Evaluation of 3,5-Dimethylphenyl Carbamoylated α-, β-, and γ-Cyclodextrins as Chiral Stationary Phases for HPLC

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Abstract
Optical resolving power of chiral stationary phases (CSPs) containing 3,5-dimethylphenyl carbamoylated β-cyclodextrin chemically bonded to silica was compared with those of two commercial stationary phases containing carbamoylated β-cyclodextrin (β-CD), Cyclobond I SN and Cyclobond I DMP. For most of examined 14 racemates, higher selectivities were obtained on our CSPs than on the commercial CSPs. This may be ascribed to the higher degree of substitution of carbamate groups on β-CD and to the opposite orientation of the immobilized β-CD on our materials. The present CSPs were evaluated under reverse, normal and supercritical fluid chromatographic conditions. The highest selectivities were usually obtained under normal phase chromatographic conditions. The influence of cyclodextrins, α-, β- and γ-CD, on the enantioselectivity was compared. Each CSP containing different cyclodextrin showed the highest enantioselectivity for different racemates. By using silica particles with different average pore size (60, 100 and 300 Å), the influences of the amount and surface concentration of immobilized carbamoylated β-CD on the enantioselectivity were studied for similar amounts of immobilized β-CD. Higher enantioselectivity was observed for the material with high surface concentration.