Advanced Tool for Chiral Separations of Anionic and Zwitterionic (Metalla)carboranes: Supercritical Fluid Chromatography.

Abstract

The continuous expansion of research in the field of stable carboranes and their wide potential in the drug design require carrying out fundamental studies regarding their chiral separations. Although supercritical fluid chromatography (SFC) is a viable technique for fast enantioseparations, no investigation concerning boron cluster compounds has been done yet. We aimed at the development of a straightforward method enabling chiral separations of racemic mixtures of anionic cluster carboranes and metallacarboranes that represent an analytical challenge. The fast gradient screening testing nine polysaccharide-based columns was used. The key parameters affecting the selectivity were the type of chiral selector, the type of alcohol, and the base in cosolvent. Moreover, the addition of acetonitrile or water to the cosolvent was identified as an effective tool for decreasing the analysis time while preserving the resolution. After the optimization, the chiral separations of 19 out of 20 selected compounds were achieved in less than 10 min. These results demonstrate the clear advantage of SFC over chiral separations using HPLC in terms of both analysis time and structural variety of successfully separated compounds.