CHIRAL DISCRIMINATION BY ALBUMIN - A MECHANISTIC STUDY OF LIQUID-CHROMATOGRAPHIC OPTICAL RESOLUTION OF NONAROMATIC CARBOXYLIC-ACIDS

In order to get further insight into the mechanism by which bovine serum albumin (BSA) discriminates between enantiomers of organic acids, some radioisotopically labeled, nonaromatic carboxylic acids were studied under varying mobile phase conditions. It was found for a series of N-alkanoyl-DL-[H-3]leucines that the D-enantiomers were much more strongly retained and that the composition of the mobile phase could be adjusted to give very large (alpha > 20) enantiomeric separation factors. The elution order was consistent with what has been found earlier for other N-acyl derivatives as well as for N-arylcarbamoyl derivatives of simple aliphatic amino acids. A marked increase in the hydrophobic interaction of the D-enantiomers with the chiral phase was found upon a lowering of the mobile phase strength, conditions under which the L-form was only slightly influenced. These and other results are consistent with a chiral recognition model by which inclusion of the compound in a hydrophobic chiral cavity of BSA with simultaneous charge interaction is assumed to take place and whereby discrimination is determined by the steric bulk and orientation of the alpha-substituent. (C) 1993 Wiley-Liss, Inc.