Chemical synthesis of polygalacic acid

Abstract

The application belongs to the technical field of organic synthesis, and particularly relates to a chemical synthesis method of natural triterpene polygalacic acid with anti-inflammatory, anti-tumor and neuroprotective activities. The polygalacic acid is a pentacyclic triterpene extracted from the traditional Chinese medicine polygala, has various physiological activities, and currently no chemical synthesis method has been reported at home and abroad. The polygalacic acid is mainly obtained by natural extraction and purification, and has low production efficiency and high cost. The method starts from the cheap and easily available oleanolic acid, and obtains the polygalacic acid through three key C-H bond oxidation reactions and directional introduction of three oxidation states in 14 steps with a total yield of 0.3%. The application is the first chemical synthesis of the compound, and provides a feasible route for synthesis and preparation of the compound and its structural analogs.

Description

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a chemical synthesis method of polygalic acid, which has anti-inflammatory, anti-tumor and neuroprotective activities. Background Technology

[0002] Neurodegenerative diseases, chronic inflammation, and tumors are major threats to human health. Neurodegenerative diseases, such as Alzheimer's disease, affect more than 50 million people worldwide and there is still no cure. Chronic inflammatory diseases, such as arthritis and enteritis, affect hundreds of millions of people, and current treatments have significant side effects and are prone to drug resistance. Meanwhile, the incidence and mortality rates of tumors continue to rise, creating an urgent need for novel, low-toxicity, and highly effective lead compounds.

[0003] Polygalic acid is an oleanane-type triterpenoid natural product isolated from the medicinal plant *Polygala tenuifolia* Willd., belonging to the Polygalaceae family. It is one of the core active ingredients that enable *Polygala tenuifolia* to exert its traditional effects of calming the mind, improving intelligence, relieving phlegm, and reducing swelling. Modern pharmacological studies have shown that polygalic acid possesses a variety of important biological activities: this substance can inhibit the expression of matrix metalloproteinases, showing potential therapeutic effects on osteoarthritis. Simultaneously, polygalic acid exhibits significant neuroprotective activity against cognitive impairment: it can inhibit acetylcholinesterase activity, increase choline acetyltransferase activity, and enhance acetylcholine content in the hippocampus and frontal cortex, thereby improving the function of the cholinergic system. Furthermore, it possesses various pharmacological effects such as antimutation, sedation, and anticonvulsant activity, making it a highly promising lead compound for new drug research.

[0004] However, the acquisition of polygalic acid currently faces significant bottlenecks. The content of polygalic acid in the natural medicinal herb *Polygala tenuifolia* is extremely low, influenced by factors such as origin, harvesting period, and growth age, with the actual content being only about 2-3%. Large-scale extraction requires a large amount of medicinal material, resulting in high costs and potentially leading to over-harvesting of wild *Polygala tenuifolia* resources and ecological damage, failing to meet the needs of industrial production. Furthermore, there are currently no reports of total chemical synthesis, both domestically and internationally. Existing preparation methods mainly rely on plant extraction or saponin hydrolysis, which involve cumbersome steps, difficult purification, and high dependence on raw materials. These factors make the large-scale preparation of polygalic acid extremely difficult, hindering further research and application of this compound. Summary of the Invention

[0005] To address the shortcomings of polygalactic acid, such as its limited natural availability, reliance on plant resources in existing preparation processes, high cost, and low efficiency, this invention provides a chemical synthesis method for polygalactic acid. This method synthesizes polygalactic acid from readily available and inexpensive oleanolic acid, providing technical support for subsequent structural modification, structure-activity relationship studies, and large-scale production of this natural product. Attached Figure Description Figure 1 The 2 synthesized in this invention 1H NMR spectrum; Figure 2 The 2 synthesized in this invention 13 C NMR spectrum; Figure 3 The 3 synthesized in this invention 1 H NMR spectrum; Figure 4 The 3 synthesized in this invention 13 C NMR spectrum; Figure 5 The 4 synthesized in this invention 1 H NMR spectrum; Figure 6 The 4 synthesized in this invention 13 C NMR spectrum; Figure 7 The 5 synthesized in this invention 1 H NMR spectrum; Figure 8 The 5 synthesized in this invention 13 C NMR spectrum; Figure 9 The 6 synthesized in this invention 1 H NMR spectrum; Figure 10 The 6 synthesized in this invention 13 C NMR spectrum; Figure 11 The 7 synthesized in this invention 1 H NMR spectrum; Figure 12 The 7 synthesized in this invention 13 C NMR spectrum; Figure 13 The 8 synthesized in this invention 1 HNMR spectrum; Figure 14 The 8 synthesized in this invention 13 C NMR spectrum; Figure 15 The 9 synthesized in this invention 1 H NMR spectrum; Figure 16 The 9 synthesized in this invention 13 C NMR spectrum; Figure 17 The 10 synthesized in this invention 1 H NMR spectrum; Figure 18 The 10 synthesized in this invention 13 CNMR spectrum; Figure 19 The polygalic acid (11) synthesized in this invention 1 H NMR spectrum; Figure 20 The polygalic acid (11) synthesized in this invention 13 CNMR spectrum. Detailed Implementation Plan

[0006] This invention provides a method for the chemical preparation of polygalic acid. The method uses inexpensive and readily available oleanolic acid as a starting material, and through strategies such as CH activation, introduces oxidized states at different sites and undergoes multiple functional group transformations, ultimately obtaining polygalic acid in 14 steps with a total yield of 0.3%. The specific steps include:

[0007] (1) Synthesis of compound 2

[0008]

[0009] Oleanolic acid 1 (41.76 g, 91.5 mmol) and K2CO3 (37.8 g, 273.27 mmol) were weighed into a 1 L round-bottom flask and dissolved in 500 mL of a 5:2 mixture of DMF and THF. MeI (6.24 mL, 100.2 mmol) was added dropwise to the reaction system, and the mixture was stirred at room temperature for approximately 8 h. After the reaction was complete, the solvent was evaporated under reduced pressure, followed by extraction with EA. The solution was dried over anhydrous sodium sulfate and concentrated, then used directly in the next reaction without column purification.

[0010] 200 mL of DCM was added to a 1 L round-bottom flask, and TFAA (23.83 mL, 170.0 mmol) was dissolved in it and cooled to -78 °C. After cooling, DMSO (18.11 mL, 255 mmol) was slowly added dropwise. After stirring for about 10 min, the crude product was dissolved in DCM and added dropwise to the system. After stirring again for about 30 min, triethylamine (59.3 mL, 425.0 mmol) was added dropwise. After the addition was completed, the system was allowed to warm to room temperature for two minutes and stirred until the system turned brownish-yellow. The solution was then quenched with water, followed by extraction with DCM, drying and concentration with anhydrous sodium sulfate, and purification of the crude product by column chromatography to give compound 2 37.4 g, with a yield of 87%.

[0011] 1 H NMR (400 MHz, CDCl3) δ 5.30 (t, J = 3.7 Hz, 1H), 3.63 (s, 3H) 2.87 (dd, J = 14.1, 4.6 Hz, 1H), 2.54 (ddd, J = 15.9, 11.2, 7.3 Hz, 1H), 2.35(ddd, J = 15.9, 6.8, 3.6 Hz, 1H), 2.05 – 1.80 (m, 4H), 1.74 – 1.52 (m, 6H), 1.51 – 1.27 (m, 8H), 1.18 (dd, J = 14.4, 3.4, Hz, 2H), 1.14 (s, 3H), 1.08 (s,3H), 1.04 (s, 6H), 0.92 (s, 3H), 0.90 (s, 3H), 0.78 (s, 3H).

[0012] 13C NMR (101 MHz, CDCl3) δ 217.9, 178.4, 144.0, 122.3, 55.5, 51.7,47.6, 47.0, 46.9, 46.0, 41.9, 41.5, 39.4, 39.3, 36.9, 34.3, 34.0, 33.2, 32.5,32.3, 30.8, 27.8, 26.6, 26.0, 23.8, 23.6, 23.2, 21.6, 19.7, 16.9, 15.1.

[0013] (2) Synthesis of compound 3

[0014]

[0015] Compound 2 (37.4 g, 79.85 mmol) and NH2OH·HCl (8.3 g, 119.77 mmol) were weighed into a round-bottom flask, dissolved in 500 mL of pyridine, and reacted at 50 °C for 4 h. After the reaction was completed, the solvent was concentrated on a rotary evaporator. The resulting concentrate was extracted with EA, washed three times with 1 N HCl, washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated. The crude product was purified by column chromatography to give compound 3 32.5 g, with a yield of 84%.

[0016] 1H NMR (600 MHz, CDCl3) δ 9.22 (s, 1H), 5.28 (t, J = 3.7 Hz, 4H), 3.62 (s, 10H), 3.08 (ddd, J = 15.5, 5.2, 3.3 Hz, 1H), 2.86 (dd, J = 13.9, 4.6 Hz,1H), 2.15 (ddd, J = 15.2, 12.8, 5.8 Hz, 1H), 1.91 (dddd, J =34.3, 15.9, 13.1,7.2 Hz, 3H), 1.74 (ddd, J = 13.1, 5.8, 3.4 Hz, 1H), 1.68 (td, J = 13.9, 4.4Hz, 1H), 1.64 – 1.49 (m, 6H), 1.46 – 1.39 (m, 2H), 1.31 (dt, J = 12.7, 3.92H), 1.20 – 1.16 (m, 1H), 1.15 (s, 3H), 1.13 (d, J = 4.1 Hz, 1H) 1.10 (s, 3H), 1.06 (s, 6H), 1.02 (s, 3H), 0.92 (s, 3H), 0.89 (s, 3H), 0.75 (s, 3H).

[0017] 13 C NMR (151 MHz, CDCl3) δ 178.4, 167.2, 144.0, 122.4, 56.0, 51.7,47.3, 46.9, 45.9, 41.8, 41.4, 40.5, 39.4, 38.6, 37.2, 34.0, 33.2, 32.5, 32.5,30.8, 27.8, 27.2, 26.0, 23.8, 23.6, 23.4, 23.2, 19.1, 17.2, 17.0, 15.0.

[0018] (3) Synthesis of compound 4

[0019]

[0020] Compound 3 (32.5 g, 67.2 mmol) was weighed and dissolved in 500 mL of a 1:1 mixture of acetic acid and acetic anhydride. The mixture was stirred at 45 °C for 2 h. Pd(OAc)2 (2.26 g, 10.08 mmol) and PIDA (36.78 g, 114.2 mmol) were added to a round-bottom flask and reacted at 45 °C for 16 h. The solvent was then evaporated, extracted with EA, washed with brine, dried over anhydrous sodium sulfate, and concentrated. The crude product was purified by column chromatography and used directly in the next reaction step.

[0021] The purified product was dissolved in 500 mL MeOH, and K2CO3 (11.14 g, 80.64 mmol) was added. The system was heated to 60 °C and reacted for 2 h. The solvent was then evaporated, extracted with EA, washed three times with an equal volume of water, washed with saturated brine, dried and concentrated with anhydrous sodium sulfate. No further purification was required, and the crude product was used directly in the next step.

[0022] The crude product was dissolved in 300 mL THF, and 300 mL 3 N HCl was added. After reacting overnight at room temperature, the product was concentrated on a rotary evaporator to remove the organic solvent. It was then extracted with EA, washed three times with an equal volume of water, washed with saturated sodium bicarbonate solution, washed with saturated brine, dried and concentrated with anhydrous sodium sulfate, and purified by column chromatography to give compound 4 16.9 g, with a yield of 44%.

[0023] 1 H NMR (600 MHz, CDCl3) δ 5.29 (s, 1H), 3.62 (s, 3H), 3.41 (dd, J =11.5, 4.9 Hz, 1H), 2.86 (dd, J = 14.0, 4.6 Hz, 1H), 2.61 (m, 1H), 2.45 (s,1H), 2.26 (m, 1H), 2.05 – 1.85 (m, 4H), 1.68 (q, J = 4.3, 3.3 Hz, 2H), 1.62(dd, J = 11.9, 9.3 Hz, 4H), 1.51 (d, J = 9.6 Hz, 3H), 1.42 – 1.31 (m, 4H),1.27 – 1.13 (m, 3H), 1.13 (s, 6H), 1.06 (dd, J = 14.2, 2.7 Hz, 1H), 1.01 (s,3H), 0.91 (s, 3H), 0.89 (s, 3H), 0.78 (s, 3H).

[0024] 13 C NMR (151 MHz, CDCl3) δ 178.4, 144.1, 122.1, 67.1, 52.5, 51.7,49.3, 46.9, 46.8, 45.9, 41.9, 41.4, 39.4, 38.9, 36.7, 35.3, 33.9, 33.2, 32.4,32.2, 30.8, 27.8, 26.1, 23.7, 23.6, 23.1, 19.2, 17.1, 17.0, 15.3.

[0025] (4) Synthesis of compound 5

[0026]

[0027] Compound 4 (16.9 g, 34.89 mmol), TBSCl (13.14 g, 87.2 mmol), and imidazole (7.12 g, 104.67 mmol) were weighed into a round-bottom flask, dissolved in 400 mL of DMF, and reacted at room temperature for 4 h. The solvent was then evaporated to dryness, washed four times with saturated brine, dried over anhydrous sodium sulfate, and concentrated. The crude product was then purified by column chromatography and used directly in the next reaction step.

[0028] Weigh the purified product (18.7 g, 31.2 mmol) and t-BuOK (38.57 g, 343.7 mmol) into a round-bottom flask, add 300 mL of tert-butanol to dissolve, react at 45 °C for 16 h, then evaporate the solvent, extract with EA, wash three times with an equal volume of water, wash with saturated brine, then dry and concentrate with anhydrous sodium sulfate. The crude product is purified by column chromatography to give 58.8 g of colorless oily liquid product, yield 43%.

[0029] 1H NMR (400 MHz, CDCl3) δ 6.30 (s, 1H), 5.86 (s, 1H), 5.34 (s, 1H), 3.87 (d, J = 9.4 Hz, 1H), 3.62 (s, 3H), 3.39 (d, J = 9.3 Hz, 1H), 2.87 (dd, J= 13.9, 4.8 Hz, 1H), 2.35 (dd, J = 10.6, 3.2 Hz, 1H), 2.08 (dt, J = 8.2, 3.9Hz, 1H), 2.05 – 1.98 (m, 1H), 1.94 (dq, J = 10.9, 6.6, 5.4 Hz, 2H), 1.76 –1.58 (m, 4H), 1.57 – 1.38 (m, 4H), 1.37 – 1.31 (m, 2H), 1.30 – 1.22 (m, 1H), 1.20 (s, 3H), 1.16 (d, J = 4.6 Hz, 1H), 1.12 (s, 3H), 1.11 – 1.06 (m, 1H), 0.93 (d, J = 3.4 Hz, 6H), 0.89 (s, 3H), 0.80 (d, J = 2.1 Hz, 12H), -0.00 (s, 3H), -0.04 (s, 3H).

[0030] 13 C NMR (101 MHz, CDCl3) δ 200.25, 178.37, 145.08, 144.20, 127.94,122.03, 77.36, 67.31, 51.69, 49.37, 46.94, 45.76, 44.94, 43.16, 42.20, 41.66,40.12, 37.90, 34.01, 33.24, 32.43, 32.32, 30.82, 27.72, 25.78, 25.74, 23.71,23.51, 23.14, 20.54, 18.33, 18.10, 17.47, 17.19, -5.58.

[0031] (5) Synthesis of compound 6

[0032]

[0033] Compound 5 (8.8 g, 15.1 mmol) was weighed into a round-bottom flask and dissolved in 150 mL of THF / EtOH (5:1). NaBH4 (1.6 g, 42.28 mmol) was weighed and added to the round-bottom flask at 0 °C. The mixture was then reacted at room temperature for 3 h, quenched with water, extracted with EA, washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated. The crude product was dissolved in 150 mL of 2,2-dimethoxypropane, and p-TsOH·H2O (287.2 mg, 1.51 mmol) was added. The mixture was stirred at room temperature for 30 min, and the organic solvent was evaporated to dryness. The mixture was extracted with an equal volume of EA, washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated. The crude product was purified by column chromatography to give product 6 (4.5 g), with a yield of 46%.

[0034] 1 H NMR (600 MHz, CDCl3) δ 5.31 (t, J = 3.7 Hz, 1H), 4.36 (t, J = 6.1Hz, 1H), 4.20 (d, J = 6.7 Hz, 1H), 3.62 (s, 3H), 3.29 (d, J = 9.7 Hz, 1H),3.17 (d, J = 9.7 Hz, 1H), 2.86 (dd, J = 13.9, 4.6 Hz, 1H), 2.22 – 2.17 (m,1H), 2.02 – 1.86 (m, 3H), 1.72 – 1.54 (m, 4H), 1.54 – 1.41 (m, 6H), 1.38 –1.29 (m, 7H), 1.27 – 1.23 (m, 2H), 1.20 – 1.16 (m, 1H), 1.14 (s, 4H), 1.10(s, 3H), 1.09 – 1.04 (m, 1H), 0.92 (s, 3H), 0.88 (s, 12H), 0.78 (s, 3H), 0.73(s, 3H), 0.03 (d, J = 3.5 Hz, 6H).

[0035] 13 C NMR (151 MHz, CDCl3) δ 178.4, 143.7, 122.7, 107.1, 76.2, 73.8,68.4, 51.7, 47.9, 47.0, 46.1, 44.5, 42.0, 41.6, 41.2, 40.6, 39.4, 35.7, 34.1,33.3, 32.5, 32.1, 30.8, 27.7, 26.1, 26.0, 25.7, 25.1, 23.8, 23.5, 23.3, 18.4,18.3, 17.0, 17.0, 16.6, -5.3, -5.5.

[0036] (6) Synthesis of compound 7

[0037]

[0038] Compound 6 (4.4 g, 6.7 mmol) was weighed into a round-bottom flask, replaced with Ar, and dissolved in 60 mL of DCM. The system was cooled to -78 °C, and then 13.4 mL of DIBAL-H (1.5 M solution in Toluene) solution was added dropwise. The reaction was continued at -78 °C for 1 h, and then MeOH and potassium sodium tartrate were added dropwise to quench the reaction. The mixture was stirred until it completely separated into layers, extracted with EA, washed with brine and concentrated. The crude product was purified by column chromatography and used directly in the next step of the reaction.

[0039] 30 mL of DCM was added to a 100 mL round-bottom flask, oxalyl chloride (1.45 mL, 17.19 mmol) was dissolved in it, and the flask was cooled to -78 °C. After cooling, DMSO (2.44 mL, 34.38 mmol) was slowly added dropwise. After stirring for about 10 min, the purified product (3.6 g, 5.73 mmol) was dissolved in DCM and added dropwise to the system. After stirring again for about 30 min, Et3N (6.4 mL, 45.84 mmol) was added dropwise. After the addition was completed, the system was allowed to warm to room temperature for two minutes and stirred until the system turned brownish-yellow. The solution was then quenched with water, followed by extraction with DCM, drying and concentration with sodium sulfate, and purification of the crude product by column chromatography to obtain 72.69 g of product, with a yield of 64%.

[0040] 11H NMR (600 MHz, CDCl3) δ 9.40 (s, 1H), 5.38 (t, J = 3.7 Hz, 1H), 4.36 (td, J = 6.3, 1.4 Hz, 1H), 4.20 (d, J = 6.8 Hz, 1H), 3.29 (d, J = 9.7 Hz, 1H), 3.17 (d, J = 9.7 Hz, 1H), 2.63 (dd, J = 13.5, 4.6 Hz, 1H), 2.20 (dd, J = 15.3, 1.5 Hz, 1H), 2.03 – 1.86 (m, 4H), 1.72 – 1.60 (m, 3H), 1.56 (q, J = 8.1, 6.3 Hz, 2H), 1.50 – 1.41 (m, 7H), 1.36 (dd, J = 10.0, 3.0 Hz, 2H), 1.33 (s, 4H), 1.32 (s, 1H), 1.31 – 1.29 (m, 2H), 1.28 (d, J = 6.6 Hz, 2H), 1.23 (s, 1H), 1.19 (ddd, J = 13.0, 4.9, 2.4 Hz, 3H), 1.14 (s, 3H), 1.11 (s, 3H), 1.10 – 1.07 (m, 1H), 0.91 (s, 6H), 0.89 (s, 12H), 0.78 (s, 3H), 0.75 (s, 3H), 0.03 (d, J = 4.2 Hz, 6H).

[0041] 13 13C NMR (151 MHz, CDCl3) δ 207.6, 142.9, 123.6, 107.1, 76.3, 73.8, 68.5, 49.3, 47.9, 45.8, 44.6, 42.1, 41.4, 40.8, 40.7, 39.7, 35.7, 33.4, 33.2, 32.2, 30.8, 29.9, 27.9, 26.8, 26.1, 26.0, 25.3, 25.1, 23.6, 23.5, 22.3, 18.4, 18.3, 17.0, 16.9, 1.2, -5.3, -5.5.

[0042] (7) Synthesis of Compound 8

[0043]

[0044] Compound 7 (2.69 g, 4.29 mmol) and p-TsOH·H₂O (81.8 mg, 0.43 mmol) were weighed and dissolved in 50 mL of toluene. (S)-1-(2-pyridyl)ethylamine (882 µL, 8.56 mmol) was added dropwise to the system, and the reaction was carried out at 80 °C for 2 h. 1 After the H NMR analysis confirmed the reaction was complete, the mixture was cooled to room temperature, diluted with EA for extraction, and washed three times with saturated ammonium chloride solution and sodium bicarbonate solution, respectively. The mixture was then dried and concentrated with sodium sulfate, and the crude product was used directly in the next step.

[0045] The crude product, Cu(OTf)₂ (2.0 g, 5.57 mmol), and sodium ascorbate (1.7 g, 8.574 mmol) were added to a flask. 50 mL of a 1:1 mixture of acetone and methanol was added to dissolve the crude product. After dissolution, O₂ was bubbled until the system turned dark green, at which point bubbling was stopped. The reaction was maintained at 50 °C for 1.5 h under O₂ atmosphere, then cooled to room temperature. The mixture was diluted with EA, quenched with saturated tetrasodium ethylenediaminetetraacetate solution, and stirred overnight. EA was then extracted, and the aqueous phase was extracted five times with EA. The organic phases were combined, washed with brine, dried over sodium sulfate, and concentrated. The crude product was purified by column chromatography to yield 8990 mg of product, with a yield of 36%.

[0046] 1H NMR (600 MHz, CDCl3) δ 9.46 (d, J = 2.7 Hz, 1H), 5.43 (s, 1H), 4.36(t, J = 5.7 Hz, 1H), 4.20 (d, J = 6.7 Hz, 1H), 4.16 (td, J = 9.7, 4.6 Hz,1H), 3.29 (d, J = 9.7 Hz, 1H), 3.18 (d, J = 9.7 Hz, 1H), 2.72 (dd, J = 13.8,4.6 Hz, 1H), 2.66 (d, J = 10.3 Hz, 1H), 2.19 (dd, J = 15.2, 1.4 Hz, 1H), 2.00– 1.89 (m, 3H), 1.83 (t, J = 12.7 Hz, 1H), 1.66 – 1.58 (m, 2H), 1.55 (dd, J =13.3, 4.9 Hz, 1H), 1.47 (s, 3H), 1.45 – 1.40 (m, 2H), 1.39 – 1.36 (m, 2H),1.35 (d, J = 3.4 Hz, 1H), 1.33 (s, 3H), 1.32 (d, J = 5.6 Hz, 2H), 1.29 (d, J= 2.8 Hz, 1H), 1.27 – 1.23 (m, 2H), 1.20 (ddd, J = 14.0, 4.8, 2.1 Hz, 1H),1.17 (s, 3H), 1.14 (s, 3H), 0.95 (s, 3H), 0.92 (s, 3H), 0.88 (s, 9H), 0.79(d, J = 1.7 Hz, 6H), 0.03 (d, J = 2.8 Hz, 6H).

[0047] 13 C NMR (151 MHz, CDCl3) δ 210.0, 141.7, 124.3, 107.1, 76.2, 73.7,68.4, 65.9, 52.7, 47.0, 45.4, 44.5, 44.1, 43.5, 41.3, 40.6, 39.8, 36.7, 35.6,33.2, 32.6, 32.1, 30.5, 26.3, 26.0, 26.0, 25.1, 23.6, 23.5, 21.8, 18.2, 17.0,17.0, 16.9, -5.3, -5.6.

[0048] (8) Synthesis of compound 9

[0049]

[0050] Compound 8 (840 mg, 1.31 mmol) was weighed into a round-bottom flask and dissolved in 13 mL of a mixed solution of tert-butanol and dimethyl sulfoxide in a volume ratio of 4.5:1. NaClO2 (829.3 mg, 9.17 mmol) and NaH2PO4·H2O (1.26 g, 9.17 mmol) were dissolved in an appropriate amount of water and added dropwise to the system. The mixture was stirred at room temperature and reacted for 1 h. The reaction was then quenched with 10% sodium bicarbonate solution until the system became alkaline. The mixture was extracted with hexane, and the aqueous phase was acidified with 1 N HCl and then extracted with DCM. The organic phase was washed with brine, dried over sodium sulfate, and concentrated. The crude product was directly used in the next step.

[0051] The crude product was dissolved in 14 mL of THF:H2O = 10:1. TBAI (48.4 mg, 0.131 mmol), K2CO3 (362.1 mg, 2.62 mmol), and AllBr (227 µL, 2.62 mmol) were added to the system. The mixture was heated to 65 °C and reacted for 2 h. The solvent was then evaporated by rotary evaporation. The solution was diluted with EA, washed three times with water, and the organic phases were combined. The mixture was washed with brine, dried over sodium sulfate, and concentrated. The crude product was purified by column chromatography to obtain 9565.7 mg of the product, with a yield of 62%.

[0052] 1H NMR (600 MHz, CDCl3) δ 5.89 (ddt, J = 16.4, 10.9, 5.6 Hz, 1H), 5.36– 5.31 (m, 2H), 5.25 (d, J = 10.4 Hz, 1H), 4.59 (dd, J = 13.3, 5.7 Hz, 1H),4.50 (dd, J = 13.4, 5.6 Hz, 1H), 4.36 (t, J = 6.2 Hz, 1H), 4.20 (d, J = 6.7Hz, 1H), 4.14 (td, J = 11.8, 4.5 Hz, 1H), 3.44 (d, J = 11.5 Hz, 1H), 3.29 (d,J = 9.7 Hz, 1H), 3.18 (d, J = 9.7 Hz, 1H), 3.04 (dd, J = 14.0, 4.7 Hz, 1H),2.25 (dt, J = 13.4, 3.4 Hz, 1H), 2.19 (d, J = 15.2 Hz, 1H), 1.93 (qdd, J =18.6, 8.8, 3.6 Hz, 2H), 1.72 – 1.58 (m, 4H), 1.53 (dd, J = 14.2, 4.1 Hz, 1H),1.48 (s, 4H), 1.46 – 1.42 (m, 2H), 1.39 – 1.35 (m, 1H), 1.33 (s, 3H), 1.31(d, J = 5.5 Hz, 1H), 1.30 – 1.22 (m, 4H), 1.17 (s, 3H), 1.13 (s, 3H), 0.96(s, 3H), 0.91 (s, 3H), 0.88 (s, 9H), 0.79 (s, 3H), 0.74 (s, 3H), 0.03 (d, J =2.8 Hz, 6H).

[0053] 13C NMR (151 MHz, CDCl3) δ 178.1, 142.3, 131.9, 123.3, 118.6, 107.1,76.2, 73.7, 68.4, 65.3, 64.9, 50.8, 47.1, 45.6, 44.5, 44.2, 43.5, 41.2, 40.6,39.5, 37.4, 35.6, 33.4, 33.2, 32.0, 30.7, 26.8, 26.6, 26.1, 26.0, 25.1, 24.0,23.5, 18.3, 17.1, 17.0, 16.7, -5.3, -5.6.

[0054] (9) Synthesis of compound 10

[0055]

[0056] Weigh compound 9 (565.7 mg, 0.81 mmol) into a round-bottom flask, add 9 mL of dissolved sodium bicarbonate (340.2 mg, 4.05 mmol) and DMP (629.1 mg, 3.24 mmol) in DCM, react at room temperature for 3 h, then dilute with DCM, quench with saturated sodium thiosulfate solution, add an appropriate amount of water and stir until the organic phase is clear, extract with DCM, extract the aqueous phase three times with DCM, combine the organic phases, wash with brine, dry with sodium sulfate and concentrate, and proceed directly to the next step with the crude product.

[0057] The crude product was dissolved in a round-bottom flask, and 6 mL of MeOH was added to dissolve it. NaBH4 (223.2 mg, 5.9 mmol) was weighed and added to the system at 0 °C. After stirring at room temperature for 2 h, the mixture was quenched with water and extracted with EA. The aqueous phase was extracted three times with EA, and the organic phases were combined. The mixture was washed with brine, dried over sodium sulfate, and concentrated. The crude product was purified by column chromatography to obtain 10,410 mg of product, with a yield of 53%.

[0058] 1H NMR (600 MHz, CDCl3) δ 5.87 (m, 1H), 5.43 (s, 1H), 5.30 (dd, J =17.2, 1.6 Hz, 1H), 5.21 (dd, J = 10.4, 1.6 Hz, 1H), 4.55 – 4.44 (m, 3H), 4.37(t, J = 6.2 Hz, 1H), 4.21 (d, J = 6.7 Hz, 1H), 3.29 (d, J = 9.7 Hz, 1H), 3.17(dd, J = 9.8, 2.5 Hz, 1H), 3.08 (dd, J = 14.5, 4.5 Hz, 1H), 2.24 – 2.13 (m,2H), 1.95 (ddd, J = 14.9, 8.7, 3.4 Hz, 2H), 1.91 – 1.87 (m, 1H), 1.81 (td, J= 13.3, 11.9, 4.0 Hz, 3H), 1.60 (d, J = 2.6 Hz, 1H), 1.48 (s, 3H), 1.37 (dd,J = 15.3, 3.6 Hz, 2H), 1.33 (d, J = 5.8 Hz, 9H), 1.31 – 1.27 (m, H), 1.15 (s,3H), 0.97 (s, 3H), 0.90 (s, 3H), 0.88 (s, 12H), 0.78 (s, 3H), 0.74 (s, 3H), 0.03 (d, J = 3.9 Hz, 6H).

[0059] 13 C NMR (151 MHz, CDCl3) δ 176.6, 142.6, 132.3, 123.3, 118.2, 107.1,76.2, 75.2, 73.8, 68.3, 65.3, 49.0, 47.0, 46.5, 44.5, 41.7, 41.3, 40.9, 40.7,39.6, 35.7, 35.6, 35.5, 32.9, 32.3, 30.8, 30.6, 26.9, 26.1, 26.0, 25.1, 24.8,23.4, 18.2, 17.2, 17.0, 16.9, 1.2, -5.3, -5.5.

[0060] (10) Synthesis of the natural product polygalic acid

[0061]

[0062] Compound 10 (80 mg, 0.12 mmol) was weighed into a round-bottom flask, dissolved in 2 mL of THF, and TBAF solution (1.2 mL, 1.2 mmol, 1 M solution in THF) was added dropwise to the system. The mixture was heated to 65 °C and reacted for 4 h. The solvent was then evaporated by rotary evaporation. The product was diluted with EA, washed three times with water, and the organic phases were combined. The mixture was washed with brine, dried over sodium sulfate, and concentrated. The crude product was dissolved in MeOH: 6 N HCl = 1:1, stirred at room temperature for 5 min, diluted with EA, washed three times with water, and the organic phases were combined. The mixture was washed with brine, dried over sodium sulfate, and concentrated. The crude product was rapidly purified by column chromatography to obtain 43.8 mg of the deprotected product, with a yield of 67%.

[0063] The above product (10 mg, 0.02 mmol) was weighed in a glove box and dissolved in 0.5 mL of degassed DCM. Pd(PPh3)4 (2.3 mg, 0.002 mmol) and barbituric acid (12.5 mg, 0.08 mmol) were added to the system. After stirring at room temperature for 20 min, the solvent was evaporated. The crude product was purified by column chromatography to obtain 119.2 mg of polysaccharide, with a yield of 90% and an overall yield of 60% for both steps.

[0064] 1H NMR (400 MHz, CD3OD) δ 5.33 (m, 1H), 4.47 (s, 1H), 4.09 (d, J = 3.6Hz, 1H), 3.63–3.57 (m, 1H), 3.51 (d, J = 11.0 Hz, 1H), 3.26 (d, J = 10.9 Hz,1H), 3.02 (dd, J = 14.5, 4.6 Hz, 1H), 2.30 (m, 1H), 2.12–2.05 (m, 1H), 2.03–1.92 (m, 4H), 1.91–1.73 (m, 3H), 1.65 (dd, J = 11.2, 6.5 Hz, 2H), 1.53–1.44(s, 2H), 1.40 (s, 3H), 1.35–1.32 (m, 1H), 1.31 (s, 3H), 1.28 (d, J = 9.0 Hz,1H), 1.20–1.12 (m, 2H), 1.08–1.00 (m, 1H), 0.99 (s, 4H), 0.92 (s, 4H), 0.89(s, 4H), 0.82 (s, 3H).

[0065] 13 C NMR (101 MHz, CD3OD) δ 181.6, 145.6, 123.9, 75.7, 73.9, 72.7,67.9, 48.9, 48.1, 48.1, 45.7, 43.3, 43.1, 42.5, 41.1, 38.2, 37.0, 36.5, 34.2,33.9, 33.2, 31.8, 27.8, 25.3, 25.0, 19.2, 18.2, 18.0, 14.5.

Claims

1. A chemical synthesis method for polygalic acid, characterized in that... Starting with readily available and inexpensive oleanolic acid 1, this method introduces oxidized states at different sites through strategies such as CH activation and undergoes multiple functional group transformations, ultimately yielding polygalic acid in 14 steps with an overall yield of 0.3%. This method represents the first chemical synthesis of polygalic acid and prepares several structural analogs, providing the necessary material basis and technical support for further research on its structure-activity relationship. The synthesis route is as follows: 。 2. The method according to claim 1, characterized in that the specific steps are as follows: 1) Weigh oleanolic acid 1 (41.76 g, 91.5 mmol) and K2CO3 (37.8 g, 273.27 mmol) into a 1 L round-bottom flask, and dissolve them in 500 mL of a 5:2 mixture of DMF and THF. Add MeI (6.24 mL, 100.2 mmol) dropwise to the reaction system, stir at room temperature for about 8 h. After the reaction is complete, evaporate the solvent under reduced pressure, then extract with EA, dry and concentrate with anhydrous sodium sulfate, and use directly in the next step of the reaction without column purification. 200 mL of DCM was added to a 1 L round-bottom flask, and TFAA (23.83 mL, 170.0 mmol) was dissolved in it and cooled to -78 °C. After cooling, DMSO (18.11 mL, 255 mmol) was slowly added dropwise. After stirring for about 10 min, the crude product was dissolved in DCM and added dropwise to the system. After stirring again for about 30 min, triethylamine (59.3 mL, 425.0 mmol) was added dropwise. After the addition was complete, the system was allowed to warm to room temperature for two minutes and stirred until the system turned brownish-yellow. The solution was then quenched with water, followed by extraction with DCM, drying and concentrating with anhydrous sodium sulfate. The crude product was purified by column chromatography to give compound 2 37.4 g, with a yield of 87%. 2) Compound 2 (37.4 g, 79.85 mmol) and NH2OH·HCl (8.3 g, 119.8 mmol) were weighed into a round-bottom flask, dissolved in 500 mL of pyridine, and reacted at 50 °C for 4 h. After the reaction was completed, the solvent was concentrated on a rotary evaporator. The resulting concentrate was extracted with EA, washed three times with 1 N HCl, washed with saturated brine, dried and concentrated with anhydrous sodium sulfate, and the crude product was purified by column chromatography to obtain compound 3 32.5 g, with a yield of 84%. 3) Weigh compound 3 (32.5 g, 67.2 mmol), dissolve it in 500 mL of a 1:1 mixture of acetic acid and acetic anhydride, and stir at 45 °C for 2 h. Add Pd(OAc)2 (2.26 g, 10.08 mmol) and PIDA (36.78 g, 114.2 mmol) to a round-bottom flask, react at 45 °C for 16 h, then evaporate the solvent, extract with EA, wash with brine, dry and concentrate with anhydrous sodium sulfate, and purify the crude product by column chromatography. The crude product is then used directly in the next step of the reaction. The purified product was dissolved in 500 mL MeOH, and K2CO3 (11.14 g, 80.64 mmol) was added. The system was heated to 60 °C and reacted for 2 h. The solvent was then evaporated, extracted with EA, washed three times with an equal volume of water, washed with saturated brine, dried and concentrated with anhydrous sodium sulfate. No further purification was required, and the crude product was used directly in the next step. The crude product was dissolved in 300 mL THF, and 300 mL 3 N HCl was added. After reacting overnight at room temperature, the product was concentrated on a rotary evaporator to remove the organic solvent. It was then extracted with EA, washed three times with an equal volume of water, washed with saturated sodium bicarbonate solution, washed with saturated brine, dried and concentrated with anhydrous sodium sulfate, and purified by column chromatography to give compound 4 16.9 g, with a yield of 44%. 4) Weigh compound 4 (16.9 g, 34.89 mmol), TBSCl (13.14 g, 87.2 mmol), and imidazole (7.12 g, 104.67 mmol) into a round-bottom flask, add 400 mL of DMF to dissolve, react at room temperature for 4 h, then evaporate the solvent, wash four times with saturated brine, dry and concentrate with anhydrous sodium sulfate, and the crude product is directly used in the next step of the reaction after simple purification by column chromatography. Weigh the purified product (18.7 g, 31.2 mmol) and t-BuOK (38.57 g, 343.7 mmol) into a round-bottom flask, add 300 mL of tert-butanol to dissolve, react at 45 °C for 16 h, then evaporate the solvent, extract with EA, wash three times with an equal volume of water, wash with saturated brine, then dry and concentrate with anhydrous sodium sulfate. The crude product is purified by column chromatography to give 58.8 g of colorless oily liquid product, yield 43%. 5) Weigh compound 5 (8.8 g, 15.1 mmol) into a round-bottom flask, add 150 mL of THF / EtOH (5:1) to dissolve it, weigh NaBH4 (1.6 g, 42.28 mmol) and add it to the round-bottom flask at 0 °C. After reacting at room temperature for 3 h, quench with water, extract with EA, wash with saturated brine, dry and concentrate with anhydrous sodium sulfate, dissolve the crude product in 150 mL of 2,2-dimethoxypropane, add p-TsOH·H2O (287.2 mg, 1.51 mmol), stir at room temperature for 30 min, evaporate the organic solvent, extract with an equal volume of EA, wash with saturated brine, dry and concentrate with anhydrous sodium sulfate, purify the crude product by column chromatography to obtain product 6 4.5 g, with a yield of 46%. 6) Weigh compound 6 (4.4 g, 6.7 mmol) into a round-bottom flask, replace with Ar, add 60 mL of DCM to dissolve, cool the system to -78 ℃, and then add 13.4 mL of DIBAL-H (1.5 M solution in Toluene) solution dropwise. Continue the reaction at -78 ℃ for 1 h, then add MeOH and potassium sodium tartrate dropwise to quench the reaction, stir until complete separation, extract with EA, wash with brine and concentrate, and then purify the crude product by column chromatography and use it directly in the next step of the reaction. 30 mL of DCM was added to a 100 mL round-bottom flask, and oxalyl chloride (1.45 mL, 17.19 mmol) was dissolved in it. The flask was then cooled to -78 °C. After cooling, DMSO (2.44 mL, 34.38 mmol) was slowly added dropwise. After stirring for about 10 min, the purified product (3.6 g, 5.73 mmol) was dissolved in DCM and added dropwise to the system. After stirring again for about 30 min, Et3N (6.4 mL, 45.84 mmol) was added dropwise. After the addition was completed, the system was allowed to warm to room temperature for two minutes and stirred until it turned brownish-yellow. The solution was then quenched with water, followed by extraction with DCM, drying and concentration with sodium sulfate, and purification of the crude product by column chromatography to obtain 72.69 g of product, with a yield of 64%. 7) Weigh compound 7 (2.69 g, 4.29 mmol) and p-TsOH·H2O (81.8 mg, 0.43 mmol), dissolve them in 50 mL of toluene, and add (S)-1-(2-pyridyl)ethylamine (882 µL, 8.56 mmol) dropwise to the system. React at 80 °C for 2 h. 1 After the H NMR analysis confirmed the reaction was complete, the mixture was cooled to room temperature, diluted with EA for extraction, and washed three times with saturated ammonium chloride solution and sodium bicarbonate solution, respectively. The mixture was then dried and concentrated with sodium sulfate, and the crude product was used directly in the next step. The crude product, Cu(OTf)₂ (2.0 g, 5.57 mmol), and sodium ascorbate (1.7 g, 8.574 mmol) were added to a flask. 50 mL of a 1:1 mixture of acetone and methanol was added to dissolve the crude product. After dissolution, O₂ was bubbled until the system turned dark green. The bubbling was stopped, and the reaction was maintained at 50 °C for 1.5 h under O₂ atmosphere. The mixture was then cooled to room temperature, diluted with EA, quenched with saturated tetrasodium ethylenediaminetetraacetate solution, and stirred overnight. The mixture was extracted with EA, and the aqueous phase was extracted five times with EA. The organic phases were combined, washed with brine, dried over sodium sulfate, and concentrated. The crude product was purified by column chromatography to obtain 8990 mg of product, with a yield of 36%. 8) Weigh compound 8 (840 mg, 1.31 mmol) into a round-bottom flask, add 13 mL of a mixed solution of tert-butanol and dimethyl sulfoxide (4.5:1) to dissolve it, dissolve NaClO2 (829.3 mg, 9.17 mmol) and NaH2PO4·H2O (1.26 g, 9.17 mmol) in an appropriate amount of water and add them dropwise to the system. Stir at room temperature and react for 1 h. Quench the reaction with 10% sodium bicarbonate solution until the system is alkaline. Extract with hexane, acidify the aqueous phase with 1 N HCl and extract with DCM, wash the organic phase with brine, dry and concentrate with sodium sulfate, and proceed directly to the next step with the crude product. The crude product was dissolved in 14 mL of THF:H2O = 10:

1. TBAI (48.4 mg, 0.131 mmol), K2CO3 (362.1 mg, 2.62 mmol), and AllBr (227 µL, 2.62 mmol) were added to the system. The mixture was heated to 65 °C and reacted for 2 h. The solvent was then evaporated by rotary evaporation. The solution was diluted with EA, washed three times with water, and the organic phases were combined. The mixture was washed with brine, dried over sodium sulfate, and concentrated. The crude product was purified by column chromatography to obtain 9565.7 mg of the product, with a yield of 62%. 9) Weigh compound 9 (565.7 mg, 0.81 mmol) into a round-bottom flask, add 9 mL of dissolved sodium bicarbonate (340.2 mg, 4.05 mmol) and DMP (629.1 mg, 3.24 mmol) in DCM, react at room temperature for 3 h, then dilute with DCM, quench with saturated sodium thiosulfate solution, add an appropriate amount of water and stir until the organic phase is clear, extract with DCM, extract the aqueous phase three times with DCM, combine the organic phases, wash with brine, dry with sodium sulfate and concentrate, and proceed directly to the next step with the crude product. The crude product was dissolved in a round-bottom flask, and 6 mL of MeOH was added to dissolve it. NaBH4 (223.2 mg, 5.9 mmol) was weighed and added to the system at 0 °C. After stirring at room temperature for 2 h, the mixture was quenched with water and extracted with EA. The aqueous phase was extracted three times with EA, and the organic phases were combined. The mixture was washed with brine, dried over sodium sulfate, and concentrated. The crude product was purified by column chromatography to obtain 10,410 mg of product, with a yield of 53%. 10) Weigh compound 10 (80 mg, 0.12 mmol) into a round-bottom flask, add 2 mL of THF to dissolve it, add 1.2 mL of TBAF solution (1.2 mmol, 1 M solution in THF) dropwise into the system, heat to 65 °C and react for 4 h, then evaporate the solvent by rotary evaporation, dilute with EA, wash three times with water, combine the organic phases, wash with brine, dry and concentrate with sodium sulfate, dissolve the crude product in MeOH: 6 N HCl = 1:1, stir at room temperature for 5 min, dilute with EA, wash three times with water, combine the organic phases, wash with brine, dry and concentrate with sodium sulfate, and rapidly purify the crude product by column chromatography to obtain 43.8 mg of deprotected product, with a yield of 67%. The above product (10 mg, 0.02 mmol) was weighed in a glove box and dissolved in 0.5 mL of degassed DCM. Pd(PPh3)4 (2.3 mg, 0.002 mmol) and barbituric acid (12.5 mg, 0.08 mmol) were added to the system. After stirring at room temperature for 20 min, the solvent was evaporated. The crude product was purified by column chromatography to obtain 119.2 mg of polysaccharide, with a yield of 90% and an overall yield of 60% for both steps.

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