Hydrogen bonding-mediated oligobenzamide foldamer receptors that efficiently bind a triol and saccharides in chloroform

Abstract

The self-assembly of two novel intramolecular hydrogen bonding-driven foldamers is described. Two linear symmetric aromatic amide oligomers, 1 and 2, which are incorporated with benzene subunits, have been prepared by continuous amide-coupling reactions. The existence of three-centred hydrogen bonds in the oligomers and consequently the folding conformation of the oligomers in solution have been characterized by ¹H NMR experiments and by comparing them with the reported solid state structure of the identical structural skeleton. Molecular modeling reveals a rigid crescent conformation for 1 with a cavity of ca. 0.9 nm in diameter and a helical conformation for 2 with a cavity of ca. 0.8 nm in diameter. Due to the existence of intramolecular hydrogen bonding, all the CO groups in both oligomers are located inwardly. The binding of 1 and 2 towards a trihydroxyl guest and four saccharide derivatives have been investigated with ¹H NMR, fluorescence, and circular dichroism spectroscopy. The association constants of the corresponding 1 ∶ 1 complexes have been determined by fluorescence titration experiments.