Synthesis method and application of bergamottin

Abstract

The application discloses a synthesis method and application of bergamottin, and comprises the following steps: (1) taking m-benzene triol as raw material, and synthesizing 5-methoxy-1,3-benzene diol through a selective etherification reaction; (2) adopting a Pechmann condensation reaction to prepare 5-methoxy-7-hydroxycoumarin; (3) obtaining 5-methoxy-7-allyloxy coumarin through an etherification reaction; (4) preparing 5-methoxy-6-allyl-7-hydroxycoumarin through a Claisen rearrangement reaction; (5) synthesizing 5-methoxypsoralen through an oxidation ring formation reaction; and (6) synthesizing the natural compound bergamottin through a demethylation reaction. The synthesis process is simple, raw materials are cheap, product separation and purification are simple, the yield is higher than 65%, the purity is above 99%, and the product can be produced on a large scale; meanwhile, the bergamottin shows superior antioxidant activity, and the antioxidant performance is superior to corresponding coumarin and benzofuran, and has potential application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, in particular to a synthesis method of bergaptol and application thereof. BACKGROUND

[0002] Bergaptol, also known as 5-hydroxyscutellarein, is a natural furanocoumarin compound, which is widely present in natural plants such as Notopterygium, lemon, bergamot and the like, and shows important antibacterial, anti-inflammatory, antitumor and other various biological pharmacological activities. In addition, when bergaptol is added to cigarettes, elegant bean aroma notes are revealed during smoking, which can significantly improve the intrinsic quality of cigarettes. Meanwhile, both coumarin and benzofuran are natural structural skeletons, and their derivatives have antioxidant activity, and the phenolic hydroxyl group is also an antioxidant functional group. Therefore, bergaptol, which integrates coumarin, benzofuran and phenolic hydroxyl group, has higher antioxidant activity and application value.

[0003] However, there are few reports on the synthesis method of bergaptol, which leads to high price of bergaptol and limits its application in cigarettes and medicines.

[0004] Therefore, it is particularly important to develop a new synthesis method of bergaptol and carry out application research in the aspect of antioxidant. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a synthesis method of bergaptol and application thereof. The synthesis method uses inexpensive phloroglucinol as raw material, and synthesizes bergaptol through six steps of etherification, Pechmann condensation, etherification, Claisen rearrangement, oxidation ring formation and demethylation. The synthesis route is simple in operation, high in yield and easy to scale up.

[0006] The technical problem to be solved by the present application is solved by the following technical scheme:

[0007] The synthesis method of bergaptol comprises the following steps: (1) using phloroglucinol as raw material, 5-methoxy-1,3-benzenediol is synthesized through selective etherification reaction, (2) 5-methoxy-7-hydroxycoumarin is prepared by Pechmann condensation reaction, (3) 5-methoxy-7-allyloxy coumarin is obtained by etherification reaction, (4) 5-methoxy-6-allyl-7-hydroxycoumarin is prepared by Claisen rearrangement reaction, (5) 5-methoxyscutellarein is synthesized by oxidation ring formation reaction, and (6) natural compound bergaptol is synthesized by demethylation reaction.

[0008] The reaction formula is as follows:

[0009]

[0010] Preferably, the method comprises the following steps:

[0011] (1) Preparation of 5-methoxy-1, 3-benzene diol: in a round bottom flask, add phloroglucinol, solvent and catalyst, cool to 0-5°C in ice bath, add iodomethane to the system, continue stirring for 0.5-2h, then react at room temperature for 8-12h, after the reaction is completed, filter, wash the solid with ethyl acetate, combine the organic phase, evaporate the solvent under reduced pressure, separate the crude product by silica gel column chromatography to obtain 5-methoxy-1, 3-benzene diol;

[0012] (2) Preparation of 5-methoxy-7-hydroxycoumarin: in a round bottom flask, add concentrated H2SO4, cool to 0- -25°C in a low temperature reactor, then slowly add 5-methoxy-1, 3-benzene diol and malic acid solid mixture to the concentrated H2SO4 under stirring, after adding 5-methoxy-1, 3-benzene diol and malic acid, continue stirring at low temperature for 0.5-2h, then react at room temperature for 12-30h, after the reaction is completed, slowly add the reaction mixture to ice water, collect the precipitate by suction filtration, wash with ice water and dry, separate the crude product by silica gel column chromatography to obtain 5-methoxy-7-hydroxycoumarin;

[0013] (3) Preparation of 5-methoxy-7-allyloxy coumarin: in a round bottom flask, add organic solvent, 5-methoxy-7-hydroxycoumarin and catalyst, slowly drop the organic solution containing allyl bromide into the reaction system under stirring, after the dropping is completed, heat to reflux for 5-12h, after the reaction is completed, evaporate the solvent under reduced pressure, add distilled water and stir, collect the solid by suction filtration, wash with water and dry, recrystallize the crude product with 95% ethanol to obtain 5-methoxy-7-allyloxy coumarin;

[0014] (4) Preparation of 5-methoxy-6-allyl-7-hydroxycoumarin: in a round bottom flask, add 5-methoxy-7-allyloxy coumarin and organic base, heat to reflux for 2-6h, after the reaction is completed, evaporate the solvent under reduced pressure, then add ice water and stir vigorously, collect the solid by suction filtration, wash with water and dry, separate the crude product by silica gel column chromatography to obtain 5-methoxy-6-allyl-7-hydroxycoumarin;

[0015] (5) Preparation of 5-methoxypsoralen (5): in a round bottom flask, add 5-methoxy-6-allyl-7-hydroxycoumarin, oxidizing agent and solvent, react at room temperature for 12-24h, after the reaction is completed, add inorganic acid and continue stirring for 0.5-2h, pour the reaction mixture into ice water, collect the solid by suction filtration, wash with water and dry, recrystallize the crude product with 95% ethanol to obtain 5-methoxypsoralen.

[0016] (6) Preparation of bergamottin: in a round-bottom flask, 5-methoxypsoralen and a solvent are added, the reactor is cooled to 0 to -20 DEG C at low temperature, and an organic solvent containing BBr3 is added dropwise into the flask under nitrogen protection, then stirring is carried out at room temperature for 6 to 10 hours, after the reaction is completed, water is slowly added dropwise at 0 to 5 DEG C to quench the reaction, white solid is precipitated, the organic solvent is removed under reduced pressure, filtration, water washing and drying are carried out, the solid is dissolved in acetone, the insoluble substance is removed by filtration, the solvent is removed under reduced pressure, and the crude product is recrystallized with 95% ethanol to obtain the target natural compound bergamottin.

[0017] Preferably, in step (1), the solvent is one of acetone, dichloromethane or trichloromethane; the catalyst is one of potassium carbonate, sodium carbonate or potassium hydroxide; and the molar ratio of m-cresol, iodomethane and the catalyst is 1:(1-1.1):(1-1.2).

[0018] Preferably, in step (2), the mass fraction of concentrated H2SO4 is 70% to 98%; and the molar ratio of 5-methoxy-1,3-benzenediol and malic acid is 1:(1-1.3).

[0019] Preferably, in step (3), the organic solvent is one of acetone, dichloromethane or trichloromethane; the catalyst is one of potassium carbonate, sodium carbonate or potassium hydroxide; and the molar ratio of 5-methoxy-7-hydroxycoumarin, the catalyst and allyl bromide is 1:(1-1.2):(1-1.3).

[0020] Preferably, in step (4), the organic base is one of triethylamine, N,N-dimethylaniline or N,N-diethylaniline; and the organic base is both a solvent and a catalyst.

[0021] Preferably, in step (5), the oxidant is one or more of osmium tetroxide, potassium periodate or potassium perchlorate; the solvent is one or more of methanol, ethanol or distilled water; and the inorganic acid is one of 98% H2SO4, 37% HCl or 85% H3PO4.

[0022] Preferably, in step (6), the organic solvent is one of anhydrous dichloromethane or anhydrous trichloromethane; and the molar ratio of 5-methoxypsoralen and BBr3 is 1:(1-2).

[0023] A bergamottin synthesized by the method.

[0024] The application further discloses an application of the bergamottin synthesized by the method in scavenging free radicals.

[0025] The technical scheme has the following beneficial effects:

[0026] The synthesis method of bergamottin has simple process, cheap and easily available raw materials, simple product separation and purification, and the yield is higher than 65%, the purity of the final bergamottin is more than 99%, and large-scale production can be carried out.

[0027] Meanwhile, the bergamottin is added into ABTS·, DPPH· and galvinoxyl· free radical ethanol solution respectively, and the ABTS·, DPPH· and galvinoxyl· free radicals can be well removed, and the bergamottin shows superior antioxidant activity, and the antioxidant performance is superior to corresponding coumarin and benzofuran, and has potential application value. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0029] Figure 1 is a nuclear magnetic resonance hydrogen spectrum of bergamottin;

[0030] Figure 2 is a nuclear magnetic resonance carbon spectrum of bergamottin;

[0031] Figure 3 is a mass spectrum of bergamottin. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions, and numerical values set forth in these embodiments are not limiting to the scope of the present application unless otherwise specifically stated.

[0033] A synthesis method of bergamottin comprises the following steps: (1) taking m-hydroxybenzoic acid as a raw material, 5-methoxy-1,3-benzenediol is synthesized by selective etherification reaction, (2) 5-methoxy-7-hydroxycoumarin is prepared by Pechmann condensation reaction, (3) 5-methoxy-7-allyloxy coumarin is obtained by etherification reaction, (4) 5-methoxy-6-allyl-7-hydroxycoumarin is prepared by Claisen rearrangement reaction, (5) 5-methoxypsoralen is synthesized by oxidation ring reaction, and (6) natural compound bergamottin is synthesized by demethylation reaction;

[0034] The reaction formula is as follows:

[0035]

[0036] Wherein, formula (1) is 5-methoxy-1,3-benzene diol, formula (2) is 5-methoxy-7-hydroxycoumarin, formula (3) is 5-methoxy-7-allyloxy coumarin, formula (4) is 5-methoxy-6-allyl-7-hydroxycoumarin, formula (5) is 5-methoxypsoralen, and formula (6) is bergamotol.

[0037] Application of a kind of bergamotol in scavenging free radicals.

[0038] The antioxidant performance test of the bergamotol obtained in the present application is carried out, and the specific method is as follows:

[0039] The bergamotol is dissolved in ethanol to form an ethanol solution, which is then added into 2,2'-azobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical (ABTS·), diphenyl picrylhydrazyl radical (DPPH·) and 2,6-di-tert-butyl-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadiene)-p-methoxy radical (galvinoxyl·) ethanol solution, respectively. Then, the change curves of the concentrations of ABTS·, DPPH· and galvinoxyl· radicals with time are determined at the maximum absorption wavelengths (734 nm, 517 nm and 428 nm), and the free radical scavenging rate of the bergamotol is calculated.

[0040] The concentrations of the bergamotol in the ABTS·, DPPH· and galvinoxyl· radical ethanol solutions are 5 μmol / L, 10 μmol / L and 50 μmol / L, respectively, and the reaction time of the bergamotol with the ABTS·, DPPH· and galvinoxyl· radicals is 30 min.

[0041] The following is described in detail in the examples:

[0042] Example 1

[0043] A synthesis method of a kind of bergamotol, comprising the following steps:

[0044] (1) Preparation of 5-methoxy-1,3-benzene diol (1): In a 250 mL round-bottom flask, 12.60 g of phloroglucinol (100 mmol), 150 mL of acetone and 13.80 g of potassium carbonate were added, cooled to 5°C in an ice bath, and 14.20 g of iodomethane was added into the system. After the dropwise addition was completed, the reaction was carried out at room temperature for 12 h. After the reaction was completed, the potassium carbonate was filtered, washed with 40 mL of ethyl acetate twice, and the organic phases were combined and dried. The solvent was removed under reduced pressure, and the crude product was separated by silica gel column chromatography to obtain 10.20 g of white 5-methoxy-1,3-benzene diol with a yield of 72.86%.

[0045] (2) Preparation of 5-methoxy-7-hydroxycoumarin (2): In a 100 mL round bottom flask, 60 mL of H2SO4 (98%) was added and cooled to below -20 °C in a low temperature reactor. 5-methoxy-1, 3-benzenediol (7.00 g, 50 mmol) and malic acid (7.40 g, 55 mmol) were mixed and added slowly to the concentrated H2SO4 under stirring at -20 °C. After the addition of the reactants, the stirring was continued at -20 °C for 1 h and then the temperature was increased to room temperature for 24 h. After the completion of the reaction, the reaction mixture was slowly added to ice water and the precipitate was collected by filtration. The precipitate was washed with ice water and dried. The crude product was recrystallized from 95% ethanol to obtain 6.63 g of white flaky 5-methoxy-7-hydroxycoumarin in 69.06% yield.

[0046] (3) Preparation of 5-methoxy-7-allyloxycoumarin (3): In a 100 mL round bottom flask, acetone (70 mL), 5-methoxy-7-hydroxycoumarin (5.76 g, 30 mmol) and potassium carbonate (4.14 g, 30 mmol) were added and an allyl bromide (4.02 g, 33 mmol) solution in acetone was slowly added dropwise to the reaction system under stirring. After the completion of the dropwise addition, the reaction was heated to reflux for 10 h. After the completion of the reaction, most of the solvent was removed under reduced pressure and water was added to precipitate a white solid. The solid was collected by filtration, washed with water and dried. The crude product was recrystallized from 95% ethanol to obtain 5.87 g of white 5-methoxy-7-allyloxycoumarin in 84.34% yield.

[0047] (4) Preparation of 5-methoxy-6-allyl-7-hydroxycoumarin (4): In a 100 mL round bottom flask, 5-methoxy-7-allyloxycoumarin (4.64 g, 20 mmol) and N, N-diethylaniline (50 mL) were added and heated to reflux for 4 h. After the completion of the reaction, the solvent was removed under reduced pressure and the crude product was separated by column chromatography using silica gel to obtain 3.21 g of white 5-methoxy-6-allyl-7-hydroxycoumarin in 69.18% yield.

[0048] (5) Preparation of 5-methoxypsoralen (5): In a 50 mL round bottom flask, 5-methoxy-6-allyl-7-hydroxycoumarin (2.32 g, 10 mmol), osmium tetroxide (0.25 g, 1 mmol), potassium periodate (1.00 g), methanol (20 mL) and distilled water (10 mL) were added and the reaction was carried out at room temperature for 20 h. After the completion of the reaction, 85% H3PO4 (8 mL) was added and the stirring was continued for 1 h. The reaction mixture was poured into ice water to precipitate a white solid. The solid was collected by filtration, washed with water and dried. The crude product was recrystallized from 95% ethanol to obtain 1.58 g of white granular 5-methoxypsoralen in 73.15% yield.

[0049] (6) Preparation of Bergamottol (6): In a 100 mL round bottom flask, 5-methoxy- psoralen (1.08 g, 5 mmol) and anhydrous dichloromethane (20 mL) were added, and the low-temperature reactor was cooled to below -20 °C under nitrogen protection. 10 mL of anhydrous dichloromethane containing BBr3 (10 mmol) was added dropwise into the flask, and then stirred at room temperature for 10 h. After the reaction was completed, 20 mL of water was slowly added dropwise under ice bath to quench the reaction, and white solids were precipitated. The organic solvent was removed under reduced pressure, filtered, washed with water, and dried. The solid was dissolved in acetone, filtered to remove insoluble substances, and the solvent was removed under reduced pressure. The crude product was recrystallized with 95% ethanol to obtain 0.93 g of the target compound bergamottol with a yield of 92.08%.

[0050] Example 2

[0051] A method for synthesizing bergamottol, comprising the following steps:

[0052] (1) Preparation of 5-methoxy-1,3-benzene-diol (1): In a 250 mL round bottom flask, m- trihydroxybenzene (12.60 g, 100 mmol), dichloromethane (150 mL), and sodium carbonate (11.66 g) were added, and the system was cooled to 5 °C in an ice bath. 14.20 g of iodomethane was added, and after the addition was completed, the reaction was carried out at room temperature for 10 h. After the reaction was completed, the potassium carbonate was filtered and washed with 40 mL of ethyl acetate twice. The organic phases were combined, dried, and then the solvent was removed under reduced pressure. The crude product was separated by silica gel column chromatography to obtain 8.54 g of white 5-methoxy-1,3-benzene-diol with a yield of 61.00%.

[0053] (2) Preparation of 5-methoxy-7-hydroxycoumarin (2): In a 100 mL round bottom flask, 60 mL of H2SO4 (90%) was added, and the low-temperature reactor was cooled to below -15 °C. Under stirring, 5-methoxy-1,3-benzene-diol (7.00 g, 50 mmol) and malic acid (8.04 g, 60 mmol) were mixed and slowly added to the concentrated H2SO4, and the reaction temperature was maintained at -15 °C. After the reactants were added, stirring was continued at -15 °C for 2 h, and then the temperature was increased to room temperature and reacted for 30 h. After the reaction was completed, the reaction mixture was slowly added to ice water, and a precipitate was precipitated. The precipitate was collected by suction filtration, washed with ice water, and dried. The crude product was recrystallized with 95% ethanol to obtain 6.22 g of white flaky 5-methoxy-7-hydroxycoumarin with a yield of 64.79%.

[0054] (3) Preparation of 5-methoxy-7-allyloxy coumarin (3): In a 100 mL round bottom flask, dichloromethane (70 mL), 5-methoxy-7-hydroxycoumarin (5.76 g, 30 mmol) and sodium carbonate (3.50 g, 33 mmol) were added, and an allyl bromide (4.02 g, 33 mmol) solution in dichloromethane was slowly added dropwise to the reaction system under stirring. After the addition was completed, it was heated to reflux for 10 h. After the reaction was completed, most of the solvent was removed by evaporation under reduced pressure, and water was added to precipitate white solids. The solids were collected by suction filtration, washed with water, and dried. The crude product was recrystallized from 95% ethanol to obtain 4.98 g of white 5-methoxy-7-allyloxy coumarin with a yield of 71.55%.

[0055] (4) Preparation of 5-methoxy-6-allyl-7-hydroxycoumarin (4): In a 100 mL round bottom flask, 5-methoxy-7-allyloxy coumarin (4.64 g, 20 mmol) and triethylamine (50 mL) were added, and it was heated to reflux for 6 h. After the reaction was completed, the solvent was removed by evaporation under reduced pressure, and the crude product was separated by silica gel column chromatography to obtain 1.56 g of white 5-methoxy-6-allyl-7-hydroxycoumarin with a yield of 33.62%.

[0056] (5) Preparation of 5-methoxypsoralen (5): In a 50 mL round bottom flask, 5-methoxy-6-allyl-7-hydroxycoumarin (2.32 g, 10 mmol), osmium tetroxide (0.25 g, 1 mmol), potassium perchlorate (1.00 g), methanol (20 mL), and distilled water (10 mL) were added, and it was reacted at room temperature for 20 h. After the reaction was completed, 37% HCl (8 mL) was added and stirred for 1 h. The reaction mixture was poured into ice water to precipitate white solids. The solids were collected by suction filtration, washed with water, and dried. The crude product was recrystallized from 95% ethanol to obtain 1.12 g of white granular 5-methoxypsoralen with a yield of 51.85%.

[0057] (6) Preparation of bergamottin (6): In a 100 mL round bottom flask, 5-methoxypsoralen (1.08 g, 5 mmol) and anhydrous chloroform (20 mL) were added, and the reactor was cooled to below -10°C at low temperature. Under nitrogen protection, 10 mL of anhydrous chloroform containing BBr3(8 mmol) was added dropwise to the flask, and then it was stirred at room temperature for 10 h. After the reaction was completed, 20 mL of water was slowly added dropwise under ice bath to quench the reaction, and white solids were precipitated. The organic solvent was removed by evaporation under reduced pressure, and the filtrate was washed with water and dried. The solids were dissolved in acetone, and the insoluble matter was removed by filtration. The solvent was removed by evaporation under reduced pressure, and the crude product was recrystallized from 95% ethanol to obtain 0.91 g of the target compound bergamottin with a yield of 90.10%.

[0058] Example 3

[0059] A method for synthesizing a bergamot alcohol, comprising the following steps:

[0060] (1) Preparation of 5-methoxy-1,3-benzene diol (1): In a 250 mL round-bottom flask, add phloroglucinol (12.60 g, 100 mmol), chloroform (150 mL), and potassium hydroxide (6.11 g), cool to 5°C in an ice bath, add 14.20 g of methyl iodide to the system, after the end of the dropwise addition, react at room temperature for 10 h, after the reaction is completed, filter, wash the potassium carbonate with 40 mL of ethyl acetate twice, combine the organic phases, dry, and evaporate the solvent under reduced pressure, separate the crude product by silica gel column chromatography to obtain 7.63 g of white 5-methoxy-1,3-benzene diol, with a yield of 54.50%.

[0061] (2) Preparation of 5-methoxy-7-hydroxycoumarin (2): In a 100 mL round-bottom flask, add 60 mL of H2SO4 (80%), cool to below -10°C in a low-temperature reactor, under stirring conditions, slowly add 5-methoxy-1,3-benzene diol (7.00 g, 50 mmol) and malic acid (7.40 g, 55 mmol) mixed solids to concentrated H2SO4, and maintain the reaction temperature at -10°C. After the reactants are added, continue to stir at -10°C for 0.5 h, then raise the temperature to room temperature and react for 20 h, after the reaction is completed, slowly add the reaction mixture to ice water, precipitate is separated out, collect the precipitate by suction filtration, wash with ice water, dry, and recrystallize the crude product from 95% ethanol to obtain 6.09 g of white flaky 5-methoxy-7-hydroxycoumarin, with a yield of 63.44%.

[0062] (3) Preparation of 5-methoxy-7-allyloxy coumarin (3): In a 100 mL round-bottom flask, add chloroform (70 mL), 5-methoxy-7-hydroxycoumarin (5.76 g, 30 mmol), and potassium hydroxide (1.85 g, 33 mmol), under stirring conditions, slowly dropwise add a chloroform solution of allyl bromide (4.02 g, 33 mmol) to the reaction system. After the end of the dropwise addition, heat to reflux for 12 h, after the reaction is completed, evaporate most of the solvent under reduced pressure, add water to precipitate white solids. Collect the solids by suction filtration, wash with water, dry, and recrystallize the crude product from 95% ethanol to obtain 5.46 g of white 5-methoxy-7-allyloxy coumarin, with a yield of 78.45%.

[0063] (4) Preparation of 5-methoxy-6-allyl-7-hydroxycoumarin (4): In a 100 mL round-bottom flask, add 5-methoxy-7-allyloxy coumarin (4.64 g, 20 mmol) and N,N-dimethylaniline (50 mL), heat to reflux for 5 h, after the reaction is completed, evaporate the solvent under reduced pressure, separate the crude product by silica gel column chromatography to obtain 2.77 g of white 5-methoxy-6-allyl-7-hydroxycoumarin, with a yield of 59.70%.

[0064] (5) Preparation of 5-methoxypsoralen (5): In a 50 mL round bottom flask, 5-methoxy-6-allyl-7-hydroxycoumarin (2.32 g, 10 mmol), osmium tetroxide (0.25 g, 1 mmol), potassium periodate (1.00 g), ethanol (20 mL) and distilled water (10 mL) were added, and the reaction was carried out at room temperature for 24 h. After the reaction was completed, 98% H2SO4(8 mL) was added and stirring was continued for 2 h. The reaction mixture was poured into ice water, and white solids were precipitated. The solids were collected by suction filtration, washed with water, and dried. The crude product was recrystallized from 95% ethanol to obtain 1.42 g of 5-methoxypsoralen in the form of white granules, with a yield of 65.74%.

[0065] (6) Preparation of bergamottin (6): In a 100 mL round bottom flask, 5-methoxypsoralen (1.08 g, 5 mmol) and anhydrous dichloromethane (20 mL) were added, and the reaction vessel was cooled to below -10°C in a low-temperature reactor. Under nitrogen protection, 10 mL of anhydrous dichloromethane containing BBr3(5 mmol) was added dropwise to the flask, and then stirring was carried out at room temperature for 8 h. After the reaction was completed, 20 mL of water was slowly added dropwise under ice-bath cooling to quench the reaction, and white solids were precipitated. The organic solvent was removed by evaporation under reduced pressure, and the solids were filtered, washed with water, and dried. The solids were dissolved in acetone, and insoluble substances were removed by filtration. The solvent was removed by evaporation under reduced pressure, and the crude product was recrystallized from 95% ethanol to obtain 0.86 g of the target compound bergamottin, with a yield of 85.15%.

[0066] Structural characterization data of the compound:

[0067] Bergamottin: 1 H NMR (600 MHz), δ: 11.29 (s, 1H), 8.24 (d, J = 9.6 Hz, 1H), 7.90 (d, J = 2.4 Hz, 1H), 7.19 (dd, J = 1.2 Hz, 2.4 Hz, 1H), 7.14 (s, 1H), 6.25 (d, J = 9.6 Hz, 1H); 13 C NMR (151 MHz,), δ: 160.92, 157.51, 153.13, 148.35, 145.45, 140.27, 112.96, 111.42, 105.19, 104.20, 91.48. HRMS m / z calcd for C 11 H6O4[M+H] + 203.0339, found 203.0345.

[0068] Antioxidant performance test

[0069] (1) ABTS·radical scavenging performance test:

[0070] Firstly, the solution was prepared: 5.0 mg of ABTS and 1.5 mg of K2S2O8 were weighed into a 2 mL volumetric flask, and distilled water was added to constant volume. After being placed in the dark at room temperature for 24 h, the color turned dark blue. Then it was transferred to a 100 mL volumetric flask, and anhydrous ethanol was added to constant volume. It was placed in a constant temperature water bath at 30°C for 30 min to obtain an ABTS· ethanol solution. The absorbance value of the solution was maximum at 734 nm, and was 1.072. The molar extinction coefficient of ABTS· at this wavelength was 1.6 x 10 4 L / (mol·cm).

[0071] The operation of quenching ABTS· free radicals by the compound was as follows: 1.9 mL of ABTS· ethanol solution and 0.1 mL of 0.1 mmol / L bergamot alcohol ethanol solution were transferred into a test tube, the final concentration of bergamot alcohol was 5 μmol / L, and the mixture was quickly mixed. The decay curve of absorbance value (A) at the maximum absorption wavelength within 30 min was recorded. The concentrations of ABTS· at the initial time and the final time were obtained by the Lambert-Beer law, and the ABTS· clearance rate of bergamot alcohol was obtained by the concentration change.

[0072] (2) DPPH· free radical clearance performance test:

[0073] Firstly, the solution was prepared: 4.0 mg of DPPH was weighed into a 20 mL beaker, and a small amount of anhydrous ethanol was added to dissolve it. Then it was transferred to a 100 mL volumetric flask, and anhydrous ethanol was added to constant volume to obtain a DPPH· ethanol solution. The maximum absorption wavelength of the solution was at 517 nm, and the absorbance value was about 1.107. The molar extinction coefficient at this wavelength was 4.09 x 10 3 L / (mol·cm).

[0074] The operation method of quenching DPPH· by the compound was consistent with that of quenching ABTS·: 1.9 mL of DPPH· ethanol solution and 0.1 mL of 0.2 mmol / L bergamot alcohol ethanol solution were transferred into a test tube, so that the final concentration of bergamot alcohol was 10 μmol / L. The mixture was quickly mixed, and the decay curve of absorbance value (A) at the maximum absorption wavelength within 30 min was recorded. The concentrations of DPPH· at the initial time and the final time were obtained by the Lambert-Beer law, and the DPPH· clearance rate of bergamot alcohol was obtained by the concentration change.

[0075] (3) Galvinoxyl· free radical clearance performance test:

[0076] Firstly, the solution was prepared: 1.0 mg of galvinoxyl was weighed into a 20 mL beaker, dissolved with a small amount of anhydrous ethanol, and then transferred to a 100 mL volumetric flask, which was diluted with anhydrous ethanol to obtain a galvinoxyl· free radical ethanol solution, which had a maximum absorbance value of about 1.523 at 428 nm, and a molar extinction coefficient of 1.4 x 10 5 L / (mol·cm) at this wavelength.

[0077] The operation method of quenching galvinoxyl· free radicals by the compound was consistent with that of quenching ABTS·: 1.9 mL of the galvinoxyl· free radical ethanol solution and 0.1 mL of the limonin ethanol solution with a concentration of 1 mmol / L were removed and added to a test tube, so that the final concentration of limonin was 50 μmol / L, the mixture was quickly mixed, and the decay curve of the absorbance value (A) at the maximum absorption wavelength within 30 min was recorded, the concentrations of galvinoxyl· free radicals at the initial time and the final time were obtained by the Lambert-Beer law, and the clearance rate of limonin on galvinoxyl· free radicals was obtained by the concentration change.

[0078] Table 1: Compound clearance rates on ABTS·, DPPH· and galvinoxyl· free radicals

[0079]

[0080] Note: The concentrations of the three compounds in the ABTS· free radical clearance performance test system were 5 μmol / L; the concentrations of the three compounds in the DPPH· free radical clearance performance test system were 10 μmol / L; and the concentrations of the three compounds in the galvinoxyl· free radical clearance performance test system were 50 μmol / L.

[0081] As shown in Table 1, the clearance rates of limonin on ABTS·, DPPH· and galvinoxyl· free radicals were 92.12%, 78.76% and 58.37%, respectively, which indicated that limonin could well clear ABTS·, DPPH· and galvinoxyl· free radicals, and the free radical clearance rate was higher than that of the corresponding coumarin and benzofuran, which showed superior antioxidant activity and had potential application value.

[0082] Although the present application has been disclosed as above, it is not intended to limit the present application, and any person skilled in the art can make various selections and modifications without departing from the spirit and scope of the present application, and therefore the protection scope of the present application is defined by the claims and their equivalent forms.

Claims

1. A method of synthesizing nerolidol, characterized by, Comprising the following steps: (1) Preparation of 5-methoxy-1,3-benzene diol (1): In a 250 mL round-bottom flask, 12.60 g, 100 mmol of m-benzene triol, 150 mL of acetone and 13.80 g of potassium carbonate were added, cooled to 5°C in an ice bath, 14.20 g of methyl iodide was added to the system, after the end of dropwise addition, the reaction was carried out at room temperature for 12 h, after the reaction was completed, the potassium carbonate was filtered, washed with 40 mL of ethyl acetate twice, the organic phases were combined, dried and the solvent was removed under reduced pressure, the crude product was separated by silica gel column chromatography to obtain 10.20 g of white 5-methoxy-1,3-benzene diol, the yield was 72.86%; (2) Preparation of 5-methoxy-7-hydroxycoumarin (2): In a 100 mL round-bottom flask, 60 mL of 98% H2SO4 was added, and the low-temperature reactor was cooled to below -20°C, 7.00 g, 50 mmol of 5-methoxy-1,3-benzene diol and 7.40 g, 55 mmol of malic acid were mixed and slowly added to the concentrated H2SO4, and the reaction temperature was maintained at -20°C; After the reactants were added, stirring was continued at -20°C for 1 h, and then the temperature was raised to room temperature and reacted for 24 h, after the reaction was completed, the reaction mixture was slowly added to ice water, the precipitate was separated, and the precipitate was collected by suction filtration, washed with ice water and dried, and the crude product was recrystallized with 95% ethanol to obtain 6.63 g of white flaky 5-methoxy-7-hydroxycoumarin, the yield was 69.06%; (3) Preparation of 5-methoxy-7-allyloxy coumarin (3): In a 100 mL round-bottom flask, 70 mL of acetone, 5.76 g, 30 mmol of 5-methoxy-7-hydroxycoumarin and 4.14 g, 30 mmol of potassium carbonate were added, and 4.02 g, 33 mmol of allyl bromide in acetone was slowly added dropwise to the reaction system under stirring; After the end of dropwise addition, heating was carried out under reflux for 10 h, after the reaction was completed, most of the solvent was removed under reduced pressure, and water was added to precipitate white solids; The solids were collected by suction filtration, washed with water and dried, and the crude product was recrystallized with 95% ethanol to obtain 5.87 g of white 5-methoxy-7-allyloxy coumarin, the yield was 84.34%; (4) Preparation of 5-methoxy-6-allyl-7-hydroxycoumarin (4): In a 100 mL round-bottom flask, 4.64 g, 20 mmol of 5-methoxy-7-allyloxy coumarin and 50 mL of N,N-diethyl aniline were added, and heating was carried out under reflux for 4 h, after the reaction was completed, the solvent was removed under reduced pressure, and the crude product was separated by silica gel column chromatography to obtain 3.21 g of white 5-methoxy-6-allyl-7-hydroxycoumarin, the yield was 69.18%; (5) Preparation of 5-methoxypsoralen (5): In a 50 mL round-bottom flask, 2.32 g, 10 mmol of 5-methoxy-6-allyl-7-hydroxycoumarin, 0.25 g, 1 mmol of osmium tetroxide, 1.00 g of potassium periodate, 20 mL of methanol and 10 mL of distilled water were added, and the reaction was carried out at room temperature for 20 h. After the reaction was completed, 8 mL of 85% H3PO4 was added and stirring was continued for 1 h. The reaction mixture was poured into ice water, and white solids were precipitated. The solids were collected by suction filtration, washed with water and dried. The crude product was recrystallized from 95% ethanol to obtain 1.58 g of white granular 5-methoxypsoralen at a yield of 73.15%. (6) Preparation of bergamottol (6): In a 100 mL round-bottom flask, 1.08 g, 5 mmol of 5-methoxypsoralen and 20 mL of anhydrous dichloromethane were added, and the low-temperature reactor was cooled to below -20°C. Under nitrogen protection, 10 mL of anhydrous dichloromethane containing 10 mmol of BBr3 was added dropwise to the flask, and then stirring was carried out at room temperature for 10 h. After the reaction was completed, 20 mL of water was slowly added dropwise under ice-bath cooling to quench the reaction, and white solids were precipitated. The organic solvent was removed by evaporation under reduced pressure, and the solids were filtered, washed with water and dried. The solids were dissolved in acetone, and the insoluble substances were removed by filtration. The solvent was removed by evaporation under reduced pressure, and the crude product was recrystallized from 95% ethanol to obtain 0.93 g of the target compound bergamottol at a yield of 92.08%.

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