Catechin and epicatechin were enantioseparated by high-performance liquid chromatography (HPLC) with a phenyl column and aqueous mobile phases containing 0.05% (w/v) and 0.6% (w/v) of β-cyclodextrin for catechin and epicatechin, respectively. β-Cyclodextrin was found to be scarcely retained on a phenyl column. Consequently, it was suggested that catechin, which was eluted earlier than epicatechin, formed more stable inclusion complex with β-cyclodextrin than epicatechin and earlier eluted enantiomers, (-)-catechin and (+)-epicatechin, formed more stable diastereomer complexes with β-cyclodextrin than the respective enantiomers. This was confirmed by β-cyclodextrin-modified micellar electrokinetic chromatography and Benesi-Hildebrand plots by fluorescence spectrophotometry. Effect of sugars (D-sucrose, D-glucose, and D-fructose) on the epimerization of (+)-catechin and (+)-epicatechin by heating was investigated by HPLC with a β-cyclodextrin stepwise elution mode, in which two kinds of aqueous eluents containing different concentrations of β-cyclodextrin were used by turns. The epimerization of the two enantiomers was suppressed only when D-fructose was added. Separation of ten kinds of catechins including catechin and epicatechin enantiomers was investigated by a β-cyclodextrin linear gradient HPLC elution mode without using organic solvents, where two kinds of aqueous eluents containing different concentrations of β-cyclodextrin were used with changing their ratio gradually. These catechins in a green tea infusion could be separated successfully by this method.
Keywords: Catechin, β-cyclodextrin; Phenyl column, Chiral separation, Gradient elution.
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