Enantioseparation of beta-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 beta-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 2moles/mole cyclodextrin, and sulfopropylated-beta-CD (SP4-beta-CD) with a degree of substitution of 4moles/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.