JPS601164A - Optically active tryptophan salt crystal and its preparation - Google Patents

Abstract

NEW MATERIAL:The optically active tryptophan monosodium pentahydrate crystal. Melting point: fluidizes at 45 deg.C, begins to melt at 55 deg.C, and melts completely at 70 deg.C. USE:Useful for the purification of colored tryptophan crystal. The crystal obtained by adding Na ion to a tryptophan-containing solution under alkaline condition has low absorption affinity to impurities such as coloring materials, and the impurities can be dissolved easily since the solution is alkaline. Tryptophan is an essential amino acid, and is useful as a nitrient source for man or cattle. PREPARATION:The titled compound is obtained by crystallizing from an aqueous solution containing optically active tryptophan at >=10.9pH in the presence of Na ion. The molar ratio of Na to tryptophan in the solution is >=1. Usually, NaOH is used as the Na ion source and the pH-controlling agent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for obtaining optically active tryptophan l-sodium pentahydrate crystals from a solution containing pentahydrate crystals and optically active tryptophan under alkaline conditions and in the presence of N and ions.

Tryptophan is one of the essential amino acids and is useful as a nutritional source for the human body or livestock. The tryptophan used in these products is required to be of high quality.

Methods for producing tryptophan include chemical synthesis method, enzymatic method,
Fermentation methods are being used. As a method for separating and purifying tryptophan in these manufacturing processes, a method of adding a metal salt to form a racemic double salt (Japanese Patent Publication No. 50-1
1 9 1 4), a method using an anion and cation exchange resin (Japanese Patent Laid-Open No. 53-111061), or a method combining an adsorption resin and an ultrafiltration membrane (Japanese Patent Laid-Open No. 58-89)
5) etc.

However, since optically active tryptophan has a strong tendency to adsorb to and desorb from resin together with colored substances, complicated steps and operations are required for its separation and purification. Additionally, colored substances are easily adsorbed and mixed into the crystals during crystallization. For this purpose, there is a method of crystallization using an organic solvent such as alcohol, but this requires complicated steps such as recovering the solvent.

Because tryptophan has such a high adsorption affinity, there is no known means for easily removing impurities such as colored substances.

The present inventors have made extensive studies to effectively remove impurities by crystallization, and have discovered that impurities can be removed extremely easily by crystallizing optically active tryptophan as a sodium salt.

That is, when alkaline Na ions are present in a solution containing optically active tryptophan, optically active tributophane monosodium pentahydrate crystals are precipitated. These crystals have extremely low adsorption affinity for impurities such as colored substances, and since the liquid is alkaline, impurities are easily dissolved and can be extracted into the mother liquor.

The physical properties of optically active tryptophan monosodium pentahydrate crystals are as follows. Incidentally, the crystals used for measuring the physical properties were obtained by the method shown in Example 1.

(1 elemental analysis: Table 1 0 58.41% 57.70 H4,904,78 N 12.38 12.25 0 14.15 14.53 Na 10.16 10.74 H2028,4828, 82 (2) Melting point = Fluidization at 45°C, melting start at 55°C, 70
Completely thawed at °C.

(3) Differential thermal analysis: temperature increase 2/miH, 45℃~300
Measured in °C.

46℃〜78℃ 3H20 withdrawal Endothermic reaction □78℃〜
114℃ 2H20 separation (anhydration) Endothermic reaction 226℃
~ Start of decomposition (carbonization) Exothermic reaction (4) Specific optical rotation: [α
) −+3.5 (C=2.H2O) (5) X-ray diffraction: C
Four turns of powder X-ray diffraction using u-Ka-X rays showed a strong peak at the following position (2θ). 4.1,
10.8, 11.9, 15.9, 16.2, 27.1 and 32.6° (6) Solubility in solvents: Easily soluble in water and ethanol, poorly soluble in acetone.

(7) Color reaction: Ninhydrin reaction produces a reddish-purple color.

(8) Liquidity of aqueous solution: strongly alkaline.

(9) Crystal form: plate crystal. However, depending on the crystallization method and solution state, it may become almost columnar, and the thickness may also vary.

Incidentally, the tryptophan salt crystals of the present invention have a better crystal habit and can be obtained with higher purity than known free tryptophan crystals, so the method of the present invention can be used, for example, to purify colored tryptophan crystals. However, the tryptophan salt crystals of the present invention can also be made into highly pure optically active tryptophan crystals by simple neutralization.

Such optically active tryptophan monosodium pentahydrate crystals precipitate at pH 10.9 or higher. The amount of Na ions is preferably 1 or more, preferably about 2 to 5 as a molar ratio of Na ions to tryptophan in the solution. Even if more than this is added, the amount of crystals obtained will not increase significantly, so it is a waste of alkali and is not a good idea. NaOH is usually used as the Na ion source and regulator, but NaCt*Na2SO4 can be mixed with sodium acetate etc. Na salt and an alkali such as KOH, LiOH or NH4OH may be used in combination. Also, even when using NaOH, the higher the amount of NaOH, the higher the crystallization rate, so N
When the amount of aOH is reduced, it is also possible to increase the crystallization rate by coexisting salts such as NaC2 and Na2So4 due to the common ion effect of Na ions.

Conveniently, the crystallization is by cooling crystallization. For example, slowly cool the solution from around 30 to 50°C, and when it reaches the saturation concentration, add seed crystals as necessary and cool it further to 0° to 30°C.
Separate nearby. When this crystal is air-dried at room temperature, it easily dehydrates and transforms into an anhydride.

The crystals of the present invention can be widely crystallized from aqueous solutions containing optically active tryptophan, and are particularly effective in removing dull substances derived from fermentation liquids and enzyme reaction liquids containing colored substances. Examples of such liquids include fermentation liquids, enzyme reaction liquids, sterilizing liquids thereof, liquids purified by using ion exchange resins, nonionic resins, ultrafiltration, reverse osmosis filtration, etc., and liquids such as these. For example, a mother liquor obtained by crystallizing and separating tricytophan from a liquid or a solution of its crystals (crude crystals) may be used. It can also be applied to crystallization of an optically active substance after optical resolution of the DL form.

The separated optically active tricytophan monosodium pentahydrate crystals can be dissolved in water and neutralized and crystallized with an acid such as hydrochloric acid to obtain optically active tricytophan crystals.

Examples are shown below.

Example I L-) Rig door 7n102. IJ7 and Na0I (50
After dissolving 1 in 190 g of water at 40°C, the solution was stirred and crystallized to 19°C while cooling.

After 20 hours, the crystallization slurry was centrifuged to obtain crystals 133.
I got JF. Yield 84.0'%. The analytical values are shown in Table 1.

Example 2 L-tributophane fermentation liquid (Japanese Patent Application Laid-Open No. 56-92796)
was passed through a strongly acidic cation exchange resin to adsorb L-) lipoan, followed by elution with a 2N NaOH solution.

The eluent was concentrated to give L-) lipoan 27.4 h, N''/L-) lig) 77 n (molar ratio) = 4.1, pH
Approximately 14 concentrates were obtained.

300 # of this concentrated solution was collected and crystallized by cooling to 10° C. over 20 hours.

The precipitated crystals were centrifuged to obtain 117 g of tryptophan sodium salt crystals. Tryptophan content 64.1%
, yield 91.2%. The transmittance of this crystal was 87% (C=1, pH adjusted to 5.9 with HCl, 430
nm).

Comparative Example 1 The concentrated solution 300 II of Example 2 was diluted with water to 800 g, and then concentrated hydrochloric acid was added to neutralize and crystallize the solution to pH 5.9.

The precipitated crystals were centrifuged and dried at 60°C under reduced pressure to obtain crystals 68.711. Tryptophan content 98.6%,
Yield 82.4%. The transmittance of this crystal was 43% (
C=1, water, 4301m).

Example 3 After dissolving the tricytophan crystal (crude crystal) 209 obtained in Comparative Example 1 and NaOH711 in 4Qml of water at 40°C,
Crystallization was performed by cooling to 5°C.

The slurry was centrifuged to obtain tryptophan sodium salt crystals 28.5#. Tryptophan content 6265%,
Yield 90.3%. The transmittance of this crystal was 96% (
Measured under the same conditions as Example 2).

Comparative Example 2 Tryptophan crystals 2019 obtained in Comparative Example 1 were dissolved in concentrated hydrochloric acid 8
．． 5- and Pii dissolved in 150 m7 of water and filtered through P paper.
A 30% NaOH solution was added to the solution to neutralize and crystallize it to pH 5.9.

The precipitated crystals were centrifuged and dried at 60°C under reduced pressure to obtain crystals 16.7.9. Tryptophan content 99.1%,
The yield was 83.9%, and the transmittance of this crystal was 58% (
Measured under the same conditions as Comparative Example 1) 0 Example 4 35% HC1t-13 was added to the L-tributophane fermentation solution and centrifuged. 30% NaOH solution was added to pi-112.5 and concentrated. did. 110 g of this concentrated solution (Lyptophan content: 15.4 L) was cooled and crystallized from 40° C. to 5° C. over 25 hours.

After the precipitated crystals were centrifuged, they were washed by spraying a small amount of cold water. The tryptophan sodium salt crystal obtained was 22.5.9 (tryptophan content 60.8%, yield 80.7%), and the transmittance of this crystal was 82%.

(Measured under the same conditions as Example 2).

Patent applicant: Ajinomoto Co., Inc.

Claims (2)

[Claims] (1) Optically active tryptophan monosodium pentahydrate crystal (2) An aqueous solution containing optically active tryptophan at -10
, 9 or more and the crystallization operation is performed in the presence of Na ions in an amount such that the molar ratio of Na ions to tryptophan in the solution is 1 or more. manufacturing method.