Application of centrifugal counter-current chromatography to the separation of macrolide antibiotic analogues I. Selection of solvent systems based on solubility and partition coefficient investigations

As the first part of our studies on counter-current chromatography. the met hodology for selecting suitable solvent systems was established based on de tailed investigations of solubility and partition coefficients (log K) of m acrolide antibiotic analogues. The solubility of two important macrolides, ascomycin and FK-506, was measured in a series of common solvents, where th eir polarities were ranked with dielectric constants, The partition coeffic ients of the two macrolides were compared in various binary, ternary, quate rnary solvent systems. Hexane-tert.-butyl methyl ether-methanol-water syste m was selected based on suitable log K of solutes and hydrogen-bonding prop erties of solvents. In the further optimisation of composition proportions in the multicomponent solvent system, hexane-tert.-butyl methyl ether-metha nol-water (1:3:6:5) showed the best solvent selectivity by giving the most prominent difference of partition coefficient (Delta log K) between ascomyc in and FK-506, With this solvent system, a baseline preparative separation of these two very closely related 23-membered macrolide antibiotics was suc cessfully achieved by employing the newly introduced Quattro counter-curren t chromatograph. (C) 1999 Elsevier Science B.V: All rights reserved.