KR20080039502A - Method for preparing gemcitabine and related intermediates - Google Patents

Abstract

The present invention provides at least a substantial portion of the α anomer of N-1-protection-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester from its anomer mixture Removing; Removing the 3'-ester, 5'-ester and N-protecting group; And optionally forming a salt, a method for preparing gemcitabine or a salt thereof. The 3'-ester and 5'-ester may be the same or different, and at least one of the esters is preferably cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcar Carbonyl, 4-methylbenzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester. The invention also provides novel intermediates, including but not limited to 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester, and such Provided are methods for preparing the intermediates.

Description

PROCESS FOR PREPARING GEMCITABINE AND ASSOCIATED INTERMEDIATES}

Gemcitabine HCl, sold under the trademark Gemzar ^{® by} Eli Lilly, is a common class of chemotherapeutic drugs known to be metabolic antagonists and nucleoside analogs that exhibit antitumor activity. Gemcitabine interferes with the synthesis of nucleic acids, preventing the cells from producing DNA and RNA, thereby inhibiting the growth of cancer cells and killing cancer cells.

Gemcitabine has the chemical name 4-amino-1- (2-deoxy-2,2-difluoro-β-D-ribofuranosyl) -pyrimidin-2 (1H) -one or 2'-de It is a synthetic glucoside analogue of cytosine, which is oxy-2 ', 2'-difluorocytidine (β isomer). Gemcitabine HCl has the following structure:

Gemzar ^® is a sterile lyophilized powder containing 200 mg or 1 g of gemcitabine HCl (as free base) formulated with sodium acetate (12.5 mg or 62.5 mg respectively) and mannitol (200 mg or 1 g respectively). It is supplied as a sterile hydrochloride in a vial as a containing, only for intravenous injection. Hydrochloric acid and / or sodium hydroxide may be added for pH adjustment.

U.S. Patent 4,808,614 (the '614 patent) describes a synthetic preparation process of gemcitabine, which process is generally shown in Scheme 1 below:

D-glyceraldehyde ketal ( 2 ) is reacted with bromodifluoroacetic acid ethyl ester (BrCF ₂ COOEt) in the presence of activated zinc to give ethyl 2,2-difluoro-3-hydroxy-3- (2 , 2-dimethyldioxolan-4-yl) -propionate ( 3 ) is obtained as a mixture of 3-R isomers and 3-S isomers. The 3-R isomer to 3-S isomer ratio is about 3: 1. The 3-R isomer has the stereochemical properties necessary to produce the desired erythro (3-R) ribose structure and can be chromatographically separated from the 3-S isomer.

The obtained product is treated with an acidic ion exchange resin such as Dowex 50W-X12 to cyclize to give 2-deoxy-2,2-difluoro-D-erythro-pentanoic acid- [gamma] -lactone ( 4 ). . The protected-butyldimethylsilyl (TBDMS) protecting group, protected lactone 3,5-bis-hydroxy groups of the lactone tert (tert-butyldimethylsilyloxy) -2-des oxy -2,2-difluoro-1- Obtained oxoribose ( 5 ) and reducing the product to give 3,5-bis- ( tert -butyldimethylsilyl) -2-desoxy-2,2-difluororibose ( 6 ).

Position 1 of the carbohydrate is activated by introducing a leaving group, for example, methanesulfonyloxy (mesylate) formed by reacting a compound ( 6 ) with methanesulfonyl chloride, thereby activating 3,5-bis- ( tert -butyl Dimethylsilyloxy) -1-methanesulfonyloxy-2-desoxy-2,2-difluororibose ( 7 ) is obtained. In the presence of a reaction initiator such as trifluoromethanesulfonyloxy trimethylsilane (trimethylsilyl triflate), compound ( 7 ) is reacted with N, O-bis- (trimethylsilyl) -cytosine ( 8 ) to form a base ring. Coupling to carbohydrates. The protecting group was removed and purified by chromatography to give gemcitabine free base.

US Pat. No. 4,526,988 describes a similar process for carrying out cyclization by hydrolyzing alkyl 3-dioxolanyl-2,2-difluoro-3-hydroxy-propionate with an acidic ion exchange resin. . Hertel et al. in J. Org . Chem . 53, No. 11, 2406 (1988).

And U.S. Patent No. 4,965,374 ( '374 patent), is to describe a process for preparing gemcitabine from the intermediate 3,5-dibenzoyl-Li Bo protected lactone of the formula:

Here, certain erythroisomers can be isolated in crystalline form from a mixture of erythroisomers and threoisomers. The process described in the '374 patent is generally outlined in Scheme 2:

3-hydroxy groups of the compound ( 3 ), in the presence of tertiary amines or catalysts such as 4- (dimethylamino) pyridine or 4-pyrrolidinopyridine, benzoyl chloride, benzoyl bromide, benzoyl cyanide, benzoyl azide, For example, ethyl 2,2-difluoro-3-benzoyloxy-3- (2,2-dimethyl) by reacting with PhCOX (where X = Cl, Br, CN or N ₃ ) and esterifying with a benzoyl protecting group Dioxolane-4-yl) -propionate ( 9 ) is obtained.

9 isoalkylidene protecting group is selectively removed using a strong acid such as concentrated sulfuric acid in ethanol, for example ethyl-2,2-difluoro-3-benzoyloxy-4,5-dihydroxypentano It generates benzoate (9A). The product was cyclized to give lactone ( 10 ), which was converted to a dibenzoate ester to give lactone 2-deoxy-2,2-difluoropentopuranos-1-ulose-3,5-dibenzoate ( 11 ) is produced as a mixture of erythroisomers and threoisomers. The '374 patent describes isolating isomers into at least some eryth from the mixture by selective precipitation. See also, Chou et al., Synthesis , 565-570, (1992).

Subsequently, compound ( 11 ) is reduced to obtain a mixture ( 12 ) of α and β anomers of 2-desoxy-2,2-difluoropentofuranos-dibenzoate, which is methanesulfonyl chloride. 2-deoxy-2,2-difluoro-D-ribofuranosyl-3,5-di-O-benzoyl-1-O-β-methanesulfonate which is activated and is an anomer mixture of mesylate ( 13 ) And a dibenzoate ester ( 14 ) of silyl-protected nucleoside, which is coupled with N, O-bis (trimethylsilyl) -cytosine ( 8 ), to a mixture of α- and β-anomers (about 1: 1 α / β anomer ratio). Ester and silyl protecting groups are removed to provide a mixture of β-anomer (gemcitabine) and α-anomer (about 1: 1 α / β anomer ratio). The '374 patent selectively isolates β-anomers (gemcitabine) by forming salts of anomer mixtures, such as hydrochloride or hydrobromide, and optionally precipitates them to provide 2'-deoxy-2', It is described to obtain 2'-difluorocytidine as a salt in a 1: 4 α / β ratio. The '374 patent also describes the selective precipitation of β-anomers in weakly basic aqueous solutions in free base form. One such process involves dissolving a 1: 1 α / β anomer mixture in hot acidic water (pH is adjusted to 2.5-5.0), and when the mixture is substantially dissolved, raises the pH to 7.0-9.0, the solution Cooling to form crystals, which are isolated by filtration.

A process for separating anomer mixture of alkylsulfonate intermediates has also been described. U.S. Pat.Nos. 5,256,797 and 4,526,988 describe a process for separating anomers of 2-deoxy-2,2-difluoro-D-ribofuranosyl-1-alkylsulfonates, and U.S. Patents 5,256,798 Describes a process for obtaining ribofuranosyl sulfonate enriched in α-anomer.

Other intermediates have been disclosed that may be useful for the preparation of gemcitabine. For example, US Pat. No. 5,480,992 discloses, for example, 2-deoxy-2,2-difluoro-D-ribofuranosyl-3,5-di-O-benzoyl-1-O to obtain azide. An anomer mixture of 2,2-difluororibosyl azide and the corresponding amine intermediate, which can be prepared by reacting a -β-methanesulfonate with an azide nucleophilic reagent such as lithium azide, is described. The azide can be reduced to produce the corresponding amine, which can be converted synthetically to nucleosides. See also US Pat. Nos. 5,541,345 and 5,594,155.

Other known intermediates include, for example, 1-alkylsulfonyl-2,2-difluoro-3-carbamoyl ribose and related nucleoside intermediates (US Pat. No. 5,521,294), tritylated intermediates (US Patent 5,559,222), 2-deoxy-2,2-difluoro-β-D-ribo-pentopyranose (US Pat. No. 5,602,262), 2-substituted-3,3-difluorofuran intermediate ( US Pat. No. 5,633,367) and α, α-difluoro-β-hydroxy thiol esters (US Pat. Nos. 5,756,775 and 5,912,366).

Other processes for preparing gemcitabine have been described, for example, in WO 2006/070985 and WO 2006/071090 for stereoselective preparation of 2'-deoxy-2 ', 2'-difluorocytidine, This is generally outlined in Scheme 3:

The process involves activating 2'-deoxy-2 ', 2'-difluoro-D-ribofuranosyl-3,5-diester ( 12A ) with diphenyl chlorophosphate and then isomer separation to Obtaining 1-bromo-ribofuranose intermediate, coupling it with N, O-bis- (trimethylsilyl) -cytosine ( 8 ) and then deprotecting to obtain gemcitabine. However, this process requires an additional step compared to the process outlined in Scheme 2, which makes this process less attractive for industrial use.

There are inherent problems associated with the production of gemcitabine, particularly those that require the production and separation of isomers, which tend to yield insufficient yields on a commercial scale. Thus, there is a need for improved methods of preparing gemcitabine and intermediates thereof, particularly on a commercial scale, which facilitate the production of gemcitabine. The present invention provides such methods and intermediates and will be apparent from the description of the invention provided herein.

Summary of the Invention

The present invention provides a process for the preparation of gemcitabine or salts thereof, which method preferably

At least a substantial portion of the α anomer was removed from the anomer mixture of N-1-protected-2'-deoxy-2 ', 2'-difluorocytidine-3', 5'-diester, Producing at least a rich product;

Removing the 3'-ester, 5'-ester and N-protecting group; And

Optionally converting the product to a salt

It includes.

The 3'-ester and 5'-ester may be the same or different, and at least one of the esters is preferably cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcar Carbonyl, 4-methylbenzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester.

N-1-protection-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester can be prepared by any suitable process. Preferably, N-1-protection-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester is

2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester is reduced to 2-deoxy-2,2-difluoro-D Producing ribofuranose-3,5-diester;

2-deoxy-2,2-difluoro is reacted with 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester and methanesulfonyl chloride in the presence of a base. Obtaining rho-D-ribofuranose-3,5-diester-1-methanesulfonate; And

N-1-protection-cytosine is coupled to the 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate to provide N-1-protection Producing -2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester

To manufacture.

3-esters and 5-esters are the same or different and at least one of said esters is preferably cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4-methyl Benzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester.

2-Deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-diester can be obtained by any suitable process. Preferably, 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-diester is a product of 2-deoxy-2,2- Obtained by separating from a mixture of erythro (3-R) isomers and threo (3-S) isomers of difluoropentofuranos-1-ulose-3,5-diester. 3-esters and 5-esters are the same or different and at least one of said esters is preferably cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4-methyl Benzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester.

The protective 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester of the present invention is particularly useful for preparing gemcitabine on a commercial scale. Do. These D-erythro derivatives are crystalline substances and can be purified from the mixture of the D-erythro isomer and the L-threo isomer, for example, by precipitation. The intermediates and methods of the present invention promote the total synthesis of gemcitabine and are easier to use and yield higher yields than the processes described in the literature.

details

The present invention provides a process for the preparation of gemcitabine or salts thereof, which method preferably

At least a substantial portion of the α anomer was removed from the anomer mixture of N-1-protected-2'-deoxy-2 ', 2'-difluorocytidine-3', 5'-diester, Producing at least a rich product;

Removing the 3'-ester, 5'-ester and N-protecting group; And

Optionally converting the product to a salt

It includes.

The 3'-ester and 5'-ester may be the same or different, and at least one of the esters is preferably cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcar Carbonyl, 4-methylbenzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester.

Anomer mixtures of N-1-protection-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diesters can be prepared by any suitable process. Preferably, the anomer mixture of N-1-protecting-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester is

2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester is reduced to 2-deoxy-2,2-difluoro-D Producing an anomer mixture of ribofuranose-3,5-diester;

2-deoxy-2,2-difluoro is reacted with 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester and methanesulfonyl chloride in the presence of a base. Obtaining rho-D-ribofuranose-3,5-diester-1-methanesulfonate; And

N-1-protection-cytosine is coupled to the 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate to provide N-1-protection Producing an anomer mixture of -2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester

To manufacture.

3-esters and 5-esters may be the same or different, and at least one of the esters is preferably cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4- Methylbenzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester.

The 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester of the present invention can be obtained by any suitable process. Preferably, the 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-diester is 2-deoxy-2,2-difluoro The product is obtained by separating the product from a mixture of erythro (3-R) isomers and threo (3-S) isomers of pentofuranos-1-ulose-3,5-diester. 3-esters and 5-esters may be the same or different, at least one of said esters preferably being cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4 -Methylbenzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester.

Mixtures of the erythro (3-R) and threo (3-S) isomers of the 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester of the present invention may be any It can be obtained by a suitable process of. In one embodiment, the erythro (3-R) isomer of the 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester and the threo (3-S) isomer The mixture is prepared by esterifying a mixture of erythro (3-R) isomers and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranos-1-ulose. When 3-ester and 5-ester are the same, 3-ester and 5-ester are preferably cinnamoyl, 1-naphthoyl or 1-naphthylmethylcarbonyl. Mixtures of the erythro (3-R) and treo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranos-l-ulose are any suitable process, for example alkyl 2 It can be prepared by cyclizing a mixture of 3-R isomer and 3-S isomer of, 2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate. have. Suitable alkyl 2,2-difluoro-3-hydroxy-3- (2,2-dimethyl-dioxolan-4-yl) propionate as a pro intermediates, such as C _{1 -6-alkyl-2,2-} Difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate such as ethyl-2,2-difluoro-3-hydroxy-3- (2, 2-dimethyldioxolan-4-yl) -propionate.

In another embodiment, the erythro (3-R) isomer and the treo (3-S) of the 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester of the present invention The mixture of isomers is esterified by esterifying a mixture of the erythro (3-R) and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester. Manufacture. The mixture of the erythro (3-R) isomer and the treo (3-S) isomer of the above 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester may be prepared by any suitable process. Mixtures of 3-R isomers and 3-S isomers, for example of alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate Can be prepared by esterifying and cyclizing the product. The cyclization reaction can be carried out using any suitable conditions, for example alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate This can be done by treating a mixture of the 3-R isomer and the 3-S isomer of with a suitable acid. In this embodiment, when the 3-ester and 5-ester are different, the 3-ester or 5-ester is preferably cinnamoyl, benzoyl or 1-naphthylmethylcarbonyl. Suitable alkyl 2,2-difluoro-3-hydroxy-3- (2,2-dimethyl-dioxolan-4-yl) propionate intermediate, such as C _{1 -6-alkyl-2,2-} Difluoro-3-hydroxy-3- (2,2-dimethyl-dioxolan-4-yl) -propionate such as ethyl-2,2-difluoro-3-hydroxy-3- (2 , 2-dimethyl-dioxolan-4-yl) -propionate.

Surprisingly, according to the invention, certain ester groups such as, for example, cinnamoyl and 1-naphthylmethylcarbonyl, not only enable the formation of the preferred isomers of 3,5-ribodiester lactones, but are also stable crystalline materials, which The material makes it possible to separate the 3,5-ribodiester lactone isomers from the 3,5-xyldiester lactone isomers using simple crystallization or precipitation techniques.

According to the invention, the ester groups of the riboprotected lactones in positions 3 and 5 may be the same or different, in other words, 2-deoxy-2,2-difluoro-D-erythro-pentofuranos The -1-ulose-3,5-diester may contain the same or different ester protecting groups in positions 3 and 5.

Particularly preferred embodiments of the invention are generally shown in Scheme 4:

According to Scheme 4, N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluorocytidine-3', 5'-diester (preferably N-1-trimethylsilylacetyl Separation of α and β anomers of -2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl-cytidine) is carried out in a solvent mixture, preferably 1, This can be carried out by selectively precipitated α-anomer from a mixture of 2-dichloroethane and methanol. Gemcitabine,

a) reducing lactone ( 15 ) using a suitable reducing agent in an organic solvent to yield 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester ( 16 ) about 1: 1 Obtaining an isomeric mixture;

b) 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate by reacting compound ( 16 ) with methanesulfonyl chloride in the presence of a base ( 17 ) obtaining;

c) N-1-trimethylsilylacetyl-2'-deoxy-2, preferably by coupling a compound ( 17 ) and bis (trimethylsilyl) -N-acetylcytosine in an organic solvent using a catalyst at room temperature Obtaining a mixture of α and β anomers of ', 2'-difluorocytidine-3,5-diester;

d) precipitating the α anomer 18 and separating the two anomers by filtration; And

e) removing the protecting group by hydrolysis to obtain gemcitabine

By doing more.

For example, the reduction of lactone ( 15 ) as shown in Scheme 4 can be, for example, one or more reducing agents selected from lithium aluminum hydride, diisobutylaluminum hydride and sodium bis- (2-methoxyethoxy) aluminum hydride and the like. It may be carried out using any suitable reducing agent. Reduction, for example, as shown in Scheme 4, is particularly preferably carried out using lithium aluminum hydride, especially on commercial scale production, where lithium aluminum hydride has a low molecular weight and a relatively high reduction capacity (4 H atoms effective per molecule). Because). Although diisobutylaluminum hydride is less preferred in terms of molecular weight and in that only one H atom per molecule is effective for reduction, reduction may also be carried out using diisobutylaluminum hydride [eg, US As taught in Patent 4,808,614 and Chou et al., Synthesis , 565-570 (1992).

For example, the coupling reaction as shown in Scheme 4 may comprise any suitable organic solvent, which may include, for example, one or more organic solvents selected from acetonitrile, dichloromethane, chloroform, 1,2-dichloroethane, toluene and xylene. It may be carried out in a solvent. In one embodiment, the coupling reaction is carried out in 1,2-dichloroethane. Optionally, the coupling reaction can be promoted using a suitable catalyst reagent such as, for example, trimethylsilyl triflate (Me ₃ SiOTf).

Removal of protecting groups, for example as shown in Scheme 4, can be carried out using any suitable conditions which may include, for example, basic hydrolysis such as methanolic ammonia.

The 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester of the present invention may be prepared by any suitable method. Scheme 5 and Scheme 6 are methods A, for obtaining exemplary 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester of the present invention. And two preferred methods, each labeled Method B.

The process shown in Scheme 5 below is a 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester of the present invention, wherein 5-esters are the same), for example 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-discinnamate, In this process, two isomers are separated by precipitation to give erythro isomers with a purity of 99.9% and an ee of at least 99.6%:

According to Scheme 5, 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester is

a) alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate such as 3 to cyclize to 2-deoxy-2 Producing, 2-difluoropentofuranos-l-ulose ( 4 );

b) 2-deoxy-2,2-difluoro by reacting 2-deoxy-2,2-difluoropentofuranos-l-ulose ( 4 ) with an appropriate acid chloride in the presence of a base in an organic solvent. Obtaining lofentopuranos-1-ulose-3,5-diester as a mixture ( 21 ) of the erythroisomer and the treo isomer; And

c) separating the isomers by selective precipitation

It can be prepared by a process comprising a.

Preferably, alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate such as compound ( 3 ) is acid in a solvent mixture Cyclization was carried out by refluxing the starting material in the presence of and then distilled to yield 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose ( 4 ). The cyclization can be carried out using ion exchange resins according to US Pat. No. 4,808,614. See also Scheme 1.

Cyclization as also shown, for example, in Scheme 5, via intermediate ( 9A ) (Scheme 2), in the presence of an acid, as described in Chou et al, Synthesis , 565-570, (1992). Alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate, such as compound ( 3 ), is refluxed in a suitable solvent mixture and then distilled This can be done by adding one more step to the process. However, the reflux / distillation process can be advantageous from a commercial standpoint that it is more economical for industrial use. Ion exchange resin routes may require reaction times of up to 4 days, which is not practical for some commercial applications.

An exemplary process for cyclizing alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate,

a) providing a solution of crude ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing an acid and Heating for a time sufficient to substantially complete the reaction;

b) reducing the solution volume by distillation;

c) adding an organic solvent and further refluxing;

d) further removing the solvent mixture by distillation to obtain an oil; And

e) optionally distilling the oil obtained under reduced pressure

And, thereby producing 2-deoxy-2,2-difluoropentofuranos-1-ulose.

Preferably, the acid containing distillation solvent is a mixture of acetonitrile, water and trifluoroacetic acid. Preferably, the acetonitrile: water: trifluoroacetic acid ratio is about 150: 12: 2.2 (v / v / v).

2-deoxy-2,2-difluoropentofuranos-1-ulose can be esterified using any suitable esterifying agent, for example as shown in Scheme 5. In one embodiment, 2-deoxy-2,2-difluoropentofuranos-l-ulose is used, for example, using an acid chloride in the presence of a base in an organic solvent, for example

a) providing a solution of 2-deoxy-2,2-difluoropentofuranos-1-ulose in an organic solvent;

b) optionally adding a base and an acid chloride dropwise at room temperature;

c) refluxing the reaction mixture for a time sufficient to substantially complete the reaction;

d) washing the reaction mixture, separating and drying the organic phase; And

e) evaporating the solvent to obtain crude diester

It is esterified by the process containing.

According to the present invention, suitable acid chlorides useful for esterifying hydroxy groups include one or more acid chlorides selected from cinnamoyl chloride, 1-naphthoyl chloride, 1-naphthyl acetyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride, and the like. Include.

According to the invention, 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester (eg, the ester groups in positions 3 and 5 are the same here) The erythroisomers and treo isomers can be separated from the crude mixture by the crystallization process. One example of such a crystallization process is

a) adding a first organic solvent to the crude mixture and stirring at room temperature;

b) adding a second organic solvent while maintaining stirring;

c) cooling for a time sufficient to precipitate; And

d) filtering to obtain the desired product

It includes.

The first solvent may include, for example, one or more solvents selected from ethyl acetate, isopropyl acetate, n -butyl acetate, isobutyl acetate, tert -butyl acetate, THF, acetonitrile and mixtures thereof. The second solvent may include, for example, one or more solvents selected from pentane, hexane, heptane, octane and petroleum ether, or mixtures thereof. In one embodiment, the first solvent is ethyl acetate and the second solvent is hexane.

The process shown in Scheme 6 (Method B) is the 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester of the present invention, wherein Particularly useful for preparing 3-esters and 5-esters)

According to Scheme 6, 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-diester (optionally an ester group not identical in positions 3 and 5) Containing)

a) alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate such as ethyl-2,2-difluoro-3- 3-hydroxyl group of hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate ( 3 ) was esterified to yield ethyl-2,2-difluoro-3-acyloxy Producing -3- (2,2-dimethyldioxolan-4-yl) -propionate ( 22 );

b) the ethyl 2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized, for example by reflux and then distilled , Obtaining 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester as a mixture ( 23 ) of the erythro (3-R) isomer and the treo (3-S) isomer ( Wherein most of the product obtained is erythroisomers);

c) esterifying the 5-hydroxyl group of 23 to obtain a diester having an ester group in positions 3 and 5 (which may be the same as or different from 24 ); And

d) the steps of selectively precipitating and isolating isomers ( 24 ) from the reaction mixture

It can be obtained by the method including.

The 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester of the present invention (whether or not the ester groups in positions 3 and 5 are the same or different) is subject to selective precipitation. Facilitates separation of the preferred isomers, thereby allowing separation of the two isomers. According to the invention, erythroisomers, for example 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-discinnamate, are at least 99% ee Can be obtained.

Exemplary methods for esterifying 3-hydroxyl groups, such as shown in Scheme 6, include

a) dissolving ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan ~ 4-yl) -propionate ( 3 ) in an organic solvent;

b) dropwise addition of a base and a suitable acid chloride, optionally at room temperature;

c) refluxing the mixture for a time sufficient to complete the reaction; And

d) The reaction mixture is washed, the organic phase is separated and dried to yield ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate Obtaining as a solid material

It includes.

Esterification of the 3-hydroxy group is any suitable alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate, such as described herein. By use of the above compounds, corresponding alkyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate, for example alkyl-2, 2-difluoro-3-acyloxy-3- (2,2-dimethyl-dioxolan-4-yl) -propionate [in the compounds, alkyl is C _{1 -6} alkyl (e.g., ethyl) and 3-acyloxy group RCO ₂ -, where R is (forming the cinnamoyl ester) ethenyl 2-phenyl, phenyl, 1-naphthyl, 1-naphthylmethyl, 2-methylbenzyl, 4-methylbenzyl May be any suitable substituent, including but not limited to.

As shown in Scheme 6, the cyclization of ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate followed by reflux, It can be achieved by distillation. Exemplary cyclization process is

a) heating a solution of crude ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing acid Performing cyclization;

b) reducing the solution volume by distillation;

c) adding an organic solvent and refluxing;

d) removing the solvent mixture by distillation until the internal temperature of the mixture reaches 90-100 ° C., and maintaining this temperature for about 1 hour; And

e) The residue of the solvent mixture is optionally evaporated under reduced pressure to afford 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester with erythro (3-R) isomer and threo ( 3-S) obtaining as a mixture of isomers

It includes.

The reaction solvent containing an acid is preferably a mixture of acetonitrile, water and trifluoroacetic acid. Preferably, the acetonitrile: water: trifluoroacetic acid ratio is about 75: 3.7: 0.65 (v / v / v). The organic solvent added after reducing the solution volume by distillation is preferably toluene. Method B is particularly advantageous in that the product obtained after cyclization surprisingly provides the erythro isomer as the main product, for example by refluxing the reaction mixture followed by distillation, so that this method is selective for the desired isomer.

For example, esterification of 5-hydroxyl groups as shown in Scheme 6 can be carried out using any suitable method to obtain diesters optionally having ester groups that are not identical in positions 3 and 5. In one embodiment, 5-hydroxyl is

a) dissolving 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester ( 23 ) in an organic solvent;

b) dropwise addition of a base and a suitable acid chloride, optionally at room temperature;

c) refluxing the mixture for a time sufficient to substantially complete the reaction; And

d) The reaction mixture is washed and the organic phase is separated and dried to give 2-deoxy-2,2-difluoropentopuranos-l-ulose-3,5-diester ( 24 ) as a solid material, R and R 'may be the same or different)

It is esterified by the process containing.

Separation of the erythro and treo isomers of 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester, as shown, for example, in Scheme 6 may be followed by any suitable process. By carrying out using, for example, 2-deoxy-2,2-difluoro-D-erythro-pentapuranos-1-ulose-3,5-diester can be obtained. Preferably, the separation

a) adding a solvent to the crude mixture and stirring at room temperature;

b) cooling to settle; And

c) separating the product by filtration

It is carried out by a process comprising a.

Exemplary solvents are selected from, for example, ethyl acetate, isopropyl acetate, n -butyl acetate, isobutyl acetate, tert -butyl acetate, THF, acetonitrile, pentane, hexane, heptane, octane, petroleum ether, and mixtures thereof It may include one or more solvents. The solvent is preferably a mixture of ethyl acetate and heptane.

According to the invention, when 3-esters and 5-esters are different, at least one of the esters in the 3 and 5 positions (or at least one of the esters in the 3 'and 5' positions) is cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4-methylbenzyl carbonyl or 9-fluorenylmethyloxycarbonyl ester, other esters are cinnamoyl, naphthoyl, naphthylmethylcarbonyl, 2 Any suitable ester including but not limited to -methylbenzylcarbonyl, 4-methylbenzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester. Other suitable esters include, for example alkyl esters, such as C _{1 -6} alkyl esters (e.g., acetyl) may include, and aromatic esters (e.g., benzoic acid and derivatives thereof). When using method B, the R substituents should be carefully selected, in some cases 9-fluorenylmethyloxycarbonyl, naphthylacetyl and acetyl are removed by hydrolysis to produce compound ( 4 ), eg, thinner This is because other esters, such as moles, remain and produce compound ( 23 ).

The following examples further illustrate the invention but, of course, should not be construed as limiting the scope of the invention in any way.

Example  One

This example illustrates the preparation of crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-discinnamate.

To a 500 mL round flask was added crude 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-discinnamate (10 g, 23.36 mmol) This was dissolved in anhydrous THF (100 mL) and cooled to 0-5 ° C. LiAlH ₄ (0.46 g, 12.1 mmol) was added over 5 minutes, then the mixture was stirred for another 1 hour. Stirring with addition of water (10 mL). Most of the solvent was removed by distillation and 1 N HCl (50 mL) was added to the remaining volume (about 30 mL) to form a clear solution having a pH value of about 2. Ethyl acetate (100 mL) was added and the organic phase was washed with 5% NaHCO ₃ (50 mL), water (50 mL), and brine (50 mL). The ethyl acetate phase was dried over MgSO ₄ and concentrated under reduced pressure to afford crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-discinnamate as an oil. Yield: 8.52 g, (19.8 mmol, 84.8%, α / β isomer ratio about 1/1).

Example  2

This example illustrates the preparation of 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-discinnamate-1-methanesulfonate.

In a 100 mL round flask, crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-discinnamate (2.5 g, 5.8 mmol) was dissolved in dichloromethane (20 mL). Triethylamine (0.7 g, 6.9 mmol) was added. Methanesulfonyl chloride (0.79 g, 6.9 mmol) was added dropwise and cooled to 0-5 占 폚. The mixture was stirred for another 1 h, washed with 1N HCl (15 mL), 5% NaHCO ₃ (15 mL) and dried over MgSO ₄ . The solvent was removed by distillation under reduced pressure to obtain crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-discinnamate-1-methanesulfonate via diesel. Yield: 2.82 g, (5.55 mmol), 95.7%, purity 99.2%. Pure anomer was obtained using preparative HPLC. ¹ H-NMR (CDCl ₃ , 300 MHz) β-anomer: δ = 3.14 (CH ₃ , 3H), 4.52 (H-4,5, 3H), 5.75 (H-1, 1H), 5.98 (H- 3, 1H), 6.50 (cinnam., 2H), 7.40 (aromatic, 6H), 7.54 (aromatic, 4H), 7.79 (cinnam., 2H).

Example  3

This example illustrates the preparation of N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl-cytidine.

1,2-dichloroethane (50 mL) was added to bis (trimethylsilyl) -N-acetylcytosine (2.2 g) to give a clear solution, followed by trimethylsilyl triflate (Me ₃ SiOTf) (2.2 mL, 2.75 g ) Was added and stirred for 30 minutes. 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-discinnamate-1-methanesulfonate (2.6 g, 5.1 mmol) in 1,2-dichloroethane (10 mL) Solution was added dropwise and the mixture was refluxed overnight. After cooling, the mixture was washed with water (30 mL), 5% NaHCO ₃ (30 mL), and brine (20 mL) and dried over MgSO ₄ . The solvent was removed by distillation to give crude N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl-cytidine as pale yellow solid (2.4 g, 4.24 mmol, 83%). Crude N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl-cytidine (2 g, 3.5 mmol) was added at room temperature to 1, It was dissolved in 2-dichloroethane (4 mL) and stirred with methanol (120 mL) dropwise.

The white solid formed was collected by filtration, dried (about 0.5 g of N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl- Cytidine, α-anomer), and the residue is concentrated to dryness to obtain crude N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3'. , 5'-Dicinnamoyl-cytidine, β-anomer was obtained as a pale yellow solid (1.6 g, 2.8 mmol), 80% yield, ee 90%. N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl-cytidine, β-anomer: ¹ H NMR CDCl ₃ : δ = 2.23 (CH ₃ , 3H), 4.52 (H-4, 1H), 4.62 (H-5, 2H), 4.79 (cyt-H, 1H), 5.50 (H-3, 1H), 6.47-6.53 (cinnam. + H-1, 3H), 7.43 (aromatic 6H), 7.54 (aromatic, 4H), 7.78 (cyt-H + cinnam. 3H) 9.2-9.35 (NH broad 1H).

Example  4

This example illustrates the preparation of gemcitabine hydrochloride.

To a solution of methanol in ammonia (about 20%, 40 mL), crude N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-discinnamoyl -Cytidine β-anomer (1.5 g, 2.6 mmol) was added and stirred at room temperature overnight. The mixture was concentrated to give a pale yellow oil, and 1N HCl (20 mL) was added followed by stirring with the addition of dichloromethane (20 mL). The aqueous phase was separated, activated charcoal (0.2 g) was added and the mixture was heated to 75 ° C. for 30 minutes. After filtration, the residue was concentrated to dryness under reduced pressure to give gemcitabine hydrochloride as a solid (1 g). The solid was dissolved in water (1 mL) at room temperature, and acetone (40 mL) was added dropwise with stirring. After 30 minutes, the precipitate was collected by filtration and dried at 70 ° C. to give crude gemcitabine. Yield: 0.3 g, 38.5% yield. Purity: 95%, ee 95%.

Example  5

This example illustrates the preparation of 2-deoxy-2,2-difluoropentofuranos-1-ulose.

In a 500 mL glass flask equipped with a reflux condenser, crude ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (30 g, 0.118 mole) was added and dissolved in a mixture of acetonitrile (150 mL), water (12 mL) and trifluoroacetic acid (2.2 mL). After refluxing for 3 hours, the reflux condenser was adjusted to distill at atmospheric pressure and the volume of 130-150 mL volume was distilled off. Toluene (70 mL) was added and the mixture was refluxed for an additional 3 hours and concentrated to give 20.2 g of oil, which was distilled under reduced pressure (140 ° C./2 mmHg) to give 12.2 g (0.073 mol) of 2-Deoxy-2,2-difluoropentofuranos-l-ulose was obtained in 61.9% yield.

Example  6

This example illustrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-discinnamate.

In a 1 liter glass flask equipped with a reflux condenser, the newly distilled 2-deoxy-2,2-difluoropentofuranos-1-ulose (2-deoxy-2,2-difluoropentanoic acid- (also termed γ-lactone) (19.5 g, 0.116 mol) was added and dissolved in ethyl acetate (200 mL). Pyridine (37 mL, 0.458 mol) was added and the mixture was stirred at room temperature. A solution of cinnamoyl chloride (56 g, 0.336 mol) in ethyl acetate (100 mL) was added dropwise at room temperature, and the mixture was refluxed for 4 hours. After cooling, the mixture was washed with water (100 mL), 1 M HCl (100 mL), 5% NaHCO ₃ (100 mL), water (100 mL), and brine (100 mL). The organic phase was dried over Na ₂ SO ₄ and concentrated on a rotary evaporator to give 46 g of crude 2-deoxy-2,2-difluoropentopuranos-1-ulose-3,5-discinnamate. Was obtained as an oil. Ethyl acetate (80 mL) was added to the obtained oil, and the mixture was stirred at room temperature, and then stirring was continued while hexane (150 mL) was added. After about 30 minutes, the mixture (two layers) was cooled to a temperature ranging from -7 ° C to -10 ° C overnight. The precipitate was collected by filtration to give 26 g (60.7 mmol) of crude solid of 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-discinnamate. Was obtained in 52.3% yield, 99.9% purity and 99.6% ee. ¹ H NMR, CDCl ₃ : δ = 4.59 (H-5, 2H), 4.88 (H-4, 1H), 5.63 (H-3, 1H), 6.50 (cinnam., 2H), 7.44 (aromatic 6H), 7.55 (aromatic 4H), 7.75-7.88 (cinnam., 2H).

Example  7

This example illustrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-dinaphthoate.

In a 100 ml glass flask with reflux condenser, 2-deoxy-2,2-difluoro-pentofuranos-1-ulose (2.2 g, 13 mmol) was dissolved in anhydrous THF (15 mL), Anhydrous pyridine (3 mL, 37 mmol) was added. A solution of 2-naphthoyl chloride (obtained by heating 2-naphthoic acid in thionyl chloride) in anhydrous THF (10 mL) was added dropwise. After refluxing for 2 hours, the mixture was cooled and washed with water (10 mL), 1 M HCl (10 mL), 5% NaHCO ₃ (10 mL), water (10 mL), and brine (10 mL). . The organic phase was dried over Na ₂ SO ₄ and concentrated on a rotary evaporator to give a solid, which was crystallized to give 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose- A white solid of 3,5-dinaphthoate was obtained with 98% purity and 90% ee.

Example  8

This example illustrates the preparation of 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-di-2-naphthylacetate.

2-deoxy-2,2-difluoropentofuranos-l-ulose (0.82 g) and pyridine (0.85 mL) were mixed in dichloromethane (10 mL) and 2- in dichloromethane (10 mL). A solution of naphthylacetyl chloride (obtained by reacting 2-naphthyl acetic acid with oxalyl chloride) was added dropwise. After refluxing for 2 hours, the mixture was cooled and washed with water (10 mL), 1 M HCl (10 mL), 5% NaHCO ₃ (10 mL), water (10 mL), and brine (10 mL). . The organic phase was dried over Na ₂ SO ₄ , concentrated on a rotary evaporator to give a residue, which was chromatographed to give 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose. An oil of -3,5-di-2-naphthyl acetate was obtained as a mixture of the erythroisomer and the treo isomer.

Example  9

This example illustrates the preparation of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-di-4-methylphenylacetate.

2-deoxy-2,2-difluoropentofuranos-l-ulose (1.61 g), pyridine (1.7 mL) and 4- (dimethylamino) -pyridine (DMAP) (300 mg) were added to dichloromethane ( 15 ml) was added dropwise with a solution of 4-methyl-phenylacetyl chloride (obtained from 3 g of 4-methylphenylacetic acid and 5 ml of oxalyl chloride) in dichloromethane (10 ml). After refluxing for 2 hours, the mixture was cooled and washed with water (10 mL), 1 M HCl (10 mL), 5% NaHCO ₃ (10 mL), water (10 mL), and brine (10 mL). . The organic phase was dried over Na ₂ SO ₄ and concentrated on a rotary evaporator to give a residue, which was chromatographed to give 2-deoxy-2,2-difluoropentopuranos-1-ulose-3,5- An oil of di-4-methylphenylacetate was obtained as a mixture of erythroisomers and threoisomers.

Example  10

This example illustrates the preparation of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-cinnamate.

In a 1 liter glass flask with reflux condenser, crude ethyl 2,2-difluoro-3-cinnamoyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (43 g , 0.112 mole) was added, dissolved in a solvent mixture (400 mL) of CH ₃ CN: H ₂ O: CF ₃ CO ₂ H [25: 1.25: 0.215 (v / v / v)] and refluxed for 4 h. I was. The reflux condenser was adjusted to distill at atmospheric pressure and about 50 ml of solvent was removed by distillation. Toluene (50 mL) was then added and distillation was continued until the internal temperature of the mixture was 95-100 ° C. After another 1 hour of heating at this temperature, the mixture was concentrated to give crude 2,2-difluoropentofuranos-1-ulose-3-cinnamate (33 g, 0.111 mol) in 99% yield. Got it. ¹ H-NMR (CDCl ₃ ): δ = 4.0 (H-5, 2H), 4.6 (H-4, 1H), 5.69 (H-3, 1H), 6.50 (cinnam., 1H), 7.44 (aromatic 3H ), 7.56 (aromatic 2H), 7.83 (cinnam., 1H).

Example  11

This example illustrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-discinnamate.

2-deoxy-2,2-difluoropentofuranos-1-ulose-3-cinnamate (33 g) was dissolved in ethyl acetate (350 mL) and pyridine (66 mL, 0.816 mmol) was added. And the mixture was stirred at room temperature. A solution of cinnamoyl chloride (40 g, 0.24 mol) in ethyl acetate (150 mL) was added dropwise at room temperature, and the mixture was refluxed for 4 hours. After cooling, the mixture was washed with water (150 mL), 1 M HCl (150 mL), 5% NaHCO ₃ (150 mL), water (150 mL), and brine (150 mL). The organic phase was dried over Na ₂ SO ₄ and concentrated on a rotary evaporator to give crude 2-deoxy-2,2-difluoro-pentofuranos-1-ulose-3,5-discinnamate as a solid ( 11.3 g, 23.5%), which was crystallized from ethyl acetate-hexane and washed with petroleum ether to 8.9 g (0.0208 mol) of 2-deoxy-2,2-difluoro-D-erythro-pento Furanos-1-ulose-3,5-discinnamate was obtained in 18.7% yield and 99% ee.

Example  12

This example illustrates the preparation of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-cinnamate-5-benzoate.

In a 500 ml glass flask equipped with a reflux condenser, crude ethyl-2,2-difluoro-3-cinnamoyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (10 g) was added and dissolved in a mixture of acetonitrile (75 mL), water (3.7 mL) and trifluoroacetic acid (0.65 mL). After heating at reflux for 3 hours, toluene (75 mL) was added and the mixture was distilled until the internal temperature of the mixture was 99-100 ° C. The mixture was concentrated to give crude 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-cinnamate (7.73 g), which was THF (50 mL), pyridine ( 4.5 mL) and 4- (dimethylamino) -pyridine (DMAP) (0.317 g). Freshly re-distilled benzoyl chloride (4.8 g) was stirred dropwise at 0? 10 占 폚. The mixture was stirred at 20-30 ° C. for 2 h and then concentrated to dryness. Ethyl acetate (30 mL) was added, the solid thus formed was removed by filtration, and the residue was concentrated to give an oil. A solvent mixture of ethyl acetate and heptane was added and the resulting solution was cooled overnight to -7 ° C to -10 ° C. The precipitate was collected by filtration to give a solid (erythro isomer, 0.5 g) of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-cinnamate-5-benzoate. ¹ H-NMR (CDCl ₃ ): δ = 4.66-4.74 (H-5, 2H), 4.92 (H-4, 1H), 5.65 (H-3, 1H), 6.49 (cinnam., 1H), 7.42- 7.48 (aromatic 5H), 7.54-7.62 (aromatic 3H), 7.82 (cinnam., 1H), 8.03 (aromatic 2H).

All references mentioned herein, including publications, patent applications, and patents, are incorporated herein by reference to the same extent as if each reference was individually and specifically incorporated by reference and is fully disclosed herein.

In the context of describing the present invention (particularly in the context of the claims below), the use of the terms “this”, “the” and “the” and similar indicators is used in the singular and the context unless otherwise specified or clearly contradicted by context. It should be interpreted as encompassing all the plurals. The terms "comprising", "having", "including" and "including" are to be construed as unlimited terms (ie, meaning "including but not limited to") unless stated otherwise. The description of a range of values herein is intended to be used as an abbreviation for individually referring to each distinct value within that range, unless stated otherwise, and each distinct value herein individually It is included in the specification as described. All methods described herein may be carried out in any suitable order unless otherwise specified herein or clearly contradicted by context. Any and all examples, or description of exemplary phrases (eg, “such as”) described herein, are intended to better describe the invention and do not limit the scope of the invention unless otherwise claimed. Do not. No phrase in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of the invention are described herein, including the best mode for carrying out the invention, which the inventors know. Modifications of such preferred embodiments will become apparent to those skilled in the art upon reading the foregoing specification. The inventors expect skilled artisans to employ such variations as appropriate, and anticipate that the invention may be practiced otherwise than as specifically described herein. Accordingly, the present invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Also included in the present invention are any combinations of the foregoing elements in all possible variations thereof, unless expressly contradicted herein or otherwise clearly contradicted by context.

Claims (64)

At least a substantial portion of the α anomer was removed from the anomer mixture of N-1-protected-2'-deoxy-2 ', 2'-difluorocytidine-3', 5'-diester, Producing at least a rich product; Removing the 3'-ester, 5'-ester and N-protecting group; And Optionally converting the product to a salt Including, Gemcitabine or a method for producing a salt thereof, The 3'-ester and the 5'-ester are the same or different and at least one of the esters is cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4-methyl Benzylcarbonyl or 9-fluorenylmethyloxycarbonyl ester. The method of claim 1, wherein the anomer mixture of N-1-protection-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester, 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-ulose-3,5-diester is reduced to 2-deoxy-2,2-difluoro-D Producing ribofuranose-3,5-diester; 2-deoxy-2,2-difluoro is reacted with 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester and methanesulfonyl chloride in the presence of a base. Obtaining rho-D-ribofuranose-3,5-diester-1-methanesulfonate; And N-1-protection-cytosine is coupled to the 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate to provide N-1-protection Producing -2'-deoxy-2 ', 2'-difluorocytidine-3', 5'-diester Prepared by a process comprising the 3-esters and 5-esters being the same or different. The compound of claim 2, wherein at least one of the esters is cinnamoyl, benzoyl, 1-naphthoyl, 1-naphthylmethylcarbonyl, 2-methylbenzylcarbonyl, 4-methylbenzylcarbonyl or 9-fluorenylmethyl The method is an oxycarbonyl ester. The 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-diester is a 2-deoxy-2,2-diester according to claim 2. Obtained separately from a mixture of erythroisomers and threoisomers of fluoropentofuranos-1-ulose-3,5-diester, wherein the 3-ester and 5-ester are as defined in claim 2 . The mixture of the erythroisomer and the treo isomer of 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester is a 2-deoxy-2. The process is prepared by esterifying a mixture of erythroisomers and threoisomers of, 2-difluoropentofuranos-1-ulose. The mixture of the erythroisomer and the treo isomer of 2-deoxy-2,2-difluoropentofuranos-l-ulose is alkyl-2,2-difluoro-3-hydric according to claim 5. Wherein the mixture of 3-R isomer and 3-S isomer of oxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized. The method of claim 5, wherein the 3-ester and 5-ester are the same. 8. The method of claim 7, wherein the 3-ester and 5-ester are cinnamoyl, 1-naphthoyl or 1-naphthylmethylcarbonyl ester. The mixture of the erythroisomer and the treo isomer of 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester is a 2-deoxy-2. A process for preparing a mixture of erythroisomers and treo isomers of, 2-difluoropentofuranos-1-ulose-3-ester. 10. The mixture of claim 9, wherein the mixture of the erythro (3-R) isomer and the treo (3-S) isomer of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester is , Esterification of a mixture of 3-R and 3-S isomers of alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate Producing an alkyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate, and Alkyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized to give 2-deoxy-2,2-difluoro Producing a mixture of erythroisomers and threoisomers of lofentopuranos-1-ulose-3-ester It is prepared by a process comprising a. The method of claim 9, wherein the 3-ester and 5-ester are different. The method of claim 11, wherein the 3-ester or 5-ester is cinnamoyl, benzoyl, 1-naphthoyl or 1-naphthylmethylcarbonyl ester. The method of claim 1, 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-diester is reduced with a reducing agent in an organic solvent to give 2-deoxy-2, Producing 2-difluoro-D-ribofuranose-3,5-diester; 2-deoxy-2,2-difluoro is reacted with 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester and methanesulfonyl chloride in the presence of a base. Obtaining rho-D-ribofuranose-3,5-diester-1-methanesulfonate; 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate and bis (trimethylsilyl) -N-, optionally in the presence of a catalyst in an organic solvent Coupling acetylcytosine to produce N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester; The α isomer of N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-cytidine-3', 5'-diester is precipitated and filtered to isolate the β isomer. Doing; And Hydrolysis to remove N-1-trimethylsilylacetyl, 3'-ester and 5'-ester to produce gemcitabine Method comprising a. The method of claim 13, wherein the reducing agent is lithium aluminum hydride, diisobutylaluminum hydride or sodium bis- (2-methoxyethoxy) -aluminum hydride. The method of claim 14, wherein the reducing agent is lithium aluminum hydride. The method of claim 13, wherein the catalyst is trimethylsilyl triflate (Me ₃ SiOTf). The process according to claim 13, wherein the α and β anomers are separated by a process comprising precipitating the α anomer in a solvent mixture comprising 1,2-dichloroethane and methanol. The method of claim 13 including hydrolyzing said N-1-trimethylsilylacetyl, said 3'-ester and 5'-ester in the presence of methanolic ammonia. The method of claim 7, wherein Ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized to give 2-deoxy-2,2-difluoro Producing lofentopuranos-1-ulose; The 2-deoxy-2,2-difluoropentofuranos-l-ulose is esterified with an acid chloride in the presence of a base in an organic solvent to give 2-deoxy-2,2-difluoropentopuranos. Producing a mixture of erythro isomers and threo isomers of -1-ulose-3,5-diester; And Selectively precipitating one of the isomers Method comprising a. The method of claim 19, wherein the cyclization, Dissolve ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing an acid and heat it to give 2 Producing deoxy-2,2-difluoropentofuranos-1-ulose; Reducing the solution volume by distillation; Adding an organic solvent and refluxing; Distilling off the solvent mixture to obtain an oil; And Optionally, distilling the oil under reduced pressure Method comprising a. The method of claim 20, wherein the reaction solvent comprises acetonitrile, water and trifluoroacetic acid. 22. The method of claim 21 wherein the acetonitrile: water: trifluoroacetic acid ratio is about 150: 12: 2.2 (v / v / v), respectively. The method of claim 19, wherein the esterification is Dissolving 2-deoxy-2,2-difluoropentofuranos-1-ulose in an organic solvent; Optionally at room temperature, adding a base or other acid scavenger and acid chloride; Refluxing the reaction mixture to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester; Washing the reaction mixture, separating and drying the organic phase; And Evaporating the solvent to isolate crude 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester Method comprising a. The method of claim 23, wherein the acid chloride is cinnamoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride, 1-naphthylacetyl chloride, or 9-fluorenylmethyloxycarbonyl chloride. . The method according to claim 19, wherein the erythro isomer and treo isomer, Adding a first organic solvent to an isomeric mixture of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester, and stirring at room temperature; Adding a second organic solvent while stirring; Cooling to selectively precipitate one of the isomers; And Filtration How to separate in a process comprising a. The method of claim 25, wherein the first solvent is ethyl acetate, isopropyl acetate, n -butyl acetate, isobutyl acetate, tert -butyl acetate, THF, acetonitrile, or mixtures thereof. The method of claim 25, wherein the second solvent is pentane, hexane, heptane, octane, petroleum ether, or mixtures thereof. The method of claim 25, wherein the 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester is 2-deoxy-2,2-difluoro-D- Erythro-pentofuranos-1-ulose-3,5-discinnamate, the first solvent is ethyl acetate, and the second solvent is hexane. The erythro isomer of 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-l-ulose-3,5-discinnamate according to claim 28, having a purity of at least 99.9% and a purity of 99.6. Method comprising isolating with an ee of at least%. The method of claim 10, Esterification of a mixture of 3-R isomers and 3-S isomers of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate Producing ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate; Ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized to give 2-deoxy-2,2-difluoro Producing lofentopuranos-1-ulose-3-ester (optionally an erythro: threo isomer ratio of greater than 1: 1); Esterifying a 5-hydroxy group to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester, wherein the 3-ester and 5-ester are Same or different); And Separation of erythroisomers and threoisomers of 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester by selective precipitation and filtration Method comprising a. 32. The 3-R isomer and 3-S isomer of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate according to claim 30. Esterifying the mixture of Dissolving ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in an organic solvent; Optionally at room temperature, adding a base and an acid chloride dropwise; Refluxing the mixture to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester; And Washing the reaction mixture, separating and drying the organic phase to obtain a solid material Method comprising a. 32. The method of claim 31, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride or 1-naphthylacetyl chloride. The method of claim 30, wherein the cyclization, Crude ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is dissolved in a solvent mixture containing an acid and heated to Performing cyclization; Reducing the solvent volume by distillation; Adding an organic solvent and refluxing; Removing the solvent mixture by distillation until the internal temperature of the mixture reaches about 90 to 100 ° C., and maintaining the temperature for about 1 hour; And Concentrating the cyclized product, optionally by evaporation under reduced pressure Method comprising a. The method of claim 33, wherein the reaction solvent comprises a mixture of acetonitrile, water and trifluoroacetic acid. 35. The method of claim 34, wherein the acetonitrile: water: trifluoroacetic acid ratio is about 75: 3.7: 0.65 (v / v / v), respectively. The method of claim 33, wherein the solvent added after the solution volume is reduced by distillation is ethyl acetate, xylene, toluene, or mixtures thereof. The method of claim 30, wherein the 5-hydroxy group, Dissolving ethyl-2,2-difluoro-3 ~ acyloxy-pentofuranos-1-ulose in an organic solvent; Optionally at room temperature, adding a base or other acid scavenger and acid chloride; Refluxing the mixture to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester; Washing the reaction mixture, separating and drying the organic layer; Removing the solvent by distillation to obtain a solid, and Optionally, crystallizing the product Esterizing by a process comprising a. 38. The method of claim 37, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride or 4-methylphenylacetyl chloride. The method of claim 30, wherein the erythroisomer and treo isomer, Adding a solvent mixture to a crude mixture of the erythro isomer and the treo isomer of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester, and stirring at room temperature; Cooling for a time sufficient to selectively precipitate one of the isomers; And Filtration How to separate in a process comprising a. The solvent mixture of claim 39 wherein the solvent mixture is ethyl acetate, isopropyl acetate, n -butyl acetate, isobutyl acetate, tert -butyl acetate, THF, acetonitrile, pentane, hexane, heptane, octane, petroleum ether, or mixtures thereof. How to include. Ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized to give 2-deoxy-2,2-difluoro Producing lofentopuranos-1-ulose; 2-deoxy-2,2-difluoropentofuranos-l-ulose was esterified with an acid chloride in the presence of a base in an organic solvent to thereby 2-deoxy-2,2-difluoropentopuranos Producing a mixture of erythro isomers and threo isomers of -1-ulose-3,5-diester; And Selectively precipitating one of the isomers A method for producing an isomer-rich 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester comprising a. 42. The method of claim 41 wherein the cyclization is Dissolve ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing an acid and heat it to give 2 Producing deoxy-2,2-difluoropentofuranos-1-ulose; Reducing the solution volume by distillation; Adding an organic solvent and refluxing; Distilling off the solvent mixture to obtain an oil; And Optionally, distilling the oil under reduced pressure Method comprising a. 43. The method of claim 42, wherein the reaction solvent comprises acetonitrile, water and trifluoroacetic acid. 44. The method of claim 43, wherein the acetonitrile: water: trifluoroacetic acid ratio is about 150: 12: 2.2 (v / v / v), respectively. 42. The method of claim 41 wherein the esterification is Dissolving 2-deoxy-2,2-difluoropentofuranos-1-ulose in an organic solvent; Optionally at room temperature, adding a base or other acid scavenger and acid chloride; Refluxing the reaction mixture to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester; Washing the reaction mixture, separating and drying the organic phase; And Evaporating the solvent to isolate crude 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester Method comprising a. 46. The method of claim 45, wherein the acid chloride is cinnamoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride, 1-naphthylacetyl chloride, or 9-fluorenylmethyloxycarbonyl chloride Way. 42. The method according to claim 41, wherein the erythroisomer and treo isomer, Adding a first organic solvent to an isomeric mixture of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester, and stirring at room temperature; Adding a second organic solvent while stirring; Cooling to selectively precipitate one of the isomers; And Filtration How to separate in a process comprising a. 48. The method of claim 47, wherein the first solvent is ethyl acetate, isopropyl acetate, n -butyl acetate, isobutyl acetate, tert -butyl acetate, THF, acetonitrile, or mixtures thereof. 48. The method of claim 47, wherein the second solvent is pentane, hexane, heptane, octane, petroleum ether, or mixtures thereof. Esterification of a mixture of 3-R isomers and 3-S isomers of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate Producing ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate; Ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized to give 2-deoxy-2,2-difluoro Producing lofentopuranos-1-ulose-3-ester (optionally an erythro: threo isomer ratio of greater than 1: 1); Esterifying a 5-hydroxy group to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester, wherein the 3-ester and 5-ester are Same or different); And Separation of erythroisomers and threoisomers of 2-deoxy-2,2-difluoropentofuranos-l-ulose-3,5-diester by selective precipitation and filtration A method for producing an isomer-rich 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester comprising a. 51. The 3-R isomer and 3-S isomer of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate according to claim 50. Esterifying the mixture of Dissolving ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in an organic solvent; Optionally at room temperature, adding a base and an acid chloride dropwise; Refluxing the mixture to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3-ester; And Washing the reaction mixture, separating and drying the organic phase to obtain a solid material Method comprising a. The method of claim 51, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride or 1-naphthylacetyl chloride. The method of claim 50, wherein the cyclization, Crude ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is dissolved in a solvent mixture containing an acid and heated to Performing cyclization; Reducing the solvent volume by distillation; Adding an organic solvent and refluxing; Removing the solvent mixture by distillation until the internal temperature of the mixture reaches about 90 to 100 ° C., and maintaining the temperature for about 1 hour; And Concentrating the cyclized product, optionally by evaporation under reduced pressure Method comprising a. The method of claim 53, wherein the reaction solvent comprises a mixture of acetonitrile, water and trifluoroacetic acid. 55. The method of claim 54, wherein the acetonitrile: water: trifluoroacetic acid ratio is about 75: 3.7: 0.65 (v / v / v), respectively. The method of claim 53, wherein the solvent added after the solution volume is reduced by distillation is ethyl acetate, xylene, toluene, or a mixture thereof. The method of claim 50, wherein the 5-hydroxy group, Dissolving ethyl-2,2-difluoro-3-acyloxy-pentofuranos-1-ulose in an organic solvent; Optionally at room temperature, adding a base or other acid scavenger and acid chloride; Refluxing the mixture to produce 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester; Washing the reaction mixture, separating and drying the organic layer; Removing the solvent by distillation to obtain a solid; And Optionally, crystallizing the product Esterizing by a process comprising a. 59. The method of claim 57, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride or 4-methylphenylacetyl chloride. The method of claim 50, wherein the erythroisomer and treo isomer, Adding a solvent mixture to a crude mixture of the erythro isomer and the treo isomer of 2-deoxy-2,2-difluoropentofuranos-1-ulose-3,5-diester, and stirring at room temperature; Cooling for one time sufficient to selectively precipitate one of the isomers; And Filtration How to separate in a process comprising a. 60. The method of claim 59, wherein the solvent mixture is ethyl acetate, isopropyl acetate, n -butyl acetate, isobutyl acetate, tert -butyl acetate, THF, acetonitrile, pentane, hexane, heptane, octane, petroleum ether, or mixtures thereof. How to include. Compounds of the formula

In the above formula, R and R 'are the same or different and each is 2-phenylethenyl, phenyl, 2-methylbenzyl, 4-methylbenzyl, 1-naphthyl, 1-naphthylmethyl or 9-fluorenyl Methyl. A compound of the formula: as erythro isomer, treo isomer, or mixtures thereof:

In the formula, R is 2-phenylethenyl, phenyl, 2-methylbenzyl, 4-methyl benzyl or 1-naphthyl methyl, Alk is a C _{1 -6} alkyl. Compounds of the formula: as α aomers, β anomers, or mixtures thereof:

Wherein R and R 'are the same or different and at least one of R and R' is 2-phenylethenyl, phenyl, 2-methylbenzyl, 4-methylbenzyl, 1-naphthyl, 1-naphthylmethyl Or 9-fluorenylmethyl, the other represents a residue of a carboxylate ester. 64. A method for preparing gemcitabine, comprising the step of converting β anomer of the compound of claim 63 to gemcitabine.