Enantioselective HPLC of Liquid Crystals Bearing a Small and Flexible 2-Methylbutyl Chiral Center.

The conformationally flexible 2-methylbutyl structural motif represents a small chiral center, which cannot engage in polar interactions with chiral stationary phases (e.g., hydrogen bonds), which often play a key role in enantioselective recognition. In this contribution, racemic liquid crystalline materials sharing the 2-methylbutyl group were analyzed by enantioselective high-performance liquid chromatography, and the studied analyte set also included diastereomeric compounds with additional chiral centers based on the lactate unit. As the non-chiral parts of the analytes are rigid and bulky, this disbalance in size and flexibility further complicates enantioseparation of such materials. The separations were done under either polar organic mode or reversed-phase liquid chromatography conditions to enhance the less polar interactions with the chiral stationary phases. Two polysaccharide chiral stationary phases were employed-coated tris(5-chloro-2-methylcarbamate) amylose and immobilized tris(3-chloro-5-methylphenylcarbamate) amylose. Baseline enantioseparation of all racemic samples was accomplished in less than 9 minutes. Effects of analytes' structural variations on enantioselectivity are discussed, and the differences between results on the two chiral stationary phases are assessed.