Synthesis process of brassinolide

Abstract

The invention relates to a synthesis process of brassinolide, which is characterized in that a compound A is used as an initial raw material, and is subjected to esterification reaction, ring-closing reaction, oxidation reaction, oxidation ring-opening reaction, dihydroxylation reaction and oxidation rearrangement reaction to prepare the brassinolide. And the technological process is simpler and more convenient, and the yield is higher. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of agrochemistry, and particularly to a synthesis process of brassinolide. Background Art

[0002] Brassinolide is a new type of green and environment-friendly plant growth regulator. In 1970, American scientist Grove isolated it from rape pollen. Through the study of its crystal structure, it was found that this is a sterol compound, which was named brassinolide. Brassinolide is a plant endogenous hormone with extremely high activity, and its chemical name is (22R,23R,24S)-2α,3α,22,23-tetrahydroxy-24-methyl-B-homo-7-oxa-5α-cholest-6-one. Brassinolide can accelerate the elongation and division of plant cells, regulate the photosynthesis of plants, and improve the stress resistance of plants (cold resistance, drought resistance, salt-alkali resistance, disease resistance, etc.). It can be applied to a variety of crops and has broad application prospects in agricultural production. Its structural formula is:

[0003] Currently reported synthesis routes of brassinolide mainly include: In 1980, Fung et al. first reported a method for the stereoselective synthesis of brassinolide from stigmasterol (2). Based on the methods for synthesizing intermediate 3 reported by Salmond, Hutchins, etc., using the C-20 chirality, intermediate 3 was reacted with the E-configuration lithium reagent (4) to synthesize compound 5. After oxidation with m-chloroperoxybenzoic acid (MCPBA) and reduction with LiBH4 / BH3·THF, the C-24 configuration was inverted to obtain compounds 7 and 8, and the regioselectivity was 3:1. The (22R,23R,24S)-configured compound 7 was subjected to acid-catalyzed rearrangement, ketalization, C-3 hydroxyl sulfonylation, hydroboration-oxidation to introduce a C-6 hydroxyl group, elimination in the Li2CO3 / DMAC system, Jones oxidation of the C-6 hydroxyl group, osmium tetroxide (OsO4) oxidation of the C-2 double bond, and trifluoroperacetic acid (CF3CO3H) to lactonize the B ring and hydrolyze the protecting group to synthesize brassinolide;

[0004]

[0005] In 1984, Mori et al. reported a method for the regioselective and stereoselective ring-opening of the C-23 and C-24 epoxy rings in the side chain. Ikekawa et al. had attempted to introduce a methyl group at C-24 of the epoxy ring using an organocopper reagent but without success. Mori used Me3Al for ring-opening during the construction of the side chain, achieving the direct attachment of a methyl group at the C-24 position and obtaining the side chain of brassinolide with the correct configuration. The addition of isopropylalkynyllithium 25 to the aldehyde group of compound 22, the reduction of the triple bond with P2-Ni / H2 / H2NCH2CH2NH2, the epoxidation of the double bond with MCPBA, and the ring-opening with Me3Al / n-BuLi gave compound 27. Brassinolide was synthesized from compound 2 through 16 steps with an overall yield of 3%. This method has good stereoselectivity, but the amount of Me3Al reagent used is large and unstable, and the reaction needs to be carried out at -70 °C under Ar protection for 69 h.

[0006]

[0007] Since the content of brassinolide compounds extracted from natural plants is extremely low, and the purity of the extracted products is not high, it is difficult to meet the research and application requirements. Currently, most synthetic methods use expensive and highly toxic osmium tetroxide as an oxidant, increasing the cost and polluting the environment. Therefore, optimizing the synthesis process of brassinolide is a key technical issue for reducing the production cost of brassinolide and realizing industrial production. Summary of the Invention

[0008] The purpose of the present invention is to provide a synthesis process of brassinolide to solve the technical problems such as high toxicity and high price of catalysts in the prior art.

[0009] To solve the above technical problems, the present invention provides a synthesis process of brassinolide, and its synthesis route is as follows:

[0010]

[0011] It includes the following steps:

[0012] 1) Using compound A as the starting material, compound B is obtained through an esterification reaction;

[0013] 2) Compound B undergoes a ring-closure reaction in the presence of a base to obtain compound C;

[0014] 3) Compound C undergoes an oxidation reaction to obtain compound D;

[0015] 4) Compound D undergoes an oxidative ring-opening reaction to obtain compound E;

[0016] 5) Compound E undergoes a hydroxylation reaction to obtain compound G;

[0017] 6) Compound G undergoes an oxidative rearrangement reaction to obtain the target product, brassinolide compound H.

[0018] The chiral ligand for the hydroxylation reaction in step 5) is:

[0019] As a preferred technical solution of the present invention, it includes the following steps:

[0020] 1) Using compound A as the starting material, compound B is obtained through an esterification reaction;

[0021] 2) Compound B is heated under reflux in the presence of a base for a ring-closure reaction to obtain compound C;

[0022] 3) Compound C is then oxidized using Jones reagent under an ice-water bath condition to obtain compound D;

[0023] 4) Compound D undergoes an oxidative ring-opening reaction to obtain compound E;

[0024] 5) Compound E undergoes a hydroxylation reaction of a diene compound under the action of a catalyst Rh(acac)(nbd) and a chiral ligand Ligand to obtain compound G;

[0025] 6) Finally, compound G uses trifluoroperacetic acid as an oxidant and H2O2 as a secondary oxidant to obtain brassinolide compound H through a Baeyer-Villiger oxidation rearrangement reaction.

[0026] As a preferred technical solution of the present invention, in step 1), the solvent for the esterification reaction is selected from one of ethyl acetate, dichloromethane, acetone, or butanone; triethylamine is added as a base reagent in the esterification reaction; in the esterification reaction, the molar ratio of compound A to p-toluenesulfonyl chloride is 1:1 - 2; the reaction time of the esterification reaction is 0.5 - 4 h, and the reaction temperature of the esterification reaction is 0 - 10 °C;

[0027] As a preferred technical solution of the present invention, in step 2), the base is selected from one of sodium bicarbonate, potassium bicarbonate, and sodium carbonate; the solvent is selected from one of acetone or butanone; the temperature of the reflux reaction is 60 - 80 °C; the reaction time of the reflux reaction is 4 - 6 hours;

[0028] As a preferred technical solution of the present invention, in step 3), the temperature of the oxidation reaction is 0 - 10 °C; the reaction time of the oxidation reaction is 2 - 6 hours;

[0029] As a preferred technical solution of the present invention, in step 4), the molar ratio of compound D:p-toluenesulfonic acid:sodium bromide is 1:(0.2 - 0.4):(0.4 - 0.8); the solvent for the oxidative ring-opening reaction is DMF or DMA; the temperature of the oxidative ring-opening reaction is 140 - 180 °C, and the reaction time of the oxidative ring-opening reaction is 3 - 6 hours;

[0030] As a preferred technical solution of the present invention, in step 5), the molar ratio of compound E to compound F is 1:1 - 2; the catalyst for the hydroxylation reaction is rhodium (norbornadiene) acetylacetonate (i.e., Rh(acac)(nbd)); the molar ratio of compound E:Rh(acac)(nbd):chiral ligand is 1:0.05 - 0.2:0.05 - 0.2, and the more preferred molar ratio is: 1:0.1:0.1; the solvent for the hydroxylation reaction is tetrahydrofuran; the reaction temperature of the hydroxylation reaction is room temperature; the reaction time of the hydroxylation reaction is 10 - 24 hours; the operation further includes: under argon protection, slowly dropwise adding an aqueous sodium hydroxide solution with a concentration of 3M and an aqueous hydrogen peroxide solution with a concentration of 30%, continuing to stir at room temperature for 3 hours, then quenching the reaction with a saturated aqueous sodium thiosulfate solution and an aqueous sodium hydroxide solution with a concentration of 1M, and then performing extraction and purification operations.

[0031] As a preferred technical solution of the present invention, in step 6), the solvent for the oxidative rearrangement reaction is dichloromethane or chloroform; the temperature of the oxidative rearrangement reaction is 0 - 5°C; the reaction time of the oxidative rearrangement reaction is 3 - 6 hours.

[0032] The beneficial effects of the present invention are as follows:

[0033] 1) The preparation method of the present invention does not need to use highly toxic and expensive osmium metal catalysts, and is more environmentally friendly.

[0034] 2) When performing the hydroxylation reaction of the present invention, rhodium (norbornadiene) acetylacetonate is used as the catalyst, as the chiral ligand, and compound G is successfully synthesized at room temperature, avoiding the use of highly toxic and expensive osmium metal catalysts, and the process is more simple and the yield is better. Specific Embodiments

[0035] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0037] Example 1

[0038] Synthesis of brassinolide compound H:

[0039]

[0040] The synthesis steps of the specific brassinolide compound H are as follows:

[0041] Synthesis of compound B:

[0042] Under the condition of an ice bath at 0 °C, 19.9 g (50 mmol) of compound A was dissolved in 300 mL of methyl ethyl ketone solution, and then 13.9 mL (10.1 g, 100 mmol) of triethylamine was added. Under stirring conditions, 9.28 g (60 mmol) of p-toluenesulfonyl chloride was slowly added dropwise. After the addition was complete, the reaction was continued with stirring for 1 h. The reaction was monitored by TLC plate spotting. After the reaction was complete, 100 mL of NaCl solution was added to quench the reaction. The mixture was allowed to stand and the upper organic phase was separated. The organic phase was washed twice with 100 mL of NaHCO3 solution and 100 mL of water in sequence. The organic phases were combined, filtered, rotary evaporated, and purified by column chromatography to obtain 23.3 g of compound B with a yield of 98%.

[0043] Synthesis of compound C:

[0044] 19.05 g (40 mmol) of the above-prepared compound B was dissolved in 300 mL of acetone, 100 mL of water and 6.72 g (80 mmol) of NaHCO3 were added, and the mixture was heated to reflux at 60 °C for 4 h. The reaction was monitored by TLC. After the reaction was complete, the reaction solution was cooled to room temperature, allowed to stand and the organic phase was separated. The organic phase was washed twice with 200 mL of saturated NaCl aqueous solution. The organic phases were combined, dried over anhydrous Na2SO4, filtered, rotary evaporated under vacuum, and purified by column chromatography to obtain 12.75 g of compound C with a yield of 80%.

[0045] Synthesis of compound D:

[0046] 7.97 g (20 mmol) of the above-prepared compound C was dissolved in 100 mL of methyl ethyl ketone solution, and the temperature was lowered to 2 °C. 9.6 mL of Jones reagent (Sigma-Aldrich, product number: G4410) was started to be added dropwise. After the addition was complete, the reaction was carried out for 3 h. The reaction was monitored by TLC. After the reaction was complete, 50 mL of saturated NaCl solution was added to the flask, stirred, allowed to stand and the organic phase was separated. The organic phase was washed three times with 50 mL × 3 saturated NaHCO3 aqueous solution and 50 mL × 3 saturated NaCl solution in sequence. The organic phase was dried over anhydrous NaSO4, filtered by suction, rotary evaporated under vacuum, and purified by column chromatography to obtain 7.53 g of compound D with a yield of 95%.

[0047] Preparation of compound E:

[0048] Dissolve 4.0 g (10 mmol) of the above-prepared Compound D in 50 mL of DMF solution. Add 0.38 g (2.2 mmol) of p-toluenesulfonic acid and 0.52 g (4 mmol) of sodium bromide to the flask. Heat to 170 °C and reflux for 4 h. Monitor the reaction by TLC. After the reaction is complete, cool to room temperature, extract twice with 200 mL of ethyl acetate, let it stand for phase separation, combine the organic phases, dry the organic phase with anhydrous NaSO4, filter, rotary evaporate under vacuum, and separate the crude product by column chromatography to obtain 3.17 g of Compound E. The yield is 80%.

[0049] Preparation of Compound G:

[0050]

[0051] Under an argon atmosphere, add 117.6 mg (0.4 mmol) of the catalyst [Rh(acac)(nbd)], 224.2 mg (0.4 mmol) of the ligand (S)-PINAP and 0.5 mL of THF to a 100 mL flask. Stir the above mixed solution for 5 minutes. Add 2.8 g (8 mmol) of Compound F under argon conditions. After stirring the solution for 5 minutes, add 1.58 g (4 mmol) of Compound E to the solution under argon. Seal the reactor and stir the mixed solution at room temperature for 14 hours. Subsequently, cool the mixed solution to 0 °C. Then, under argon protection, slowly add dropwise 12.8 mL of a 3 M aqueous sodium hydroxide solution and 12.8 mL of a 30% aqueous hydrogen peroxide solution. Continue to stir at room temperature for 3 hours. Then, quench the reaction with 16 mL of a saturated aqueous sodium thiosulfate solution and 150 mL of a 1 M aqueous sodium hydroxide solution. Extract three times with 200 mL * 3 of ethyl acetate, combine the organic phases, dry with anhydrous sodium sulfate, filter, rotary evaporate, and purify by silica gel column chromatography to obtain 1.5 g of Compound G. The eluent is petroleum ether / ethyl acetate (volume ratio 2:1). The yield is 82%, and ee% = 90%.

[0052] Preparation of Compound H:

[0053] Take 929.4 mg (2 mmol) of the above-prepared Compound G and dissolve it in 30 mL of dichloromethane solution (for later use). Add (5.5 mL, 0.025 mol) of trifluoroperacetic acid and 30 mL of dichloromethane to a beaker. Place the beaker in an ice bath and cool it to 0 °C. Control the temperature at 0 °C and slowly add hydrogen peroxide (2 mL). After the addition is complete, stir at 0 °C for 30 minutes. Then, quickly add the above-prepared dichloromethane solution to the flask. The system quickly becomes clear. Control the temperature at 0 °C and react for 4 h. Monitor the reaction by TLC plate. After the reaction is complete, add 50 mL of water to the flask, stir for a period of time, separate the upper aqueous phase, and extract it twice with 100 mL of ethyl acetate. Let it stand for layering, separate the organic phase and combine them. Wash the organic phase twice with 200 mL of NaHCO3 and 200 mL of NaHSO3 solution respectively, and then wash it with 100 mL of saturated NaCl. Separate the upper ethyl acetate phase, dry it with anhydrous Na2SO4, filter, concentrate, and separate by column chromatography to obtain 721.0 mg of Compound H, with a yield of 75%.

[0054] 1 HNMR(400MHz,CDCl3)δ4.13 - 4.07(m,2H),4.01(d,1H),3.82(d,2H),3.52(d,1H),3.33 - 3.29(m,1H),2.54 - 2.23(m,5H),2.04–1.82(m,7H),1.61 - 1.44(m,5H),1.31 - 1.16(m,6H),0.98(d,3H),0.94 - 0.81(m,12H),0.71(s,3H).

[0055] Comparative Example 1

[0056] Preparation of Brassinolide Compound G

[0057] The synthetic route of Comparative Example 1 is basically the same as that of Example 1, with the only difference being the ligand used in the preparation of Compound G. The ligand used in Example 1 is: ligand (S)-PINAP; while Comparative Example 1 uses ligand (S)-Quinap. The specific synthetic route and steps for preparing Compound G in Comparative Example 1 are as follows:

[0058]

[0059] Under an argon atmosphere, 117.6 mg (0.4 mmol) of the catalyst [Rh(acac)(nbd)], 175.8 mg (0.4 mmol) of the ligand (S)-Quinap and 0.5 mL of THF were added to a 100 mL flask. The above mixed solution was stirred for 5 minutes. Under argon, 2.8 g (8 mmol) of compound F was added. After the solution was stirred for 5 minutes, 1.58 g (4 mmol) of compound E was added to the solution under argon. The reactor was sealed, and the mixed solution was stirred at room temperature for 14 hours. Subsequently, the mixed solution was cooled to 0 °C. Then, under argon protection, 12.8 mL of an aqueous sodium hydroxide solution with a concentration of 3 M and 12.8 mL of a 30% aqueous hydrogen peroxide solution were slowly added dropwise. Stirring was continued at room temperature for 3 hours. Subsequently, the reaction was quenched with 16 mL of a saturated aqueous sodium thiosulfate solution and 150 mL of an aqueous sodium hydroxide solution with a concentration of 1 M. The mixture was extracted three times with 200 mL × 3 of ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, rotary evaporated, and purified by silica gel column chromatography to obtain 1.3 g of compound G. The eluent was petroleum ether / ethyl acetate (volume ratio 2:1), and the yield was 70%, ee% = 46%.

[0060] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A synthesis process of brassinolide, characterized in that: The steps include: 1) Using compound A as the starting material, compound B is obtained through esterification reaction; 2) Compound B is heated under reflux in the presence of a base to undergo a ring-closing reaction to obtain compound C; 3) Compound C is then oxidized using Jones reagent in an ice-water bath to obtain compound D; 4) Compound D is subjected to an oxidative ring-opening reaction to obtain compound E; 5) Compound E undergoes a hydroxylation reaction of a diene compound under the action of a catalyst Rh(acac)(nbd) and a chiral ligand to obtain compound G; 6) Finally, compound G is subjected to Baeyer-Villiger oxidative rearrangement reaction with trifluoroperacetic acid as an oxidant and H2O2 as a secondary oxidant to obtain brassinolide compound H; Its synthetic route is as follows: The chiral ligand for the hydroxylation reaction in step 5) is:

2. The synthesis process of brassinolide according to claim 1, characterized in that: The solvent for the esterification reaction in step 1) is selected from one of ethyl acetate, dichloromethane, acetone or butanone; triethylamine is added as an alkaline reagent in the esterification reaction in step 1); in the esterification reaction in step 1), the molar ratio of compound A to p-toluenesulfonyl chloride is 1:1-2; in step 1), the reaction time of the esterification reaction is 0.5-4h; and the reaction temperature of the esterification reaction is 0-10°C.

3. The synthesis process of brassinolide according to claim 1, characterized in that: In the step 2), the base is selected from one of sodium bicarbonate, potassium bicarbonate and sodium carbonate; the solvent for the ring-closing reaction is selected from one of acetone and butanone; the reflux temperature is 60-80° C.; and the reflux time is 4-6 hours.

4. The synthesis process of brassinolide according to claim 1, characterized in that: In the step 3), the temperature of the oxidation reaction is 0-10° C.; and the time of the oxidation reaction is 2-6 hours.

5. The synthesis process of brassinolide according to claim 1, characterized in that: In the step 4), the molar ratio of compound D: p-toluenesulfonic acid: sodium bromide is 1:(0.2-0.4):(0.4-0.8); the solvent of the oxidative ring-opening reaction is DMF or DMA; the temperature of the oxidative ring-opening reaction is 140-180° C., and the reaction time of the oxidative ring-opening reaction is 3-6 hours.

6. The synthesis process of brassinolide according to claim 1, characterized in that: In the step 5), the molar ratio of compound E: compound F is 1: 1-2; the catalyst of the hydroxylation reaction is Rh(acac)(nbd); the molar ratio of compound E: Rh(acac)(nbd): chiral ligand is 1: 0.05-0.2: 0.05-0.2; the solvent of the hydroxylation reaction is tetrahydrofuran; the reaction temperature of the hydroxylation reaction is room temperature; the reaction time of the hydroxylation reaction is 10-24 hours; the operation further comprises: under argon protection, slowly dropping a 3M sodium hydroxide aqueous solution and a 30% hydrogen peroxide aqueous solution, continuing stirring at room temperature for 3 hours, then quenching the reaction with a saturated sodium thiosulfate aqueous solution and a 1M sodium hydroxide aqueous solution, and then performing extraction and purification operations.

7. The synthesis process of brassinolide according to claim 1, characterized in that: In the step 6), the solvent for the oxidative rearrangement reaction is dichloromethane or chloroform; the temperature for the oxidative rearrangement reaction is 0-5° C.; and the reaction time for the oxidative rearrangement reaction is 3-6 hours.

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