A method for synthesizing 28-homobrassinolide

Abstract

The application discloses an environment-friendly synthesis method of 28-homobrassinolide, wherein (2,22)-diene-24S-ethyl-5alpha-cholesta-6-ketone P1 is used as a starting material, double bonds on a ring of P1 are simultaneously epoxidized, namely, double epoxidation, ring opening, acetylation, one-time hydrolysis and two-time hydrolysis are carried out to obtain a tetrahydroxy compound, and finally, lactonization is carried out to obtain the target 28-homobrassinolide. The 28-homobrassinolide is synthesized by a brand-new organic synthesis method, which is energy-saving, efficient, environment-friendly, simple in process and good in industrial application value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of synthesis of steroidal plant growth hormone, and particularly relates to a synthesis method of 28-homobrassinolide. BACKGROUND

[0002] Brassinolide is a new type of green and environmentally friendly plant growth hormone without toxicity and harm, which is the latest plant growth regulator found in nature and is known as the sixth type of plant growth regulator. Its biological activity far exceeds the existing five hormones, i.e., auxin, gibberellin, cytokinin, abscisic acid and ethylene.

[0003] More than 60 brassinolide analogues have been found so far, but few of them have high biological activity and practical value. Among them, 28-homobrassinolide has relatively high biological activity and is the only plant hormone with high activity for monocotyledonous and dicotyledonous plants and woody plants. Therefore, as a product with high added value and broad application prospects, it is of great theoretical and practical significance to develop the synthesis route and production process of 28-homobrassinolide.

[0004] There are many literatures on the synthesis of 28-homobrassinolide. The most commonly used synthesis route is as follows: using stigmasterol as the raw material, the target product is obtained through six steps of hydroxyl sulfonylation, cyclization, oxidation of secondary alcohol, rearrangement, asymmetric oxidation of olefin and Baeyer-Villiger oxidation reaction. However, the key step in this synthesis route uses the highly toxic and expensive osmium tetroxide (OsO4) as a catalyst, and a chiral ligand of quinidine needs to be added during the reaction process to improve its stereoselectivity. Therefore, it is of great significance to develop a process for synthesizing brassinolide without osmium.

[0005] Chinese invention patent CN110452284A discloses a preparation method of 28-homobrassinolide, specifically discloses a method for obtaining 28-homobrassinolide through two steps of Sharpless asymmetric dihydroxylation and Baeyer-Villiger oxidation reaction, using (2,22)-dien-24S-ethyl-5α-cholestan-6-one as the raw material under the action of a chiral catalyst and an oxidizing agent.

[0006] However, the patent uses potassium osmate dihydrate as a catalyst, and potassium osmate dihydrate is a highly toxic and expensive compound. In addition, under the conditions of high temperature, humidity and light, potassium osmate dihydrate may decompose to produce dangerous osmium ions.

[0007] Chinese invention patent CN112851744B discloses a synthesis method of 28-homobrassinolide, specifically discloses a synthesis method of 28-homobrassinolide, which selects stigmasterol B as a starting material, carries out esterification reaction to obtain compound C, heats and refluxes C under alkaline conditions to obtain compound D; D is oxidized to obtain compound E; E is oxidized to open a ring to obtain compound F; F is subjected to dihydroxylation reaction to obtain compound G; and G is subjected to oxidation rearrangement reaction to obtain compound A 28-homobrassinolide.

[0008] Although the patent avoids the use of osmium tetroxide as a catalyst, it is similar to the use of osmium tetroxide as a catalyst, uses ruthenium trioxide as an oxidizing agent, and sodium periodate as an auxiliary oxidizing agent to generate in-situ ruthenium tetroxide; According to the data, ruthenium tetroxide is also a highly toxic volatile oxidant, and ruthenium tetroxide is strictly prohibited from contacting with reducing organic matter to prevent explosion. Ruthenium tetroxide can easily oxidize human tissues, leaving ruthenium dioxide deposits, and its vapor can strongly irritate the eyes and respiratory tract, so it must be avoided when in use. And the product obtained by using ruthenium tetroxide in the tetrahydroxylation reaction post-processing may contain residual heavy metal ruthenium; The waste water produced after the reaction is a heavy metal wastewater containing ruthenium, which has a great impact on the environment and organisms. Chinese invention patent CN110483611B discloses a preparation method of 28-homobrassinolide, which uses (2,22)-diene-24S-ethyl-5α-cholestan-6-one as a raw material to obtain the corresponding asymmetric epoxide under the action of a chiral catalyst and an oxidizing agent, and then undergoes esterification, oxidation and hydrolysis reactions.

[0009] Although the invention patent does not use osmium tetroxide (OsO4) as a catalyst, the invention uses a chiral metal salen Mn(III) complex as a first chiral catalyst, and a binary catalyst composed of tetrabutylammonium bromide (TBAB) and graphene oxide (GO) as a second catalyst. The preparation process of the two catalysts is complex, the raw materials are difficult to obtain and expensive, and the industrial production is limited.

[0010] Therefore, it is necessary to develop a new synthesis method of 28-homobrassinolide, which does not use highly toxic and expensive osmium catalysts, does not need to add chiral ligands to improve its stereoselectivity, and has a simple synthesis route and cheap and easily available raw materials. SUMMARY

[0011] The application provides a novel synthesis method of 28-homobrassinolide, which can effectively reduce the production cost of 28-homobrassinolide.In the existing dihydroxylation reaction, OsO4 is mostly used as a catalyst, and the method is widely used in the synthesis of fine chemicals and natural products.However, due to the high price and toxicity of osmium metal, the industrial production is greatly limited.In the dihydroxylation reaction, the double bond is opened by using an olefin epoxidation ring-opening method, then the chiral is changed by esterification using acetic anhydride, and finally the dihydroxylation product is obtained by hydrolysis.The use of toxic and expensive osmium metal as a catalyst is avoided, and the process is simple, pollution-free and has a better yield.

[0012] The object of the application is achieved by the following technical solutions:

[0013] The application provides a synthesis method of 28-homobrassinolide, which comprises the following steps:

[0014] (1) Double epoxidation reaction: starting material (2,22)-dien-24S-ethyl-5α-cholestan-6-one P1 is reacted under the action of m-chlorobenzoic acid, alkali metal bicarbonate and a first solvent to obtain an intermediate P2 after treatment;

[0015] (2) Double epoxide ring-opening reaction: P2 is reacted under the action of hydrobromic acid and a second solvent to obtain an intermediate P3 after treatment;

[0016] (3) Acetylation reaction of all hydroxyl groups: P3 is reacted under the action of an organic base, 4-dimethylaminopyridine and acetic anhydride at normal temperature to obtain an intermediate P4 after treatment;

[0017] (4) First hydrolysis reaction: P4 is hydrolyzed under the action of acetic acid, potassium acetate and water at 115-125 DEG C to obtain an intermediate P5 after treatment;

[0018] (5) Second hydrolysis reaction: P5 is hydrolyzed under the action of an alkali metal hydroxide aqueous solution and a third solvent at 70-75 DEG C to obtain an intermediate P6 after treatment;

[0019] (6) Baeyer-Villiger oxidation reaction: P6 is reacted under the action of trifluoroperacetic acid and a fourth solvent in an inert gas environment to obtain a target product P7, i.e., 28-homobrassinolide, after treatment.

[0020] The specific reaction equation is shown in the following:

[0021]

[0022] Further, the alkali metal bicarbonate in the step (1) is one of sodium bicarbonate and potassium bicarbonate or a mixture of the two;

[0023] Further, the first solvent in step (1) is dichloromethane;

[0024] Further, the molar ratio of P1, m-chlorobenzoic acid and alkali metal bicarbonate in step (1) is 1:3.5~5:1.0~1.5;

[0025] Further, the reaction condition of step (1) is that the intermediate is dissolved with P1, alkali metal bicarbonate is added, and m-chloroperoxybenzoic acid is added in batches under stirring condition;

[0026] Further, the post-treatment of step (1) is that after the reaction is completed, excess anhydrous sodium sulfite and water are added for quenching, then filtration is performed, the filter cake is washed with dichloromethane, filtration is performed again, the filtrate is combined, and after being dissolved in ethyl acetate, sodium bicarbonate solution is added for washing, and the organic phase is concentrated to obtain the crude product P2 of the diepoxy intermediate.

[0027] Further, the hydrobromic acid used in step (2) is an aqueous solution of hydrobromic acid with a mass concentration of 48%;

[0028] Further, the molar ratio of P2 and hydrobromic acid in step (2) is 1:4~6;

[0029] Further, the second solvent in step (2) is butanone and / or acetone;

[0030] Further, the reaction temperature of step (2) is 5~10℃;

[0031] Further, the post-treatment of step (2) is that after the reaction is completed, the reaction system is poured into an ice water bath, and sodium chloride solid is added to be supersaturated, and then the system is separated; the water phase is extracted with butanone, the organic phase is washed with saturated sodium bicarbonate until it is neutral, the water phase is extracted with butanone again, the combined organic phase is dried by azeotropic dehydration with n-hexane, and a brominated ring-opening intermediate P3 solution is obtained.

[0032] Further, the organic base in step (3) is triethylamine or pyridine;

[0033] Further, the reaction condition of step (3) is that P3 solution is added to the organic base, 4-dimethylaminopyridine is added, and acetic anhydride is added dropwise under inert gas environment, and then stirring is performed at room temperature for 3 days;

[0034] Further, the post-treatment of step (3) is that after the reaction is completed, excess organic base is evaporated under reduced pressure, water and dichloromethane are added for extraction, the organic phase is collected, and then the organic phase is washed with sodium bicarbonate solution twice and water twice, and then the organic phase is desolvated to obtain a black gel, and then the black gel is subjected to flash column chromatography to obtain a yellow-white acetylated intermediate P4 crude product.

[0035] Further, the post-treatment in step (4) is: after the reaction is completed and the solvent is removed under reduced pressure, the remaining solid kettle bottom material is added with water and dichloromethane solvent extraction, and the organic phase is removed to obtain a first hydrolysis intermediate P5 crude product.

[0036] Further, the aqueous alkali metal hydroxide solution in step (5) is a 30wt% aqueous potassium hydroxide solution and / or a 30wt% aqueous sodium hydroxide solution;

[0037] Further, the reaction condition in step (5) is refluxing at 70-75℃ for 4-8 hours;

[0038] Further, the post-treatment in step (5) is: after the reaction is completed, acetic acid is added to adjust the pH to neutral, the methanol is removed, the remaining solid is added with water and ethyl acetate to dissolve and extract, the organic phase is washed twice with saturated sodium bicarbonate solution, and then washed twice with water, and then removed to obtain a second hydrolysis intermediate crude product. The crude product is washed by soaking in ethyl acetate to obtain a tetrahydroxylated intermediate P6;

[0039] Further, the molar ratio of P6 to trifluoroperacetic acid in step (6) is 1:10-15;

[0040] Further, the reaction condition in step (6) is: under inert gas environment, dropwise addition of trifluoroperacetic acid at a temperature of-5-0℃, and after the dropwise addition is completed, stirring at 0-5℃ for 4h-6h;

[0041] Further, the post-treatment in step (6) is: after the reaction is completed, ice water is slowly added to the reaction kettle for stirring and washing, and there is a violent heat release phenomenon during the water addition process, and attention should be paid to maintain the temperature not to exceed 10℃, and after stirring for 10min, stand for 10min, separate the organic phase into a transfer tank; the water phase is transferred into a transfer plastic cup and extracted twice with dichloromethane, and the combined organic phase is returned to the kettle. Then slowly add 10% sodium sulfite solution to the material under stirring until the starch iodine potassium paper does not change color, and then slowly add 10% sodium carbonate solution until the pH is 6; slowly open the bottom valve to discharge and add water, stand (accelerate aging to facilitate filtration), and after aging, perform pressure filtration, wash the filter cake with dichloromethane, collect the filtrate and separate the phases, extract the water phase with dichloromethane, combine the organic phases, remove the dichloromethane from the organic phase, combine the filter cake with the residual material after the dichloromethane recovery, and dry to obtain a crude product, the crude product is dissolved in ethanol by heating to filter out impurities, concentrated to crystallize to obtain a product and a mother liquor, and the mother liquor is concentrated again to perform secondary crystallization.

[0042] Compared with the prior art, the present application has the following outstanding advantages and beneficial effects:

[0043] The application synthesizes 28-homobrassinolide by a brand-new organic synthesis method, avoids the use of toxic oxidants, co-oxidants and other expensive chiral catalysts required for direct oxidation of carbon-carbon double bond into asymmetric hydroxyl, is energy-saving and efficient, environment-friendly, simple in process and easy to operate, and has good industrial application value.

[0044] P3 obtained by ring opening of hydrobromic acid is protected by acetylation to obtain P4, as shown in the following formula, and there is an SN2 process of adjacent group participation in the reaction of hydrolysis to remove halogen, Walden inversion occurs, a diol propionyl-protected transition state intermediate is formed, there are three carbon-oxygen single bonds on a carbon atom of the transition state intermediate, which is unstable and prone to elimination reaction, the transition state intermediate can improve the selectivity of RR / SS product without adding expensive chiral catalysts, and the industrialized production is facilitated.

[0045] BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is the gas phase peak graph of the crude product P2 of the double epoxy intermediate in Example 1;

[0047] The 24.49min peak represents the double epoxy intermediate crude product P2;

[0048] Figure 2 It is the HPLC spectrum of the crude product P6 in Example 1;

[0049] The 22.6min peak represents S,S-P6, and the 31.8min peak represents R,R-P6;

[0050] Figure 3 It is the HPLC spectrum of the once purified product in Example 1;

[0051] The 19min peak and the 21min peak represent O6 and O7 isomers of 28-homobrassinolide, respectively;

[0052] Figure 4 It is the HPLC spectrum of the once purified product in Example 1;

[0053] The 24.49min peak represents the double epoxy intermediate crude product P2;

[0054] Figure 5 It is the HPLC spectrum of the crude product P6 in Example 2;

[0055] Figure 6 It is the HPLC spectrum of the once purified product in Example 2;

[0056] wherein the 19 min peak and the 21 min peak represent the O6 and O7 isomers of 28- homobrassinolide, respectively;

[0057] Figure 7 HPLC chart of the once purified product of Example 1;

[0058] Figure 8 HPLC chart of the once purified product of Example 4;

[0059] Figure 9 HPLC chart of the once purified product of Example 5;

[0060] Figure 10 HNMR chart of the product;

[0061] Figure 11 Mass chart of the product. DETAILED DESCRIPTION

[0062] The application will be further described in connection with the following examples, but the embodiments of the application are not limited thereto.

[0063] Example 1

[0064] The present example provides a method for synthesizing 28-homobrassinolide, which specifically comprises the following steps:

[0065] (1) Double epoxidation reaction: the starting material (2,22)-dien-24S-ethyl-5α-cholesta-6- one P1 is reacted with m-chloroperbenzoic acid, alkali metal bicarbonate and a first solvent to obtain an intermediate P2 after treatment:

[0066] Into a 3L flask, 124.50 g (0.3 mol) of purified P1 was added and dissolved with 1615 g of dichloromethane, then 31.23 g (0.31 mol) of potassium bicarbonate was added, 1.05 mol of m-chloroperbenzoic acid was added in four portions, and 514 g of dichloromethane was added. After the reaction was completed, 30 g of water and 62 g of anhydrous sodium sulfite were added for quenching, then suction filtration was performed, the filter cake was washed with 2 times 250 g of dichloromethane, and suction filtration was performed. After the filtrate was combined, it was dissolved in ethyl acetate after being dissolved under reduced pressure, then a sodium bicarbonate solution was added for washing, and the organic phase was concentrated to obtain 158.29 g of a double epoxide intermediate crude product P2, as shown in Figure 1 the peak area ratio of intermediate P2 was 84.03%.

[0067] (2) Ring opening reaction: P2 is reacted with hydrobromic acid and a second solvent to obtain an intermediate P3 after treatment:

[0068] The obtained 158.29 g of P2 crude product (0.3 mol) was dissolved in 633.20 g of butanone, and 226 g (1.34 mol) of 48% hydrobromic acid was added dropwise under ice water bath at about 10°C. After stirring for 3 min, the mixture was poured into 500 g of ice water, and sodium chloride was added to saturation, and the mixture was separated. The water phase was extracted with 317 g of butanone, and the organic phase was washed with saturated sodium bicarbonate until neutral, and the water phase was extracted with 160 g of butanone, and the combined organic phase was dried by azeotropic dehydration with 50 g of n-hexane to obtain a brominated open-loop intermediate P3 solution.

[0069] (3) Acetylation reaction: P3 was reacted with an organic base, 4-dimethylaminopyridine and acetic anhydride to obtain an intermediate P4 after treatment:

[0070] The dried brominated open-loop intermediate P3 solution was directly added with 183 g (1.8 mol) of triethylamine, and then 23.85 g (0.195 mol) of 4-dimethylaminopyridine was added, and 122.51 g (1.2 mol) of acetic anhydride was added dropwise under nitrogen protection, and stirred at room temperature for 3 days. The excess triethylamine was evaporated under reduced pressure, 500 g of water and 500 g of dichloromethane were added for extraction, and the organic phase was collected, washed with 200 g of sodium bicarbonate solution twice, and washed with 200 g of water twice, and then the organic phase was desolved to obtain 194.05 g of black gel, and then the gel was decolorized by flash column chromatography to obtain 144.6 g of yellow-white acetylated intermediate P4 crude product.

[0071] (4) First hydrolysis reaction: P4 was reacted with acetic acid, potassium acetate and water to obtain an intermediate P5 after treatment:

[0072] The obtained 144.6 g (about 0.21 mol according to 100% content) of acetylated intermediate P4 was dissolved in 810 g of acetic acid, and then 420 g (4.2 mol) of potassium acetate and 154 g of water were added, and the mixture was heated to reflux for 20 h, and then the reaction was completed, and the remaining solid was added with 500 g of water and 500 g of dichloromethane solvent to separate the liquid, and the organic phase was desolved to obtain 152.9 g of first hydrolysis intermediate P5 crude product.

[0073] (5) Second hydrolysis reaction: P5 was reacted with an aqueous alkali metal hydroxide solution and a third solvent to obtain an intermediate P6 after treatment:

[0074] The obtained primary hydrolysis intermediate P5 was dissolved and dispersed in 2293.5 g of methanol, 2.10 mol of 30 wt% potassium hydroxide aqueous solution was added, and the temperature was raised to reflux for 5 h. After the reaction was completed, acetic acid was added to adjust the pH to neutral, methanol was removed by dissolution, and the remaining solid was dissolved in 500 g of water and 500 g of ethyl acetate to extract and separate, the organic phase was washed twice with 200 g of saturated sodium bicarbonate solution, and then washed twice with 200 g of water, and then dissolved to obtain 112.8 g of a secondary hydrolysis intermediate crude product. The crude product was washed by spraying with ethyl acetate to obtain a tetrahydroxylated intermediate P6, as shown in the HPLC spectrum of the P6 crude product; the ratio of R,R-P9 to S,S-P6 in the P6 crude product was 66.19%:14.15%, and after column chromatography elution and separation with dichloromethane-methanol 3:1 as the eluent, 76 g of R,R-P6 with a liquid phase content of 94.5% was obtained, and the total yield of P1 to P6 R,R-P6 was 52.92%. Figure 2

[0075] (6) Baeyer-Villiger oxidation reaction: P6 was reacted in a fourth solvent under the action of trifluoroperacetic acid in an inert gas environment, and after treatment, the target product P7, i.e., 28-homocamphor lactone, was obtained:

[0076] A 5 L reaction flask was dried and replaced with nitrogen, 3300 g of dichloromethane was weighed into the 5 L reaction flask; 180.5 g (1.59 mol) of 30% hydrogen peroxide was added to the reaction flask; the stirring was started at 200 r / min and the circulation refrigeration was started at -5~0°C, 1598.8 g (7.38 mol) of trifluoroacetic anhydride was slowly added to the reaction flask through a 1 L constant-pressure dropping funnel; the internal temperature was maintained at 0~5°C during the addition process, and the addition time was about 2 h, after the addition was completed, 70 g of dichloromethane was added to wash the constant-pressure dropping funnel, and then the temperature was maintained and stirred for 1 h to prepare a trifluoroperacetic acid solution;

[0077] A 10 L reaction kettle was dried and replaced with nitrogen, 1906.8 g of dichloromethane was weighed into the 10 L reaction kettle, and the stirring was started at 200 r / min; 76 g of tetrahydroxylated intermediate P6 with a purity of 94.5% (0.15 mol) was added to the 10 L reaction kettle, the refrigeration cycle was started, and the refrigeration temperature was set to -10°C, so that the temperature in the kettle was reduced to about -5~0°C, under stirring conditions, the prepared trifluoroperacetic acid was slowly pumped into the 10 L reaction kettle using a metering pump, and then the temperature was maintained at 0~5°C for 4 h of stirring reaction;

[0078] ​Weigh 2000g of ice water and slowly add it to the reactor for stirring and washing. During the water addition process, there will be a violent exothermic reaction; ensure the temperature does not exceed 10℃. After stirring for 10 minutes, let it stand for 10 minutes, then separate the organic phase and transfer it to a 10L transfer tank. Transfer the aqueous phase to a 5L transfer plastic cup and extract it twice using 408g of dichloromethane. Combine the organic phases and return them to the 10L reactor. Then, slowly add 10% sodium sulfite solution while stirring until the material no longer causes discoloration on starch-potassium iodide test paper. Next, slowly add 10% sodium carbonate solution until the pH reaches 6.

[0079] Slowly open the bottom valve to discharge the material and add water to allow it to stand (to accelerate aging for filtration). After aging, perform pressure filtration. The filter cake is washed with 75g of water and 75g of dichloromethane. Collect the filtrate and separate the phases. The aqueous phase is extracted with 100g of dichloromethane and then combined with the organic phase. The organic phase is desolventized and 3.5L (5300g) of dichloromethane is recovered. The filter cake and the residue after recovering dichloromethane are combined and dried to obtain 77.83g of crude product with a mixed content of 60.08%. The crude yield of step (6) is 63.01%. The crude product is heated and dissolved in 40 times the amount of ethanol to remove impurities. After concentration and crystallization, 36.6g of the first purified product with a mixed content of 96.5% is obtained. After secondary concentration and crystallization, 11.6g of the second purified product with a mixed content of 74.9% is obtained. The total yield is 29.65%. Figure 3 The HPLC chromatogram of the purified product of Example 1 is shown; the peaks at 19 min and 21 min represent the O6 and O7 isomers of 28-homobrassinolide, respectively.

[0080] The O6 and O7 isomers are shown in the following formula. Academician Zhou Weishan clearly pointed out in his monograph "Residual Chemistry" that the O6 and O7 isomers also have biological activity and do not need to be removed during the production process to avoid increasing purification costs.

[0081]

[0082] like Figure 10 To obtain the HNMR spectrum of the product; such as Figure 11 This is the mass spectrum of the product.

[0083] Example 2

[0084] This embodiment provides a method for synthesizing 28-homobrassinolide, which specifically includes the following steps:

[0085] (1) Bicyclic oxidation reaction: The starting material (2,22)-diene-24S-ethyl-5α-cholest-6-one P1 reacts with m-chlorobenzoic acid P1 in the presence of m-chlorobenzoic acid, alkali metal bicarbonate and a first solvent, and is then post-treated to obtain intermediate P2:

[0086] Into a 3L flask, 124.55g (0.3mol) of purified P1 was dissolved in 1615g of dichloromethane, then 41.44g (0.41mol) of potassium bicarbonate was added, followed by 1.5mol of meta-chloroperoxybenzoic acid and 514g of dichloromethane. After the reaction was completed, 60g of water and 125g of anhydrous sodium sulfite were added to quench the reaction, then the filter cake was washed with 2 times 250g of dichloromethane. The filtrate was combined and concentrated under reduced pressure, then dissolved in ethyl acetate, washed with sodium bicarbonate solution, and the organic phase was concentrated to obtain 187.21g of the crude bis-epoxide intermediate P2, as shown in Figure 4 the gas chromatogram, the peak area ratio of intermediate P2 was 66.83%.

[0087] (2) Ring-opening reaction: P2 was reacted with hydrobromic acid and a second solvent to obtain intermediate P3 after work-up:

[0088] The obtained crude P2 was dissolved in 1140g of acetone, and 223g of 48% hydrobromic acid was added dropwise under ice water bath at about 10°C. After stirring for another 3min, the mixture was poured into a 500g ice water bath, dissolved in 1L of dichloromethane, and separated. The aqueous phase was extracted with 200ml of dichloromethane, and the combined organic phase was washed twice with 200g of saturated sodium bicarbonate and saturated sodium chloride, respectively, dried over anhydrous sodium sulfate, and concentrated to obtain about 260g of the orange-yellow viscous solid bromo-ring-opening P3.

[0089] (3) Acetylation reaction: P3 was reacted with an organic base, 4-dimethylaminopyridine, and acetic anhydride to obtain intermediate P4 after work-up:

[0090] The above P3 was added to a 2000ml three-necked flask, 540.04g of pyridine was added and stirred to dissolve, then 23.82g (0.195mol) of 4-dimethylaminopyridine and 245g (2.4mol) of acetic anhydride were added. After reaction at room temperature for 72h under nitrogen protection, TLC monitoring showed that the starting material was completely converted. The pyridine was removed under reduced pressure, 500ml of dichloromethane and 500ml of water were added, 200ml of 3% hydrochloric acid was added to acidify, stirred and extracted, the organic phase was collected, washed twice with 100ml of sodium bicarbonate and twice with 100ml of saturated brine, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation. Column chromatography was used for purification to obtain about 225g of acetylated intermediate P4.

[0091] (4) First hydrolysis reaction: P4 was reacted with acetic acid, potassium acetate, and water to obtain intermediate P5 after work-up:

[0092] The obtained acetylated intermediate P4 was added to a 2000 ml three-necked flask, dissolved in 1200 ml acetic acid, and then 647.85 g (6.54 mol) potassium acetate and 240 g water were added. The mixture was heated to reflux and reacted for 20 h. After the reaction was completed, the solvent was removed under reduced pressure. The remaining solid bottom material was separated by adding 500 g water and 500 g dichloromethane solvent. The organic phase was desolventized to obtain 190 g crude primary hydrolysis intermediate P5.

[0093] (5) Second hydrolysis reaction: P5 reacts with an aqueous solution of alkali metal hydroxide and a third solvent, and after post-treatment, yields intermediate P6:

[0094] The 190g P5 obtained above was added to 1900ml of methanol in a 3000mL three-necked flask. The mixture was heated to reflux with stirring until completely dissolved. Then, 2.70mol / L 30wt% potassium hydroxide aqueous solution was slowly added, and the mixture was refluxed (approximately 72℃) with stirring for 5 hours. After the reaction was complete, the mixture was cooled to 10℃ in an ice bath, and the pH was adjusted to 6-7 with approximately 10% dilute hydrochloric acid. The solvent was removed under reduced pressure. The remaining solid was dissolved and extracted with 500g of water and 500g of ethyl acetate. The organic phase was desolvated to obtain 96.08g of crude secondary hydrolysis intermediate. Figure 5 As shown, the ratio of R,R-P6 to S,S-P6 in the crude P6 intermediate was 69.18%:6.28%. After washing with ethyl acetate, the crude product was separated by column chromatography with dichloromethane:methanol = 3:1 elution agent to obtain 58.25g of R,R-P6 with a purity of 94.92%; the yield of R,R-P6 from P1 to P6 was 38.50%.

[0095] (6) Baeyer-Villiger oxidation reaction: P6 reacts in an inert gas environment with trifluoroperacetic acid and a fourth solvent to obtain the target product P7, namely 28-homobrassinolide, after post-treatment.

[0096] The 5L reaction flask was dried and purged with nitrogen beforehand. 2450g of dichloromethane was weighed into the 5L reaction flask. 131g (1.15mol) of 30% hydrogen peroxide was weighed into the reaction flask. The stirring was turned on to 200r / min and the circulating cooling was turned on to -5~0℃. 1225g (5.77mol) of trifluoroacetic anhydride was weighed and slowly added into the reaction flask through a 1L constant pressure dropping funnel. The internal temperature was maintained at 0~5℃ during the dropping process, and the dropping time was about 2h. After the dropping was completed, 50g of dichloromethane was added to rinse the constant pressure dropping funnel and then the temperature was kept warm and stirred for 1h to obtain a trifluoroperacetic acid solution.

[0097] Take 10 L reactor dry and replace with nitrogen, weigh 2330 g of dichloromethane in 10 L reactor, open the stirring to 200 r / min; add the above 58.25 g of purity of 94.9% (0.115 mol) tetrahydroxyl intermediate P6 into the 10 L reactor, open the refrigeration cycle, set the refrigeration temperature to -10℃, and reduce the temperature in the reactor to about -5~0℃, under stirring conditions, slowly inject the prepared trifluoroperacetic acid into the 10 L reactor using a metering pump, and then continue to maintain 0~5℃ stirring for 4 h;

[0098] Weigh 1250 g of ice water and slowly add it to the reactor for stirring and washing. There is a violent exothermic phenomenon during the water addition process. Pay attention to maintain the temperature not exceeding 10℃. After stirring for 10 min, stand for 10 min, and then separate the organic phase into a 10 L transfer tank. Transfer the aqueous phase into a 5 L plastic cup and extract twice with 250 g of dichloromethane. Combine the organic phases and return them to the 10 L reactor. Then slowly add 10% sodium sulfite solution to the material under stirring until the starch iodine potassium paper no longer changes color. Then slowly add 10% sodium carbonate solution until the pH is 6;

[0099] Slowly open the bottom valve to discharge and add water. Stand (accelerate aging to facilitate filtration). After aging, perform pressure filtration. Wash the filter cake with 50 g of water and 50 g of dichloromethane. Collect the filtrate and separate the phases. Extract the aqueous phase with 100 g of dichloromethane. Combine the organic phases. Recover 3.5 L of dichloromethane from the organic phase. Combine the filter cake and the recovered dichloromethane residue after recovery. Dry to obtain 60.24 g of crude product. The mixed content is 65.39%. The crude yield of step (6) is 69.00%. The crude product is dissolved by heating with 40 times ethanol. Impurities are filtered out. Concentration and crystallization obtain 29.18 g of once purified product. The mixed content is 96.82%. Secondary concentration and crystallization obtain 5.60 g of twice purified product. The mixed content is 65.18%. The total yield is 21.49%. As shown in FIG. 2, it is an HPLC spectrum of the once purified product of Example 2. The peaks at 19 min and 21 min represent the O6 and O7 isomers of 28-homobrassinolide, respectively. Figure 6 As shown in FIG. 3, it is an HPLC spectrum of the twice purified product of Example 2.

[0100] Example 3

[0101] Compared with Example 1, the difference of the present example is that:

[0102] In step (1), the molar ratio of P1, m-chlorobenzoic acid, and alkali metal bicarbonate is 1:3.5:1.0.

[0103] In step (1), the alkali metal bicarbonate is sodium bicarbonate.

[0104] In step (2), the molar ratio of P2 to hydrobromic acid is 1:6.

[0105] The alkali metal hydroxide aqueous solution in step (5) is a 30% sodium hydroxide aqueous solution;

[0106] The ratio of P6 and trifluoroperacetic acid in step (6) is 1:10;

[0107] This example is synthesized according to the same method as example 1 to obtain the target product P7, i.e. 28-homobrassinolide.

[0108] Finally, 29.02 g of the first purification product is obtained, with a mixed content of 94.53%, and 8.80 g of the second purification product is obtained, with a mixed content of 74.98%, and the total yield is 22.93%. As shown in the following table, the first purification product of example 3 is analyzed by HPLC. Figure 7

[0109] Example 4

[0110] The difference between this example and example 1 is that:

[0111] The molar ratio of P1, m-chlorobenzoic acid, and alkali metal bicarbonate in step (1) is 1:5:1.5;

[0112] The molar ratio of P2 and hydrobromic acid in step (2) is 1:4;

[0113] This example is synthesized according to the same method as example 1 to obtain the target product P7, i.e. 28-homobrassinolide.

[0114] Finally, 25.34 g of the first purification product is obtained, with a mixed content of 94.80%, and 6.72 g of the second purification product is obtained, with a mixed content of 71.97%, and the total yield is 19.44%. As shown in the following table, the first purification product of example 4 is analyzed by HPLC. Figure 8

[0115] Example 5

[0116] The difference between this example and example 1 is that:

[0117] The ratio of P6 and trifluoroperacetic acid in step (6) is 1:15;

[0118] This example is synthesized according to the same method as example 1 to obtain the target product P7, i.e. 28-homobrassinolide.

[0119] Finally, 33.23 g of the first purification product is obtained, with a mixed content of 96.96%, and 13.05 g of the second purification product is obtained, with a mixed content of 72.26%, and the total yield is 28.06%. As shown in the following table, the first purification product of example 5 is analyzed by HPLC. Figure 9

[0120] [Table 1] Product acquisition and yield of examples 1-5​​​

[0121]

[0122] As can be seen from Table 1, although the final yield of the present application is not particularly high, the present application does not add expensive and toxic catalysts such as osmium tetroxide, potassium osmium dihydrate and ruthenium trioxide during the reaction, which is energy-saving and environmentally friendly, and does not add expensive chiral catalysts, which are expensive and although they improve the stereoselectivity to a certain extent, they cannot be reused due to the difficulty in separating the reaction substrate and the catalyst from the product, which causes high cost, complicated operation and other problems, greatly limiting their application, so the present application does not add toxic catalysts and chiral ligands, does not use expensive raw materials, and has high economic benefits, simple product purification and is suitable for industrial production.

[0123] The above examples are only for better illustrating the present application, and are not used to limit the scope of the present application, any modification, equivalent replacement, improvement, etc. based on the above content of the present application shall be included in the protection scope of the present application.

Claims

1. A method of synthesizing 28-homobrassinolide, characterized by: Comprising the following steps: (1) Double epoxidation reaction: the starting material (2,22)-dien-24S-ethyl-5α-cholestan-6-one P1 reacts under the action of meta-chloroperoxybenzoic acid, alkali metal bicarbonate and a first solvent to obtain an intermediate P2 after treatment; (2) Double epoxide ring-opening reaction: P2 reacts under the action of hydrobromic acid and a second solvent to obtain an intermediate P3 after treatment; (3) Acetylation of all hydroxyl groups: P3 reacts under the action of an organic base, 4-dimethylaminopyridine and acetic anhydride at room temperature to obtain an intermediate P4 after treatment; (4) First hydrolysis reaction: P4 is hydrolyzed under the action of acetic acid, potassium acetate and water at 115-125 DEG C to obtain an intermediate P5 after treatment; (5) Second hydrolysis reaction: P5 is hydrolyzed under the action of an aqueous alkali metal hydroxide solution and a third solvent at 70-75 DEG C to obtain an intermediate P6 after treatment; (6) Baeyer-Villiger oxidation reaction: P6 reacts under the action of trifluoroperacetic acid and a fourth solvent in an inert gas environment to obtain the target product P7, i.e. 28-homobrassinolide, after treatment; The specific reaction equation is shown as follows: 。 2. The method of synthesis of claim 1, wherein: In the step (1), the molar ratio of P1, meta-chloroperoxybenzoic acid and alkali metal bicarbonate is 1:3.5-5:1.0-1.

5.

3. The method of synthesis of claim 2, wherein: In the step (1), after the reaction is completed, excess anhydrous sodium sulfite and water are added for quenching, then filtration is performed, the filter cake is washed with dichloromethane, the filtrates are combined, and then, after being dissolved in ethyl acetate, the solution is washed with a sodium bicarbonate solution, and the organic phase is concentrated to obtain the double epoxide intermediate P2.

4. The method of claim 1, wherein: In the step (2), the molar ratio of P2 and hydrobromic acid is 1:4-6.

5. The method of claim 4, wherein: In the step (2), after the reaction is completed, the reaction system is poured into an ice water bath, and sodium chloride is added until it is supersaturated, then the system is separated, the water phase is extracted with butanone, the organic phase is washed with a saturated sodium bicarbonate solution until it is neutral, the water phase is extracted with butanone again, the combined organic phase is dried by azeotropic dehydration with n-hexane to obtain a bromo ring-opening intermediate P3 solution.

6. The method of claim 1, wherein: In the step (3), after the reaction is completed, excess organic base is evaporated under reduced pressure, water and dichloromethane are added for extraction, the organic phase is collected, washed with a sodium bicarbonate solution twice, washed with water twice, and then, the organic phase is desolventized to obtain a black gel, which is further subjected to flash column chromatography to remove color to obtain a yellow-white acetylated intermediate P4 crude product.

7. The method of claim 1, wherein: In the step (4), after the reaction is completed, the remaining solid at the bottom of the kettle is dissolved in water and dichloromethane for extraction, and the organic phase is desolventized to obtain a first hydrolysis intermediate P5 crude product.

8. The method of claim 1, wherein: In the step (5), after the reaction is completed, acetic acid is added to adjust the pH to neutral, methanol is removed by desolventization, the remaining solid is dissolved in water and ethyl acetate for extraction, the organic phase is washed with a saturated sodium bicarbonate solution twice, washed with water twice, and then, desolventized to obtain a second hydrolysis intermediate crude product; the crude product is washed with ethyl acetate to obtain a tetrahydroxylated intermediate P6.

9. The method of claim 1, wherein: In the step (6), the molar ratio of P6 and trifluoroperacetic acid is 1:10-15.

10. The method of synthesis of claim 9, wherein: The post-treatment in the step (6) is that after the reaction is completed, ice water is slowly added into the reaction kettle for stirring and washing, and after stirring, the organic phase is separated and discharged into a transfer tank; the water phase is transferred into a transfer plastic cup and extracted twice with dichloromethane, and the combined organic phase is returned to the kettle; then, under stirring, sodium sulfite solution is slowly added until the starch iodine potassium paper is no longer discolored, and then sodium carbonate solution is slowly added until pH = 6; the bottom valve is slowly opened to discharge and add water, and after standing and aging, pressure filtration is performed, the filter cake is washed with dichloromethane, the filtrate is collected and separated, the water phase is extracted with dichloromethane, and the combined organic phase is recovered from the dichloromethane, the filter cake and the residual material after recovery of dichloromethane are combined and dried to obtain a crude product, the crude product is dissolved in ethanol for heating, impurities are filtered out, and the product and mother liquor are obtained by concentration and crystallization; the mother liquor is concentrated again for secondary crystallization.

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