Method for preparing tetrandrine by green electrolysis

Abstract

The present application relates to the technical field of electrochemical synthesis, and discloses a method for preparing tetrandrine by green electrolysis, which comprises the following steps: mixing tetrandrine, tetramethylammonium chloride and a reaction solvent in a diaphragm-free electrolytic cell, and performing a methylation reaction under a constant current electrolysis condition; and after the reaction is completed, extracting, vacuum concentration, hot dissolution and filtration, and recrystallization are sequentially performed on the reaction liquid to obtain tetrandrine. The present application has the advantages of mild conditions, no need of stoichiometric oxidants, reducing agents and strong alkaline reagents, environmental friendliness, simple operation, high preparation efficiency, high raw material utilization rate and yield, low cost, and the like, and has a good application prospect and is easy to realize industrial production.

Description

Technical Field

[0001] This invention relates to the field of electrochemical synthesis technology, specifically to a green electrolytic method for preparing tetrandrine. Background Technology

[0002] Tetrandrine is a dibenzylisoquinoline alkaloid extracted from the tuberous roots of *Stephania tetrandra*, a plant in the Menispermaceae family. It belongs to the category of novel calcium channel blockers and calmodulin antagonists, possessing multiple excellent pharmacological activities, including anti-inflammatory, analgesic, antispasmodic, anti-myocardial ischemia, antihypertensive, antitumor, hepatoprotective, and autophagy-regulating effects. In the clinical pharmaceutical field, tetrandrine can be specifically used to treat various conditions such as silicosis, autoimmune diseases, inflammatory lung diseases, cardiovascular diseases, and hypertension, demonstrating high medicinal value and a wide range of clinical applications. Furthermore, with the rapid development of the modern biopharmaceutical industry and the continuous growth in clinical drug demand, the market demand for tetrandrine is steadily increasing. Developing efficient, green, low-cost, and scalable tetrandrine preparation technologies is of significant economic and social value for ensuring the supply of clinical drugs, reducing pharmaceutical production costs, and promoting the green and low-carbon development of the pharmaceutical industry.

[0003] Currently, the preparation technologies for tetrandrine in the industrial field are mainly divided into two categories: natural plant extraction processes and chemical synthesis and conversion processes. Among them, patent CN1903856A discloses a natural plant extraction and separation technology, specifically using dried root tubers of *Stephania tetrandra* as raw material, and purifying tetrandrine through multiple refining processes such as ethanol extraction, reflux extraction, chromatographic separation, and recrystallization. To improve the low utilization rate of natural extraction resources, the industry has further developed a chemical conversion and synthesis process, using tetrandrine B, a natural extraction byproduct, as raw material, and directionally converting low-value-added tetrandrine B into highly active tetrandrine through a phenolic hydroxymethylation reaction. Early chemical synthesis processes of this type mainly used dimethyl sulfate (e.g., literature: China Pharmaceutical Industry Magazine, 2015, 46 (9), 948–949) and iodomethane (e.g., patent: CN116804017A) as methylating agents to complete the methylation reaction. In order to solve the pollution problem of highly toxic reagents, the existing improved technology uses dimethyl carbonate to replace traditional highly toxic reagents (e.g., patents: CN116804017, CN117534679A; literature: Pharmaceutical Frontiers, 2025, 29 (4), 560–566), which reduces the production toxicity and environmental pressure to a certain extent, and has become a relatively preferred synthesis improvement scheme at this stage.

[0004] However, the existing tetrandrine preparation process still has many technical bottlenecks that are difficult to overcome, and cannot meet the industrial demand for green production, high yield, low cost and large-scale mass production. These include: (1) The utilization rate of raw materials in the natural plant extraction process is extremely low. The tetrandrine content in Stephania tetrandra is only about 1%, and the tetrandrine with similar structure is close to its polarity and difficult to separate. The overall preparation process is complicated and the production cycle is long. At the same time, the natural plant extraction process requires the use of toxic organic solvents such as chloroform, which causes serious environmental pollution and high environmental protection costs. A large amount of tetrandrine by-products are discarded, resulting in resource waste and solid waste pollution. The production capacity is limited and cannot meet the incremental market demand. (2) The methylating reagents such as dimethyl sulfate and iodomethane used in the traditional chemical synthesis process are highly toxic and pose great safety hazards. They do not meet the standards for green pharmaceutical manufacturing. Moreover, the chemical selectivity of the reaction is poor, which can easily lead to the over-methylation of tertiary amine groups to generate quaternary ammonium salt by-products. The product purification is difficult and the yield is low. At the same time, the reaction requires the addition of a metric strong base, which generates a large amount of inorganic salt waste residue and has poor industrial adaptability. (3) The existing green improvement process for dimethyl carbonate still has obvious defects, including high activation energy of dimethyl carbonate, easy decomposition at high temperature, the need for high temperature and high pressure conditions for reaction, large amount of catalyst, and high energy consumption; in addition, the reaction conversion rate is low, the raw material residue is large, the side reaction is difficult to control effectively, the product yield is low, and it is still impossible to achieve low-cost and large-scale industrial production.

[0005] In summary, there is an urgent need to develop a novel preparation process for tetrandrine that features mild reaction conditions, high selectivity, is green and pollution-free, has excellent yield, and is suitable for industrial mass production. Summary of the Invention

[0006] The present invention aims to provide a green electrolytic method for preparing tetrandrine, in order to solve the technical problems of low raw material conversion rate and large residue in existing tetrandrine preparation processes, as well as numerous and difficult-to-remove byproducts, resulting in low product yield.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for green electrolytic preparation of tetrandrine, comprising adding tetrandrine, tetramethylammonium chloride and reaction solvent into a diaphragmless electrolytic cell and mixing them, and carrying out a methylation reaction under constant current electrolysis conditions; after the reaction is completed, the reaction solution is sequentially extracted, concentrated under reduced pressure, hot dissolved and filtered, and recrystallized to obtain tetrandrine.

[0008] Beneficial effects: This scheme uses tetramethylammonium chloride as an electrolyte and methylating agent, which effectively improves the utilization rate of reagents, reduces the types of reagents required for production, lowers costs, reduces side reactions, and improves product purity.

[0009] Preferably, as an improvement, the structure of the tetrandrine is as shown in formula (1): Equation (1): ; The structure of the tetrandrine is shown in formula (2): Equation (2): .

[0010] Preferably, as an improvement, the reaction solvent is any one of dichloromethane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexafluoroisopropanol, and acetonitrile, and the amount used is 10~20 mL / mmol tetrandrine.

[0011] Preferably, as an improvement, the molar ratio of tetrandrine to tetramethylammonium chloride is 1:1 to 5.

[0012] Preferably, as an improvement, the anode material used in the electrolysis reaction is any one of a carbon rod electrode, a platinum sheet electrode, a nickel foam electrode, a carbon felt electrode, or a mesh glassy carbon electrode; the cathode material is any one of a carbon rod electrode, a platinum sheet electrode, or a nickel foam electrode; and the electrolysis is performed under a constant current of 1–10 mA for 1–10 h.

[0013] Preferably, as an improvement, the extraction involves adding water to the reaction solution, mixing well, and then extracting with dichloromethane 2-3 times, combining the organic phases obtained from the extraction.

[0014] Add ethyl acetate, mix, stir and heat to 80~85℃ and reflux for 30~60 min to obtain a reddish-brown translucent solution; cool to 65~75℃, filter while hot, collect the filtrate and concentrate under reduced pressure at 45℃ to obtain a yellow solid.

[0015] Preferably, as an improvement, the recrystallization involves recrystallizing the yellow solid obtained in the hot dissolution and filtration stage twice with acetone and anhydrous ethanol, followed by filtration, washing, and drying to obtain a white solid powder, namely tetrandrine.

[0016] Preferably, as an improvement, the recrystallization includes the following: First recrystallization: The yellow solid obtained by hot dissolution and filtration was mixed with acetone, stirred and heated under reflux, and then concentrated by atmospheric distillation until a white solid gradually precipitated out. The mixture was then slowly stirred and cooled to room temperature, cooled to 0-5 ℃ in an ice-water bath and kept at that temperature with stirring for 3 hours. The filter cake obtained by filtration was washed with a small amount of ice-cold acetone and dried to obtain a white solid. Second recrystallization: The above-mentioned off-white solid was mixed with anhydrous ethanol, stirred and heated until dissolved to obtain a reddish-brown clear solution; the solution was concentrated by vacuum distillation under a vacuum degree ≤ 0.07 MPa until a white solid gradually precipitated out; the solution was slowly stirred and cooled to room temperature and kept stirred for 3 h; the filter cake obtained by suction filtration was washed twice with anhydrous ethanol and dried to obtain an off-white solid powder, which is tetrandrine.

[0017] The principle and advantages of this scheme are: 1. This invention prepares tetrandrine by methylation of tetrandrine using an electrochemical method. Tetramethylammonium chloride, which is inexpensive and low in toxicity, is used as the methylation reagent and electrolyte. It has unique advantages such as mild conditions, no need for stoichiometric oxidants, reducing agents, or strong alkaline reagents, environmental friendliness, simple operation, high preparation efficiency, high raw material utilization and yield, and low cost. It has good application prospects and is easy to realize industrial production.

[0018] 2. This invention solves the technical problems of existing preparation methods, such as low raw material utilization, cumbersome processes, expensive and highly toxic methylating reagents, significant pollution, poor reaction selectivity, difficulty in removing residual tetrandrine, high energy consumption, and high industrialization costs. Furthermore, the synthesis method provided by this invention achieves a conversion rate of over 90% in converting tetrandrine to tetrandrine A, yielding a tetrandrine A product with a purity of over 99%, containing <0.5% tetrandrine residue, no quaternary ammonium salt byproduct residue, stable quality, and a yield of over 80%. The green electrolytic synthesis method provided by this invention can improve the yield and output of tetrandrine A. Attached Figure Description

[0019] Figure 1 This is the core reaction route diagram for the green electrolytic preparation of tetrandrine in this embodiment of the invention.

[0020] Figure 2 The hydrogen nuclear magnetic resonance spectrum of tetrandrine prepared in Example 1 of this invention.

[0021] Figure 3 The carbon nuclear magnetic resonance spectrum of tetrandrine prepared in Example 1 of this invention.

[0022] Figure 4 This is a high-performance liquid chromatogram of the reaction solution at the endpoint of the preparation of tetrandrine in Example 1 of the present invention.

[0023] Figure 5 This is a high-performance liquid chromatogram of tetrandrine prepared in Example 1 of the present invention.

[0024] Figure 6 This is a high-performance liquid chromatogram of tetrandrine prepared in Example 2 of the present invention.

[0025] Figure 7 This is a high-performance liquid chromatogram of tetrandrine prepared in Example 3 of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials and reagents used can all be obtained commercially.

[0027] Example 1 This scheme provides a green electrolytic method for preparing tetrandrine, the core reaction route of which is as follows: Figure 1 As shown, tetramethylammonium chloride and a reaction solvent were added to a diaphragm-free electrolytic cell and mixed, and a methylation reaction was carried out under constant current electrolysis conditions. After the reaction was completed, the reaction solution was successively extracted, concentrated under reduced pressure, thermally dissolved and filtered, and recrystallized to obtain tetramethylammonium chloride. Tetramethylammonium chloride is the electrolyte and methylating agent in this method.

[0028] The specific steps are as follows: Step S1, Electrolysis: In a diaphragm-free electrolytic cell, 183 mg (0.3 mmol) of tetramethylammonium chloride, 33 mg (0.3 mmol) of tetramethylammonium chloride, and 5 mL of N,N-dimethylformamide (DMF) were added sequentially. Platinum electrodes (10 mm × 10 mm × 0.2 mm) were used as the anode and cathode. Electrolysis was carried out for 10 h under constant current of 1 mA with stirring. The reaction was monitored by TLC (developing solvent: dichloromethane: methanol = 5:1) to ensure complete reaction. The ratio of tetrandrine to tetrandrine in the reaction solution was 91.6:6.0 by HPLC.

[0029] Step S2, Extraction: Add 10 mL of water to the reaction mixture and extract three times with 15 mL of dichloromethane each time; Step S3, Concentration under reduced pressure: Combine the organic phases and dry with anhydrous sodium sulfate. Filter under vacuum, and concentrate the filtrate at 40 °C to obtain a yellow solid; Step S4, hot dissolution and filtration: Add 20 mL of ethyl acetate to the obtained yellow solid, stir and heat the mixture to 80~85℃ and reflux for 30 min to obtain a reddish-brown translucent solution; cool to 75℃, filter while hot, wash the filter cake 3 times with a small amount of ethyl acetate. The filter cake is a quaternary ammonium salt byproduct and should be discarded; concentrate the filtrate under reduced pressure at 45℃ to obtain 235 mg of yellow solid.

[0030] Step S5, First recrystallization: Add 235 mg of the above yellow solid and 5.5 mL of acetone to a dry flask. Stir and heat the mixture to reflux for 30 min. Distill at normal pressure, concentrating until the residual solvent in the flask is about 2.0 mL. At this point, a small amount of white solid gradually precipitates out. Stir slowly, cool slowly to room temperature, then cool to 0-5 °C in an ice-water bath and maintain the temperature with stirring for 3 h. Filter by suction, wash the filter cake once with a small amount of ice-cold acetone, and dry to obtain 176 mg of off-white solid.

[0031] Step S6, Second Recrystallization: Add 176 mg of the above-mentioned off-white solid and 5.5 mL of anhydrous ethanol to a dry flask. Stir and heat the mixture to 50-55 °C to dissolve, yielding a clear reddish-brown solution. Distill under reduced pressure (vacuum degree ≤0.07 MPa) to concentrate until the residual solvent in the flask is about 0.9 mL. During concentration, a white solid gradually precipitates out. Stir slowly, cool slowly to room temperature, and maintain the temperature with stirring for 3 h. Filter, wash the filter cake twice with anhydrous ethanol, and dry to obtain 150 mg of off-white solid powder, i.e., tetrandrine.

[0032] This method uses high-performance liquid chromatography (HPLC) to determine the chemical purity of the product, under the following specific conditions: The chromatographic column was a C18 column, the mobile phase was water:acetonitrile:methanol:triethylamine = 650:300:50:3 (pH adjusted to 2.0 with perchloric acid), the flow rate was 1.0 mL / min, the sample concentration was 0.1 mg / mL, the injection volume was 20 μL, the detection wavelength was 280 nm, the column temperature was 30 ℃, the run time was 35 min, and the reference retention times were 17.1 min for tetrandrine and 13.0 min for tetrandrine.

[0033] In the examples, the yield refers to the molar yield, and the calculation formula is: yield (%) = (actual product moles / theoretical product moles) × 100%, where the theoretical product moles are calculated based on the number of moles of tetrandrine in the feed.

[0034] The HPLC purity of tetrandrine A obtained in Example 1 was 99.72% (of which tetrandrine B residue was 0.07%). Figure 5 As shown in the figure, the yield was 80%. 1HNMR (400 MHz, CDCl3) δ:7.38 (dd, J = 1.8, 8.2Hz, 1H), 7.18 (dd, J = 2.4, 8.2 Hz, 1H), 6.94 – 6.88 (m, 2H), 6.84 (dd, J =2.4, 8.3 Hz, 1H), 6.58 (s, 1H), 6.55 (s, 1H), 6.35 – 6.32 (m, 2H), 6.03 (s,1H), 3.97 (s, 3H), 3.91 (q, J = 5.5 Hz, 1H), 3.80 – 3.79 (m, 4H), 3.60 – 3.44(m, 2H), 3.41(s, 3H), 3.30 (dd, J = 5.4, 12.3 Hz, 1H), 3.22 (s, 3H), 3.04 –2.89 (m, 4H), 2.86 – 2.72 (m, 3H), 2.66 (s, 3H), 2.56 (d, 13.9 Hz, 1H), 2.50– 2.46 (m, 1H), 2.38 (s, 3H); 13 CNMR (101 MHz, CDCl3) δ: 153.9, 153.1, 151.5, 149.4, 148.7, 148.5, 147.1, 143.8, 137.9, 135.2, 132.7, 130.2, 122.8, 122.0 × 2 (122.02, 121.97), 120.2, 116.2, 112.8, 111.6, 105.8, 64.0, 61.5, 60.3, 56.2, 55.9, 45.3, 42.6, 42.4, 42.0, 38.4, 25.3, 22.1 (e.g.) Figures 2-3 (As shown).

[0035] Example 2 This scheme provides a green electrolytic method for preparing tetrandrine, the core reaction route of which is as follows: Figure 1 As shown, the specific steps are as follows: In a diaphragm-free electrolyzer, 183 mg (0.3 mmol) of tetramethylammonium chloride, 99 mg (0.9 mmol) of tetramethylammonium chloride, and 3 mL of acetonitrile were added sequentially. A carbon rod was used as the anode, and a platinum electrode (10 mm × 10 mm × 0.2 mm) was used as the cathode. Electrolysis was carried out under constant current of 5 mA with stirring for 5 h. The reaction was monitored by TLC (developing solvent: dichloromethane: methanol = 5:1) to ensure complete reaction. The reaction mixture was concentrated under reduced pressure at 45 °C to obtain a yellow solid. 20 mL of ethyl acetate was added to the obtained yellow solid, and the mixture was stirred and heated to 80-85 °C and refluxed for 45 min to obtain a reddish-brown translucent solution. The solution was cooled to 65 °C and filtered while hot. The filter cake was washed three times with a small amount of ethyl acetate. This filter cake was a quaternary ammonium salt byproduct and was discarded. The filtrate was concentrated under reduced pressure at 45 °C to obtain a yellow solid. The resulting yellow solid was recrystallized twice with acetone and anhydrous ethanol, filtered, washed, and dried to obtain 156 mg of a white solid powder, namely tetrandrine A, with an HPLC purity of 99.37% (of which tetrandrine B residue was 0.06%). Figure 6 As shown in the figure, the yield was 84%.

[0036] The operational details not shown are basically the same as in Example 1, and will not be repeated here.

[0037] Example 3 This scheme provides a green electrolytic method for preparing tetrandrine, the core reaction route of which is as follows: Figure 1 As shown, the specific steps are as follows: In a diaphragm-free electrolyzer, 183 mg (0.3 mmol) of tetramethylammonium chloride, 164 mg (1.5 mmol) of tetramethylammonium chloride, and 6 mL of dimethyl sulfoxide were added sequentially. A carbon felt electrode (10 mm × 10 mm) was used as the anode, and a nickel foam electrode (10 mm × 10 mm × 0.3 mm) was used as the cathode. Electrolysis was carried out under constant current of 10 mA with stirring for 2 h. The reaction was monitored for completeness by TLC (developing solvent: dichloromethane: methanol = 5:1). 10 mL of water was added to the reaction mixture, and the mixture was extracted three times with 15 mL of dichloromethane each time. The organic phases were combined and dried over anhydrous sodium sulfate. The mixture was filtered, and the filtrate was concentrated under reduced pressure at 40 °C to obtain a yellow solid. 20 mL of ethyl acetate was added to the obtained yellow solid, and the mixture was stirred and heated to 80-85 °C and refluxed for 60 min to obtain a reddish-brown translucent solution. The solution was cooled to 70 °C and filtered while hot. The filter cake was washed three times with a small amount of ethyl acetate. This filter cake was a quaternary ammonium salt byproduct and was discarded. The filtrate was concentrated under reduced pressure at 45 °C to obtain a yellow solid. The obtained yellow solid was recrystallized twice, successively with acetone and anhydrous ethanol. After filtration, washing, and drying, 153 mg of a white solid powder was obtained, namely tetrandrine A, with an HPLC purity of 99.08% (of which tetrandrine B residue was 0.37%). Figure 7 As shown in the figure, the yield was 82%.

[0038] The operational details not shown are basically the same as in Example 1, and will not be repeated here.

[0039] Comparative Example 1: Replacing the methylating agent and electrolyte This comparative example is basically the same as Example 1, except that the methylating agent is iodomethane and the electrolyte is tetrabutylammonium perchlorate.

[0040] In this comparative example, the yield of tetrandrine was 45%, and the HPLC purity was 99.10% (of which tetrandrine B residue was 0.33%). The inventors analyzed that the reason was that iodomethane, as a methylating reagent, easily generates a large amount of quaternary ammonium salt byproducts, leading to a decrease in reaction yield and recrystallization yield.

[0041] Comparative Example 2: Insufficient Tetramethylammonium Chloride This comparative example is basically the same as Example 1, except that the molar ratio of tetrandrine and tetramethylammonium chloride is 1:0.9.

[0042] In this comparative example, the yield of tetrandrine A was 75%, and the HPLC purity was 99.04% (of which tetrandrine B residue was 0.52%). The inventors analyzed that the reason was that the reaction was incomplete due to insufficient tetramethylammonium chloride in the reaction system, resulting in a higher residual amount of tetrandrine B, which was difficult to remove completely through post-processing and recrystallization. Therefore, the yield of tetrandrine A was reduced, and the residual amount of tetrandrine B increased.

[0043] Comparative Example 3: Excess Tetramethylammonium Chloride This comparative example is basically the same as Example 1, except that the molar ratio of tetrandrine and tetramethylammonium chloride is 1:5.5.

[0044] In this comparative example, the yield of tetrandrine was 71%, and the HPLC purity was 99.14% (of which tetrandrine B residue was 0.35%). The inventors analyzed that the reason was that the excessive amount of tetramethylammonium chloride in the reaction system increased the formation of quaternary ammonium salt byproducts, resulting in significant product loss during post-processing and recrystallization, thus reducing the yield of tetrandrine.

[0045] Comparative Example 4: The anode and cathode materials used in electrolysis are unsuitable. This comparative example is basically the same as Example 1, except that the anode material used in electrolysis is a zinc rod electrode and the cathode material is a carbon felt electrode.

[0046] The yield of tetrandrine in this comparative example was 0%. The inventors analyzed that the reason was that the anode and cathode materials used in the electrolysis of this comparative example were unsuitable, which prevented the methylation reaction from proceeding.

[0047] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A green electrolytic method for preparing tetrandrine, characterized in that: The process involves mixing tetramethylammonium chloride and a reaction solvent in a diaphragm-free electrolytic cell and carrying out a methylation reaction under constant current electrolysis conditions. After the reaction is completed, the reaction solution is sequentially extracted, concentrated under reduced pressure, thermally dissolved and filtered, and recrystallized to obtain tetramethylammonium chloride.

2. The method for green electrolytic preparation of tetrandrine according to claim 1, characterized in that: The structure of the tetrandrine is shown in formula (1): Equation (1): ; The structure of the tetrandrine is shown in formula (2): Equation (2): .

3. The method for green electrolytic preparation of tetrandrine according to claim 1, characterized in that: The reaction solvent is any one of dichloromethane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexafluoroisopropanol, and acetonitrile, and the amount used is 10~20 mL / mmol tetrandrine.

4. The method for green electrolytic preparation of tetrandrine according to claim 1, characterized in that: The molar ratio of tetrandrine to tetramethylammonium chloride is 1:1 to 5.

5. The method for green electrolytic preparation of tetrandrine according to claim 4, characterized in that: The anode material used in the electrolysis reaction is any one of carbon rod electrode, platinum sheet electrode, nickel foam electrode, carbon felt electrode, and mesh glassy carbon electrode; the cathode material is any one of carbon rod electrode, platinum sheet electrode, and nickel foam electrode; the electrolysis is performed under a constant current of 1 to 10 mA for 1 to 10 h.

6. The method for green electrolytic preparation of tetrandrine according to claim 5, characterized in that: The extraction process involves adding water to the reaction solution, mixing it thoroughly, and then extracting it 2-3 times with dichloromethane. The resulting organic phases are then combined.

7. The method for green electrolytic preparation of tetrandrine according to claim 6, characterized in that: The hot dissolution filtration process involves adding the yellow solid obtained from vacuum concentration to ethyl acetate, mixing, stirring, heating to 80-85°C, refluxing for 30-60 minutes to obtain a reddish-brown translucent solution; cooling to 65-75°C, filtering while hot, collecting the filtrate, concentrating under vacuum at 45°C, and then obtaining the yellow solid again.

8. The method for green electrolytic preparation of tetrandrine according to claim 7, characterized in that: The recrystallization process involves recrystallizing the yellow solid obtained during the hot dissolution and filtration stage twice with acetone and anhydrous ethanol, followed by filtration, washing, and drying to obtain a white solid powder, namely tetrandrine.

9. The method for green electrolytic preparation of tetrandrine according to claim 8, characterized in that: The recrystallization includes the following: First recrystallization: The yellow solid obtained by hot dissolution and filtration was mixed with acetone, stirred and heated under reflux, and then concentrated by atmospheric distillation until a white solid gradually precipitated out. The mixture was then slowly stirred and cooled to room temperature, cooled to 0-5 ℃ in an ice-water bath and kept at that temperature with stirring for 3 h. The filter cake obtained by filtration was washed with a small amount of ice-cold acetone and dried to obtain a white solid. Second recrystallization: The above-mentioned off-white solid was mixed with anhydrous ethanol, stirred and heated until dissolved to obtain a reddish-brown clear solution; the solution was concentrated by vacuum distillation under a vacuum degree ≤ 0.07 MPa until a white solid gradually precipitated out; the solution was slowly stirred and cooled to room temperature and kept stirred for 3 h; the filter cake obtained by suction filtration was washed twice with anhydrous ethanol and dried to obtain an off-white solid powder, which is tetrandrine.

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