RU2144924C1 - Method of preparing azitromicyn and methods for production of intermediates - Google Patents

Abstract

FIELD: pharmaceutical chemistry. SUBSTANCE: method is distinguished by that erythromycin is converted to oxime by hydroxylamine hydrochloride in presence of sodium carbonate in aqueous ethanol (20-40% water) medium at starting erythromycin-to-solvent g/ml ratio from 1:1.4 to 1:1.7 at temperature 50-80 C. Oxime product is isolated from reaction mixture by extraction with chlorinated hydrocarbon at pH 9-11 and subjected to Beckmann rearrangement by agency of arenesulfonic acid chloride in two-phase water-chlorinated hydrocarbon system to form erythromycin imino-ester. The latter is isolated by crystallization at pH 9-11 and temperature 60+-5 C and reduced in aqueous medium at room temperature with 0 to 0.2 molar excess of complex metal borohydride to give azaerythromycin. The latter is methylated, in the form of borate complex with mineral or organic acid (preferably, hydroxyacid), at pH 2.5, with formaldehyde in chloroform in presence of formic acid. Methylation product is isolated by reextraction with water at pH 4.5-5.5. Borate complex, if necessary, is hydrolyzed and product is precipitated form aqueous solution at pH 9-11 and 50-80 C and then recrystallized from acetone-water (2:1 to 1:2) mixture. EFFECT: simplified process and increased yield of final product. 4 cl, 5 ex

Description

 The invention relates to an improved method for producing a macrolide semi-synthetic antibiotic derived from erythromycin A, and in particular to a method for producing N-methyl-11-aza-10-deoxo-10-dihydroerythromycin-azithromycin (I), which has a wide spectrum of antimicrobial activity.

 Known methods for producing azithromycin by N-methylation of 11-aza-10-deoxy-10-dihydroerythromycin (hereinafter azaerythromycin). Two methods of N-methylation of azaerythromycin are described (V, Scheme 1). The first, by pre-oxidizing azaerythromycin with hydrogen peroxide to form N-oxide, followed by alkylation with methyl iodide in the presence of a hydrogen iodide acceptor and catalytic reduction of the obtained alkyl derivative over Pd / C or over Raney Ni (US patent N 4474468, CL C 07 H 17/08, 1984 [1]. And the second, the action of formaldehyde on azaerythromycin in the presence of formic acid in a chlorinated hydrocarbon such as chloroform or carbon tetrachloride (US patent N 4517359, CL C 07 H 17/08, 1981 [2] ). To highlight I the target product is re-extracted with water at pH 5.0, then the product is again extracted with 4 times the volume of chloroform at pH 7.5, the extract is dried and evaporated to dryness. The yield of azithromycin thus isolated is 83.0% ([ 2], example 1).

 The second method is closest to the present invention and is its prototype.

The starting azaerythromycin (V) according to all known methods is obtained from erythromycin (II) according to the following scheme (Scheme 1):
- erythromycin (II) hydroxylation to produce erythromycin (III) oxime;
- the conversion of oxime III to the imino ester of erythromycin (IV) by Beckmann rearrangement;
- restoration of iminoether IV to azaerythromycin (V).

 The erythromycin oximation, according to all known methods, is carried out in anhydrous methanol by the action of hydroxylamine, which is used either in the form of a free base, partially neutralized with acid (European patent N 0342990, class C 07 H 17/086, 1989 [3]), or hydrochloride in the presence of an acceptor of hydrogen chloride; erythromycin reacts with hydroxylamine hydrochloride in the presence of barium carbonate in absolute methanol at the boiling point (England patent N 1100504, CL C 07 H 21/00, 1968, [4]); the initial erythromycin / methanol ratio is 1: 5, the reaction mixture is boiled for 22 h, the reaction mixture is filtered to isolate the product, concentrated in vacuo to 1/3 of the volume, erythromycin oxime crystallizes when the concentrate is cooled, the yield of oxime III is 48.3% ( [4], example 1) is a prototype according to claim 2 of the claims.

The Beckman rearrangement of erythromycin (III) oxime according to the described methods is carried out by the action of arylsulfonic acid chlorides in a mixture of acetone-water (J. Chem. Soc. Perkin. Traus, 1986, p. 1881-90 [6], US patent N 4328334, class C 07 H 17/08, 1982 [7]. According to USSR patent N 1447288, class C 07 H 17/08, 1983 [5] oxime III is subjected to Beckmann rearrangement by a 2-4 molar excess of p-toluenesulfonyl chloride, p-iodobenzenesulfonyl chloride or p -atsetilaminobenzolsulfohlorida in the presence of 2-8 molar excess of sodium bicarbonate or triethylamine at a temperature of 0-5 ^o C in an acetone-water. By ca. pv 2 [5] to isolate the reaction product IV acetone was evaporated in vacuo, the aqueous residue was pH-gradient extraction with chloroform, the extract obtained at pH 8,0, was dried and evaporated to dryness. Yield of the thus obtained imino ether IV is 74.3%.

The reduction of the imoester IV by known methods is carried out by catalytic hydrogenation at a pressure of 65-70 ati in glacial acetic acid as a solvent, using noble metals or their oxides such as Pd / C or PtO ₂ as a catalyst, the yield of azaerythromycin (V) in this case is 80.0% (US patent N 4328334, class C 07 H 17/08, 1982 [7]), by the electrochemical method in a cell with a synthetic diaphragm on a mercury cathode with a lead anode in the presence of tetrabutylammonium iodide using acetic acid as a catholyte acid, and as the anolyte of an aqueous solution of sodium acetate, the yield of azaerythromycin by this method is 81.5% (USSR patent N 1530096, class C 07 H 17/08, 1990 [8]); chemical reduction with complex metal hydrides, such as sodium borohydride in absolute methanol at a temperature of about 4 ^o C [7]. According to Example 4 [7] to restore IV iminoether use 20-fold molar excess of sodium borohydride, to separate product recovery - azaerythromycin (V), the reaction mixture after bubbling CO ₂ was filtered, the filtrate was evaporated to dryness, the residue dissolved in chloroform, water is added, carry out a pH gradient extraction, the extract is dried, evaporated to dryness, the dry residue is extracted with ether, the extract is evaporated to dryness. The yield of azaerythromycin thus obtained is 60.5%.

 The aim of the invention is to simplify the process (simplifying technology, reducing energy intensity, improving fire and environmental safety) and increasing the yield of the target product.

 This goal is achieved by the following method.

Erythromycin is oximelated with hydroxylamine hydrochloride in the presence of sodium carbonate in ethanol-water (20-40% water), with an initial erythromycin / solvent ratio of 1: (1.4-1.7) at a temperature of 50-80 ^o C, to highlight the product of the oximelation use the extraction method, for which the reaction mass is extracted with chlorinated hydrocarbon at a pH of 9-11. The yield of erythromycin oxime is 75-80%.

 The implementation of this stage described above can significantly increase the concentration of reacting substances, which is significant, because the erythromycin oxymethylation reaction is always accompanied by the process of erythromycin dehydration with the formation of anhydroerythromycin; this side reaction is monomolecular and, therefore, its rate does not depend on concentration, while the rate of the target reaction increases in proportion to the concentration of the reacting substances. Thus, an increase in the concentration of reacting substances leads to a decrease in the content of anhydroerythromycin impurities in the reaction mass and an increase in the yield of erythromycin oxime. In addition, the use of methanol-toxic and flammable solvent and the need for evaporation of the reaction mass at the end of the reaction are eliminated, which significantly reduces the energy intensity of the process. Using the extraction method for the separation of oxime III allows you to easily and completely separate (and if necessary regenerate) the excess hydroxylamine, while by the known method [4], the excess hydroxylamine decomposes to a large extent with prolonged boiling of the reaction mixture and partially crystallizes with oxime III after concentration of the reaction mixture and cooling the concentrate, which contaminates the reaction product.

To carry out Beckmann rearrangement under the action of aryl sulfonic acid chloride, a two-phase solvent system is used: chlorinated hydrocarbon - water. This allows at the end of the reaction to easily separate impurities and precipitate the erythromycin imino ester from the aqueous solution in crystalline form. At the end of the reaction, during the separation of the aqueous phase, all inorganic impurities are separated; upon subsequent re-extraction of the iminoether into water at pH 4.5-5.5, all organic impurities remain in chloroform. Pure iminoether IV crystallizes from the aqueous stripping after establishing a pH of 9-11 at a temperature of (60 ± 5) ^o C. The use of a two-phase solvent system eliminates the need for evaporation of acetone from the reaction mass at the end of the reaction, as well as stepwise extraction of impurities. The product is isolated by crystallization, instead of a low-tech dry-off solution. The yield of iminoether in this method is 82.0%.

When reducing the iminoether IV with complex metal borohydrides, water is used as a solvent, the reaction is carried out at ambient temperature (16-20) ^o C, the reducing agent is used in an amount of 1.0-1.2 mol per mol of the iminoether. We found that under the action of metal borohydrides or during the preliminary treatment of iminoether IV with boric acid, water-soluble borane complexes of the iminoether are formed, which makes it possible to carry out the reduction reaction in an aqueous solution at pH 9-11, which is the optimal area when working with complex metal borohydrides. Therefore, to complete the restoration of iminoether IV under these conditions, an equimolar amount of a reducing agent is sufficient. In this case, the product of the reduction reaction is the azaerythromycin borate complex, which is used to obtain azithromycin by methylation and subsequent hydrolysis of the borate complex, or the azaerythromycin borate complex is hydrolyzed before methylation. In both cases, the borate complex is hydrolyzed by treatment with dilute mineral or organic acid at a pH of 2.5, usually for 5-15 minutes at a temperature of 18-20 ^o C. It is preferable to use hydroxy acid for hydrolysis. their presence prevents the reverse reaction of complexation. Azaerythromycin (V) is isolated after hydrolysis of the complex by extraction with chloroform. The yield of azaerythromycin is 85-88%, counting on iminoether IV.

Azithromycin (I) is obtained from azaerythromycin (V) or its borate complex by methylation in chloroform with formaldehyde and formic acid, the methylation product is re-extracted with water at pH 4.5-5.5, and if necessary, the azithromycin borate complex is hydrolyzed with mineral or organic acid at pH 2.5, the target product is precipitated from an aqueous solution at a pH of 9-11 and a temperature of 50-80 ^o C (azithromycin yield is 76-78%, counting as erythromycin iminoether) and purified by recrystallization from acetone-water or ethanol-water in soo relations from (2: 1) to (1: 2). The use of a mixture of acetone-water or ethanol-water for the purification of azithromycin in a wide range of ratios makes it possible to control the quality of the obtained product: when using more water mixtures, the yield of the target product increases, but impurities partially crystallize, while a decrease in the amount of water in the crystallization mixture reduces the yield of the target product, but provides a preparation of a high degree of purity. The output at the stage of recrystallization is 70-94%.

Thus, the proposed method for producing azithromycin is as follows:
Erythromycin (II) is oxidized by the action of hydroxylamine hydrochloride in the presence of sodium carbonate in ethanol-water (20-40% water) at an initial erythromycin / solvent ratio of 1: (1.4-1.7) (mass / volume) and temperature (50 -80%) ^o C, the reaction product - erythromycin (III) oxime is isolated from the reaction mass by extraction with chlorinated hydrocarbon at a pH of 9-11. Oxime III is subjected to Beckmann rearrangement by the action of aryl sulfonic acid chloride in a two-phase mixture of solvents: the water-chlorinated hydrocarbon, the obtained erythromycin imino ester (IV) is isolated from the aqueous solution by crystallization at pH 9-11 and a temperature of (60 ± 5) ^o C. Iminoether IV is reduced by the action of the complex metal borohydride taken in a 0-0.2 molar excess in an aqueous medium, the resulting azaerythromycin borate complex is isolated by extraction with chloroform and, in the form of a borate complex or after hydrolysis of the complex of action a mineral or organic acid, preferably hydroxy acids, at pH 2.5, are methylated in chloroform with formaldehyde in the presence of formic acid, the methylation product is re-extracted with water at pH 3.5-5.5, if necessary, the borate complex is hydrolyzed, and azithromycin is isolated by precipitation from an aqueous solution at a pH of 9-11 and a temperature of (50-30) ^o C. Azithromycin is purified by recrystallization from a mixture of acetone-water or ethanol-water in a ratio of (2: 1) to (1: 2).

 This method allows you to get azithromycin with quality indicators that meet the requirements of the US Pharmacopoeia and the VFS RF, and a yield of 35-40%, counting on erythromycin.

 Another objective of the invention is to increase the yield and simplify the process of producing erythromycin (III) oxime.

 The closest analogue to the prototype of the proposed method is a method for producing erythromycin oxime according to the patent [4].

This goal is achieved by the fact that when erythromycin (II) is oxylated with hydroxylamine hydrochloride in the presence of sodium carbonate, an ethanol-water mixture (20-40% water) is used as a solvent, which allows creating high concentrations of reactants (the initial erythromycin / solvent ratio is 1: 1.4 - 1: 1.7 mass / volume), the reaction is carried out at a temperature of (50-80) ^o C, while the oximelation process ends in 2-0.3 hours, the erythromycin (III) oxime is isolated by extraction with a chlorinated hydrocarbon, such like chloride me thylene or chloroform. The yield of oxime III is 75-80%.

 A third object of the invention is to increase the yield of azaerythromycin (V) obtained by reducing the erythromycin (IV) imino ester with a complex metal borohydride.

 The closest analogue to the prototype of the proposed method is a method for producing azaerythromycin [7], example 4.

 This goal is achieved in that the erythromycin (IV) imino ester is reduced in an aqueous solution by the action of a complex metal borohydride taken in 0-0.2 molar excess at ambient temperature, the reduction product, the azaerythromycin borate complex, is hydrolyzed by the action of a mineral or organic acid, preferably hydroxy acid , at pH 2.5, azaerythromycin (V) is isolated by extraction with chloroform at pH 9-11. The yield of azaerythromycin is 85-88%.

 The method can be illustrated by the following examples.

 Example 1. Obtaining erythromycin (III) oxime.

Erythromycin (200 g) is dissolved in 210 ml of ethanol when heated to 60 ^o C. To the resulting solution of erythromycin is added a solution containing 36.0 g of sodium carbonate and 90.0 g of hydroxyamine hydrochloride in 90 ml of water, with a temperature of 60 ^o C. Receive water-alcohol solution (30% water) with an initial erythromycin / solvent ratio of 1: 1.5 g / ml. The reaction mass is stirred at a temperature of 60 ^o C for 1 h, then transferred to an extractor containing 1.5 l of water and 1.5 chloroform. With stirring, add a 20% solution of sodium hydroxide to establish the pH of the aqueous phase in the range of 9-11. The layers are separated, the chloroform extract is washed with 300 ml of water. 2.15 L of a chloroform solution containing 66.0 mg / ml erythromycin oxime is obtained (polarimetrically). Yield 77.3%.

The crystalline erythromycin oxime is isolated after evaporation of the chloroform solution to a volume of 400 ml and cooling of the concentrate to (8-10) ^o C for 16 hours. 134.0 g of colorless crystals are obtained with a melting point of 157-159 ^o C, which corresponds to the literature (Tetrahedren Letters, 1970, p. 157-160 [9]). The yield of 72.8%.

 Example 2. Obtaining iminoether erythromycin (IV).

In a glass reactor, a chloroform solution of erythromycin oxime is loaded (Example 1), a solution of 54.0 g of sodium bicarbonate in 2 L of water is added. The mixture was cooled to (5 ± 2) ^° C and a solution of p-toluenesulfonyl chloride in chloroform (64.0 g p-TLC in 250 ml of chloroform) was added from a dropping funnel with stirring. The addition of the reagent continues for 1 hour. The reaction mass is kept under stirring and at a temperature of (7-10) ^o C for another 2 hours, then the layers are separated. 1.5 L of water and dilute hydrochloric acid are added to the chloroform layer until the pH of the aqueous phase reaches 4.5-5.5. The mass is stirred for 30 minutes, controlling the pH of the aqueous phase, which should remain within the specified limits. Then the layers are separated. 120 ml of conc. ammonia, while the pH is set between 9-11. The crystallization mass is heated with stirring to (60 ± 5) ^o C and maintained at this temperature for 15 minutes, continuing stirring. The precipitate of iminoether IV is filtered off and washed on a filter with 400 ml of water at a temperature of ~ 60 ^° C. The product is dried to constant weight. 115.0 g of a fine crystalline white powder are obtained, mp. 129-130 ^o C, [α] $\genfrac{}{}{0ex}{}{\text{20}}{\text{D}}$ minus 55 ^o (in chloroform). The yield of iminoether 82.2%, counting on oxime III or 63.5%, counting on erythromycin (II).

 Example 3. Obtaining azaerythromycin (V).

100.0 g of erythromycin iminoether (Example 2) and 1.2 L of water are placed in a glass reactor. To the suspension, 20% sulfuric acid is added from a dropping funnel with stirring until the iminoether is completely dissolved (pH 5.6-6.4). A solution of 13.8 g of potassium borohydride in 100 ml of water is added to the solution while stirring. The reaction mass is left at room temperature for 16-18 hours to complete the recovery reaction. The reaction mass is a colorless solution with a pH of 9.0-11.0. At the end of the reaction, 1.3 L of chloroform was added to the solution, stirred for 30 minutes, the layers were separated. To the chloroform layer (Solution A) containing the azaerythromycin borate complex, 1.0 L of water and 20% sulfuric acid solution are added until the pH of the aqueous phase is established (2.5 ± 0.1). The reaction mass is maintained at this pH for 15 minutes at a temperature of (18-20) ^o C, then 130 ml of 20% sodium hydroxide solution are added, the mixture is stirred for 30 minutes, after which the layers are separated. The pH of the aqueous phase is in the range of 9-11. The chloroform extract of azaerythromycin is dried with sodium sulfate. 1.22 L of a chloroform solution of azaerythromycin is obtained, with a basic substance content of 65 mg / ml (polarimetrically) - Solution B. The extract is evaporated to dryness, 87.3 g of an amorphous powder are obtained. The content of azaerythromycin 90.0% [α] $\genfrac{}{}{0ex}{}{\text{20}}{\text{D}}$ minus 34.7 ^o (1% in chloroform). Yield 88.0%, counting on iminoether IV.

 Example 4. Obtaining azithromycin.

A) Solution A (example 3) containing an azaerythromycin borate complex was placed in a flask equipped with a reflux condenser, 18.0 ml of formaldehyde (40%) and 9.7 ml of formic acid (99%) were added. The reaction mass is heated to boiling and boiled for 6 hours. Then the mass is cooled, if necessary add 20% sulfuric acid solution to establish the pH value of the aqueous phase in the range of 4.5-5.5. The layers are separated, citric acid (19.5 g) is added to the aqueous layer to pH (2.5 ± 0.1), the solution is stirred for 15 minutes, then 1.4 L of chloroform and 20% sodium hydroxide solution are added until the pH of the aqueous solution is established. phase in the range of 9-11. The layers are separated. 1.4 L of water and a 20% sulfuric acid solution are added to the chloroform layer to a pH of 4.5-5.5. The mixture was stirred for 30 minutes while controlling the pH of the aqueous phase. The layers were separated, the aqueous layer was placed in a crystallizer, 1.5 L of water and 82.0 ml of conc. ammonia. In this case, the pH of the crystallization mass is set in the range of 9-11. The crystallization mass is heated to a temperature of about 70 ^o C, stirred at this temperature for 15 minutes and filtered. The precipitate is washed on the filter with 300 ml of water with a temperature of about 70 ^o C and dried to constant weight. Obtain 75.5 g of a white crystalline powder, the mass fraction of azithromycin 86.0% (microbiological method). Yield 74.8%, counting on the imino ester of erythromycin (IV).

 B. Solution B (Example 3) containing azaerythromycin was transferred to a flask equipped with a reflux condenser, 9.7 ml of formic acid and 18.0 ml of formalin (40%) were added. The reaction mass is heated to boiling and boiled for 6 hours. Then the mass is cooled, 1.4 l of water and 20% sulfuric acid solution are added until the pH of the aqueous phase reaches 4.5-5.5. The mixture is stirred for 30 minutes, controlling the pH of the aqueous phase, which should remain in the range of 4.5-5.5. The layers are separated. The aqueous layer was placed in a crystallizer and 1.5 L of water and 82 ml of conc. ammonia. In this case, the pH of the crystallization mass is set in the range of 9-11. Crystallization of azithromycin is carried out as described in paragraph A. Get 76.2 g. Yield 75.3%, counting on the imino ester of erythromycin.

 Example 5. Recrystallization of azithromycin.

 To 75.5 g of azithromycin obtained in Example 4, 225 ml of acetone are added and the suspension is stirred until azithromycin is completely dissolved. The resulting solution was filtered through a Vladipor MFC membrane N 2, the membrane was washed with 75.0 ml of acetone. The combined filtrate was transferred to a crystallizer and water was added with stirring until crystallization began. The crystallization mass is stirred for 1 h, then water is added from the dropping funnel so that the total amount of water added is 150 ml and the acetone-water ratio in the crystallization mass is 2: 1. The mass is stirred for another two hours at room temperature to complete crystallization, then filtered. The precipitate was washed on the filter with a mixture of acetone-water (2: 1). The product is dried to constant weight, 66.8 g of a white non-hygroscopic crystalline substance are obtained, with a mass fraction of the basic substance of 94.0% and a water content of 4.8%. The yield of azithromycin is 37.5%, counting on erythromycin.

Specific rotation: minus 41 ^o
Specific Impurities: Less than 0.5%
Sulphated Ash: Trace
pH of an aqueous suspension: 8.6
Acetone Content: 0.10%
The diffraction pattern of the product corresponds to a standard sample of azithromycin.

Claims (3)

1. The method of producing azithromycin (I), characterized in that, in order to simplify the process and increase the yield of the target product, erythromycin A (II) is oxidized by the action of hydroxylamine hydrochloride in the presence of sodium carbonate in ethanol - water (20-40% water) at the initial ratio of erythromycin / solvent, g / ml, 1: 1.4 - 1: 1.7 and a temperature of 50-80 ^o C, the product of the oximelation - erythromycin (III) oxime is isolated from the reaction mass by extraction with chlorinated hydrocarbon at pH 9-11 and subjected to Beckman rearrangement by arylsul chloride oic acid in a biphasic solvent system - water / chlorinated hydrocarbon, the resulting imino ether of erythromycin (IV) is isolated by crystallization from aqueous solution at pH 9-11 and temperature of 60 ± 5 ^o C, followed by reduction of imino ether IV in aqueous medium at room temperature influence complex borohydride metal taken in 0-0.2 molar excess, the reduction product is azaerythromycin (V) in the form of a borate complex or after hydrolysis of the complex with a mineral or organic acid, preferably hydroxy acid, at pH 2, 5, methylated in chloroform with formaldehyde in the presence of formic acid, the methylation product is isolated by reextraction with water at pH 4.5-5.5, if necessary, hydrolysis of the borate complex is carried out, the target product is precipitated from an aqueous solution at pH 9-11 and a temperature of 50-80 ^o C, followed by recrystallization from a mixture of acetone - water or ethanol - water, taken in a ratio of from 2: 1 to 1: 2. 2. The method of producing erythromycin (III) oxime from erythromycin A (II) by the action of hydroxylamine hydrochloride in the presence of sodium carbonate, characterized in that, in order to increase the yield and simplify the process, the reaction is carried out in an aqueous-alcoholic medium with a water content of 20-40% , at a temperature of 50-80 ^o C and the initial ratio of erythromycin / solvent, g / ml, 1: 1.4 - 1: 1.7 and the target product is isolated by extraction with chlorinated hydrocarbon.  3. The method of producing azaerythromycin (V) by reducing the erythromycin (IV) imino ester by the action of a complex metal borohydride, characterized in that, in order to increase the yield of the target product, the reduction is carried out in an aqueous medium using a reducing agent in 0-0.2 molar excess, the reaction product - the azaerythromycin borate complex is hydrolyzed by the action of a mineral or organic acid, preferably hydroxy acid, at pH 2.5, the target product is isolated from the hydrolyzate by extraction with chloroform at pH 9-11.

Images