Helical Aromatic Oligoamides:  Reliable, Readily Predictable Folding from the Combination of Rigidified Structural Motifs

Abstract

Factors responsible for the folding of aromatic oligoamides with backbones rigidified by local three-center H-bonds were investigated. The stability of the three-center H-bonds was quantified by the half-lives of amide proton-deuterium exchange reactions, which show that the three-center H-bonds were largely intact at room temperature in the oligomer examined. This result is consistent with our current and previous 2D NMR studies. The overall helical conformation of nonamer 1 was found by variable-temperature NOESY studies to be dynamic. As temperature rose, the end-to-end NOEs rapidly disappeared, while the amide side chain NOEs were still readily detectable, corresponding to the "breath" and stretching of the helix by slightly twisting the local H-bonded rings. Based on the simple repetition of the same structural motif and local conformational preference, undecamer 2 was found to fold into well-defined helical conformation. The predictability of the folding of these backbone-rigidified aromatic oligoamides was demonstrated by a simple modeling method using structural parameters from oligomers with known crystal structures. The reliability and generality of the modeling methods were shown by the excellent agreement between the modeled structures corresponding to 1 and 2 and data from NOESY studies.

Strong Stacking between F⋅⋅⋅HN Hydrogen‐Bonded Foldamers and Fullerenes: Formation of Supramolecular Nano Networks

“…[15,17] We have recently demonstrated that rationally designed hydrogenbonded foldamers from aromatic oligoamides represent versatile self-assembling scaffolds [18] and acyclic receptors for the recognition of discrete guests. [19] Herein, we describe that 1) strong interactions are generated between F···H À N hydrogen-bonding-induced foldamers and fullerenes (C 60 and C 70 ), and 2) that these interactions may be utilized for the construction of structurally unique supramolecular nano networks.…”

Observations on the Influence of Precursor Conformations on Macrocyclization Reactions

“…14 More recently, conformational and configurational pre-organization in macrocyclization has been studied, e.g. folding of oligoamides, 15 synthesis of cycloparaphenylens, 16 and peptidomimetic macrocycles. 17 In order to address the dearth of novel macrocyclic scaffolds for screening campaigns, we have undertaken a research program aimed at developing methods for facile synthesis of macrocycles from simple precursors.…”

Shape-persistent macrocycles: efficient extraction towards lanthanide and actinide elements

“…Recently, the one-step condensation reaction of monomeric diamines and diacid chlorides was found to lead to the highly efficient formation of a series of shape-persistent cyclized oligoamide products in yield of 60-80% [10]. Different from ordinary cyclic aromatic oligoamides that are often associated with flexible amide bonds, these macrocycles are backbone rigidified by intramolecular hydrogen bonds with few degrees of conformation freedom, and thus have well-defined cavities containing introverted O atoms [11].…”