Stereodynamic Chemosensor with Selective Circular Dichroism and Fluorescence Readout for in Situ Determination of Absolute Configuration, Enantiomeric Excess, and Concentration of Chiral Compounds

A stereodynamic chemosensor having a parallel arrangement of a substrate-binding salicylaldehyde unit and an adjacent pyridyl N-oxide fluorophore undergoes rapid condensation with chiral amino alcohols and subsequent asymmetric transformation of the first kind toward a single rotamer. Crystallographic analysis shows that the concomitant central-to-axial chirality imprinting is controlled by minimization of steric repulsion and by intramolecular hydrogen bonding between the bound amino alcohol and the proximate N-oxide group. The substrate binding event results in strong CD effects and characteristic fluorescence changes which can be used for instantaneous in situ determination of the absolute configuration, enantiomeric composition and total concentration of a variety of chiral amino alcohols. This chemosensing approach avoids time-consuming workup and purification steps, and it is applicable to minute sample amounts which reduces the use of solvents and limits waste production.