CHIRAL RECOGNITION BY THE COPPER(II) COMPLEX OF EOXY-6-N-(2-METHYLAMINOPYRIDINE)-BETA-CYCLODEXTRIN

A modified beta-cyclodextrin bearing a 2-aminomethylpyridine binding s ite for copper (II) -6-[N-(2-methylamino)pyridine)]-beta-cyclodextrin, CDampy) was synthesized by C-6-monofunctionalization. The acid-base p roperties of the new ligand in aqueous solution were investigated by p otentiometry and calorimetry, and its conformations as a function of p H were studied by NMR and circular dichroism (c.d.). The formation of binary copper(II) complexes was studied by potentiometry, EPR, and c.d .. The copper(II) complex was used as chiral selector for the HPLC ena ntiomeric separation of underivatized aromatic amino acids. Enantiosel ectivity in the overall stability constants of the ternary complexes w ith D- or L-Trp was detected by potentiometry, whereas the complexes o f the Ala enantiomers did not show any difference in stability. These results were consistent with a preferred cis coordination of the amino group of the ligand and of the amino acid in the ternary complexes (' 'cis effect''), which leads to the inclusion of the aromatic side chai n of D-Trp, but not of that of L-Trp. In Trp-containing ternary comple xes, the two enantiomers showed differences in the fluorescence lifeti me distribution, consistent with only one conformer of D-Trp and two c onformers of L-Trp, and the latter were found to be more accessible to fluorescence quenching by acrylamide and KI. (C) 1997 Wiley-Liss, Inc .