A method for preparing high-purity estetrol

Abstract

The present invention discloses a method for preparing high-purity estragen-1,3,5(10)-triene-3,15α,16α,17β-tetrol (abbreviated as estragen-1,3,5(10),15-tetraene) using 3-hydroxy-17β-hydroxy-estragen-1,3,5(10),15-tetraene as a raw material, and preparing estragen-1 through three steps of phenolic hydroxyl protection, asymmetric dihydroxylation, and hydrolysis. In the preparation method of the present invention, 3-hydroxy-17β-hydroxy-estragen-1,3,5(10),15-tetraene is used as a raw material, alkoxy-substituted benzoyl is used to protect the 3-hydroxyl group, potassium osmate is used to catalyze oxidation to perform an asymmetric dihydroxylation reaction, and di-α-hydroxy groups are introduced at the 15,16 positions. The preparation method does not require the use of expensive chemical reagents and catalysts, the dihydroxylation has high stereoselectivity, is easy to purify and separate, has mild reaction conditions, and is simple and convenient to operate, thereby achieving efficient preparation of high-purity estragen-1,3,5(10),15-tetraene (≥99.5%).

Description

Technical Field

[0001] The invention belongs to the technical field of organic compound preparation and relates to a method for preparing high-purity estetrol. Background Art

[0002] Estetrol, a female hormone, is produced exclusively by the fetus's liver during pregnancy. Clinical studies have shown that estetrol can be used in hormone replacement therapy and female oral contraceptives. Furthermore, estetrol has important applications in treating autoimmune diseases, preventing and treating breast and colon tumors, osteoporosis, skin care, and wound healing (WO02 / 094276, WO02 / 094279, WO02 / 094278, WO02 / 094275, WO03 / 041718, and WO03 / 018026).

[0003] The chemical name of estratetrol is estradiol-1,3,5(10)-triene-3,15α,16α,17β-tetrol, and its structure is shown in Formula 1. The main characteristic structural part is 15α,16α,17β-triol.

[0004]

[0005] Early methods for the synthesis of estetrol mainly used 3,17-diacetyl-protected estradiol-1,3,5(10),15-tetraene-3,17β-diol to undergo asymmetric dihydroxylation with osmium tetroxide (J.Org.Chem.1968,33,3133-3135; Steroids,1976,27,111-121; Steroids,1995,60,277-284). Using estrone as the starting material, the total yield of estetrol was 7-8%, the yield of the asymmetric dihydroxylation reaction was 46-47%, and the product / isomer ratio of the dihydroxylation was 74 / 26, that is, the 15α,16α- / 15β,16β- ratio was 74 / 26. Unfortunately, the purity of the product estetrol was not reported. The reaction route is shown in Scheme 1.

[0006]

[0007] When acetyl is used as a protecting group for 3-phenolic hydroxyl group, not only is the protecting group unstable during the reaction, but also when the intermediate product is purified by crystallization, the production of by-products will increase once a protic solvent such as methanol is used.

[0008] In 2004, patent WO 2004 / 041839 described the synthesis of estetrol from estrone by protecting the 3-hydroxyl group with a benzyl group and the 17-hydroxyl group with an acetyl group. The total reaction yield was 10.8%. The carbonyl reduction step employed a NaBH4 / CeCl3 system, and the key asymmetric dihydroxylation step also employed osmium tetroxide as an oxidant. Starting from compound K, dihydroxylation afforded compound L with a crude yield of 84%. After three recrystallizations, compound L had a purity of 98.7% and a refined yield of 43%. The purity of the final product, estetrol, was not reported, as shown in Scheme 2.

[0009]

[0010] The same scheme was repeated in patent WO 2013 / 012328, replacing osmium tetroxide with PVP-osmium tetroxide. The data for dihydroxylation were consistent. After deprotection by catalytic hydrogenation (92% yield) and alkaline hydrolysis (92.5% yield), the resulting estetrol had a purity of 99.5%. The total impurities in the estetrol process reported in the patent did not exceed 1%, but the content information of individual impurities was not provided.

[0011] Patent WO 2013 / 012328 similarly reports a method for preparing estetrol through an asymmetric dihydroxylation reaction with different protecting groups protecting the 3-hydroxyl group and leaving the 17-hydroxyl group unprotected. The 3-hydroxyl group is protected as a benzyl ether, benzoyloxy, alkyl ether, or silyl ether, among others. The asymmetric dihydroxylation was performed using PVP-osmium tetroxide, with a 15α,16α- / 15β,16β- ratio of 90 / 10. However, the purified yield of the asymmetric dihydroxylation was not reported. As a control experiment, the patent also reports the results of a direct asymmetric dihydroxylation reaction with the 3-hydroxyl group unprotected. The yield was low (62%), and the resulting estetrol contained impurities, had a poor solid form, and was difficult to purify.

[0012] Patent WO 2013 / 034780 in 2013 reported the limitation of 3-phenolic hydroxyl protecting groups. As shown in Formula 2, R is limited to benzoyl, acetyl, and benzyl.

[0013]

[0014]

[0015] Patent CN 103890001 (related patent number WO 2013050553) in 2014 also reported the limitation of the 3-phenolic hydroxyl protecting group, wherein it was reported that P1 was a protecting group selected from R1CO-, and R1 was a group selected from C1-C6 alkyl or C3-C6 cycloalkyl, as shown in Formula 3.

[0016]

[0017] 3-Hydroxy-17β-hydroxyestra-1,3,5(10),15-tetraene as a starting material can be synthesized according to the literature [J. Org. Chem. 1968, 33, 3133-3135; Steroids, 1976, 27, 111-121; Steroids, 1995, 60, 277-284].

[0018] In all the above patents publicly reporting asymmetric dihydroxylation, the 3-phenolic hydroxyl group is mainly protected by an ester group or an ether bond. The main problem is that after dihydroxylation, the presence of isomers and impurities makes purification difficult. Repeated purification is required to obtain a high-purity dihydroxylation product, and the yield is low.

[0019] Regarding the effective purification of the dihydroxylated product, patents CN 114514237 and CN 114302889 (related to WO 2021044302) reported in 2022 that the three hydroxyl groups at positions 15, 16, and 17 were first converted into ester derivatives, followed by purification and separation, as shown in Scheme 3. After preparing Compound III, it was recrystallized from methanol with a refined yield of 69.8%, resulting in Compound III with a purity of 99.2%, but with significant material losses. After purification, it undergoes two steps of hydrogenation debenzylation and hydrolysis, ultimately achieving a purity of 99.67% for estetrol, with isomers <0.04% and all impurities <0.10%. However, this derivatization method requires a longer route, a low refining yield, and significant losses.

[0020]

[0021] In summary, how to directly purify the asymmetric dihydroxylation product after asymmetric dihydroxylation without derivatization or repeated purification, and ensure that the purity of estetrol after hydrolysis is ≥99.5%, and that the single impurity content is <0.04% and the total impurity content is <0.1%, is a very challenging task. Summary of the Invention

[0022] The technical problem to be solved by the present invention is how to provide a method for preparing high-purity estetrol. By optimizing and screening the 3-hydroxyl protecting functional group, the present invention proposes using an alkoxy-substituted benzoyl group to protect the 3-phenolic hydroxyl group. This method not only increases the dihydroxylation ratio (from 93:7 to 95:5), but more importantly, improves the physical properties of the dihydroxylated product (melting point, solubility, solid crystal form, etc.), making it easier to effectively separate the dominant product structure (15α, 16α, 17β-) from impurities and isomers (15β, 16β, 17β-). Through a simple solvent purification step, a dihydroxylated product with a purity of ≥98.5% can be obtained. Subsequently, through subsequent hydrolysis and deprotection, high-purity estetrol (≥99.5%) can be prepared.

[0023] The present invention uses 3-hydroxy-17β-hydroxyestra-1,3,5(10),15-tetraene as a raw material and utilizes an alkoxy-substituted benzoyl group to protect the 3-phenolic hydroxyl group, thereby effectively solving the subsequent dihydroxylation yield, stereoselectivity and product purification. The alkoxy-containing benzoyl group provides greater steric hindrance, making the dihydroxylation have higher stereoselectivity, while increasing the solubility of the dihydroxylated product, which has a great advantage in the subsequent purification of the material. Compared with the benzoyl or ether protective group introduced without a substituent reported in the prior art, the present invention has a better separation and purification effect, the advantage of a higher dihydroxylation ratio, avoids tedious post-processing and a reduction in yield, and improves the preparation yield of high-purity estetrol.

[0024] In the preparation method of the present invention, 3-hydroxy-17β-hydroxyestra-1,3,5(10),15-tetraene is used as a raw material, and estetrol is prepared through three steps of phenolic hydroxyl protection, dihydroxylation and hydrolysis.

[0025] The reaction process of the above-mentioned preparation method of the present invention is shown in reaction formula (I):

[0026]

[0027] Wherein, R is an alkoxy group, and the position of R is at the ortho position, meta position or para position of the aromatic ring.

[0028] The R group is located at one or more of the ortho, meta or para positions of the benzene ring; preferably, at the para position.

[0029] The R group on the benzene ring is an alkoxy group containing a C1-C6 alkane, which is one or more of methoxy, ethoxy, isopropoxy, tert-butoxy, etc.; preferably, it is methoxy.

[0030] The method of the present invention comprises the steps of:

[0031] Step 1, 3-phenolic hydroxyl protection: In a first solvent, the compound of formula (1) and a hydroxyl-protecting aromatic reagent are subjected to a hydroxyl protection reaction in the presence of a base to obtain a compound of formula (2); the reaction process is shown in reaction formula (A):

[0032]

[0033] Step 2, asymmetric dihydroxylation reaction: dissolving the compound of formula (2) obtained in step 1 in a second solvent, and reacting under temperature control in the presence of a catalyst and an oxidant to obtain a compound of formula (3); the reaction process is shown in reaction formula (B):

[0034]

[0035] Step 3, hydrolysis reaction: The compound of formula (3) obtained in step 2 is dissolved in a third solvent and deprotected under alkaline conditions to obtain the target product estratetrol; the reaction process is shown in reaction formula (C):

[0036]

[0037] In step 1 of the present invention, the 3-phenolic hydroxyl protection reaction is specifically as follows: the compound of formula (1) reacts with an aromatic reagent for protecting the hydroxyl group in the first solvent under the action of a base to obtain a compound of formula (2).

[0038] The aromatic reagent for protecting the hydroxyl group is selected from one or more of p-methoxybenzoyl chloride, o-methoxybenzoyl chloride, p-ethoxybenzoyl chloride, p-isopropoxybenzoyl chloride, p-tert-butoxybenzoyl chloride, etc.; preferably, p-methoxybenzoyl chloride.

[0039] Wherein, the base is selected from one or more of triethylamine, diisopropylethylamine, imidazole, pyridine, DMAP, etc.; preferably, it is pyridine.

[0040] The first solvent is selected from one or more of ethyl acetate, dichloromethane, chloroform, DMF, toluene, tetrahydrofuran, 2-methyltetrahydrofuran, etc.; preferably, it is dichloromethane.

[0041] The molar ratio of the compound of formula (1), the aryl reagent for protecting the hydroxyl group, and the base is 1:(1-4):(0.05-5); preferably, 1:1.1:1.1.

[0042] Wherein, the reaction temperature is 0-50°C; preferably, 25°C.

[0043] The reaction time is 2 to 24 hours, preferably 3 hours.

[0044] In step 2, the second solvent is selected from one or more of dichloromethane, chloroform, acetone, toluene, ethyl acetate, methanol, ethanol, tetrahydrofuran, 2-methyltetrahydrofuran, etc.; preferably, it is acetone.

[0045] In step 2, the oxidant is selected from one or more of N-methylmorpholine oxide (NMO), trimethylamine N-oxide, etc.; preferably, it is N-methylmorpholine oxide (NMO).

[0046] In step 2, the catalyst is selected from one or more of osmium tetroxide, potassium osmate, etc.; preferably, it is potassium osmate.

[0047] In step 2, the mass ratio of the compound of formula (3), the oxidant, and the catalyst is 1:(1-2):(0.001-0.01); preferably, it is 1:1.2:0.005.

[0048] In step 2, the temperature of the oxidation reaction is 0°C-50°C; preferably, 50°C.

[0049] In step 2, the oxidation reaction time is 6-12 hours; preferably, 6 hours.

[0050] In step 3, the hydrolysis reaction is specifically as follows: the compound of formula (2) undergoes a hydrolysis reaction in the third solvent under the action of a base to obtain estetrol.

[0051] Wherein, the base is selected from one or more of LiOH, KOH, NaOH, t-BuOK, K2CO3, etc.; preferably, it is NaOH.

[0052] Wherein, the molar ratio of the compound of formula (3) to the base is 1:(0.5-2); preferably, it is 1:2.

[0053] Wherein, the third solvent is selected from one or two of water, methanol, ethanol, etc.; preferably, it is methanol.

[0054] Wherein, the temperature of the hydrolysis reaction is 10-75°C; preferably, 65°C.

[0055] The hydrolysis reaction time is 0.5 to 12 hours, preferably 6 hours.

[0056] In the present invention, the phenolic hydroxyl group at the 3-position is protected by an alkoxy-containing benzoyl group, which provides significant steric hindrance, alters the physical properties of the dihydroxylated product, and improves its lipid solubility. A high-purity dihydroxylated product (purity ≥ 98.5%) can be obtained through a single purification step. Subsequently, high-purity estetrol (purity ≥ 99.5%) can be efficiently prepared through hydrolysis and deprotection. During the present invention, the reaction conditions for the 3α-hydroxyl protection, dihydroxylation, and hydrolysis reactions are safe and mild, and no strong base or strong acid system is involved. This does not affect the configuration of the 15α, 16α-hydroxyl, and 17β-hydroxyl groups, preserving their unique stereo configurations and providing the advantage of efficient separation.

[0057] The beneficial effects of the present invention are as follows: 3-hydroxy-17β-hydroxyestra-1,3,5(10),15-tetraene is used as a raw material, a benzoyl group containing an alkoxy group is used to protect the 3-hydroxyl group, a dihydroxyl reaction is carried out by catalytic oxidation with potassium osmate, and a di-α-hydroxyl group is introduced at the 15,16-positions; the preparation method does not require the use of costly chemical reagents and catalysts; the dihydroxylization reaction has the characteristics of high stereoselectivity, easy purification and separation, mild reaction conditions, and simple and convenient operation, thereby realizing the efficient preparation of high-purity estetrol. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is the HPLC spectrum of high-purity estetrol in Example 12 of the present invention.

[0059] Figure 2 The high-purity estetrol in Example 12 of the present invention 1 HNMR spectrum. DETAILED DESCRIPTION

[0060] The invention is further described in detail with reference to the following specific examples. The processes, conditions, experimental methods, and the like used in implementing the present invention, except as specifically mentioned below, are generally known in the art and are not particularly limiting. (The results shown in the examples are all obtained under optimized experimental conditions and have potential application value.)

[0061] Example 1 (protection of p-methoxybenzoyl)

[0062]

[0063] In a 1L dry three-necked flask, 54.0g (0.2mol) of the compound of formula (1), 540ml of dichloromethane, and 17.5g (0.22mol) of pyridine were added, and the mixture was stirred and the temperature was adjusted to 25°C; 37.4g (0.22mol) of p-anisyl chloride was added dropwise at 25°C to control the temperature of the reaction system to be no higher than 25°C; after the addition, the mixture was kept at 25°C and stirred for 3 hours. After the reaction was completed, 100ml of 1mol / L sodium carbonate solution was added, and the mixture was stirred for 30 minutes, and the aqueous phase was separated. The organic phase was added with 100ml of water, and the mixture was stirred for 15 minutes, and the aqueous phase was separated; the organic phase was dried over anhydrous sodium sulfate for 2 hours, filtered, and concentrated to dry dichloromethane, and 150g of methanol was added and stirred at 10°C for 2h; filtered, and dried to obtain 80.0g of the compound of formula (2) with a purity of 99.5% and a molar yield of 99.0%.

[0064] Example 2 (protection of p-methoxybenzoyl)

[0065]

[0066] To a 1L three-necked flask, add 80.0g (0.198mol) of the compound of formula (2), 400ml of acetone, and 32g (0.236mol) of NMO monohydrate, and stir evenly. Add 362mg (1mmol) of potassium osmate dihydrate, and stir at 50°C for 6h. After the reaction, cool the internal temperature to 10°C and add 300ml of NaHSO3 (15%) dropwise. The internal temperature is controlled at 25°C due to the exotherm during the addition. Stir for 1 hour after the addition is complete, then add 400ml of dichloromethane and stir again for 0.5 hour. Allow to stand and separate, remove the aqueous phase, and wash the organic phase with 300ml of water. Allow to stand and separate, concentrate the organic phase, add 300ml of methanol, stir at 25°C for 2 hours, filter, and dry the filter cake to obtain 63.5g of the compound of formula (3). Purity: 98.5%, molar yield: 73.2%.

[0067] Example 3 (protection of p-methoxybenzoyl, THF as solvent)

[0068]

[0069] To a 1L three-necked flask, add 80.0g (0.198mol) of the compound of formula (2), 400ml of tetrahydrofuran, and 32g (0.236mol) of NMO monohydrate, and stir evenly. Add 362mg (1mmol) of potassium osmate dihydrate, and stir at 50°C for 6h. After the reaction, cool the internal temperature to 10°C and add 300ml of NaHSO3 (15%) dropwise. The internal temperature is controlled at 25°C due to the exotherm during the addition. Stir for 1 hour after the addition is complete, then add 400ml of dichloromethane and stir again for 0.5 hour. Allow to stand and separate, remove the aqueous phase, and wash the organic phase with 300ml of water. Allow to stand and separate, concentrate the organic phase, add 300ml of methanol, stir at 25°C for 2 hours, filter, and dry the filter cake to obtain 62.4g of the compound of formula (3). Purity: 98.3%, molar yield: 71.9%.

[0070] Example 4 (Protection of p-Anisyl Group, Using Trimethylamine N-Oxide as Oxidant)

[0071]

[0072] In a 1L three-necked flask, 80.0g (0.198mol) of the compound of formula (2), 400ml of acetone, and 17.7g (0.236mol) of trimethylamine N-oxide were added and stirred uniformly. 362mg (1mmol) of potassium osmate dihydrate was added, and the mixture was stirred at 50°C for 6h. After the reaction, the internal temperature was lowered to 10°C and 300ml of NaHSO3 (15%) was added dropwise. The internal temperature was controlled at 25°C due to the exotherm during the addition. After the addition was completed, the mixture was stirred for 1 hour. 400ml of dichloromethane was added and stirred again for 0.5 hour. The mixture was allowed to stand and the aqueous phase was separated. The organic phase was washed with 300ml of water. The organic phase was allowed to stand and the organic phase was concentrated. 300ml of methanol was added, stirred at 25°C for 2 hours, and filtered. The filter cake was dried to obtain 61.8g of the compound of formula (3). Purity: 98.1%, molar yield: 71.2%.

[0073] Example 5 (protection of p-methoxybenzoyl group)

[0074]

[0075] In a 1L three-necked flask, add 63.5g (0.145mol) of the compound of formula (3) and 600ml of methanol, stirring uniformly at 25°C. Add 11.6g (0.29mol) of sodium hydroxide in portions, reflux at 65°C, and stir for 6 hours. After the reaction, neutralize the pH to neutral with acetic acid. Concentrate to remove most of the methanol. Add 300ml of purified water, stir at room temperature for 2 hours, filter, wash with purified water, and dry the filter cake to obtain 33.1g of estetrol. Purity ≥99.5%, molar yield: 75.0%.

[0076] Example 6 (protection of p-methoxybenzoyl, base is lithium hydroxide)

[0077]

[0078] In a 1L three-necked flask, add 63.5g (0.145mol) of the compound of formula (3) and 600ml of methanol, and stir uniformly at 25°C. Add 12.2g (0.29mol) of lithium hydroxide monohydrate in batches, and reflux at 65°C with stirring for 6 hours. After the reaction, neutralize the pH to neutral with acetic acid. Concentrate to remove most of the methanol. Add 300ml of purified water, stir at room temperature for 2 hours, filter, wash with purified water, and dry the filter cake to obtain 32.9g of estetrol. Purity ≥99.5%, molar yield: 74.5%.

[0079] Example 7 (o-Anisyl Protection)

[0080]

[0081] In a 1L dry three-necked flask, 54.0g (0.2mol) of the compound of formula (1), 540ml of dichloromethane, and 17.5g (0.22mol) of pyridine were added, and the mixture was stirred and the temperature was adjusted to 25°C; 37.4g (0.22mol) of o-anisyl chloride was added dropwise at 25°C to control the temperature of the reaction system to be no higher than 25°C; after the addition, the mixture was kept at 25°C and stirred for 3 hours. After the reaction was completed, 100ml of 1mol / L sodium carbonate solution was added, the mixture was stirred for 30 minutes, and the aqueous phase was separated. The organic phase was added with 100ml of water, stirred for 15 minutes, and the aqueous phase was separated; the organic phase was dried over anhydrous sodium sulfate for 2 hours, filtered, and concentrated to dry dichloromethane, 150g of methanol was added, and the mixture was stirred at 10°C for 2h; filtration was performed and the mixture was dried to obtain 78.4g of the compound of formula (2) with a purity of 99.2% and a molar yield of 97.0%.

[0082] Example 8 (o-Anisyl Protection)

[0083]

[0084] To a 1L three-necked flask, add 80.0g (0.198mol) of the compound of formula (2), 400ml of acetone, and 32g (0.236mol) of NMO monohydrate, and stir evenly. Add 362mg (1mmol) of potassium osmate dihydrate, and stir at 50°C for 6h. After the reaction, cool the internal temperature to 10°C and add 300ml of NaHSO3 (15%) dropwise. The internal temperature is controlled at 25°C due to the exotherm during the addition. Stir for 1 hour after the addition is complete, then add 400ml of dichloromethane and stir again for 0.5 hour. Allow to stand and separate, remove the aqueous phase, and wash the organic phase with 300ml of water. Allow to stand and separate, concentrate the organic phase, add 300ml of methanol, stir at 25°C for 2 hours, filter, and dry the filter cake to obtain 62.9g of the compound of formula (3). Purity: 98.3%, molar yield: 72.5%.

[0085] Example 9 (o-Anisyl Protection)

[0086]

[0087] In a 1L three-necked flask, add 63.5g (0.145mol) of the compound of formula (3) and 600ml of methanol, stirring uniformly at 25°C. Add 11.6g (0.29mol) of sodium hydroxide in portions, reflux at 65°C, and stir for 6 hours. After the reaction, neutralize the pH to neutral with acetic acid. Concentrate to remove most of the methanol. Add 300ml of purified water, stir at room temperature for 2 hours, filter, wash with purified water, and dry the filter cake to obtain 32.5g of estetrol. Purity ≥99.4%, molar yield: 73.3%.

[0088] Example 10 (Protection of p-isopropoxybenzoyl)

[0089]

[0090] In a 1L dry three-necked flask, 54.0g (0.2mol) of the compound of formula (1), 540ml of dichloromethane, and 17.5g (0.22mol) of pyridine were added, and the mixture was stirred and the temperature was adjusted to 25°C; 43.6g (0.22mol) of p-isopropoxybenzoyl chloride was added dropwise at 25°C to control the temperature of the reaction system to be no higher than 25°C; after the addition, the mixture was kept at 25°C and stirred for 3 hours. After the reaction was completed, 100ml of 1mol / L sodium carbonate solution was added, the mixture was stirred for 30 minutes, and the aqueous phase was separated. The organic phase was added with 100ml of water, stirred for 15 minutes, and the aqueous phase was separated; the organic phase was dried over anhydrous sodium sulfate for 2 hours, filtered, and concentrated to dry dichloromethane, 150g of methanol was added, and the mixture was stirred at 10°C for 2h; filtration was performed and the mixture was dried to obtain 84.6g of the compound of formula (2) with a purity of 99.2% and a molar yield of 98.0%.

[0091] Example 11 (Protection of p-isopropoxybenzoyl)

[0092]

[0093] In a 1L three-necked flask, 85.5g (0.198mol) of the compound of formula (2), 400ml of acetone, and 32g (0.236mol) of NMO monohydrate were added and stirred uniformly. 362mg (1mmol) of potassium osmate dihydrate was added, and the mixture was stirred at 50°C for 6h. After the reaction, the internal temperature was lowered to 10°C and 300ml of NaHSO3 (15%) was added dropwise. The internal temperature was controlled at 25°C due to the exotherm during the addition. After the addition was completed, the mixture was stirred for 1 hour. 400ml of dichloromethane was added and stirred again for 0.5 hour. The mixture was allowed to stand and the aqueous phase was separated. The organic phase was washed with 300ml of water. The organic phase was allowed to stand and the organic phase was concentrated. 300ml of methanol was added, stirred at 25°C for 2 hours, and filtered. The filter cake was dried to obtain 65.7g of the compound of formula (3). Purity: 98.7%, molar yield: 71.2%.

[0094] Example 12 (Protection of p-isopropoxybenzoyl)

[0095]

[0096] In a 1L three-necked flask, add 67.6g (0.145mol) of the compound of formula (3) and 600ml of methanol, and stir uniformly at 25°C. Then add 11.6g (0.29mol) of sodium hydroxide in batches, and reflux at 65°C with stirring for 6 hours. After the reaction, neutralize the pH to neutral with acetic acid. Concentrate to remove most of the methanol. Add 300ml of purified water, stir at room temperature for 2 hours, filter, wash with purified water, and dry the filter cake to obtain 32.6g of estetrol. Purity ≥99.5%, molar yield: 74%.

[0097] 1 H NMR (400MHz, CD3OD) δ7.09 (d, J = 8.0 Hz, 1H), 6.50-6.57 (m, 2H), 3.86-3.93 (m, 1H), 3.44 (d, J = 4.0 Hz,2H),2.75-2.89(m,2H),2.17-2.34(m,3H),1.90-1.93(m,1H),1.18-1.65(m,5H),0.81(s,3H).

[0098] Example 13 (Control Experiment, Benzoyl Protection)

[0099]

[0100] In a 1L three-necked flask, 74.1g (0.198mol) of the compound of formula (2), 400ml of acetone, and 32g (0.236mol) of NMO monohydrate were added and stirred evenly; 362mg (1mmol) of potassium osmate dihydrate was added, and the mixture was kept warm at 50°C and stirred for 6h; after the reaction was completed, the internal temperature was lowered to 10°C and 300ml of NaHSO3 (15%) was added dropwise, and the internal temperature was controlled to 25°C due to heat release during the addition. After the addition was completed, the mixture was stirred for 1 hour, and 400ml of dichloromethane was added and stirred again for 0.5 hour; the mixture was allowed to stand and separate, and the aqueous phase was separated; the organic phase was washed with 300ml of water; the mixture was allowed to stand and separate, and the organic phase was concentrated, and 300ml of methanol was added, stirred at 25°C for 2 hours, and filtered. The filter cake was dried to obtain 58.1g of the compound of formula (3).

[0101] Purity: 96.7%, molar yield: 72%.

[0102]

[0103] In a 1L three-necked flask, add 59.2g (0.145mol) of the compound of formula (3) and 600ml of methanol, stirring uniformly at 25°C. Add 11.6g (0.29mol) of sodium hydroxide in portions, reflux at 65°C, and stir for 6 hours. After the reaction, neutralize the pH to neutral with acetic acid. Concentrate to remove most of the methanol. Add 300ml of purified water, stir at room temperature for 2 hours, filter, wash with purified water, and dry the filter cake to obtain 32.2g of estetrol. Purity: 97.6%, molar yield: 73%.

[0104] The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention and are protected by the appended claims.

Claims

1. A method for preparing high-purity estetrol, characterized in that: The reaction process of the method is shown in reaction formula (I): The method comprises the following steps: Step 1, 3-phenolic hydroxyl protection: In a first solvent, the compound of formula (1) reacts with a hydroxyl-protecting aromatic reagent in the presence of a base to obtain a compound of formula (2); the hydroxyl-protecting aromatic reagent is selected from one or more of p-methoxybenzoyl chloride, o-methoxybenzoyl chloride, p-ethoxybenzoyl chloride, p-isopropoxybenzoyl chloride, and p-tert-butoxybenzoyl chloride; the reaction process is shown in Reaction Formula (A): Step 2, asymmetric dihydroxylation reaction: dissolving the compound of formula (2) obtained in step 1 in a second solvent, and reacting under temperature control in the presence of a catalyst and an oxidant to obtain a compound of formula (3); the catalyst is selected from one or both of osmium tetroxide and potassium osmate; the oxidant is selected from one or both of N-methylmorpholine oxide NMO and trimethylamine N-oxide; the reaction process is shown in reaction formula (B): Step 3, hydrolysis reaction: The compound of formula (3) obtained in step 2 is dissolved in a third solvent and deprotected under alkaline conditions to obtain the target product estetrol; the reaction process is shown in reaction formula (C):

2. The method according to claim 1, wherein In step 1, the first solvent is selected from one or more of ethyl acetate, dichloromethane, chloroform, DMF, toluene, tetrahydrofuran, and 2-methyltetrahydrofuran; and / or the base is selected from one or more of triethylamine, diisopropylethylamine, imidazole, pyridine, and DMAP.

3. The method according to claim 1, wherein In step 1, the molar ratio of the compound of formula (1), the aryl reagent for protecting the hydroxyl group, and the base is 1:(1-4):(0.05-5); and / or the reaction temperature is 0-50° C.; and / or the reaction time is 2-24 h.

4. The method according to claim 1, wherein In step 2, the second solvent is selected from one or more of dichloromethane, chloroform, acetone, toluene, ethyl acetate, methanol, ethanol, tetrahydrofuran, and 2-methyltetrahydrofuran.

5. The method according to claim 1, wherein In step 2, the mass ratio of the compound of formula (2), the oxidant, and the catalyst is 1:(1-2):(0.001-0.01); and / or the temperature of the oxidation reaction is 0°C-50°C; and / or the time of the oxidation reaction is 6-12h.

6. The method according to claim 1, wherein In step 3, the hydrolysis reaction is specifically as follows: the compound of formula (3) undergoes a hydrolysis reaction in the third solvent under the action of a base to obtain estetrol.

7. The method according to claim 6, wherein The base is selected from one or more of LiOH, KOH, NaOH, t-BuOK, and K2CO3; and / or the molar ratio of the compound of formula (3) to the base is 1:(0.5-2); and / or the third solvent is selected from one or two of water, methanol, and ethanol.

8. The method according to claim 6, wherein The temperature of the hydrolysis reaction is 10 to 75° C.; and / or the time of the hydrolysis reaction is 0.5 to 12 hours.

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