A process for the preparation of 17-epioestradiol

Abstract

The application discloses a preparation method of 17-epiestriol and belongs to the technical field of organic synthesis. The method comprises the following steps: dissolving a compound 1 in an organic solvent, reacting with potassium borohydride in the presence of a Lewis acid and an alkali, and obtaining the 17-epiestriol; wherein the Lewis acid is selected from anhydrous calcium chloride or anhydrous cerium chloride. By introducing a specific Lewis acid into the reaction system, the stereoselectivity of 16alpha, 17alpha-epoxide ring opening is changed, 17-epiestriol is changed from a by-product under conventional conditions to a main product, the content of the crude product can be up to more than 81%, and the purity can be up to more than 97% after simple recrystallization. The method is simple in operation, high in yield, low in cost, suitable for industrial production, and the prepared 17-epiestriol can be used as an impurity control sample of estriol.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for preparing 17-epistenetriol. Background Technology

[0002] Estriol, an important estrogen, is widely used to alleviate urogenital tract atrophy symptoms caused by estrogen deficiency in postmenopausal women. In current industrial production, estriol is mainly synthesized from estrone through a multi-step process involving acetylation, epoxidation, and reduction. During the reduction step, due to the limitations of the reaction mechanism, the byproduct 17-epistestriol is inevitably produced. This byproduct differs from estriol only in the stereoconfiguration of the hydroxyl group at the 17-position; the remaining chemical structures are completely identical. This high degree of structural similarity directly results in their remarkably similar physical properties.

[0003] Because estriol and 17-epiestrylestradiol have only minor differences in physical properties, conventional purification methods such as solvent crystallization are insufficient for efficient separation. This makes it highly likely that 17-epiestrylestradiol will remain as a major impurity in the final estriol product. According to the European Pharmacopoeia, edition 11.2, the content of 17-epiestrylestradiol (i.e., estriol impurity E) in estriol raw materials is strictly controlled to below 0.3%. To ensure the safety and quality control of the drug, rigorous quality studies and limit control of this specific impurity are essential.

[0004] Currently, although 17-epiestrol is listed in the pharmacopoeia as a key impurity, there is a lack of reports in existing patent literature regarding efficient and specific synthetic methods for 17-epiestrol. Meanwhile, the supply of reference standards for this impurity is relatively scarce and expensive in the market. Therefore, developing a simple, high-yield synthetic method for preparing high-purity 17-epiestrol is of paramount practical significance and application value for preparing impurity reference standards, improving the quality research of estriol, establishing impurity analysis methods, and ensuring the safety of clinical drug use. Summary of the Invention

[0005] In view of this, the present invention proposes a method for preparing 17-epistenetriol that is simple to operate, has a high yield, and produces a high purity product.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a method for preparing 17-epistenetriol, characterized by comprising the following steps: Compound 1 was dissolved in an organic solvent and reacted with potassium borohydride in the presence of a Lewis acid and a base to give the 17-epistenetriol. The structures of compound 1 and 17-epistestriol are shown below: , .

[0007] Based on the above technical solutions, preferably, compound 1 is an intermediate in the synthesis of estriol, which is obtained by acetylation and epoxidation of estradiol.

[0008] More preferably, the reaction temperature is -20℃ to 0℃; the reaction time is 2 to 4 hours.

[0009] More preferably, the Lewis acid includes one of anhydrous calcium chloride and anhydrous cerium chloride.

[0010] More preferably, the molar ratio of the Lewis acid to compound 1 is 2.0:1 to 3.0:1.

[0011] More preferably, the alkali includes one of sodium hydroxide and potassium hydroxide; the molar ratio of the alkali to compound 1 is 3.7:1 to 6.0:1.

[0012] More preferably, the molar ratio of potassium borohydride to compound 1 is 2.0:1 to 3.0:1.

[0013] More preferably, the organic solvent includes methanol.

[0014] In a further preferred embodiment, after the reaction is completed, the pH is adjusted to 6-7 at -20℃ to 0℃ for quenching. After quenching, the product is concentrated under negative pressure at 40-45℃ to obtain crude 17-epistenetriol.

[0015] Secondly, the present invention also provides 17-epiestradiol prepared by the above preparation method as an impurity reference standard for estriol.

[0016] The present invention has the following advantages over the prior art: (1) By introducing a specific Lewis acid into the reaction system, the stereoselectivity of 16α,17α-epoxy ring opening was unexpectedly changed, and 17-epistenetriol (17α-OH) was transformed from a by-product (about 9%) under normal conditions into a major product (up to 81.6%).

[0017] (2) The method of the present invention is a one-pot reaction, the raw materials are readily available (compound 1 is a common intermediate in the synthesis of estriol), the reagents are all conventional industrial products, the reaction conditions are mild (low temperature and normal pressure), and the post-processing is simple, making it very suitable for industrial production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the HPLC chromatogram of 17-epistenetriol obtained in Example 3 of the present invention.

[0020] Figure 2 This is the LC-MS spectrum of 17-epiestrone obtained in Example 3 of the present invention.

[0021] Figure 3 The 17-epistestriol obtained in Example 3 of this invention 1 H NMR spectrum. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available products. Among them, compound 1 (16α,17α-epoxy-1,3,5(10)-estritotriene-3,17β-diol diacetate) was sourced from Hubei Gedian Renfu Pharmaceutical Co., Ltd., with an HPLC purity of 99.492%.

[0024] Example 1: Take 15g of compound 1 (16α,17α-epoxy-1,3,5(10)-estradiol-3,17β-diol diacetate), add 100mL of methanol, stir well, and cool to -20℃~-15℃. Add 2.937g of anhydrous calcium chloride, 1.960g of sodium hydroxide, and 1.428g of potassium borohydride to the reaction solution, and react at -20℃ for 4 hours. After the reaction is complete, add acetic acid at -20℃ to adjust the pH to 6-7. After quenching, concentrate to dryness under negative pressure at 40~45℃ to obtain the crude product. HPLC analysis showed that the content of 17-epistenes in the crude product was 74.748%.

[0025] Example 2: Take 15g of compound 1, add 100mL of methanol, stir well, and cool to -10℃~0℃. Add 14.445g of anhydrous cerium chloride, 3.177g of potassium hydroxide, and 2.142g of potassium borohydride to the reaction solution, and react at 0℃ for 2 hours. After the reaction is complete, add acetic acid at 0℃ to adjust the pH to 6-7. After quenching, concentrate to dryness under negative pressure at 40~45℃ to obtain the crude product. HPLC analysis showed that the content of 17-epistenes in the crude product was 62.252%.

[0026] Example 3: Take 15g of compound 1, add 100mL of methanol, stir well, and cool to 0-5℃. Add 3.083g of anhydrous calcium chloride, 1.961g of sodium hydroxide, and 1.500g of potassium borohydride to the reaction solution, and react at 0℃ for 3 hours. After the reaction is complete, add acetic acid at 0℃ to adjust the pH to 6-7. After quenching, concentrate to dryness under negative pressure at 40-45℃ to obtain the crude product. HPLC analysis showed that the content of 17-epistenes in the crude product was 81.600%.

[0027] The crude product was slurried with water and then recrystallized with methanol to obtain 2.512 g of white solid 17-epistenetriol with an HPLC purity of 97.809%.

[0028] The structure of the obtained 17-epistestriol was determined by... 1 H NMR ( Figure 3 ), LC-MS ( Figure 2 Confirmation: 1 H NMR (400 MHz, DMSO- d 6) δ ppm 0.65-0.68 (m, 3 H) 1.21-1.31 (m, 3 H)1.43-1.46 (m, 2 H) 1.70-1.82 (m, 4 H) 2.07 (m, 1 H) 2.23-2.25 (m, 1 H) 2.68-2.72 (m, 2 H) 3.41-3.43 (m, 1 H) 4.25-4.29 (m, 2 H) 4.61-4.63 (m, 1 H) 6.42 (m, 1 H) 6.48-6.50 (m, 1 H) 7.03-7.05 (m, 1 H) 8.97 (m, 1 H).

[0029] LC-MS: m / z = 289.2 [M+H] + This is consistent with the molecular weight of 17-epiestrone.

[0030] Comparative Example 1: Unlike Example 3, no Lewis acid was added. The remaining steps were the same as in Example 3 and will not be repeated here. HPLC analysis showed that the crude product contained 9.020% 17-epistenetriol.

[0031] Without the addition of a Lewis acid, after the epoxy ring of compound 1 is opened, the 17-acetoxy group migrates to the 16 position, followed by reduction of the 17-ketone group by potassium borohydride. Because the methyl group at 13 is in the β-configuration and the substituent at 16 is in the α-configuration, the steric hindrance effect formed by both influences the attack direction of potassium borohydride, thus determining the stereoconfiguration of the resulting 17-hydroxyl group. Under these conditions, estriol is mainly formed in the product, with only a small amount of 17-epiestriol.

[0032] When anhydrous calcium chloride is added to the reaction system, calcium chloride reacts with potassium borohydride to form calcium borohydride; when anhydrous cerium chloride is added, cerium chloride promotes the reaction of potassium borohydride with methanol to form alkoxyborohydrides. These two in-situ generated borohydrides have greater steric hindrance, changing the original attack orientation of potassium borohydride, thereby significantly increasing the content of 17-epistenes in the product.

[0033] Comparative Example 2: The difference from Example 3 is that anhydrous calcium chloride was replaced with 3.94 g of boron trifluoride diethyl ether. The remaining steps are the same as in Example 3 and will not be repeated here. HPLC analysis showed that the crude product contained 21.03% 17-epistenesole.

[0034] Comparative Examples 3-4: Unlike Example 3, the amounts of anhydrous calcium chloride added were 1.469 g (molar ratio to compound 1 of 1.0:1) and 7.345 g (molar ratio to compound 1 of 5.0:1), respectively. The remaining steps were the same as in Example 3 and will not be repeated here. HPLC analysis showed that the contents of 17-epistenes in the crude products were 25.247% and 46.813%, respectively.

[0035] When the Lewis acid content was reduced to a molar ratio of 1.0:1, the effective calcium borohydride formation in the system was insufficient, failing to adequately alter the attack orientation of the borohydride reagent. This resulted in a significantly lower 17-epistenesole content compared to Example 3, only slightly higher than the level without Lewis acid (Comparative Example 1). When the Lewis acid content was excessive to a molar ratio of 5.0:1, the excess calcium chloride reacted with other components in the reaction system, or caused changes in the local alkaline environment, which conversely reduced the selectivity of the reaction. Although the 17-epistenesole content was higher than in Comparative Example 2, it was still far lower than the optimal value in Example 3. Furthermore, excess Lewis acid would increase the difficulty and cost of post-processing.

[0036] Application Example 1: Application of 17-Epistethrin as an impurity reference standard Accurately weigh 17-epiestriol (HPLC purity 97.809%) prepared in Example 3, dissolve and dilute it in methanol to prepare a solution containing 0.1 mg per mL, which serves as the reference solution. Separately, take an appropriate amount of estriol raw material, dissolve and dilute it in methanol to prepare a test solution containing 1 mg per mL. Measure the chromatogram using high-performance liquid chromatography (Chinese Pharmacopoeia General Chapter 0512). The results show that the retention time of the 17-epiestriol peak in the test solution is consistent with the retention time of the main peak in the reference solution, indicating that the 17-epiestriol prepared in this invention can be used as a localization and quantitative reference for this impurity in estriol.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing 17-epistestriol, characterized in that, Includes the following steps: Compound 1 was dissolved in an organic solvent and reacted with potassium borohydride in the presence of a Lewis acid and a base to give the 17-epistenetriol. The structures of compound 1 and 17-epistestriol are shown below: 、 。 2. The preparation method according to claim 1, characterized in that, Compound 1 is a synthetic intermediate for estriol, prepared from estrone via acetylation and epoxidation.

3. The preparation method according to claim 1, characterized in that, The reaction temperature is -20℃ to 0℃; the reaction time is 2 to 4 hours.

4. The preparation method according to claim 1, characterized in that, The Lewis acid includes one of anhydrous calcium chloride and anhydrous cerium chloride.

5. The preparation method according to claim 3, characterized in that, The molar ratio of the Lewis acid to compound 1 is 2.0:1 to 3.0:

1.

6. The preparation method according to claim 1, characterized in that, The alkali includes one of sodium hydroxide and potassium hydroxide; the molar ratio of the alkali to compound 1 is 3.7:1 to 6.0:

1.

7. The preparation method according to claim 1, characterized in that, The molar ratio of potassium borohydride to compound 1 is 2.0:1 to 3.0:

1.

8. The preparation method according to claim 1, characterized in that, The organic solvent includes methanol.

9. The preparation method according to claim 1, characterized in that, After the reaction was completed, the pH was adjusted to 6-7 at -20℃ to 0℃ for quenching. After quenching, the product was concentrated under negative pressure at 40-45℃ to obtain crude 17-epistenetriol.

10. The 17-epiestradiol prepared by the preparation method according to any one of claims 1 to 9 is used as an impurity reference standard for estriol.

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