Process and intermediates of 2,2'-DifluoronucIeosides
Field of the invention;
The present invention relates to novel l-trihaloacetimido-2-deoxy-2,2*-difluoro-3,5-di-0- protected ribose derivates and its use in the process for the preparation of antiviral alpha or beta or mixtures of anomeric nucleosides and its pharmaceutical^ acceptable salts and more particularly the invention relates to novel 1-trihaloacetimido- 2-deoxy-2,2-difluoro-3-carbomyI- 5-O-protected ribose and its use in the preparation of 2-deoxy-2,2'-difluoro-beta-cytidine and its pharmaceutically acceptable salts as antiviral and anticancer agent.
Background of the invention:
US Patent No. 4,526,988 teaches the preparation of 2'-deoxy-2,2'-difluoro nucleosides as useful antiviral agents. European Patent Application 184,365 also teaches the use of the same compound as anticancer agents. The process for the preparation is also described in these patents.
US Patent No. 4,526,988 teaches the preparation of 3R and 3S-hydroxy enantiomers of an alkyl- 2,2-difluoro-3-hydroxy-3-(2,2-dialkyl dioxalan-4-yl)propionate.
US Patent No. 4,526,988 particularly refers to the use of t-butyldimethyl silyl as a protecting group and its use in the synthesis of 2'-deoxy-2,2'-difluoro nucleosides composed of 4 : 1 a / (3 anomeric ratio. The required P anomer was obtained by employing tedious and expensive purification method of column chromatography.
Bull.Chem Soc. (Japan), 62 (3), 845-852 (1989) has described the concept of using substituent on the 3-hydroxy deoxyribose derivates to direct beta synthesis.
US Patent No. 5,521,294 reveals the use of l-sulfonate-3-carbomyl-5-protected 2'-deoxy-2,2'- difluororibose to produce high yield of (3-anomer nucleoside compare to alpha anomer when used in the preparation of intermediate to 2'-deoxy-2,2'-difluoro-beta-cytidine.
Accordingly, the present invention provides novel l-trihaloacetimido-3,5-di-o-protected-2'- deoxy-2,2'-difluororibose intermediate in the preparation of enhanced yield of P-anomer of 2- deoxy-2,2'-difluoronucleosides and more particularly beta anomer of 2-deoxy-2,2'- difluorocytidine and its salts.
In accordance with the prior art knowledge the glycosidation process step in the preparation of 2-deoxy-2,2'-difluoro nucleoside has provided a / p anomeric ratio up to 40 : 60. The present invention provides a / p anomeric ratio up to 30 : 70.
The surprising result of the present invention is achieved by obtaining enhanced proportion of P- anomer 2-deoxy-2,2'-difluro nucleoside in the mixture of a and P anomer 2-deoxy-2,2'-difluoro nucleoside obtained in the glycosidation process by contacting silylated nucleobase and 1- trihaloacetimido 3,5-diprotected-2-deoxy ribose derivative in presence of a lewis acid(s) followed by deprotection. However it is also observed that generally the same anomeric ratio of protected nucleoside is obtained after removing the protecting groups.
Objects of the invention:
An object of the invention is to provide ribose derivatives of formula (1) as novel intermediates which produce high yield of the P-anomer nucleoside, more particularly beta anomer of 2- deoxy-2,2'-difluoro cytidine.
Another object of the invention is to provide beta anomer nucleosides from ribose derivatives as novel intermediate compounds.
Yet another object of the invention is to provide a process for producing compounds which is simple and economical and can be used to produce P-anomer 2-deoxy-2,2'-difluro nucleosides and particularly P-anomer 2-deoxy 2,2'-difluoro cytidine in bulk.
Still another object of the invention is to provides a process for the preparation of enhanced proportion of P-anomer 2'-deoxy-2,2'-difluoro cytidine from mixture of a and p anomer 2-deoxy -2,2'-difluoro cytidine.
The above objects will become apparent by reference to the following description. Summary of the invention:
The invention provides a process for the preparation of enantiomeric mixture of novel 1-trihalo acetimido-2 -deoxy-2,2'-difluoro-3,5-di-0-protected ribose of formula (1);
Formula (1)
Wherein, R and Ri each is a hydroxy protecting group X = CI or Br.
which comprises hydrolysing a enantiomeric mixture of an alkyl 2,2-difluoro-3-hydroxy-3-(2,2- dialkyl dioxalan-4-yl)propionate or a protective derivative thereof of formula.(2);

Formula (2)
Wherein, R is as defined above, R3 and R4 are independently Ci - C4 alkyl, by using a strong acid as a hydrolytic reagent, followed by azeotropic distillation of water to obtain the lactone of formula (3);
Formula (3)
Wherein, R is hydroxy protecting group and Rt is either hydrogen or hydroxy protecting group. When Ri is a hydrogen it may be protected by contacting with a hydroxy protecting reagent before reduction of lactone to its corresponding lactol.
The lactone obtained above is further converted into its corresponding lactol of formula (4) by reduction using an appropriate reducing agent at a temperature ranging between - 80°C to - 20°C in a suitable inert solvent.

The lactol thus obtained above is contacted with trihaloacetonitrile in presence of a base preferably organic base in a chlorinated solvent at a temperature ranging between + 10°C to - 10°C to yield the required ribose derivative of formula (1) as novel intermediates. Inert solvents used in the present invention are those solvents which do not participate in the essential reaction.
Detailed description of the invention:
US Patent No. 4,526,988 reveals alkyl 2,2-difluoro-3-hydroxy-3-(2,2-dialkyI dioxalan-4-yl) propionate of the formula. (2.R = H)
Formula (2)
Wherein, R3 and R4 are independency CM alkyl. The compound consist of 3-hydroxy enantiomeric mixture. The present invention provides a process for converting the 3-hydroxyl or its protected derivative to the compound of the formula (3).
Wherein, R is hydrogen or a hydroxy protecting group.
The above mentioned 3-hydroxy protected propionate derivative of formula (2) can be prepared by contacting the corresponding 3-hydroxyl compound with a suitable hydroxy protecting reagent under appropriate reaction conditions known to skilled person in the art.
The 3-hydroxy protected derivatives are converted to the lactone compound of formula (3, R=H) by mixing with strong acid and dissolving it in a suitable solvent and diluting with water to provide 1 to 6 molar equivalents of water relative to the hydroxy protected derivative. The solvents may include alcoholic solvents, acetonitrile and related polar solvents.
The 3-protected propionate starting material, solvent, acid and water are mixed. The solution is heated for about 4 h to 8 h to substantially remove the isoalkyldine protecting group. Once the isoalkylidine group is substantially removed the resulting pentanoate is cyclised to lactone derivative by azeotropic distillation with hydrocarbon solvent preferably aromatic hydrocarbon solvent.
Further 3-hydroxy protected lactone of formula (3, Ri = H) obtained above is contacted with suitable hydroxy protecting reagent to yield 3,5-di-O-protected lactone of formula (3).
3,5-di-O-protected 2-deoxy-2,2'-difluoro pentofurano-l-ulose derivative may be further subjected to azeotropic distillation with toluene containing p-toluene sulphonic acid, followed by solvent purification to obtain purified D-erytho-3,5-di-o-protected-2-deoxy-2,2-difluoro- pentfurano-l-ulose derivative.
After obtaining 3,5-di-O-protected 2-deoxy-2,2 -difluoro-pentofurano-l-ulose derivative, it is converted into its corresponding 1-trihaloacetimido derivate of formula (1) by sequence of process steps involving reduction to lactol derivative of formula (4), followed by contacting with trihaloacetonitrile reagent in presence of a base and a suitable solvent under appropriate reaction conditions.
The trihaloacetimido group of the above mentioned derivative is a leaving group, when couple with nucleobase of the formula mentioned below.
NHR4
Wherein, R1 = H, alkyl or halogen; R2 = OH; R3 = H or halogen and R4 = H or nitrogen protective group.
to produce anomeric mixture of 2-deoxy-2,2'-difluoro nucleosides. The above mentioned glycosidation reaction between nucleobase and ribose derivative as novel intermediates may be carried out using Lewis acid as coupling initiator at a temperature ranging between 20°C to about 130°C. The reaction is substantially completed in about 4 h to 20 h of time period to yield anomeric mixture of protected nucleosides. The anomeric mixture of 2-deoxy-2,2'-difluoro nucleoside obtained after deprotection may be as such subjected to purification or by preparing its hydrohalide salt, followed by crystallization to enhance the purity level of 2-deoxy-2,2'- difluoro nucleoside or its hydrohalide salt, which may be further used to obtain p-anomer of 2- deoxy-2,2'-difluoro nucleoside hydrohalide salt of purity up to 99.80%.
The nucleobase mentioned above forms as a part of the nucleobase used in this invention and not restricted to these.
Removal of hydroxyl and amino protecting group may be conveniently carried out in any solvent selected from alkanols, polyols, tetrahydrofuran, acetone, dimethylsulfoxide and like solvents.
The preferred process utilizes cytosine to produce a mixture of 2'-deoxy-2,2,-difluorocytidine of about (30 : 70) a / p anomeric mixture. The invention also reveals process for selectively isolating p-2-deoxy-2,2'-difluorocytidine or its pharmaceutical^ acceptable salts from a anomeric mixture of a / P 2-deoxy-2,2'-difluorocytidine.
Lewis acid as a coupling initiator that may be used are trimethylsilyl trifluoromethane sulfonate, tin tetrachloride, aluminum chloride, borontrifluoride etherate, borontribromide and the like.
The present invention is not restricted to the preparation and isolation of beta nucleosides but also relates to the preparation and isolation of alpha nucleoside and mixture of a / P nucleosides and their pharmaceutically acceptable salts.
Hydroxy protecting groups include such as formyl, benzyl, triphenylmethyl, diphenylmethyl, benzoyl, chloroacetyl, 4-nitrobenzyl, substituted or unsubstituted carbomyl, phenyl carbomyl, substituted phenyl carbomyl, benzyloxy carbonyl and the like.
Amino protecting groups for nucleobase derivatives are selected from the group consisting of such as trialkylsilyl, t-butyldialkylsilyl, t-butyldiamyl silyl, carbomates such as 1-t-butoxy carbomyl, benzyloxy carbonyl, 4-methoxy-benzyloxy carbonyl, 4-nitrobenzyloxy carbonyl ether forming group such as a trimethylsilyl, alkyl, benzyl, t-butyl and the like hydroxy protecting group of the nucleobase are selected from silyl ether forming groups t-butoxy carbonyl, substituted or unsubstituted benzyloxy carbonyl, formyl, acetyl and the like.
The protecting groups of carbohydrate moiety and nucleobase can be removed with acid or base catalyst under appropriate conventional reaction conditions known to the person skilled in the art.
The term appropriate condition of the present invention refers to the selection of features like time, temperature and work up procedure adapted etc related to that particular process step to obtain the required product.
In the process of present invention the molar ratio of compound of formula (4) to trihaloacetonitrile ranges between 1:5 to 1:12 preferably between 1:5 to 1:10.
In the process of present invention the molar ratio of compound of formula (4) to base ranges between 1:1 to 1:1.5.
In the process of present invention the molar ratio of intermediate compound of formula (1) to nucleobase ranges between 1:1.2 to 1:2.0.
In the process of present invention the molar ration of intermediate compound of formula (1) to lewis acid ranges between 1 :2 to 1 : 5 preferably 1: 2 to 1 : 3.
The following examples illustrate the specific embodiments of the present invention. The examples are not to be construed to limit the scope of the invention in any respect.
EXAMPLES:
Example-l: Preparation of enantiomeric mixture of D-Glyceraldehyde ketonide;
a) charge D-mannitol (100 g), 2,2-dimethoxy propane (152 g) and p-toluenesulphonic acid (1.0 g) to dimethyl sulphoxide (200 ml). The mixture is stirred for 2 h at a temperature of about 20°C to 25°C to dissolve completely the reactants. The mixture is maintained between 20°C to 25°C for further 16 h. Check TLC of the reaction mixture for completion, quench the reaction mixture at a temperature of 0°C to 5°C by adding aqueous sodium bicarbonate solution (15 g in 600 ml H20). Raise the temperature to 20°C to 25°C, extract with ethyl acetate (800 ml), wash ethyl acetate layer with water, dry over anhydrous sodium sulphate, filter and concentrate to one tenth of its volume and add n-hexane to crystallize the title compound (70 g).
b) Compound (70 g) obtained in Step (a) is taken in methylene dichloride (600 ml) and to it charged aqueous NaHC03 solution (9 g in 30 ml H20) and maintained between 20°C to 25°C. Added sodium metaperiodate (112 g) in portion over a period of 2 h. Filter the reaction mixture, collect methylene chloride layer, wash methylene chloride layer with sodium bicarbonate solution, dried over anhydrous sodium sulfate, filtered and distilled methylene chloride at NTP, followed by distillation under vacuum (50-60 mm of Hg) at a temperature ranging between 55°C to 70°C to obtain the title compound (27 g) [a-]D + 60° to 80° (C = 2.25 in ethyl acetate).
Example-2: Preparation of enantiomeric mixture of ethyI-2,2-difluoro-3-hydroxy-3-(2,2- dimethyldioxalan-4-yl) propionate.
To a clean, dry RB flask fitted with a stirrer and condenser is charged activated Zn dust (137 g). Separately dissolved a mixture of title compound of Example-1 (300 g) and ethyl bromo difluoroacetate (426 g) in dry THF (1500 ml). Added one length volume of the THF solution to Zn dust and heated to gentle reflux for 15 mts. Then added rest of the THF solution drop-wise over a period of 1 to 2 h maintaining gentle reflux and continued further refluxing for a period of at least an hour. Reaction mixture cooled to room temperature, worked up by quenching it in 10% aqueous HC1 (7.25 Its) at about 0 to 5°C. Extract with methylene chloride (4X1000 ml). Washed methylene chloride layer with aqueous bicarbonate solution, followed by water, dried over anhydrous sodium sulphate filtered and evaporated to dryness to yield title compound (360 g) as an yellow oil.
Example-3: Preparation of enantiomeric mixture of ethyl 2,2-difluoro-3-benzoyloxy-3-(2,2- dimethyIdioxaIon-4-yI) propionate (formula2, R=C6HsCO);
Compound prepared as per Example-2 (100 g; 0.394 mole) is taken in dry ethyl acetate (1000 ml) and to it added dry pyridine (84.9 g; 1.08 mole) and 4-dimethylamino pyridine (10 g). Then added benzoyl chloride (75.6 g; 0.538 mole) dissolved in ethyl acetate over a period of 2 h. The reaction mixture is heated to 60°C to 70°C for a period of 3 h to 4 h and then stirred at room temperature for an overnight. Worked up the reaction mixture by washing successively with water (500 ml), 10% aqueous HC1 (500 ml), water (500 ml), aqueous 10% NaHC03 solution (500 ml) and finally saturated brine solution (500 ml). Dried organic layer over anhydrous Na2S04, filtered and evaporated to dryness to yield title compound (140 g).
Example-4; Preparation of enantiomeric mixture of 2-deoxy-2,2-difluoropentafuranose-l- ulose-3-benzoate (formula3,R=C6H5CO;Ri=H);
To a mixture solution consisting enantiomeric mixture of ethyl 2-deoxy-2,2-difluoro-3- (benzoyloxy)-3-(2,2-dimethyldioxolan-4-yl) propionate (140 g; 0.392mole), trifluoroacetic acid (11.6 g,0.102 mole) and acetonitrile (1484 ml) is added water (36 ml; 2.0 mole). The mixture is refluxed with stirring at a temperature of about 80°C for 5 h to 6 h. After this, reaction mixture is distilled under atmospheric pressure to remove solvent (370 ml). To the resulting solution toluene (210ml)is added and distilled of volatiles (370 ml). The procedure is repeated further five to eight times to remove total volatiles of about 2200 ml. The resulting reaction mixture is cooled to room temperature under nitrogen stream and solution on evaporation under reduced presence to yield a residue comprising title compound.
Example-5: Preparation of an enantiomeric mixture of 3-benzyloxy-5-(4-methoxyphenyl
carbomyl2-deoxy-2,2-difluoropentafurnose-l-lose(formula3,R=C6HsCO;R,=C6HsNHCO);
To a solution of compound prepared as per Example-4 in ethyl acetate (10.5 1) added triethylamine (79.0 g; 0.784 mole), followed by the addition of p-methoxyphenylisocyanate (38.6 g; 0.784 mole) and stirred the mixture at room temperature under nitrogen atmosphere for an overnight. The reaction was partially complete and further hence added quantities of p- methoxy phenyl isocyanate (38.6 g; 0.784 mole) and continued stirring the reaction mixture at room temperature for further few hours. Finally reaction mixture is filtered to remove the precipitated solid and clear mother liquor was evaporated to dryness to obtain an oily residue comprising title compound (190 g).
Example-6: Preparation of an enantiomeric mixture of 3-benzoyloxy-5-(4-methoxyphenyl carbomyl)-2-deoxy-2,2-difluoro ribose (formula4,R=C6HsCO;Ri=C6H5NHCO);
Compound obtained in Example-5 (100 g, 0.236 mole) is dissolved in moisture free tetrahydrofuran (1.95 L) and cooled to a temperature of about -50°C. To this cooled solution, 70% vitride solution in toluene (54.76 ml; 0.189 mole) is added drop-wise with stirring over a period of 1 h to 2 h maintaining the temperature at about -50°C. The reaction mixture is further stirred at this temperature for 2 h to 3 h. and treated with methanol (70 ml) at a temperature not above -20°C. Slowly the reaction mixture is brought to ambient temperature and quenched with 0.1 N aqueous HC1 (2.0 L). The aqueous layer is then washed with toluene three times, combined organic layer is then washed with aqueous sodium carbonate followed by saturated sodium chloride solution, dried over anhydrous sodium sulphate, filtered and clear mother liquor evaporated to yield a residue comprising title compound of [formula (4), 100 g].
ExampIe-7: Preparation of enantiomeric mixture of l-trichIoroacetimido-3-benzoyloxy-5- (4-methoxyphenyIcarbomyl)-2-deoxy-2,2-difluororibose of formuia(l) [R=C6HsCO, Ri=p- MeO-CeHgNHCO];
Trichloracetonitrile (452 ml; 4.51 mole) is taken in ethylene dichloride (60 ml) and diisopropyl ethyl amine (28 ml;0.165 mole) is added to it. The mixture is cooled to 0 to 5°C and a solution of compound of formula (4) prepared as per Example-6 (160 g: 0.376 mole) in ethylene chloride (500 ml) is added drop-wise over a period of 1 h to 2 h maintaining the temperature between 0 to 5°C.
The reaction mixture is further stirred overnight at this temperature and evaporated to dryness under high vacuum at a temperature not more than 50°C to yield a comprising the title compound of formula (1) (190 g).
ExampIe-8: Preparation of a / p anomeric mixture of protected 2-deoxy-2,2'- difluorocytidine;
Tol-trichloroacetimido-3-benzoyloxy-5-(4-methoxyphenylcarbomyl)-2-deoxy-2,2'- difluororibose (120 g; 0.229 mole) in ethylene dichloride (900 ml) were added bis- trimethylsilyl-N-acetylcytosine (120 g; 0.466mole) and trimethylsilyl trifluoromethane sulfonate (128.9 g; 0.488 mole) and refluxed for about 8h to 16h. Worked up the reaction mixture by pouring on to aqueous IN hydrochloric acid and extracting with water immiscible organic solvent, followed by washing the organic layer with sodium bicarbonate, brine drying over anhydrous sodium sulfate, filtering and evaporating the organic layer to dryness to obtain a residue comprising the title compound (90 g).
Example-9: Preparation of a / p anomeric mixture of protected 2-deoxy-2,2'- difluorocytidine;
Tol-trichloroacetimido-3-benzoyloxy-5-(4-methoxyphenylcarbomyl)-2-deoxy-2,2'- difluororibose (120 g; 0.229 mole) in ethylene dichloride (900 ml) were added bis- trimethylsilyl-N-acetylcytosine ( 120 g; 0.466mole) and tin tetrachloride (155 g; 0.595 mole) and refluxed for about 8 h to 16 h. Worked up the reaction mixture by pouring on to aqueous IN hydrochloric acid and extracting with water immiscible organic solvent, followed by washing the organic layer with sodium bicarbonate, brine drying over anhydrous sodium sulfate, filtering and evaporating the organic layer to dryness to obtain a residue comprising the title compound. (110 g).
Example-10: Preparation of a / p anomeric mixture of 2-deoxy-2,2'-difluorocytidine;
Tol-trichloroacetimido-3-benzoyloxy-5-(4-methoxyphenylcarbomyl)-2-deoxy-2,2'- difluororibose (120 g; 0.229 mole) in ethylene dichloride (900 ml) were added bis- trimethylsilyl-N-acetylcytosine (120 g; 0.466 mole) tin tetrachloride (155 g; 0.595 mole) and trimethylsilyl trifluoromethane sulfonate (128.9 g; 0.488 mole) and refluxed for about 8 h to 16 h. Worked up the reaction mixture by pouring on to aqueous IN hydrochloric acid and extracting with water immiscible organic solvent, followed by washing the organic layer with sodium bicarbonate, brine diying over anhydrous sodium sulfate, filtering and evaporating the organic layer to dryness to obtain a residue comprising the title compound. (116 g).
Example-11: Preparation of crude beta-2-deoxy-2,2'-difluoro cytidine hydrochloride (% purity can be mentioned);
Compound (100 g) obtained in Example-8 is contacted with 25% ammonium hydroxide solution (240 ml) in methanol (600 ml) and the mixture is stirred at room temperature for about 24 h. Remove methanol under reduced pressure to obtain a residual (70 g). The residue is dissolved in methanol, stirred with activated charcoal and filtered. To the filtrate added concentrated hydrochloric acid, cooled the mixture to 00C to 50C for 4 h. Separated the precipitated solid, dried the solid to obtain alpha/beta mixture of ribonucleoside hydrochloride (16 g).
Example-12: Preparation of beta-2-deoxy-2,2'-difluoro-cytidine hydrochloride (99.80%);
Compound (16 g) obtained in Example-11 is dissolved in DM water (112 ml) by heating. The clear solution is treated with activated charcoal (1200 mg) and filtered. The filtrate in treated with glacial acetic acid (1280 ml), mixture stirred at room temperature, separated the ciystallied solid, dried under vacuum to obtain P-anomer 2-deoxy-2,2'-difluoro cytidine hydrochloride (10.4 g) of anomeric purity upto 99.80%.
Example-13; Preparation of enantiomeric mixture of ethyI-2,2-difluoro-3-(4-methoxy phenyl carbomy!)-3-(2,2-dimethyldioxalan-4-yl) propionate (formula 2; R = CONHC6H4OMe);
Compound prepared as per Example-2 (100 g; 0.394 mole) is dissolved in dry ethyl acetate (7500 ml), followed by addition of Triethylamine (109.6 ml) and 4-methoxy phenyl isocyanate (38.9 ml; 0.394 mole) and the mixture stirred at room temperature under N2 atmosphere for an overnight. Again added 4-methoxy-phenylisocyanate (38.9 ml; 0.394 mole) and stirred for further 4 to 5 h at room temperature. Filtered the precipitated solid and clear mother liquor obtained is concentrated to approximately one tenth of its volume and again filtered to remove the solid. The clear mother liquor is further evaporated to dryness to obtain the title compound (158 g).
Example-14: Preparation of enantiomeric mixture of 2-deoxy-2,2-difluoropentafuranose-3- (4-methohy phenylcarbomyl) l-ulose[formula3,R=p-MeOC6H4NHCO;Ri=H);
To a mixture solution consisting enantiomeric mixture of ethyl 2-deoxy-2,2-difluoro-3-(4- methohy phenylcarbomyl) 3-(2,2-dimethyldioxolan-4-yl) propionate (158 g; 0.392 mole), trifluoroacetic acid (11.6 g, 0.102 mole) and acetonitrile (1674 ml) is added water (18 ml; 1.0 mole). The mixture is refluxed with stirring at a temperature of about 80°C for 5 h to 6 h. After this, reaction mixture is distilled under atmospheric pressure to remove solvent (420 ml). To the resulting solution toluene (420 ml) is added and distilled of volatiles (420 ml). The procedure is repeated further five to eight times to remove total volatiles of about 2400 ml. The resulting reaction mixture is cooled to room temperature under nitrogen stream and solution on evaporation yielded the title compound (3),
Example-15: Preparation of an enantiomeric mixture of 3-(4-methoxyphenyl carbomyl)-5- benzyloxy-2-deoxy-2,2-difluoropentafurnose-l-ulose (formula3, R=p-MeOC6H4NHCO; R,= C6H5CO);
To a solution of compound (158 g, 0.392 mole) prepared as per Example-14 in ethyl acetate (1600 ml) added pyridine (83.3 g; 1.05 mole) and 4-dimethyl amino pyridine (15 g; 0.123 mole). The mixture is heated upto 60°C and benzoylchloride (76.26 g; 0.542 mole) in ethyl acetate (1600 ml) is added drop-wise over a period of 2 h to 3 h. After the completion of addition, the reaction mixture is maintained about 60°C for 3 h and then cooled to room temperature stirred overnight and reaction mixture worked by washing with water (1600 ml) followed by successively with aqueous HC1 (1600 ml), water (1600 ml), aqueous NaHC03 (1600 ml) and saturated brine (1600 ml). Finally organic layer is dried over anhydrous sodium sulfate, filtered and evaporated to dryness to obtain title compound (125 g)
Example-16; Preparation of an enantiomeric mixture of 3-(4-methoxyphenyl carbomyl) 5 - benzoyloxy-2-deoxy-2,2-difluoro ribose [formula4,R=p-MeOC6H4NHCO;Ri=C6H5CO];
Compound obtained in Example-15 (lOOg, 0.236 mole) is dissolved in moisture free tetrahydrofuran (1.95 L) and cooled to a temperature of about -50°C. To this cooled solution, 70% vitride solution in toluene (54.76 ml, 0.189 mole) is added drop-wise with stirring over a period of 1 h to 2 h maintaining the temperature at about -50°C. The reaction mixture is stirred at this temperature for further 2 h to 3 h and then treated with methanol (70 ml) at a temperature not above -20°C. Slowly the reaction mixture is brought to ambient temperature and quenched with 0.1 N aqueous HC1 (2.0 L). The aqueous layer is then washed with toluene three times, combined organic layer is then washed with aqueous sodium carbonate followed by saturated sodium chloride solution, dried over anhydrous sodium sulphate, filtered and clear mother liquor evaporated to yield a residue comprising of title compound of [formula (4); 100 g]
Example-17: Preparation of enantiomeric mixture of l-trichloroacetimido-3-(4- methoxyphenylcarbomyl)- 5 -benzoyloxy-2-deoxy-2,2-difluororibose of formula (l)[R=p- MeO-C6H4NHCO,R,= C6H5CO|;
Trichloracetonitrile (452 ml; 4.51 mole) is taken in ethylene dichloride (60 ml) and diisopropyl ethyl amine (28 ml; 0.165 mole) is added to it. The mixture is cooled to 0 to 5°C and a solution of compound 4 (160g; 0.376 mole) in ethylene chloride (500 ml) is added drop-wise over a period of 1 h to 2 h maintaining the temperature between 0 to 5°C.The reaction mixture is stirred overnight at this temperature and then evaporated to dryness under high vacuum at a temperature not more than 50°C. The residue obtained comprises of title compound of (formula 1, 185 g)
Example-18: Preparation of a / 0 anomeric mixture of protected 2-deoxy-2,2'- difluorocytidine;
Tol-trichloroacetimido-3-(4-methoxyphenylcarbomyl)-5-benzoyloxy-2-deoxy-2,2'- difluororibose (120 g; 0.229 mole) in ethylene dichloride (900 ml) were added bis- trimethylsilyl-N-acetylcytosine (120 g; 0.466mole) and trimethylsilyl trifluoromethane sulfonate (128.9 g; 0.488 mole) and refluxed for about 8 h to 16 h. Worked up the reaction mixture by pouring on to aqueous IN hydrochloric acid and extracting with water immiscible organic solvent, followed by washing the organic layer with sodium bicarbonate, brine drying over anhydrous sodium sulfate, filtering and evaporating the organic layer to dryness to obtain a residue comprising of the title compound. (110 g).
Example-19: Preparation of a / p anomeric mixture of protected 2-deoxy-2,2'- difluorocytidine;
To l-trichloroacetimido-3-(4-methoxyphenylcarbomyl)-5-benzoyloxy-2-deoxy-2,2'-difluoro ribose (120 g; 0.229 mole) in ethylene dichloride (900 ml) were added bis-trimethylsilyl-N- acetylcytosine (128.9 g; 0.488 mole) and tin tetrachloride (155 g ; 0.595 mole) and refluxed for about 8 h to 16 h. Worked up the reaction mixture by pouring on to aqueous IN hydrochloric acid and extracting with water immiscible organic solvent, followed by washing the organic layer with sodium bicarbonate, brine drying over anhydrous sodium sulfate, filtering and evaporating the organic layer to dryness to obtain a residue comprising of the title compound (105 g).
Example-20: Preparation of a / p anomeric mixture of protected 2-deoxy-2,2'- difluorocytidine;
Tol-trichloroacetimido-3-(4-methoxyphenylcarbomyl)-5-benzoyloxy-2-deoxy-2,2'- difluororibose (120 g; 0.229 mole) in ethylene dichloride (900 ml) were added bis- trimethylsilyl-N-acetylcytosine (128.9 g; 0.488 mole) tin tetrachloride (155 g; 0.595 mole) and trimethylsilyl trifluoromethane sulfonate (128.9 g; 0.488 mole) and refluxed for about 8 h to 16 h. Worked up the reaction mixture by pouring on to aqueous IN hydrochloric acid and extracting with water immiscible organic solvent, followed by washing the organic layer with sodium bicarbonate, brine drying over anhydrous sodium sulfate, filtering and evaporating the organic layer to dryness to obtain a residue comprising of the title compound (112 g).
Example-21: Preparation of crude beta-2,2 -difluorocytidine hydrochloride (% purity);
Compound (120 g) obtained in Example-18 is contacted with 25% ammonium hydroxide solution (240ml) in methanol (600 ml) and the mixture is stirred at room temperature for about 24 h. Remove methanol under reduced pressure to obtain a residue (70 g).The residue is dissolved in methanol, stirred with activated charcoal and filtered. To the filtrate added concentrated hydrochloric acid, cooled the mixture to 0 to 50C for 4 h. Separated the precipitated solid, dried the solid to obtain alpha/beta mixture of ribonucleoside (18 g).
Example-22: Preparation of beta-2,2 -difluorocytidine hydrochloride (99.80% purity);
Compound (18 g) obtained as per Example-21 is dissolved in DM water (126 ml) by heating. The clear solution is treated with activated charcoal (1400 mg) and filter, clear filtrate is treated with glacial acetic acid (1440 ml), stirred at room temperature, separated the crystallized solid, dried under vacuum to yield P anomer 2-deoxy-2,2'-difluorocytidine hydrochloride of anomeric purity up to 99.8% (11.8 g)

We claim:
1. An intermediate of formula (1)


Wherein R and Ri each is a hydroxy protecting group X = CI or Br.
2. Preferred intermediate of claim 1;
Wherein R and Ri are each selected from a group consisting of benzoyl, substituted or unsubstituted carbomyl and substituted or unsubstituted phenyl carbomyl. X = CI or Br.
3. The most preferred intermediate of claim 2
Wherein R3 and R4 are each selected from a group consisting of hydrogen substituted or unsubstituted phenyl. X is CI or Br
4. The intermediate of claim 3, wherein R3 is hydrogen, R4 is phenyl and X= CI or Br.
5) The intermediate of Claim 3, wherein R3 is hydrogen, R4 is 4-methoxy phenyl and X = CI or Br.
6) The more preferred intermediate of Claim 2

Wherein R3 and R4 are each selected from a group consisting of hydrogen and substituted or unsubstituted phenyl; X = CI or Br
7) The intermediate of 6, wherein R3 is hydrogen, R4 is phenyl and X = CI or Br
8) The intermediate of 6, wherein R3 is hydrogen, R4 is 4-methoxxy phenyl and X = CI or Br
9) The preferred intermediate of Claim 2

10) The intermediate of Claim 9, wherein R3 is hydrogen, R4 is phenyl and X = CI or Br
11) The intermediate of Claim 9, wherein R3 is hydrogen, R4 is 4-methoxy phenyl and X = CI or Br.
12. A process for the preparation of a beta nucleoside of the formula represented below.


Wherein R and Ri each is a hydroxy protecting group, NB is a protected nucleobase, which comprises reacting an intermediate of the formula below.
Wherein R, R] and X have the same definition mentioned above with a protected nucleobase in the presence of a lewis acid(s) initiator in an inert solvent at a temperature ranging from about 70°C to 130°C.
13. The process of Claim 12, wherein the nucleobase is a pyrimidine or purine derived nucleobase.
14. The process of Claim 13, wherein the pyrimidine nucleobase is a cytosine derivative.
15. The process of Claim 12, wherein the coupling initiator is a lewis acid.
16. The process of Claim 15, wherein Lewis acid used is selected from a group consisting of trimethyl silyl trifluoromethane sulfonate, tin-tetrachloride, titanium tetrachloride boron trifluoride etherate, borontrihalide and mixture thereof.
17. The process of Claim 12, wherein the solvent is ethylene dichloride or xylene.
18. The process of Claim 12, further comprising the step of deprotection of the resulting nucleoside and selectively isolating the required beta nucleoside hydrohalide salt.