An enantioselective NMR shift reagent for cationic aromatics

structure: see text] The water-soluble tetra l-prolinylmethyl derivative of a tetrasulfonated calix4]resorcarene is an effective chiral NMR solvating agent for compounds with bicyclic aromatic or indole rings. Complexation of bicyclic substrates with the calix4]resorcarene is likely promoted by hydrophobic effects. The bicyclic substrates have larger association constants with the calix4]resorcarene than similar phenyl-containing compounds. Substantial enantiomeric discrimination is observed for several resonances in the (1)H NMR spectra of these substrates.