JP3220484B2 - Method for producing N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing L-phenylalanine methyl ester and N-benzyloxycarbonyl-L-
The present invention relates to a method for producing N-benzyloxycarbonyl-α-L aspartyl-L-phenylalanine methyl ester with high selectivity from aspartic anhydride.

[0002] α-L-aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as α-APM)
Is widely known as a dipeptide-based sweetener, has good sweetness characteristics and a high sweetness nearly 200 times that of sucrose, and its demand as a diet sweetener is greatly growing.

[0003]

2. Description of the Related Art α-APM is obtained by a condensation reaction between N-protected L-aspargic anhydride and L-phenylalanine methyl ester (hereinafter abbreviated as L-PM) in an organic solvent. -Α-L-aspartyl-L-phenylalanine methyl ester (hereinafter referred to as N-protected-α-APM
Abbreviated. ), And N-
The most common method is to remove the protecting group to obtain the desired α-APM (USP-3,786,039).

[0004]

In the known production examples, in addition to the desired N-protected-α-APM, its isomer, N-protected-β-L-aspartyl-L-phenylalanine, is used. Methyl ester (hereinafter abbreviated as N-protected-β-APM) is inevitable.

[0005] β-A obtained from N-protected-β-APM
Since PM has no sweetness, the by-product of Z-β-APM is
The yield of α-APM, which is the final target, is reduced.

Further, β- by-produced with the desired α-APM
From a mixture of L-aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as β-APM), α-
As a method for separating APM, α-APM and β-AP
M in aqueous medium with β-resorcylic acid, α-A
A method is known in which PM is separated as a sparingly soluble adduct from β-APM as an impurity (JP-A-49-6305).

[0007] Further, by contacting α-APM with hydrohalic acid in an aqueous medium, the hardly soluble α-AP
There is also known a method of generating a hydrohalide of M and separating β-APM coexisting as an impurity (JP-A-49-41425).

In order to obtain α-APM from the α-APM salt once isolated as an acid adduct, a neutralization step is required. Usually, in the neutralization operation, a method is used in which a salt of α-APM is dissolved in water, and a base is added thereto for neutralization to separate α-APM formed as crystals.

[0009] However, in these methods, the yield is low because a considerable amount of α-APM is lost in the aqueous solution.
Further, α-APM isolated by this method contains a large amount of salts, and requires operations such as recrystallization and desalting in order to obtain a final product, which further lowers the yield.

We have previously described a water suspension of benzyloxycarbonyl-β-L-aspartyl-L-phenylalanine methyl ester containing up to 30% by weight of benzyloxycarbonyl-β-L-aspartyl-L-phenylalanine methyl ester. After the solution was hydrogenated in the presence of a platinum group catalyst, the catalyst was separated at a temperature at which the formed α-L-aspartyl-L-phenylalanine methyl ester was completely dissolved, and the filtrate was β-L-aspartyl- L
-Phenylalanine methyl ester was cooled to a temperature at which it did not precipitate, and the precipitated α-L-aspartyl-L-phenylalanine methyl ester was separated. A method for producing α-L-aspartyl-L-phenylalanine methyl ester to be circulated and used for suspension was found and filed.

However, even in this method, α-A
There is a disadvantage in that the same amount of α-APM as β-APM is lost in the process of separating PM. Reducing the formation of β-forms in the condensation step reduces the purification loss in addition to increasing the α-formation rate. To achieve a double effect.

[0012]

Means for Solving the Problems The inventors of the present invention have made intensive studies to overcome the above-mentioned drawbacks, and as a result, surprisingly, L-PM and N-benzyloxycarbonyl-L-aspartate in an organic solvent have been surprisingly obtained. An anhydride (hereinafter abbreviated as Z-Asp anhydride) is reacted to produce N-benzyloxycarbonyl-α-L aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as Z-α-APM). In the method, the reaction is performed under conditions such that the L-PM concentration in the reaction solution is 1% or less, and the addition rate is controlled so that the Z-Asp anhydride in the system becomes excessive with respect to L-PM. It was found that the desired α selectivity was drastically improved by adding a small amount at a time and reacting, thereby completing the present invention.

L-PM used in the method of the present invention
Can be obtained by subjecting L-phenylalanine to methyl esterification in the presence of an acid catalyst, and is usually obtained in the form of an addition salt with an acid. Can be directly subjected to the reaction. LP
There is no particular limitation on the concentration of M.

Z-As used in the method of the present invention
The p-anhydride is, for example, N-benzyloxycabonyl-L
It is known that aspartic acid can be obtained by dissolving or suspending it in an organic solvent and allowing it to react with a dehydrating agent.

As the reaction solvent used in the method of the present invention, any solvent can be used as long as it is not particularly active in reactants and products. Aromatic hydrocarbons such as benzene, toluene and xylene, chlorinated hydrocarbons such as dichloromethane, 1.2-dichloroethane chloroform and carbon tetrachloride, ethers such as tetrahydrofuran and dioxane, and acetonitrile and propionitrile Typical examples thereof include nitriles, esters such as ethyl acetate / n-butyl acetate / methyl propionate, and ketones such as acetone / methyl ethyl ketone, and a mixed solvent of any two or more of these is used. You can also. Particularly, aromatic hydrocarbons such as toluene and esters such as n-butyl acetate are preferred. Also, the solvent is
Z-APM may be included.

The reaction method may be a batch method or a continuous method. In the case of the batch method, L-PM may be added dropwise to the solution containing Z-Asp anhydride, or both may be added simultaneously, but the latter method is preferred. L-
It is necessary to control the rate of addition of PM in consideration of the rate of the condensation reaction, and the rate must be such that the L-PM concentration in the system becomes 1% or less. LP in solution
The M concentration may be obtained by analyzing the reaction solution with an analyzer such as HLC. The addition rate can also be controlled by a pH meter equipped with a commercially available glass composite electrode, using the indicated value as an index. pH meter reading is 3.0
It is preferred to add the L-PM solution as follows.

The addition time is adjusted in accordance with the L-PM consumption rate in the system, but is usually 1 to 3 hours. When the addition is performed for 30 minutes or less, unreacted L-PM in the reaction solution increases,
The α selectivity is lowered, which is not preferable.

The addition temperature and the reaction temperature are 100 ° C. or lower, preferably 80 ° C. or lower, from the viewpoint of minimizing racemization of the product. The lower the temperature, the higher the α selectivity.

The reaction time after completion of the addition of the Z-Asp anhydride and L-PM is not particularly limited, but is generally maintained for several hours in order to complete the reaction. Although it depends on the reaction temperature, usually within 6 hours is sufficient.

The molar ratio of Z-Asp anhydride to L-PM is:
The range of 0.8 to 1.2 is preferred. The reaction proceeds almost quantitatively, and when one of them is used in excess, that amount is wasted and is not economical.

[0021]

EXAMPLES The method of the present invention will be described below in detail with reference to examples.

Example 1 133.61 g (0.5%) of N-benzylcarboxy-L-aspartic acid was placed in a 1000 ml reaction vessel equipped with a stirrer.
0 mol), 56.15 g (0.55 mol) of acetic anhydride and 400 g of toluene were mixed and reacted at 55 ° C. for 3 hours with stirring. The obtained reaction solution was cooled to 30 ° C., filtered, washed with toluene, and dried to obtain 109.7 g (0.44 mol) of anhydrous Z-Asp crystals.

38.3 g of n-butyl acetate was placed in a 300 ml reaction vessel equipped with a stirrer, cooled to 3 ° C.
12.84 g (0.0515 mol) of Asp anhydride crystals
Was added to 65 g of n-butyl acetate and dissolved in parallel with 8.96 g (0.05 mol) of L-phenylalanine methyl ester.
66.0 g of butyl was simultaneously dropped and sampled over time to confirm that the concentration of L-PM was 1% or less. Further, a glass electrode pH meter manufactured by Ikeda Seisakusho (model PT-3S) After the dropwise addition was completed in 2 hours while controlling the indicated value of 3.0 or less, the mixture was reacted at the same temperature for 2 hours. Z-α-APM and Z-β-APM in the reaction solution
Was determined and the yield of Z-α-APM was determined.
8.0%.

Further, n-butyl acetate of the condensed liquid was distilled off under reduced pressure, and 310 g of water was added to obtain a suspended state.
After heating, 0.5% of 5% palladium-carbon was added, and catalytic reduction was performed at normal pressure for 3 hours. Then, the catalyst was separated by filtration at the same temperature, the toluene layer was separated, and the aqueous layer was cooled. After stirring at 5 ° C. for 1 hour, the precipitated crystals were filtered at the same temperature, washed with 30 ml of 5 ° C. cold water, dried and α-APM 10.36
g (0.0352 mol) were obtained. (70.4% yield)

Comparative Example 1 104.3 g of n-butyl acetate containing 8.96 g (0.05 mol) of L-phenylalanine methyl ester was placed in a 300 ml reaction vessel equipped with a stirrer, and cooled to 3 ° C.
Crystals of Z-Asp anhydride obtained in Example 1 12.84
g (0.0515 mol) was added to and dissolved in 65 g of n-butyl acetate.
Allowed to react for hours. At that time, the reading of the pH meter was 5.
As a result of sampling over time and analyzing the concentration of L-PM, it was 1% or more. Z in this reaction solution
-Α-APM and Z-β-APM were quantified, and the Z-α-
When the yield of APM was determined, it was 75.5%.

Example 2 Example 1 except that the dropping and reaction temperature was 40 ° C.
The reaction was carried out according to the method described above. Z-α- in this reaction solution
APM and Z-β-APM were quantified, and the Z-α-APM
Was 80.8%.

Example 3 The reaction was carried out in the same manner as in Example 1 except that the dropping temperature and the reaction temperature were -20 ° C. Z-α in this reaction solution
-APM and Z-β-APM were quantified and their Z-α-AP
The yield of M was 87.0%.

Example 4 38.3 g of 1.4-dioxane was placed in a 300 ml reactor equipped with a stirrer, cooled to 3 ° C., and then 12.84 g of the anhydrous Z-Asp crystal obtained in Example 1 ( 0.05
15 mol) was added to 65 g of 1.4-dioxane and, while preceding the dropwise addition of a solution, 66.0 g of 1.4-dioxane containing 8.96 g (0.05 mol) of L-phenylalanine methyl ester was added. At the same time, the mixture was dropped and sampled over time to confirm that the concentration of L-PM was 1% or less, and the pH meter indicated a value of 3.0.
After the dropping was completed in 2 hours while controlling as follows, the reaction was carried out at the same temperature for 2 hours. Z-α-A in this reaction solution
When PM and Z-β-APM were quantified and the yield of Z-α-APM was determined, it was 84.0%.

Examples 5 to 9 The results obtained in Example 1 by changing the kind of the solvent are shown in the following Table.
It is shown in FIG. The reaction was carried out according to the method of Example 1 except that the type of the solvent was changed. Example 10 12.84 g (0.051) of the anhydrous Z-Asp crystal obtained in Example 1 was placed in a 1000 ml reaction vessel equipped with a stirrer.
5 mol) in 300 g of toluene and cooled to 3 ° C., and then a toluene solution containing 8.96 g (0.05 mol) of phenylalanine methyl ester 90.
0 g was dropped in 2 hours, and the pH meter indicated a value of 3.
The reaction was controlled at 0 or less and reacted at the same temperature for 2 hours. Z-α-APM and Z-β-APM in this reaction solution were quantified, and the yield of Z-α-APM was determined.
6.5%.

[0030]

According to the present invention, it is possible to produce Z-α-APM with a higher α selectivity than any of the values described in the reports known so far, particularly in an ester solvent, as compared with the ordinary batch insertion method. This is industrially extremely advantageous in that the yield can be greatly improved in the subsequent α-APM isolation step.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akihiro Yamaguchi 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Examiner, Mitsui Toatsu Chemicals, Inc. Natsuko Honma (58) Field surveyed (Int.Cl. ⁷ , DB name) C07K 5/075 C07K 1/06 BIOSIS (DIALOG) WPI (DIALOG)

Claims (2)

(57) [Claims] In an organic solvent, L-phenylalanine methyl ester is reacted with N-benzyloxycarbonyl-L-aspartic anhydride to form N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester. N-benzyloxycarbonyl, characterized in that the reaction is carried out under conditions such that the concentration of L-phenylalanine methyl ester in the reaction solution is 1% or less and the pH of the reaction solution is 3.0 or less. A method for producing α-L-aspartyl-L-phenylalanine methyl ester. 2. The process according to claim 1, wherein the N-benzyloxycarbonyl-L-aspartic anhydride is added simultaneously, in parallel with the L-phenylalanine methyl ester.