JP2008099661A - Process for producing optically active (s)-7-hydroxy-6-methylheptan-2-one and precursor thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process capable of simply, efficiently and industrially producing optically active (S)-7-hydroxy-6-methylheptan-2-one and precursor thereof. <P>SOLUTION: The process for producing optically active (S)-2-methyl-6-oxoheptanoate ester represented by formula (III) (wherein, R<SP>1</SP>is the same as the above defined), in which an esterase derived from a microorganism of the genus Aspergillus, capable of preferentially hydrolyzing R form is allowed to act on 2-methyl-6-oxoheptanoate ester represented by formula (II) (wherein, R<SP>1</SP>is a 1-5C alkyl group) to optically resolve it, is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing optically active (S) -7-hydroxy-6-methylheptan-2-one and its precursor.

  The epothilone derivative represented by the following formula is useful as an anticancer agent.

In the synthesis of an epothilone derivative, optically active (S) -7-hydroxy-6-methylheptan-2-one is useful as a C _{7 to} C ₁₂ building block, and the compound is optically active (S) -2. It can be derived from methyl-6-oxoheptanoic acid via its ester (see Patent Documents 1 and 2, Non-Patent Documents 1 and 2). Various production methods have been proposed for 2-methyl-6-oxoheptanoic acid (see Non-Patent Documents 3 to 8). However, since the production methods described in Non-Patent Documents 3 to 6 are methods for extracting and isolating corresponding natural products and oxidizing them, there was a problem in obtaining raw materials. Moreover, the manufacturing method of a nonpatent literature 6 is a manufacturing method of the (R) body. Furthermore, the production methods described in Non-Patent Documents 7 and 8 are methods in which 2,6-dimethylcyclohexanone is oxidized using potassium permanganate, and the resulting product is obtained from 2-methyl-6-oxoheptanoic acid. It was racemic and optically inactive.

DE 19751200 WO2005 / 003071 J. et al. A. C. S. , 119, 7974 (1997) Chem. Eur. J. et al. , 2, 1477 (1996) Natural Product Letters, 3,189 (1993) J. et al. Nat. Prod. , 66, 251 (2003) Natural Product Letters, 4, 51 (1994) Helv. Chim. Acta, 73, 733 (1990) J. et al. Med. Chem. , 26, 426 (1983) Collect. Czech. Chem. Commun. , 30, 1214 (1965)

  The present invention provides optically active (S) -7-hydroxy-6-methylheptan-2-one and its precursor, optically active (S) -2-methyl-6-oxoheptanoic acid ester, etc. simply and efficiently. It aims at providing the method which can be manufactured industrially.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have obtained high optical purity when 2-methyl-6-oxoheptanoic acid ester (RS mixture) is optically resolved by the action of a specific esterase ( If the knowledge that S) isomer is obtained and this optical resolution is used, optically active (S) -7-hydroxy-6-methylheptan-2-one can be easily and efficiently industrially produced. As a result, the present invention has been completed.

That is, the present invention is as follows.
[1] Formula (II):

(In the formula, R ¹ represents a C _1-5 alkyl group.)
Aspergillus, which can preferentially hydrolyze the R-form to 2-methyl-6-oxoheptanoic acid ester represented by the formula (hereinafter also referred to as 2-methyl-6-oxoheptanoic acid ester (II)) Optical resolution by the action of esterases derived from microorganisms of the genus, formula (III):

(Wherein R ¹ represents the same meaning as described above.)
A method for producing an optically active (S) -2-methyl-6-oxoheptanoic acid ester (hereinafter also referred to as optically active (S) -2-methyl-6-oxoheptanoic acid ester (III)).

[2] The carbonyl group of optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) is protected to give a compound of formula (IV):

(In the formula, A represents an oxygen atom or a sulfur atom, R ¹ represents the same meaning as described above, and R ² and R ³ each independently represent a C _1-5 alkyl group or bonded to each other. Represents a C _2-5 alkylene group.)
The production method according to [1], further including a step of obtaining an optically active (S) -ketal ester represented by (hereinafter also referred to as optically active (S) -ketal ester (IV)).

[3] Reduction of the optically active (S) -ketal ester (IV) to give the formula (V):

(In the formula, A, R ² and R ³ represent the same meaning as described above.)
The production method according to [2], further including a step of obtaining an optically active (S) -ketal alcohol represented by the formula (hereinafter also referred to as optically active (S) -ketal alcohol (V)).

[4] By optically resolving 2-methyl-6-oxoheptanoic acid ester (II) with an esterase derived from a microorganism of the genus Aspergillus that can preferentially hydrolyze the R-form, the optical activity (S ) Obtaining 2-methyl-6-oxoheptanoic acid ester (III);
Protecting the carbonyl group of optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) to obtain optically active (S) -ketal ester (IV);
Reducing the optically active (S) -ketal ester (IV) to obtain the optically active (S) -ketal alcohol (V); and deprotecting the optically active (S) -ketal alcohol (V) to obtain a compound of formula (I):

An optically active (S) -7-hydroxy-6-methylheptan-2-one (hereinafter also referred to as optically active (S) -7-hydroxy-6-methylheptan-2-one (I)) Obtaining step;
A process for producing optically active (S) -7-hydroxy-6-methylheptan-2-one (I).

[5] The production method according to any one of the above [1] to [4], wherein the optical purity of the optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) is 95 to 100% ee.

[6] The production method according to any one of the above [1] to [5], wherein R ¹ is a methyl group.

[7] The production method according to any one of the above [2] to [6], wherein R ² and R ³ are both methyl groups or bonded to each other to represent an ethylene group or a propylene group.

[8] The production method according to any one of [1] to [7], wherein the microorganism of the genus Aspergillus is Aspergillus flavus.

[9] The production method according to any one of [1] to [8], wherein the microorganism of the genus Aspergillus is Aspergillus flavus ATCC 11492 strain.

[10] Formula (IV ′):

(Wherein A is an oxygen atom or a sulfur atom, R ^{1 ′} is a methyl group, an ethyl group, a propyl group or a butyl group, and R ^{2 ′} and R ^{3 ′} are both methyl groups, or A is an oxygen atom or a sulfur atom, R ^{1 ′} is a methyl group, and R ^{2 ′} and R ^{3 ′} are bonded to each other to represent an ethylene group or a propylene group.)
An optically active (S) -ketal ester (hereinafter also referred to as optically active (S) -ketal ester (IV ′)).

[11] The optically active (S) -ketal ester according to the above [10], wherein A is an oxygen atom, and R ^{1 ′} , R ^{2 ′} and R ^{3 ′} are all methyl groups.

  According to the production method of the present invention, optically active (S) -7-hydroxy-6-methylheptan-2-one (I) and its precursor, optically active (S) -2-methyl-6-oxoheptane The acid ester (III) can be easily and efficiently produced industrially.

The present invention is described in detail below.
First, the definition of the group used in this specification will be described below.
The “C _1-5 alkyl group” is a linear or branched alkyl group having 1 to 5 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and n-butyl. Group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1,2-dimethylpropyl group and the like. Among these, a methyl group, an ethyl group, and an n-propyl group are preferable, and a methyl group is more preferable.

The “C _2-5 alkylene group” is a linear or branched alkylene group having 2 to 5 carbon atoms, and examples thereof include an ethylene group, a propylene group, a butylene group, and a pentylene group. Preferably, they are an ethylene group and a propylene group.

R ¹ is preferably a methyl group, an ethyl group or an n-propyl group, more preferably a methyl group.
R ² and R ³ are preferably both methyl groups or together form an ethylene or propylene group.

  In the present invention, first, 2-methyl-6-oxoheptanoic acid ester (II) is optically resolved by causing an esterase derived from a microorganism of the genus Aspergillus that can preferentially hydrolyze the R-form, The active (S) -2-methyl-6-oxoheptanoic acid ester (III) is prepared (step a).

2-Methyl-6-oxoheptanoic acid ester (II) has two optical isomers (S-form and R-form) having an asymmetric center at the α-position of the —CO ₂ R ¹ group. However, even if the 2-methyl-6-oxoheptanoic acid ester (II) used in the production method of the present invention is a racemate containing an equivalent amount of these optical isomers, an excess of one optical isomer ( It may be a mixture containing (in any proportion). A racemate is preferable. The wavy line in the formula (II) represents a single bond with a methyl group, and the 2-methyl-6-oxoheptanoic acid ester (II) has the above-mentioned asymmetric center at the carbon atom to which the methyl group is bonded. It represents a mixture containing a racemate or one of the optical isomers in excess (in any proportion).

  For example, 2-methyl-6-oxoheptanoic acid ester (II) is obtained by referring to the descriptions in Patent Documents 1, 2, 7, Non-Patent Documents 1, 2, etc. It can be obtained by esterification. In addition, as for 2-methyl-6-oxoheptanoic acid, for example, referring to Non-Patent Documents 7 and 8, etc., 2,6-dimethylcyclohexanone that is easily available industrially is used as potassium permanganate. Can be obtained by oxidation.

  The esterase used in step a can preferentially hydrolyze the R form. In the present invention, an esterase derived from a microorganism of the genus Aspergillus that can preferentially hydrolyze the R-form (hereinafter also simply referred to as esterase) is used, and preferably the R-form can be preferentially hydrolyzed. Esterase derived from Aspergillus flavus, more preferably esterase derived from Aspergillus flavus ATCC 11492 strain is used. Furthermore, these esterases are derived from these microorganisms by treatment with a mutagen or ultraviolet rays, even if they are produced by recombinant microorganisms transformed by introducing the enzyme genes of these microorganisms. Even if it is an esterase derived from a mutant or a mutant esterase in which one or several specific amino acids in the amino acid sequence of these esterases are missing, added or substituted by genetic engineering techniques, etc. Good. These microorganisms can be easily subjected to liquid culture by a normal method, for example, a method in which the microorganism is inoculated into a sterilized liquid medium and reciprocally shake cultured at 20 to 40 ° C. In addition, solid culture may be performed as necessary. Examples of those derived from animals include those derived from steapsin, pancreatin, porcine, and sheep. Examples of plant-derived materials include those derived from wheat germ.

  The form of esterase is not particularly limited, and various forms such as purified esterase, crude esterase, esterase-containing material, microbial culture solution, microbial culture, microbial cell, microbial cell culture solution, and those obtained by treating them However, from the viewpoint of providing an industrial production method, it is preferable to use one in which various forms of esterase as described above are immobilized. As an immobilization method, for example, the esterase is adsorbed, polyacrylamide method, sulfur-containing to an inorganic carrier such as silica gel or ceramics, a natural resin such as cellulose, or a synthetic resin such as styrene-divinylbenzene copolymer. Examples of the method include immobilization using a known method such as a polysaccharide gel method, an alginate gel method, an agar gel method, and the like. Of these, esterases immobilized by an adsorption method are preferably used.

  The amount of esterase used may be appropriately selected according to the form of esterase, enzyme activity, etc. so that hydrolysis proceeds well with good stereoselectivity. For example, when the esterase is in the form of purified esterase or crude esterase, the amount used is usually in the range of 0.001 to 2 parts by weight relative to 1 part by weight of 2-methyl-6-oxoheptanoic acid ester (II). Preferably, it is the range of 0.002-0.5 weight part. Moreover, the usage-amount in the form of microbial culture, a microbial cell, and those processed materials is 0.01-200 weight normally with respect to 1 weight part of 2-methyl-6-oxoheptanoic acid ester (II). Parts, preferably 0.1 to 50 parts by weight.

Hydrolysis by esterase is performed in water or a mixed solvent of water and an organic solvent.
The amount of water used is usually 0.5 to 200 parts by weight, preferably 0.5 to 20 parts by weight per 1 part by weight of 2-methyl-6-oxoheptanoic acid ester (II).

  Examples of the organic solvent include a hydrophobic organic solvent and a hydrophilic organic solvent. Examples of the hydrophobic organic solvent include ethers such as methyl tert-butyl ether and isopropyl ether; ketones such as methyl isobutyl ketone and methyl ethyl ketone; toluene , Hydrocarbons such as hexane, cyclohexane and heptane. Examples of the hydrophilic organic solvent include alcohols such as tert-butanol, methanol, ethanol, isopropanol, and n-butanol; ethers such as tetrahydrofuran; sulfoxides such as dimethyl sulfoxide; ketones such as acetone; N, N— Amides such as dimethylformamide; and nitriles such as acetonitrile. These hydrophobic organic solvent and hydrophilic organic solvent may be used alone or in combination of two or more kinds, or a hydrophobic organic solvent and a hydrophilic organic solvent may be used in combination.

  The amount of the organic solvent used is usually 200 parts by weight or less, preferably 0.1 to 100 parts by weight with respect to 1 part by weight of 2-methyl-6-oxoheptanoic acid ester (II).

Moreover, although it depends on the type of esterase, hydrolysis with esterase is carried out while maintaining the value such that the stereoselectivity of hydrolysis does not decrease, usually pH 4 to 10, preferably pH 6 to 8.
To adjust the pH to the above range, a buffered aqueous solution is used. Examples of the buffered aqueous solution include buffered aqueous solutions of inorganic acid salts such as alkali metal phosphate aqueous solutions (sodium phosphate aqueous solution, potassium phosphate aqueous solution, etc.), acetic acid, and the like. Examples include buffered aqueous solutions of organic acid salts such as aqueous alkali metal salt solutions (sodium acetate aqueous solution, potassium acetate aqueous solution, etc.). The concentration of this buffer is preferably 0.01 to 0.3M, more preferably 0.05 to 0.1M. This buffer also serves as a solvent.

  Moreover, in order to maintain pH in said range, you may adjust by adding a base to a reaction system as needed. Examples of the base include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, alkaline earth metal carbonates such as calcium carbonate; sodium hydrogen carbonate, carbonate Alkali metal bicarbonates such as potassium hydrogen, sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, etc .; organic bases such as triethylamine, pyridine; ammonia etc. Can be mentioned. These bases may be used alone or in combination of two or more. The base is usually added as an aqueous solution, but may be added as a mixed solvent solution of an organic solvent and water. Examples of the organic solvent include the same ones as described above. The base may be added as a solid or as a suspension.

  The method for performing the hydrolysis is not particularly limited. For example, water (for example, buffered aqueous solution), 2-methyl-6-oxoheptanoic acid ester (II) and esterase (for example, those immobilized on a resin or the like) ). When an organic solvent is used, water, 2-methyl-6-oxoheptanoic acid ester (II) and esterase may be mixed in the organic solvent.

  If the reaction temperature is too high, the esterase stability tends to decrease, and if it is too low, the reaction rate tends to decrease. The reaction temperature is preferably in the range of about 5 to 65 ° C, more preferably in the range of about 10 to 50 ° C. Although reaction time changes also with reaction temperature, it is 1 to 100 hours normally.

  By the above hydrolysis, the R form in 2-methyl-6-oxoheptanoic acid ester (II) is stereoselectively hydrolyzed to a carboxylic acid while maintaining its configuration (that is, optically active (R)). 2-methyl-6-oxoheptanoic acid is formed).

Thus, a reaction mixture comprising unreacted optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) and hydrolysis product optically active (R) -2-methyl-6-oxoheptanoic acid Is obtained.
In order to separate these compounds in the reaction mixture, or in order to separate these compounds from esterases, buffer agents (components of buffered aqueous solution), etc. used in the reaction, further post-treatment operations may be performed. . Examples of the post-treatment operation include a method of separating and purifying using silica gel chromatography after distilling off the solvent in the reaction mixture, and a method of separating and purifying by liquid separation operation. Specifically, the optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) can be isolated by subjecting the reaction mixture after hydrolysis to, for example, the following treatment. it can. First, when insoluble esterase, an immobilization support, etc. are present in the reaction mixture, the reaction mixture is filtered through a filter aid as necessary to remove these insoluble matters. Here, in order to improve the filterability, the esterase may be subjected to heat-denaturation or acid-denaturation treatment, or may be subjected to body feed filtration (filtering by mixing a filter aid with the reaction mixture). . Then, if necessary, the pH of the filtrate is adjusted to 6 to 9, and then the aqueous layer and the organic layer are separated, and the organic layer is optically active (S) -2-methyl-6-oxoheptanoic acid ester (III). A solution of Here, in order to improve the liquid separation property, alcohols such as methanol, ethanol and n-butanol may be added to the filtrate. When a hydrophobic organic solvent is used in the hydrolysis, the obtained reaction mixture may be separated as it is, but when the hydrophobic organic solvent is not used in the hydrolysis, the amount used is small. In the case where the liquid cannot be easily separated or in the case where the liquid cannot be easily separated due to the small amount of water used, the liquid may be separated after appropriately adding a hydrophobic organic solvent or water. Examples of the hydrophobic organic solvent include ethers such as methyl tert-butyl ether and isopropyl ether, hydrocarbons such as toluene, hexane, cyclohexane and heptane, and halogenated carbonization such as dichloromethane, dichloroethane, chloroform, chlorobenzene and orthodichlorobenzene. Examples thereof include hydrogens, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and esters such as ethyl acetate, methyl acetate and butyl acetate.

  Next, by distilling off the organic solvent from the obtained organic solvent solution of the optically active (S) -2-methyl-6-oxoheptanoic acid ester (III), the desired optically active (S) -2-methyl- The 6-oxoheptanoic acid ester (III) can be removed. The obtained optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) may be further purified by distillation, column chromatography or the like.

  In addition, the optically active (R) -2-methyl-6-oxoheptanoic acid, which is a hydrolysis product, is contained in the aqueous layer after the liquid separation. This may be caused by distilling off water or neutralization. It can be easily removed from the aqueous layer by extraction with an organic solvent after the treatment. The obtained optically active (R) -2-methyl-6-oxoheptanoic acid is reused as 2-methyl-6-oxoheptanoic acid ester (II) by subjecting it to esterification and racemization treatments. Can do.

  The optical purity of the optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) thus obtained is preferably 90 to 100% ee, more preferably 95 to 100% ee. Yes, most preferably 98-100% ee.

  This optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) is converted into the desired optically active (S) -7-hydroxy-6-methylheptane-2-ester by the following steps b to d. Can be turned on (I).

(Process b)
In this step, the optically active (S) -ketal ester (IV) is obtained by protecting the carbonyl group of the optically active (S) -2-methyl-6-oxoheptanoic acid ester (III). In the present invention, the optically active (S) -ketal ester (IV) includes an optically active (S) -thioketal ester.

The method for protecting the carbonyl group is not particularly limited, and is used in the art to convert the carbonyl group into a ketal group (A = O) or a thioketal group (A = S) (that is, to protect the carbonyl group). Any commonly used method can be employed. For example, optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) is converted to alcohols or orthoformates or thiols corresponding to R ² and R ³ in the presence of an acid catalyst in an organic solvent. The method of making it react with is mentioned.

  The organic solvent is not particularly limited as long as it does not hinder the progress of the reaction. For example, ethers such as methyl tert-butyl ether and isopropyl ether; hydrocarbons such as toluene, hexane, cyclohexane, heptane, octane and isooctane Halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, chlorobenzene and orthodichlorobenzene. The amount of the organic solvent used may be appropriately adjusted according to the type of optically active (S) -2-methyl-6-oxoheptanoic acid ester (III) and the like, and usually optically active (S) -2-methyl- It is 0.5-50 weight part with respect to 1 weight part of 6-oxoheptanoic acid ester (III).

  The acid catalyst is not particularly limited. For example, inorganic acids such as hydrochloric acid and ammonium chloride; organic acids such as camphorsulfonic acid and p-toluenesulfonic acid monohydrate; strong acid ion exchange such as amberlist Resins etc. are mentioned. The amount of the acid catalyst to be used is preferably 0.001 to 0.5 equivalent, more preferably 0.001 to 1 equivalent of optically active (S) -2-methyl-6-oxoheptanoic acid ester (III). 005 to 0.2 equivalents.

The alcohols corresponding to R ² and R ³ are not particularly limited, and examples thereof include methanol, ethanol, ethylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, and the like. Is mentioned. The amount of alcohol used is preferably 1 to 50 equivalents, more preferably 2 to 10 equivalents, with respect to 1 equivalent of optically active (S) -2-methyl-6-oxoheptanoic acid ester (III). In some cases, the amount may be a solvent amount.

Orthoformates corresponding to R ² and R ³ are not particularly limited, and examples thereof include methyl orthoformate, ethyl orthoformate, and propyl orthoformate. The amount of orthoformate used is preferably 1 to 50 equivalents, more preferably 2 to 10 equivalents with respect to 1 equivalent of optically active (S) -2-methyl-6-oxoheptanoate (III). is there.

Thiols corresponding to R ² and R ³ are not particularly limited, and examples thereof include methanethiol, ethanethiol, propanethiol, isopropanethiol, butanethiol, 1,2-ethanedithiol, 1,3- Examples include propanedithiol. The amount of thiols used is preferably 1 to 50 equivalents, more preferably 2 to 10 equivalents, relative to 1 equivalent of optically active (S) -2-methyl-6-oxoheptanoic acid ester (III). In some cases, the amount may be a solvent amount.

  The reaction temperature is preferably 10 to 120 ° C, more preferably 20 to 60 ° C. The reaction time varies depending on the reaction temperature, but is usually 10 minutes to 50 hours.

  The optically active (S) -ketal ester (IV) can be isolated by subjecting the reaction mixture obtained by the above reaction to, for example, a liquid separation operation. The isolated optically active (S) -ketal ester (IV) can be purified by conventional means such as distillation and chromatography, if necessary.

(Process c)
This step is a step of reducing the optically active (S) -ketal ester (IV) to obtain the optically active (S) -ketal alcohol (V). In the present invention, the optically active (S) -ketal alcohol (V) includes optically active (S) -thioketal alcohol.

  The reduction method is not particularly limited, and any method commonly used in the art for reducing a carboxylic acid ester to an alcohol can be employed. For example, the method of making optically active (S) -ketal ester (IV) react with a reducing agent in an organic solvent is mentioned.

  The organic solvent is not particularly limited as long as it does not hinder the progress of the reaction. For example, ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran (THF), 1,4-dioxane, methyl tert-butyl ether; hexane, Hydrocarbons such as heptane and toluene; halogenated hydrocarbons such as dichloromethane, dichloroethane, chlorobenzene, and orthodichlorobenzene. What is necessary is just to adjust the usage-amount of an organic solvent suitably according to the kind etc. of optically active (S) -ketal ester (IV), and is 1 normally with respect to 1 weight part of optically active (S) -ketal ester (IV). ~ 100 parts by weight.

  As the reducing agent, one that usually reduces an ester to give an alcohol is used. For example, borohydride alkali metal salts such as sodium borohydride and lithium borohydride; trialkylborohydride alkali metal salts such as lithium triethylborohydride; aluminum hydride alkali metal salts such as lithium aluminum hydride; hydrogen Dialkylaluminum hydride such as diisobutylaluminum hydride; and the like. The amount of the reducing agent used is preferably 0.5 to 20 equivalents and more preferably 1 to 10 equivalents with respect to 1 equivalent of the optically active (S) -ketal ester (IV).

  The reaction temperature is preferably −78 to 60 ° C., more preferably −40 to 30 ° C. Although reaction time changes also with reaction temperature, it is 1 to 70 hours normally.

(Process d)
In this step, optically active (S) -ketal alcohol (V) is deprotected to obtain optically active (S) -7-hydroxy-6-methylheptan-2-one (I).
The deprotection method is not particularly limited, and the carbonyl group protected in step b is deprotected (that is, the ketal group (A = O) or the thioketal group (A = S) is converted into a carbonyl group). Therefore, any method usually used in the field can be employed. For example, the method of acid-treating in water or an organic solvent is mentioned.

  The organic solvent is not particularly limited as long as it does not hinder the progress of the reaction. For example, alcohols such as methanol and ethanol; diethyl ether, diisopropyl ether, tetrahydrofuran (THF), 1,4-dioxane, methyl tert- Ethers such as butyl ether; Halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, chlorobenzene and orthodichlorobenzene; Ketones such as acetone; Hydrocarbons such as toluene, hexane, cyclohexane, heptane, octane and isooctane; and these And the like. The amount of the organic solvent used may be appropriately adjusted according to the type of the optically active (S) -ketal alcohol (V), and is usually 2 with respect to 1 part by weight of the optically active (S) -ketal alcohol (V). ~ 50 parts by weight. These organic solvents may be used alone or in combination with water.

  The acid is not particularly limited. For example, inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as trifluoroacetic acid, p-toluenesulfonic acid, formic acid, acetic acid, and oxalic acid; strong acids such as amberlist Ion exchange resins and the like. The amount of acid used is preferably 0.001 to 50 equivalents and more preferably 0.1 to 10 equivalents with respect to 1 equivalent of optically active (S) -ketal alcohol (V).

  The reaction temperature is preferably 0 to 100 ° C, more preferably 20 to 80 ° C. The reaction time varies depending on the reaction temperature, but is usually 30 minutes to 24 hours.

In the case of a thioketal group (A = S), in addition to the above acid treatment, there is a method using a reaction reagent such as a metal salt, an oxidizing agent, a halogenating agent, etc., which is preferable from the viewpoint of reactivity. .
Examples of the metal salt include silver salts such as silver perchlorate (I), silver oxide and silver nitrate; mercury salts such as mercury chloride and mercury oxide; thallium salts such as thallium nitrate (III) and thallium trifluoroacetate (III); Examples thereof include copper salts such as copper chloride (I) and copper oxide (I). As the oxidizing agent, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), m-chloroperbenzoic acid (mCPBA), cerium ammonium nitrile, sodium periodate, hydrogen peroxide, molecular oxygen Etc. Examples of the halogenating agent include iodine, N-bromosuccinimide, N-chlorosuccinimide and the like. The amount of these reaction reagents to be used is preferably 1 to 20 equivalents, more preferably 1 to 10 equivalents, with respect to 1 equivalent of optically active (S) -ketal alcohol (V).

  As the reaction solvent, an organic solvent or a mixed solvent of an organic solvent and water is used. The organic solvent is not particularly limited as long as it does not hinder the progress of the reaction. For example, alcohols such as methanol and ethanol; diethyl ether, diisopropyl ether, tetrahydrofuran (THF), 1,4-dioxane, methyl tert- Ethers such as butyl ether; Halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, chlorobenzene and orthodichlorobenzene; Ketones such as acetone; Hydrocarbons such as toluene, hexane, cyclohexane, heptane, octane and isooctane; and these And the like. The amount of the organic solvent used may be appropriately adjusted according to the type of optically active (S) -ketal alcohol (V) and the like, and is usually 1 per 1 part by weight of optically active (S) -ketal alcohol (V). ~ 100 parts by weight. These organic solvents may be used alone.

  The reaction temperature is preferably −45 to 160 ° C., more preferably 0 to 80 ° C. The reaction time varies depending on the reaction temperature, but is usually 5 minutes to 20 hours.

  The optically active (S) -7-hydroxy-6-methylheptan-2-one (I) thus obtained can be purified by conventional means such as distillation and chromatography, if necessary. . Steps b to d may be performed independently as separate steps or may be performed as a single continuous step.

Alternatively, the following steps A and B may be performed instead of the steps a and b.
Step A: Protecting the carbonyl group of 2-methyl-6-oxoheptanoic acid ester (II) to give a compound of formula (VI):

(Wherein A, R ¹ , R ² and R ³ are as defined above.)
And a step B: esterase derived from a microorganism of the genus Aspergillus, which can preferentially hydrolyze the R-form into the ketal ester (VI). To obtain optically active (S) -ketal ester (IV) by optical resolution.

  Step A can be performed by the same method as in step b. Moreover, the process B can be performed by the same method as the process a.

  Of the optically active (S) -ketal ester (IV), the formula (IV ′):

(Wherein A is an oxygen atom or a sulfur atom, R ^{1 ′} is a methyl group, an ethyl group, a propyl group or a butyl group, and R ^{2 ′} and R ^{3 ′} are both methyl groups, or A is an oxygen atom or a sulfur atom, R ^{1 ′} is a methyl group, and R ^{2 ′} and R ^{3 ′} are bonded to each other to represent an ethylene group or a propylene group.)
Is a novel compound. Optically active (S) -ketal alcohol (V) is also a novel compound.

  EXAMPLES Hereinafter, although a reference example and an Example demonstrate this invention concretely, this invention is not limited to these.

Reference example 1
Synthesis of racemic 2-methyl-6-oxoheptanoic acid (Part 1)
Suspension of potassium permanganate (195.7 g, 1.24 mol) in water (1390 ml) while vigorously stirring a mixture of 2,6-dimethylcyclohexanone (120.0 g, 0.95 mol) and water (600 ml). The solution was carefully added at about 30 ° C. over about 1 hour and stirred overnight at room temperature. The produced manganese dioxide was filtered and the filter cake was washed with methyl tert-butyl ether (250 ml) and water (250 ml). The organic layer of the filtrate was separated, the aqueous layer was adjusted to pH 1.0 with 35% concentrated hydrochloric acid (about 150 ml), sodium chloride (400 g) was added, and the mixture was extracted with ethyl acetate (300 ml × 5). After drying over magnesium, the solvent was distilled off under reduced pressure, and the resulting oil residue was distilled under reduced pressure using a vacuum pump. A fraction having a boiling point of 130 to 144 ° C./267 Pa was collected to obtain 79.92 g (yield 53.2%) of a racemic 2-methyl-6-oxoheptanoic acid.

Reference example 2
Synthesis of racemic 2-methyl-6-oxoheptanoic acid (Part 2)
2,6-dimethylcyclohexanone (93.0 g, 0.737 mol), water (1057 ml) and acetone (333 ml) were charged into 2 L of Kolben, and the temperature was raised to an internal temperature of 50 ° C. with a hot water bath. Under stirring at 45 to 55 ° C., potassium permanganate (326 g, 2.06 mol) was added in 9 portions over about 9 and a half hours. The mixture was stirred at the same temperature for about 2 hours. At the same temperature, the produced manganese dioxide was filtered using a Nutsche having a diameter of 12 cm, and the material on the filter was washed with water (300 ml) and acetone (100 ml). The filtrate was stirred under reduced pressure at a bath temperature of 40 ° C. and 14.7 to 17.3 kPa, and acetone was distilled off.
Sodium chloride (330 g) was added to the aqueous solution thus obtained for dissolution, and the solution was washed with ethyl acetate (200 ml). After further washing with THF (200 ml), THF (500 ml) was added and 35% synthetic hydrochloric acid (107 ml) was added dropwise to acidify the pH of the aqueous solution from 8.7 to 0.81. After separating into a THF layer and an aqueous layer, the aqueous layer was further extracted with THF (150 ml) and combined with the first THF layer.
Magnesium chloride (4.0 g) was added to the resulting THF solution and stirred for 30 minutes. The aqueous layer separated from the THF layer was separated and removed. Thereafter, THF was distilled off under reduced pressure at a bath temperature of 40 ° C., and further, the mixture was swept by a vacuum pump (133 Pa) for 60 minutes while stirring with a magnetic stirrer at a bath temperature of 50 ° C. to obtain 106.27 g (content 93.9%). A racemate of 2-methyl-6-oxoheptanoic acid (gas chromatography (GC); distillate), purity conversion yield 85.7%) was obtained.

Reference example 3
Synthesis of racemic 2-methyl-6-oxoheptanoic acid methyl ester After dissolving 43 g of racemic 2-methyl-6-oxoheptanoic acid (purity 99.65%, 0.27 mmol) in 214.25 g of methanol 2.14 g of concentrated sulfuric acid was added and mixed. Next, the mixture was heated to 65 ° C. and reacted at the same temperature for 5 hours. After completion of the reaction, the reaction mixture was cooled to room temperature. Next, the reaction mixture was concentrated under reduced pressure until it became about one quarter of the original weight, and then 30 g of water was added. Further, 128.55 g of methyl tert-butyl ether (MTBE) was added, and 55.06 g of 5% aqueous sodium hydrogen carbonate solution was added dropwise at room temperature with stirring. The resulting mixture was sufficiently stirred at room temperature and then separated, and the aqueous layer was further separated with 64.27 g of MTBE. The obtained organic layers were combined and concentrated under reduced pressure to give 45.4 g (content 94.3%, yield 92%) of a racemic crude product of 2-methyl-6-oxoheptanoic acid methyl ester as a colorless oil. Obtained as a thing. The obtained crude product was used in the next reaction as it is (note that the obtained crude product may be used in the next reaction after distillation (boiling point 107 ° C./1333 Pa) if necessary).

Example 1
Optical resolution by hydrolysis using 2-methyl-6-oxoheptanoic acid methyl ester racemic esterase derived from Aspergillus flavus ATCC 11492 (Part 1)
Racemic 1.0 g (5.75 mmol) of 2-methyl-6-oxoheptanoic acid methyl ester was suspended in 5.0 g of 0.1 M phosphate buffer (pH 7.0). After cooling the suspension to 10 ° C., 0.7 g of immobilized esterase derived from Aspergillus flavus ATCC 11492 strain (prepared by the method described in Japanese Patent Application Publication No. 2003-70471) (water content 56%, enzyme activity 4028 KU / Kg) Then, the mixture was stirred at 10 ° C. for 23 hours while appropriately adding a 4% NaOH aqueous solution to maintain the pH at 6-7. Thereafter, a part of the reaction solution was taken and analyzed by HPLC [Chiralpak AS-H, 4.6 mm × 25 cm (manufactured by Daicel)], and optically active (S) -2-methyl-6-oxoheptanoic acid methyl ester. The optical purity and reaction yield of the ester were determined. As a result, the optical purity was 100% ee, and the reaction yield was 47% (value calculated from the optical purity).
For reference, optically active (R) -2-methyl-6-oxoheptanoic acid, which is a hydrolysis product, has an optical purity of 90.4% ee and a reaction yield of 52.5% (value calculated from the optical purity). Met.

Example 2
Optical resolution by hydrolysis using 2-methyl-6-oxoheptanoic acid methyl ester racemic esterase derived from Aspergillus flavus ATCC 11492 (part 2)
To 5.0 g of 0.1 M phosphate buffer (pH 7.0), 1.0 g (5.75 mmol) of racemic methyl 2-methyl-6-oxoheptanoate and 2.0 g of methyl tert-butyl ether (MTBE) Was suspended. After cooling the suspension to 10 ° C., 0.7 g of immobilized esterase derived from Aspergillus flavus ATCC 11492 strain (prepared by the method described in Japanese Patent Application Publication No. 2003-70471) (water content 56%, enzyme activity 4028 KU / Kg) The solution was stirred at 10 ° C. for 23 hours while appropriately adding a 4% NaOH aqueous solution to maintain the pH at 6-8. Thereafter, a part of the reaction solution was taken and analyzed by HPLC [Chiralpak AS-H, 4.6 mm × 25 cm (manufactured by Daicel)], and optically active (S) -2-methyl-6-oxoheptanoic acid methyl ester. The optical purity and reaction yield of the ester were determined. As a result, the optical purity was 100% ee, and the reaction yield was 47% (value calculated from the optical purity).
For reference, the optical purity of the hydrolyzed product, optically active (R) -2-methyl-6-oxoheptanoic acid, was 88.2% ee, and the reaction yield was 53% (value calculated from the optical purity). It was.

Example 3
Optical resolution by hydrolysis using 2-methyl-6-oxoheptanoic acid methyl ester racemic esterase derived from Aspergillus flavus ATCC 11492 (part 3)
Racemic 1.0 g (5.75 mmol) of 2-methyl-6-oxoheptanoic acid methyl ester and 2.0 g of MTBE were suspended in 5.0 g of 0.1 M phosphate buffer (pH 7.0). After cooling the suspension to 10 ° C., 0.1 g of an immobilized esterase derived from Aspergillus flavus ATCC 11492 strain (prepared by the method described in Japanese Patent Application Laid-Open No. 2003-70471) (water content 56%, enzyme activity 4028 KU / Kg) The solution was stirred at 10 ° C. for 99 hours while appropriately adding a 4% aqueous NaOH solution to maintain the pH at 6-8. Thereafter, a part of the reaction solution was taken and analyzed by HPLC [Chiralpak AS-H, 4.6 mm × 25 cm (manufactured by Daicel)], and optically active (S) -2-methyl-6-oxoheptanoic acid methyl ester. The optical purity and reaction yield of the ester were determined. As a result, the optical purity was 99.8% ee, and the reaction yield was 48.5% (value calculated from the optical purity).
For reference, the optical purity of the optically active (R) -2-methyl-6-oxoheptanoic acid, which is a hydrolysis product, is 94.2% ee, and the reaction yield is 51.5% (value calculated from the optical purity). Met.

Example 4
Optical resolution by hydrolysis using 2-methyl-6-oxoheptanoic acid methyl ester racemic esterase derived from Aspergillus flavus ATCC 11492 (Part 4)
Racemic 10.6 g of 2-methyl-6-oxoheptanoic acid methyl ester (content 94.3%, 5.75 mmol) and 20.0 g of MTBE were added to 50.0 g of 0.1 M phosphate buffer (pH 7.0). Suspended. After cooling the suspension to 10 ° C., 2.0 g of immobilized esterase derived from Aspergillus flavus ATCC 11492 strain (prepared by the method described in Japanese Patent Laid-Open No. 2003-70471) (moisture content 56%, enzyme activity 4028 KU / Kg) Then, the mixture was stirred at 10 ° C. for 51 hours while appropriately adding a 4% aqueous NaOH solution to maintain the pH at 7.0 to 7.5. Thereafter, the reaction solution was filtered using radiolite (filter aid, trade name: Showa Chemical Industries) to remove esterase. The obtained filtrate was extracted twice with 25 g and 12.5 g of methyl isobutyl ketone (MIBK), and then the obtained organic layers were combined and washed with 15% brine to obtain optically active (S) -2- A MIBK solution of methyl-6-oxoheptanoic acid methyl ester (optical purity 98.9% ee, yield 41.5%) was obtained. The optical purity was analyzed by HPLC [Chiralpak AS-H, 4.6 mm × 25 cm (manufactured by Daicel)] in the same manner as in Example 1.

Example 5
Optical resolution by hydrolysis using 2-methyl-6-oxoheptanoic acid methyl ester racemic esterase derived from Aspergillus flavus ATCC 11492 (Part 5)
Racemic 10.6 g of 2-methyl-6-oxoheptanoic acid methyl ester (content 94.3%, 5.75 mmol) and 20.0 g of MTBE were added to 50.0 g of 0.1 M phosphate buffer (pH 7.0). Suspended. After cooling the suspension to 10 ° C., 2.0 g of immobilized esterase derived from Aspergillus flavus ATCC 11492 strain (prepared by the method described in Japanese Patent Laid-Open No. 2003-70471) (moisture content 56%, enzyme activity 4028 KU / Kg) And 4% NaOH aqueous solution was added as appropriate to maintain the pH at 7.5 to 8.0, and the mixture was stirred at 10 ° C. for 48 hours. Thereafter, the reaction solution was filtered using radiolite (filter aid, trade name: Showa Chemical Industries) to remove esterase. The obtained filtrate was extracted twice with 25 g and 12.5 g of MIBK, and then the obtained organic layers were combined and washed with 15% brine to obtain optically active (S) -2-methyl-6-oxoheptane. An acid methyl ester MIBK solution (optical purity 98.8% ee, yield 40.3%) was obtained. The optical purity was analyzed by HPLC [Chiralpak AS-H, 4.6 mm × 25 cm (manufactured by Daicel)] in the same manner as in Example 1.

Reference example 4
Synthesis of 6,6-dimethoxy-2 -methylheptanoic acid methyl ester 15.4 g of 2-methyl-6-oxoheptanoic acid methyl ester (content 84.4%, 75.5 mmol) was converted to 24.2 g (0.75 mol) of methanol. Then, 40.1 g (0.38 mol) of methyl orthoformate and 0.14 g (0.75 mmol) of p-toluenesulfonic acid monohydrate were added and mixed. Next, the mixture was heated to 65 ° C. and reacted at the same temperature for 1.5 hours. After completion of the reaction, the reaction mixture was cooled to room temperature. Next, 39 g of toluene and 26 g of 3% aqueous sodium hydrogen carbonate solution were added to the reaction mixture, and the mixture was sufficiently stirred. After separating the reaction mixture, the obtained organic layer was concentrated under reduced pressure to give 22.8 g of a crude product of 6,6-dimethoxy-2-methylheptanoic acid methyl ester (content 69.5%, reaction yield 95). %). The obtained crude product of 6,6-dimethoxy-2-methylheptanoic acid methyl ester was directly used in the next reaction.
In addition, a portion of the resulting crude product of 6,6-dimethoxy-2-methylheptanoic acid methyl ester was purified by column chromatography to obtain colorless oily 6,6-dimethoxy-2-methylheptanoic acid methyl ester. Obtained.
¹ H-NMR (CDCl ₃ , 300 MHz): δ 1.15 (3H, d, J = 7.0 Hz), 1.24 (2H, s), 1.27-1.47 (3H, m), 1. 56-1.74 (3H, m), 2.45 (1H, dt, J = 7.0, 14.0 Hz), 3.15 (6H, s), 3.67 (3H, s).

Reference Example 5
Synthesis of 7-hydroxy-6-methylheptan-2-one (Part 1)
Racemic 1.90 g (content 84.4%, 7.3 mmol) of 6,6-dimethoxy-2-methylheptanoic acid methyl ester was dissolved in 4.8 g of THF, 0.93 g (21.9 mmol) of lithium chloride and hydrogen 1.66 g of sodium borohydride (content 90%, 39.5 mmol) was sequentially added and mixed. Next, 8.80 g of methanol was added dropwise to the reaction mixture at room temperature over 4 hours, and then stirred overnight at the same temperature. Next, 32.07 g of 5% hydrochloric acid was added dropwise to the reaction mixture at room temperature, and 45.3 g of a homogeneous solution containing 0.96 g (yield 90.7%) of 7-hydroxy-6-methylheptan-2-one was added. Obtained.

Reference Example 6
Synthesis of 7-hydroxy-6-methylheptan-2-one (2)
Lithium aluminum hydride 0.74 g (content 80%, 15.6 mmol) was suspended in 7.0 g of THF, and the resulting suspension was cooled to 0 ° C. Next, a solution prepared by dissolving 2.37 g (content 84.4%, 9.2 mmol) of 6,6-dimethoxy-2-methylheptanoic acid methyl ester in 3.0 g of THF was added to the suspension at 1.degree. It was dripped over 5 hours. Subsequently, after stirring the reaction mixture at the same temperature for 3 hours, 1.47 g (45.9 mmol) of methanol was added dropwise to quench unreacted lithium aluminum hydride. Next, 2.74 g of a 2% aqueous sodium hydroxide solution was added dropwise to the reaction mixture at room temperature, and the resulting aluminum hydroxide was removed by filtration using radiolite (filter aid, trade name: Showa Chemical Industries). Subsequently, an acid treatment was performed to obtain a homogeneous solution containing 7-hydroxy-6-methylheptan-2-one (1.07 g, yield: 80.9%).

Example 6
Synthesis of (S) -6,6-dimethoxy-2 -methylheptanoic acid methyl ester 21.52 g (content 94.0%, 0.117 mol) of (S) -2-methyl-6-oxoheptanoic acid methyl ester After dissolving in 37.2 g (1.16 mol), 62.4 g (0.59 mol) of methyl orthoformate and 0.22 g (1.2 mmol) of p-toluenesulfonic acid monohydrate were added and mixed. Next, the reaction mixture was heated to 65 ° C. and reacted at the same temperature for 3 hours. After completion of the reaction, the reaction mixture was cooled to room temperature. Next, 61 g of toluene and 40.4 g of 3% aqueous sodium hydrogen carbonate solution were added to the reaction mixture, and the mixture was sufficiently stirred. After liquid separation, the obtained organic layer was concentrated under reduced pressure to give 25.14 g of a crude product of (S) -6,6-dimethoxy-2-methylheptanoic acid methyl ester (content 96.2%, reaction yield). 94.4%). The crude product of (S) -6,6-dimethoxy-2-methylheptanoic acid methyl ester was directly used in the next reaction. At this time, a part of the crude product of (S) -6,6-dimethoxy-2-methylheptanoic acid methyl ester obtained was purified by column chromatography to obtain colorless oil (S) -6,6-dimethoxy- 2-methylheptanoic acid methyl ester was obtained.
[Α] _D ²⁷ = 22.6 ° (5.01% in EtOH)

Example 7
Synthesis of (S) -7-hydroxy-6-methylheptan-2-one To a suspension obtained by adding 15 g of THF to 0.65 g (content 90%, 26.6 mmol) of lithium borohydride, (S) -6, A solution prepared by dissolving 5.13 g (content 96.2%, 22.6 mmol) of 6-dimethoxy-2-methylheptanoic acid methyl ester in 10 g of THF was added dropwise at room temperature. Next, the reaction mixture was heated to 55 ° C. and reacted at the same temperature for 9 hours to obtain (S) -6,6-dimethoxy-2-methylheptanol. Next, 7.32 g of methanol was added dropwise to the reaction mixture at room temperature over about 1 hour, followed by stirring at the same temperature for 4 hours. Next, 25.08 g of 5% hydrochloric acid was added dropwise to this reaction mixture at room temperature, and the mixture was further stirred at the same temperature for 30 minutes. This solution was extracted twice with 15 g and 12.5 g of methyl isobutyl ketone, and then the obtained organic layers were combined and washed twice with 10 g of 15% aqueous sodium carbonate solution to obtain (S) -7-hydroxy-6- 51.7 g of MIBK solution containing 2.95 g of methylheptan-2-one (yield 89.5%) was obtained. The solvent was distilled off under reduced pressure to obtain 3.68 g of a crude product of (S) -7-hydroxy-6-methylheptan-2-one as a pale yellow oil. This may be used for the next reaction without purification, or may be purified by vacuum distillation as necessary. A part of the obtained crude product of (S) -7-hydroxy-6-methylheptan-2-one was purified by distillation to obtain colorless oil (S) -7-hydroxy-6-methylheptane-2-one. Got on.
[Α] _D ²⁷ = −13.9 ° (5.03% in EtOH)

Reference Example 7
Acquisition of esterase 10 ml of 50 mg / ml ampicillin aqueous solution and 10 μl of E. coli with 10 ml of sterilized liquid medium (dissolved 5 ml of glycerol, 6 g of yeast extract, 4 g of 1 potassium phosphate, and 9.3 g of 2 potassium phosphate in 1000 ml of water) E. coli JM105 / pYHNK2 strain glycerol stock (see JP 2001-46084 A) 0.1 ml was added and shaken at 30 ° C. for 9 hours (the resulting culture medium is referred to as culture medium A).
Sterilized liquid medium (dissolve glycerol 225g, yeast extract 150g, total amino acid F225g, monopotassium phosphate 60g, magnesium sulfate 36g, ferrous sulfate heptahydrate 0.6g and calcium chloride dihydrate in 13000ml water) Further, water was added to make a total amount of 150,000 ml) 4M phosphoric acid aqueous solution and 14% (W / W) ammonia water were added to 15000 ml to adjust the pH to 7.0. To this, 7.5 ml of the above-mentioned culture solution A was added and cultured with aeration and stirring at 30 ° C. A sterilized liquid medium (a mixture of 1100 g of water and 1500 g of glycerol dissolved in 280 g of yeast extract and 420 g of total amino acid F) was gradually added after 14 hours from the start of the culture. Further, isopropyl thio-β-D-galactoside was added to 50 μM 18 hours after the start of the culture.
40 hours after the start of the culture, 1950 ml of ethanol was added to the culture solution, and the mixture was further stirred at 30 ° C. for 24 hours. Thereafter, 6000 g of this mixture was taken and mixed with 6200 g of water. This solution was continuously centrifuged (20000 rpm, flow rate 130 g / min) to obtain 11200 g of a centrifugal supernatant. 220 g of Radiolite # 200 (trade name of Showa Chemical Industry Co., Ltd.) was added to this centrifugal supernatant and stirred, and further filtered through Radiolite # 200 to obtain a protein clarified liquid.

Reference Example 8
Diaion HP20SS (trade name of Mitsubishi Chemical Co., Ltd.) washed with water with immobilized esterase (12 g of Diaion HP20SS and 300 ml of water mixed, stirred for 30 minutes, filtered, and further washed with 400 ml of water) and Reference Example 7 Was mixed with 600 g of the protein clarification solution produced by the above and stirred at 10 ° C. for 18 hours. Thereafter, the mixture was filtered and washed with 400 g of water to obtain 12.5 g of an immobilized enzyme.

According to the production method of the present invention, optically active (S) -7-hydroxy-6-methylheptan-2-one (I) and its precursor, optically active (S) -2-methyl-6-oxoheptane The acid ester (III) can be easily and efficiently produced industrially. This optically active (S) -7-hydroxy-6-methylheptan-2-one (I) is useful as a C ₇ -C ₁₂ building block in the synthesis of epothilone derivatives used as anticancer agents.

Claims (11)

Formula (II):

(In the formula, R ¹ represents a C _1-5 alkyl group.)
An optical resolution is carried out on the 2-methyl-6-oxoheptanoic acid ester represented by the formula (III) by acting an esterase derived from a microorganism of the genus Aspergillus that can preferentially hydrolyze the R-form. :

(Wherein R ¹ represents the same meaning as described above.)
A method for producing an optically active (S) -2-methyl-6-oxoheptanoic acid ester represented by the formula: Formula (III):

(In the formula, R ¹ represents a C _1-5 alkyl group.)
The carbonyl group of the optically active (S) -2-methyl-6-oxoheptanoic acid ester represented by formula (IV) is protected:

(In the formula, A represents an oxygen atom or a sulfur atom, R ¹ represents the same meaning as described above, and R ² and R ³ each independently represent a C _1-5 alkyl group or bonded to each other. Represents a C _2-5 alkylene group.)
The manufacturing method of Claim 1 which further includes the process of obtaining the optically active (S) -ketal ester represented by these. Formula (IV):

(In the formula, A represents an oxygen atom or a sulfur atom, R ¹ represents a C _1-5 alkyl group, and R ² and R ³ each independently represent a C _1-5 alkyl group, or bonded to each other. And represents a C _2-5 alkylene group.)
An optically active (S) -ketal ester represented by formula (V):

(In the formula, A, R ² and R ³ represent the same meaning as described above.)
The manufacturing method of Claim 2 which further includes the process of obtaining optically active (S) -ketal alcohol represented by these. Formula (II):

(Wherein R ¹ represents the same meaning as described above.)
Is optically resolved by acting esterase derived from microorganisms of the genus Aspergillus, which can preferentially hydrolyze R-form, to 2-methyl-6-oxoheptanoic acid ester represented by formula (III):

(Wherein R ¹ represents the same meaning as described above.)
A step of obtaining an optically active (S) -2-methyl-6-oxoheptanoic acid ester represented by:
The carbonyl group of the optically active (S) -2-methyl-6-oxoheptanoic acid ester represented by the formula (III) is protected to give the formula (IV):

(In the formula, A represents an oxygen atom or a sulfur atom, R ¹ represents the same meaning as described above, and R ² and R ³ each independently represent a C _1-5 alkyl group or bonded to each other. Represents a C _2-5 alkylene group.)
Obtaining an optically active (S) -ketal ester represented by:
The optically active (S) -ketal ester represented by the formula (IV) is reduced to give the formula (V):

(In the formula, A, R ² and R ³ represent the same meaning as described above.)
A step of obtaining an optically active (S) -ketal alcohol represented by formula (I); and deprotecting the optically active (S) -ketal alcohol represented by formula (V) to obtain formula (I):

Obtaining an optically active (S) -7-hydroxy-6-methylheptan-2-one represented by:
A process for producing optically active (S) -7-hydroxy-6-methylheptan-2-one represented by formula (I), comprising:   The production method according to claim 1, wherein the optical purity of the optically active (S) -2-methyl-6-oxoheptanoic acid ester represented by the formula (III) is 95 to 100% ee. The process according to any one of claims 1 to 5 R ¹ is a methyl group. The production method according to any one of claims 2 to 6, wherein R ² and R ³ are both methyl groups or bonded to each other to represent an ethylene group or a propylene group.   The production method according to any one of claims 1 to 7, wherein the microorganism of the genus Aspergillus is Aspergillus flavus.   The production method according to any one of claims 1 to 8, wherein the microorganism of the genus Aspergillus is Aspergillus flavus ATCC 11492 strain. Formula (IV ′):

(Wherein A is an oxygen atom or a sulfur atom, R ^{1 ′} is a methyl group, an ethyl group, a propyl group or a butyl group, and R ^{2 ′} and R ^{3 ′} are both methyl groups, or A is an oxygen atom or a sulfur atom, R ^{1 ′} is a methyl group, and R ^{2 ′} and R ^{3 ′} are bonded to each other to represent an ethylene group or a propylene group.)
An optically active (S) -ketal ester represented by The optically active (S) -ketal ester according to claim 10, wherein A is an oxygen atom, and R ^{1 ′} , R ^{2 ′} and R ^{3 ′} are all methyl groups.