DE2305187A1 - PROCESS FOR THE SEPARATION OF A MIXTURE OF 3-FLUORINE-D- AND -L-ALANINE COMPOUNDS - Google Patents

Description

The invention relates generally to the production of 3-fluoro-D-alanine, which is an effective antibacterial agent and inhibits the growth of both gram-positive and gram-negative pathogenic bacteria. In particular, the invention relates to the preparation of 3-fluoro-D-alanine in practically pure form by direct separation of 3-fluoro-DL-alanine or a salt thereof. This direct separation process consists in preparing an aqueous solution of the DL mixture of 3-pluoroalanine and converting the solution into a supersaturated aqueous solution of the DL mixture (which is expediently achieved by increasing the temperature in the dissolving tank to about 30 ^° C. and maintaining a temperature difference between the dissolving tank and the crystallization tank of about 5 ⁰ G),

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the supersaturated solution is inoculated with crystals of the undesired L-isomer, the mother liquor is separated off and with or without brings further increase in supersaturation with the desired D-isomer in contact. Usually is preferred initially the undesired L-isomer crystallizes out, since this first crystallization a major change in the impurity occurs. While doing this continuously In the process, the mother liquor from the second crystallization (i.e. the crystallization of the D-isomer) is transferred to the dissolving tank recycled, and crystallized D- and L-isomer are continuously or from time to time from each crystallization vessel deducted.

This continuous direct separation is in the same way on salts of 3-pluoro-DL-alanine with acids or bases, for example the hydrochloride, benzenesulfonate or the sodium, Potassium or quaternary ammonium salt, as well as derivatives of 3-pluoroalanine, such as the N-acetyl or N-benzoyl derivative, applicable. If the benzenesulfonate is used, it will do so the separation is expedient in solution in a low molecular weight alkanol, preferably ethanol. A solution to the jJ-Fluoro-D-alanine-benzenesulfonate in ethanol, prepared in the It keeps dissolved, is converted into a supersaturated solution in ethanol, this is mixed with crystals of 3-fluoro-L-alanine benzene sulfonate inoculated, the mother liquor is separated from the crystallized material and .mit crystals of 3-Pluor-D-alanine-benzenesulfonate inoculated, and the mother liquor from this second crystallization is returned to the dissolving tank.

Although the individual steps of the continuous process are preferably carried out sequentially, they can

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if desired, can also be carried out in parallel, i.e. the solution from the dissolving tank can be divided into two equal parts, · - each solution converted into a supersaturated solution, the one inoculated with crystals of the D-isomer and the other with crystals of the L-isomer and put both mother liquors in the dissolving tank are recycled, and the crystallized D- and L-isomer can be separated from their slurries continuously or at certain time intervals.

Alternatively, the direct separation can be carried out in a continuous process consisting of only two stages, i.e. a dissolving and a take place in a crystallization stage. This is done in the dissolving container a saturated solution of a 3-pluoro-DL-alanine produced, and this solution is transferred to a crystallization zone, where it is converted into a supersaturated state preferably by lowering its temperature. The supersaturated solution is then inoculated with crystals of 5-fluorine-D-alanine, so that the D-isomer selectively crystallizes out in practically pure form, and this crystalline 5-fluoro-D-alanine is then filtered off or centrifuged off. The mother liquors are returned to the dissolving tank and the temperature is brought back to the the original value in the dissolving tank is increased. The solution obtained is brought into contact with further j5-fluoro-DL-alanine, whereby the D-isomer is selectively dissolved while the L-isomer remains undissolved in practically pure form. In this way a

the continuous selective separation of a / enantiomorph, -die form the DL mixture, i.e. the L-isomer in the dissolution zone and the separation of the other enantiomorph (i.e. the D-isomer) into the crystallization zone, and the D- and the L-isomer can continuously or at certain time intervals from the crystallization zone or taken from the dissolution zone.

As mentioned above, the 3'-fluoro-D-alanine is an effective antibacterial agent, while the isomeric 5-fluoro-L-alanine (ob-

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probably also this antibacterial effect) is generally an undesirable isomer. The racemization of the L-isomer to the DL mixture is expediently carried out by heating the 3-fluoro-L-alanine with acetic anhydride to an increased level Temperature of about 80 ° C, under which conditions the acetylation and racemization with the formation of N-acetyl-j5-fluoro-D-alanine is practically finished in about J5 hours. The N-acetyl-3-fluoro-DL-alanine is then conveniently with an aqueous mineral acid, such as aqueous hydrochloric acid, hydrolyzed, after which by Addition of aqueous ammonia the jJ-Fluor-DL-alanine, i.e. the Starting material for the above direct resolution.

The following examples illustrate the method according to the invention.

example 1

The device consists of three containers, each with a stirrer and means for temperature control is equipped. The three containers are about to form a closed circle Lines connected to one another, with a filter being arranged at the input end of each line and the solution by means of a Pump is pumped to the next container. Additional filters can be placed behind each pump outlet. The first of the The container arranged for the circulation, the dissolving container, also has means for adding solid j5-fluoro-DL-alanine and Solvent on. The other two tanks are the crystallization tanks for the D and L isomers. The procedure is carried out as follows:

2 liters of water are added to the dissolving tank, and 300 "g

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jJ-Fluor-DL-alanine are added. The slurry is equilibrated by holding it at 25 ° C for one hour after which time pumping to the L-crystallizer is started. When the volume in the L crystallization vessel has increased to 500 ml, the pump between the L and D crystallization vessels is switched on and the pumping speed is adjusted so that the volume of solution in the L crystallization vessel is kept at 500 ml. When the volume in the D-crystallization vessel has increased to 500 ml, the pump between the D-crystallization vessel and the dissolving vessel is switched on and the pumping speed is adjusted so that the volume is kept constant. 1 more water and 150 g of 3-fluoro-DL-alanine are introduced ^{into the dissolving container, and the system is brought into equilibrium at 25 °} C. by pumping the solution from one container into the other container. 20 g of 3-fluorine-L-alanine are added to the L-crystallization vessel and 20 g of 3-fluoro-D-alanine are added to the D-crystallization vessel.

Then, the temperature is increased in the dissolution vessel at 30 ⁰ C, so that a, supersaturation of about l6 g / l builds up, which is maintained at 25 ⁰ C in the crystallization vessels. To maintain a solid phase, additional solid 3-fluoro-DL-alanine is added to the dissolving tank.

The solid phase in each crystallization vessel is kept roughly constant by adding some of the Withdraws crystal slurry from each crystallization vessel. By filtering the slurry from the L-crystallizer practically pure j5-fluoro-L-alanine is obtained. By filtering the slurry off. the D-crystal feature container practically pure 5-fluoro-D-alanine is obtained.

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The filtrates are returned to the dissolving tank. Example 2

In the manner described in Example 1, 400 g of 2-fluoro-DL-alanine-benzenesulfonate are introduced into the dissolving container which contains 2 liters of absolute ethanol. The L-crystallization vessel is seeded with 25 g of solid 3-fluoro-L-alanine-benzene sulphonate and the D-crystallization vessel with 25 g of 3-fluoro-D-alanine-benzene sulphonate. The temperature difference between the dissolving container and the crystallization containers is kept at 5 ^° C. (ie the temperature in the dissolving container is 30 ^° C. and that in the crystallization containers is 25 ^° C.). Production speed can be increased by increasing the temperature of the dissolving tank and maintaining solid phase. However, the risk of contamination and the production of less pure 3-fluoro-D-alanine benzenesulfonate increases with higher supersaturation. In the event of contamination, das.Produkt can be purified in individual batches by simple recrystallization from absolute ethanol.

The 3-5 ^l luoro-D-alanine benzenesulfonate is converted into 3-alanine by dissolving the salt in water and ^{absorbing the amino acid on a sulfonic acid resin (H +} cycle). The column is washed with water and then eluted with dilute aqueous ammonia. The eluate is concentrated to a small volume and the 3-fluoro-D-alanine crystallizes when isopropanol is added.

Example 3

About 10 g of 3-fluoro-L-alanine are added to 50 ml of acetic anhydride, and the mixture is ^{heated to 80 °} C. for 3 hours. Then the mixture is evaporated to dryness. About 100 ml of 6N aqueous hydrochloric acid are added, the mixture is heated to reflux temperature for 8 hours, and the resulting solution is evaporated to dryness. The residue is in

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the minimum amount of water dissolved, and the PH is with ko ^ -. ι centered aqueous ammonium hydroxide adjusted to 4.8. The mixture is ^{cooled to 0} ° C. and the precipitated material

is filtered off, washed with ice water and dried, whereby 3-fluoro-DL-alanine is obtained. Alternatively, this will be. crude hydrochloride of 3-Fluc-r-DL-alanine, which is obtained by evaporation of the hydrolysis mixture is obtained, washed in water and replaced by a strongly acidic cation exchange resin (H. cycle) guided. The column is washed with water to separate the chloride ions and then with dilute aqueous ammonium hy- ■ droxyd eluted. The eluate is evaporated and the precipitate which forms is filtered off and dried, 3-fluoro-DL-alanine- being obtained will.

The procedure of this Example 3 is for racemization of all N-acyl and N-aroyl derivatives of 3-fluoro-L-alanine jjdem unwanted isomer obtained in the separation), which are able to form the oxazolin-5-one ring, applicable in which In cases it is not necessary to remove the N-acyl group by hydrolysis.

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Claims (6)

937 ! Pat enta η sayings Process for the separation of a mixture of 3 ~ and-L-alanine compounds, characterized by the fact that one is saturated in a solution zone Solution of the mixture produces, the solution converted into a supersaturated solution of the mixture, from the supersaturated solution L-isomer crystallized out by inoculation with crystals of the L-isomer, the mother liquor separates from the crystals, and the ^ -fluoro-D-alanine compound crystallized out by seeding with crystals of the D-isomer and the 3-fluorine-D-alanine compound wins. 2. The method according to claim 1, characterized by h that the j5-fluoro-DL-alanine compound 3-fluorine-DL-alanine-benzenesulfonate, the obtained D-isomer 3-fluoro-D-alanine-benzenesulfonate is. ^. Method according to claim 1, characterized in that that the j5 ~ fluoro-DL-alanine compound is an N-acyl derivative and the N-acyl - ^ - fluoro-L-alanine isomer is racemized by heating with acetic anhydride to form N-acyl-2-fluoro-DL-alanine. 4. A method for the separation of 3-fluoro-DL-alanine, characterized in that in a dissolving zone a saturated solution of the DL mixture produces, this solution is converted into a supersaturated solution of the DL mixture that is supersaturated 30983 2/1175 14 937 Solution seeded with crystals of the L-isomer and thereby the L-isomer crystallizes out of the solution, which Separates mother liquor from the crystals and brings them into contact with crystals of the D-isomer and thereby the 3-fluorine-D-alanine crystallizes out and the 3-fluoro-D-alanine wins. 5. The method according to claim 4, characterized in that the mother liquor of the crystallization of the 3-fluoro-D-alanine is returned to the dissolving tank and the separation is carried out continuously. 6. The method according to claim 4, characterized in that that the J-Pluor-L-alanine with acetic anhydride heated and the acetylated product to 3-fluoro-DL-alanine, which is returned to the dissolving tank is, is hydrolyzed. 309832/1175