SK5499A3 - Process for the preparation of the disodium salt of z-l-aspartic acid from fumaric acid - Google Patents

Abstract

Manufacture of lysodic compound of Z-L-asparaginic acid from fumaric acid comprises fumaric acid in inert solvent in presence of aspartase or microorganism and ammonia.

Description

METHOD FOR MANUFACTURING Z-L-ASPARAGIC BISODIC SALT FROM FUMARIC ACID

Technical field

The invention relates to a process for the preparation of a disodium salt of Z-L-aspartic acid from fumaric acid.

BACKGROUND OF THE INVENTION

L-aspartic acid is an edible starting material for the synthesis of aspartame dipeptide, an artificial sweetener 200 times sweeter than sucrose.

Numerous chemical and enzymatic methods have been described for the synthesis of aspartame, in which L-aspartic acid and phenylalanine methyl ester, with or without enzymatic catalysis, bind to each other differently. For example, the starting material is a solid aspartic acid which, after reaction in the disodium salt with benzyloxycarbonyl chloride (Z-Cl) in aqueous solution, reacts to the disodium salt of Z-L-aspartic acid. In this connection, as described in EP-A-0 127 940, aspartic acid is prepared from maleic acid, which isomerizes to fumaric acid, enzymatically via ammonium L-aspartate and subsequent crystallization in the presence of acid. In this case, an equimolar amount of ammonium salts is formed in the mother liquor and must be removed accordingly. In this process, moreover, a number of process steps are required to obtain the disodium salt of Z-L-aspartic acid. Furthermore, it should be noted that the Z-L-aspartic acid disodium salt solution is subject to stringent specifications with respect to residual ammonia content, residual fumaric acid content, color and optical purity.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a process which avoids the formation of waste waters containing ammonium ions, reduces the number of steps to reach the disodium salt of Z-L-aspartic acid and meets the necessary specifications.

Unexpectedly, this problem is solved in a manner in which, starting from fumaric acid, ammonium L-aspartate is converted directly to the disodium salt of L-aspartic acid while quantitatively recovering the ammonia.

The present invention therefore provides a process for the preparation of a disodium salt of Z-L-aspartic acid from fumaric acid, characterized in that:

(a) fumaric acid in an inert solvent reacts with an excess of ammonia in the presence of aspartase or aspartase-producing micro-organisms to give ammonium L-aspartate, then

(b) sodium hydroxide is added to the ammonium L-aspartate-containing solution, whereby sodium or disodium L-aspartate or a mixture thereof is formed depending on the amount of sodium hydroxide used; and

(c) the continuous distillation is removed at ambient pressure and at a reflux temperature of 90 to 120 ° C in an interval of 0.2 to 2 minutes, cleaved and excess ammonia and returned to the fumaric acid suspension, which is used as the main solution for further enzymatic reactions whereby

d) the solution containing the remaining sodium L-aspartate is reacted with benzyloxycarbonyl chloride at a pH between 9-14 and sodium hydroxide added to form the Z-Lasparagic acid disodium salt.

In the first step a) of the process according to the invention, fumaric acid is reacted in an enzymatic reaction to ammonium L-aspartate. The main product for the process of the invention, i. fumaric acid, can be prepared, for example, by isomerization of maleic acid.

For the enzymatic reaction, fumaric acid is mixed up to the solubility limit in an inert solvent so as to obtain a suspension. As the inert solvent, water, a water / ethanol mixture, or a water / acetone mixture and the like are suitable. Preferably, water is used. Liquid ammonia or in the form of a solution of 10 to 35% by weight is then introduced into the fumaric acid suspension at ambient temperature, raising the temperature up to 60 ° C and adjusting the pH between 8 and 9. Preferably, an aqueous ammonia solution of 20 to 35 is used. 30 wt. The ammonia is added in excess, preferably 1 to 30%.

The aspartase enzyme or aspartase-producing microorganism is then mixed into the system, preferably solution, at 20 to 60 ° C, preferably at 30 to 50 ° C. In this addition of the enzyme or aspartase-producing microorganism, it is advantageous to obtain a solution by the addition of ammonia, since in the case of a suspension a larger amount of the enzyme is required, due to its adsorption and thus the loss of activity due to it. An enzyme activity of 30 to 50 IU per mole of fumaric acid is required for an almost quantitative reaction after 24 to 30 hours.

Aspartase-producing microorganisms are, for example, Pseudomonas fluorescens, Protens vulgaris, Pseudomonas aeruginosa, Serratia marcescens, Bacterium succinium, Bacillus subtilis, Aerobacter aerogenes, Micrococcus sp. , Escherichia coli and the like. Other suitable aspartase producing microorganisms are described, for example, in US 3,791,926 and US 3,198,712.

Furthermore, purified or synthetic aspartase may be used in the method of the invention. The aspartase-producing enzyme or microorganism can be added to a liquid or immobilized form, as described in EP 0 127 940, for example. 20 ° C to 30 ° C and in the second step b) sodium hydroxide is added. The amount of sodium hydroxide added depends on the desired sodium salt or the desired pH of the production solution. Both sodium and disodium salts as well as mixtures thereof are suitable for further reactions. Sodium hydroxide is preferably used. The reaction solution is heated to 10-30 ° C.

According to the invention, the ammonia is removed by distillation continuously, preferably on a thin film evaporator, a downstream film evaporator and a short path evaporator. The reaction temperature and the reflux temperature, respectively, are 90 to 120 ° C, preferably 100 to 110 ° C.

The distillation is carried out at ambient pressure and at a very short interval of 0.2 to 2 minutes, preferably 0.5 to 1.5 minutes. The distilled ammonia is then recycled to the fumaric acid slurry, which, after a further addition of ammonia, can be reused as the main solution for the subsequent enzymatic reaction. According to this method, the ammonia separation practically ensures a quantitative separation of ammonia and suppresses or completely prevents racemic reactions (D4 asp. <0.1 wt%) as well as the yellowish coloration of the remaining solution and the fission to fumaric acid.

The sodium L-aspartate solution thus obtained is then added to benzyloxycarbonyl chloride (Z-Cl) at a temperature of 30 to 60 ° C in a subsequent step d), maintaining the pH between 9 and 14, preferably between 11 and 12, by simultaneous dropwise addition of sodium hydroxide. Z-Cl can be added in equimolar amounts, but also in a slight excess. After the addition of Z-Cl, the reaction mixture is allowed to stand for 0.5 to 4 hours at the reaction temperature and then cooled to ambient temperature while phase separation is carried out.

The aqueous phase is then washed, for example with tertiary methylbutyl ether, diisobutyl ether, toluene or other water-insoluble solvents.

The organic phase is shifted to give the Z-Lasparagic acid disodium salt in aqueous solution. To remove any residual amounts of organic solvents in the aqueous phase, they are placed under vacuum at ambient temperature.

The process according to the invention yields the disodium salt of Z-L-aspartic acid as a clear, slightly yellowish solution which, if necessary, can be used, by coupling with phenylalanine, for further processing to aspartame. The process of the invention avoids waste water containing ammonium ions and the ammonia is quantitatively recycled to further fumaric acid enzymatic reactions.

Furthermore, it is not necessary to isolate Lasparagic acid or one of the intermediates in the process of the invention.

The ZL-aspartic acid disodium salt solution thus obtained complies with all specifications in relation to residual fumaric acid (<0.3 wt%) and ammonia (<100 mol%), color (APHA color <25) and optical purity (Dasp. <0.1 wt%)

DETAILED DESCRIPTION OF THE INVENTION

Example 1

(a) Enzymatic reaction

2070 ml of drinking water was added to a 5 L double-jacketed vessel and 973 g of fumaric acid (8.38 mol) was added. 1450 ml of 25 wt.% Was then added to the fumaric acid slurry over 30 minutes. ammonia solution (1314 g). A reaction temperature of 45-50 ° C and a pH of 8.5 was achieved. 1.4 ml aspartase solution (245 IU / ml) was added to the clear solution at 45 ° C and gentle stirring. Stirring was then stopped and the reaction solution was maintained at 45 ° C. The reaction was determined photometrically. An almost quantitative response (<99%) was achieved after 25.5 hours.

(b) and (c) Ammonia desorption

To 2445 ml of the ammonium L-aspartate solution obtained according to step a), after cooling to 25 ° C for 15 minutes, 842.5 g of 50 wt. sodium hydroxide solution. The solution was heated to 50 ° C. A pH of 11.5 was measured. Subsequently, cleaved and excess ammonia were separated from the L-aspartic acid sodium salt solution by means of a thin-film evaporator with a diaphragm metering pump.

The oil bath temperature was 175 ° C, the rotor speed was 300 rpm.

time gatherer ml sludge temperature ° C head ml sludge ml oh 1000 88.2 after 40 min. 500 94.3 230 270 1 h 22 min. 0 82.3 480 510

A solution of disodium L-aspartate having a content of 33.5% by weight was obtained. L-aspartic acid. No racemis was observed. The content of Dasparagic acid was 0.04% by weight. (D-asp: L-asp = <0.1:> 99.9%). The distilled ammonia was introduced into a fumaric acid slurry which served as the main solution for further reactions. The residual ammonia content was 20 mol%. The fumaric acid content was <0.04 wt. %, malic acid and asparagine were not detected.

d) Preparation of disodium Z- (L) aspartate ml of a disodium L-aspartate solution, prepared in analogy to Examples 1a) to 1c), with 18.1 wt. of L-aspartic acid (0.11 mol) was heated to 45 ° C. While stirring, 20.5 g of benzyloxycarbonyl chloride (Z-Cl) was added dropwise over an hour. Simultaneously, 50% w / w sodium hydroxide was added dropwise. maintained the pH between 10.9 and 13.8. In total, 7.8 g of sodium hydroxide solution of 50 wt. After dropwise addition, the reaction solution was maintained at 45-47 ° C for 2.5 hours. The pH was constant 12.1. After cooling to 25 ° C, the aqueous solution was treated twice with 92 ml of tertiary methylbutyl ether. The organic phases were transferred, the aqueous phase was freed of solvent residues for 20 minutes at 20 ° C and 20 mbar. 101 g of a slightly yellowish, clear solution were obtained. Disodium Z- (L) -aspartate content, 30.8% by weight.

Example 2

Production of sodium L-aspartate solution

In analogy to Example 1b) and 1c), 588 g of 20% sodium hydroxide solution were added to 1300 ml of the solution obtained according to 1a) after cooling to 25 ° C for 15 minutes. The solution was heated to 50 ° C. At ambient pressure, all ammonia was removed by distillation analogously to Example 1c) and the reaction solution was concentrated to 1200 ml. The residual ammonia content was <100 mol%.

A solution of sodium L-aspartate containing L-aspartic acid was obtained

No racemis was observed. The fumaric acid content was <0.1 wt. %, malic acid and asparagine were not detected. The solution was further processed to the disodium Z- (L) aspartate analogously to Example 1d).

Example 3

Production of Z- (L) -aspartate disodium by excess Z-CI

64.2 ml of disodium L-aspartate solution with 18.1 wt. % of Lasparagic acid (0.09 mol), prepared analogously to Examples 1a) to 1c), was heated to 45 ° C. 17.7 g of benzyloxycarbonyl chloride (0.10 mol) was added dropwise over 1 hour of stirring. Simultaneously, 50 wt. % sodium hydroxide solution reached a pH between 9.4 and 11.8. In total, it was added

8.8 g sodium hydroxide 50% wt. After the dropwise addition, the reaction solution was maintained at 45 ° C for 2.5 hours. The pH was constant 11.3. After cooling to 25 ° C, the aqueous solution was treated twice with 46 ml of tertiary methylbutyl ether. The organic phases were transferred, the aqueous phase was freed of solvent residues for 20 minutes at 20 ° C and 20 mbar. 84.2 g of a slightly yellowish, clear solution was obtained. The content of Z- (L) -aspartate disodium was 31.4% by weight.

Claims (10)

PATENT CLAIMS A process for producing a disodium salt of Z-L-aspartic acid from fumaric acid, characterized in that: (a) fumaric acid in an inert solvent reacts with an excess of ammonia in the presence of aspartase or aspartase-producing micro-organisms to give ammonium L-aspartate, then (b) sodium hydroxide is added to the ammonium L-aspartate-containing solution, whereby sodium or disodium L-aspartate or a mixture thereof is formed depending on the amount of sodium hydroxide used; and (c) the continuous distillation is removed at ambient pressure and at a reflux temperature of up to 120 ° C in an interval of 0.2 to 2 minutes, cleaved and excess ammonia and returned to the fumaric acid suspension, which is used as a starting solution for further enzymatic reactions, d) the solution containing the remaining sodium L-aspartate is reacted with benzyloxycarbonyl chloride at a pH of between 9 and 14 with the addition of sodium hydroxide to form the disodium salt of Z-Lasparagic acid. Process according to Claim 1, characterized in that water, a water / ethanol mixture or a water / acetone mixture is used as the inert solvent. Process according to claim 1, characterized in that the fumaric acid reacts at an enzymatic activity of 30 to 50 IU per 1 mole of fumaric acid. Process according to claim 1, characterized in that ammonia liquid or aqueous form of 10 to 35 wt. solution. The process according to claim 1, characterized in that the ammonia is introduced in an excess of 1 to 30%. The process according to claim 1, characterized in that the ammonia is removed by means of a thin film evaporator, a downstream film evaporator and a short path evaporator. Process according to claim 1, characterized in that the ammonia is removed at a reflux temperature of 100 to 110 ° C. A process according to claim 1, characterized in that benzyloxycarbonyl chloride is added to the solution containing sodium Laspartate at a temperature of 30 to 60 ° C. The process according to claim 1, characterized in that, following the reaction of Laspartate and benzyloxycarbonyl chloride, after phase separation, the aqueous phase is washed with a water-insoluble solvent. The process according to claim 9, characterized in that the aqueous phase containing the disodium salt of Z-L-aspartic acid is bound to phenylalanine to aspartame.