Synthesis method of soapberry acid

Abstract

The invention discloses a synthesis method of soapberry acid, which takes commercially purchased oleanolic acid as a raw material and prepares soapberry acid through multi-step reaction, and the synthesis route is as follows: # imgabs0 # R1 is Bn, C1-C5 saturated groups and alkyl groups, MOM, BOM, Fmoc, TBS, TBDPS or allyl; r2 is an alkanoyl group, an aroyl group or a silicon group; r is # imgabs1 # imgabs2 # G represents 1-3 identical or different substituent groups, each G is independently selected from H, F, Cl, Br, C1-C4 saturated alkyl, nitryl, methoxyl and acetoxy, R3 is Bn, C1-C5 saturated and alkyl groups, MOM, BOM, Fmoc or TBS; the method has the advantages of mild conditions, large-scale synthesis, simple operation and high yield.

Description

Technical Field

[0001] The present invention belongs to the field of the synthesis of triterpenoid compounds, and particularly relates to a method for synthesizing quillaic acid. Background Art

[0002] Vaccines play an irreplaceable role in preventing diseases and maintaining human health. Among them, modern novel vaccines (such as DNA vaccines, recombinant vaccines, and subunit vaccines) have more significant safety and targeting properties, but their immunogenicity is relatively low. To ensure that modern novel vaccines can elicit sufficient immune responses, they need to be used in conjunction with immunoadjuvants. Immunoadjuvants can not only ensure that subunit vaccines have ideal immunogenicity, but also significantly reduce the dosage of subunit vaccines, thereby reducing the usage cost of this type of novel vaccine.

[0003] The triterpenoid saponin QS-21 isolated from Quillaja saponaria Molina has good immunoadjuvant activity (Expert Rev. Vaccines 2011, 10, 463 - 470.), and as an immunoadjuvant, QS-21 has been applied to clinical studies of vaccines for anti-tumor, anti-infectious diseases including pneumonia, HIV, malaria, and tuberculosis, as well as anti-neurodegenerative diseases such as Alzheimer's disease (Expert Opin. Drug Discov. 2015, 10, 1133 - 1144. J. Neurochem. 2016, 137, 687 - 700.). However, due to the extremely low natural content of QS-21, it is difficult to obtain and widely apply it in large quantities. Therefore, chemical synthesis has become the preferred and reliable method for obtaining sufficient QS-21. In terms of chemical structure, QS-21 is composed of a left-wing branched trisaccharide, a core triterpenoid quillaic acid, a right-wing linear tetrasaccharide, and an acyl side chain. To chemically synthesize QS-21, the first problem to be solved is the acquisition of the aglycone quillaic acid. Although quillaic acid is commercially available, its price is expensive (about 55,000 yuan per gram). Therefore, developing an efficient method for synthesizing quillaic acid is of great significance. In 2020, our research group reported a method for synthesizing expensive quillaic acid from protoaescigenin as a raw material, but the route is lengthy (24 steps) and the practicability is poor (Org. Lett. 2020, 22, 8613 - 8617.). Therefore, a more efficient and practical synthetic route for quillaic acid needs to be established. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for synthesizing quillaic acid.

[0005] Based on the above purpose, the present invention adopts the following technical solutions:

[0006] A method for synthesizing quillaic acid, the synthetic route is as follows:

[0007]

[0008] R 1 is Bn, a saturated alkyl group of C1-C5, MOM, BOM, Fmoc, TBS, TBDPS or allyl; R 2 is an alkanoyl group, an aroyl group or a silyl group; R is G represents 1 to 3 identical or different substituents, and each G is independently selected from H, F, Cl, Br, a saturated alkyl group of C1-C4, nitro, methoxy, acetoxy, R 3 is Bn, a saturated alkyl group of C1-C5, MOM, BOM, Fmoc, TBS;

[0009] The specific preparation process is as follows:

[0010] (1) Oleanolic acid is reacted to obtain compound I;

[0011] (2) Compound I is reacted to obtain compound II;

[0012] (3) Compound II is reacted to obtain compound III;

[0013] (4) The hydroxyl group at the C-28 position of compound III is oxidized to an aldehyde group, and then the methylene group at the C-16 position is oxidized to a hydroxyl group to obtain compound IV;

[0014] (5) The C-28 position of compound IV is oxidized to a carboxyl group, and then R 3 protecting group is introduced to obtain compound V;

[0015] (6) The hydroxyl group at the C-16 position of compound V is oxidized to a carbonyl group, and then reduced to obtain compound VI;

[0016] (7) Compound VI is deprotected from the protecting group R to obtain compound VII;

[0017] (8) The hydroxyl group at the C-23 position of compound VII is oxidized to a carbonyl group to obtain compound VIII;

[0018] (9) The protecting group R at the C-28 position of compound VIII is removed 3 to obtain the target compound, sapienic acid.

[0019] Furthermore, the specific process of step (1) is as follows:

[0020]

[0021] S1. The carboxyl group at the 28th position of oleanolic acid is protected with the protecting group R 1 to obtain compound I-1;

[0022] S2. Oxidize the hydroxyl group at the 3-position of compound I-1 to a carbonyl group to obtain compound I-2;

[0023] S3. Generate an oxime group at the 3-position carbonyl of compound I-2 to obtain compound I.

[0024] Further, the specific process of step (3) is as follows:

[0025]

[0026] a. Remove R from compound II 2 to obtain a deprotection product; generate a carbonyl group at the oxime group at the C-3 position of the deprotection product to obtain compound III-1; b. Reduce the carbonyl group at the C-3 position and the ester group at the 28-position of compound III-1 to hydroxyl groups to obtain compound III-2;

[0027] c. Protect the two hydroxyl groups of compound III-2 with an R protecting group to obtain compound III.

[0028] Further, the specific process of step (4) is as follows:

[0029]

[0030] Oxidize the hydroxyl group of compound III to an aldehyde group to obtain compound IV-1, and oxidize the C16 position of compound IV-1 to a hydroxyl group to obtain compound IV.

[0031] Preferably, in step S1, oleanolic acid reacts with a halide of R in the presence of potassium carbonate to obtain compound I-1, and the molar ratio of oleanolic acid, potassium carbonate, and the halide of R is 1:(2 - 3):(2 - 3). 1 and the halide of R 1 is 1:(2 - 3):(2 - 3).

[0032] Preferably, in step S2, compound I-1 reacts with DMP in the presence of NaHCO 3 to obtain compound I-2, and the molar ratio of compound I-1, NaHCO 3 and DMP is 1:(4 - 5):(1 - 2), and the reaction temperature is -5 to 5°C;

[0033] Preferably, in step S3, compound I-2 reacts with hydroxylamine hydrochloride in the presence of NaOAc to obtain compound I, and the molar ratio of compound I-2, NaOAc, and hydroxylamine hydrochloride is 1:(2 - 4):(1 - 2).

[0034] Further, the process of step a is as follows: Compound II removes R in the presence of a base 2 , and dissolve the product after removing R 2 in a solvent, and add NH 4OAc, then add TiCl 3 hydrochloric acid solution of, react completely at room temperature to obtain compound III-1, the product of deacetylation, NH 4 OAc and TiCl 3 The molar ratio of is 1:(9-11):(1-3);

[0035] Specifically, in the step a, the base is sodium carbonate or potassium carbonate, and the molar ratio of compound II to the base is 1:(5-7).

[0036] Further, the process of step b is as follows: dissolve compound III-1 in an organic solvent, add LAH at -5°C to 5°C to reduce to obtain compound III-2, and the molar ratio of compound III-1 to LAH is 1:(2-3);

[0037] Further, the process of step c is as follows: react compound III-2 with the alkoxy or chloride of RCH in the presence of TsOH to obtain compound III, and the molar ratio of compound III-2, TsOH and the alkoxy or chloride of RCH is 1:(0.4-0.6):(0.1-0.3).

[0038] Further, the process of step (2) is as follows. Dissolve compound I in a mixed solvent of AcOH / Ac 2 O, add Pd(OAc) 2 , PIDA, stir and react completely at 40-50°C to obtain compound II, wherein the molar ratio of compound I, PIDA and Pd(OAc) 2 is 1:(1-2):(0.1-0.2).

[0039] Preferably, the process of step (4) is as follows

[0040] React compound III with the oxidant IBX to obtain compound IV-1, react compound IV-1 with (S)-DG in the presence of TsOH at 70-90°C to obtain a crude imine product, dissolve the crude imine product in a solvent, add Cu(OTf) 2 and sodium L-ascorbate, after the system changes color, bubble in oxygen, after the system changes color, react completely at 45-55°C, quench the reaction with saturated Na 4 EDTA solution, and perform post-treatment to obtain compound IV, wherein the structure of (S)-DG is The molar ratio of compound III to the oxidant IBX is 1:(1-3); the molar ratio of compound IV-1, TsOH and (S)-DG is 1:(0.1-0.2):(2-4); the molar ratio of the crude imine product, Cu(OTf) 2 and sodium L-ascorbate is 1:(1-1.5):(1-3).

[0041] Further, the specific process of step (5) is as follows:

[0042] Dissolve Compound IV in an organic solvent, add 2-methyl-2-butene, stir evenly, and then add NaClO 2 and NaH 2 PO 4 aqueous solution. After the reaction is complete at room temperature and through post-treatment, a crude product with the C-28 position oxidized to a carboxyl group is obtained. The crude product with the C-28 position oxidized to a carboxyl group reacts with a halide of an R 3 protecting agent in the presence of potassium carbonate to obtain Compound V. The molar ratio of Compound IV, 2-methyl-2-butene, NaClO 2 and NaH 2 PO 4 is 1:(9 - 11):(4 - 6):(6 - 8); the molar ratio of the crude product with the C-28 position oxidized to a carboxyl group, potassium carbonate, and the halide of the R 3 protecting agent is 1:(1 - 2):(1 - 2).

[0043] Further, the specific process of step (6) is as follows: React Compound V with DMP in the presence of NaHCO 3 to obtain a compound with the C-16 position oxidized to a ketone. The compound with the C-16 position oxidized to a ketone reacts with NaBH 4 at -50 to -80 °C to obtain Compound VI. Among them, the molar ratio of Compound V, NaHCO 3 and DMP is 1:(3 - 5):(1 - 3), and the molar ratio of the compound with the C-16 position oxidized to a ketone and NaBH 4 is 1:(5 - 7).

[0044] Further, the specific process of step (7) is as follows: Remove the protecting group from Compound VI in the presence of an acetic acid solution. The concentration of acetic acid in the acetic acid solution is 70 - 90 wt%, and the reaction conditions are 100 - 120 °C; the concentration of Compound VI in the acetic acid solution is 0.1 - 0.2 mmol / mL.

[0045] Further, the specific process of step (8) is as follows: Dissolve KBr and TBACl in a saturated NaHCO 3 solution to prepare a mixed solution A, and then prepare a solution B by mixing a (2 - 8) wt% NaClO solution with a saturated NaCl solution and a saturated NaHCO 3 solution; dissolve Compound VII in an organic solvent, then add TEMPO and solution A in sequence, and then add solution B at -5 to 5 °C and react at this temperature. Add solution B in batches every 0.5 h - 1.5 h until the reaction is complete as monitored by TLC.

[0046] Preferably, the molar ratio of compound VII, KBr, TBACl, and TEMPO is 1:(1-1.5):(0.5-0.7):(0.1-0.2); the concentration of KBr in the saturated NaHCO 3 solution is 0.5-0.6 mmol / mL, and the volume ratio of the NaClO solution, saturated NaCl solution, and saturated NaHCO 3 in solution B is (6-8):(1-3):(2-4); the volume ratio of solution A, solution B, and the organic solvent is 1:(10-15):(13-17), and the addition amount of solution B each time is 0.5-1 mL.

[0047] Furthermore, the specific process of step (9) is as follows: Compound VIII reacts with hydrogen in the presence of Pd / C, and the reaction temperature is 35-45 °C. The molar ratio of compound VIII to Pd is 1:(0.1-0.3).

[0048] The present invention uses commercially available oleanolic acid as a raw material and prepares quillaic acid through multiple steps. The method has mild conditions, can be synthesized in large quantities, is easy to operate, and has a high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the 1 HNMR spectrum of the quillaic acid synthesized by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] The technical solutions of the present invention will be further described in detail below with reference to specific examples.

[0051] Example 1

[0052]

[0053] Commercially available oleanolic acid (60 g, 0.13 mol) and potassium carbonate (45.4 g, 0.33 mol) were placed in a flask, a magnetic stirrer was added, and 500 mL of DMF was added to dissolve them. Then, MeI (20 mL, 0.33 mol) was slowly added dropwise, and the reaction was carried out at room temperature for 7 h under N 2 protection and detected by TLC. After the reaction was completed, it was diluted with EA, washed successively with water and saturated NaCl solution, the organic phase was collected, and anhydrous Na 2 SO 4 was added for drying, and the solvent was evaporated and purified by column chromatography (PE / EA = 20:1) to obtain white solid compound 1 (58.7 g, 95%). 11H NMR (400 MHz, Chloroform-d) δ 5.28 (t, J = 3.7 Hz, 1H), 3.62 (s, 3H), 3.21 (dd, J = 11.2, 4.7 Hz, 1H), 2.86 (dd, J = 14.0, 4.5 Hz, 1H), 2.00 - 1.86 (m, 3H), 1.70 (dd, J = 13.7, 4.3 Hz, 1H), 1.66 - 1.49 (m, 10H), 1.45 - 1.41 (m, 3H), 1.38 - 1.26 (m, 4H), 1.20 - 1.15 (m, 1H), 1.13 (s, 3H), 1.07 - 1.03 (m, 1H), 0.98 (s, 3H), 0.92 (s, 3H), 0.90 (s, 3H), 0.89 (s, 3H), 0.78 (s, 3H), 0.72 (s, 3H).

[0054]

[0055] Compound 1 (60 g, 0.12 mol) and NaHCO 3 (42.8 g, 0.51 mol) were placed in a 1 L flask, dissolved in 500 mL of dry DCM, and then DMP (81 g, 0.19 mol), an oxidant, was slowly added under an ice bath. The reaction was stirred at room temperature for 6 h. After monitoring by TLC and completion of the reaction, it was diluted with DCM and quenched with saturated Na 2 S 2 O 3 solution, and then washed successively with saturated NaHCO 3 solution and NaCl solution. The organic layer was placed in a conical flask, dried with Na 2 SO 4 , rotary evaporated, and purified by column chromatography (PE / EA = 30:1) to obtain white solid Compound 2 (51.4 g, 86%). 1 1H NMR (400 MHz, Chloroform-d) δ 5.30 (t, J = 3.7 Hz, 1H), 3.63 (s, 3H), 2.95 - 2.80 (m, 1H), 2.54 (ddd, J = 15.9, 11.2, 7.2 Hz, 1H), 2.35 (ddd, J = 15.9, 6.8, 3.6 Hz, 1H), 2.01 - 1.85 (m, 4H), 1.73 - 1.57 (m, 6H), 1.55 - 1.47 (m, 4H), 1.44 - 1.23 (m, 5H), 1.22 - 1.15 (m, 1H), 1.14 (s, 3H), 1.08 (s, 3H), 1.04 (s, 6H), 0.92 (s, 3H), 0.90 (s, 3H), 0.77 (s, 3H).

[0056]

[0057] Place compound 2 (60 g, 0.12 mol) in a 1 L flask, add 250 mL of DCM and 500 mL of MeOH to dissolve it, then add NaOAc (31.5 g, 0.37 mol) and hydroxylamine hydrochloride (13.3 g, 0.19 mol), stir at room temperature for 5 h, monitor by TLC. After the reaction is complete, dilute with DCM, wash with H 2 O and saturated NaCl solution, place the organic phase in a conical flask, add Na 2 SO 4 to dry, filter and evaporate to dryness, perform column chromatography (PE / EA = 30:1) to obtain white solid compound 3 (60.68 g, 98%). 1 1H NMR (400 MHz, Chloroform-d) δ 5.34 - 5.19 (m, 1H), 3.62 (s, 3H), 3.08 (ddd, J = 16.2, 5.2, 3.1 Hz, 1H), 2.86 (dd, J = 13.9, 4.5 Hz, 1H), 2.15 (ddd, J = 15.5, 12.7, 5.7 Hz, 1H), 2.02 - 1.81 (m, 3H), 1.74 (ddd, J = 13.0, 5.8, 3.4 Hz, 1H), 1.70 - 1.24 (m, 11H), 1.15 (s, 3H), 1.11 (s, 3H), 1.05 (s, 3H), 1.02 (s, 3H), 0.92 (s, 3H), 0.89 (s, 3H), 0.76 (s, 3H).

[0058]

[0059] Place compound 3 (50 g, 0.1 mol) in a 500 mL flask, add AcOH / Ac 2 O (230 mL / 230 mL), stir at 45 °C for 1.5 h, then add Pd(OAc) 2 (3.48 g, 0.015 mol) and PIDA (56.6 g, 0.175 mol), stir and react at 45 °C for 12 h, monitor by TLC. After the reaction is complete, dilute with EA, wash with water first, then wash with saturated NaHCO 3 solution to remove the excess acid, then wash with saturated NaCl solution, collect the organic phase, add Na 2 SO 4 to dry, evaporate to dryness, perform column chromatography (PE / EA = 10:1 - 5:1) to obtain yellow solid compound 4 (32 g, 53%) and compound 5 (9.9 g, 15%). 11H NMR (400 MHz, Chloroform-d) δ 5.28 (d, J = 3.3 Hz, 1H), 4.17 (s, 2H), 3.59 (s, 3H), 2.84 (dd, J = 14.0, 4.5 Hz, 1H), 2.75 (ddd, J = 16.8, 7.0, 3.7 Hz, 1H), 2.47 (ddd, J = 17.3, 10.6, 7.2 Hz, 1H), 2.14 (s, 3H), 2.02 (s, 3H), 1.98 - 1.85 (m, 3H), 1.76 - 1.54 (m, 6H), 1.53 - 1.36 (m, 6H), 1.35 - 1.16 (m, 5H), 1.13 (s, 3H), 1.09 (s, 3H), 0.95 (s, 3H), 0.89 (s, 3H), 0.86 (s, 3H), 0.73 (s, 3H); 13 13C NMR (150 MHz, Chloroform-d) δ 178.2, 170.9, 170.5, 169.7, 143.9, 122.1, 68.1, 51.6, 48.5, 46.8 (2C), 45.8, 43.9, 41.8, 41.7, 39.25, 37.0, 36.5, 33.9, 33.15, 32.4, 32.0, 30.7, 27.7, 25.8, 23.7, 23.5, 23.1, 21.0, 20.3, 20.05, 19.4 (2C), 16.8, 15.3.

[0060]

[0061] Dissolve compound 4 (20 g, 0.034 mol) in 600 mL of MeOH, add Na 2 CO 3 (8.4 g, 0.21 mol), stir the reaction at room temperature for 8 h. Monitor by TLC. After the reaction is complete, dilute with EA and wash with saturated NaCl solution. Place the organic phase in a conical flask, add Na 2 SO 4 to dry, evaporate to dryness, and perform column chromatography (PE / EA = 8:1) to obtain the product with the acetyl group removed (15.4 g, 90%).

[0062] Dissolve the above deacetylated product (15.4 g, 0.031 mol) in THF / H 2 O (300 mL / 300 mL), add NH 4 OAc (23.7 g, 0.31 mol) to it, and then add a 15 wt% hydrochloric acid solution of TiCl 3 (42 mL, TiCl 3The molar amount was 0.054 mmol), and the reaction was stirred at room temperature for 6 h. TLC was used for detection. After the reaction was complete, it was diluted with EA, washed with saturated NaCl solution and NaHCO 3 solution, and the organic phase was placed in a conical flask. Add Na 2 SO 4 for drying, rotary evaporation, and column chromatography (PE / EA = 10:1) to obtain white solid compound 6 (14.2 g, 95%). 1 1H NMR (600 MHz, Chloroform-d) δ 5.29 (d, J = 3.7 Hz, 1H), 3.63 (d, J = 11.3 Hz, 1H), (s, 3H), 3.42 (d, J = 11.3 Hz, 1H), 2.87 (dd, J = 13.9, 4.7 Hz, 1H), 2.63 (ddd, J = 16.1, 13.3, 6.8 Hz, 1H), 2.41 (s, 1H), 2.26 (ddd, J = 16.1, 5.4, 2.6 Hz, 1H), 2.01 - 1.89 (m, 4H), 1.71 - 1.57 (m, 6H), 1.54 - 1.47 (m, 3H), 1.43 - 1.30 (m, 4H), 1.21 - 1.17 (m, 1H), 1.16 - 1.13 (m, 1H), 1.13 (s, 6H), 1.09 - 1.04 (m, 1H), 1.02 (s, 3H), 0.92 (s, 3H), 0.89 (s, 3H), 0.79 (s, 3H).

[0063]

[0064] Dissolve compound 6 (16 g, 0.033 mol) in 300 mL of THF, and then slowly add LAH (3.13 g, 0.082 mol) under an ice bath. Stir the reaction at room temperature for 3 h. TLC was used to detect the completion of the reaction. Slowly add the reaction system to a beaker containing ethyl acetate and anhydrous Na 2 SO 4 . Quench the excess LAH with ethyl acetate, and then wash with saturated NaCl solution. Place the organic phase in a conical flask and use anhydrous Na 2 SO 4 for drying, rotary evaporation, and column chromatography (PE / EA = 3:1) to obtain white solid compound 7 (9.6 g, 64%) and compound 8 (3.6 g, 24%). For 7: 11H NMR (400 MHz, Chloroform-d) δ 5.19 (t, J = 3.7 Hz, 1H), 3.73 (d, J = 10.3 Hz, 1H), 3.64 (dd, J = 9.0, 7.1 Hz, 1H), 3.54 (d, J = 11.0 Hz, 1H), 3.43 (d, J = 10.3 Hz, 1H), 3.20 (d, J = 11.0 Hz, 1H), 2.58 (brs, 1H), 1.97 (dd, J = 13.6, 4.7 Hz, 1H), 1.92 - 1.84 (m, 3H), 1.75 - 1.24 (m, 17H), 1.20 - 1.17 (m, 1H), 1.16 - 1.14 (m, 3H), 1.06 (ddd, J = 13.4, 4.7, 2.4 Hz, 1H), 0.97 (s, 3H), 0.94 (s, 3H), 0.90 (s, 3H), 0.88 (s, 3H), 0.87 (s, 3H).

[0065]

[0066] Dissolve compound 7 (10 g, 0.22 mol) in CH 3 CN, then add TsOH (1.87 g, 0.11 mol) and PhCH(OMe) 2 (16 mL, 0.043 mol), react at room temperature for 8 h, monitor by TLC. After the reaction is complete, dilute with EA, wash with saturated NaHCO 3 solution and NaCl solution. Place the organic phase in a conical flask, add anhydrous Na 2 SO 4 to dry, filter by suction, evaporate to dryness, and perform column chromatography (PE / EA = 20:1) to obtain white solid compound 9 (9.9 g, 83%). 1 1H NMR (400 MHz, Acetone-d 6 ) δ 7.52 - 7.45 (m, 2H), 7.40 - 7.31 (m, 3H), 5.56 (s, 1H), 5.20 (t, J = 3.6 Hz, 1H), 3.91 (d, J = 10.3 Hz, 1H), 3.57 - 3.47 (m, 3H), 3.15 (d, J = 10.6 Hz, 1H), 1.95 - 1.67 (m, 9H), 1.66–1.45 (m, 5H), 1.44 - 1.25 (m, 8H), 1.22 (s, 3H), 1.17 (s, 3H), 1.15 - 1.07 (m, 2H), 0.99 (s, 3H), 0.89 (s, 6H); 13 13C NMR (100 MHz, Acetone-d 6)δ145.6,140.4,129.3,128.7,127.3,122.7,103.0,86.5,79.1,69.0,52.0,48.5,47.5,43.2,42.5,40.8,39.7,37.9,37.75,37.3,35.0,33.6,32.9,32.0,31.6,26.5,26.3,24.2,24.1,24.0,22.8,18.45,17.2,17.0,13.85,11.7.

[0067]

[0068] Dissolve compound 9 (7 g, 0.013 mol) in DMSO / THF (300 mL / 300 mL), add the oxidant IBX (7.17 g, 0.026 mol), react at room temperature for 5 h. After detecting the completion of the reaction by TLC, dilute with EA, and wash with saturated NaHCO 3 solution and NaCl solution. Place the organic phase in a conical flask, add anhydrous Na 2 SO 4 to dry, filter by suction, rotary evaporate, and perform column chromatography (PE / EA = 35:1) to obtain white solid compound 10 (5.8 g, 83%). 1 1H NMR (400 MHz, Chloroform-d) δ9.40 (s, 1H), 7.54 - 7.46 (m, 2H), 7.45 - 7.28 (m, 3H), 5.53 (s, 1H), 5.36 (s, 1H), 3.94 (d, J = 10.4 Hz, 1H), 3.46 (t, J = 8.7 Hz, 2H), 2.64 (dd, J = 13.8, 4.5 Hz, 1H), 2.04 - 1.85 (m, 3H), 1.80 - 1.54 (m, 7H), 1.51 - 1.41 (m, 3H), 1.36 - 1.22 (m, 5H), 1.20 (s, 3H), 1.17 (s, 3H), 1.11 - 1.04 (m, 2H), 1.00 (s, 3H), 0.93 (s, 3H), 0.92 (s, 3H), 0.87 - 0.81 (m, 1H), 0.75 (s, 3H); 13C NMR(100MHz,Chloroform-d)δ207.4,143.1,138.8,129.0,128.5,128.4,126.5,126.4,123.2,102.8,86.2,78.9,51.6,49.2,47.7 ,45.7,41.8,40.5,39.85,39.0,37.3,36.8,33.25,33.2,32.4,30.8,27.8,26.85,25.7,23.5,23.4,22.2,17.9,17.1,16.6,13.6.

[0069]

[0070] Compound 10 (4 g, 7.3 mmol) and TsOH (126 mg, 0.73 mmol) were dissolved in toluene dried over molecular sieves, (S)-DG (2.8 mL, 22 mmol) was added, and the mixture was stirred in an oil bath at 80 °C for 5 h. After the reaction was completed, EA was added to dilute the mixture, and saturated NH 4 Cl solution, saturated NaHCO 3 The organic phase was placed in a conical flask and anhydrous Na 2 SO 4 The mixture was dried, filtered and spin-dried to obtain a yellow foamy solid crude imine product.

[0071] The dried imine crude product was dissolved in a mixed solvent of dry methanol and acetone (150 mL / 150 mL), and Cu(OTf) was added. 2 (3.4 g, 9.5 mmol) and Na L-ascorbate (2.9 g, 14.6 mmol) were stirred at room temperature for 5 min, and the system turned brown. 2 The system was stirred with oxygen gas and reacted at room temperature for 5 min. The system changed from brown to green. The system was placed in a 50°C oil bath for 1.5 h. The reaction was monitored by TLC. After the reaction was completed, the system was cooled to room temperature, diluted with EA, and washed with saturated Na 4 The reaction was quenched with EDTA solution and stirred at room temperature for 1.5 h. The aqueous phase was stripped with EA, combined with the organic phase, washed with saturated NaCl solution, and the organic phase was collected and placed in a conical flask. Anhydrous Na 2 SO 4 The residue was dried, filtered, and spin-dried. The residue was purified by column chromatography (PE / EA=15:1) to obtain compound 11 (2.1 g, 52%) as a white solid. 11H NMR (400 MHz, Chloroform-d) δ 9.47 (d, J = 2.7 Hz, 1H), 7.55 - 7.47 (m, 2H), 7.41 - 7.27 (m, 3H), 5.53 (s, 1H), 5.41 (t, J = 3.7 Hz, 1H), 4.18 (t, J = 11.7 Hz, 1H), 3.95 (d, J = 10.4 Hz, 1H), 3.47 (td, J = 9.0, 8.4, 4.1 Hz, 2H), 2.73 (dd, J = 13.9, 4.6 Hz, 1H), 2.67 (d, J = 10.2 Hz, 1H), 1.99 - 1.69 (m, 6H), 1.65 - 1.62 (m, 1H), 1.58 (s, 6H), 1.55 - 1.26 (m, 11H), 1.23 (s, 3H), 1.20 (s, 3H), 1.10 - 1.04 (m, 1H), 1.00 (s, 3H), 0.96 (s, 3H), 0.95 (s, 3H), 0.90 - 0.83 (m, 2H), 0.79 (s, 3H).

[0072]

[0073] Compound 11 (3.5 g, 6.2 mmol) was dissolved in a mixed solvent of t-BuOH / THF (120 mL / 40 mL), 2-methyl-2-butene (6.5 mL, 62 mmol) was added, and the mixture was stirred at room temperature for 5 min. Then, NaClO 2 (2.8 g, 31.2 mmol) and NaH 2 PO 4 (5.2 g, 43.4 mmol) in 10 mL of aqueous solution were added, and the reaction was carried out at room temperature for 3 h. After monitoring by TLC, when the reaction was completed, it was diluted with EA and washed with saturated NaCl solution. The organic phase was placed in a conical flask, and anhydrous Na 2 SO 4 was added for drying. After filtration and evaporation, a crude product with a carboxyl group oxidized at the C-28 position was obtained.

[0074] The obtained crude product was dissolved in DMF (30 mL), K 2 CO 3 (1.67 g, 9.3 mmol) and BnBr (1.4 mL, 9.3 mmol) were added, and the reaction was carried out at room temperature for 6 h. After monitoring by TLC, when the reaction was completed, it was diluted with EA and washed successively with H 2 O and saturated NaCl solution. The organic phase was placed in a conical flask, and anhydrous Na 2 SO 4 was added for drying. After filtration and evaporation, column chromatography (PE / EA = 15:1) gave white solid compound 12 (3.3 g, 82%). 11H NMR (400 MHz, Chloroform-d) δ 7.53 - 7.50 (m, 2H), 7.40 - 7.31 (m, 8H), 5.54 (s, 1H), 5.31 (t, J = 3.7 Hz, 1H), 5.14 - 5.06 (m, 2H), 4.21 - 4.14 (m, 1H), 3.95 (d, J = 10.3 Hz, 1H), 3.49 - 3.43 (m, 3H), 3.08 (dd, J = 14.0, 4.6 Hz, 1H), 2.28 (dt, J = 12.8, 3.2 Hz, 1H), 1.87 - 1.41 (m, 14H), 1.23 (s, 3H), 1.20 (s, 3H), 1.17 - 1.01 (m, 3H), 0.97 (s, 3H), 0.96 (s, 3H), 0.94 (s, 3H), 0.85 - 0.81 (m, 1H), 0.59 (s, 3H).

[0075]

[0076] Compound 12 (2.5 g, 3.7 mmol) was dissolved in DCM, and NaHCO 3 (1.26 g, 15.0 mmol) was added. Then DMP (3.17 g, 7.4 mmol) was slowly added under an ice bath, and the reaction was carried out at room temperature for 5 h. Monitored by TLC, after the reaction was completed, it was diluted with DCM, and washed with saturated Na 2 S 2 O 3 solution and saturated NaCl solution. The organic phase was placed in a conical flask, and anhydrous Na 2 SO 4 was added for drying. After filtration and evaporation, column chromatography (PE / EA = 20:1) gave the white solid compound with a ketone group oxidized at the 16th position (2.1 g, 86%).

[0077] The obtained compound above (2.1 g, 3.1 mmol) was dissolved in ethanol, and NaBH 4 (0.72 g, 18.9 mmol) was slowly added under an ice bath. The reaction was stirred at -78 °C for 4 h, then transferred to room temperature and stirred for 15 h. Monitored by TLC, after the reaction was completed, it was diluted with EA, and the reaction was slowly quenched with water under an ice bath, and then washed with saturated NaCl solution. The organic phase was placed in a conical flask, and anhydrous Na 2 SO 4 was added for drying. After filtration and evaporation and column chromatography (PE / EA = 15:1), the white product compound 13 (1.8 g, 89%) was obtained. 1 1H NMR (400 MHz, CDCl 3) δ 7.44 (dd, J = 7.8, 1.3 Hz, 1H), 7.35 (dd, J = 7.5, 1.6 Hz, 1H), 7.21 (td, J = 7.6, 1.7 Hz, 1H), 7.15 (td, J = 7.5, 1.4 Hz, 1H), 5.27 (t, J = 9.3 Hz, 1H), 5.15 (dd, J = 10.1, 9.3 Hz, 1H), 5.11 (t, J = 9.3 Hz, 1H), 4.95 (d, J = 10.1 Hz, 1H), 4.24 (dd, J = 12.3, 5.7 Hz, 1H), 4.14 (dd, J = 12.4, 2.3 Hz, 1H), 3.80 (ddd, J = 10.0, 5.8, 2.4 Hz, 1H), 2.06 (s, 3H), 2.04 (s, 3H), 2.03 (s, 3H), 2.01 (s, 3H), 1.32 (s, 9H).

[0078]

[0079] Compound 13 (1.5 g, 2.4 mmol) was dissolved in 15 mL of EAA, then 20 mL of 80 wt% AcOH was added, and the mixture was refluxed at 100 °C for 8 h. After monitoring the reaction by TLC and completion of the reaction, it was cooled to room temperature, diluted with EAA, and quenched with saturated NaHCO 3 solution. The organic phase was washed with saturated NaCl solution, placed in a conical flask, and dried over anhydrous Na 2 SO 4 and filtered. After evaporation to dryness, column chromatography (PE / EAA = 3:1) gave the white solid compound 14 (1.1 g, 85%). 1 1H NMR (400 MHz, CDCl 3 ) δ 7.39 - 7.28 (m, 5H), 5.37 (t, J = 3.6 Hz, 1H), 5.14 - 4.97 (m, 2H), 4.54 (t, J = 3.8 Hz, 1H), 3.71 (d, J = 10.4 Hz, 1H), 3.63 (dd, J = 8.9, 6.9 Hz, 1H), 3.42 (d, J = 10.3 Hz, 1H), 3.08 (dd, J = 14.4, 4.5 Hz, 1H), 2.15 (t, J = 13.7 Hz, 1H), 1.94 - 1.72 (m, 6H), 1.68 - 1.52 (m, 4H), 1.33 (s, 3H), 1.30 - 1.06 (m, 5H), 0.94 (d, J = 10.2 Hz, 6H), 0.89 (d, J = 6.7 Hz, 6H), 0.59 (s, 3H).

[0080]

[0081] Dissolve KBr (63.6 mg, 0.52 mmol) and TBACl (71 mg, 0.312 mmol) in 1 mL of saturated NaHCO 3 solution to prepare a mixed solution A. Then, prepare solution B by mixing 7 mL of 5 wt% NaClO solution, 2 mL of saturated NaCl solution, and 3 mL of saturated NaHCO 3 solution. Dissolve compound 14 (0.3 g, 0.52 mmol) in 15 mL of DCM, then sequentially add TEMPO (8.1 mg, 0.052 mmol) and solution A. Next, add 0.5 mL of solution B at 0 °C and react at this temperature. Add solution B in batches every 1 h until the reaction is complete as monitored by TLC. After the reaction is completed, dilute with DCM, wash with saturated NaCl solution, place the organic phase in a conical flask, add anhydrous Na 2 SO 4 to dry, filter by suction and rotary evaporate to dryness, and perform column chromatography (PE / EA = 4:1) to obtain white solid compound 15 (0.24 g, 81%). 1 1H NMR (400 MHz, CDCl 3 ) δ 9.40 (d, J = 1.5 Hz, 1H), 7.33 (dhept, J = 8.5, 3.5 Hz, 5H), 5.38 (d, J = 3.9 Hz, 1H), 5.17 - 4.98 (m, 2H), 4.55 (s, 1H), 3.77 (d, J = 11.1 Hz, 1H), 3.09 (dd, J = 14.6, 4.5 Hz, 1H), 2.16 (t, J = 13.7 Hz, 1H), 1.97 - 1.62 (m, 13H), 1.36 (d, J = 1.5 Hz, 3H), 1.06 (d, J = 1.6 Hz, 3H), 0.95 (dd, J = 9.1, 1.5 Hz, 6H), 0.92 - 0.90 (m, 3H), 0.59 (d, J = 1.5 Hz, 3H).

[0082]

[0083] Place compound 15 (50 mg, 0.086 mmol) and Pd / C (20 mg, 10% Pd / C) in a flask, evacuate and replace the gas for 10 min, then add 5 mL of DMF and Et 3 N (36 μL, 0.56 mmol), evacuate and replace the gas for 20 min under hydrogen protection. Then react at 40 °C overnight under hydrogen. Detect by TLC. After the reaction is completed, dilute with EA, wash with saturated NaCl solution, collect the organic phase in a conical flask, add anhydrous Na 2 SO 4 to dry, filter by suction and rotary evaporate to dryness to obtain white solid final product 16 of sapienic acid (0.24 g, 81%); 1The \(^1\)H NMR spectrum is shown in Figure 1 .

[0084] 1 \(^1\)H NMR (400 MHz, MeOD) δ 9.32 (s, 1H), 5.33 (d, J = 3.8 Hz, 1H), 4.48 (d, J = 3.8 Hz, 1H), 3.79 (dd, J = 10.9, 5.2 Hz, 1H), 3.03 (dd, J = 14.5, 4.5 Hz, 1H), 2.32 (t, J = 13.6 Hz, 1H), 2.02 - 1.67 (m, 11H), 1.66 - 1.49 (m, 3H), 1.43 (s, 3H), 1.32 (ddt, J = 20.3, 18.0, 6.0 Hz, 6H), 1.17 (dd, J = 12.3, 6.9 Hz, 3H), 1.04 - 0.97 (m, 9H), 0.91 (s, 3H), 0.82 (s, 3H).

Claims

1. A method for synthesizing saponin, characterized in that: The synthetic route is as follows: R1 is Bn, a saturated or alkyl group of C1 to C5, MOM, BOM, Fmoc, TBS, TBDPS or allyl group; R2 is an alkanoyl group, an aromatic acyl group or a silicon group; R is G represents 1 to 3 identical or different substituents, and each G is independently selected from H, F, Cl, Br, C1-C4 saturated alkyl, nitro, methoxy, acetoxy, R3 is Bn, C1-C5 saturated and alkyl, MOM, BOM, Fmoc or TBS; The specific preparation process is as follows: (1) reacting oleanolic acid to obtain compound I; (2) Compound I is reacted to obtain Compound II; (3) Compound II is reacted to obtain compound III; (4) oxidizing the C-28 hydroxyl group of compound III to an aldehyde group, and then oxidizing the C-16 methylene group to a hydroxyl group to obtain compound IV; (5) Oxidizing the C-28 position of compound IV to a carboxyl group, and then adding an R3 protecting group to obtain compound V; (6) oxidizing the C-16 hydroxyl group of compound V to a carbonyl group, and then reducing it to obtain compound VI; (7) removing the protecting group R from compound VI to obtain compound VII; (8) The C-23 hydroxyl group of compound VII is oxidized to a carbonyl group to obtain compound VIII; (9) The C-28 protecting group R3 of compound VIII is removed to obtain the target compound saponin.

2. The method for synthesizing saponin according to claim 1, characterized in that: The specific process of step (1) is as follows: S1, the 28-position carboxyl group of oleanolic acid is protected with a protecting group R1 to obtain compound I-1; S2, oxidizing the 3-hydroxyl group of compound I-1 to a carbonyl group to obtain compound I-2; S3. The 3-carbonyl group of compound I-2 is converted into an oxime group to obtain compound I.

3. The method for synthesizing saponin according to claim 1, characterized in that: The specific process of step (3) is as follows: a. removing R2 from compound II to obtain a removal product; The oxime group at the C-3 position of the product is removed to generate a carbonyl group to obtain compound III-1; b. Reducing the carbonyl group at position C-3 and the ester group at position 28 of compound III-1 to a hydroxyl group to obtain compound III-2; c. Protect the two hydroxyl groups of compound III-2 with R protecting groups to obtain compound III.

4. The method for synthesizing saponin according to claim 1, characterized in that: The process of step (4) is as follows: The hydroxyl group of compound III is oxidized to an aldehyde group to obtain compound IV-1, and the C16 position of compound IV-1 is oxidized to a hydroxyl group to obtain compound IV.

5. The method for synthesizing saponin according to claim 1, characterized in that: The specific process of step (5) is as follows: Compound IV is dissolved in an organic solvent, 2-methyl-2-butene is added, and after stirring, an aqueous solution of NaClO2 and NaH2PO4 is added. The reaction is completely carried out at room temperature, and after post-treatment, a crude product oxidized to a carboxyl group at C-28 is obtained. The crude product oxidized to a carboxyl group at C-28 is reacted with a halide of an R3 protective agent in the presence of potassium carbonate to obtain compound V. The molar ratio of compound IV, 2-methyl-2-butene, NaClO2 and NaH2PO4 is 1:(9-11):(4-6):(6-8); the molar ratio of the crude product oxidized to a carboxyl group at C-28, potassium carbonate and the halide of an R3 protective agent is 1:(1-2):(1-2).

6. The method for synthesizing saponin according to claim 1, characterized in that: The specific process of step (6) is: compound V is reacted with DMP in the presence of NaHCO3 to obtain a compound oxidized to ketone at C-16, and the compound oxidized to ketone at C-16 is reacted with NaBH4 at -50 to -80°C to obtain compound VI, wherein the molar ratio of compound V, NaHCO3 and DMP is 1:(3 to 5):(1 to 3).

7. The method for synthesizing saponin according to claim 1, characterized in that: The specific process of step (8) is as follows: KBr and TBACl are dissolved in a saturated NaHCO3 solution to prepare a mixed solution A, and then (2 to 8) wt% NaClO solution, a saturated NaCl solution, and a saturated NaHCO3 solution are prepared to prepare a solution B; compound VII is dissolved in an organic solvent, and then TEMPO and solution A are added in sequence, and then solution B is added at -5 to 5°C, and reacted at this temperature, and solution B is added in batches every 0.5h to 1.5h until the reaction is complete as monitored by TLC.

8. The method for synthesizing saponin according to claim 7, characterized in that: The molar ratio of compound VII, KBr, TBACl and TEMPO is 1:(1-1.5):(0.5-0.7):(0.1-0.2); the concentration of KBr in saturated NaHCO3 solution is 0.5-0.6 mmol / mL, the volume ratio of NaClO solution, saturated NaCl solution and saturated NaHCO3 in solution B is (6-8):(1-3):(2-4); the volume ratio of solution A, solution B and organic solvent is 1:(10-15):(13-17), and the amount of solution B added each time is 0.5-1 mL.

9. The method for synthesizing saponin according to claim 3, characterized in that: The process of step a is as follows: Compound II is de-R2ed in the presence of a base, the de-R2ed product is dissolved in a solvent, NH4OAc is added thereto, and then a hydrochloric acid solution of TiCl3 is added, and the reaction is completed at room temperature to obtain compound III-1, wherein the molar ratio of the de-R2ed product, NH4OAc and TiCl3 is 1:(9-11):(1-3); The process of step b is as follows: dissolving compound III-1 in an organic solvent, adding LAH for reduction to obtain compound III-2, wherein the molar ratio of LAH to LAH is 1:(2-3); The process of step c is as follows: Compound III-2 is reacted with an alkoxy group or chloride of RCH in the presence of TsOH to obtain compound III, and the molar ratio of compound III-2, TsOH and the alkoxy group or chloride of RCH is 1:(0.4-0.6):(0.4-0.6):(0.2-0.5).

10. The method for synthesizing saponin according to claim 4, characterized in that: Compound III is reacted with IBX in an organic solvent to obtain compound IV-1. Compound IV-1 is reacted with (S)-DG in the presence of TsOH to obtain a crude imine product. The crude imine product is dissolved in a solvent, Cu(OTf)2 and sodium L-ascorbate are added, oxygen is bubbled into the system after the system changes color, and the reaction is completed at 45-55°C after the system changes color. The reaction is quenched with a Na4EDTA solution, and post-processed to obtain compound IV, wherein the structure of (S)-DG is The molar ratio of compound III and oxidant IBX is 1:(1-3); the molar ratio of compound IV-1, TsOH and (S)-DG is 1:(0.1-0.2):(2-4); the molar ratio of crude imine, Cu(OTf)2 and sodium L-ascorbate is 1:(1-1.5):(1-3).

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