Supramolecular approach for synthesis and functionalization of cyclic macromolecules

Abstract

This report highlights our recent findings concerning the synthesis of cyclic polymers based on supramolecular chemistry as well as the stereochemical recognition of helices by a cyclic macromolecule consisting of helical peptides and porphyrins. The first part will focus on an electrostatic self-assembly and covalent fixation strategy for the efficient synthesis of cyclic polymers. It has been shown that a unimeric polymer assembly is formed exclusively from the linear polymer precursor having cyclic ammonium salt end groups carrying dicarboxylate counter ions. An effective synthesis of cyclic polymers has been achieved by the subsequent covalent transformation of the ammonium salt groups. The process has been extended to the synthesis of cyclic macromonomers, which produced a unique polymer network having both covalent and mechanical linkages. The second part will focus on the stereochemical recognition of helices by a cyclic host. α-Aminoisobutyric acid (Aib) peptide-based cyclic hosts having metalloporphyrin units have been synthesized for guest binding and chiroptical sensing. By using these cavities, biologically important “peptide bundling” has been realized through complexation of helical peptide guests, where the three helical chains, two of which are from the host and one from the guest, are harmonized stereochemically in a confined cavity, leading to intense chiroptical outputs in the absorption bands of the metalloporphyrin units. The selective peptide bundling events based on helical senses of the host/guest molecules has also been achieved with a chiral conformational matching.