Synthesis, analytical characterization and capillary electrophoretic use of the single-isomer...

This contribution reports the synthesis, characterization and capillary electrophoretic application of heptakis-(6-O-sulfobutyl-ether)-β-cyclodextrin sodium salt, (6-(SB)₇-β-CD). The compound was obtained through a five-steps synthesis and it represents the first example of single-isomer sulfobutylated cyclodextrin that carries the negatively charged functions exclusively on its primary side and it is unmodified on the lower rim. The purity of each intermediate was determined by appropriate liquid chromatographic methods, while the isomeric purity of the final product was established by an ad-hoc developed HPLC method based on a CD-Screen-IEC column. The structural identification of 6-(SB)₇-β-CD was carried out by 1D, 2D NMR spectroscopy and ESI-MS. The chiral separation ability of 6-(SB)₇-β-CD was studied by chiral capillary electrophoresis using the single-isomer host as a background electrolyte additive to separate the enantiomers of a representative set of pharmacologically significant model compounds such as verapamil, dapoxetine, ondansetron, propranolol, atenolol, metoprolol, carvedilol, terbutaline, amlodipine and tadalafil. The enantiomer migration order and the effects of the selector concentration on the enantiorecognition properties were investigated. NMR spectroscopy was applied to deepen and further confirm the host-guest interactions and in the case of the model compound dapoxetine a potential representation for the supramolecular assembly was developed based on the dataset collected by the extensive 2D NMR analysis. This single-isomer chiral selector offers a new alternative to the widely applied randomly sulfobutylated- and sulfated-beta-cylodextrins as well as to the single-isomer sulfated and carboxymethylated derivatives in chiral separations.