HK1009451B - Process for the synthesis of nucleoside analogues - Google Patents

Description

Method for synthesizing nucleoside analogue

The present invention relates to a process for preparing antiviral 1, 3-oxathiolane (oxathiolane) nucleosides that utilizes an intramolecular glycosylation process to produce a single β -diastereomer. The invention also relates to novel intermediates obtained by this process.

1, 3-oxathiolane nucleosides have two chiral centers (at the C1 '-and C4' positions, depending on the furanose numbering system) and generally exist as pairs of α -and β -diastereoisomers, each type containing two enantiomers. The α -and β -type diastereomers will have different antiviral activities, with the β -form generally being more effective. Similarly, the enantiomeric pair of each diastereomer will have different properties.

The β -diastereomer is traditionally prepared by preparing a mixture of diastereomers followed by tedious separation by physical means such as differential solubility or chromatography. The overall yield of the beta-isomer thus obtained is generally less than 50%.

International patent application No. wo91/11186 describes a process for obtaining 1, 3-oxathiolane nucleosides by high β -diastereoselective condensation of a sugar or sugar-like moiety with a heterocyclic base in the presence of a specific Lewis acid, such as stannic chloride. The method is further exemplified in international patent application No. wo 92/14743.

In addition, diastereoselective methods for preparing nucleoside analogues involving the condensation of a sugar or analogous moiety thereof with a purine or pyrimidine base have been described in WO92/20669 and WO 95/29174.

We have developed an efficient novel process that provides a single β -diastereomer of a 1, 3-oxathiolane pyrimidine nucleoside free of α contamination. The key step involved in this synthesis is the cyclization of the appropriate heterocyclic acetaldehyde with 1, 4-dithiane-2, 5-diol to give the "5 '-defined" 1, 3-oxathiolane nucleoside analogue, followed by intramolecular glycosylation on the same face of the sugar ring to give the single (1' -defined) β -diastereomer. The method of intramolecular glycosylation of 5' -qualified furanose nucleosides is disclosed in particular in Japanese patent No.06263792-A, but the use of this method to prepare antiviral 1, 3-oxathiolane nucleosides has not been reported in the prior art. The resulting β -diastereomer can be hydrolyzed to give the corresponding cytidine analog or resolved using appropriate techniques known to those skilled in the art, e.g., esterification followed by selective enzymatic hydrolysis, removal of the undesired enantiomer and hydrolysis of the ester of the desired enantiomer. Alternatively, a substantially enantiomerically pure intermediate can be obtained by a process such as with a chiral auxiliary, from which the desired enantiomerically pure product can be produced.

In one aspect the invention provides a process for the preparation of a compound of formula (I),

wherein R is hydrogen, C_1-6Alkyl, or halogen and Y is hydroxy, amino, C_1-6Alkoxy OR OR¹Wherein R is¹Is a chiral auxiliary, which process comprises reacting a compound of the formula (II)

Wherein R and Y are as defined above, R²Represents hydrogen, C_1-6Acyl radical, C_1-6Alkyl OR halogen, with appropriate Lewis acids OR groups OR²Appropriate reagent treatment for conversion to a leaving group.

Suitable Lewis acids include, for example, tin chloride or trimethylsilyl triflate. The reaction with the Lewis acid is suitably carried out at reduced temperature (e.g.from 0 ℃ to-20 ℃) in a polar aprotic solvent, followed by treatment with a base.

If R is²Is H, can be substituted by a group OR²By reaction with halogenating agents, e.g. thionyl chloride OR oxalyl chloride, OR tosyl chloride OR mesyl chloride, the group OR can be readily reacted²Converted to a leaving group. Others will OR²Methods for conversion to a leaving group (i.e., a group that is readily substituted with a ring nitrogen atom) will be apparent to those skilled in the art.

It is to be understood that if the variable R occurs more than once in a formula, it can represent the same group at each position, or different groups.

Halogen as used herein means bromine, chlorine, fluorine or iodine, especially chlorine or fluorine, more preferably fluorine.

The term "chiral auxiliary" refers to an asymmetric molecule used to perform resolution of a racemic mixture. Such chiral auxiliary may have one chiral centre such as α -methylbenzylamine or several chiral centres such as menthol. Once the chiral auxiliary is added to the starting materialsThe purpose of the chiral auxiliary is to simplify the separation of the diastereomeric mixture. See, e.g., J Jacques et al, &Enantiomers, racemates and splitting》( Enantiomers，Racemates and Resolutions)，pp.251-369，JohnWiley & Sons，New York(1981)。

If R is¹Represents a chiral auxiliary, R¹Preferably selected from the group consisting of (d) -menthyl, (1) -menthyl, (d) -8-phenylmenthyl, (1) -8-phenylmenthyl, (+) -norephedrine and (-) -norephedrine. More preferably R¹Is a (1) -menthylgroup, or a (d) -menthylgroup, most preferably a (1) -menthylgroup.

In another aspect the invention provides a process for the preparation of a compound of formula (Ia),

wherein R and Y are as defined above, which process comprises reacting a compound of formula (IIa)

Wherein R, Y and R²With appropriate Lewis acids OR groups OR, as defined above²Appropriate reagent treatment for conversion to a leaving group.

In a further aspect the invention provides a process for the preparation of a compound of formula (II), which process comprises reacting a compound of formula (III)

Wherein R and Y are as defined above, with 1, 4-dithiane-2, 5-diol at elevated temperature (e.g. 100 ℃) in a non-polar aprotic solvent to give a compound wherein R is²A compound of formula (II) which is H. Wherein R is²Compounds of formula (II) other than H can be prepared from the corresponding hydroxy compound by derivatization using any standard methodFor example, treatment with an alkanoyl halide/base or carboxylic anhydride/base.

Reaction of a compound of formula (III) with 1, 4-dithiane-2, 5-diol to produce a compound wherein R²An isomeric mixture of a compound of formula (II) which is H. If Y is OR¹The compounds of formula (IIa) can be selectively crystallized from a mixture of diastereomers. Thus, in a further aspect the invention further provides a process for obtaining R from a mixture of isomers wherein R is H and Y is OR¹By at least partially in solution by using a compound of formula (IIa) in which R is H and Y is OR, the desired single enantiomer (IIa) is not completely inhibited by enabling isomeric interconversion¹) The crystallizing reagent treats the isomer mixture. Other compounds of formula (IIa) can be prepared in a conventional manner from those in which R is H and Y is OR¹A compound of formula (IIa).

Agents capable of effecting isomer interconversion without completely inhibiting crystallization of the trans isomer include, for example, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, and organic bases, particularly tertiary amines such as pyridine and triethylamine and Hunig's base. The preferred reagent is triethylamine.

Interconversion of isomers may be carried out in any suitable solvent or solvent mixture which does not react with the alcohol of formula (II), under concentrated conditions and at a temperature which allows crystallization of the desired isomer or isomers without causing significant decomposition of the desired isomer or isomers. Suitable solvents include, for example, aliphatic or aromatic hydrocarbons, ethers, esters and chlorinated hydrocarbons. Interconversion is preferably carried out at a temperature of about-20 ℃ to 120 ℃, more preferably between about-10 ℃ to 80 ℃, such as between about 0 ℃ to 50 ℃.

It will be understood by those skilled in the art that the solvent, temperature, amount of the tautomerization agent, particularly the tautomerization agent, are best based on the R, R present in the isomer¹And R²Is selected taking into account the properties of (a). However, when an organic base is used as the tautomerism agent, it is preferably used in an amount of generally less than 2 molar equivalents, based on the total amount of all isomers (II) present.

The interconversion of isomers can be carried out separately from the preparation of the mixture of isomers; however, the interconversion of isomers is more advantageous as this preparation proceeds.

Interconversion processes may also be used to increase the purity of the isolated isomer (IIa).

By using the tautomerization process, the isolated yield of the desired isomer (IIa) can be increased to more than 50% of the theoretical yield (based on all stereoisomers formed), typically to about 60% to 90% of the theoretical yield; but it is not excluded to obtain a yield close to 100% of the theoretical yield.

Compounds of formula (III) can be prepared by reacting compounds of formula (IV)

Wherein R (which may be the same or different) and Y are as defined above, with aqueous trifluoroacetic acid (90%) at elevated temperature.

Compounds of formula (IV) can be prepared by reacting compounds of formula (V)

Wherein R and Y are as defined above and Z is a suitable leaving group, e.g. chloro, with a compound of formula (VI)

Wherein R (which may be the same or different) are as defined above, in a polar aprotic solvent in the presence of a base at reduced temperature.

Compounds of formula (V) can be prepared by reacting compounds of formula (VII)

Wherein R and Z (which may be the same or different) are as defined above, with a suitable nucleophile, if Y in the compound of formula (V) is ethoxy, with a nucleophile EtO (NaOEt/EtOH).

The compounds of formula (VI) and (VII) may be commercial products or prepared by methods known to those skilled in the art starting from commercial sources, for example, for compounds of formula (VII) wherein R is fluoro and Z is chloro, they may be prepared by treating 5-fluorouracil with phosphorus oxychloride at elevated temperature in the presence of a base.

As mentioned above, wherein Y at position C4-is C_1-6Alkoxy OR OR¹The compounds of formula (I) can be converted to cytosine analogues (Y ═ NH) by heating with methanolic ammonia₂) Or, if racemic, can be resolved by any suitable technique known to those skilled in the art, for example by one of the enzymatic methods described in international patent No. wo 92/14743.

According to this method, the C5 '-position of the racemic β -diastereomer is esterified, for example with butyric anhydride, and the racemic ester is treated with a suitable enzyme, for example porcine liver esterase, to preferentially hydrolyze the "unwanted" enantiomer back to the water-soluble 5' -OH compound (IX) and separate it from the desired (unhydrolyzed) enantiomer (X). The latter is converted by heating with methanol with ammonia into 4-NH of the desired enantiomeric configuration₂5' -OH compound.

The process of the invention is particularly useful for the preparation of (2R, 5S) -5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine, (2R, 5S) -1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine, (+ -) -cis-5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine and (. + -) -cis-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine.

The invention further provides novel compounds of formulae (IV), (III), (II) and (I) (which later include the racemate (2S, 5R) -enantiomer (IX), the esterified racemate (VIII) and esterification to give the (2R, 5S) -enantiomer (X)). Specific intermediate compounds for the preparation of (2R, 5S) -5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine, (2R, 5S) -1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine, (+ -) -cis-5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine and (+ -) -cis-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine include:

2- (2, 2-Dimethoxyethoxy) -4-ethoxy-5-fluoropyrimidine

2- (2, 2-Dimethoxyethoxy) -4-ethoxypyrimidine

2- [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] acetaldehyde

2- [ (4-ethoxy-2-pyrimidinyl) oxy ] acetaldehyde

2- { [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-ol

2- { [ (4-ethoxy-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-ol

2- { [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-yl acetate

2- { [ (4-ethoxy-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-yl acetate

(2S^*，5R^*) -4-ethoxy-5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

(2S^*，5R^*) -4-ethoxy-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

(2S^*，5R^*) -4-ethoxy-5-fluoro-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

(2S^*，5R^*) -4-ethoxy-1- [2- (butyryloxymethyl) -1, 3-oxathiolane-5-yl]Pyrimidin-2-ones

(2S, 5R) -4-ethoxy-5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] pyrimidin-2-one

(2S, 5R) -4-ethoxy-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] pyrimidin-2-one

(2R, 5S) -4-ethoxy-5-fluoro-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl ] pyrimidin-2-one

(2R, 5S) -4-ethoxy-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl ] pyrimidin-2-one.

The following examples of the process according to the invention are intended only to illustrate the invention and do not limit the scope of the invention in any way. In all of the cases where the first and second substrates are to be treated,¹h NMR and C, H, N elemental analysis results were consistent with the recommended structure.

Example 1

Preparation of (2R, 5S) -5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine

(a)2, 4-dichloro-5-fluoropyrimidine

To a suspension of 5-fluorouracil (Aldrich 8.00g, 61.5mmol) in phosphoryl chloride (25.0mL, 41.12g, 268mmol) was added N, N-diethylaniline (12.6mL, 11.81g, 80mmol) and the mixture was heated at 100 ℃ for 1.5 h. Evaporate the solvent in vacuo and pour the residue into cold H₂O/Et₂O (400mL, 1: 1). With Et₂O extract the aqueous phase and dry the combined organic phases (Na)₂5O₄) And evaporated (suction pump, 35 ℃) to give the desired product (10.2g, 99%) as a yellowish solid: mp34-36 deg.C (35-36 deg.C).

(b) 2-chloro-4-ethoxy-5-fluoropyrimidines

To a solution of the product of step (a) (10.0g, 59.9mmol) in absolute EtOH (40mL) at 0 ℃ under nitrogen was added 1M NaOEt/EtOH (61mL, 61mmol) and the mixture was stirred for 1 h. Vacuum evaporation of solventAnd the remainder is taken up in H₂O and Et₂And (4) distributing among the O. With Et₂The aqueous phase was O extracted and the combined organic phases were washed with brine and dried (Na)₂SO₄) And evaporated (suction pump, 35 ℃) to give the desired product (8.74g, 83%) as a yellowish solid: mp30-32 deg.C (literature 31-32 deg.C).

¹H NMR(CDCl₃): δ 1.46(t, J ═ 7.0Hz, 3H), 4.53 (quartet, J ═ 7Hz, 2H), 8.17(d, J ═ 2.1Hz, 1H); MS M/z179(M +3, 17%), 177(M +1, 50%), 149 (100%).

C₆H₆ClFN₂Elemental analysis of O:

C H N

theoretical value 40.813.4215.86

Found value 40.903.4515.81

(c)2- (2, 2-Dimethylethoxy) -4-ethoxy-5-fluoropyrimidine

To a suspension of 60% NaH/mineral oil (2.88g, 72.2mmol) in anhydrous DMF (70mL) at 0 deg.C under nitrogen was slowly added ethanol dimethyl acetal (Lancaster, 6.13g, 57.7 mmol). The mixture was stirred at room temperature for 1 hour and then transferred over 15 minutes to a-55 deg.C solution of the product of step (b) (8.5g, 48.1mmol) in anhydrous DMF (70 mL). The mixture was allowed to warm to-20 ℃ over a 2 hour period and then neutralized with AcOH. The solvent was evaporated in vacuo and the residue was taken up in H₂O and CH₂Cl₂Are distributed among the devices. By CH₂Cl₂The aqueous phase was extracted and dried (Na)₂SO₄) The combined organic phases were evaporated. The residue was purified by flash chromatography (EtOAc/hexane, 1: 5) to give the desired product (9.75g, 82%) as an oil.

¹H NMR(CDCl₃): δ 1.42(t, J ═ 7.0Hz, 3H), 3.43(s, 6H), 4.32(d, J ═ 5.2Hz, 2H), 4.50 (quartet, J ═ 7.0Hz, 2H), 4.75(t, J ═ 5.2Hz, 1H), 8.03(d, J ═ 2H), and so on.4Hz，1H)；MS m/z 215(M-OCH₃，100％).

C₁₀H₁₅FN₂O₄Elemental analysis of (2):

C H N

theoretical value 48.786.1411.38

Found value 48.846.0611.36

(d)2- [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] acetaldehyde

The product of step (c) (6.0g, 24.4mmol) and 90% TFA/H₂A mixture of O (50mL) was heated at 50 ℃ for 2.5 hours. The solvent was evaporated in vacuo and the residue taken up in CHCl₃And saturated NaHCO₃/H₂And (4) distributing among the O. With CHCl₃(. times.2) extraction of the aqueous phase, drying (Na)₂SO₄) The combined extracts were evaporated to give the desired product (4.82g, 99%) as a colourless oil which was used in the next reaction without further purification. Purification by flash chromatography (EtOAc/hexane, 1: 2) afforded the analytically pure material as a colorless oil.

¹H NMR(CDCl₃): δ 1.43(t, J ═ 7.0Hz, 3H), 4.40 (quartet, J ═ 7.0Hz, 2H), 4.81(s, 2H), 8.03(d, J ═ 1.8Hz, 1H), 9.74(s, 1H); MS M/z201(M +1, 100%).

C₈H₉FN₂O₃·0.25H₂Elemental analysis of O:

C H N

theoretical value 46.954.6813.69

Found value 46.814.6113.64

(e)2- { [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-ol

Step (d)A mixture of the product of (4.6g, 23.0mmol) and 1, 4-dithiane-2, 5-diol (Aldrich, 1.92g, 12.65mmol) in dry toluene (90mL) was heated at 100 ℃ for 2 hours. The mixture was filtered, the filtrate was concentrated and evaporated in vacuo to give the desired product (6.27g, 99%) as a waxy pale yellow solid which was used in the next reaction (using no further purification)¹H NMR spectroscopy analysis, diastereomer ratio was about 1: 1). Purification by flash chromatography (EtOAc/hexanes, 1: 2) afforded analytically pure material as a white solid.¹HNMR(CDCl₃): δ 1.41(t, J ═ 7.0Hz, 3H), 2.42(br s, 1H), 3.10(d, J ═ 11.0Hz, 1H), 3.20(dd, J ═ 11.0, 3.5Hz, 1H), 4.40(dd, J ═ 12.0, 3.5Hz, 1H), 4.43 (quartet, J ═ 7.0Hz, 2H), 4.77(dd, J ═ 12.0, 7.0Hz, 1H), 5.70(dd, J ═ 7.0, 3.5Hz, 2H), 5.92(d, J ═ 3.5Hz, 1H), 8.04(d, J ═ 2.5Hz, 1H);

shows a similar signal for the other diastereomer; MS M/z201 (M-C)₂H₃OS，100％)。C₁₀H₁₃FN₂O₄Elemental analysis of S:

C H N S

theoretical value 43.474.7410.1411.61

Found value 43.564.7810.0411.66

(f)2- { [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-yl acetate

To the product of step (e) (1.0g, 3.62mmol) and pyridine (0.8mL, 0.78g, 9.88mmol) in CH at 0 deg.C₂Cl₂To the solution (12mL) was added AcCl (0.35mL, 0.37g, 4.7 mmol). After 1 hour at room temperature saturated NaHCO was added₃/H₂O, aqueous phase with CHCl₃And (4) extracting. The combined organic phases were washed with brine and dried (Na)₂SO₄) Evaporated and dried in vacuo to give the desired product (1.13g, 99%) as a yellow oil which was used in the next reaction without further purification (fractionated on a 1HNMR spectrometer)The diastereomer ratio was about 2: 1). Purification by flash chromatography (acetone/CH)₂Cl₂1: 24) gave the analytically pure substance as a colorless oil.

¹H NMR(CDCl₃)：δ1.42(t，J＝7.0Hz，3H)，2.07(s，3H)，3.15(d，J＝11.5Hz，1H)，3.38(dd，J＝11.5，4.0Hz，1H)，4.40-4.60(m，4H)，5.73(m，1H)，6.70(d，J＝4.0Hz，1H)，8.03(d，J＝2.5Hz，1H)；

Similar signals were shown for a smaller portion of diastereomers; MS M/z259(M-OAc, 9%), 159 (100%). C₁₂H₁₅FN₂O₅Elemental analysis of S:

C H N S

theoretical value 45.284.758.8010.07

Found value 45.354.768.8310.11

(g)(2S^*，5R^*) -4-ethoxy-5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

To the product of step (f) (0.21g, 0.66mmol) and 4 angstrom molecular sieves (0.3g) anhydrous CH at-20 deg.C under nitrogen₃CN (20mL) was added slowly to a mixture of trimethylsilyl triflate (Aldrich, 0.14mL, 0.16g, 0.73 mmol). Stirring at-20 deg.C for 2 hr, adding 1M NaOH/H₂O (2.0mL, 2.0 mmol). The mixture was neutralized with AcOH after 2 hours at 0 ℃. The solvent was evaporated in vacuo and the residue was purified by flash chromatography (EtOAc/hexanes, 9: 1) to give the desired product (0.11g, 60%) as a white solid. mp162-164 deg.C;¹H NMR(DMSO-d₆): δ 1.39(t, J ═ 7.0Hz, 3H), 3.29(dd, J ═ 12.0, 2.7Hz, 1H), 3.60(dd, J ═ 12.0, 5.4Hz, 1H), 3.82(ddd, J ═ 12.5, 5.4, 3.5Hz, 1H), 3.95(ddd, J ═ 12.5, 5.4, 3.5Hz, 1H), 4.45 (quartet J ═ 7.0Hz, 2H), 5.31(t, J ═ 3.5Hz, 1H), 5.63(t, J ═ 5.4Hz, 1H), 6.20(m, 1H), 8.74 (J ═ 7.0Hz, 2H), 5.31(t, J ═ 3.5Hz, 1H), 6.20(m, 1H), 8.74 (J ═ 1H)(d，J＝6.7Hz，1H)；MS m/z 277(M+1，4％)，159(100％).

C₁₀H₁₃FN₂O₄Elemental analysis of S:

C H N S

theoretical value 43.474.7410.1411.61

Found value 43.544.7610.1811.52

(h)(2S^*，5R^*) -4-ethoxy-5-fluoro-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

To a solution of the product of step (g) (90mg) in pyridine (0.2mL) was added butyric anhydride (1.0mL), and the resulting mixture was stirred at room temperature for 18 hours. Adding ice water, and adding 1N HCl/H₂O the aqueous solution was adjusted to pH2 and CHCl was used₃Extraction was carried out three times. The combined organic phases were washed with saturated NaHCO₃/H₂Washed with brine and dried (Na)₂SO₄) And concentrated in vacuo. The resulting oil was dried under vacuum at 50 ℃ under a stream of nitrogen for 18 hours to give the desired product (100mg) as a colorless solid.¹H NMR(CDCl₃): δ 0.99(t, 3H), 1.42(t, 3H), 1.70 (hexameric peak, 2H), 2.42(t, 2H), 3.23(d, 1H), 3.60(dd, 1H), 4.45(dd, 1H), 4.50 (quarter peak, 2H), 4.65(dd, 1H), 5.40(m, 1H), 6.30(m, 1H), 8.15(d, 1H); MS M/z347(M +1, 25%), 159 (100%).

(i) (2R, 5S) -4-ethoxy-5-fluoro-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl ] pyrimidin-2-one

20% CH of product (10mg) in step (h)₃PLE (pig liver esterase, 1.5. mu.L, Sigma) was added to a CN/buffer (3.0mL, 0.05M, pH8.0, phosphate) solution, and the mixture was stirred at room temperature for 24 hours. The aqueous solution was extracted twice with hexane and dried (Na)₂SO₄) The combined extracts were concentrated in vacuo. HPLC (Chiral) of the organic extractsPack AS; EtOH; 1.5ml/min) analysis indicated the presence of the single enantiomer butyrate (4 mg). Enantiomeric alcohols can be detected in the aqueous phase. Ester:¹H NMR(CDCl₃): δ 0.97(t, J ═ 7.4Hz, 3H), 1.42(t, J ═ 7.0Hz, 3H), 1.67 (hexameric, J ═ 7.4Hz, 2H), 2.40(t, J ═ 7.4Hz, 2H), 3.23(d, J ═ 12.8Hz, 1H), 3.60(dd, J ═ 12.8, 5.3Hz, 1H), 4.46(dd, J ═ 12.6, 2.5Hz, 1H), 4.52 (quarter J ═ 7.0Hz, 2H), 4.65(dd, J ═ 12.6, 4.0Hz, 1H), 5.37(m, 1H), 6.29(m, 1H), 8.12(d, J ═ 6, 1H).

(j) (2R, 5S) -5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine

(ii) reaction of the ester obtained in step (i) (4mg) with NH₃the/MeOH (2mL) solution was charged into a teflon (teflon) lined steel cylinder, sealed and heated at 70 deg.C for 18 hours. The solvent was evaporated in vacuo to give the desired product (2 mg). The performance of the HPLC is improved by carrying out the HPLC,¹h NMR and MS are consistent with the properties of these authentic samples.

Example 2

Preparation of (2R, 5S) -1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine

(a) 2-chloro-4-ethoxypyrimidine

To a solution of 2, 4-dichloropyrimidine (Aldrich 10.0g, 67.12mmol) in absolute EtOH (120mL) was slowly (2 h) forced in 1M NaOEt/EtOH (68mL, 68mmol) at-3 ℃ under nitrogen, and the resulting mixture was stirred for 1 h. Evaporate the solvent in vacuo and leave the residue in H₂O and Et₂And (4) distributing among the O. With Et₂The aqueous phase was extracted and the combined organic phases were washed with brine and dried (Na)₂SO₄) And evaporated (suction pump, 35 ℃). The resulting residue was filtered and washed with petroleum ether to give the desired product (8.05g, 75%) as a yellowish solid: mp30-31 deg.C (document 35 deg.C).¹H NMR(CDCl₃): δ 1.40(t, J ═ 7.2Hz, 3H), 4.44 (quartet, J ═ 7.2Hz, 2H), 6.62(d, J ═ 5.7Hz, 1H), 8.27(d, J ═ 5.7Hz, 1H); MS M/z 161(M +3, 34%), 159(M +1, 100%). C₆H₇ClN₂Elemental analysis of O:

C H N Cl

theoretical value 45.444.4517.6622.36

Found value 45.324.4117.6022.43

(b)2- (2, 2-Dimethylethoxy) -4-ethoxypyrimidine

To a suspension of 60% NaH/mineral oil (2.55g, 63.96mmol) in anhydrous DMF (70mL) at 0 deg.C under nitrogen was slowly added ethanol aldehyde dimethyl acetal (Aldrich, 5.65g, 53.3 mmol). The mixture was stirred at room temperature for 1 hour and then added over 15 minutes to a-55 deg.C solution of the product of step (a) (8.05g, 53.3mmol) in anhydrous DMF (70 mL). The mixture was allowed to warm to-20 ℃ over a 2 hour period and then neutralized with AcOH. The solvent was evaporated in vacuo and the residue was taken up in H₂O and CH₂Cl₂Are distributed among the devices. By CH₂Cl₂The aqueous phase was extracted and dried (Na)₂SO₄) The combined organic phases were evaporated in vacuo. The residue was purified by flash chromatography (EtOAc/hexane, 1: 4) to give the desired product (7.92g, 69%) as a colorless oil.¹H NMR(CDCl₃)：δ1.37(t，J＝7.0Hz，3H)，3.44(s，6H)，4.36-4.43(m，4H)，4.78(t，J＝5.0Hz，1H)，6.34(d，J＝6.0Hz，1H)，8.15(d，J＝6.0Hz，1H)；MS m/z 229(M＝1，13％)，197(100％).

C₁₀H₁₆N₂O₄Elemental analysis of (2):

C H N

theoretical value 52.627.0712.27

Found value 52.457.0112.26

(c)2- [ (4-ethoxy-2-pyrimidinyl) oxy ] acetaldehyde

The product of step (b) (6.0g, 24.4mmol) and 90% TFA/H₂A mixture of O (50mL) was heated at 50 ℃ for 2.5 hours. The solvent was evaporated in vacuo and the residue taken up in CHCl₃And saturated NaHCO₃/H₂And (4) distributing among the O. With CHCl₃(. times.2) extraction of the aqueous phase, drying (Na)₂SO₄) The combined extracts were evaporated in vacuo to give the desired product (4.48g, 94%) as a colourless oil.

¹H NMR(CDCl₃): δ 1.38(t, J ═ 7.0Hz, 3H), 4.37 (quartet J ═ 7.0Hz, 2H), 4.80(s, 2H), 6.40(d, J ═ 6.0Hz, 1H), 8.15(d, J ═ 6.0Hz, 1H), 9.74(s, 1H); MS M/z 183(M +1, 100%).

C₈H₁₀N₂O₃·0.25H₂Elemental analysis of O:

C H N

theoretical value 51.475.5715.01

Found value 51.385.6914.76

(d)2- { [ (4-ethoxy-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-ol

A mixture of the product of step (c) (4.0g, 22.0mmol) and 1, 4-dithiane-2, 5-diol (Aldrich, 1.67g, 11.0mmol) in dry toluene (80mL) was heated at 100 ℃ for 2 hours. The mixture was filtered, the filtrate concentrated and evaporated in vacuo to give the desired product (6.27g, 99%) as a waxy pale yellow oil which was used in the next reaction without further purification¹H NMR spectroscopy analysis, diastereomer ratio was about 1: 1). Purification by flash chromatography (EtOAc/hexanes, 2: 3) afforded the analytically pure material as a colorless oil.¹H NMR(CDCl₃)：δ1.37(t，J＝7.0Hz，3H)，3.07(d，J＝11.0Hz，1H)，3.18(d，J＝2.3Hz，1H)，3.26(dm，J＝1 1.0Hz，1H)，4.38-4.58(m，3H)，4.85(dd，J＝12.0，6.0Hz，1H)，5.72(dd，J＝6.0，4.5Hz，1H)，5.92(m，1H)，6.39(d，J＝6.0Hz，1H)，8.15(d，J＝6.0Hz，1H)；

Shows a similar signal for the other diastereomer; MSm/z197 (M-C)₂H₅O，41％)，133(100％)。C₁₀H₁₄N₂O₄Elemental analysis of S:

C H N S

theoretical value 46.505.4610.8512.41

Found value 46.405.4410.7912.49

(e)2- { [ (4-ethoxy-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-yl acetate

The product of step (d) (1.0g, 3.9mmol), pyridine (0.7mL, 0.68g, 8.65mmol) and Ac₂A mixture of O (2.0ml, 2.26g, 21.2mmol) was stirred at room temperature for 1.5 hours. After the addition of ice water, the mixture was stirred for 15 minutes. The mixture was extracted with EtOAc and the combined extracts were extracted with saturated NaHCO₃/H₂O washing and drying (Na)₂SO₄) Evaporated and dried in vacuo to give the desired product (1.15g, 99%) as an orange oil which was used in the next reaction without further purification¹H NMR spectroscopy analysis, diastereomer ratio was about 2: 1).¹H NMR(CDCl₃)：δ1.40(t，3H)，2.05(s，3H)，3.08(d，1H)，3.27(dd，1H)，4.40-4.70(m，4H)，5.79(m，1H)，6.38(d，1H)，6.75(d，1H)，8.18(d，1H)；

Similar signals were shown for a smaller portion of diastereomers; MS M/z 241(M-OAc, 4%), 141 (100%). C₁₂H₁₆N₂O₅Elemental analysis of S:

C H N S

theoretical value 47.995.379.3310.68

Found value 47.885.439.2210.60

(f)(2S^*，5R^*) -4-ethoxy-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

To the product of step (e) (0.20g, 0.66mmol) anhydrous CH at 0 deg.C under nitrogen₃CN (12mL) was added slowly to a solution of tin chloride (Aldrich, 0.12mL, 0.27g, 1.05 mmol). Stirring at 0 deg.C for 2 hr, adding 1M NaOH/H₂O (5.5mL, 5.5 mmol). The mixture was neutralized with AcOH after 1 hour at 0 ℃. The solvent was evaporated in vacuo and the residue taken up in CHCl₃And water. Aqueous phase with CHCl₃Extracted twice and dried (Na)₂SO₄) The combined extracts were concentrated in vacuo. The residue was purified by flash chromatography (EtOAc/hexanes, 2: 1 then EtOAc) to afford the desired product (0.10g, 60%) as a white solid. mp117-118 ℃;¹H NMR(CDCl₃): δ 1.26(t, J ═ 7.0Hz, 3H), 3.15(dd, J ═ 12.0, 3.5Hz, 1H), 3.51(dd, J ═ 12.0, 5.5Hz, 1H), 3.71-3.84(m, 2H), 4.26 (quartet J ═ 7.0Hz, 2H), 5.22(t, J ═ 4.0Hz, 1H), 5.40(t, J ═ 6.0Hz, 1H), 6.0(d, J ═ 7.4Hz, 1H), 6.18(dd, J ═ 5.5, 3.5Hz, 1H), 8.25(d, J ═ 7.4Hz, 1H); MS M/z259(M +1, 4%), 141 (100%).

C₁₀H₁₄N₂O₄Elemental analysis of S:

C H N S

theoretical value 46.505.4610.8512.41

Found value 46.585.4910.8412.34

(g)(2S^*，5R^*) -4-ethoxy-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-ones

To a solution of the product of step (f) (0.30g, 1.16mmol) in pyridine (0.19mL, 0.18g, 2.32mmol) was added butyric anhydride (0.37mL, 0.36g, 2.32mmol), and the mixture was stirredThe mixture was stirred at room temperature for 2 hours. Adding NaHCO₃/H₂O, 1h later the mixture was extracted twice with EtOAc. Drying (Na)₂SO₄) The combined extracts were concentrated in vacuo and purified by flash chromatography (EtOAc/hexanes, 1: 1) to give the desired product (0.21g, 55%) as a yellowish solid. mp59-61 ℃;¹H NMR(CDCl₃): δ 0.96(t, J ═ 7.4Hz, 3H), 1.36(t, J ═ 7.1Hz, 3H), 1.68 (hexameric, J ═ 7.4Hz, 2H), 1.80(br s, 1H), 2.36(t, J ═ 7.4Hz, 2H), 3.14(dd, J ═ 12.3, 3.5Hz, 1H), 3.59(dd, J ═ 12.3, 5.2Hz, 1H), 4.40(m, 3H), 4.59(dd, J ═ 12.3, 5.2Hz, 1H), 5.36(dd, J ═ 5.2, 3.4Hz, 1H), 5.89(d, J ═ 7.3Hz, 1H), 6.34(dd, J ═ 5.2, 3.91, 7.3Hz, 1H), 7.91.3H, 7.3H, 1H); MS M/z 329(M ═ 1, 11%), 141 (100%).

C₁₄H₂₀N₂O₅Elemental analysis of S:

C H N S

theoretical value 51.216.148.539.76

Found value 51.086.158.399.69

(h) (2R, 5S) -4-ethoxy-1- [2- (butyryloxymethyl) -1, 3-oxathiolan-5-yl ] pyrimidin-2-one

20% CH of product (10mg) in step (g)₃PLE (pig liver esterase, 1.5. mu.L, Sigma) was added to a CN/buffer (3.0mL, 0.05M, pH8.0, phosphate) solution, and the mixture was stirred at room temperature for 24 hours. The aqueous solution was extracted twice with hexane and dried (Na)₂SO₄) The combined extracts were concentrated in vacuo to give the desired product. HPLC analysis of the organic phase indicated the presence of the single enantiomer butyrate. Enantiomeric alcohols can be detected in the aqueous phase.

(i) (2R, 5S) -1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl ] cytosine

Will be described in detail with reference to the following steps (h)NH of the resulting ester (4mg)₃the/MeOH (2mL) solution was charged into a teflon (teflon) lined steel cylinder, sealed and heated at 70 deg.C for 18 hours. The solvent was evaporated in vacuo to afford the desired product. The performance of the HPLC is improved by carrying out the HPLC,¹h NMR and MS are consistent with the properties of these authentic samples.

Example 3

(2S^*，5R^*) -5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Cytosine

The product of step (g) (10mg) was taken up in NH₃A solution of/MeOH (2mL MeOH saturated with NH3 gas at 0 ℃ for 45 minutes) was placed in a teflon (teflon) -lined steel cylinder, sealed and heated at 70 ℃ for 18 hours. The solvent was evaporated in vacuo and acetone was added to give the desired product (8.8mg, 99%) as a white solid. mp195-196 ℃;¹H NMR(DMSO-d₆)：δ3.10(dd，J＝12.0，4.2Hz，1H)，3.40(dd，J＝12.0，5.3Hz，1H)，3.70(ddd，J＝12.0，5.5，3.5Hz，1H)，3.77(ddd，J＝12.0，5.5，3.5Hz，1H)，5.16(t，J＝3.5Hz，1H)，5.39(t，J＝5.5Hz，1H)，6.11(m，1H)，7.56(br s，1H)，7.80(br s，1H)，8.17(d，J＝7.4Hz，1H)；MS m/z 248(M+1，34％)，130(100％).

C₈H₁₀FN₃O₃elemental analysis of S:

C H N S

theoretical value 38.864.0817.0012.97

Found value 38.974.0516.9612.95

Example 4

(2S^*，5R^*) -1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Cytosine

Will be (2S)^*，5R^*) -4-ethoxy-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-one (0.21g) in ammonia/methanol (at 0 deg.C)8mL of methanol saturated with ammonia gas for 45 minutes) was put into a steel cylinder with a Teflon (teflon) liner, sealed and heated at 70 ℃ for 18 hours. The solvent was evaporated in vacuo and the residue was purified by flash chromatography to give the desired product (0.16g, 89%) as a white solid. mp184-185 ℃;¹H NMR(DMSO-d₆)：δ3.00(dd，J＝11.8，5.0Hz，1H)，3.38(dd，J＝11.8，5.5Hz，1H)，3.63-3.80(m，2H)，5.15(t，J＝4.5Hz，1H)，5.30(t，J＝6.0Hz，1H)，5.70(d，J＝7.3Hz，1H)；6.18(t，J＝5.0Hz，1H)，7.20(brd，2H，NH₂)，7.79(d，J＝7.3Hz，1H)；MS m/z 229.8(M+1，4％)，112(100％).

C₈H₁₁N₃O₃elemental analysis of S:

C H N S

theoretical value 41.914.8418.3313.99

Found value 41.974.8318.2413.93

Claims (12)

1. A process for the preparation of a compound of formula (I),

wherein

R is hydrogen, C_1-6Alkyl, or halogen and

y is hydroxy, amino, C_1-6Alkoxy OR OR¹Wherein R is¹Is a chiral auxiliary; the method comprises reacting a compound of formula (II)

Wherein R and Y are as defined above, R²Represents hydrogen, C_1-6Acyl radical, C_1-6An alkyl group or a halogen, in which,

with appropriate Lewis acids OR groups OR²Appropriate reagent treatment for conversion to a leaving group.

2. The method according to claim 1, wherein the compound of formula (I) is a compound of formula (Ia):

wherein

R is hydrogen, C_1-6Alkyl, or halogen and

y is hydroxy, amino, C_1-6Alkoxy OR OR¹Wherein R is¹Is a chiral auxiliary, which process comprises reacting a compound of the formula (IIa)

Wherein R, Y and R²As defined above, the above-mentioned,

with appropriate Lewis acids OR groups OR²Appropriate reagent treatment for conversion to a leaving group.

3. A process according to claim 1 or 2 wherein the lewis acid is tin chloride or trimethylsilyl triflate.

4. A process according to claim 3, wherein the Lewis acid is tin chloride and the treatment is carried out at reduced temperature in a polar aprotic solvent.

5. A process according to claim 1, 3 or 4, wherein the compound of formula (II) is prepared by reacting a compound of formula (III)

Wherein

R is hydrogen, C_1-6Alkyl, or halogen and

y is hydroxy, amino, C_1-6Alkoxy OR OR¹Wherein R is¹Is a chiral auxiliary, is reacted with 1, 4-dithiane-2, 5-diol and is prepared, if necessary or desired, by derivatization.

6. A process according to claim 5, wherein the reaction with 1, 4-dithiane-2, 5-diol is carried out at elevated temperature and in a non-polar aprotic solvent.

7. The process according to claim 6, wherein the reaction with 1, 4-dithiane-2, 5-diol is carried out in anhydrous toluene and at a temperature of about 100 ℃.

8. The method according to any one of claims 2 to 4, wherein in the compound of formula (IIa), R is H; y is OR¹The compound of formula (IIa) is obtained from a mixture of isomers by treating the mixture of isomers, at least partially in solution, with a reagent capable of effecting isomeric interconversion without complete inhibition of crystallization of the desired single enantiomer (IIa).

9. A compound:

2- { [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-ol,

2- { [ (4-ethoxy-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-ol,

2- { [ (4-ethoxy-5-fluoro-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-yl acetate, or

2- { [ (4-ethoxy-2-pyrimidinyl) oxy ] methyl } -1, 3-oxathiolan-5-yl acetate.

10. A compound of the formula (IIa),

wherein R represents hydrogen, C_1-6Alkyl, or halogen, R²Represents hydrogen, C_1-6Acyl radical, C_1-6Alkyl OR halogen, and Y represents OR¹Wherein R is¹Represents (d) -menthyl, (1) -menthyl, (d) -8-phenylmenthyl, (1) -8-phenylmenthyl, (+) -norephedrine or (-) -norephedrine.

11. The compound of claim 10, wherein R¹Represents (1) -menthyl.

12. A compound:

(2S^*，5R^*) -4-ethoxy-5-fluoro-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]Pyrimidin-2-one, or

(2S^*，5R^*) -4-ethoxy-1- [2- (hydroxymethyl) -1, 3-oxathiolan-5-yl]A pyrimidin-2-one.