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 C-2-symmetry toward the enantiomers of protonated primary amines was examined by isothermal titration calorimetry.