Lanthanide-chiral carboxylate and chiral ester mixtures as NMR shift reagents.

Abstract

Achiral lanthanide tris beta-diketonate complexes are added to the acid and ester derivatives of the chiral NMR solvating agents dinitrobenzoyl-L-leucine and N-1-(1-naphthyl)ethylaminocarbonyl-L-valine to enhance enantiomeric discrimination. With the acid derivative, the solvating agent bonds directly to the lanthanide(III) complex to create an anionic species, and larger shifts are usually observed for the resonances of the enantiomer that associates more strongly with the solvating agent. With the ester derivative, the solvating agent generally does not bind to the lanthanide, whereas the substrate does. In this situation, the enantiomer that associates less strongly with the solvating agent exhibits the larger lanthanide-induced shifts. The effectiveness of adding neutral lanthanide complexes containing two beta-diketonate ligands and one chiral carboxylate ligand is compared to the anionic species with three beta-diketonate ligands and a chiral carboxylate ligand.