Preparation method for pharmaceutical-grade sodium 3-hydroxybutyrate

Abstract

A method for preparing pharmaceutical-grade sodium 3-hydroxybutyrate, the method comprising the following steps: A, hydrolyzing methyl(ethyl) 3-hydroxybutyrate at 55°C to 60°C by using sodium hydroxide, so as to obtain a sodium 3-hydroxybutyrate crude product; B, dissolving the crude product obtained in step A with methanol and water, adding an addition catalyst thereto, and maintaining the temperature at 20°C-30°C for reaction, so as to obtain an addition reaction product; and C, filtering the reaction liquid from step B, subjecting the mother liquid to reduced pressure distillation, and removing methanol by means of evaporation until the mother liquid is thick; and adding acetone thereto for crystallization, and cooling, filtering and drying the mixture, so as to obtain a finished product. The content of crotonic acid in the sodium 3-hydroxybutyrate prepared by means of the method is not higher than 16 ppm, and the content of sodium 3-hydroxybutyrate reaches 99.5% or above.

Description

Method for preparing medical grade sodium 3-hydroxybutyrate TECHNICAL FIELD

[0001] The present application belongs to the field of fine chemical technology, and particularly relates to a method for preparing medical grade sodium 3-hydroxybutyrate. BACKGROUND

[0002] Sodium 3-hydroxybutyrate is also known as sodium beta-hydroxybutyrate, DL-3-hydroxybutyric acid sodium, and is simply referred to as BHB sodium salt. It has been widely used as a dietary supplement ingredient for supplementing ketones. It is a stable sodium salt supplier for 3-hydroxybutyric acid, which can provide energy for the brain, heart and muscles in the absence of glucose and under low-carbohydrate intake.

[0003] In recent years, in the medical field, sodium 3-hydroxybutyrate has also been used for the treatment of brain dysfunction, glutaric aciduria type II and other diseases.

[0004] The conventional preparation method of sodium 3-hydroxybutyrate is to use methyl (or ethyl) 3-hydroxybutyrate as the main raw material, and to perform hydrolysis under the action of sodium hydroxide, followed by decolorization, pressure filtration, concentration, and spray drying to obtain the finished product. However, the main disadvantage of the product prepared by this method is high impurity content, which is mainly due to the following reasons: 1. In the process of hydrolysis and salt formation, whether strong base sodium hydroxide or other sodium salts are used, the production of crotonate is inevitable, and this by-product will cause certain harm to the human body. 2. The use of conventional chemical raw materials inevitably introduces some heavy metal ions, resulting in excessive content. 3. The use of spray drying results in many types of impurities and high residue.

[0005] Medical grade sodium 3-hydroxybutyrate needs to meet the requirements of high main product content, low impurity content, and low heavy metal content. Since the sodium 3-hydroxybutyrate prepared by the existing technology has high impurity content, it is difficult to meet the basic requirements, and additional purification processes must be performed in several steps to be used in medicine. Each step of purification will cause product loss, reduce the total yield of the finished product, and result in high cost. SUMMARY

[0006] In order to overcome the above-mentioned defects of the prior art method for preparing high-purity sodium 3-hydroxybutyrate, we have innovated the hydrolysis process, and through the control of raw materials and the separation and purification method of the product, medical grade sodium 3-hydroxybutyrate product can be prepared in the shortest process route, the yield is significantly improved, and the production cost of medical grade sodium 3-hydroxybutyrate is significantly reduced. Specifically, the present application provides the following technical scheme.

[0007] A method for preparing medical grade sodium 3-hydroxybutyrate, comprising the following steps:

[0008] A. Hydrolysis reaction: 3-hydroxybutyric acid methyl (ethyl) ester, methyl (ethyl) alcohol, water are added into the reactor; the temperature is kept at 15-45°C, more preferably 20-40°C, more preferably 25-30°C, sodium hydroxide is added in batches, the temperature is raised to 45-70°C, preferably 50-65°C, more preferably 55-60°C, and the hydrolysis reaction is carried out, after cooling, 3-hydroxybutyric acid sodium is precipitated, filtered, washed, and dried to obtain 3-hydroxybutyric acid sodium crude product; wherein the alcohol (methanol or ethanol) can be added with water, if water-containing alcohol is used directly, such as 95% ethanol, water does not need to be added additionally.

[0009] B. Addition reaction: the crude product obtained in step A is added into the reactor, an appropriate amount of alcohol solvent and water are added, after dissolution, the addition product is added, and the reaction is carried out at 15-40°C, preferably 18-35°C, more preferably 20-30°C, to obtain the addition reaction product;

[0010] C. Purification: the reaction liquid of step B is filtered to remove a small amount of insoluble matter; the mother liquor is distilled under reduced pressure, and the alcohol is distilled off until it is thick; acetone is added for crystallization, preferably acetone is slowly added, such as dropwise added, stirred, cooled, filtered, and dried to obtain the finished product.

[0011] In one embodiment, the 3-hydroxybutyric acid methyl ester in step A corresponds to the solvent alcohol, that is, when the raw material is 3-hydroxybutyric acid methyl ester, methanol is used, and when the raw material is 3-hydroxybutyric acid ethyl ester, ethanol is used.

[0012] The addition product in step B is used for catalyzing the hydration addition reaction of crotonic acid (butenoic acid), and is selected from sodium bisulfite, sodium sulfite, sodium metabisulfite, sodium thiosulfate, and a mixture of two or more thereof. More preferably, the addition product is sodium metabisulfite.

[0013] Preferably, the amount of the addition product in step B is 0.5-0.7 times, for example, about 0.6 times, of the purity of crotonic acid detected by HPLC method.

[0014] More preferably, the amount of the solvent used in step B is 3-10 times, preferably 4-8 times, more preferably about 5 times, of the amount of the crude product, and the reaction is carried out at 20-30°C. This condition is conducive to the addition reaction.

[0015] It should be understood that, when expressing numerical characteristics herein, the term "about" or "around" means that the indicated number can have an error range or floating range of ±10%, ±9%, ±8%, ±7%, ±6%, or ±5%.

[0016] The alcohol solvent used in step B above is selected from methanol, ethanol, isopropyl alcohol, isopentyl glycol, or a mixture of two or more thereof. More preferably, the alcohol used in step B is methanol.

[0017] Preferably, the HPLC purity of the product of step C is less than 0.32%, and the content of the external standard is less than 0.016%; the HPLC purity of the sodium 3-hydroxybutyrate is more than 99.2%, and the content of the external standard is more than 99.5%.

[0018] The reagents used in the above preparation method include sodium hydroxide (industrial grade, referred to as flake alkali), alcohol solvents such as methanol / ethanol and acetone, which are preferably of food grade or pharmaceutical grade in terms of specifications and purity to avoid the introduction of toxic and harmful substances such as heavy metals.

[0019] In one embodiment, the organic solvent alcohols such as methanol and acetone used in steps B and C above can be reused after recovery and distillation separation, achieving the effect of recycling.

[0020] The method not only can efficiently prepare sodium 3-hydroxybutyrate with safety reaching the pharmaceutical grade, but also can effectively reduce the production cost of the sodium 3-hydroxybutyrate of this specification, which is suitable for industrialized production and application. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is an HPLC spectrum of a commercially available food grade commodity sodium 3-hydroxybutyrate produced by a conventional method. The retention times of the substances in the figure are as follows: 3-hydroxybutyric acid, 4.3 min; crotonic acid, 15.4 min.

[0022] Figure 2 is an HPLC spectrum of sodium 3-hydroxybutyrate prepared in one embodiment of the present application. The retention times of the substances in the figure are as follows: 3-hydroxybutyric acid, 4.3 min; crotonic acid, 15.8 min. DETAILED DESCRIPTION

[0023] The hydrolysis product of 3-hydroxybutyrate, 3-hydroxybutyric acid, contains a hydroxyl group and a carboxyl group, which are active, and under weak alkaline conditions, the hydroxyl group is more likely to be removed to form crotonic acid, which is a toxic substance that seriously affects the quality of 3-hydroxybutyric acid and 3-hydroxybutyrate.

[0024] The product of sodium 3-hydroxybutyrate produced by a conventional method (for example, a method including a spray drying step) has a high content of impurities, and the content of crotonate is also high. For example, referring to Figure 1, a certain batch of product produced in large quantities was taken, and the HPLC determination of the purity of crotonate was 4.877%, the content of the external standard was 0.244%, the purity of sodium 3-hydroxybutyrate was 94.074%, and the content of the external standard was 98.35%.

[0025] In view of the fact that crotonic acid (butenoic acid) is a major by-product which seriously affects the use of sodium 3-hydroxybutyrate as a medicine, the design idea of the present application is to avoid the generation of impurity crotonate (crotonic acid salt), reduce the residual impurities in the finished product, and replace spray drying which needs a higher temperature with a crystallization process.

[0026] To this end, we conceived to use the principle of reversible reaction chemical equilibrium to replenish the intermediate reactants by addition reaction which can cause the reverse reaction of crotonic acid (crotonic acid) to generate 3-hydroxybutyric acid, as shown in the following reaction formula.

[0027] That is, the method for reducing crotonate (crotonic acid salt) is to add a certain amount of addition product which can convert the generated by-product crotonate into 3-hydroxybutyrate, so as to achieve the purpose of reducing crotonate. The addition product is also called addition catalyst, which is used to catalyze the hydration addition reaction of crotonic acid (crotonic acid), including but not limited to sodium bisulfite, sodium sulfite, sodium metabisulfite, sodium thiosulfate and a mixture of two or more thereof, and more preferably sodium metabisulfite.

[0028] The design idea of the process is to mix the hydrolysis reaction crude product with a suitable solvent, dissolve it, add the addition product, and reverse the crotonic acid generated by the dehydroxylation of 3-hydroxybutyric acid to 3-hydroxybutyric acid, and then generate its sodium salt.

[0029] The catalysis of the above-mentioned addition product makes the degree of olefin hydration reaction of crotonic acid controllable. The addition product of crotonic acid prepared by using the addition product as a catalyst does not contain other by-products such as sodium 2-hydroxybutyrate, sodium 3-ketobutyrate, sodium 2-ketobutyrate, etc., and at least no other by-products are detected by HPLC.

[0030] In the purification, i.e. refining, of the hydrolysis / addition reaction product sodium 3-hydroxybutyrate, through comparison of a large number of organic solvent additives which can promote the crystallization of the product sodium 3-hydroxybutyrate, it is found that the effect of using acetone as a crystallization additive is the best, the yield of pure product is the highest, more impurities can be removed, and the purity of the finished product is improved.

[0031] In this paper, the term "impurity (in the product)" should be understood in a broad sense, not only limited to the main by-product crotonate (crotonic acid salt), but also including impurities such as heavy metal elements carried in the raw materials. The "impurities" in the product sodium 3-hydroxybutyrate even include unreacted raw materials themselves, for example, methyl (ethyl) 3-hydroxybutyrate.

[0032] As used herein, the term "increase," "enhance," or "boost" can mean an increase of at least 10% compared to a reference level, such as a prior art process product, for example, an increase of at least about 20%, or at least about 30%, or at least about 40%, or at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or up to and including 100% compared to a reference level.

[0033] Accordingly, as used herein, the term "decrease," "reduce," or "decrease" can mean a decrease of at least 10% compared to a reference level, such as a prior art process product, for example, a decrease of at least about 20%, or at least about 30%, or at least about 40%, or at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or up to and including 100% compared to a reference level, or any decrease between 10% and 100%, or an increase of at least about 2-fold, or at least about 3-fold, or at least about 4-fold, or at least about 5-fold, or at least about 10-fold compared to a reference level.

[0034] The sodium 3-hydroxybutyrate prepared by the process of the present application has a purity of 3-hydroxybutyric acid sodium salt of 0.311% or less as determined by HPLC, and a content of 0.016% or less, i.e., less than 16 ppm as determined by external standard method; the HPLC purity of the sodium 3-hydroxybutyrate is 99.288% or more, and the content is 99.56% or more, which meets the quality standards of pharmaceutical grade established by the enterprise.

[0035] The term "pharmaceutical grade" as used herein can also be referred to as "drug grade" or "drug product grade", which represent the same meaning and can be used interchangeably, and all refer to the safety of the product meeting the safety standards of injection drugs and / or oral drugs, which is higher than that of food grade.

[0036] As a specific embodiment, the preparation method of the present application generally comprises the following steps:

[0037] A. Hydrolysis reaction: 3-hydroxybutyric acid ethyl ester, ethanol, and water are added to a reactor, the temperature is maintained at 25-30°C, sodium hydroxide is added in batches, and the reaction is carried out at 55-60°C. After cooling, 3-hydroxybutyric acid sodium is precipitated, filtered, washed, and dried to obtain 3-hydroxybutyric acid sodium crude product. Alternatively, if water-containing ethanol such as 95% ethanol is used directly, no additional water needs to be added.

[0038] B. Addition reaction: the crude product obtained in step A is added to a reactor, an appropriate amount of alcohol and water are added, and after dissolution, an additive is added, and the reaction is carried out at 20-30°C to obtain an addition reaction product;

[0039] C. Refining: the reaction solution of step B is filtered to remove a small amount of insoluble matter; the mother liquor is distilled under reduced pressure to remove methanol until it is thick; slowly add acetone to crystallize, stir, cool, filter, and dry.

[0040] In the above addition reaction step, the alcohol used is particularly preferably methanol. Compared with other alcohols such as ethanol, isopropyl alcohol, isopentyl glycol, etc., the use of methanol promotes the addition reaction and significantly reduces the production of crotonic acid (butenoic acid) salt.

[0041] The organic solvents methanol and acetone used in the above steps B and C can be recovered and separated by rectification, and can be reused, achieving the effect of recycling.

[0042] The reagents used in the above preparation method include sodium hydroxide (industrial grade, referred to as flake alkali), methanol / ethanol, and acetone, all of which are preferably of food grade specifications and purity, and are preferably of pharmaceutical grade, to avoid the introduction of toxic and harmful substances such as heavy metal elements.

[0043] Starting from experimentally pure methyl (or ethyl) 3-hydroxybutyrate, the total yield of pharmaceutical grade sodium 3-hydroxybutyrate prepared by the process of the present application can reach more than 80%, which is much higher than the total yield (about 61%) obtained by using conventional preparation methods and purification processes, and does not require high energy consumption spray drying, avoiding the investment in production equipment such as spray drying tower and supporting cyclone separator and other devices, production site investment, etc., which helps to greatly reduce the production cost of pharmaceutical grade sodium 3-hydroxybutyrate, and significantly improves the economic efficiency.

[0044] As a person skilled in the art would readily understand, the addition and replenishment technology of the present application is also applicable to other 3-hydroxybutyric acid metal salts such as calcium 3-hydroxybutyrate, magnesium 3-hydroxybutyrate, potassium 3-hydroxybutyrate, zinc 3-hydroxybutyrate, iron 3-hydroxybutyrate, etc.

[0045] It should be understood that in order to ensure the safety of 3-hydroxybutyric acid sodium product for food and medical use, the inorganic raw material flake alkali, the organic solvents such as ethanol, methanol, and acetone approved by the National Food and Drug Administration and FDA are preferably food safety grade raw materials.

[0046] Examples

[0047] The present application is further illustrated by the following examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the present application. Various changes or modifications made by a person skilled in the art based on the concept of the present application shall fall within the scope of the present application.

[0048] In this paper, the addition amount, content and concentration of various substances are mentioned, and the percentage content mentioned herein refers to mass percentage content unless otherwise specified.

[0049] In the examples herein, if no specific temperature is mentioned for the operating temperature, this temperature generally refers to room temperature (15-35 °C).

[0050] HPLC detection method of sodium 3-hydroxybutyrate in the examples:

[0051] Instrument: liquid chromatograph Agilent 1260

[0052] Column: Agilent ZORBAX SB-Aq 4.6 mm x 250 mm x 5 μm or equivalent

[0053] Mobile phase: 0.1% aqueous perchloric acid: acetonitrile = 95:5 (v / v);

[0054] Flow rate: 1.0 ml / min

[0055] Column temperature: 30 °C

[0056] Detector: differential refractive index detector

[0057] Detection wavelength: 214 nm

[0058] Injection volume: 10 μl

[0059] External standard method to calculate the content of the components.

[0060] Enterprise quality standards:

[0061] The pharmaceutical grade quality standards we have established are: sodium 3-hydroxybutyrate content ≥ 99.0%; total impurities ≤ 1.0%, of which: tiglic acid residue ≤ 0.05% i.e. no more than 50 ppm.

[0062] Example 1: Preparation of crude sodium 3-hydroxybutyrate

[0063] In a 500 ml three-necked flask, add 50 g (0.378 mol) of ethyl 3-hydroxybutyrate, 250 ml of 95% ethanol, and stir to dissolve. Keep the temperature at 25-30 °C, and add 15.1 g of sodium hydroxide (0.378 mol) in batches over 4 hours. After the addition of sodium hydroxide is complete, warm to 55-60 °C until the system is clear, and react for 3 hours. Cool to 10 °C, and filter under suction, and dry at 80 °C. Take a sample, and detect the purity of tiglic acid by HPLC to be 2.869%, and the dry product weight yield is 81%, which is the crude sodium 3-hydroxybutyrate.

[0064] Example 2: Addition reaction and purification

[0065] In a 500 ml three-necked flask, add 20 g of the crude product obtained in Example 1, and then add 100 ml of methanol and 3 ml of deionized water, and heat to 25 °C. After dissolution, add 1.5 g of sodium pyrosulfite, and react at 23 °C for 5 hours.

[0066] The filtrate was evaporated under reduced pressure to remove methanol. 100 ml of acetone was added slowly to the filtrate and stirred for 0.5 hour. The temperature was lowered to 10°C and the mixture was stirred for 1 hour. The mixture was filtered and the residue was dried at 80°C. The yield of the dried product was 0.91 g. The purity of the dried product was 0.311% as determined by HPLC and the content of the dried product was 0.016% as determined by external standard method.

[0067] Example 3: Addition reaction and purification

[0068] In a 500 ml three-necked flask, 20 g of the crude product obtained in Example 1 was added and 100 ml of 95% methanol was added. The mixture was heated to 25°C. After the solution was clear, 1.5 g of sodium pyrosulfite was added and the mixture was stirred at 25°C for 5 hours.

[0069] The filtrate was evaporated under reduced pressure to remove methanol. 100 ml of acetone was added slowly to the filtrate and stirred for 0.5 hour. The temperature was lowered to 10°C and the mixture was stirred for 1 hour. The mixture was filtered and the residue was dried at 80°C. The yield of the dried product was 0.91 g. The purity of the dried product was 0.311% as determined by HPLC and the content of the dried product was 0.016% as determined by external standard method.

[0070] Example 4: Addition reaction and purification

[0071] In a 500 ml three-necked flask, 20 g of the crude product obtained in Example 1 was added and 100 ml of methanol was added. The mixture was heated to 30°C. After the solution was clear, 1.5 g of sodium pyrosulfite was added and the mixture was stirred at 30°C for 5 hours.

[0072] The filtrate was evaporated under reduced pressure to remove methanol. 100 ml of acetone was added slowly to the filtrate and stirred for 0.5 hour. The temperature was lowered to 10°C and the mixture was stirred for 1 hour. The mixture was filtered and the residue was dried at 80°C. The yield of the dried product was 0.91 g. The purity of the dried product was 0.311% as determined by HPLC and the content of the dried product was 0.016% as determined by external standard method.

[0073] Example 5: Addition reaction and purification

[0074] In a 500 ml three-necked flask, 20 g of the crude product obtained in Example 1 was added and 100 ml of 95% methanol was added. The mixture was heated to 25°C. After the solution was clear, 1.5 g of sodium pyrosulfite was added and the mixture was stirred at 25°C for 5 hours.

[0075] The filtrate was evaporated under reduced pressure to remove methanol. 100 ml of acetone was added slowly to the filtrate and stirred for 0.5 hour. The temperature was lowered to 10°C and the mixture was stirred for 1 hour. The mixture was filtered and the residue was dried at 80°C. The yield of the dried product was 0.91 g. The purity of the dried product was 0.311% as determined by HPLC and the content of the dried product was 0.016% as determined by external standard method.

[0076] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of pharmaceutical grade sodium 3-hydroxybutyrate, characterized in that, The method comprises the following steps: A. Hydrolysis reaction: 3-hydroxybutyric acid methyl (ethyl) ester, methyl (ethyl) alcohol and water are added into a reactor, the temperature is kept at 15-45°C, more preferably 20-40°C, and more preferably 25-30°C, sodium hydroxide is added in batches, the temperature is raised to 45-70°C, preferably 50-65°C, and more preferably 55-60°C, and the hydrolysis reaction is carried out, and after cooling, 3-hydroxybutyric acid sodium is precipitated, filtered, washed and dried to obtain 3-hydroxybutyric acid sodium crude product; B. Addition reaction: the crude product obtained in step A is added into a reactor, an alcohol solvent and water are added, after dissolution, an additive is added, and the reaction is carried out at 15-40°C, preferably 18-35°C, and more preferably 20-30°C, to obtain an addition reaction product; C. Refining: the reaction liquid in step B is filtered to remove a small amount of insoluble substances, the mother liquor is distilled under reduced pressure to remove the alcohol, acetone is added for crystallization, stirred, cooled, filtered and dried to obtain a finished product.

2. The method of claim 1, wherein, The 3-hydroxybutyric acid methyl ester in step A corresponds to the solvent alcohol, that is, when the raw material is 3-hydroxybutyric acid methyl ester, methanol is used, and when the raw material is 3-hydroxybutyric acid ethyl ester, ethanol is used.

3. The method of claim 1, wherein, The additive in step B is selected from sodium bisulfite, sodium sulfite, sodium metabisulfite, sodium thiosulfate and a mixture of two or more thereof.

4. The method of claim 1, wherein, The additive in step B is sodium metabisulfite.

5. The method of claim 3, wherein, The amount of the additive is 0.5-0.7 times the purity of crotonic acid detected by HPLC.

6. The method of claim 3, wherein, In step B, the amount of solvent used is 3-10 times, preferably 4-8 times, and more preferably 5 times the amount of crude product, and the reaction is carried out at 20-30°C.

7. The method of claim 1, wherein, The alcohol solvent used in step B is selected from methanol, ethanol, isopropyl alcohol, isopentyl glycol or a mixture of two or more thereof.

8. The method of claim 1, wherein, The alcohol used in step B is methanol.

9. The method of claim 1, wherein, The HPLC purity of crotonic acid or its salt in the 3-hydroxybutyric acid sodium finished product obtained in step C is 0.32% or less, and the content measured by external standard method is 0.016% or less; the HPLC purity of 3-hydroxybutyric acid sodium is 99.2% or more, and the content measured by external standard method is 99.5% or more.

10. The method of claim 1, wherein, The reagents used in the preparation method include sodium hydroxide, alcohol solvent and acetone, which are of food grade or pharmaceutical grade specifications and purity.

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