A method for synthesizing the diterpenoid natural product przewalskin B

Abstract

This invention relates to the utilization of intermolecular S N The 2' reaction rapidly constructs the reaction precursor and, for the first time, achieves an intramolecular [5+2] cycloaddition reaction between α-hydroxy-o-benzoquinone and the carbon-oxygen double bond, rapidly constructing a [5,5] fused ring structure with a high oxidation state, yielding the natural product przewalskin B. Previous synthetic methods often required complex steps to construct the ring system and introduce the oxidation state. The key to solving the problem in this invention lies in: 1. Utilizing intermolecular S... N 2' reaction can effectively introduce a chiral center to complete the asymmetric synthesis of przewalskin B molecule; 2. It realizes the [5+2] cycloaddition reaction of α-hydroxy-o-benzoquinone with carbon-oxygen double bond.

Description

Technical Field

[0001] This invention relates to the field of synthetic chemistry, specifically to a method for synthesizing the diterpenoid natural product przewalskin B. Background Technology

[0002] *Salvia przewalskii*, a plant belonging to the subgenus *Salvia* of the genus *Salvia* in the family Lamiaceae, is also known as Purple Salvia, Plateau Salvia, and Red Gentiana. It is widely distributed in western Gansu, western Sichuan, northwestern Yunnan, and Tibet in my country, and is a well-known Tibetan medicine. The *Jingzhu Materia Medica* records that it has the effects of "clearing liver heat and treating oral diseases." In May 1995, the Gansu Provincial Health Department officially included it in the Gansu Provincial Local Standards and promulgated a trial implementation. In the 1980s, this medicinal material was already included in the Yunnan Provincial Local Standards. Because its roots and stems have similar pharmacological activities to *Salvia miltiorrhiza*, it is widely used in China as a high-quality substitute for *Salvia miltiorrhiza*. Due to the increasing demand for *Salvia miltiorrhiza*, it is trending towards becoming a mainstream commodity.

[0003] As research into *Salvia miltiorrhiza* in Ganxi deepens, our understanding of its phytochemical components and pharmacological effects is becoming increasingly profound. This type of plant contains a variety of components, including polysaccharides, sesquiterpenes, diterpenes, triterpenes, flavonoids, and polyphenols, exhibiting anti-inflammatory, antibacterial, antioxidant, and anti-cardiovascular activities. Tanshinone II A and salvianolic acid B, as the main components of tanshinone II-sulfonate sodium injection and salvianolic acid salt for injection, respectively, have shown remarkable efficacy in treating coronary heart disease, angina pectoris, and myocardial infarction.

[0004] Przewalskin B is a diterpenoid natural product isolated from *Salvia miltiorrhiza*, possessing certain anti-HIV activity (EC50 = 30 μg / mL), and can serve as an important source for further structural modification and activity studies. However, current methods for isolating przewalskin B from plants are inefficient, complex, and difficult to obtain in large quantities for subsequent modification and improvement studies. Therefore, rapid and efficient chemical synthesis for large-scale preparation has become an important means to solve this problem. However, current synthetic routes for przewalskin B all face problems such as long steps, low overall yield, and high cost, making them unsuitable as a strategy for large-scale synthesis. Summary of the Invention

[0005] In view of this, the present invention provides an efficient and economical method for synthesizing the diterpenoid compound przewalskin B. Compared with the prior art, this method has the advantages of low cost, short production cycle and high production efficiency.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for synthesizing a diterpenoid compound, przewalskin B, the structural formula of which is as follows:

[0008]

[0009] The synthesis path is as follows:

[0010] Synthesis of fragment 4:

[0011]

[0012] Synthesis of Fragment 8:

[0013]

[0014] Segment docking:

[0015]

[0016] The specific steps are as follows:

[0017] (1) Compound 1 was dissolved in anhydrous pyridine, iodine was added at room temperature and stirred for 1 hour at this temperature, the reaction was quenched with 1 mol / L hydrochloric acid aqueous solution, then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure under vacuum to obtain crude product. The crude product was purified by silica gel column chromatography to obtain compound 2.

[0018] (2) Dissolve (S)-2-methyl-CBS-oxazolium borane in anhydrous dichloromethane, add a borane dimethyl sulfide solution at 0°C, and react at this temperature for 30 minutes. Then, slowly add a dichloromethane solution of compound 2 dropwise, and continue the reaction for 2 hours. Quench the reaction with H2O at 0°C, extract with ethyl acetate, wash with saturated sodium chloride aqueous solution, dry with anhydrous sodium sulfate, filter under reduced pressure, and concentrate under reduced pressure to obtain a crude product. The crude product is purified by silica gel column chromatography to obtain compound 3.

[0019] (3) Compound 3 was dissolved in anhydrous dichloromethane, imidazole was added at 0°C, followed by redistilled triethyl chlorophosphate. The reaction was detected by TLC. After about 1 hour, H2O was added to quench the reaction. The product was extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure under vacuum to obtain crude product. The crude product was purified by silica gel column chromatography to obtain compound 4.

[0020] (4) Compound 5 was dissolved in anhydrous dichloromethane, 1,1-dichloromethyl ether was added at 0°C, and SnCl4 was slowly added dropwise. The mixture was brought back to room temperature and stirred for 1 hour. The reaction was quenched with 1 mol / L hydrochloric acid aqueous solution at 0°C. The mixture was then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure under vacuum to obtain crude product. The crude product was purified by silica gel column chromatography to obtain compound 6.

[0021] (5) Triphenylmethylphosphine bromide was dissolved in anhydrous tetrahydrofuran, and a 2.4 mol / L n-butyllithium solution was added dropwise at 0°C. The mixture was stirred for 30 minutes at this temperature, and then a tetrahydrofuran solution of compound 6 was added. The mixture was allowed to return to room temperature and reacted for 10 minutes. The reaction was quenched with a saturated ammonium chloride aqueous solution at 0°C, and then extracted with ethyl acetate, washed with a saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under vacuum to obtain a crude product. The crude product was purified by silica gel column chromatography to obtain compound 7.

[0022] (6) Compound 7 was dissolved in anhydrous tetrahydrofuran, and a 1 mol / L tetrahydrofuran solution of zirconium hydrogen was added dropwise at 0°C. The mixture was stirred for 30 minutes at this temperature, then iodine was added, and the mixture was stirred for another 30 minutes. The reaction was quenched with a saturated ammonium chloride aqueous solution at 0°C, then extracted with ethyl acetate, washed with a saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure to obtain a crude product. The crude product was purified by silica gel column chromatography to obtain compound 8.

[0023] (7) Compound 8 was dissolved in anhydrous tetrahydrofuran, and a 2.4 mol / L tert-butyllithium solution was added dropwise at -78°C. The mixture was stirred for 30 minutes at this temperature. Then, a tetrahydrofuran solution of cuprous cyanide was added, and the mixture was stirred for another 30 minutes. Next, a tetrahydrofuran solution of compound 4 was slowly added dropwise, and the mixture was allowed to warm naturally to room temperature (about 2 hours). The reaction was quenched with a saturated ammonium chloride aqueous solution at 0°C. The mixture was then extracted with ethyl acetate, washed with a saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure to obtain a crude product. The crude product was purified by silica gel column chromatography to obtain compound 9.

[0024] (8) Compound 9 was dissolved in anhydrous tetrahydrofuran, and 2.4 mol / L tert-butyllithium solution was added dropwise at -78°C. The mixture was stirred for 30 minutes at this temperature. Then, a formylation reagent was added, and the reaction was quenched with saturated ammonium chloride aqueous solution at 0°C. The mixture was then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure under vacuum to obtain crude product. The crude product was purified by silica gel column chromatography to obtain compound 10.

[0025] (9) Compound 10 was added to anhydrous dichloromethane at -78°C, stirred at room temperature for 1 hour, quenched with H2O at 0°C, extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under vacuum to obtain crude product. The crude product was purified by silica gel column chromatography to obtain compound 11.

[0026] (10) Compound 11 was dissolved in anhydrous tetrahydrofuran, potassium ferricyanide was added dropwise at room temperature, followed by triethylamine, and the reaction was carried out at room temperature for 30 minutes. The reaction was quenched with H2O at 0°C, then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under vacuum to obtain crude product. The crude product was purified by silica gel column chromatography to obtain przewalskin B.

[0027] The advantages of this invention are:

[0028] 1. Most of the reagents used in this invention are commercially available and inexpensive, requiring no special processing.

[0029] 2. This invention is easy to operate and simple to process, which greatly reduces the cost of product separation.

[0030] 3. This invention utilizes asymmetric reduction to obtain chiral alcohols, which induces the generation of subsequent chiral centers, enabling the efficient production of optically pure products.

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 The attached figure shows the hydrogen spectrum of compound 8 prepared in this invention;

[0033] Figure 2 The attached figure shows the carbon 8 spectrum of the compound prepared in this invention;

[0034] Figure 3 The attached figure is the proton NMR spectrum of compound 9 prepared in this invention;

[0035] Figure 4 The attached figure shows the carbon spectrum of compound 9 prepared in this invention;

[0036] Figure 5 The attached figure is the proton NMR spectrum of compound 10 prepared in this invention;

[0037] Figure 6 The attached figure shows the carbon spectrum of the compound prepared in this invention.

[0038] Figure 7 The attached figure is the proton NMR spectrum of compound 11 prepared in this invention;

[0039] Figure 8 The attached figure is the carbon spectrum of compound 11 prepared in this invention;

[0040] Figure 9 The attached figure is the proton NMR spectrum of the compound przewalskin B prepared in this invention;

[0041] Figure 10 The attached figure shows the carbon spectrum of the compound przewalskin B prepared in this invention; Specific implementation methods

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1:

[0044]

[0045] Compound 8 (2 mmol) was dissolved in 10 mL of anhydrous tetrahydrofuran. 1.6 mL of 2.4 mol / L (4 mmol) tert-butyllithium solution was added dropwise at -78 °C, and the mixture was stirred at 400 rpm for 30 minutes. Then, 5 mL of cuprous cyanide (2 mmol) tetrahydrofuran solution was added, and the mixture was stirred at 400 rpm for another 30 minutes. Next, 0.6 mmol of compound 4 tetrahydrofuran solution was slowly added dropwise, and the mixture was allowed to warm naturally to room temperature (approximately 2 hours). The reaction was quenched at 0 °C with 10 mL of saturated ammonium chloride aqueous solution, followed by extraction with 5 mL of ethyl acetate and washing with 10 mL of saturated sodium chloride aqueous solution. The mixture was dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain compound 9 (232 mg, yield 82%).

[0046] The detection data for compound 9 are as follows:

[0047] 1H NMR (400MHz, Chloroform-d) δ6.78 (s, 1H), 6.30 (t, J = 3.8Hz, 1H), 3.90 (s, 3H), 3.88 (s, 3H), 3.84 (s, 3H), 3.34-3.15 (m, 1H), 2.62 (dddd, J = 33.8, 13 .0, 11.0, 5.9Hz, 2H), 2.15-2.01(m, 3H), 1.90-1.69(m, 2H), 1.62-1.50(m , 1H), 1.30-1.24 (m, 1H), 1.21 (d, J=6.9Hz, 6H), 1.06 (s, 3H), 1.01 (s, 3H).

[0048] 13 C NMR (400MHz, Chloroform-d) δ149.7, 149.4, 146.1, 137.4, 136.4, 131.3, 121.4, 10 5.3, 61.3, 61.2, 60.7, 56.2, 35.3, 33.6, 30.7, 30.3, 28.1, 27.7, 27.2, 26.9, 23.8.

[0049] HRMS(m / z): [M+H] + calcd for C 22 H 34 IO3 + 473.1553, found 473.1546.

[0050] Example 2:

[0051]

[0052] (1) Compound 9 (0.49 mmol) was dissolved in 5 mL of anhydrous tetrahydrofuran. 0.3 mL of 2.4 mol / L (0.73 mmol) tert-butyllithium solution was added dropwise at -78 °C. The mixture was stirred at this temperature (400 rpm) for 30 minutes. Then, a formylation reagent (0.83 mmol) was added, and the mixture was stirred at 400 rpm for 30 minutes. The mixture was allowed to warm naturally to room temperature (about 2 hours). The reaction was quenched at 0 °C with 10 mL of saturated ammonium chloride aqueous solution. The mixture was then extracted with 5 mL of ethyl acetate and washed with 10 mL of saturated sodium chloride aqueous solution. The mixture was dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain compound 10 (130 mg, yield 71%).

[0053] (2) Compound 10 (0.35 mmol) was dissolved in 3.5 mL of anhydrous dichloromethane. Boron tribromide (1.75 mmol) was added dropwise at -78 °C, and the mixture was stirred at 400 rpm for 30 minutes. The temperature was then raised to 0 °C, and the mixture was stirred at 400 rpm for 30 minutes. The reaction was quenched with 10 mL of H₂O at 0 °C, extracted with 5 mL of ethyl acetate, washed with 10 mL of saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain compound 11 (93 mg, yield 81%).

[0054] (3) Compound 11 (0.28 mmol) was dissolved in 2 ml of anhydrous tetrahydrofuran, and triethylamine (1.12 mmol) was added dropwise at 25 °C. Then, potassium ferricyanide (0.56 mmol) was added at the same temperature, and the mixture was stirred (400 rpm) for 30 minutes. The solid impurities were filtered through diatomaceous earth, and the crude product was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain compound przewalskin B (60 mg, yield 65%).

[0055] The detection data for compound 10 are as follows:

[0056] 1 H NMR (400MHz, Chloroform-d) δ9.51 (s, 1H), 6.75 (t, J = 3.6Hz, 1H), 6.67 (s, 1 H), 3.88 (s, 3H), 3.82 (s, 3H), 3.81 (s, 3H), 3.32-3.14 (m, 1H), 2.52 (dtd, J=3 5.5, 13.2, 5.1Hz, 2H), 2.41-2.28 (m, 2H), 1.82-1.61 (m, 2H), 1.32 (ddd, J=31 .3, 13.3, 6.9Hz, 3H), 1.18 (dd, J=6.9, 1.8Hz, 6H), 1.07 (s, 3H), 0.82 (s, 3H).

[0057] 13 C NMR (400MHz, Chloroform-d) δ194.6, 150.3, 149.5, 149.3, 146.1, 145.9, 137.2, 131.7 , 121.2, 61.2, 61.0, 60.6, 41.3, 34.3, 32.0, 30.7, 30.5, 28.1, 26.9, 26.9, 24.7, 23.7.

[0058] HRMS(m / z): [M+H] + calcd for C 23 H 35 O4+ 375.2535, found 375.2529.

[0059] The detection data for compound 11 are as follows:

[0060] 1 H NMR (400MHz, Chloroform-d) δ9.42 (s, 1H), 7.19 (s, 1H), 6.84 (t, J = 3.8Hz, 1H), 6.41 (s, 1H), 5.56 (s, 1H), 5.22 (s, 1H), 3.38-3.03 (m, 1H), 2.62 (ddd, J=9.9, 6.2, 4.0Hz, 2H), 2.39 (qd, J= 9.6, 8.4, 3.2Hz, 2H), 2.04 (t, J=4.7Hz, 1H), 1.82 (dtd, J=12.9, 8.9, 3.6Hz, 1H), 1.56 (ddd, J =13.7, 9.7, 7.0Hz, 1H), 1.35-1.26 (m, 2H), 1.20 (t, J = 6.6Hz, 6H), 0.88 (s, 3H), 0.77 (s, 3H).

[0061] 13 C NMR (400MHz, Chloroform-d) δ197.1, 153.9, 146.8, 139.8, 139.7, 132.2, 127.1, 119.6, 117.1, 41.5, 34.3, 31.9, 30.8, 30.5, 27.4, 27.0, 26.6, 25.2, 23.0, 22.9.

[0062] HRMS(m / z): [MH]-calcd for C 20 H 27 O4 - 331.1909, found 331.1917.

[0063] The detection data for compound przewalskin B are as follows:

[0064] 1H NMR(400MHz,Chloroform-d)δ7.10(d,J=1.4Hz,1H),5.80(q,J=4.0,3.3Hz,1H),4.79(q,J=2.6Hz,1H),3.66(s,1H),2.63(pd,J=6.9,1.4Hz,1H),2.15-1.95(m,2H),1.87-1.66(m,3H),1.62-1.48(m,2H),1.42(ddd,J=13.1,8.9,6.2Hz,1H),1.30-1.18(m,1H),1.14(d,J=6.8Hz,3H),1.09(d,J=6.9Hz,3H),0.95(s,3H),0.89(s,3H).

[0065] 13 C NMR(400MHz,Chloroform-d)δ200.5,173.2,158.5,149.2,136.0,121.3,82.3,54.4,45.1,32.5,31.4,29.6,27.7,26.5,25.4,25.3,22.5,20.7,20.6.

[0066] HRMS(m / z):[M+NH4] + calcd for C 20 H 30 NO4 - 348.2175found 348.2170.

Claims

1. A method for synthesizing a diterpene natural product, przewaIskin B, characterized by, The reaction process is as follows: Compound 11 is dissolved in anhydrous tetrahydrofuran, and potassium ferricyanide is added dropwise at room temperature, followed by the addition of triethylamine, and the reaction is stirred at 15-50℃ for 0.5-6 h; the reaction is quenched with H2O at 0℃, and then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure in vacuum to obtain a crude product, which is purified by silica gel column chromatography to obtain przewalskin B.

2. The method of synthesis according to claim 1, characterized in that: The solution concentration after the addition of tetrahydrofuran is 0.05-0.4 mol / L; the molar ratio of triethylamine to compound 11 is (3-6):1, and the molar ratio of potassium ferricyanide to compound 11 is (2-4):1; The stirring speed is 100-1000 rpm; The temperature for quenching the reaction is 15-50℃, and the time is 1-3 min; The vacuum degree for concentration under reduced pressure is 50-600 mbar.

3. The method of synthesis of claim 2, wherein, The preparation process of compound 11 is as follows: Compound 10 is dissolved in anhydrous dichloromethane, and boron tribromide is added at -78℃, and then the temperature is restored to room temperature and stirred for 1 h; the reaction is quenched with H2O at 0℃, and then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure in vacuum to obtain a crude product, which is purified by silica gel column chromatography to obtain compound 11.

4. The method of synthesis of claim 3, wherein, The preparation process of compound 10 is as follows: Compound 9 is dissolved in anhydrous tetrahydrofuran, and a tert-butyllithium solution is added dropwise, stirred, and then a formylating reagent is added, and the reaction is quenched with saturated ammonium chloride aqueous solution; Then extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure in vacuum to obtain a crude product, which is purified by silica gel column chromatography to obtain compound 10.

5. The method of synthesis according to claim 4, characterized in that: When preparing compound 10, the solution concentration after the addition of anhydrous tetrahydrofuran is 0.05-0.4 mol / L; the concentration of the tert-butyllithium solution is 1.0-2.4 mol / L, and the molar ratio of the formylating reagent to compound 9 is (1.8-2):1; The stirring temperature is -78--50℃, the time is 0.5-6 h, and the stirring speed is 100-1000 rpm; The temperature for quenching the reaction is -78--50℃, and the time is 1-3 min; The vacuum degree for concentration under reduced pressure is 50-600 mbar.

6. The method of synthesis according to claim 4 or 5, wherein, The preparation process of compound 9 is as follows: Compound 8 is dissolved in anhydrous tetrahydrofuran, and a tert-butyllithium solution is added dropwise, and then stirred at -78-20℃ for 0.5-1 h; a cuprous cyanide tetrahydrofuran solution is added, and then stirred for 30 min; a compound 4 tetrahydrofuran solution is slowly added dropwise, and then naturally warmed to room temperature; the reaction is quenched with saturated ammonium chloride aqueous solution at -20-0℃; The above quenching reaction product is extracted with ethyl acetate, washed with saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered under reduced pressure, and concentrated under reduced pressure in vacuum to obtain a crude product, which is purified by silica gel column chromatography to obtain compound 9.

7. The method of synthesis according to claim 6, wherein: When preparing compound 9, the concentration of the solution after adding anhydrous tetrahydrofuran is 0.1-0.2 mol / L; the concentration of the added tert-butyllithium solution is 1.0-2.4 mol / L, and the volume ratio of the tetrahydrofuran solution of cuprous cyanide to the substrate solution is 1:(1-2); The stirring speed is 100-1000 rpm; The time for quenching the reaction is 20-30 min; The vacuum degree for concentration under reduced pressure is 50-600 mbar.

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