Preparation and purification method of levocarnitine and intermediate thereof

Abstract

The invention provides a preparation and purification method of (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride, which comprises the following steps: dissolving trimethyl hydrochloride in methanol to obtain a solution, adding S-epichlorohydrin into the solution for reaction, partially or completely removing a reaction solvent after the reaction is finished, and then adding dichloromethane for pulping to remove impurities. According to the technical scheme, high-temperature distillation treatment is not needed, byproducts are few, especially biquaternary ammonium salt impurities grow slowly, hydrolysis impurities and basic toxic impurities such as S-epichlorohydrin can be effectively removed, and medication safety and effectiveness of the levocarnitine product are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of drug synthesis, specifically relating to a method for the preparation and purification of levocarnitine and its intermediates. Background Technology

[0002] L-carnitine, also known as L-(-)-carnitine, was discovered in meat extracts in 1906. It is a compound with multiple physiological functions, such as acting as a carrier in lipid metabolism to transport long-chain fatty acids to mitochondria, and participating in fatty acid oxidation and energy metabolism. It was first approved in the United States in 1985 under the brand name Carnitor for the treatment of acute and chronic carnitine deficiency due to congenital metabolic errors, and for the prevention and treatment of carnitine deficiency in end-stage renal disease patients undergoing dialysis.

[0003] The chemical name of levocarnitine is (R)-3-carboxy-2-hydroxy-N,N,N-trimethyl-1-propylamine hydroxide, inner salt (Formula I), and its structural formula is as follows:

[0004]

[0005] Industrially, (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride is mainly produced by reacting (S)-(+)-epoxychloropropane with trimethylammonium chloride. Levocarnitine is then obtained via cyanidation and hydrolysis. The preparation and purification of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride are crucial steps. Epichlorochloropropane in the reactants readily initiates side reactions such as polymerization and hydrolysis. The former may lead to the formation of bisquaternary ammonium salts. The structure of the hydrolyzed impurities is shown in Formula II, and the structure of the bisquaternary ammonium salts is shown in Formula III.

[0006]

[0007] Both hydrolysis impurities and S-epoxychloropropane are toxic impurities. During subsequent reaction steps, a small portion of them will be converted into general impurities, while the majority will remain in the final product, affecting its medication safety. Therefore, their content must be strictly controlled in the preparation of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride. Numerous studies have published research on the process and purification optimization of this step. Traditional purification methods, such as solvent extraction or vacuum distillation, often lead to an increase in the content of quaternary ammonium salts in the product after high-temperature concentration, and the removal of toxic impurities is not very effective.

[0008] Chinese patent CN102329243A discloses a tubular reaction synthesis method for levocarnitine. This method involves storing a methanol solution of (S)-(+)-epoxychloropropane and an aqueous solution of trimethylamine hydrochloride in two separate tanks. The methanol solution of (S)-(+)-epoxychloropropane and the aqueous solution of trimethylamine hydrochloride are then rapidly mixed using a Y-type jet mixer after being metered by a pump before entering a tubular reactor for reaction. The reaction temperature is controlled between 45-65℃, and the residence time in the tubular reactor is controlled between 4-15 minutes. After the reaction, the reaction solution enters a distillation purification vessel for separation and purification to obtain (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride. The tubular reaction method effectively reduces the formation of byproducts such as bisquaternary ammonium compounds, but this method requires specialized reaction equipment.

[0009] The literature (Synthesis of L-(-)-carnitine, Gu Songlin et al., Synthetic Chemistry, Vol. 12, No. 4, 2004) reports a method for preparing L-carnitine. Trimethylammonium is added to a reaction flask, cooled in an ice-water bath, and concentrated hydrochloric acid is slowly added dropwise with stirring to adjust the pH to 6-7. After reacting for 30 min, the temperature is slowly raised to 40 °C, and epichlorohydrin is added dropwise. After the addition is complete, the reaction is carried out at 40 °C for 3 h. The water is removed by vacuum distillation to obtain the crude product. The crude product is refluxed with methanol to completely dissolve it, then frozen to below 5 °C and filtered. The filter cake is dried to obtain solid (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride.

[0010] Chinese patent CN117776935A discloses a method for preparing (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride. A 50% aqueous solution of trimethylamine hydrochloride is added to a reaction vessel, and the temperature of the reaction vessel is controlled to 10-20°C. An equal mass of water is added and stirred until dissolved. S-epoxychloropropane is then added dropwise to the reaction vessel over approximately 10-14 hours. After the reaction is complete, the reaction solution is transferred to a vacuum distillation vessel to remove water. A vacuum pump is used to stabilize the pressure inside the vessel at -0.08 MPa, and the temperature is controlled at 50°C-65°C until no distillate remains, yielding the (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride product. The product contains 0.09% (R)-3-chloro-2-hydroxypropyltrimethylammonium chloride, 0.36% hydrolysis impurities and trimethylamine, and 0.25% bisquaternary ammonium salt impurities.

[0011] To address the problems existing in traditional processes and overcome operational complexity, it is still necessary to develop an efficient and simple method for preparing (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride with high purity. Summary of the Invention

[0012] The purpose of this invention is, on the one hand, to provide a method for purifying (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride, the method comprising slurrying a crude product containing (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride in an organic solvent B, and filtering to obtain a solid. In some embodiments, the organic solvent B is selected from one or more of hydrocarbon solvents, aromatic solvents, and ketone solvents.

[0013] In some embodiments, the hydrocarbon solvent is dichloromethane, the aromatic solvent is toluene, and the ketone solvent is acetone; dichloromethane is more preferably used.

[0014] In some embodiments, the mass-to-volume ratio of the crude (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride to organic solvent B is 1:1 to 3.

[0015] In some embodiments, the pulping time is 0.5 to 10 hours; preferably, the pulping time is 1 to 4 hours.

[0016] In some embodiments, the pulping temperature is 30°C or below; preferably, the pulping temperature is 20 to 25°C, for example, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, or any value or range thereof.

[0017] In some embodiments, the crude (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride has a purity of 80% or higher, for example, it may be 80%, 85%, 90%, 95% or any of these values.

[0018] In some embodiments, the crude (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride contains one or more of (S)-epoxychloropropane, hydrolyzed impurities, or bisquaternary ammonium salts.

[0019] In some embodiments, the crude (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride contains one or more of the following: (S)-epoxychloropropane 0.01-0.1%, hydrolyzed impurities 5-8%, or bisquaternary ammonium salt 0.5-1%.

[0020] In some embodiments, the crude (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride is obtained by reacting trimethylamine hydrochloride and S-epoxychloropropane in organic solvent A.

[0021] In some embodiments, the reaction temperature is below 30°C, preferably 15–30°C.

[0022] In some embodiments, the organic solvent A is selected from methanol and ethanol, preferably methanol.

[0023] In some embodiments, after the reaction is completed, the reaction solvent A is partially or completely removed at a temperature below 30°C.

[0024] In some embodiments, the reaction solvent A is removed by azeotropic reaction with reaction solvent B.

[0025] Another aspect of the present invention provides a method for preparing (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride, the method comprising the following steps:

[0026] Step 1: Dissolve the trimethyl hydrochloride solid in organic solvent A to obtain a solution;

[0027] Step 2: Add S-epoxychloropropane to the solution obtained in Step 1 to carry out the reaction;

[0028] Step 3: After the reaction is completed, the (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride is obtained by post-processing.

[0029] In some embodiments, the reaction temperature is below 30°C, preferably between 15°C and 30°C.

[0030] In some embodiments, the organic solvent A is selected from methanol and ethanol, preferably methanol.

[0031] In some embodiments, the mass-to-volume ratio of S-epoxychloropropane, trimethyl hydrochloride solid, and organic solvent A is 1:0.95 to 1.1:1 to 5, preferably 1:1.01 to 1.05:1.5 to 3.

[0032] In some embodiments, S-epoxychloropropane can be added in batches in step 2, wherein 10-50% of the total amount of S-epoxychloropropane is first added to the solution obtained in step 1, and then the remaining amount is added dropwise to the solution.

[0033] In some embodiments, after the reaction in step 3 is completed, the reaction solvent is partially or completely removed, and then the mixture is pulped in organic solvent B and filtered to obtain a solid. This step can be repeated once or more, for example, twice, three times or four times.

[0034] In some embodiments, the organic solvent B in step 3 is dichloromethane, wherein the amount of organic solvent B is 2 to 4 times the volume of S-epoxychloropropane, the stirring temperature is 20 to 25°C, and the stirring time is 1 to 4 hours.

[0035] Another aspect of the present invention provides (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride, wherein the (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride has an HPLC purity of ≥99.8%.

[0036] In some embodiments, the content of hydrolysis impurities in the (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride is not greater than 50 ppm; the content of S-epoxychloropropane is not greater than 1 ppm; and the content of bisquaternary ammonium salt impurities is not greater than 0.2%; wherein the impurity content is determined by external standard method.

[0037] In some embodiments, the (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride contains 10-40 ppm of hydrolysis impurities; 0.01-0.5 ppm of S-epoxychloropropane; and 0.01-0.1% of bisquaternary ammonium salt impurities.

[0038] A third aspect of the present invention provides a method for preparing levocarnitine, wherein levocarnitine is prepared by cyanidation and hydrolysis of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride obtained according to the present invention.

[0039] A fourth aspect of the present invention provides a levocarnitine, wherein the levocarnitine contains a total amount of toxic impurities of less than 15 ppm, said toxic impurities being (S)-(+)-epoxychloropropane and hydrolytic impurities of formula II; preferably less than 10 ppm, more preferably less than 2.5 ppm, and even undetectable.

[0040] Compared with the prior art, the positive technical effects achieved by the present invention are as follows:

[0041] 1. The method for preparing (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride provided by the present invention does not require high-temperature distillation, has a high reaction yield, few by-products, and slow growth of quaternary ammonium salt impurities. The reagents are green and environmentally friendly, making it suitable for large-scale industrial production.

[0042] 2. The (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride and its purification method provided by the present invention can effectively remove hydrolytic impurities and S-epoxychloropropane and other toxic impurities. The method is simple to operate and low in cost.

[0043] 3. The L-carnitine and its preparation method provided by this invention reduce the risk of further residues in the final product by controlling the generation of hydrolysis impurities and the residues of toxic impurities in key steps, thus ensuring the safety and effectiveness of the product. Detailed Implementation

[0044] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0045] All ranges described in this invention include the endpoints of the range between two values, whether or not indicated. All values ​​listed in this invention include the degree of expected experimental error, technical error, and instrumental error of the given technique used to measure that value. When the degree of error is not stated, all values ​​listed in this invention encompass a range of ±10% of the stated value.

[0046] In this invention, unless otherwise stated, % is a percentage of weight / weight (w / w).

[0047] In this invention, the terms "organic solvent A" and "organic solvent B" actually still refer to organic solvents, and A and B are only used to distinguish them as organic solvents used in different reactions.

[0048] In this invention, "mass-volume ratio" is the ratio of the volume (ml) of the reaction solvent to the weight (g) of the reaction raw materials.

[0049] Unless otherwise specified, all materials used in this invention are commercially available.

[0050] The GC-MS analysis method used for the content of related substances in (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride of this invention is as follows:

[0051] Instruments: Gas chromatograph equipped with detector, CTC injector, 5975MS detector

[0052] Column: Agilent VF624ms (30m x 0.25mm x 1.4um)

[0053] Inlet temperature: 260℃

[0054] Flow split ratio: 5:1

[0055] Column temperature: Initial temperature 50℃, hold for 5 min; then increase to 140℃ at a rate of 20℃ / min, hold for 0 min; then increase to 165℃ at a rate of 5℃ / min, hold for 0 min.

[0056] MS conditions

[0057] Ion source temperature: 230℃

[0058] Quadrupole temperature: 150℃

[0059] Data acquisition time: 6 min – 14.5 min

[0060] Example 1: Preparation of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride

[0061] Add 51.6 g of trimethylamine hydrochloride and 100 mL of methanol to the reaction flask, stir to dissolve, and then add 16.6 g of (S)-epimchlorohydrin. Maintain the temperature at 25℃±2℃ and add 33.3 g of (S)-epimchlorohydrin dropwise over 3 hours. After the addition is complete, maintain the temperature at 25℃±2℃ for 3-4 hours. After the reaction is complete, concentrate the reaction solution at 20℃-30℃ to 2.6-2.8 times the weight of (S)-epimchlorohydrin added. Add 100 mL of dichloromethane and concentrate to 3.0-3.2 times the weight of (S)-epimchlorohydrin. Repeat this process three times. At 20℃-25℃, add 150mL of dichloromethane, slurry for 1-2 hours, filter, and wash the filter cake with 50mL of dichloromethane. At 20℃-25℃, add 150mL of dichloromethane to the solid, slurry for 1-2 hours, filter, and wash the filter cake with 50mL of dichloromethane. Dry the solid under reduced pressure at 60℃ to obtain 85.4g with a purity of 99.9%, including 32.8ppm of hydrolytic impurities, 0.04ppm of S-epimeric chloropropane, and 0.01% of bisquaternary ammonium salt impurities.

[0062] Example 2:

[0063] Preparation of L-carnenitrile

[0064] Add 50g of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride and 950ml of methanol to a reaction flask, stir to dissolve, add sodium cyanide in three batches, heat to 55±2℃, and maintain the temperature for 7-9h. After the reaction is complete, add 2% activated carbon and stir for 0.5h to decolorize, filter, wash with 50ml of methanol, concentrate the reaction solution at 25-30℃ to 2.5-3.0 times the weight of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride, slurry at 40-45℃ for 0.5h, cool to 0-5℃ and stir for 0.5-1h, filter, wash with 100ml of ethanol, and dry at 60℃. The yield is 89% and the purity is 99.8%.

[0065] Example 3

[0066] Preparation of L-carnitine

[0067] Add 50g of intermediate B to the reaction flask, add 100ml of concentrated hydrochloric acid, heat to 65±2℃, maintain the temperature for 8-10h, cool to 20-25℃, add 180ml of purified water to dissolve, add 2% activated carbon and stir for 0.5h to decolorize, filter, add 30% sodium hydroxide aqueous solution to adjust the pH to 6-6.5, perform electrodialysis to remove salt, concentrate the reaction solution at 65℃ until there are almost no distillates, add 125ml of ethanol to dissolve, dissolve at 50-55℃, add 400ml of acetone to induce crystallization, cool to 0-5℃ and stir for 1-2h, filter, dry the material, yield 70%; purity: 99.9%, hydrolysis impurities and S-epimchlorohydrin were not detected.

[0068] Example 4:

[0069] Preparation of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride

[0070] Add trimethylamine hydrochloride (31g) and methanol (60mL) to the reaction flask, stir to dissolve, and add (S)-epimchlorohydrin (10g). Maintain the temperature at 25℃±2℃, and add (S)-epimchlorohydrin (20g) dropwise over 3 hours. After the addition is complete, maintain the temperature at 25℃±2℃ for 3-4 hours. After the reaction is complete, concentrate the reaction solution to 2.6-2.8 times the weight of S-epimchlorohydrin at 20℃-30℃. Add dichloromethane (60mL) and concentrate to 3.0-3.2 times the weight of S-epimchlorohydrin, repeating 3 times. Add dichloromethane (90mL) at 20℃-25℃, slurry for 1-2 hours, filter, and wash the filter cake with dichloromethane (30mL). The solid was dried under reduced pressure at 60°C to obtain 50.5g of a purity of 99.8%, with hydrolysis impurities of 14.6ppm, S-epoxychloropropane content of 0.15ppm, and bisquaternary ammonium salt impurity content of 0.08%.

[0071] Example 5:

[0072] Preparation of (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride

[0073] Trimethylamine hydrochloride (31 g) and methanol (60 mL) were added to a reaction flask and stirred to dissolve. Then, (S)-epimchlorohydrin (10 g) was added. The temperature was maintained at 25℃±2℃, and (S)-epimchlorohydrin (20 g) was added dropwise over 3 hours. After the addition was complete, the reaction mixture was kept at 25℃±2℃ for 3-4 hours. After the reaction was complete, the reaction solution was concentrated to dryness at 20℃-30℃ to obtain 55 g of crude product with a purity of 93.8%, a hydrolysis impurity content of 5.6%, an S-epimchlorohydrin content of 0.09%, and a bisquaternary ammonium salt impurity content of 0.53%.

[0074] The crude product was then added to dichloromethane (60 mL) and concentrated to 3.0-3.2 times the weight of S-epimchloropropane, repeated three times. At 20-25°C, dichloromethane (90 mL) was added, and the mixture was stirred for 1-2 hours, filtered, and the filter cake was washed with DCM (30 mL). At 20-25°C, DCM (90 mL) was added to the solid, and the mixture was stirred for 1-2 hours, filtered, and the filter cake was washed with DCM (30 mL). The solid was dried under reduced pressure at 60°C to obtain 46 g of product with a purity of 99.8%, containing 35.1 ppm of hydrolytic impurities and 0.32 ppm of S-epimchloropropane. No quaternary ammonium salt impurities were detected.

[0075] The specific embodiments described in this invention are merely illustrative of the spirit of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A process for purifying (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride, characterized in that, The method comprises beating the (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride crude product in an organic solvent B, and filtering to obtain a solid.

2. The method of claim 1, wherein, The organic solvent B is selected from one or more of a hydrocarbon solvent, an aromatic hydrocarbon solvent and a ketone solvent; preferably, the hydrocarbon solvent is dichloromethane, the aromatic hydrocarbon solvent is toluene, and the ketone solvent is acetone; further preferably, the organic solvent B is dichloromethane.

3. The method of claim 1, wherein, The mass-volume ratio of the (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride crude product to the organic solvent B is 1:1-3.

4. The method of claim 1, wherein, The beating time is 0.5-10 hours, and the beating temperature is 30°C or lower; preferably, the beating time is 1-4 hours, and the beating temperature is 20-25°C.

5. The method of claim 1, wherein, The (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride crude product is obtained by reacting trimethylamine hydrochloride and S-epichlorohydrin in an organic solvent A.

6. The method of claim 1, wherein, The reaction temperature is 30°C or lower, the organic solvent A is selected from methanol and ethanol, and part or all of the reaction solvent A is removed at 30°C or lower after the reaction is completed; preferably, the reaction temperature is 15-30°C, the organic solvent A is methanol, and the reaction solvent A is removed by azeotropy with the reaction solvent B after the reaction is completed.

7. A process for the preparation of (S)-3-chloro-2-hydroxypropyl trimethylammonium chloride, characterized in that, The method comprises the following steps: Step 1: dissolving trimethylamine hydrochloride solid in an organic solvent A to obtain a solution; Step 2: adding S-epichlorohydrin to the solution obtained in Step 1 to react; Step 3: obtaining the (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride by post-treatment after the reaction is completed.

8. The method of claim 7, wherein, The reaction temperature is 30°C or lower, the organic solvent A is selected from methanol and ethanol, and the mass-volume ratio of the S-epichlorohydrin, the trimethylamine hydrochloride solid and the organic solvent A is 1:0.95-1.1:1-5; preferably, the reaction temperature is 15-30°C, the organic solvent A is methanol, and the mass-volume ratio of the S-epichlorohydrin, the trimethylamine hydrochloride solid and the organic solvent A is 1:1.01-1.05:1.5-3.

9. The preparation method according to claim 7, characterized in that, In Step 2, the S-epichlorohydrin is added in batches, wherein 10-50% of the total amount of the S-epichlorohydrin is first added to the solution obtained in Step 1, and the remaining amount is added dropwise to the solution.

10. The method of claim 7, wherein, After Step 3, part or all of the reaction solvent A is removed, and then beating in an organic solvent B and filtering a solid are performed.

11. The preparation method according to claim 7, characterized in that, The organic solvent B is dichloromethane, and the amount of the organic solvent B is 2-4 times the volume of the S-epichlorohydrin; the stirring temperature is 20-25°C, and the stirring time is 1-4 hours.

12. A (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride, wherein the (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride HPLC purity is > 99.8%, characterized in that, The content of the hydrolysis impurity in the (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride is not more than 50 ppm, the content of the S-epichlorohydrin is not more than 1 ppm, and the content of the bis-quaternary ammonium salt impurity is not more than 0.2%; wherein the impurity content is determined by an external standard method, the hydrolysis impurity is shown as Formula II, and the bis-quaternary ammonium salt impurity is shown as Formula III, 13. (S)-3-chloro-2-hydroxypropyltrimethylammonium chloride according to claim 12, characterized in that The content of the hydrolysis impurity in the (S)-3-chloro-2-hydroxypropyl trimethyl ammonium chloride is 10-40 ppm, the content of the S-epichlorohydrin is 0.01-0.5 ppm, and the content of the bis-quaternary ammonium salt impurity is 0.01-0.1%.

14. A process for the preparation of levocarnitine, characterized in that, The (S)-3-chloro-2-hydroxypropyl trimethylammonium chloride obtained by the method according to any one of claims 1-13 is prepared into Levemiracetam by cyanation reaction and hydrolysis reaction.

15. Levocarnitine, characterized in that, The Levemiracetam contains less than 15 ppm of total amount of toxic impurities, wherein the toxic impurities are (S)-(+)-epichlorohydrin and hydrolysis impurities of formula II; preferably less than 10 ppm, more preferably less than 2.5 ppm, and even not detected.

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