Synthetic method of L-leucyl-L-glutamine

Abstract

The invention discloses a synthetic method of L-leucyl-L-glutamine, and belongs to the technical field of organic synthesis. The preparation method comprises the following steps: protecting amino of L-leucine through phthalic anhydride to obtain phthaloyl-L-leucine, and then carrying out chlorination reaction by using a chlorination reagent to obtain phthaloyl-L-leucyl chloride; then carrying out a reaction with L-glutamine so as to obtain phthaloyl-L-leucyl-L-glutamine; then removing a protecting group through hydrazinolysis reaction to obtain an L-leucyl-L-glutamine crude product; and finally, purifying by adopting water as a solvent to obtain the L-leucyl-L-glutamine. According to the invention, cheap L-leucine and L-glutamine are used as raw materials, the synthesis route is simple, water is used as a solvent in the purification process, the use of an organic solvent is avoided, and the obtained product is excellent in purity, high in yield and easy for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and particularly relates to a synthesis method of L-leucyl-L-glutamine. BACKGROUND

[0002] L-leucine is one of the essential amino acids for human body, which belongs to branched-chain amino acid (BCAA), and its main functions include promoting protein synthesis, maintaining muscle health, regulating blood sugar, supporting immune function and promoting wound repair. It cannot be synthesized by the human body itself and needs to be obtained through diet or supplements.

[0003] Glutamine provides essential nitrogen for the body and promotes the synthesis of proteins in muscle cells. It can enhance strength and endurance. Glutamine is an important fuel for the immune system and can enhance the function of the immune system. Glutamine is the basic energy source for the cells of the gastrointestinal tract. Glutamine can improve brain function. Glutamine can improve the body's antioxidant capacity. Supplementing glutamine can improve the body's antioxidant capacity, stabilize cell membranes and protein structures by maintaining and increasing the glutamine reserves in tissue cells. Glutamine can strengthen nutritional support, improve the body's metabolic nitrogen balance, promote protein synthesis and increase the total number of lymphocytes. Glutamine can maintain the intestinal permeability of patients with severe acute pancreatitis, reduce the occurrence of intestinal bacterial translocation, inhibit the release of inflammatory mediators, reduce the degree of body stress response and shorten the hospitalization time. Glutamine can be used for biochemical research and as a bacterial culture medium.

[0004] The stability of glutamine mainly depends on its chemical and physical environment. In terms of chemical properties, glutamine is relatively stable in neutral solution, but it is easily decomposed into glutamol or propylated into pyrrole carboxyl alcohol in alcohol, alkali or hot water. In addition, glutamine is also unstable under acidic, heated and other conditions. However, L-leucyl-L-glutamine, as a small peptide containing leucine and glutamine, has good stability and its function is basically the same as that of glutamine. At the same time, it has good ACE inhibitor function. It is widely used and has good market prospects.

[0005] At present, there are few literatures about the synthesis method of L-leucyl-L-glutamine. Shimonishi, Y. reported the following synthesis method. This method has high raw material cost, long synthesis route, and uses Cbz and other protecting groups, which is not conducive to industrial production.

[0006] .

[0007] E. Wunsch et al. reported the following synthesis method, which also has high raw material cost and limitations in subsequent Cbz removal, making it difficult to realize industrial production.

[0008] .

[0009] Therefore, finding a synthetic method with low raw material cost, easy operation and being conducive to industrial production is the main task of the present application. SUMMARY

[0010] The present application discloses a synthetic method of L-leucyl-L-glutamine, and a reaction formula of the synthesis is as follows: .

[0011] The method comprises the following steps: (1) Synthesis of phthalyl-L-leucyl chloride Phthalyl-L-leucine is obtained by amino protection of L-leucine with phthalic anhydride, and then phthalyl-L-leucyl chloride is obtained by reacting with a chlorinating reagent.

[0012] (2) Synthesis of phthalyl-L-leucyl-L-glutamine Phthalyl-L-leucyl-L-glutamine is obtained by reacting phthalyl-L-leucyl chloride and L-glutamine in a mixed solvent of water and solvent A under the action of a base at-5-10℃. The molar ratio of L-glutamine, phthalyl-L-leucyl chloride and the base is 1:1.0-1.2:2.0-2.5.

[0013] In step (2), glutamine is easily soluble in water under alkaline conditions; while the water solubility of acyl chloride is poor, and water-soluble aprotic solvents such as acetone, tetrahydrofuran or acetonitrile are used, which can facilitate the reaction of acyl chloride with glutamine in water. If water-soluble solvents are not used or no solvent is used, acyl chloride will be quenched by water and become carboxylic acid before it is dissolved in water, and the acid-amine condensation cannot be carried out.

[0014] In step (2), the reaction needs to be carried out at a relatively low temperature. Since the activity of acyl chloride is high, too high or too low reaction temperature will cause the selectivity of acyl chloride to decrease, the selectivity of the reaction of acyl chloride with the amino group of glutamine and water in the system will greatly decrease, and the reaction yield will greatly decrease.

[0015] (3) Synthesis of L-leucyl-L-glutamine crude product L-leucyl-L-glutamine crude product is obtained by deprotection of phthalyl-L-leucyl-L-glutamine.

[0016] (4) Purification of L-leucyl-L-glutamine crude product The crude L-leucyl-L-glutamine is dissolved in water at room temperature using an acid solution or a base solution, and then solid-liquid separation is performed. A base solution or an acid solution is added dropwise to the filtrate to adjust the pH to 5.5-7.5, and then solid-liquid separation is performed to obtain a refined L-leucyl-L-glutamine product. In one scheme, when the crude L-leucyl-L-glutamine is dissolved using an acid solution, the molar ratio of the crude L-leucyl-L-glutamine to the acid solution is 1:0.8-1.2, and the pH at the end of the dissolution is 1-2. In another scheme, when the crude L-leucyl-L-glutamine is dissolved using a base solution, the molar ratio of the crude L-leucyl-L-glutamine to the base solution is 1:0.8-1.2, and the pH at the end of the dissolution is 9-10.

[0017] In step (4), a refining method is obtained according to the characteristics of L-leucyl-L-glutamine. Because the solubility of L-leucyl-L-glutamine is very small in a single solvent such as water, methanol, ethanol, etc., or in a mixed solvent such as water and methanol, water and ethanol, etc., L-leucyl-L-glutamine cannot be completely dissolved, and impurities cannot be effectively removed to obtain purification. Therefore, we purify according to the characteristics of L-leucyl-L-glutamine dissolved in an acid or a base. The impurities brought in steps (1)-(3) are very easy to remove in this step, the purification process is very simple, and the yield is very high.

[0018] Specifically, step (1) comprises: refluxing L-leucine and phthalic anhydride in toluene under catalysis of triethylamine to obtain a phthalyl-L-leucine solution; after the reaction is completed, the temperature is lowered to 60-70°C, a chlorinating reagent is added dropwise, and after the dropwise addition is completed, the reaction is maintained. After the reaction is completed, the pressure is reduced to concentrate to no obvious solvent is evaporated, and then solvent A is added to obtain a phthalyl-L-leucyl chloride solution. The molar ratio of L-leucine, phthalic anhydride, chlorinating reagent and triethylamine is 1:1.0-1.1:1.0-1.5:0.01-0.05. The chlorinating reagent is selected from thionyl chloride, phosphorus trichloride, phosphorus pentachloride or oxalyl chloride, etc., and is preferably thionyl chloride.

[0019] The solvent A is selected from tetrahydrofuran, acetone, 1.4-dioxane or acetonitrile, etc., and is preferably acetone. In the mixed solvent of water and solvent A, the mass ratio of solvent A to water is 1:1-5, and the mass ratio of solvent A to L-leucine is 3-8:1. Preferably, the solvent A is acetone, and the mass ratio of solvent A to water is 1:2.

[0020] Specifically, step (2) comprises: dissolving the base in water, cooling to -5-10℃; adding L-glutamine, and then quickly adding o-phthalyl-L-leucyl chloride solution (specifically, acetone solution), dropping for 10-30 minutes, and reacting for 1-2 hours; after the reaction is completed, adjusting the pH to 1-2 with hydrochloric acid, solid-liquid separation, water leaching, and drying to obtain o-phthalyl-L-leucyl-L-glutamine. The base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, triethylamine, and pyridine. Preferably, the base is selected from sodium hydroxide and sodium carbonate, and the mass ratio of sodium carbonate to sodium hydroxide is 2-4:1, which has a very good effect.

[0021] Specifically, step (3) comprises: reacting o-phthalyl-L-leucyl-L-glutamine in solvent B under the action of a deprotection reagent, and the reaction temperature is 60-90℃. After the reaction is completed, cooling to room temperature, adding acid to pH=1-2, solid-liquid separation, water leaching, adjusting the pH of the filtrate to 6.0-6.5 with ammonia water, solid-liquid separation, leaching, and drying to obtain L-leucyl-L-glutamine crude product. The solvent B is selected from water, methanol or ethanol, and preferably water. The deprotection reagent is selected from hydrazine hydrate, n-propylamine or n-butylamine, and preferably hydrazine hydrate. The molar ratio of o-phthalyl-L-leucyl-L-glutamine to the deprotection reagent is 1:1.0-20.0.

[0022] In step (4), the acid solution is selected from hydrochloric acid aqueous solution or acetic acid aqueous solution, and preferably hydrochloric acid aqueous solution. The base solution is selected from sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or ammonia water, and preferably sodium hydroxide solution. The concentration of the acid solution is 5-30wt%, and the concentration of the base solution is 5-30wt%.

[0023] Preferably, in step (4), the L-leucyl-L-glutamine crude product is dissolved in sodium hydroxide solution at room temperature in water, the molar ratio of the L-leucyl-L-glutamine crude product to the sodium hydroxide solution is 1:0.8-1.2, and the pH at the end of dissolution is 9-10. After solid-liquid separation, hydrochloric acid is added to the filtrate to adjust the pH to 6.0-6.5, and then solid-liquid separation, leaching and drying are performed to obtain L-leucyl-L-glutamine refined product. The stability of L-leucyl-L-glutamine at room temperature and pH 9-10 is better than that at room temperature and pH 1-2, and the preparation of sodium hydroxide solution is more accurate when the alkali is adjusted first, and the volatilization of hydrochloric acid is avoided. Therefore, it is more convenient to adjust the alkali first.

[0024] Specifically, the L-leucyl-L-glutamine synthesis method provided by the embodiments of the present application comprises the following steps: (1) Synthesis of o-phthalyl-L-leucyl chloride L-leucine and phthalic anhydride are subjected to a dehydration reaction in toluene under catalysis of triethylamine to obtain a phthalyl-L-leucine solution; after the reaction is completed, the temperature is lowered to 60-70°C, and thionyl chloride is added dropwise, and after the dropping is completed, the reaction is maintained; after the reaction is completed, the solution is concentrated under reduced pressure until no obvious solvent is distilled out, and then acetone is added to obtain a phthalyl-L-leucine chloride solution. The molar ratio of L-leucine, phthalic anhydride, thionyl chloride and triethylamine is 1:1.0-1.1:1.0-1.5:0.01-0.05.

[0025] (2) Synthesis of phthalyl-L-leucyl-L-glutamine The base is dissolved in water, and the temperature is lowered to -5-10°C; L-glutamine is added, and then the phthalyl-L-leucine chloride solution is added dropwise quickly, the dropping is completed in 10-30 minutes, the reaction is maintained for 1-2 hours, after the reaction is completed, the pH is adjusted to 1-2 by using hydrochloric acid, and then solid-liquid separation is performed, water washing is performed, and drying is performed to obtain phthalyl-L-leucyl-L-glutamine. The molar ratio of L-glutamine, phthalyl-L-leucine chloride and the base is 1:1.0-1.2:2.0-2.5; the mass ratio of acetone to water is 1:1-5; and the mass ratio of acetone to L-leucine is 3-8:1. The base is selected from sodium hydroxide and sodium carbonate, and the mass ratio of sodium carbonate to sodium hydroxide is 2-4:1.

[0026] (3) Synthesis of L-leucyl-L-glutamine crude product Phthalyl-L-leucyl-L-glutamine is subjected to a reaction in water under the action of hydrazine hydrate, and the reaction temperature is 60-90°C; after the reaction is completed, the temperature is lowered to room temperature, hydrochloric acid is added dropwise until the pH is 1-2, solid-liquid separation is performed, water washing is performed, the pH of the filtrate is adjusted to 6.0-6.5 by using ammonia water, solid-liquid separation is performed, washing is performed, and drying is performed to obtain an L-leucyl-L-glutamine crude product. The molar ratio of phthalyl-L-leucyl-L-glutamine to hydrazine hydrate is 1:1.0-20.0.

[0027] (4) Purification of L-leucyl-L-glutamine crude product In water at room temperature, crude L-leucyl-L-glutamine is dissolved in acid or alkaline solution, followed by solid-liquid separation. The pH of the filtrate is adjusted to 5.5-7.5 by adding more alkaline or acidic solution, and the solid-liquid separation yields refined L-leucyl-L-glutamine. When dissolving crude L-leucyl-L-glutamine in acid, the molar ratio of crude L-leucyl-L-glutamine to acid solution is 1:0.8-1.2, with the final pH set at 1-2. When dissolving crude L-leucyl-L-glutamine in alkaline solution, the molar ratio is 1:0.8-1.2, with the final pH set at 9-10. The acid solution is selected from aqueous hydrochloric acid or acetic acid; the alkaline solution is selected from aqueous sodium hydroxide, potassium hydroxide, or ammonia solution; the concentration of both the acid and alkaline solutions is 5-30 wt%.

[0028] This invention uses inexpensive L-leucine and L-glutamine as raw materials. L-leucine is protected with phthalic anhydride to obtain phthaloyl-L-leucine, which is then reacted with a chlorinating agent to obtain phthaloyl-L-leucyl chloride. This chloride is then condensed with L-glutamine, and deprotected to obtain crude L-leucyl-L-glutamine. Finally, L-leucyl-L-glutamine is purified. The synthetic route is simple, the deprotection conditions are mild, and the purification process uses water as a solvent, avoiding the use of organic solvents. The purity is excellent (greater than 99%), and the yield is high (overall yield around 80%, with the first three steps achieving yields of over 90%), making it suitable for industrial production. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0030] Example 1: Synthesis of phthaloyl-L-leucyl chloride Add 500g of toluene, 100.0g of L-leucine, and 113.6g of phthalic anhydride sequentially to a four-necked flask, then heat to reflux for water separation. After the reaction is complete, cool to 60-70℃ and add 108.4g of thionyl chloride dropwise. After the addition is complete, maintain the temperature for further reaction. After the reaction is complete, concentrate under reduced pressure until no obvious solvent evaporates, then stop the concentration. Add 500g of acetone for later use. The yield is calculated as 100.0%.

[0031] Example 2: Synthesis of phthaloyl-L-leucyl-L-glutamine Into a four-necked flask, add water 1000g, sodium hydroxide 30.4g, sodium carbonate 80.5g, stir to dissolve, cool to -5~10℃, add L-glutamine 100.9g, quickly add the solution of phthalyl-L-leucyl chloride in acetone from Example 1, dropwise, 10~30 minutes dropwise, 1-2 hours reaction, adjust pH to 1-2 with hydrochloric acid, a large amount of solid precipitates, filter, wash with water, dry to obtain phthalyl-L-leucyl-L-glutamine 266.4g, yield 99.1%.

[0032] Example 3: Synthesis of L-leucyl-L-glutamine crude product Into a four-necked flask, add water 1500g, 80% hydrazine hydrate 60.3g and phthalyl-L-leucyl-L-glutamine 250.0g, heat to 75~85℃ and react. After the reaction is completed, cool to room temperature, add 30% hydrochloric acid dropwise to pH=1~2, filter, wash with water, obtain the filtrate, then adjust the pH of the filtrate to 6~6.5 with 25% ammonia water, a large amount of solid precipitates, filter, wash, dry to obtain L-leucyl-L-glutamine crude product 162.7g, yield 91.4%.

[0033] Example 4: Purification of L-leucyl-L-glutamine Into a four-necked flask, add water 450g and L-leucyl-L-glutamine crude product 30.0g, at room temperature, add 10% ammonia water dropwise until the system is almost clear, pH=9~10, consume about 10% ammonia water 20.2g, filter to obtain the filtrate, then slowly add 10% hydrochloric acid to the filtrate until the system pH=6~6.5, stir for 1~2 hours, filter, wash, dry to obtain L-leucyl-L-glutamine 26.5g, yield 88.3%, purity 99.2%.

[0034] Example 5: Purification of L-leucyl-L-glutamine Into a four-necked flask, add water 450g and L-leucyl-L-glutamine crude product 30.0g, at room temperature, add 10% sodium hydroxide solution dropwise until the system is almost clear, pH=9~10, consume about 10% sodium hydroxide solution 47.6g, filter to obtain the filtrate, then slowly add 10% hydrochloric acid to the filtrate until the system pH=6~6.5, stir for 1~2 hours, filter, wash, dry to obtain L-leucyl-L-glutamine 27.4g, yield 91.3%, purity 99.6%.

[0035] Example 6: Purification of L-leucyl-L-glutamine A four-necked flask was charged with water 450 g and L-leucyl-L-glutamine crude product 30.0 g, and 10% potassium hydroxide solution was added dropwise at room temperature until the system was almost clear, pH = 9-10, and 10% potassium hydroxide solution was consumed about 66.7 g, the filtrate was obtained by filtration, then 10% hydrochloric acid was slowly added dropwise to the filtrate until the system pH = 6-6.5, stirred for 1-2 hours, washed and dried by filtration to obtain L-leucyl-L-glutamine 27.6 g, yield 92.0%, purity 99.1%.

[0036] Example 7: Purification of L-leucyl-L-glutamine A four-necked flask was charged with water 450 g and L-leucyl-L-glutamine crude product 30.0 g, and 10% potassium hydroxide solution was added dropwise at room temperature until the system was almost clear, pH = 9-10, and 10% potassium hydroxide solution was consumed about 66.7 g, the filtrate was obtained by filtration, then 10% hydrochloric acid was slowly added dropwise to the filtrate until the system pH = 6-6.5, stirred for 1-2 hours, washed and dried by filtration to obtain L-leucyl-L-glutamine 27.6 g, yield 92.0%, purity 99.1%.

[0037] Example 8: Purification of L-leucyl-L-glutamine A four-necked flask was charged with water 450 g and L-leucyl-L-glutamine crude product 30.0 g, and 10% potassium hydroxide solution was added dropwise at room temperature until the system was almost clear, pH = 9-10, and 10% potassium hydroxide solution was consumed about 66.7 g, the filtrate was obtained by filtration, then 10% hydrochloric acid was slowly added dropwise to the filtrate until the system pH = 6-6.5, stirred for 1-2 hours, washed and dried by filtration to obtain L-leucyl-L-glutamine 27.6 g, yield 92.0%, purity 99.1%.

[0038] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application, 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 method for synthesizing L-leucyl-L-glutamine, characterized in that, The method includes the following steps: (1) Synthesis of phthaloyl-L-leucyl chloride Phthaloyl-L-leucine was obtained by amino protection of L-leucine with phthalic anhydride, and then reacted with a chlorinating agent to obtain phthaloyl-L-leucyl chloride. (2) Synthesis of phthaloyl-L-leucyl-L-glutamine In a mixed solvent of water and solvent A, phthaloyl-L-leucyl chloride and L-glutamine react at -5 to 10°C under the action of an alkali to obtain phthaloyl-L-leucyl-L-glutamine; the molar ratio of L-glutamine, phthaloyl-L-leucyl chloride and alkali is 1:1.0-1.2:2.0-2.

5. (3) Synthesis of crude L-leucyl-L-glutamine Phthaloyl-L-leucyl-L-glutamine was deprotected to give crude L-leucyl-L-glutamine. (4) Purification of crude L-leucyl-L-glutamine In water at room temperature, crude L-leucyl-L-glutamine is dissolved in acid or alkaline solution, and the solid and liquid are separated. Alkaline or acid solution is added dropwise to the filtrate to adjust the pH to 5.5-7.5, and the solid and liquid are separated to obtain refined L-leucyl-L-glutamine. When the crude L-leucyl-L-glutamine is dissolved in an acid solution, the molar ratio of crude L-leucyl-L-glutamine to acid solution is 1:0.8-1.2, and the pH at the dissolution endpoint is 1-2. When the crude L-leucyl-L-glutamine is dissolved in an alkaline solution, the molar ratio of crude L-leucyl-L-glutamine to alkaline solution is 1:0.8-1.2, and the pH at the dissolution endpoint is 9-10.

2. The method for synthesizing L-leucyl-L-glutamine according to claim 1, characterized in that, Step (1) specifically includes: in toluene, under the catalysis of triethylamine, L-leucine and phthalic anhydride are refluxed and dehydrated to obtain a phthaloyl-L-leucine solution; after the reaction is completed, the temperature is lowered to 60-70℃, and a chlorination reagent is added dropwise. After the addition is completed, the reaction is kept at the temperature; after the reaction is completed, the solution is concentrated under reduced pressure until no obvious solvent is distilled off, and then solvent A is added to obtain a phthaloyl-L-leucyl chloride solution; the molar ratio of L-leucine, phthalic anhydride, chlorination reagent and triethylamine is 1:1.0-1.1:1.0-1.5:0.01-0.05; the chlorination reagent is selected from thionyl chloride, phosphorus trichloride, phosphorus pentachloride or oxalyl chloride.

3. The method for synthesizing L-leucyl-L-glutamine according to claim 2, characterized in that, Solvent A is selected from tetrahydrofuran, acetone, 1,4-dioxane, or acetonitrile; in the mixed solvent of water and solvent A, the mass ratio of solvent A to water is 1:1-5; the mass ratio of solvent A to L-leucine is 3-8:

1.

4. The method for synthesizing L-leucyl-L-glutamine according to claim 2, characterized in that, Solvent A is acetone, and the mass ratio of solvent A to water is 1:

2.

5. The method for synthesizing L-leucyl-L-glutamine according to claim 2, characterized in that, Step (2) specifically includes: dissolving the alkali in water and cooling it to -5 to 10°C; adding L-glutamine, and then rapidly adding phthaloyl-L-leucyl chloride solution over 10 to 30 minutes, allowing the reaction to proceed for 1 to 2 hours. After the reaction is complete, the pH is adjusted to 1 to 2 with hydrochloric acid, the solid and liquid are separated, washed with water, and dried to obtain phthaloyl-L-leucyl-L-glutamine; the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, triethylamine, and pyridine.

6. The method for synthesizing L-leucyl-L-glutamine according to claim 5, characterized in that, The alkali is selected from sodium hydroxide and sodium carbonate, and the mass ratio of sodium carbonate to sodium hydroxide is 2-4:

1.

7. The method for synthesizing L-leucyl-L-glutamine according to claim 2, characterized in that, Step (3) specifically includes: phthaloyl-L-leucyl-L-glutamine reacts in solvent B under the action of a deprotecting agent at a reaction temperature of 60-90℃; after the reaction is completed, the temperature is lowered to room temperature, acid is added dropwise to pH=1-2, solid-liquid separation is performed, water is rinsed, the pH of the filtrate is adjusted to 6.0-6.5 with ammonia, solid-liquid separation is performed, rinsing is performed, and drying is carried out to obtain crude L-leucyl-L-glutamine; the solvent B is selected from water, methanol or ethanol; the deprotecting agent is selected from hydrazine hydrate, n-propylamine or n-butylamine; the molar ratio of phthaloyl-L-leucyl-L-glutamine to the deprotecting agent is 1:1.0-20.

0.

8. The method for synthesizing L-leucyl-L-glutamine according to claim 1, characterized in that, In step (4), the acid solution is selected from hydrochloric acid aqueous solution or acetic acid aqueous solution; the alkaline solution is selected from sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or ammonia solution; the concentration of the acid solution is 5-30 wt%, and the concentration of the alkaline solution is 5-30 wt%.

9. The method for synthesizing L-leucyl-L-glutamine according to claim 8, characterized in that, In step (4), crude L-leucyl-L-glutamine is dissolved in water at room temperature using sodium hydroxide solution. The molar ratio of crude L-leucyl-L-glutamine to sodium hydroxide solution is 1:0.8-1.

2. The pH at the dissolution endpoint is set to 9-10. After solid-liquid separation, hydrochloric acid is added dropwise to the filtrate to adjust the pH to 6.0-6.

5. After solid-liquid separation, the product is washed and dried to obtain refined L-leucyl-L-glutamine.

10. The method for synthesizing L-leucyl-L-glutamine according to claim 1, characterized in that, The method includes the following steps: (1) Synthesis of phthaloyl-L-leucyl chloride In toluene, L-leucine and phthalic anhydride react under triethylamine catalysis by reflux to remove water, yielding a phthaloyl-L-leucine solution. After the reaction is complete, the temperature is lowered to 60-70℃, and thionyl chloride is added dropwise. After the addition is complete, the reaction is maintained at this temperature. After the reaction is complete, the solution is concentrated under reduced pressure until no obvious solvent evaporates, and then acetone is added to obtain a phthaloyl-L-leucyl chloride solution. The molar ratio of L-leucine, phthalic anhydride, thionyl chloride, and triethylamine is 1:1.0-1.1:1.0-1.5:0.01-0.

05. (2) Synthesis of phthaloyl-L-leucyl-L-glutamine The alkali was dissolved in water and cooled to -5 to 10°C. L-glutamine was added, followed by rapid dropwise addition of phthaloyl-L-leucyl chloride solution over 10-30 minutes. The reaction was allowed to proceed for 1-2 hours. After the reaction was complete, the pH was adjusted to 1-2 with hydrochloric acid. The solid and liquid phases were separated, washed with water, and dried to obtain phthaloyl-L-leucyl-L-glutamine. The molar ratio of L-glutamine, phthaloyl-L-leucyl chloride, and alkali was 1:1.0-1.2:2.0-2.

5. The mass ratio of acetone to water was 1:1-5. The mass ratio of acetone to L-leucine was 3-8:

1. The alkali was selected from sodium hydroxide and sodium carbonate, with a mass ratio of sodium carbonate to sodium hydroxide of 2-4:

1. (3) Synthesis of crude L-leucyl-L-glutamine Phthaloyl-L-leucyl-L-glutamine reacts in water with hydrazine hydrate at a temperature of 60-90℃. After the reaction is complete, the mixture is cooled to room temperature, and hydrochloric acid is added dropwise until the pH reaches 1-2. The solid and liquid phases are separated, and the mixture is washed with water. The pH of the filtrate is adjusted to 6.0-6.5 with ammonia, and the solid and liquid phases are separated again. The mixture is then washed and dried to obtain crude L-leucyl-L-glutamine. The molar ratio of phthaloyl-L-leucyl-L-glutamine to hydrazine hydrate is 1:1.0-20.

0. (4) Purification of crude L-leucyl-L-glutamine In water at room temperature, crude L-leucyl-L-glutamine is dissolved in an acidic or alkaline solution, followed by solid-liquid separation. The pH of the filtrate is adjusted to 5.5-7.5 by adding an acidic or alkaline solution, and the solid-liquid separation yields refined L-leucyl-L-glutamine. When dissolving crude L-leucyl-L-glutamine in an acidic solution, the molar ratio of crude L-leucyl-L-glutamine to acidic solution is 1:0.8-1.2, with the final pH set at 1-2. When dissolving crude L-leucyl-L-glutamine in an alkaline solution, the molar ratio of crude L-leucyl-L-glutamine to alkaline solution is 1:0.8-1.2, with the final pH set at 9-10. The acidic solution is selected from aqueous hydrochloric acid or acetic acid; the alkaline solution is selected from aqueous sodium hydroxide, potassium hydroxide, or ammonia; the concentration of both the acidic and alkaline solutions is 5-30 wt%.