A method for synthesizing s-acetyl-l-glutathione

Abstract

The application provides a synthesis method of S-acetyl-L-glutathione, steps of which comprise the following steps: dissolving L-glutathione in acetic acid, adding inorganic strong acid, stirring to obtain a first solution; adding acetic anhydride dropwise into the first solution, performing complete reaction to obtain a second solution; adding water into the second solution, adding alkali to adjust pH, adding a crystallization solvent to crystallize and filter to obtain a solid crude product, and performing post-treatment to obtain the S-acetyl-L-glutathione; wherein the temperature of the first solution is 16-25 DEG C, and the temperature of the second solution is 16-25 DEG C. The preparation method is simple, convenient to operate, has mild reaction conditions, high yield and purity, low cost, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the fields of medicinal chemistry and organic synthesis technology, and particularly relates to a method for synthesizing S-acetyl-L-glutathione. Background Technology

[0002] S-acetyl-L-glutathione is a derivative of glutathione and a potent antioxidant and cell protectant. L-glutathione is a polypeptide composed of three amino acids: glutamic acid, cysteine, and glycine. The (-SH) functional group of L-glutathione is its main active ingredient, exhibiting strong reducing and detoxifying effects in biological cells. The sulfhydryl group in L-glutathione is readily acetylated by acetylation agents to form S-acetyl-L-glutathione. Therefore, S-acetyl-L-glutathione has better stability and solubility than L-glutathione and is more easily absorbed by cells. In the medical and health fields, S-acetyl-L-glutathione can enhance the antioxidant capacity of cells, reduce oxidative stress and inflammatory responses, and has a positive impact on improving cell health and protecting cell function. The structural formula of S-acetyl-L-glutathione is:

[0003]

[0004] In existing technologies, trifluoroacetic acid is used as the reaction solvent, and Lewis acid salts such as aluminum trichloride and zinc chloride are added as catalysts to synthesize S-acetyl-L-glutathione via acetyl chloride acylation. However, this reaction requires a large amount of trifluoroacetic acid, which must be recovered at high temperatures, and side reactions are prone to occur. Another method involves protecting the amino group with trifluoroacetic acid first, and then synthesizing S-acetyl-L-glutathione using acetyl chloride catalysis in a mixed solvent such as DMF. However, large amounts of DMF solvent react with acetyl chloride, generating impurities that affect recovery rate and product purity, and there are also issues with DMF recovery and disposal, resulting in high production costs. Summary of the Invention

[0005] The main objective of this invention is to provide a method for synthesizing S-acetyl-L-glutathione, aiming to solve the technical problems of low yield and high cost in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for synthesizing S-acetyl-L-glutathione, comprising the following steps:

[0007] L-glutathione was dissolved in acetic acid, and an inorganic protic strong acid was added. After stirring, the first solution was obtained.

[0008] Acetic anhydride was added dropwise to the first solution to allow for a complete reaction, resulting in a second solution.

[0009] Water and alkali were added to the second solution to adjust the pH, followed by the addition of a crystallization solvent for crystallization and filtration to obtain a solid crude product. After post-processing, the S-acetyl-L-glutathione was obtained.

[0010] The temperature of the first solution is 16–25°C, and the temperature of the second solution is 16–25°C.

[0011] According to an embodiment of this application, the mass of L-glutathione added to each milliliter of the acetic acid is 3 to 8 g.

[0012] According to the embodiments of this application, the inorganic protic strong acid, by mass fraction, is one of 70-72% perchloric acid, 80-95% sulfuric acid, and 47-49% hydrobromic acid.

[0013] According to an embodiment of this application, in the inorganic protic strong acid, the molar amount of hydrogen ions is 1 to 1.5 times the molar amount of L-glutathione.

[0014] According to an embodiment of this application, the amount of acetic anhydride used is 1.0 to 1.8 times the molar amount of L-glutathione.

[0015] According to an embodiment of this application, the amount of water used is 10 to 20% of the molar amount of L-glutathione.

[0016] According to the embodiments of this application, an alkali is added to adjust the pH to 3-6, wherein the alkali is one of triethylamine, ammonia, sodium carbonate, and sodium bicarbonate.

[0017] According to the embodiments of this application, the crystallization solvent is one of methanol, ethanol, and acetone.

[0018] In each milliliter of the crystallization solvent, the mass of L-glutathione is 8 to 15 g.

[0019] The crystallization temperature is 5–15℃.

[0020] According to an embodiment of this application, the post-processing step includes:

[0021] The solid crude product is added to an aqueous solution of methanol or ethanol, stirred for 1 to 3 hours, filtered, washed, and dried to obtain the S-acetyl-L-glutathione.

[0022] In the methanol or ethanol aqueous solution, the volume fraction of the solute is 50-90%.

[0023] According to an embodiment of this application, the stirring temperature is 10–25°C.

[0024] The beneficial effects of this invention are:

[0025] This invention uses acetic acid as the reaction solvent. L-glutathione is dissolved in acetic acid, and an inorganic protic strong acid is added to completely protonate the amino group of L-glutathione, ensuring that the amino group does not participate in the acetylation reaction. After stirring, acetic anhydride is added dropwise as an acylation reagent to carry out the complete reaction. Simultaneously, the inorganic protic strong acid catalyzes the acetylation reaction, as it can donate protons (H+). + This process promotes the protonation of thiol groups, enhances their nucleophilicity, and enables them to effectively attack the carbonyl carbon atom in acetic anhydride, thus promoting the synthesis of S-acetyl-L-glutathione. The reaction is completed at low temperatures, and the reaction rate is increased. Adding water to the second solution to quench the reaction and adjusting the pH with alkali avoids esterification side reactions, thereby ensuring that the synthesized S-acetyl-L-glutathione has high yield and purity.

[0026] Furthermore, the preparation method of this invention is simple, easy to operate, has mild reaction conditions, high yield and purity, and low cost, making it suitable for large-scale industrial production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 This is a high-performance liquid chromatography (HPLC) detection result of the synthesized S-acetyl-L-glutathione in the embodiments of the present invention.

[0029] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0032] To achieve the above objectives, the present invention provides a method for synthesizing S-acetyl-L-glutathione, comprising the following steps:

[0033] S1: Dissolve L-glutathione in acetic acid, add an inorganic protic strong acid, and stir to obtain the first solution.

[0034] In some embodiments, a three-necked flask is used. L-glutathione is added to acetic acid and stirred until partially dissolved. Then, an inorganic protic strong acid is added and stirred until the L-glutathione is completely dissolved, yielding a clear first solution. Acetic acid serves as the reaction solvent, and the inorganic protic strong acid completely protonates the amino group of L-glutathione, ensuring that the amino group does not participate in the acetylation reaction. This significantly reduces the activity of the amino group and decreases the byproducts of the reaction between the amino group and the acetylation reagent, thereby improving the purity and yield of S-acetyl-L-glutathione. The inorganic protic strong acid can provide protons (H... + It promotes the protonation of thiol, enhances its nucleophilicity, and can effectively attack the carbonyl carbon atom in acetic anhydride, thus promoting the synthesis of S-acetyl-L-glutathione.

[0035] S2: Add acetic anhydride dropwise to the first solution to allow for complete reaction and obtain the second solution.

[0036] In some embodiments, the temperature of the first solution is 16–25°C. Acetic anhydride is slowly added dropwise to the first solution until the addition is complete, and an acetylation reaction is carried out. The reaction is completed to obtain the second solution. For example, if the addition is completed in 30–60 minutes, the temperature of the first solution is controlled at 16–20°C, and the reaction is allowed to proceed for 20 minutes. The reaction is then confirmed to be complete by HPLC analysis of a sample.

[0037] In some embodiments, because L-glutathione has high solubility in water and is easily decomposed, the acetic anhydride initially added dropwise is used to consume water in the reaction system, and the subsequently added acetic anhydride is used for the acetylation reaction. Acetic anhydride acts as an acylation reagent, directly acylating the thiol group (-SH) in L-glutathione. Because the reactivity and selectivity of the thiol group are higher than those of the amino group, the amino group of L-glutathione does not participate in the reaction, allowing the acetylation of the thiol group to be completely converted, generating S-acetyl-L-glutathione. The yield can reach 90-95%, and the purity can reach over 99.5%.

[0038] The synthetic reaction formula for S-acetyl-L-glutathione of the present invention is as follows:

[0039]

[0040] S3: Water and alkali were added to the second solution to adjust the pH, crystallization solvent was added to crystallize and the solution was filtered to obtain a solid crude product. After post-processing, the S-acetyl-L-glutathione was obtained.

[0041] In some embodiments, the temperature of the second solution is 16–25°C. Water is added to the second solution to decompose excess acetic anhydride, quench the reaction, and prevent excess acetic anhydride from reacting with other components in the system in subsequent steps, thus avoiding the formation of impurities. Acetic anhydride undergoes vigorous hydrolysis to acetic acid upon contact with water, which is a strongly exothermic reaction. Adding water and controlling the temperature of the second solution can prevent a sudden temperature rise during the reaction from damaging the product structure and causing side reactions.

[0042] In some embodiments, the temperature of the second solution is 16–20°C. Water is added to the second solution to decompose excess acetic anhydride and quench the reaction for 30 minutes.

[0043] In some embodiments, a large amount of white precipitate is generated by rapidly adding a crystallization solvent. After the crystallization solvent has been added, the mixture is stirred to crystallize and then filtered to obtain a solid crude product. After post-processing, the S-acetyl-L-glutathione is obtained.

[0044] The above-described method for synthesizing S-acetyl-L-glutathione involves using acetic acid as the reaction solvent to dissolve L-glutathione. An inorganic protic strong acid is added to completely protonate the amino group of L-glutathione, ensuring that the amino group does not participate in the acetylation reaction. After stirring, acetic anhydride is added dropwise as an acylation reagent to allow for complete reaction. Simultaneously, the inorganic protic strong acid catalyzes the acetylation reaction, enabling the reaction to be completed at low temperatures and increasing the reaction rate. The reaction is quenched with water, the pH is adjusted with alkali, and a crystallization solvent is added to the second solution for crystallization. The crystals are then filtered to obtain a solid crude product, which is further processed to obtain S-acetyl-L-glutathione. This ensures that the synthesized S-acetyl-L-glutathione has a high yield and purity.

[0045] Furthermore, the preparation method of this invention is simple, easy to operate, has mild reaction conditions, high yield and purity, reduces costs, and is suitable for large-scale industrial production.

[0046] In some embodiments, the mass of L-glutathione added to each milliliter of acetic acid is 3-8 g. That is, the volume-to-mass ratio of acetic acid to L-glutathione is 1 mL: 3-8 g.

[0047] In some embodiments, such as 10 ml of acetic acid, 30-80 g of L-glutathione is added to achieve partial dissolution of L-glutathione in acetic acid.

[0048] In some embodiments, the mass of L-glutathione added to each milliliter of acetic acid is 4 to 6 g.

[0049] In some embodiments, the inorganic protic strong acid, by mass fraction, is one of 70-72% perchloric acid, 80-95% sulfuric acid, and 47-49% hydrobromic acid.

[0050] In some embodiments, the molar amount of hydrogen ions in the inorganic protic strong acid is 1 to 1.5 times the molar amount of L-glutathione.

[0051] In some embodiments, the molar amount of hydrogen ions in the inorganic protic strong acid is 1 to 1.5 times the molar amount of L-glutathione. This ensures that the amino group in L-glutathione is completely protonated and does not participate in subsequent acetylation reactions.

[0052] In some embodiments, the molar amount of hydrogen ions in the inorganic protic strong acid is 1.1 to 1.3 times the molar amount of L-glutathione.

[0053] In some embodiments, the amount of acetic anhydride used is 1.0 to 1.8 times the molar amount of L-glutathione. By controlling the amount of acetic anhydride used as the acylation agent, the acetylation of the thiol group can be completely converted to generate S-acetyl-L-glutathione.

[0054] In some embodiments, the amount of acetic anhydride used is 1.1 to 1.3 times the molar amount of L-glutathione.

[0055] In some embodiments, the amount of water used is 10-20% of the molar amount of L-glutathione. This is to decompose excess acetic anhydride, quench the reaction, and prevent excess acetic anhydride from reacting with other components in the system in subsequent steps, thus avoiding the generation of impurities.

[0056] In some embodiments, alkali is added to adjust the pH to 3-6.

[0057] In some embodiments, alkali is added to adjust the pH to 3-4. This neutralizes the acidity of acetic acid produced from excess acetic anhydride during hydrolysis and also maintains the stability of the product.

[0058] In some embodiments, the alkali is one of triethylamine, ammonia, sodium carbonate, and sodium bicarbonate.

[0059] In some embodiments, sodium bicarbonate is selected to neutralize the acidity of acetic acid generated from acetic anhydride by water quenching, so as to avoid hydrolysis or decomposition of reactants or products under acidic conditions.

[0060] In some embodiments, the crystallization solvent is one of methanol, ethanol, and acetone.

[0061] In each milliliter of the crystallization solvent, the mass of L-glutathione is 8 to 15 g.

[0062] The crystallization temperature is 5–15℃.

[0063] In some embodiments, methanol is selected as the crystallization solvent. With the addition of methanol, a large amount of white precipitate gradually forms. After the methanol addition is complete, the crystallization temperature is 5–6°C, and the crystallization is maintained at this temperature for 2 hours. The product is then filtered to obtain a solid crude product. The volume of the crystallization solvent is related to the mass of L-glutathione. For example, if the mass of L-glutathione is 8–15 g, then 1 mL of methanol needs to be added. That is, the mass-to-volume ratio of L-glutathione to the crystallization solvent is 8–15 g: 1 mL.

[0064] In some embodiments, the post-processing step includes:

[0065] The solid crude product is added to an aqueous solution of methanol or ethanol, stirred for 1 to 3 hours, filtered, washed, and dried to obtain the S-acetyl-L-glutathione.

[0066] In the methanol or ethanol aqueous solution, the volume fraction of the solute is 50-90%.

[0067] In some embodiments, the solid crude product is added to an 80% methanol aqueous solution, the stirring temperature is controlled at 10-25°C, and the mixture is stirred for 1 hour. After filtration, it is washed with an 80% methanol aqueous solution and then dried in a hot air circulating drying oven at 65°C for 16 hours to obtain S-acetyl-L-glutathione.

[0068] In some embodiments, the stirring temperature is 10–25°C.

[0069] In some embodiments, the stirring temperature is 10–15°C. By controlling the temperature, hydrolysis of S-acetyl-L-glutathione during stirring is avoided, which would reduce the purity of the product.

[0070] To further illustrate the present invention, the following examples are provided:

[0071] Example 1

[0072] Add 120 mL of acetic acid and 30 g of L-glutathione to a 500 mL three-necked flask, start mechanical stirring, and then add 14.7 g of 70–72% perchloric acid. After stirring, the first solution is obtained. Adjust the temperature of the first solution to 16–20 °C, and slowly add 36 g of acetic anhydride dropwise to the first solution over 0.5–1 hour. The reaction is complete in 20 minutes, yielding the second solution.

[0073] The reaction was quenched by adding 0.3 g of water to the second solution at a temperature of 16–20 °C for 30 min. Saturated sodium bicarbonate was added dropwise until the pH reached 4, followed by rapid addition of 300 mL of methanol. A large amount of white precipitate gradually formed in the reaction solution. After the methanol addition was complete, the crystallization temperature was 5–6 °C, and the crystallization was maintained at this temperature for 2 h. The mixture was then filtered, and the filter cake was washed with 30 mL of methanol. After filtration, 45 g of wet solid crude product was obtained. This 45 g solid crude product was transferred to a 250 mL three-necked flask, and 135 mL of 80% methanol aqueous solution was added. The mixture was stirred at 10–15 °C for 1 h, followed by vacuum filtration. The filter cake was washed with 20 mL of 80% methanol aqueous solution and then dried in a hot air circulating drying oven at 65 °C for 16 h to obtain 32.0 g of S-acetyl-L-glutathione. The yield was 93.8%, and the purity was 99.5%.

[0074] Example 2

[0075] Add 140 mL of acetic acid and 30 g of L-glutathione to a 500 mL three-necked flask, start mechanical stirring, and then add 15.4 g of 70–72% perchloric acid. After stirring, the first solution is obtained. Adjust the temperature of the first solution to 16–20 °C, and slowly add 38 g of acetic anhydride dropwise to the first solution over 0.5–1 hour. The reaction is complete in 20 minutes, yielding the second solution.

[0076] The reaction was quenched by adding 0.35 g of water to the second solution at a temperature of 16–20 °C for 30 min. Saturated sodium bicarbonate was added dropwise until the pH reached 4, followed by rapid addition of 300 mL of methanol. A large amount of white precipitate gradually formed in the reaction solution. After the methanol addition was complete, the crystallization temperature was 5–6 °C, and the crystallization was maintained at this temperature for 2 h. The mixture was then filtered, and the filter cake was washed with 30 mL of methanol. After filtration, 42 g of wet solid crude product was obtained. This 42 g of solid crude product was transferred to a 250 mL three-necked flask, and 100 mL of 80% methanol aqueous solution was added. The mixture was stirred at 10–15 °C for 1 h, followed by suction filtration. The filter cake was washed with 20 mL of 80% methanol aqueous solution and then dried in a hot air circulating drying oven at 65 °C for 16 h to obtain 31.9 g of S-acetyl-L-glutathione. The yield was 93.5%, and the purity was 99.6%.

[0077] Example 3

[0078] Add 100 mL of acetic acid and 20 g of L-glutathione to a 500 mL three-necked flask, start mechanical stirring, and then add 3.5 g of 90% sulfuric acid. After stirring, the first solution is obtained. Adjust the temperature of the first solution to 16–20 °C, and slowly add 24 g of acetic anhydride dropwise to the first solution over 0.5–1 hour. The reaction is complete in 30 minutes, yielding the second solution.

[0079] The reaction was quenched by adding 0.23 g of water to the second solution at a temperature of 16–20 °C for 30 min. Triethylamine was added dropwise until the pH reached 4, followed by the rapid addition of 250 mL of methanol. A large amount of white precipitate gradually formed in the reaction solution. After the methanol was completely added, the crystallization temperature was 8–10 °C, and the crystallization was maintained at this temperature for 2 h. The mixture was then filtered, and the filter cake was washed with 20 mL of methanol. After filtration, 27 g of wet solid crude product was obtained. The 27 g of solid crude product was transferred to a 250 mL three-necked flask, and 81 mL of 80% methanol aqueous solution was added. The mixture was stirred at 8–10 °C for 1 h, followed by suction filtration. The filter cake was washed with 15 mL of 80% methanol aqueous solution, and then dried in a hot air circulating drying oven at 65 °C for 16 h to obtain 21.4 g of S-acetyl-L-glutathione. The yield was 94.1%, and the purity was 99.5%.

[0080] Example 4

[0081] Add 100 mL of acetic acid and 20 g of L-glutathione to a 500 mL three-necked flask, start mechanical stirring, and then add 10.3 g of perchloric acid (70-72% by mass). After stirring, the first solution is obtained. Adjust the temperature of the first solution to 16-20 °C, and slowly add 25 g of acetic anhydride dropwise to the first solution over 0.5-1 hour. The reaction is complete in 20 minutes, yielding the second solution.

[0082] The reaction was quenched by adding 0.24 g of water to the second solution at a temperature of 16–20 °C for 30 min. Triethylamine was added dropwise until the pH reached 4, followed by the rapid addition of 250 mL of methanol. A large amount of white precipitate gradually formed in the reaction solution. After the methanol was completely added, the crystallization temperature was 8–10 °C, and the crystallization was maintained at this temperature for 2 h. The mixture was then filtered, and the filter cake was washed with 25 mL of methanol. After filtration, 25.5 g of wet solid crude product was obtained. The 25.5 g of solid crude product was transferred to a 250 mL three-necked flask, and 76 mL of 80% methanol aqueous solution was added. The mixture was stirred at 8–10 °C for 1 h, followed by suction filtration. The filter cake was washed with 15 mL of 80% methanol aqueous solution, and then dried in a hot air circulating drying oven at 65 °C for 16 h to obtain 21.2 g of S-acetyl-L-glutathione. The yield was 93.3%, and the purity was 99.7%.

[0083] Example 5

[0084] Add 100 mL of acetic acid and 20 g of L-glutathione to a 500 mL three-necked flask, start mechanical stirring, and then add 11 g of 70-72% perchloric acid. After stirring, the first solution is obtained. Adjust the temperature of the first solution to 16-20 °C, and slowly add 27 g of acetic anhydride dropwise to the first solution over 0.5-1 h. The reaction is complete in 30 min, yielding the second solution.

[0085] The reaction was quenched by adding 0.25 g of water to the second solution at a temperature of 16–20 °C for 30 min. Triethylamine was added dropwise until the pH reached 4, followed by the rapid addition of 250 mL of methanol. A large amount of white precipitate gradually formed in the reaction solution. After the methanol was completely added, the crystallization temperature was maintained at 8–10 °C for 2 h. The mixture was then filtered, and the filter cake was washed with 25 mL of methanol. After filtration, 26 g of wet solid crude product was weighed. The 26 g of solid crude product was transferred to a 250 mL three-necked flask, and 76 mL of 80% methanol aqueous solution was added. The mixture was stirred at 8–10 °C for 1 h, followed by suction filtration. The filter cake was washed with 15 mL of 80% methanol aqueous solution and then dried in a hot air circulating drying oven at 65 °C for 16 h to obtain 21.3 g of S-acetyl-L-glutathione. The yield was 93.7%, and the purity was 99.6%.

[0086] Comparative Example 1

[0087] Add 120 mL of trifluoroacetic acid, 60 mL of DMF, 0.3 g of zinc chloride, and 30 g of L-glutathione to a 500 mL three-necked flask. Turn on the mechanical stirrer and adjust the temperature of the solution to 8–15 °C. Then slowly add 9.0 g of acetyl chloride dropwise over 0.5–1 h. The reaction is complete in 20 min, yielding a fully reacted solution.

[0088] The reaction was quenched by adding 1g of methanol to the completely reacted solution. The temperature of the completely reacted solution was 8-12℃, and the reaction was carried out for 30 minutes. Triethylamine was added dropwise until the pH reached 4, followed by the rapid addition of 380mL of acetone. A large amount of white precipitate gradually formed in the reaction solution. After the acetone was completely added, the crystallization temperature was 5-10℃, and the crystallization was maintained at this temperature for 2 hours. The mixture was then filtered, and the filter cake was washed with 30mL of acetone. After filtration, 37.1g of wet solid crude product was obtained. The 37.1g of solid crude product was transferred to a 250mL three-necked flask, and 100mL of 80% methanol aqueous solution was added. The mixture was stirred at 8-10℃ for 1 hour, then filtered under vacuum. The filter cake was washed with 20mL of 80% methanol aqueous solution, and then dried in a hot air circulating drying oven at 65℃ for 16 hours to obtain 29.4g of S-acetyl-L-glutathione. The yield was 86.3%, and the purity was 97.8%.

[0089] Comparative Example 2

[0090] Add 120 mL of trifluoroacetic acid, 90 mL of dichloromethane, 0.3 g of aluminum trichloride, and 30 g of L-glutathione to a 500 mL three-necked flask. Turn on the mechanical stirrer and adjust the temperature of the solution to 8–15 °C. Then slowly add 8.8 g of acetyl chloride dropwise over 0.5–1 h. The reaction is complete in 20 min, yielding a fully reacted solution.

[0091] The reaction was quenched by adding 0.5 g of water to the completely reacted solution at a temperature of 8–12 °C for 30 min. Triethylamine was added dropwise until the pH reached 4, followed by rapid addition of 360 mL of acetone. A large amount of white precipitate gradually formed in the reaction solution. After the acetone was completely added, the crystallization temperature was maintained at 5–10 °C for 2 h. The crystallization was then filtered, and the filter cake was washed with 30 mL of acetone. After filtration, 36.6 g of wet solid crude product was obtained. The 36.6 g of solid crude product was transferred to a 250 mL three-necked flask, and 100 mL of 80% methanol aqueous solution was added. The mixture was stirred at 8–10 °C for 1 h, followed by suction filtration. The filter cake was washed with 20 mL of 80% methanol aqueous solution and then dried in a hot air circulating drying oven at 65 °C for 16 h to obtain 29.6 g of S-acetyl-L-glutathione. The yield was 87.0%, and the purity was 98.2%.

[0092] Combination Figure 1 The high-performance liquid chromatography (HPLC) results of the synthesized S-acetyl-L-glutathione shown indicate that in Examples 1-5, L-glutathione was dissolved in acetic acid as a reaction solvent, and different inorganic protic strong acids were added to completely protonate the amino group of L-glutathione, ensuring that the amino group did not participate in the acetylation reaction. Acetic anhydride was then added dropwise as an acylation reagent after stirring to ensure complete reaction. Simultaneously, the amounts of each substance were controlled to achieve a rapid acylation reaction at a lower temperature. The reaction was then quenched with water, the pH was adjusted with alkali, and a crystallization solvent was added for crystallization and filtration to obtain a solid crude product. After post-processing, the yield of S-acetyl-L-glutathione was 92-95%, and the purity was above 99%.

[0093] Comparative Example 1 shows that using trifluoroacetic acid as the reaction solvent and amino protonating agent, with Lewis salts such as aluminum trichloride and zinc chloride as catalysts, and acetyl chloride added dropwise for acylation, the reaction proceeds smoothly. Using methanol to decompose excess acetic acid chloride reagent easily leads to side reactions, such as the esterification of the carboxyl group on the generated S-acetyl-L-glutathione with methanol, affecting the yield of S-acetyl-L-glutathione to only 86.3%. The trifluoroacetic acid and DMF used in the reaction need to be recycled, increasing production costs. Furthermore, the reuse of the recycled trifluoroacetic acid affects the yield and purity of S-acetyl-L-glutathione.

[0094] As shown in Comparative Example 2, although this method can synthesize S-acetyl-L-glutathione in the laboratory, the synthesis cost is high, and the control of reaction conditions and operating procedures are relatively complex. Furthermore, the yield of the obtained S-acetyl-L-glutathione was 87.0%, and the purity was 98.2%. The yield and purity of the product are relatively low.

[0095] Therefore, by selecting a suitable reaction solvent and an inorganic protic strong acid, the amino group of L-glutathione is completely protonated, ensuring that the amino group does not participate in the acetylation reaction. After stirring, a suitable acylation reagent and quencher are added dropwise, and the appropriate temperature and solvent addition amount are controlled. These steps work together to obtain S-acetyl-L-glutathione with high yield and purity as described in this application. Furthermore, the preparation method of this invention is simple, convenient to operate, has mild reaction conditions, high yield and purity, reduces costs, and is suitable for large-scale industrial production.

[0096] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for synthesizing S-acetyl-L-glutathione, characterized in that the step... include: S1: Dissolve L-glutathione in acetic acid, then add an inorganic protic strong acid, and stir to obtain the first solution; S2: Add acetic anhydride dropwise to the first solution to allow the reaction to proceed completely, resulting in a second solution; S3: Water and alkali were added to the second solution to adjust the pH, crystallization solvent was added to crystallize and the solution was filtered to obtain a solid crude product. After post-processing, the S-acetyl-L-glutathione was obtained. The temperature of the first solution is 16~25℃, and the temperature of the second solution is 16~25℃. The inorganic protic strong acid is 70-72% perchloric acid or 90-95% sulfuric acid by mass fraction.

2. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, The mass of L-glutathione added to each milliliter of the acetic acid is 3-8 g.

3. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, In the inorganic protic strong acid, the molar amount of hydrogen ions is 1 to 1.5 times the molar amount of L-glutathione.

4. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, The amount of acetic anhydride used is 1.0 to 1.8 times the molar amount of L-glutathione.

5. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, The amount of water used is 10-20% of the molar amount of the L-glutathione.

6. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, The pH is adjusted to 3-6 by adding an alkali, wherein the alkali is one of triethylamine, ammonia, sodium carbonate, or sodium bicarbonate.

7. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, The crystallization solvent is one of methanol, ethanol, and acetone; The mass of L-glutathione in each milliliter of the crystallization solvent is 8-15 g; The crystallization temperature is 5~15℃.

8. The method for synthesizing S-acetyl-L-glutathione according to claim 1, characterized in that, The post-processing steps include: The solid crude product is added to an aqueous methanol or ethanol solution, stirred for 1 to 3 hours, filtered, washed, and dried to obtain the S-acetyl-L-glutathione. In the methanol or ethanol aqueous solution, the volume fraction of the solute is 50-90%.

9. The method for synthesizing S-acetyl-L-glutathione according to claim 8, characterized in that, The stirring temperature is 10~25℃.

Images