Preparation and purification method of methyl isoglycyrrhizinate

Abstract

This invention provides a method for preparing and purifying methyl isoglycyrrhizate. The preparation method includes reacting isoglycyrrhizic acid (of formula I) or its salt in a mixed solvent of methanol and methyl acetate in the presence of acetyl chloride. The purification method involves adding crude methyl isoglycyrrhizate to a mixed solvent of organic solvent and water after the reaction, heating and stirring to dissolve; then adding water dropwise, cooling to allow crystallization, and filtering to obtain a solid. This invention, by adding a certain amount of methyl acetate during the reaction, can ensure the conversion rate, control the acidity of the reaction environment, reduce the degradation of methyl isoglycyrrhizate, and greatly improve the product yield and material utilization. The purification method for methyl isoglycyrrhizate provided by this invention can efficiently remove impurity A from the product, is simple to operate, uses little solvent, has a high yield, and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical chemistry, specifically to magnesium isoglycyrrhizate, and more specifically to a method for preparing and purifying methyl isoglycyrrhizate. Background Technology

[0002] Magnesium isoglycyrrhizinate is a hepatoprotective agent with anti-inflammatory, hepatocyte membrane protective, detoxifying, antioxidant, and liver function improving effects. Its chemical name is (18α,20β)-20-carboxy-11-oxo-30-norolean-12-en-3β-yl-2-O-β-D-glucuronide-α-D-glucuronide magnesium isoglycyrrhizinate, and its structural formula is as follows:

[0003]

[0004] Patent CN1381462A discloses a method for producing magnesium isoglycyrrhizate. This method utilizes the characteristic that isoglycyrrhizic acid precipitates as a methyl ester in methanol. The product of the alkali-catalyzed isomerization reaction is added to methanol, along with a small amount of dehydrating agent. Methyl isoglycyrrhizate precipitates rapidly, and after filtration, high-purity magnesium isoglycyrrhizate methyl ester is obtained. Since natural glycyrrhizic acid and impurities do not precipitate in the mother liquor, methyl isoglycyrrhizate is almost completely separated from unconverted glycyrrhizic acid and impurities. Furthermore, based on the readily hydrolyzable nature of methyl isoglycyrrhizate, it is hydrolyzed in an alkaline solution, neutralized with acid, and extracted with n-butanol to obtain refined isoglycyrrhizic acid. Finally, a calculated amount of inorganic or organic salt is added to form isoglycyrrhizate salt. This patent achieves a 55% yield of methyl isoglycyrrhizate, but does not disclose its purity.

[0005] Patent CN107488207 discloses a purification method for methyl isoglycyrrhizinate. The inventors discovered through repeated experiments that an impurity A, introduced from the raw materials during the reaction process, is difficult to remove and directly affects the quality of the finished product. The structure of impurity A is shown in the following formula:

[0006]

[0007] The specification also discloses that the crude methyl isoglycyrrhizate contains approximately 2.5% impurity A, which cannot be effectively removed by conventional washing methods such as methanol washing. This invention involves dissolving the crude methyl isoglycyrrhizate in a mixed solution of DMF and methanol-purified water, stirring at 70–80°C for 1–2 hours, cooling to 20–25°C and stirring to crystallize for 8–12 hours, then filtering. The filter cake is then slurried with methanol at 35°C for 2 hours, filtered, and the filter cake is added to tetrahydrofuran, refluxed and stirred until dissolved, stirred for 1 hour, slowly cooled to 0°C to crystallize for 8 hours, filtered, and dried under reduced pressure at 50°C for 12 hours to obtain refined methyl isoglycyrrhizate with a purification yield of 80% and an impurity A content of 0.3%.

[0008] Given the shortcomings and deficiencies of existing technologies, it is necessary to develop a method with high conversion rate in preparation and high efficiency in purification. Summary of the Invention

[0009] The present invention aims to provide a method for preparing methyl isoglycyrrhizate, the method comprising reacting isoglycyrrhizic acid of formula 1 or its salt in a mixed solvent of methanol and methyl acetate in the presence of acetyl chloride, the reaction formula of which is shown below:

[0010]

[0011] In some embodiments, the molar volume ratio of isoglycyrrhizic acid or its salt, acetyl chloride, methyl acetate and methanol is 1:2 to 5:2 to 6:5 to 10 mol / mol / mol / ml.

[0012] In some typical embodiments, the molar volume ratio of isoglycyrrhizic acid or its salt, acetyl chloride, methyl acetate and methanol is 1:2.5-3.5:4.5-5.5:5-8 mol / mol / mol / ml.

[0013] In some embodiments, the reaction is carried out at a temperature of 30–50°C for a reaction time of 1–8 hours; in some typical embodiments, the reaction is carried out at a temperature of 35–45°C for a reaction time of 2–6 hours.

[0014] Another objective of this invention is to provide a method for purifying methyl isoglycyrrhizinate, the method comprising adding crude methyl isoglycyrrhizinate to a mixed solvent of organic solvent and water, heating and stirring to dissolve; then adding water dropwise, cooling to crystallize, and filtering to obtain a solid.

[0015] In some embodiments, the organic solvent is an ether solvent, selected from ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and propylene glycol monomethyl ether; wherein the volume ratio of the organic solvent to water in the mixed solvent is 50 to 5:1, preferably 20 to 5:1.

[0016] In some embodiments, the mass-to-volume ratio of crude methyl isoglycyrrhizinate, mixed solvent, and added water is 1:10-15:1.2-10 g / ml / ml; in some typical embodiments, the mass-to-volume ratio of crude methyl isoglycyrrhizinate, mixed solvent, and added water is 1:11-15:1.5-5 g / ml / ml.

[0017] In some embodiments, the heating temperature is 50–100°C, the cooling temperature is 0–40°C, and the crystallization time is 0.5–10 hours. In some typical embodiments, the heating temperature is 70–90°C, the cooling temperature is 20–30°C, and the crystallization time is 1–5 hours.

[0018] In some embodiments, the crude methyl isoglycyrrhizate is obtained by reacting isoglycyrrhizic acid or its salt in a mixed solvent of methanol and methyl acetate in the presence of acetyl chloride.

[0019] A third aspect of the present invention is to provide a method for preparing magnesium isoglycyrrhizate, wherein the methyl isoglycyrrhizate obtained by the method according to the present invention is further subjected to a hydrolysis reaction to form magnesium isoglycyrrhizate by reacting with inorganic or organic magnesium salts.

[0020] Compared with the prior art, the present invention achieves positive technical effects:

[0021] 1. In the preparation of methyl isoglycyrrhizinate, methyl acetate, formed by the reaction of acetyl chloride and methanol, is typically used as a methylating agent. During the experiment, the inventors unexpectedly discovered that methyl isoglycyrrhizinate is easily degraded into impurity B under strongly acidic conditions during its preparation, with the following structural formula:

[0022]

[0023] Reducing the amount of acetyl chloride to lower the acidity of the reaction environment leads to a decrease in conversion rate. The inventors have solved this problem by adding a certain amount of methyl acetate during the reaction process, which ensures both conversion rate and acidity control, reduces the degradation of methyl isoglycyrrhizinate, and significantly improves product yield and material utilization.

[0024] 2. The purification method for methyl isoglycyrrhizinate provided by this invention can efficiently remove impurity A from the product, is simple to operate, requires less solvent, has a high yield, and is environmentally friendly. Detailed Implementation

[0025] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0026] Definitions and Explanations

[0027] Unless otherwise specified, the following terms have the following meanings:

[0028] "Crude product" refers to substances that have not undergone further purification during the synthesis process. These substances may contain various impurities, such as unreacted raw materials, byproducts, solvents, or other impurities. Typically, it refers to substances directly separated from the reaction mixture that can be further purified into a pure product using various purification methods. In this invention, crude isoglycyrrhizic acid methyl ester refers to a refined product with an isoglycyrrhizic acid methyl ester content of 80% or higher but less than 98%, where impurities include, but are not limited to, impurity A.

[0029] The sources of crude methyl isoglycyrrhizinate in this invention include, but are not limited to, preparations made according to existing technologies such as CN1381462A, or preparations made using the preparation method of this invention.

[0030] Those skilled in the art will readily understand that the error range of the parameters listed in this invention also falls within the scope of protection of this invention. The error range includes, but is not limited to, the degree of expected experimental error, technical error, instrument error, and industrial operational error of the given technique used to measure the value. When the degree of error is not specified, all values ​​listed in this invention encompass a range of ±10% of the specified value.

[0031] The HPLC test parameters for methyl isoglycyrrhizinate used in this invention are as follows:

[0032]

[0033] Example 1: Synthesis of isoglycyrrhizic acid according to the method in patent CN1381462A

[0034] Weigh 1280g of sodium hydroxide and put it into a reaction vessel. Add 8400ml of water to dissolve it into a concentrated alkaline solution (4mol / L). Add 1680g of monoammonium glycyrrhizate and stir to dissolve. Heat under normal pressure and reflux for 8 hours. Cool the reaction solution to room temperature, add hydrochloric acid to adjust the pH to 2-3, filter the precipitate, wash with water to pH 4-5, and dry to obtain isoglycyrrhizic acid.

[0035] Example 2: Synthesis of Methyl Isoglycyrrhizinate under Different Reaction Conditions

[0036] 400 ml of methanol was added to each of the 2000 ml three-necked flasks. 80 g of isoglycyrrhizic acid obtained in Example 1 was taken, and 0 g, 0 g, 33.3 g, and 40.7 g of methyl acetate were added respectively. The temperature was controlled, and 62.8 g, 27.4 g, 27.4 g, and 19.6 g of acetyl chloride were added dropwise respectively. After the addition was complete, the temperature was increased and the reaction was maintained. After the reaction was completed, the reaction solutions obtained under different reaction conditions were analyzed by high-performance liquid chromatography (HPLC). The amounts of methyl isoglycyrrhizic acid and impurity B are shown in the table below:

[0037]

[0038] Example 3: Synthesis of Methyl Isoglycyrrhizinate

[0039] Add 400 ml of methanol to a 1 L jacketed bottle, along with 80 g of isoglycyrrhizic acid obtained in Example 1 and 33.3 g of methyl acetate. Maintain the temperature at 25 ± 5 °C and add 27.5 g of acetyl chloride dropwise. After the addition is complete, raise the temperature to 40 ± 3 °C and maintain the temperature with stirring for 6 hours. After the reaction is complete, lower the temperature to 20-25 °C, filter, and obtain 59.4 g of crude methyl isoglycyrrhizic acid, with impurity A content of 2.5%.

[0040] Example 4: Refining of methyl isoglycyrrhizinate

[0041] 2.3 g of crude methyl isoglycyrrhizinate obtained in Example 3 was added to a mixed solvent of 23 ml diethylene glycol monomethyl ether and 2.3 ml water. The mixture was heated to 80 °C and stirred until dissolved. Then, 3.9 ml of water was added dropwise, the mixture was cooled to 25 °C, filtered, and the filter cake was dried at 50 °C to obtain 2.1 g of methyl isoglycyrrhizinate. The yield was 91.3%, the purity was 99.4%, and the content of impurity A was 0.23%.

[0042] Example 5: Refining of methyl isoglycyrrhizinate

[0043] 2.3 g of crude methyl isoglycyrrhizinate obtained in Example 3 was added to a mixed solvent of 23 ml of ethylene glycol monomethyl ether and 2.3 ml of water. The mixture was heated to 80 °C and stirred until dissolved. Then, 4.6 ml of water was added dropwise, the mixture was cooled to 25 °C, filtered, and the filter cake was dried at 50 °C to obtain 2.0 g of methyl isoglycyrrhizinate. The yield was 87%, the purity was 99.5%, and the content of impurity A was 0.20%.

[0044] Example 6: Preparation of magnesium isoglycyrrhizate

[0045] Take 2.1 g of methyl isoglycyrrhizinate obtained in Example 4, add 6.3 ml of 3N sodium hydroxide solution, heat to reflux until the solution is clear, maintain the reaction temperature for 2 h, cool to room temperature, add dilute sulfuric acid to adjust the pH to 3.0, extract with 10 mL of 2-methyltetrahydrofuran, and concentrate the organic phase to 4 mL. Add the organic phase to 12.5 ml of isopropanol, add 1.15 g of 30% magnesium acetate aqueous solution, heat to 75 °C and stir for 4 hours, then cool to 25 °C, filter, and collect the filter cake.

[0046] Add 10 ml of water to the filter cake, beat for 2 hours, filter, and dry the filter cake at 50℃ to obtain magnesium isoglycyrrhizate product with a purity of 99.75% and a single impurity of <0.08%.

[0047] Comparative Example 1:

[0048] 2.3 g of crude methyl isoglycyrrhizinate obtained in Example 3 was added to 400 ml of methanol, heated to 60-65 °C and stirred for 2 h, then cooled to 20-25 °C and filtered. The methanol stirring operation was repeated once more. The resulting filter cake was dried at 40-45 °C with a drying loss of ≤4.0%, yielding 1.95 g of methyl isoglycyrrhizinate, with a yield of 84.8%, a purity of 96.5%, and an impurity A content of 2.3%.

[0049] Comparative Example 2:

[0050] 4.6 g of crude methyl isoglycyrrhizinate obtained in Example 3 was added to a reaction flask, along with 9.2 ml of DMF. The mixture was stirred until dissolved, heated to 70°C, and a methanol-purified water mixture (5:1) was slowly added dropwise until the system just became turbid. The mixture was then cooled to 25°C and stirred for 8 hours. After filtration, the filter cake was slurried with 46 ml of methanol at 35°C for 2 hours. After filtration, the filter cake was added to 36 ml of tetrahydrofuran, refluxed, stirred until dissolved, and stirred for 1 hour. The mixture was then slowly cooled to 0°C to crystallize for 6 hours. After filtration, the crystals were dried under reduced pressure at 50°C for 2 hours to obtain 3.6 g of purified methyl isoglycyrrhizinate, with a yield of 78.3% and an impurity A content of 0.58%.

[0051] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing methyl isoglycyrrhizinate, characterized in that, This method involves reacting compound I, isoglycyrrhizic acid or a salt thereof, in a mixed solvent of methanol and methyl acetate in the presence of acetyl chloride, as shown in the following reaction formula:

2. The preparation method according to claim 1, characterized in that, The molar volume ratio of isoglycyrrhizic acid or its salt, acetyl chloride, methyl acetate and methanol is 1:2-5:2-6:5-10 mol / mol / mol / ml; preferably, the molar volume ratio of isoglycyrrhizic acid or its salt, acetyl chloride, methyl acetate and methanol is 1:2.5-3.5:4.5-5.5:5-8 mol / mol / mol / ml.

3. The preparation method according to claim 2, characterized in that, The reaction is carried out at a temperature of 30–50°C for a time of 1–8 hours; preferably, the reaction is carried out at a temperature of 35–45°C for a time of 2–6 hours.

4. A method for purifying methyl isoglycyrrhizinate, characterized in that, The method involves adding crude methyl isoglycyrrhizinate to a mixed solvent of organic solvent and water, heating and stirring to dissolve it; then adding water dropwise, cooling to allow crystals to precipitate, and filtering to obtain a solid.

5. The purification method according to claim 4, characterized in that, The organic solvent is an ether solvent, selected from ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and propylene glycol monomethyl ether; wherein the volume ratio of the organic solvent to water in the mixed solvent is 50 to 5:1, preferably 20 to 5:

1.

6. The purification method according to claim 4, characterized in that, The mass-to-volume ratio of crude methyl isoglycyrrhizinate, mixed solvent, and water is 1:10-15:1.2-10 g / ml / ml, preferably 1:11-15:1.5-5 g / ml / ml.

7. The purification method according to claim 4, characterized in that, The heating temperature is 50–100°C, the cooling temperature is 0–40°C, and the crystallization time is 0.5–10 hours; preferably, the heating temperature is 70–90°C, the cooling temperature is 20–30°C, and the crystallization time is 1–5 hours.

8. The purification method according to claim 4, characterized in that, The crude methyl isoglycyrrhizate is obtained by reacting isoglycyrrhizic acid or its salt in a mixed solvent of methanol and methyl acetate in the presence of acetyl chloride.

9. A method for preparing magnesium isoglycyrrhizate, characterized in that, The method according to claims 1-8 yields methyl isoglycyrrhizate, which is further hydrolyzed to form magnesium isoglycyrrhizate with inorganic or organic magnesium salts.

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