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

4-Sulfobutyl ether derivatives of cyclomaltoheptaose (beta-cyclodextrin) (SBE-beta-CD) are being developed as parenterally safe solubilizing and stabilizing agents. SBE-beta-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-beta-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-beta-CD mixture was calculated.

Effect of alkyl chain length and degree of substitution on the complexation of sulfoalkyl ether beta-cyclodextrins with steroids.

This study was designed to test how the sulfoalkyl ether (SAE) modification of beta-cyclodextrin (beta-CD) affects the binding capacity of testosterone and progesterone, thereby enhancing their solubility. The SAE-beta-CD derivatives contain either sulfopropyl ether (SPE) or sulfobutyl ether (SBE) groups on the 2-, 3-, and 6-hydroxyl positions of the dextrose moieties. SAE-beta-CDs are a mixture of positional and regional isomers containing from one to as many as 12 SAE groups per CD. The effect of chain length and the degree of substitution on complexation behavior was investigated by the phase-solubility method. The results were compared with those obtained with beta-CD, where possible, and with hydroxypropyl-beta-CD (HP-beta-CD). To determine the effect of degree of substitution (DS) on the binding, mixtures of SAE-beta-CDs with multiple substitution levels and varying average degrees of substitution were studied as well as mixtures of SAE-beta-CDs that contained the same degree of substitution. Mixtures that contained SAE-beta-CDs of the same degree of substitution were isolated from the multiple substitution level mixtures by ion-exchange chromatography and purified for investigation. Unlike the parent beta-CD, linear increases in the apparent solubilities of testosterone and progesterone were observed, and the binding potentials were comparable to those of beta-CD or better. The results demonstrate that the binding potentials of the SAE-beta-CD derivatives were dependent on the guest molecule, the degree of substitution, and the alkyl ether chain length. Our previous study showed the inhibition of complexation by direct sulfonation of the beta-CD. However, in the present work, interferences with the charged sulfonate groups were avoided by repositioning them away from the cavity. Increasing the degree of substitution assisted in complex formation; however, its effects were limited. Reduction of the alkyl chain length, as in the case of SPE-beta-CD compared with SBE-beta-CD, decreased the complexation potential. This decrease in complexation potential was further suppressed with an increase in the number of substituents placed on the CD torus. Generally, the binding potential of SAE-beta-CD derivatives increased with increasing alkyl chain length. However, placement of more than an optimum number of SAE groups on the CD torus resulted in inhibition of complexation.

Evaluation of the utility of capillary electrophoresis for the analysis of sulfobutyl ether beta-cyclodextrin mixtures.

A capillary electrophoresis (CE) method for the analysis of a sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) mixture is described. The SBE-beta-CD has been prepared as a parenterally safe solubilizing agent and has historically been characterized by elemental analysis and nuclear magnetic resonance spectroscopy. While these methods provide gross values for the degree of substitution, the CE method described resolves the mixture of positional and regional isomers based on the degree of SBE substitution. The method uses benzoic acid in the running buffer and detects the CD by a decrease in background absorbance of the benzoic acid due to complexation. The necessity of a defined column was sequence between injections was evaluated. The reproducibility of migration times and peak areas/heights for 10 components of the mixture was determined. The modular CE system gave a relative standard deviation of 2.5% (n = 3) for six of the 10 peaks. Further refinements (pH buffer effects) were explored to improve the reproducibility with remaining components. The method was used to evaluate the reproducibility of the synthesis (21 different lots) and the effect of reaction variables (time, temperature and base) on the composition pattern of the modified CD.