PL194994B1 - Method of obtaining azithromycin - Google Patents

Abstract

Method for producing azithromycin from 9-deoxy-9a-aza-9a-homoerythromycin A, significant in that 9-deoxy-9a-aza-9a-homoerythromycin And in a polar solvent it gives up exhaustive N-methylation in the presence of a base, while converting it into dihalides 3'-N, N, N-trimethyl-9a-N, N-dimethylammonium 9-deoxy-9a-aza-9a-homoerythromycin A, which then undergoes a thermolysis reaction in a high-boiling non-polar solvent, simultaneously taking away the halide formed methyl.

Description

Description of the invention

The present invention relates to a process for the production of the macrolide azithromycin antibiotic from 9-deoxy-9a-aza-9a-homoerythromycin A.

Azithromycin is a synthetic analogue of erythromycin A that is more stable in an acidic environment, e.g. gastric juice, and is active against a greater number of strains and species of Gram positive and Gram negative bacteria than the parent compound. Particularly valuable is the high activity of azithromycin (the highest macrolide antibiotic known to date) against many important strains of gram-negative bacteria, e.g. Haemophilus influenza, Neisseria gonorrhoeae, Branhamella catarrhalis. Moreover, compared to erythromycin A, azithromycin is much better absorbed from the digestive system, achieves higher tissue concentrations and is characterized by a significantly longer period of elimination from the body. Azithromycin does not cause unpleasant gastrointestinal side effects, which are typical for the use of erythromycin. Resistance of bacterial strains to azithromycin has not been a problem in clinical practice so far.

The growing interest in azithromycin applications is reflected, inter alia, in the development of new forms of the drug, e.g. intravenous injections (Ann. Chemother, 1999 (33), 218-228) and research into new medical indications for this drug.

The generally recognized advantages of this antibiotic simultaneously necessitate the development of technologically improved methods of its synthesis.

The methods for the synthesis of anhydrous azithromycin described in the patent literature are based on a series of chemical transformations of erythromycin A, from which first (E) -oxime is obtained, then subjected to Beckmann rearrangement to the 6,9-iminoether of erythromycin A, in accordance with the description of European patent application EP 109253, which in turn is reduced to 9-deoxy-9a-aza-9a-homoerythromycin A. 9-deoxy-9a-aza-9a-homoerythromycin A or directly N-methylated by the Eschweiler-Clarke method by reaction with formaldehyde in the presence of formic acid to azithromycin (Polish patent specification 131784) or it is protected in the form of a 9a-N-hydroxy-3'-N-oxide derivative, which is subjected to exhaustive N-methylation and subsequent catalytic reduction with hydrogen in an inert solvent to azithromycin ( Polish patent no. 141 924). The European patent application EP 879823 also discloses a method in which the reduction of 6,9-iminoether to 9-deoxy-9a-homoerythromycin A is carried out on a noble metal catalyst and then reductively methylated with formaldehyde in the same reaction vessel. azithromycin.

The methods of converting 9-deoxy-9a-aza-9a-homoerythromycin A into azithromycin used in the above methods are not without difficulties.

The high acidity of the formic acid used in the Eschweiler-Clarke method leads to the contamination of azithromycin with 3-O-descladinose-9a-deoxy-9a-aza-homoerythromecin A, which is the product of acidic hydrolysis of the glycosidic bond of cladinose. A serious limitation of this method is also the necessity to use formaldehyde, which is known, like formic acid, for its strong toxic properties. The disadvantage of the reduction step is the contamination of the product with the metal reduction catalyst, which is a significant problem, especially on a technical scale, especially in the case of amines having an additional alcohol hydroxyl group in the molecule due to the formation of stable complexes and the high costs associated with its use.

Unexpectedly, it turned out that the above disadvantages can be avoided by the preparation of azithromycin according to the method of the invention, in which 9-deoxy-9a-aza-9a-homoerythromycin A is subjected to exhaustive N-methylation while simultaneously converting it into a 3'-N, N, dihalide, N-trimethyl-9a-N, N-dimethylammonium 9-deoxy-9a-aza-9a-homoerythromycin A, which is then thermolyzed in a high-boiling non-polar solvent while simultaneously receiving the methyl halide formed.

A suitable methylating agent for 9-deoxy-9a-aza-9a-homoerythromycin A (Formula 1) is the art-known methylating agents of formula CH ₈ X, where X is a halogen or other moiety, preferably methyl sulfate (CH3OSO3). However, the advantageous effect of the invention is achieved by methylation with methyl halide. In the case of using the compound CH ₈ X for methylation, where X is a group other than a halogen atom, the disolate obtained after N-methylation can be converted into the appropriate form without isolation from the reaction medium.

3'-N, N, N-trimethyl-9a-N, N-dimethylammonium 9-deoxy-9a-aza-9a-homoerythromycin A dihalide by counter-ion exchange by washing the disalts with an aqueous alkali metal halide solution.

In the N-methylation reaction of 9-deoxy-9a-aza-9a-homoerythromycin A, a molar excess of the methylating agent is used. The stoichiometric ratio of the methylating agent to the starting compound is not critical to the course of the reaction, but it is important to ensure that the amount is sufficiently methylated (exhaustive methylation). This goal is achieved by using 3-5 molar equivalents of the methylating agent relative to 9-deoxy-9a-aza-9a-homoerythromycin A. The N-methylation reaction is carried out in a polar solvent, for example a C1-C4 alcohol or dimethylformamide, in the presence of rules. Suitable bases are the carbonates or hydrogen carbonates of alkaline earth metals such as NaHCO 3 or Cs ₂ CO 3 or sodium hydride.

It turned out that the thus obtained quaternary methylammonium salts of 9-deoxy-9a-aza-9a-homoerythromycin A (formula 2) undergo thermolysis reaction to azithromycin (formula 3) at a temperature above 100 ° C in nonpolar solvents (formula 3) with good efficiency and without the need for additional reagents.

The thermolysis reaction of the 3'-N, N, N-trimethyl-9a-N, N-dimethylammonium dihalide 9-deoxy-9a-aza-9a-homoerythromycin A dihalide is carried out under a nitrogen atmosphere in a simple apparatus, e.g. a simple distillation apparatus. The reaction is carried out at the reflux temperature of a non-polar solvent under atmospheric pressure to remove the liberating low-boiling methyl halide from the reaction medium.

The use of a non-polar high-boiling solvent is essential for the course of the thermolysis reaction, which at the same time facilitates the control of the course of the reaction and the separation of the product from the reaction mixture. Suitable solvents are aliphatic or aromatic hydrocarbons such as xylenes (o-, m-, p-xylene or mixtures thereof), mesitylene or tert-butylbenzene. The use of a more polar solvent results in a reduction in the reaction yield and formation of undesirable polar by-products as observed in Comparative Example 4.

In order to dissolve the dense precipitate of unreacted disolate that forms over time, a low-boiling polar solvent (e.g. methanol) can be added to the reaction vessel after a temporary cooling, which is then easily distilled off while continuing the thermolysis of the disolate. After 2-12 hours of thermolysis reaction, the reaction mixture is cooled, a solvent such as ethyl acetate is added, and the resulting product is isolated. The solution is concentrated and dried in vacuo or, in order to obtain the product of the highest chromatographic purity, it is washed with a dilute alkali metal bicarbonate solution, the organic phase is dried and the solvents are removed in vacuo. Anhydrous azithromycin is obtained in the form of a colorless glassy solid. The yield of azithromycin based on the starting 9-deoxo-9a-aza-9a-homoerythromycin A is 50-80%. The anhydrous azithromycin obtained by the method according to the invention can be converted into a therapeutic azithromycin dihydrate of high chromatographic purity, in a manner known from the state of the art, e.g. as described in Polish patent no. 157 145, consisting in crystallization from a mixture of THF and an aliphatic hydrocarbon in the presence of at least 2 equivalents of water or by crystallization from an acetone-water solvent system as described in European application EP 827965 A1.

The process according to the invention enables the production of chromatographically pure azithromycin with high yield, which is determined by the use of a non-polar high-boiling solvent in the thermolysis step. The method avoids high consumption of reagents, since both the solvent used and the alkyl halide can be easily recovered using an uncomplicated procedure.

The following examples illustrate the invention.

P r z k ł a d 1.

Preparation of anhydrous azithromycin by thermolysis of ammonium dibromide.

9-Deoxy-9a-aza-9a-homoerythromycin A (2.25 g, 3.06 mmol) was dissolved in MeOH (50 ml), NaHCO ₃ (2.0 g, 23.8 mmol) was added and iodomethane (2, 5 ml, 5.70 g, 40.1 mmol). It was stirred at room temperature for 22 hours, then the precipitate was filtered off. The filtrate was concentrated in vacuo. CH ₂ Cl ₂ (50 ml) and a 30% aqueous NaBr solution (50 ml) were added. The mixture was vigorously stirred at room temperature, shaking the thickened mixture every few minutes. After 30 minutes, added

PL 194 994 B1

1-butanol (120 ml) and 30% aqueous NaBr solution (100 ml). The mixture was shaken in the separating funnel and the layers were separated. The aqueous layer was washed with 1-butanol (50 ml). The combined organic layers were concentrated in vacuo to give a dibromide solution of ca. 5 ml. A mixture of xylenes (200 ml) was added with vigorous stirring. The suspension formed in this way was slowly boiled under nitrogen atmosphere, at a rate allowing for the collection of distillate in the amount of about 1 drop / minute. After 3 hours, the mixture was cooled to ca. 70 ° C, ethyl acetate (50 ml) was added and stirred for 10 minutes. The solution was filtered, concentrated, and dried thoroughly in vacuo. A colorless glassy solid (0.92 g, 40%) was obtained, identical to a standard sample of anhydrous azithromycin (NMR, TLC, C-18 HPLC). The thermolysis residue (yellowish glassy mass) was dissolved in MeOH (25 mL). With vigorous stirring, tert-butylbenzene (100 ml) was added. The suspension thus obtained was vigorously stirred and heated to reflux under a nitrogen atmosphere. In this way, methanol was distilled off and the residue was slowly heated to boiling, while the distillate was collected at a rate of about 1 drop / minute. After 3 hours, heating was discontinued, the mixture was cooled, EtOAc (30 mL) was added and stirred for 10 minutes. The solution was filtered, concentrated in vacuo, and dried thoroughly in vacuo. A glassy solid (0.90 g) was obtained, with the properties above. Cumulative yield of azithromycin: 1.82 g (79.4%).

P ricycles 2

Preparation of anhydrous azithromycin by thermolysis of ammonium diiodide.

9-Deoxo-9a-aza-9a-homoerythromycin A (1.60 g, 2.18 mmol) was dissolved in MeOH (30 ml), NaHCO ₃ (3.2 g, 38 mmol) and iodomethane (2.0 ml , 4 _; 56 g, 32 mmol). The mixture was stirred in a sealed flask at room temperature for 48 hours. The precipitate was then filtered off, washed with MeOH (15 mL) and the combined methanol solutions were concentrated to dryness in vacuo. The precipitate was partitioned in a separatory funnel between 40% aqueous NaI solution and the stirred phase [CH 3 Cl 2 (80 ml) plus isopropyl alcohol (20 ml)]. After extraction, the upper, organic layer was dried anhydrous. Na ₃ SO ₄ , filtered, concentrated and dried under vacuum. A white, crystalline precipitate of 4th order diiodide was obtained. Ammonium ^{e g} of ^{(2 16} g, 96%); ¹ H ^- NMR (CD 3 OD, 200 MH ^z) d 5.04 ⁽ 1H; d ^: 4.6 Hz), 4.88 ⁽ 1H; d ^: 2.6 Hz), 4.67 (1H, bd ^: 6.4 Hz), 3.59 ⁽ 1H ^; d ^: 1.5 Hz ), 3.38 (3H, s), 3.28 ⁽ 12H ^; bs) ^pp m ^{; 13} C ^- NMR (CD3OD, 50 MHz) d: 179.6, 102.7, 96.4, 85.6, 79.8, 79.1,78.1.75.7, 75.5, 74.9, 74.6, 74.0, 73.0, 70.6 (m), 67.4, 66.5, 64.7, 63.8 (m), 53.9, 50.0, 46.7, 43.3, 43.1, 36.7, 35.9, 34.6, 27.9, 27.7, 25.3, 22.3, 21.8, 21.7, 18.9, 17.4, 15.6, 11.5, 9.9, and 7.7 ppm.

Part of this sample (1.96 g, 1.90 mmol) was dissolved in MeOH (50 mL). A mixture of xylenes (200 ml) was added with vigorous stirring. The suspension formed was heated to reflux with vigorous stirring. After the methanol had been distilled off, the mixture was heated gently to reflux under nitrogen, while the distillate was collected at a rate of about 1 drop / minute. After 12 hours, the mixture was cooled, EtOAc (50 mL) added, stirred for 5 minutes. The solution was filtered, washed with 10% aqueous KHCO3, dried over anh. K2CO3, filtered, concentrated in vacuo and dried in vacuo. A glassy, colorless solid was obtained (anhydrous azithromycin, 0.90 g, 60.8%). The thermolysis precipitate was dissolved in MeOH (30 ml), the mixture of xylenes was added with vigorous stirring and heated to reflux under a nitrogen atmosphere. After the methanol had been distilled off, the xylene fraction was collected as before. After 3 hours, the isolation of the thermolysis product was repeated according to the procedure described above. An additional portion of anhydrous was obtained. azithromycin (0.160 g). In total, 1.06 g of azithromycin (65%) was obtained in the two thermolysis steps; TLC, C-18 HPLC and NMR data as for the reference azithromycin.

P ricycles 3

Preparation of anhydrous azithromycin by thermolysis of ammonium dichloride.

9-Deoxo-9a-aza-9a-homoerythromycin A (1.42 g, 1.93 mmol) was dissolved in MeOH (10 ml), NaHCO3 (2.0 g, 23.8 mmol) was added and iodomethane (2.0 ml, 4.56 g, 32 mmol). The mixture was stirred in a sealed flask at room temperature for 20 hours. The reaction mixture was then shaken with brine (60 ml) and CH 2 Cl 2 (70 ml). The aqueous layer after extraction was washed with CH2Cl2 (50 ml). The combined organic layers were dried over K2CO3, filtered, concentrated and dried under vacuum. A white, glassy solid was obtained (1.18 g, 71.8%). To this sample was added CH 2 Cl 2 (10 ml) and a mixture of xylenes (150 ml). It was slowly heated to reflux with vigorous stirring, first the CH2Cl2 fraction was collected, and then the xylene fraction was collected at a rate of ca. 1 drop / minute. After 6 hours, the mixture was cooled to room temperature, the solution was decanted and concentrated in vacuo. A glassy yellow solid (0.89 g) was obtained containing impurities. This sample was purified on a Si-gel column (230-400m, 40g) eluting with 5% MeOH / CH2Cl2 / + 0.2% Et3N. A glassy white solid (0.506 g, ca. 49%) was obtained with C-18 HPLC, TLC and NMR characteristics of the main component consistent with anhydrous. azithromycin, containing a small amount of impurities.

PL 194 994 B1

P r z k ł a d 3 (comparative)

Obtaining anhydrous azithromycin by thermolysis of ammonium diiodide in a solvent of higher polarity

4th tier ammonium diiodide was prepared from 9-deoxo-9a-aza-9a-homoerythromycin A and iodomethane in the same manner as in Example 1.

Diglyme (25 ml) and mesitylene (170 ml) were added to a sample of diiodide (2.30 g, 2.22 mmol). With vigorous stirring, the formed suspension was heated to reflux under a nitrogen atmosphere. The distillate was collected at a rate of 1 drop / minute. After 2 hours, the mixture was cooled to 60 ° C and MeOH (50 ml) was added to dissolve the formed precipitate. Heating was continued under nitrogen atmosphere, withdrawing first the methanol and then the diglyme-mesitylene mixture boiling at 162 ° C at 1 drop of distillate / minute. After 6 hours, the mixture was cooled to room temperature, EtOAc (40 ml) was added and extracted with 10% aq. KHCO3 solution. The organic layer was dried over anh. K2CO3, filtered, concentrated and dried thoroughly in vacuo. A yellowish solid (0.86 g, ca 51%) with TLC and NMR characteristics of the main component consistent with anhydrous was obtained. azithromycin, but additionally containing approx. 10% polar impurities.

P ricycles 5

Crystallization of anhydrous azithromycin to azithromycin dihydrate.

The anhydrous azithromycin (3.10 g) obtained by thermolysis in nonpolar solvents was dissolved in CHCl2 (150 ml). A 10% aqueous KH2PO4 solution (150 ml) was added. While stirring vigorously, a 6N aqueous HCl solution was added until pH = 3. After extraction, the layers were separated, and CHCl 3 (150 ml) was added to the aqueous layer. While stirring vigorously, a 6N aqueous NaOH solution was added until pH = 11. After extraction, the layers were thoroughly separated. The organic layer was concentrated and dried in vacuo. A glassy solid (2.5 g) was obtained. This sample was dissolved in acetone (15 ml), and with vigorous stirring under nitrogen atmosphere, H 2 O (17 ml) was added dropwise over 30 minutes. The mixture was stirred at room temperature under nitrogen for 20 hours. The crystals were filtered off, washed with H 2 O (10 mL) and dried under vacuum at room temperature. A white, fine crystalline precipitate of azithromycin dihydrate (2.73 g, 84%) was obtained. M.p. 130-136 ° C. This material has TLC and RP HPLC purity identical to the standard of azithromycin dihydrate pharmaceutical substance.

Claims (6)

1. The method for the preparation of azithromycin from 9-deoxy-9a-aza-9a-homoeryttomycin A, characterized in that 9-deoxy-9a-aza-9a-homoerythromycin A in a polar solvent is subjected to exhaustive N-methylation in the presence of a base by it simultaneously into 3'-N, N, N-trimethyl-9a-N, N-dimethylammonium dihalide 9-deoxy-9a-aza-9a-homoerythromycin A, which is then thermolyzed in a high-boiling non-polar solvent, simultaneously receiving the halide formed methyl. 2. The method according to p. A compound according to claim 1, characterized in that the methylating agent is a compound of formula CH ₇ X, in which X is a halogen atom or another group that can be replaced with a halogen atom, preferably methylsulfate, where if X is a non-halogen atom, then obtained from The N-methylation of the disolate is converted to the 3'-N, N, N-trimethyl-9a-N, N-dimethylammonium dihalide 9-deoxy-9a-aza-9a-homoerythromycin A by washing with an aqueous alkali metal halide solution. 3. The method according to principles. 1, in that the N-methylation reaction uses a molar excess of the methylating agent relative to 9-deoxy-9a-aza-9a-homoerythromycin A, preferably from 3 to 5 molar equivalents per equivalent of 9-deoxy-9a-aza-9a -homoerythromycin A. 4. Way according to zassi ^. 1, I know that the N-methyl reaction is carried out. it is in C1-C4 alcohol or dimethylformamide. 5. The method according to p. A process as claimed in claim 1, characterized in that the N-meylation reaction is carried out in the presence of a base selected from carbonates and bicarbonates of alkaline earth metals or sodium hydride. 6. The method according to Ss. The process of claim 1, characterized in that the reemollysis reaction is carried out in a solvent selected from C1-C10 aliphatic or C6-C12 aromatic hydrocarbons, optionally halogenated, preferably in o-, m- or p-xylene or a mixture thereof.