Diastereotopic fluorine substituents as 19F NMR probes of screw-sense preference in helical foldamers

Abstract

Ligating simple amino alcohol or amino ester monomers containing enantiotopic fluorine substituents to the C-terminus of a helical peptide places the fluorine atoms in diastereotopic environments, and gives two distinct and easily identifiable signals in the ¹⁹F NMR spectrum. In the case of a dynamically inverting helix built from achiral monomers, the chemical shift separation between the ¹⁹F signals provides a simple means of analysing the ratio of screw-sense conformers in the oligomer, in cases where an asymmetric bias leads to a screw-sense preference.