Larger Groups, Smaller Enantioselectivity? Two Anthracene-Containing, Pyridino-Crown Ether-Based Fluorescent Sensor Molecules

(R,R)- and (S,S)-enantiomers of anthracene-containing pyridino-18-crown-6 ether having tert-butyl groups at the stereogenic centers were prepared with the aim of achieving higher enantioselectivity than for the reported (S,S)-analogue having isobutyl groups. The enantiomeric recognition abilities of the new sensor molecules toward chiral protonated primary amines and amino acid esters were studied in acetonitrile by UV–vis and fluorescence spectroscopies. The pKa values of these pyridino-crown ethers and their reported (S,S)-analogues having methyl or isobutyl groups have also been determined in acetonitrile

Push or Pull for a Better Selectivity? A Study on the Electronic Effects of Substituents of the Pyridine Ring on the Enantiomeric Recognition of Chiral Pyridino-18-Crown-6 Ethers

Seven dimethyl-substituted optically active pyridino-18-crown-6 ethers containing various substituents at position 4 of the pyridine ring were studied with regards to the electron-donating and -withdrawing effects of substituents on enantiomeric recognition. In order to compile this set of compounds, we prepared four novel pyridino-18-crown-6 ethers, including an intermediate of a new synthetic route for a formerly reported crown ether. The discriminating ability of these pyridino-crown ethers with C2-symmetry toward the enantiomers of protonated primary amines was examined by isothermal titration calorimetry