DE2111522A1 - Method of Purification of Cephalexin - Google Patents

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Cephalosporin 127

GLAXO LABORATORIES LIMITED, Greenford, Middlesex, England

Method of Purification of Cephalexin

The invention relates to an improved method of cleaning from cephalexin, i.e. 7ß- (D-2-amino-2-phenylacetamido) -3-methyl- " ceph-3 ~ em-4 - carboxylic acid.

Cephalexin becomes in crystalline form from an aqueous medium obtained, it shows a rod-like structure that is very hygroscopic and tends to remove impurities from the manufacturing process to include. The cephalexin obtained in this way is unsuitable for pharmaceutical use and further cleaning stages are required. Such further stages of purification entail the loss of some cephalexin and it is therefore desirable to have no more than a minimum number of steps to use in the additional cleaning process.

It has now been found that Cephalexin is in a high state of purity and can be obtained in an advantageous crystalline form from impure solutions by treating such solutions with acetonitrile treated, the pH value close to the isoelectric point

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so that an acetonitrile solvate of cephalexin crystallizes begins to suspend this solvate in warm water and then the crystalline solvate is allowed to dissolve in it, whereby pure, essentially acetonitrile-free cephalexin crystallized out. It is of interest to note that the crystalline Structure of the extracted gephalexin differs from that of the solvate.

In one embodiment of the inventive method for the purification of cephalexin, the impurities, an aqueous acid solution of the Cephalexins with acetonitrile is treated in such quantities that the volume of 70 * i is the volume of water to at least vorhandenein acetonitrile. Ilan then brings the pH of the solution to 3.5 to 4.5 by adding a base, so that a crystalline acetonitrile solvate of cephalexin is formed. Subsequently, the solvate obtained is separated and suspended in ater V / at a temperature of at least 58 ⁰ C. The crystalline solvate is allowed to dissolve in the water and pure, essentially acetonitrile-free crystalline cephalexin is recovered from the solution.

The pure cephalexin is usually in the form of large crystals with a diameter of several hundred microns and it has the shape of thick leaflets and it has a crystalline form different from that of acetonitrile solvate. The crystalline form of the cephalexin obtained from the process according to the invention is referred to as the β-form and the X-ray crystallographic data relating to this material are given in Table I which follows the examples.

It is an advantage of the process according to the invention that reaction solutions can be used as the aqueous starting cephalexin solution. For example, you can use the reaction solution that is obtained when 2,2,2-trichloroethyl-7ß- _< / BN- (2,2,2-triohloräthoxycarbonyl) -2-amino-2-phenylacetamido7-3-methylceph- 3-em-4-carboxylate or similar precursors reduced, for example with zinc / acetic acid.

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Acetonitrile is preferably added to the aqueous solution of impure cephalexin in such amounts that the added volume of acetonitrile is substantially the same as the volume of the aqueous cephalexin solution. If desired, the formation of acetonitrile solvate can be accelerated by adding a water-miscible organic solvent, such as, for example, a water-miscible ketone, for example acetone. The acetonitrile solvate can crystallize in the form of flat needles. The crystals tend to slowly lose acetonitrile in a vacuum, while in the surrounding atmosphere they take up 4 to 6 generally water and give off essentially all of the acetonitrile they contain over 2 to 3 days.

Cephalexin's acetonitrile solvate has a crystalline form that differs from the ß-form. This Kristlline The form of the solvate is called the fr-form. It should be noted that when the acetonitrile solvate is bound acetonitrile gives off by evaporation, no Y / echsel in the crystalline Form of cephalexin occurs.

The base that is used to adjust the pH of the water-acetonitrile solution to adjust to a, n value that the acetonitrile solvate of cephalexin from the solution is close to the isoelectric Crystallized point, can be any water-soluble base, for example an alkali metal hydrogen carbonate or preferably a lower trialkylamine, for example triethylamine or Ammonium hydroxide.

The aqueous solution of impure cephalexin that is used as the starting material is used in the inventive method, can have any concentration you want. It was, however, in general found that it is inexpedient to work with solutions that have an initial concentration of cephalexin that is bigger than about $ 25. After adding acetonitrile it is preferred that the concentration of the solution be about 10; ' amounts to.

'322

The acetonitrile solvate can be obtained from the aqueous acetonitrile medium by any convenient method such as Mitration or centrifugation followed by washing with acetonitrile or aqueous acetonitrile and then, if desired, [drying under reduced pressure. The additional The step of washing the acetonitrile solvate with acetonitrile or aqueous acetonitrile is advantageous when this step is used the purity and crystalline form of endcephalexin are improved.

The acetonitrile solvate can be suspended in water at a concentration of 10 to 40 ^c / o, for example 20 to 30 $, expediently at about 25 foj. The temperature of the water should be at least 58 ⁰ C or from 60 to 75 ⁰ C, preferably from 65 to 70 ⁰ C, and the formation of the ß-form can be followed by visual observation with the aid of a microscope. The small needles of the CX - The shape of the solvate quickly disappears, forming thick β-shaped leaflets. The aqueous suspension of the crystals can be filtered hot, washed with cold water and dried, if desired under reduced pressure.

It is an advantage of the method according to the invention that the The cephalexin obtained is essentially free of foreign ions.

There is another advantage of the process according to the invention, that the cephalexin is obtained in high yield from the acetonitrile solvate.

The following examples illustrate the invention without, however to restrict.

example 1

a) Production of acetonitrile solvate

2,2,2-trichloroethyl-7ß- / S- (ir-2,2,2-trichloroethoxycarbonyl) -2- 'mino-2-phenylaoe-tamido7-3-methylceph-3-em-4-carboxylate, the

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-. 5 -

0.5 mole of methyl isobutyl ketone (300 g) became one stirred zinc dust suspension in 98% formic acid. After the reaction and removal of the zinc, the formic acid became evaporated and replaced by acetic acid. This solution (450 ml) was diluted with v / water (400 ml) and extracted with ether. The aqueous layer was separated and back extracted for a total of 750 ml. Parts of this solution were then treated as follows:

i) Formation of acetonitrile solvate using acetone

19.7 ^ of the total volume were diluted with the same volume of acetonitrile (150 ml) at 35 ° and the pH of the solution was adjusted to 4.0 with triethylamine. The suspension was diluted with acetone (300 ml), cooled to 0 ° for 3 hours, filtered, washed with acetone and dried under reduced pressure at 40 ° to give cephalexin acetonitrile solvate. 26.29 g, / ^ 7-n + 142.5 ° (c, 0.5 in H ₂ O), A _max 263 µm, E ^ 204 (HpO) with a typical NMR spectrum showing the presence of acetonitrile and a trace of acetone indicated

ii) Formation of acetonitrile solvate without the use of acetone

26.5 ° / ° of the total volume was treated with 1 volume of acetonitrile as in i), but after the pH had been adjusted, no acetone was added. Cephalexinacetcmitrilsolvat, 36.32 g / AE7-Q ⁺ H2,5 ° '(o, 0.5 in H ₂ O) / t _max 263 nm, e] ^ 208 was obtained. The IR spectrum in Nujol was typical of the hygroscopic crystalline form of cephalexin, referred to as the CX form, and the NMR spectrum was typical of cephalexin, which contained acetonitrile «

The calculated /peJj.-VJe-rt for acetonitrile solvate, calculated on / piJ-Q of 154 ° for cephalexin, is + 138 °. Under normal drying conditions, a sample loses acetonitrile at a remarkable rate, the specific rotation lies between the two values,

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b) Crystallization of cephalexin

The cephalexin acetonitrile solvate obtained in ii) (10.0 g) was suspended in water / water (30 ml), stirred and kept at 65 to 70 °. After 5 minutes the nature of the suspension changed and large well-defined crystals became clearly visible under the microscope. After a further 5 minutes had passed, the suspension was filtered hot, the product was washed by replacement with cold water (40 ml) and dried at 40 ° in vacuo to give cephalexin. 7.79 g (87% recovery, assuming the starting material was pure solvate), {C {J- ^ + 154 ° (c, 0.5 in H ₂ O), A _max 263 nm, e ] J 233 (both calculated on the dry material), moisture content according to Karl Fischer $ 0.7, acetonitrile (TLC) 0.1 #. The IR spectrum was typical of the ß-form of cephalexin and the NMR spectrum was similar to that of a standard with no detectable impurities. Since the weight / weight yield in b) was 77.9 ° , the total yield from the starting material was 71 fo dry cephalexin.

Example 2

The implementation of Example 1 a) was repeated on the same scale. The combined aqueous layers from the ether extraction were diluted with an equal volume of acetonitrile for 15 minutes. Towards the end of the addition, the solvate began to crystallize. Another volume of acetonitrile was added with stirring over 15 minutes. The slurry was then adjusted to pH 4.0 with aqueous ammonia solution (0.880 diluted with an equal volume of v / water), the addition taking approximately 20 minutes. The suspension was cooled to 0 °, filtered and washed with 80% acetonitrile-water (500 ml), acetonitrile (1000 ml) and dried in vacuo at 40 ° for 3 to 4 hours to give cephalexin acetonitrile solvate, 132.32 g {ptf-Q ⁺ H2 ° (c, 0.5 in H ₂ O) nm, A _max 263, B] J _n 222nd

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This material (127.32 g) was added to rapidly stirring water (380 ml) held "at 65Ms 70 °. The suspension was stirred for an additional 10 minutes and then a portion of vacuum was applied" until the boiling stopped ( approx. 30 minutes). The suspension was filtered, washed with cold water (200 ml) substitute, and dried under reduced pressure at 40 overnight to give thick flaky crystals of cephalexin, 104.53 g, 73.3 # total theoretical yield, A7 _D + 152 ° (c, 0.5 in H ₂ O), A _max 263 mn, E ¹ ^ _m 238. The infrared spectrum is typical for the β-form of cephalexin and the NMR spectrum is typical for the pure compound, no impurities being observed will.

Example 3

Crude cephalexin (200 g) was suspended in cold water (400 ml). The suspension was dissolved by concentrating Hydrochloric acid (50 ml) added, with water (50 ml) diluted to give an orange colored solution. Activated animal charcoal (10 g) was then added and the suspension stirred for an additional 30 minutes and then filtered through a previously produced kieselguhr layer. The layer was made with water (50 ml). The yellow piltrate and wash waters were combined and mixed with acetonitrile (500 ml). Ammonia solution (0.88 s.g.) was steadily added to the stirred solution during Given for 15 minutes with inoculation until the pH increased from 1.7 to 4.5. The thick white crystal slurry became Stirred for a further 10 minutes at 20 °, filtered and 'washed with aqueous acetonitrile (1; 1, 750 ml). The solvate was in vacuo dried at 40 ° overnight, being a colorless electro. static powder (199 g) that was less than 0.5 mole Acetonitrile contained (IR spectrum).

The solvate (189 g »95 $> of the product) was in water at 75 °

(600 ml) suspended and stirred. The suspension was after ■ / · ■ ·

5 minutes a bit thin and became granular. The microscopic

Investigation showed that the 'change from the small needle-

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shaped CX shape to the thick platelet-like crystals of the ß-Porra was complete. The suspension was stirred for a total of 20 minutes at 75 °, filtered hot and washed with cold water (750 ml) by displacement. The product was dried in vacuo overnight, giving pure cephalexin in the form of a colorless crystalline powder (158 g, $ 83 total recovery), / Q (Z ₁ ) + 154 ° (c, 0.5 in H ₂ O), A _max 262 nm, έ] ^{/ 0} 227; the IR spectrum (Nujol) was characteristic of the ß-form of cephalexin with no trace of acetonitrile at 2245 cm ". The PMR spectrum in D ₂ O / trifluoroacetic acid was identical to that of a pure sample.

Example 4

An aqueous reaction solution obtained according to Example 1, from 81.25 g of starting material a volume of 180 ml had. * Added acetonitrile (180 ml) Wurd ¹ for 30 seconds with stirring. The pH rose from 2.45 to 3.35 and crystallization began after 5 minutes. Stirring was stopped and then stirred again 5 minutes later. The suspension was stirred for a further 5 minutes, then the pH had dropped to 2.8.

Triethylamine was added in 2 ml portions over 2 minutes until the pH had reached 4.5 (19.3 ml in total). The suspension was cooled to 10 ° for 3 hours and then filtered. The filter cake was washed by displacement with acetonitrile-water (1: 1, 90 ml) and acetonitrile (90 ml) and dried in vacuo at 40 ° overnight to give the solvate, 34.15 g, / 0 (J ^ ⁰ + 148 ° (c, 0 _s 5, H ₂ O) (yield, calculated on 32.8 g, 82 io theory); A _max 261.5 nm, E ^ _m 219

The product (15g) was added to stirred water (50ml) at 70 ° and the temperature was held for 5 minutes. The purified cephalexin was filtered off, washed with cold water / water (20 ml) and dried in vacuo overnight to give 13.28 g (91.5 step yield; 75 1 ° overall yield); ßj ^ + 153 (c, 0.52, H ₂ O), the crystals showed the typical size

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Prismatic structure when examined under the microscope.

The X-ray crystallographic results of the crystalline O / L and β forms of cephalexin are given in the tables below. The interplanar distances / Ά {%) _ J as well as the relative intensities of the lines, determined with copper-CX radiation, are given below, the following abbreviations being used:

s = strong ν = very m = medium f = low w = weak d = diffuse

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- 10 - I. there) τ Table I. S. 3.53 VW ß-form cephalexin S. 3.48 VW d (X) m 3.26 vwd 15.55 VW 3.13 ra 11.86 W. 3.06 m 10.67 W. 2.94 W. 9.47 VW 2.89 W. 8.28 VW 2.86 m 7.93 W. 2.76 m 5.87 V8 2.69 W. 5.76 m 2.65 W. 5.49 m 2.62 wd 5.33 wd 2.58 VW 5.21 W. 2.57 VW 4.86 m 2.51 VW 4.73 "m 2.47 VW 4.48 VW 2.42 wd 4.33 W. 2.40 W. 4.16 VW 2.26 wd 4.02 VW 2.10 VW 3.95 m 1.86 VW 3.90 m 1.85 VW 3.87 md 1.84 vwd 3.81 3.73 3.57

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- 11 ~ Table II

Acetonitrile solvate - Oi form

9.60 S. 8.62 m 6.80 m 6.37 m 5.68 m 5.53 S. 5.33 W. 4.72 W. 4.60 S. 4.14 VS 3.93 m 3.50 VW 3.37 m 3.32 m

3.18 m 3.10 m 3.05 W. 3.00 W. 2.95 W. 2.90 VW 2.86 VW 2.75 wd 2.71 VW 2.61 W. 2.55 wd 2.32 vwd 2.07 VW

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Claims (16)

Claims 1. A method for purifying cephalexin which contains impurities, characterized in that an aqueous acidic solution of the cephalexin is treated with acetonitrile in such amounts that the volume of acetonitrile present is at least 70 ia of the Y / as servo lumen s, the pH -Adjusts the value of the solution to 3.5 to 4.5 by adding a base, so that a crystalline acetonitrile solvate of cephalexin is formed, the solvate obtained is separated off, the solvate is suspended in water at a temperature of at least 58 ° C, the crystalline Solvate can be dissolved therein and pure, essentially acetonitrile-free crystalline cephalexin is obtained from the solution. 2. The method according to claim 1, characterized in that the The original aqueous cephalexin solution is the reaction solution obtained when 2,2,2-trichloroethyl-7β- / BE "- (2,2,2-trichloroethoxycarbonyl) ~ 2-amino-2-phenylacetamido7-3-methylceph ~ 3 -em-4-carboxylate reduced in solution. 3. The method according to claim 1 or 2, characterized in that the acetonitrile to the aqueous solution of the impure Cephalexin is added in such amounts that the added volume of acetonitrile is substantially equal to that Volume of the aqueous cephalexin solution. 4. The method according to any one of the preceding claims, characterized in that the formation of the acetonitrile solvate by Addition of a water-miscible organic solvent is accelerated. 109840/1822 5. The method according to claim 4, characterized in that the organic solvent is a water-miscible ketone. 6. The method according to claim 5 »characterized in that the Ketone is acetone. 7. The method according to any one of the preceding claims, characterized in that .that the base that is used to adjust the
pH of the water-acetonitrile solution is used, a low trialkylamine or ammonium hydroxide. 8. The method according to claim 7, characterized in that the Base is triethylamine. 9. The method according to any one of the preceding claims, characterized in that the initial concentration of cephalexin in the aqueous solution is not more than 25 i ° . 10. The method according to any one of the preceding claims, characterized in that after adding acetonitrile, the concentration of cephalexin in the aqueous solution is approximately 10 $
amounts to. 11. The method according to any one of the preceding claims, characterized in that the crystalline acetonitrile solvate, the
separated from the aqueous solution with acetonitrile
or aqueous acetonitrile. 12. The method according to any one of the preceding claims, characterized in that the acetonitrile solvate is suspended in water at a concentration of 10 to 40 # . 13. The method according to claim 12, characterized in that thea the concentration is 20 to 30 #. 14. The method according to claim 13, characterized in that the concentration is approximately 25 i » . 109840/1822 15. The method according to any one of the preceding claims, characterized in that the temperature of the water in which the acetonitrile solvate is dissolved is 60 to 75 ^° C. 16. The method according to claim 16, characterized in that the temperature is 65 to 70 ⁰ G. 109840/1822