Helical Foldamers Incorporating Photoswitchable Residues for Light-Mediated Modulation of Conformational Preference

An E unsaturated fumaramide linkage may be introduced into Aib peptide foldamer structures by standard coupling methods and photoisomerized to its Z (maleamide) isomer by irradiation with UV light. As a result of the photoisomerization, a new hydrogen-bonded contact becomes possible between the peptide domains located on either side of the unsaturated linkage. Using the fumaramide/maleamide linker to couple a chiral and an achiral fragment allows the change in hydrogen bond network to communicate a conformational preference, inducing a screw sense preference in the achiral domain of the maleamide-linked foldamers that is absent from the fumaramides. Evidence for the induced screw sense preference is provided by NMR and CD, and also by the turning on by light of the diastereoselectivity of a peptide chain extension reaction. The fumaramide/maleamide linker thus acts as a "conformational photodiode" that conducts stereochemical information as a result of irradiation by UV light.