GB782926A - Purification of polymyxin - Google Patents

Abstract

Polymyxin is recovered from an aqueous liquid containing it by contacting the liquid with an ion exchange material which derives its exchange capacity from carboxyl groups, thereby adsorbing the polymyxin on to the said ionexchange material, eluting the polymyxin with an electrolyte, contacting the eluate with an ionexchange material A in order to remove anion impurities and with an ion exchange material B to remove cation impurities and then recovering the purified polymyxin thus produced. The polymyxin solution is any aqueous solution containing it including a fermentation broth, the unfiltered broth being preferred since residual polymyxin retained in the bacterial cells is adsorbed. The carboxyl ion-exchange material may be a copolymer of acrylic or methacrylic acid with divinyl benzene, e.g. Amberlite IRC50, Permutit H70 and Zeocarb 226, or a condensation product of formaldehyde and resorcyclic acid, e.g. Wofatit C. The resin may be used in the free acid form or wholly or in part as a salt with a weakly basic cation such as ammonium. It is preferred to use the resin in the acid form and to add the weakly basic substance, e.g. aqueous ammonia, continuously or intermittently to the broth during adsorption to maintain the pH of the effluent between 6 and 7. The preferred eluant is aqueous mineral acid, e.g. sulphuric or hydrochloric. Material A is an anion exchange material having a basic nitrogen, especially modified phenol-formaldehyde polymers having amine groups or styrene polymers having quaternary amine groups, e.g. Amberlite IR4B and Amberlite IRA400, and is used in the hydroxyl form. Material B is a cationexchange material possessing strongly acidic groups, especially sulphonic acid groups, e.g. Amberlite IR120, which is a sulphonated styrene copolymer. Cations present as impurities are adsorbed while polymyxin is largely unadsorbed. A mixed bed of ion exchange materials A and B may be used. The polymyxin is recovered from the purified solution by adjusting the pH to 3 to 4, preferably using ion exchange material A, concentrating, and adding alkali, e.g. aqueous ammonia, to pH above 7 in order to precipitate the polymyxin. Heating to 70 DEG C. facilitates precipitation. The adsorption may be batch or continuous. The continuous process is illustrated in the drawing (not shown) by equipment consisting of two columns of the carboxylic ion-exchange material and one of ion-exchange material B, a vessel for the eluant and a vessel for ion-exchange material A. The micro-organism may be Bacillus polymyxa or B. aerosporus. Reference has been directed by the Comptroller to Specification 742,589.