FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
"IMPROVED PROCESSES FOR THE PREPARATION OF GEMCITABINE HYDROCHLORIDE"
We, CADILA HEALTHCARE LIMITED, a company incorporated under the Indian companies Act, 1956, of Zydus Tower, Satellite Cross Road, Ahmedabad 380015, Gujarat, India.
The following specification particularly describes the nature of the invention and the manner in which it is performed:

Field of invention:
The present invention relates to an improved process for the preparation of Gemcitabine hydrochloride.
Background Art:
Gemcitabine HC1, marketed by Eli Lilly under the trademark Gemzar, is a nucleoside
analogue that exhibits antitumor activity and belongs to a general group of chemotherapy drugs known as antimetabolites. Gemcitabine prevents cells from producing DNA and RNA by interfering with the synthesis of nucleic acids, thus stopping the growth of cancer cells and causing them to die.
Gemcitabine is a synthetic glucoside analog of cytosine, which is chemically described as
4-amino-l-(2-deoxy-2,2-difluoro-p-D-ribofuranosyl)-pyrimidin-2(lH)-one or 2'-deoxy-
2,2'difluorocytidine (P-isomer). Gemcitabine HC1 has the following structure:

(I) Methods for preparing gemcitabine are known in the art. For example US 4808614
disclose Gemcitabine hydrochloride, compositions containing Gemcitabine hydrochloride and
their use in the treatment of herpes viral infections. It also describes a process for the preparation
of Gemcitabine hydrochloride. US 5223608 discloses a process for the preparation of
Gemcitabine hydrochloride by using hydrolysis reagents such as strong acids in the preparation
of 2-deoxy-2,2-diflouro-D-erythro-pentofuranos-l-ulose-3,5-dibenzoate. US 4965374 describes
a process for producing gemcitabine from an intermediate 3,5-dibenzoyl ribo protected lactone,
where the desired erythro isomer can be isolated in a crystalline form from a mixture of erythro
and threo isomers. International Application Publication No. WO 2005/095430 discloses a
process for the preparation of gemcitabine hydrochloride. This application describes the use of
hydrolysis reagents like strong acids for the preparation of 2- deoxy-2, 2-diflouro-D-erythro-
pentofuranos-l-ulose-3, 5-dibenzoate and its purification process. This application also
describes a process for the purification of gemcitabine hydrochloride by the dissolution of 95 %
enriched P-anomer of gemcitabine hydrochloride in water and isolating it by using solvents like
isopropyl alcohol or acetonitrile or acetone. The above approaches employ mildly acidic ion
exchange resins and strong acids as the hydrolyzing agents during the formation of unprotected

or protected lactone. Both types of hydrolyzing agents suffer from the disadvantage of formation of a lactone ring, undesirable reaction products, impurities eind often a lactone reverts back to its open chain precursor because of its sensitivity to strong acids and resins. US 5945547 discloses a process for the purification of Gerncitabine hydrochloride with respect to its anomeric impurity, comprising dissolution of a 1 :1 α /β anomeric mixture in hot water, followed by the addition of acetone at reflux, and cooling tlie solution to a temperature of about -10 to 50 °C. The precipitated Gerncitabine hydrochloride was collected and subjected to further purification by repeating the above process to afford purified p-anomeric Gerncitabine hydrochloride. WO 2006095359 discloses a process for the preparation of gerncitabine hydrochloride. This application describes process for preparing gerncitabine by using a protecting group such as p-chloro or p-methyl or p-nitro benzoyl. This application also describes a process for the purification of gerncitabine hydrochloride, by slurrying 95 % enriched p-anomer of gerncitabine hydrochloride in water and then the forming a solid with acetone. Gerncitabine hydrochloride was again purified with water and acetone or acetonitrile or isopropanol to obtain a 99.9 % p-enriched gerncitabine hydrochloride.
recrystallization with water and acetic acid to get 99.94% of the P-anomer from the original 95% of the p-anomer. This application also relates to a process for the preparation of intermediates, and improvements in the purification techniques to afford the desired p-anomer of gerncitabine hydrochloride substantially free from the a-anomer. Processes for separating anomeric mixtures of alkylsulfonate intermediates also have been described. US5256797 and 4526988 describe processes for separating anomers of 2-deoxy-2, 2-difluoro-D-ribofuranosyI-I-alkyI sulfonates, and US 5256798 describes a process for obtaining a-anomer-enriched ribofuranosyl sulfonates Other intermediates that may be useful for preparing gerncitabine have been disclosed. For instance, US 5480992 describes anomeric mixtures of 2}2- difluororibosyl azide and corresponding amine intermediates that can be prepared, eg., by reacting a 2-deoxy-2, 2-difluoro-D-ribofuranosyl-3, 5-di-0-benzoyl-l-β -methanesulfonate with an azide nucleophile, such as lithium azide, to obtain the azide. Reduction of the azide produces the corresponding amine, which can be synthetically converted into a nucleoside. See also US 5541345 and 5594155. Other known intermediates include, e.g., tritylated intermediates (US 5559222), 2-deoxy-2, 2-difluoro-p-D-ribo-pento [ribo]pyranose (US 5602262), 2-substituted-3, 3"difluorofuran intermediates (5633367), and a, a difluoro-β-hydroxy thiol esters (US 5756775 and 5,912,366). There are inherent problems associated with the production of gerncitabine, particularly for processes that require the production and separation of isomers, and tend to produce poor yields on a commercial scale. Accordingly, there is a need for improved methods

of preparing gemcitabine and intermediates thereof, which facilitate the production of gemcitabine, particularly on a commercial scale. The present invention provides such methods and intermediates, as will be apparent from the description of the invention provided herein.
According to the present invention there is provided a convenient process for the preparation of Gemcitabine hydrochloride and its intermediates with desired purity and yield by using better preparation techniques, which are simple, ecofriendly, cost-effective, robust and well suited for use on an industrial scale. Objects of the invention:
The object of the present invention is to provide an improved process for the preparation of Gemcitabine hydrochloride
Another object of the present invention is to provide an improved process for the preparation of compound of formula 5.
The above and other embodiment of the present invention is described in details below. Detailed description:
As used herein, the term "reflux temperature" refers to the boiling point of the solvent. As used herein, the term "TEA" refers to triethyl amine. As used herein, the term "DMSO" refers to dimethyl sulfoxide. As used herein, the term "IPA" refers to isopropyl alcohol. As used herein, the term "EBDFA" refers to ethyl bromodifluoroacetate. As used herein, the term "TFA" refers to trifluoroacetic acid. As used herein, the term "DMAP" refers to 4-dimethylaminopyridine. As used herein, the term "RT" refers to room temperature. As used herein, the term "RM" refers to reaction mass As used herein, the term "DMF" refers to dimethylformamide As used herein, the term "MDC" refers to Dichloromethane As used herein, the term "EDC" refers to Dichloroethane As used herein, the term "THF" refers to Tetrahydrofuran As used herein, the term "DME" refers to Dimethoxyethane As used herein, the term "DMP" refers to Dimethoxypropane As used herein, the term "DIBAL" refers to Diisobutylaluminium hydride As used herein, the term "Bz" refers to Benzoyl group.
The present invention provides an improved process for the preparation of Gemcitabine hydrochloride as depicted in Scheme A.


Accordingly, the invention provides a process for the preparation of Gemcitabine hydrochloride comprising the steps of,
1A) 1, 2:5, 6-diisopropylidene-D-mannitol of formula (I) was prepared as per method similar to that disclosed in Organic synthesis. 9, 450, (1998).
2A) reacting the compound of formula (I) with suitable reagent in a suitable solvent(s) and in presence of suitable base to get compound of the formula (II). Optionally, the step-(2A) is performed insitu after the completion of step-(lA).
3A) reacting the compound of formula (II) with EBDFA and Zn in a suitable solvent(s) to get compound of the formula (111).
4A) Cyclization of the compound of formula (III) by using acid/water in a suitable solvent and subsequently, aziotropic distillation of reaction mixture using suitable solvent to get compound of formula (IV)

5A) reacting the compound of the formula (TV) with benzoyl chloride in a suitable solvent(s) and
in presence of suitable base to get compound of the formula (V). Optionally, the step-(5A) is
performed insitu after the completion of step-(4A).
6A) Optionally, compound of formula (V) can be further converted to Gemcitabine
hydrochloride.
The suitable bases in step (2A) is suitable organic or inorganic bases wherein, the organic base may be selected from C1.-5 alkyl amines, C1-.5 substituted alkyl amines preferably, triethyl amine (TEA), diisopropyl amine, diisopropylethyl amine, heterocyclic saturated or unsaturated amines, preferably morpholine, piperidine, pyrollidine and pyridine; the suitable inorganic bases used is selected from hydroxides such as NaOH, KOH, carbonates such as NaHC03, Na2C03, K2C03 and like.
The reaction mixture in step (2A) is maintained at 0 °C to 50 °C. Preferably, the temperature is at 20-30 °C.
The suitable solvents used in step (2A) is suitable organic solvents may be selected from suitable hydrocarbons such as benzene, toluene, xylene, ethyl benzene, trimethyl benzene and tetrahydrofuran, halogenated hydrocarbons solvents such as chloroform, dichloromethane, dichloroethane and the like or mixtures thereof, alcohols such as methanol, ethanol, t-butanol and like or mixtures thereof, ketones such as acetone. Preferably, it is one or more solvents selected from the group consisting of halogenated hydrocarbons, hydrocarbons and ketones.
More preferably, halogenated hydrocarbons and ketones; particularly, dichloromethane and acetone.
The reagent used in step (2A) may be selected form sodium periodate, Pb(OAc)4 and alkaline H202, preferably sodium periodate
The duration of the reaction may be from 30 min. to 20 hrs, more specifically 1 to 4 hrs.
The suitable solvents used in step (3A) is suitable organic solvents but are not limited to ethers such as THF, dioxane and the like, inert solvent such as benzene, toluene, xylene, mesitylene and like; aportic polar solvents such as N, N-dimethyl formamide, N,N-dimethylacetamide, dimethyl sulfoxide and like; or mixtures thereof.
Optionally, the reaction of step-(3A) may be carried out in an inert atmosphere such as N2, He or Ar. The duration of the reaction may be from 30 min to 5 hrs, more specifically 1 to 2 hrs.
The reaction mixture in step (3A) is maintained at 40 to 70 °C. Preferably, the temperature is at 50 to 60 °C.

The suitable water miscible solvents used in step (4A) may be selected from polar solvents such as the alcohols, for example methanol, ethanol, isopropanol, and the like; acetonitrile; and related polar solvents and their suitable mixtures thereof.
The suitable acids used in step (4A) may be selected from suitable organic and suitable inorganic acids. Suitable inorganic acid is selected from hydrochloric acid, sulphuric acid and like. Suitable organic acid is selected from p-toluene sulphonic acid, TFA and like,
The water content of the solution can be adjusted to provide between about 1 to about 5 equivalents of water in several ways; by adding additional water to the water already present in the organic or inorganic strong acid, by choosing an inorganic acid which has the proper normality to provide the desired quantity of water, or by choosing a solvent, such as 95% ethanol, which contains a small amount of water. In general, about 1 to 2 molar equivalents of water relative to the formula 3, starting material are preferred since the lower water content is easily removed when cyclizing to the lactone.
The reaction of step-(4A), wherein the duration of the reaction may from 1 hrs to 7 hrs, more specifically 2 hrs to 4 hrs.
The suitable solvent for the azeotropic distillation used in step (4A) is selected from suitable hydrocarbons such as toluene, xylenes and their suitable mixtures thereof.
The suitable bases in step (5A) is suitable organic bases may be selected from C1.-5 alkyl amines, C1-5 substituted alkyl amines preferably, triethyl amine (TEA), diisopropyl amine, diisopropylethyl amine, heterocyclic saturated or unsaturated amines, preferably morpholine, piperidine, pyrollidine, pyridine, DMAP and like.
The suitable solvents used in step (5A) may be selected from ethers such as THF, 1, 4-dioxane, diisopropyl ether, diethyl ether and like; halogenated hydrocarbons solvents such as chloroform, dichloromethane, trichloroethane; esters such as ethyl acetate; hydrocarbons such as toluene, xylenes and their suitable mixtures thereof.
In one of the embodiment of the present invention is disclosed a process for the preparation of Gemcitabine hydrochloride using the compound of formula (V) as prepared in scheme-A.


Accordingly, the invention provides a process for the preparation of Gemcitabine hydrochloride comprising the steps of,
IB) reacting the compound of the formula (V) with suitable reducing agent in a suitable solvent(s) to get compound of the formula (VI).
2B) reacting the compound of the formula (VI) with Methane sulfonyl Chloride in a suitable solvent(s) and in presence of suitable base to get compound of the formula (VII). 3B) reacting the compound of the formula (VII) with the compound of the formula (VIII) and suitable reagents in a suitable solvent(s) to get compound of the formula (IX). 4B) reacting the compound of formula (IX) with suitable base in a suitable solvent to get Gemcitabine free base.
5B) Gemcitabine free base is converted to Gemcitabine hydrochloride by reacting with hydrochloric acid in suitable solvents.
6B) Crystallization of Gemcitabine hydrochloride by using suitable solvent. The suitable reducing agents in step (IB) may be selected from vitride, DIBAL, lithium tri(tert-butoxy)aluminium hydride, lithium bis(tert-butoxy)aluminium hydride.

The reaction mixture in step (IB) is maintained at -30 to 30 °C preferably, the temperature is at 0-10 °C.
The suitable solvents used in step (IB) is suitable organic solvents which may be selected from suitable hydrocarbons such as benzene, toluene, xylene, ethyl benzene, trimethyl benzene and like; halogenated hydrocarbons solvents such as chloroform, dichloromethane, dichloroethane and the like or mixtures thereof, ethers such as THF, glyme, diglyme, dioxane and like.
Optionally, the reaction may be carried out in an inert atmosphere such as N2, He or Ar. The suitable solvent used in step (2B) is suitable organic solvents which are not limited to, inert solvent such as benzene, toluene, xylene and like; halogenated hydrocarbons solvents such as chloroform, dichloromethane, dichloroethane and the like; esters used such as ethyl acetate and like; or mixtures thereof.
The suitable base in step (2B) may be suitable organic bases selected from C1-5 alkyl amines, Ci_5 substituted alkyl amines preferably, triethyl amine (TEA), diisopropyl amine, diisopropylethyl amine, heterocyclic saturated or unsaturated amines, preferably morpholine, N-methly morpholine, piperidine pyridine, DMAP and like .
Optionally, the reaction of step-(2B) may be carried out in an inert atmosphere such as N2, He or Ar.
The reaction mixture in step (2B) is maintained at 0°C to 40, preferably 0-5°C.
The suitable solvents used in step (3B) may be selected from hydrocarbons such as benzene, toluene, xylene and like; halogenated hydrocarbons solvents such as chloroform, dichloromethane, dichloroethane, flouro benzene and the like; esters such as ethyl acetate and like; nitriles such as acetonitrile or mixtures thereof.
The suitable reagent used in step (3B) may be selected from trimethylsilyl trifluoromethane sulfonate, SnCl4 and ZnCl2
The reaction mixture in step (3B) is maintained at 60 to 100 °C.
The reaction of step-(3B), wherein the duration of the reaction may from 13 hrs to 48 hrs, more specifically 16 hrs to 18 hrs.
The suitable base used in step (4B) may be ammonia, monomethylamine and dimethyl amine.
The suitable solvent used in step (4B) is suitable organic solvents may be selected from suitable alcohols such CrC6 lower alcohol, preferably methanol.
The suitable solvent used in step (5B) is suitable organic solvent may be selected from suitable alcohols such C1-C6 lower alcohol, preferably IPA.

The suitable solvent used in step (6B) is suitable organic solvents may be selected from suitable alcohols such C1-C6 lower alcohol; ketone such as acetone and ether such as dioxane or mixtures thereof.
The process is further described by the following non-limiting examples, which provides the preferred mode of carrying out the process of the present invention. It is to be appreciated that several alterations, modifications, optimizations of the processes described herein are well within the scope of a person skilled in the art and such alterations, modifications, optimizations etc. should be construed to be within the scope of the present inventive concept as is disclosed anywhere in the specification. Example-1 Process for 2,3-(0)-isopropylidene-D-grvceraldehyde: Formula-2
D-Mannitol (250gm, 1.37mol), Dimethoxypropane (400mT, 3.26mol) and anhydrous
SnCl2 (250mg, 0.001 mol) were added to Dimethoxyethane (600mL) and the mixture was
refluxed for 1.5H. Cooled the reaction mass up to 60-62 °C and added pyridine (0.5mL,
0.006mol).The solvent was removed under vacuum, cooled to RT, added 1.8L of MDC and
refluxed for 30min.Cooled the reaction mass to RT and filtered. Added saturated Sodium
bicarbonate solution and Sodium periodate (325gm, 1.5moI) under stirring and stirring
continued for 2H. Added anhydrous Magnesium sulphate (90gm) and further stirred for 30 min.
Filtered and concentrate under vacuum. Applied high vacuum and 120-140 °C temperature for
high vacuum fractional distillation using cow head receiver. Weight of said compound was
121.7gm. Yield: 68.15%. GC Purity: 99.4%
Exam ple-2
Process for Ethyl 2, 2-difluoro-3-hvdroxv-3-f2, 2-dimethvl dioxolan-4-yI) propionate: Formula-3
Activated Zinc (56.3gm, 0.86mol) added to the dry THF (125mL) under atmosphere of dry nitrogen and started stirring and reflux. Prepared a solution of (lllmL, 0.567 mol) Ethyl bromo difluoro acetate and (460mL) dry THF and Charged 20 mL drop wise to the Reaction mass for activation of Zinc surface. Added (125gm, 0.96 mol) of 2, 3-(0)-isopropylidene-D-glyceraldehyde in above prepared solution and charged drop wise in Reaction mixture and refluxed for further 1H. Cooled the reaction mass to RT and poured in to chilled 500ml of 2N HC1 and stirred for 15 min, extracted with 2 x 375 ml of ethyl acetate and organic layer washed with water and saturated sodium bicarbonate solution and brine solution. Dry the organic layer over Na2SO4 and distilled the solvent under vacuum to give 179 gm of desired product Ethyl (3R, S) 2, 2-difluoro-3-hydroxy-3-(2, 2-dimethyl dioxolan-4-yl) propionate. Yield: 75 %, HPLC Purity: 90.50 %, Assay: 91.20 %

Example-3
Process for Ethyl 2. 2-difluoro-3-hydroxv-3-(2. 2-dimethvl dioxolan-4-vn propionate:
Formula-3
Activated Zinc (2.26gm, 0.034mol) added to the dry THF (5mL) under atmosphere of
dry nitrogen and started stirring and reflux. Prepared a solution of (4.44mL, 0.023 mol) Ethyl bromo difiuoro acetate and (24mL) diethyl ether and Charged 2mL drop wise to the Reaction mass for activation of Zinc surface. Added (5gm, 0.038 mol) of 2, 3-(0)-isopropylidene-D-glyceraldehyde in above prepared solution and charged drop wise in Reaction mixture and refluxed for further 1H. Cooled the reaction mass to RT and poured in to chilled 45ml of IN HC1 & 45gm of ice. Stirred for 15 min, extracted with 2 x 25 ml of ethyl acetate and organic layer washed with water, saturated sodium bicarbonate solution and brine solution. Dry the organic layer over Na2S04 and distilled the solvent under vacuum to give 6.8gm of desired product Ethyl (3R, S) 2, 2-difluoro-3-hydroxy-3-(2, 2-dimethyl dioxolan-4-yl) propionate. Yield: 70 %, HPLC Purity: 80 % Example-4 Process for 2-Deoxy-2,2-difluoro pentofuranose-3, 5- dibezoate:
Acetonitrile (1L) added to the (180gm, 0.73mol) Ethyl 2, 2-difluoro-3-hydroxy-3-(2J 2-dimethyl dioxolan-4-yl) propionate, (9 mL, 0.12mol) TFA and (51.5 mL, 2.86mol) water under stirring. Refluxed for 3H. Started aziotropic distillation using Dean-Stark, under N2 atmosphere. 500ml of aziotropic solvent was recovered and 500 ml of toluene was charged. Again distilled 500ml aziotropic solvent and 500ml toluene was charged. Cool the Reaction mass to 0-5°C and added (155 mL, 1.92 mol) Pyridine. Solution of (203 ml, 1.75mol) Benzoyl chloride in (203 ml) Toluene was added drop wise over the period of 30 min. Heated the Reaction mass at 80-85°C for 3H. Cool the reaction mass to RT and added (18gm) of charcoal, filtered and washed with water, IN HC1, again water and brine solution (1286 mL each). Dry the organic layer over Na2S04 and distilled solvent under vacuum to give (296.8 gm) crude 2-Deoxy-2, 2-difluoro pentofuranose-3, 5- dibezoate. HPLC Purity: 67.17 %, Assay: 60.50 % Example-5 Crystallization of 2-Deoxv-2,2-difluoro pentofuranose-3, 5- dibezoate: Formula-5
The solution of 280ml of Hexane and 173ml of MDC charged to the above crude mass. Reflux maintained for 30min, cooled to RT and then 5-7°C, maintained for 30min, Filtered and wet cake washed with chilled 133 ml mixture of 82ml Hexane and 51ml MDC. The wet product was charged for drying under high vacuum at 60°C for 4H. Finally we got the desire compound 2-Deoxy-2, 2-difluoro pentofuranose-3, 5- dibezoate as a White solid. Dried Weight: 117.6 gm, Yield: 44 %, HPLC Purity: 99.48% and Assay: 99.27%

Example-6
Process for 2-Deoxy-2,2-difluoro pentofuranose-3,5- dibezoate:
Acetonitrile (780mL) added to the (140gm, 0.57mol) Ethyl 2, 2-difluoro-3-hydroxy-3-(2, 2-dimethyl dioxolan-4-yl) propionate, (7 mL, 0.09mol) TFA and (40 mL, 2.22mol) water under stirring. Reflux for 3H. Started aziotropic distillation using Dean-Stark, under N2 atmosphere. 390ml of aziotropic solvent was recovered and 390 ml of toluene was charged. Acetonitrile was slowly distilled from the reaction mass. Simultaneously toluene charged drop wise in to the RB Flask at the rate acetonitrile was distilling off. This process was continued until the mass temperature rose to about 110°C. Later toluene was distilled off completely under reduced pressure at 60°C. Cool the Reaction mass to RT and added 700mL of MDC followed by 120 mL (1.48mol) of Pyridine. Solution of 150ml (1.29mol) Benzoyl chloride in 700ml of MDC was added drop wise over the period of 1H. Heated the Reaction mass at 40-45°C for 3H. Cool the reaction mass to RT and added (14gm) of charcoal, filtered and washed with water, IN HC1, again water and bicarbonate solution (1L each). Dry the organic layer over Na2SO4 and distilled solvent under vacuum to give (212,7 gm) crude 2-Deoxy-2, 2-difluoro pentofuranose-3, 5-dibezoate. HPLC Purity: 63.2 %, Assay: 51.8 % Exam ple-7
Crystallization of 2-Deoxy-2, 2-difluoro pentofuranose-3, 5- dibezoate: Formula -5
Dissolve 207.2 gm of above crude residue in 145mL of MDC and added 221 ml of
Hexane as an antisolvent. Stirred it at RT for 1H and Filtered and wet cake washed with chilled
93 ml mixture of 57.3ml Hexane and 35.7ml MDC. The wet product dried under high vacuum at
60°C. Finally the desire compound 2-Deoxy-2, 2-difluoro pentofuranose-3, 5- dibezoate
obtained as a White solid. Weight: 82.8 gm, Yield: 40 %, HPLC Purity: 99.04%.
Example-8
Process for 2-Deoxy-2,2-difluoro-D-ribofuranose-3,5-dibezoate: FormuIa-6
Toluene (1L) added to 2-Deoxy-2, 2-difluoro pentofuranose-3, 5- dibezoate (100 gm, 0.267mol) under atmosphere of dry nitrogen and started stirring and cooling to obtained 0-5°C temp. Mixture of 70% Vitride (64ml, 0.35mol) in 60ml toluene was added drop wise to the Reaction mass over the period of 30 min. Stirring and cooling were continued for 2H. Added 15ml methanol followed by 300ml of 10% HC1 under stirring. Reaction mass stirred at RT for 30 min and organic layer was separated. Aqueous layer (PH=1.36) was extracted with 200ml of toluene. Combined organic layers and washed with 300ml of 10% NaHCO3 and 300ml of Brine. Finally dried over Na2SO4 and distilled organic layer under vacuuo to give desire product as a pale yellow colour thick oily mass. Weight: 87.80gm, Yield: 87.30%, HPLC Purity: 85% Assay: 86.70%

Exam plc-9
Process for 2-Deoxy-2, 2-difluoro-D-ribofuranose-3, 5-dibezoate: Formula-6
Tetrahydrofuran (260ml) added to 2-Deoxy-2, 2-difluoro pentofuranose-3, 5- dibezoate (26 gm, 0.069mol) under atmosphere of dry nitrogen and started stirring and cooling to obtain -20°C temp. Mixture of 70% Vitride (20.5ml, O.105mol) was added drop wise to the Reaction mass over the period of 15 min. Stirring and cooling were continued for 1H. Added 4ml methanol followed by 78ml of IN HC1 under stirring. Reaction mass stirred at RT for 30 min and organic layer was separated. Aqueous layer was extracted with 120ml of Ethyl acetate. Combined organic layers and washed with 10% NaHCO3 and Brine. Finally dried over Na2S04 and distilled organic layer under vacuuo to give desire product as a pale yellow colour thick oily mass. Weight: 27gm, Yield: 95.6%
Example-10
Process for 2-Deoxy-2, 2-difluoro-D-ribofuranose-3, 5-dibezoate: Formula-6
Toluene (100ml) added to 2-Deoxy-2, 2-difluoro pentofuranose-3, 5-dibezoate (10 gm,
0.026mol) under atmosphere of dry nitrogen and started stirring and cooling to obtain 0-5°C
temp. 1M solution of Lithium tri(tert-butoxy)aluminum hydride LiAlH[OC(CH3)3]3 in THF (30
ml, 0.03mol) was added drop wise to the Reaction mass over the period of 40 min. Stirring and
cooling were continued for 2H. Added 2ml methanol followed by 30ml of 10% HC1 under
stirring. Reaction mass stirred at RT for 30 min and organic layer was separated. Aqueous layer
was extracted with Toluene. Combined organic layers and washed with 10% NaHCC>3, Brine
and Purified Water. Finally dried over Na2SO4 and distilled organic layer under vacuuo to give
desire product as a pale yellow colour thick oily mass. Weight: 9gm, Yield: 89.5 %, Purity
91.5%
Example-11
Process for 2-Deoxy-2, 2-difluoro-D-ribofuranose-3, 5-dibezoate-l-methane sulfonate: Formula-7
Dichloromethane (900 mL) added to the above thick oily mass of 2-Deoxy-2, 2-difluoro-
D-ribofuranose-3, 5-dibezoate (90 gm, 0.238mol) under atmosphere of dry nitrogen and started stirring and cooling to obtained 0-5°C temp. TEA (48.6 mL, 0.35mol) was added and Stirring was continued for 30 min. Mixture of (25.9 mL, 0.335mol) Methane sulfonyl Chloride in (60 ml) MDC was added drop wise over the period of 30 min. Stirring continued for 15 min at 0-5°C temp, removed cooling and Stirring continued for 1H at RT. Organic layer washed with 5% NaHCOs and Brine. Finally organic layer dried over Na2S04 and distilled organic layer under vacuuo to give desire product as a pale yellow colour thick oily mass. Weight: 103.5 gm, Yield: 99.8%, HPLC Purity: 94% Assay: 81%

Example-12
Process for 2-Deoxv-2,2-difluoro-D-ribofuranose-3, 5-dibezoate-l-methane sulfonate: Formula-7
Dichloromethane (10 mL) added to the above thick oily mass of 2-Deoxy-2, 2-difluoro-D-ribofuranose-3, 5-dibezoate (lgm, 2.6mmol) under atmosphere of dry nitrogen and started stirring and cooling to obtained 0-5°C temp. N-Methyl morpholine (0.41mL, 3.73mmol) was added and Stirring was continued for 30 min. Mixture of (0.29 mL, 3.72mol) Methane sulfonyl Chloride in (1 ml) MDC was added drop wise over the period of 15 min. Stirring continued for 15 min at 0-5°C temp, removed cooling and Stirring continued for 1H at RT. Organic layer washed with 5% NaHCO3 and Brine. Finally organic layer dried over Na2S04 and distilled organic layer under vacuuo to give desire product as a pale yellow color thick oily mass. Weight: 11 gm, Yield: 91.6%, HPLC Purity: 85 %. Example-13 Process for Silyl protected N-Acetyl Cytosine: Formula-8
In to Dichloroethane (1L) charged (50 gm, 0.326mol) N-Acetyl cytosine, (77.5 ml, 0.372 mol) Hexamethyldisilazane and (2.75 ml, 0.02mol) Chlorotrimethylsilane under atmosphere of dry nitrogen and started stirring and heating to obtained reflux temp and refluxed for 3H. Purity of Monosilyl Product: 94.80%, Purity of Disilyl Product: 4.80%. Distill out the solvent from Reaction mass at 80°C under vacuum. Off white solid residue obtained is Silyl protected N-Acetyl Cytosine. (In situ, we could not isolate)
Example-14
Process for N-acetvl-2,-Deoxv-2^ 2'-diflluoro-3, 5'- dibezoate-cytidine: Formula -9
Charged (1L) EDC to the above flask containing Silyl protected N-Acetyl Cytosine under atmosphere of dry nitrogen and started stirring. Cool the reaction mass to 20-25°C temp and added (72 mL, 0.389 mol) Tri methyl silyl trifluoromethane sulfonate-TMSOTf, stirred for 30min. Added (1OOgm, 0.219 mol) 2-Deoxy-2, 2-difluoro-D-ribofuranose-3, 5-dibezoate-l-methane sulfonate and Applied heating to get reflux temp and maintained for 16H. Reaction mass cool to cool to RT and washed with Purified water and 3% sodium bicarbonate solution. Distillation of solvent in vacuum gives N-acetyI-2'-Deoxy-2', 2'-difluoro-3', 5'-dibezoate-cytidine as a Brownish foam like solid mass. Weight: 112.4gm (In situ), Yield: Quantitative, HPLC Purity: 90.17%. Assay: 68.50% Exam ple-15 Process for Silyl protected N-Acetvl Cytosine: Formula-8
In to Toluene (200mL) charged (10 gm, 0.065mol) N-Acetyl cytosine (27.8 ml, 0.133 mol), Hexamethyldisilazane (6.8 ml, 0.053mol) and Chlorotrimethylsilane under atmosphere of

dry nitrogen and started stirring and heating to obtained reflux temp and refluxed for 3H. Purity of Monosilyl Product: 84 %, Purity of Disilyl Product: 10 %. Distill out the solvent from Reaction mass at 125°C. Off white solid residue obtained is Silyl protected N-Acetyl Cytosine. (In situ, we could not isolate)
Exampie-16
Process for N-aeetvl-2'-Deoxv-2,; 2'-dtfluoro-3', 5'- dibezoate-cytidine: Formula -9
Charged (200mL) Toluene to the above flask containing Silyl protected N-Acetyl Cytosine under atmosphere of dry nitrogen and started stirring. Cool the reaction mass to 20-25°C temp and added (15.6 mL, 0.086 mol) Trimethylsilyl triftuoromethane sulfonate-TMSOTf, stirred for 30min. Added (20gm, 0.044mol) 2-Deoxy-2, 2-difluoro-D-ribofuranose-3, 5-dibezoate-1-methane sulfonate and Applied heating to get reflux temp and maintained for 18H. Reaction mass cool to RT and washed with 140mL of 5% HC1, 140ml of 5% sodium bicarbonate solution and I40ml of Brine. Finally organic layer dried over Na2S04 and filter through hyflow. Distillation of solvent in vacuum gives N-acetyl-2'-Deoxy-2', 2'-difluoro-3', 5'-dibezoate-cytidine as a Brownish foam like solid mass. Weight: 18.6gm, Yield: 82.66%, HPLC Purity: 66.35%. Assay: 41.9%
Exam ple-17
Process for 2 -Deoxy-2, 2 difluoro-cytidine: Formula -10
Charged (1125mL) Methanol in above flask having (112.5 gm, 0.219mol) N-acetyI-2'-Deoxy-2', 2'-difluoro-3', 5'-dibezoate-cytidine prepared in Example-14 and stirred it to make it clear solution. Applied cooling to get 0-5°C. Ammonia bubbled for 3H. Reaction mass was stirred for 16H at RT. Distilled the solvent under vacuum to give thick gummy mass. Dissolved the obtained mass in Purified water and organic impurities extracted with ethyl acetate. Added (5.5gm) charcoal (Darco-G60) to the aqueous layer, filtered and evaporated. Isopropyl alcohol was added and again distilled under high vacuum to remove traces of water. Light yellow foam like mass obtained as 2'-Deoxy-2', 2'-difluoro-cytidine.(Gemcitabine Freebase), Weight: 57.7gm (In situ), Yield: Quantitative, Assay: β -anomer (28.88%) & a-anomer (40.06%).
Exam pie-18
Process for 2,-Deoxy-2,2'-difluoro-cvtidine: Formula -10
Charged (lOOmL) Methanol in above flask having (10 gm, 19.5mmol) N-acetyl-2'-Deoxy-2', 2'-difluoro-3, 5'-dibezoate-cytidine and stirred it to make it clear solution. Applied cooling to get 0-5°C. Added 33 gm of 10% Ammonia solution of Methanol drop wise over the period of 30min. Stirred the Reaction mass for 5H at 0-5°C and for 20H at RT. Distilled the

solvent under vacuum to give thick gummy mass. Dissolved the obtained mass in Purified water and organic impurities extracted with ethyl acetate. Organic layer back washed with 10 ml of Purified water. Combined aqueous layer having desire compound and added (lgm) charcoal (Darco-G60) to the aqueous layer, filtered and evaporated. Added Isopropyl alcohol and again distilled under high vacuum to remove traces of water. Light yellow foam like mass obtained as 2'-Deoxy-2, 2'-difluoro-cytidine. (Gemcitabine Freebase), Weight: 4.lgm, Yield: 79.98 %, Assay: p-anomer (26.52%) & a-anomer (37.88%) Example-19 Process for Gemcitabine Hydrochloride:
Charged 1PA (750 ml) into above flask having 2'-Deoxy-2', 2'-difluoro-cytidine (57.7 gm, 0.219mol) prepared in Example-17. Applied heating to obtained clear solution. Mixture of Cone HC1 (19.4 mL, 0.219mol) in IPA (57.6mL) was added drop wise in Reaction mass within 30 min, stirring continued for 2H at RT and 1H at 0-5°C. Filtered light yellow compound under suction and washed with 173 ml of Acetone. Crude Gemcitabine Hydrochloride was dried under vaccume to obtain as a light yellow solid. Weight: 42.7 gm, Yield: 65%, Assay: p (43.16%) & a (53.67%).
Charged crude Gemcitabine hydrochloride (40gm) and purified water (40mL). Stirred at RT for 30 min, at 60°C for 1H and again at RT for 1H. Slurry was filtered under suction. Wet cake washed with acetone and dried under vacuum to obtained Purified Gemcitabine Hydrochloride obtained as an off white solid. Weight: 16.1 lgm, Yield: 40.66% Assay: 96.75%, Content of a-anomer: 3.36%
Charged purified water and Purified crude Gemcitabine Hydrochloride (16 gm) and applied stirring and heating to get 70-75°C temp. RM became clear solution stirring continued for 15min. Charged Charcoal (Darco-G60) (800mg), filtered through hyflow and bed washed with hot purified water. Distilled out water from filtrate and added acetone drop wise at 50-55 C.Cool the reaction to RT and stirred for 1H. Filtered the solid mass under suction and washed with 32 ml acetone. Dried the wet solid compound to get Gemcitabine Hydrochloride in a white crystalline solid.. Weight: 13.4 gm, Yield: 83.75%. Assay: 99.9%. Example-20 Process for Gemcitabine Hydrochloride:
Charged IPA (67.5 ml) into above flask having 2'-Deoxy-2', 2'-difluoro-cytidine (4.8 gm, 0.018mol). Applied heating to obtained clear solution. Mixture of Cone. HC1 (7.5 mL, 0.085mol) in IPA (57.6mL) was added drop wise in Reaction mass within 30 min at 72°C Stirring continued for 12H at RT and 3H at 0-5°C. Filtered light yellow compound under suction and washed with 25 ml of Acetone. Wet compound dried under vacuum to obtained Crude

Gemcitabine Hydrochloride as a light yellow solid. Weight: 0.96 gm, Yield: 15%, Purity: β (' %)
Charged purified water (2.25mL) and 14mL of Methanol to the Gemcitabir Hydrochloride (1 gm, 97% pure) and applied stirring and heating to get 70-75°C temp. RN became clear solution stirring continued for 15min. Charged Charcoal (Darco-G60) (lOOmg) filtered through hyflow. Added 15mL of 1PA to the filtrate and stirred for 30 min. filtered the solid mass under suction. Dried the wet solid compound to get Gemcitabine Hydrochloride in a white crystalline solid. Weight: 0.455 gm, Yield: 45.5%, Assay: 99.8%

We claim:
1. A process for the preparation of compound of Gemcitabine hydrocloride comprising, 1A) reacting D-mannitol with suitable reagent in a suitable solvent(s) and in presence of suitable base to get compound of the formula (1).

2A) reacting the compound of the formula (1) with sodium periodate in a suitable solvent(s) and in presence of suitable base to get compound of the formula (2). Optionally, the step-(2A) is performed insitu after the completion of step-(l A).

3A) reacting the compound of the formula (2) with EBDFA and Zn in a suitable solvent(s) to get compound of the formula (3)

4A). cyclization of the compound of formula (3) by using acid/water in a suitable solvent and subsequently, aziotropic distillation of reaction mixture using suitable solvent to get compound of formula (4)

5A) reacting the compound of the formula (4) with benzoyl chloride in a
suitable solvent(s) and in presence of suitable base to get compound of the formula (5). Optionally, the step-(5A) is performed insitu after the completion of step-(4A).


2. A process as claimed in claim 1 in step (1 A), wherein said suitable reagent used is SnCl2 suitable solvent used is DMP and DME, suitable base used is pyridine.
3. A process as claimed in claim 1 in step (2A), wherein suitable solvent used is selected from suitable hydrocarbons; halogenated hydrocarbons; alcohols; ketones and mixtures thereof. Preferably, dichloromethane and acetone.
4. A process as claimed in claim 1 in step (2A), wherein said suitable organic base is
selected from C1-5 alkyl amines, C1-5 substituted alkyl amines; heterocyclic saturated or unsaturated amines; and the inorganic base is selected from hydroxides, carbonates and bicarbonates.
5. A process as claimed in claim ] in step (2A), wherein the suitable reagent used is selected
form sodium periodate, Pb(OAc)4 and alkaline H2O2, preferably sodium periodate.
6. A process as claimed in claim 1 in step (3A), wherein the suitable solvents is selected
from ethers; inert solvent; aportic polar solvents and mixtures thereof and the suitable
solvents used in step (4A), is selected from polar solvents such as the alcohols such as
methanol, ethanol, isopropanol, acetonitrile and their suitable mixtures thereof.
7. A process as claimed in claim 1 in step (4A), wherein the suitable acids used is selected
from suitable organic and suitable inorganic acids. Suitable inorganic acid is selected
from hydrochloric acid and sulphuric acid. Suitable organic acid is selected from p-
toluene sulphonic acid and TFA.
8. A process as claimed in claim 1 in step (5A), wherein suitable base is selected from C1-5
alkyl amines, C1-5 substituted alkyl amines preferably, triethyl amine (TEA), diisopropyl
amine, diisopropyl ethyl amine, heterocyclic saturated or unsaturated amines, preferably
morpholine, piperidine, pyrollidine, pyridine and DMAP,

9. A process as claimed in claim 1 in step (5A), wherein suitable solvent used is selected from ethers; halogenated hydrocarbons; esters; hydrocarbons and their suitable mixtures thereof..
10. A process as claimed in claim 1 step (6A), wherein the compound of formula (5) is converted to Gemcitabine hydrochloride by the process comprising,
IB) reacting the compound of the formula (5) with Suitable reducing agent in a suitable solvent(s) to get compound of the formula (6).

2B) reacting the compound of the formula (6) with Methane sulfonyl chloride in a suitable solvent(s) and in presence of suitable base to get compound of the formula (7).

IUIIIIIMO-U rUIIIIUlU-'
3B) reacting the compound of the formula (7) with the compound of the formula (8) and suitable reagent in a suitable solvent(s) to get compound of the formula (9).

4B) reacting the compound of formula (9) with suitable base in a suitable solvent to get Gemcitabine free base.

5B) Gemcitabine free base is converted to Gemcitabine hydrochloride by reacting with hydrochloric acid in suitable solvent.

6B) Optionally purifying the Gemcitabine hydrochloride by crystallization from suitable solvent.
11. A process as claimed in claim 10 in step (IB), wherein suitable reducing reagent used is selected from vitride, DIBAL, lithium tri(tert-butoxy) aluminium hydride, lithium bis(tert-butoxy) aluminium hydride and suitable solvent used is selected from hydrocarbons; halogenated hydrocarbons; ethers such as THF, glyme, diglyme, dioxane or mixtures thereof.
12. A process as claimed in claim 10 in step (2B), wherein suitable base used is selected from C 1-5 alkyl amines, C1.5 substituted alky] amines preferably, triethyl amine (TEA), diisopropyl amine, diisopropylethyl amine, heterocyclic saturated or unsaturated amines, preferably morpholine, N-methyl morpholine, piperidine, pyrollidine, pyridine and DMAP and suitable solvent used is selected from ethers; halogenated hydrocarbons; esters and their suitable mixtures thereof..
13. A process as claimed in claim 10 in step (3B), wherein suitable reagent used is selected from trimethylsilyl trifluoromethane sulfonate, SnCl2 and ZnCl2 and suitable solvent used is selected from hydrocarbons; halogenated hydrocarbons; esters: nitriles and mixtures thereof.
14. A process as claimed in claim 10 in step (4B), wherein suitable base used is selected from ammonia, monomethylamine and dimethyl amine and suitable solvent used is selected from alcohols such C1-C6 lower alcohol and mixtures thereof.
15. A process as claimed in claim 10 in step (5B): wherein suitable solvent used is selected from alcohols such C1-C6 lower alcohol and mixtures thereof and suitable solvent used in step (6B) is selected from alcohols; ketone and ether or mixtures thereof.