Synthesis method of L-selenium-methyl selenocysteine

Abstract

The invention provides an L-selenium-methyl selenocysteine synthesis method, which comprises: mixing dimethyl diselenide and sodium borohydride, and adding a sodium hydroxide solution to carry out a reaction to obtain a sodium methyl selenol solution; 3-chloro-L-alanine methyl ester hydrochloride is prepared, and the prepared 3-chloro-L-alanine methyl ester hydrochloride and a sodium methyl selenol solution are subjected to a stirring reaction; acidifying the solution subjected to the stirring reaction, extracting, removing impurities, leaving a water phase, heating, carrying out reduced pressure distillation to obtain solid crystals, carrying out secondary extraction on the solid crystals by adopting methanol, adding triethylamine, and carrying out stirring crystallization to obtain an L-selenium-methyl selenocysteine solid crude product; the L-selenium-methyl selenocysteine solid crude product is subjected to hydration and recrystallization, and an L-selenium-methyl selenocysteine solid is obtained; the L-selenium-methyl selenocysteine synthesized by the method is simple in process route, mild in condition and high in purity and yield.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and particularly relates to a method for synthesizing L-seleno-methylselenocysteine. Background Art

[0002] Selenium is an essential trace element for the human body, but it cannot be synthesized in the human body and needs to be completely supplemented through external intake. Selenium deficiency in the human body can cause dysfunctions of some important organs and lead to the occurrence of many serious diseases. L-seleno-methylselenocysteine (SeMCYS) is a natural selenium-containing amino acid and also an approved new generation of nutritional fortifier. It has various functions such as inhibiting tumors, antioxidation, assisting in the treatment of cardiovascular diseases, and detoxifying.

[0003] Currently, the commonly used method for synthesizing seleno-methylselenocysteine is the sodium methylselenolate substitution method. Existing technologies usually use alanine intermediates protected by methyl esters or amide groups to carry out nucleophilic substitution reactions with sodium methylselenolate, and subsequent hydrolysis reactions are required to remove the methyl ester or amide group protecting groups to obtain the target product; this step-by-step process design results in the conversion of key intermediates to end products through two independent reaction stages of substitution and hydrolysis, thereby causing material losses and side reaction accumulation in multiple steps, resulting in a long process route and low overall product yield, seriously restricting the improvement of production efficiency. In addition, conventional nucleophilic substitution reactions are carried out in an organic phase reaction system, and a large amount of organic solvents such as tetrahydrofuran, dioxane, and sodium methoxide are used in the reaction process. These solvents significantly increase production costs and environmental protection treatment pressures, and the use of strong alkaline reagents such as sodium methoxide also greatly increases the operation difficulty. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a method for synthesizing L-seleno-methylselenocysteine to solve the problems existing in the prior art.

[0005] The present invention provides a method for synthesizing L-seleno-methylselenocysteine, comprising the following steps: S10, adding dimethyldiselenide and sodium borohydride into a first reaction flask for mixing, and adding a sodium hydroxide solution into the mixed first reaction flask for reaction to obtain a sodium methylselenolate solution; S20, preparing 3-chloro-L-alanine methyl ester hydrochloride, and adding the prepared 3-chloro-L-alanine methyl ester hydrochloride into the first reaction flask to carry out a stirring reaction with the sodium methylselenolate solution; S30, acidifying the solution after the stirring reaction and then performing extraction, removing impurities, leaving the aqueous phase, heating and performing reduced pressure distillation to obtain solid crystals, performing secondary extraction on the solid crystals with methanol, and then adding triethylamine for stirring crystallization to obtain a crude solid of L-seleno-methylselenocysteine; S40, subject the crude L-seleno-methylselenocysteine solid to hydration and then recrystallization to obtain the L-seleno-methylselenocysteine solid.

[0006] Preferably, in step S10: The molar ratio of dimethyldiselenide, sodium borohydride, and sodium hydroxide is (1:5:5) - (5:1:1); The initial temperature of the sodium hydroxide solution is less than 10 °C; React in the first reaction flask for 4 h - 10 h to obtain the sodium selenomethoxide solution.

[0007] Preferably, the steps for preparing 3-chloro-L-alanine methyl ester hydrochloride in step S20 include: S21, add dichloromethane and acetonitrile to the second reaction flask and stir; S22, prepare L-serine methyl ester hydrochloride, add L-serine methyl ester hydrochloride to the second reaction flask, and add thionyl chloride followed by a normal temperature water bath; S23, heat the second reaction flask to the preset temperature, add a supplementary solvent dropwise to the second reaction flask and react at the preset temperature, and a solid precipitates in the reaction solution; S24, filter out the solid in the reaction solution and wash it to obtain the wet crude 3-chloro-L-alanine methyl ester hydrochloride, and dry the wet crude 3-chloro-L-alanine methyl ester hydrochloride to obtain 3-chloro-L-alanine methyl ester hydrochloride.

[0008] Preferably, in step S21, the addition ratio of dichloromethane to acetonitrile is 1:3 - 3:1; In step S23, the preset temperature is from room temperature to 50 °C, the supplementary solvent is a mixed solvent of dichloromethane and acetonitrile, the solution in the second reaction flask reacts at the preset temperature for 6 h - 10 h, then stop heating and stirring, and refrigerate to precipitate a solid; In step S24, wash the solid precipitated in step S23 with dichloromethane.

[0009] Preferably, the steps for preparing L-serine methyl ester hydrochloride in step S22 include: S221, add methanol to the third reaction flask and perform an ice-water bath, add thionyl chloride to the third reaction flask in the ice-water bath and stir to react to obtain an intermediate product; S222, mix the obtained intermediate product with L-serine and then perform a heating and stirring reaction; S223, after the stirring reaction ends, perform reduced pressure concentration on the reaction solution, rotary evaporate with methanol until no liquid distills out from the third reaction flask to obtain the wet crude L-serine methyl ester hydrochloride, and dry the wet crude L-serine methyl ester hydrochloride to obtain L-serine methyl ester hydrochloride.

[0010] Preferably, in step S221, the temperature of the ice-water bath is 0°C - 10°C, and the stirring reaction time is 0.5 h - 1 h; In step S222, after the intermediate product is mixed with L-serine, the temperature is raised to 40°C - 50°C, and the stirring reaction time after the temperature rise is 2 h - 3 h. Among them, the molar ratio of L-serine, thionyl chloride, and methanol is (1:0.8:10) - (1:1.2:15).

[0011] Preferably, in step S20, the step of adding the prepared methyl 3-chloro-L-alaninate hydrochloride to the first reaction flask and stirring and reacting with sodium selenomethanethiol solution includes: Cool the sodium selenomethanethiol solution obtained in step S10 to below 10°C and stir for 10 min - 15 min; Add methyl 3-chloro-L-alaninate hydrochloride to the first reaction flask and then stir for 10 min - 15 min; Heat the solution in the first reaction flask to 25°C - 35°C and react for 8 h - 15 h.

[0012] Preferably, step S30 specifically includes: S31, Cool the reaction solution after the reaction in step S20 to below 10°C, add hydrochloric acid to adjust the pH value of the reaction solution, and stir for 1 h - 2 h; S32, Extract with ethyl acetate 2 - 3 times, retain the aqueous phase and perform heating under reduced pressure distillation to obtain solid crystals; S33, Perform secondary extraction on the solid crystals with a methanol solution, filter off the remaining solids to obtain a methanol extract; S34, Raise the temperature under a water bath condition, add triethylamine dropwise to the methanol extract, adjust the solution pH, then cool and stir until the solids completely precipitate and then filter; S35, Collect the filter cake in S34, wash it with methanol to obtain a crude product of L-seleno-methylselenocysteine solid.

[0013] Preferably, in step 31, adjust the pH of the reaction solution to 1 - 2 with hydrochloric acid; In step 32, the volume ratio of the extractant ethyl acetate to the reaction solution to be extracted is 2:1 - 1:2; In step 33, the ratio of the mass m of the solid crystals to the volume v of the extractant methanol solution is m:v = 1:1 - 1:5; In step 34, the temperature of the water bath heating is 45°C - 55°C, adjust the solution pH to 5.5 - 6.5 with triethylamine, and the temperature of the cooling and stirring is lower than 15°C - 20°C.

[0014] Preferably, step S40 specifically includes: S41. Add the crude L-seleno-methylselenocysteine solid to purified water and completely dissolve it under the condition of 55°C - 65°C. S42. Add activated carbon to the dissolved solution and perform suction filtration for decolorization. S43. Heat and reduce the pressure of the decolorized filtrate to saturation, and dropwise add ethanol under the water bath condition of 45°C - 55°C until turbidity appears, then stop, and stir for 25 min - 30 min. S44. After stirring, continue to dropwise add ethanol and then stir for 0.5 h - 4.0 h, let it stand and cool naturally, stir and crystallize until the solid completely precipitates, filter, collect the filter cake, and wash the filter cake with ethanol to obtain the L-seleno-methylselenocysteine solid.

[0015] The beneficial effects of the present invention are as follows: The synthesis method of L-seleno-methylselenocysteine provided in this application shows outstanding innovation and technological advancement. First, by innovatively using an aqueous reaction system to replace the traditional organic phase reaction system, a one-step direct conversion of chiral L-serine as the starting material to 3-chloro-L-alanine methyl ester hydrochloride is realized. While avoiding the hydrolysis process in the prior art, steps such as group protection, hydroxyl activation, and subsequent deprotection are reduced, significantly shortening the process route and greatly improving the total reaction yield. Second, through the in-situ generation strategy of sodium methylselenol, the technical bottleneck of poor stability and difficult separation and purification of this intermediate is effectively solved, ensuring the reliability of the reaction system while simplifying the operation process. Third, the selected raw materials are inexpensive and easily available, the reaction medium is green and environmentally friendly, and the process conditions are mild and controllable, with significant economic benefits and environmental friendliness. The synergistic effect of the above technical features makes this solution particularly suitable for industrial continuous production, has important application value in the field of L-seleno-methylselenocysteine synthesis, and is suitable for large-scale promotion.

[0016] Additional aspects and advantages of the present invention will be given in part in the following description, will become apparent in part from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the synthesis method of L-seleno-methylselenocysteine provided by the present invention; Figure 2 It is a high-resolution mass spectrum of the L-serine methyl ester hydrochloride sample prepared by the invention; Figure 3 It is an infrared spectrum analysis chart of the L-serine methyl ester hydrochloride sample prepared by the invention; Figure 4 It is a standard hydrogen spectrum of L-seleno-methylselenocysteine; Figure 5It is the standard carbon spectrum of L-seleno-methylselenocysteine; Figure 6 It is the hydrogen spectrum of L-seleno-methylselenocysteine prepared by the present invention; Figure 7 It is the carbon spectrum of L-seleno-methylselenocysteine prepared by the present invention.

[0018] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. Specific Embodiments

[0019] For the convenience of understanding the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing alternative embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0021] Example 1 This example provides a method for synthesizing L-seleno-methylselenocysteine. As Figure 1 shown, the preparation method includes steps S10-S40: S10, Add dimethyldiselenide and sodium borohydride into the first reaction flask for mixing, and add sodium hydroxide solution into the mixed first reaction flask for reaction to obtain sodium selenomethanol solution; S20, Prepare 3-chloro-L-alanine methyl ester hydrochloride, and add the prepared 3-chloro-L-alanine methyl ester hydrochloride into the first reaction flask to stir and react with the sodium selenomethanol solution; S30, Acidify the solution after the stirring reaction, then extract it, remove impurities, leave the aqueous phase, heat and distill it under reduced pressure to obtain solid crystals. Use methanol to extract the solid crystals twice, and then add triethylamine to stir and crystallize to obtain the crude solid of L-seleno-methylselenocysteine; S40, Hydrate the crude solid of L-seleno-methylselenocysteine and then recrystallize it to obtain the solid of L-seleno-methylselenocysteine.

[0022] In this embodiment, step S10 specifically includes: adding dimethyldiselenide and sodium borohydride with a molar ratio of 1:2 into a 250 ml reaction flask, and then preparing an aqueous sodium hydroxide solution, with the molar ratio of sodium borohydride to sodium hydroxide being 1:1; that is, the molar ratio of dimethyldiselenide, sodium borohydride, and sodium hydroxide is 1:2:2; cooling the sodium hydroxide solution to 8 °C in advance. Cooling the sodium hydroxide solution in advance can absorb the heat released when dimethyldiselenide, sodium borohydride, and sodium hydroxide come into contact, preventing the solution temperature from being too high. Then, stir and let it react naturally to room temperature. It can be understood that the room temperature is the ambient temperature, the reaction time is 8 h, and an aqueous solution of sodium selenomethoxide is obtained. This application prepares sodium selenomethoxide through an in-situ generation strategy, effectively solving the technical bottlenecks of poor stability and difficult separation and purification of this intermediate, and ensuring the reliability of the reaction system while simplifying the operation process.

[0023] In step S20, the steps for preparing 3-chloro-L-alanine methyl ester hydrochloride include: S21, adding dichloromethane and acetonitrile into a second reaction flask and stirring; S22, preparing L-serine methyl ester hydrochloride, adding L-serine methyl ester hydrochloride into the second reaction flask, and adding thionyl chloride followed by a constant temperature water bath at room temperature; S23, heating the second reaction flask to a preset temperature, adding a supplementary solvent dropwise to the second reaction flask to react at the preset temperature, and a solid precipitates in the reaction solution; S24, filtering out the solid in the reaction solution and washing it to obtain a wet crude product of 3-chloro-L-alanine methyl ester hydrochloride, and drying the wet crude product of 3-chloro-L-alanine methyl ester hydrochloride to obtain 3-chloro-L-alanine methyl ester hydrochloride.

[0024] In this embodiment, first add 200 ml of dichloromethane and 300 ml of acetonitrile into the reaction flask, with the addition ratio of dichloromethane to acetonitrile being 1:1.5; stir evenly, and the stirring rate can be 260 r / min; then add 100 g of L-serine methyl ester hydrochloride into the reaction flask, and weigh 91.8 g of thionyl chloride and add it thereto, with the constant temperature of the water bath at 30 °C; then start heating, heat up to 45 °C, and after 50 min, add 150 ml of dichloromethane and 150 ml of acetonitrile as a supplementary solvent dropwise to the reaction flask to react at 45 °C. The total reaction time is 7 h after the reaction flask is heated to 45 °C. The stirring parameters during the reaction can be 380 r / min. Then turn off the heating, stop stirring, refrigerate overnight to precipitate a solid, filter the reaction solution the next day, remove the brown filtrate to obtain a yellowish-brown filter cake; wash the yellowish-brown filter cake with dichloromethane to obtain a wet crude product of 3-chloro-L-alanine methyl ester hydrochloride, and dry the wet crude product of 3-chloro-L-alanine methyl ester hydrochloride to obtain 3-chloro-L-alanine methyl ester hydrochloride.

[0025] The steps for preparing L-serine methyl ester hydrochloride in step S22 include: S221, adding methanol to a third reaction flask and then performing an ice-water bath. Add thionyl chloride to the third reaction flask in the ice-water bath and stir for reaction to obtain an intermediate product; S222, mixing the obtained intermediate product with L-serine and then performing a temperature-raising stirring reaction; S223, after the stirring reaction ends, concentrate the reaction solution under reduced pressure until dry, and spin-dry with methanol until no liquid distills out of the third reaction flask to obtain wet crude L-serine methyl ester hydrochloride. Dry the wet crude L-serine methyl ester hydrochloride to obtain L-serine methyl ester hydrochloride.

[0026] In this example, add 1320 ml of methanol to a 2 L four-necked flask, stir in an ice-water bath at 5 °C, and the stirring rate can be 260 r / min. Then weigh 148.8 g of thionyl chloride and slowly add it to the system. After the addition of thionyl chloride is completed, stir in the ice-water bath for 0.5 h to obtain an intermediate product; weigh 110.1 g of L-serine and mix it with the intermediate product, then raise the temperature to 45 °C and stir for reaction at 45 °C for 3 h. The molar ratio of L-serine, thionyl chloride, and methanol is 1:1.2:12; after the reaction ends, turn off the heating device, cool naturally, and stir at room temperature overnight, and the stirring rate can be 200 r / min; the next day, concentrate the reaction solution under reduced pressure until dry, repeatedly add 500 ml of methanol and spin-dry twice until no liquid distills out of the flask to obtain wet crude L-serine methyl ester hydrochloride. Dry the wet crude L-serine methyl ester hydrochloride to obtain L-serine methyl ester hydrochloride; the chemical name of L-serine methyl ester hydrochloride is L-2-amino-3-hydroxypropionic acid methyl ester hydrochloride, and the molecular formula is C4H 10 ClNO3;: Optionally, in this example, high-resolution mass spectrometry and infrared spectroscopy analysis are performed on the prepared sample, and the analysis results are as Figure 2 and Figure 3 shown. The high-resolution first-order mass spectrometry in the ESI positive ion mode of the sample shows that the measured value of the mass-to-charge ratio of the target peak plus hydrogen C4H9NO3H [M+H] + is 120.0655, which is consistent with the theoretical mass-to-charge ratio of 120.0655 for L-serine methyl ester plus hydrogen; the infrared spectrum of the sample shows characteristic absorption peaks of groups such as hydroxyl, amino, alkyl, carbonyl, ester group, and amine salt, which are consistent with the structure of the compound L-serine methyl ester hydrochloride.

[0027] In the present application, an aqueous reaction system is innovatively adopted to replace the traditional organic-phase reaction system, realizing the one-step direct conversion of chiral L-serine as the starting material to methyl 3-chloro-L-alaninate hydrochloride. While avoiding the methyl ester hydrolysis process in the prior art, the process route is significantly shortened, reducing the problems of reaction material loss and side reaction accumulation caused by multiple reaction steps, and improving the overall reaction yield.

[0028] In step S20, the step of adding the prepared methyl 3-chloro-L-alaninate hydrochloride to the first reaction flask and stirring it with sodium methylselenolate solution includes: Cool the sodium methylselenolate solution obtained in step S10 to 8°C and stir for 10 min; After adding methyl 3-chloro-L-alaninate hydrochloride to the first reaction flask, stir for another 10 min; Heat the solution in the first reaction flask to 30°C and react for 10 h.

[0029] In the present application, the intermediate L-serine methyl ester hydrochloride and methyl 3-chloro-L-alaninate hydrochloride are prepared separately, ensuring the quality and stability of the intermediate, and ultimately improving the product quality. Methyl 3-chloro-L-alaninate hydrochloride is prepared by chiral synthesis technology, with easily available and inexpensive raw materials, convenient operation, mild and green reaction conditions, single product, easy separation, high yield, suitable for industrial production, and good quality; the process conditions are mild and controllable, with significant economic benefits and environmental friendliness.

[0030] Step S30 specifically includes: S31, Cool the reaction solution after the reaction in step S20 to 8°C, add hydrochloric acid to adjust the pH of the reaction solution to 1, and stir for 1 h; S32, Extract twice with ethyl acetate, the volume ratio of ethyl acetate to the reaction solution to be extracted is 1:2, retain the aqueous phase and perform heating under reduced pressure distillation to obtain solid crystals; S33, Perform secondary extraction on the solid crystals with methanol solution, the ratio of the mass m (g) of the solid crystals to the volume v (ml) of the extraction agent methanol solution is 1:3, filter off the remaining solid to obtain the methanol extract; S34, Heat to 50°C under water bath conditions, add triethylamine dropwise to the methanol extract, adjust the pH of the solution to 6, then cool to 15°C and stir until the solid completely precipitates and then filter; S35, Collect the filter cake in S34, wash with methanol to obtain the crude solid of L-seleno-methylselenocysteine.

[0031] Step S40 specifically includes: S41, Add 5 g of the crude solid of L-seleno-methylselenocysteine to 50 ml of purified water and completely dissolve it under the condition of 60°C; S42. Add activated carbon to the dissolved solution and perform suction filtration for decolorization; S43. Heat and distill the decolorized filtrate under reduced pressure until it reaches a saturated state. At 50 °C under a water bath condition, add ethanol dropwise until turbidity appears and then stop. Stir for 30 min; S44. After stirring, continue to add ethanol dropwise and then stir for 2 h. Let it stand and cool naturally. Stir and crystallize until the solid completely precipitates, then filter. Collect the filter cake and wash the filter cake with 50 ml of ethanol to obtain L-seleno-methylselenocysteine solid.

[0032] Optionally, the standard hydrogen spectrum and carbon spectrum of L-seleno-methylselenocysteine are as shown in Figure 4 and Figure 5 shown. The hydrogen spectrum and carbon spectrum of L-seleno-methylselenocysteine prepared in this example are as shown in Figure 6 and Figure 7 shown. By comparing Figure 4 and Figure 6 and Figure 5 and Figure 7 it can be seen that the hydrogen spectrum and carbon spectrum of L-seleno-methylselenocysteine prepared in this example are almost the same as those of the standard L-seleno-methylselenocysteine, that is, the L-seleno-methylselenocysteine prepared in this example has a high purity; Example 2 The difference between this example and Example 1 is as follows: Step S10 specifically includes: The molar ratio of dimethyldiselenide, sodium borohydride, and sodium hydroxide is 1:5:5; the sodium hydroxide solution is pre-cooled to 5 °C, and the reaction time is 4 h to obtain a solution of sodium selenomethanol.

[0033] The steps for preparing 3-chloro-L-alanine methyl ester hydrochloride in step S20 specifically include: In step S21, the ratio of dichloromethane to acetonitrile added is 1:3; In step S22, 80 g of L-serine methyl ester hydrochloride and 75 g of thionyl chloride are added; In step S23, the preset temperature is 25 °C, and the supplementary solvent is a mixed solvent of 100 ml of dichloromethane and 150 ml of acetonitrile. The solution in the second reaction flask reacts at 25 °C for 6 h, then the heating is turned off and the stirring is stopped. The solid precipitates after refrigeration.

[0034] The steps for preparing L-serine methyl ester hydrochloride in step S22 specifically include: In step S221, the temperature of the ice-water bath is 8 °C, and the stirring reaction time is 0.7 h; In step S222, the intermediate product is mixed with L-serine and then heated to 40°C, and the stirring reaction time after heating is 2 h. Among them, the molar ratio of L-serine, thionyl chloride, and methanol is 1:0.8:10.

[0035] The step of adding the prepared methyl 3-chloro-L-alaninate hydrochloride to the first reaction flask in step S20 and carrying out a stirring reaction with sodium selenomethanethiol solution specifically includes: Cool the sodium selenomethanethiol solution obtained in step S10 to 5°C and stir for 12 min; Add methyl 3-chloro-L-alaninate hydrochloride to the first reaction flask and then stir for 13 min; Heat the solution in the first reaction flask to 25°C and react for 8 h.

[0036] Step S30 specifically includes: S31, cool the reaction solution after the reaction in step S20 to 5°C, add hydrochloric acid to adjust the pH of the reaction solution to 1.5, and then stir for 1.5 h; S32, extract 3 times with ethyl acetate, the volume ratio of ethyl acetate to the reaction solution to be extracted is 1:1, retain the aqueous phase and carry out heating under reduced pressure distillation to obtain solid crystals; S33, carry out secondary extraction on the solid crystals with methanol solution, the ratio of the mass m (g) of the solid crystals to the volume v (ml) of the extraction agent methanol solution is 1:1, filter off the remaining solid to obtain a methanol extraction solution; S34, heat to 45°C under a water bath condition, add triethylamine dropwise to the methanol extraction solution, adjust the pH of the solution to 5.5, then cool to 18°C and stir until the solid completely precipitates and then filter; S35, collect the filter cake in S34, wash it with methanol to obtain a crude solid of L-seleno-methylselenocysteine.

[0037] Step S40 specifically includes: S41, add the crude solid of L-seleno-methylselenocysteine to purified water and completely dissolve it under the condition of 55°C; S42, add activated carbon to the dissolved solution and carry out suction filtration for decolorization; S43, carry out heating under reduced pressure distillation on the decolorized filtrate to the saturated state, dropwise add ethanol under the condition of a 45°C water bath until turbidity appears and then stop, and stir for 25 min; S44, continue to dropwise add ethanol after stirring and then stir for 0.5 h, let it stand and cool naturally, stir and crystallize until the solid completely precipitates and filter, collect the filter cake, wash the filter cake with ethanol to obtain a solid of L-seleno-methylselenocysteine.

[0038] Example 3 Step S10 specifically includes: The molar ratio of dimethyldiselenide, sodium borohydride and sodium hydroxide is 5:1:1; the sodium hydroxide solution is pre-cooled to 6 °C, and the reaction time is 10 h to obtain a sodium selenomethanol solution.

[0039] The steps for preparing 3-chloro-L-alanine methyl ester hydrochloride in step S20 specifically include: In step S21, the ratio of dichloromethane to acetonitrile added is 3:1; In step S22, 120 g of L-serine methyl ester hydrochloride and 105 g of thionyl chloride are added; In step S23, the preset temperature is 50 °C, the supplementary solvent is a mixed solvent of 300 ml of dichloromethane and 200 ml of acetonitrile. The solution in the second reaction flask reacts at 50 °C for 10 h, then the heating is turned off and the stirring is stopped. After refrigeration, a solid precipitates.

[0040] The steps for preparing L-serine methyl ester hydrochloride in step S22 specifically include: In step S221, the temperature of the ice-water bath is 6 °C, and the stirring reaction time is 1 h; In step S222, the intermediate product is mixed with L-serine and then heated to 50 °C. The stirring reaction time after heating is 2.5 h. Among them, the molar ratio of L-serine, thionyl chloride and methanol is 1:1.2:15.

[0041] The steps for adding the prepared 3-chloro-L-alanine methyl ester hydrochloride to the first reaction flask and stirring and reacting with the sodium selenomethanol solution in step S20 specifically include: Cool the sodium selenomethanol solution obtained in step S10 to 6 °C and stir for 15 min; After adding 3-chloro-L-alanine methyl ester hydrochloride to the first reaction flask, stir for another 15 min; Heat the solution in the first reaction flask to 35 °C and react for 15 h.

[0042] Step S30 specifically includes: S31, cool the reaction solution after the reaction in step S20 to 5 °C, add hydrochloric acid to adjust the pH of the reaction solution to 2, and stir for 2 h; S32, extract with ethyl acetate 3 times. The volume ratio of ethyl acetate to the reaction solution to be extracted is 2:1. Retain the aqueous phase and perform heating under reduced pressure distillation to obtain a solid crystal; S33, perform secondary extraction on the solid crystal with a methanol solution. The ratio of the mass m (g) of the solid crystal to the volume v (ml) of the extraction agent methanol solution is 1:5. After filtering off the remaining solid, a methanol extract is obtained; S34. Heat it up to 55 °C under a water bath condition, add triethylamine dropwise to the methanol extract, adjust the pH of the solution to 6.5, then cool it down to 20 °C and stir until the solid completely precipitates, and then filter it. S35. Collect the filter cake in S34, wash it with methanol to obtain the crude solid of L-seleno-methylselenocysteine.

[0043] Step S40 specifically includes: S41. Add the crude solid of L-seleno-methylselenocysteine to purified water and completely dissolve it under the condition of 65 °C. S42. Add activated carbon to the dissolved solution and filter it by suction for decolorization. S43. Heat and distill the decolorized filtrate under reduced pressure to a saturated state, add ethanol dropwise under the water bath condition of 55 °C until turbidity appears and then stop, and stir for 28 min. S44. After stirring, continue to add ethanol and then stir for 4 h, let it stand and cool naturally, stir and crystallize until the solid completely precipitates, filter it, collect the filter cake, and wash the filter cake with ethanol to obtain the solid of L-seleno-methylselenocysteine.

[0044] Comparative Example This comparative example adopts a conventional synthesis method of L-seleno-methylselenocysteine, which specifically includes the following steps: (a) Under stirring conditions, add L-serine methyl ester hydrochloride to tetrahydrofuran and cool it to 0 - 5 °C. (b) Add triethylamine (acid-binding agent), stir evenly, then add acetyl chloride dropwise. After the reaction is completed, add thionyl chloride dropwise, heat up to 45 °C, and after the reaction is completed, cool it down to 0 °C to obtain the amide group-protected alanine intermediate. (c) Add saturated sodium bicarbonate solution, stir evenly, then add the tetrahydrofuran solution of sodium selenomethanethiol for nucleophilic substitution reaction. After the addition is completed, continue to stir and let it warm up to room temperature naturally to obtain the reaction mixture. (d) Slowly add HCl to adjust the pH of the reaction mixture to less than 4.0, then extract it 3 times with ethyl acetate, combine the extraction solutions, wash with water, dry with anhydrous sodium sulfate, filter, and remove ethyl acetate under reduced pressure to obtain the crude product of L-2-acetamido-3-methylselenopropionic acid. (e) Dissolve the crude product obtained in step (d) in an aqueous solution of cobalt chloride, adjust the pH to 7.5 with NaOH solution, add acylated amino acid hydrolase for hydrolysis reaction to remove the protecting group, control the temperature at 37 °C, stir until the hydrolysis is completed, neutralize the pH to 5.0 - 6.0 with acetic acid; add activated carbon and heat for decolorization, concentrate the filtrate under reduced pressure, then separate it with a cation exchange resin, wash it successively with water and ammonia water, evaporate the ammonia water eluate under reduced pressure, and recrystallize it with water-ethanol to obtain L-selenomethylselenocysteine.

[0045] The L-seleno-methylselenocysteine synthesized in the examples and comparative examples of this application is shown in Table 1; Table 1

[0046] As can be seen from Table 1, the L-seleno-methylselenocysteine prepared by the synthesis method of L-seleno-methylselenocysteine provided in this application has a higher purity, the total product yield reaches over 90%, the overall reaction time is shorter, and the preparation efficiency is improved.

[0047] In summary, the synthesis method of L-seleno-methylselenocysteine provided in this application demonstrates outstanding innovation and technological advancement: First, by innovatively adopting an aqueous reaction system to replace the traditional organic phase reaction system, a one-step direct conversion of chiral L-serine as the starting material to 3-chloro-L-alanine methyl ester hydrochloride is achieved. While avoiding the methyl ester hydrolysis process in the prior art, the process route is significantly shortened, and the total reaction yield is increased to over 90%; Second, through the in-situ generation strategy of sodium methylselenol, the technical bottleneck of poor stability and difficult separation and purification of this intermediate is effectively solved, while simplifying the operation process and ensuring the reliability of the reaction system; Third, the use of tetrahydrofuran and sodium methoxide is reduced during the reaction process. The selected raw materials are low-cost and easy to obtain, the reaction medium is green and environmentally friendly, and the process conditions are mild and controllable, with significant economic benefits and environmental friendliness. The synergistic effect of the above technical features makes this solution particularly suitable for industrial continuous production and has important application value in the field of L-seleno-methylselenocysteine synthesis.

[0048] It should be noted that the above implementation process is only to illustrate the feasibility of this application, but this does not mean that there are the above several implementation processes for the L-seleno-methylselenocysteine synthesis method of this application. On the contrary, as long as the L-seleno-methylselenocysteine synthesis method of this application can be implemented, it can be included in the feasible implementation solutions of this application.

[0049] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0050] The above embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for synthesizing L-seleno-methylselenocysteine, characterized in that, It includes the following steps: S10. Add dimethyldiselenide and sodium borohydride into the first reaction flask for mixing, and add sodium hydroxide solution into the mixed first reaction flask for reaction to obtain sodium selenomethanol solution; S20. Prepare 3-chloro-L-alanine methyl ester hydrochloride, and add the prepared 3-chloro-L-alanine methyl ester hydrochloride into the first reaction flask to carry out stirring reaction with the sodium selenomethanol solution; S30. Acidify the solution after the stirring reaction, then carry out extraction, remove impurities, leave the aqueous phase, heat under reduced pressure for distillation to obtain solid crystals, carry out secondary extraction on the solid crystals with methanol, and then add triethylamine for stirring crystallization to obtain crude L-seleno-methylselenocysteine solid; S40. Hydrate the crude L-seleno-methylselenocysteine solid and carry out recrystallization to obtain L-seleno-methylselenocysteine solid.

2. The method for synthesizing L-seleno-methylselenocysteine according to claim 1, characterized in that, In step S10: The molar ratio of dimethyldiselenide, sodium borohydride and sodium hydroxide is (1:5:5)-(5:1:1); The initial temperature of the sodium hydroxide solution is less than 10 °C; React in the first reaction flask for 4 h - 10 h to obtain sodium selenomethanol solution.

3. The method for synthesizing L-seleno-methylselenocysteine according to claim 1, wherein The steps for preparing 3-chloro-L-alanine methyl ester hydrochloride in step S20 include: S21. Add dichloromethane and acetonitrile into the second reaction flask for stirring; S22. Prepare L-serine methyl ester hydrochloride, add L-serine methyl ester hydrochloride into the second reaction flask, and add thionyl chloride, then carry out constant temperature water bath; S23. Heat up the second reaction flask to the preset temperature, dropwise add supplementary solvent into the second reaction flask to carry out reaction at the preset temperature, and solids precipitate out in the reaction solution; S24. Filter out the solids in the reaction solution and wash them to obtain wet crude 3-chloro-L-alanine methyl ester hydrochloride, and dry the wet crude 3-chloro-L-alanine methyl ester hydrochloride to obtain 3-chloro-L-alanine methyl ester hydrochloride.

4. The method for synthesizing L-seleno-methylselenocysteine according to claim 3, characterized in that In step S21, the addition ratio of dichloromethane to acetonitrile is 1:3 - 3:1; In step S23, the preset temperature is from room temperature to 50 °C, the supplementary solvent is a mixed solvent of dichloromethane and acetonitrile, the solution in the second reaction flask reacts at the preset temperature for 6 h - 10 h, then turn off heating, stop stirring, and solids precipitate out after refrigeration; In step S24, the solids precipitated in step S23 are washed with dichloromethane.

5. The method for synthesizing L-seleno-methylselenocysteine according to claim 3, wherein The steps for preparing L-serine methyl ester hydrochloride in step S22 include: S221. Add methanol into the third reaction flask and carry out ice-water bath, add thionyl chloride into the third reaction flask in the ice-water bath for stirring reaction to obtain an intermediate product; S222. Mix the obtained intermediate product with L-serine and then carry out heating and stirring reaction; S223. After the stirring reaction ends, carry out reduced pressure concentration on the reaction solution, rotary dry with methanol until no liquid distills out from the third reaction flask to obtain wet crude L-serine methyl ester hydrochloride, and dry the wet crude L-serine methyl ester hydrochloride to obtain L-serine methyl ester hydrochloride.

6. The method for synthesizing L-seleno-methylselenocysteine according to claim 5, wherein in step S221, the temperature of the ice-water bath is 0°C - 10°C, and the stirring reaction time is 0.5 h - 1 h; in step S222, after the intermediate product and L-serine are mixed, the temperature is raised to 40°C - 50°C, and the stirring reaction time after heating is 2 h - 3 h, wherein the molar ratio of L-serine, thionyl chloride, and methanol is (1:0.8:10) - (1:1.2:15).

7. The method for synthesizing L-seleno-methylselenocysteine according to claim 1, characterized in that, In step S20, the step of adding the prepared 3-chloro-L-alanine methyl ester hydrochloride to the first reaction flask and stirring it with sodium selenomethanethiol solution includes: cooling the sodium selenomethanethiol solution obtained in step S10 to below 10°C and stirring for 10 min - 15 min; adding 3-chloro-L-alanine methyl ester hydrochloride to the first reaction flask and then stirring for 10 min - 15 min; raising the temperature of the solution in the first reaction flask to 25°C - 35°C and reacting for 8 h - 15 h.

8. The method for synthesizing L-seleno-methylselenocysteine according to claim 1, wherein Step S30 specifically includes: S31, cooling the reaction solution after the reaction in step S20 to below 10°C, adding hydrochloric acid to adjust the pH value of the reaction solution, and stirring for 1 h - 2 h; S32, extracting with ethyl acetate 2 - 3 times, retaining the aqueous phase and performing heating under reduced pressure distillation to obtain solid crystals; S33, performing secondary extraction on the solid crystals with a methanol solution, filtering off the remaining solids to obtain a methanol extract; S34, raising the temperature under a water bath condition, dropping triethylamine into the methanol extract, adjusting the pH of the solution, and then cooling and stirring until the solids completely precipitate and then filtering; S35, collecting the filter cake in S34, washing it with methanol to obtain a crude L-seleno-methylselenocysteine solid.

9. The method for synthesizing L-seleno-methylselenocysteine according to claim 8, wherein in step 31, the pH of the reaction solution is adjusted to 1 - 2 by hydrochloric acid; in step 32, the volume ratio of the extraction agent ethyl acetate to the reaction solution to be extracted is 2:1 - 1:2; in step 33, the mass m of the solid crystals and the volume v of the extraction agent methanol solution ratio is m:v = 1:1 - 1:5; in step 34, the temperature of the water bath heating is 45°C - 55°C, the pH of the solution is adjusted to 5.5 - 6.5 by triethylamine, and the temperature of the cooling and stirring is lower than 15°C - 20°C.

10. The method for synthesizing L-seleno-methylselenocysteine according to claim 1, wherein step S40 specifically includes: S41, adding the crude L-seleno-methylselenocysteine solid to purified water and completely dissolving it under the condition of 55°C - 65°C; S42, adding activated carbon to the dissolved solution and performing suction filtration for decolorization; S43, heating and distilling the decolorized filtrate under reduced pressure to a saturated state, dropping ethanol under the water bath condition of 45°C - 55°C until turbidity appears and then stopping, and stirring for 25 min - 30 min; S44, continue to dropwise add ethanol after stirring and then stir for 0.5 h - 4.0 h, let it stand and cool naturally, stir and crystallize until the solid completely precipitates, filter, collect the filter cake, wash the filter cake with ethanol to obtain L-seleno-methylselenocysteine solid.

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