in the presence of a base and optionally a catalyst to give compound of Formula Va.

In a most preferred embodiment, the present invention provides an improved process for the preparation of intermediate compound of Formula Va which comprises:
i) reacting the compound of Formula IIa

Formula IIa
with a compound of Formula IIIa

Formula IIIa
in anhydrous pyridine in the presence of molecular sieves to give compound of Formula IVa and

Formula IVa
ii) reacting the compound of Formula IVa with alanine isopropyl ester in acetonitrile in the presence of a triethylamine to give compound of Formula Va.
While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention. The invention is illustrated below with reference to inventive and comparative examples and should not be construed to limit the scope of the invention.

EXAMPLES
Example 1: Synthesis of compound Va:

To pyridine (10 V) and diphenyl phosphite (0.0305 mol) was added a solution of compound IIa in pyridine at 0-5°C. After addition, the mass was maintained at room temperature. Maintained the reaction mass for 1hr at room temperature. To the mass was added a solution of alanine isopropyl ester in acetonitrile and triethyl amine at room temperature. Maintained the reaction mass for 6hrs at room temperature. Concentrated the solvent completely below 60°C under vacuum, furnished compound Va. The pure compound was isolated in column chromatography.

Ex-2: Synthesis of Sofosbuvir compound of formula I:

To THF (10 V) was added compound Va at room temperature. To this was added sodium sulfite solution (sodium thiosulfate and sodium metabisulfite dissolved in water). Maintained the mass for 24 hrs at room temperature. The reaction mass was diluted with water and isolated in ethyl acetate. The pure compound was isolated in water and methanol mixture by seeding with pure compound. (HPLC purity: 99.3%).

Dated this Nineteenth (19th) day of February 2016.
__________________________________
Dr. S. Padmaja
Agent for the Applicant
IN/PA/883
,CLAIMS:We Claims:

1. An improved process for the preparation of Sofosbuvir of Formula I or its salts

Formula I
which comprises:
a) reacting the compound of Formula II

Formula II
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I); with a compound of Formula III

Formula III
wherein L represents a suitable leaving group; in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IV,

Formula IV
b) optionally isolating compound of formula IV,
c) reacting the compound of Formula IV with alanine isopropyl ester in a solvent in the presence of a base and optionally in the presence of a catalyst to give compound of Formula V,

Formula V
wherein Pg and Nu are as defined above,
d) deprotecting the compound of Formula V in a suitable solvent and a reagent to give compound of Formula I, and
e) optionally converting the compound of Formula I when Nu is other than F to compound of Formula I where Nu is F.

2. An improved process for the preparation of intermediate compound of Formula V

Formula V
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I), which comprises:
a) reacting the compound of Formula II

Formula II
wherein Pg and Nu are as defined above; with a compound of Formula III

Formula III
wherein L represents a suitable leaving group; in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IV and

Formula IV
wherein Pg and Nu are as defined above, and
b) optionally isolating compound of formula IV, and
c) reacting the compound of Formula IV with alanine isopropyl ester in a solvent in the presence of a base and optionally in the presence of a catalyst to give compound of Formula V.

3. The process as claimed in claim 2, wherein the compound of Formula V is further converted to compound of formula I by a process, which comprises deprotecting the compound of Formula V in a suitable solvent and a reagent to give compound of Formula I.

4. An improved process for the preparation of intermediate compound of Formula IV

Formula IV
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I), which comprises reacting the compound of Formula II

Formula II
wherein Pg and Nu are as defined above; with a compound of Formula III

Formula III
wherein L represents a suitable leaving group; in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IV.

Formula IV

5. The process as claimed in claim 4, wherein the compound of Formula IV is further converted to compound of formula I by a process, which comprises
a) reacting the compound of Formula IV with alanine isopropyl ester in a solvent in the presence of a base and optionally in the presence of a catalyst to give compound of Formula V,

Formula V
wherein Pg is a protecting group and Nu is halogen (F, Cl, Br, I), and
b) deprotecting the compound of Formula V in a suitable solvent and a reagent to give compound of Formula I.

6. An improved process for the preparation of Sofosbuvir of Formula I which comprises:
a) reacting the compound of Formula IIa

Formula IIa
with a compound of Formula IIIa

Formula IIIa
in the presence of a base and optionally in the presence of molecular sieves to give compound of Formula IVa,

Formula IVa
b) reacting the compound of Formula IVa with alanine isopropyl ester in a solvent in the presence of a base and optionally in the presence of a catalyst to give compound of Formula Va, and

Formula Va
c) deprotecting the compound of Formula Va in a suitable solvent and a reagent to give compound of Formula I.

7. An improved process for the preparation of Sofosbuvir of Formula I which comprises:
a) reacting the compound of Formula IIa

Formula IIa
with a compound of Formula IIIa

Formula IIIa
in anhydrous pyridine to give compound of Formula IVa,

Formula IVa
b) reacting the compound of Formula IVa with alanine isopropyl ester in acetonitrile in the presence of a triethylamine to give compound of Formula Va, and

Formula Va
c) deprotecting the compound of Formula Va using THF / water or mixture and sodium sulfite / sodium metabisulfite to give compound of Formula I.

8. The process as claimed in any of the preceding claims, wherein the base used is independently selected from either inorganic base like alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide; alkali metal carbonates such as sodium carbonate, potassium carbonate, cesium carbonate and lithium carbonate; Alkali metal bicarbonates such as sodium bicarbonate and potassium bicarbonate; alkali metal alkoxides such as sodium methoxide, potassium methoxide, sodium tertiary butoxide, potassium tertiary butoxide or mixtures thereof or organic bases such as triethylamine, triethanolaminetributylamine, N-methylmorpholine, N,N-diisopropylethylamine, di-n-propylamine, N-methylpyrrolidine, pyridine, 4-(N,N-dimethylamino)pyridine, morpholine, imidazole, 2-methylimidazole, 4-methylimidazole, 1,4-diazabicyclo[2,2,2]octane or mixture thereof; the solvent used in any of the preceding claims is independently selected from aprotic solvents such as pentane, hexane, heptane, benzene, toluene, xylene, diethyl ether, diisopropyl ether, tert-butyl methyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, dioxane, diglyme, triglyme, N,N-dimethylformamide, N,N-dimethylacetamide, DMSO, acetonitrile, chloroform, dichloromethane, dichloroethane, carbon tetrachloride or mixture thereof.

9. The process as claimed in any of the preceding claims, compound of formula IV is reacted with alanine isopropyl ester either in the absence of catalyst or in the presence of catalyst wherein the catalyst is selected from chiral crown ethers such as 8-crown-6 or 15-crown-5 18-crown-6 or dibenzo-18-crown-ether and the like or cinchona alkaloids such as N-(acridin-9-ylmethyl)quininium bromide or N-(anthracenylmethyl)quininium bromide, N-(anthracenylmethyl)cinchonidinium chloride, O(9)-allyl-N-9-anthracenylmethylcinchonidium bromide, (8S,9R)-(-)-N-benzyl cinchonidium chloride.

10. The process as claimed in any of the preceding claims, Pg is selected from methyl, t-butyl, formyl, acetyl, benzyl, 4-methoxybenzyl, tetrahydropyranyl, methoxymethyl, 2-methoxyethoxymethyl, or R"C(O)-; wherein R" is a straight or branched alkyl, or cycloalkyl, amino acid, aryl, alkylaryl, aralkyl, alkoxyalkyl, aryloxyalkyl or substituted alkyl, substituted aryl, wherein the substitution may comprise at least one selected from chloro, bromo, fluoro, iodo, nitro, C=O, substituted or unsubstituted C1 to C4 alkyl or C1 to C4 alkoxy, sulfonate esters, mono, di, or triphosphate ester, trityl or monomethoxy-trityl, substituted alkaryl, aralkyl, alkoxyalkyl, or aryloxyalkyl;trityl, trialkylsilyl, isopropyldialkylsilyl, alkyldiisopropylsilyl, triisopropylsilyl, tetraisopropyldisilyl, t-butyldialkylsilyl or t-butyldiphenylsilyl and Leaving groups used is selected from amino acid, substituted or unsubstitutedaryloxy, alkoxyalkyloxy, aryloxyalkyloxy, C1 to C4 alkoxy, sulfonate esters, mono, di, or triphosphate ester, trityl, monomethoxy-trityl, trialkylsilyl, isopropyldialkylsilyl, alkyldiisopropylsilyl, triisopropylsilyltetraisopropyldisilyl, t-butyldialkylsilyl or t-butyldiphenylsilyl or halogens such as chlorine, bromine, iodine or trifluoroacetate or alkylsulfonyloxy group such as methanesulfonyloxy and the like or trifluoroalkylsulfonyloxy such as a trifluoromethanesulfonyloxy and the like or arylsulfonyloxy group such as benzenesulfonyloxy, p-toluenesulfonyloxy, p-nitrobenzenesulfonyloxy, o-nitrobenzenesulfonyloxy, fluorosulfonyl, camphorsulfonyl and the like or phenoxides such as pentafluorophenoxide, p-NO2-phenoxide and the like or thio phenyls and the like or 2,2-dimethyl-3-(3-(trifluoromethyl)phenyl)propanoyl chloride and the like; bicyclic compounds such as indole,benzotriazoles or tricyclic compounds such as Fmoc or menthol or compounds represented by the Formula