RU2764597C1 - Method for synthesising disodium salt of dexamethasone 21-phosphate applied for treating patients with coronavirus infection (covid-19) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to a method for synthesising disodium salt of dexamethasone (11,17βα-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20-dione) 21-phosphate by the formula (I) - a corticosteroid medicinal product exhibiting a desensitising, antishock, immunosuppressive, antiallergic, anti-inflammatory effect. The compound by the formula I is produced from dexamethasone (11β,17α,21-trihydroxy-9α-fluoro-16α-methylpregna-1,4-diene-3,20-dione) by the formula (II) by means of a reaction with pyrophosphoryl chloride taken at the rate of no less than 1.0 mol per 1.0 mol of the compound II, in the environment of a cyclic ether, followed by hydrolysis of the resulting 21-phosphate dexamethasone dichloro-derivative, removal of steroid impurities from the aqueous medium by the method of liquid-phase extraction using chlorinated hydrocarbon, extraction of the formed dexamethasone (11β,17α-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20-dione) 21-phosphate by the formula (III) from the aqueous medium by the method of solid-phase extraction at room temperature using non-ionogenic polymers selected from Macronet MN-200, Macronet MN-202, AmberLite XAD-4, AmberLite XAD-16, desorption thereof by a mixture of chlorinated hydrocarbon and aliphatic alcohol, and processing of 21-phosphate dexamethasone with sodium alcoholate in the environment of the corresponding aliphatic alcohol, wherein no less than 1.94 moles of sodium alcoholate is taken per 1 mol of the compound III.

EFFECT: proposed method provides a possibility of synthesising a target product of the appropriate quality while ensuring a molar yield of at least 90%.

10 cl, 3 ex

Description

Technical field

The present invention relates to the field of organic synthesis, specifically for the production of water-soluble derivatives of steroid compounds (corticosteroids), such as dexamethasone, and can be used in the chemical and pharmaceutical industries, as well as in industrial biotechnology, for the production of steroid medicines used to treat patients with a severe course of coronavirus infection (COVID-19).

State of the art

Corticosteroid C ²¹ -monoefiry phosphoric acids are important precursors in the production of water-soluble dosage forms of steroidal anti-inflammatory drugs used in the form of sodium salts, such as prednisolone, dexamethasone, betamethasone [https://www.rlsnet.ru/].

Dexamethasone 21-phosphate disodium salt (CAS No. 2392-39-4) is a water-soluble derivative of dexamethasone (11β,17α,21-trihydroxy-9α-fluoro-16α-methylpregna-1,4-diene-3,20-dione, CAS No. 50-02-2) - a corticosteroid drug that has a desensitizing, anti-shock, immunosuppressive, anti-allergic, anti-inflammatory effect. Dexamethasone 21-phosphate disodium salt is used in the form of a solution for parenteral and local (including conjunctival) administration. This compound can be used as an active ingredient not only in injectable preparations and solutions for ophthalmology, but also in the form of water-soluble tablets (including for oral administration).

According to WHO, dexamethasone is currently the only therapeutic agent that has been shown to be effective against the novel coronavirus SARS-CoV2 (COVID-19) in patients with severe disease. According to a study reported by WHO, dexamethasone has reduced mortality by one-third in patients on mechanical ventilation and by one-fifth in patients requiring oxygen therapy [https://www.who.int/ru/news-room/qa- detail/qa-dexamethasone-and-covid-19]. On September 2, 2020, WHO issued "interim guidance on the use of dexamethasone and other corticosteroids for the treatment of COVID-19" [https://apps.who.int/iris/bitstream/handle/10665/334125/WHO-2019-nCoV-Corticosteroids -2020.1-rus.pdf?sequence=9&isAllowed=y]. These recommendations have been developed by a team of WHO experts, as well as international experts and researchers, and are based on evidence from seven clinical trials. WHO has recommended a range of oral or intramuscular corticosteroids, including dexamethasone, for the treatment of patients with severe and critical COVID-19. However, dexamethasone (DSM) has significant advantages over other recommended steroids, as it is used in a much lower daily dose, namely 6 mg instead of 160 mg for hydrocortisone, 40 mg for prednisolone and 32 mg for methylprednisolone, and is practically devoid of the negative mineralocorticoid effect inherent in these drugs.

An intermediate in the synthesis of DSM 21-phosphate disodium salt from DSM is DSM 21-phosphate (11β,17α,-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20- dione, CAS no. 312-93-6).

DSM 21-phosphate is obtained by esterification of the hydroxyl group of the DSM molecule at the C21 atom or by chemical modification of its 21-deoxy structural analog.

Known methods for obtaining the disodium salt of 21-phosphate DSM from DSM with the release of crystalline 21-phosphate DSM, and without isolation.

Thus, a method is known for obtaining the disodium salt of 21-phosphate DSM [DE2022695, 1970, example 3] without isolating 21-monophosphate DSM (III), including the interaction of DSM and a triethylamine salt with N- p- nitrobenzoyl-phosphoric acid amide in a dimethylformamide medium. The reaction mass after the reaction is concentrated in vacuo, the residue is dissolved in methanol and treated with a cation exchange resin based on polystyrene with SO3H groups (Type IR-120). Remove part of the solvent in vacuo, add NaOH in methanol to pH 9 and dilute with acetone. The sodium salt of 21-phosphate DSM precipitates, which is filtered off, washed with acetone, benzene and ether to remove p-nitrobenzamide, dried in vacuum to constant weight. Get the sodium salt of 21-phosphate DSM with a yield of 85%. Quality indicators are not given.

Also known is a method for the synthesis of the disodium salt of 21-phosphate DSM from DSM with the release of crystalline 21-phosphate DSM [GB952193, 1964, (example 3)], which is obtained through the formation of 21-dimorpholido-phosphate DSM by the reaction of 16α-methyl-9α-fluoroprednisolone (DSM ) with dimorpholidophosphoryl chloride. DSM 21-dimorpholidophosphate is converted to DSM 21-phosphate by a complex procedure involving treatment with an ion exchange resin in aqueous ethanol at 60°C, isolation and purification of DSM 21-phosphate using a solution-precipitation method using caustic soda and sulfuric acid, extraction with ethyl acetate to remove impurities from an aqueous solution. The disodium salt is obtained from DSM 21-phosphate by neutralization with an equivalent amount of NaOH in a methanol solution, followed by evaporation of the methanol to dryness, dissolution of the residue in methanol, and precipitation of the sodium salt from this solution with water. The yield of the disodium salt of 21-phosphate DSM is not indicated, however, it is obvious that such a complex procedure does not allow a satisfactory yield to be obtained.

The most well-known are the use of two methods for obtaining DSM 21-phosphate from DSM:

- a three-stage method, which includes the sequential conversion of DSM to 21-methanesulfonate (mesylate), the transformation of DSM 21-mesylate into a 21-iodine derivative and the replacement of an iodine atom with a phosphorus group to form DSM 21-phosphate (method 1);

- one-step method of direct phosphorylation (method 2).

Of industrial interest is the production of 21-phosphate DSM by method 2, carried out in one stage.

Method (2) of direct phosphorylation consists in the interaction of 21-hydroxysteroid II with pyrophosphoryltetrachloride (pyrophosphoryl chloride, diphosphoryl chloride, PPC) and hydrolysis of the resulting 21-ester of the dichloro derivative of phosphoric acid IIa with the formation of 21-phosphate DSM (III) (Scheme 1). In this case, the hydrolysis reaction is carried out without isolating the intermediate IIa.

Scheme 1

Known methods for producing disodium salt of dexamethasone phosphate (I) from DSM (II) using the method of direct phosphorylation with the release of crystalline 21-phosphate DSM (III) [CN101397320, 2009; CN103936809, 2014 (example 3); CN 109134581, 2019]. Obtaining 21-phosphate DSM from DSM is carried out by reaction with PPC in a tetrahydrofuran (THF) medium at a temperature of from minus 60°C to minus 45°C, followed by dilution of the reaction mass with water and the addition of NaHCO ₃ at a temperature of 5 to 15°C to pH 8 After standing, NaHCO _{3 is} filtered off, washed with water, the layers are separated, the organic layer is concentrated to remove THF. At the same time, in patents [CN101397320, 2009; CN 109134581, 2019] after evaporation of the solvent, hydrochloric acid is added to the residue to pH 1-2, the suspension is kept for 2 hours, and the precipitate is filtered off. After drying, 21-phosphate DSM (III) is obtained with a yield of 11.1 g from 10 g of DSM and 10.86 g from 10.02 g of DSM, respectively. The content of the main substance in the products is not specified. In the patent [CN103936809, 2014, example 3], after removal of THF in a vacuum, the residue is extracted with ethyl acetate, the layers are separated, and the aqueous layer is treated with activated carbon at 30-40°C for 1 hour. Ethyl acetate is removed from the filtrate in vacuo and concentrated hydrochloric acid is added to the residue cooled to 10-20°C. After 6-8 hours of stirring at 10-20°C, the suspension is settled for 30 minutes, the precipitate is filtered and dried in vacuum at 60°C. Get 21-phosphate DSM with a weight yield of 116.2% and with a basic substance content of 99.3%.

In the patent [WO 201706227, 2017, example 1-1], after alkalizing the reaction mass with a saturated solution of NaHCO ₃ to pH ~ 8, the resulting solution is acidified with a 1N HCl solution and extracted with ethyl acetate. The organic phase is washed with brine, dried over sodium sulfate and evaporated. Get 21-phosphate DSM with a molar yield of 103%, which indicates a low quality of the product.

Known methods of obtaining the disodium salt of 21-phosphate DSM (I) in methanol by the action of a solution of NaOH. According to the patent [CN101397320, 2009], 13.2 g of DSM 21-phosphate disodium salt with m.p. 230-235℃ (which corresponds to a molar yield of 108.82% without taking into account the % content of the main substance in the original DSM 21-phosphate). In the patent [CN 109134581, 2019], by the same method, 13.11 g of 21-disodium phosphate DSM (I) is obtained from 10.86 g of DSM phosphate (which corresponds to a molar yield of 101.2% without taking into account the % content of the main substance in the original DSM 21-phosphate, but taking into account water content, which is 8.36% according to Karl Fischer analysis or 8.42% according to the result of thermogravimetric analysis).

A known method of obtaining the disodium salt of 21-phosphate DSM from 21-phosphate DSM in ethanol by adding 10% (w/v) NaOH solution to pH 11. To a solution of dexamethasone sodium phosphate at 25°C add 4000 ml of a mixture of ether and water in a volume ratio 9:1. After crystallization, the precipitate is centrifuged and washed with acetone. The crystals are dried at 70° C. under vacuum. In the patent [CN1763067, 2006, (option 1)], a crystalline product is obtained with a weight yield of 102.8% and a basic substance content of 99.3%. In the patent [CN 109134581, 2019], from 12.03 g of DSM 21-phosphate, the authors obtain 11.53 DSM 21-phosphate disodium salt trihydrate (which corresponds to a molar yield of 87.7%, taking into account the content of water of crystallization, which is 8.66% according to Karl Fischer analysis or 8.73 % according to the result of thermogravimetric analysis).

In addition, the patent [CN 109134581, 2019] proposes an alternative method for obtaining the disodium salt of DSM 21-phosphate, which consists in the fact that a solution of DSM 21-phosphate in a mixture of water, acetone and methanol containing sodium acetate and sodium hydrosulfite is decolorized by activated carbon, sodium isooctanoate is added to the filtrate and the pH is adjusted to 10.7 with NaOH solution (1 mol/l). Then, isopropanol and seed crystals are added to the solution. After settling at 5-10°C, the precipitate is filtered off, washed with acetone and dried in vacuum. DSM 21-phosphate disodium salt dihydrate is obtained with a purity of 99.32% (HPLC) and a water content of 6.49% according to the result of the analysis by the K. Fischer method and 6.5% according to the thermogravimetric analysis).

Also known are methods for obtaining the disodium salt of 21-phosphate DSM from epoxide 21-acetate DSM through the formation of DSM [CN 105326787, 2016; CN105326788, 2016; CN105348358, 2016; CN105348360, 2016; CN105342993, 2016; CN105342992, 2016; СN105342991, 2016]. The examples describe the synthesis of DSM 21-phosphate disodium salt from DSM without isolation of DSM 21-phosphate. DSM esterification is carried out with PPC in THF medium and 21-phosphate DSM is obtained, which is then converted into the disodium salt of DSM 21-phosphate by the action of NaOH in methanol.

Thus, known methods for the preparation of the disodium salt of DSM 21-phosphate use the reaction of DSM 21-phosphate with NaOH in a medium containing methanol or ethanol, preferably in a methanol medium.

The closest in essence to the proposed is a method for obtaining 21-disodium phosphate DSM from DSM [US3966778, 1976, example 3], which consists in the reaction of DSM (7.8 g) with PPC (10 g) in a THF solution at a temperature of -40°C. After 2 hours of incubation, water, 20 g of activated carbon are added to the reaction mass, and THF is evaporated under reduced pressure. The carbon containing the adsorbed steroid is filtered off and washed with water to remove inorganic acid. Charcoal is added to methanol (100 ml) and the suspension is basified to pH 8.0 by adding 15 ml of 2N NaOH in methanol. The coal is filtered off and washed with methanol. The methanol solution was concentrated in vacuo to give 6.5 g of DSM 21-phosphate sodium salt (corresponding to a yield of 63.35%), which was recrystallized from methanol and acetone to give a colorless powder.

The disadvantages of this method are:

- low-temperature mode (minus 40°С) for carrying out the phosphorylation reaction;

- a laborious process of isolation and purification of the product, which consists in sorbing the reaction product on coal by evaporating in vacuum a suspension of coal in a water-tetrahydrofuran solution of the product, which is undesirable in industrial production;

- a combined process of desorption of 21-phosphate DSM from coal and obtaining a disodium salt by reaction with NaOH, which leads to contamination of the salt solution with coloring and other impurities;

- evaporation of a methanol solution of the sodium salt of 21-phosphate DSM, probably before the end of the shoulder strap, as can be assumed from the description of example 3;

- low yield of the crude target product (6.5 g out of 7.8 g of DSM), which corresponds to a molar yield of 63.35%, which can be explained by losses during the washing of coal with water, which indicates an unsatisfactory sorption capacity of coal;

- the need to use purification by recrystallization from methanol and acetone, which indirectly confirms the unsatisfactory quality of the crude product, while the yield of the recrystallized product is not indicated, which does not allow us to judge the effectiveness of the proposed purification method;

- extremely low efficiency of the method for isolating 21-phosphate DSM from the reaction mass and purifying its disodium salt.

These shortcomings significantly complicate the process.

It should be noted that the problem of purification of water-soluble derivatives of corticosteroids is of a general nature. The essence of purification of disodium salts of 21-phosphates of 21-hydroxy-corticosteroids is to remove color and impurities of unreacted 21-hydroxy-steroid, organic phosphates and other water-soluble by-products. Impurities that are insoluble or sparingly soluble in water can be removed from an aqueous solution of the corticosteroid 21-phosphate or its disodium salt by extraction with a water-immiscible solvent in which the impurities are readily soluble.

Thus, the main problem of the known methods for obtaining the disodium salt of DSM 21-phosphate is the isolation of DSM 21-phosphate from an aqueous solution and its purification to the quality required to obtain further its disodium salt.

The technical problem is the lack of a high-tech, easily scalable method for obtaining the disodium salt of 21-phosphate DSM.

Disclosure of invention

The technical result of the claimed invention is the development of a method for obtaining the disodium salt of dexamethasone 21-phosphate from dexamethasone while ensuring the molar yield of the target product is not less than 90% and the quality meets the requirements of the State Pharmacopoeia of the Russian Federation (the content of the main substance is not less than 97%).

The technical result is achieved by a method for producing disodium salt of dexamethasone 21-phosphate (11β,17α,-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20-dione) of formula I

from dexamethasone (11β,17α,21-trihydroxy-9α-fluoro-16α-methylpregna-1,4-diene-3,20-dione) of formula II,

through the formation of an intermediate dexamethasone 21-phosphate (11β,17α,-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20-dione) of formula III,

including the reaction of direct phosphorylation of the hydroxyl group at the C21 atom of compound II by the action of pyrophosphoryl chloride, taken at the rate of at least 1.0 mol per 1 mol of compound II, in an aprotic organic solvent, removal of steroid impurities by extraction of an aqueous medium by the liquid-phase extraction method, extraction of the formed compound III from an aqueous medium by solid-phase extraction, desorption of compound III and its interaction with sodium alcoholate, taken at the rate of 1 mol of compound III, not less than 1.94 mol of sodium alcoholate, in an aliphatic alcohol medium. The esterification of the 21-hydroxyl group of compound II is carried out in an aprotic solvent, which is used as cyclic ethers, in particular, tetrahydrofuran. To remove steroid impurities by liquid-phase extraction, chlorinated hydrocarbons are used, taken in an amount equal to the amount of cyclic ether (by volume), and the extraction is carried out at room temperature. Dichloromethane, chloroform, 1,2-dichloroethane are used as chlorinated hydrocarbons. To extract compound III by solid-phase extraction, nonionic macronet polymers are used, which are copolymers of ethylstyrene and divinylbenzene. The desorption of compound III is carried out after the purification of compound III adsorbed on the polymer from inorganic compounds by washing with water, while the desorption of compound III is carried out with a mixture of organic solvents containing chlorinated hydrocarbon and aliphatic alcohol in a 1:1 volume ratio and the minimum required amount for complete desorption of the product . Chloroform, dichloromethane, dichloroethane are used as chlorinated hydrocarbon, and ethyl or methyl alcohol is used as aliphatic alcohol.

The preparation of a compound of formula I can be carried out without isolating the crystalline compound of general formula III.

Achievable indicators of the method are provided:

1) the use of a chlorinated hydrocarbon to remove the residual amount of DSM, other possible steroid compounds, and insoluble or slightly water-soluble impurities from the aqueous medium by liquid-phase extraction;

2) using the method of solid-phase extraction to extract 21-phosphate DSM from the reaction mass and achieve its almost complete extraction at ambient temperature (i.e. at room temperature);

3) carrying out a continuous technological process for obtaining the disodium salt of 21-phosphate DSM without isolating the intermediate 21-phosphate DSM and thereby eliminating not only its losses in the mother liquors, but also mechanical losses that usually occur in the technological operations of extraction, filtration, drying and etc.;

4) the use of sodium alcoholates, in particular sodium ethylate, to obtain the disodium salt of 21 DSM phosphate. The result is a high yield of the final product I (not less than 90%), counting from DSM (II);

5) exclusion from the technological process of the operation of recrystallization of the disodium salt of 21-phosphate DSM and, thereby, its losses in the mother liquors.

According to the literature data, the preparation of the disodium salt is carried out by treating DSM 21-phosphate in a methanol medium with a methanolic NaOH solution, followed by evaporation of the solvent. However, this method does not allow obtaining a product with quality characteristics that meet the requirements of the pharmacopoeia. Subsequent purifications (recrystallization with solvents, or a combination of "dissolution in water - precipitation" using acid and alkali) lead to significant product losses and a decrease in yield.

Additional purification of 21-phosphate DSM with coal according to the present invention in a solution of a mixture of aliphatic alcohol and chlorinated hydrocarbon allows the reaction to obtain a disodium salt without isolating the purification product in crystalline form.

In addition, when using a mixture of ethanol and chlorinated hydrocarbon, rectified ethanol of 96.2% content can be used in the purification operation. Since the solubility of DSM 21-phosphate increases in the presence of water, the use of rectified ethanol makes it possible to use a minimum amount of a mixture of ethanol and chlorinated hydrocarbon to dissolve DSM 21-phosphate without losing the quality of clarification of the solution with coal. For example, when using a mixture of ethanol and chloroform in the process of evaporating chloroform from a solution, azeotropic drying of a solution of DSM 21-phosphate in ethanol occurs. Evaporation of chloroform in the form of an azeotropic mixture with ethyl alcohol and water (composition: 91% chloroform, 5% ethanol and 4% water; boiling point 55.5°C) makes it possible to completely remove chloroform and water from the reaction mass. Then the neutralization reaction is carried out in anhydrous ethanol, and sodium ethoxide is used as a reagent. When using, for example, a mixture of methanol and chloroform (azeotropic mixture: 81% chloroform, 15% methanol and 4% water; boiling point 53°C), the neutralization reaction is carried out in anhydrous methanol, and sodium methoxide is used as a reagent.

The essence of the claimed invention concerning the preparation of the disodium salt of 21-phosphate DSM is that, in order to increase the yield and simplify the process, after the completion of the esterification reaction of DSM and the hydrolysis of the dichloro derivative of 21-phosphate DSM, steroid impurities are first removed by liquid extraction, then solid-phase extraction is carried out extraction of 21-phosphate DSM from an aqueous medium, 21-phosphate DSM adsorbed on the polymer is purified from inorganic impurities with water, desorbed with a mixture of organic solvents, the resulting solution is clarified with charcoal, and after concentrating the solution, the disodium salt is obtained by reaction with sodium alcoholate.

For solid-phase extraction, hypercrosslinked macroreticulated neoinogenic polymers based on ethylstyrene and divinylbenzene are used.

The advantages of the proposed method are as follows:

- it is possible to use not only dexamethasone of pharmacopoeial quality with the content of the main substance of at least 97%, but also of technical quality with the content of the main substance in the range from 85 to 97%;

- the use of organochlorine hydrocarbons to remove steroid impurities, which is more technologically advanced and efficient than the use of simple or complex ethers for this purpose, for example, diethyl ether or ethyl acetate;

- carrying out the operation of extracting 21-phosphate DSM from the aqueous medium by the method of solid-phase extraction at room temperature;

- the process of desorption of 21-phosphate DSM is carried out at room temperature with a mixture of aliphatic alcohol and chlorinated hydrocarbon;

- the sorbent can be used repeatedly in cycles "sorption-desorption" without additional conditioning;

- there is no need to use multiple repetitions of dissolution operations with the addition of an alkaline agent and precipitation by acidification for the purification of 21-phosphate DSM;

- a significant reduction in the loss of the main product during its isolation and purification, which is ensured by the high sorption capacity of the polymer;

- the use of sodium alcoholate makes it possible to carry out the process of obtaining the disodium salt of 21-phosphate DSM in an anhydrous medium, which ensures a greater yield of the product by minimizing losses during washing of the precipitate with a solvent to remove a possible excess of sodium alcoholate.

- a combination of the proposed methods (sorption method for extracting DSM 21-phosphate and sodium alcoholate) for obtaining DSM 21-phosphate disodium salt makes it possible to exclude from the technological process the operations of cleaning DSM 21-phosphate disodium salt by crystallization and recrystallization methods, to significantly increase the achieved total yield of disodium salt 21 -phosphate DSM from DSM (at least 90%, taking into account the percentage of the main substance in the original DSM) and obtain the target product with a quality that meets the requirements of the State Pharmacopoeia of the Russian Federation XIV edition [FS.2.1.0090.18 "Dexamethasone sodium phosphate". GF RF XIV, 2018, volume III, p. 3741-3748. http://femb.ru/femb/pharmacopea.php];

- the proposed sorption method for the extraction of 21-phosphate DSM can be used for additional extraction of it from the mother aqueous solutions using the known extraction methods described above.

Implementation of the invention

Dexamethasone (II), CAS No. 50-02-2, C₂₂H₂₉FO₅(USP quality or EP or BP quality) is commercially available, can be purchased, for example, from the company Steraloids (USA), or from other manufacturers. Dexamethasone of technical quality can be obtained by known methods, for example, the method according to the patent [RU 2532902, 2014, example 16]. Pyrophosphoryl chloride (97.0%) can be purchased from Sigma-Aldrich Co or synthesized by a method known from the literature [H.Grunze; Chemische Berichte, Vol. 92 (1959), P. 850]. Sodium methylate (methoxide) (95%) sodium ethylate (ethoxide) (95%) are commercially available, can be purchased, for example, from Sigma-Aldrich Co or prepared by known methods [for example, sodium ethoxide - method according to patent RU2093504, 1997 ; sodium methoxide - by the method according to the patent SU92152, 1950]. Other reagents, solvents, and inert gases are commercially available and can be purchased, for example, from Russian manufacturers.

Drinking tap water was used to isolate the products at the end of the reactions by diluting the reaction masses with water, as well as to wash the precipitates and extracts in organic solvents, unless otherwise noted. Distilled water was used to prepare aqueous solutions of acids, sodium chloride, and sodium bicarbonate.

All procedures, unless otherwise noted, were carried out at room temperature or ambient temperature, that is, in the range from 20 to 25ºC. For processes requiring temperatures lower than room temperature, cooling was provided by cold tap water (in the range of 10 to 20°C), or a mixture of crushed ice and cold water (in the range of 5 to 10°C), or a mixture of crushed ice and chloride. calcium (at temperatures below 5°C). An electric mantle heater was used to heat the reactions at a temperature above room temperature and to evaporate the solvents at atmospheric pressure.

Evaporation of the solvents in vacuo was carried out using a rotary vacuum evaporator Rotavapor (Büchi Labortechnik AG), at a residual pressure of 0.35 ± 0.05 kg / cm ² (35 ± 5 psi) and the water temperature in the bath in the range of 35-50ºC depending from the nature of the evaporated solvent.

Drying of product crystals to constant weight was carried out at a temperature of 40 to 60°C at atmospheric pressure or using a vacuum oven at a residual pressure of 0.35±0.05 kgf/cm ² (35±5 kPa).

To determine the pH of the wash water, we used universal indicator paper with a range of values from 0 to 12 (Lakhema, Czech Republic).

Dry (anhydrous) solvents (acetone, methanol, ethanol) were obtained by well-known methods of organic chemistry.

The reaction progress was monitored by thin layer chromatography (TLC) using Silica gel 60 F254 plates (Merck, Germany).

The structure and purity of all isolated compounds were confirmed by at least one of the following methods: TLC (TLC plates Silica gel 60 F254 (Merck, Germany)), mass spectrometry, elemental analysis or nuclear magnetic resonance (NMR), high performance liquid chromatography (HPLC).

The melting points of the isolated compounds were determined on an M-565 melting point apparatus (Büchi Labortechnik AG).

Spectra NMR^oneH and³¹Р was recorded in parts per million (ppm) on a Bruker Avance-400 spectrometer (Bruker BioSpin GmbH) with an operating frequency of 400 MHz and 161.9 MHz, respectively, using deuterated dimethyl sulfoxide (99.9% D, Sigma-Aldrich) or deuterated water ( 99.9% D, Sigma-Aldrich) as solvent; as internal standard, residual solvent signals were used.

The ratio and amount of solvents and reagents is given only to illustrate the proposed method. An increase in the amount of solvents and reagents used does not lead to a decrease in the yield of the target product.

Used solvents contained in the waste can be recovered and reused. Can be regenerated and returned to the process: at least 90% chloroform, at least 90% acetone; not less than 95% ethanol and not less than 80% tetrahydrofuran.

DSM and DSM 21-phosphate can be recovered from the organochlorine extract and returned to the process. 21-Phosphate DSM can be recovered from the mother liquor obtained by filtering and washing the disodium salt of 21-phosphate DSM and reused to obtain the disodium salt.

The method for obtaining the disodium salt of dexamethasone 21-phosphate of formula (I) is carried out according to the scheme shown in scheme 1.

Dexamethasone (11β,17α,21-trihydroxy-9α-fluoro-16α-methylpregna-1,4-diene-3,20-dione) of formula (II),

subjected to the reaction of phosphorylation of the hydroxyl group at the C21 atom by the action of pyrophosphoryl chloride in an aprotic solvent medium. To do this, 1-1.7 moles of pyrophosphoryl chloride are used per 1 mol of dexamethasone. Obtained with a yield of more than 93% (taking into account the% content of the main substance in the original DSM) 21-phosphate-dexamethasone (III) is subjected to neutralization with the formation of a disodium salt by the action of sodium alcoholate at a molar ratio of 1.94 to 2 moles of sodium alkoxide per 1 mole of 21- dexamethasone phosphate. In this case, the reaction with sodium alcoholate can be carried out both with preliminary isolation and without isolation of 21-phosphate DSM (III).

The total yield of the disodium salt of 21-phosphate DSM (I) with the content of the main substance of 97.6-99.4% and the quality that meets the requirements of the State Pharmacopoeia of the Russian Federation of the XIV edition, taking into account the% content of the main substance in the starting compound (II), is from 90.1 to 96.66 %.

According to the present invention, the preparation of the disodium salt of 21-phosphate DSM (I) from DSM (II) can be carried out both with and without isolation of intermediate product III from the reaction mass. In accordance with the purpose of the present invention, it is preferable to carry out the process without isolation. However, the 21-phosphate DSM (III) obtained according to the present invention can be used as an initial substrate for other purposes, for example, for obtaining other organic compounds and salts of other metals without additional purification.

The claimed invention is illustrated by the following examples. Reaction times are for illustration purposes only. Yields are for illustration purposes only. The use of Macronet MN-200 non-ionic macrocrosslinked polymer (The Purolite Company) is for illustration purposes only. Any other nonionic hypercrosslinked copolymers of ethylstyrene and divinylbenzene can be used instead without loss of efficiency, for example, Macronet MN-202 (The Purolite Company), AmberLite XAD-4, AmberLite XAD-16 (Rohn and Haas Company and other manufacturers).

Example 1 Obtaining disodium salt of 21-phosphate DSM from DSM

Option 1

To a solution of 2 g of DSM (II) 87.7% content (4.469 mmol in 100% calculation of the main substance) in 20 ml of THF, cooled to 0–2°C, 1.2 ml (2.184 g, 8.675 mmol) of PPC was added dropwise with stirring and stirred at this temperature for 1 hour. Upon completion of the reaction, the reaction mixture was added dropwise with stirring to 105 ml of water cooled to 2–4°C, stirred for 15 min, and extracted with chloroform twice, 20 ml each. The layers were separated (according to HPLC, the dry residue obtained after evaporation of the combined chloroform extract (0.132 g) contained 19.0% dexamethasone 21-phosphate and 18.6% dexamethasone). 20 g of Macronet MN-200 sorbent (preliminarily aged for 2 hours in ethanol and washed with water) was added to the aqueous layer and stirred at room temperature for 20 hours. The sorbent was filtered off, washed on the filter 3 times with 30 ml of distilled water until the pH of the wash water was neutral, then the steroid was desorbed by passing 120 ml of a mixture of ethanol 96.2% and chloroform (1:1 by volume) through the sorbent on the filter. The completion of the desorption process was monitored by TLC. 0.205 g of activated charcoal was added to the ethanol–chloroform solution, and the mixture was stirred at room temperature for 30 min. The coal was filtered off and washed on the filter 2 times with 5 ml of a mixture of ethanol-chloroform (1:1). The filtrate was concentrated at atmospheric pressure to a vapor temperature of 78°C and a residual volume of ~10 ml, then to a solution cooled to 5°C in an inert gas flow, 8 ml of a 1 N solution of sodium ethoxide in ethanol was slowly added with stirring to pH 8–9, then kept under stirring and a temperature of 0-2°C for 2 hours. The precipitate formed was filtered off, washed on the filter with 5 ml of anhydrous water cooled to 0–2°C. ethanol and twice 5 ml of dry acetone. Dried in a vacuum oven at 40°C. 2.09 g (4.047 mmol) of DSM 21-phosphate disodium salt was obtained in the form of a white crystalline powder with a molar yield of 90.56% (based on the loaded DSM in 100% terms of the main substance) and a basic substance content of 99% (according to HPLC data). T. pl. 234-236 ºС. The DSM impurity content (HPLC) was 0.046%; the total impurity content was 0.59%. The water content determined by the thermogravimetric method was 0.24%; the content of residual ethanol (GLC) was 0.035%; there was no residual acetone. The pH value of a 1% solution in water was 7.71, and the specific rotation was +79⁰. In terms of solubility, transparency and color of the solution (1 g in 20 ml of water) and the content of inorganic phosphates, the product met the requirements of the RF SP XIV.

Option 2

Under the conditions of option 1, 2.48 g (4.802 mmol) of DSM 21-phosphate disodium salt was obtained from 2 g of pharmacopoeial quality dexamethasone with a content of the main substance of 97.5% (4.969 mmol in 100% calculation of the main substance) with a yield of 96.66% (based on loaded DSM in 100% calculation of the main substance) and the content of the main substance of 99.4% (according to HPLC).

Option 3

Under the conditions of option 1, 1.625 g (3.147 mmol) of the disodium salt of DSM 21-phosphate was obtained from 2 g of technical grade dexamethasone with a content of the main substance of 87.7% (4.469 mmol in 100% of the main substance) using a 5 N solution of NaOH in methanol with a yield of 70.41% (based on the loaded DSM in 100% terms of the main substance) and the content of the main substance of 98.2% (according to HPLC).

Option 4

Under the conditions of option 1, from 2 g of technical grade dexamethasone with a content of the main substance of 85% (4.332 mmol in 100% of the main substance), using dichloromethane instead of chloroform, 2.032 g (3.935 mmol) of the disodium salt of 21-phosphate DSM was obtained with a yield of 90.84% (considering the loaded DSM in 100% terms of the main substance) and the content of the main substance 98.4% (according to HPLC).

Option 5

Under the conditions of option 2, 2.312 g (4.477 mmol) of the disodium salt of 21-phosphate DSM with a yield of 90.1% (based on the loaded DSM in 100% terms of the main substance) and the content of the main substance of 98.2% (according to HPLC).

Option 6

Under the conditions of option 1, from 2 g of technical grade dexamethasone with a content of the main substance of 87% (4.434 mmol in 100% of the main substance), using 1.2-dichloroethane instead of chloroform, 2.1 g (4.066 mmol) of the disodium salt of 21-phosphate DSM was obtained with a yield of 91, 7% (based on the loaded DSM in 100% terms of the main substance) and the content of the main substance 98.8% (according to HPLC).

Example 2 Preparation of dexamethasone 21-phosphate from dexamethasone

Option 1

To a solution of 2 g of DSM (II) 87.7% content (4.469 mmol in 100% calculation of the main substance) in 20 ml of THF, cooled to 0–2°C, 1.2 ml (2.184 g, 8.675 mmol) of PPC was added dropwise with stirring and stirred at this temperature for 1 hour. Upon completion of the reaction, the reaction mixture was added dropwise with stirring to 105 ml of water cooled to 2–4°C, stirred for 15 min, and extracted with chloroform twice, 20 ml each. The layers were separated. To the aqueous layer was added 20 g of the sorbent (previously aged for 2 hours in ethyl alcohol and washed with water) and stirred at room temperature for 20 hours. The sorbent was filtered off, washed on the filter 3 times with 30 ml of distilled water until the pH of the wash water was neutral, then the steroid was desorbed by passing 120 ml of a mixture of 96.2% ethanol and chloroform (1:1 by volume) through the sorbent on the filter. The completion of the desorption process was monitored by TLC. 0.205 g of activated charcoal was added to the ethanol–chloroform solution, and the mixture was stirred at room temperature for 30 min. The coal was filtered off and washed on the filter 2 times with 5 ml of a mixture of ethanol-chloroform (1:1 by vol.). The filtrate was concentrated at atmospheric pressure to a vapor temperature of 78°C and a residual volume of ~ 10 ml; 15 minutes. The precipitate that formed was filtered off, washed on the filter with 5 ml of distilled water cooled to 5°С. Dried in a vacuum oven at 60°C to constant weight. Received 2.05 g (4.339 mmol) of compound III in the form of white crystals with a yield of 97.09% (based on loaded DSM in 100% calculation of the main substance) and the content of the main substance of 95.2% (according to HPLC). So pl. 162-164°C.

¹ H NMR Spectrum ²¹ C-phosphate (δ, ppm .; DMSO-d ^6): 7.28 (1H, d, J 10.1 Hz, H-1), 6.22 (1H, dd, J 1.6 Hz, 10.1 Hz, H-2), 6.00 (1H, br. s, H-4), 4.90 (1H, dd, J 7.4 Hz, 18.1 Hz, H-21), 4.50 (1H, dd, J 6.1 Hz, 18.1 Hz, H -21), 1.47 (3H, s, H-19), 0.86 (3H, s, H-18), 0.77 (3H, d, J 7.2 Hz, H-16).

³¹ P NMR spectrum of ^{C 21} -phosphate (δ, ppm; DMSO-d ⁶ ): -0.90.

Option 2

Under the conditions of option 1, 2.185 g (4.625 mmol) of 21-phosphate DSM was obtained from 2 g of dexamethasone of pharmacopoeial quality with a content of the main substance of 97.5% (4.969 mmol in 100% calculation of the main substance) with a yield of 93.08% and a content of the main substance of 95.6 %.

Option 3 (without using the solid phase extraction method)

To a solution of 2 g of pharmacopoeial quality dexamethasone 97.5% (4.969 mmol in 100% of the main substance) in 20 ml of THF, cooled to 0-2℃, 1.2 ml (2.184 g, 8.675 mmol) of PPC was added dropwise with stirring and stirred at this temperature for 1 hour. Upon completion of the reaction, the reaction mass was added dropwise to 104 ml of a saturated aqueous solution of NaHCO ₃ cooled to 0-2℃ and then kept under stirring for 15 minutes. Chloroform (40 ml) was added to the resulting solution (pH 7.5), the mixture was intensively stirred, and the layers were separated after settling. The aqueous layer (pH 7.5) was added with stirring to a saturated solution of NaCl in hydrochloric acid (prepared from 53 g of NaCl, 200 ml of distilled water and 50 ml of concentrated HCl and cooled to 5°C) and stirred at the same temperature for 30 min. The precipitate formed was filtered off, washed on the filter 2 times with 10 ml of distilled water to pH ~ 4–5, and dried to constant weight at 60°C in vacuum.

Received 1.59 g (3.365 mmol) of compound III in the form of white crystals with a yield of 67.72% (based on loaded DSM in 100% calculation of the main substance) and the content of the main substance of 94.7% (according to HPLC).

Example 3 Preparation of DSM 21-phosphate disodium salt from DSM 21-phosphate

2.05 g of 21-phosphate DSM 95.2% of the content of the main substance obtained according to example 2, option 1 (4.131 mmol in 100% calculation of the main substance) was dissolved with stirring in 120 ml of a mixture of ethanol 96.2% and chloroform (1:1 by vol.). 0.205 g of activated carbon was added to the solution and stirred at room temperature for 30 min. The coal was filtered off and washed on the filter 2 times with 5 ml of a mixture of ethanol and chloroform (1:1 by vol.). The filtrate was evaporated at atmospheric pressure at a vapor temperature of up to 78°C to a residual volume of ~10 ml. To a solution cooled to 5°C in an inert gas stream, 8 ml (6.56 g) of a 1 N solution of sodium ethoxide (0.544 g, 8 mmol) in ethanol was slowly added with stirring to pH 8–9, after which it was kept under stirring at a temperature of 0– 2°C for 2 hours. The precipitate that formed was filtered off, washed on the filter with 5 ml of anhydrous ethanol cooled to 0–2°C and twice with 5 ml of dry acetone. Dried in a vacuum oven at 40°C. Received 2.09 g (4.047 mmol) disodium salt of 21-phosphate DSM with a yield of 97.97% (calculated on the loaded 21-phosphate DSM in 100% calculation of the main substance) and the content of the main substance 98.4% (according to HPLC).

¹ H NMR spectrum of disodium salt of C ²¹ -phosphate ¹ H (δ, ppm; D ₂ O): 7.53 (1H, d, J 10.1 Hz, H-1), 6.41 (1H, dd, J 1.6 Hz, 10.1 Hz, H-2), 6.20 (1H, br. s, H-4), 4.90 (1H, dd, J 5.4 Hz, 19.0 Hz, H-21), 4.56 (1H, dd, J 5.0 Hz, 19.0 Hz, H-21), 4.39 (1H, m, 17-OH), 3.04 (1H, m, 11-OH), 1.53 (3H, s, H-19), 0.98 (3H, s, H-18) , 0.88 (3Н, d, J 7.2 Hz, Н-16).

Claims (16)

1. Method for the preparation of dexamethasone (11β,17α-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20-dione) disodium salt of 21-phosphate of formula I

from dexamethasone (11β,17α,21-trihydroxy-9α-fluoro-16α-methylpregna-1,4-diene-3,20-dione) formula II

, characterized in that they carry out a reaction with pyrophosphoryl chloride, taken at the rate of at least 1.0 mol per 1.0 mol of compound II, in a cyclic ether medium, followed by hydrolysis of the formed dexamethasone 21-phosphate dichloride derivative, removal of steroid impurities from the aqueous medium by liquid-phase extraction using a chlorinated hydrocarbon, extraction of the formed dexamethasone 21-phosphate (11β,17α-dihydroxy-9α-fluoro-16α-methyl-21-(phosphonooxy)pregna-1,4-diene-3,20-dione) of formula (III)

from an aqueous medium by solid-phase extraction at room temperature using non-ionic polymers selected from Macronet MN-200, Macronet MN-202, AmberLite XAD-4, AmberLite XAD-16, its desorption with a mixture of chlorinated hydrocarbon and aliphatic alcohol and treatment with dexamethasone 21-phosphate sodium alcoholate in the medium of the corresponding aliphatic alcohol, while sodium alkoxide is taken at least 1.94 mol per 1 mol of compound III. 2. The method according to p. 1, characterized in that tetrahydrofuran is used as the cyclic ether. 3. The method according to claim 1, characterized in that to remove steroid impurities by liquid-phase extraction, chlorinated hydrocarbons are used, taken in an amount equal to the amount of cyclic ether (by volume), and the extraction is carried out at room temperature. 4. The method according to p. 1, characterized in that dichloromethane, chloroform, 1,2-dichloroethane are used as chlorinated hydrocarbons. 5. The method according to p. 1, characterized in that the desorption of the compound III is carried out after the purification of the compound III adsorbed on the polymer from inorganic compounds. 6. The method according to p. 5, characterized in that the purification of compound III adsorbed on the polymer from inorganic compounds is carried out by washing with water. 7. The method according to p. 1, characterized in that the desorption is carried out using a mixture of chlorinated hydrocarbon and aliphatic alcohol in a volume ratio of 1:1 and the minimum required amount for complete desorption of the product. 8. The method according to p. 7, characterized in that chloroform, dichloromethane, 1,2-dichloroethane are used as the chlorinated hydrocarbon. 9. The method according to claim 7, characterized in that ethyl or methyl alcohol is used as aliphatic alcohol. 10. The method according to claim 1, characterized in that the preparation of the compound of formula I can be carried out without isolating the crystalline compound of general formula III.