Alpha Salon Synthesis

Abstract

A method for preparing and purifying alfasalone (3α-hydroxy-5α-pregnane) from a crude mixture of 3α- and 3β-hydroxy-5α-pregnane, and subsequently purifying the 17α- and 17β-enantiomers to obtain the 17β-enantiomer (alfasalone).

Description

[0001] This invention relates to a novel method for preparing and purifying steroidal 3α-hydroxy-5α-pregnane (alphasalon) from a crude mixture of 3α- and 3β-hydroxy-5α-pregnane to obtain alphasalon with a purity >95%. Background Technology

[0002] Steroids are known to have a significant inhibitory effect on the central nervous system and function pharmacologically as anesthetics or hypnotics. These compounds have become the subject of extensive research in search of viable alternatives to known anesthetics.

[0003] Anesthetic steroids are typically relatively simple pregnane derivatives, often hydroxylated at the 3-position. Historically, 3β-hydroxy steroids have been more favored in research compared to 3α-steroid compounds. Many useful properties have now been discovered in 3α-hydroxy steroids; in particular, 5α-pregnane steroids with a 3α-hydroxy group (hereinafter referred to as 3α-hydroxy-5α-steroids) have been found to possess desirable anesthetic properties and are included as active ingredients in pharmaceutical formulations. For pharmaceutical applications, it is desirable to obtain the 3α-hydroxy stereoisomer of the 5α-pregnane steroid in the purest possible form. Preparing high-purity products through catalysis and various purification techniques remains a challenging task.

[0004] 3α-Hydroxy-5α-steroids can be formed through biotransformation or chemical synthesis. Many different synthetic routes have been proposed in the past to prepare 3α-hydroxy-5α-steroids. One method involves using an iridium catalyst reduction system to reduce the corresponding 3-oxosteroid. However, the yield and purity of the desired 3α-hydroxy product are unsatisfactory due to isomerization at the 17-position of, for example, 20-oxopregnane and the formation of the 3β-hydroxy isomer. In an improved version of this method, 3-oxo-5α-steroids are reduced in the presence of an organic base using an iridium catalyst system prepared from a trivalent phosphorus compound, an iridium compound, and water. It was found that reducing the 3α-hydroxy-5α-steroid in the presence of a sufficient amount of added organic base to maintain a substantially neutral pH improves the desired 3α-hydroxy-5α-steroid ratio and controls the 17-position isomerization. Alternatively, a ruthenium catalyst (US Patent No. 11,472,833B2) can be used to catalytically reduce C3 ketones (C=O; as shown below) in the presence of carbonates in an organic solvent such as isopropanol to prepare C3-hydroxy (C-OH) steroids.

[0005]

[0006] C3 refers to the third carbon in an organic molecule. The use of a ruthenium catalyst achieves a stereoselectivity of approximately 80:20 between the 3α-hydroxy compound of formula (1a) and the 3-β-hydroxy compound of formula (1b). However, preparing the product of formula (1a) in high purity via catalysis and various purification techniques remains a challenging task. Furthermore, the inventors have found that the desired purity of the 3α-hydroxy-5α-steroid remains unacceptable, especially for commercial pharmaceutical manufacturing purposes.

[0007] There is clearly a need for a method to prepare the 3α-hydroxy stereoisomer of 5α-pregnane steroids with relatively high purity, especially a method that is easy to perform and inexpensive. The inventors have recently discovered a means to further control and improve the purity of the desired 3α-hydroxy-5α-pregnane steroids by modifying the hydrolysis reaction and purification stages. Summary of the Invention

[0008] This paper describes a novel method for purifying a crude mixture of 3α- and 3β-hydroxy-5α-pregnane as defined below by formulas (1a; alfasal) and (1b) to provide separate 3α-hydroxy stereoisomers and 3β-hydroxy stereoisomers, particularly the 3α-hydroxy stereoisomer with relatively high purity. The inventors have surprisingly discovered that this can be achieved by converting both the 3α-hydroxy and 3β-hydroxy groups on the 5α-pregnane steroid to their corresponding 3-acetoxy isomers (2a and 2b), which are surprisingly easier to separate from each other than their corresponding 3-hydroxy isomers. Each separate or desired 3-acetoxy isomer is then hydrolyzed to convert the acetate back to the hydroxyl group. This novel method overcomes previous technical difficulties by providing, relatively easily, synthetically the 3α-hydroxy-5α-pregnane steroid in a substantially monomeric form.

[0009] In one aspect of the invention, a method is provided for purifying a crude mixture of compounds of formula (1a) and (1b) into individual stereoisomers to substantially obtain a single stereoisomer of formula (1a), comprising:

[0010] a) Treating a mixture of compounds of formula (1a) and (1b) in at least one aprotic solvent with an acylating agent to form a mixture of compounds according to formula (2a) and (2b).

[0011] in

[0012] R 1 The alkyl group may be substituted or unsubstituted, and the alkyl group may be substituted by at least one or more substituents selected from hydroxyl, chlorine and oxo; b) Separate the compounds of formula (2a) and (2b) to obtain essentially a single stereoisomer of (2a) and (2b); c) Hydrolyzing the acetylated compound of formula (2a) in one or more solvents under alkaline conditions to form a compound of formula (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomers to obtain >95% of the 17β-enantiomers.

[0013] In another aspect, a method for purifying a crude mixture of compounds of formula (1a) and (1b) into individual stereoisomers to substantially obtain a single stereoisomer of formula (1a) includes:

[0014] a) Treating a mixture of compounds of formula (1a) and (1b) in at least one aprotic solvent with an acylating agent to form a mixture of compounds according to formula (2a) and (2b).

[0015] in

[0016] R 1 The alkyl group may be substituted or unsubstituted, and the alkyl group may be substituted by at least one or more substituents selected from hydroxyl, chlorine and oxo; b) Separate the compounds of formula (2a) and (2b) to obtain essentially a single stereoisomer of (2a) and (2b); c) Hydrolyzing the acetylated compound of formula (2a) in one or more solvents under alkaline conditions to form a compound of formula (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane, methanol and water, or ethanol and water to obtain >95% of the 17β-enantiomer.

[0017] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0018] It includes the following steps: a) A mixture of compounds of formula (1a) and (1b) is treated;

[0019] The treatment uses an acylating agent selected from acetic anhydride, acetyl chloride, propionic anhydride, and propionyl chloride in at least one aprotic solvent selected from tetrahydrofuran, pyridine, diethyl ether, dimethylformamide, dioxane, and triethylamine, or mixtures thereof, and optionally in the presence of a catalyst, for a duration of about 5 to 40 hours at a temperature of about 15-30°C; to form a mixture of compounds according to formulas (2a) and (2b).

[0020] in

[0021] R 1 The alkyl group may be substituted or unsubstituted, and the alkyl group may be substituted by at least one or more substituents selected from hydroxyl, chlorine and oxo; b) Separating compounds of formula (2a) and (2b) by recrystallization of the mixture in a solvent / antisolvent to obtain a substantially single stereoisomer of formula (2a), wherein the solvent is selected from acetone and ethyl acetate, and the antisolvent is selected from hexaane, pentane, and heptane. c) Hydrolyzing compound (2a) under alkaline conditions using sodium hydroxide, potassium hydroxide, or potassium carbonate in an aqueous solution of an alcohol solvent selected from methanol, ethanol, propanol, and isopropanol, and water, to prepare compound (1a) as a substantially monostereomer, comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane, methanol and water, or ethanol and water to obtain >95% of the 17β-enantiomer.

[0022] In another aspect, the preferred R 1 The substituent is methyl.

[0023] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0024] It includes the following steps: a) A mixture of compounds of formulas (1a) and (1b) is treated using an acylating agent selected from acetic anhydride or acetyl chloride, in

[0025] In an aprotic solvent selected from tetrahydrofuran, pyridine, or mixtures thereof, in the presence of a catalyst selected from 4-dimethylaminopyridine, 1-hydroxy-7-azabenzotriazole, or 1-hydroxy-7-azabenzotriazole, at a temperature of about 15-30°C for about 5 to 40 hours, a mixture of 3-acetoxy compounds of formulas (2a') and (2b') is formed. ; b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a solvent mixture selected from acetone and hexane, ethyl acetate and hexane, methanol and water, or ethanol and water to obtain a substantially single stereoisomer of (2a'); c) Hydrolyzing compound (2a') under alkaline conditions using sodium hydroxide in an aqueous solution of an alcohol solvent selected from methanol, ethanol, propanol, and isopropanol, and water, to form compound (1a) in a substantially monolithic stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane, methanol and water, or ethanol and water to obtain >95% of the 17β-enantiomer.

[0026] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0027] It includes the following steps: a) A mixture of compounds of formulas (1a) and (1b) is treated.

[0028] The treatment uses acetic anhydride in a mixture of tetrahydrofuran and pyridine, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxy compounds of formulas (2a') and (2b'). ; b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to about 1:10 to obtain substantially a single stereoisomer; c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water, or ethanol and water, to form compound (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane, methanol and water, or ethanol and water to obtain >95% of the 17β-enantiomer.

[0029] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0030] It includes the following steps: a) A mixture of compounds of formulas (1a) and (1b) is treated.

[0031] The treatment uses acetic anhydride in a mixture of tetrahydrofuran and pyridine in a ratio of about 4:1, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxy compounds of formulas (2a') and (2b'). ; b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to 1:10 to obtain a substantially single stereoisomer of formula (2a'); c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water, or ethanol and water, in an amount of 1 to 2 molar equivalents relative to formula (2a'), to form compound (1a) in a substantially monolithic stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane in a ratio of about 1:4 or 2:5, methanol and water in a ratio of about 1:1 to 1:2, or ethanol and water in a ratio of about 1:1 to 1:2, to obtain >95% of the 17β-enantiomer.

[0032] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0033] It includes the following steps: a) A mixture of compounds of formulas (1a) and (1b) is treated.

[0034] The treatment uses acetic anhydride in a mixture of tetrahydrofuran and pyridine in a ratio of about 4:1, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxy compounds of formulas (2a') and (2b'). ; b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to 1:10 to obtain a substantially single stereoisomer of formula (2a'); c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water, or ethanol and water, in an amount equivalent to 1 molar equivalent of formula (2a'), to form compound (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane in a ratio of about 1:4 or 2:5, methanol and water in a ratio of about 1:1 to 1:2, or ethanol and water in a ratio of about 1:1 to 1:2, to obtain >95% of the 17β-enantiomer.

[0035] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0036] It includes the following steps: a) A mixture of compounds of formulas (1a) and (1b) is treated.

[0037] The treatment uses acetic anhydride in a mixture of tetrahydrofuran and pyridine in a ratio of about 4:1, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxy compounds of formulas (2a') and (2b'). ; b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to 1:10 to obtain a substantially single stereoisomer of formula (2a'); c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water, or ethanol and water, in an amount of 2 molar equivalent relative to formula (2a'), to form compound (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers and said mixture containing >95% of the 17β-enantiomer; and d) Enantiomer enrichment of the enantiomers by recrystallization of the mixture in a ratio of about 1:1 to 1:2 of methanol and water or in a ratio of about 1:1 to 1:2 of ethanol and water to obtain the 17β-enantiomer.

[0038] In another aspect, a method for preparing a substantially single stereoisomer of formula (1a) is provided.

[0039] It includes the following steps: a) A mixture of compounds of formulas (1a) and (1b) is treated.

[0040] The treatment uses acetic anhydride in a mixture of tetrahydrofuran and pyridine in a ratio of about 4:1, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxy compounds of formulas (2a') and (2b'). ; b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to 1:10 to obtain a substantially single stereoisomer of formula (2a'); c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water at a concentration of 2 molar equivalents relative to formula (2a') to form compound (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers and said mixture containing >98% of the 17β-enantiomer, and d) Enantiomer enrichment of the enantiomers by recrystallization of the mixture in a ratio of about 1:1 to 1:2 of methanol and water or in a ratio of about 1:1 to 1:2 of ethanol and water to obtain the 17β-enantiomer.

[0041] Compared to the British Pharmacopoeia 2019 standard, the purity of alfasalol obtained by this invention is about 95-100%. A more preferred range is about 97-100%. Typically, other impurities such as 3... -Hydroxy isomer and 17 - The percentage of enantiomers is <2%.

[0042] Preferably, the mixture of 3α- and 3β-hydroxy compounds according to formulas (1a) and (1b) is formed by the Henbest reduction of allogeneic trione. Even more preferably, allogeneic trione is synthesized via a series of steps starting from readily available 11-hydroxyprogesterone or 11-ketoprogesterone, as indicated in Scheme 1.

[0043] Throughout this specification, the word “comprise” or its variations such as “comprises” or “comprising” should be understood to imply inclusion of the stated elements, integers or steps or groups of elements, integers or steps, but does not exclude the inclusion of any other elements, integers or steps or groups of elements, integers or steps, or including but not limited to.

[0044] In the description of this specification, reference may be made to subject matter that is not within the scope of the appended claims. Such subject matter should be readily recognized by those skilled in the art and may facilitate the practice of the invention as defined in the appended claims. Detailed Implementation

[0045] This invention relates to a method for preparing alfasal. Alfasal is a neuroactive steroid and general anesthetic, currently used in veterinary practice as an injectable anesthetic for induction and maintenance of anesthesia. Alfasal is a preferred anesthetic due to its minimal inhibitory effect on the cardiovascular system. The most common side effect in current veterinary practice when alfasal is administered alone or concurrently with other sedatives and anesthetics is respiratory depression. Alfasal acts as a positive allosteric modulator of the γ-aminobutyric acid A (GABA-A) receptor and, at high concentrations, as a direct agonist of the GABA-A receptor. The GABA-A receptor is an ion channel-type receptor and a ligand-gated ion channel. Its endogenous ligand is type A γ-aminobutyric acid (GABA); it is the major inhibitory neurotransmitter receptor responsible for rapid inhibition in the basal ganglia. Alfasal is rapidly cleared by the liver, resulting in a relatively short terminal half-life and preventing its accumulation in the body, thereby reducing the possibility of overdose.

[0046] Alphasalone is used as an injectable anesthetic for induction and maintenance of anesthesia, or as a sedative in animals. While commonly used in cats and dogs, it has also been successfully used in other animals such as rabbits, horses, sheep, pigs, and exotic animals (turtles, iguanas, marmosets, bears, and fish). As an inducer, alphasalone fully relaxes the animal for endotracheal intubation, allowing for the administration of inhalation anesthesia. Preoperative administration reduces the dosage requirement of alphasalone as an inducer. In surgeries shorter than 30 minutes, alphasalone can be used instead of gaseous anesthetics, administered intravenously via a constant-rate infusion; this is particularly useful in procedures such as bronchoscopy or tracheal tear repair, as inhalation anesthesia is not required and therefore there is no obstruction to endotracheal intubation. Once alphasalone administration is discontinued, minimal intervention is required for the animal to recover from anesthesia. Alphasalone can also be used as a sedative when administered intramuscularly. Based on the commercial use of alphasalone in veterinary medicine, there is a need for better manufacturing methods to reduce time, lower product costs, and increase yield. The method described in this paper provides a new, more efficient, and more cost-effective approach for the preparation of alfasal.

[0047] As described herein, the term enantiomer enrichment refers to a) the method of epimerizing the 17α-enantiomer under basic conditions to obtain a higher amount of the 17β-enantiomer (alphasalon) and / or b) the method of enantiomerizing any mixture of 17α- and 17β-enantiomers in a solvent / antisolvent system ( For example 17β-alphasalon was recrystallized in acetone / hexane, methanol / water, and ethanol / water to obtain a purer 17β-alphasalon.

[0048] Alphasalon, formula (1a), is also described herein as 3α-hydroxy-5α-pregnane, 3α-hydroxy-17β-alphasalon, and 17β-alphasalon.

[0049] The following shows the structural numbering of Alpha Salon:

[0050] In general, progesterone and 11-ketoprogesterone are examples of 3-ketosteroids and are useful starting materials for 3-hydroxypregnane steroids. In particular, 11-ketoprogesterone is a useful starting material for the synthesis of some cortical steroids, such as alfasalone and hydrocortisone. The synthesis of these cortical steroids requires the separation of the 3α- and 3β-hydroxy isomers using a simple, high-yield method to isolate the substantially pure 3α-hydroxy isomer. To obtain 3α-hydroxy isomers in even higher yields and with higher purity, the applicant converts a mixture of 3α- and 3β-hydroxy isomers into a mixture of 3α- and 3β-acetoxy isomers, which can be selectively crystallized from a solvent / antisolvent system to yield the substantially pure 3α-acetoxy isomer. Further epimerization of C17 can be controlled depending on the hydrolysis conditions of the acetoxy isomer. To overcome the problem of this diastereomeric mixture at C17 and to obtain essentially >97% 17β-alphasalon, the hydrolysis conditions for removing the 3-acetic acid protecting group are: at a lower temperature, using a minimum of 2 molar equivalents of sodium hydroxide in a small amount of water to allow the equilibrium to shift to the preferred thermodynamically stable 17β-alphasalon. Recrystallization from the solvent / antisolvent system provides an even higher yield of the 17β enantiomer (i.e., alphasalon), while reducing the preparation time by approximately 40% and requiring less solvent. The synthesis of alphasalon is illustrated in Scheme 1.

[0051] Option 1. Preparation of Alfasal

[0052] Scheme 2. Preparation of 3α-acetoxyalfasalone (2a') (Step 4 of Scheme 1)

[0053] Scheme 3. Hydrolysis of 3α-acetoxyalfasalone and preparation of alfasalone (1a) - (Step 5 of Scheme 1)

[0054] Scheme 4. Hydrolysis of 3α-acetoxyalphasalon (2a') and hydrolysis of crude 17α:17β-enantiomer (1c:1a) to prepare alphasalon (1a) - (Step 5 of Scheme 1)

[0055] In general, step 1 describes the process in an acidic aqueous solution ( For example In the presence or absence of solvents (such as sulfuric acid and acetic acid), example likeIn the presence of acetone and isopropanol, 11α-hydroxyprogesterone is oxidized to 11-ketoprogesterone using chromium trioxide (yield 80-85%). The reaction is very smooth and produces few byproducts. The product is separated by precipitation, including dilution with water and filtration.

[0056] In step 2, 11-ketoprogesterone is catalytically hydrogenated (Pd / C) in ethanol and / or ethyl acetate to give a 4:1 mixture of 5α- and 5β-pregnanetrione (allogracetrione). The desired 5α-product is readily crystallized from the ethyl acetate / ethanol solution in a yield of about 55-60%. Undesirable 5β-isomers are retained in solution. The prior separation is performed by column chromatography. It has been found that the 5α:5β-isomer ratio depends on the pH of the reaction medium; the higher the pH, the more undesirable 5β-isomers are produced. Preferably, the pH of the reaction medium is neutral. Overall, hydrogenation is simple and has been previously described. Purification is performed by fractional crystallization, with the yield determined by the 5-α / β ratio formed in the reaction.

[0057] In step 3, using Henbest reaction conditions, the 3-keto group of pregnanetrione is selectively reduced by transfer hydrogenation using an in-situ formed catalyst (iridium), which selectively reduces the 3-keto group of pregnanetrione to a mixture of 8.5:1.5 to 9.4:0.6 of 3α-hydroxy (1a) and 3β-hydroxy (1b) stereoisomers, respectively. The use of hexachloroiridium(iv) acid hydrate, isopropanol, triethylamine, trimethyl phosphite, and water facilitates the C3 reduction reaction. These stereoisomers have similar physical properties and co-crystallize in a variety of different solvent systems. Separating these stereoisomers by fractional crystallization can be extremely difficult. The reaction has been extensively studied by varying the reaction conditions, the properties of the reagents, and the pH of the medium to prevent or reduce the formation of undesirable 3β-isomers and other unwanted byproducts. Under acidic pH (<6) conditions, the reaction is slow and results in higher levels of impurities. An ideal pH range of 6–7 will produce the best yields and the fewest impurities without affecting the 3α:3β ratio. At higher pH levels, the reaction rate is faster, but the amount of impurities is higher, including the formation of undesirable 3β isomers. Using trimethyl phosphite at pH 6–7 yields 3α:3β isomers in ratios of approximately 8.5:1.5 to 9.4:0.6 in 90–95% (crude) yield. Changing the phosphite reagent to tributyl phosphite, triisopropyl phosphite, or triethyl phosphite does not significantly change the 3α:3β ratio. The use of tri(2-chloroethyl) phosphite increases the 3α:3β ratio to 12:1. However, the percentage of impurities is higher. Surprisingly, the 3α:3β isomers can be separated by derivatization of the 3-hydroxy group using a three-step chemical approach comprising (a) acetylation of the 3-hydroxy group; (b) separation of the stereoisomers by fractional crystallization; and (c) hydrolysis of the acetyl group. It should be understood that known methods can be used for acylation, separation, and hydrolysis.

[0058] In step 4 (Scheme 2), the 3-hydroxy isomer is derived into an acetate analog, which can be accomplished using any number of non-limiting acetylation agents such as acetic anhydride, acetyl chloride, propionic anhydride, propionyl chloride, etc. Preferred acetylation agents are acetic anhydride and acetyl chloride. More preferably, the acetylation agent is acetic anhydride. It should be understood that the acylation step will be carried out in one or more suitable solvents. Preferably, the acylation step is carried out in an aprotic solvent in the presence of a base, wherein the base is also a solvent. The base can act as a solvent and / or co-solvent. Non-exclusive examples of suitable solvents include tetrahydrofuran (THF), pyridine, diethyl ether, dimethylformamide (DMF), dioxane, methanol, hexane, acetone, triethylamine (TEA), or mixtures thereof. Preferably, the acylation step is carried out in THF and pyridine. It should be understood that one or more catalysts can be used in the acylation reaction. The role of the catalyst is to improve the efficiency of the reaction. Examples of suitable catalysts include, but are not limited to, 4-dimethylaminopyridine (DMAP); 1-hydroxy-7-azabenzotriazole (HOAt) and 1-hydroxy-7-azabenzotriazole (HOBt). DMAP is the preferred catalyst.

[0059] It should be understood that the acylation reaction can be carried out under certain conditions for a period of time to allow the desired conversion of the alcohol to the acetate to occur. The reaction can be carried out at a temperature in the range of about 0-30°C, preferably about 15-30°C. The time required for the acylation step will depend on many factors, including but not limited to the percentage of conversion achieved by acylation, the reaction temperature, the solvent used, and the presence of a catalyst. For example, the acylation reaction can be carried out for about 5 to 40 hours. Preferably, at least about 98% conversion from 3-hydroxyl to 3-acetoxy is achieved, more preferably >98%. It should be understood that the extent of the reaction can be monitored using thin-layer chromatography (TLC) or HPLC analysis. Preferably, the acylating agent is combined with the catalyst and mixed with formulas (1a) and (1b) combined with one or more solvents. In a preferred embodiment, formulas (1a) and (1b) are dissolved in THF / pyridine (4:1) and mixed with acetic anhydride / DMAP while stirring at room temperature (about 20-25°C) for about 20 hours to prepare 3α- and 3β-acetoxy compounds. The reaction is very smooth and produces no other byproducts or impurities. The 3α- and 3β-acetoxy compounds can be precipitated from solution by adding a large amount of methanol, followed by hot water and then cooling to room temperature. The yields of the 3α-isomer and the 3β-isomer are approximately 95-85% and 5-15%, respectively.

[0060] It should be understood that the separation of 3α- and 3β-acetoxy compounds can be performed using known methods, including but not limited to recrystallization and chromatography. Preferably, recrystallization, and more preferably fractional crystallization, is used to achieve the separation of the 3α- and 3β enantiomers. 。Recrystallization can be carried out using a solvent in which the crude 3α-acetoxy group is preferably slightly soluble at lower temperatures (about room temperature or lower, preferably ≤25°C) and soluble at higher temperatures (at or near the solvent boiling point). Preferably, the 3α-acetoxy group is separated from the 3β-acetoxy group isomer by fractional crystallization. Preferably, fractional crystallization is achieved using a solvent and antisolvent mixture system in which both compounds are soluble at or near the solvent boiling point, such that the target compound crystallizes out at a lower temperature (room temperature or lower). Examples of suitable solvent systems include, but are not limited to, acetone and ethyl acetate, and non-exclusive examples of suitable antisolvents include hexane, pentane, and heptane, including the corresponding isomers. Hexane isomers include n-hexane, 2-methylpentane, 3-methylpentane, cyclopentane, 2,3-dimethylbutane, and 2,2-dimethylbutane. Heptane isomers include n-heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, and 2,2,3-trimethylbutane. Pentane isomers include n-pentane, isopentane, and neopentane. Preferably, a mixture of 3α- and 3β-acetoxy groups is dissolved in hot acetone, followed by the addition of hot hexane as an antisolvent, and the mixture is cooled to allow selective crystallization of the 3α-acetoxy group. The 3α-acetoxy crystals can be collected by standard filtration methods. The filtrate can be distilled to remove the acetone fraction, followed by cooling to precipitate additional 3α-acetoxy crystals. Preferably, the solvent system is a mixture of acetone and hexane in a ratio of about 1:2 to 1:10. Recrystallization from the mixture of acetone and hexane yields 3α-acetoxyalphasalt as a white crystalline solid in about 70% yield and >98% purity. The 3β-acetoxy isomer is retained in hexane solution.

[0061] In step 5 (Scheme 3), the hydrolysis process is preferably carried out under alkaline conditions. Examples of aqueous solutions that can be used in the hydrolysis reaction include, but are not limited to, alkaline saline solutions, including: sodium hydroxide, potassium hydroxide, lithium hydroxide, potassium carbonate, sodium carbonate, and calcium carbonate. Preferred alkaline saline solutions are sodium hydroxide or potassium hydroxide. More preferably, alkaline saline solutions are sodium hydroxide. Preferably, the hydrolysis reaction also includes a solvent, more preferably a solvent in which 3α- and / or 3β-acetoxy groups are soluble. Examples of suitable solvents include, but are not limited to, alcohols, such as methanol, ethanol, isopropanol, n-propanol, or mixtures thereof. Preferred hydrolysis solvents are methanol or ethanol. It should be understood that the hydrolysis reaction can be carried out at 10°C to reflux, and the extent of the hydrolysis reaction can be determined by standard methods (…). For example Monitoring (TLC or HPLC).

[0062] In one aspect, 3α- and / or 3β-acetoxy groups are hydrolyzed with an aqueous sodium hydroxide solution, more preferably, 3α- and 3β-acetoxy groups are dissolved in methanol or ethanol and heated under reflux in the presence of an aqueous sodium hydroxide solution until hydrolysis is complete. Due to base-catalyzed isomerization at the C17 position of the molecule, hydrolysis of 3α-acetoxyalphasalone with an aqueous sodium hydroxide solution (1 molar equivalent) yields alphasalone in two enantiomeric forms: the 17β-isomer (…). Right now The desired 17β:17α-isomer (formula (1a)) and the undesirable 17α-isomer (formula (1c)) are present. This results in an enantiomer ratio of approximately 75:25 for the 17β:17α-isomers, requiring further purification and selective crystallization of the precipitate to improve the yield of 17β-alphasalon. Selective crystallization of the 75:25 mixture of precipitates can be performed to purify the mixture of 3α-hydroxy-17α- and 3α-hydroxy-17β- compounds formed during the hydrolysis reaction to obtain 17β-alphasalon. This selective recrystallization process yields approximately 50% of the desired 3α-hydroxy-17β-compound (formula (1a)) and the undesirable 17α-isomer (formula (1c)). Right now Alphasalane. It should be understood that a variety of solvents (solvent for dissolution and antisolvent for recrystallization) can be used in the recrystallization step. Non-limiting examples of suitable solvents include acetone, ethyl acetate, ethanol, and methanol; and non-limiting examples of antisolvents include water, pentane, heptane, and hexane. For a 17β:17α enantiomer ratio of 75:25, a preferred solvent / antisolvent mixture is acetone and hexane. The desired 17β-isomer is readily crystallized from a mixture of acetone and hexane (1:4 or 2:5) to obtain pure alphasalane, which can be separated by basic filtration techniques. As described, 1 molar equivalent of sodium hydroxide produces a 17β:17α-enantiomer ratio of 75:25 with an overall yield of about 50%. Once the 17β-alphasalane crystals are collected after crystallization, the mother liquor, still containing 17α- and 17β-isomers (1:1), can be reprocessed after solvent distillation and then further hydrolyzed by adding a hydrolytic reagent ( Right nowThe 17α-enantiomer is further epimerized to 17β-alphasalone using a 1-molar aqueous solution of methanol, ethanol, and water. Each consecutive batch harvest yields a 75:25 ratio of 17β:17α-enantiomers, with subsequent harvests yielding approximately 1:1 of the two isomers. These conditions can be used for multiple batch harvests to increase the yield of 17β-alphasalone to >97%. Furthermore, at any stage of batch harvest, the precipitate mixture of the 17α- and 17β- isomers can be epimerized in a mixture of methanol, water, and 2 molar equivalents of sodium hydroxide to obtain a mixture of 17α- and 17β- isomers with a ratio of <2:>98; this mixture can then be recrystallized from the solvent / antisolvent to obtain 17β-alphasalone in approximately 88-92% yield, thus eliminating the need for multiple batch harvest steps (Scheme 4B).

[0063] Alternatively, to eliminate the batch harvesting steps described above, if the hydrolysis reactants are increased, particularly by increasing the molar equivalent of sodium hydroxide to 2 molar equivalents, the hydrolysis of 3α-acetoxyalfalone will produce 17β- and 17α-isomers in a ratio of >98:<2 (Scheme 4A). This mixture is then recrystallized from the solvent / antisolvent system to obtain 17β-alfalone (1a) in a yield of approximately 88-92%. The precipitated 17β- and 17α-enantiomers can be recrystallized from a mixture of acetone and hexane (1:4 or 2:5), or preferably from a mixture of ethanol and water (1:1 to 1:2) or methanol and water (1:1 to 1:2), to obtain pure alfalone, which can be separated by basic filtration techniques. The preferred hydrolysis reaction for 3-acetoxyalfasalone is as follows: 3α-acetoxyalfasalone is dissolved in an aqueous sodium hydroxide solution (2 molar equivalents) of methanol or ethanol (preferably methanol) to obtain 17β-alfasalone and 17α-enantiomers in a ratio >98:<2, and then the enantiomer mixture is recrystallized from ethanol and water to obtain 3α-17β-alfasalone. This material meets the requirements for alfasalone in the British Pharmacopoeia (2019).

[0064] experiment

[0065] Those skilled in the art will understand that various modifications and variations can be made to the invention as illustrated in the specific embodiments without departing from the spirit or scope of the invention as broadly described. Therefore, the embodiments of the invention should be considered illustrative rather than restrictive in all respects.

[0066] All reactions were performed under standard laboratory conditions and by thin-layer chromatography (TLC) on pre-coated silica gel TLC plates or pre-coated reversed-phase C24 plates.18 The reaction progress was monitored on a bonded TLC plate or by HPLC. Products were separated by precipitation with water as an antisolvent and by filtration. All products were purified by recrystallization. Melting points were determined using an uncalibrated electrothermal digital melting point apparatus. 1 H NMR and 13 C10 NMR spectra were recorded using a Bruker AC300F spectrometer running at 300 MHz and 75 MHz at the Department of Chemistry, University of New South Wales; or using a Bruker NMR spectrometer running at 300 MHz and 75 MHz at the Department of Chemistry, Newcastle University. Purity was determined by HPLC analysis and recorded relative to the British Pharmacopoeia (2019) quality reference standards. Industrial-grade reagents and solvents were used unless otherwise specified.

[0067] Example

[0068] Step 1. Oxidation of 11-hydroxyprogesterone: A solution of chromium trioxide (12.5 kg) in 25 L of water was added very slowly to a solution of 25 kg of 11α-hydroxyprogesterone (11-α-hydroxy-4-pregnen-3,20-dione) in 95 L of 90% acetic acid. The initial reaction is exothermic, and therefore the rate of addition of the chromium trioxide solution should be carefully controlled to maintain the reaction temperature below 70 °C. The mixture was stirred overnight at room temperature. Water (420 L) was added and the product was allowed to crystallize. It was stored in a cold room for two days and then filtered using a basket centrifuge. The product was washed several times with water to remove residual chromium oxide impurities. It was dried in air to give 11-ketoprogesterone as a white powder. Typical yields are ~80-82%. The crude product is sufficiently pure, so no further purification is required.

[0069] Step 2. Preparation of 5-α-pregnane-3,11,20-trione (allogrenonetrione) by selective reduction: Add 8.0 g of 10% palladium / activated carbon to a solution of 1.65 kg of 11-ketoprogesterone in 27 L of ethyl acetate and 13 L of 96% ethanol and hydrogenate. Degas the reaction mixture for 30 minutes using a suction pump, then connect to the hydrogen supply line and adjust the hydrogen pressure to slightly above atmospheric pressure. Stir vigorously until all 11-ketoprogesterone is hydrogenated (~1 day). Warm the reaction mixture to dissolve the precipitated product and filter using a 30 cm disc filter and an S-10 packed filter pad. Allow the filtrate to cool to room temperature and then store overnight in a cold room (4°C). Allogeneic trione crystallizes out as white crystals. Collect the crystals by filtration and wash with cold ethyl acetate / ethanol (30%) (using the solvent recovered from the fractionation). Allow the product to dry in a ventilated area or in a drying oven. Concentrate the filtrate (mother liquor) to one-third of its volume by distillation, then store in a cold room for several days and filter. This yields the second batch of allogeneic trione. Typical yield is approximately 55-60%. Repeat the procedure several times to convert all 11α-hydroxyprogesterone into allogeneic trione.

[0070] Step 3: Crude mixture of 3α- and 3β-hydroxy-5α-pregnane-11,20-dione prepared

[0071] 12 g of chloroiridium acid and 4.85 L of trimethyl phosphite were heated under reflux for 20 hours in 28 L of isopropanol and 4.7 L of water. The solution was cooled to about 50-60 °C, and the pH was adjusted to pH 6.5-7 by adding triethylamine (5.17 L). Allogeneic trione (4.6 kg) was added, and the reaction was heated to reflux and maintained for 24 hours. The progress of the reaction was monitored by TLC and HPLC. About 15 L of solvent was removed by distillation, and the concentrated reaction mixture was then transferred to a 100 L stainless steel container. Water (60 L) was slowly added with stirring. The mixture was allowed to cool to room temperature and then stored overnight in a cold room. The white crystalline solid was filtered using a basket centrifuge, washed several times with water to remove residual solvent, and dried in a hot air drying oven. The typical yield was about 95%. HPLC analysis showed a 9:1 mixture of 3α and 3β isomers. A small sample was recrystallized from a mixture of acetone and hexane (1:4) to obtain needle-like crystals with a melting point of 165-166℃.

[0072] Step 4. Preparation of 3α-acetoxy-5α-pregnane-11,20-dione (3α-acetoxyalfasalone (2a')): In a very dry 50 L glass reaction vessel, 5.7 kg of 3-α / β-hydroxy-5α-pregnane-11,20-dione (a 9:1 mixture of 3α and 3β isomers) was dissolved in 12 L of pre-chilled tetrahydrofuran and 2.76 L of pre-chilled pyridine. 2.5 L of acetic anhydride and 18.08 g of 4-dimethylaminopyridine (DMAP) were added, and the mixture was stirred at room temperature for 20 hours. The reaction progress was monitored using TLC. 2.7 L of methanol was added, and the mixture was stirred at room temperature for one hour. Under vigorous stirring, the reaction mixture was added to 145 L of hot water. The mixture was allowed to cool to room temperature and then stored in a cold room for 1–2 days. The resulting white, oily precipitate was collected by filtration and washed several times with water. The crude acetoxy mixture was dried in a fume hood and then in a hot air drying oven. The product was purified by fractional crystallization as described below.

[0073] The dried crude product was dissolved in 8 L of hot acetone, and then 54 L of hot hexane was added with stirring. The hot solution was allowed to cool slowly to room temperature and then stored in a cold room for two days. Crystals were collected by filtration. The filtrate was distilled to remove the acetone fraction (~20 L) and allowed to cool to room temperature before being stored in a cold room. A second batch of product was obtained by filtration. The first and second batches were combined to give 5.1 kg of the 3α-acetoxy compound. The product was analyzed by reversed-phase TLC. 1 H NMR and HPLC analyses of the product showed a 3α:3β ratio >99:1. The calculated purity of 3α-acetoxyalfasalone was >98%.

[0074] Step 5. Hydrolysis of 3α-acetoxyalfasalone (2a'): Add 5.0 L of 10% sodium hydroxide (1.0 mol equivalent) to a suspension of 4.4 kg of 3α-acetoxyalfasalone in 44 L of methanol, and heat under reflux for 3–4 hours (until all acetates are hydrolyzed). Monitor the progress of the reaction by TLC, and then distill off 20 L of methanol. Transfer the reaction mixture to a larger vessel and stir overnight at room temperature. Then add 80 L of reverse osmosis (RO) water with stirring and allow it to cool in a cold room for two days. Filter the precipitate using a basket centrifuge and wash several times with water. Collect the product and dry it in a hot air drying oven. TLC analysis of the product showed it to be a mixture of 17α and 17β optical isomers.

[0075]

[0076] The separated mixture of 17α- and 17β-enantiomer precipitates can be further enriched to a 17β-alphasalin content >95% by dissolving the precipitate in methanol or ethanol and an aqueous sodium hydroxide solution (2.0 molar equivalents) at room temperature. For example, 2.0 kg of alphasalin precipitate (at any 17α and 17β ratio) was dissolved in methanol (7.2 kg) and treated with a 10% aqueous sodium hydroxide solution (0.47 kg sodium hydroxide / 7.4 kg RO water). The reaction mixture was heated to reflux for 1 hour and then cooled to <20°C and kept at a sufficient time to allow it to equilibrate. For example (Overnight). RO water at <30°C was added to the cooled reaction slurry and aged for 1 hour with stirring, followed by filtration through a Buchner funnel or centrifuge. The filter cake was thoroughly washed with water and then dried in an oven at 60°C. Typically, the recovery rate of 17β-alphasalon is >97%. The same yield was obtained when methanol was replaced with ethanol. Using 1.0 molar equivalent of sodium hydroxide (0.24 kg) and the same amount of aphasalon precipitate (17β-alphasalon and 17α-enantiomer) and solvent input, and with the same process, the ratio of 17β-alphasalon to 17α-enantiomer was 75:25.

[0077] As described herein, the crystallization of alfasal is carried out as follows: The crude product (17β-alfasal and 17α-enantiomer (75:25)) is dissolved in a minimal amount of hot acetone (approximately 20 L), and the hot solution is filtered through a 10S disc filter pad. The filter pad is washed with 2–3 L of acetone. The solution is concentrated to ~15 L, 60 L of hot hexane is added, and the solution is allowed to cool to room temperature and then stored overnight in a cold room. Gentle agitation has been found to reduce the co-crystallization of the unwanted isomer (17α-enantiomer) with alfasal. Fine needle-like crystals are collected by filtration. The mother liquor containing the mixture of 3α-hydroxy-17α (undesirable) and 3α-hydroxy-17β-alfasal (desirable) is evaporated, the residue is dissolved in 8.8 kg of methanol, and stirred with 400 mL of 10% sodium hydroxide solution for 24 hours. Alfasal is precipitated by adding water and collected by filtration. The drying and recrystallization as described above yielded pure alpha-salt. This was combined with the first batch of harvest. Similarly, the mother liquor was evaporated and the residue dissolved in methanol, 10% sodium hydroxide was added, and the mixture was stirred overnight. Water was then added, the solution was filtered, and the product was dried. The product was purified by recrystallization as described above to collect the third batch of harvest. This procedure was repeated twice more with the mother liquor to collect the fourth and fifth batches of harvest. Right now(Harvested in batches). The purity of alfasal was analyzed by HPLC according to the British Pharmacopoeia (Veterinary) standard method. The purity of alfasal was ~96.4%. The amount of the 17α-isomer was <0.1%. The product may optionally be recrystallized again from acetone and hexane. Alternatively, the mother liquor (any batch) may be reduced to 70% of the initial volume, cooled to <30°C, optionally mixed with an antisolvent, and aged for 3 hours, followed by filtration and drying.

[0078] Alternatively, the hydrolysis of 3α-acetoxyalfasalane in step 5 can be carried out under different hydrolysis conditions to produce the desired 17β-alfasalane drug product as the main product, while minimizing 17α-enantiomers, thereby simplifying crystallization and batch harvesting steps, reducing the need for additional solvent use / waste generation, and providing a more cost-effective route for the preparation of 17β-alfasalane drug products.

[0079] Unlike the procedure described above (which resulted in a 75:25 (17β:17α) ratio and approximately 50% yield in the first batch of harvest), this method uses a short-chain alcohol (such as methanol or ethanol), increases sodium hydroxide (2 molar equivalents) and water, then heats to >55°C and holds for >10 minutes, cools to <25°C, and ages the mixture at this temperature for a sufficient time to allow it to equilibrate, followed by precipitation with water. The holding time is crucial for the 17-α / β-enantiomer ratio to allow the equilibrium to shift in favor of the 17β-enantiomer (alphasalon). With optimized reaction conditions, >97% 17β-alphasalon will be provided after the precipitation step without further recrystallization and batch harvesting. When enriching the product for enantiomers, alcohols (methanol or ethanol) and water, instead of acetone and hexane, can be used as high-yield and safer crystallization solvents for recrystallization and further purification. This optimized method can be used to prepare alpha-salt in higher yields while reducing solvent / antisolvent usage and saving approximately 40% of the time.

[0080] As an example of optimized conditions using methanol or ethanol, a suspension of 660 g of 3α-acetoxyalphasalone in 1.5 L of methanol was heated to >60 °C / reflux and a 20% aqueous solution of sodium hydroxide was added (sodium hydroxide (150 g) / RO water (760 g)). The mixture was held at this temperature for 20 minutes and then cooled to 20 °C. As the reaction cooled, the 17β-enantiomer began to precipitate from the solution preferentially over the 17α-enantiomer. The slurry mixture was held at this temperature for at least 12 hours and then RO water (12 kg) was added to complete the precipitation and essentially obtain the desired 17β-enantiomer. The precipitate was separated by filtration, washed with RO water, and dried. HPLC analysis revealed that the analyzed material had >98% 17β-alphasalone (1a). The alphasalone precipitate was recrystallized from hot ethanol (3 wt% and hot water (3 to 4.5 wt%), and the mixture was then slowly stirred and cooled to (10 °C) overnight. The product was separated by any filtration method, washed with cold ethanol:water, and then dried. HPLC analysis showed that the purity of alfasalamine was greater than 99% and met the quality standards of the 2019 British Pharmacopoeia. The overall yield of this optimized process (covering the two separable steps) was 88-92%. If necessary, additional material can be separated from the filtrate by reducing the mother liquor volume through distillation (atmospheric or vacuum distillation) to precipitate (1a) and (1b). The precipitate can be separated by filtration, dried, and further enriched using the enrichment methods described above to obtain formula (1a). 1 HNMR, 13 The product was characterized by CNMR and MS spectroscopy. Formula (1a) has a melting point of 172-173 °C and a specific rotation [α] at 18 °C. D It is 110.11.

Claims

1. A method for preparing the compound of formula (1a), Alphasalen, The method includes: a) Treatment of a mixture of compounds of the 3α-hydroxy form (1a) and the 3β-hydroxy form (1b), The treatment is carried out in at least one aprotic solvent using an acylating agent in the presence of a catalyst to form a mixture of acetylated 3α-form (2a) and 3β-form (2b) compounds. Where R 1 The alkyl group may be substituted or unsubstituted, wherein the alkyl group may be substituted by at least one or more substituents selected from hydroxyl, chlorine and oxo; b) Separate the compounds of formula (2a) and (2b) to obtain their essentially single stereoisomers; c) Hydrolyzing the acetylated compound of formula (2a) under alkaline conditions in one or more solvents to form a compound of formula (1a) as a substantially single stereoisomer, said substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers, and optionally, d) Enantiomer enrichment of the enantiomer mixture, comprising epimerizing the 17α-enantiomer in an alkaline aqueous solution containing 1-2 molar equivalents of sodium hydroxide or potassium hydroxide in methanol and water, or ethanol and water, and then recrystallizing the resulting product from a mixture of acetone and hexane, methanol and water, or ethanol and water to obtain >95% of the 17β-enantiomer.

2. The method according to claim 1, wherein the acetylation in step (a) is carried out using an acetylation agent selected from acetic anhydride, acetyl chloride, propionic anhydride and propionyl chloride; and wherein the aprotic solvent in step (a) is selected from tetrahydrofuran, pyridine, diethyl ether, dimethylformamide, dioxane, triethylamine or mixtures thereof; and wherein the catalyst is selected from 4-dimethylaminopyridine, 1-hydroxy-7-azabenzotriazole and 1-hydroxy-7-azabenzotriazole.

3. The method according to claim 2, wherein the acetylation agent is acetic anhydride or acetyl chloride, and the aprotic solvent is a mixture of tetrahydrofuran and pyridine.

4. The method of claim 3, wherein the acetylation agent is acetic anhydride and the ratio of tetrahydrofuran to pyridine is about 4:

1.

5. The method according to claim 4, wherein the catalyst is 4-dimethylaminopyridine.

6. The method according to claim 1, step (b), wherein formula (2a) is separated from formula (2b) by dissolving the compound in ethyl acetate or acetone and then recrystallizing the compound from a solvent and antisolvent mixture, wherein the solvent is acetone and the antisolvent is hexane, in an amount ratio of about 1:2 to 1:10, and then filtering the solvent / antisolvent mixture to obtain the compound of formula (2a).

7. The method according to claim 1, wherein the hydrolysis in step (c) is carried out by using an alkaline salt selected from potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate and calcium carbonate, and the solvent is selected from acetone, methanol or ethanol.

8. The method according to claim 7, wherein the alkaline salt is sodium hydroxide, and wherein the molar equivalent of sodium hydroxide is at least 1 to 2 moles relative to the amount of formula (1a).

9. The method of claim 1, wherein the method further comprises step (d), and wherein the enantiomer enrichment of the 17β-enantiomer is accomplished by causing the 17α-enantiomer to undergo epimerization in methanol and an aqueous solution of 1 or 2 molar equivalents of sodium hydroxide, and wherein the 17β product is recrystallized from a mixture of acetone and hexane, methanol and water, or ethanol and water.

10. The method according to claim 9, wherein the ratio of the mixture of acetone and hexane is about 1:4 or about 2:5; and the ratio of the mixture of methanol and water, or the mixture of ethanol and water, is about 1:1 to 1:

2.

11. The method of claim 10, wherein the 17β product is recrystallized from a mixture of methanol and water, or ethanol and water, in an amount ratio of about 1:1 to 1:2, and preferably 1:1.

5.

12. A method for preparing the compound of formula (1a), Alphasalen, The method includes: a) Treatment of a mixture of compounds of the 3α-hydroxy form (1a) and the 3β-hydroxy form (1b), The treatment uses acetic anhydride in a solvent mixture of tetrahydrofuran and pyridine, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxyalphasalane compounds of formula (2a') and (2b'). b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to about 1:10 to obtain substantially a single stereoisomer; c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water, or ethanol and water, in an amount of 1 molar equivalent relative to formula (2a'), to prepare compound (1a) as a substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and optionally, d) Enantiomer enrichment of the enantiomers in an aqueous solution containing 1 or 2 molar equivalents of sodium hydroxide in methanol and water, or ethanol and water, and recrystallization of the resulting product from a mixture of acetone and hexane, methanol and water, or ethanol and water to obtain >95% of the 17β-enantiomers.

13. The method of claim 12, further comprising step (d), wherein the amount of sodium hydroxide in step (d) is about 1 molar equivalent, and the 17β product is recrystallized from a mixture of acetone and hexane in an amount ratio of about 1:4 or 2:

5.

14. The method according to claim 13, wherein the sodium hydroxide in step (d) is in a 2 molar equivalent and the product is recrystallized from a mixture of methanol and water, or ethanol and water; the ratio of the amounts of each is from about 1:1 to 1:2, and preferably about 1:1.

5.

15. A method for preparing the compound of formula (1a), alpha-salone, The method includes: a) Treatment of a mixture of compounds of the 3α-hydroxy form (1a) and the 3β-hydroxy form (1b), The treatment uses acetic anhydride in a solvent mixture of tetrahydrofuran and pyridine in a ratio of about 1:4, in the presence of a catalyst of 4-dimethylaminopyridine, at a temperature of about 15-30°C for about 5 to 40 hours; to form a mixture of 3-acetoxyalphasal compounds of formula (2a') and (2b'). b) The compounds of formula (2a') and (2b') were separated by fractional crystallization in a mixture of acetone and hexane in a ratio of about 1:2 to about 1:10 to obtain substantially a single stereoisomer; c) Hydrolyzing compound (2a') under alkaline conditions using an aqueous solution of sodium hydroxide in methanol and water at a concentration of 2 molar equivalents relative to compound (2a') to form compound (1a) as a substantially single stereoisomer comprising a mixture of 17α- and 17β-enantiomers; and d) Enantiomer enrichment of the enantiomers by recrystallization of the 17β product in a mixture of methanol and water, or ethanol and water, in an amount ratio of about 1:1 to 1:2, and preferably 1:1:1.5.

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