Synthetic method of stevioside Rebaudioside A and Rebaudioside M

Abstract

The invention discloses a synthesis method of stevioside Rebaudioside A and Rebaudioside M, and belongs to the technical field of synthesis of stevioside. According to the invention, a synergistic catalysis glycosylation method taking gold trichloride as a catalyst and pivalononitrile as a ligand is established, a trisaccharide glycosyl donor and an aglycone receptor are subjected to efficient glycosylation, a beta-configuration compound is obtained at a relatively high yield, and then stevioside Rebaudioside A and Rebaudioside M are obtained at a relatively high yield, so that the method has the advantages of high efficiency, simplicity, convenience, high stereoselectivity and the like, and is suitable for industrial production. And an effective reference is provided for efficient preparation of stevioside.

Description

Technical Field

[0001] The present invention relates to the technical field of steviol glycoside synthesis, and in particular to a method for synthesizing steviol glycosides Rebaudioside A and Rebaudioside M. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to enhance the overall understanding of the present invention and is not necessarily to be regarded as an admission or an implication in any form that such information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Steviol glycosides are a type of glycoside extracted from the leaves of the Compositae plant Stevia rebaudiana. In recent years, steviol glycoside substances have received extensive attention from researchers and production enterprises as a new type of sweetener that can replace sucrose. Compared with other sweeteners, steviol glycosides have the characteristics of natural origin, high sweetness, and zero calories. Currently, they have been approved as sweeteners in many countries, including China, the United States, the European Union, Japan, Brazil, and other countries. They also have various pharmacological effects, such as anti-cancer, anti-hypertensive, anti-hyperglycemic, anti-diarrheal, etc. Among the steviol glycoside compounds isolated and identified from Stevia rebaudiana, most have the same ent-kaurene type diterpene steviol backbone (ent-13-hydroxy kaur-16-en-19-oic-acid), except for a few isomers. The differences between different types of steviol glycosides lie in the different sugar groups attached to the C-13 and C-19 positions. Research shows that oral administration of steviol glycosides has a blood pressure-lowering effect on hypertensive patients, especially showing certain effects in long-term interventions. Steviol glycosides also have anti-hyperglycemic, insulin-promoting, and glucagon-inhibiting effects. In addition, steviol glycosides also exhibit strong physiological activities, such as antibacterial and anti-tumor effects.

[0004] Although steviol glycosides have potential biological significance, current research on their activities and mechanisms still relies on extraction and isolation from plant materials. Since the content of steviol glycoside compounds in plants is relatively low, and the content of most rare components with high research value is even less than 1%, it restricts the research and application of steviol glycoside sweeteners. Therefore, how to efficiently and highly produce steviol glycosides with a single configuration has become a key task for researchers. Due to substrate specificity, lack of enzymes, and limitations in enzyme expression levels, enzymatic synthesis cannot be an effective approach. Chemical synthesis, with its flexible and variable characteristics, has become a powerful means. In recent decades, researchers have made great efforts in the synthesis of steviol glycosides. The construction of the C-19β bond is achieved by the orthoester method and obtained through the phase transfer method of brominated sugar. Currently, the construction of the C-13β bond is almost all achieved through neighboring group participation. However, all of these methods invariably introduce complex protection and deprotection group operations, severely restricting the overall efficiency of the synthesis process. In addition, when synthesizing steviol glycosides using existing technologies, there is also a problem of low β / α selectivity (β / α < 3). Therefore, to date, no technology has been able to achieve the efficient, highly selective, and large-scale preparation of steviol glycosides. This current situation highlights the limitations of the current synthesis methods and makes the efficient preparation of steviol glycosides a synthetic challenge. Summary of the Invention

[0005] In view of this, the present invention provides a method for synthesizing steviol glycosides Rebaudioside A and Rebaudioside M, which can achieve the efficient, simple, and highly stereoselective synthesis of Rebaudioside A and Rebaudioside M.

[0006] The present invention provides a method for synthesizing steviol glycosides Rebaudioside A and Rebaudioside M, comprising the following steps:

[0007] (1) Oxidize compound 7 with ammonium cerium nitrate to obtain compound 8;

[0008]

[0009] (2) React compound 8 with trichloroacetonitrile to obtain compound 4;

[0010]

[0011] (3) React compound 4 with compound 3 under the action of gold(III) chloride and pivalonitrile to obtain compound 10;

[0012]

[0013] (4) Deprotect the compound 10 in the β-configuration under the action of tetrabutylammonium fluoride to obtain the compound 11;

[0014]

[0015] (5) React the compound 11 with the compound 14 or the compound 18 under the action of tetrabutylammonium bromide to obtain the compound 15 or the compound 19;

[0016]

[0017] (6) Remove all protecting groups from the compound 15 or the compound 19 to obtain Rebaudioside A or Rebaudioside M;

[0018]

[0019] In some embodiments of the present invention, the compound 7 is obtained by reacting the compound 5 and the compound 6 under the catalysis of trimethylsilyl trifluoromethanesulfonate;

[0020]

[0021] In some embodiments of the present invention, the compound 3 is obtained by reacting steviol with tert-butyldimethylchlorosilane.

[0022] In some embodiments of the present invention, in step (3), the molar ratio of the compound 4, the compound 3, gold(III) chloride and pivalonitrile is 1:(0.7 - 0.9):(0.25 - 0.4):(170 - 200).

[0023] In some embodiments of the present invention, the reaction time of step (3) is 30 - 40 min, and the reaction temperature is -70 - -50 °C.

[0024] In some embodiments of the present invention, dichloromethane is further included in the reaction system of step (3), and the volume ratio of dichloromethane to pivalonitrile is 1:(0.8 - 1.2).

[0025] In some embodiments of the present invention, the synthesis method of the compound 14 is: reacting the compound 12 with benzoyl chloride to form the compound 13, and reacting the compound 13 with hydrogen bromide in acetic acid to obtain the compound 14;

[0026]

[0027] In some embodiments of the present invention, the compound 18 is obtained by reacting the compound 17 with hydrogen bromide in acetic acid;

[0028]

[0029] Furthermore, Compound 17 is obtained by reacting Compound 16 with acetic anhydride under the action of 4-dimethylaminopyridine;

[0030]

[0031] Furthermore, Compound 16 is obtained by first reacting Compound 7 with p-toluenesulfonic acid and then with ammonium cerium(IV) nitrate.

[0032] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0033] The present invention provides a method for gold(III)-nitrile co-catalyzed glycosylation, which realizes the efficient and selective connection of glycosyl donors and aglycones. This reaction uses a convergent synthesis method, directly glycosylates a trisaccharide without participation of neighboring groups with a steviol aglycone sensitive to acid under mild reaction conditions, and obtains the β-configured Compound 11β with a high yield, with a β / α value greater than 6 and high stereoselectivity; starting from commercially available steviol, Rebaudioside A and Rebaudioside M are finally obtained with a total yield higher than 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 is the 1H NMR spectrum of Compound 10α in Example 3 of the present invention;

[0036] Figure 2 is the 13C NMR spectrum of Compound 10α in Example 3 of the present invention;

[0037] Figure 3 is the 1H NMR spectrum of Compound 10β in Example 3 of the present invention;

[0038] Figure 4 is the 1H NMR spectrum of Compound 1 in Example 4 of the present invention;

[0039] Figure 5 is the 1H NMR spectrum of Compound 2 in Example 5 of the present invention;

[0040] Figure 6 is the 13C NMR spectrum of Compound 2 in Example 5 of the present invention;

[0041] Figure 7 is the structural formula and synthetic strategy schematic diagram of Compound 1 and Compound 2 in Example 5 of the present invention. Detailed implementation manners

[0042] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0043] The technical solution of the present invention will be further described below in conjunction with specific embodiments. The present invention has no special restrictions on the sources of the reagents used in the following embodiments, and commercially available products well-known to those skilled in the art can be used.

[0044] Example 1

[0045] This example provides a method for synthesizing a trisaccharide glycosyl donor (Compound 5).

[0046] The synthetic route of Compound 5 (2,3-di-O-(2,3,4,6-tetra-O-benzoyl-β-D-glucopyranosyl)-4,6-di-O-benzyl-α-D-glucopyranosyl trichloroacetimidate) is as follows:

[0047]

[0048] 1. Preparation of Compound 7:

[0049] Put 2.7 g of activated molecular sieve into a 100 mL two-necked flask. Under an argon atmosphere, dissolve Compound 6 (4.9 g, 6.7 mmol) and Compound 5 (1.0 g, 2.7 mmol) in 27 mL (c = 0.1 M) of dichloromethane. Add TMSOTf (trimethylsilyl trifluoromethanesulfonate) (97 μL, 0.5 mmol) at 0 °C and react for 30 min. After detecting the reaction of the raw materials by TLC, add 0.5 mL of triethylamine to quench the reaction, dilute with dichloromethane, filter through diatomaceous earth, spin dry, and purify by column chromatography (petroleum ether:ethyl acetate = 2:1) to obtain a white foamy solid, namely Compound 7 (3.7 g, 90%), and the yield is 90%. 1 H NMR (400 MHz, CDCl 3)δ8.22 - 8.15 (m, 2H, ArH), 8.15 - 8.07 (m, 2H, ArH), 7.92 - 7.85 (m, 2H, ArH), 7.83 - 7.71 (m, 9H, ArH), 7.66 - 7.06 (m, 30H, ArH), 6.84 - 6.76 (m, 2H), 6.52 - 6.43 (m, 2H), 5.76 - 5.68 (m, 2H, 3b - H, 3c - H), 5.55 - 5.45 (m, 2H, 2c - H, 4c - H), 5.46 - 5.37 (m, 2H, PhCH, 2b - H), 5.33 (t, J = 9.7 Hz, 1H, 4b - H), 4.83 (d, J = 6.8 Hz, 1H, 1a - H), 4.77 (d, J = 7.7 Hz, 1H, 1b - H), 4.66 (d, J = 7.7 Hz, 1H, 1c - H), 4.29 - 4.08 (m, 5H, 6a - H, 6b - H, 6b’ - H, 6c - H, 6c’ - H), 3.98 - 3.87 (m, 2H, 2a - H, 3a - H), 3.69 - 3.53 (m, 5H, 4a - H, 6a’ - H, OCH 3 ), 3.31 (td, J = 9.7, 4.9 Hz, 1H, 5a - H), 2.64 - 2.54 (m, 2H, 5b - H, 5c - H). 13 C NMR (100 MHz, CDCl 3 )δ165.97, 165.95, 165.9, 165.74, 165.2, 165.1, 165.02 165.00, 155.2, 151.5, 137.2, 133.7, 133.6, 133.5, 133.3, 133.1, 133.0, 130.2, 130.1, 129.9, 129.8, 129.74, 129.72, 129.69, 129.6, 129.5, 129.44, 129.41, 129.04, 128.99, 128.98, 128.84, 128.81, 128.5, 128.42, 128.40, 128.3, 128.1, 126.0, 118.1, 114.5, 101.3, 101.0, 100.5, 100.1, 79.8, 79.5, 78.2, 72.8, 72.7, 72.6, 72.5, 71.5, 71.4, 70.1, 69.0, 68.7, 66.1, 63.4, 62.4, 55.6. HRMS (ESI) Calcd for C 88 H 74 NaO 25 + [M + Na] +: 1553.4412, found: 1553.4454.

[0050] 2. Preparation of Compound 8:

[0051] Dissolve Compound 7 (3.7 g, 2.4 mmol) in a mixed solution of 50 mL of water and acetonitrile (v:v = 4:1) (c = 0.05 M). Add ammonium cerium(IV) nitrate (CAN, 4.0 g, 7.3 mmol) at 0 °C and react for 30 min. Monitor the reaction by TLC until the raw materials are completely reacted. Quench the reaction with saturated sodium bicarbonate solution, extract with 100 mL of dichloromethane, wash three times with 100 mL of saturated sodium bicarbonate, wash once with 100 mL of saturated sodium chloride, dry over anhydrous sodium sulfate, filter by suction, evaporate to dryness, and purify by column chromatography (petroleum ether:ethyl acetate = 1.5:1) to obtain a pale yellow foamy solid, namely Compound 8 (2.9 g, 85%).

[0052] 3. Preparation of Compound 4

[0053] Dissolve Compound 8 (2.9 g, 2.1 mmol) in 20 mL of redistilled dichloromethane, cool to 0 °C, and successively add trichloroacetonitrile (2 mL, 21 mmol) and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene, 93 μL, 0.6 mmol) under argon. Warm to room temperature and stir overnight. Monitor the reaction by TLC until the raw materials are completely reacted. Evaporate the reaction solution to dryness and purify by column chromatography (petroleum ether:ethyl acetate volume ratio = 2:1) to obtain a white foamy solid, namely Compound 4 (2.4 g, 73%). 1 H NMR (600 MHz, CDCl 3)δ8.46(s,1H,NH),8.30 - 8.26(m,2H,ArH),8.23 - 8.19(m,2H,ArH),8.01 - 7.97(m,2H,ArH),7.93 - 7.89(m,3H,ArH),7.89 - 7.83(m,5H,ArH),7.77(t,J = 7.8Hz,2H,ArH),7.71 - 7.65(m,2H,ArH),7.62 - 7.48(m,5H,ArH),7.46 - 7.37(m,10H,ArH),7.37 - 7.33(m,2H,ArH),7.29(t,J = 7.8Hz,3H,ArH),7.25 - 7.23(m,2H,ArH),7.20 - 7.14(m,5H,ArH),6.30(d,J = 4.1Hz,1H,1a - H),5.69 - 5.64(m,2H,3b - H,3c - H),5.57(dd,J = 9.9,7.7Hz,1H,2b - H),5.53(s,1H,PhCH),5.49 - 5.42(m,3H,2c - H,4b - H,4c - H),4.67(d,J = 7.7Hz,1H,1b - H),4.59(d,J = 7.7Hz,1H,1c - H),4.39 - 4.34(m,2H),4.30 - 4.21(m,3H,6a - H),4.19(t,J = 9.2Hz,1H,3a - H),3.92(td,J = 10.0,4.9Hz,1H,5a - H),3.89(dd,J = 9.0,4.1Hz,1H,2a - H),3.68(t,J = 10.3Hz,1H,6a’ - H),3.59(t,J = 9.6Hz,1H,4a - H),2.86(ddd,J = 9.5,5.7,3.3Hz,1H),2.70(ddd,J = 10.0,4.8,3.4Hz,1H). 13 C NMR(150MHz,CDCl 3)δ166.05,166.00,165.96,165.90,165.22,165.14,165.09,164.6,138.0,137.1,133.8,133.7,133.64,133.60,133.43,133.40,133.3,133.2,130.3,130.0,129.94,129.89,129.86,129.80,129.77,129.70,129.66,129.60,129.55,129.2,129.1,128.6,128.4,128.2,125.9,125.4,101.1,100.4,100.3,95.7,91.0,78.4,77.0,75.9,72.9,72.8,72.3,72.12,72.07,71.5,69.7,69.5,68.7,64.7,63.4,62.3.HRMS(ESI)Calcd for C 83 H 68 Cl 3 NNaO 24 + [M+Na] + :1590.3090,found:1590.3052。

[0054] Example 2

[0055] This example provides the synthesis of steviol tert-butyldiphenylsilyl ester (Compound 3).

[0056] The synthetic route is as follows:

[0057]

[0058] Steviol (Compound 9, 800 mg, 2.5 mmol) was dissolved in DMF. Under an argon atmosphere, imidazole (1.0 g, 15.1 mmol) and TBDPSCl (tert-butyldimethylchlorosilane) (763 μL, 3 mmol) were added. The reaction was carried out for 1.5 h. After the reaction of the raw materials was completed as detected by TLC, the reaction was quenched with 5 mL of methanol. The reaction solution was extracted with 100 mL of ethyl acetate and washed three times with 100 mL of saturated sodium chloride. The organic phase was dried over anhydrous sodium sulfate, filtered by suction and evaporated to dryness, and purified by column chromatography (petroleum ether:ethyl acetate = 3:1) to obtain a white foamy solid, namely Compound 3 (1.3 g, 90%). 1 H NMR(400MHz,CDCl 3)δ 7.71 - 7.63 (m, 4H), 7.45 - 7.32 (m, 6H), 4.96 (s, 1H), 4.80 (s, 1H), 2.28 - 2.14 (m, 2H), 2.11 - 1.98 (m, 2H), 1.92 - 1.67 (m, 5H), 1.61 - 1.47 (m, 6H), 1.45 - 1.38 (m, 1H), 1.26 (s, 4H), 1.24 - 1.18 (m, 1H), 1.14 (d, J = 1.5 Hz, 9H), 1.04 (t, J = 10.2 Hz, 1H), 0.94 (d, J = 7.7 Hz, 1H), 0.90 - 0.78 (m, 1H), 0.75 (s, 3H).

[0059] Example 3

[0060] This example provides a method for synthesizing the trisaccharide glycosyl donor (Compound 11).

[0061] The synthetic route of Compound 11 (13 - O - [2,3 - di - O - (2,3,4,6 - tetra - O - benzoyl - β - D - glucopyranosyl) - 4,6 - di - O - benzyl - α / β - D - glucopyranosyl] steviol tert - butyldiphenylsilyl ester) is as follows:

[0062]

[0063]

[0064] 1. Preparation of Compound 10

[0065] Put 2 g of activated molecular sieve into a 50 mL two - necked flask. Under an argon atmosphere, dissolve Compound 4 (809 mg, 0.5 mmol) and Compound 3 (230 mg, 0.41 mmol) in 10 mL of dichloromethane and pivalonitrile (10 mL, 86.5 mmol), cool to - 60 °C, add AuCl 3 (46 mg, 0.155 mmol), react for 30 min. After detecting the completion of the reaction of the raw materials by TLC, add 0.5 mL of triethylamine to quench the reaction, dilute with dichloromethane, filter through diatomaceous earth, extract with 100 mL of dichloromethane, wash once with 100 mL of saturated sodium bicarbonate, wash once with 100 mL of saturated sodium chloride, dry over anhydrous sodium sulfate, filter, evaporate to dryness, and purify by column chromatography (petroleum ether:dichloromethane:ethyl acetate = 15:15:1) to obtain a white foamy solid, namely Compound 10 (89 mg, 11%, α; 648 mg, 80%, β).

[0066] The nuclear magnetic resonance hydrogen spectrum ( 1 1H NMR) of the α - isomer (Compound 10α) is as Figure 1As shown, the carbon-13 NMR spectrum is as follows: Figure 2 As shown, the data are summarized as follows: 1 H NMR (600 MHz, CDCl 3 ) δ 8.31 (d, J = 8.2 Hz, 2H, ArH), 8.28 (d, J = 8.2 Hz, 2H, ArH), 7.99 (t, J = 8.3 Hz, 2H, ArH), 7.95 - 7.84 (m, 10H, ArH), 7.80 (t, J = 7.3 Hz, 2H, ArH), 7.70 (t, J = 7.5 Hz, 2H, ArH), 7.68 - 7.64 (m, 4H, ArH), 7.61 - 7.55 (m, 3H, ArH), 7.55 - 7.51 (m, 3H, ArH), 7.48 - 7.42 (m, 7H, ArH), 7.39 (t, J = 7.9 Hz, 2H, ArH), 7.37 - 7.28 (m, 10H, ArH), 7.19 - 7.16 (m, 3H, ArH), 5.74 - 5.69 (m, 2H, 3b-H, 3c-H), 5.61 (dd, J = 9.8, 7.7 Hz, 1H, 2b-H), 5.57 - 5.49 (m, 3H, PhCH, 2c-H, 4b-H), 5.45 (t, J = 9.8 Hz, 1H, 4c-H), 5.39 (s, 1H, =CH 2 ), 5.04 (d, J = 3.9 Hz, 1H, 1a-H), 4.99 (s, 1H, =CH 2 ), 4.73 (d, J = 7.8 Hz, 1H, 1b-H), 4.65 (d, J = 7.9 Hz, 1H, 1c-H), 4.44 - 4.32 (m, 2H, 6c-H, 6b-H), 4.30 (dd, J = 12.0, 5.3 Hz, 1H, 6b’-H), 4.26 (t, J = 9.2 Hz, 1H, 3a-H), 4.15 (dd, J = 12.3, 4.9 Hz, 1H, 6c’-H), 4.06 (dd, J = 10.1, 4.8 Hz, 1H, 6a’-H), 3.97 (td, J = 10.0, 4.9 Hz, 1H, 5a-H), 3.68 (dd, J = 9.3, 3.9 Hz, 1H, 2a-H), 3.61 (t, J = 10.2 Hz, 1H, 6a’-H), 3.46 (t, J = 9.5 Hz, 1H, 4a-H), 2.87 - 2.81 (m, 1H, 5a-H), 2.65 - 2.61 (m, 1H, 5c-H), 2.26 - 2.19 (m, 1H, CH 2 ×1), 1.93 - 1.77 (m, 7H, CH 2 ×7), 1.68 - 1.56 (m, 4H, CH 2×4), 1.53 - 1.41 (m, 3H, CH 2 ×3), 1.35 - 1.31 (m, 1H, CH 2 ×1), 1.27 (s, 3H), 1.15 (s, 9H), 1.06 - 1.00 (m, 2H, CH×1, CH 2 ×1), 0.95 - 0.75 (m, 2H, CH×1, CH 2 ×1), 0.69 (s, 3H, CH 3 ×3). 13 C NMR (150 MHz, CDCl 3 ) δ 177.0, 166.02, 165.99, 165.9, 165.20, 165.17, 165.1, 164.8, 149.9, 137.7, 135.8, 133.67, 133.6, 133.5, 133.4, 133.34, 133.25, 133.0, 132.0, 131.9, 130.3, 130.2, 130.1, 129.92, 129.86, 129.8, 129.73, 129.68, 129.6, 129.5, 129.2, 129.1, 129.03, 128.94, 128.59, 128.56, 128.47, 128.46, 128.4, 128.0, 127.69, 127.67, 126.0, 106.1, 100.8, 100.6, 99.9, 94.3, 86.0, 79.7, 77.8, 75.5, 73.1, 72.9, 72.6, 72.2, 71.7, 71.2, 70.0, 69.5, 69.0, 63.5, 62.1, 57.2, 53.7, 47.7, 45.2, 43.9, 41.7, 41.4, 40.7, 39.5, 39.4, 38.7, 29.8, 29.4, 27.3, 22.31, 22.30, 20.0, 19.4, 16.0. HRMS (ESI) Calcd for C 117 H 114 NaO 26 Si + [M + Na] + : 1986.7294, found: 1986.7287。

[0067] The ¹H NMR spectrum of the β - isomer (Compound 10β) is as follows Figure 3 shown, and the data are summarized as follows: 1 ¹H NMR (400 MHz, CDCl 3)8.32(d, J = 7.7 Hz, 2H, ArH), 8.20(d, J = 7.5 Hz, 2H, ArH), 7.95(m, 14H, ArH), 7.78 - 7.73(m, 5H, ArH), 7.71 - 7.26(m, 39H, ArH), 5.96 - 5.85(m, 2H), 5.67(dd, J = 9.8, 7.8 Hz, 1H), 5.58 - 5.49(m, 4H), 5.15(s, 1H, =CH 2 ), 5.00(d, J = 7.8 Hz, 1H, 1b - H), 4.89(d, J = 7.8 Hz, 1H, 1c - H), 4.72(s, 1H, =CH 2 ), 4.67(d, J = 7.3 Hz, 1H, 1a - H), 4.40 - 4.18(m, 5H), 4.05(t, J = 8.7 Hz, 1H), 3.92(t, J = 7.8 Hz, 1H), 3.72(q, J = 9.6, 9.0 Hz, 2H), 3.32(m, 1H), 2.86(m, 2H), 2.36(d, J = 13.3 Hz, 1H), 2.14(d, J = 17.0 Hz, 1H), 2.05(d, J = 11.1 Hz, 1H), 2.01 - 1.78(m, 8H), 1.64(s, 6H), 1.62 - 1.53(m, 1H), 1.42(t, J = 6.3 Hz, 1H), 1.33(s, 3H), 1.23(s, 9H), 1.11(q, J = 6.0, 5.5 Hz, 1H), 0.97(d, J = 7.7 Hz, 1H), 0.86(s, 3H).

[0068] 2. Preparation of Compound 11

[0069] Dissolve compound 10β (455 mg, 0.23 mmol) in 4.6 mL of tetrahydrofuran. Mix a tetrahydrofuran solution of AcOH (40 μL, 0.69 mmol) and 1M TBAF (tetrabutylammonium fluoride) (290 μL, 1.14 mmol) and add it to the reaction system. React for 0.5 h. When TLC detects that the raw materials have reacted completely, extract with 50 mL of ethyl acetate, wash with 50 mL of water, wash with 50 mL of saturated sodium chloride solution, dry over anhydrous sodium sulfate, filter by suction, evaporate to dryness, and then purify by column chromatography to obtain a white foamy solid, which is compound 11 (375 mg, 96%). 1 HNMR(400 MHz, DMSO - d 6)δ11.93(s,1H,COOH),8.00 - 7.80(m,12H,ArH),7.80 - 7.74(m,4H),7.68 - 7.30(m,26H),6.12(t,J=9.6Hz,1H),6.00(t,J=9.5Hz,1H),5.87(t,J=9.5Hz,1H),5.83 - 5.75(m,1H),5.73(s,1H),5.60(d,J=7.9Hz,1H),5.57 - 5.46(m,2H),5.32(dd,J=9.6,7.8Hz,1H),4.96(s,1H),4.73(d,J=6.9Hz,1H),4.52 - 4.06(m,8H),3.97(t,J=9.0Hz,1H),3.88(t,J=9.3Hz,1H),3.63 - 3.42(m,2H),2.12 - 1.55(m,13H),1.52 - 1.19(m,7H),1.11(s,3H),1.02 - 0.92(m,5H),0.86(s,4H),0.77(d,J=11.1Hz,2H).

[0071] Example 4

[0072] This example provides a method for synthesizing Rebaudioside A (Compound 1).

[0073] The synthetic route of Compound 1 is as follows:

[0074]

[0075] 1. Preparation of Compound 13

[0076] Dissolve Compound 12 (1.0 g, 5.5 mmol) in 16 mL of dry pyridine. Add BzCl (benzoyl chloride) (5.1 mL, 44.3 mmol) at 0 °C. React at room temperature for 6 h. Monitor the reaction by TLC until the raw materials are completely reacted. Quench with 5 mL of methanol and evaporate to dryness. Then wash with 100 mL of 1 M hydrochloric acid and 100 mL of saturated sodium chloride solution. Dry the organic phase with anhydrous sodium sulfate, filter, evaporate to dryness, and recrystallize with petroleum ether and ethyl acetate to obtain a white solid, namely Compound 13 (3.3 g, 85%).

[0077] 2. Preparation of Compound 14

[0078] Compound 13 (536 mg, 0.76 mmol) was dissolved in 5 mL of dry dichloromethane. It was cooled to 0 °C, and 33% HBr / HOAc solution (5.4 mL, 2.8 mmol) was added under an argon atmosphere. The reaction was allowed to warm to room temperature and stirred for 6 h. When the raw materials were completely reacted as detected by TLC, the reaction mixture was extracted with 50 mL of dichloromethane, washed with 50 mL of water, 50 mL of 1% sodium bicarbonate solution, 50 mL of saturated sodium bicarbonate solution, and 50 mL of saturated sodium chloride solution. The organic phase was dried over anhydrous sodium sulfate, filtered, evaporated to dryness, and purified by column chromatography (petroleum ether:ethyl acetate = 3:1) to obtain a white foamy solid, namely compound 14 (494 mg, 94%). 1 H NMR (400 MHz, CDCl 3 ) δ 8.03 - 7.96 (m, 2H, ArH), 7.96 - 7.90 (m, 2H, ArH), 7.91 - 7.85 (m, 2H, ArH), 7.84 - 7.77 (m, 2H, ArH), 7.53 - 7.17 (m, 12H, ArH), 6.79 (d, J = 4.0 Hz, 1H, 1-H), 6.19 (t, J = 9.8 Hz, 1H, 3-H), 5.75 (t, J = 10.0 Hz, 1H, 4-H), 5.26 (dd, J = 10.0, 4.0 Hz, 1H, 2-H), 4.66 (ddd, J = 10.3, 4.5, 2.7 Hz, 1H, 5-H), 4.60 (dd, J = 12.5, 2.7 Hz, 1H, 6a-H), 4.44 (dd, J = 12.5, 4.5 Hz, 1H, 6b-H).

[0079] 3. Preparation of Compound 15

[0080] Compound 11 (70 mg, 0.04 mmol) was dissolved in a mixed solution of 2.6 mL of chloroform and water (v:v = 1:1). At room temperature, TBAB (tetrabutylammonium bromide) (36 mg, 0.08 mmol) and K 2 CO 3 (17 mg, 0.12 mmol) were added. After reacting for 10 min, compound 14 (54 mg, 0.08 mmol) was added, and then the reaction was heated to 40 °C and stirred for 6 h. When the raw materials were completely reacted as detected by TLC, the reaction mixture was extracted with 50 mL of ethyl acetate, washed with 50 mL of saturated sodium chloride solution. The organic phase was dried over anhydrous sodium sulfate, filtered, evaporated to dryness, and purified by column chromatography (petroleum ether:ethyl acetate = 2:1) to obtain a white solid, namely compound 15 (153 mg, 82%). 1 H NMR (400 MHz, CDCl 3)δ 8.27 - 8.20 (m, 2H, ArH), 8.12 - 8.06 (m, 2H, ArH), 8.03 - 7.98 (m, 2H, ArH), 7.95 - 7.78 (m, 17H, ArH), 7.77 - 7.72 (m, 2H, ArH), 7.65 - 7.13 (m, 41H, ArH), 6.15 (d, J = 7.9 Hz, 1H, 1d - H), 5.91 - 5.66 (m, 5H, 2d - H, 3c - H, 3b - H, 3d - H, 4d - H), 5.59 (dd, J = 9.9, 7.8 Hz, 1H, 2c - H), 5.52 - 5.38 (m, 4H, PhCH, 2b - H, 4b - H, 4c - H), 5.08 (s, 1H, =CH 2 ), 4.93 (d, J = 7.8 Hz, 1b - H), 4.81 (d, J = 7.7 Hz, 1H, 1c - H), 4.66 (s, 1H, =CH 2 ), 4.64 - 4.57 (m, 2H, 1a - H, 6d - H), 4.50 (dd, J = 12.2, 4.6 Hz, 1H, 6d’ - H), 4.35 - 4.12 (m, 6H, 5d - H, 6a - H, 6b - H, 6b’ - H, 6c - H, 6c’ - H), 3.98 (t, J = 8.8 Hz, 1H, 3a - H), 3.85 (t, J = 7.8 Hz, 1H, 2a - H), 3.70 (t, J = 10.2 Hz, 1H, 6a’ - H), 3.64 (t, J = 9.3 Hz, 1H, 4a - H), 3.31 (td, J = 9.7, 5.0 Hz, 1H, 5a - H), 2.83 - 2.68 (m, 2H, 5b - H, 5c - H), 2.21 (d, J = 13.2 Hz, 1H, CH 2 ), 2.12 - 1.97 (m, 2H, CH 2 ), 1.94 - 1.36 (m, 14H, CH 2 ), 1.38 - 1.23 (m, 2H, CH 2 ), 0.96 (s, 5H, CH, CH 2 , CH 3 ), 0.84 (d, J = 8.1 Hz, 1H, CH), 0.73 (s, 3H, CH 3 ). 13 C NMR (100 MHz, CDCl 3)δ175.1,166.0,165.93,165.90,165.89,165.68,165.65,165.21,165.19,165.10,165.08,164.9,152.3,137.5,133.6,133.5,133.44,133.41,133.36,133.33,133.29,133.1,133.0,130.2,130.0,129.9,129.84,129.76,129.73,129.70,129.66,129.61,129.56,129.38,129.36,129.3,129.2,129.1,129.01,128.96,128.9,128.84,128.80,128.77,128.7,128.5,128.41,128.39,128.36,128.33,128.28,128.2,128.0,126.1,105.1,101.3,100.1,99.9,96.8,91.5,86.1,80.4,78.9,78.5,72.9,72.83,72.81,72.77,72.7,72.6,72.0,71.5(2C),70.9,70.2,69.8,69.3,68.9,65.9,63.4,63.1,62.6,57.2,54.1,47.5,44.1,43.6,42.5,41.3,40.4,39.4,37.8,36.8,28.8,21.6,20.3,19.2),16.3.HRMS(ESI)Calcd for C 135 H 126 NO 35 + [M+NH 4 + :2321.8139,found:2321.8155。

[0081] 4. Preparation of Compound 1

[0082] ​Compound 15 (60 mg, 0.026 mmol) was dissolved in a mixed solution of 1.2 mL of dichloromethane and methanol (v:v = 1:1), and p-TsOH (p-toluenesulfonic acid) (22.4 mg, 0.13 mmol) was added. The reaction was carried out overnight at room temperature. After the raw materials were detected by TLC to have reacted completely, the reaction was quenched with 0.5 mL of triethylamine. After evaporation to dryness, the intermediate was separated and purified by column chromatography (petroleum ether:ethyl acetate = 1:1). Then the intermediate was dissolved in 5 mL of methanol, and freshly prepared sodium methoxide solution was added to adjust the pH to 9. The reaction was carried out for 2 h. After the raw materials were detected by TLC to have reacted completely, the pH was adjusted to 7 with cation exchange resin, filtered, and after evaporation to dryness, it was separated and purified by a C18 chromatographic column (methanol:water = 2:1) to obtain a white solid, namely Compound 1 (19.1 mg, 76%), and its 1H NMR spectrum is as follows Figure 4 shown. 1 1H NMR (400 MHz, DMSO-d 6 ) δ 5.28 (d, J = 8.1 Hz, 1H, 1d-H), 5.05 (s, 1H, =CH 2 ), 4.74 (s, 1H, =CH 2 ), 4.64 (d, J = 7.8 Hz, 1H, 1b-H), 4.45 (dd, J = 15.8, 7.7 Hz, 2H, 1a-H, 1c-H), 3.75 - 2.92 (m, 42H), 2.17 - 1.24 (m, 13H), 1.15 (s, 4H), 1.08 - 0.72 (m, 6H).

[0083] Example 5

[0084] This example provides a method for synthesizing Rebaudioside M (Compound 2).

[0085] The synthetic route is as follows:

[0086]

[0087] 1. Preparation of Compound 16

[0088] Compound 7 (100 mg, 0.07 mmol) was dissolved in a mixed solution of 6.6 mL of dichloromethane and methanol (v:v = 1:1). p-TsOH (p-toluenesulfonic acid) (56 mg, 0.33 mmol) was added, and the reaction was carried out at room temperature for 4 h. When the reaction of the raw materials was completed as detected by TLC, the reaction was quenched with 0.5 mL of triethylamine. After evaporation to dryness, the intermediate was obtained. The intermediate was dissolved in a mixed solution of 6 mL of dichloromethane and methanol (v:v = 4:1), and CAN (cerium ammonium nitrate) (153 mg, 0.28 mmol) was added at 0 °C. The reaction was carried out for 0.5 h. When the reaction of the raw materials was completed as detected by TLC, the reaction was then quenched with saturated sodium bicarbonate solution. The reaction solution was extracted with 50 mL of ethyl acetate, washed with 50 mL of saturated sodium bicarbonate solution, washed with 50 mL of saturated sodium chloride solution, the organic phase was dried over anhydrous sodium sulfate, filtered, evaporated to dryness, and purified by column chromatography (petroleum ether:ethyl acetate = 1:2) to obtain a white foamy solid, namely compound 16 (73 mg, 84%).

[0089] 2. Preparation of Compound 17

[0090] Compound 16 (300 mg, 0.22 mmol) was dissolved in 2.5 mL of dry pyridine. Ac 2 O (acetic anhydride) (1 mL, 10.6 mmol) and DMAP (4-dimethylaminopyridine) (13 mg, 0.11 mmol) were added at 0 °C. The reaction was allowed to warm to room temperature overnight. When the reaction of the raw materials was completed as detected by TLC, the reaction was quenched with 1 mL of methanol, evaporated to dryness, extracted with 50 mL of ethyl acetate, washed with 50 mL of 1M HCl, washed with 50 mL of saturated sodium bicarbonate solution, washed with 50 mL of saturated sodium chloride solution, the organic phase was dried over anhydrous sodium sulfate, filtered, evaporated to dryness, and purified by column chromatography (petroleum ether:ethyl acetate = 1:1) to obtain a white foamy solid, namely compound 17 (303 mg, 93%).

[0091] 3. Preparation of Compound 18

[0092] Compound 17 (303 mg, 0.2 mmol) was dissolved in 85 mL of dry dichloromethane, cooled to 0 °C, and 33% HBr / HOAc solution (1.4 mL, 7.66 mmol) was added under an argon atmosphere. The reaction was warmed to room temperature and carried out for 3 h. When the reaction of the raw materials was completed as detected by TLC, the reaction solution was extracted with 50 mL of dichloromethane, washed with 50 mL of water, washed with 50 mL of 1% sodium bicarbonate solution, washed with 50 mL of saturated sodium bicarbonate solution, washed with 50 mL of saturated sodium chloride solution, the organic phase was dried over anhydrous sodium sulfate, filtered, evaporated to dryness, and purified by column chromatography (petroleum ether:ethyl acetate = 2:1) to obtain a white foamy solid, namely compound 18 (295 mg, 96%). 1 H NMR (400 MHz, CDCl 3)δ 8.36 - 8.23 (m, 4H, ArH), 7.99 (d, J = 8.5 Hz, 4H, ArH), 7.95 - 7.90 (m, 2H, ArH), 7.90 - 7.85 (m, 6H, ArH), 7.81 (t, J = 7.6 Hz, 2H, ArH), 7.76 - 7.67 (m, 3H, ArH), 7.65 - 7.52 (m, 5H, ArH), 7.49 - 7.38 (m, 10H, ArH), 7.31 (t, J = 7.7 Hz, 4H, ArH), 6.37 (d, J = 4.2 Hz, 1H, 1a - H), 5.74 (t, J = 9.8 Hz, 1H, 3c - H), 5.62 - 5.38 (m, 5H, 2b - H, 2c - H, 3b - H, 4b - H, 4c - H), 4.97 (t, J = 9.8 Hz, 1H, 4a - H), 4.57 - 4.52 (m, 2H, 1b - H, 1c - H), 4.40 (dd, J = 12.3, 3.0 Hz, 1H, 6c - H), 4.32 (dd, J = 12.3, 2.8 Hz, 1H, 6b - H), 4.26 - 4.00 (m, 6H, 3a - H, 5a - H, 6a - H, 6a’ - H, 6b’ - H, 6c’ - H), 3.66 (dd, J = 9.2, 4.2 Hz, 1H, 2a - H), 2.70 (m, 2H, 5b - H, 5c - H), 2.06 (s, 3H, CH 3 ), 1.90 (s, 3H, CH 3 ). 13 C NMR (100 MHz, CDCl 3 ) δ 170.6, 169.2, 165.91, 165.89, 165.85, 165.7, 165.0, 164.9, 164.54, 164.51), 133.8, 133.7, 133.6, 133.40, 133.37, 133.3, 130.2, 130.1, 129.8, 129.73, 129.70, 129.66 129.54, 129.47, 129.4, 129.3, 129.2, 128.82, 128.78, 128.75, 128.7, 128.6, 128.5, 128.41, 128.39, 100.2, 100.0, 90.3, 76.64, 76.58, 72.73, 72.68, 72.3, 72.07, 72.06, 71.9, 71.3, 69.13, 69.09, 66.8), 62.6, 62.0, 61.6, 20.8, 20.6. HRMS (ESI) Calcd for C 78 H 67 BrNaO 25+ [M+Na] + : 1505.3047, found: 1505.3067。

[0093] 4. Preparation of Compound 19

[0094] Dissolve Compound 11 (160 mg, 93 μmol) in a mixed solution of 5.8 mL of chloroform and water (v:v = 1:1). Add TBAB (tetrabutylammonium bromide) (60 mg, 185 μmol) and K 2 CO 3 (38 mg, 278 μmol) at room temperature. After reacting for 10 min, add Compound 18 (275 mg, 185 μmol), then raise the reaction temperature to 40 °C and react for 19 h. When TLC detects that the raw materials have reacted completely, extract the reaction solution with 50 mL of ethyl acetate, wash it with 50 mL of saturated sodium chloride solution, dry the organic phase with anhydrous sodium sulfate, filter, evaporate to dryness, and purify by column chromatography (petroleum ether:ethyl acetate = 1.5:1) to obtain a white solid, namely Compound 19 (260 mg, 89%). 1 1H NMR (400 MHz, CDCl 3 ) δ 8.22 - 8.14 (m, 8H, ArH), 8.05 (d, J = 7.9 Hz, 2H, ArH), 7.91 - 7.69 (m, 31H, ArH), 7.66 - 7.56 (m, 4H, ArH), 7.55 - 7.09 (m, 64H, ArH), 5.79 - 5.69 (m, 4H, 3b-H, 3c-H, 3e-H, 3f-H), 5.53 - 5.46 (m, 1H, 2b-H), 5.44 - 5.28 (m, 11H, PhCH, 1d-H, 2c-H, 2e-H, 2f-H, 4b-H, 4c-H, 4e-H, 4f-H), 4.96 (s, 1H, =CH 2 ), 4.90 (t, J = 9.7 Hz, 1H, 4d-H), 4.81 (d, J = 7.7 Hz, 1H, 1b-H), 4.71 (d, J = 7.7 Hz, 1H, 1e-H), 4.68 (d, J = 7.6 Hz, 1H, 1c-H), 4.61 (d, J = 7.6 Hz, 1H, 1f-H), 4.54 (s, 1H, =CH 2), 4.49 (d, J = 7.6 Hz, 1H, 1a-H), 4.22 - 4.04 (m, 9H, 6a-H, 6b-H, 6b’-H, 6c-H, 6c’-H, 6e-H, 6e’-H, 6f-H, 6f’-H), 3.98 (dd, J = 12.5, 4.8 Hz, 1H, 6d-H), 3.95 - 3.70 (m, 5H, 2a-H, 2d-H, 3a-H, 3d-H, 6d’-H), 3.60 - 3.47 (m, 2H, 4a-H, 6a’-H), 3.36 - 3.29 (m, 1H, 5d-H), 3.20 - 3.10 (m, 1H, 5a-H), 2.68 - 2.58 (m, 2H), 2.43 - 2.32 (m, 2H), 2.17 (dd, J = 10.7, 3.6 Hz, 1H), 2.06 - 1.94 (m, 3H), 1.89 (s, 3H), 1.85 - 1.43 (m, 9H), 1.40 - 1.04 (m, 8H), 0.93 - 0.71 (m, 7H), 0.71 - 0.49 (m, 1H). 13 C NMR (100 MHz, CDCl 3δ 175.0, 170.33, 169.29, 165.99, 165.95, 165.93), 165.88, 165.80, 165.64, 165.21, 165.17, 165.10, 165.07, 164.9, 164.8, 164.6 152.5, 137.5, 133.73, 133.67, 133.65, 133.64, 133.56, 133.5, 133.4, 133.28, 133.26, 133.01, 132.96, 130.2, 130.1, 129.9, 129.79, 129.76, 129.75, 129.74, 129.71, 129.70, 129.68, 129.62, 129.59, 129.53 129.48, 129.44, 129.42, 129.37, 129.32, 129.27 129.1, 129.0, 128.90, 128.87, 128.8, 128.62, 128.57, 128.52, 128.49, 128.42, 128.39, 128.32, 128.25, 128.0, 105.0, 101.2, 100.22, 100.15, 100.0, 97.0, 91.1, 86.0, 80.3, 79.9, 78.9, 78.5, 76.3, 72.8, 72.7, 72.6, 72.4, 72.1, 71.5, 71.4, 71.3, 70.3, 69.7, 69.6, 69.5, 68.9, 67.7, 65.9, 63.4, 63.3, 63.0, 62.8, 61.8, 57.3, 54.0, 47.4, 44.0, 43.2, 42.7, 41.4, 40.3, 39.4, 29.7, 29.2, 22.6, 21.5, 20.89, 20.86, 20.8, 20.7, 20.3, 19.2, 16.6. HRMS(ESI) Calcd for C 179 H 166 NO 51 + [M + NH 4 + : 3146.0455, found: 3146.0501。

[0095] 5. Preparation of Compound 2

[0096] ​Compound 19 (145 mg, 0.046 mmol) was dissolved in a mixed solution of 1.1 mL of dichloromethane and methanol (v:v = 1:1), and p-TsOH (p-toluenesulfonic acid) (40 mg, 0.23 mmol) was added. The reaction was carried out overnight at room temperature. After the reaction of the starting material was completed as detected by TLC, the reaction was quenched with 0.5 mL of triethylamine. After evaporation to dryness, the intermediate was separated and purified by column chromatography (petroleum ether:ethyl acetate = 1:1). Then the intermediate was dissolved in 5.5 mL of methanol, and freshly prepared sodium methoxide solution was added to adjust the pH to 9. The reaction was carried out at room temperature for 5 h. After the reaction of the starting material was completed as detected by TLC, the pH was adjusted to 7 with cation exchange resin, filtered, and evaporated to dryness. The product was separated and purified by a C18 column (methanol:water = 2:1) to obtain a white solid, namely compound 2 (47 mg, 79%). Its 1H NMR spectrum is as Figure 5 shown, and its 13C NMR spectrum is as Figure 6 shown. 1 1H NMR (600 MHz, DMSO-d 6 ) δ 5.71 (d, J = 4.9 Hz, 1H, OH), 5.58 (d, J = 5.3 Hz, 1H, OH), 5.52 (d, J = 8.0, 1H, 1d-H), 5.37 (d, J = 6.5 Hz, 1H, OH), 5.29 (d, J = 6.9 Hz, 1H, OH), 5.10 (s, 1H, =CH 2 ), 5.08 - 5.05 (m, 4H, OH×4), 4.97 - 4.90 (m, 3H, OH×3), 4.86 (d, J = 4.3 Hz, 1H, OH), 4.81 - 4.45 (m, 11H, =CH 2 , 1a-H, 1b-H, 1c-H, 1e-H, 1f-H, OH×5), 4.43 (t, J = 5.8 Hz, 1H, OH), 4.33 (t, J = 5.3 Hz, 1H, OH), 4.07 - 4.01 (m, 1H, OH), 3.83 (t, J = 6.0 Hz, 1H), 3.74 - 3.67 (m, 6H), 3.67 - 3.58 (m, 2H), 3.54 - 3.48 (m, 1H), 3.36 (d, J = 1.6 Hz, 12H), 3.26 - 3.17 (m, 3H), 3.17 - 3.11 (m, 3H), 3.11 - 3.01 (m, 4H), 3.01 - 2.95 (m, 2H), 2.95 - 2.88 (m, 2H), 2.33 - 2.28 (m, 1H, CH 2 ×1), 2.08 (d, J = 10.6 Hz, 1H, CH 2 ×1), 2.00 (s, 2H, CH 2 ×2), 1.95 - 1.87 (m, 1H, CH 2×1), 1.77 (d, J = 10.8 Hz, 5H, CH 2 ×5), 1.67 (d, J = 13.6 Hz, 1H, CH 2 ×1), 1.47 (d, J = 12.1 Hz, 2H, CH 2 ×2), 1.41 (d, J = 10.0 Hz, 1H, CH 2 ×1), 1.34 (s, 1H, CH 2 ×1), 1.16 (s, 3H, CH 3 ×3), 0.99 (t, J = 6.9 Hz, 1H, CH×1), 0.91 (d, J = 7.2 Hz, 2H, CH×1, CH 2 ×1), 0.82 (s, 3H, CH 3 ×3), 0.76 (s, 1H, CH 2 ×1). 13 C NMR (150 MHz, DMSO-d 6 ) δ 174.7, 152.8, 104.1, 102.9, 102.8, 102.5, 101.7, 95.9, 92.0, 86.7, 86.5, 85.6, 79.0, 77.2, 77.0 (2C), 76.8, 76.7, 76.6, 76.5, 76.4, 76.1, 75.3, 74.5, 74.1, 73.8 (2C), 71.2, 70.8, 70.1, 68.6, 68.2, 61.9, 61.6, 60.99, 60.96, 60.4, 56.5, 53.2, 46.7, 43.4, 42.8, 41.3, 40.0, 38.9, 36.9, 36.6, 28.1, 21.5, 19.7, 19.2, 16.1. HRMS (ESI) Calcd for C 56 H 89 O 33 - [M - H] - : 1289.5291, found: 1289.5288。

[0097] The structural formulas and synthetic strategy diagrams of Compound 1 and Compound 2 are as Figure 7 shown.

[0098] Comparative Examples 1 - 4

[0099] Compound 10 was prepared from Compound 3 and Compound 4 under the conditions in Table 1. Except for the parameter changes listed in the table, the remaining preparation steps were the same as those for the preparation of Compound 10 in Example 3. The synthesis results are summarized in Table 1.

[0100] Table 1 Preparation Conditions and Results of Comparative Examples 1-4 and Example 3

[0101]

[0102] Note: *The concentration of Compound 4 refers to the concentration of Compound 4 in dichloromethane.

[0103] As can be seen from Table 1, when the amount of pivalonitrile is too small, the selectivity of β / α will decrease. When no pivalonitrile is contained, the product is mainly α, and the selectivity of β / α is 1:1.6. When the concentration of Compound 4 is 0.01 mol / L, the reaction time is long, and the reaction ends in 60 minutes, with a yield of only 80%. However, by using the method of Example 3 of the present invention, the selectivity of β / α is high, the reaction time is short, and the yield is high.

[0104] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for synthesizing steviol glycosides Rebaudioside A and Rebaudioside M, characterized in that: The steps include: (1) Compound 7 is oxidized by ammonium cerium nitrate to obtain compound 8; (2) reacting compound 8 with trichloroacetonitrile to obtain compound 4; (3) Compound 4 is reacted with compound 3 in the presence of gold trichloride and pivalonitrile to obtain compound 10; (4) removing the protecting group of the β-configuration compound 10 under the action of tetrabutylammonium fluoride to obtain compound 11; (5) reacting compound 11 with compound 14 or compound 18 under the action of tetrabutylammonium bromide to obtain compound 15 or compound 19; (6) removing all protecting groups from compound 15 or compound 19 to obtain Rebaudioside A or Rebaudioside M; 2. The synthesis method according to claim 1, characterized in that Compound 7 is obtained by reacting compound 5 and compound 6 under the catalysis of trimethylsilyl trifluoromethanesulfonate; 3. The synthesis method according to claim 1, characterized in that Compound 3 is obtained by the reaction of steviol and tert-butyldimethylsilyl chloride.

4. The synthesis method according to claim 1, characterized in that In step (3), the molar ratio of compound 4, compound 3, gold trichloride and pivalonitrile is 1:(0.7-0.9):(0.25-0.4):(170-200).

5. The synthesis method according to claim 1, characterized in that The reaction time of step (3) is 30 to 40 minutes, and the reaction temperature is -70 to -50°C.

6. The synthesis method according to claim 1, characterized in that The reaction system of step (3) also includes dichloromethane, and the volume ratio of dichloromethane to pivalonitrile is 1:(0.8-1.2).

7. The synthesis method according to claim 1, characterized in that The synthesis method of compound 14 is as follows: compound 12 is reacted with benzoyl chloride to generate compound 13, and compound 13 is reacted with hydrogen bromide in acetic acid to obtain compound 14; 8. The synthesis method according to claim 1, characterized in that Compound 18 is obtained by reacting compound 17 with hydrogen bromide in acetic acid; 9. The synthesis method according to claim 8, characterized in that Compound 17 is obtained by reacting compound 16 with acetic anhydride under the action of 4-dimethylaminopyridine; 10. The synthesis method according to claim 9, characterized in that Compound 16 is prepared by reacting compound 7 with p-toluenesulfonic acid and then with ammonium cerium nitrate.

Images