JP2007051126A - Method for producing optically active diphenylalanine compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for production with which a diphenylalanine compound can industrially and advantageously be obtained in good yield. <P>SOLUTION: A diphenylmethylene halide compound represented by formula (1) is reacted with a malonic diester compound represented by formula (2) in the presence of an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N,N-dimethylformamide and a base selected from an alkali metal hydride and an alkali metal t-butoxide to provide a diester compound represented by formula (3). The resultant diester compound is then subjected to hydrolysis and decarboxylation to afford the diphenylalanine compound represented by formula (4). In the formulas, the symbols are each especially defined. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a diphenylalanine compound and a method for producing the same, and a method for producing an optically active diphenylalanine compound useful as a synthetic intermediate such as an anti-HIV drug or a dipeptidyl peptidase inhibitor.

  A diphenylalanine compound, particularly an optically active diphenylalanine compound (including a protected form of an amino group) is a compound useful as a synthetic intermediate of a pharmaceutical compound. For example, an anti-HIV drug (Patent Document 1), dipeptidyl peptidase It is used as a synthetic intermediate for inhibitors (Patent Document 2).

  As a method for producing 3,3-diphenylalanine, in Patent Document 3, as shown in the following reaction scheme, diethylacetamidomalonate and diphenylbromomethane are reacted in ethanol in the presence of sodium ethoxide, Diethyl 2-acetamido-2- (diphenylmethyl) malonic acid ester is obtained, hydrolyzed in the presence of hydrogen bromide, neutralized with aqueous sodium hydroxide solution, and 3,3-diphenylalanine is obtained by column purification. Although the method is described, there is no specific description about the yield.

Therefore, the present inventors tried to produce 3,3-diphenylalanine by reacting diethylacetamidomalonate with diphenylchloromethane or diphenylbromomethane according to the above reaction scheme. However, diphenylmethyl ethyl ether was obtained as the main product, and the desired 3,3-diphenylalanine was obtained only in a very low yield.
As another method, as shown in the following reaction scheme, a method of reacting N- (diphenylmethylene) glycine ester synthesized from benzophenone imine and glycine ester with diphenylbromomethane is known (Patent Document 4). .

  However, in the above method, it is difficult to obtain benzophenone imine as a raw material compound, and benzophenone imine is only used as a leaving group. Therefore, an efficient production method using the raw material compound effectively It's hard to say.

  On the other hand, as a method for producing optically active diphenylalanine, Patent Document 4 described above describes an optical resolution method of N-acetyldiphenylalanine using (−)-cinchonidine. However, this method is not as efficient as the yield of the optical resolution step is 25 to 30%. In addition, this document describes that optical resolution of 3,3-diphenylalanine compounds by porcine kidney acylase and carboxypeptidase was not possible.

  As another method, Non-Patent Document 1 and Non-Patent Document 2 describe an asymmetric synthesis method of N-Boc-diphenylmethylalanine. However, these methods use a stoichiometric amount of asymmetric source and have a large number of steps. In addition, they are expensive, such as a low-temperature reaction tank or KHMDS (hexamethyldisilazane potassium) for reaction at -78 ° C. Cost is high because of the need for such a reagent, and it is difficult to say that the method is industrially advantageous.

Thus, a method for producing an optically active diphenylalanine compound by a biological technique has not yet been reported.
WO04 / 056764 pamphlet International Publication No. 03/002531 Pamphlet U.S. Pat. No. 4,766,109 US Pat. No. 5,198,548 HETEROCYCLES, vol.57, No.6, pp1143 (2002) Tetrahedron Letter, vol.33, No.23, pp3293 (1992)

  The present invention has been made in view of such circumstances, and the problem to be solved is to provide a production method capable of obtaining a diphenylalanine compound and an optically active diphenylalanine compound in an industrially advantageous yield. There is to do. Another object is to provide racemic N-acetyldiphenylalanine and racemic N-acetylbis (4-fluorophenyl) alanine as crystals.

  As a result of intensive studies to solve the above problems, the present inventors have obtained diphenylmethylene halide compounds and malonic acid diester compounds as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N- It has been found that a diphenylalanine compound can be easily obtained in high yield by reacting in the presence of an organic solvent selected from dimethylformamide and a base selected from an alkali metal hydride and a t-butoxy alkali metal. The present inventors also found that penicillin amidase can react with a diphenylalanine compound having a specific structure in a substrate-specific manner to easily produce an optically active diphenylalanine compound with high yield. Furthermore, it has been found that racemic N-acetyldiphenylalanine and racemic N-acetylbis (4-fluorophenyl) alanine can be crystallized by a specific method. Based on these findings, the present inventors have completed the present invention.

That is, the present invention is as follows.
[1] The following formula (1):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And X represents a chlorine atom, a bromine atom or an iodine atom. ]
And a diphenylmethylene halide compound represented by the following formula (2):

[Wherein, R ³ and R ⁴ each independently represent an alkyl group or an aralkyl group, or R ³ and R ⁴ together form an alkylene group, and P ¹ is an amino-protecting group. Indicates. ]
A malonic acid diester compound represented by the formula: an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and an alkali metal hydride and a t-butoxy alkali metal The reaction is carried out in the presence of a selected base, the following formula (3):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of the diester compound represented by these.

[2] The production method of the above-mentioned [1], wherein the base is selected from sodium hydride, sodium t-butoxy and potassium t-butoxy.
[3] The production method of the above-mentioned [1], wherein the organic solvent is selected from N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.
[4] The production method according to any one of [1] to [3], wherein R ¹ and R ² are fluorine atoms.
[5] The production method according to any one of [1] to [4], wherein R ³ and R ⁴ are ethyl groups.
[6] P ¹ is an acetyl group or phenylacetyl group, the manufacturing method according to any one of the above [1] to [5].
[7] The production method according to any one of [1] to [6], wherein X is a chlorine atom or a bromine atom.
[8] The production method according to any one of [1] to [7], which is performed in the presence of an iodine compound or a bromine compound.
[9] The production method according to any one of [1] to [7], which is performed in the presence of metal iodide or quaternary ammonium iodide.

[10] A method for producing a diphenylalanine compound represented by the following formula (4) or a salt thereof, comprising the following steps (a) and (b):
Step (a): Formula (1) below:

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And X represents a chlorine atom, a bromine atom or an iodine atom. ]
And a diphenylmethylene halide compound represented by the following formula (2):

[Wherein, R ³ and R ⁴ each independently represent an alkyl group or an aralkyl group, or R ³ and R ⁴ together form an alkylene group, and P ¹ is an amino-protecting group. Indicates. ]
A malonic acid diester compound represented by the formula: an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and an alkali metal hydride and a t-butoxy alkali metal Reaction in the presence of a selected base gives the following formula (3):

[Wherein each symbol has the same meaning as defined above. ]
Step of obtaining a diester compound represented by formula (b): Step (b): The diester compound is subjected to hydrolysis and decarboxylation, and the following formula (4):

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ² represents a hydrogen atom or an amino-protecting group. ]
The process of obtaining the diphenylalanine compound or its salt represented by these.

[11] The production method of the above-mentioned [10], wherein P ² is a hydrogen atom, an acetyl group or a phenylacetyl group.

[12] The following formula (4):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And P ² represents a hydrogen atom or an amino-protecting group (provided that the following formula (5):

(Wherein R ⁵ represents a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ³ represents an integer of 0 to 5)). Show. ]
Wherein P ² of the diphenylalanine compound represented by the formula or a salt thereof is converted to a substituted phenylacetyl group represented by the formula (5):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of the acyl-substituted diphenylalanine compound or its salt represented by these.

[13] The following formula (6):

[Wherein R ¹ , R ² and R ⁵ each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ , n ² and n ³ each independently And represents an integer of 0 to 5. ]
Penicillin amidase is allowed to act on an acyl-substituted diphenylalanine compound represented by the formula:

[Wherein each symbol has the same meaning as defined above. ]
Or an L-diphenylalanine compound represented by the following formula (6b):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of the D-acyl substituted diphenylalanine compound represented by these, or its salt.

[14] A method for producing an optically active diphenylalanine compound represented by the following formulas (7a) and (6b) or a salt thereof, comprising the following steps (a), (b), (c) and (d):
Step (a): Formula (1) below:

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And X represents a chlorine atom, a bromine atom or an iodine atom. ]
And a diphenylmethylene halide compound represented by the following formula (2):

[Wherein, R ³ and R ⁴ each independently represent an alkyl group or an aralkyl group, or R ³ and R ⁴ together form an alkylene group, and P ¹ is an amino-protecting group. Indicates. ]
A malonic acid diester compound represented by the formula: an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and an alkali metal hydride and a t-butoxy alkali metal Reaction in the presence of a selected base gives the following formula (3):

[Wherein each symbol has the same meaning as defined above. ]
A step of obtaining a diester compound represented by:
Step (b): The diester compound is subjected to hydrolysis and decarboxylation to obtain the following formula (4):

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ² represents a hydrogen atom or an amino-protecting group. ]
A step of obtaining a diphenylalanine compound represented by the formula:
Step (c): the diphenylalanine compound [wherein P ² is represented by the following formula (5):

(Wherein R ⁵ represents a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ³ represents an integer of 0 to 5). except. Or P ² of the salt thereof is converted into a substituted phenylacetyl group represented by the above formula (5), and the following formula (6):

[Wherein each symbol has the same meaning as defined above. ]
A step of obtaining an acyl-substituted diphenylalanine compound or a salt thereof represented by: and step (d): a penicillin amidase is allowed to act on the acyl-substituted diphenylalanine compound or a salt thereof, and the following formula (7a):

[Wherein each symbol has the same meaning as defined above. ]
Or an L-diphenylalanine compound represented by the following formula (6b):

[Wherein each symbol has the same meaning as defined above. ]
A step of obtaining a D-acyl-substituted diphenylalanine compound represented by the formula:

[15] According to the method described in [13] above, the following formula (7a):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represent 0 to 5 Indicates an integer. ]
After obtaining the L-diphenylalanine compound or its salt represented by the following formula (8a), the amino group of the compound or its salt is protected:

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ³ represents an amino-protecting group. ]
The manufacturing method of the LN protection diphenylalanine compound or its salt represented by these.

[16] The production method of the above-mentioned [15], wherein P ³ is a tert-butoxycarbonyl group.

[17] According to the method described in [13] above, the following formula (6b):

[Wherein R ¹ , R ² and R ⁵ each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ , n ² and n ³ each independently And represents an integer of 0 to 5. ]
After obtaining a D-acyl-substituted diphenylalanine compound or a salt thereof represented by the following formula (7b):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of D-diphenylalanine compound or its salt represented by these.

[18] According to the method described in [17] above, the following formula (7b):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represent 0 to 5 Indicates an integer. ]
After obtaining the D-diphenylalanine compound or salt thereof represented by the following formula (8b), the amino group of the compound or salt thereof is protected:

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ³ represents an amino-protecting group. ]
The manufacturing method of DN protected diphenylalanine compound or its salt represented by these.

[19] The production method of the above-mentioned [18], wherein P ³ is a tert-butoxycarbonyl group.

[20] The following formula (6):

[Wherein R ¹ , R ² and R ⁵ each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ , n ² and n ³ each independently And represents an integer of 0 to 5. ]
Or an acyl-substituted diphenylalanine compound or a salt thereof.

[21] In an X-ray diffraction pattern obtained by powder X-ray diffraction using Cu—Kα rays, diffraction angles 2θ are 5.8 °, 11.5 °, 21.6 °, 23.2 ° and 28.7 °. Racemic N-acetyldiphenylalanine crystals with characteristic peaks.
[22] The crystal according to [21] above, which is obtained by adding a poor solvent to a racemic N-acetyldiphenylalanine acetate solution.
[23] In an X-ray diffraction pattern obtained by powder X-ray diffraction using Cu—Kα rays, 17.1 °, 21.8 °, 22.0 °, 22.7 °, 23.1 ° and 25.4 ° A racemic N-acetylbis (4-fluorophenyl) alanine crystal having a characteristic peak at a diffraction angle of 2θ.
[24] X-ray diffraction pattern obtained by powder X-ray diffraction with Cu-Kα ray has characteristic peaks of diffraction angle 2θ at 12.8 °, 17.6 °, 19.2 ° and 24.3 ° Racemic N-acetylbis (4-fluorophenyl) alanine crystals.
[25] The crystal according to [23] above, which is obtained by adding a poor solvent to a racemic N-acetylbis (4-fluorophenyl) alanine acetate solution.
[26] The crystal according to [24] above, which is obtained by cooling a racemic N-acetylbis (4-fluorophenyl) alanine acetate solution.

  According to the present invention, a novel diphenylalanine compound or a salt thereof capable of reacting with penicillin amidase in a substrate-specific manner is provided. Further, the diphenylalanine compound or a salt thereof and the optically active diphenylalanine compound or a salt thereof can be easily produced in a high yield. Furthermore, racemic N-acetyldiphenylalanine and racemic N-acetylbis (4-fluorophenyl) alanine can be obtained in the form of crystals having high purity and convenient for storage and transportation.

Hereinafter, the present invention will be described in detail.
First, definitions of symbols in each formula used in this specification will be described.

Examples of the halogen atom in R ^{1, R 2} and ^{R 5,} chlorine atom, bromine atom, fluorine atom is preferable, and fluorine atom is more preferable.

The alkyl group in R ¹ , R ² , R ³ , R ⁴ and R ⁵ is preferably linear or branched having 1 to 10 carbon atoms, more preferably 1 to 7 carbon atoms, and still more preferably 1 to 4 carbon atoms. In the form of alkyl. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group. A methyl group, ethyl group, propyl group, isopropyl group, butyl group, tert-butyl group and the like are preferable. The alkyl group may be substituted with one or more halogen atoms (for example, chlorine atom, bromine atom, fluorine atom), hydroxyl group, alkoxy group having 1 to 6 carbon atoms (for example, methoxy group) and the like. Good.

The alkoxy group in R ¹ , R ² and R ⁵ is preferably a linear or branched alkoxy group having 1 to 10 carbon atoms, more preferably 1 to 7 carbon atoms, and still more preferably 1 to 4 carbon atoms. . Specifically, methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group, etc. Among them, methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, tert-butoxy group and the like are preferable. The alkoxy group may be substituted with one or more halogen atoms (for example, chlorine atom, bromine atom, fluorine atom), hydroxyl group, alkoxy group having 1 to 6 carbon atoms (for example, methoxy group) and the like. Good.

The amino group in R ¹ , R ² and R ⁵ may be 1 or 2 substituted with the aforementioned alkyl group, aryl group or aralkyl group, and the amino group in P ¹ , P ² and P ³ described later It may be protected with a group exemplified as a protecting group.

The hydroxyl group in R ¹ , R ² and R ⁵ may be protected, and examples of the protecting group include those conventionally known. Specifically, benzyl group, trimethylsilyl group, triethylsilyl group, tert -A butyl dimethyl silyl group etc. are mentioned.

Note that n ¹ R ^{1 s} may be the same or different, and n ² R ² and n ³ R ⁵ may be the same or different, respectively.

The aralkyl group in R ³ and R ⁴ refers to an alkyl group substituted with an aryl group. Carbon number of this alkyl group becomes like this. Preferably it is 1-6, More preferably, it is 1-3, and a methyl group, an ethyl group, a propyl group, an isopropyl group etc. are mentioned specifically ,. As this aryl group, C6-C14 (preferably 6-8) is preferable, and a phenyl group, a naphthyl group, etc. are mentioned specifically ,. The total carbon number of the aralkyl group is preferably 7-20, more preferably 7-11. Specific examples include a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, etc. Among them, a benzyl group is preferable. The aralkyl group includes a halogen atom (for example, a chlorine atom, a bromine atom, and a fluorine atom), a hydroxyl group, an alkyl group having 1 to 6 carbon atoms (for example, a methyl group), and an alkoxy group having 1 to 6 carbon atoms (for example, , A methoxy group), a haloalkyl group (for example, trifluoromethyl group), a haloalkoxy group (for example, trifluoromethoxy group) and the like, may be substituted one or more.

Examples of the alkylene group formed by combining R ³ and R ⁴ include linear or branched alkylene groups having preferably 2 to 6 carbon atoms, more preferably 2 to 4 carbon atoms. Specific examples include an ethylene group, a trimethylene group, a propylene group, and a tetramethylene group, and among them, a trimethylene group and a tetramethylene group are preferable.

Examples of the protecting group for the amino group in P ¹ , P ² and P ³ include groups described in Protecting Groups in Organic Chemistry 2nd edition (John Wiley & Sons, Inc. 1991). Specific examples include an acyl group, an alkyl group, an aralkyl group, and a silyl group. Examples of the acyl group include a formyl group, a C _1-6 alkyl-carbonyl group (eg, acetyl group), a C _6-8 aryl-carbonyl group, a C _7-11 aralkyl-carbonyl group (eg, phenylacetyl group), and the like. Is mentioned. As an alkyl group, the same thing as the alkyl group in R < ¹ >, R < ² >, R < ³ >, R < ⁴ > and R < ⁵ > is mentioned, for example. Examples of the aralkyl group include the same aralkyl groups as those represented by R ³ and R ⁴ . Examples of the silyl group include trialkyl-substituted silyl groups such as a trimethylsilyl group, a triethylsilyl group, and a tert-butyldimethylsilyl group. The alkyl group preferably has 1 to 4 carbon atoms, specifically, A methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a tert-butoxy group, etc. are mentioned. In addition, methoxymethyl group, methylthiomethyl group, benzyloxymethyl group, methoxyethoxymethyl group, tetrahydropyranyl group, methoxycarbonyl group (Moc group), 9-fluorenylmethoxycarbonyl group (Fmoc group), 2,2, Examples also include 2-trichloroethoxycarbonyl group, benzyloxycarbonyl group (Cbz group), tert-butoxycarbonyl group (Boc group) and the like.

Particularly preferred embodiments for each symbol are as follows.
R ¹ and R ² are each preferably a halogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a halogen atom, and particularly preferably a fluorine atom. Incidentally, R ¹ and R ² may be the same or different.
R ³ and R ⁴ are each preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and particularly preferably an ethyl group. R ³ and R ⁴ may be the same or different.
R ⁵ is preferably a halogen atom or an alkyl group having 1 to 10 carbon atoms.
P ¹ is preferably an acyl group having 1 to 7 carbon atoms, particularly preferably an acetyl group or a phenylacetyl group.
P ² is preferably a hydrogen atom or an acyl group having 1 to 7 carbon atoms, particularly preferably a hydrogen atom, an acetyl group, or a phenylacetyl group.
P ³ is preferably a Moc group, an Fmoc group, a Cbz group, or a Boc group, and particularly preferably a Boc group.
X is preferably a chlorine atom or a bromine atom.
n ¹ , n ² and n ³ are each independently preferably 0, 1 or 2. n ¹ and n ² are each independently preferably 0 or 1, and n ³ is particularly preferably 0.

  Next, the manufacturing method of this invention is demonstrated. The production method of the present invention is represented by the following reaction scheme.

[Wherein each symbol has the same meaning as defined above. ]

Step (a)
Step (a) includes a diphenylmethylene halide compound represented by formula (1) (hereinafter referred to as “compound (1)”) and a malonic acid diester compound represented by formula (2) (hereinafter referred to as “compound (1)”). 2) ") is selected from organic solvents selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and alkali metal hydrides and t-butoxy alkali metals. This is a step of reacting in the presence of a base to obtain a diester compound represented by the formula (3) (hereinafter referred to as “compound (3)”).

  The reaction in the step (a) is performed in the presence of a base selected from an alkali metal hydride and a t-butoxy alkali metal. Here, examples of the alkali metal hydride include lithium hydride, potassium hydride, sodium hydride and the like. Sodium hydride and potassium hydride are preferable, and sodium hydride is particularly preferable. Examples of the t-butoxy alkali metal include t-butoxy sodium and t-butoxy potassium, and t-butoxy potassium is particularly preferable. The amount of the base used is generally 1 to 1.5 equivalents, preferably 1.1 to 1.3 equivalents, relative to compound (2).

  The above reaction can also be performed in the presence of an iodine compound or a bromine compound in order to promote the reaction. In this case, when X is a chlorine atom, it is carried out in the presence of an iodine compound and / or a bromine compound, and preferably in the presence of an iodine compound. When X is a bromine atom, the reaction is carried out in the presence of an iodine compound.

  As the iodine compound, metal iodide and quaternary ammonium iodide are preferably used. As the metal iodide, an alkali metal iodide is preferable, and examples thereof include lithium iodide, potassium iodide, sodium iodide and the like, and potassium iodide and sodium iodide are particularly preferable. Examples of the quaternary ammonium iodide include tetrabutylammonium iodide and tetraheptylammonium iodide. Among them, tetrabutylammonium iodide is particularly preferable. As the bromine compound, metal bromide and quaternary ammonium bromide are preferably used. As the metal bromide, an alkali metal bromide is preferable, and examples thereof include lithium bromide, potassium bromide, sodium bromide and the like, and potassium bromide and sodium bromide are particularly preferable. Examples of the quaternary ammonium bromide include tetrabutylammonium bromide and tetraheptylammonium bromide. Among them, tetrabutylammonium bromide is particularly preferable. The usage-amount of an iodine compound or a bromine compound is 0.05-1.0 equivalent normally with respect to a compound (1), Preferably it is 0.5-1.0 equivalent.

  The reaction of step (a) is carried out under an organic solvent selected from N-methyl-2-pyrrolidone (also known as N-methylpyrrolidinone or 1-methylpyrrolidinone), N-ethyl-2-pyrrolidone and N, N-dimethylformamide. Done. From the viewpoint of improving the yield, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone are preferable, and N-methyl-2-pyrrolidone is particularly preferable. N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide may be used by mixing two or more of them in an appropriate ratio. Further, a solvent other than N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N, N-dimethylformamide may be mixed and used within a range in which the effect of this reaction is exhibited. As such a solvent, an aprotic organic solvent is preferably used, and examples thereof include dimethyl sulfoxide, hexamethylphosphoric triamide, acetonitrile, toluene and the like. Although the usage-amount of an organic solvent can be suitably selected according to the kind of compound, it is 3-20 times weight normally with respect to a compound (1), Preferably it is 5-10 times weight.

  The amount of compound (2) to be used is generally 1 to 1.5 equivalents, preferably 1.1 to 1.3 equivalents, relative to compound (1). When the amount of compound (2) used is less than the above range, the reaction tends to be insufficient.

  As reaction conditions, when the base is an alkali metal hydride, the reaction temperature is usually 30 to 60 ° C., preferably 40 to 50 ° C., and the reaction time is usually 1 to 16 hours, preferably 3 to 6 hours. is there. When the base is t-butoxy alkali metal, the reaction temperature is usually 30 to 80 ° C., preferably 60 to 70 ° C., and the reaction time is usually 3 to 24 hours, preferably 3 to 8 hours.

  After completion of the reaction, an organic solvent (for example, hydrocarbons such as toluene) and water are added to the reaction liquid and the mixture is separated, and the resulting organic layer is washed with water and concentrated to give compound (3). Can be obtained. Alternatively, after the completion of the reaction, the step (b) can be continuously performed in the same reaction vessel without performing the above-described post-treatment.

Step (b)
Step (b) is a step of subjecting compound (3) to hydrolysis and decarboxylation to obtain a diphenylalanine compound represented by formula (4) or a salt thereof (hereinafter referred to as “compound (4)”). is there. Thereby, a compound (4) can be easily obtained with a sufficient yield.

  Hydrolysis and decarboxylation can be carried out by a conventionally known method. For example, compound (3) is mixed with an alcohol (for example, ethanol) or a mixed solvent of water and water with a base (for example, sodium hydroxide). The method of making it react is mentioned. The above reaction is usually carried out within the range of the reflux temperature of the solvent used from 80 ° C. (preferably 85 to 90 ° C.), and the reaction time is usually 1 to 16 hours, preferably 3 to 6 hours. After completion of the reaction, an organic solvent (for example, hydrocarbons such as toluene) and water are added to the reaction liquid and the mixture is separated. Acetic esters (for example, ethyl acetate and isopropyl acetate) and water are added to the resulting aqueous layer. Further, an acid (for example, hydrochloric acid or sulfuric acid) is added to make it acidic (usually pH 0.5 to 3, preferably 1 to 2), followed by extraction. The obtained organic layer is washed with water and then concentrated to obtain the compound (4).

  Step (a) and step (b) can also be carried out continuously in the same reaction vessel. For example, after completion of the reaction in the step (a), a method of adding a base (for example, sodium hydroxide, potassium hydroxide) and reacting it can be mentioned. This reaction is usually carried out within the range of the reflux temperature of the solvent used from 50 ° C. (preferably 60 to 70 ° C.), and the reaction time is usually 1 to 16 hours, preferably 3 to 6 hours.

  After completion of the reaction, the mixture is separated and acid (eg, hydrochloric acid, sulfuric acid) is added to the resulting aqueous layer to make it neutral (usually pH 6-8, preferably 7-8), followed by acetate esters (eg, acetic acid). Ethyl and isopropyl acetate) are added, and further acid (for example, hydrochloric acid and sulfuric acid) is added to make it acidic (usually pH 0.5 to 3, preferably 1 to 2), followed by extraction. The obtained organic layer is washed with an acid (for example, hydrochloric acid) and saturated brine, and then concentrated to obtain compound (4).

  The property of the compound (4) obtained by the concentration is amorphous, but after performing the concentration to a certain degree without performing the concentration to the end, the acetate (eg, ethyl acetate, isopropyl acetate) solution is cooled as it is or Crystallization by adding a specific poor solvent (for example, toluene) to an acetic acid ester (for example, ethyl acetate, isopropyl acetate) solution can also be performed to obtain the compound (4) as crystals.

  For example, a racemic N-acetyldiphenylalanine (also known as 2-acetylamino-3,3-diphenylpropanoic acid) crystal is prepared by adding toluene as a poor solvent to an acetic acid ester (eg, ethyl acetate, isopropyl acetate) solution. In the X-ray diffraction pattern obtained by the crystallization method and obtained by powder X-ray diffraction with Cu-Kα rays, it was 5.8 °, 11.5 °, 21.6 °, 23.2 ° and 28.7 °. It has a characteristic peak of diffraction angle 2θ.

  In addition, for the racemic N-acetylbis (4-fluorophenyl) alanine (also known as 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid) crystal, Two crystal forms were found to exist.

  For example, racemic N-acetylbis (4-fluorophenyl) alanine crystals obtained by a crystallization method in which toluene is added as a poor solvent to an acetic ester (eg, ethyl acetate, isopropyl acetate) solution are Cu-Kα rays. In the X-ray diffraction pattern obtained by powder X-ray diffraction according to the characteristics of diffraction angle 2θ at 17.1 °, 21.8 °, 22.0 °, 22.7 °, 23.1 ° and 25.4 ° Has a peak.

  In addition, racemic N-acetylbis (4-fluorophenyl) alanine crystals obtained by a crystallization method of cooling an acetate ester (eg, ethyl acetate, isopropyl acetate) solution are powder X-ray diffraction by Cu-Kα rays. In the X-ray diffraction pattern obtained at 12.8 °, 17.6 °, 19.2 ° and 24.3 ° have characteristic peaks of diffraction angle 2θ.

  In this way, racemic N-acetyldiphenylalanine and racemic N-acetylbis (4-fluorophenyl) alanine can be obtained as crystals having high purity and convenient for storage and transportation.

  In addition, the value of the diffraction angle (2θ) in the powder X-ray diffraction spectrum can have a measurement error of about ± 0.2 degrees, and such an error does not deny the identity of the crystal form. Is clear.

Step (c)
Step (c), it converts the P ² of the compound (4) substituted phenyl acetyl group, acyl substituted diphenylalanine compound represented by the formula (6) (hereinafter, referred to as "compound (6)". ).

That is, among the compounds (4), P ² is represented by the formula (5):

(In the formula, each symbol is as defined above.)
In compound is other than the groups represented, as shown in the following reaction scheme, an amino group is deprotected (Compound P ² is a hydrogen atom is not required), a compound represented by the formula (4c) or A salt (hereinafter referred to as “compound (4c)”) was obtained, and then the compound (4c) was reacted with an acyl halide represented by formula (5c) (hereinafter referred to as “compound (5c)”). By introducing a substituted phenylacetyl group represented by the formula (5), the compound (6) can be easily obtained in a high yield.

(In the formula, X ′ represents a chlorine atom, a bromine atom or an iodine atom, and other symbols are as defined above.)

  Deprotection of the amino group of compound (4) can be carried out by a known method, and examples thereof include acid treatment, catalytic reduction and the like.

  For example, in the acid treatment, an acid (for example, hydrochloric acid or sulfuric acid) is added to the compound (4) and usually at 80 to 100 ° C. (preferably 90 to 100 ° C.), usually 1 to 16 hours (preferably 3 to 6 hours). This is done by reacting. Here, compound (4c) may be obtained as an acid addition salt.

  The catalytic reduction is performed by a conventionally known method, for example, by introducing hydrogen into the compound (4) in the presence of a reduction catalyst such as palladium carbon.

  Next, compound (6) can be obtained in good yield by reacting compound (4c) with compound (5c) under basic conditions (usually pH 10-13, preferably pH 11-12). Examples of the base include sodium hydroxide and potassium hydroxide. The amount of compound (5c) to be used is generally 1-1.2 equivalents, preferably 1.05-1.1 equivalents, relative to compound (4). When the amount of compound (5c) used is less than the above range, the reaction tends to be insufficient. The reaction temperature is usually 0 to 40 ° C., preferably 20 to 30 ° C. The reaction time is usually 1 to 5 hours, preferably 2 to 3 hours.

  After completion of the reaction, an acetate ester (for example, ethyl acetate) is added to the reaction solution, and an acid (for example, hydrochloric acid or sulfuric acid) is added to make the solution acidic (usually pH 0.5 to 3, preferably 1 to 2). The compound (6) can be obtained by separating the liquid and concentrating the obtained organic layer or by adding a crystallization solvent (for example, hydrocarbons such as hexane) for crystallization.

In addition, among the compounds (4), the compound in which P ² is a group represented by the formula (5) is not subjected to the step (c) after the step (b), and the step (d) described later is performed. Just do it.

Step (d)
In the step (d), penicillin amidase is allowed to act on the racemic compound (6) to produce an L-diphenylalanine compound represented by the formula (7a) or a salt thereof (hereinafter referred to as “compound (7a)”). In this step, a D-acyl-substituted diphenylalanine compound represented by the formula (6b) or a salt thereof (hereinafter referred to as “compound (6b)”) is obtained. Penicillin amidase acts on the compound (6) in a substrate-specific manner, and the L-form, that is, the compound represented by the formula (6a) (hereinafter referred to as “compound (6a)”) is deacylated by hydrolysis. To form compound (7a), but D-form, that is, compound (6b) is hardly hydrolyzed.

[Wherein each symbol has the same meaning as defined above. ]

  Examples of penicillin amidase include E. coli produced from microorganisms such as bacteria, actinomycetes, and fungi. C. Any enzyme can be used without particular limitation as long as it is classified into the number 3.5.1.11. Examples of such microorganisms include, for example, Acetobactor, Xanthomonas, Mycoplana, Protaminobacter, Aeromonas, Pseudomonas, Flavobacterium, and Aphanobacterium. Jum (Aphanocladium), Cephalosporium, Acetobacter pasteurianum, Bacillus megaterium, Xanthomonas citrii, Kluyvera citrophila, Kluyvera citrophila (Escherichia coli). Penicillin amidase can be used as a free water-soluble enzyme or as a water-insoluble immobilized enzyme.

  In the above reaction, for example, penicillin amidase is added to compound (6) under basic conditions (usually pH 6.8 to 8.5, preferably pH 7.2 to 7.9), and usually 30 to 40 ° C. (preferably Is 36 to 38 ° C.) and is usually performed for 2 to 48 hours (preferably 8 to 24 hours). Examples of the base include sodium hydroxide and potassium hydroxide.

  The substrate concentration of compound (6) is usually 0.01 to 0.2 mol / L (preferably 0.02 to 0.1 mol / L). The concentration of penicillin amidase is usually 10 to 1000 U / mL (preferably 10 to 100 U / mL). The above reaction can also be performed using a commonly used buffer such as a phosphate buffer.

  After completion of the reaction, the compound (7a) and the compound (6b) are separated. Specifically, an organic solvent (for example, an acetate such as ethyl acetate) is added to the reaction solution, and the acid (for example, hydrochloric acid, sulfuric acid) is acidic (usually pH 0.5 to 2.0, preferably pH 1.0 to 2). 0.0), liquid separation is performed, and then the compound (7a) is isolated from the aqueous layer and the compound (6b) is isolated from the organic layer. Furthermore, although it may refine | purify by attaching | subjecting recrystallization as needed, you may use the water layer obtained by extraction operation as it is for the process (e) mentioned later.

  When an immobilized enzyme is used, for example, the immobilized penicillin amidase is removed by filtration after completion of the reaction, and then the compound (7a) and the compound (6b) can be obtained by the same operation as described above. . The immobilized penicillin amidase can be reused by washing with water or the like.

  By such a method, the compound (7a) useful as a synthetic intermediate for pharmaceuticals such as anti-HIV drugs and dipeptidyl peptidase inhibitors can be easily obtained in high yield.

Step (e)
In the step (e), the amino group of the compound (7a) is protected to obtain an LN-protected diphenylalanine compound represented by the formula (8a) or a salt thereof (hereinafter referred to as “compound (8a)”). It is a process. Step (e) can be performed by a known method, for example, the method described in Protecting Groups in Organic Chemistry 2nd edition (John Wiley & Sons, Inc. 1991).

  Hereinafter, as a preferred embodiment of the step (e), protection of an amino group by a Boc group will be described. The amino group is protected by the Boc group, for example, when an aqueous solution of the compound (7a) obtained in the step (d) (the aqueous layer obtained by the extraction operation in the step (d) may be used as it is) is basic ( After adjusting to pH 7-9 (preferably pH 8), alcohol (for example, methanol) and di-t-butyl dicarbonate are added to this, and it is usually 1-24 at 0-50 ° C (preferably 20-40 ° C). The reaction can be carried out for a time (preferably 1 to 6 hours). As the base, for example, potassium hydrogen carbonate or the like is used. The amount of di-t-butyl dicarbonate used is usually 1 to 1.2 equivalents (preferably 1.05 to 1.1 equivalents) relative to compound (7a). The usage-amount of alcohol is 2-100 times weight normally with respect to a compound (7a) (preferably 5-20 times weight). After completion of the reaction, an acid (for example, hydrochloric acid or sulfuric acid) is added to the reaction solution to make it acidic (usually pH 0.5 to 3, preferably pH 1 to 2), followed by liquid separation. The obtained organic layer is washed with water and then concentrated to obtain compound (8a). Furthermore, if necessary, the compound (8a) may be purified by crystallization or column chromatography. Thereby, the compound (8a) useful as a synthetic intermediate of pharmaceuticals such as anti-HIV drugs and dipeptidyl peptidase inhibitors can be easily obtained in high yield. In addition, since the compound (8a) is a crystal, it has high purity and excellent handling properties such as storage and transportation.

Step (f)
Step (f) is a step of deacylating compound (6b) to obtain a D-diphenylalanine compound represented by formula (7b) or a salt thereof (hereinafter referred to as “compound (7b)”). Deacylation can be performed by the same method as the acid treatment for deprotecting the amino group described in step (c).

Step (g)
In the step (g), the amino group of the compound (7b) is protected to obtain a DN-protected diphenylalanine compound represented by the formula (8b) or a salt thereof (hereinafter referred to as “compound (8b)”). It is a process. Step (g) is performed by introducing an amino-protecting group in the same manner as in step (e). Thereby, an optically active compound (8b) can be easily obtained with good yield.

  In each step, compound (4), compound (4c), compound (6), compound (6a), compound (6b), compound (7a), compound (7b), compound (8a) and compound (8b) are: It may be in the form of a salt. In addition, the compound (1), the compound (2), the compound (3), and the compound (5c) may also be in the form of a salt when the substituent has an amino group. Examples of the acid addition salt include salts with inorganic acids (for example, hydrochloric acid, sulfuric acid), organic acids (for example, acetic acid, trifluoroacetic acid, p-toluenesulfonic acid, methanesulfonic acid), and the like. Examples of such salts include alkali metal salts (for example, sodium salts and potassium salts), alkaline earth metal salts (for example, calcium salts and magnesium salts), and organic salts (for example, triethylamine salts and dicyclohexylamine salts).

  Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

Example 1
Synthesis of 2-acetylamino-3,3-diphenylpropanoic acid To a solution of diethyl acetamidomalonate (6.79 g, 31.25 mmol) in N-methyl-2-pyrrolidone (25 mL, 1.25 M), 60% sodium hydride ( 1.25 g, 31.25 mmol) was added, and the mixture was stirred at room temperature for 1 hour, and then diphenylmethylene chloride (4.45 mL, 25.0 mmol) and potassium iodide (4.15 g, 25 mmol) were added at 50 ° C. Stir for 7 hours. After completion of the reaction, toluene (75 mL) and water (31.5 mL) were added to the reaction solution for liquid separation, and the organic layer was washed twice with water (31.5 mL) and concentrated. Ethanol (31.5 mL) and 2M aqueous sodium hydroxide solution (37.5 mL) were added to the concentrated solution, and the mixture was stirred at 80 ° C. for 11 hours. Then, it cooled to 25 degreeC and toluene (9 mL) was added and liquid-separated. When the aqueous layer was concentrated in half and the pH was adjusted to 1.1 with concentrated hydrochloric acid, white crystals were precipitated. The crystals were filtered and dried in vacuo to give 5.0 g of the title compound.

Example 2
Synthesis of 2-amino-3,3-diphenylpropanoic acid hydrochloride After stirring a concentrated hydrochloric acid solution (21 mL) of 2-acetylamino-3,3-diphenylpropanoic acid (2.83 g, 10 mmol) at 90 ° C. for 5 hours. The reaction solution was ice-cooled to precipitate a solid. The solid was filtered and dried to give 2.65 g of the title compound.

Example 3
Synthesis of 2-phenylacetylamino-3,3-diphenylpropanoic acid To an aqueous solution (14 mL) of 2-amino-3,3-diphenylpropanoic acid hydrochloride (2.0 g, 7.2 mmol), 1M aqueous sodium hydroxide solution was added. After adjusting the pH to 12, phenylacetyl chloride (1.05 mL, 7.9 mmol) was added dropwise at 0 to 10 ° C. while adjusting to pH 11 to 12 with a 1 M aqueous sodium hydroxide solution, and the mixture was stirred at room temperature for 4 hours. . Thereafter, 40 mL of ethyl acetate was added to the reaction solution, and the pH was adjusted to 1.1 with concentrated hydrochloric acid, followed by liquid separation. The obtained organic layer was heated to 50 ° C., hexane (30 mL) was added, and the mixture was ice-cooled to precipitate a solid. The solid was filtered and dried to give 2.41 g of the title compound.
Melting point 173 ° C
¹ H NMR (400 MHz, DMSO-d ₆ ) δ 3.26-3.34 (m, 2H), 4.33 (d, 1H, J = 7.2 Hz), 5.19 (dd, 2H, J = 5.6 Hz, 10.7 Hz), 6.88 -7.34 (m, 15H), 8.51 (d, 1H, J = 5.6 Hz)
¹³ C NMR (100 MHz, DMSO-d ₆ ) δ172.62, 170.00, 162.53, 141.54, 141.43, 136.45, 129.05, 128.74, 128.64, 128.53, 128.51, 128.37, 127.03, 126.81, 126.43, 55.52, 53.43, 42.13
MS (FAB), m / z 360 [M + + H]

Example 4
Synthesis of L-2-amino-3,3-diphenylpropanoic acid Phosphate buffer (pH 7.2, 80 mL) was added to 2-phenylacetylamino-3,3-diphenylpropanoic acid (0.80 g, 2.2 mmol) Dissolved and warmed to 37 ° C. Then, penicillin amidase (1250 U, manufactured by SIGMA) was added and stirred at 37 ° C. for 6 hours. It was found by HPLC analysis that the desired product was produced at a conversion rate of 30.2% (92.9% ee, Daicel CHIRALPAK WH, 2 mM aqueous copper sulfate solution: acetonitrile = 6: 4, 220 nm, 1.0 mL / min. , Rt). Thereafter, ethyl acetate (100 mL) was added to the reaction solution, the pH was adjusted to 1 with concentrated sulfuric acid, liquid separation was performed, and the target product was extracted into the aqueous layer. Thereafter, the aqueous layer was adjusted to pH 7, separated, extracted into the organic layer, and concentrated to obtain the title compound.

Example 5
Synthesis of L-2-t-butoxycarbonylamino-3,3-diphenylpropanoic acid To an aqueous solution of L-2-amino-3,3-diphenylpropanoic acid (0.10 g, 0.28 mmol, 92.9% ee) Sodium bicarbonate was added to adjust the pH to 8 to 9, and then ethyl acetate (1.0 mL) and di-t-butyl dicarbonate (0.1 g, 0.45 mmol) were added thereto. Stir for hours. Thereafter, the reaction solution was returned to room temperature, pH was adjusted to 2 with 6N hydrochloric acid, and the mixture was separated to extract the desired product into the organic layer. After the organic layer was concentrated, heptane was added and the mixture was stirred overnight, whereby crystals were precipitated. The crystals were filtered, dried and 97% ee (SUMICHIRAL OA-4100, hexane: methanol: 2-propanol: trifluoroacetic acid = 98: 1: 1: 0.1, 220 nm, 1.0 mL / min, rt) Of the title compound.

Example 6
Synthesis of 2-acetylamino-3,3-diphenylpropanoic acid To a solution of diethyl acetamidomalonate (10.94 g, 50.57 mmol) in N-methyl-2-pyrrolidone (40 mL, 1.25 M), t-butoxypotassium (5 .90 g, 52.60 mmol) was added and stirred at room temperature for 1 hour, and then diphenylmethylene bromide (10.0 g, 46.46 mmol) was added and stirred at 70 ° C. for 5 hours. After completion of the reaction, 2M aqueous sodium hydroxide solution (45 mL) was added to the reaction solution, and the mixture was stirred at 70 ° C. for 3 hours. After cooling to room temperature, toluene (19 mL) was added and the layers were separated, concentrated hydrochloric acid (8.8 mL) was added to the aqueous layer to adjust the pH to 7.0, ethyl acetate (80 mL) was added, and concentrated hydrochloric acid (13 (0.0 mL) was added for liquid separation. The aqueous layer was further extracted with ethyl acetate (40 mL), the organic layers were combined, and the organic layer was washed 3 times with 2M hydrochloric acid (40 mL), washed with saturated brine (10 mL), and concentrated. Toluene (30 mL) was added to the concentrate, and the mixture was concentrated at 50 ° C., further toluene (30 mL) was added, and the mixture was stirred for 30 min. Then, white crystals precipitated by cooling to 0 ° C. over 5 hours. The crystals were filtered and dried under reduced pressure to give 9.18 g of the title compound.

Example 7
Synthesis of 2-acetylamino-3,3-diphenylpropanoic acid To a solution of diethyl acetamidomalonate (13.33 g, 61.8 mmol) in N-methyl-2-pyrrolidone (40 mL, 1.25 M), t-butoxypotassium (7 .20 g, 64.3 mmol) was added, and the mixture was stirred at room temperature for 1 hour, and then diphenylmethylene chloride (10.0 g, 49.3 mmol) and potassium iodide (4.10 g, 24.7 mol) were added thereto. For 6 hours. After completion of the reaction, 2M aqueous sodium hydroxide solution (45 mL) was added to the reaction solution, and the mixture was stirred at 60 ° C. for 5 hours. After cooling to room temperature, the mixture was separated, and concentrated hydrochloric acid (4.4 mL) was added to the aqueous layer to adjust the pH to 7.0, ethyl acetate (80 mL) was added, and concentrated hydrochloric acid (6.9 mL) was further added to separate the layers. Liquid. The aqueous layer was further extracted with ethyl acetate (40 mL), and the organic layers were combined, washed 3 times with 2M hydrochloric acid (20 mL), washed with saturated brine (10 mL), and concentrated. Toluene (30 mL) was added to the concentrate, and the mixture was concentrated at 50 ° C., further toluene (30 mL) was added, and the mixture was stirred for 30 min. Then, white crystals precipitated by cooling to 0 ° C. over 5 hours. The crystals were filtered and dried under reduced pressure to give 11.69 g of the title compound. As shown in FIG. 1, the powder X-rays (Cu-Kα ray) of the dried crystals have characteristic peaks at 5.8 °, 11.5 °, 21.6 °, 23.2 ° and 28.7 °. showed that.

Example 8
Synthesis of 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid 55% hydrogenated into a solution of diethyl acetamidomalonate (22.79 g, 105.4 mmol) in N-methyl-2-pyrrolidone (84 mL) Sodium (4.58 g, 105.2 mmol) was added and stirred at room temperature for 1 hour, and then bis (4-fluorophenyl) methylene chloride (16.5 mL, 84.7 mmol) and potassium iodide (13.95 g, 84.84). 0 mmol) was added and the mixture was stirred at 50 ° C. for 5 hours. After completion of the reaction, toluene (200 mL) and water (100 mL) were added to the reaction solution for liquid separation. The obtained organic layer was washed twice with water (100 mL) and then concentrated. Ethanol (108 mL) and 2M aqueous sodium hydroxide solution (127 mL) were added to the concentrated solution, and the mixture was stirred at 90 ° C. for 2.5 hours. Thereafter, the reaction solution was cooled to 25 ° C., and toluene (200 mL) and water (50 mL) were added for liquid separation. The aqueous layer was concentrated to half volume, isopropyl acetate (60 mL) and water (130 mL) were added, the pH was adjusted to 1.1 with concentrated hydrochloric acid, and the mixture was separated and washed with water (200 mL). The organic layer was concentrated and dried in vacuo to give 28.24 g of the title compound.

Example 9
Synthesis of 2-amino-3,3-bis (4-fluorophenyl) propanoic acid hydrochloride Concentration of 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid (25.34 g, 79.9 mmol) A hydrochloric acid solution (144 mL) was stirred at 90 ° C. for 5 hours, and then ice-cooled to precipitate a solid. The solid was filtered and dried to give 22.79 g of the title compound.

Example 10
Synthesis of 2-phenylacetylamino-3,3-bis (4-fluorophenyl) propanoic acid 2-amino-3,3-bis (4-fluorophenyl) propanoic acid hydrochloride (21.50 g, 68.9 mmol) A 1M aqueous sodium hydroxide solution (154.2 g) was added to the aqueous solution (188 mL) to adjust the pH to 12.2, and then the pH was adjusted from 11 to 12 with a 1M aqueous sodium hydroxide solution, while phenylacetyl chloride (10. 8 mL, 81.7 mmol) was added dropwise at 0 to 10 ° C., and the mixture was stirred at room temperature for 3 hours. Thereafter, 400 mL of ethyl acetate was added to the reaction solution, and the pH was adjusted to 1.1 with concentrated hydrochloric acid, followed by liquid separation. The obtained organic layer was heated to 40 ° C., hexane (525 mL) was added, and the mixture was ice-cooled to precipitate a solid. The solid was filtered and dried to give 21.75 g of the title compound.
Melting point 187 ° C
¹ H NMR (400 MHz, DMSO-d ₆ ) δ 3.25-3.35 (m, 2H), 4.35 (d, 1H, J = 7.2 Hz), 5.13 (dd, 2H, J = 5.6 Hz, 10.7 Hz), 6.68 -7.39 (m, 13H), 8.52 (d, 1H, J = 5.6 Hz)
¹³ C NMR (100 MHz, DMSO-d ₆ ) δ172.49, 170.04, 162.53, 160.16, 160.12, 137.57, 137.39, 136.39, 130.45, 130.38, 130.30, 129.02, 128.29, 126.47, 115.60, 115.44, 115.39, 115.23, 55.67, 51.82, 42.18
MS (FAB), m / z 396 [M + + H]

Example 11
Synthesis of L-2-amino-3,3-bis (4-fluorophenyl) propanoic acid An aqueous solution of 2-phenylacetylamino-3,3-bis (4-fluorophenyl) propanoic acid (5 g, 12.6 mmol) ( 500 mL) was adjusted to pH 7.8 by adding 0.8 M aqueous potassium hydroxide solution (6 mL), penicillin amidase (10000 U, manufactured by SIGMA) was added, and the mixture was stirred at 37 ° C. for 24 hours. It was found by HPLC analysis that the target product was produced at a conversion rate of 47% (88% ee, Daicel CHIRALPAK WH, 2 mM aqueous copper sulfate solution: acetonitrile = 6: 4, 220 nm, 1.0 mL / min, rt). Thereafter, ethyl acetate (400 mL) and activated carbon (500 mg) were added to the reaction solution, and the pH was adjusted to 1.1 with concentrated hydrochloric acid, followed by filtration. The filtrate was separated and the title compound was extracted into the aqueous layer.

Example 12
Synthesis of L-2-t-butoxycarbonylamino-3,3-bis (4-fluorophenyl) propanoic acid L-2-amino-3,3-bis (4-fluorophenyl) propane obtained in Example 11 The aqueous acid solution was adjusted to pH 8 with an aqueous potassium hydrogen carbonate solution, methanol (50 mL) and di-t-butyl dicarbonate (1.37 g, 6.3 mmol) were added, and the mixture was stirred at 37 ° C. for 3 hr. Thereafter, the pH of the reaction solution was adjusted to 1.1 with concentrated hydrochloric acid, liquid separation was performed, and the target product was extracted into the organic layer. The organic layer was concentrated and dried to give a solid (1.75 g). This solid was recrystallized to have an optical purity of 99.3% ee (SUMICHIRAL OA-4100, hexane: methanol: 2-propanol: trifluoroacetic acid = 98: 1: 1: 0.2, 210 nm, 1.0 mL / min, rt) of the title compound was obtained.

Example 13
Synthesis of D-2-amino-3,3-bis (4-fluorophenyl) propanoic acid The organic layer separated in the previous Example 11 was analyzed by HPLC. As a result, D-2-phenylacetylamino-3,3 It was found that bis (4-fluorophenyl) propanoic acid was present in a yield of 50% (78% ee: Daicel CHIRALPAK WH, 2 mM aqueous copper sulfate solution: acetonitrile = 6: 4, 220 nm, 1.0 mL / min, rt). The organic layer was concentrated, concentrated hydrochloric acid was added, and the mixture was stirred at 100 ° C. for 16 hours. The precipitated crystals were filtered and dried to obtain 0.99 g of the title compound (78% ee: Daicel CHIRALPAK WH, 2 mM aqueous copper sulfate solution: acetonitrile = 6: 4, 220 nm, 1.0 mL / min, rt) .

Example 14
Synthesis of 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid To a solution of diethyl acetamidomalonate (1.09 g, 5 mmol) in N-methyl-2-pyrrolidone (4 mL), 55% sodium hydride ( (219 mg, 5 mmol) was added and stirred at room temperature for 1 hour, bis (4-fluorophenyl) methylene bromide (990 mg, 4 mmol) was added, and the mixture was stirred at 50 ° C. for 4 hours. After completion of the reaction, toluene (20 mL) and water (10 mL) were added to the reaction solution for liquid separation. The obtained organic layer was washed twice with water (10 mL) and then concentrated. Ethanol (4.5 mL) and 2M aqueous sodium hydroxide solution (5 mL) were added to the concentrated solution, and the mixture was stirred at 90 ° C. for 16 hours. Thereafter, the reaction solution was cooled to 25 ° C., and toluene (8 mL) and water (5 mL) were added for liquid separation. The aqueous layer was concentrated to half volume, isopropyl acetate (8 mL) and water (10 mL) were added, the pH was adjusted to 1.1 with concentrated hydrochloric acid, and the mixture was separated and washed with water (10 mL). The organic layer was concentrated and dried in vacuo to give 973 mg of the title compound.

Example 15
Synthesis of diethyl (acetylamino) (bis (4-fluorophenyl) methyl) malonate To a solution of diethyl acetamidemalonate (238 mg, 1.1 mmol) in N, N-dimethylformamide (1 mL), 55% sodium hydride (44 mg, 1.1 mmol) and stirred at room temperature for 1 hour, and then added bis (4-fluorophenyl) methylene chloride (93 μL, 0.5 mmol) and tetra n-butylammonium iodide (24 mg) at 50 ° C. The mixture was stirred for 16 hours and further stirred at 80 ° C. for 16 hours. After completion of the reaction, quantitative analysis by HPLC confirmed 161 mg of the title compound (Inertsil ODS-2, 0.03 M phosphate buffer: acetonitrile = 90: 10 to 25:75 (20 minutes), 220 nm, 1.0 mL / min, rt).

Example 16
Synthesis of 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid N-methyl-2-pyrrolidone (18.2 mL, 1.25 M) of diethyl acetamidomalonate (5.17 g, 23.80 mmol) To the solution was added t-butoxypotassium (2.77 g, 24.69 mmol), and the mixture was stirred at room temperature for 1 hour, and then a toluene solution of bis (4-fluorophenyl) methylene chloride (4.54 g, 19.02 mmol) (21 .79 g) and potassium iodide (3.19 g, 19.10 mol) were added, and the mixture was stirred at 70 ° C. for 6 hours. After completion of the reaction, 2M aqueous sodium hydroxide solution (45 mL) was added to the reaction solution, and the mixture was stirred at 60 ° C. for 5 hours. After cooling to room temperature, the mixture was separated, and concentrated hydrochloric acid (4.4 mL) was added to the aqueous layer to adjust the pH to 7.0, ethyl acetate (30 mL) was added, and concentrated hydrochloric acid (6.9 mL) was further added. Liquid. The aqueous layer was further extracted with ethyl acetate (6 mL), the organic layers were combined, and the content of the title compound was examined by HPLC. As a result, it was found that 5.678 g was contained in the organic layer. The organic layer was washed 3 times with 2M hydrochloric acid (9 mL), washed with saturated brine (4.5 mL), and concentrated. Toluene (13.5 mL) was added to the concentrate, and the mixture was concentrated at 50 ° C., and further toluene (13.5 mL) was added and stirred for 30 minutes. Then, white crystals precipitated by cooling to 0 ° C. over 5 hours. The crystals were filtered to obtain wet crystals. As shown in FIG. 2, the wet crystal powder X-rays (Cu-Kα rays) are 17.1 °, 17.6 °, 18.8 °, 20.7 °, 21.8 °, 22.0 °. , 22.7 °, 23.1 ° and 25.4 °. The wet crystals were dried under reduced pressure to give 5.39 g of the title compound as dry crystals. As shown in FIG. 3, the powder X-rays (Cu-Kα rays) of the dried crystals are 17.1 °, 21.8 °, 22.0 °, 22.7 °, 23.1 ° and 25.4 °. Showed a characteristic peak.

Example 17
Synthesis of 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid N-methyl-2-pyrrolidone (19.0 mL, 1.25 M) of diethyl acetamidomalonate (5.14 g, 23.66 mmol) T-Butoxy sodium (2.38 g, 24.76 mmol) was added to the solution, and the mixture was stirred at room temperature for 1 hour, and then a toluene solution of bis (4-fluorophenyl) methylene chloride (4.54 g, 19.02 mmol) (22 0.07 g) and potassium iodide (3.17 g, 19.10 mol) were added, and the mixture was stirred at 60 ° C. for 6 hours. After completion of the reaction, 2M aqueous sodium hydroxide solution (45 mL) was added to the reaction solution, and the mixture was stirred at 60 ° C. for 4 hours. After cooling to room temperature, the mixture was separated, and concentrated hydrochloric acid (4.4 mL) was added to the aqueous layer to adjust the pH to 7.0, ethyl acetate (30 mL) was added, and concentrated hydrochloric acid (6.9 mL) was further added. Liquid. The aqueous layer was further extracted with ethyl acetate (6 mL), the organic layers were combined, and the content of the title compound was examined by HPLC. As a result, it was found that 5.914 g was contained in the organic layer. The organic layer was washed 3 times with 2M hydrochloric acid (9 mL), washed with saturated brine (4.5 mL), concentrated at 40 ° C., and cooled to about a quarter to precipitate crystals. After cooling to 0 ° C., the crystals were filtered to obtain wet crystals. As shown in FIG. 4, the wet crystal X-ray powder (Cu-Kα ray) showed characteristic peaks at 12.8 °, 17.6 °, 19.2 °, and 24.3 °.

Example 18
Synthesis of 2-acetylamino-3,3-bis (4-fluorophenyl) propanoic acid N-ethyl-2-pyrrolidone (4.0 mL, 1.1 M) of diethyl acetamidomalonate (1.15 g, 5.29 mmol) To the solution was added t-butoxypotassium (0.58 g, 5.41 mmol), and the mixture was stirred at room temperature for 1 hour, and then bis (4-fluorophenyl) methylene chloride (1.0 g, 4.21 mmol) and potassium iodide ( 0.70 g, 4.21 mol) was added, and the mixture was stirred at 60 ° C. for 6 hours. After completion of the reaction, toluene (5 mL) and 2M aqueous sodium hydroxide solution (5 mL) were added to the reaction solution, and the mixture was stirred at 60 ° C. for 5 hours. After cooling to room temperature, the mixture was separated, concentrated hydrochloric acid was added to the aqueous layer to adjust the pH to 7.0, ethyl acetate (8 mL) was added, and concentrated hydrochloric acid was further added for separation. The aqueous layer was further extracted with ethyl acetate (2 mL), the organic layers were combined, and the content of the title compound was examined by HPLC. As a result, it was found that 1.10 g was contained in the organic layer (Inertsil ODS). -2, 0.03 M phosphate buffer: acetonitrile = 90: 10 to 25:75 (20 minutes), 220 nm, 1.0 mL / min, rt).

  According to the present invention, optically active diphenylalanine compounds useful as synthetic intermediates for anti-HIV drugs, dipeptidyl peptidase inhibitors and the like are obtained from a novel diphenylalanine compound by a substrate-specific reaction with penicillin amidase. It can be easily manufactured at a rate. Furthermore, racemic N-acetyldiphenylalanine and racemic N-acetylbis (4-fluorophenyl) alanine can be obtained in the form of crystals having high purity and convenient for storage and transportation.

1 is a powder X-ray diffraction pattern of a racemic N-acetyldiphenylalanine dry crystal in Example 7. FIG. The vertical axis represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ [deg]. 2 is a powder X-ray diffraction pattern of racemic N-acetylbis (4-fluorophenyl) alanine wet crystals in Example 16. FIG. The vertical axis represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ [deg]. 3 is a powder X-ray diffraction pattern after drying of racemic N-acetylbis (4-fluorophenyl) alanine crystals in Example 16. FIG. The vertical axis represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ [deg]. 4 is a powder X-ray diffraction pattern of racemic N-acetylbis (4-fluorophenyl) alanine wet crystals in Example 17. FIG. The vertical axis represents the diffraction intensity, and the horizontal axis represents the diffraction angle 2θ [deg].

Claims (26)

Following formula (1):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And X represents a chlorine atom, a bromine atom or an iodine atom. ]
And a diphenylmethylene halide compound represented by the following formula (2):

[Wherein, R ³ and R ⁴ each independently represent an alkyl group or an aralkyl group, or R ³ and R ⁴ together form an alkylene group, and P ¹ is an amino-protecting group. Indicates. ]
A malonic acid diester compound represented by the formula: an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and an alkali metal hydride and a t-butoxy alkali metal The reaction is carried out in the presence of a selected base, the following formula (3):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of the diester compound represented by these.   The production method according to claim 1, wherein the base is selected from sodium hydride, sodium t-butoxy and potassium t-butoxy.   The production method according to claim 1, wherein the organic solvent is selected from N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The manufacturing method in any one of Claims 1-3 whose R < ¹ > and R < ² > is a fluorine atom. R ³ and ^{R 4} is an ethyl group, The process according to claim 1. P ¹ is an acetyl group or phenylacetyl group, the manufacturing method according to claim 1.   The manufacturing method in any one of Claims 1-6 whose X is a chlorine atom or a bromine atom.   The manufacturing method in any one of Claims 1-7 performed in coexistence of an iodine compound or a bromine compound.   The production method according to any one of claims 1 to 7, which is carried out in the presence of metal iodide or quaternary ammonium iodide. A method for producing a diphenylalanine compound represented by the following formula (4) or a salt thereof including the following steps (a) and (b);
Step (a): Formula (1) below:

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And X represents a chlorine atom, a bromine atom or an iodine atom. ]
And a diphenylmethylene halide compound represented by the following formula (2):

[Wherein, R ³ and R ⁴ each independently represent an alkyl group or an aralkyl group, or R ³ and R ⁴ together form an alkylene group, and P ¹ is an amino-protecting group. Indicates. ]
A malonic acid diester compound represented by the formula: an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and an alkali metal hydride and a t-butoxy alkali metal Reaction in the presence of a selected base gives the following formula (3):

[Wherein each symbol has the same meaning as defined above. ]
Step of obtaining a diester compound represented by formula (b): Step (b): The diester compound is subjected to hydrolysis and decarboxylation, and the following formula (4):

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ² represents a hydrogen atom or an amino-protecting group. ]
The process of obtaining the diphenylalanine compound or its salt represented by these. P ² is a hydrogen atom, an acetyl group or phenylacetyl group, The method according to Claim 10. Following formula (4):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And P ² represents a hydrogen atom or an amino-protecting group (provided that the following formula (5):

(Wherein R ⁵ represents a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ³ represents an integer of 0 to 5)). Show. ]
Wherein P ² of the diphenylalanine compound represented by the formula or a salt thereof is converted to a substituted phenylacetyl group represented by the formula (5):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of the acyl-substituted diphenylalanine compound or its salt represented by these. Following formula (6):

[Wherein R ¹ , R ² and R ⁵ each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ , n ² and n ³ each independently And represents an integer of 0 to 5. ]
Penicillin amidase is allowed to act on an acyl-substituted diphenylalanine compound represented by the formula:

[Wherein each symbol has the same meaning as defined above. ]
Or an L-diphenylalanine compound represented by the following formula (6b):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of the D-acyl substituted diphenylalanine compound represented by these, or its salt. A method for producing an optically active diphenylalanine compound represented by the following formulas (7a) and (6b) or a salt thereof, comprising the following steps (a), (b), (c) and (d);
Step (a): Formula (1) below:

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represents an integer of 0 to 5] And X represents a chlorine atom, a bromine atom or an iodine atom. ]
And a diphenylmethylene halide compound represented by the following formula (2):

[Wherein, R ³ and R ⁴ each independently represent an alkyl group or an aralkyl group, or R ³ and R ⁴ together form an alkylene group, and P ¹ is an amino-protecting group. Indicates. ]
A malonic acid diester compound represented by the formula: an organic solvent selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and N, N-dimethylformamide, and an alkali metal hydride and a t-butoxy alkali metal Reaction in the presence of a selected base gives the following formula (3):

[Wherein each symbol has the same meaning as defined above. ]
A step of obtaining a diester compound represented by:
Step (b): The diester compound is subjected to hydrolysis and decarboxylation to obtain the following formula (4):

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ² represents a hydrogen atom or an amino-protecting group. ]
A step of obtaining a diphenylalanine compound represented by the formula:
Step (c): the diphenylalanine compound [wherein P ² is represented by the following formula (5):

(Wherein R ⁵ represents a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ³ represents an integer of 0 to 5). except. Or P ² of the salt thereof is converted into a substituted phenylacetyl group represented by the above formula (5), and the following formula (6):

[Wherein each symbol has the same meaning as defined above. ]
A step of obtaining an acyl-substituted diphenylalanine compound or a salt thereof represented by: and step (d): a penicillin amidase is allowed to act on the acyl-substituted diphenylalanine compound or a salt thereof, and the following formula (7a):

[Wherein each symbol has the same meaning as defined above. ]
Or an L-diphenylalanine compound represented by the following formula (6b):

[Wherein each symbol has the same meaning as defined above. ]
A step of obtaining a D-acyl-substituted diphenylalanine compound represented by the formula: According to the method of claim 13, the following formula (7a):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represent 0 to 5 Indicates an integer. ]
After obtaining the L-diphenylalanine compound or its salt represented by the following formula (8a), the amino group of the compound or its salt is protected:

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ³ represents an amino-protecting group. ]
The manufacturing method of the LN protection diphenylalanine compound or its salt represented by these. The production method according to claim 15, wherein P ³ is a tert-butoxycarbonyl group. According to the method of claim 13, the following formula (6b):

[Wherein R ¹ , R ² and R ⁵ each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ , n ² and n ³ each independently And represents an integer of 0 to 5. ]
After obtaining a D-acyl-substituted diphenylalanine compound or a salt thereof represented by the following formula (7b):

[Wherein each symbol has the same meaning as defined above. ]
The manufacturing method of D-diphenylalanine compound or its salt represented by these. According to the method of claim 17, the following formula (7b):

[Wherein, R ¹ and R ² each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ and n ² each independently represent 0 to 5 Indicates an integer. ]
After obtaining the D-diphenylalanine compound or salt thereof represented by the following formula (8b), the amino group of the compound or salt thereof is protected:

[Wherein, R ¹ , R ² , n ¹ and n ² have the same meaning as defined above, and P ³ represents an amino-protecting group. ]
The manufacturing method of DN protected diphenylalanine compound or its salt represented by these. The production method according to claim 18, wherein P ³ is a tert-butoxycarbonyl group. Following formula (6):

[Wherein R ¹ , R ² and R ⁵ each independently represent a halogen atom, an alkyl group, an alkoxy group, an amino group, a nitro group or a hydroxyl group, and n ¹ , n ² and n ³ each independently And represents an integer of 0 to 5. ]
Or an acyl-substituted diphenylalanine compound or a salt thereof.   Characteristic peak of diffraction angle 2θ at 5.8 °, 11.5 °, 21.6 °, 23.2 ° and 28.7 ° in the X-ray diffraction pattern obtained by powder X-ray diffraction with Cu-Kα ray Racemic N-acetyldiphenylalanine crystals having:   The crystal according to claim 21, which is obtained by adding a poor solvent to an acetic ester solution of racemic N-acetyldiphenylalanine.   In the X-ray diffraction pattern obtained by powder X-ray diffraction with Cu-Kα ray, diffraction angles are 17.1 °, 21.8 °, 22.0 °, 22.7 °, 23.1 ° and 25.4 °. Racemic N-acetylbis (4-fluorophenyl) alanine crystals with a characteristic peak of 2θ.   Racemate having characteristic peaks of diffraction angle 2θ at 12.8 °, 17.6 °, 19.2 ° and 24.3 ° in an X-ray diffraction pattern obtained by powder X-ray diffraction with Cu-Kα ray Of N-acetylbis (4-fluorophenyl) alanine.   The crystal | crystallization of Claim 23 obtained by adding a poor solvent to the acetic ester solution of a racemic N-acetylbis (4-fluorophenyl) alanine.   The crystal | crystallization of Claim 24 obtained by cooling the acetate ester solution of a racemic N-acetylbis (4-fluorophenyl) alanine.

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