A synthetic method of natural-identical raspberry ketone

Abstract

The present invention provides a method for synthesizing natural-identical raspberry ketone, belonging to the field of pharmaceutical synthesis. Using natural anisaldehyde and natural acetone as starting materials, the final natural-identical raspberry ketone is obtained through three consecutive reactions: Claisen-Schmidt condensation catalyzed by basic resin, enzymatic reduction, and demethylation with sodium ethanethiolate. The preparation method of the present invention is safe, clean, and has a stable yield, reaching about 85%, providing a basis for industrial continuous production. The preparation method of the present invention not only meets the requirements of clean production but also saves labor costs by virtue of the continuous process, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of drug preparation, and particularly relates to a method for synthesizing natural-identical raspberry ketone. Background Art

[0002] Natural-identical raspberry ketone has a clear berry aroma just like natural extracted raspberry ketone. Compared with conventionally chemically synthesized raspberry ketone, it is more easily absorbed and has higher safety. In 2013, Gu Yuncui et al. (Flavors and Fragrances of China, 2013 (Supplementary Issue 1): 39-41) used natural anisaldehyde as a raw material, carried out an aldol condensation reaction with fermented acetone, then obtained anisylacetone through hydrogenation, and finally prepared natural raspberry ketone through a demethylation reaction, with a naturalness of over 98%. In 2014, Xu Dongqing et al. (Chemical Research and Application, 2014, 26, 301-305) prepared natural-grade raspberry ketone by the same method. The total yield based on anisaldehyde was 75.75%, and the content could reach 98.65%. Currently, it has been widely used in the fields of daily chemicals, food, fuels, pharmaceutical intermediates, etc.

[0003] However, in the above processes, a large amount of acids and bases are used, which easily cause corrosion of equipment and environmental pollution; using heavy metals such as palladium-carbon as catalysts is expensive and has poor selectivity, resulting in low content of intermediates, and reacting with hydrogen under high temperature and high pressure, once the operation is improper, serious dangerous accidents are likely to occur; the cost of refluxing and demethylating with hydrobromic acid is relatively high, and the requirements for reaction conditions are high, and the product yield fluctuates between 42% and 80%. Summary of the Invention

[0004] In view of this, the present invention provides a microchannel synthesis method for natural-identical raspberry ketone. Based on the three basic reactions of condensation reaction, catalytic reduction reaction and demethylation reaction, the specific reaction methods and reaction conditions are improved to provide a continuous reaction method more suitable for industrial applications, which is a stable, efficient and green synthesis method.

[0005] A method for synthesizing natural-identical raspberry ketone according to the present invention comprises the following steps:

[0006] (1) Claisen-Schmidt condensation: Mix anisaldehyde and acetone to obtain a reaction solution, pass the reaction solution through a microchannel with a diameter of about 2.5 mm into a reactor filled with basic anion resin for reaction, collect the effluent and rinse the pipeline with a small amount of acetone, dilute with water until the solid completely precipitates to obtain 4-(p-methoxyphenyl)-3-en-2-one; the inner diameter of the reactor filled with basic anion resin is 13 mm and the filling is about 60 mm;

[0007] (2) Enzymatic catalytic reduction: Dimethyl sulfoxide (DMSO), glucose, 4-(p-methoxyphenyl)-3-en-2-one, enoate reductase, glucose dehydrogenase, and nicotinamide adenine dinucleotide (NAD+) were added to a phosphate buffer solution to obtain a mixed solution, which was stirred and reacted at a temperature of 35 °C for 24 hours. The pH of the reaction solution was adjusted by dropping saturated sodium bicarbonate solution with a pH titrator, controlling the pH at 7.0, and the reaction was detected to be completed by TLC; the reaction solution was extracted three times with isopropyl acetate, the isopropyl acetate phases were combined, washed with saturated brine, dried over anhydrous magnesium sulfate, and filtered to obtain a filtrate. The solvent was removed from the filtrate under reduced pressure to obtain the product anisylacetone;

[0008] (3) Demethylation with sodium ethanethiolate: Under a nitrogen atmosphere, an anhydrous DMF solution of ethanethiol was added to a suspension of sodium hydride in anhydrous DMF, and the mixture was stirred for 5 - 8 minutes to mix well to obtain a sodium ethanethiolate solution. Then, the anisylacetone prepared in step (2) was added, and the mixture was heated under reflux for 3 hours; after adjusting to pH = 6, it was extracted twice with chloroform, the organic phases were combined, washed twice with water, separated, the chloroform was recovered by atmospheric distillation, and the anisylacetone was recovered by reduced pressure distillation for recycling. Raspberry ketone was obtained by recrystallization.

[0009] Preferably, the volume fraction of anisaldehyde in the reaction solution in step (1) is 1% - 30%.

[0010] Preferably, the flow rate of the reaction solution in the microchannel in step (1) is 1.0 - 1.5 mL / min.

[0011] Preferably, the basic anion resin in step (1) is a hydroxide form strongly basic anion exchange resin.

[0012] Preferably, in the mixed solution in step (2), the ratio of dimethyl sulfoxide, glucose, 4-(p-methoxyphenyl)-3-en-2-one, enoate reductase, glucose dehydrogenase, and nicotinamide adenine dinucleotide to the total volume of the mixed solution is 0.05 - 0.25 mL: 20 - 60 mg: 170 - 180 mg: 0.03 - 0.67 mg: 0.01 - 0.2 mg: 0.002 - 0.01 mg: 2 mL.

[0013] Preferably, the pH of the phosphate buffer solution is 7.0 and the concentration is 0.2 mol / L.

[0014] Preferably, the stirring speed in step (2) is 400 rpm.

[0015] Preferably, the concentration of ethanethiol in the anhydrous DMF solution of ethanethiol in step (3) is 0.03 - 0.035 g / mL; the concentration of sodium hydride in the anhydrous DMF suspension of sodium hydride is 0.01 - 0.015 g / mL.

[0016] Preferably, the volume ratio of the anhydrous DMF solution of ethanethiol to the anhydrous DMF suspension of sodium hydride is 1:1.

[0017] Preferably, the mass ratio of ethanethiol, sodium hydride and sodium hydride in step (3) is 0.3 - 0.35:0.1 - 0.15:1.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a method for synthesizing natural identical raspberry ketone. Using natural anisaldehyde and natural acetone as starting materials, through three-step continuous reactions of Claisen-Schmidt condensation catalyzed by basic resin, enzymatic reduction and demethylation with sodium ethanethiolate, the final natural identical raspberry ketone is obtained. Among them, the Claisen-Schmidt condensation reaction catalyzed by basic resin adopts microchannel technology. This reaction method is safe, clean, and the yield is stable, reaching about 85%, providing a basis for industrial continuous production. The preparation method of the present invention not only meets the requirements of clean production, but also saves labor costs by virtue of the continuous process, and is suitable for large-scale industrial production. Detailed Embodiments

[0020] The present invention provides a microchannel synthesis method for natural identical raspberry ketone.

[0021] In a specific embodiment of the present invention, the basic anion resin used is purchased from Tianjin Xinyue Huamei Environmental Protection Technology Co., Ltd., and the model is: 201x7(OH);

[0022] The ene reductase used in the present invention is ene reductase (ERED) purchased from Shangke Biopharmaceuticals (Shanghai) Co., Ltd., and the product number is ES-ERED-128.

[0023] The present invention will be further described below in conjunction with embodiments.

[0024] Example 1

[0025] A method for synthesizing natural identical raspberry ketone, the steps are as follows:

[0026] (1) Mix anisaldehyde and acetone to obtain a reaction solution according to the volume fraction of natural anisaldehyde being 10%. Prepare a microchannel device (the diameter of the supporting pipeline is about 2.5 mm), set the flow rate of the reaction solution at 1.5 ml / min, and pass the reaction solution through the supporting pipeline into a reactor filled with alkaline anion resin (the inner diameter of the reactor is 13 mm and the filling is 60 mm) for reaction. The reaction can be cycled and repeated until the reaction is complete (detected by TLC). Collect the effluent and rinse the pipeline with a small amount of acetone, then dilute with water until the solid completely precipitates to obtain 4-(p-methoxyphenyl)-3-en-2-one; filter and calculate the yield to be about 99.1%;

[0027] (2) Add 54 mg of glucose, 176 mg of (E)-4-(4-methoxyphenyl)but-3-en-2-one, 0.05 ml of co-solvent DMSO, 0.15 mg of dry powder of eno reductase, 0.08 mg of dry powder of glucose dehydrogenase, and 0.01 mg of nicotinamide adenine dinucleotide (NAD+) to the catalytic buffer solution (200 mM sodium phosphate buffer solution at pH 7.0), and supplement the buffer solution to make the volume of the reaction system 2 mL; keep the reaction temperature at 30 °C and react at 400 rpm for 18 hours. The pH of the reaction solution is adjusted by dropping saturated sodium bicarbonate solution with a pH titrator to control the pH at 7.0, and the reaction is detected by TLC when it ends. Extract with isopropyl acetate three times, 5 mL each time, combine the isopropyl acetate phases, wash with saturated brine, dry with anhydrous magnesium sulfate, filter, and remove the solvent under reduced pressure from the filtrate to obtain 220.0 mg of the product 4-(4-methoxyphenyl)butan-2-one, with a yield of 98.8% and a purity of 100% (HPLC);

[0028] (3) Under a nitrogen atmosphere, dissolve 0.31 g of ethanethiol in 10 mL of anhydrous DMF to obtain an anhydrous DMF solution of ethanethiol; dissolve 0.12 g of sodium hydride in 10 mL of anhydrous DMF to obtain an anhydrous DMF suspension of sodium hydride. Add the anhydrous DMF solution of ethanethiol to the anhydrous DMF suspension of sodium hydride, stir for 5 minutes to fully mix the mixture, then add 1 g of the anisylacetone prepared in step (2), and heat under reflux for 3 hours; adjust to pH = 6 and then extract twice with chloroform. Combine the organic phases, wash twice with water, separate the layers, recover chloroform by atmospheric distillation, and recover anisylacetone by reduced pressure distillation for recycling. Recrystallize to obtain 0.768 g of the natural identical raspberry ketone, with a content of 97.93% and a yield of 83.36% (calculated based on anisylacetone).

[0029] The total yield of raspberry ketone (calculated based on natural anisaldehyde) is 83.33%.

[0030] Example 2

[0031] (1) Mix anisaldehyde and acetone to obtain a reaction solution according to the volume fraction of natural anisaldehyde being 30%. Prepare a microchannel device (the diameter of the supporting pipeline is about 2.5 mm), set the flow rate of the reaction solution at 1.0 ml / min, and pass the reaction solution through the supporting pipeline into a reactor filled with alkaline anion resin (the inner diameter of the reactor is about 13 mm and the filling is about 60 mm) for reaction. The reaction can be cycled and repeated until the reaction is complete (detected by TLC). Collect the effluent and rinse the pipeline with a small amount of acetone, then dilute with water until the solid completely precipitates to obtain 4-(p-methoxyphenyl)-3-en-2-one; filter and calculate the yield to be about 93.8%;

[0032] (2) Add 25 mg of D-glucose to the catalytic buffer solution (200 mM sodium phosphate buffer at pH 7.5), add 176 mg of (E)-4-(4-methoxyphenyl)but-3, 0.1 ml of co-solvent DMSO, 0.075 mg of dry enoate reductase powder, 0.020 mg of dry D-glucose dehydrogenase powder, and 0.002 mg of nicotinamide adenine dinucleotide phosphate (NADP+), and supplement the buffer solution to make the volume of the reaction system 2 mL; keep the reaction temperature at 35 °C and react at 400 rpm for 20 hours. The pH of the reaction solution is adjusted by dropwise adding saturated sodium bicarbonate solution with a pH titrator to control the pH at 7.5, and detect the end of the reaction by TLC. Extract three times with isopropyl acetate, 5 mL each time, combine the isopropyl acetate phases, wash with saturated brine, dry with anhydrous magnesium sulfate, filter, and remove the solvent under reduced pressure from the filtrate to obtain 214.59 mg of the product 4-(4-methoxyphenyl)butan-2-one, with a yield of 96.37% and a purity of 100% (HPLC);

[0033] (3) Under a nitrogen atmosphere, dissolve 0.31 g of ethanethiol in 10 mL of anhydrous DMF to obtain an anhydrous DMF solution of ethanethiol; dissolve 0.12 g of sodium hydride in 10 mL of anhydrous DMF to obtain an anhydrous DMF suspension of sodium hydride. Add the anhydrous DMF solution of ethanethiol to the anhydrous DMF suspension of sodium hydride, stir for 5 minutes to fully mix the mixture, then add 1.5 g of the anisylacetone prepared in step (2), and heat under reflux for 4 hours; adjust to pH = 6 and then extract twice with chloroform, combine the organic phases, wash twice with water, separate the layers, recover chloroform by atmospheric distillation, recover anisylacetone by reduced pressure distillation for recycling, and obtain 1.167 g of the natural-identical raspberry ketone by recrystallization, with a yield of 84.44% (calculated based on anisylacetone).

[0034] The total yield of raspberry ketone (calculated based on natural anisaldehyde) is 72.83%.

[0035] Comparative Example 1

[0036] (1) Add 6.8 g of water and 0.24 g of NaOH to a 50 mL three-necked flask, stir to dissolve. Add 4.34 g of natural acetone. Then add 2.24 g of anisaldehyde, and finally stir and react at 20 - 25 °C for 30 minutes to complete the reaction. Add 16 mL of water to the reaction solution to fully precipitate the reaction product anisalacetone from the reaction solution, then perform suction filtration under reduced pressure, and dry the filtered solid product to obtain 2.68 g of the intermediate anisalacetone, with a yield of 92.5%.

[0037] (2) Add 13 mL of ethanol, 2.0 g of anisalacetone, and 0.2 g of palladium-carbon catalyst to a 50 mL round-bottom flask. Connect a three-way valve, first check the airtightness with nitrogen, evacuate the gas in the reaction device, and then introduce hydrogen until the hydrogen in the device is replaced three times. Stir and react at room temperature. After reacting for 14 hours, detect that the reaction is complete by TLC. Filter and recover the palladium-carbon, and rotary evaporate the ethanol to obtain 1.80 g of anisylacetone, with a yield of 89.1%.

[0038] (3) Add 1 g of anisylacetone, 0.6 mL of glacial acetic acid, and 6 mL of 48% hydrobromic acid to a 50 mL glass three-neck reaction flask. Slowly heat and stir, and reflux and react at a temperature of 105 - 110 °C for about 9 h. Detect that the reaction is complete by TLC. Extract the reactant three times with ethyl acetate and then treat it with 30% sodium hydroxide solution. Detect that the reaction is complete by TLC and separate the layers. Add hydrochloric acid to the aqueous layer until pH = 6, extract three times with ethyl acetate, combine the organic phases, and evaporate to dryness to obtain 0.837 g of the product, with a purity of 78.6% and a yield of 69.7% (calculated based on anisylacetone).

[0039] The total yield of raspberry ketone (calculated based on natural anisaldehyde) is 57.5%.

[0040] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A synthetic method of natural identical raspberry ketone, characterized in that, it comprises the following steps: (1) Claisen-Schmidt condensation: Mix anisaldehyde and acetone to obtain a reaction solution, pass the reaction solution through a microchannel with a diameter of 2.5 mm into a reactor filled with basic anion resin for reaction, collect the effluent and rinse the pipeline with a small amount of acetone, dilute with water until the solid completely precipitates to obtain 4-(p-methoxyphenyl)-3-en-2-one; the inner diameter of the reactor filled with basic anion resin is 13 mm and the filling is 60 mm; (2) Enzyme-catalyzed reduction: Add dimethyl sulfoxide, glucose, 4-(p-methoxyphenyl)-3-en-2-one, enoate reductase, glucose dehydrogenase, and nicotinamide adenine dinucleotide to a phosphate buffer solution to obtain a mixed solution, stir and react at a temperature of 35 °C for 24 hours, adjust the pH of the reaction solution by dropwise adding saturated sodium bicarbonate solution with a pH titrator, control the pH at 7.0, and detect the end of the reaction by TLC; extract the reaction solution three times with isopropyl acetate, combine the isopropyl acetate phases, wash with saturated brine, dry over anhydrous magnesium sulfate, filter to obtain a filtrate, remove the solvent from the filtrate under reduced pressure to obtain the product anisylacetone; the catalog number of the enoate reductase is ES-ERED-128; (3) Demethylation with sodium ethanethiolate: Under a nitrogen atmosphere, add an anhydrous DMF solution of ethanethiol to a suspension of sodium hydride in anhydrous DMF, stir for 5 - 8 minutes to fully mix the mixture to obtain a sodium ethanethiolate solution, then add the anisylacetone prepared in step (2), and heat under reflux for 3 hours; adjust to pH = 6 and then extract twice with chloroform, combine the organic phases, wash twice with water, separate the layers, recover chloroform by atmospheric distillation, recover anisylacetone by reduced pressure distillation for recycling, and obtain raspberry ketone by recrystallization.

2. The synthetic method of natural identical raspberry ketone according to claim 1, characterized in that, the volume fraction of anisaldehyde in the reaction solution in step (1) is 1% - 30%.

3. The synthetic method of natural identical raspberry ketone according to claim 1, characterized in that, the flow rate of the reaction solution in the microchannel in step (1) is 1.0 - 1.5 ml / min.

4. The synthetic method of natural identical raspberry ketone according to claim 1, characterized in that, the basic anion resin in step (1) is a hydroxide-type strongly basic anion exchange resin.

5. The synthetic method of natural identical raspberry ketone according to claim 1, characterized in that, in the mixed solution in step (2), the ratio of dimethyl sulfoxide, glucose, 4-(p-methoxyphenyl)-3-en-2-one, enoate reductase, glucose dehydrogenase, and nicotinamide adenine dinucleotide to the total volume of the mixed solution is 0.05 - 0.25 mL: 20 - 60 mg: 170 - 180 mg: 0.03 - 0.67 mg: 0.01 - 0.2 mg: 0.002 - 0.01 mg: 2 mL.

6. The synthetic method of natural identical raspberry ketone according to claim 5, characterized in that, The pH of the phosphate buffer solution is 7.0 and the concentration is 0.2 mol / L.

7. The method for synthesizing natural-identical raspberry ketone according to claim 1, characterized in that the stirring speed in step (2) is 400 rpm.

8. The method for synthesizing natural-identical raspberry ketone according to claim 1, characterized in that in the anhydrous DMF solution of ethanethiol in step (3), the concentration of ethanethiol is 0.03 - 0.035 g / mL; in the anhydrous DMF suspension of sodium hydride, the concentration of sodium hydride is 0.01 - 0.015 g / mL.

9. The method for synthesizing natural-identical raspberry ketone according to claim 8, characterized in that the volume ratio of the anhydrous DMF solution of ethanethiol to the anhydrous DMF suspension of sodium hydride is 1:

1.

10. The method for synthesizing natural-identical raspberry ketone according to claim 1, characterized in that in step (3), the mass ratio of ethanethiol, sodium hydride and sodium hydride is 0.3~0.35:0.1~0.15:1.