Homeomorphic Isomerism in a Peptidic Macrobicycle

Bicyclic compounds can exist as in–out isomers, which can interconvert when one chain passes through the ring that it bridges, as shown schematically on the right. A novel peptide macrobicycle exhibits this property and two separate in–out isomers, which can be distinguished by their NMR spectra because of stereocenters in one of the three chains, have been separated and found to interconvert in solution over several days.