Fractionation and characterization of 4-sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin)

Abstract

4-Sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin) (SBE-β-CD) are being developed as parenterally safe solubilizing and stabilizing agents. SBE-β-CDs are a mixture of positional and regional isomers containing from one to as many as twelve sulfobutyl ether (SBE) groups per cyclodextrin. Capillary electrophoretic (CE) analysis of these mixtures resolves these isomers based on the molar degree of SBE substitution (ds), and the electropherogram shows an almost symmetrical distribution of SBE incorporation centered around the band which represents the apparent average degree of substitution for the mixture. The objectives of this study were to isolate the different substitution bands for their characterization and to evaluate their mass contribution to the mixture. Mixtures of SBE-β-CDs containing from mono- up to deca-SBE substitutions were fractionated by preparative anion-exchange chromatography with salt concentration gradient elution. The bands for each ds were well resolved as characterized by CE analysis with indirect UV detection. The isolated materials were desalted and lyophilized to obtain white solids, which were then characterized by nuclear magnetic resonance ( 1H NMR) spectroscopy, capillary electrophoresis (CE), and fast-atom-bombardment mass spectrometry (FABMS). The CE molar response factor of each ds was then determined, and the actual percent mass composition of a SBE-β-CD mixture was calculated. 4-Sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin) of ds 1–10 were prepared, separated by anion-exchange chromatography, analyzed by capillary electrophoresis, and characterized by 1H NMR spectroscopy and FAB mass spectrometry.