TWI485126B - Methods for the production of l-carnitine - Google Patents

Description

Method for producing L-carnitine

This invention relates to a process for the manufacture of L-carnitine.

Carnitine (vitamin Bt; 3-hydroxy-4-trimethylammonium-butyric acid) is a quaternary ammonium compound biosynthesized from amino acid lysine and methionine. In living cells, it is desirable to transport fatty acids from the cytosol to the mitochondria during lipid dissociation to produce metabolic energy. Carnitine is used as a nutritional supplement.

Carnitine exists in two stereoisomeric forms. The biologically active form is L-carnitine and the enantiomer D-carnitine is not biologically active. When L-carnitine is produced by an industrial process, it is desirable to produce a high purity biologically active L-form. High purity L-carnitine can be obtained by a microbiological method. EP 0 195 944 discloses a microbiological process in which L-carnitine is produced in a bioreactor by means of a specific microorganism from crotonobetain and gamma-butyricine. A mixture of enantiomerically pure L-carnitine and gamma-butyric acid betaine is obtained. To remove gamma-butyric acid betaine, the final product was recrystallized from methanol and isobutanol.

DD 296702 discloses another microbial process for obtaining substantially pure L-carnitine. The L-carnitine in the culture solution was depleted by electrodialysis and recrystallization of L-carnitine. In such microbial methods, substantially no D-carnitine is produced, and thus the enantiomeric separation step is not necessary. The L-carnitine is recrystallized from the solvent to remove other substances.

When non-microbial or non-enzymatic methods are used, obtaining high purity L-carnitine will become more complicated. D-carnitine and L-肉 are usually obtained by means of organic synthesis a mixture of bases. In order to obtain pure L-carnitine, DE 689 01 889 T2 proposes the use of a phosphonium phosphine complex in the stereoselective asymmetric hydrogenation. Such complexes are relatively complex and expensive and are therefore not suitable for the preparation of large amounts of L-carnitine in industrial processes.

Therefore, a method of separating L-carnitine from a mixture of L-carnitine and D-carnitine has been developed. In general, such methods are based on the separation of carnitine into a salt with an optically active acid and the separation of L-carnitine from D-carnitine due to differences in physical properties such as solubility.

In this regard, DD 93 347 discloses a method for separating D-carnitine and L-carnitine from an alcohol solution in the presence of camphoric acid, benzhydryl tartaric acid or a combination thereof. D-carnitine is separated from L-carnitine by the solubility of the salt.

DE 35 36 093 discloses a process for the preparation of L-carnitine from a racemic mixture, wherein D-carnitine and L-carnitine are converted to optically active salts with benzoyl-L-tartaric acid, followed by fractional crystallization .

However, the method of converting carnitine to an optically active salt or acid is relatively complicated because the methods include the steps of adding a separating agent and removing the separating agent after the separation process. This makes the entire process relatively time-saving and labor-saving.

Problem of the invention

The problem underlying the present invention is to provide a method of making L-carnitine which overcomes the above problems.

The method should be adapted to produce high purity L-carnitine from an enantiomeric mixture comprising L-carnitine and D-carnitine. Thereby the enantiomeric purity is significantly increased and the yield will become high.

This method will be carried out in a simple manner. In particular, additional compounds (such as optically active auxiliaries) that must be removed after use will be avoided. Moreover, the number of method steps is relatively small and the method does not require complex equipment. Overall, the method will be cost effective and labor intensive.

Disclosure of the present invention

Surprisingly, the problems of the present invention can be solved by the method according to the scope of the patent application. Other inventive examples are disclosed throughout the description.

The present invention relates to a process for producing L-carnitine comprising the steps of (a) providing a solution comprising at least 5% (w/w) carnitine in a first solvent, wherein the carnitine is D-carnitine and L-肉a mixture of bases, (b) seeding the solution with L-carnitine crystals as appropriate, (c) adding a second solvent in which L-carnitine is insoluble or has low solubility, and (d) is isolated from L - Crystals of carnitine.

Carnitine is a zwitterion containing a carboxyl group and a quaternary ammonium group. The carnitine used in step (a) is preferably a zwitterionic carnitine. However, it is also possible to use salts such as chlorides, sulfates or nitrates. The carnitine used in the step (a) is preferably not a salt formed by carnitine and an optically active anion.

By the method of the present invention, L-carnitine having an increased purity can be obtained. The method of the present invention is therefore also a method of purifying L-carnitine, a method of obtaining high-purity L-carnitine, or a method of increasing the enantiomeric excess of L-carnitine.

According to the present invention, crystalline L-carnitine can be obtained from a solution comprising D-carnitine and L-carnitine. In a preferred embodiment, the solution in step (a) consists essentially of a solvent and a carnitine. In the method of the present invention, L- meat can be improved The enantiomeric excess of the base (e.e.). The enantiomeric excess value is preferably increased by more than 1% or more than 2%. The increase in the enantiomeric excess value depends on the enantiomeric excess in the initial solution in step (a). The enantiomeric excess (e.e.) is defined as the absolute difference between the mole fractions of each enantiomer in percent. For example, a sample with 90% L-isomer and 10% D-isomer has an enantiomeric excess of 80% L-isomer.

In a preferred embodiment of the invention, in step (a), the carnitine comprises more than 50%, 80%, 90%, 95% or 98% (e.e.) of L-carnitine. Preferably, the L-carnitine which is isolated in step (d) comprises more than 90%, 95%, 98%, 99% or 99.5% (e.e.) of L-carnitine. Preferably, when a solution containing more than 95% (ee) of L-carnitine is used in step (a), a crystal containing more than 99% (ee) of L-carnitine can be obtained in step (d). .

In a preferred embodiment of the invention, the first solvent is selected from the group consisting of ethanol, methanol, water, acetonitrile, and mixtures thereof. The solvent is a good solvent for carnitine. This means that the solubility of carnitine at room temperature is at least 5%, preferably at least 10% or at least 20% (w/w). Preferably, the first solvent is ethanol. In a particular embodiment, the first solvent can comprise up to 0.5%, up to 2% or up to 5% (w/w) water. Therefore, the solvent can be industrial grade.

In a preferred embodiment, the solution in step (a) is a saturated solution or a supersaturated solution. The solution is also preferably near saturation, which means that the carnitine concentration is a saturation concentration of more than 80% or more than 90%. In a preferred embodiment of the invention, the concentration of total carnitine in the first solvent is from 5% to 75%. In ethanol The concentration is preferably from 10% to 50% or from 15% to 40% (w/w). In methanol, the concentration is preferably from 20% to 70% (w/w).

Preferably, the carnitine dissolved in the solution in step (a) is pure carnitine or a high purity carnitine. In this embodiment, the solution in step (a) contains only minor amounts of additional material. The amount of additional material may be less than 0.5%, less than 1% or less than 2% (w/w), based on the total amount of carnitine in the solution (D-carnitine and L-carnitine). In another embodiment, the carnitine dissolved in the solution of step (a) comprises an amount of by-product or other compound, such as a starting compound from the manufacturing process. In this embodiment, the solution in step (a) may comprise up to 5%, up to 10% or up to 15% (w/w) of other compound, based on the total amount of carnitine. For example, the synthetic carnitine may comprise less than 1% (w/w) hydroxybutenoic acid.

In a preferred embodiment, the solution in step (a) is substantially free of water. This means that the carnitine and solvent should be substantially free of water or contain as little water as possible. It has been found that the method is more effective when only a small amount of water is present. Preferably, the total water content in solution (a) is less than 2%, less than 1% or less than 0.5% (w/w).

In a preferred embodiment of the invention, step (a) comprises heating the solution (preferably) until all carnitine is dissolved, for example to a temperature above 40 °C or above 50 °C. Optionally, residual solid carnitine and/or residual solids can then be removed by filtration, for example. In the step (a), the temperature can be adjusted to 40 ° C to 80 ° C or 50 ° C to 75 ° C. The temperature is selected depending on the solvent. When ethanol is used, a temperature between 50 ° C and 75 ° C is preferred, for example, about 65 ° C.

In step (b), the seed crystal from the solution of step (a) can be seeded with L-carnitine crystals. Preferably, the seeded seed solution is a saturated or supersaturated solution. When a saturated solution is prepared at a high temperature in the step (a) and the saturated solution is slowly cooled so that the carnitine has not precipitated or crystallized, a supersaturated solution can be obtained.

Crystal growth was induced by seeding and cultivating the solution with L-carnitine crystals. Therefore, when the seeding step (b) is included in the method of the present invention, the average size of the finally obtained crystal is large. However, it is also possible to obtain a carnitine crystal having high purity in a high yield without adding a seed crystal in the seeding step (b). The crystal consists essentially of L-carnitine or is rich in L-carnitine. Only a small amount of seed crystal is required for seeding. Seed crystals should be of high purity and very fine. Preferably, the seed crystals are added while the solution is still clear (i.e., when the crystal or precipitate has not or is substantially not spontaneously formed). This can be achieved by seeding at elevated temperatures. In a preferred embodiment of the invention, in the seeding step (b), the solution has a temperature between 25 ° C and 50 ° C, preferably between 30 ° C and 45 ° C. However, the solubility of carnitine was still quite high during and after seeding and before the addition of the second solvent, and substantially no rapid formation of crystals or only a limited degree of rapid formation of crystals was observed.

In a preferred embodiment, the temperature of the solution is lowered after seeding with crystals. Preferably, the temperature is lowered to 10 ° C to 30 ° C, for example to about 20 ° C.

In the step (c), a second solvent in which L-carnitine is insoluble or has low solubility therein is added. Crystallization of L-carnitine was observed during and after the addition of the second solvent. During the crystallization of L-carnitine, the L-carnitine in the solution is depleted and the solution becomes a suspension. Thus, after crystallization, the composition can be considered a solution or suspension. When referring to "solution" with respect to step (b) and subsequent steps, it refers to this solution/suspension.

In a preferred embodiment of the present invention, the second solvent is selected from the group consisting of acetone, isopropanol, isobutanol, 2-propanol, 1-pentanol, 2-butanone, methyl acetate, ethyl acetate, Butyl acetate, tetrahydrofuran, toluene, and mixtures thereof. Preferably, the second solvent is acetone.

The second solvent is a solvent in which L-carnitine is insoluble or has only low solubility therein. In a preferred embodiment of the invention, the solubility of L-carnitine in the second solvent is less than 3%, less than 2% or less than 1% (w/w) at 25 °C. When the second solvent is added, the total solubility of the carnitine in the solution is lowered, and the carnitine is crystallized. Therefore, when the second solvent is added, solid carnitine crystals are formed in the solution.

In an excellent embodiment of the invention, the first solvent is ethanol and the second solvent is acetone.

In a preferred embodiment of the present invention, in the step (c), the ratio of the first solvent to the second solvent is 1:1 and 1:10 (w/w), more preferably 1:1.5 and 1:6. Or between 1:2 and 1:4 (w/w). This ratio should be adjusted so that the solubility of the carnitine in the solvent mixture is significantly reduced, allowing most of the carnitine to crystallize.

In a preferred embodiment of the invention, after the optional seeding step (b), or before or during step (c), or after adding the second solvent in step (c), the solution is The temperature is adjusted between 10 ° C and 30 ° C. However, the second solvent can be added before or after the temperature of the solution is lowered.

Preferably, the second solvent in step (c) is added slowly (e.g., dropwise). In a preferred embodiment of the invention, in step (c), a second solvent is added to the solution over a period of from 20 minutes to 24 hours, from 20 minutes to 8 hours, or from 1 hour to 6 hours. L-carnitine crystallizes during the addition of acetone and during incubation. The amount of crystalline L-carnitine can generally be increased by incubation at low temperatures.

Preferably, the composition is incubated at low temperature after the addition of the second solvent. For example, the temperature can be lowered to 5 ° C to 20 ° C, or below 15 ° C. The composition can be incubated at this temperature for 10 minutes to 2 days, or 30 minutes to 24 hours. In a preferred embodiment of the invention, after the second solvent is added in step (c), the composition is incubated at a temperature below 20 ° C for 10 minutes to 2 days.

In step (d), the solid crystal is isolated by known means (for example by filtration or deposition). The crystals are washed as appropriate (preferably with a second solvent). The solvent is removed by drying under reduced pressure as appropriate. For example, acetone can be removed by drying at 55 ° C under a pressure of less than 100 mbar.

According to the invention, all solid carnitines which are separated in step (d) are referred to as "crystals". The solid was found to have a crystalline structure. However, especially in the rapid addition of the second solvent, the solid "carnitine" of the carnitine may also at least partially contain the carnitine precipitate.

The total yield of L-carnitine is preferably higher than 80% or higher than 85% based on the total L-carnitine in the starting solution.

In a preferred embodiment of the invention, the method comprises the steps of (a) providing a solution comprising at least 5% (w/w) carnitine in ethanol, wherein the carnitine comprises at least 50% (ee) L-meat a base in which the solution is heated until all carnitine is dissolved, (a1) the temperature of the solution is adjusted to 25 ° C to 50 ° C, (b) seeding the solution with L-carnitine crystals, (b1) adjusting the temperature to 10 ° C to 30 ° C as appropriate, (c) such that the ratio of ethanol to acetone is between 1:1 and 1:10 ( The amount between w/w) is added with acetone, (c1) the composition is optionally cooled to a temperature lower than 20 ° C, and (d) the crystal containing L-carnitine is preferably isolated by filtration.

In the method described above, steps (a) to (d) are continuously performed.

In a particular embodiment of the invention, the entire process of the invention is repeated with the crystals obtained in step (d). In this particular example, a solution of crystals in a first solvent is prepared. When the entire process is repeated two or more times, even high purity L-carnitine can be obtained from carnitine having a low enantiomeric purity.

The method of the present invention solves the above problems. High purity L-carnitine can be obtained from the mixture of D-carnitine and L-carnitine by the method of the present invention. When a mixture of D-carnitine and L-carnitine is isolated, it is not necessary to add the optically active compound as disclosed, for example, in DE 35 36 093 or DD 93 347. In the process of the invention, the carnitine is not converted to an optically active salt in an intermediate step. Surprisingly, the process of the present invention is highly efficient because it is generally accepted in the art that efficient separation of zwitterions is difficult without optically active additives (see DD 93 347, column 2, pages 8-11). Row). Therefore, it is not conceivable that a substantial increase in the L-enantiomeric form can be achieved by the relatively simple method of the present invention.

The method of the invention can be applied in a simple manner with a small number of method steps. This method does not require precipitation of the optically active salt of L-carnitine, isolation and decomposition by additional crystallization steps. This process provides L-carnitine in high enantiomeric purity and high yield. This method is less costly and labor intensive than methods known in the art. This method can be used to purify L-carnitine from a mixture of enantiomers, such as an enantiomeric mixture obtained by an industrial synthetic process.

Example

Example 1

The laboratory reactor was filled with 100 g of carnitine and 300 g of ethanol. The reactor was heated up to 65 ° C and stirred until all carnitine had dissolved. After that, the reactor temperature was set to 37 °C. Seed crystals of pure L-carnitine were added at 37 °C. The reactor temperature was lowered to 20 ° C at a rate of -0.2 K/min. 900 g of acetone was added over 2 hours at 20 °C. The suspension was then lowered to 10 ° C. The solid was isolated at 10 ° C and washed with acetone and dried at 55 ° C and <100 mbar.

Thus, 86.1 g of a white crystalline dry solid was obtained. The solid contained 99.036% (w/w) total carnitine. The enantiomeric purity was 99.60% (e.e.). The residual solvent content was 349 mg/kg ethanol and 386 mg/kg acetone. The total yield of L-carnitine was 88.6%.

Example 2

The laboratory reactor was filled with 60.2 g of carnitine and 60 g of methanol. The reactor was heated up to 50 ° C and stirred until all carnitine had dissolved. After that, the reactor temperature was set to 25 °C. At 25 ° C, 0.74 g of pure L-carnitine seed crystals were added. The reactor temperature was lowered to 20 ° C at a rate of -0.2 K/min. 180 g of acetone was added over 1 hour at 20 °C. After that, the suspension was lowered to 10 ° C in 50 minutes. At this temperature, the suspension was stirred for another 30 minutes. Thereafter, the solid was filtered through a Nutsch filter and washed twice with about 60 g of acetone and then dried at 55 ° C and a pressure of 250 mbar for 8 h.

Thus 45.78 g of a white crystalline dry solid were obtained. The solid contained 98.94% (w/w) total carnitine. The enantiomeric purity was 99.78% (e.e.).

Example 3

The laboratory reactor was filled with 30.1 g of carnitine and 90 g of ethanol. The reactor was heated up to 65 ° C and stirred until all carnitine had dissolved. Thereafter, the reactor temperature was set to 37 °C. At 37 ° C, 0.91 g of pure L-carnitine seed crystals were added. The reactor temperature was lowered to 20 ° C at a rate of -0.2 K/min. 270 g of ethyl acetate was added over 1 hour at 20 °C. Thereafter, the suspension was lowered to 10 ° C in 50 minutes. At this temperature, the suspension was stirred for another 30 minutes. Thereafter, the solid was filtered through a suction filter, and washed twice with about 30 g of ethyl acetate and then dried at 55 ° C and a pressure of 250 mbar for 8 h.

Thus 28.66 g of a white crystalline dry solid were obtained. The solid contained 98.51% (w/w) total carnitine. The enantiomeric purity was 99.46% (e.e.).

Claims (15)

A method of producing L-carnitine comprising the steps of (a) providing a solution comprising at least 5% (w/w) carnitine in a first solvent, wherein the carnitine is D-carnitine and L- a mixture of carnitine, (b) seeding the solution with L-carnitine crystals as appropriate, (c) adding a second solvent in which the L-carnitine is insoluble or has low solubility, (d) single From the crystal containing L-carnitine. The method of claim 1, wherein the first solvent is selected from the group consisting of ethanol, methanol, water, acetonitrile, and mixtures thereof. The method of claim 1 or 2, wherein in step (a), the concentration of total carnitine in the first solvent is from 5% to 75% (w/w). The method of claim 1 or 2, wherein in step (a), the carnitine comprises more than 80% (ee) L-carnitine, and in step (d), the crystal comprises more than 95% (ee) L-carnitine. The method of claim 1 or 2, wherein the step (a) comprises heating the solution to a temperature above 40 °C. The method of claim 1 or 2, wherein the second solvent is selected from the group consisting of acetone, isopropanol, isobutanol, 2-propanol, 1-pentanol, 2-butanone, methyl acetate, acetic acid Ethyl ester, butyl acetate, tetrahydrofuran, toluene, and mixtures thereof. The method of claim 1 or 2, wherein the solubility of L-carnitine in the second solvent is less than 2% (w/w) at 25 °C. The method of claim 1 or 2, wherein in the seeding step (b), the solution has a temperature of from 25 ° C to 50 ° C. The method of claim 1 or 2, wherein in the step (c), the ratio of the first solvent to the second solvent is between 1:1 and 1:10 (w/w). The method of claim 1 or 2, wherein the solution is after the seeding step (b), before or during the step (c), or after the second solvent is added in the step (c) The temperature is adjusted to be between 10 ° C and 30 ° C. The method of claim 1 or 2, wherein in step (c), the second solvent is added to the solution over a span of 20 minutes and 24 hours. The method of claim 1 or 2, wherein after the second solvent is added in the step (c), the composition is incubated at a temperature lower than 20 ° C for 10 minutes to 2 days. The method of claim 1 or 2, wherein in the step (d), the crystal contains more than 99% (e.e.) of L-carnitine. The method of claim 1 or 2, wherein in step (d), the crystal is isolated by filtration or deposition. The method of claim 1 or 2, wherein the first solvent is ethanol and the second solvent is acetone.