JPH0832718B2 - Method for producing α-L-aspartyl-L-phenylalanine methyl ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to α-L-aspartyl-L-phenylalanine methyl ester useful as a sweetener (hereinafter, α-AP).
(Abbreviated as M)), which relates to a significantly improved method of producing α-APM by neutralizing an acid addition salt of α-APM with a base.

More specifically, an acid addition salt of α-APM is used as a base in an aqueous medium using ammonia or an organic amine,
After the aging operation in the pH range, the isoelectric point is neutralized and α
-It relates to a method of manufacturing an APM.

The α-APM of the present invention is a dipeptide-based sweetener having a sweetness about 200 times higher than that of sucrose, and is a substance that has been heavily used in recent years as a diet sweetener.

(Prior Art) Regarding the method for producing α-APM, many methods have been disclosed so far. The following methods are typical methods. For example, (1) a method of condensing a strong acid addition salt of L-aspartic acid anhydride and L-phenylalanine methyl ester, (2) condensation of N-protected-L-aspartic acid anhydride and L-phenylalanine methyl ester to produce (3) N-formyl-L-aspartic acid anhydride and L-phenylalanine are prepared by removing the protecting group of N-protected-α-L-aspartyl-L-phenylalanine methyl ester by a suitable method. As a starting material, there is a method of leading to α-APM via α-L-aspartyl-L-phenylalanine.

In addition, a method in which L-aspartic acid anhydride is not used as a starting material is disclosed, but (N-protected) -L-aspartic acid anhydride is used as one of the starting materials from the viewpoints of production and stability of the starting material. The method is considered to be the mainstream of the method for chemically producing α-APM.

However, this method of using (N-protected) -L-aspartic anhydride is not only the desired product but also unnecessary β-
A step of producing an isomer by-product and separating this is required.

In addition, there may be cases where other impurities are by-produced through each reaction step.

Therefore, in order to separate the finally produced α-APM from other contaminants, noting that the hydrochloride salt of α-APM is generally sparingly soluble in an aqueous medium, A method is employed in which the product is isolated with a hydrochloride and then neutralized with a base to convert it into free α-APM.

By the way, α-APM hydrochloride is neutralized with a base and α-APM
As a method for producing a., A method of using alkali hydroxide, alkali carbonate or alkali bicarbonate as a neutralizing agent in water is known. For example, Japanese Patent Publication Sho 55-26133
JP-A-55-35059 discloses an example of using an aqueous solution of sodium hydroxide as a neutralizing agent, and JP-A-55-35059 discloses an example of using an aqueous solution of sodium hydrogen carbonate.

(Problems to be Solved by the Invention) However, the present inventors have found that α-
It has been found that there are the following problems in neutralizing APM hydrochloride.

That is, when alkali hydroxide is used as a base, hydrolysis of the ester group of α-APM and intramolecular cyclization reaction occur during neutralization, resulting in α-L-aspartyl-L-phenylalanine and diketopiperazine compounds. (5-benzyl-3,6-dioxopiperazine-2-acetic acid) is likely to be produced, which lowers the yield of α-APM, and neutralization with alkali carbonate or bicarbonate is not effective. The foaming caused by the generation of carbon dioxide gas during the neutralization is remarkable, which causes a temporary increase in the volume of the neutralization mass, which causes a problem in workability.

The method for neutralizing α-APM hydrochloride is usually carried out by dissolving α-APM hydrochloride in water and adding or dropping a base into this solution. It was also found that in the method of continuously dropping to the point, precipitation of α-APM was likely to occur at one time during the process, so that only the peripheral portion of the stirrer was stirred and fluidity was lost.

In order to eliminate such a phenomenon, the amount of water used during neutralization must be excessively large and neutralization treatment must be performed in a dilute concentration, which not only reduces the volumetric efficiency but also the α-APM recovery rate. Is also a disadvantage.

As described above, when converting α-APM hydrochloride into α-APM by neutralizing it with a base, conventional methods include a method that is always satisfactory in terms of stability, workability, volumetric efficiency, etc. of α-APM. The current situation is that there are none.

(Means for Solving Problems) In view of the current state of the α-APM hydrochloride neutralization method as described above, the present inventors have repeatedly studied a more efficient neutralization method, and as a result, ammonia as a base has been obtained. Further, they have found that the above problems can be solved all at once by using an organic amine and adding an aging operation during the neutralization operation, and have completed the present invention.

That is, the present invention is a method of converting an acid addition salt of α-APM to α-APM by neutralizing the isoelectric point with a base, in an aqueous medium,
A process for producing α-APM, which comprises using ammonia or an organic amine as a base, aging in the range of pH 2.5 to 3.5 during neutralization, and then neutralizing to the isoelectric point.

In the method of the present invention, an acid addition salt of α-APM is used.
As the acid addition salt, there are mineral salts such as hydrochloride, hydrobromide, sulfate or phosphate, and the hydrochloride is often used.

Neutralization of the acid addition salt of α-APM is carried out in an aqueous medium. Usually, water is used alone, but methanol, ethanol, n-propanol, isopropanol, tertiary butanol, acetone, dioxane, tetrahydrofuran, acetonitrile, 2-methoxyethanol or 2 is used.
It is also possible to use a mixed solvent of water and one or more polar solvents such as ethoxyethanol. In this case, the ratio of water to the organic solvent can be arbitrarily selected within a range in which the ammonium salt or organic amine salt produced by neutralization does not precipitate outside the medium system.

The amount of the aqueous medium used is not particularly limited, but if it is used too much, the volume efficiency and the α-APM recovery rate decrease, which is not preferable, and if it is too small, the workability during neutralization deteriorates. Therefore, usually, the range of 3 to 20 times by weight based on α-APM in the acid addition salt of α-APM is preferable.

The base used is ammonia or organic amine. Ammonia may be introduced by the method of introducing ammonia gas, but it is preferable to use it in the form of an aqueous solution from the viewpoint of workability. Also, as an organic amine, its basicity is α
-It is not particularly limited as long as it is higher than the basicity of APM and the salt formed by an acid and an organic amine produced by neutralization is soluble in the aqueous medium used.

Specifically, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, tripropylamine, butylamine, hexylamine, ethanolamine, diethanolamine, triethanolamine, aliphatic amines such as ethylenediamine, cyclohexylamine or dicyclohexylamine, and pyridine. Representative aromatic amines are exemplified.

The amount of the base used is the amount necessary to make the acid addition salt of α-APM have the isoelectric point of α-APM.

In a specific embodiment of the method of the present invention, the acid addition salt of α-APM is first suspended or dissolved in an aqueous medium. At this time α
-The acid addition salt of APM does not necessarily have to be in a dissolved state, and even if it is in a suspended state, there is no problem in neutralization. On the contrary, when the suspension is carried out, the amount of the aqueous medium used can be reduced and the volume efficiency can be improved.

Next, ammonia (ammonia water) or an organic amine (which may be used in the form of an aqueous solution or the like if necessary) is added for neutralization to convert the α-APM acid addition salt into α-APM. At this time, α-AP was added continuously until the isoelectric point.
If it is converted to M, it tends to become muddy on the way, and it becomes difficult to smoothly stir around the flask. In the middle of adding the base
By suspending the addition once between pH 2.5 and 3.5 and performing the aging operation under stirring, the precipitation of α-APM can be gradually and smoothly advanced, and the neutralization process up to the subsequent isoelectric point can be performed. Thus, the neutralization can be carried out smoothly without troubles such as a problem of stirring due to the decrease in the fluidity of α-APM.

The aging time in the range of pH 2.5 to 3.5 is 15 minutes or longer, preferably 30 minutes or longer. The upper limit is not particularly limited, but it is not necessary to ripen for a long time, and usually 3 hours or less is sufficient.

The temperature conditions of the neutralization process including the aging process are 0 to 50 ° C,
It is preferably 5 to 40 ° C. If the temperature is raised more than necessary, side reactions such as hydrolysis of the ester are likely to occur and the yield may be reduced, which is not preferable.

After the aging operation, ammonia or organic amine is added again to neutralize to the isoelectric point. After neutralizing to the isoelectric point,
If necessary, it is cooled, and α-APM is isolated by a filtration operation such as centrifugation or pressure filtration.

(Effect) According to the method of the present invention, stability of α-APM at the time of neutralization observed when using an alkali hydroxide, an alkali carbonate or an alkali bicarbonate as an α-APM acid addition salt as a neutralizing agent, Not only the problems such as a decrease in workability due to the bubbling of carbon dioxide gas are solved, but also the problem of fluidity at the time of neutralization is solved.

That is, the method of the present invention is a method having a high industrial value because α-APM of stable quality can be obtained.

Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 36.7 g (0.1 mol) of α-APM hydrochloride dihydrate are suspended in 300 ml of water. 28% ammonia water was slowly added dropwise with stirring at room temperature, and the addition was stopped when the pH reached 2.7. Stir for 1 hour at room temperature. The pH dropped to 2.55. After that, ammonia water was added again and ammonia water was added until the pH reached 5.2. During this period, the neutralization reaction proceeded smoothly without any trouble such as sedimentation of mud. After cooling to 5 ° C, 27.10 g (yield 92.2
%) Of α-APM was obtained. As a result of analysis of α-APM in the filter wash liquid, 2.23 g (7.6% / α-APM hydrochloride) of α-APM was contained.

Comparative Example 1 In Example 1, neutralization was carried out by continuously dropping ammonia water without performing an aging operation in the middle. At around pH 3.5, it became extremely mud-like, and the fluidity was lost except for the surrounding area of the stirring rod, and the whole was in a solidified state. The stirring was stopped, the whole was loosened and then neutralized to pH 5.2. During this time, it was necessary to loosen the precipitated cake from time to time.

Comparative Example 2 36.7 g (0.1 mol) of α-APM hydrochloride dihydrate was added to 750 ml of water.
Dissolved in. While stirring at room temperature, 45% sodium hydroxide was slowly added dropwise to neutralize the pH to 5.2. By cooling to 5 ° C, filtering and washing with water, 22.80 g of α-APM (yield 77.6
%) To obtain a wet cake.

On the other hand, as a result of analysis, α-APM in the washing liquid was 4.72 g (16.0% /
α-APM hydrochloride), and α-L-aspartyl-L-phenylalanine and 5-benzyl-
3,6-dioxopiperazine-2-acetic acid total 6.2% / α
-APM hydrochloride was detected, indicating that a part of the hydrolysis reaction of α-APM apparently occurred during neutralization.

Comparative Example 3 20% in place of 45% sodium hydroxide in Comparative Example 2
The same procedure as in Comparative Example 2 was carried out except that% sodium carbonate was used.

The temporary increase in the apparent volume due to the generation of carbon dioxide gas after the precipitation of α-APM started to occur was large, and the sodium carbonate aqueous solution had to be dropped intermittently. After neutralization, the mixture was cooled to 5 ° C., filtered, and washed with water to obtain a wet cake containing 24.21 g (yield 82.3%) α-APM.

On the other hand, as a result of analysis, α-APM in the filter wash liquid was 4.65 g (15.8%
/ Α-APM hydrochloride).

Example 2 Example 1 was repeated except that triethylamine was used instead of aqueous ammonia as the base. The same results as in Example 1 were obtained, and the neutralization reaction could be carried out smoothly without the problem of stirring trouble due to mud formation of crystals during the neutralization.

Example 3 36.7 g (0.1 mol) of α-APM hydrochloride dihydrate was added to 240 ml of 50% (volume%) methanol water and dissolved. 28% Ammonia water was added dropwise with stirring at 30 ° C, and when the pH reached 3.1, the addition was stopped and the mixture was aged by stirring at the same temperature for 1 hour. α-APM crystals gradually precipitate, and during this aging time,
H dropped to 3.0. Then restart the dropping of ammonia water.
Neutralized to pH 5.2. During this neutralization process, there was no trouble in stirring due to the mudification of the precipitate, and the neutralization reaction proceeded smoothly. After neutralization, the mixture was cooled to 5 ° C., and the precipitated crystals were filtered and washed with cooled 50% methanol water. As a result of analysis of the obtained wet cake, 26.93 g (yield 91.5%) of α-AP was obtained.
M recovered. Α-APM in the filtrate was 2.39 g (8.1% / α-
APM hydrochloride).

Example 4 30% of 50% methanol water in Example 3 (volume%)
A neutralization reaction was performed in the same manner as in Example 3 except that ethanol water was used and ammonia water was changed to monoethanolamine. The stirring state during neutralization was the same as in Example 3.

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Claims (2)

[Claims] 1. A method for producing α-L-aspartyl-L-phenylalanine methyl ester by neutralizing an acid addition salt of α-L-aspartyl-L-phenylalanine methyl ester with a base to produce α-L-aspartyl-L-phenylalanine methyl ester in an aqueous medium. , Ammonia or organic amine as the base, pH during neutralization
A method for producing α-L-aspartyl-L-phenylalanine methyl ester, which comprises aging in the range of 2.5 to 3.5. 2. The method according to claim 1, wherein the acid addition salt of α-L-aspartyl-L-phenylalanine methyl ester is a hydrochloride.