IE44704B1 - Lactam antibiotic - Google Patents

Abstract

An aqueous solution of a salt of clavulanic acid with the exception of the calcium salt is treated with a cation exchanger resin in the form of the calcium salt. The calcium diclavulanate which is formed is eluted from the exchanger resin, resulting in a solution of calcium diclavulanate which is virtually free of cations other than calcium ions. Calcium diclavulanate dihydrate is allowed to crystallise out of the resulting solution and is isolated in crystalline form. The resulting salt is suitable as active component in pharmaceutical compositions, especially for oral administration.

Description

The present invention relates ts a new process for the preparation of the crystalline calcium salt of clavulanic acid, to the salt produced hy this process and to pharmaceutical compositions containing it.

Patent Specification No. 792/75'discloses inter alia that the calcium salt of clavulanic acid, which is cf the formulas say he isolated from a fermentation broth containing salts of clavulanic acid fey adsorbing the clavulanic acid residues onto a weak sr strong has© exchange resin and eluting off with a suitable salt solution and also by hydrogenation of a benzyl or like ester of clavulanic acid in the presence of a suitable base. We have now found that crystalline calcium di-clavulanate dihydrate may conveniently be prepared from other salts of clavulanic acid in high yield and good purity. - 2 The present invention provides a process for the preparation of crystalline calcium di-clavulanate dihydrate which process comprises contacting an aquscus solution of a salt of clavulanic acid other than the calcium salt 'with a cation exchange resin in the salcina fore and eluting the thus fesaed calcium di-clcvulajiate from the resin to yi.?ld c. solution cf calcium di-clavular •;;.;'33t,.5noiairy frea from cations ether than calciu3 ond thareaftor causing the crystallisation c£ the ealeizn di-elavulsnute dthyira~e from the solution and itolttiui. che desired salt.

The iri.tial salt of e?avulanic acid used tn thia process ai;.·· he any convenient metal (other than calcium;, -•anonium or substituted asmoriux salt but in general it is aost co;ivena*nt to use a aonc-v?.X$nt salt such as the lithium, sodium or potassiw salt of clavulrnic acid.

Of these the lithium and sodium salts are often the most convenient. In general we prefer to use the sodium salt which can lead to a product of particularly acceptable purity.

The salt used to form the solution to be exchanged should be as pure as can be conveniently obtained in order to allow the preparation of a pure product. - 3 Suitable cation exchange resins for use are crosslinked polystyrene-divinylbenzene co-polymers substituted by acid groups in the fora of the calcium salt. The preferred acid group is the sulphonic acid group. The resins chosen will generally have 2-20% cross-linking and usually 4-10% cross-linking,for example about 8% cross-linking. The resin is usually in the fora of beads, for example spherical beads of 14-52 Π.Κ. mesh size.

Suitable resins include the calcium fora of Amberlite 10 resins such as 1R-120, IR-121, IR-122, 200, 2000, 252; Bowex resins such as 50WX1, 50VJX2, 50X4, 5O’S8, 5X10, WQQ, 50WX16; Bio Rad resins such as AG 50VJX1, 40WX2, AG 50WX4, AG 50VIX8, AG 50WX12; lonac resins such as 0250, 0258 or C255?and Zerolit resins such as 225, 325, 425,· 525, 625. (Amberlite, Dowsx and Zerolit are Registered Trade Marks) The resin is normally used in large excess. The quantity of resin used should be sufficient to provide an exchange capacity of at least 10 times, more suitably at least 20 times and preferably at least 30 times, the total exchangeable capacity in the solution of the salt of clavulanic acid to be applied.

In use the resin is in a bed through which the solution is percolated. Generally this bed is in the form of a column. - 4 ,· / 'j -J a ihe c;nc.c.itruticn οϊ ϊϊέ solution οϊ ·ώ« salt to he exchingci is not critical out very dilute solutions (fcr sxaaplo, less than 1% w/v) should bs avoided as low concentrations can lead to inconveniently low loriir? and inccrplste e::cht:.'i£e. Similarly vary ii.D concentrations (for example those appi-w-aehing saturation) should ca avoided as such solutions can have too high :. vicoocri-y far iuey usi··, in general for meet salts concentrations of 2-303 w/v ars accoptahio, a range ci about 5 to 25# being sosa suitable and a range οϊ about fi to 2C# being proferrod. for example about 10)h The solution to be exchanged is normally applied slowly to ths top to the cclur.t. The band is then uilowod tc percolate slowly into the top of the resin after which a little· -water is applied to ---ash the band c short •a&j into the resin. She revaininy necessary water is then slowly run through ths column co that the band pusses through the- column in as tight a band as conveniently possible.

The presence cf calcium elavulanate in the eluate is usually readily detectable by a change in the refractive index of ths eluate. This may bs determined using a refractometer or visually, for example by the presence of striations. Alternatively fractions asy be taken and tested in convenient manner, for example by spotting en s t.l.c. plate and spraying with permanganate which is cscoicusi-ii ay ths clavularate os by listhcds using the tasyae inhibitory effects of the material, «» The desired calcium salt may he obtained from solution in conventional manner, for example from a relatively concentrated solution by the slow addition of a water-miscible organic solvent such as acetone until crystallisation commences or reducing the solvent volume prior to the addition of an organic solvent, for example, by concentrating under reduced pressure to a syrup, followed by adding small quantities of acetone, acetonitrile, or acetone/ether to initiate crystallisation. t Most suitably crystallisation is initiated at 10 ambient or slightly elevated temperature, for example, 12-30°C, more suitably 20-25°C. Once crystallisation has begun the mixture may be cooled, for example to about -5° to -10°C,until no further crystals appear.

Once the desired crystals have formed they may be 15 filtered off and dried. Vigorous drying conditions (such as vacuum drying) are best avoided as they tend to lead to breakdown of the crystal structure and partially dehydrated crystals. Wet air should not be used for drying as it can lead to wet crystals. Drying should preferably be effected at atmospheric pressure.

The calcium di-clavulanate dihydrate produced by the process of this invention is also an aspect of this invention.

An infra-red spectrum of the salt according to this 25 invention is shown in Table 1. - 6 d 4 V 'J d Στ should Is appreciated thct 1.1¾ cryvtulline salt within this invention can contain small amounts of partly dehydrated calcium di-clavulaaate or small aswats of water which forms no part of the crystal structure and probably simply wets the οχιιΧ faces, however, the crystalline salt cf tXo invintio··. mors suitably contains 6.2 to 7,7% (wsi-X A/ilyit, cf ’.iatsr, Xi is it should act contain -uater X.oh fo.-ns i.e xX X the crystal structure althcuyh it c·- iiu^eixXr X -’or it to contain small amovnrs of partly XrXauru material. We have found that a salt cvXainiry Approximatsly IX to 7-S)a (weight/weight) of total water to· iavs poXXXcXy suitable stability properties., Xst suitably the water content cf the cryorals is aXuu 7X7 ths water contents referred to above x-s total water, for exanple as determined by XX xs-chsr analysis.

The present invention also extends to a pharmaceutical composition which comprises the said crystalline calcium di-clavulanate dihydrate and a pharmaceutically acceptable carrier therefor.

Such compositions are most suitably adapted for oral administration.

The compositions of this invention may also comprise a penicillin or cephalosporin. Particularly suitable penicillins include amgiciilin (as che anhyvravc or crihydrsts or a phar;:';dcsvcicaliy acceptable sale? and anoyycj.iiin fss the t.vhywrate oy a pharmaceutically acciptafclo salt; and also disodium. earbeniciilin, disodium tioarcillan, cX sodium. sales -~q or -χ ohenyi or inearyl a-esters ol carbeniciliin or ticarcxllin, - 7 Suitable forms of the compositions of this invention, are described in Belgian Patent Specification No, 827926.

Table 1 INFRA-RED SPECTRUM OF CALCIUM DI-CLAVULANATE DIHYDRATE 5 (IN NUJOL MULL)_ 3630 shoulder, 3520 shoulder, 3315 strong, broad, 1785 strong, 1695 medium, 1660 shoulder, 1605 strong, 1575 shoulder, 1555 shoulder., 1450 shoulder, 1418 weak, 1350 weak, 1315 strong, 1200 medium, 1147 medium, 1124 strong, 1096 medium, 1072 medium, 1050 strong, 1024 strong, 1004 strong, 976 weak, 960 shoulder, 897 strong, 850 medium, 803 medium, 748 strong, 708 weak, 659 weak.

(Note no significant peak at 2330) (Nujol is a Trade Hark).

The following Examples illustrate the invention: Example 1 Sodium clavulanate (290 mg) in water (1 ml) was passed through Amberlite IP-120 calcium salt (10 ml wet resin).

The eluate (20 ml) was concentrated to less than 1 ml volume and acetonitrile (10 ml) added. Fine crystals of calcium di-clavulanate dihydrate were obtained which had i.r. absorbances thus: 1782 (8-lactam 0=0), 1695 (C=C), 1605 cm}· (CO2"). Water (by Karl Fischer): 7.A%, calcium diclavulanate dihydrate requires 7.6%. 64704 SsssleJ ρ...... Prsparatlon of Resin in MFei-rz /7:/.7 Antealits 13-120 resit (SCO ri) ees- ε;/; i~t:o a cejrwa (15° H . x M ) and hydrochloric acid 1.1 & .7zz.co: passed through ths resin until ths 77 -J:v offiuent was consistently cslcw C.3. ana resin -'’as t-isn. washed with distillid water (initially upflow mi ihcu domil-sw) until rh-5 pH ci ths ·:;ζ.·ά co:, distantly cc about 3.3. A ablucian af calcium chloride d/J h; wa.s than pam-d through the resin (hy dow.-.fl .;.?.·) mail ths pS oi the percolate dreppad to lorn thm l.C, lurcher calcium chloride solution was paasei through tZ:e &ii& until ths pH oi the percolate --.¾... aa...s2sdii.; at 3.33.5. lit rscin was then washed (tp downflow) with distilled water (aloat 2 1) until aha pH of the percolate was consistently approxinaaily -a Sodium clavulanate tetrehydraae (equivalent to 30 g of purs free acid) was made up to 300 al with distilled water. The solution was stirred with ’i?orit{ (segistacea Trade Mark) gsx charcoal (3 p) and fiiisrsd to give a clear pale yellow tinged solution at pH c.9. The solution was applied to the previously prepared 1.1-120 calcium cycle column st 200 ml/hour. 7/hen loading ---::.3 complete the column was then washed wial distilled at 200 sl/bour. 4^705 As the calcium salt began to be eluted the pH of the eluate changed to about 6.0. Fractions (approximately 60 ml) were then collected until a small aliquot of the final fraction produced little or no precipitation with acetone. This final fraction was colourless and had a pH of about 6.6. The first collected aliquot was discarded and the remaining aliquots were then combined to yield the desired solution of calcium clavulanate. (if desired the sodium clavulanate tetrahydrate may bs 10 replaced by equivalent amounts of potassium clavulanate or lithium clavulanate). c. Preparation of Crystalline Calcium Clavulanate Dihydrate The solution prepared as described above (370 sal) was stirred and acetone slowly added. After about 3.5 volumes of acetone had been added a slightly hazyprecipitate formed and was filtered off via Celite (Registered Trade Mark). Further acetous was added to the solution until a total t f of 15 volumes had been added. The resulting solid was filtered off to give a pale buff crystalline material.

This voluminous material collapsed on the filter and was then washed with acetone (3 x 150 ml) and pressed down on the filter to remove residual acetone. The solid was then dried under reduced pressure (about 10 torr for 18 hours) to yield the desired crystalline calcium clavulanate dihydrate (28 g, total water 6.¾ purity >90%). - 10 4 4 7 0 4 The low moisture contents in the above sample probablyresulted from drying under reduced pressure. Avoidance of reduced pressures leads to the preparation of crystals containing amounts of water closer to the theoretical amount needed for the dihydrate. It will be therefore understood that in this example air drying st the final step is usually to be preferred. - 11 Example 3 a. Sodium clavulanate tetrahydrate (150 mg) was dissolved in distilled water (l ml) and passed down a column of Amberlite IR-120 resin (Ca2' fora, «*7 ml wet resin). Tbe resin was then washed with distilled water (25 ml). She eluate was evaporated under reduced pressure at ambient temperature (about 22°C) to a syrup (^0.5 ml) and then triturated with acetonitrile (25 ml). She calcium salt crystallised, and it was cooled to 2-3°C for 2 hours, collected by filtration and washed with dry ether (25 ml). The product was air-dried to yield the desired crystalline calcium di-clavulanate dihydrate (75 mg of substantially pure product, water content i>7.4%) b. Amberlite IR-120 in the calcium form was produced as follows; The resin (Ηψ form, 20 ml wet resin, exchange capacity 38 m. moles) in water (50 ml) was treated with calcium hydroxide (0.5 g, excess) with stirring. The excess calcium hydroxide was removed by passing a current of distilled water up through a column containing the resin ('back-washing’) until the eluate had a pH approximately 8-8.5. (This also removes the’fines’-debris and minor organic impurities).

Claims (15)

1. A process for the preparation of crystalline calcium di-clavulanate dihydrate which comprises contacting an aqueous solution of a salt of clavulanic acid other than 5 the calcium salt with a cation exchange resin in the calcium form and eluting the thus formed calcium diclavulanate from the resin to yield a solution of calcium ii-clavulanate substantially free iiOJi Cct UXvJiiis 0 GiiuZ? than calcium and thereafter causing the crystallisation lo of the calcium di-clavulanate dihydrate from the solution and isolating the desired crystalline salt.

2. A process as claimed in claim 1 wherein the original salt of clavulanic acid is the lithium, sodium or potassium salt. 15

3. A process as claimed in claim 1 wherein the original salt of clavulanic acid is the sodium salt.

4. A process as claimed in any of claims 1-3 wherein the resin is a cross-linked polystyrene-divinylbenzene co-polymer substituted by sulphonic acid groups in the 20 form of the calcium salt.

5. A process as claimed in any of claims 1-4 wherein the quantity of resin used provides an exchange capacity of at least 10 times the total exchangeable cation capacity in the solution to be applied. - 13

6. « A process as claimed in any of claims 1-5 wherein the contacting of the solution with the resin takes the form of percolation through a bed of resin.

7. A process as claimed in any of claims 1-6 5 wherein the solution of the salt to be exchanged contains 2 = 30% w/v of the salt of clavulanic acid.

8. » A process as claimed in claim 7 wherein the solution contains 8 to 20% w/v of the salt.

9. A process as claimed in any of claims 1-8 io wherein the crystallisation of the calcium di-clavulanate dihydrate is initiated by the addition of a water miscible organic solvent.

10. A process as claimed in claim 9 wherein the solvent volume is reduced prior to the addition of the organic 15 solvent.

11. A process as claimed in any of claims 1-10 wherein the crystals are dried at atmospheric pressure.

12. A process as claimed in claim 1 substantially as described in any Example herein. - 14 4 4 7 0 IJ. Crystalline calcium di-clavulanate dihydrate whenever prepared hy a process as claimed in any of claims 1-12.

13. 14. A pharmaceutical composition which comprises the 5 compound claimed in claim 13 and a pharmaceutically acceptable carrier therefor.

14. 15« A composition as claimed, in claim 14 adapted for oral administration. lo. A composition as claimed in claim 14 or 15 which 10 also comprises a penicillin or cephalosporin.

15. 17. A composition as claimed in claim 15 which comprises ampicillin anhydrate* ampicillin trihydrate, pharmaceutically acceptable salt of ampicillin, amoxycillin trihydrate or a pharmaceutically acceptable salt 15 of amoxycillin.