Patent Application
20060173174
The invention is directed to the novel difluoronucleoside, 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine, and to the process for preparation thereof.
Gemcitabine HCl is the beta isomer of 2′-deoxy-2′,2′-difluorocytidine monohydrochloride, having the following structure
It is a white to off-white solid, marketed under the name Gemzar® as a nucleoside analogue that exhibits antitumor activity. Gemcitabine, which is the free base of Gemcitabine hydrochloride, exhibits cell phase specificity, primarily killing cells undergoing DNA synthesis (S-phase), and also blocking the progression of cells through the G1/S-phase boundary. Gemcitabine is metabolized intracellularly by nucleoside kinases to the active diphosphate (dFdCDP) and triphosphate (dFdCTP) nucleosides. The cytotoxic effect of gemcitabine is attributed to a combination of two actions of the diphosphate and the triphosphate nucleosides, which leads to inhibition of DNA synthesis.
Gemcitabine hydrochloride is prepared from Gemcitabine, which is a 2′,2′-difluoronucleoside derivative that is usually prepared by the attack of a suitable protected base on the 1-position of a corresponding protected sugar derivative.
U.S. Pat. No. 4,965,374 discloses the coupling reaction between 1-sulphonyloxy-2-deoxy-2,2,-difluoropentofuranoses and a protected cytidine, to yield the precursor of Gemcitabine as a mixture of cc/p isomers in a ratio of 1:1.
U.S. Pat. No. 5,371,210 discloses the coupling reaction between 1-sulphonyloxy-2-deoxy-2,2,-difluoropentofuranoses and a protected cytidine, but the reaction is carried out without any solvent. However, a pre-purification process of the 1-sulphonyloxy-2-deoxy-2,2,-difluoropentofuranoses is conducted to obtain an isomerically enriched starting material, that after the coupling reaction leads to the precursor of Gemcitabine having an α/β ratio of up to 1 to 1.8.
U.S. Pat. No. 5,594,124 discloses the coupling reaction between 1-sulphonyloxy-2-deoxy-2,2,-difluoropentofuranoses and a protected cytidine at −78° C., giving the final product with an α/β ratio of up to 1 to 2.5.
U.S. Pat. No. 5,744,597 discloses the coupling reaction between 1-sulphonyloxy-2-deoxy-2,2,-difluoropentofuranoses and a protected cytidine, after a pre-purification process, as described in U.S. Pat. No. 5,371,210.
The US Pharmacopoeia sets a very strict limitation on the level of the a isomer in Gemcitabine (the β isomer), thus allowing a level of no more than 0.1% area by HPLC. Therefore, there is a need in the art for an improved process for the preparation of 2′,2′-difluoronucleosides.
In one aspect, the present invention provides a process for the preparation of a 2′,2′-difluoronucleoside of formula I,
having an α/β ratio of about 1:4 to about 1:6 by HPLC, comprising combining a fluorinated protected sugar derivatives of formula II,
having an α/β ratio of about 1:1 to 1:2 as determined by HPLC, a water immiscible organic solvent and an organic base of formula III
with a Lewis acid, to obtain a mixture. The mixture is then heated to a temperature of about 40° C. to about 140° C. until the conversion is of at least 80%, followed by quenching to give 2′,2′-difluoronucleoside of the formula I; wherein, L is a leaving group selected from the group consisting of C1-10 alkyl, C1-10 haloalkyl, C1-10 aryl-esters, C1-10 alkyl and C1-10 aryl-sulphonates, and halogens; R is an alcohol protecting groups selected from the group consisting of C1-10 alkyl- and C1-10 aryl-ester ester, ether, carbamate and acetal; P1 is a C1-6 trialkyl silyl ether, wherein each alkyl group can be the same or different, and X is either NH and O.
In another aspect, the present invention provides a process for preparing Gemcitabine comprising preparing 2′,2′-difluoronucleoside of formula I as described above, and further converting it to Gemcitabine.
In yet another aspect, L in the process described above, is acetate group, R is a benzyl group and P1 is trimethylsilyl group, and the obtained product is 3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia.
In one aspect, the present invention provides a process for preparing Gemcitabine comprising preparing 3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia, as described above, and further converting it to Gemcitabine.
In another aspect, the present invention provides the novel compound, 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia.
In yet another aspect, the present invention provides 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia having α/β ratio of about 1:4 to about 1:6, as determined by HPLC.
In one aspect, the present invention provides the novel β isomer of 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia-β, of the following structure.
The present invention provides a process to obtain Gemcitabine, by a stereoselective coupling reaction, which is done under mild condition, leading to the β enriched precursor of Gemcitabine, hence, avoiding purification steps such as, chromatography. Thus, the process of the present invention can be adapted to an industrial scale.
The present invention provides a process for the preparation of a 2′,2′-difluoronucleoside of formula I,
having an α/β ratio of about 1:4 to about 1:6 by HPLC, comprising combining a fluorinated protected sugar derivatives of formula II,
having α/β ratio of about 1:1 to 1:2, as determined by HPLC, a water immiscible organic solvent and an organic base of formula III
with a Lewis acid, to obtain a mixture. The mixture is then heated to a temperature of about 40° C. to about 140° C. until the conversion is of at least about 80%, followed by quenching to give 2′,2′-difluoronucleoside of the formula I; wherein, L is a leaving group selected from the group consisting of C1-10 alkyl, C1-10 haloalkyl, C1-10 aryl-esters, C1-10 alkyl and C1-10 aryl-sulphonates, and halogens; R is an alcohol-protecting group selected from the group consisting of C1-10 alkyl, C1-10 aryl ester, ether, carbamate and acetal; P1 is a C1-6 trialkyl silyl ether, wherein each alkyl group can be the same or different, and X is either NH and O.
Preferably, the process of the invention may be used for the synthesis of 2′-deoxy-2′,2′-difluoroadenosine, 2′-deoxy-2′,2′-difluorouridine, 2′-deoxy-2′,2′-difluorothymidine, 2′-deoxy-2′,2′-difluoroguanosine, 2′-deoxy-2′,2′-difluorocytidine, and analogues thereof, which are obtained after a deprotection reaction of the protected 2′,2′-difluoronucleoside, obtained by the process of the present invention. The deprotection reaction may be done according to process known in the art, such as the ones described in J. Chem. Soc. Perkin Trans. I, 1982, 1171, J. Org. Chem., 1988, 53, 2406, Helv. Chim. Acta, 1995, 490 and in Org. Proc. Res. Dev., 2004, 8, 564
Preferably, R is either C1-10 alkyl- or C1-10 aryl-ester, more preferably, C1-10 aryl-ester and most preferably, benzoyl ester. A more preferred P1 is C1-3 alkyl and most preferably, trimethylsilyl, Preferably, L is either C1-10 alkyl, or C1-10 aryl-esters, more preferably, C1-10 alkyl ester, and most preferably, methylester.
The present invention further provides a process for preparing Gemcitabine comprising preparing 2′,2′-difluoronucleoside of formula I as described above, and further converting it to Gemcitabine.
The present invention also provides the process described above wherein, L is methyl ester and R is benzoyl ester, hence, the fluorinated protected sugar derivatives of formula II corresponds to 1-acetyl-2-deoxy-3,5-dibenzoate-2,2-difluoro-ribofuranose of the formula II-a,
and wherein P1 is trimethylsilyl group, hence, the organic base of formula III corresponds to 2,4-bis-O-trimethylsilyluracil of formula IIIa,
and the obtained 2′,2′-difluoronucleoside of formula I corresponds to 3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia.
The 1-acetyl-2-deoxy-3,5-dibenzoate-2,2-difluoro-ribofuranose of formula IIa, may be prepared as exemplified in example 2. According to the process exemplified in example 3, the compound of formula IV,
is combined with an organic base and an acetylating reagent, to obtain a mixture. The mixture is then maintained at a temperature of about 0° C. to about 40° C. for about 1 to about 18 h to give 1-acetyl-2-deoxy-3,5-dibenzoate-2,2-difluoro-ribofuranose, which is then recovered.
Preferably, the water immiscible organic solvent is selected from the group consisting of C1-4 halogenated hydrocarbon, more preferably, either dichloroethane or dichloromethane, most preferably, dichloroethane.
Preferably, the organic base in the coupling step is commercial.
Preferably, the organic base in the coupling step is selected from the group consisting of pyrimidine and purine derivatives. Preferably, the pyrimidine derivative is cytosine, uracil or thymine. A preferred purine derivative is either guanine or adenine.
Preferably, the base is a protected base in which each oxygen atom is protected with a protecting group. Preferably, the base is a protected base in which each oxygen atom is protected with a protecting group. Preferably, the protected base is selected from the group consisting of 2-O-trimethylsilylcytosine, 2-O-trimethyl-N-trimethylsilylacetylcytosine, 2,4-bis-O-trimethylsilyluracil, 2,4-bis-O-trimethylsilylthymine, and 6-O-trimethylsilylguanine. Most preferably, the protected base is 2,4-bis-O-trimethylsilyluracil.
Preferably, the Lewis acid is TiCl4, AlCl3, BF3, ZnCl2, SnCl2 or SnCl4, more preferably, SnCl4.
Preferably, the Lewis acid is used in an amount of 1.5 mole equivalent to 6 mole equivalent per mole equivalent of the compound of formula IV.
Preferably, the mixture is heated to a temperature of about 60° C. to about 120° C.
Preferably, the reaction is maintained at a temperature of about 60° C. to about 120° C. for about 1 to about 24 hours, preferably, for about 6 to about 24 hours until obtaining a conversion of at least 80%. Wherein, at this stage, the isomeric ratio is fixed, and the reaction can be stopped by quenching. Conveniently, the observed α/β ratio in 3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia is not determined by the initial ratio of anomers in the starting sugar, but is driven by the nature of the catalyst and by the reaction solvent.
The conversion is preferably measured by HPLC.
Preferably, the mixture is cooled to a temperature of about 25° C. to about 20° C., prior to recovering of the product.
Preferably, quenching is done using a saturated aqueous solution of potassium or sodium bicarbonate, more preferably, potassium bicarbonate.
The 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine, of the formula Ia may be recovered from the reaction mixture by filtering the suspension obtained after quenching, followed by washing the filtrate with a saturated sodium bicarbonate solution and concentrating under reduced pressure.
The recovered 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine, of the formula Ia having an isomeric ratio of about 1:4 to about 1:6, determined by HPLC, is triturated in a mixture of heptane and ethyl acetate, in a ratio of 2 to 1 and filtered, to give 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine, of the formula Ia having an α/β ratio of about 2:98, as determined by HPLC.
The present invention provides a process for preparing Gemcitabine comprising preparing 3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia, as described above, and further converting it to Gemcitabine, for example, according to processes known in the art, such as the ones described in J. Chem. Soc. Perkin Trans. I, 1982, 1171, J. Org. Chem., 1988, 53, 2406; Helv. Chim. Acta, 1995, 490 or in Org. Proc. Res. Dev., 2004, 8, 564.
The present invention further provides the novel compound, 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia.
The present invention also provides 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia having α/β ratio of about 1:4 to about 1:6, as determined by HPLC.
The 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia of the present invention is characterized by an 1H-NMR spectrum having peaks at about 4.85-4.55, 4.85, 5.25, 5.77, 5.95-5.80, 6.37, 6.60, 7.75-7.42, 7.90, 7.95-8.10 and 11.65 ppm. The
1H-NMR spectrum for this compound is illustrated in
The present invention provides the novel 0 isomer of 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia-β, of the following structure.
The β isomer of 2-deoxy-3,5-dibenzoate-2,2-difluoro-uridine of the formula Ia-β of the present invention is characterized by an 1H-NMR spectrum having peaks at about 4.92-4.85, 5.77, 5,95-5.85, 6.37, 7.80-7.42, 7.90, 8.10 and 11.65 ppm. The 1H-NMR spectrum of this compound is illustrated in
HPLC
The isomeric ratio was determined by the following HPLC method:
In accordance with the invention, the difluoro sugar derivative was dissolved in 20 to 30 volumes of solvent, then 1.5 to 4.5 equivalents of 2,4-bis-O-trimethylsilyluracil and 2 to 4.5 equivalents of Sn (II) or (IV) salts were added at room temperature. The mixture was heated at temperatures between 20° C. and 105° C., and the reaction was monitored by HPLC. When the desired conversion was observed, the mixture was cooled to room temperature, and then a saturated sodium bicarbonate solution was added. The mixture was filtered, and the filtrate was concentrated to dryness. Optionally, the crude mixture of stereoisomers was triturated in heptane/ethyl acetate and filtered to yield pure beta anomer as a white solid.
A 0.46 g sample of 1-acetyl-2-deoxy-3,5-dibenzoate-2,2-difluoro-ribofuranose (compound IV that can be obtained from commercially available material e.g. by method reported in patent application WO2005095430) was dissolved in 15 ml of dichloroethane, and 1.26 g of 2,4-bis-O-trimethylsilyluracil and 0.89 ml of SnCl4 were added at room temperature. The mixture was then heated to 83° C. for 22 hours. The mixture was then allowed to cool to room temperature, and quenched via addition of 20 ml of a saturated sodium bicarbonate solution. The suspension was filtered over a pad of Celite eluting with 100 ml of dichloromethane. The filtrate was washed with 20 ml of saturated sodium bicarbonate solution, dried over Na2SO4, and filtered and concentrated under reduced pressure to obtain an off-white foam.
The crude product, a 1:5 mixture of anomers, was triturated in a 2:1 heptane/ethyl acetate mixture, and filtered. The undissolved solid was identified (1H, 19F NMR, HPLC) as β-anomer (95% de) of the title compound.
1H NMR: δ (300 MHz, DMSO): 11.65 (1H, s); 8.10 (2H, d); 7.90 (2H, d); 7.80-7.42 (7H, m); 6.37 (1H, t); 5.95-5.85 (1H, m); 5.77 (1, d); 4.92-4.85 (3H, m)
A 4.0 g sample of 2-deoxy-3,5-dibenzoate-2,2-difluoro-ribofuranose was dissolved in 40 ml of triethylamine, and 20 ml of acetic anhydride was added slowly. The mixture was stirred at room temperature for 17 hours, and then partitioned between 100 ml of dichloromethane and 40 ml of a saturated solution of sodium bicarbonate. The organic phase was dried over Na2SO4, and concentrated under reduced pressure. Chromatography of the residue over silica gel with a heptane/ethyl acetate eluent yielded the title compound (3.78 g, 1:1.19 mixture of anomers via 1H, 19F NMR and HPLC), as a white solid.
δ (300 MHz, DMSO): 8.10-7.90 (4H, d); 7.85-7.50 (6H, d); 6.40 and 6.31 (1H, d); 6.00-5.90 (1H, m); 4.95-4.45 (3H, m); 2.18 and 2.00 (3H, s)
A 4.0 g sample of 2-deoxy-3,5-dibenzoate-2,2-difluoro-ribofuranose was dissolved in 1.92 ml of triethylamine and 50 ml of dichloromethane. Then, 1.00 ml of methanesulphonyl chloride was added slowly. The resulting mixture was stirred at room temperature for 17 hours. The mixture was then partitioned between 100 ml of dichloromethane and 40 ml of a saturated solution of sodium bicarbonate. The organic phase was dried over Na2SO4, and concentrated under reduced pressure. Chromatography of the residue over silica gel (eluent heptane/ethyl acetate) yielded 4.91 g of the title compound in a 1:1 mixture of anomers via 1H, 19F NMR and HPLC, as a white solid.
2-Deoxy-3,5-dibenzoate-2,2-difluoro-1-methylsulphonyloxy-ribofuranose (500 mg) obtained as described above was dissolved in a pressure-proof vessel with dichloroethane (10 ml).
2,4-O-Bis-trimethylsilyluracil (420 mg) and trimethylsilyltriflate (0.297 mL) were added to the solution. The mixture was heated to 83° C. for 17 h, then cooled to 25° C. and partitioned twice between dichloromethane (40 mL) and saturated sodium bicarbonate solution (20 mL).
The combined organic extracts were dried over Na2SO4 and concentrated over reduced pressure to yield the crude product as an off-white foam (540 mg); α/β anomeric ratio (1.14/1, HPLC).
This application claims the benefit of U.S. provisional application No. 60/634,376, filed Dec. 8, 2004, hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60634376 | Dec 2004 | US |
