A method for synthesizing a natural product Sokotrasterol sulfate

Abstract

The application relates to the field of chemical synthesis, and first proposes a semi-synthetic method of a natural product Sokotrasterol sulfate. Swine deoxycholic acid is used as raw material, methyl ester and tert-butyl dimethyl silyl ether are used to protect the carboxyl and different-position hydroxyl groups of the swine deoxycholic acid; after selective oxidation of the 3-position hydroxyl group, bromination, hydrolysis, introduction of a 2-position beta-configuration hydroxyl group and borohydride oxidation-reaction introduction of an alpha-configuration hydrogen at the 5-position are carried out; then, methyl ester hydrolysis, iodination and decarboxylation are carried out to introduce iodine at the 17-position; hydrolysis and bromination are carried out on the iodine to introduce bromine at the 17-position; then, halogen-lithium exchange reaction, lithiation reaction and elimination of a tertiary alcohol are carried out to introduce a side chain at the 17-position; finally, the protective groups are removed, and the hydroxyl groups at different positions are subjected to sulfation reaction to obtain the target natural product. Through the technical scheme, the problems that the natural product is directly obtained from a marine sponge, extraction and purification are difficult, the yield is low, and the natural product cannot be effectively structurally modified are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and in particular to a method for synthesizing a natural product, Sokotrasterol sulfate. Background Art

[0002] The development of new blood vessels from existing vascular networks, a process known as angiogenesis, contributes to various pathological processes, such as tumor progression and chronic inflammatory processes. On the other hand, the generation of new blood vessels in response to ischemia can alleviate the sequelae of tissue hypoxia, and therapeutic angiogenesis is also an effective strategy for treating occlusive vascular diseases. To date, clinical research to promote the development of new blood vessels in ischemic tissues has focused primarily on the use of angiogenic growth factors, using two main strategies: one strategy involves the direct delivery of recombinant proteins to the ischemic tissue via intramuscular or intraarterial injection, and the other strategy involves the use of gene therapy, either through direct transfer of expression vectors or through cell-based approaches. However, the optimal delivery strategy has not yet been devised. The use of small molecules for therapeutic angiogenesis would eliminate many of the difficulties associated with the use of protein or gene therapies.

[0003] Currently, the use of exogenous drugs to promote angiogenesis in ischemic tissues has become a hot topic in clinical treatment. Sokotrasterol Sulfate (structural formula shown below 19) is a steroid extracted from marine sponges. Siun Murphy, Bruno Larriveé, et al. reported in Circ Res. 2006;99:257-265 that this natural product can induce angiogenesis in vitro and in vivo, including angiogenesis in the chicken chorioallantoic membrane (CAM) and reperfusion in a mouse hindlimb ischemia model. It is used to promote angiogenesis and alleviate the sequelae of vascular occlusive diseases, and has promising research prospects.

[0004]

[0005] However, obtaining this natural product directly from marine sponges has problems such as extraction and purification difficulties, low yield, and inability to structurally modify the compound. Furthermore, there is still no complete synthetic route for the natural product Sokotrasterol sulfate, which has hindered further research, development, and utilization of this natural product. Summary of the Invention

[0006] The present invention proposes for the first time a method for synthesizing the natural product Sokotrasterol sulfate, which solves the problems in the prior art of obtaining the natural product directly from marine sponges, such as difficulty in extraction and purification, low yield, and inability to structurally modify the compound.

[0007] The technical solutions of the present invention are as follows:

[0008] A preparation method of a natural product, Sokotrasterol sulfate, is characterized in that: using hyodeoxycholic acid (HDCA) as a raw material, using methyl ester to protect the carboxyl group, N-bromosuccinimide to selectively oxidize the 3-position hydroxyl group, acetyl group to protect the 6-position hydroxyl group, copper bromide to selectively bromine at the 2-position, then hydrolyzing with potassium carbonate to introduce a β-configuration hydroxyl group at the 2-position, lithium tri-sec-butylborohydride to selectively reduce the 3-position carbonyl group to an α-configuration hydroxyl group, tert-butyldimethylsilyl ether to protect the 2- and 3-position hydroxyl groups, sodium methoxide to remove the acetyl group, phosphorus oxychloride to eliminate the 6-position hydroxyl group to introduce a double bond, and borane tetrahydrofuran to perform borohydride. The α-configuration hydrogen at position 5 is introduced by a chemical-oxidation reaction, the hydroxyl group at position 6 is protected by tert-butyldimethylsilyl ether, the methyl ester is hydrolyzed by sodium hydroxide solution, N-iodosuccinimide and iodine are used for iodide decarboxylation, the iodide is hydrolyzed by sodium bicarbonate, carbon tetrabromide and triphenylphosphine are used for bromination, tert-butyl lithium and the bromide are subjected to a halogen-lithium exchange reaction, and then a lithiation reaction with 3,3,4-trimethyl-2-pentanone is carried out to introduce a side chain, the tert-butyldimethylsilyl ether is removed by tetrabutylammonium fluoride, the tertiary alcohol is eliminated by p-toluenesulfonic acid monohydrate, and finally the hydroxyl groups at positions 2, 3, and 6 are sulfated to obtain the target product;

[0009] The reaction formula is as follows:

[0010]

[0011] As a further technical solution, the following steps are included:

[0012] Under nitrogen protection, hyodeoxycholic acid was used as raw material, concentrated hydrochloric acid was used as catalyst, and reacted with methanol as solvent to obtain intermediate 1. The intermediate structure is as follows:

[0013]

[0014] Under nitrogen protection, intermediate 1 was used as raw material and N-bromosuccinimide was used as a selective oxidant to obtain intermediate 2. The intermediate structure is as follows:

[0015]

[0016] Under nitrogen protection, intermediate 2 was used as raw material, 4-dimethylaminopyridine as catalyst, triethylamine as acid binding agent, and reacted with acetic anhydride to obtain intermediate 3. The intermediate structure is as follows:

[0017]

[0018] Under nitrogen protection, intermediate 3 was used as a raw material to react with copper bromide to obtain intermediate 4, the structure of which is as follows:

[0019]

[0020] Under nitrogen protection, intermediate 4 was used as a raw material to react with potassium carbonate to obtain intermediate 5, the structure of which is as follows:

[0021]

[0022] Under nitrogen protection, intermediate 5 was used as a raw material to react with lithium tri-sec-butylborohydride to obtain intermediate 6, the structure of which is as follows:

[0023]

[0024] Under nitrogen protection, intermediate 6 was used as raw material and imidazole as acid binding agent to react with tert-butyldimethylsilyl ether to obtain intermediate 7. The intermediate structure is as follows:

[0025]

[0026] Under nitrogen protection, intermediate 7 was used as a raw material to react with sodium methoxide to obtain intermediate 8, the structure of which is as follows:

[0027]

[0028] Under nitrogen protection, intermediate 8 was used as raw material and pyridine as solvent to react with phosphorus oxychloride to obtain intermediate 9. The intermediate structure is as follows:

[0029]

[0030] Under nitrogen protection, intermediate 9 was used as a raw material to react with borane tetrahydrofuran. After the raw material reacted completely, it was reacted with sodium hydroxide and 30% hydrogen peroxide to obtain intermediate 10. The intermediate structure is as follows:

[0031]

[0032] Under nitrogen protection, intermediate 10 was used as raw material and imidazole as acid binding agent to react with tert-butyldimethylsilyl ether to obtain intermediate 11. The intermediate structure is as follows:

[0033]

[0034] Under nitrogen protection, intermediate 11 was used as a raw material and reacted with 0.5 mol / L sodium hydroxide solution to obtain intermediate 12. The intermediate structure is as follows:

[0035]

[0036] Under nitrogen protection, intermediate 12 was reacted with iodine and N-iodosuccinimide respectively to obtain intermediate 13, the structure of which is as follows:

[0037]

[0038] Under nitrogen protection, intermediate 13 was reacted with sodium bicarbonate to obtain intermediate 14, the structure of which is as follows:

[0039]

[0040] Under nitrogen protection, intermediate 14 was reacted with carbon tetrabromide and triphenylphosphine to obtain intermediate 15, the structure of which is as follows:

[0041]

[0042] Under nitrogen protection, intermediate 15 was reacted with tert-butyllithium and 3,3,4-trimethyl-2-pentanone respectively to obtain intermediate 16, the structure of which is as follows:

[0043]

[0044] Under nitrogen protection, intermediate 16 was reacted with tetrabutylammonium fluoride to obtain intermediate 17, the structure of which is as follows:

[0045]

[0046] Under nitrogen protection, intermediate 17 was reacted with p-toluenesulfonic acid monohydrate to obtain intermediate 18, the structure of which is as follows:

[0047]

[0048] Under nitrogen protection, intermediate 18 was reacted with sulfur trioxide pyridine and saturated sodium bicarbonate solution to obtain target natural product 19, the structure of which is as follows:

[0049]

[0050] Design idea:

[0051] The natural product Sokotrasterol sulfate is a polyhydroxylated sulfate steroid, i.e. the trisulfate derivative of 24,25,26,26-tetramethyl-5α-cholest-23E-ene-2β,3α,6α-triol. It contains a steroidal nucleus structure, i.e. a four-fused ring nucleus structure of cyclopenta-perhydrophenanthrene. Sokotrasterol sulfate has three sulfated alcohol hydroxyl groups at the C-2 position, the C-3 position, and the C-6 position, is alkylated at the C-10 position and the C-13 position, and has an olefinated long side chain at the C-17 position. On the basis of cholesterols, the long side chain involves olefination at the C-23 position, alkylation at the C-24 position, and the addition of two additional methyl groups at the C-26 position and one additional methyl group at the C-25 position. By analyzing its structure, we found that the synthetic difficulties of the natural product are concentrated on the construction of the three chiral hydroxyl groups at the 2,3,6 positions of the steroidal nucleus and the construction of the 5-position α-configuration hydrogen, and the construction of the 17-position olefinated long side chain is also a difficulty. We analyzed the reverse synthesis of the compound, and selected the commercially available material pig deoxycholic acid similar to the structure of Sokotrasterol sulfate. By consulting relevant literature, we found that in the traditional method, due to the existence of the chiral hydroxyl group on the steroidal nucleus, it is difficult to accurately control the chiral β-configuration hydroxyl group at the 2 position and the yield of the obtained product is low. Secondly, the selected raw material pig deoxycholic acid has a β-configuration hydrogen at the 5 position, and the synthesis of the natural product Sokotrasterol sulfate requires the inversion of the configuration of the 5-position hydrogen. Due to the rigid structure of the steroidal nucleus, the configuration inversion is difficult to achieve. The reported method such as lithium metal and liquid ammonia reduction of double bond to construct 5-position α-hydrogen has harsh reaction conditions and the reaction raw material is difficult to obtain. Finally, the construction of the 17-position long side chain has not been reported in the synthesis of similar structures, and the applicability of the traditional method of constructing carbon-carbon double bond needs to be explored due to the difference of the substrate.

[0052] In view of the above synthetic difficulties, the following synthetic strategy is designed:

[0053] 1. Construction of 2-position β-configuration hydroxyl group:

[0054] Through research on related literature, we found that Zhang lei research team reported a method for constructing 2-position β-configuration hydroxyl group with pig deoxycholic acid as raw material in Steroids 157 (2020): 108594, and the synthetic route is as follows:

[0055]

[0056] We cited the route they constructed for the β-configuration hydroxyl group at the 2nd position and optimized the synthesis steps therein: In the original synthetic route, when intermediate H5 was used as the raw material to synthesize intermediate H6, the research team used sodium borohydride to reduce the 3rd carbonyl group. This reducing agent is non-selective and will reduce the 3rd carbonyl group to α and β-configuration hydroxyl groups in a ratio of 1:1, with a yield of only 50%. We optimized this step and used the selective reducing agent lithium tri-sec-butylborohydride to reduce the 3rd carbonyl group, which can obtain intermediate H6 with a yield of 97%. The synthetic route is as follows:

[0057]

[0058] 2. Construction of α-configuration hydrogen at position 5:

[0059] By consulting relevant literature, we used a hydroboration-oxidation reaction to construct the α-configuration hydrogen at position 5. After the hydroxyl group at position 2 was constructed, tert-butyldimethylsilyl ether was used to protect the hydroxyl groups at positions 2 and 3. Then, sodium methoxide was used to remove the acetyl group at position 6 and eliminate the hydroxyl group at position 6. The α-configuration hydrogen at position 5 was obtained by a hydroboration-oxidation reaction with a yield of 90%. The synthetic route is as follows:

[0060]

[0061] 3. Construction of the 17-position side chain:

[0062] When constructing the 17-position side chain, we tried different methods, such as olefin cross-metathesis, Grignard reaction, Wittig reaction, and lithiation reaction. After comprehensive analysis and comparison of the results of the above methods, we finally chose lithiation reaction to construct the 17-position side chain. The specific method results are compared as follows:

[0063] (The substrates used in the reaction route exploration stage are related derivatives)

[0064] ①Olefin cross metathesis reaction:

[0065]

[0066] This method does not produce the target product. In this reaction, 2,3,3,4-tetramethyl-1-pentene is a relatively inactive olefin, and the product obtained by the reaction is a dimer generated by the olefin cross-metathesis reaction of the raw material itself.

[0067] ②Grignard reaction:

[0068]

[0069] This method cannot obtain the target product. The reaction fails to successfully form an organomagnesium Grignard reagent with the raw materials, metallic magnesium and iodine in the first step. No obvious initiation phenomenon is observed during the reaction, and the raw materials do not react.

[0070] ③Wittig reaction:

[0071]

[0072] This method failed to produce the target product. Intermediate b was too active and could not produce a stable phosphorus ylide after reacting with potassium tert-butoxide, and could not proceed to the next step of reaction with 3,3,4-trimethyl-2-pentanone.

[0073]

[0074] When raw material a is replaced with raw material c, intermediate d is less active than intermediate b and can exist stably in the reaction system. However, when the next step of the reaction is continued, the target product is still not obtained. Considering that the steric hindrance of 3,3,4-trimethyl-2-pentanone is large, the reaction is difficult to proceed:

[0075] ④Lithiation reaction:

[0076]

[0077] This method can produce the target product. Raw material a first undergoes a halogen-lithium exchange reaction with tert-butyl lithium, followed by a lithiation reaction with 3,3,4-trimethyl-2-pentanone, yielding intermediate e in a 20% yield. Intermediate e is then deprotected using tetrabutylammonium fluoride to yield intermediate f. Intermediate f is heated at 80°C under acidic conditions to eliminate the tertiary alcohol, yielding derivative g. Derivative g is then subjected to a sulfation reaction with sulfur trioxide-pyridine and a saturated sodium bicarbonate solution to yield the target derivative h. This route successfully yields the target product, providing the technical solution (partial steps) protected by the present invention.

[0078] The beneficial effects of the present invention are:

[0079] This invention utilizes the method developed by Zhang Lei's research team to construct a β-configured hydroxyl group at position 2 and further optimizes the reaction route to improve the reaction yield. A hydroboration-oxidation reaction is used to construct an α-configured hydrogen at position 5 with high yield. The side chain is constructed using lithiation. This invention is the first to achieve the semi-synthesis of the natural product Sokotrasterol sulfate using hyodeoxycholic acid as a raw material. The 19-step synthetic route achieves an overall yield of 0.81%, overcoming the difficulties and low yields associated with traditional methods of direct extraction and purification from marine sponges. Furthermore, this synthetic route also enables the synthesis of a series of derivatives, further promoting the research, development, and utilization of this natural product.

[0080] The details are as follows:

[0081] In the present invention, hyodeoxycholic acid is used as a raw material, and the reaction is divided into 19 steps. The carboxyl group is protected by methyl ester, the hydroxyl group at the 3rd position is selectively oxidized by N-bromosuccinimide, the hydroxyl group at the 6th position is protected by acetyl group, copper bromide is selectively brominated at the 2nd position, and then hydrolyzed with potassium carbonate to introduce a β-configuration hydroxyl group at the 2nd position, lithium tri-sec-butylborohydride selectively reduces the carbonyl group at the 3rd position to an α-configuration hydroxyl group, tert-butyldimethylsilyl ether protects the hydroxyl groups at the 2nd and 3rd positions, sodium methoxide removes the acetyl group, phosphorus oxychloride eliminates the hydroxyl group at the 6th position to introduce a double bond, and borane tetrahydrofuran is used for a hydroboration-oxidation reaction to introduce the hydroxyl group at the 2nd position. The α-hydrogen at the 5-position is introduced, the hydroxyl group at the 6-position is protected with tert-butyldimethylsilyl ether, the methyl ester is hydrolyzed with sodium hydroxide solution, iodide decarboxylation is carried out with N-iodosuccinimide and iodine, the iodide is hydrolyzed with sodium bicarbonate, carbon tetrabromide and triphenylphosphine are used for bromination, tert-butyllithium and the bromide undergo a halogen-lithium exchange reaction, and then a lithiation reaction with 3,3,4-trimethyl-2-pentanone is carried out to introduce a side chain. The tert-butyldimethylsilyl ether is removed with tetrabutylammonium fluoride, and the tertiary alcohol is eliminated with p-toluenesulfonic acid monohydrate. Finally, the hydroxyl groups at the 2, 3, and 6 positions are sulfated to obtain the target product. The reaction raw materials are widely available, the chemical stability is high, and the post-reaction treatment is simple, making it suitable for mass production. The reaction route has wide applicability and can be used to synthesize a series of derivatives. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0083] Figure 1 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 7 in Example 1 of the present invention;

[0084] Figure 2 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 8 in Example 1 of the present invention;

[0085] Figure 3 This is the H-NMR carbon spectrum of intermediate 9 in Example 1 of the present invention;

[0086] Figure 4 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 10 in Example 1 of the present invention;

[0087] Figure 5 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 11 in Example 1 of the present invention;

[0088] Figure 6 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 12 in Example 1 of the present invention;

[0089] Figure 7 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 13 in Example 1 of the present invention;

[0090] Figure 8This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 14 in Example 1 of the present invention;

[0091] Figure 9 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 15 in Example 1 of the present invention;

[0092] Figure 10 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 16 in Example 1 of the present invention;

[0093] Figure 11 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 17 in Example 1 of the present invention;

[0094] Figure 12 This is the H-NMR nuclear magnetic resonance hydrogen spectrum of intermediate 18 in Example 1 of the present invention;

[0095] Figure 13 is the H-NMR nuclear magnetic resonance hydrogen spectrum of the derivative g of the present invention;

[0096] Figure 14 is the H-NMR nuclear magnetic resonance hydrogen spectrum of the derivative h of the present invention;

[0097] (The H NMR spectra of intermediates 1-6 have been reported in Steroids 157(2020):108594) DETAILED DESCRIPTION

[0098] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0099] Example 1

[0100]

[0101] S1. Add 1 g of hyodeoxycholic acid and 15 mL of methanol to a reaction flask, stir until dissolved, then add 100 μL of concentrated hydrochloric acid dropwise, and heat under reflux at 80°C for 6 h.

[0102] After the reaction was completed, sampling was performed to check that the raw material was completely converted. Saturated sodium bicarbonate solution was added to the reaction solution to quench the reaction, and the mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected, washed with saturated sodium bicarbonate aqueous solution (10 mL × 2) and saturated sodium chloride aqueous solution (20 mL × 2), and concentrated to obtain 1.04 g of intermediate 1 as a white solid with an isolation yield of 99%;

[0103] S2. Add 200 mg of intermediate 1, 12 mL of acetone, and 4 mL of water to a reaction flask, stir to dissolve, slowly add 33 μL of acetic acid dropwise under an ice-water bath, stir thoroughly, then add 160 mg of N-bromosuccinimide, and react at 0°C to room temperature for 2 h;

[0104] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw materials was complete. Saturated aqueous sodium bisulfite solution was added to the reaction solution to quench the reaction. The mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated aqueous sodium bicarbonate solution (10 mL × 2) and saturated aqueous sodium chloride solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 227 mg of intermediate 2 as a white solid with an isolation yield of 100%.

[0105] S3. Add 700 mg of intermediate 2 and 15 mL of ethyl acetate to a reaction flask, stir until dissolved, add 211 mg of 4-dimethylaminopyridine and 595 μL of triethylamine, and react at room temperature for 1.5 h.

[0106] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw material was complete, and a saturated aqueous sodium bicarbonate solution was added to quench the reaction. The mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected, washed with a saturated aqueous sodium bicarbonate solution (10 mL × 2) and a saturated aqueous sodium chloride solution (20 mL × 2), and concentrated to obtain 780 mg of intermediate 3 as a white solid with an isolation yield of 99%;

[0107] S4. Add 760 mg of intermediate 3 and 20 mL of ethyl acetate to a reaction flask, stir to dissolve, add 684 mg of copper bromide, and reflux at 100°C for 5 h;

[0108] After the reaction was completed, sampling was performed under nitrogen protection. If the conversion of the starting material was complete, water was added to quench the reaction. The solid was removed by filtration on celite and extracted three times with ethyl acetate (20 mL). The organic phase was collected, washed with saturated sodium chloride aqueous solution (20 mL × 2), and concentrated to obtain 875 mg of intermediate 4 as a yellow solid with an isolated yield of 98%.

[0109] S5. Add 800 mg of intermediate 4, 24 mL of acetone, and 8 mL of water to a reaction flask, stir to dissolve, add 670 mg of potassium carbonate, and heat to react at 45°C for 7 h.

[0110] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw materials was complete. 1 mol / L hydrochloric acid aqueous solution was added to the reaction solution to neutralize the pH, and the mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected, washed with saturated sodium bicarbonate aqueous solution (10 mL × 2) and saturated sodium chloride aqueous solution (20 mL × 2), and purified by column chromatography to obtain 500 mg of intermediate 5 as a white solid with an isolation yield of 71%.

[0111] S6. Add 2 g of intermediate 5 and 30 mL of tetrahydrofuran to a reaction flask, stir at -78 °C to dissolve, and slowly add 5.19 mL of lithium tri-sec-butylborohydride dropwise after 10 minutes. React at -78 °C for 4 h.

[0112] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw materials was complete. Saturated aqueous ammonium chloride was added to the reaction solution to quench the reaction. The mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated aqueous sodium chloride (20 mL × 2). The organic phase was purified by column chromatography to obtain 1.94 g of intermediate 6 as a white solid with an isolation yield of 97%.

[0113] S7. Add 1.94 g of intermediate 6 and 30 mL of N,N-dimethylformamide to a reaction flask, stir under an ice bath until dissolved, add 1.14 g of imidazole and 2.27 g of tert-butyldimethylsilyl chloride, and react at 0°C to room temperature overnight;

[0114] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the starting material was complete. Water was added to the reaction solution to quench the reaction. The mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 2.8 g of intermediate 7 as a white solid with an isolation yield of 97%.

[0115] The NMR spectrum of intermediate 7 is as follows Figure 1 As stated;

[0116] S8. Add 1.4 g of intermediate 7, 20 mL of methanol, and 10 mL of dichloromethane to a reaction flask, stir to dissolve, add 546 mg of sodium methoxide, and heat at 40°C to react overnight;

[0117] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw materials was complete. Water was added to the reaction solution to quench the reaction. The reaction solution was neutralized with 1 mol / L hydrochloric acid aqueous solution to pH 7 and extracted three times with dichloromethane (30 mL). The organic phase was collected and washed with saturated sodium bicarbonate aqueous solution (10 mL × 2) and saturated sodium chloride aqueous solution (20 mL × 2). Column chromatography was used for purification to obtain 1.02 g of intermediate 8 as a white solid with an isolation yield of 78%.

[0118] The NMR spectrum of intermediate 8 is as follows Figure 2 As stated;

[0119] S9. Add 1.53 g of intermediate 8 and 30 mL of pyridine to a reaction flask, stir under an ice bath to dissolve, slowly add 2.15 mL of phosphorus oxychloride dropwise, and heat at 40°C to react overnight;

[0120] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the starting material was complete. Saturated aqueous sodium bicarbonate solution was slowly added dropwise to the reaction solution under ice bath to quench the reaction. The mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated aqueous sodium chloride solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 0.86 g of intermediate 9 as a white solid with an isolation yield of 58%.

[0121] The NMR spectrum of intermediate 9 is as follows Figure 3 As stated;

[0122] S10, 40 mg of intermediate 9 and 5 mL of tetrahydrofuran were added to a reaction flask, stirred and dissolved, 0.19 mL of borane tetrahydrofuran solution was slowly added under ice bath, and the reaction was allowed to react at room temperature for 4 h. After the conversion of the raw materials was complete, water was added to the reaction solution under ice bath to quench the reaction, and then 0.147 mL of 3 mol / L sodium hydroxide aqueous solution and 0.147 mL of 30% hydrogen peroxide solution were added, and the reaction was allowed to react from 0°C to room temperature for 2 h;

[0123] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw materials was complete. 1 mol / L hydrochloric acid aqueous solution was added to the reaction solution to neutralize the reaction solution to pH 7, and extracted three times with ethyl acetate (20 mL). The organic phase was collected, washed with saturated sodium bicarbonate aqueous solution (10 mL × 2) and saturated sodium chloride aqueous solution (20 mL × 2), and purified by column chromatography to obtain 31 mg of intermediate 10 as a white solid with an isolation yield of 90%;

[0124] The NMR spectrum of intermediate 10 is as follows Figure 4 As stated;

[0125] S11. Add 632 mg of intermediate 10 and 15 mL of N,N-dimethylformamide to a reaction flask, stir under an ice bath to dissolve, add 199 mg of imidazole and 351 mg of tert-butyldimethylsilyl chloride, and react at 0°C to room temperature for 2 h;

[0126] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the starting material was complete. Water was added to the reaction solution to quench the reaction. The mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 628 mg of intermediate 11 as a white solid with an isolation yield of 85%.

[0127] The NMR spectrum of intermediate 11 is as follows Figure 5 As stated;

[0128] S12, 628 mg of intermediate 11 and 15 mL of tetrahydrofuran were added to a reaction flask, stirred to dissolve, 4.92 mL of 0.5 mol / L sodium hydroxide solution was added, and the mixture was heated at 50°C and reacted overnight;

[0129] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the raw materials was complete. Ethyl acetate was added to the reaction solution to dilute the reaction solution. The pH of the reaction solution was adjusted to 4-5 with 1 mol / L hydrochloric acid aqueous solution. The solution was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 590 mg of intermediate 12 as a white solid with an isolation yield of 96%.

[0130] The NMR spectrum of intermediate 12 is as follows Figure 6 As stated;

[0131] S13. Add 590 mg of intermediate 12 and 15 mL of 1,2-dichloroethane to a reaction flask, stir to dissolve, add 199 mg of iodine and 529 mg of N-iodosuccinimide, and heat under reflux at 100°C for overnight reaction;

[0132] After the reaction was completed, sampling was performed under nitrogen protection. If the starting material was not completely reacted, water was added to the reaction solution to quench the reaction, and the mixture was extracted three times with dichloromethane (20 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 385 mg of intermediate 13 as a white solid with an isolated yield of 59% (191 mg of intermediate 12 was recovered).

[0133] The NMR spectrum of intermediate 13 is as follows Figure 7 As stated;

[0134] S14, 475 mg of intermediate 13, 6 mL of N,N-dimethylformamide, 6 mL of tetrahydrofuran, and 3 mL of water were added to a reaction flask, stirred to dissolve, and then 96 mg of sodium bicarbonate was added, and the reaction was heated at 100°C overnight;

[0135] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the starting material was complete. Ethyl acetate was added to the reaction solution to dilute the reaction solution, and the mixture was extracted three times with ethyl acetate (20 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (20 mL × 2). The organic phase was purified by column chromatography to obtain 300 mg of intermediate 14 as a white solid with an isolation yield of 73%.

[0136] The NMR spectrum of intermediate 14 is as follows Figure 8 As stated;

[0137] S15. Add 150 mg of intermediate 14 and 2 mL of dichloromethane to a reaction flask, stir to dissolve, then add 109 mg of triphenylphosphine and 103 mg of carbon tetrabromide, and react at 0°C for 0.5 h.

[0138] After the reaction was completed, sampling was performed under nitrogen protection. The conversion of the starting material was complete. Water was added to the reaction solution to quench the reaction, and the mixture was extracted three times with dichloromethane (5 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (5 mL × 2). The organic phase was purified by column chromatography to obtain 140 mg of intermediate 15 as a white solid with an isolation yield of 86%.

[0139] The NMR spectrum of intermediate 15 is as follows Figure 9 As stated;

[0140] S16. Add 100 mg of intermediate 15 and 2 mL of tetrahydrofuran to a reaction flask, protect with nitrogen, ventilate three times, stir at -78°C for ten minutes, add 0.196 mL of tert-butyl lithium, react at -78°C for 0.5 h, add 49 mg of 3,3,4-trimethyl-2-pentanone (dissolved in 0.5 mL of tetrahydrofuran), react at -78°C for 1 h, and then slowly raise the temperature from -78°C to room temperature to react overnight.

[0141] After the reaction was completed, sampling was performed under nitrogen protection. The reaction of the starting material was complete. Saturated ammonium chloride solution was added to the reaction solution to quench the reaction. The mixture was extracted three times with ethyl acetate (10 mL). The organic phase was collected and washed with saturated sodium chloride aqueous solution (10 mL × 2). The organic phase was purified by column chromatography to obtain 21 mg of intermediate 16 as a white solid with an isolation yield of 20%.

[0142] The NMR spectrum of intermediate 16 is as follows Figure 10 As stated;

[0143] S17, add 20 mg of intermediate 16 and 2 mL of tetrahydrofuran to a reaction flask, stir until dissolved, add 1 mL of tetrabutylammonium fluoride, and react at 60°C overnight;

[0144] After the reaction was completed, sampling was performed under nitrogen protection. The reaction of the starting material was complete. Saturated ammonium chloride solution was added to the reaction solution to quench the reaction. The mixture was extracted three times with ethyl acetate (10 mL). The organic phase was collected and washed with saturated ammonium chloride aqueous solution (10 mL × 2) and saturated sodium chloride aqueous solution (10 mL × 2). The organic phase was purified by column chromatography to obtain 10 mg of intermediate 17 as a white solid with an isolation yield of 85%.

[0145] The NMR spectrum of intermediate 17 is as follows Figure 11 As stated;

[0146] S18, 10 mg of intermediate 17 and 2 mL of tetrahydrofuran were added to a reaction flask, stirred to dissolve, 4 mg of p-toluenesulfonic acid monohydrate was added, and the reaction was carried out at 80°C overnight;

[0147] After the reaction was completed, sampling was performed under nitrogen protection. The reaction of the starting material was complete, and a saturated aqueous sodium bicarbonate solution was added to quench the reaction. The mixture was extracted three times with ethyl acetate (10 mL). The organic phase was collected, washed with a saturated aqueous sodium bicarbonate solution (10 mL × 2) and a saturated aqueous sodium chloride solution (10 mL × 2), and purified by column chromatography to obtain 8 mg of intermediate 18 as a white solid with an isolation yield of 83%.

[0148] The NMR spectrum of intermediate 18 is as follows Figure 12 As stated;

[0149] S19, 5 mg of intermediate 18 and 1 mL of N,N-dimethylformamide were added to a reaction flask, stirred to dissolve, and 10 mg of sulfur trioxide pyridine was added, and the reaction was allowed to proceed at room temperature overnight;

[0150] After the reaction was completed, sampling and testing were performed under nitrogen protection. The raw material reaction was complete, the solvent was dried, 2 mL of saturated sodium bicarbonate solution was added, the solution was dried, and methanol was extracted three times. The product was purified by column chromatography to obtain 6 mg of the target natural product 19 as a white solid with an isolation yield of 73%.

Claims

1. A method for synthesizing the natural product Sokotrasterol sulfate, characterized in that: Using hyodeoxycholic acid as the starting material, the carboxyl group on the 17-position side chain was protected with methyl ester to obtain intermediate 1; N-bromosuccinimide selectively oxidized the 3-position hydroxyl group to obtain intermediate 2; acetyl protected the 6-position hydroxyl group to obtain intermediate 3; copper bromide selectively brominated the 2-position to obtain intermediate 4; potassium carbonate was then used for hydrolysis to introduce a β-configuration hydroxyl group at the 2-position to obtain intermediate 5; lithium tri-sec-butylborohydride selectively reduced the 3-position carbonyl group to an α-configuration hydroxyl group to obtain intermediate 6; tert-butyldimethylsilyl ether protected the 2- and 3-position hydroxyl groups to obtain intermediate 7; sodium methoxide removed the acetyl group to obtain intermediate 8; phosphorus oxychloride eliminated the 6-position hydroxyl group to introduce a double bond to obtain intermediate 9; borane tetrahydrofuran was subjected to a hydroboration-oxidation reaction to introduce an α-configuration hydrogen at the 5-position to obtain intermediate 10 ; tert-butyldimethylsilyl ether is used to protect the 6-hydroxyl group to obtain intermediate 11; sodium hydroxide solution is used to hydrolyze the methyl ester to obtain intermediate 12; N-iodosuccinimide and iodine undergo iodide decarboxylation reaction to obtain intermediate 13; sodium bicarbonate is used to hydrolyze the iodide to obtain intermediate 14; carbon tetrabromide and triphenylphosphine are used to bromine to obtain intermediate 15; tert-butyl lithium is used to exchange the bromide 15 with lithium halide, and then the bromide 15 is subjected to a lithiation reaction with 3,3,4-trimethyl-2-pentanone to introduce a side chain to obtain intermediate 16; tetrabutylammonium fluoride is used to remove the tert-butyldimethylsilyl ether protecting group to obtain intermediate 17; p-toluenesulfonic acid monohydrate is used to eliminate the tertiary alcohol on the side chain 17 to obtain intermediate 18, and finally the hydroxyl groups at positions 2, 3, and 6 are sulfated to obtain the target product 19; 2. The method for synthesizing the natural product Sokotrasterol sulfate according to claim 1, wherein: Prepared according to the following steps: in: S1. Under nitrogen protection, hyodeoxycholic acid was used as raw material and concentrated hydrochloric acid was used as catalyst to react with methanol as solvent to obtain intermediate 1. The intermediate structure is as follows: S2. Under nitrogen protection, intermediate 1 is used as a raw material and N-bromosuccinimide is used as a selective oxidant to obtain intermediate 2. The intermediate structure is as follows: S3. Under nitrogen protection, intermediate 2 was reacted with acetic anhydride using 4-dimethylaminopyridine as a catalyst and triethylamine as an acid binding agent to obtain intermediate 3. The intermediate structure is as follows: S4. Under nitrogen protection, intermediate 3 is reacted with copper bromide to obtain intermediate 4. The intermediate structure is as follows: S5. Under nitrogen protection, intermediate 4 is reacted with potassium carbonate to obtain intermediate 5. The intermediate structure is as follows: S6. Under nitrogen protection, intermediate 5 was reacted with lithium tri-sec-butylborohydride to obtain intermediate 6. The intermediate structure is as follows: S7. Under nitrogen protection, intermediate 6 was used as a raw material and imidazole was used as an acid binding agent to react with tert-butyldimethylsilyl ether to obtain intermediate 7. The intermediate structure is as follows: S8. Under nitrogen protection, intermediate 7 is reacted with sodium methoxide to obtain intermediate 8. The intermediate structure is as follows: S9. Under nitrogen protection, intermediate 8 was used as raw material and pyridine was used as solvent to react with phosphorus oxychloride to obtain intermediate 9. The intermediate structure is as follows: S10. Under nitrogen protection, intermediate 9 was reacted with borane tetrahydrofuran. After the reaction of the raw materials was complete, the reaction was continued with 3 mol / L sodium hydroxide and 30% hydrogen peroxide to obtain intermediate 10. The intermediate structure is as follows: S11, under nitrogen protection, using intermediate 10 as raw material and imidazole as acid binding agent, reacting with tert-butyldimethylsilyl ether to obtain intermediate 11, the intermediate structure of which is as follows: S12. Under nitrogen protection, intermediate 11 was reacted with 0.5 mol / L sodium hydroxide solution to obtain intermediate 12, the structure of which is as follows: S13. Under nitrogen protection, intermediate 12 was reacted with iodine and N-iodosuccinimide to obtain intermediate 13. The intermediate structure is as follows: S14. Under nitrogen protection, intermediate 13 was reacted with sodium bicarbonate to obtain intermediate 14. The intermediate structure is as follows: S15. Under nitrogen protection, intermediate 14 is reacted with carbon tetrabromide and triphenylphosphine to obtain intermediate 15. The intermediate structure is as follows: S16. Under nitrogen protection, intermediate 15 was reacted with tert-butyl lithium and 3,3,4-trimethyl-2-pentanone respectively to obtain intermediate 16. The intermediate structure is as follows: S17. Under nitrogen protection, intermediate 16 is reacted with tetrabutylammonium fluoride to obtain intermediate 17. The intermediate structure is as follows: S18. Under nitrogen protection, intermediate 17 was reacted with p-toluenesulfonic acid monohydrate to obtain intermediate 18. The intermediate structure is as follows: S19. Under nitrogen protection, intermediate 18 was reacted with sulfur trioxide pyridine and saturated sodium bicarbonate solution to obtain the target natural product 19. The structure of the natural product Sokotrasterol sulfate is as follows:

3. The method for synthesizing the natural product Sokotrasterol sulfate according to claim 2, wherein: In said S1, the reaction temperature is 80°C; In S2, the reaction temperature is 0°C, acetone and water are used as solvents in a volume ratio of 3:1, and N-bromosuccinimide is used as a selective oxidant; In S3, the reaction temperature is room temperature, ethyl acetate is the solvent, 4-dimethylaminopyridine is the catalyst, and triethylamine is the acid binding agent; In said S4, the reaction temperature is 100°C and ethyl acetate is used as the solvent; In S5, the reaction temperature is 45°C, acetone and water are used as solvents, and the volume ratio is 3:1; In S6, the reaction temperature is -78°C, tetrahydrofuran is used as solvent, and lithium tri-sec-butylborohydride is used as a selective reducing agent; In said S7, the reaction temperature is 0°C to room temperature, N,N-dimethylformamide is the solvent, and imidazole is the acid binding agent; In the S8, the reaction temperature is 40°C, methanol and dichloromethane are used as solvents, and the volume ratio is 2:1; In said S9, the reaction temperature is 40°C and pyridine is used as the solvent; In the S10, the reaction temperature is 0°C to room temperature, the solvent is tetrahydrofuran, and after the intermediate 9 and borane tetrahydrofuran react completely, water is added to quench the reaction, and then 3 mol / L sodium hydroxide solution and 30% hydrogen peroxide are added respectively; In S11, the reaction temperature is 0°C to room temperature, N,N-dimethylformamide is the solvent, and imidazole is the acid binding agent; In said S12, the reaction temperature is 50°C and tetrahydrofuran is used as the solvent; In the S13, the reaction temperature is 100° C. and 1,2-dichloroethane is used as the solvent; In S14, the reaction temperature is 100° C., and N,N-dimethylformamide, tetrahydrofuran, and water are used as solvents in a volume ratio of 2:2:1; In said S15, the reaction temperature is 0°C and dichloromethane is used as the solvent; In S16, the reaction temperature is -78°C to room temperature, tetrahydrofuran is used as the solvent, and the intermediate 15 is first subjected to a halogen-lithium exchange reaction with tert-butyl lithium, and then subjected to a lithiation reaction with 3,3,4-trimethyl-2-pentanone; In said S17, the reaction temperature is 60°C and tetrahydrofuran is used as the solvent; In said S18, the reaction temperature is 80°C and tetrahydrofuran is used as the solvent; In the above S19, the reaction temperature is room temperature, N,N-dimethylformamide is used as solvent, the intermediate 18 is first reacted with sulfur trioxide pyridine, and after the intermediate 18 is completely reacted, the solvent is dried and then a saturated sodium bicarbonate solution is added for reaction.

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