A method for refining levodopa

Abstract

This invention provides a method for refining levodopa. The method includes dissolving crude levodopa in an acidic aqueous solution under antioxidant protection, crystallizing at low temperature to obtain needle-like levodopa crystals, filtering, and then slurrying the filter cake in high-temperature purified water to obtain flake-like levodopa crystals. The filtered and dried products yield refined levodopa. The refining method provided by this invention effectively removes water-soluble impurities from crude levodopa through crystal transformation during the high-temperature purified water slurry process, resulting in a high-content, high-bulk-density refined levodopa. This refining method is suitable for large-scale production, and the obtained levodopa exhibits excellent crystal morphology.

Description

Technical Field

[0001] This invention relates to a method for refining levodopa, belonging to the field of pharmaceutical technology. Background Technology

[0002] In 1970, Roche's levodopa was approved for marketing in the United States. Levodopa has been used to treat Parkinson's disease for nearly 50 years and remains the most effective drug for the disease. Levodopa can cross the blood-brain barrier and enter the brain, where it is decarboxylated by dopamine to exert its effect.

[0003] There are several methods for preparing levodopa, including chemical methods, enzymatic synthesis, microbial fermentation, and plant extraction. To achieve the quality standards of the active pharmaceutical ingredient, levodopa generally requires further purification after synthesis or extraction using these methods.

[0004] L-DOPA is an amino acid compound with an isoelectric point of 3.5. It is highly soluble in strong acid or strong alkaline solutions but insoluble in organic solvents such as ethanol and dichloromethane. The ortho-diphenol hydroxyl group in the L-DOPA molecule is stable under acidic conditions but is easily oxidized to dopaquinone under neutral and alkaline conditions, ultimately converting into melanin. Therefore, the purification of crude L-DOPA generally involves dissolving it under acidic conditions and then purifying it through methods such as column chromatography, isoelectric point crystallization, or cooling crystallization.

[0005] Levodopa finished products exist in various dosage forms: tablets, capsules, etc. Each dosage form has different requirements for the physical properties of the API (bulk density, tap density, angle of repose, etc.) during production. In order to maintain the stability of the production process, each formulation manufacturer puts forward its own requirements for the physical properties of the API.

[0006] US3592843A (1971) reported a purification method for levodopa (L-DOPA) to remove its isomer (D-DOPA). This method involves decolorizing crude levodopa under nitrogen protection and the protection of the antioxidant vitamin C, dissolving it in approximately 40 times its weight of boiling water, cooling to room temperature, stirring to crystallize for 20 hours, and then drying. Alternatively, crude levodopa can be slurried in an aqueous solution of methanol or other alcohols at room temperature for 2 days. Taking advantage of the good solubility of D-DOPA in aqueous alcohol solutions, D-DOPA is removed by slurrying. This method can yield levodopa with a purity close to 100%, but it generates a large amount of wastewater and has a long production cycle, making it unsuitable for large-scale production. Furthermore, current enzyme-catalyzed synthesis processes have achieved large-scale production, effectively eliminating the production of the D-DOPA isomer impurity.

[0007] CN106946721B reports a method for simultaneously extracting high-purity tyrosine and levodopa from cat's bean. The recrystallization steps are as follows: crude levodopa is added to an acidic alcoholic aqueous solution, stirred and dissolved at room temperature, filtered, the pH is adjusted with alkali, cryo-crystallized, filtered, and vacuum dried. The cryo-crystallization temperature is 5–10°C, and the crystallization time is 6–12 hours. This method is suitable for purifying crude levodopa obtained by extraction. However, when levodopa is synthesized using pyruvate or sodium pyruvate as raw materials via enzymatic catalysis, this recrystallization method, employing low-temperature (5–10°C) crystallization, cannot effectively remove residual pyruvate. The product obtained by this method has a bulk density of only 0.40, while some levodopa formulation manufacturers (such as Mylan) require a bulk density of over 0.60 when purchasing APIs.

[0008] CN109485581A reports a method for purifying levodopa. The recrystallization steps are as follows: levodopa is added to 8 times its weight of 0.2 mol / L hydrochloric acid to adjust the pH to 1.0, and heated to 55°C to dissolve. The mixture is then cooled to allow levodopa crystals to precipitate, which are collected and dried to obtain refined levodopa. This method has a very low yield because the main factor affecting the solubility of levodopa is pH; levodopa is readily soluble in strong acids and bases, and temperature has little effect on solubility. Therefore, this method is suitable for preparing small quantities of high-purity samples but not for large-scale production.

[0009] CN107382760B reports a method for the separation and purification of levodopa: levodopa is dissolved under alkaline conditions under the protection of an antioxidant (vitamin C), and then acetic acid is added at 2–7°C to bring the pH to 3–5. This method inhibits oxidation by adding an antioxidant. However, in planned production, to increase batch size and reduce wastewater, dissolution under strong alkalinity is required to obtain a high-concentration levodopa solution. This necessitates a large amount of antioxidant, which can lead to excessive residues or impurities in the final levodopa solution.

[0010] After long-term research, the inventors discovered that when using crystallization to remove impurities, crystallization is generally carried out at low temperatures (0-10℃) to improve the yield. Further research revealed that:

[0011] 1) Crystallization at low temperatures (0–10°C) yields needle-shaped crystals. The bulk density of levodopa in this crystalline state is low, at around 0.40 g / mL, making it unsuitable for capsule production. Furthermore, according to the European Pharmacopoeia, the titration content is only at 99.2% (the required level is 99.0–101.0%), posing a risk of non-compliance.

[0012] 2) When crystallized at high temperature (approximately 40°C), irregular flaky crystals are obtained. The bulk density of levodopa in this crystalline state is relatively high, at the level of 0.50 g / mL. However, according to the EU Pharmacopoeia testing, the pH value is 4.5–4.8 (the required value is 4.5–7.0), which poses a risk of non-compliance. This is likely because a small amount of acid is trapped within the crystals during the high-temperature crystallization process.

[0013] 3) XRD patterns show that the needle-like crystals and plate-like crystals mentioned above belong to the same type of amorphous crystals, only with different crystal habits. Summary of the Invention

[0014] Based on our long-term research on the effect of crystallization temperature on crystal habit and impurities, this invention provides a purification method for levodopa that is suitable for large-scale production and can obtain high bulk density (≥0.60 g / mL) and high titration content (≥99.5%).

[0015] A method for refining levodopa specifically includes the following steps:

[0016] a. Dissolution: Take crude levodopa, add it to purified water, add antioxidant, add acid to adjust the pH of the solution to 0-1.5, and stir until dissolved;

[0017] b. Low-temperature crystallization: Cool the dissolved solution from step a to 0-15℃, add alkali to adjust the pH of the solution to 3.0-5.0, stir to induce crystallization, and filter.

[0018] c. High-temperature pulping: The filter cake obtained in step b is put into purified water, antioxidants are added, the temperature of the liquid is controlled, the mixture is stirred to crystallize, the temperature is lowered to 0-15℃, and then filtered.

[0019] d. Drying: The filter cake from the previous step is dried to obtain the refined L-DOPA product. Electron microscopy shows that the resulting crystals are regular square plate-like crystals.

[0020] Preferably, the crude levodopa in step a is prepared by the following method: levodopa is synthesized by catalysis of catechol, pyruvic acid and ammonia with tyrosine phenol lyase, dissolved in acid, filtered, and the filtrate is crystallized with alkali and then filtered again to obtain crude levodopa.

[0021] Preferably, the acid in step a includes, but is not limited to, hydrochloric acid, nitric acid, dilute sulfuric acid, formic acid, or acetic acid, and more preferably hydrochloric acid or sulfuric acid.

[0022] Preferably, the antioxidants in steps a and c include, but are not limited to, vitamin A, vitamin E, vitamin C, or sodium sulfite, with vitamin C being more preferred.

[0023] Preferably, in step a, the weight-to-volume ratio (g / mL) of crude levodopa to purified water is 1:5 to 1:15.

[0024] Preferably, in step a, the weight ratio of crude levodopa to antioxidant is 50:1 to 200:1.

[0025] Preferably, the alkali in step b includes, but is not limited to: sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, triethylamine, or DBU, and more preferably sodium hydroxide or sodium carbonate.

[0026] Preferably, in step c, the weight-to-volume ratio (g / mL) of the filter cake to the purified water is 1:5 to 1:15.

[0027] Preferably, the weight ratio of filter cake to antioxidant in step c is 50:1 to 200:1.

[0028] Preferably, the stirring and crystallization speed in steps b and c is 30–90 rpm.

[0029] Preferably, the stirring time in step c is determined according to the crystal transformation rate. The crystals are completely transformed into plate-like crystals, and the time is controlled in the range of 10 to 120 minutes. Studies have shown that the higher the temperature, the faster the transformation rate.

[0030] Preferably, the temperature of the liquid material in step c is controlled at 40-90°C. Studies have shown that the higher the temperature, the faster the needle-like crystals transform into plate-like crystals. To balance production efficiency and energy consumption, a further preferred temperature is 60-70°C.

[0031] Currently, the refining method used in large-scale production involves dissolving the crude product in an acidic aqueous solution, then adding alkali to adjust the pH to the isoelectric point for crystallization. Low-temperature crystallization is ineffective at removing pyruvic acid impurities, and the product's pH value and titration content are at the lower limit of the European Pharmacopoeia standard, posing a quality risk. Regardless of whether it's high or low temperature, crystals precipitate rapidly during alkali crystallization, trapping some impurities within them. Unlike ordinary pulping processes, levodopa undergoes a crystal habit transformation process during high-temperature pulping, effectively releasing impurities trapped within the crystals during crystallization.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. This invention uses low-temperature crystallization followed by high-temperature pulping, which can effectively remove impurities trapped in the crystals during crystallization. At the same time, the bulk density of the product is significantly higher than that of the product obtained by low-temperature crystallization, which can meet the needs of formulation customers with special requirements for bulk density.

[0034] 2. The refining method provided by this invention can effectively remove water-soluble impurities from crude levodopa through crystal transformation during the high-temperature purified water pulping process, and obtain levodopa refined product with high content and high bulk density. This refining method is suitable for large-scale production, and the obtained levodopa has a good crystal morphology.

[0035] 3. The refining method provided by this invention has no special requirements for equipment or special raw materials, is suitable for large-scale production, and uses water as a solvent, which is environmentally friendly. Attached Figure Description

[0036] Figure 1 The irregular sheet-like crystals prepared in Comparative Example 1 are shown.

[0037] Figure 2 The needle-like crystals prepared in Comparative Example 3 are shown.

[0038] Figure 3 The regular square-shaped plate-like crystals prepared in Example 1. Detailed Implementation

[0039] The following specific preparation examples are provided to illustrate the present invention in detail. These examples are for more detailed and specific explanation only and are not intended to limit the present invention in any way.

[0040] Reference Example 1: Preparation of crude levodopa.

[0041] 3000 mL of water, 140 g of catechol, 117.1 g of pyruvic acid, 165 g of 25% ammonia, 70 g of ammonium acetate, 3 g of pyridoxal 5-phosphate, and 500 g of tyrosine phenol lysin solution were added to a reaction vessel. The mixture was kept at 25 °C until the catechol was essentially completely reacted. Hydrochloric acid was added to adjust the pH to 1.0, and 2 g of activated carbon was added. The mixture was stirred at 30 °C for 30 minutes and then filtered. Sodium hydroxide solution was added to the filtrate to adjust the pH to 4.0, and the temperature was lowered to 10 °C. The mixture was then filtered and dried to obtain crude levodopa. The obtained crude levodopa was pale yellow in color, with an HPLC purity of 99.50% and a titration content of 98.9%.

[0042] Comparative Example 1:

[0043] In a four-necked flask, 10g of crude levodopa, 100mL of drinking water, and 0.1g of vitamin C were added. The temperature of the solution was controlled at 20-40℃. Hydrochloric acid was added dropwise until the pH of the solution reached 0.8, and the solution was stirred until dissolved. The temperature of the solution was controlled at 45±2℃, and the stirring speed was 120rpm. Sodium hydroxide solution was added dropwise until the pH of the solution reached 3.5, and the solution was stirred for 30 minutes. The temperature was then lowered to 5℃. The solution was filtered and dried to obtain purified levodopa, with a yield of 91.5%. The obtained purified levodopa was off-white, with an HPLC purity of 99.95%, a titration content of 99.3%, a pH of 4.6, and a bulk density of 0.55g / mL. Electron microscopy revealed that the obtained crystals were irregularly shaped plate-like crystals, such as... Figure 1 As shown.

[0044] Comparative Example 2:

[0045] In a four-necked flask, 10g of crude levodopa, 100mL of drinking water, and 0.1g of vitamin C were added. The temperature of the solution was controlled at 20-40℃. Sulfuric acid solution was added dropwise until the pH of the solution reached 0.7, and the solution was stirred until dissolved. The temperature of the solution was controlled at 30±2℃, and the stirring speed was 120rpm. Potassium hydroxide solution was added dropwise until the pH of the solution reached 3.8, and the solution was stirred for 30 minutes. The temperature was then lowered to 5℃. The solution was filtered and dried to obtain purified levodopa, with a yield of 91.0%. The obtained purified levodopa was off-white, with an HPLC purity of 99.93%, a titration content of 99.1%, a pH of 4.5, and a bulk density of 0.50g / mL. Electron microscopy revealed that the obtained crystals were irregularly shaped flaky crystals.

[0046] Comparative Example 3:

[0047] 10g of crude levodopa, 100mL of drinking water, and 0.1g of vitamin C were added to a four-necked flask. The temperature of the solution was controlled at 20-40℃. Sulfuric acid solution was added dropwise until the pH of the solution reached 0.7, and the mixture was stirred until dissolved. The temperature of the solution was controlled at 5±2℃, and the stirring speed was 120rpm. Potassium hydroxide solution was added dropwise until the pH of the solution reached 3.7, and the mixture was stirred for 30 minutes. The solution was filtered and dried to obtain purified levodopa, with a yield of 90.5%. The obtained purified levodopa was off-white, with an HPLC purity of 99.80%, a titration content of 99.5%, and a bulk density of 0.43g / mL. Electron microscopy revealed that the obtained crystals were needle-like. Figure 2 As shown.

[0048] Example 1:

[0049] In a four-necked flask, 10g of crude levodopa, 100mL of drinking water, and 0.1g of vitamin C were added. The temperature of the solution was controlled at 20-40℃. Sulfuric acid solution was added dropwise until the pH of the solution reached 0.8, and the solution was stirred until dissolved. The temperature of the solution was controlled at 7±2℃ and the stirring speed at 60rpm. Potassium hydroxide solution was added dropwise until the pH of the solution reached 3.4, and the solution was stirred for 30 minutes. The solution was filtered, and the filter cake was added to 50mL of purified water. 0.1g of vitamin C was added, and the temperature was raised to 65℃, and the solution was stirred for 30 minutes. The solution was cooled to 4℃, filtered, and dried to obtain purified levodopa with a yield of 89.5%. The obtained purified levodopa was white, with an HPLC purity of 99.97%, a titration content of 99.8%, a pH of 5.3, and a bulk density of 0.60g / mL. Electron microscopy showed that the obtained crystals were regular square plate-like crystals. Figure 3 As shown.

[0050] Example 2

[0051] In a four-necked flask, add 10g of crude levodopa, 100mL of drinking water, and 0.1g of vitamin C. Maintain the temperature of the solution at 20-40℃, and add hydrochloric acid dropwise until the pH reaches 0.8, stirring until dissolved. Maintain the temperature at 5±2℃ and the stirring speed at 90rpm, and add sodium hydroxide solution dropwise until the pH reaches 3.5, stirring for 30 minutes, then filter. Prepare 50mL of purified water, heat to 70℃, add the filter cake from the previous step and 0.1g of vitamin C, and stir for 10 minutes. Cool the solution to 10℃, filter, and dry to obtain purified levodopa with a yield of 90.0%. The obtained purified levodopa is white, with an HPLC purity of 99.96%, a titration content of 99.9%, a pH of 5.5, and a bulk density of 0.65g / mL.

[0052] Example 3

[0053] In a four-necked flask, add 10g of crude levodopa, 100mL of drinking water, and 0.1g of vitamin C. Maintain the temperature of the solution at 20-40℃, and add sulfuric acid dropwise until the pH reaches 0.8, stirring until dissolved. Maintain the temperature at 5±2℃ and the stirring speed at 90rpm, and add sodium carbonate solution dropwise until the pH reaches 3.5, stirring for 30 minutes, then filter. Prepare 50mL of purified water, heat to 50℃, add the filter cake from the previous step and 0.1g of vitamin C, and stir for 10 minutes. Cool the solution to 10℃, filter, and dry to obtain purified levodopa with a yield of 90.0%. The obtained purified levodopa is white, with an HPLC purity of 99.98%, a titration content of 99.7%, a pH of 5.5, and a bulk density of 0.62g / mL.

Claims

1. A method for refining levodopa, characterized in that... Specifically, the following steps are included: a. Dissolution: Take crude levodopa, add it to purified water, add antioxidant, add acid to adjust the pH of the solution to 0~1.5, and stir until dissolved; b. Low-temperature crystallization: Cool the dissolved solution from step a to 0~15℃, add alkali to adjust the pH of the solution to 3.0~5.0, stir to induce crystallization, and filter. c. High-temperature pulping: Add the filter cake obtained in step b to purified water, add antioxidant, control the temperature of the liquid at 40~90℃, stir to precipitate crystals, cool to 0~15℃, and filter. d. Drying: The filter cake from the previous step is dried to obtain the refined L-DOPA product. Electron microscopy shows that the resulting crystals are regular square plate-like crystals.

2. The method for refining levodopa according to claim 1, characterized in that... In step a, crude levodopa is prepared by the following method: catechol, pyruvic acid and ammonia are synthesized into levodopa by tyrosine phenol lyase catalysis, dissolved in acid, filtered, the filtrate is crystallized by adding alkali, and then filtered again to obtain crude levodopa.

3. The method for refining levodopa according to claim 1, characterized in that... The acid used in step a is selected from hydrochloric acid or dilute sulfuric acid.

4. The method for refining levodopa according to claim 1, characterized in that... The antioxidants in steps a and c include: vitamin A, vitamin E, vitamin C, or sodium sulfite.

5. The method for refining levodopa according to claim 4, characterized in that... The antioxidants used in steps a and c are selected from vitamin C.

6. The method for refining levodopa according to claim 1, characterized in that... In step a, the weight-to-volume ratio of crude levodopa to purified water is 1:5 to 1:15 (g / ml).

7. The method for refining levodopa according to claim 1, characterized in that... In step a, the weight ratio of crude levodopa to antioxidant is 50:1 to 200:

1.

8. The method for refining levodopa according to claim 1, characterized in that... The alkali used in step b includes: sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, and sodium bicarbonate.

9. The method for refining levodopa according to claim 8, characterized in that... The alkali used in step b is selected from sodium hydroxide or sodium carbonate.

10. The method for refining levodopa according to claim 1, characterized in that... In step c, the weight-to-volume ratio of filter cake to purified water is 1:5 to 1:15 (g / ml); the weight ratio of filter cake to antioxidant in step c is 50:1 to 200:

1.

11. The method for refining levodopa according to claim 1, characterized in that... The stirring speed for crystallization in steps b and c is 30-90 rpm; the stirring time in step c is controlled within the range of 10-120 min.

12. The method for refining levodopa according to claim 1, characterized in that, In step c, the temperature of the liquid feed is controlled at 60~70℃.

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