KR20010039189A - Process for the stereoselective synthesis of nucleoside analogues - Google Patents

Abstract

PURPOSE: Provided is a method for stereoselectively synthesizing nucleoside analogues in higher yield with low costs. CONSTITUTION: The method for stereoselectively synthesizing nucleoside analogues comprises the steps of: coupling (2R,5R)-5-hydroxy- (1,3)-oxathiolan-2-carboxylic acid(1'R,2'S,5'R) menthylester with 5-fluorouracyl to produce (1'R,2'S,5'R)-menthyl- 5S-5-(5"-fluorouracyl-1"-yl)- 1,3-oxathiolan-2R-carboxylate; activating (1'R,2'S,5'R)- menthyl- 5S-5-(5"-fluorouracyl-1"-yl)- 1,3-oxathiolan-2R-carboxylate and amidating it to produce (1'R,2'S,5'R)-menthyl- 5S-5- (5"-fluorocytosine-1"-yl)- 1,3-oxathiolan-2R- carboxylate; and reducing (1'R,2'S,5'R)-menthyl- 5S-5- (5"-fluorocytosine-1"-yl)- 1,3-oxathiolan-2R- carboxylate to produce 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'yl)- 1,3-oxathiolan.

Description

Process for the stereoselective synthesis of nucleoside analogues

The present invention relates to stereoselective synthesis of nucleoside analogs, in particular 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane ((-)- To a method of synthesizing FTC).

Nucleoside analogs with antiviral activity against human immunodeficiency virus and hepatitis B virus are known. These nucleoside analogues mostly have two or more chiral centers, and largely have pairs of cis and trans optical isomers, respectively. Only one cis isomer generally shows biological activity and low cytotoxicity. Therefore, the technique of stereoselective synthesis of one such cis-nucleoside is very important.

Methods for preparing nucleoside analogs include glycosylation of purine or pyrimidine bases on 1.3-oxa thiolane derivatives using Lewis acids, as disclosed in WO 92/20669 and WO 95/29176. have. However, this method has a disadvantage in that the yield of the cis form with biological activity is low because the nucleoside analogue of the cis form and the trans form must be separated.

International Patent Publication No. WO94 / 29301 discloses 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3 by synthesizing nucleosides stereoselectively using bicyclic intermediates. A method for preparing oxathiolane ((-)-FTC) is disclosed. However, all of the above methods have the disadvantage of using Lewis acid.

A method for synthesizing nucleoside analogs without the use of Lewis acids has been published in WO95 / 29174, but this method also did not synthesize nucleoside analogs of only one cis form. Therefore, there is a problem in that the optical isomers generated together must be separated by enzymes or chromatograms.

It is therefore an object of the present invention to provide a method for preparing nucleoside analogs that are stereoselectively without the use of Lewis acids.

Another object of the present invention is to provide 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane ((-)-FTC) in high yield using inexpensive raw materials. It is to provide a method for producing.

The object of the present invention is a) 5-fluoro to (2R, 5R) -5-hydroxy- [1,3] -oxathiolane-2-carboxylic acid (1'R, 2'S, 5'R) menthyl ester Coupling the lauracil to (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylay B) (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R- After activating the carboxylate, it is then aminated to (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane- 2R-carboxylate, and c) the above (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxa To a process for producing 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane, characterized by reducing thiolane-2R-carboxylate. Is achieved.

The synthesis method of 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane of the present invention is shown in the following chemical scheme.

1) to tartaric acid (I) (1'R, 2'S, 5'R) -dimentyl ester (II) is prepared by reacting menthol with p-toluenesulfonic acid. At this time, it is effective to use a mixed solvent which can be azeotropic as a solvent. For example, a mixed solvent of one of toluene, benzene, and ethyl acetate and one of tetrahydrofuran and acetonitrile can be used, and it is particularly preferable to use a mixed solvent of toluene and tetrahydrofuran.

2) Tartaric acid (1'R, 2'S, 5'R) -dimentyl ester (II) using sodium iodide and sodium thiosulfate Made with t (III).

3) (1'R, 2'S, 5'R) -Mentylglycolate (III) is reacted with 1,4-dithiane-2,5-diol (IV) to give (2R, 5R) -5-hydride Roxy- [1,3] -oxathiolane-2-carboxylic acid (1'R, 2'S, 5'R) mentyl ester (V) is prepared.

4) 5-fluorouracil in (2R, 5R) -5-hydroxy- [1,3] -oxathiolane-2-carboxylic acid (1'R, 2'S, 5'R) mentyl ester (V) Coupling to (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylate (VII ). In this coupling reaction, a weak organic acid such as p-nitrophenol or phenol is used as a catalyst.

5) (1'R, 2'S, 5'R) -Mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylate (VII) Was activated and then aminated to give (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane-2R-carboxyl To prepare the plate (VIII). Sulfonyl chloride compounds are used for activation, and amine compounds such as ammonia, alkyl amines and dialkyl amines are used for amination.

6) (1'R, 2'S, 5'R) -Mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane-2R-carboxylate (VIII) To reduce 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane (IX).

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 Tartaric Acid (1'R, 2'S, 5'R) -Dymentyl Ester (II)

Tartaric acid (69.6 g), l-menthol (135.2 g), p-toluenesulfonic acid (35.6 g), 300 ml Tol, and 150 ml THF were added to a 1-flask (Dean-Stark-Trap equipped) and refluxed for 6 hours. In the meantime, about 22g of water was produced. The reaction solution was cooled to room temperature and then added dropwise with stirring to 400 ml of a 5% -NaHCO ₃ aqueous solution prepared in advance. The organic layer was separated and the reaction solution was washed again with 200 g of water, and then the solvent was distilled off under reduced pressure.

Example 2: (1'R, 2'S, 5'R) -mentylglyoxylate (III)

560 ml of methanol was added to the residue (II), followed by stirring for 10 minutes to dissolve it.

After adding 30 ml of water and heating (60-65 ° C.), 92 g of sodium periodate was added and refluxed for 4 hours, followed by cooling (10 ° C.). The reaction solution was filtered over celite and washed with methanol. The filtrate was distilled under reduced pressure. 550 ml of toluene and 80 ml of 5% sodium thiosulfate were added to the residue, followed by stirring until the solid was dissolved. The organic layer was separated and washed with 100 ml of brine. Basic charcoal 10g / 10g anhydrous sodium sulfate was added to the organic layer, and filtered after stirring for 1 hour.

Example 3: (2R, 5R) -5-hydroxy- [1,3] -oxathiolane-2-carboxylic acid (1'R, 2'S, 5'R) menthyl ester (V)

Add the reaction solution (III) to 1 L flask (Dean-Stark-Trap equipped), add 12 g of acetic acid, reflux (external temperature: 140 ° C), remove water, and distill the reaction solution under reduced pressure to obtain 520 residue. To ml. 60 g of 1,4-dithiane-2,5-diol (IV) was added thereto, refluxed for 2 hours, and water was removed (about 20 g). The temperature of the reaction mixture was lowered to about 80 ° C., filtered and the internal temperature was reduced to 0-5 ° C., followed by addition of hexane / TEA (1.2 L: 12 ml) over about 2 hours, followed by stirring at the temperature for about 6 hours. The solid was filtered and washed with 40 ml x 2 of toluene / hexane (1: 3). The resulting white solid was dried under reduced pressure (10 hours at 50-55 ℃). mp = 93.8 ° C. [a] ²⁵ _D = -45 (c = 0.1, MC). ¹ H NMR (DMSO-d6) 5.56 (d, 1H), 4.72 (t, 1H), 3.1 (dd, 1H), 2.8 (dd, 1H), 1.4-2.0 (m, 7H), 1.0 (m, 2H ), 0.9 (t, 6H), 0.8 (d, 3H). MS; 288 (2, M +), 271 (3), 139 (72, menthol x H ₂ O), 105 ((50), 83 (100).

Example 4 (1'R, 2'S, 5'R) -Mentyl-5S-5- (5 "-Fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylate VII)

50 g of the compound (V) and 500 ml of MC were added to 0.11 ml of methanesulfonic acid and 14.3 ml of DMF. 13.3 mL of thionyl chloride is added dropwise for about 1 hour while maintaining the above temperature, and then the temperature of the reaction vessel is raised to 10-15 ° C. and stirred for 1.5 hours. The reaction solution was distilled at atmospheric pressure for 1.5 hours (about 300 mL).

Into a 500 ml three-necked flask, 47.6 g of 5-fluorouracil distilled from distillation, 100 ml of chloroform and 5.74 g of p-nitrophenol were added thereto, and the solution was added dropwise for 30 minutes and refluxed for 5 hours. To the mixture of 50 mL of water and 12.2 mL of TEA was slowly added dropwise the reaction solution, which was stirred for 30 minutes and the organic layer was separated. After completely distilling off the solvent under reduced pressure, 75 ml of isopropyl acetate was added thereto, and the mixture was stirred at 10-15 ° C. for 5 hours and filtered. The resulting white solid was dried under reduced pressure at 55-60 ° C. for 6 hours. 55 g of (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylate were obtained ( Yield 80%). mp = 220 ° C. (dec.). [a] ²⁵ _D = -57.9 (c = 1.02, DMF). ¹ H NMR (DMSO-d 6); 8.2 (d, 1H), 6.3 (t, 1H), 4.7 (t, 1H), 3.5 (dd, 1H), 3.2 (dd, 1H), 1.4-2.0 (m, 7H), 1.0 (m, 2H) , 0.9 (t, 6H), 0.8 (d, 3H). MS; 401 (5, M + 1), 270 (26), 189 (16), 139 (30, menthol x H ₂ O), 83 (100).

Example 5: (1'R, 2'S, 5'R) -Mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane-2R-carboxylate ( VIII)

In a 100 ml flask, 5.0 g of the compound (VII), 3.45 g of anhydrous K ₂ CO ₃ , and 4.76 g of tosyl chloride (Tosyl-Cl) were added to 50 ml of acetonitrile and refluxed for 2 hours. After cooling to room temperature, ammonia was added for 1-2 hours. 50 ml of methylene chloride and 50 ml of water were added thereto, followed by stirring for 30 minutes to separate an organic layer. The solvent was distilled under reduced pressure, 10 ml of isopropyl acetate was added thereto, stirred for 30 minutes, and filtered. The resulting solid was dried under reduced pressure to obtain 4.0 g of (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane-2R -Carboxylate was obtained (yield 80%). mp = 220 ° C. (dec.). [a] ²⁵ _D = -20 (c = 0.07, MeOH). ¹ H NMR (DMSO-d 6); 8.1 (b, 1H), 6.4 (t, 1H), 5.8 (b, 1H), 4.8 (dt, 1H), 3.5 (dd, 1H), 3.1 (dd, 1H), 1.4-2.0 (m, 7H) , 1.0 (m, 2H), 0.9 (t, 6H), 0.8 (d, 3H).

Example 6 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane (IX)

4.58 g K ₂ HPO ₄ was dissolved in 50 mL of water. 3.5 g of the compound (VIII) and 35 ml of ethanol were added thereto, followed by stirring for 10 minutes. Pre-prepared mixtures of NaBH ₄ 0.7 g / 7㎖ water /0.07㎖ 25% NaOH aqueous solution was added dropwise over a period of about 2 hours. After the reaction was completed, the organic layer was separated after standing for 30 minutes. The organic layer solution was adjusted to pH 4-4.5 with 1 ml of concentrated HCl and again between pH 6.8-7.2 with 4 ml of 2N-NaOH. After distilling the organic solvent completely under reduced pressure, 20 ml of water was added thereto and extracted twice with toluene. After distilling under reduced pressure, the water layer containing (IX) was separated by flash column chromatography (MC / MeOH, 95: 5). 1.95 g of (-)-FTC were obtained (yield 95%). mp = 195 ° C., [a] ²⁵ _D = −130 (c = 1.02, MeOH). ¹ H NMR (DMSO-d 6); 8.2 (d, 1H), 7.83 (br, 1H), 7.59 (br, 1H), 6.1 (m, 1H), 5.4 (t, 1H), 5.2 (m, 1H), 3.7 (m, 2H), 3.4 (dd, 1H), 3.1 (dd, 1H). MS; 248 (1, M + 1), 130 (26, 5-fluorocytosine + 1), 118 (95), 87 (100).

Comparative Example (Compound (VIII) of Example 5 was synthesized using 5-fluorocytosine as starting material according to the method described in WO 95/29174).

In a 100 ml flask, 6.7 g of the compound (V), 67 ml of methylene chloride, 0.02 ml of methanesulfonic acid, and 2.0 ml of DMF were added and cooled to 5-10 ° C. 1.9 ml of thionyl chloride was slowly added dropwise, stirred for 1-2 hours at 10-15 ° C., and 35 ml of MC was distilled off at atmospheric pressure. Into a 100 ml three-necked flask, add 3.0 g 5-fluorocytosine, 5.3 ml hexamethyldisilazane, 0.02 ml methanesulfonic acid, 10 ml toluene, reflux until a clear solution, and cool to 50 ° C. 3.2 mL was added, and the chlorination reaction solution of (V) was slowly added dropwise to a 5-fluorocytosine solution silylated at 50 ° C, and then refluxed for 5 hours. The reaction solution was suspended in 25 mL of 1.65 mL TEA / water, stirred for 60 minutes, and then slowly added dropwise with 27 mL of hexane, followed by stirring at room temperature overnight. It was filtered, washed with isopropyl acetate and dried. 3.25 g of white solid (VIII) were obtained (yield 35%).

mp = 220 ° C. (dec.). [a] ²⁵ _D = -20 (c = 0.07, MeOH). ¹ H NMR (DMSO-d 6); 8.1 (b, 1H), 6.4 (t, 1H), 5.8 (b, 1H), 4.8 (dt, 1H), 3.5 (dd, 1H), 3.1 (dd, 1H), 1.4-2.0 (m, 7H) , 1.0 (m, 2H), 0.9 (t, 6H), 0.8 (d, 3H).

As can be seen in the description and examples of the present invention, the preparation method of the present invention does not require the separation of additional isomers in a stereoselective reaction without using Lewis acids. In addition, inexpensive 5-fluorouracil is used as a base instead of expensive 5-fluorocytosine in the coupling reaction, and the yield is much higher than that of the conventional method.

Claims (7)

a) 5-fluorouracil is coupled to (2R, 5R) -5-hydroxy- [1,3] -oxathiolane-2-carboxylic acid (1'R, 2'S, 5'R) mentyl ester Prepare (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylate, b) activating the (1'R, 2'S, 5'R) -menthyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3-oxathiolane-2R-carboxylate And then aminated to (1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane-2R-carboxylate Manufacturing the c) reducing said (1'R, 2'S, 5'R) -menthyl-5S-5- (5 "-fluorocytosine-1" -yl) -1,3-oxathiolane-2R-carboxylate Method for producing 2R-hydroxymethyl-5S- (5'-fluorocytosine-1'-yl) -1,3-oxathiolane, characterized in that consisting of The (2R, 5R) -5-hydroxy- [1,3] -oxathiolane-2-carboxylic acid (1'R, 2'S, 5'R) according to claim 1, which is a starting material of step a). Menthyl ester is i) to tartaric acid (I) (1'R, 2'S, 5'R) -dimentyl ester was prepared by reacting menthol with p-toluenesulfonic acid, followed by ii) tartaric acid (1'R, 2'S, 5'R) -dimentyl ester. (1'R, 2'S, 5'R) -Mentylglyoxylate was prepared using sodium periodide and iii) (1'R, 2'S, 5'R) -mentylglyoxylate was prepared using 1,4-dithiane. Prepared by reacting with -2,5-diol. 3. The method of claim 2, wherein the solvent of step i) is azeotropic mixed solvent. The method of claim 3, wherein the mixed solvent is a mixed solvent of one of toluene, benzene, and ethyl acetate, and one of tetrahydric furan and acetonitrile. The process of claim 1, wherein the coupling reaction of step a) uses a weak organic acid as a catalyst. 6. The method of claim 5 wherein the weak organic acid is p-nitrophenol or phenol. The process of claim 1, wherein the amination reaction of step b) is 1'R, 2'S, 5'R) -mentyl-5S-5- (5 "-fluorouracil-1" -yl) -1,3- Oxatiola-2R-carboxylate is activated with a sulfonyl chloride compound and then reacted with an amine.