DE2109029A1 - Cleaning process - Google Patents

Description

Dr. Ing.A. van der Wenn Dr. f raw Lederer _n r. _H PATENT Attorneys £ 3. ΓβΟ.

RAN 4007/23

F. HofFmann-La Roche & Co. Aktiengesellschaft, Basel / Switzerland Cleaning process

L-Serine is a well-known amino acid that is used as a medicinal product and cosmetic is used. L-Serine is also used as a starting material for peptides and is also used for further syntheses of organic compounds.

L-serine can be obtained from synthetically produced DL-serine by separating it into the optical antipodes. This process is laborious and only succeeds in several steps, the yields being of course low.

L-serine is more easily accessible through microbiological methods. Methods have been described in which DL-G-Iy-

109839/1735 As / 1/20/71

ceric acid must be used as a substrate. Cheaper Methods (for example the one described in German Offenlegungsschrift No. 1.916.421), "which use carbohydrates as nutrient sources, Use hydrocarbons and other carbon sources, and those with certain bacteria, such as Arthrobacter, Brevibacterium or Gorynebacterium strains also produce! -Serin.

The crude L-serine obtainable by these methods is often due to certain amounts of other amino acids, in particular L-threonine, which makes its use difficult or impossible. The separation of the unwanted amino acids can only be achieved with relatively complicated and expensive methods, such as separation on ion exchange resins. These methods are often difficult to implement technically.

It is therefore the aim of the present invention to provide a technically simple process for obtaining pure L-serine, bzv /. of pure L-serine methyl ester hydrochloride, from one L-serine and other amino acids, especially L-threonine, containing mixture, for example from microbiologically produced, raw L-serine, which contains mainly L-threonine as an impurity.

The method according to the invention is characterized in that that the amino acids present in the mixture in the

109839/1735

corresponding methyl ester hydrochloride transferred to the L-serine methyl ester hydrochloride isolated by crystallization and optionally converted into! -Serine.

The resulting L-serine methyl ester hydrochloride can also be used as such, without prior conversion to serine, as an intermediate for various syntheses.

The method according to the invention is particularly suitable for obtaining L-serine from a mixture containing L-serine and L-threonine, which contains at most about 30 % L-threonine, in particular about 75 ° L-serine and about 25 ° L-threonine , contains.

The conversion of the amino acids present in the mixture in the corresponding methyl ester hydrochloride can in an known manner by reaction with an esterifying agent releasing the methyl group in the presence of or with subsequent Treatment with hydrochloric acid can be carried out, e.g. by adding the mixture of amino acids in methanol with thionyl chloride boils under reflux and then evaporates excess methanol. The residue obtained from the mixture of Hydrochloride of the methyl esters of amino acids (the hydrochloride. ride of L-serine methyl ester and L-threonine methyl ester) consists, can be purified by crystallization from a mixture of methanol and ethyl acetate, with pure L-

109839/1735

Serine methyl ester hydrochloride is obtained. An advantageous embodiment of the process according to the invention consists, for example, in that the crude mixture of the diethyl ester hydrochloride of! -Serine and L-threonine, as obtained by esterification of parts by weight of crude L-serine, which is converted to T6fo from L-serine and to 24 ° L-threonine, in addition to small amounts of other substances, is dissolved in about 400 parts of methanol and crystallized by adding 100 parts of ethyl acetate and cooling at 0 °, whereby about 70 parts by weight of L-serine diethyl ester hydrochloride are isolated, which Contains less than 0.5 f ° L-threonine methyl ester hydrochloride. Further quantities can be obtained from the mother liquor, so that the yield, based on the L-serine originally present, is about 90 % . This pure L-serine methyl ester hydrochloride melts at 163-165 and is uniform in the thin-layer chromatogram. The mixture remaining in the mother liquor, which consists mainly of L-threonine methyl ester hydrochloride and to a lesser extent of L-serine methyl ester hydrochloride, can be worked up to pure L-serine methyl ester hydrochloride as well as L-threonine methyl ester hydrochloride by further enrichment will.

The conversion of the L-serine methyl ester hydrochloride into the L-serine can by known hydrolysis methods, e.g. by treatment with a strong acid, e.g. Hydrochloric acid, and subsequent conversion of the hydrochloride from L-serine

1 09839/1735

in. the free! -Serin.

The conditions suitable for carrying out the process can be limited within certain limits. can be varied and are of course in the range of the usual chemical technology. A "particularly favorable embodiment is shown in the following example described:

example

100 g raw L-serine (after determination by the method von Stein and Moore in the Beckraan Uriichrom Amino-ac id analyzer the mixture consisted of 76 # L-serine and 24 7 »threonine, besides minor other impurities) are in 400 ml abs.

Dissolved methanol, treated with 77 ml of thionyl chloride and refluxed for about 12 hours. Then the reaction mixture is evaporated under reduced pressure and the residue redissolved in 400 ml of methanol. The crystallization of the L-serine methyl ester hydrochloride is initiated in that 100 ml of ethyl acetate are added and the mixture is left to stand at 0 ° for 4-5 hours. In this way a first crystallization is obtained of about 69 g of colorless crystals. The mother liquor becomes almost completely evaporated and the residue left to stand with 100 ml of alcohol for 3-4 hours at 0 °, again about 30 g of L-serine methyl ester hydrochloride are obtained. The total yield

109839/1735

is 99 g, which corresponds to about 88 % . The first crystallization is completely free of threonine according to the thin-layer orcatogram (acetic acid ester-n-butanol-porraamide-triethyla.niin / 50:50! 10: 5) with kinhydrin as the reagent. In the Beckinan amino acid analyzer, the first fraction showed 0.16 °, the second 1.63 ° L-threonine in addition to L-serine.

The hydrolysis of the pure L-serine methyl ester hydrochloride can be quoted as follows:

The L-serine methyl ester hydrochloride is 1.5 η Added hydrochloric acid, refluxed overnight, evaporated to dryness and taken up in ethyl alcohol, whereupon the alcoholic solution with diethylamine to a pH of 5 is discontinued, whereby L-serine precipitates.

109839/1735

Claims (4)

Claims 1. A method for obtaining L-serine methyl ester hydrochloride ¹ or L-serine from a mixture containing L-serine and other amino acids, in particular L-threonine, characterized in that the amino acids present in the mixture are converted into the corresponding methyl ester Hydrochloride transferred, the L-serine methyl ester hydrochloride isolated by crystallization and optionally converted into L-serine. 2. The method according to claim 1, characterized in that one starts from a mixture of L-serine and L-threonine, which contains a maximum of about $ 30 L-threonine. 3. The method according to claim 1 or 2, characterized in that one of a mixture of L-serine and L-threonine goes out, which was obtained by microbiological means. 4. The method according to claim 1, 2 or 3 »characterized in that one starts from a mixture which contains about 75 i ° L-serine and about 25 % L-threonine. 5 · The method according to any one of claims 1 - A, characterized in that the mixture of methyl ester hydrochloride is crystallized fractionally, the first 109839/1735 BATH Fraction from a solution in methanol by adding ethyl acetate and the second fraction crystallized from ethanol. 109839/1735