JPS6216498A - Production of alpha-l-aspartyl-l-phenylalanite methyl ester hydrochloride - Google Patents

Abstract

PURPOSE:To obtain the titled compound useful as a low-calorific sweetener, etc., economically on an industrial scale, by contacting alpha-L-aspartyl-R- phenylalanine methyl ester with an aqueous solvent containing specific amount of hydrogen chloride and inorganic chloride, and separating the crystallized product. CONSTITUTION:The objective compound is produced by contacting alpha-L-aspartyl- L-phenylalanine methyl ester with an aqueous medium containing <=2mol of hydrogen chloride (based on 1 liter of aqueous medium) (provided that the amount of the hydrogen chloride is >=1mol per 1mol of alpha-L-aspartyl-L- phenylalanine methyl ester) and >=50g of an inorganic chloride (e.g. sodium chloride) (based on 1l of the aqueous solvent), and separating the crystallized hydrochloride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing u, α-L-aspartyl-monophenylalanine methyl ester hydrochloride.

α-L-Aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as α-APM) is a substance that exhibits good sweetness and is attracting attention for its usefulness as a low-calorie sweetener.

As a method for producing this α-APMt-, after reacting N-L-protected aspartic acid anhydride and L-phenylalanine methyl ester in an organic solvent, the protecting group is removed by a conventional method (USP 3,786). ,039),L
- A method of directly reacting a strong acid addition salt of aspartic acid anhydride with L-phenylalanine methyl ester (Japanese Patent Publication No. 4)
9-14, 21l) and L-phenylalanine t-N-formyl-L-aspartic anhydride in glacial acetic acid, and the formyl group was removed from the resulting product to obtain α
-L-aspartyl-L-phenylalanine (α-AP
) and esterifying it with methanol (USP 3g33,781) is known.

In these methods, in addition to the α-isomer such as α-APM or α-AP, a large amount of its isomer β-isomer is produced as a by-product.
In addition, the reaction solution contained L-ame/4 used as a raw material.
Derivatives of lagic acid and L-phenylalanine are also present. Therefore, when producing α-APM industrially, it is particularly important to efficiently separate and purify such impure α-APM. As this method, β-L-aspartyl-L-phenylalanine methyl ester (β-L-aspartyl-L-phenylalanine methyl ester
α-APM containing impurities such as -APM) is brought into contact with hydrochloric acid such as hydrochloric acid in water alone or in an aqueous solvent consisting of methanol and water to crystallize the hydrohalide salt of α-APM. A method (as
p3.798, 207) is known.

On the other hand, as an improved method of USP 3,933,781, when α-AP is esterified with methanol, α
- AP is methyl esterified by contacting with a reaction medium consisting of methanol, hydrohalic acid, and water, converting α-AP to α-APM, and immediately precipitating the 710 hydroginate as crystals. Method of esterifying α-AP to α-APM (USP A in a solvent consisting of small jujube water, or in a solvent consisting of α-APt-methanol and water)・Contact with hydrorhodanic acid let me,
The method of precipitating the hydrohalide of α-APM as crystals is a method for precipitating the hydrohalide of α-APM when industrially producing
This method is particularly useful as a method for increasing efficiency in the purification of 1 m of APMO and the conversion of α-AP to α-APM.

However, in this method, α-APM's 710 hydrogen chloride 5
As is clear from the solubility relationship shown in Figure 1, in order to efficiently precipitate the 1-salt, a high concentration of no-rhodanhydric acid, for example, about 2 moles or more per liter of aqueous medium, is required. Since it has to be carried out in a region where an excess of about 3 moles or more of hydrohalic acid exists, the yield decreases due to hydrolysis of the ester bond or peptide bond of α-APM, and in order to neutralize the excess hydrohalic acid. In addition, especially in industrial scale production, hydrohalic acids are highly corrosive to metal materials, so equipment costs are reduced due to higher quality equipment materials. It had disadvantages such as close-up of the image.

The inventors of the present invention selected hydrochloric acid as the hydrohalodanic acid from the viewpoint of industrialization and conducted intensive studies on measures to overcome this drawback.
When precipitating the hydrochloride of M, it is possible to efficiently precipitate the hydrochloride of α-APM even if the excess amount of hydrogen chloride, which has the above-mentioned drawbacks, is greatly reduced by allowing inorganic chloride to coexist to a certain extent. We have discovered that this is possible and have completed the present invention.

In the present invention, when precipitating hydrochloride crystals of α-APM from an aqueous solvent, an inorganic chloride is coexisted in the aqueous solvent.
- A method for producing α-APM hydrochloride, characterized in that the excess amount of APM is brought into contact with hydrogen chloride in a greatly reduced amount to efficiently precipitate the crystals.

According to the present invention, α
- APM is contacted with a low concentration of hydrogen chloride to precipitate the hydrochloride of α-APM, or α-AP is contacted with methanol and a low concentration of hydrogen chloride in an aqueous solvent in the presence of an inorganic chloride, and then α− produced by the equilibrium reaction shown
APM i α-AP+MeOH: By immediately precipitating α-APM+H20 as a hydrochloride, a method for producing α-APM hydrochloride is provided which overcomes the above-mentioned drawbacks from the viewpoint of production on an industrial scale.

The concentration of hydrogen chloride in the present invention is due to the corrosivity of equipment materials, especially metal materials, which is a problem in industrial production, and α-AP.
The concentration range to be used should be determined experimentally, taking into account the adverse effects of M on the hydrolyzability of ester bonds and peptide bonds.

Regarding the effects of hydrogen chloride concentration on these, the present inventors have determined that α-APM has poor thermal stability, especially in the extremely acidic region such as the method of the present invention, and therefore is not suitable for practical use. A detailed study was carried out at a temperature of 30° C. or lower in consideration of the properties. As a result, as shown in Tables 1 and 2, if the hydrogen chloride concentration is 2 mol or less per liter of aqueous solvent, the actual effect will be extremely small, and more preferably if it is 1 mol or less, there will be almost no effect. It became clear that there was no. Therefore, the present invention is carried out at a temperature of 30° C. or lower and in a region where the hydrogen chloride concentration is 92 mol or less, preferably 1 mol or less per liter of aqueous solvent.

Table 1 Table 2 (Storage time = 7 hours) *Initial (E-APM concentration 101/1 The inorganic chloride used in the present invention has a solubility in an aqueous solvent of 1 liter of solvent) of at least 50 g, α- Those that do not inhibit the precipitation of APH hydrochloride, for example, NaCt# KCL e NHaC2e CaCL2
*ZnC22 etc. are used. Also, efficiently α
- In order to precipitate the hydrochloride of APM, it is desirable that the concentration of inorganic chloride be as high as possible, but a certain level of concentration is required depending on the concentration of coexisting hydrogen chloride.

The required concentration of this inorganic chloride varies somewhat depending on the type of inorganic chloride, but as shown in Figure 2,
In a concentration range where hydrogen chloride is less than 2 moles per liter of aqueous solvent and more than about 1 mole per liter of aqueous solvent, ! 750g
It is appropriate that hydrogen chloride is
l! In the low concentration range of 91 mol or less, it is appropriate to use about 100 g or more per 1 liter of the aqueous solvent. In either case, it goes without saying that the inorganic chloride is used at a concentration that does not precipitate it.

An aqueous solvent containing an inorganic chloride can be prepared by adding a crystalline inorganic chloride or an aqueous solution of an inorganic chloride to an aqueous solvent, or by adding hydrogen chloride in an aqueous solvent to NaOH or KOH.

Neutralize with a metal hydroxide solution such as N Ca (OH) 2 Zn (OH) 2 or jeH water to remove inorganic chlorides on the spot (
1) or, on an industrial scale, a method that utilizes inorganic chloride produced as a by-product during the process.

The solvent used in the present invention may be water alone or a mixed solvent of methanol and water depending on the purpose;
There is no problem in mixing other solvents that do not override the addition reaction between α-APM and hydrogen chloride, such as methanol, ethylene glycol, acetone, etc., in an amount that does not significantly reduce the solubility of the inorganic chloride.

Furthermore, the present inventors brought α-M into contact with methanol in such a system in which inorganic chlorides coexist, and the α-M produced in situ
As a result of investigating the amount of methanol that is useful when APM is immediately precipitated as an addition group with hydrogen chloride, it was found that α-R can be efficiently converted to α-APM hydrochloride even if the amount of methanol present in the aqueous solvent is quite low. I discovered that.

In other words, if more methanol is used than necessary, the α
-APM is further methyl esterified, and the production of a methyl ester of the β-carboxyl group of the as/IP lytic acid residue of α-APM (α-A(M)PM) increases significantly. It was found that the conversion rate to α-APM hydrochloride was significantly reduced. On the other hand, reducing the amount of methanol more than necessary will reduce the amount of methanol from α-APM to α-A (M
) is advantageous in suppressing side reactions to PM, but α-A
This is not preferable because it lowers the conversion rate of P to α-APM.

Based on this, we investigated the amount of methanol useful when obtaining α-APM hydrochloride from α-AP using this method.
As shown in Example 6, useful amounts of methanol range from about 0.5 to about 0.5 methanol per liter of aqueous reaction medium. I made it clear that there was one.

According to this finding, the amount of methanol in the reaction medium is consumed by the methyl esterification of α-AP, and if the concentration range of the amount of methanol that is useful is to be exceeded, it is necessary to newly add methanol during the reaction. is effective, and adding the required amount of methanol from the beginning increases the production of α-A(M)PM, which is not preferable.

The total amount of methanol used at this time varies from α-li to α-
Considering the esterification reaction to APM, α-Apl-1
It goes without saying that at least 1 mole of methanol per methanol is required.

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

Example 1 25 g of α-APM was added to 2N hydrochloric acid at 1000° C. at 40°C.
Divide the solution into three equal parts, each using a 500 mm tube with a stirrer.
d flask. One was dissolved as it was (4) and the other two were dissolved with 3.3 g ω) and 16.7 g of common salt, respectively, and then stirred and crystallized in a constant temperature water bath at 5° C. overnight.

The precipitated crystals were separated, washed with a small amount of cold 2N hydrochloric acid, and dried under vacuum at 50°C. The infrared absorption spectra of these crystals correspond to α-APM hydrochloride, each with 98
% or more (liquid chromatography method). The results are shown in Table 3.

Table 3 Note: A and B are control examples.

Example 2 495 d of an aqueous solution containing 15 g of α-APM and 30 g of calcium chloride was placed in a 1 liter flask with a stirrer and the temperature was raised to 5.
After gradually adding 35% hydrochloric acid 105% while keeping the temperature at ℃,
- Crystallization was performed with stirring overnight.

The precipitated crystals were treated in the same manner as in Example 1 to give 1 l. 2
Crystals of g were obtained. Yield: 90.2. Purity 9 eup 7 me.

Example 3 15g of α-APM was dissolved in a mixed solvent of 500d of 1.1N hydrochloric acid and 50al of methanol, and the solution was divided into two equal parts.
One (G) was left as is, and the other (B) was dissolved with 60I of ammonium chloride and stored in a refrigerator overnight.

The precipitated crystals were treated in the same manner as in Example 1 to obtain 6.1 g (A) and 8.7 J (B) of crystals, respectively.

The crystal purity (and yield) is 98.2% (s4.1
1 (4) and 97.6% (90.8 chi) (B). Purity is determined by liquid chromatography.

Note that A is a control example.

Example 4 28 g of α-APM and 12 g of β-APM, 5 g' of water
00 ml and add 35% hydrochloric acid at room temperature.
was adjusted to 2.2 and dissolved. The solution was divided into two equal parts, and to the other half, 150 d of 35% hydrochloric acid was added and crystallization was carried out with stirring at 15C for 15 hours. The other (B) is 150 rLt of 35% hydrochloric acid.
After adding powdered anhydrous carbonic acid), 61 g of IJum was gradually added to neutralize a part of the excess hydrochloric acid, and then heated at 15°C for 15 minutes.
Crystallization was performed with stirring for hours.

The precipitated crystals were treated in the same manner as in Example 1.

The results are shown in Table 4. In addition, A is a control example.

Table 4 Incidentally, the hydrogen chloride concentrations in the mother liquor were as follows: 0 A: 4 mol/l B: 1.4 mol/73 (Na(, tl 501/l
) Example 5 α-AP 143 # with a purity of 98.2% was dissolved in methanol 3
The solution was dissolved in a mixed solvent of 8d and 900 Inl of 2N hydrochloric acid, and the solution was divided into two equal parts, one (G) was left as is and 51 g of ammonium chloride crystals were added and dissolved in the other (B).

Each solution was kept under stirring at 25°C for 3 days and then at 10°C for 1 day and night to precipitate crystals of α-APM hydrochloride.

Each precipitated crystal was treated in the same manner as in Example 1, and 32
．． Obtained crystals of 0g and 62gfI(B). The infrared absorption spectra of these crystals match α-APM hydrochloride,
The composition was analyzed by liquid chromatography, and the results were as shown in Table 5. A is a control example.

Table 5 *Purity as α-APM-HC1・2H20**
Methyl ester of β-carboxyl group of as/gragic acid residue of α-AP Incidentally, initial methanol concentration 1 to, 9z mol/1 l or a
3) NH4C2 concentration in Offi liquid 101/A? Deah fc.

Example 6 215.6 g of α-AP with a purity of 97.5% and 200 g of salt
Dissolve g in 1509ml of IN hydrochloric acid, divide the solution into 5 equal parts, and place each in a 500rR1 four-way flask (A to E) with a stirrer.
).

Next, add methanol to each solution for 5d (4), 7
wtl (B), 14d(C'), 39ml) and 50t/(llj) were added, and α-APM hydrochloride was crystallized according to the same procedure as in Example 5, and 1l of each crystal was added.
．． 5,9 (A), 28.6 g (B), 33.3 N (
C), 33.0g0)) and 21.6Jil) were obtained.

The crystal composition and yield of these are shown in Table 6 (liquid chroma dog 2 fee method). In Table 6, A and E are control examples; when the methanol concentration is low, a large amount of α-AP is produced, and when the methanol concentration is high, α-AP is produced.
It will be understood that -A(M)PM is produced in large amounts.

[Brief explanation of drawings]

Figure 1 shows the preliminary results of measuring the relationship between hydrogen chloride concentration and α-APM solubility at different temperatures, and Figure 2 shows the relationship between chloride concentration and α-APM solubility.
-Represents the results of measuring the relationship with the solubility of APM by changing the hydrogen chloride concentration.

Claims (4)

[Claims] (1) α-L-aspartyl-L-phenylalanine methyl ester is mixed with not more than about 2 moles of hydrogen chloride per 1 liter of aqueous solvent (however, at least 1 mole of hydrogen chloride per 1 mole of α-L-aspartyl-L-phenylalanine methyl ester). ) and an aqueous solvent containing at least about 50 g of inorganic chloride per liter of aqueous solvent;
A method for producing α-L-aspartyl-L-phenylalanine methyl ester hydrochloride, which comprises separating the crystallized α-L-aspartyl-L-phenylalanine methyl ester hydrochloride. (2) the aqueous solvent contains not more than about 1 mole of hydrogen chloride per liter of aqueous solvent (provided that at least 1 mole of hydrogen chloride is present per mole of α-L-aspartyl-L-phenylalanine methyl ester) and per liter of aqueous solvent; The method of claim 1 containing at least about 100 g of inorganic chloride. (3) α-L-aspartyl-L-phenylalanine with hydrogen chloride of about 2 mol or less per liter of aqueous solvent (however,
at least 1 mole of hydrogen chloride per mole of α-L-aspartyl-L-phenylalanine) and at least about 50 g of inorganic chloride per liter of aqueous solvent, with the additional addition of methanol,
Methanol is added in an amount of at least 1 mol or more per 1 mol of α-L-aspartyl-L-phenylalanine), and then the crystallized α-L-aspartyl-L-phenylalanine methyl ester hydrochloride is separated. A method for producing α-L-aspartyl-L-phenylalanine methyl ester hydrochloride. (4) the aqueous solvent contains not more than about 1 mole of hydrogen chloride per liter of aqueous solvent (provided that at least 1 mole of hydrogen chloride is present per mole of α-L-aspartyl-L-phenylalanine) and at least about 100 g per liter of aqueous solvent; About 0.5 mol or more and about 2 mol or less (however, α
4. The method according to claim 3, wherein at least 1 mole of methanol is added per mole of L-aspartyl-L-phenylalanine.