Remote conformational responses to enantiomeric excess in carboxylate-binding dynamic foldamers

Abstract

A zinc(ii)-capped Aib oligomer senses enantiomeric excess and transmits this information to a remote reporter group which provides a 1H spectroscopic output.

Molecular Recognition by Zn(II)‐Capped Dynamic Foldamers

“…The X‐ray crystal structure of Zn( 1 ) ⋅ 2ClO 4 has been reported, so samples of both Zn( 2 ) ⋅ 2ClO 4 and Zn( 3 ) ⋅ 2ClO 4 were subjected to crystallization trials. Although Zn( 3 ) ⋅ 2ClO 4 did not provide good quality crystals, Zn( 2 ) ⋅ 2ClO 4 did provide crystals from methanol that were suitable for structure determination by X‐ray crystallography.…”

“…Metal complexes of these BQPA‐capped Aib foldamers have been used to relay chemical information through the length of Aib foldamers to a reporter group, information that is encoded either in ligand shape (chiral ligands) or in the e.e . of a scalemic mixture of carboxylates . This relay terminates at a C‐terminal reporter group on the foldamer, such as a bispyrene group, difluorinated Aib, or a glycinamide (GlyNH 2 ) residue.…”

“…This relay terminates at a C‐terminal reporter group on the foldamer, such as a bispyrene group, difluorinated Aib, or a glycinamide (GlyNH 2 ) residue. The latter is a particularly well‐characterized and chemically stable reporter group . The 3 10 helical conformation of the foldamer renders the GlyNH 2 methylene protons diastereotopic, but since achiral Aib foldamers exist as a racemic mixture of left‐handed ( M ) and right‐handed ( P ) 3 10 helices, at fast exchange on the NMR timescale the methylene resonance coalesces to a single 2H signal.…”

“…. Although these BQPA‐capped Aib foldamers have proved to be remarkably successful for detecting chiral stimuli, the basic and nucleophilic BQPA headgroup limits subsequent chemical transformations of the C‐terminus. Simpler structural variants of BQPA are of interest, especially if they are more robust and easier to synthesise in better yield.…”

“…Using foldamer 1 as the inspiration for our design (Zn(II) complex shown in Figure ), two modifications were proposed. The first modification was replacement of the quinolinyl groups with pyridyl, providing analogue 2 that is capped with an N , N ‐bis(pyrid‐2‐ylmethyl)‐ N ‐(5’‐carboxypyrid‐2‐ylmethyl)amine (BPPA) group.…”