Enantioseparation of β-substituted tryptophan analogues with modified cyclodextrins by capillary zone electrophoresis

Direct capillary zone electrophoretic methods were developed for the separation of the enantiomers of unnatural P-substituted tryptophan analogues such as erythro- and threo-beta-methyl-, beta-2-propyl-, beta-3-pentyl-, beta-phenyl- and beta-2,5-dimethoxyphenyltryptophan. Cyclodextrins (CDs) were chosen as chiral selectors because of their favorable properties (stability, commercial availability, low cost, UV transparency, inertness, etc.). Capillary zone electrophoresis was carried out using sulfopropylated-alpha-CD (SP2-alpha-CD), sulfopropylated-beta-CD (SP2-beta-CD) both with a degree of substitution of 2 moles/mole cyclodextrin, and sulfopropylated-beta-CD (SP4-beta-CD) with a degree of substitution of 4 moles/mole beta-cyclodextrin. With this technique all compounds investigated are baseline resolved using different background electrolytes and chiral additives. The elution sequence was determined in all cases. (C) 2009 Elsevier B.V. All rights reserved.