Investigation of a dual CD chiral CE system for separation of glitazone compounds

A dual CD-CE method for chiral separation of enantiomers of pioglitazone, rosiglitazone and balaglitazone was investigated for the purpose of optimizing the chiral separation. In a previous work a dual CD chiral CE method was used for investigation of glitazone compounds in drug substance and pharmaceutical formulation and the studies showed that all studied glitazones were racemic mixtures. This CE method could separate the enantiomers with a resolution (R(S)) of about 3. However, another study on single glitazone enantiomers pointed out that a higher R(S) is needed to achieve more accurate results for separation of a small amount of one enantiomer in the presence of a high amount of the other enantiomers. The focus of this investigation was thus directed toward the effect of CDs and the pH of the running buffer to achieve a better enantioseparation. Initially CE systems with each of heptakis(2,6-di-O-methyl)-beta-CD (DM-beta-CD) and heptakis(6-sulfobutylether)-beta-CD (SB-beta-CD) as single CD added were investigated at three different pH values (2.5, 5.0 and 9.3). After having chosen the best of these three pH values a dual CD system was further investigated and optimized. The optimization work was then focused on the concentration of the two CDs and the pH of the running buffer and was performed using factorial design experiments. A mixture of a DM-beta-CD and SB-beta-CD was found to be optimal and necessary to achieve enantioseparation with sufficiently high R(S). In order to further verify the importance of the SB-beta-CD, a CE system with the DM-beta-CD added and substitution or partial substitution of the SB-beta-CD by SDS was studied for comparison. (1)H-NMR studies were performed to get a more detailed understanding of the interactions between the glitazones and the CDs used.The optimized dual CD-CE method for chiral separation of the enantiomers of pioglitazone, rosiglitazone and balaglitazone using a running buffer containing 50 mM borate buffer pH 9.7, 12 mM of SB-beta-CD and 3 mM of DM-beta-CD provided a high R(S) (R(S) between 5.5 and 8.8).