Separation of cis-/trans-diastereomers and enantiomers of aminoindanol and aminoindan using capillary electrophoresis.

Aminoindanol poses an interesting separation problem because it contains two chiral centers and exists as four stereoisomers. The capillary electrophoretic separation of the cis- and the larger trans-diastereomers of aminoindanol is simply achieved by pH control of the tris buffer background electrolyte. In accordance with theory, maximum separation occurs at the pH equal to the mean value of the pKA values of the isomers. The separation of the enantiomers of both the cis- and trans-diastereomers is effected using the chiral selector alpha-cyclodextrin (alpha-CD). The cis-enantiomeric pair is better separated than the trans-pair, as reflected by the larger difference in the binding constants, K, for the cis-enantiomers with the alpha-CD, K values were measured from the change in electrophoretic mobility with selector concentration, over the temperature range 15 degrees C-35 degrees C. The associated delta H degrees and delta S degrees values were determined for the transfer of each enantiomer from the aqueous buffer phase to the alpha-CD phase. The corresponding K values and associated thermodynamic quantities were also measured for the aminoindan enantiomers, which lack the hydroxyl group of aminoindanol. The effect of chiral selector size was evaluated for the aminoindanols by measuring K and the associated values using beta-CD, which has a larger cavity than the alpha-CD. The better fit of the larger trans-isomers leads to larger K values for the trans-isomers but reduced Ks for the cis-. The gamma-CD cavity is too large to produce chiral discrimination. The low solubility of the beta-CD requires the addition of high concentrations of urea to the tris buffer. Urea has little effect on the K values of the trans-aminoindanols with alpha-CD, but leads to larger values for the cis-isomers.