Dysprosium(III)-diethylenetriaminepentaacetate complexes of aminocyclodextrins as chiral NMR shift reagents

A metal chelating ligand is bonded to alpha-, beta-, and gamma-cyclodextrin by the reaction of diethylenetraminepentaacetic dianhydride with the corre sponding 6-mono- and 2-mono(amine)cyclodextrin. Adding Dy(III) to the cyclo dextrin derivatives causes shifts in the H-1-NMR spectra of substrates such as propranolol, tryptophan, aspartame, carbinoxamine, pheniramine, doxylam ine, and 1-anilino-8-naphthalenesulfonate. The Dy(III)-induced shifts enhan ce the enantiomeric resolution in the NMR spectra of several substrates. En hancements in enantiomeric resolution using cyclodextrin derivatives with t he amine tether are compared to previously described compounds in which the chelating ligand is attached through an ethylenediamine tether. In general , the Dy(III) complex of the 6-beta-derivative with the amine tether is a m ore effective chiral resolving agent than the complex with the ethylenediam ine tether. The opposite trend is observed with the 2-beta-derivatives. The presence of the chelating ligand in the 2-beta-derivative hinders certain substrates from entering the cavity. For cationic substrates, evidence sugg ests that a cooperative association involving inclusion in the cavity and a ssociation with the Dy(III) unit occurs. Enhancements in enantiomeric resol ution in the spectrum of tryptophan are greater for the secondary alpha- an d gamma-derivatives than the beta-derivative. (C) 2000 Wiley-Liss, Inc.