A new chiral lanthanide NMR probe for the determination of the enantiomeric purity of α-hydroxy acids and the absolute configuration of α-amino acids in water

Abstract

A water-soluble, enantiopure lanthanide complex, SSS-[Ln x L3], has been assessed as an effective chiral derivatizing agent for the determination of the enantiomeric purity of alpha-hydroxy acids in aqueous solution. The complex displays superior chemical shift non-equivalence (DeltaDeltadelta approximately 2-11 ppm) for the diastereomeric resonances of interest compared to lanthanide shift reagents reported in the literature (DeltaDeltadelta <0.1 ppm, typically). 1H NMR studies have also revealed that SSS-[Ln x L3] can be used to determine the absolute configuration of alpha-amino acids at physiological pH, in water. The ability of SSS-[Ln x L3] to signal anion binding and, in particular, to distinguish between diastereomers through optical techniques such as lanthanide luminescence and circular dichroism has also been assessed.