JPH0232096A - Preparation of n-benzyloxycarbonyl-alpha-l-aspartyl-l-phenylalanine methyl ester - Google Patents

Abstract

PURPOSE:To provide the subject substance useful as a sweetener intermediate by reacting N-benzyloxycarbonyl-L-aspartic acid anhydride with L-phenylalanine methyl ester mineral acid salt in the presence of an alkali metal, etc., in an organic carboxylic acid and subsequently adding water to the reaction solution. CONSTITUTION:N-benzyloxycarbonyl-L-aspartic acid anhydride is reacted with an L-phenylalanine methyl ester mineral acid salt in the presence of an alkali(ne earth) metal or the hydroxide, oxide, carbonate, bicarbonate or organic acid salt thereof or ammonium carbonate or an organic carboxylic acid ammonium salt in an organic carboxylic acid (preferably acetic acid or propionic acid), followed by adding water to the reaction solution to deposit the objective compound.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to the production of N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as N-protected-α-APM). Regarding the manufacturing method.

N-protected-α-APM is an α-APM used as a sweetener.
It is an important compound as an intermediate of L-aspartyl-L-phenylalanine methylnester (hereinafter abbreviated as α-APM). α-APM is widely known as a dipeptide-based sweetener, and has high quality sweetness characteristics and a sweetness level nearly 200 times that of sucrose, and its demand as a dietary sweetener is rapidly increasing.

[Conventional technology and problems to be solved] α-APM
is a dipeptide compound consisting of L-aspartic acid and L-phenylalanine methyl ester, and many methods for its production are already known, mainly chemical production methods.

The method generally uses N-protected-L-aspartic acid anhydride as a starting material, for example, N-protected-L-aspartic acid anhydride.
A manufacturing method in which aspartic acid anhydride and L-phenylalanine methyl ester are condensed in an organic solvent and then the protective group is removed by a conventional method (US Pat. No. 3,786).
No. 039) is known.

As a method that does not use L-phenylalanine methyl ester, N-formyl-thi-aspartic acid anhydride and L-phenylalanine methyl ester are used.
- After condensing with phenylalanine in acetic acid, deformylation is performed in the coexistence of hydrohalic acid, and esterification is performed by treatment with water, alcohol, and hydrohalic acid, and αAPM is converted into hydrohalic acid. A method for isolating it as (Japanese Patent Publication No. 55-26133) is known.

However, N-acyl groups, especially N-formyl groups, are retained.
! When used as a group, it is common to remove the protective group by contacting it with a strong acid in an aqueous solvent, but under this condition, some of the methyl ester of α-APM tends to undergo hydrolysis; Even in the presence of methanol, α-L-aspartyl-monophenylalanine-β-methyl ester and α-■.

-Aspartyl-L-phenylalanine dimethyl ester is produced, making it difficult to selectively obtain only the desired α-APM.

On the other hand, when a benzyloxycarbonyl group is used as an N-protecting group, the protecting group can be easily removed by catalytic reduction, so there is no problem of hydrolysis of methyl ester, and it can be removed with high selectivity. known to be protective. Japanese Patent Publication No. 57-25538 describes the hydrogenation of N-benzyloxycarbonyl-α-APM obtained from N-benzyloxycarbonyl-shi-aspartic acid anhydride and L-phenylalanine methyl ester in the presence of a mineral acid. A method for obtaining α-APM by neutralizing the reaction solution is shown.

Generally, when N-protected-L-aspartic acid anhydride is used as a starting material, the by-product of the β-isomer in addition to the α-isomer cannot be avoided. The derived β-L-aspartyl-12-enylalanine methyl ester does not have a sweetening effect, but rather exhibits a bitter taste, so its presence reduces the commercial value of α-APM.

Therefore, N-protected-L-aspartic anhydride and I, -
It is necessary to efficiently isolate only the α-isomer from the reaction solution condensed with phenylalanine methyl ester.

JP-A-46-1370 uses I2-phenylalanine methyl ester as a reaction raw material, and N-ho 1-15-
A method is presented for reacting with aspartic anhydride in an inert reaction medium.

According to this method, an ethyl acetate solution of N-benzyloxycarbonyl-di-aspartic acid anhydride and an ethyl acetate solution of L-phenylalanine methyl ester hydrochloride are mixed, an IN sodium carbonate aqueous solution is added to the ethyl acetate solution, and L - After reacting the hydrochloride of phenylalanine methyl ester while neutralizing it, the target product is recrystallized from an aqueous ethyl acetate solution and then isolated by adding acetone.

Also known is a method in which N-benzyloxycarbonyl-d-aspartic acid anhydride and L-phenylalanine methyl ester hydrochloride are reacted in the presence of a base in an inert organic solvent (Japanese Patent Application Laid-open No. 7068/1983). , specifically N
-benzyloxycarbonyl-aspartic acid anhydride and L-phenylalanine methyl ester hydrochloride are dissolved in ethyl acetate, and then reacted while adding sulfur/lium carbonate or potassium carbonate aqueous solution to the solution,
2. Remove unreacted L-phenylalanine methyl ester from the organic solution, then extract the target product with a sodium hydroxide solution, and further extract this solution with ethyl acetate. By drying, N-benzyloxycarbonyl-α-
L-aspartyl-L-phenylalanine methyl ester is obtained. Tertiary amines are also used as bases in this reaction. However, in any of the reactions, the hydrochloride of L-phenylalanine methyl ester is used and the reaction is carried out in an organic solvent while being neutralized with an aqueous alkali solution, and after the reaction, other solvents are added or water is added. L-phenylalanine methyl ester and N-protected-α can be extracted by extraction with sodium oxide solution.
- The disadvantage that APM causes hydrolysis of the ester by aqueous alkaline solutions is unavoidable. Furthermore, when isolating the target product, operations such as extraction with ethyl acetate and drying are complicated, and it cannot be said to be an effective isolation method.

In addition, N-formyl-shi-aspartic acid anhydride and L-
A method in which the reaction with phenylalanine methyl ester is carried out in a solvent in the presence of acetic acid or formic acid (Japanese Unexamined Patent Publication No. 62-14
No. 9669) is known.

That is, in this method, the desired α-isomer ratio is improved by carrying out the reaction in the presence of a mixture of acetic acid or formic acid in a reaction solvent, but the yield is not described.

In this way, using an organic carboxylic acid, N-protected-L-aspartic anhydride and L-phenylalanine or L-
When reacted with phenylalanine methyl ester,
Although it has the effect of improving the α-isomer ratio, the target product is dissolved, so operations such as concentration are required to isolate it in high yield.

[Means to solve the problem]

The present inventors have discovered that, in the reaction of N-benzyloxycarbonyl-dis-aspartic acid anhydride and L-phenylalanine methyl ester, there is no drawback of the conventional method as described above, and N-benzyloxycarbonyl is selectively removed from the reaction mixture. As a result of extensive research into a method that isolates only carbonyl-α-L-aspartyl-L-phenylalanine methyl ester and is also satisfactory as an industrial production method, we found that N-benzyloxycarbonyl-dis-aspartic acid anhydride and L-
In reaction with phenylalanine methyl ester 1.
I,-phenylalanine methyl ester in the form of a mineral salt, that is, without isolating the mineral salt as L-phenylalanine methyl ester by neutralization, extraction, dehydration, etc. as in conventional methods. , and in organic carboxylic acids, alkali metals, alkaline earth metals, hydroxides, oxides, carbonates, bicarbonates, or organic carboxylates of these metals, or ammonium carbonate, ammonium organic carboxylates are added. After a condensation reaction with N-benzyloxycarbonyl-5-aspartic anhydride, water is added to selectively crystallize the N-
A method for isolating protected-α-APM was discovered and the present invention was completed.

That is, the present invention provides N-benzyloxycarbonyl-
L-aspartic anhydride and a mineral acid salt of L-phenylalanine methyl ester in an organic carboxylic acid, an alkali metal, an alkaline earth metal, or a hydroxide of these metals,
oxides, carbonates, bicarbonates or organic carboxylates,
Alternatively, by adding and reacting ammonium carbonate or ammonium organic carboxylate, and then adding water,
This is a method for producing N-protected-α-APM, which is characterized by selectively crystallizing N-protected-α-APM.

The method of the present invention is characterized in that the mineral acid salt of L-phenylalanine methyl ester is added to an alkali metal, an alkaline earth metal, or a hydroxide, oxide, carbonate, bicarbonate, or organic carboxylic acid of these metals in an organic carboxylic acid. When a salt, ammonium carbonate, or ammonium organic carboxylate is added, it substantially reacts as L-phenylalanine methyl ester, but L-phenylalanine methyl ester undergoes a self-ring-closing reaction even in its free state in an organic carboxylic acid. It has the characteristic of not occurring at all.

N-benzyloxycarbonyl- used in the method of the present invention
Shi-aspartic acid anhydride is obtained by a known method of reacting L-aspartic acid and carbobenzoxy chloride to obtain N-benzyloxycarbonyl-shi-aspartic acid, and then applying a dehydrating agent such as acetic anhydride. Obtainable.

Further, the L-phenylalanine methyl ester mineral salt used in the present invention can be produced by esterifying L-phenylalanine in methanol in the presence of a mineral acid by a conventional method.

The organic carboxylic acids used in the method of the present invention include carboxylic acids such as formic acid, acetic acid, and propionic acid, but acetic acid and propionic acid are preferably used.

The amount of these organic carboxylic acids to be used is not particularly limited, but is usually 2 to 5 times the amount of N-hensyloxycarbonyl-aspartic anhydride used as the raw material.
0 weight! It is preferable to use the range of 1' times.

Examples of the alkali metals and alkaline earth metals used in the method of the present invention include sodium and magnesium.

Examples of the hydroxides of alkali metals and alkaline earth metals include hydroxides such as thorium hydroxide, potassium hydroxide, lithium hydroxide, and magnesium hydroxide. Examples of oxides of alkali metals and alkaline earth metals include calcium oxide and magnesium oxide. Examples of carbonates of alkali metals and alkaline earth metals include lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, and magnesium carbonate.

As bicarbonates of alkali metals and alkaline earth metals,
Lithium bicarbonate, sodium bicarbonate, potassium bicarbonate,
Examples include bicarbonates such as calcium bicarbonate. Examples of organic carboxylates of alkali metals and alkaline earth metals include lithium acetate, sulfur and lithium acetate, potassium acetate, calcium acetate, and magnesium acetate, preferably sulfur acetate.
-lium, potassium acetate is used. Ammonium carbonate or ammonium organic carboxylates can also be used.

The amount of alkali metals, alkaline earth metals, hydroxides, oxides, carbonates, bicarbonates, or organic carboxylates of these metals, or ammonium carbonate or ammonium organic carboxylates is as follows: -Phenylalanine methyl An equimolar amount relative to the mineral acid salt of the ester is sufficient, but the molar ratio is usually in the range of 1.0 to 3.0. , N
- Protection - Suspending or dissolving L-aspartic anhydride, alkali metals, alkaline earth metals, or hydroxides, oxides, carbonates, bicarbonates or organic carboxylates of these metals, or ammonium carbonate. , after adding ammonium organic carboxylate, a mineral acid salt of L-phenylalanine methyl ester may be added, or after adding a mineral acid salt of L-phenylalanine methyl ester, an alkali metal, alkaline earth metal , or hydroxides, oxides, carbonates, bicarbonates or organic carboxylates of these metals, or ammonium carbonate or ammonium organic carboxylates may be added.

In the present invention, there is no particular restriction on the reaction temperature, which is usually in the range of -15 to 80°C, preferably in the range of 5 to 25°C.

A reaction time of 0.5 to 10 hours is usually sufficient.

In the present invention, water is added after the reaction, and the amount of water added is preferably selected so that the concentration of the organic carboxylic acid is 5 to 90% by weight. Particularly preferred concentration is 45-70
Weight%. If the concentration is less than 45% by weight, the β-isomer will be mixed in. On the other hand, when the concentration exceeds 70% by weight, the isolation yield of N-protected-α-APM decreases.

By-produced N-benzyloxycarbonyl-β-aspartyl-L-phenylalanine methyl ester (hereinafter referred to as N
-Ho! -β-APM) is relatively soluble in an aqueous organic carboxylic acid solution, so the target N-α-APM can be easily isolated by filtering and washing the precipitated crystals.

〔Effect of the invention〕

According to the method of the present invention, in the production of N-protected-α-APM, which is an important compound as an intermediate for α-APM,
-Benzyloxycarbonyl-L-aspartic acid can be efficiently obtained in a short time under mild conditions, and the method of the present invention can be a highly valuable industrial production method.

〔Example〕

Hereinafter, the method of the present invention will be explained in detail with reference to Examples.

Example 1 N-benzyloxycarbonyl- to 100.4 g of acetic acid
After adding and suspending 25.1 g (0.1 mol) of di-aspartic acid, 9.2 g (0.11 mol) of sodium acetate was added at 10-15°C with stirring, and then L-phenyl was added at the same temperature. 21.6g of 1-ranine methyl esterate
(0.1 mol) was added. Stir at the same temperature for 4 hours (↑ After the reaction, 87.1 g of water was added at the same temperature to make the organic carboxylic acid concentration 53.5% by weight. Then, after cooling to 0 to 5 °C, precipitation Crystals were obtained by filtering, washing and drying the crystals.

Yield: 31.0 g (yield 72.4%/vs., -phenylalanine methyl ester salt M salt) Analysis of the obtained crystals by high performance liquid chromatography revealed that only α was present.

Melting point 123.8-124.9°C Elemental analysis value (%) CtzHz4Nz (h as HN Demonstration H direct 61.56 5.70 6.
53 Calculation Direct 61.68 5.65
6.54 Example 2 The same procedure as in Example 1 was conducted except that the organic carboxylic acid and organic carboxylate shown in Table 1 were used.

The results are shown in Table-1.

Table 1 Example 3 N-benzyloxycarbonyl-L in acetic acid 100.48
- After adding and suspending 25.1 g (0.1 mol) of aspartic acid anhydride, 9.2 g (0.11 mol) sodium acetate was added at 10-15°C with stirring, and then at the same temperature. L-phenylalanine methyl ester hydrochloride 21.6g
(0.1 mol) was added. After stirring and reacting at the same temperature for 4 hours, 70.9 g of water was added at the same temperature to adjust the organic carboxylic acid concentration to 58.6% by weight. Next, after cooling to 0 to 5°C, the precipitated crystals were filtered, washed, and dried to obtain crystals.

Yield: 27.0 g (yield: 63.1%/based on L-phenylalanine methyl ester hydrochloride) Analysis of the obtained crystals by high performance liquid chromatography revealed that only α was present.

Example 4 N-benzyloxycarbonyl I to 100.4 g of 9-acid,
- After adding and suspending 25.1 g (0.1 mol) of aspartic acid anhydride, sodium acetate L. 6g (0.21 mol) was added, and then at the same temperature L-phenylalanine methyl ester sulfur M122.7
g (0.1 mol) was added. After stirring and reacting at the same temperature for 4 hours, 87.1 g of water was added at the same temperature to make the organic carboxylic acid concentration 53.3% by weight.
After cooling to , the precipitated crystals were filtered, washed, and dried to obtain crystals.

Yield 29.5g (yield 68.9%/vs. -phenylalanine methyl ester hydrochloride) Example 5 N-benzyloxycarbonyl=■ in 100.4g of vinegar H
, -aspartic anhydride 25.1 g (0.1 mol)
After adding and suspending, 421.6 g of L-phenylalanine methyl ester hydrochloric acid (0,
Then, at the same temperature, sodium acetate, 9
．． 2 g (0.1 mol) were added. After reacting with stirring at the same temperature for 4 hours, 87.1 g of water was added at the same temperature to adjust the organic carboxylic acid concentration to 53.5% by weight.
After cooling to °C, the precipitated crystals were filtered, washed, and dried to obtain crystals.

Revenue i! 31.2 g (yield 72.9%/vs., -phenylalanine methyl ester salt M salt) Analysis of the obtained crystals by high performance liquid chromatography revealed that only α was present.

Example 6 25.1 g (0.1 mol) of N-benzyloxycarbonyl monoaspartic acid anhydride was added to 100.4 g of vinegar u and suspended, and L-phenylalanine methyl ester was added at 5 to 10 °C with stirring. [22.7 g (0.1 mol) of acid [was added, and then at the same temperature sodium acetate L. 6g
(0.21 mol) was added. After reacting with stirring at the same temperature for 4 hours, 87.1 g of water was added at the same temperature to reduce the concentration of the remaining carboxylic acid to 53.5% by weight.Then, after cooling to 0 to 5°C, the precipitate was precipitated. Crystals were obtained by filtering them six times, washing and drying them.

Yield: 31.2 g (yield: 73.1%/based on L-phenylalanine methyl ester 6m acid salt) Analysis of the obtained crystals by high performance liquid chromatography revealed that only α was present.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. N-benzyloxycarbonyl-L-aspartic acid anhydride and a mineral acid salt of L-phenylalanine methyl ester in an organic carboxylic acid, an alkali metal, an alkaline earth metal, or a hydroxide or oxide of these metals, carbonate,
N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester is produced by adding bicarbonate or organic carboxylate, or ammonium carbonate, or ammonium organic carboxylate, and then adding water. A method for producing N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester, which comprises selectively crystallizing.