WO2018145578A1

WO2018145578A1 - Method for synthesizing astragaloside iv

Info

Publication number: WO2018145578A1
Application number: PCT/CN2018/074149
Authority: WO
Inventors: 孙建松; 廖进喜; 刘婷
Original assignee: 江西师范大学
Priority date: 2017-02-07
Filing date: 2018-01-25
Publication date: 2018-08-16
Also published as: CN106831927A; CN106831927B

Abstract

Disclosed is a method for synthesizing astragaloside IV, comprising the following steps: protecting hydroxyl groups at the 3-position and 6-position of cycloastragenol using protecting groups R1; after protecting hydroxyl groups at the 16-position and 25-position using protecting groups R2, removing the protecting groups R1 at the 3-position and 6-position to obtain a compound 4; protecting a hydroxyl group at the 3-position of the compound 4 using a protecting group R3 to obtain a compound 5; performing glycosidation on the compound 5, then removing the protecting group R3 at the 3-position, and continuing performing glycosidation to obtain a compound 8; and removing all protecting groups to obtain astragaloside IV. The present invention implements highly-efficient and highly-stereoselective preparation of astragaloside IV, fills the gap in the prior art, and greatly pushes the process of the research in the mechanism of the activity astragaloside compounds and the development of drugs thereof forward.

Description

Method for synthesizing astragaloside IV

Technical field

The invention belongs to the field of chemical synthesis, and more particularly relates to a preparation method of astragaloside IV.

Background technique

Astragalus is the first of the tonics and belongs to the genus Astragalus. In recent years, with the development of modern separation and identification techniques, a large number of triterpenoid saponins, flavonoids and polysaccharides have been isolated from Astragalus. Later biochemical experiments showed that the medicinal effects of Astragalus membranaceus were mainly expressed by Astragalus saponins. Recent studies have shown that xanthine saponins have shown promising medicinal prospects in immunomodulation, hypoglycemic, insulin resistance, anti-tumor, cardiovascular system regulation, antiviral and antioxidant activities, and in many jaundices. Among the saponins, the activity of astragaloside IV and isoflavone is the best.

Although the wide application prospect of Astragalus saponins has prompted people to deepen their research, the current Astragalus saponins used for activity testing are mostly isolated and extracted from Astragalus membranaceus. Because of the variety of saponins contained in Astragalus membranaceus and similar structure, this provides separation and purification. It brings great difficulties. There are also some astragalosides, which are secondary saponins, which are very low in Astragalus. It is not easy to obtain sufficient amount for the activity test. This has become a bottleneck restricting the activity of Astragalus saponins. Report on the chemical synthesis of astragaloside.

Astragaloside IV is particularly low in Astragalus membranaceus, its structural formula is shown in Formula I, and its saponin part is cycloxanthine. It has 4 positions in 6-position, 6-position, 16-position and 25-position of cyclodextrose (Compound 1). The inert OH, especially the hydroxyl group at position 25, has a low activity of the tertiary hydroxyl group, the glycosidation reaction is difficult, and the reactivity of the four inert OHs before each other is indistinguishable, and selective glycosidation of some of the hydroxyl groups is more difficult.

The hydroxyprotective reaction of cycloxanthine is difficult and the product is complex and variable. It has been reported in the literature that under the action of excess acetylating reagent, only 60% yield of peracetylation can be obtained at 60 ° C for up to 50 days. Ring of xanthanol. Shortening the reaction time or lowering the reaction temperature results in a very complicated reaction product, which is a random 1 or 2 hydroxyl group protected cycloxanthine in 4 hydroxyl groups.

The methods commonly used in the literature for the protection of large sterically hindered, inert hydroxy groups also do not work in the protection of cycloxanthine, such as the Lewis acid catalyzed acetylation reaction without the selective protection of cycloxanthine.

This shows that the synthesis of astragaloside IV is difficult, and there have been no successful reports at home and abroad.

References: a) Mamedova, RP; Agzamova, MA; Isaev, MIChem. Nat. Compd. 2001, 37, 533-536.b) Isaev, IM; Iskenderov, DA; Isaev, MIChem. Nat. Compd. , 45, 381-384.c) Isaev, IM; Iskenderov, DA; Isaev, MIChem. Nat. Compd. 2010, 46, 407-411.d) Procopiou, PA; Baugh, SPD; Flack, SS; Inglis, GGJOrg.Chem.1998, 63, 2342-2347.

Summary of the invention

OBJECT OF THE INVENTION The technical problem to be solved by the present invention is to provide a highly efficient and highly selective chemical synthesis method of astragaloside IV, which provides sufficient raw materials for the research and application of astragaloside IV, and provides a reference for the synthesis of baicalin compounds. .

Technical Solution: In order to solve the above technical problems, the technical solution adopted by the present invention is:

A method for synthesizing astragaloside IV, comprising the following steps:

(1) protecting the 3-position and 6-position hydroxyl groups of cycloxanthine 1 with a protecting group R1 to obtain a compound 2;

(2) protecting the 16th and 25th hydroxyl groups of compound 2 with a protecting group R ^{2 to} give compound 3;

(3) removing the 3-position and 6-position protecting group R ^{1 of} compound 3 to obtain compound 4;

(4) protecting the 3-hydroxyl group of compound 4 with a protecting group R ^{3 to} give compound 5;

(5) glycosidation reaction of compound 5 with glycosyl donor compound 9 to obtain compound 6;

(6) The 3-position protecting group R ^{3 of} compound 6 is removed to obtain compound 7;

(7) a compound 7 and a glycosyl donor compound 10 glycosidation reaction to obtain a compound 8;

(8) removing all protecting groups of compound 8 to obtain astragaloside IV;

Wherein R ^{1 is} selected from substituted or unsubstituted C ² -C 6 alkanoyl; said R ^{2 is} selected from substituted or unsubstituted C ² -C 6 alkanoyl; said R ^{3 is} selected from substituted or unsubstituted C 1 -C 9 Alkylsilyl; said R ⁴ or R ⁵ are each independently selected from a C 1 -C 6 aroyl group; said X is selected from a substituted or unsubstituted alkynyloxy group, preferably, said R ¹ is a Lev; R ² is Ac; the R ^{3 is} selected from TBS, TES, TBDMS, TBDPS, DIPS, DPS or TIPDS; the R ⁴ or R ⁵ is Bz;

In the step (1), the method for protecting comprises the steps of: dissolving cycloxanthine 1, DMAP and levulinic acid in a first solvent at 0 ° C, adding DCC, slowly raising the reaction temperature to room temperature, stirring Until the TLC tracking shows that the cycloxanthine reaction is complete; the first solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane, pyridine, One or more of tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably dichloromethane; the molar ratio of the cycloxanthine, DMAP, levulinic acid and DCC is 1: 1.2:5:5 to 1:2:10:10, preferably 1:2:5:5 to 1:2:10:10; the concentration of the cycloxanthine in the first solvent is 0.05 to 1 mol /L is preferably 0.05 to 0.068 mol/L.

In the step (2), the method for protecting comprises the steps of: dissolving compound 2 and PPy in a second solvent below 0 ° C, adding acetic anhydride, DIPEA, slowly raising the reaction temperature to room temperature, and then heating to 100. ～120°C, preferably 105～110°C, stirring is continued until TLC tracking shows that compound 2 is completely reacted; the second solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF One or more of toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably toluene; The molar ratio of PPy, acetic anhydride and DIPEA is 1:1.5:8:12 to 1:2:15:20, preferably 1:2:10:15 to 1:2:15:20; The concentration in the second solvent is 0.1 to 1 mol/L, preferably 0.108 to 0.5 mol/L.

In the step (3), the method for removing the protecting group R ¹ comprises the steps of: dissolving the compound 3 in a third solvent below 0 ° C, adding cerium acetate, slowly raising the reaction temperature to room temperature, and stirring until TLC The trace shows that the compound 3 is completely reacted; the third solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, One or more of tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably a mixed solvent of pyridine and acetic acid, the volume ratio of the pyridine to acetic acid is 1:1 to 5 :1, preferably from 1.5:1 to 3:1; the molar ratio of the compound 3 to cerium acetate is from 1:15 to 1:40, preferably from 1:20 to 1:27; the compound 3 is in the third solvent. The concentration is 0.05 to 1.5 mol/L, preferably 0.092 to 0.2 mol/L.

In the step (4), the method for protecting comprises the steps of: dissolving the compound 4 in a fourth solvent at 0 ° C, adding a halosilane and an imidazole, slowly raising the reaction temperature to room temperature, and stirring until TLC tracking shows Compound 4 is completely reacted; the fourth solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, One or more of triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably DMF; the molar ratio of the compound 4, halosilane and imidazole is 1:2:3~1 5:10, preferably 1:2:3 to 1:4:6; the concentration of the compound 4 in the fourth solvent is 0.1 to 1 mol/L, preferably 0.45 to 0.5 mol/L, the halogenation The silane is selected from the group consisting of TBSCl, TESCl, TBDMSCl, TBDPSCl, DIPSCl, DPSCl or TIPDSCl.

In the step (5), the glycosidation reaction comprises the steps of: dissolving the compound 5 and the glycosyl donor compound 9 in a fifth solvent under the protection of an inert gas, adding a desiccant, and stirring at room temperature for 0.5 to 2 The catalyst was further added in an hour and continued to stir at room temperature until the TLC trace showed that the compound 5 was completely reacted; the fifth solvent was selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, One or more of benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably dichloromethane; the catalyst is selected from a monovalent gold complex, preferably PPh ₃ AuNTf ₂ or PPh ₃ AuOTf; the desiccant is selected from molecular sieves, preferably

Molecular sieve or pickled

The molecular sieve, more preferably 4A molecular sieve; the molar ratio of compound 5, glycosyl donor compound 9 to the catalyst is 1:1:0.1 to 1:5:0.8, preferably 1:1:1:1 to 1:2: 0.5, the concentration of the compound 5 in the fifth solvent is 0.001 to 1 mol/L, preferably 0.006 to 0.05 mol/L.

In the step (6), the reaction of removing the protecting group R ³ comprises the steps of: dissolving the compound 6 in the sixth solvent, adding camphorsulfonic acid at room temperature, stirring until TLC tracking shows that the compound 6 is completely reacted; The solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, One or more of acetone, methanol, ethanol, DMSO or diethyl ether, preferably methanol; the molar ratio of the compound 6 to camphorsulfonic acid is from 1:1 to 1:10, preferably from 1:1 to 1:4. The concentration of the compound 6 in the sixth solvent is 0.001 to 1 mol/L, preferably 0.001 to 0.004 mol/L.

In the step (7), the glycosidation reaction comprises the steps of dissolving the compound 7 and the glycosyl donor compound 10 in a seventh solvent, adding a desiccant, stirring at room temperature for 0.5 to 2 hours, and then adding a catalyst to continue. Stir at room temperature until TLC tracking shows that compound 7 is completely reacted; the seventh solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane One or more of pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably dichloromethane; the catalyst is selected from the complexation of monovalent gold a substance, preferably PPh ₃ AuNTf ₂ or PPh ₃ AuOTf; the desiccant is selected from the group consisting of molecular sieves, preferably

Molecular sieve or pickled

More preferably, the molecular sieve is 4A molecular sieve; the molar ratio of the compound 7, the glycosyl donor compound 10 to the catalyst is 1:1:0.1 to 1:5:0.8, preferably 1:1:0.1 to 1:2.5: 1; The concentration of the compound 7 in the seventh solvent is 0.001 to 1 mol/L, preferably 0.001 to 0.003 mol/L.

In the step (8), the reaction of removing the protecting group comprises the steps of dissolving the compound 8 in the eighth solvent, adding a base, and stirring at room temperature until TLC tracking shows that the compound 8 is completely reacted; the base is selected from the group consisting of methanol Sodium, sodium hydroxide, potassium carbonate, potassium hydroxide, preferably sodium methoxide; the eighth solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene One or more of dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, preferably methanol.

Preferably, any of steps (1) to (8) is carried out under inert gas protection conditions selected from nitrogen, argon or helium.

In the step (1), when the molar ratio of xanthanol, levulinic acid and DCC is 1:2.5:2.5, a mixture of compounds partially or completely protected by the 3-position of the cycloxanthine and the hydroxyl group at the 6-position is obtained.

In the step (2), the TLC tracking shows that the reaction of the compound 2 is completed in about 2 hours, and the reaction rate, the reaction yield and the reaction selectivity are greatly improved compared with the prior art.

Advantageous Effects: The present invention efficiently and highly stereoselectively prepares astragaloside IV, fills the gap of the prior art, and is a scutellaria saponin, which will greatly advance the activity mechanism of the saponin compound and the progress of drug development.

detailed description

The invention can be better understood in light of the following examples. However, those skilled in the art will understand that the description of the embodiments is only intended to illustrate the invention and should not be construed as limiting the invention as described in the claims.

In the present invention, PPy represents 4-pyrrolidinopyridine (English name: 4-(1-pyrrolidino)-pyridine), DMAP represents 4-dimethylaminopyridine, DCC represents dicyclohexylcarbodiimide, and DIPEA represents N. N-diisopropylethylamine; the purity of the product obtained in each of the following steps is relatively high, and no impurity peak is observed in the 400 M nuclear magnetic resonance spectrum.

Bz protected sugars 11 and 12 are synthesized according to conventional methods in the art:

The synthesis of Compound 9-1 is as follows:

Under nitrogen protection, all-Bz-glucose (100 mg, 0.17 mmol) exposed to anomeric hydroxyl groups was dissolved in dry dichloromethane (4 mL), and o-ynylbenzoic acid (37.4 mg, 0.2 mmol) was added to the system. DMAP (28.1 mg, 0.23 mmol), EDCI (43.9 mg, 0.23 mmol), DIPEA (74 μL), stirring at room temperature overnight until TLC tracking showed that the starting material was completely reacted, and the reaction system was extracted with dichloromethane, and then 1 mol/l. HCl, saturated sodium bicarbonate, washed with saturated NaCl, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure and the crude product, then column chromatography to give a white solid compound 9-1 (121mg, 93%): 1 H NMR (400MHz, CDCl ₃ ) δ ¹ H NMR (400MHz, CDCl ₃ ) δ 8.07 (d, J = 7.5 Hz, 2H), 7.92 - 7.87 (m, 6H), 7.44 - 7.28 (m, 17H), 6.94 (d, J) =3.3 Hz, 1H), 6.38 (dd, J = 9.6, 9.9 Hz, 1H), 5.94 (dd, J = 9.9, 10.2 Hz, 1H), 5.76 (dd, J = 3.3, 9.9 Hz, 1H), 4.80 -4.66 (m, 2H), 4.54 (dd, J = 3.3, 6.0 Hz, 1H), 1.56 (m, 1H), 0.84 (d, J = 6.6 Hz, 4H).

The synthesis of Compound 10-1 is as follows:

Similarly to the synthesis of compound 9-1, a white solid compound 10-1 (612 mg, 89%) was obtained from the all-Bz-glucose exposed to the anomeric hydroxyl group: [α] _D ²⁵ = 0.02 (c 1.0, CHCl ₃ ); ¹ H NMR (400MHz, CDCl ₃ ) δ 8.04-7.98 (m, 6H), 7.90 (dd, J = 1.2, 8.0 Hz, 1H), 7.58-7.51 (m, 3H), 7.49-7.42 (m, 2H), 7.38 -7.30 (m, 6H), 7.21 (td, J = 1.6, 7.6 Hz, 1H), 6.42 (d, J = 7.6 Hz, 1H), 5.81 (t, J = 5.2 Hz, 1H), 5.58 (dd, J=4.0, 5.2 Hz, 1H), 5.36-5.32 (m, 1H), 4.63 (dd, J=3.6, 12.8 Hz, 1H), 4.06 (dd, J=4.8, 12.4 Hz, 1H), 1.54-1.47 (m, 1H), 0.90-0.84 (m, 4H); ¹³ C NMR (100MHz, CDCl ₃ ) δ 164.9, 164.4, 164.3, 163.3, 133.7, 132.8, 129.9, 129.7, 129.4, 129.3, 128.5, 128.3, 127.8(2C),126.3,124.7,99.7,91.4,73.6,67.8,67.6,67.2,60.9,8.2,-0.0;HRMS(ESI-TOF)m/z:[M+H] ⁺ calcd for C ₃₈ H ₃₁ O ₉ 631.1968; found 631.1966.

Example 1. Synthesis of astragaloside IV

(1) Synthesis of 3, 6-hydroxy protected cycloxanthine derivative 2

In a nitrogen atmosphere, at 0 ° C, cycloxanol (300 mg, 0.61 mmol), DMAP (160 mg, 1.22 mmol) and levulinic acid (350 mg, 3.06 mmol) were dissolved in dry dichloromethane (9 mL). DCC (630 mg, 3.06 mmol) was added to the system, the system was slowly warmed to room temperature, stirred until the TLC trace showed that the starting material was completely reacted, and the reaction system was extracted with ethyl acetate, and sequentially diluted with 1 mol/l HCl, saturated sodium hydrogen carbonate, and saturated. NaCl, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure and the crude product, then column chromatography to give a white solid compound 2 (413mg, 98.3%): [α] D 25 = 39.6 (c = 1, CHCl 3); ^{_{1 H NMR (400MHz, CDCl 3}} ) δ4.78 (td, J = 4.8,9.2Hz, 1H), 4.71 (dd, J = 7.6,14.4Hz, 1H), 4.60 (dd, J = 4.4,10.8Hz, 1H), 3.77 (t, J = 7.2 Hz, 1H), 3.52-3.45 (m, 1H), 2.77-2.70 (m, 4H), 2.59 (t, J = 6.4 Hz, 2H), 2.51 (t, J = 6.8 Hz, 2H), 2.34 (d, J = 7.6 Hz, 1H), 2.19 (s, 3H), 2.18 (s, 3H), 2.01-1.88 (m, 6H), 1.30 (s, 3H), 1.24 (s, 3H), 1.22 (s, 3H), 1.15 (s, 3H), 0.99 (s, 3H), 0.94 (s, 3H), 0.87 (s, 3H), 0.60 (d, J = 4.8 Hz) , 1H), 0.34 (d, J = 4.4 Hz, 1H); ¹³ C NMR (100 MHz, CDCl ₃ ) δ 206.6, 206.4, 172.4, 172.0, 87.0, 81.4, 79.9, 73.3, 71.7, 70.7, 57.3, 49.7 , 49.2, 45.9, 45.8, 45.1, 44.7, 40.2, 38.1, 37.8, 34.4, 33.9, 33.0, 32.7, 31.4, 29.8, 28.8, 28.4, 28.2, 27.8, 27.7, 26.5 (2C), 25.8, 25.6 (2C) , 24.9, 20.8, 20.7, 19.7, 16.3; HRMS (ESI) calcd for C ₄₀ H ₆₂ O ₉ Na[M+Na] ⁺ 709.4286, found 709.4288.

(2) Synthesis of a fully hydroxyl protected cycloxanthine derivative 3

Under nitrogen protection, 0 ° C, compound 2, PPy was dissolved in dry toluene, then acetic anhydride, DIPEA was added to the system, the system was slowly warmed to room temperature and then heated to 105 ° C, stirred until TLC tracking showed complete reaction of the raw materials. The reaction system was extracted with ethyl acetate and washed successively with 1 mol/l HCl, saturated sodium hydrogen carbonate and saturated NaCl, dried over anhydrous sodium sulfate, filtered, filtered, and then evaporated. 3 (yield: 84%): [α] _D ²⁵ = 63.2 (c = 1, CHCl ₃ ); ¹ H NMR (400 MHz, CDCl ₃ ) δ 5.35-5.30 (m, 1H), 4.74 (td, J = 4.4, 9.2 Hz, 1H), 4.60 (dd, J = 4.8, 11.2 Hz, 1H), 4.02 (t, J = 7.6 Hz, 1H), 2.77 - 2.69 (m, 4H), 2.59 (t, J = 6.4 Hz, 2H), 2.50 (t, J = 6.8 Hz, 2H), 2.43 (d, J = 8.0 Hz, 1H), 2.19 (s, 3H), 2.18 (s, 3H), 2.01 (s, 3H) , 1.96 (s, 3H), 1.43 (s, 3H), 1.41 (s, 3H), 1.323 (s, 3H), 1.316 (s, 3H), 0.98 (s, 3H), 0.96 (s, 3H), 0.88 (s, 3H), 0.60 (d, J = 4.8 Hz, 1H), 0.37 (d, J = 4.8 Hz, 1H); ¹³ C NMR (100 MHz, CDCl ₃ ) δ 206.5, 206.3, 172 .3,172.1,170.4,170.2,85.5,83.0,81.2,79.8,75.8,70.7,57.4,49.8,46.4,46.2,45.4,45.1,40.2,38.0,37.8,37.3,32.8,32.2,31.3,29.8,29.3 , 28.7, 28.4, 28.3, 26.9, 26.6, 26.5, 26.1, 26.0, 22.8, 22.5, 21.6, 21.5, 20.7, 20.3, 20.0, 16.2; HRMS (ESI) calcd for C ₄₄ H ₆₆ O ₁₁ Na [M+Na ] ⁺ 793.4497, found 793.4496.

(3) Synthesis of 16,25-hydroxyl-protected cycloxanthine derivatives 4

Compound 3 (530 mg, 0.69 mmol) was dissolved in dry pyridine and acetic acid (7.5 mL, v/v = 1.5:1) under nitrogen atmosphere at 0 ° C, and then acetic acid (0.9 mL) was added to the system. 18.6mmol), the system was slowly warmed to room temperature and then stirred until the TLC trace showed that the reaction of the starting material was complete. The reaction was extracted with ethyl acetate and washed sequentially with 1 mol/l HCl, saturated sodium hydrogen carbonate, saturated NaCl and dried over anhydrous sodium sulfate. After suction filtration, the crude product was concentrated under reduced pressure and then purified to afford white crystals Compound 4 (yield: 99%): [α] _D ²⁵ = 59.0 (c = 1, CHCl ₃ ); ¹ H NMR (400 MHz, CDCl) ₃ ) δ 5.36-5.30 (m, 1H), 4.02 (t, J = 7.2 Hz, 1H), 3.56 (td, J = 3.2, 9.2 Hz, 1H), 3.33 (dd, J = 4.8, 11.2 Hz, 1H), 2.43 (d, J = 8.0 Hz, 1H), 2.26-2.13 (m, 2H), 2.02 (s, 3H), 1.97 (s, 3H), 1.43 (s, 3H), 1.42 (s, 3H) ), 1.34 (s, 3H), 1.33 (s, 3H), 1.25 (s, 3H), 0.98 (s, 3H), 0.96 (s, 3H), 0.52 (d, J = 4.0 Hz, 1H), 0.37 (d, J = 4.4 Hz, 1H); ¹³ C NMR (100 MHz, CDCl ₃ ) δ 170.5, 170.3, 85.6, 83.1, 81.3, 78.3, 75.9, 68.8, 57.6, 53.6, 46. 6,46.4,46.3,41.5,37.6,37.3,32.3,32.0,30.8,30.2,29.4,28.0,27.0,26.2,26.0,22.8,22.5,21.6,20.8,20.6,20.2,15.2; HRMS(ESI)calcd for C ₃₄ H ₅₄ O ₇ Na[M+Na] ⁺ 597.3762,found 597.3764.

Synthesis of (4) hydroxy-exposed cycloxanthine derivative 5

Compound 4 was dissolved in dry DMF under nitrogen atmosphere at 0 ° C. Then, TBSCl, imidazole was added to the system, and the system was slowly warmed to room temperature and stirred until TLC tracking showed that the starting material was completely reacted, and the reaction system was extracted with ethyl acetate. It was washed with 1 mol/l HCl, saturated sodium hydrogencarbonate and saturated NaCl, dried over anhydrous sodium sulfate, filtered, filtered, and then evaporated. α] _D ²⁵ =81.8 (c=1, CHCl ₃ ); ¹ H NMR (400 MHz, CDCl ₃ ) δ 5.36-5.31 (m, 1H), 4.02 (t, J = 7.2 Hz, 1H), 3.55 (td) , J=4.0, 9.2 Hz, 1H), 3.28 (dd, J=4.8, 10.0 Hz, 1H), 2.44 (dd, J=7.6 Hz, 1H), 2.58-2.15 (m, 2H), 2.02 (s, 3H), 1.97 (s, 3H), 1.43 (s, 3H), 1.42 (s, 3H), 1.33 (s, 6H), 1.15 (s, 3H), 0.98 (s, 3H), 0.92 (s, 3H) ), 0.89 (s, 9H), 0.50 (d, J = 4.4 Hz, 1H), 0.33 (d, J = 4.4 Hz, 1H); ¹³ C NMR (100 MHz, CDCl ₃ ) δ 170.5, 170.2, 85.6, 83.1, 81.4, 78.8, 75.9, 68.6, 57.6, 53.7, 46.5, 46.3, 46.2, 45.6, 42.0, 37.4, 37.2, 32.3, 31.9, 30.8, 30.4 , 29.7, 29.2, 28.4, 26.9, 26.1, 26.0, 25.9, 22.8, 22.5, 21.6, 20.7, 20.5, 20.1, 18.1, 15.7, -3.8, -4.9; HRMS (ESI) calcd for C ₄₀ H ₆₉ O ₇ Si [M+H] ⁺ 689.4807, found 689.4808.

(5) Synthesis of 6-hydroxyglycosylation product 6

Compound 5 and glucanyl ester donor were dissolved in dry dichloromethane under nitrogen, and added to 4A molecular sieve. Stir at room temperature for half an hour and then add catalyst Ph ₃ PAuOTf, continue to stir at room temperature until TLC tracking The reaction of the starting material was shown to be complete. The crude product was concentrated under reduced pressure and then purified to afford white solid compound 6 (yield: 79.6%): [α] _D ²⁵ =72.6 (c=1, CHCl ₃ ); ¹ H NMR (400 MHz, CDCl ₃ ) δ8.00-7.95 (m, 4H), 7.91 (dd, J = 1.2, 8.4 Hz, 2H), 7.85 (dd, J = 1.2, 8.0 Hz, 2H), 7.56-7.48 (m, 3H) , 7.44 - 7.33 (m, 7H), 7.30-7.27 (m, 2H), 5.92 (t, J = 9.6 Hz, 1H), 5.58 (t, J = 10.0 Hz, 1H), 5.50 (dd, J = 8.0 , 10.0 Hz, 1H), 5.29-5.26 (m, 1H), 5.20 (d, J = 8.0 Hz, 1H), 4.74 (td, J = 4.0, 9.2 Hz, 1H), 4.60-4.56 (m, 2H) , 4.47 (dd, J = 6.8, 12.0 Hz, 1H), 4.16-4.11 (m, 1H), 3.70 (t, J = 7.2 Hz, 1H), 2.41 (d, J = 8.0 Hz, 1H), 2.18 ( Dd, J=8.0, 14.0 Hz, 1H), 2.05 (s, 3H), 2.00 (s, 3H), 1.97 (s, 3H), 1.30 (s, 3H), 1.22 (s, 3H), 1.16 (s) , 3H), 1.12 (s, 3H), 0.98 (s, 3H), 0. 97 (s, 3H), 0.86 (s, 3H), 0.60 (d, J = 4.8 Hz, 1H), 0.38 (d, J = 4.8 Hz, 1H); ¹³ C NMR (100 MHz, CDCl ₃ ) δ 170.8 , 170.4, 170.2, 166.0, 165.9, 165.3, 164.9, 133.4, 133.2, 133.1, 129.8 (2C), 129.7 (2C), 129.6, 128.9 (2C), 128.4 (2C), 128.3, 96.1, 85.8, 82.7, 80.0 , 79.6, 76.0, 73.2, 72.1, 72.0, 70.5, 70.3, 63.8, 57.6, 49.8, 46.4, 46.3, 45.6, 45.4, 40.1, 37.4, 33.2, 32.2, 31.4, 29.8, 29.7, 28.6, 26.7, 26.6 (2C ), 25.9, 23.2, 22.2, 21.8, 21.5, 21.2, 20.6, 20.4, 20.1, 16.3; HRMS (ESI) calcd for C ₇₀ H ₈₂ O ₁₇ Na[M+Na] ⁺ 1217.5444, found 1217.5447.

(6) Synthesis of 3-hydroxyl-exposed compound 7

Compound 6 was dissolved in dry methanol under nitrogen atmosphere, and camphorsulfonic acid was added at room temperature, stirred until TLC tracking showed that the starting material was completely reacted, and the crude product was concentrated under reduced pressure. : 83.5%): [α] _D ²⁵ = 21.5 (c = 1, CHCl ₃ ); ¹ H NMR (400 MHz, CDCl ₃ ) δ 7.57-7.46 (m, 4H), 7.43-7.32 (m, 7H), 7.28 (m, 1H), 5.90 (t, J = 9.6 Hz, 1H), 5.62 (t, J = 10.0 Hz, 1H), 5.54 (dd, J = 8.0, 9.6 Hz, 1H), 5.36-5.31 (m) , 1H), 4.98 (d, J = 8.0 Hz, 1H), 4.60 (dd, J = 2.8, 12.0 Hz, 1H), 4.50 (dd, J = 6.8, 12.0 Hz, 1H), 4.19-4.14 (m, 1H), 3.99 (t, J = 7.2 Hz, 1H), 3.56-3.51 (m, 1H), 3.11 (dd, J = 4.4, 10.4 Hz, 1H), 2.38 (d, J = 8.0 Hz, 1H), 2.26 (dd, J=8.0, 13.6 Hz, 1H), 1.98 (s, 3H), 1.97 (s, 3H), 1.43 (s, 3H), 1.41 (s, 3H), 1.29 (s, 3H), 1.26 (s, 3H), 1.14 (s, 3H), 0.92 (s, 3H), 0.78 (s, 3H), 0.76 (s, 3H), 0.45 (d, J = 4.4 Hz, 1H), 0.15 (d, ^{J = 4.4Hz, 1H); 13} C NMR (100MHz, CDCl 3) δ170.5,170.0,165.8,165.2,165.0,133.4 133.1(2C), 129.9, 129.8, 129.7 (2C), 129.4, 128.9, 128.4, 128.2, 101.3, 85.6, 83.2, 81.7, 78.8, 78.0, 75.5, 73.8, 72.5, 72.4, 70.0, 63.8, 57.5, 50.7, 46.5, 46.1, 44.5, 44.0, 41.2, 38.8, 32.8, 32.4, 31.3, 29.8, 29.7, 28.3, 27.4, 26.7, 26.9, 26.7, 26.0 (2C), 22.9, 22.6, 21.6, 21.5, 21.0, 19.6, 19.5 , 15.3; HRMS (ESI) calcd for C ₆₈ H ₈₁ O ₁₆ [M+H] ⁺ 1153.5519, found 1153.5523.

(7) Synthesis of 3,6-hydroxyglycosylation products 8

Compound 7 and xyloyl alkyl ester donor were dissolved in dry dichloromethane under nitrogen, and added to 4A molecular sieve. Stir at room temperature for half an hour and then add catalyst Ph ₃ PAuOTf, continue stirring at room temperature until TLC The reaction showed that the starting material was completely reacted, and the crude product was concentrated under reduced pressure, and then purified by column chromatography to yield Compound 8 (yield: 79.5%) as a white solid: [α] _D ²⁵ = -4.1 (c = 1, CHCl ₃ ); ¹ H NMR ( 400MHz, CDCl ₃ ) δ8.00-7.90 (m, 12H), 7.84 (dd, J = 1.2, 8.0 Hz, 2H), 7.67-7.63 (m, 1H), 7.61 (m, 1H), 7.56-7.51 ( m, 4H), 7.48-7.33 (m, 13H), 7.30 (m, 2H), 5.90 (t, J = 9.6 Hz, 1H), 5.65 (t, J = 8.0 Hz, 1H), 5.60 (t, J =10.0 Hz, 1H), 5.55 (dd, J=8.0, 10.0 Hz, 1H), 5.40-5.34 (m, 1H), 5.30 (dd, J=6.4, 8.0 Hz, 1H), 5.25-5.20 (m, 1H), 4.86 (d, J = 7.6 Hz, 1H), 4.58 (dd, J = 3.2, 12.0 Hz, 1H), 4.49 (dd, J = 7.2, 12.0 Hz, 1H), 4.35 (dd, J = 4.8) , 11.6 Hz, 1H), 4.20 (d, J = 6.4 Hz, 1H), 4.16-4.11 (m, 1H), 3.99 (t, J = 7.2 Hz, 1H), 3.40 (dd, J = 8.0, 11.6 Hz) , 1H), 3.01 (dd, J=4.4, 11.2Hz, 1H), 2.43 (d, J = 8.0 Hz, 1H), 2.31 (dd, J = 8.0, 13.6 Hz, 1H), 1.98 (s, 3H), 1.96 (s, 3H), 1.43 (s, 3H), 1.41(s,3H), 1.30(s,3H), 1.12(s,3H),0.98(s,3H),0.56(s,3H),0.55(s,3H),0.37(d,J=4.4Hz , 1H), 0.03 (d, J = 4.8 Hz, 1H); ¹³ C NMR (100 MHz, CDCl ₃ ) δ 170.5, 170.0, 165.9, 165.8, 165.6, 165.5, 165.2, 164.9 (2C), 102.4, 101.6, 87.3, 85.8, 83.2, 81.8, 77.7, 75.5, 73.1, 72.2, 70.9, 70.7, 70.2, 69.7, 63.9, 61.7, 57.4, 50.6, 46.6, 46.0, 43.8, 41.6, 37.8, 32.5, 31.9, 31.1, 31.0, 29.7(2C), 29.4, 28.7, 27.1, 26.9, 26.7, 26.0, 23.9, 22.9, 22.7, 22.6, 21.6, 21.5, 21.0, 19.0, 18.9, 15.6, 14.1; HRMS (ESI) calcd for C ₉₄ H ₁₀₄ O ₂₃ N[M+NH ₄ ] ⁺ 1614.69937.found 1614.70085.

(8) Synthesis of astragaloside IV

Under the protection of nitrogen, compound 8 was dissolved in dry methanol, then sodium methoxide was added, and stirred at room temperature until TLC tracking showed that the reaction of the starting material was complete. The pH was neutralized with acidic resin to neutral neutral acidity, suction filtration and concentration under reduced pressure. The crude product was then subjected to column chromatography to give a white solid compound as a saponin (yield: 75.6%): [α] _D ²⁵ = 16.3 (c = 0.4, CH ₃ OH); ¹ H NMR (400 MHz, C ₅ D ₅ N ) δ 6.55 (bs, 1H), 5.81 (d, J = 2.8 Hz, 1H), 4.93 (d, J = 8.0 Hz, 1H), 4.88 (d, J = 7.2 Hz, 1H), 4.52 (dd, J=2.8, 11.6 Hz, 1H), 4.39-4.31 (m, 2H), 4.27-4.21 (m, 3H), 4.19 (t, J = 8.8 Hz, 1H), 4.06 (m, 2H), 3.94-3.87 (m, 2H), 3.83 (td, J = 3.6, 8.4 Hz, 1H), 3.74 (t, J = 10.4 Hz, 1H), 3.56 (dd, J = 4.0, 11.6 Hz, 1H), 3.18 (dd, J=11.2, 20.8 Hz, 1H), 2.55 (d, J=7.6 Hz, 1H), 2.41-2.27 (m, 4H), 2.06 (s, 3H), 1.60 (s, 3H), 1.43 (s, 3H) ), 1.39 (s, 3H), 1.31 (s, 6H), 0.95 (s, 3H), 0.61 (d, J = 3.6 Hz, 1H), 0.22 (d, 4.0 Hz, 1H); ¹³ C NMR (100 MHz) , C ₅ D ₅ N) δ 107.5, 105.0, 88.3, 87.0, 81.4, 79.1, 79.0, 7 8.3, 77.9, 75.4, 73.2, 71.6, 71.0, 66.8, 62.9, 58.0, 52.3, 46.0, 45.5, 44.8, 42.4, 34.7, 34.4, 33.2, 32.0, 30.0, 28.8, 28.6, 28.4, 28.0, 26.9, 26.2, 26.0, 20.9, 19.6, 16.4; HRMS (ESI) calcd for C ₄₁ H ₆₉ O ₁₄ [M+H] ⁺ 785.46818, found 785.46748.

Comparative Example 1: In the step (5) or (7), when the glycosidation reaction was carried out with the trichloroacetimidate ester donor instead of the alkyne ester donor, the reaction system was very mixed and the product was small, indicating that the alkyne ester donor was synthesized in the scutellaria Glycosides are more advantageous.

Comparative Example 2: In the step (4), when the molar ratio of the compound 3, halosilane and imidazole was 1:1.2:2, the other reaction parameters were the same, and the reaction yield was 40%.

Comparative Example 3: In the step (2), when the concentration of the compound 2 was 0.001 mol/L, the other reaction parameters were the same, and only the 16 hydroxyl group of the compound 2 was protected.

Claims

A method for synthesizing astragaloside IV, characterized in that it comprises the following steps:

(1) protecting the 3- and 6-hydroxyl groups of the cycloxanthine with a protecting group R 1 to obtain a compound 2;

(2) protecting the 16th and 25th hydroxyl groups of compound 2 with a protecting group R 2 to give compound 3;

(3) removing the 3-position and 6-position protecting group R 1 of compound 3 to obtain compound 4;

(4) protecting the 3-hydroxyl group of compound 4 with a protecting group R 3 to give compound 5;

(5) glycosidation reaction of compound 5 with glycosyl donor compound 9 to obtain compound 6;

(6) The 3-position protecting group R 3 of compound 6 is removed to obtain compound 7;

(7) a compound 7 and a glycosyl donor compound 10 glycosidation reaction to obtain a compound 8;

(8) removing all protecting groups of compound 8 to obtain astragaloside IV;

Wherein R 1 is Lev; R 2 is Ac; R 3 is selected from TBS, TES, TBDMS, TBDPS, DIPS, DPS or TIPDS; said R 4 or R 5 is Bz;

In the step (1), the method for protecting comprises the steps of: dissolving cycloxanol, DMAP and levulinic acid in a first solvent below 0 ° C, adding DCC, slowly raising the reaction temperature to room temperature, stirring until TLC tracking showed complete reaction of cycloxanthine 1;

In the step (2), the method for protecting comprises the steps of: dissolving compound 2 and PPy in a second solvent below 0 ° C, adding acetic anhydride, DIPEA, slowly raising the reaction temperature to room temperature, and then heating to 100. ～120 ° C, continue to stir until TLC tracking shows compound 2 reaction is complete, the concentration of the compound 2 in the second solvent is 0.1 ~ 1 mol / L;

In the step (3), the method for removing the protecting group R 1 comprises the steps of: dissolving the compound 3 in a third solvent below 0 ° C, adding cerium acetate, slowly raising the reaction temperature to room temperature, and stirring until TLC Tracking shows that Compound 3 is completely reactive;

In the step (4), the method for protecting comprises the steps of: dissolving the compound 4 in a fourth solvent at 0 ° C, adding a halosilane and an imidazole, slowly raising the reaction temperature to room temperature, and stirring until TLC tracking shows Compound 4 is completely reactive;

In the step (5), the glycosidation reaction comprises the steps of: dissolving the compound 5 and the glycosyl donor compound 9 in a fifth solvent under the protection of an inert gas, adding a desiccant, and stirring at room temperature for 0.5 to 2 The catalyst was further added in an hour and stirring was continued at room temperature until TLC tracking showed that Compound 5 was completely reacted;

In the step (6), the reaction of removing the protecting group R 3 comprises the steps of: dissolving the compound 6 in the sixth solvent, adding camphorsulfonic acid at room temperature, stirring until TLC tracking shows that the compound 6 is completely reacted;

In the step (7), the glycosidation reaction comprises the steps of dissolving the compound 7 and the glycosyl donor compound 10 in a seventh solvent, adding a desiccant, stirring at room temperature, and then adding a catalyst to continue at room temperature. Stir until TLC tracking shows compound 7 is completely reacted;

In the step (8), the reaction of removing the protecting group comprises the steps of dissolving the compound 8 in the eighth solvent, adding a base, and stirring at room temperature until TLC tracking shows that the compound 8 is completely reacted.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (1), the first solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, One or more of DMF, toluene, benzene, dioxane, pyridine, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether; the cycloxanthine, DMAP, acetyl-propyl The molar ratio of acid to DCC is 1:1.2:5:5 to 1:2:10:10, and the concentration of the cycloxanthine in the first solvent is 0.05 to 1 mol/L.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (2), the second solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, One or more of DMF, toluene, benzene, dioxane, pyridine, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether; the compound 2, PPy, acetic anhydride and The molar ratio of DIPEA is 1:1.5:8:12 to 1:2:15:20.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (3), the third solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, One or more of DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether; the compound 3 and cerium acetate The molar ratio is 1:15 to 1:40; the concentration of the compound 3 in the third solvent is 0.05 to 1.5 mol/L.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (4), the fourth solvent is selected from the group consisting of dichloromethane, dichloroethane, chloroform, carbon tetrachloride, 1,2- One or more of dichloroethane, DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, The molar ratio of the compound 4, the halosilane and the imidazole is 1:2 to 3 to 1:5:10; and the concentration of the compound 4 in the fourth solvent is 0.1 to 1 mol/L.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (5), the fifth solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, One or more of DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether, compound 5, glycosyl donor The molar ratio of the compound 9 to the catalyst is 1:1:0.1 to 1:5:0.8; the concentration of the compound 5 in the fifth solvent is 0.001 to 1 mol/L; the catalyst is selected from the group consisting of monovalent gold The desiccant is selected from the group consisting of molecular sieves.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (6), the sixth solvent is selected from the group consisting of dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, One or more of DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, DMSO or diethyl ether; the compound 6 and camphorsulfonate The molar ratio of the acid is from 1:1 to 1:10, and the concentration of the compound 6 in the sixth solvent is from 0.001 to 1 mol/L.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (7), the step of stirring at room temperature after adding the desiccant is 0.5 to 2 hours; and the seventh solvent is selected from the group consisting of dichloro Methane, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol, One or more of DMSO or diethyl ether; the molar ratio of the compound 7, the glycosyl donor compound 10 to the catalyst is 1:1:0.1 to 1:5:0.8; the compound 7 is in the seventh solvent The concentration in the range is 0.001 to 1 mol/L; the catalyst is selected from the group consisting of monovalent gold complexes; and the desiccant is selected from the group consisting of molecular sieves.
The method for synthesizing astragaloside IV according to claim 1, wherein in the step (8), the base is selected from the group consisting of sodium methoxide, sodium hydroxide, potassium carbonate and potassium hydroxide; and the eighth solvent is selected from the group consisting of Methyl chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, DMF, toluene, benzene, dioxane, pyridine, glacial acetic acid, tetrahydrofuran, triethylamine, ethyl acetate, acetone, methanol, ethanol One or more of DMSO or diethyl ether.
The method for synthesizing astragaloside according to claim 1, wherein any one of steps (1) to (8) is carried out under inert gas protection conditions.