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·L³], has been assessed as an effective chiral derivatising agent for the determination of the enantiomeric purity of α-hydroxy acids in aqueous solution. The complex displays superior chemical shift non-equivalence (ΔΔδ ∼2–11 ppm) for the diastereomeric resonances of interest compared to lanthanide shift reagents reported in the literature (ΔΔδ <0.1 ppm, typically). ¹H NMR studies have also revealed that SSS-[Ln·L³] can be used to determine the absolute configuration of α-amino acids at physiological pH, in water. The ability of SSS-[Ln·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.