The first chiral HPLC separation of dicarba-nido-undecarborate anions and their chromatographic behavior

Boron cluster compounds are extensively studied due to their possible use in medicinal chemistry, mainly in the boron neutron capture anticancer therapy and as new innovative pharmacophores. Concerning this research, the chiral separations of exceptionally stable anionic 7,8-dicarba-nido-undecaborate(1-) and metal bis(dicarbollide (1-) derivatives with asymmetric substitutions remain the unsolved challenge of the chiral chromatography nowadays. Although the successful enantioseparation of some anionic 7,8-dicarba-nido-undecaborate(1-) ion derivatives were achieved in CZE with native beta-cyclodextrins, it has not been observed with HPLC, yet. This study aimed to systematically investigate the enantioseparation of selected compounds in HPLC using native beta-cyclodextrin and brominated beta-cyclodextrin. The findings revealed positively charged strong adsorption sites on a stationary phase, identified as the cationic metal impurities in the silica-gel backbone. All the anionic species under the study were at least partially enantioseparated when a chelating agent blocked these cationic sites. Consequently, the first-ever HPLC enantioseparations of the 7,8-dicarba-nido-undecaborates(1-) were achieved. The brominated beta-cyclodextrin seemed to be a better chiral selector for separation of these species, whereas the native beta-cyclodextrin separated the anionic cobalt bis(dicarbollide(1-). The results of this study bring new information concerning the chiral separation of anionic boron clusters and might be used in the chiral method development process on other chiral selectors. Furthermore, the possibility of chiral separation of these species could influence the ongoing research areas of anionic boron clusters.

Automated summary

The chiral separations of stable anionic boron cluster derivatives with asymmetric substitutions remain a challenge in chiral chromatography, but this study successfully achieved the first-ever HPLC enantioseparations of 7,8-dicarba-nido-undecaborates(1-) by blocking cationic sites on the stationary phase. Brominated beta-cyclodextrin showed better chiral selectivity for separation of these species, providing new insights into chiral separation of anionic boron clusters.