PROCESS FOR REFINING PHENYLALANINE

Abstract: Phenylalanine is refined by a process which comprises the steps of bringing a phenylalanine solution containing tyrosine as the main impurity and other impurities into contact with a non-polar highly porous synthetic adsorbent, adsorbing phenylalanine on this adsorbent selectively, and eluting and recovering the adsorbed phenylalanine.

Description: This invention relates to a new process for refining phenylalanine In particular it relates to a process for eliminating impurities such as tyrosine as the main impurity, amino acids, organic acids, and salts, from phenylalanine solutions. Examples of such phenylalanine solutions are as follows: L-phenylalanine fermentation liquids containing L-tyrosine; intermediate process liquids used to recover L-phenylalanine from such fermentation liquids; dissolved liquids of the crude crystals of L-phenylalanine containing L-tyrosine obtained from such intermediate process liquids; and other phenylalanine solutions containing at least tyrosine as impurity and possibly containing other amino acids, salts, etc. The process of the present invention may be applied to any L-phenylalanine solution. The present invention is particularly applicable to L-phenylalanine fermentation liquid, from which various by-products such as amino acids, etc., can be easily separated from the L-phenylalanine by recrystallization, etc., but from which L-tyrosine is hardly separable from the L-phenylalanine by conventional refining processes such as recrystallization processes and ion-exchange processes (see Japanese Patent Publication No. 3789/1958). As the result of intensive and extensive studies, the present inventors have found it possible to refine phenylalanine by an extremely simple process. According to the invention, there is provided a process for refining phenylalanine,which comprises bringing a phenylalanine solution containing tyrosine as an impurity and optionally one or more other impurities into contact with a particular non-porous synthetic adsorbent, namely SP-207, which is a styrene-divinylbenzene copolymer made by Mitsubishi Chemical Industries Ltd., whereby the phenylanine is selectively adsorbed on the adsorbent,and eluting and recovering the adsorbed phenylalanine. In an embodiment of the invention, the process of separating phenylalanine from a phenylalanine solution containing tyrosine as the main impurity needs only contact of the solution with the adsorbent. Thus, the present invention is concerned with a process for obtaining a highly pure phenylalanine solution by contacting a phenylalanine solution containing tyrosine, etc., with the adsorbent, adsorbing only the phenylalanine on the resin, and then eluting the phenylalanine adsorbed on the resin by an appropriate solvent. As occasion demands, by concentrating this phenylalanine solution, highly pure phenylalanine crystals can be obtained. As for the manner of contact of the phenylalanine solution with the adsorbent, a batch process or a process effected in a column can be used. However, it is preferred to carry out this invention as a chromatography process of that column type. For instance, by filling a column with the adsorbent and then passing the phenylalanine solution containing impurities such as tyrosine downwardly through the column, the adsorbent adsorbs phenylalanine selectively, while the other materials are eliminated as effluent. The concentration of the phenylalanine solution is not critical, and it would be agreeable if only within the saturated solubility at the operational temperature of adsorption. The pH of the phenylalanine solution, considering that the quantity of adsorption reaches a maximum at the isoelectric point, can be maintained between about 3 and 9, preferably about 5 and 6. Moreover the upper limit of the operational temperature of adsorption will depend upon the heat-resistance of the adsorbent, because phenylalanine is stable even at high temperatures. The operational temperature of adsorption,according to the heat-resistance of the adsorbent, for instance, may be kept below 60°C or within the range of 0 to 90°C. Even within this temperature range, as the quantity of adsorption is varied in such a way that, for example, the quantity of phenylalanine adsorbed on the adsorbent may reach a maximum at around 30°C, the best adsorption operational temperature should be selected according to a preliminary experiment. Furthermore, when the concentration of salts (e.g. inorganic salts such as Na₂SO₄, NaCl, NH₄Cl, etc) in a phenylalanine solution increases, the quantity of phenylalanine adsorbed on the adsorbent also increases, so the adsorption may favorably be operated in accordance with a column system after these salts have been added to the aqueous phenylalanine solution (see Example 2). Since the adsorbent has stronger affinity for phenylalanine than for tyrosine, if, irrespective of the quantity of tyrosine as the main impurity, the adsorption is operated in order to attain a saturated adsorption of phenylalanine, the phenylalanine recovered by the elution will not contain tyrosine. The saturation rate of the adsorption, relative to phenylalanine, depends upon the desired purity of the phenylalanine. The elution for the recovery of the phenylalanine adsorbed on the adsorbent is not difficult. For instance, the elution of the phenylalanine can be easily performed by water, acid, alkali, lower aliphatic alcohol (e.g. methanol, ethanol, isopropyl alcohol, etc.), and mixtures thereof ( e.g. aqueous solutions of methanol, ethanol, isopropyl alcohol, etc.). The invention will now be illustrated by the following Examples. Example 1 2.5 litres (pH = 6.0) of an aqueous solution containing 3 g/dl of L-phenylalanine and 40 mg/dl of L-tyrosine was passed through a 100 ml bed(80 cm in height and 4 cm in diameter) of non-polar highly porous synthetic adsorbent, namely SP-207, in the form of a column, at an SV (space velocity in elution) of 1, whereby L-phenylalanine was adsorbed selectively. Then, the L-phenylalanine was eluted using water as an elution solvent(SV= 2). Consequently, the quantity of water required for the elution was 20 litres, and more than 98% of the L-phenylalanine adsorbed was eluted. By the deposition of crystals by the concentration of the eluate, 65g of L-phenylalanine crystals not containing any L-tyrosine, etc., were obtained. The purity of these crystals is more than 99.5%; furthermore, no L-tyrosine was detected by T.L.C. (thin layer chromatography) analysis. Example 2 3.5 litres (pH= 5.0) of L-phenylalanine solution containing 3 g/dl of L-phenylalanine, 40 mg/dl of L-tyrosine, 100 mg/dl of each of L-glutamic acid, L-alanine and L-lysine, 10 g/dl of NaCl and 2 g/dl of Na₂SO₄ was passed through a 1000 ml bed (80 cm in height and 4 cm in diameter) of non-polar porous synthetic adsorbent, namely SP-207, in the form of a column, at an SV of 1, whereby L-phenylalaine was adsorbed selectively. Then, the L-phenylalaine was eluted by an aqueous EtOH (1% v/v) and NaOH (0.2N) solution (SV = 2). The quantity of aqueous solution required for the elution was 3.5 litres, and more than 98% of the L-phenylalanine adsorbed was eluted. By the desposition of crystals, by neutralization with HCl after concentration of the eluate, 80g of L-phenylalanine crystals not containing any L-tyrosine, etc, were obtained. The purity of these crystals was more than 99.5%; furthermore, no L-tyrosine or other amino acids were detected by T.L.C. analysis.

Claims: A process for the selective adsorption of amino acids by bringing a solution of said amino acids into contact with a non-polar porous synthetic adsorbent, characterised in that said non-polar porous synthetic adsorbent is SP-207 and in that said process is a process for refining phenylalanine which comprises bringing a phenylalanine solution containing tyrosine as an impurity and optionally one or more other impurities into contact with said non-polar porous synthetic adsorbent whereby the phenylalanine is selectively adsorbed on the adsorbent, and eluting and recovering the adsorbed phenylalanine. A process according to claim 1, wherein the adsorbent is in the form of a column, and wherein the phenylalanine solution is passed downwardly through the column. A process according to claims 1 or 2 wherein the phenylalanine solution contains a salt.

Inventors: KUSUMOTO, ISAO, OTANI, MASARU, SANO, CHIAKI
Applicants: AJINOMOTO CO., INC.
Application year: 1984
Main classification: C12P13
IPC codes: C07C67, C07C227, C07C229, C12P13