DE932670C - Process for the preparation of tetracycline and its salts - Google Patents

Description

Process for the preparation of tetracycline and its salts The invention refers to the production of bactericidal tetracycline from chlortetracycline (known in trade as "Aureomycin").

A number of remedies have been found which can be used against different microorganisms are therapeutically effective. Some of these connections have such low toxicity that they can be used for human and animal treatment various diseases can be administered. However, these connections have often defects that limit or limit their value.

It has now been found that, under certain conditions, chlortetracycline can be catalytically hydrogenated to a compound that is not bound to carbon Contains more chlorine. This compound is microbiologically effective and has opposite the parent compound chlortetracycline certain advantages, e.g. B. it is in aqueous Preparations, especially at weakly alkaline pH values, more stable. the Compound is known as a tetracycline.

To prepare the new compound can be chlortetracycline or his Salts are used. It is recommended to use the chlortetracycline base as the starting product to use, d. H. the amphoteric compound that is free of metal ions or acid is. If an acid salt like chlorotetracycline hydrochloride is used, recommends a weakly soluble, weakly alkaline compound such as barium, Calcium or strontium carbonate to add, which in the course of the implementation hydrogen chloride formed neutralized. The procedure will be like this carried out that a solution of the chlorotetracycline in an organic inert Solvent reduced with hydrogen in the presence of a catalyst such as palladium. Various solvents can be used for this purpose, particularly suitable is a. Mixture of methanol and dioxane, although one also uses methanol alone as well can use other organic solvents such as ethanol or isopropanol. Even Ethers, such as glycol ethyl ether, tetrahydrofuran, dimethoxyethane, can also be used. In general, the solvent or solvent mixture should be proportionate be dry. However, a small amount of moisture does not seriously interfere with the reaction.

The reaction can be carried out with hydrogen at atmospheric pressure. Meanwhile, a slightly increased pressure accelerates the rate of the reaction. Pressures up to about 14 atmospheres are well suited for this purpose, but pressures of about 0.3 to 3.5 atmospheres are generally also useful. The reaction can be carried out at room temperature and also at slightly elevated temperatures of up to 50 °, as a result of which the reaction is not seriously disturbed. Palladium in any form can be used as the catalyst. Palladium animal charcoal or finely divided metal has been found to be very suitable by itself. A catalyst concentration of at least about 5 percent by weight of the chlorotetracycline used is necessary. In general there is no need to use more than the same amount by weight of catalyst.

Although the implementation mostly takes 1 to 12 hours, to one a noticeable amount of reaction product has formed can be changed by changing the reaction conditions, such as temperature, pressure, concentration of chlorotetracycline and catalyst type, too the implementation period can be influenced.

In general, starting solutions with a concentration of about i to io weight percent used. One can also be more dilute or stronger use concentrated solutions, but there is no particular benefit to this. In general, the rate of absorption decreases or becomes zero when about i Mole of hydrogen is absorbed. The product can then be obtained in any way The easiest way to do this is to remove the catalyst and concentrate the solution. A solid mass is obtained from the concentrated solutions, preferably by an organic non-polar solvent is added. Such nonsolvers include Diethyl ether, pentane, benzene, toluene and chloroform. It is recommended while to avoid elevated temperatures in the extraction of the product. although somewhat higher Temperatures as room temperature do not have a harmful effect. A light yellow, water soluble tetracycline. If amphoteric chlorotetracycline as a starting material was used, tetracycline hydrochloride is formed first. By setting the pH value of an aqueous solution of this product to a weakly alkaline reaction you can get the free tetracycline yourself. The free base is also noticeable water soluble. By evaporation or other careful removal of the water one can get the product firmly.

The tetracycline melts in a pure, crystalline form at 17 ° to 175 ° with decomposition. A i% solution in methanol has a specific rotation of [a] ö = - 239 °. When titrating in 50% aqueous dimethylformamide, two acid constants are observed, pkQ 8.9 and 10.2. Analysis of the Crystalline Product Found. . C 59.35%, H5.410 / 0 "N 6, 15%, calcd as C22 H24" \ T2 O8 C59.451 / @, H 5.44 0/0, N 6, 3%. The equivalent weight was determined to be 227 by titration. The calculated molecular weight is 444. In the ultraviolet absorption maxima occur at about 270 and 362 my when the material is dissolved in o, oi n-meüllyla'1'kdhol.is'chem hydrogen chloride. In o, oi n-methyl alcoholic sodium hydroxide, the absorption maxima are at 245, 265 and 382 m, u.

The acid salts are obtained from the tetracycline by treating it with about i equivalent of an acid treated. The reaction can be in aqueous solution or in a suitable solvent. With careful evaporation of the solvent the solid salt is created. If the product is made in aqueous solution, can the solid can be recovered by freeze drying. You can also use the acid salts separate by adding a precipitant, for example by adding Ether to a methyl alcoholic solution of the product. The phosphate, Hydrobromide, nitrate and other salts prepared according to the methods described will.

Tetracycline is very effective against many microorganisms, both gram-positive and gram-negative. This effect was determined quantitatively with the aid of a serial dilution test such as that used for testing antibiotics. Some of these values are given in the table below. Effectiveness of tetracycline in vitro Microorganisms Lowest inhibitory con 3 ze n trio n, yj e cm Aerobacter aerogenes .......... 50.00 Klebsiella pneumoniae .......... 12.50 Escherichia coli ............... 1.56 Sahnonella typhosa ........... 0.78 Sahnonella paratyphi ......... 0.78 Staphylococcus aureus ......... o, ig Proteus species. . . . . . . . . . . . . . . 50.00 Pseudomonas species. . . . . . . . . . 12.50 Brucella bronchisepticae ....... 0.39 Mycobacterium ranae. . . . . . . . . o, ig Streptococcus faecalis ......... o, 19 The products prepared by the process according to the invention can, for. B. used to sterilize pharmaceutical systems of various types or to separate certain microorganisms from solutions that contain mixtures of different microorganisms. They are also of value in the treatment of animals infected with certain organisms that are sensitive to these substances.

The invention is illustrated in the examples below. Example i 4.8 g of chlorotetracycline base were suspended in 100 cm3 of methanol. About the same volume of anhydrous dioxane was added to completely dissolve the product. 0.5 g of 5% palladium-activated carbon were added to this solution as a catalyst. The mixture was introduced into the usual hydrogenation apparatus and exposed to a hydrogen pressure of 3.5 atmospheres with stirring. After the initial pressure drop due to the absorption of hydrogen by the catalyst and solvent, the pressure continued to drop due to the hydrogenation of the chlorotetracycline. After about 1 mole of hydrogen had been absorbed, no further hydrogen uptake took place after about 2 hours. The catalyst was filtered off and washed with boiling methanol and dioxane. The test of the solution for chlorine ions was positive. The solution also reacted strongly acidic, a sign that the chlorine had been released in the form of hydrogen chloride. A biological analysis of the crude product in the solution showed an effectiveness of about 58o y per mg when using oxytetracycline (known under the trade name "Terramycin") as the standard with an effectiveness of 100 y per mg. The solution was concentrated in vacuo at room temperature and the remaining liquid was subjected to freeze-drying in vacuo. 0.31 g of pale yellow, amorphous tetracycline hydrochloride was obtained.

This product was converted to tetracycline by placing it in water again dissolved, the solution carefully with dilute sodium hydroxide solution to pH 4.5 and the product was obtained by evaporating the solution.

The crystalline base was obtained by extracting the aqueous solution of the base, which was prepared as described above, with butanol (other solvents such as ether can also be used for this purpose) and the solvent extracts were concentrated to a small volume. The crystalline base was recrystallized from toluene in order to obtain an analytically pure tetracycline, the composition and physical constants of which have already been given above. Example e approach chlortetracycline. . . . . . . . . . . . . . . 5J9 5 °! 1 platinum on activated carbon ....... 2.49 Mixture of equal parts by volume of methanol and dioxane. . . . . . . . . 150 cm3 If this mixture is shaken under a hydrogen pressure of 3.5 at, the hydrogen uptake was over after 2 hours. The catalyst was filtered off and one mole of Na OH was added. The solvent was distilled off from the filtrate under a pressure of 5 mm. 5 cms of water was added to the residue, followed by crystallization. The crystals were filtered off and then slurried in 20 cm3 of a mixture of 50% water and 50% acetone. After a further sufficient addition of acetone, the crystals dissolved with heating. The solution was then treated with activated charcoal, filtered and cooled, whereupon 1.6 g of tetracycline base could be filtered off. This tetracycline has a biological effectiveness of about 80o units per mg. The optical rotation was -236 °. Example 3 Chlorotetracycline approach. . . . . . . . . ...... 25 g Raney nickel. . . . . . . . . . . . . . . 259 methanol-dioxane mixture ...... Zoo cms The mixture was stirred for a few hours at 35 ° in a stirred autoclave under 9i at hydrogen pressure, the catalyst was filtered off and washed with methanol, whereupon the total volume of the filtrate was 420 cm3. The filtrate was concentrated to 100 cm3 by stripping off the solvent in vacuo. One equivalent of NaOH in 100 cm3 of water was then added, and the solution was stirred, 2 g of crystals gradually separating out. The product had a biological effectiveness of about 700 units per mg. The absorption maxima in the ultraviolet were at 220 m, u (log 8 = 1.43), at 2.68 m, u (1.og a = 1.49) and at 362 m, u (log 8 = 1.37 ).

Claims (2)

PATENT CLAIM: i. Process for the preparation of tetracycline and its salts, characterized in that one chlorotetracycline or its salts with hydrogen in an organic solvent, advantageously under somewhat increased Pressure reduced to about 14 atmospheres in the presence of a catalyst. 2. Procedure according to claim i, characterized in that the catalyst used is palladium. Referred publications: Journ. At the. chem. Soc., Vol. 75, 1953, p. 4621.