JPH0656775A - Production of n-acetyl-dl-tryptophan - Google Patents

Abstract

PURPOSE:To obtain this compound in a high quality and in a high yield by producing N-acetyl-L-tryptophan in a high quality in a high yield in an improved acetylation reaction rate while reducing the by-production of impurities, and subsequently racemizing the produced N-acetyl-L-tryptophan in a homogeneous state. CONSTITUTION:The method for producing the N-acetyl-DL-tryptophan from L-tryptophan is characterized by simultaneously adding acetic anhydride and an alkali metal hydroxide aqueous solution to the aqueous solution of the L- tryptophan and an alkali metal hydroxide in the substantially same molar amount as that of the L-tryptophan while maintaining the pH of the aqueous solution to 11 or higher, heating the aqueous solution of the acetylation product, and further treating the heated aqueous solution with acetic anhydride.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an improved process for the preparation of N-acetyl-DL-tryptophan from L-tryptophan and acetic anhydride in aqueous alkali metal hydroxide solution.

[0002]

2. Description of the Prior Art L-Tryptophan is used in N-acetyl-DL with acetic anhydride in an aqueous solution of an alkali metal hydroxide.
-Method for manufacturing tryptophan [The Journal of
Biological Chemistry Vol. XCVI N
o. 2 P511-517 (The Journal
of Biological Chemistry)]
Is known. According to the method, L-tryptophan is dissolved in an aqueous caustic soda solution having a molar ratio of about 2-fold to L-tryptophan, and about 6-fold mol of acetic anhydride is added to L-tryptophan in several batches with vigorous stirring. After that, when the temperature of the solution is kept at 35 to 40 ° C. for 3 hours, crystals start to precipitate. Therefore, the mixture is cooled, crystals are separated, and post-treatments such as washing are performed to obtain the desired product. However, the yield by this method was as low as 75%, and improvement was desired.

[0003]

DISCLOSURE OF THE INVENTION The present invention overcomes the disadvantage of the conventional method in that the yield is low, and can be carried out by a simple operation and industrially advantageously, N-acetyl-DL-.
It is to provide a method for producing tryptophan.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the pH during acetylation is low.
Is controlled to 11 or more, and the reaction liquid during racemization is performed in a uniform state, so that N-acetyl-DL-
They have found that tryptophan can be produced, and completed the present invention.

That is, according to the present invention, L-tryptophan is reacted with acetic anhydride in an aqueous alkaline solution to produce N-acetyl-DL.
In the method for producing tryptophan, the pH of the aqueous solution is added to an aqueous solution of L-tryptophan and an alkali metal hydroxide in a substantially equimolar amount to L-tryptophan.
While maintaining the value of 11 or more, acetic anhydride and an aqueous solution of an alkali metal hydroxide are simultaneously added to effect acetylation, and then the aqueous solution is treated with acetic anhydride under heating.
-Acetyl-DL-tryptophan production method.
The L-tryptophan used in the method of the present invention can be produced by any of synthetic method, enzymatic method and fermentation method.

The alkali metal hydroxide used in the method of the present invention includes, for example, potassium hydroxide, sodium hydroxide and the like, and a substantially equimolar amount is used for the preparation of the L-tryptophan aqueous solution. If it is less than equimolar, impurities will be produced as by-products and the racemization rate will decrease. If it is used in excess of the equimolar amount, a large amount of mineral acid is required for the precipitation of N-acetyl-DL-tryptophan after racemization, which is not preferable because it causes deterioration in quality and yield.

In the method of the present invention, the acetylation reaction is first carried out as the first step, and then the racemization is carried out to obtain the desired product. Acetylation is carried out by intermittently or continuously adding acetic anhydride to an aqueous solution of an alkali metal hydroxide of L-tryptophan. It is not preferable to add acetic anhydride at one time because the acetylation yield will decrease. Furthermore, the amount of acetic anhydride used during acetylation was 1 for L-tryptophan.
˜2 times mole, preferably 1 times mole. The pH of the reaction solution when acetic anhydride is added is 11 or higher, preferably pH 1
It is carried out while keeping the range of 1 to 13. If the pH of the reaction solution is less than 11, impurities are by-produced and the purity is lowered.

In order to control the pH of the reaction solution at the time of acetylation to 11 or more, the pH of the reaction solution or the pH of the reaction solution is constantly measured with a pH meter or the like, and alkali metal hydroxide is added so that the pH is maintained at 11 or more. This is achieved by adding an aqueous solution. The reaction temperature at the time of acetylation is 0 to 50 ° C., preferably 20 to 40 ° C., the addition time of acetic anhydride at the time of acetylation is 1 to 5 hours, preferably 2 to 3 hours, and the acetylation aging time is 1 to Two hours is sufficient.

After the acetylation is completed, racemization is continued. For racemization, the acetylation reaction solution is 60-100
C., preferably 70 to 80.degree. C., the crystals precipitated in the reaction solution are dissolved and brought into a uniform state, and acetic anhydride is added to the L-tryptophan in an amount of 2 to 5 times the molar amount of L-tryptophan.
It is preferably carried out by adding 3 to 4 times by mole. The addition time of acetic anhydride during racemization is 1 to 4 hours, preferably 2 to 3
It's time. After the aging of the racemization reaction, the reaction solution is cooled, acid precipitation is carried out, crystals are separated, and post-treatments such as washing with water are carried out to obtain the desired product.

[0010]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 102.1 g (0.5 mol) L-tryptophan and 44.4 g (0.5 mol) 45% NaO in 300 g water.
Aqueous H solution was added, and 53.1 g (0.5
2 mol) acetic anhydride and 53.5 g (0.6 mol) 45
% NaOH reacts simultaneously and is added continuously. The pH of the solution during the reaction was kept at 11-13 and the addition of the two solutions was completed in 2.5 hours. When this reaction liquid was analyzed by liquid chromatography, 123.1 g of N-acetyl-L-tryptophan was obtained.
(100% of acetylation selectivity). The reaction solution was heated to 70 ° C., 153.1 g (1.5 mol) of acetic anhydride was added in 2.5 hours, cooled to 5 ° C., and concentrated hydrochloric acid was added to 10 ° C.
When 2.4 g was added dropwise, filtered, washed with water and dried, 115.7 g of N-acetyl-DL-tryptophan was obtained (L-
94 mol% relative to tryptophan). (Specific rotation ±
0.0 (measurement temperature 20 ° C)]

COMPARATIVE EXAMPLE 1 102.1 g (0.5 mol) of L-tryptophan and 97.9 g (1.1 mol) of 45% NaO in 300 g of water.
53.1 g (0.52 mol) to the solution containing H aqueous solution
Acetic anhydride was added and the reaction temperature was kept at 40 ° C. to complete the acetylation reaction in 2.5 hours. When this reaction liquid was analyzed by liquid chromatography, N-acetyl-L-tryptophan was found to be 98.
4 g (80% of acetylation selectivity), the reaction solution was cooled to 5 ° C., 120.5 g of concentrated hydrochloric acid was added dropwise, filtered, washed with water and dried to obtain 91.6 g of N-acetyl-L-tryptophan. (74. to L-tryptophan.
4 mol%).

Comparative Example 2 The N-acetyl-L-tryptophan obtained in Comparative Example 1 was added to 250 g of water and 72.7 g (0.82 mol) of 45%.
Aqueous NaOH solution was added, and the reaction temperature was 40 ° C. at 114.0.
g (1.1 mol) acetic anhydride was added over 2.5 hours, and 5
After cooling to ° C, 81.1 g of concentrated hydrochloric acid was added dropwise, filtered, washed with water and dried to obtain 86.1 g of N-acetyl-DL-tryptophan (69.9 with respect to L-tryptophan).
Mol%) [specific rotation +4.3 (measurement temperature 20 ° C.)].

Comparative Example 3 40 g (0.195 mol) of L-tryptophan was added to 1N.
Dissolved in 400 ml of NaOH aqueous solution, 130 g of acetic anhydride
Was added dropwise into 6 times and vigorously stirred. Then, the reaction liquid was kept at 35 to 40 ° C. and stirred at the same temperature for 3 hours. After a while, the reaction liquid in which crystals were precipitated was cooled to 5 ° C. and the crystals were separated by filtration. The obtained crystals were washed with water, diluted hydrochloric acid and water in this order. After drying, 36 g of N-acetyl-DL-tryptophan was obtained (75 mol% from L-tryptophan). mp204-205 ° C

[0014]

INDUSTRIAL APPLICABILITY By the method of the present invention, the by-product of impurities is suppressed, the reaction rate of acetylation is improved, and N of high quality and high yield is obtained.
By obtaining -acetyl-L-tryptophan and then racemizing it in a homogeneous state, it is possible to obtain the desired product with high quality and high yield, which is an industrially useful method.

Claims (2)

[Claims] 1. A method for producing N-acetyl-DL-tryptophan by reacting L-tryptophan with acetic anhydride in an alkaline aqueous solution, wherein L-tryptophan and an alkali in a substantially equimolar amount to L-tryptophan. While keeping the pH of the aqueous solution of metal hydroxide at 11 or more, acetic anhydride and an aqueous solution of alkali metal hydroxide are simultaneously added for acetylation, and the aqueous solution is further heated and further treated with acetic anhydride. A method for producing N-acetyl-DL-tryptophan, which is characterized. 2. The heating temperature after acetylation is 60 to 100.
The method according to claim 1, wherein the amount of acetic anhydride used at 2 ° C is 2 to 5 times mol of L-tryptophan.