JP6287528B2 - Method for producing optically active 3,3-difluorolactic acid derivative - Google Patents

Description

  The present invention relates to a method for producing an optically active 3,3-difluorolactic acid derivative that is important as an intermediate for medicines and agricultural chemicals.

  Optically active 3,3-difluorolactic acid and its derivatives are important compounds as various pharmaceutical and agrochemical intermediates. So far, as a method for producing this compound, a method of performing an asymmetric hydrolysis reaction with an enzyme using a furanol having a difluoromethyl group as a substrate and obtaining an optically active substance, followed by an oxidation reaction (Non-patent Document 1) or Discloses a method of optical resolution by recrystallization of a diastereomeric salt composed of racemic 3,3-difluorolactic acid and an optically active amine (Non-patent Document 2).

Tetrahedron Asymmetry, 4, p. 889-892 (1993) CrystEngComm, 8, p. 320-326 (2006)

  In synthesizing various optically active 3,3-difluorolactic acid derivatives, the optically active 3,3-difluorolactic acid represented by the formula [4]

(* Represents an asymmetric atom. The same applies hereinafter.)
Is one of the key compounds, and it is important to produce this compound.

  However, there are few examples of synthesis of optically active 3,3-difluorolactic acid, and all are excellent synthesis methods at the laboratory level, but problems still remain in the synthesis on a large scale. In the method of Non-Patent Document 1, the hydrolysis reaction by an enzyme is performed using furanol having a difluoromethyl group as a raw material, so that the unreacted raw material can be obtained with a high optical purity of 98% ee or more at a conversion rate of 47%. Although a product can be obtained and an optically active form can be obtained with a high yield, many steps are required for synthesizing the raw material furanol, and the raw material and the product are isolated after the enzymatic reaction. However, since it is necessary to carry out an oxidation reaction for each, it is complicated as a whole and cannot be said to be an economical method. In Non-patent Document 2, optically active 3,3-difluorolactic acid is easily obtained by reacting racemic 3,3-difluorolactic acid with an optically active amine to form a diastereomeric salt and recrystallization. However, in order to obtain 3,3-difluorolactic acid having a high optical purity required for a pharmaceutical and agrochemical intermediate, recrystallization must be repeated.

  On the other hand, as a method for producing the optically active 3,3-difluorolactic acid represented by the formula [4], a “racemic or low optical purity formula [5a] corresponding to the“ chemical species immediately before being subjected to hydrolysis ”. Or a compound represented by the formula [5b] "

(In the formula, R ¹ is a linear or branched acyl group having 2 to 11 carbon atoms which may have a substituent, and R ² is a linear or branched chain having 1 to 10 carbon atoms which may have a substituent. A branched alkyl group, aryl group, or cycloalkyl group is shown.)
As a raw material, a hydrolase is brought into contact with this to selectively hydrolyze one of the optical isomers (R isomer, S isomer) of each chemical species and to lead to an optically active target product. Hydrolysis reaction is conceivable.

  However, when the present inventors tried a hydrolysis reaction using the compound of the formula [5a] as a reaction raw material, it was found that although the hydrolysis proceeds, the stereoselectivity of the enzyme is low (see “Comparison” described later). See Example). When the stereoselectivity of the enzyme is low, the optically active 3,3-difluorolactic acid represented by the formula [4] produced by hydrolyzing the compound of the formula [5a] has a low optical purity.

  On the other hand, as the hydrolysis reaction proceeds, among the compounds represented by the formula [5a], the optical isomer that does not react with the enzyme remains in the system as the compound of the formula [3a]. When this compound is taken out and subjected to further hydrolysis, the optically active 3,3-difluorolactic acid represented by the formula [4] (as opposed to that obtained by hydrolysis of the compound of the formula [5a] above) Having the same optical isomerism). However, as described above, since the stereoselectivity of the enzyme in this reaction is low, when the reaction is allowed to proceed excessively in order to obtain a compound of formula [3a] with high optical purity, the yield of the compound of formula [3a] Becomes extremely low. That is, there is a problem that it is difficult to obtain the target product in a practical yield depending on the method of obtaining the optically active 3,3-difluorolactic acid represented by the formula [4] by hydrolyzing the compound of the formula [3a]. (This is sometimes referred to as “comparative invention”).

On the other hand, the compound [5b] has a problem in isolating the target product because the unreacted raw material after hydrolysis and the product cannot adopt an efficient separation method such as extraction operation. .
That is, there has been a demand for a method for producing optically active 3,3-difluorolactic acid that can be efficiently isolated and efficiently isolated by an enzymatic asymmetric hydrolysis method.

  The inventor has intensively studied to solve the above problems. As a result, the “racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester” represented by the formula [1] is used as a raw material, and this substance is subjected to asymmetric hydrolysis by an enzyme. It was found that can be solved.

  That is, the inventors have obtained a racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1].

(In the formula, R ¹ is a linear or branched acyl group having 2 to 11 carbon atoms which may have a substituent, and R ² is a linear or branched chain having 1 to 10 carbon atoms which may have a substituent. A branched alkyl group, aryl group, or cycloalkyl group is shown.)
Is subjected to asymmetric hydrolysis by an enzyme, a highly stereoselective asymmetric hydrolysis reaction occurs, and the optically active compound represented by the formula [3a] or the formula [3b] (respectively R-form or S-form) It was found that high optical purity was obtained.

  The compound of the formula [3a] and the compound of the formula [3b] are products corresponding to the compound of the formula [4] in the comparative invention, but compared with the compound of the formula [4] generated in the comparative invention, The optical purity of the compound of formula [3a] or the compound of formula [3b] produced in the present invention is significantly high.

  The obtained optically active compound represented by the formula [3a] or the formula [3b] (respectively R-form or S-form) is subjected to hydrolysis using an acid as a catalyst, thereby impairing optical purity. It was also found that the compound can be smoothly induced to the optically active 3,3-difluorolactic acid represented by the formula [4].

  On the other hand, along with the asymmetric hydrolysis, among the compounds, the optical isomer that does not react with the enzyme is represented by the formula [2].

(The meanings of R ¹ and R ² are the same as above. * Represents an asymmetric carbon.)
The knowledge that it remains in the system as an optically active 3,3-difluoro-2-acyl lactic acid ester (R-form or S-form) represented by the following formula was also obtained. The compound of the formula [2] corresponds to the substance of the formula [3a] which is a product in the comparative invention. In the present invention, the improvement in the optical purity of the compound of the formula [2] accompanying the asymmetric hydrolysis reaction is significantly faster than the improvement in the optical purity of the compound of the formula [3a] in the above comparative invention. Since the optical purity of the compound of the formula [2] is increased at a time earlier than the rate reduction, it has been found that the compound can be obtained in a high yield.

  Next, the optically active 3,3-difluorolactic acid represented by the formula [4] is obtained by taking out the compound of the formula [2] thus obtained and subjecting it again to hydrolysis (hydrolysis under acidic conditions). It was found that it can be guided efficiently.

  The compound represented by the formula [1] has two “ester bond sites” and when viewed from the optically active 3,3-difluorolactic acid represented by the formula [4] which is the target substance of the present invention, It corresponds to “an additional precursor of the precursor”. The compound of formula [2], the compound of formula [3a], or the compound of formula [3a] remaining as an unreacted raw material by subjecting such a compound to selection as a raw material and subjecting it to asymmetric hydrolysis using an enzyme A significant feature of the present invention is that the compound 3b] can be obtained in a balanced manner from both the viewpoints of optical purity and yield.

  In addition, this inventor also discovered that a lipase was preferable as an enzyme used for the hydrolysis (asymmetric hydrolysis) of the said 1st step. More preferable reaction conditions in the asymmetric hydrolysis were also found.

  In the present invention, the 3,3-difluoro-2-acyl lactic acid ester (R-form or S-form) represented by the formula [2] is obtained in advance by the first stage hydrolysis (asymmetric hydrolysis). It is also important that stopping the hydrolysis reaction when the optical purity set as a value is reached can be easily achieved by controlling the reaction conditions of the hydrolysis. For this reason, after completion of the first stage hydrolysis (asymmetric hydrolysis), the optically active compound represented by the formula [2] can be efficiently removed from the system, represented by [2]. And the optically active compound represented by the formula [3a] or the formula [3b] can be separated from each other.

  As described above, if both hydrolysis of the compound represented by the formula [2] and hydrolysis of the optically active compound represented by the formula [3a] or the formula [3b] are carried out, the formula [4] Both isomers of the compound can be obtained. However, depending on the purpose, only one isomer can be produced.

  Further, the 3,3-difluoro-2-acyl lactic acid ester (R-form or S-form) represented by the formula [2] or the optically active compound represented by the formula [3a] or the formula [3b] Hydrolysis using an acid as a catalyst to be performed on (each R-form or S-form) has a high reaction conversion rate, and the optical purity is not impaired through the reaction. They found out.

  As described above, according to the present invention, an important optically active 3,3-difluorolactic acid or a derivative thereof can be efficiently produced by utilizing an asymmetric hydrolysis reaction using an enzyme, thereby making the compound more efficient. It was also possible to produce on a large scale.

  As in the present invention, the knowledge of stereoselectively hydrolyzing 3,3-difluoro-2-acyl lactic acid esters with racemic or low optical purity has never been known.

  In this specification, each of the following steps may be called as follows.

  (1) In Formula [2], the racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by Formula [1] is subjected to asymmetric hydrolysis by an enzyme and remains as an unreacted raw material. It is obtained as an optically active 3,3-difluoro-2-acyl lactic acid ester represented, and at the same time, an optically active compound of formula [3a] or formula [3b] (respectively R-form or S-form) is produced in the system. Step; “first step”.

  (2) A step of purifying the reaction mixture obtained in the first step and taking out the optically active 3,3-difluoro-2-acyl lactic acid ester represented by the formula [2]; “Second step”.

  (3) The optically active 3,3-difluoro-2-acyl lactic acid ester represented by the formula [2] obtained in the second step is subjected to hydrolysis with an acid to produce an optical compound represented by the formula [4]. Step of obtaining active 3,3-difluorolactic acid; “third step”.

  (4) A step of purifying the reaction mixture obtained in the first step and taking out the optically active compound of the formula [3a] or the formula [3b]; “fourth step”.

  (5) The optically active 3,3-difluorolactic acid represented by the formula [4] by subjecting the optically active compound of the formula [3a] or the formula [3b] obtained in the fourth step to hydrolysis with an acid. Step 5: obtaining a “fifth step”.

  The steps related to the present invention are summarized below.

[Substituent]
The functional groups R ¹ and R ^{2 in} the formula [1], formula [2], formula [3a], and formula [3b] of the present invention will be described. In the present invention, what is important in the selectivity of the asymmetric hydrolysis reaction is that the raw material compound has a basic skeleton of 3,3-difluorolactic acid, and R ¹ is “having a substituent having 2 to 11 carbon atoms. A linear or branched acyl group, and R ² is an optionally substituted linear or branched alkyl group, aryl group, or cycloalkyl group having 1 to 10 carbon atoms. Certainly, R ¹ and R ² can take a wide variety of groups as long as the condition is met.

R ¹ is “an optionally substituted linear or branched acyl group having 2 to 11 carbon atoms”, but from the availability of raw materials, an unsubstituted acyl group having 2 to 7 carbon atoms. Is preferred. Specifically, formyl group, acetyl group, propionyl group, butanoyl group, butanoyl group, pentanoyl group, hexanoyl group, cyclohexanoyl group and benzoyl group are preferable. Of these, an acetyl group is particularly advantageous in terms of cost, and the reaction of the present invention also proceeds favorably, so that it is particularly preferable. These acyl groups may further have a reaction-inactive substituent. Examples of such a substituent include an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, phenyl group, tolyl group, a halogen group (-F, Cl, Br, I), a halogenated alkyl group _(-CF 3, _-C etc. 2 _{F 5),} and the like (provided that the R ¹ and "backbone""Substituent" does not mean the same type (eg alkyl). However, in the end, R ¹ is eliminated when obtaining the target compound of the formula [4]. From the viewpoint of cost, it is preferable to use an acyl group having no substituent.

R ² is “an optionally substituted linear or branched alkyl group, aryl group, or cycloalkyl group having 1 to 10 carbon atoms”. From the availability of raw materials, R ² has 1 carbon atom. -6 unsubstituted alkyl groups are preferred. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a cyclohexyl group, and a phenyl group. Among them, a methyl group and an ethyl group are particularly preferable because they are advantageous in terms of cost and the reaction of the present invention proceeds well. In addition, these alkyl groups, aryl groups, or cycloalkyl groups may further have a reaction-inactive substituent. Examples of such a substituent include an alkyl group having 1 to 6 carbon atoms and carbon. Examples include an alkoxy group of formulas 1 to 6, a phenyl group, a toluyl group, a halogen group (—F, Cl, Br, I), a halogenated alkyl group (—CF ₃ , —C ₂ F ₅ etc.), etc. The “main chain” and the “substituent” of R ² do not mean the same kind (eg, alkyl). Examples of the “alkyl group having a substituent” include a benzyl group (—CH ₂ —Ph: Ph represents a phenyl group). However, in the end, R ² is eliminated when obtaining the target compound of the formula [4]. From the viewpoint of cost, it is preferable to use a group having no substituent.

As described above, in the present invention, R ¹ is an unsubstituted acyl group having 2 to 7 carbon atoms, and R ² is an unsubstituted alkyl group having 1 to 6 carbon atoms. .

  Thus, the present inventors have found an excellent method for producing an optically active 3,3-difluorolactic acid derivative by an asymmetric hydrolysis reaction using an enzyme, and completed the present invention.

  That is, the present invention provides the inventions described in the following [Invention 1] to [Invention 11].

[Invention 1]
Racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1]

Including a step of bringing a hydrolase into contact with the asymmetric hydrolysis reaction,
Optically active 3,3-difluoro-2-acyl lactic acid ester represented by the formula [2]

When,
Optically active compound represented by formula [3a] or formula [3b] (R-form or S-form, respectively)

When,
Optically active 3,3-difluorolactic acid represented by the formula [4]

Among them, a method for producing at least one compound.
(In the above formulas, * represents an asymmetric carbon atom. R ¹ is a linear or branched acyl group having 2 to 11 carbon atoms that may have a substituent, and R ² has a substituent. A C1-C10 linear or branched alkyl group, aryl group or cycloalkyl group.

[Invention 2]
The manufacturing method of the optically active 3, 3- difluoro lactic acid represented by Formula [4] including the following 1st process-3rd process.
(First step)
A racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] is brought into contact with a hydrolase and subjected to an asymmetric hydrolysis reaction, thereby being represented by the formula [2]. A step of obtaining a reaction mixture containing the optically active 3,3-difluoro-2-acyl lactic acid ester and the optically active compound represented by the formula [3a] or the formula [3b] (each R-form or S-form).
(Second step)
The step of purifying the reaction mixture obtained in the first step and taking out the optically active 3,3-difluoro-2-acyl lactic acid ester represented by the formula [2] from the reaction mixture.
(Third step)
The optical activity represented by the formula [4] is obtained by hydrolyzing the optically active 3,3-difluoro-2-acyl lactic acid ester represented by the formula [2] taken out in the second step under an acidic condition. A step of obtaining 3,3-difluorolactic acid.
(Here, the meanings of Formula [1], Formula [2], Formula [3a], Formula [3b], and Formula [4] are the same as in Invention 1.)

[Invention 3]
A method for producing an optically active 3,3-difluorolactic acid represented by the formula [4], comprising the following first step, fourth step and fifth step.
(First step)
A racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] is brought into contact with a hydrolase and subjected to an asymmetric hydrolysis reaction, thereby being represented by the formula [2]. A step of obtaining a reaction mixture containing the optically active 3,3-difluoro-2-acyl lactic acid ester and the optically active compound represented by the formula [3a] or the formula [3b] (each R-form or S-form).
(4th process)
The reaction mixture obtained in the first step is purified, and the optically active 3,3-difluorolactic acid ester represented by the formula [3a] and the optically active 3,3 represented by the formula [3b] are obtained from the reaction mixture. A step of removing at least one of difluoro-2-acyllactic acid.
(5th process)
One of the optically active 3,3-difluorolactic acid ester represented by the formula [3a] taken out in the fourth step and the optically active 3,3-difluoro-2-acyllactic acid represented by the formula [3b] The process of obtaining the optically active 3,3-difluorolactic acid represented by Formula [4] by hydrolyzing under acidic conditions.
(Here, the meanings of Formula [1], Formula [2], Formula [3a], Formula [3b], and Formula [4] are the same as in Invention 1.)

[Invention 4]
The method according to any one of Inventions 1 to 3, wherein R ¹ is an unsubstituted acyl group having 2 to 7 carbon atoms, and R ² is an unsubstituted alkyl group having 1 to 6 carbon atoms.

[Invention 5]
The method according to any one of Inventions 1 to 3, wherein the 3,3-difluoro-2-acyl lactic acid ester is 3,3-difluoro-2-acetyl ethyl lactate.

[Invention 6]
6. The method according to any one of inventions 1 to 5, wherein the hydrolase is a lipase.

[Invention 7]
The method according to invention 6, wherein the lipase is derived from Rhizomucor miehei or Thermomyces langinosa.

[Invention 8]
The asymmetric hydrolysis reaction is performed in the presence of a phosphate buffer, and the concentration of the phosphate buffer stock solution is 0.2 mol / l (mol / dm ³ ) to 2 mol / l (mol / dm ³ ). The method according to any one of inventions 1 to 7, wherein:

[Invention 9]
The method according to any one of inventions 1 to 8, wherein the temperature of the asymmetric hydrolysis reaction is 10 ° C to 60 ° C.

[Invention 10]
The method according to any one of Inventions 1 to 9, wherein the asymmetric hydrolysis reaction is carried out under the condition of a pH of 5.0 to 9.0.

[Invention 11]
After obtaining the optically active 3,3-difluorolactic acid represented by the formula [4] by the method according to any one of Inventions 1 to 10, the optically active 3,3-difluorolactic acid is recrystallized or reprecipitated. A method for producing optically active 3,3-difluorolactic acid, which is subjected to at least one purification means.

  The optically active 3,3-difluorolactic acid and its derivatives, which are important as pharmaceutical and agricultural chemical intermediates, can be efficiently produced using an asymmetric hydrolysis reaction using an enzyme. Thereby, the compound can be produced more efficiently and on a large scale.

  The present invention is described in detail below. First, the “first step” to “fifth step” will be described in this order. Finally, the [purification step] (the step of purifying the compound of the formula [4] obtained in the third step or the fifth step) will also be described.

(1) [About the first step]
First, the first step will be described. In the first step, the racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] is subjected to asymmetric hydrolysis by an enzyme, and remains as an unreacted raw material. 2] optically active 3,3-difluoro-2-acyl lactic acid ester (R-form or S-form) represented by the formula [3a] or formula [3b] at the same time (each R-form or R-form) S-form) is generated in the system.

  As described above, in the process of performing this step, among the compounds represented by the formula [1], the optical isomer that does not react with the enzyme is the optically active 3,3-difluoro-2 of the formula [2]. -As an acyl lactic acid ester, it remains in the system and the optical purity is significantly improved. At the same time, an optically active compound of formula [3a] or formula [3b] is obtained. That is, the first step is the most characteristic step common to the inventions of the present application.

  The 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] used in the present invention is a known compound, and may be appropriately adjusted by those skilled in the art based on the prior art, or is commercially available. A thing may be used. Here, “racemic or low optical purity” means “racemic (with 0% ee: where ee is an enantiomeric excess indicating enantiomeric excess)” or optically usually required as an intermediate for medicines and agricultural chemicals The purity of “ee is less than 99%” shall be broadly indicated. Then, when the reaction of the first step is performed on 3,3-difluoro-2-acyl lactic acid ester exhibiting such a wide range of ee, the ee of 3,3-difluoro-2-acyl lactic acid ester is further significant. To improve. The essence of the first step of the present invention is to improve the optical activity through an asymmetric hydrolysis reaction using an enzyme. Therefore, the raw material compound is expressed as “racemic” as in formula [1], and the product is expressed as “chiral compound” as in formula [2], or in formulas [3a] and [3b]. However, the present invention is by no means limited to an embodiment using “a raw material having an optical purity of 0%”. Further, the ee of the product of the formula [2], the formula [3a], or the formula [3b] as a product is not always required to be “99% or more”, and the optical purity is significantly high. It only has to be satisfied.

In 3,3-difluoro-2-acyl lactic acid ester, the ester group may be hydrolyzed by enzymatic reaction, the acyl group may be hydrolyzed, or both may be hydrolyzed. It may be decomposed. That is, the ester group of the 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] may be any one that can be hydrolyzed by an enzyme, and R ² constituting the ester moiety includes a methyl group, A linear or branched alkyl group, aryl group, or cycloalkyl group having 1 to 10 carbon atoms such as an ethyl group or a butyl group can be used.

Similarly, as the acyl group (R ¹ ), a linear or branched acyl group having 2 to 11 carbon atoms such as an acetyl group, a propanoyl group, a butanoyl group, and a benzoyl group can be used.

Among the compounds of the formula [1], 3,3-difluoro-2-acetylethyl lactate in which R ¹ is an acetyl group and R ² is an ethyl group is particularly easy to obtain, and the asymmetric hydrolysis reaction of the present invention Since the reactivity and stereoselectivity are also good, it is one of the particularly preferred ones.

  The reaction in the first step can be preferably carried out in a solution. The concentration of the substrate (referred to as the compound represented by the formula [1]) in the solution (concentration at the start of the reaction) proceeds smoothly, and the substrate or product is easily recovered from the reaction solution after the reaction. It is sufficient that the concentration is as high as possible, preferably 5 to 80% by mass, and more preferably 10 to 50% by mass. In addition, the substrate can be added to the reaction solution according to the progress of the enzyme reaction (the decomposed substrate is excluded from the concentration, and the substrate is added so that the amount of the enzyme is within the above range based on the amount of the remaining substrate. Just add).

  As the enzyme used in the present invention, a wide range of commercially available hydrolases (lipase, acylase, esterase, peptidase, protease) can be used. However, the enzyme is highly stereoselective and the reaction proceeds even when the substrate concentration is high. Lipase is preferable. As the lipase, a lipase derived from Rhizomucor miehei and a lipase derived from Thermomyces lanuginosa are particularly preferable since they exhibit high reactivity and stereoselectivity.

  These enzymes that can be used in the present invention are commercially available and can be purchased on a scale that allows mass production.

  The amount of the enzyme used for the reaction in the first step is not particularly limited as long as the reaction proceeds smoothly, and is preferably 0.01 to 50 with respect to the substrate represented by the formula [1]. It is 0.1 mass%, More preferably, it is 0.1-20 mass%.

  Enzymes are disadvantageous in cost even if they are used in excessive amounts. In addition, as already explained, in the first step, it is a particularly preferable aspect of the present invention to efficiently stop the reaction when the compound of the formula [2] is efficiently produced. It is not always preferable to perform the reaction at a rapid rate using a large amount of enzyme.

  The solvent used in the reaction is not particularly limited as long as it is a “solvent containing water”, but water (in particular, as described later, a buffering agent in which a buffering agent used in a normal biological experiment is dissolved). A containing aqueous solution (referred to herein as a buffer solution) can be preferably used. In addition to water, an ether-based organic solvent such as t-butyl methyl ether or an alcohol-based organic solvent such as ethanol (preferably an alcohol having 1 to 4 carbon atoms) can be used as a cosolvent.

  As a result of the first step, the optically active compound represented by the formula [3b] and the optically active 3,3-difluorolactic acid represented by the formula [4] produced by further hydrolysis of this compound are: Since they are carboxylic acids, their formation lowers the pH of the reaction solution. In particular, when the substrate concentration is high, the pH is greatly lowered by the product carboxylic acid, and the enzyme reaction may be inhibited. Therefore, it is preferable to keep the pH constant.

  The pH of the reaction is not particularly limited as long as it is suitable for the stability of the enzyme, and is preferably 4.0 to 10.0, and more preferably 5.0 to 9.0. Is racemized at an alkaline pH, the pH is preferably 5.0 to 7.0. Examples thereof include a method of controlling pH using a buffer solution and a method of automatically adding an alkali such as sodium hydroxide using a pH automatic controller. Among these, the method of controlling the pH using a buffer solution is simple and is particularly preferable when performing the reaction in the first step of the present invention.

  Since many enzymes are active near neutrality, sodium cacodylate-hydrochloric acid buffer, sodium maleate-sodium hydroxide buffer, phosphate buffer, imidazole-hydrochloric acid buffer, 2,4,6-trimethylpyridine -Hydrochloric acid buffer, triethanolamine / hydrochloric acid-sodium hydroxide buffer, veronal-hydrochloric acid buffer, N-ethylmorpholine-hydrochloric acid buffer, Tris buffer, glycylglycine-sodium hydroxide buffer, pH 5-9 Although a buffer solution having a buffering action can be adopted, any buffer solution suitable for enzyme stability may be used, and a phosphate buffer solution is one of the particularly preferable ones.

The buffer concentration can be used in the range of ^{0.01~3mol / l (mol / dm 3} ), preferably ^{0.2~2mol / l (mol / dm 3} ). The “concentration” here refers to the concentration of phosphate groups (the concentration of the following chemical species).

  The temperature of the asymmetric hydrolysis reaction may be a temperature at which the enzyme reaction proceeds smoothly and the enzyme is not inactivated by the substrate, and is preferably 5 to 70 ° C, more preferably 10 to 45 ° C. Generally, an enzyme denatures at a temperature of 70 ° C. or higher, so that the temperature of 70 ° C. or higher is unsuitable. Further, since the growth temperature of a normal microorganism is 10 to 45 ° C., the optimum temperature range of the microorganism-derived enzyme is equal to this . If the optimum temperature is known in advance depending on the type of enzyme, the reaction can be carried out at a temperature other than the above.

  The temperature of the reaction can be appropriately set within the above range by those skilled in the art so that the reaction rate (conversion rate) and the optical activity of the chemical species to be obtained increase in a well-balanced manner.

  In order to advance the reaction efficiently, the reaction solution is preferably stirred while a stirring blade, a magnetic stirrer, a shaker, a circulation column, or the like connected to a motor can be used. When using a stirring blade, a magnetic stirrer, etc., it is preferable to carry out stirring at 50-1000 rpm.

  As described above, in the first step of the present invention, if the reaction is advanced excessively, the unreacted product represented by the formula [2] may undergo excessive hydrolysis, and the yield of the formula [2] descend. As a result, the yield of the target product of the formula [4] obtained in the “third step” (hydrolysis with acid) described later also decreases.

  On the other hand, if the reaction in the first step is advanced too much, there arises a problem that the optical purity of the compounds of the formulas [3a] and [3b] is lowered. When the compounds of formula [3a] and formula [3b] having low optical purity are obtained, the compound of formula [4] which is a target substance obtained by subjecting them to the “fifth step” (hydrolysis with acid) described later The optical activity of is also low.

  Therefore, the hydrolysis reaction in the first step is appropriately sampled, the composition of the reaction mixture is measured by gas chromatography or the like, and immediately when the optical purity of the compound of the formula [2] reaches the target purity or the formula It is preferable to stop the reaction when the optical purity of [3a] and formula [3b] does not fall below the target. As reaction time which reaction is easy to monitor and can employ | adopt industrially, 1 hour-3 days are employable, for example.

(2) [About the second step]
Next, the second step will be described. In the second step, the reaction mixture obtained in the first step is purified, and the optically active 3,3-difluoro-2-acyl represented by the formula [2], which is the stereoisomer that has not reacted with the enzyme This is a step of taking out a lactic acid ester.

  Although the specific method is not particularly limited, for example, it can be separated by distillation or extraction with an organic solvent. In extraction with an organic solvent, the reaction mixture obtained in the first step is brought into contact with an organic solvent (extraction solvent), and optically active substances of the formulas [2] and [3a] are recovered in the organic layer (formula [3b] And the compound of the formula [2] and the formula [3a] are separated from each other by a conventional method such as distillation.

In performing this extraction operation, if the pH in the aqueous layer is 5 or more, the carboxyl group of the compound of the formula [3b] forms an anion (—COO ⁻ ), and is difficult to be extracted into the organic layer. Even more preferred.

  The extraction solvent may be anything as long as it can be separated from the aqueous layer, such as aliphatic hydrocarbons such as n-heptane and n-hexane, aromatic hydrocarbons such as benzene and toluene, halogens such as methylene chloride and chloroform. And hydrocarbons, ester solvents such as ethyl acetate, ether solvents such as diethyl ether and t-butyl methyl ether, and the like. Preferred are ethyl acetate and t-butyl methyl ether.

  The organic layer obtained by the extraction operation can then be separated into a compound of formula [2] and an optically active substance of formula [3a] by subjecting it to distillation or the like. What is important in this step is to separate the optically active compound of the formula [2] from the compound of the formula [3a] or the formula [3b] to significantly improve the abundance of the compound of the formula [2]. By doing so, it is possible to prevent the optical purity of the target compound of the formula [4] from being lowered in the next third step. For this reason, the compound of the formula [2] does not necessarily need to be isolated and purified, and may be subjected to the next third step in the presence of impurities such as an extraction solvent.

(3) [About the third step]
Next, the third step will be described. In the third step, the optically active 3,3-difluorolactic acid represented by the formula [4] is obtained by subjecting the compound represented by the formula [2] obtained in the second step to hydrolysis under acidic conditions. It is the process of obtaining.

  By applying hydrolysis using an acid as the reaction in the third step, hydrolysis can occur without substantially impairing the high optical purity already obtained in the compound of formula [2]. The present inventor found. This is much cheaper than asymmetric hydrolysis using an enzyme. Acidic substances used for hydrolysis include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, hydrobromic acid, phosphoric acid, boric acid, acetic acid, citric acid, formic acid, p-toluenesulfonic acid, etc. Of these, hydrochloric acid and sulfuric acid are more preferable, and hydrochloric acid is more preferable.

The reaction temperature may be a temperature at which the reaction proceeds smoothly, and is preferably 25 to 100 ° C. After the reaction, the target product can be isolated by concentration.
In addition, although the hydrolysis using a base is also considered as the third step, according to the study by the inventors, racemization gradually occurs through the reaction, and the optical purity of the compound of the formula [4] decreases. It is not preferable.

  Through the above operation, the optically active 3,3-difluorolactic acid represented by the formula [4] can be obtained in the water-soluble fraction. For organic compounds such as alcohols produced in the third step, an extraction operation, etc. Can also be removed.

(4) [About the fourth step]
The fourth step will be described. The fourth step is a step of purifying the reaction mixture obtained in the first step and taking out the optically active compound of formula [3a] or formula [3b]. Specifically, it is a step of separating the optically active compound of formula [3a] or formula [3b] from the compound represented by formula [2] remaining in the system without causing further hydrolysis. .

  Separation / purification in the fourth step is not particularly limited as long as it is a means suitable for the above-mentioned purpose. However, when recovering the compound of the formula [3a], for example, the reaction mixture obtained in the first step is used as an extraction solvent. The compounds of formula [2] and formula [3a] are recovered in the extraction solvent (leaving the carboxylic acid compound of formula [3b] in the aqueous layer) and then in the extraction solvent. The method of separating the compound of [2] and the compound of formula [3a] from each other and taking out the compound of formula [3a] can be mentioned.

  The extraction solvent may be anything as long as it can be separated from the aqueous layer, such as aliphatic hydrocarbons such as n-heptane and n-hexane, aromatic hydrocarbons such as benzene and toluene, halogens such as methylene chloride and chloroform. And hydrocarbons, ester solvents such as ethyl acetate, ether solvents such as diethyl ether and t-butyl methyl ether, and the like. Preferred are ethyl acetate and t-butyl methyl ether.

In performing this extraction operation, if the pH in the aqueous layer is 5 or more, the carboxyl group of the compound of the formula [3b] forms an anion (—COO ⁻ ) and is difficult to be extracted into the organic layer. Even more preferred.

  The extract thus obtained can be separated into a compound of the formula [2] and a compound of the formula [3a] by subjecting to conventional separation means such as distillation.

On the other hand, when the compound of the formula [3b] is recovered from the reaction mixture of the first step, the reaction mixture is subjected to an extraction operation with an extraction solvent as described above, and the compound of the formula [2] and the formula [3a] The compound of the formula [3b] may be separated and purified from the aqueous layer. Specifically, when hydrochloric acid or the like is added to the aqueous layer to make it strongly acidic, the carboxyl group of the compound [3b] returns from the anion (—COO ⁻ ) state to the neutral group (—COOH), and depends on the organic solvent. Since extraction becomes easy, if this is extracted with an organic solvent, it can be easily taken out.

  In addition, the compound of the formula [3a] or the compound of the formula [3b] obtained in the fourth step may be subjected to the subsequent fifth step after completely isolating and purifying the simple substance. There is no problem even if it is used in the fifth step in the coexisting state.

(5) [About the fifth step]
Next, the fifth step will be described. In the fifth step, the optically active compound of formula [3a] or formula [3b] obtained in the fourth step is further hydrolyzed under acidic conditions to give optical activity 3 represented by formula [4]. , 3-Difluorolactic acid.

  When hydrolysis using an acid is applied as the reaction of the fifth step, hydrolysis occurs without substantially impairing the high optical purity already obtained in the compound of formula [3a] or formula [3b]. be able to. This is much cheaper than asymmetric hydrolysis using an enzyme. Acidic substances used for hydrolysis include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, chloric acid, perchloric acid, hydrobromic acid, phosphoric acid, boric acid, acetic acid, citric acid, formic acid, p-toluenesulfonic acid, etc. Examples of the organic acid include hydrochloric acid and sulfuric acid, and hydrochloric acid is more preferable.

  The reaction temperature may be a temperature at which the reaction proceeds smoothly, and is preferably 25 to 100 ° C. After the reaction, the target product can be isolated by concentration.

  As the fifth step, hydrolysis using a base may be considered, but according to the study by the inventors, racemization gradually occurs through the reaction, and the optical purity of the compound of the formula [4] decreases. It is not preferable.

(6) Purification operation after reaction Finally, the purification operation after reaction will be described.

  The optically active difluorolactic acid represented by the formula [4] obtained in the third step and the fifth step can be further improved in optical purity by operations such as recrystallization and reprecipitation.

Among these, when performing reprecipitation, the solvent used is an aliphatic hydrocarbon such as n-heptane or n-hexane, an aromatic hydrocarbon such as benzene or toluene, or a halogen such as methylene chloride or chloroform. Examples thereof include ether hydrocarbons, ester solvents such as ethyl acetate, and ether solvents such as diethyl ether, t-butyl methyl ether and diisopropyl ether, with ethyl acetate and diisopropyl ether being preferred. These solvents can be used alone or in combination. For example, to optically active 3,3-difluoro lactic ^1g, the heating using a solvent 0.1ml (cm 3) ~50ml (cm 3), to form a liquid suspension, then cooled and filtered Thus, crystals can be obtained.

  These recrystallization and reprecipitation operations can be appropriately performed when it is desired to obtain the optically active difluorolactic acid represented by the formula [4] through the first to fifth steps described above and to further increase the optical purity. Good.

[About a particularly preferred embodiment of the present invention]
Hereinafter, particularly preferred embodiments of the present invention will be described.

  As the “racemic or 3,3-difluoro-2-acyl lactic acid ester having low optical purity” represented by the formula [1] used as the raw material of the first step of the present invention, “racemic 3,3-difluoro-2” "Ethyl acetyl lactate" is one of the particularly preferred ones.

Particularly preferred as the enzyme used in the first step is a lipase, among which a lipase derived from Rhizomucor miehei or Thermomyces lanuginosa is preferred. The asymmetric hydrolysis reaction is carried out in the presence of a phosphate buffer, and the concentration of the stock solution of the phosphate buffer is 0.2 mol / l (mol / dm ³ ) to 2 mol / l (mol / dm ³ ). It is preferable. The temperature of the asymmetric hydrolysis reaction is preferably 10 ° C. to 60 ° C., and is preferably carried out under conditions where the pH is 5.0 to 9.0.

  When the above-mentioned “racemic 3,3-difluoro-2-acetylethyl lactate” is subjected to an asymmetric hydrolysis reaction (first step) using a lipase derived from Rhizomucor miehei or Thermomyces lanuginosa as an enzyme, it is asymmetrically hydrolyzed. As the compound of the formula [2] that is not decomposed, “S-form of 3,3-difluoro-2-acetylethyl lactate” is formed. At the same time, the reaction product of the asymmetric hydrolysis includes “S form of ethyl 3,3-difluorolactic acid” as the compound of formula [3a] and “3,3-difluoro- "R-isomers of 2-acetyllactic acid" are produced respectively. In this reaction system, “R-form of 3,3-difluoro-2-acetyllactic acid” corresponding to the compound of formula [3b] is a major product, and “S of ethyl 3,3-difluorolactic acid corresponding to the compound of formula [3a] is used. "Body" is a minor product.

  In the reaction of the first step, “S form of 3,3-difluorolactic acid” represented by the formula [4] is slightly produced, but the amount is very small. As already described, if the asymmetric hydrolysis reaction is continued excessively in an attempt to increase the amount of the target compound represented by the formula [4] in the first step, not only the optical purity of the compound decreases, This is not preferable because it decreases the yield or optical purity of the compound of the formula [3a], the compound of the formula [3b], and the compound of the formula [2], which is the main target product of the first step.

  When the reaction mixture obtained in the first step in this system is subjected to an extraction operation with an extraction solvent, preferably in a state where the pH of the aqueous layer is 5 or more, the organic layer contains “3,3-difluoro-2- The “S form of ethyl acetyl lactate” (major) and the “S form of ethyl 3,3-difluorolactate” (minor) are selectively extracted. On the other hand, “R-form of 3,3-difluoro-2-acetyllactic acid” (major) and “S-form of 3,3-difluorolactic acid” (minor) remain in the water layer.

  If the organic layer obtained by this extraction operation is further subjected to separation means such as distillation, the major product “S-form of 3,3-difluoro-2-acetylethyl lactate” can be taken out. In this case, the entire separation operation becomes the “second step” together with the previous solvent extraction operation.

  If the "S form of 3,3-difluoro-2-acetylethyl lactate" taken out in the "second step" is subsequently subjected to "hydrolysis with acid (third step)", the optical purity is substantially impaired. In addition, as the target compound represented by the formula [4], “S form of 3,3-difluorolactic acid” can be obtained.

On the other hand, as a result of the extraction operation, the obtained water layer contains “R-form of 3,3-difluoro-2-acetyllactic acid” (major) and “S-form of 3,3-difluorolactic acid” (minor). The carboxyl group is dissolved mainly in the state of “—COO ⁻ ”. When a strong acid such as hydrochloric acid is added to this aqueous layer, the —COO 2 ^— groups of both compounds are returned to —COOH, and are easily extracted into an organic solvent. That is, “R form of 3,3-difluoro-2-acetyllactic acid” can be extracted into an organic solvent. The purity can be increased by subsequent conventional purification means (such as recrystallization) (a series of these operations together with the previous solvent extraction operation is the “fourth step”).

  When the “R form of 3,3-difluoro-2-acetyllactic acid” thus taken out is subjected to hydrolysis under acidic conditions, the objective represented by the formula [4] is obtained without substantially impairing the optical purity. As the compound, “R form of 3,3-difluorolactic acid” can be obtained (fifth step). In the fourth step, if the “S form of 3,3-difluorolactic acid” is not sufficiently removed even though it is a minor product, “3,3- As a result, the optical purity (ee) of the R form of difluorolactic acid is pushed down. Therefore, as much as possible, it is better to carry out the fifth step after removing the minor “S form of 3,3-difluorolactic acid” by purification. However, the fifth step may be carried out without intentionally removing the minor “S form of 3,3-difluorolactic acid” (in that case, by the above-mentioned “purification operation after reaction” described above after the fifth step, The optical purity of the target product can be increased).

  The “S-form of 3,3-difluorolactic acid” obtained in the third step and the “R-form of 3,3-difluorolactic acid” obtained in the fifth step are the “purification operation after the reaction”, that is, recrystallization. Alternatively, the optical purity can be further increased by subjecting to at least one purification means of reprecipitation.

  Embodiments of the present invention will be specifically described below, but the present invention is not limited to these examples.

[Examples 1-2]
[Asymmetric hydrolysis by enzyme]
0.03 g of each commercially available enzyme was dissolved in ³ ml (cm ³ ) of phosphate buffer (pH 7.0) prepared to 0.85 mol / l (mol / dm ³ ), and approximately 300 μl (mm ³ ) of racemic 3, 3-Difluoro-2-acetylethyl lactate was added respectively. The reaction was carried out at 25 ° C. for 1 day with stirring. Table 1 shows the results of optical purity and production amount analyzed under the analysis conditions described later.

  Thus, when racemic 3,3-difluoro-2-acetylethyl lactate is used as a raw material, a hydrolytic enzyme is brought into contact therewith, and an asymmetric hydrolysis reaction is carried out, an isomer that does not undergo hydrolysis.

Remained with significantly higher optical purity. Along with this, the isomer of the hydrolyzed one is

In this form, it was found that it was also produced in the system with high optical purity. The high optical purity of these chemical species is clear even when compared with Comparative Examples 1 to 5 described later.

  On the other hand, the following two chemical species

Although the production amount is small compared to the above two chemical species, it can be seen that these are also produced in a state in which the optical purity is significantly high.

[Comparative Examples 1 to 5] (Substrate: Racemic 3,3-difluoroethyl lactate)
0.005 g of each commercially available enzyme was dissolved in 0.5 ml (cm ³ ) of a phosphate buffer (pH 7.0) prepared to 0.85 mol / l (mol / dm ³ ), and approximately 50 μl (mm ³ ) of racemic material was dissolved. 3,3, -Difluoroethyl lactate was added respectively. The reaction was carried out at 25 ° C. for 1 day with stirring. Table 2 shows the results of optical purity and production amount analyzed under the analysis conditions described later.

  Thus, also in “Comparative Examples 1-5” in which racemic 3,3-difluoroethyl lactate was set as a raw material substrate, the hydrolysis reaction proceeded to produce an isomer that was not subjected to hydrolysis,

Along with this, the hydrolyzed isomer

Was confirmed to generate. However, the stereoselectivity of the enzyme is lower than that of “Example”, and it has been found that it is difficult to efficiently increase the optical purity in this reaction.

[Example 3]
To 200 ml (cm ³ ) of 0.85 mol / l (mol / dm ³ ) phosphate buffer, 20 g (101 mmol) of racemic 3,3-difluoro-2-acetylethyl lactate and 4 g of Lipozyme® RM IM were added, and 25 Reacted at ° C. After 88 hours, since the optical purity of 3,3-difluoro-2-acetylethyl lactate which was an unreacted raw material became sufficiently high, the reaction was stopped. After the reaction, extraction was performed with MTBE (t-butyl methyl ether). In the organic layer, 37 mmol (99.0% ee (S)) of ethyl 3,3-difluoro-2-acetyl lactate and 1.8 mmol (84.2% ee (S)) of ethyl 3,3-difluoro lactate were recovered. did. In the aqueous layer, 54 mmol (78.7% ee (R)) of 3,3-difluoro-2-acetyllactic acid and 5.1 mmol (0.4% ee (S)) of 3,3-difluorolactic acid were recovered.

Next, 13.5 ml (cm ³ ) of concentrated hydrochloric acid was added to the aqueous layer, and extraction was performed with MTBE. As a result, 41 mmol of 3,3-difluoro-2-acetyllactic acid (R-form) and 3.7 mmol of 3,3-difluorolactic acid (S-form) were recovered. This was concentrated, 0.3 ml (cm ³ ) of concentrated hydrochloric acid and 1.6 g of water were added, and a hydrolysis reaction was carried out at 65 ° C. for 1 day to obtain 3,3-difluorolactic acid (76% ee (76% ee ( R)).

  Thus, it is clear that hydrolysis of 3,3-difluoro-2-acetyllactic acid (R form) using concentrated hydrochloric acid can be induced to the target substance without substantially reducing the optical purity. became.

  In this example, since “hydrolysis with acid” is carried out without intentionally separating minor 3,3-difluorolactic acid (S form), the final product 3,3-difluorolactic acid (R The optical purity of the body is moderate. However, if the optical purity is increased to this level, the optical purity of the target product can be sufficiently increased by the subsequent purification operation (see Example 4).

[Example 4]
To 4.3 g of 3,3-difluorolactic acid (78% ee (R)), 0.8 ml (cm ³ ) of ethyl acetate was added and stirred at 35 ° C. for 10 minutes. After becoming a slurry, it was cooled in ice water, and the crystals were collected by filtration. The obtained crystal was 1.3 g (95% ee (R)).
Thus, it was revealed that the optical purity can be further improved by simply applying 3,3-difluorolactic acid having an optical purity of 78% ee to a simple method of reprecipitation using ethyl acetate.

[Analysis conditions]
Optical purity analysis of 3,3-difluorolactic acid ester: The optical purity of 3,3-difluoro-2-acetylethyl lactate and 3,3-difluoroethyl lactate was measured by gas chromatography. Further, 3,3-difluoro-2-acetyllactic acid and 3,3-difluorolactic acid were methyl esterified with TMS diazomethane, and the optical purity was measured by gas chromatography.
Column: BGB (30 m × 0.25 mm × 0.25 μm) (manufactured by BGB Analytic AG)
Temperature conditions: 50 ° C. (5 min) → 5 ° C./min→150° C. (5 min)
Inlet temperature: 230 ° C
Detector temperature: 230 ° C
[Retention time of each enantiomer]
3,3-difluoro-2-acetylethyl lactate: R-form 16.7 min, S-form 16.3 min
3,3-difluoroethyl lactate: R-form 19.7 min, S-form 20.6 min
3,3-difluoro-2-acetyllactic acid: R-form 15.8 min, S-form 15.0 min
3,3-difluorolactic acid: R-form 20.2min, S-form 21.6min
The production amount of the optically active 3,3-difluorolactic acid derivative produced by the asymmetric hydrolysis reaction was determined by ¹⁹ F-NMR analysis using benzotrifluoride as an internal standard substance.

  The optically active difluorolactic acid targeted in the present invention can be derived into various optically active difluorolactic acids, which can be used as intermediates for medicines and agricultural chemicals.

Claims (11)

Racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1]

Including a step of bringing a hydrolase into contact with the asymmetric hydrolysis reaction,
Optically active 3,3-difluoro-2-acyl lactic acid ester represented by the formula [2]

When,
Optically active compound represented by formula [3a] or formula [3b] (R-form or S-form, respectively)

When,
Optically active 3,3-difluorolactic acid represented by the formula [4]

Among them, a method for producing at least one compound.
(In the above formulas, * represents an asymmetric carbon atom. R ¹ is a linear or branched acyl group having 2 to 11 carbon atoms that may have a substituent, and R ² has a substituent. A C1-C10 linear or branched alkyl group, aryl group or cycloalkyl group. The manufacturing method of the optically active 3, 3- difluoro lactic acid represented by Formula [4] including the following 1st process-3rd process.
(First step)
A racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] is brought into contact with a hydrolase and subjected to an asymmetric hydrolysis reaction, thereby being represented by the formula [2]. A step of obtaining a reaction mixture containing the optically active 3,3-difluoro-2-acyl lactic acid ester and the optically active compound represented by the formula [3a] or the formula [3b] (each R-form or S-form).
(Second step)
The step of purifying the reaction mixture obtained in the first step and taking out the optically active 3,3-difluoro- 2-acyl lactic acid ester represented by the formula [2] from the reaction mixture.
(Third step)
The optical activity represented by the formula [4] is obtained by hydrolyzing the optically active 3,3-difluoro- 2-acyl lactic acid ester represented by the formula [2] taken out in the second step under an acidic condition. A step of obtaining 3,3-difluorolactic acid.
(Here, the meanings of Formula [1], Formula [2], Formula [3a], Formula [3b], and Formula [4] are the same as in claim 1). A method for producing an optically active 3,3-difluorolactic acid represented by the formula [4], comprising the following first step, fourth step and fifth step.
(First step)
A racemic or low optical purity 3,3-difluoro-2-acyl lactic acid ester represented by the formula [1] is brought into contact with a hydrolase and subjected to an asymmetric hydrolysis reaction, thereby being represented by the formula [2]. A step of obtaining a reaction mixture containing the optically active 3,3-difluoro-2-acyl lactic acid ester and the optically active compound represented by the formula [3a] or the formula [3b] (each R-form or S-form).
(4th process)
The reaction mixture obtained in the first step is purified, and an optically active 3,3-difluoro-2-acyllactic acid derivative represented by the formula [3a] and an optical represented by the formula [3b] are obtained from the reaction mixture. Removing at least one of the active 3,3-difluoro-2-acyllactic acid derivatives.
(5th process)
The optically active 3,3-difluoro-2-acyllactic acid derivative represented by the formula [3a] and the optically active 3,3-difluoro-2-acyllactic acid derivative represented by the formula [3b] taken out in the fourth step The process of obtaining the optically active 3,3-difluorolactic acid represented by Formula [4] by hydrolyzing one of these under acidic conditions.
(Here, the meanings of Formula [1], Formula [2], Formula [3a], Formula [3b], and Formula [4] are the same as in claim 1). The method according to any one of claims 1 to 3, wherein R ¹ is an unsubstituted acyl group having 2 to 7 carbon atoms, and R ² is an unsubstituted alkyl group having 1 to 6 carbon atoms.   4. The method according to claim 1, wherein the 3,3-difluoro-2-acyl lactic acid ester is 3,3-difluoro-2-acetyl ethyl lactate.   6. The method according to claim 1, wherein the hydrolase is a lipase.   The method according to claim 6, wherein the lipase is derived from Rhizomucor miehei or Thermomyces langinosa. The asymmetric hydrolysis reaction is performed in the presence of a phosphate buffer, and the concentration of the phosphate buffer stock solution is 0.2 mol / l (mol / dm ³ ) to 2 mol / l (mol / dm ³ ). 8. A method according to any one of claims 1 to 7, characterized in that   The method according to any one of claims 1 to 8, wherein the temperature of the asymmetric hydrolysis reaction is 10 ° C to 60 ° C.   The method according to any one of claims 1 to 9, wherein the asymmetric hydrolysis reaction is carried out under conditions where the pH is 5.0 to 9.0. By a method according to any one of claims 1乃optimum 1 0, after obtaining the optically active 3,3-difluoro-lactic acid of the formula [4], the optically active 3,3-difluoro lactic recrystallization or A method for producing optically active 3,3-difluorolactic acid, which is subjected to at least one purification means of reprecipitation.