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(.)L(3)], has been assessed as an effective chiral derivatising agent for the determination of the enantiomeric purity of a-hydroxy acids in aqueous solution. The complex displays superior chemical shift non-equivalence (Delta Delta delta similar to 2-11 ppm) for the diastereomeric resonances of interest compared to lanthanide shift reagents reported in the literature (Delta Delta delta < 0.1 ppm, typically). H-1 NMR studies have also revealed that SSS-[Ln(.)L(3)] can be used to determine the absolute configuration of a-amino acids at physiological pH, in water. The ability of SSS-[Ln(.)L(3)] 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.