JP2009506118A - Method for producing gemcitabine and related intermediates - Google Patents

Abstract

  A method for producing gemcitabine or a salt thereof, wherein at least most of the α anomer of 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position A method is provided that includes removing from the mixture; removing the ester at the 3 ′ position, the ester at the 5 ′ position, and the N-protecting group; and optionally forming a salt. The ester at the 3 ′ position and the ester at the 5 ′ position are the same or different and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthyl ester Methyl carbonyl ester, 2-methylbenzyl carbonyl ester, 4-methylbenzyl carbonyl ester, or 9-fluorenylmethyloxycarbonyl ester. Also provided are novel intermediates including, but not limited to, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester, and methods for making such intermediates.

Description

  Gemcitabine HCl, marketed by Eli Lilly under the trade name Gemzar®, is a nucleoside analog with antitumor activity and belongs to the general group of chemotherapeutic drugs known as antimetabolites. . Gemcitabine blocks cellular DNA and RNA synthesis by preventing nucleic acid synthesis, thereby stopping the growth of cancer cells and causing their death.

Gemcitabine is a synthetic glucoside analog of cytosine, chemically 4-amino-1- (2-deoxy-2,2-difluoro-β-D-ribofuranosyl) -pyrimidin-2 (1H) -one or 2 It is described as '-deoxy-2', 2'-difluorocytidine (β isomer). Gemcitabine HCl has the following structure:

  Gemzar® is provided in vials as a sterile form of the hydrochloride salt, only for intravenous injection, containing either 200 mg or 1 g of gemcitabine HCl (calculated as the free base) and mannitol (200 mg or 1 g, respectively) And formulated as a sterile lyophilized powder with sodium acetate (12.5 mg or 62.5 mg, respectively). Hydrochloric acid and / or sodium hydroxide can be added to adjust the pH.

  US Pat. No. 4,808,614 (“the '614 patent”) discloses a method for synthetically producing gemcitabine, which is typically illustrated in Scheme 1.

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

  The resulting product is cyclized by treatment with an acidic ion exchange resin such as Dowex 50W-X12 to give 2-deoxy-2,2-difluoro-D-erythro-pentanoic acid-γ-lactone 4. Protecting the hydroxy group of the lactone with the tert-butyldimethylsilyl (TBDMS) protecting group, the protected lactone 3,5-bis- (tert-butyldimethylsilyloxy) -2-deoxy-2,2-difluoro-1-oxoribose 5 and the product is further reduced to give 3,5-bis- (tert-butyldimethylsilyl) -2-deoxy 2,2-difluororibose 6.

  For example, by introducing a leaving group such as methanesulfonyloxy (mesylate) formed by reacting compound 6 with methanesulfonyl chloride, the 1-position of the sugar is activated, and 3,5-bis- (tert-butyl Dimethylsilyloxy) -1-methanesulfonyloxy-2-deoxy-2,2-difluororibose 7 is obtained. For example, by reacting compound 7 with N, O-bis- (trimethylsilyl) -cytosine 8 in the presence of a reaction initiator such as trifluoromethanesulfonyloxytrimethylsilane (trimethylsilyltriflate), the base ring is coupled to the sugar. Let Removal of the protecting group and purification by chromatography gives gemcitabine free base.

  U.S. Pat. No. 4,526,988 discloses a similar method of cyclization by hydrolyzing alkyl 3-dioxolanyl-2,2-difluoro-3-hydroxy-propionate with an acidic ion exchange resin. See also Hertel et al., J. Org. Chem. 53, 2406 (1998).

の中間体3,5-ジベンゾイルリボ保護ラクトンからゲムシタビンを製造する方法を開示している。ここで、所望のエリスロ異性体は、エリスロ-およびスレオ-異性体混合物から、結晶形態で単離することができる。'374特許で開示されたこの方法は、一般にスキーム２で概説される。 US Pat. No. 4,965,374 (“the '374 patent”) has the following formula:

Discloses a process for preparing gemcitabine from the intermediate 3,5-dibenzoylriboprotected lactone. Here, the desired erythro isomers can be isolated in crystalline form from erythro- and threo-isomer mixtures. This method disclosed in the '374 patent is generally outlined in Scheme 2.

Benzoyl chloride, benzoyl bromide, benzoyl cyanide, benzoyl azide and the like (eg, PhCOX (where X ==) in the presence of a tertiary amine or a catalyst (eg, 4-dimethylaminopyridine or 4-pyrrolidinopyridine). Cl, Br, CN, or N ₃ )) by esterification of the 3-hydroxy group of compound 3 with a benzoyl protecting group and 2,2-difluoro-3-benzoyloxy-3- (2,2-dimethyl) Ethyl dioxolan-4-yl) propionate 9 is obtained.

  For example, by using a strong acid such as concentrated sulfuric acid in ethanol, the 9 isoalkylidene protecting group is selectively removed to give ethyl 2,2-difluoro-3-benzoyloxy-4,5-dihydroxypentanoate 9A. To manufacture. This product is cyclized to lactone 10 and converted to dibenzoate ester to convert 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-dibenzoate lactone 11 to erythro- and Produced as a threo-isomer mixture. The '374 patent discloses the isolation of at least a portion of the erythro isomer by selective precipitation from a mixture. See also Chou et al., Synthesis, 565-570, (1992).

  Compound 11 is then reduced to obtain a mixture of α and β anomers of 2-deoxy-2,2-difluoropentofuranose dibenzoate 12 and activated with methanesulfonyl chloride to give the mesylate 2-deoxy-2,2 An anomeric mixture of 2-difluoro-D-ribofuranosyl-3,5-di-O-benzoyl-1-O-β-methanesulfonate 13 was further coupled with N, O-bis (trimethylsilyl) -cytosine 8; The dibenzoate silyl protected nucleoside 14 is obtained as a mixture of α- and β-anomers (α / β anomeric ratio of about 1: 1). Removal of the ester and silyl protecting groups results in a mixture of β anomer (gemcitabine) and α-anomer (approximately 1: 1 α / β anomeric ratio). The '374 patent describes the step of selectively isolating β-anomer (gemcitabine) by forming a salt (eg, hydrochloride or hydrobromide) of an anomeric mixture, and selectively precipitating, Disclosed is a process for obtaining 2′-deoxy-2 ′, 2′-difluorocytidine as a salt with an α / β ratio of 1: 4. The '374 patent also discloses the step of selectively precipitating the free base form of the β-anomer in a slightly basic aqueous solution. One such method is to dissolve a 1: 1 α / β anomeric mixture in hot acidic water (pH adjusted to 2.5-5.0), as soon as the mixture is fully dissolved, the pH is adjusted to 7.0-9.0. And crystallizing the solution by cooling the solution and isolating the crystal by filtration.

  A method for separating an anomeric mixture of alkyl sulfonate intermediates is also disclosed. U.S. Pat. Discloses a process for obtaining ribofuranosyl sulfonate enriched.

  Other intermediates have been disclosed that can be useful in preparing gemcitabine. For example, U.S. Pat.No. 5,480,992 describes, for example, 2-deoxy-2,2-difluoro-D-ribofuranosyl-3,5-di-O-benzoyl-1-O-β-methanesulfonate, such as lithium azide. Disclosed is an anomeric mixture of 2,2-difluororibosyl azide and the corresponding amine intermediate that can be prepared by reacting with an azide nucleophile to give the azide. Reduction of the azide can produce the corresponding amine, which can be synthetically converted to a nucleoside. See also US Pat. Nos. 5,541,345 and 5,594,155.

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

  Other methods for preparing gemcitabine are disclosed, for example, in WO 2006/070985 and 2006/071090 for the stereoselective preparation of 2'-deoxy-2 ', 2'-difluorocytidine. Yes. These methods are generally outlined in Scheme 3 below.

This method comprises the steps of activating 2'-deoxy-2 ', 2'-difluoro-D-ribofuranosyl-3,5-diester 12A with diphenyl chlorophosphate, then isolating the isomer, followed by the corresponding 1 A step of obtaining a -bromo-ribofuranose intermediate, which is coupled with N, O-bis- (trimethylsilyl) -cytosine 8 and then deprotected to give gemcitabine. However, this method requires additional steps compared to the method outlined in Scheme 2, which diminishes the attractiveness for industrial implementation.
U.S. Pat.No. 4,808,614 U.S. Pat.No. 4,965,374

  With respect to the production of gemcitabine, there is an inherent problem that production yields tend to be poor on a commercial scale, particularly in processes that require the production and separation of isomers. Accordingly, there is a need for improved methods for the preparation of gemcitabine and its intermediates that 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 herein.

The present invention is a method for producing gemcitabine or a salt thereof, preferably,
At least most of the α anomer is removed from the anomeric mixture of 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position to enrich at least the β anomer Producing a finished product;
A method is provided comprising: removing the ester at the 3 ′ position, the ester at the 5 ′ position, and the N-protecting group; and optionally converting the product to a salt.

  The ester at the 3 ′ position and the ester at the 5 ′ position are the same or different, and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthoyl ester, Naphthylmethylcarbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester.

The 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position can be produced by any appropriate method. Preferably,
Reduction of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester yields 2-deoxy-2,2-difluoro-D-ribofuranose-3,5- Producing a diester;
The 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester is reacted with methanesulfonyl chloride in the presence of a base to give 2-deoxy-2,2-difluoro-D-ribofuranose Obtaining a -3,5-diester-1-methanesulfonate; and
By coupling cytosine protected at the N-1 position with the 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate, the N-1 position is protected. 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester is obtained by a method comprising a step of obtaining 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester. An anomeric mixture of difluorocytidine-3 ′, 5′-diester is prepared.

  The ester at the 3 position and the ester at the 5 position are the same or different, and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethyl Carbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester.

  2-Deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester can be prepared by any suitable method. Preferably, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester is 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5 -Obtained by separating the product from a mixture of erythro (3-R) and threo (3-S) isomers of diesters. The ester at the 3 position and the ester at the 5 position are the same or different, and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethyl Carbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester.

  The protected 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester of the present invention is particularly useful for commercial scale production of gemcitabine. These D-erythro derivatives are crystalline materials and can be purified by separation (eg, precipitation) from D-erythro- and L-threo-isomer mixtures. These intermediates and methods of the present invention facilitate total synthesis of gemcitabine, are easy to handle, and achieve higher yields than methods described in the literature.

The present invention is a method for producing gemcitabine or a salt thereof, preferably,
At least most of the α anomer is removed from the anomeric mixture of 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position to enrich at least the β anomer Producing a finished product;
A method is provided comprising: removing the ester at the 3 ′ position, the ester at the 5 ′ position, and the N-protecting group; and optionally converting the product to a salt.

  The ester at the 3 ′ position and the ester at the 5 ′ position are the same or different, and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthoyl ester, Naphthylmethylcarbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester.

The 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position can be produced by any appropriate method. Preferably,
Reduction of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester yields 2-deoxy-2,2-difluoro-D-ribofuranose-3,5- Producing an anomeric mixture of diesters;
The 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester is reacted with methanesulfonyl chloride in the presence of a base to give 2-deoxy-2,2-difluoro-D-ribofuranose Obtaining a -3,5-diester-1-methanesulfonate; and
By coupling cytosine protected at the N-1 position with the 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate, the N-1 position is protected. 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester is obtained by a method comprising a step of obtaining 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester. An anomeric mixture of difluorocytidine-3 ′, 5′-diester is prepared.

  The ester at the 3 position and the ester at the 5 position are the same or different, and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethyl Carbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester.

  The 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester of the present invention can be prepared by any suitable method. Preferably, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester is replaced with 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5 It can be obtained by separating the product from a mixture of erythro (3-R) and threo (3-S) isomers of diesters. The ester at the 3-position and the ester at the 5-position are the same or different, and at least one of these esters is preferably cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethyl Carbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester.

The mixture of erythro (3-R) and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester of the present invention can be obtained by any suitable method. Can be manufactured. In one embodiment, a mixture of erythro (3-R) and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester is converted to 2-deoxy Prepared by esterifying a mixture of erythro (3-R) and threo (3-S) isomers of -2,2-difluoropentofuranose-1-urose. When the 3-position ester and the 5-position ester are the same, the 3-position ester and 5-position ester are preferably cinnamoyl, 1-naphthoyl, or 1-naphthylmethylcarbonyl. This mixture of erythro (3-R) and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranos-1-urose can be obtained by any suitable method, such as alkyl-2,2- It can be prepared by cyclizing a mixture of 3-S- and 3-R-isomers of difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate. Suitable alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate intermediates include, for example, C _1-6 alkyl-2,2-difluoro-3 -Hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate intermediate (eg ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -Propionate].

In another embodiment, the mixture of erythro (3-R) and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester of the present invention comprises: Prepared by esterifying a mixture of erythro (3-R) and threo (3-S) isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester. The mixture of erythro (3-R) and threo (3-S) isomers of the 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester can be obtained by any suitable method, such as alkyl- Esterify the mixture of 3-S- and 3-R-isomers of 2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate and cyclize the product It can manufacture by the method to make. Cyclization can be accomplished using any suitable conditions, for example, alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate 3-R- and 3 This can be done by treating the -S-isomer mixture with a suitable acid. In this embodiment, when the 3-position ester and the 5-position ester are different, it is preferred that either the 3-position ester or the 5-position ester is cinnamoyl, benzoyl, or 1-naphthylmethylcarbonyl. Suitable alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate intermediates include, for example, C _1-6 alkyl-2,2-difluoro-3 -Hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (eg ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate ] Is included.

  Surprisingly, according to the present invention, certain ester groups (eg cinnamoyl and 1-naphthylmethylcarbonyl etc.) not only allow the formation of the preferred isomers of 3,5-ribodiester lactones, By using simple crystallization or precipitation techniques, a stable crystalline material is formed that makes it possible to separate the 3,5-ribodiester lactone isomer from the 3,5-xylodiester lactone isomer.

  According to the present invention, the ester groups at the 3-position or 5-position of the riboprotected lactone may be the same or different. That is, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester may have the same ester protecting group at the 3-position or 5-position, It may have different ester protecting groups.

  A particularly preferred embodiment of the present invention is generally represented in Scheme 4.

According to Scheme 4, N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester (N-1-trimethylsilylacetyl-2′-deoxy-2 ′, Separation of the α and β anomers of 2′-difluoro-3 ′, 5′-dicinnamoyl-cytidine) selectively removes the α anomer from a solvent mixture, preferably a mixture of 1,2-dichloroethane and methanol. It can be carried out by precipitation. Gemcitabine is obtained by performing the following steps.
a) Reduction of lactone 15 with an appropriate reducing agent in an organic solvent to give 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester 16 in approximately 1: 1 isomer Obtaining as a mixture;
b) reacting compound 16 with methanesulfonyl chloride in the presence of a base to give 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-l-methanesulfonate 17;
c) Compound 17 is coupled with bis (trimethylsilyl) -N-acetylcytosine in an organic solvent using a catalyst, preferably at ambient temperature, to give N-1-trimethylsilylacetyl-2′-deoxy-2 ′, Obtaining a mixture of α and β anomers of 2′-difluorocytidine-3 ′, 5′-diester;
d) precipitating the alpha anomer 18 and separating the two anomers by filtration; and
e) A step of removing the protecting group by hydrolysis to obtain gemcitabine.

  The reduction of lactone 15 is selected from any suitable reducing agent such as lithium aluminum hydride, diisobutylaluminum hydride, or sodium bis (2-methoxyethoxy) aluminum hydride, as shown, for example, in Scheme 4. One or more reducing agents can be used. The reduction is preferably carried out with lithium aluminum hydride, especially for commercial scale production, as shown, for example, in Scheme 4. This is in particular due to its low molecular weight and relatively high reduction capacity (4 hydrogen atoms are obtained per molecule). The reduction can also be carried out using diisobutylaluminum hydride (eg taught in US Pat. No. 4,808,614 and Chou et al., Synthesis, 565-570 (1992)). Diisobutylaluminum hydride is less preferred in terms of its molecular weight and the fact that it has only one hydrogen atom available for reduction.

For example, as shown in Scheme 4, the coupling reaction may be performed using any suitable solvent (for example, one or more organic solvents selected from acetonitrile, dichloromethane, chloroform, 1,2-dichloroethane, toluene, xylene, and the like). Included). In one embodiment, the coupling reaction is performed in 1,2-dichloroethane. In some cases, the coupling reaction can be facilitated by using a suitable catalyst reagent [eg, trimethylsilyl triflate (Me ₃ SiOTf), etc.].

  Removal of the protecting group can be carried out using any suitable conditions [eg, including basic hydrolysis (eg, ammonia in methanol), as shown, for example, in Scheme 4.

  The 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester of the present invention can be produced by any method. Schemes 5 and 6 show two preferred methods (Methods A and A) for obtaining the typical 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-urose-3,5-diester of the present invention. Respectively).

  The method shown in Scheme 5 is the 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5- of the present invention in which the ester at the 3 position is the same as the ester at the 5 position. It is particularly useful for the preparation of diesters (eg, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate). In this case, the two isomers are separated by precipitation to obtain the erythro isomer 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-pentofuranose-1-urose-3,5-diester can be obtained by a method including the following steps.
a) Cyclization of alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (eg 3) to give 2-deoxy-2,2-difluoro Producing pentofuranose-1-urose-4;
b) 2-deoxy-2,2-difluoropentofuranos-1-urose 4 is reacted with an appropriate acid chloride in an organic solvent in the presence of a base to give 2-deoxy as a mixture of erythro and threo isomers. Obtaining 2,2-difluoropentofuranose-1-urose-3,5-diester 21; and
c) separating the isomers by selective precipitation.

  Preferably, alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (eg, compound 3) is prepared as a starting material in a solvent mixture in the presence of an acid. And then cyclized by distillation to produce 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose4. This cyclization can be carried out using ion exchange resins according to US Pat. No. 4,808,614 (see also Scheme 1).

  Cyclization can also be carried out via intermediate 9A, for example as shown in Scheme 5 (Scheme 2). Alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (eg, compound 3) is refluxed in the presence of an acid in a suitable solvent mixture; Distillation can then be performed as described in Chou et al., Synthesis, 565-570, (1992), but this method adds one additional step. However, this reflux / distillation method is advantageous from a commercial point of view because it is more economical for industrial applications. The ion exchange resin route may require up to 4 days of reaction time and is not practical for commercial applications.

An exemplary method for cyclizing alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate includes the following steps.
a) Crude ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is dissolved in a solvent mixture containing acid and sufficient to complete the reaction Heating for a long time;
b) reducing the volume of the solution by distillation;
c) adding an organic solvent and further refluxing;
d) removing the solvent mixture by distillation to obtain an oil; and
e) Optionally, the oil is distilled under reduced pressure to produce 2-deoxy-2,2-difluoropentofuranose-1-urose.

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

2-deoxy-2,2-difluoropentofuranose-1-urose can be esterified using any suitable esterifying agent, for example as shown in Scheme 5. In one embodiment, 2-deoxy-2,2-difluoropentofuranose-1-urose is esterified with an acid chloride in an organic solvent in the presence of a base by a method comprising the following steps.
a) preparing a solution of 2-deoxy-2,2-difluoropentofuranose-1-urose in an organic solvent;
b) optionally adding base and acid chloride dropwise at ambient temperature;
c) refluxing the reaction mixture for a time sufficient to substantially complete the reaction;
d) washing and separating the reaction mixture and rendering the organic phase anhydrous; and
e) evaporating the solvent to obtain the crude diester.

  According to the present invention, suitable acid chlorides useful for esterification of hydroxy groups include cinnamoyl chloride, 1-naphthoyl chloride, 1-naphthyl acetyl chloride, 2-methylphenyl acetyl chloride, 4-methylphenyl acetyl chloride. One or more acid chlorides selected from the above are included.

According to the present invention, the erythro and threo isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester (eg when the ester groups at the 3 and 5 positions are the same) Can be separated from the crude mixture by a crystallization method. One example of such a crystallization method includes the following steps.
a) adding a first organic solvent to the crude mixture and stirring at ambient temperature;
b) adding the second organic solvent with stirring;
c) cooling for a sufficient time to precipitate; and
d) filtering to obtain the desired product.

  The first solvent includes, for example, one or more solvents selected from ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, THF, acetonitrile, or mixtures thereof. The second solvent includes, 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 method shown in Scheme 6 (Method B) is a 2-deoxy-2,2-difluoro-D-erythro-pentofuranos-1-urose-3,5- of the present invention in which the 3- and 5-position ester groups are different. It is particularly useful for the production of diesters.

According to Scheme 6, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester (optionally having non-identical ester groups at the 3 and 5 positions) Can be obtained by a method comprising the following steps.
a) Alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate [e.g. ethyl-2,2-difluoro-3-hydroxy-3- (2, 2-Dimethyldioxolan-4-yl) -propionate 3] is esterified to give ethyl-2,2-difluoro-3-acetoxy-3- (2,2-dimethyldioxolan-4-yl)- Producing propionate 22;
b) Ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized, for example by refluxing and then distilled to give 2-deoxy-2 , 2-difluoropentofuranose-1-urose-3-ester as erythro (3-R) and threo (3-S) isomer mixture 23 (in this case, the main product obtained is erythro isomerism) Body);
c) esterifying the hydroxy group at position 5 of 23 to obtain a diester 24 having the same or different ester groups at the 3 and 5 positions; and
d) isolating the erythro isomer 24 by selectively precipitating from the reaction mixture.

  The 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester of the present invention is selective precipitation (regardless of whether the 3- and 5-position ester groups are the same or different). Makes it possible to easily separate the desired isomers and thus the two isomers can be separated by filtration. According to the present invention, erythro isomers such as 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate can be obtained with at least 99% ee. .

A typical example of esterification of a 3-hydroxyl group includes the following steps, as shown in Scheme 6.
a) dissolving ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in an organic solvent;
b) adding a base and a suitable acid chloride, optionally dropwise at ambient temperature;
c) refluxing the mixture for a time sufficient to complete the reaction; and
d) The reaction mixture is washed and separated, the organic phase is made anhydrous and ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate as a solid Step to get as.

Esterification of the 3-hydroxyl group can be any suitable alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (eg, as described herein). And the corresponding alkyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate [eg, the alkyl group is C ₁ Alkyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate, which is _˜6 alkyl (eg ethyl) and the 3-acyloxy group is RCO ₂ — Can be manufactured. In this case, R is any suitable substituent, including but not limited to 2-phenylethenyl (forms a cinnamoyl ester), phenyl, 1-naphthyl, 1-naphthylmethyl, 2- Including methylbenzyl, 4-methylbenzyl and the like.

Cyclization of ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is accomplished by reflux and then distillation as shown in Scheme 6. can do. A typical cyclization method includes the following steps.
a) Cyclization by heating a solution of crude ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing acid Process;
b) reducing the volume of the solvent by distillation;
c) adding a solvent mixture and refluxing;
d) removing the solvent mixture by distillation until the internal temperature of the mixture reaches about 90-100 ° C. and keeping at said temperature for about 1 hour; and
e) The remaining solvent mixture is optionally evaporated under reduced pressure to convert the 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester into erythro (3-R) and threo (3-S ) Obtaining as a mixture of isomers.

  The reaction solvent containing an acid is preferably a mixture of acetonitrile, water, and trifluoroacetic acid. Preferably, the ratio of acetonitrile: water: trifluoroacetic acid is about 75: 3.7: 0.65 (v / v / v). The organic solvent added after the step of reducing the volume of the solvent by distillation is preferably toluene. Method B shows that the product obtained after cyclization (eg, cyclization by refluxing the reaction mixture followed by distillation) surprisingly gives the erythro isomer as the major component and thus the desired isomer. It is particularly advantageous if it is selective.

The esterification of the 5-hydroxyl group can be carried out using a suitable method, for example as shown in Scheme 6 and can optionally yield diesters having ester groups that are not the same at the 3 and 5 positions. it can. In one embodiment, the 5-hydroxyl can be esterified by a method comprising the following steps.
a) dissolving 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester 23 in an organic solvent;
b) optionally adding base and acid chloride dropwise at ambient temperature;
c) refluxing the mixture for a time sufficient to substantially complete the reaction; and
d) washing the reaction mixture, separating and dehydrating the organic phase to obtain 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester as a solid. In this case, R and R ′ may be the same or different.

Separation of the erythro- and threo-isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester can be performed using any suitable method, for example as shown in Scheme 6. For example, 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester can be obtained. Preferably, the separation is performed by a method comprising the following steps.
a) adding solvent to the crude mixture and stirring at ambient temperature;
b) cooling to precipitate; and
c) Separating the product by filtration.

  Typical 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. One or more solvents may be included. Preferably, the solvent is a mixture of ethyl acetate and heptane.

According to the present invention, when the 3-position ester and the 5-position ester are different, at least one of the 3-position and 5-position esters (or at least one of the 3′-position and the 5′-position) is cinnamoyl. Ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethylcarbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl ester, and the remaining esters are Any suitable ester may be used, including but not limited to cinnamoyl ester, naphthoyl ester, naphthylmethylcarbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenyl Contains methyloxycarbonyl ester. Other suitable esters can include, for example, alkyl esters [eg, C _1-6 alkyl esters (eg, acetyl)] and aromatic esters (eg, esters of benzoic acid and its derivatives). When using Method B, the substituent R should be carefully selected. This is because in some cases 9-fluorenylmethyloxycarbonyl, naphthylacetyl, and acetyl are removed by hydrolysis to produce compound 4, whereas other esters (such as cinnamoyl) are This is because the compound 23 remains as it is.

  The invention is further illustrated by the following examples, which should, of course, not be construed as limiting the scope of the invention in any way.

[Example 1]
This example demonstrates the preparation of crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamate.

To a 500 ml round bottom flask was added crude 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate (10 g, 23.36 mmol) and anhydrous THF (100 ml) and cooled to 0-5 ° C. After LiAlH ₄ (0.46 g, 12.1 mmol) was added over 5 minutes, the mixture was stirred for an additional hour. Water (10 ml) was added with stirring. When most of the solvent was removed by distillation and 1N HCl (50 ml) was added to the remaining amount (about 30 ml), a clear solution with a pH value of about 2 was formed. Ethyl acetate (100 ml) was added and the organic phase was washed with 5% NaHCO3 (50 ml), water (50 ml), and brine (50 ml). The ethyl acetate phase was dried over MgSO ₄ and concentrated under reduced pressure to give crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamate as an oil. Yield: 8.52 g (19.8 mmol, 84.8%, α / β isomer ratio approximately 1/1).

[Example 2]
This example demonstrates the preparation of 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamate-1-methanesulfonate.

In a 100 ml round bottom flask, crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamate (2.5 g, 5.8 mmol) was dissolved in dichloromethane (20 ml) and triethylamine (0.7 g 6.9 mmol). Methanesulfonyl chloride (0.79 g, 6.9 mmol) was added dropwise while cooling to 0-5 ° C. The mixture was stirred for an additional hour, 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 give crude 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-disinnamate-1-methanesulfonate as a light oil. Yield: 2.82 g (5.55 mmol), 95.7%, purity 99.2%. The 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 (cinnamoyl, 2H), 7.40 (aromatic, 6H), 7.54 (aromatic, 4H), 7.79 (cinnamoyl, 2H).

[Example 3]
This example demonstrates the preparation of N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluoro-3 ′, 5′-dicinnamoyl-cytidine.

1,2-Dichloroethane (50 ml) was added to bis (trimethylsilyl) -N-acetylcytosine (2.2 g) to give a clear solution, then trimethylsilyl triflate (Me ₃ SiOTf) (2.2 ml, 2.75 g) ) Was added and stirred for 30 minutes. A solution of 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamate-1-methanesulfonate (2.6 g, 5.1 mmol) in 1,2-dichloroethane (10 ml) was added dropwise, The mixture was stirred 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′-dicinnamoyl-cytidine as a pale yellow solid (2.4 g, 4.24 mmol , 83%). This crude N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-dicinnamoyl-cytidine (2 g, 3.5 mmol) was added to 1,2-dichloroethane ( 4 ml) and methanol (120 ml) was added dropwise with stirring.

The white solid formed was collected by filtration and dried (about 0.5 g N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluoro-3 ′, 5′-dicinnamoyl-cytidine, α-anomer Containing). The remaining liquid was concentrated to give crude N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluoro-3 ′, 5′-dicinnamoyl-cytidine, β anomer, a pale yellow solid (1.6 g, 2.8 mmol) as 80% and ee 90%. N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluoro-3 ′, 5′-dicinnamoyl-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 (cytidine-H, 1H), 5.50 (H-3, 1H), 6.47-6.53 (cinnamoyl + H1, 3H) 7.43 (fragrance Family, 6H), 7.54 (aromatic, 4H), 7.78 (cytidine-H + cinnamoyl, 3H), 9.2-9.35 (NH broad 1H).

[Example 4]
This example demonstrates the production of gemcitabine hydrochloride.

  A solution of methanol in ammonia (ca. 20%, 40 ml) was added to crude N-1-trimethylsilylacetyl-2'-deoxy-2 ', 2'-difluoro-3', 5'-dicinnamoyl-cytidine beta anomer (1.5 g, 2.6 mmol) was added and stirred at ambient temperature overnight. The mixture was concentrated to a light yellow oil and 1N HCl (20 ml) was added followed by dichloromethane (20 ml) with stirring. The aqueous phase was separated, activated carbon (0.2 g) was added, and the mixture was heated at 75 ° C. for 30 minutes. After filtration, the remaining liquid was concentrated and dried under reduced pressure to give gemcitabine hydrochloride as a solid (1 g). This solid was dissolved in water (1 ml) at ambient 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 obtain crude gemcitabine. Yield: 0.3 g, 38.5%. Purity: 95%, ee 95%.

[Example 5]
This example demonstrates the preparation of 2-deoxy-2,2-difluoropentofuranose-1-urose.

  In a 500 ml glass flask equipped with a reflux condenser, add crude ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (30 g, 0,118 mol). 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 adapted for atmospheric distillation and a volume of 130-150 ml of solvent was removed by distillation. Toluene (70 ml) was added and the mixture was refluxed for an additional 3 hours and concentrated to give 20.2 g of oil. This was distilled under reduced pressure (140 ° C./2 mm Hg) to obtain 12.2 g (0.073 mol) of 2-deoxy-2,2-difluoropentofuranos-1-urose in a yield of 61.9%.

[Example 6]
This example demonstrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate.

In a 1 liter glass flask equipped with a reflux condenser, freshly distilled 2-deoxy-2,2-difluoropentofuranose-1-urose (also called 2-deoxy-2,2-difluoropentanoic acid-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 ambient temperature. A solution of cinnamoyl chloride (56 g, 0.336 mol) in ethyl acetate (100 ml) was added dropwise at ambient temperature and the mixture was refluxed for 4 hours. After cooling, the mixture was washed with water (100 ml), 1M HCl (100 ml), 5% NaHCO ₃ (100 ml), water (100 ml), and brine (100 ml). The organic phase was dried over MgSO ₄ and concentrated by rotary evaporator to give 46 g of crude 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-dicinnamate as an oil. To the resulting oil was added ethyl acetate (80 ml) and the mixture was stirred at ambient temperature, then hexane (150 ml) was added with continued stirring. After about 30 minutes, the mixture (two phases) was cooled overnight in the temperature range of -7 ° C to -10 ° C. The precipitate was collected by filtration to yield 26 g (60.7 mmol) of solid crude 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate at a yield of 52.3%. Rate, purity 99.9%, and 99.6% ee were obtained.
¹ H-NMR CDCl ₃ : δ = 4.59 (H-5, 2H), 4.88 (H-4, 1H), 5.63 (H-3, 1H), 6.50 (cinnamoyl, 2H), 7.44 (aromatic, 6H) 7.55 (aromatic, 4H), 7.75-7.88 (cinnamoyl, 2H).

[Example 7]
This example demonstrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dinaphthoate.

In a 100 ml glass flask equipped with a reflux condenser, 2-deoxy-2,2-difluoropentofuranose-1-urose (2.2 g, 13 mmol) was dissolved in anhydrous THF (15 ml) and 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, water (10 ml), 1M HCl ( 10 ml), 5% NaHCO 3 (10 ml), water (10 ml), and washed with brine (10 ml). The organic phase was dried over Na ₂ SO ₄ and concentrated by rotary evaporator to give a residue. This was crystallized to give a white solid of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dinaphthoate with a purity of 98% and 90% ee.

[Example 8]
This example demonstrates the preparation of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-di-2-naphthyl acetate.

2-Deoxy-2,2-difluoropentofuranose-1-urose (0.82 g) and pyridine (0.85 ml) were mixed in dichloromethane (10 ml), and 2-naphthylacetyl chloride (2-naphthylacetic acid was converted to oxalyl chloride). (Obtained by reacting with) in dichloromethane (10 ml) was added dropwise. After refluxing for 2 hours, the mixture was cooled and washed with water (10 ml), 1M 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 by rotary evaporator to give a solid. This was purified by chromatography to give oil of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-di-2-naphthyl acetate as a mixture of erythro and threo isomers.

[Example 9]
This example demonstrates the preparation of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-di-4-methylphenyl acetate.

2-deoxy-2,2-difluoropentofuranose-1-urose (1.61 g), pyridine (1.7 ml), and 4- (dimethylamino) -pyridine (DMAP) (300 mg) in dichloromethane (15 ml) After mixing, 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) was added dropwise. After refluxing for 2 hours, the mixture was cooled and washed with water (10 ml), 1M 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 by rotary evaporator to give a residue. This was purified by chromatography to give an oil of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-di-4-methylphenylacetate as a mixture of erythro and threo isomers. .

[Example 10]
This example demonstrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3-cinnamate.

To a 1 liter glass flask equipped with a reflux condenser was added crude ethyl-2,2-difluoro-3-cinnamoyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (43 g, 0.0112 mol). ) And dissolved in a solvent mixture (400 ml) in which CH ₃ CN: H ₂ O: CF ₃ CO ₂ H was 25: 1.25: 0.125 (v / v / v) and refluxed for 4 hours. The reflux condenser was adapted for atmospheric distillation and about 50 ml of solvent was removed by distillation. Toluene (50 ml) was then added and distillation continued until the internal temperature of the mixture was 95 ° C-100 ° C. After heating for an additional hour at this temperature, the mixture was concentrated to give crude 2-deoxy-2,2-difluoropentofuranose-1-urose-3-cinnamate (33 g, 0.0112 mol) in 99% yield. Obtained at a rate.
¹ H-NMR CDCl ₃ : δ = 4.0 (H-5, 2H), 4.6 (H-4, 1H), 5.69 (H-3, 1H), 6.50 (cinnamoyl, 1H), 7.44 (aromatic, 3H) 7.56 (aromatic, 2H), 7.83 (cinnamoyl, 1H).

[Example 11]
This example demonstrates the preparation of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate.

2-Deoxy-2,2-difluoropentofuranose-1-urose-3-cinnamate (33 g) is dissolved in ethyl acetate (350 ml), pyridine (66 ml, 0.816 mmol) is added and the mixture is Stir at temperature. A solution of cinnamoyl chloride (40 g, 0.24 mol) in ethyl acetate (150 ml) was added dropwise at ambient temperature and the mixture was stirred for 4 hours. After cooling, the mixture was washed with water (150 ml), 1M 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-difluoropentofuranose-1-urose-3,5-dicinnamate as a solid (11.3 g, 23.5 %). This was crystallized from ethyl acetate-hexane and washed with petroleum ether to give 8.9 g (0.0208 mol) of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate. ) Was obtained in 18.7% yield and 99% ee.

[Example 12]
This example demonstrates the preparation of 2-deoxy-2,2-difluoropentofuranose-1-urose-3-cinnamate-5-benzoate.

Crude ethyl-2,2-difluoro-3-cinnamoyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate (10 g) was added to a 500 ml glass flask equipped with a reflux condenser. , 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-difluoropentofuranose-1-urose-3-cinnamate (7.73 g). This was dissolved in a mixture of THF (50 ml), pyridine (4.5 ml), and 4- (dimethylamino) -pyridine (DMAP) (0.317 g). Freshly redistilled benzoyl chloride (4.8 g) was added dropwise with stirring at 0-10 ° C. The mixture was stirred at 20-30 ° C. for 2 hours and then concentrated to dryness. Ethyl acetate (30 ml) was added, the formed solid was removed by filtration and the remaining liquid was concentrated to give an oil. A solvent mixture of ethyl acetate and hexane was added and the formed solution was cooled at −7 ° C. to −10 ° C. overnight. The precipitate was collected by filtration to give a solid of 2-deoxy-2,2-difluoropentofuranose-1-urose-3-cinnamate-5-benzoate (erythro isomer, 0.5 g).
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 (cinnamoyl, 1H), 7.42-7.48 (Aromatic, 5H), 7.54-7.62 (aromatic, 3H), 7.82 (cinnamoyl, 1H), 8.03 (aromatic, 2H).

  All references, including publications, patent applications, and patents cited herein, are individually and clearly indicated that each reference is incorporated herein by reference, To the same extent as if it had been shown here in its entirety, it is incorporated herein by reference.

  In describing the present invention (especially with respect to the appended claims), the use of the terms "a", "an", and "the" and similar indicating subject matter is the context or content otherwise indicated herein. Unless otherwise clearly contradicted by, it shall be construed to cover both the singular and plural. The terms `` comprising '', `` having '', `` including '', and `` containing '' unless otherwise indicated, are words without limitation (i.e., including but not limited to `` Meaning "not to be done"). The recitation of value ranges herein is intended to serve as a convenient way to individually refer to each discrete value falling within that range, except where otherwise indicated herein. In addition, each discrete value is incorporated herein as if it were individually listed herein. All methods described herein can be performed in any suitable order except where otherwise indicated or otherwise clearly contradicted by content. The use of any and all examples, or exemplary words (e.g., "such as") provided herein are merely intended to better describe the invention and unless otherwise required. It is not intended to limit the scope of the invention. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

  Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations on these preferred embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors anticipate that those skilled in the art will use such variations as necessary, and that the inventors will implement the invention in a manner other than the specific examples described herein. Intended. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Furthermore, any combination of the above-described components in all possible variations thereof is intended to be encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by content.

Claims (64)

A method for producing gemcitabine or a salt thereof,
At least most of the α anomer is removed from the anomeric mixture of 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position to enrich at least the β anomer Producing a finished product;
Removing the ester at the 3 ′ position, the ester at the 5 ′ position, and the N-protecting group; and optionally converting the product to a salt (in this case, the ester at the 3 ′ position and the 5 ′ position). The esters may be the same or different and at least one of these esters may be cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethylcarbonyl ester, 2-methylbenzylcarbonyl ester, 4 -Methylbenzylcarbonyl ester or 9-fluorenylmethyloxycarbonyl ester)
Including a method. Reduction of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester yields 2-deoxy-2,2-difluoro-D-ribofuranose-3,5- Producing a diester;
The 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester is reacted with methanesulfonyl chloride in the presence of a base to give 2-deoxy-2,2-difluoro-D-ribofuranose Obtaining a -3,5-diester-1-methanesulfonate; and
By coupling cytosine protected at the N-1 position with the 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate, the N-1 position is protected. Obtaining 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester (in this case, the ester at the 3-position and the ester at the 5-position are the same or different)
The method according to claim 1, wherein the anomeric mixture of 2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester protected at the N-1 position is prepared by a method comprising:   At least one of the esters is cinnamoyl ester, benzoyl ester, 1-naphthoyl ester, 1-naphthylmethylcarbonyl ester, 2-methylbenzylcarbonyl ester, 4-methylbenzylcarbonyl ester, or 9-fluorenylmethyloxycarbonyl The method of claim 2 which is an ester.   The 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester is converted to 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester A process according to claim 2, obtained by separation from a mixture of erythro- and threo-isomers, wherein the ester at the 3-position and the ester at the 5-position are as defined in claim 2.   The erythro- and threo-isomer mixture of the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester is converted into an erythro of 2-deoxy-2,2-difluoropentofuranose-1-urose. The process according to claim 4, wherein the-and threo-isomer mixtures are prepared by esterification.   The erythro- and threo-isomer mixture of the 2-deoxy-2,2-difluoropentofuranos-1-urose is converted to alkyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolane-4 6. The process of claim 5, wherein the process is prepared by cyclizing a 3-R- and 3-S-isomer mixture of -yl) -propionate.   6. The method of claim 5, wherein the 3-position ester and the 5-position ester are the same.   The method according to claim 7, wherein the ester at the 3-position and the ester at the 5-position are cinnamoyl ester, 1-naphthoyl ester, or 1-naphthylmethylcarbonyl ester.   The erythro- and threo-isomer mixture of the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester is converted to 2-deoxy-2,2-difluoropentofuranose-1-urose-3. Process according to claim 4, wherein the erythro- and threo-isomer mixtures of esters are prepared by esterification. 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 yields alkyl-2, Producing 2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate;
The alkyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is cyclized to produce the 2-deoxy-2,2-difluoropentofuranose-1- And erythro- (3- (3-deoxy-2,2-difluoropentofuranos-1-ester) by a method comprising the step of producing an erythro- and threo-isomer mixture of urose-3-ester. The process according to claim 9, wherein a mixture of R-) and threo- (3-S-) isomers is produced.   10. The method of claim 9, wherein the 3-position ester and the 5-position ester are different.   The method according to claim 11, wherein the ester at the 3-position or the ester at the 5-position is a cinnamoyl ester, a benzoyl ester, a 1-naphthyl ester, or a 1-naphthylmethylcarbonyl ester. The 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-diester is reduced with a reducing agent in an organic solvent to give 2-deoxy-2,2- Producing difluoro-D-ribofuranose-3,5-diester;
The 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester is reacted with methanesulfonyl chloride in the presence of a base to give 2-deoxy-2,2-difluoro-D-ribofuranose Obtaining -3,5-diester-1-methanesulfonate;
The 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-diester-1-methanesulfonate is reacted with bis (trimethylsilyl) -N-acetylcytosine in an organic solvent, optionally in the presence of a catalyst. Coupling to produce N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester;
Precipitating the α isomer of the N-1-trimethylsilylacetyl-2′-deoxy-2 ′, 2′-difluorocytidine-3 ′, 5′-diester and filtering to isolate the β isomer; The method according to claim 1, further comprising the step of producing gemcitabine by removing the N-1-trimethylsilylacetyl, the 3′-position ester, and the 5′-position ester by hydrolysis.   14. 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 catalyst is trimethylsilyl triflate (Me ₃ SiOTf), The method of claim 13.   14. The method of claim 13, wherein the α and β anomers are separated by a method comprising the step of precipitating the α anomer in a solvent mixture comprising 1,2-dichloroethane and methanol.  14. The method of claim 13, comprising hydrolyzing the N-1-trimethylsilylacetyl, the 3'-position ester, and the 5'-position ester in the presence of methanolic ammonia. Cyclization of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate yields 2-deoxy-2,2-difluoropentofuranose-1-urose. Manufacturing process;
The 2-deoxy-2,2-difluoropentofuranose-1-urose is esterified with an acid chloride in the presence of a base in an organic solvent, and the 2-deoxy-2,2-difluoropentofuranose-1-ulose is obtained. 8. The method of claim 7, comprising the steps of producing an erythro- and threo-isomer mixture of -3,5-diester; and selectively precipitating one of the isomers. The cyclization is
The ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is dissolved in a solvent mixture containing acid and heated to produce the 2-deoxy- Producing 2,2-difluoropentofuranose-1-urose;
Reducing the volume of the solution by distillation;
Adding an organic solvent to reflux;
20. The method of claim 19, comprising the steps of removing the solvent mixture by distillation to obtain an oil; and optionally distilling the oil under reduced pressure.   21. The method of claim 20, wherein the reaction solvent comprises acetonitrile, water, and trifluoroacetic acid.   24. The method of claim 21, wherein the acetonitrile: water: trifluoroacetic acid ratio is about 150: 12: 2.2 (v / v / v), respectively. The esterification is
Dissolving 2-deoxy-2,2-difluoropentofuranose-1-urose in an organic solvent;
Adding a base or other acid scavenger and acid chloride, optionally at ambient temperature;
Refluxing the reaction mixture to produce the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester;
Washing the reaction mixture, separating and dehydrating the organic phase; and evaporating the solvent to remove the crude 2-deoxy-2,2-difluoro-pentofuranos-1-urose-3,5-diester. 20. A method according to claim 19 comprising the step of isolating.   The acid chloride is cinnamoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride, 1-naphthylacetyl chloride, or 9-fluorenylmethyloxycarbonyl chloride. 24. The method according to 23. Adding a first organic solvent to an isomeric mixture of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester and stirring at ambient temperature;
Adding a second organic solvent with stirring;
20. The method of claim 19, wherein the erythro- and threo-isomers are separated by a method comprising cooling to selectively precipitate one of the isomers; and filtering.   26. 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 a mixture thereof.   26. The method of claim 25, wherein the second solvent is pentane, hexane, heptane, octane, petroleum ether, or a mixture thereof.   The 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester is 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate 26. The method of claim 25, wherein the first solvent is ethyl acetate and the second solvent is hexane.   Isolating the erythro isomer of 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-1-urose-3,5-dicinnamate with at least 99.9% purity and at least 99.6% ee 30. The method of claim 28. Esterification of a mixture of 3-R- and 3-S-isomers of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate yields ethyl-2, Producing 2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate;
Cyclization of said ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate optionally having an erythro: threo isomer ratio greater than 1: 1 Producing 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester;
Esterifying the hydroxy group at the 5-position to produce 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester (in this case, the ester at the 3-position and the ester at the 5-position are And the erythro- and threo-isomers of the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester by selective precipitation and filtration. The method of claim 10, comprising the step of separating. Esterifying the 3-R- and 3-S-isomer mixture of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate,
Dissolving ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in an organic solvent;
Adding a base and an acid chloride optionally dropwise at ambient temperature;
Refluxing the mixture to produce the deoxy-2,2-difluoropentofuranose-1-urose-3-ester; and washing the reaction mixture, separating, rendering the organic phase anhydrous, 32. The method of claim 30, comprising the step of obtaining.   32. The method of claim 31, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride, or 1-naphthylphenylacetyl chloride. The cyclization is
Dissolving crude ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing an acid and heating to cyclize;
Reducing the volume of the solvent by distillation;
Adding an organic solvent and refluxing;
Removing the solvent mixture by distillation until the internal temperature of the mixture reaches about 90-100 ° C. and keeping at said temperature for about 1 hour; and concentrating the cyclized product by evaporation, optionally under reduced pressure. 32. The method of claim 30, comprising.   34. 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.   34. The method of claim 33, wherein the solvent added after the step of reducing the volume of the solution by distillation is ethyl acetate, xylene, toluene, or a mixture thereof. Dissolving ethyl-2,2-difluoro-3-acyloxy-pentofuranose-1-urose in an organic solvent;
Adding a base or other acid scavenger and acid chloride, optionally at ambient temperature;
Refluxing the mixture to produce the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester;
Washing the reaction mixture, separating and rendering the organic phase anhydrous;
31. The method of claim 30, wherein the 5-position hydroxy group is esterified by a method comprising distilling the solvent to obtain a solid; and optionally crystallizing the product.   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. Adding the solvent mixture to the crude mixture of erythro- and threo-isomers of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester and stirring at ambient temperature;
31. The method of claim 30, wherein the erythro- and threo-isomers are separated by a method comprising cooling for a time sufficient to selectively precipitate one of the isomers; and filtering.   40. The solvent mixture of claim 39, wherein the solvent mixture comprises ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, THF, acetonitrile, pentane, hexane, heptane, octane, petroleum ether, or mixtures thereof. The method described. A process for the production of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester enriched in one isomer comprising:
Cyclization of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate produces 2-deoxy-2,2-difluoropentofuranose-1-urose The step of:
2-deoxy-2,2-difluoropentofuranose-1-urose is esterified with an acid chloride in an organic solvent in the presence of a base, and the 2-deoxy-2,2-difluoropentofuranose-1-urose- Producing a erythro- and threo-isomer mixture of 3,5-diesters; and selectively precipitating one of the isomers. The cyclization is
The ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate is dissolved in a solvent mixture containing acid and heated to the 2-deoxy-2. Producing 2-, 2-difluoropentofuranose-1-urose;
Reducing the volume of the solution by distillation;
Adding an organic solvent and refluxing;
42. The method of claim 41, comprising removing the solvent mixture by distillation to obtain an oil; and optionally distilling the oil under reduced pressure.   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. The esterification is
Dissolving 2-deoxy-2,2-difluoropentofuranose-1-urose in an organic solvent;
Adding a base or other acid scavenger and acid chloride, optionally at ambient temperature;
Refluxing the reaction mixture to produce the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester;
Washing the reaction mixture, separating and rendering the organic phase anhydrous; and evaporating the solvent to give the crude 2-deoxy-2,2-difluoropentofuranos-1-urose-3,5-diester alone. 42. The method of claim 41, comprising the step of releasing.   The acid chloride is cinnamoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride, 4-methylphenylacetyl chloride, 1-naphthylacetyl chloride, or 9-fluorenylmethyloxycarbonyl chloride. 45. The method according to 45. Adding a first organic solvent to an isomeric mixture of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester and stirring at ambient temperature;
Adding a second organic solvent with stirring;
42. The method of claim 41, wherein the erythro- and threo-isomers are separated by a method comprising cooling to selectively precipitate one of the isomers; and filtering.   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 a mixture thereof.   48. The method of claim 47, wherein the second solvent is pentane, hexane, heptane, octane, petroleum ether, or a mixture thereof. A process for the production of 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester enriched in one isomer comprising:
Esterification of a mixture of 3-R- and 3-S-isomers of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate yields ethyl-2, Producing 2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate;
Cyclization of ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate, optionally having an erythro: threo isomer ratio greater than 1: 1; Producing 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester;
Esterifying the hydroxy group at the 5-position to produce 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester (in this case, the ester at the 3-position and the ester at the 5-position are And the erythro- and threo-isomers of the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester by selective precipitation and filtration. A method comprising the step of separating. Esterifying the 3-R- and 3-S-isomer mixture of ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate,
Dissolving ethyl-2,2-difluoro-3-hydroxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in an organic solvent;
Adding a base and an acid chloride optionally dropwise at ambient temperature;
Refluxing the mixture to produce the 2-deoxy-2,2-difluoropentofuranose-1-urose-3-ester; and washing and separating the reaction mixture, rendering the organic phase anhydrous, 51. The method of claim 50, comprising obtaining a solid.   52. The method of claim 51, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 2-methylphenyl acetyl chloride, 4-methylphenyl acetyl chloride, or 1-naphthyl acetyl chloride. The cyclization is
Dissolving crude ethyl-2,2-difluoro-3-acyloxy-3- (2,2-dimethyldioxolan-4-yl) -propionate in a solvent mixture containing an acid and heating to cyclize;
Reducing the volume of the solvent by distillation;
Adding an organic solvent and refluxing;
Removing the solvent mixture by distillation until the internal temperature of the mixture reaches about 90-100 ° C. and keeping at that temperature for about 1 hour; and concentrating the cyclized product by evaporation, optionally under reduced pressure. 51. The method of claim 50, comprising.   54. The method of claim 53, wherein the reaction solvent comprises 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.   54. The method of claim 53, wherein the solvent added after the step of reducing the volume of the solution by distillation is ethyl acetate, xylene, toluene, or a mixture thereof. Dissolving ethyl-2,2-difluoro-3-acyloxy-pentofuranose-1-urose in an organic solvent;
Adding a base or other acid scavenger and acid chloride, optionally at ambient temperature;
Refluxing the mixture to produce the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester;
Washing the reaction mixture, separating and rendering the organic phase anhydrous;
51. The method of claim 50, wherein the 5-position hydroxy group is esterified by a method comprising distilling the solvent to obtain a solid; and optionally crystallizing the product.   58. The method of claim 57, wherein the acid chloride is cinnamoyl chloride, benzoyl chloride, 1-naphthoyl chloride, 2-methylphenylacetyl chloride, or 4-methylphenylacetyl chloride. Adding a solvent mixture to the crude mixture of erythro- and threo-isomers of the 2-deoxy-2,2-difluoropentofuranose-1-urose-3,5-diester and stirring at ambient temperature;
51. The method of claim 50, wherein the erythro- and threo-isomers are separated by a method comprising cooling for a time sufficient to selectively precipitate one of the isomers; and filtering.   The solvent mixture comprises ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, THF, acetonitrile, pentane, hexane, heptane, octane, petroleum ether, or mixtures thereof. The method described. Following formula:

Wherein R and R ′ are the same or different and are each 2-phenylethenyl, phenyl, 2-methylbenzyl, 4-methylbenzyl, 1-naphthyl, 1-naphthylmethyl, or 9 -Fluorenylmethyl)
Compound. An erythro isomer, a threo isomer, or a mixture thereof, the following formula:

Wherein R is 2-phenylethenyl, phenyl, 2-methylbenzyl, 4-methylbenzyl, or 1-naphthylmethyl, and Alk is C _1-6 alkyl.
Compound. α anomer, β anomer, or a mixture thereof, the following formula:

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 rest representing the carboxylate ester residues)
Compound.   64. A method for producing gemcitabine, comprising a step of converting a β anomer of the compound of claim 63 into gemcitabine.