Helical Folding of Meta-Connected Aromatic Oligoureas

Cavity-containing aromatic oligoamide foldamers and macrocycles: progress and future perspectives

As a major class of foldamers, aromatic oligoamide foldamers have attracted intense interest. The rigidity of aromatic residues and amide linkages allows the development of foldamers with readily predictable, stable conformations. Aromatic oligoamide foldamers having backbones fully constrained by intramolecular hydrogen bonds have attracted wide attention. Depending on their lengths, such foldamers adopt crescent or helical conformations with highly negative inner cavities. Cyclizing the backbone of the aromatic oligoamides affords the corresponding macrocycles which are characterised by persistent shapes and non-deformable inner cavities. With their defined, inner cavities, such aromatic oligoamide foldamers and macrocycles have served as hosts for cationic and polar guests, and as transmembrane channels for transporting ions and molecules. Recent synthetic progress resulted in the construction of multi-turn hollow helices that offer three-dimensional inner pores with adjustable depth. Reducing the number of backbone-constraining hydrogen bonds leads to oligoamides which, with their partially constrained backbones, undergo either solvent- or guest-dependent folding. One class of such aromatic olgioamide foldamders, which offer multiple backbone amide NH groups as hydrogen-bond donors, are designed to bind anions with adjustable affinities.

The helical supramolecular assembly of oligopyridylamide foldamers in aqueous media can be guided by adenosine diphosphates

A metal-free and achiral tri-pyridylamide foldamer, DM 11, containing a critical naphthalimide side chain self-assembles in a left-handed helical manner in the presence of chiral adenosine phosphates, under physiological conditions. Surprisingly, a very high degree of helicity in the foldamer assemblies was observed with ADP compared to other nucleoside phosphates, including ATP.

Self-Assembly of Size-Controlled m-Pyridine-Urea Oligomers and Their Biomimetic Chloride Ion Channels

The m-pyridine urea (mPU) oligomer was constructed by using the intramolecular hydrogen bond formed by the pyridine nitrogen atom and the NH of urea and the intermolecular hydrogen bond of the terminal carbonyl group and the NH of urea. Due to the synergistic effect of hydrogen bonds, mPU oligomer folds and exhibits strong self-assembly behaviour. Affected by folding, mPU oligomer generates a twisted plane, and one of its important features is that the carbonyl group of the urea group orientates outwards from the twisted plane, while the NHs tend to direct inward. This feature is beneficial to NH attraction for electron-rich species. Among them, the trimer self-assembles into helical nanotubes, and can efficiently transport chloride ions. This study provides a novel and efficient strategy for constructing self-assembled biomimetic materials for electron-rich species transmission.

Oligo(5-amino-N-acylanthranilic acids): Amide Bond Formation without Coupling Reagent and Folding upon Binding Anions

Oligomers of 5-amino-N-acylanthranilic acid, previously unknown aromatic oligoamides that cannot be obtained with known amide coupling methods, are synthesized based on a new, highly efficient amide-bond formation strategy that takes advantage of the ring-opening of benzoxazinone derivatives. These oligoamides offer multiple backbone NH groups as H-bond donors which, in the presence of iodide or chloride ion, are convergently arranged and H-bonded, which enforces a folded, crescent conformation. These aromatic oligoamides provide a versatile platform based on which anion-dependent foldamers, or anion binders with tunable affinity and specificity, are being constructed.

Multiturn Hollow Helices: Synthesis and Folding of Long Aromatic Oligoamides

Aromatic oligoamides adopting helical conformations are synthesized by coupling carboxyl-terminated basic units having two, four, and eight residues to amine-terminated oligomer precursors. Coupling yields show no noticeable reduction with the size of the basic units or the final product. One- and two-dimensional NMR spectroscopy and computational studies demonstrate the reliable helical folding of these oligomers. The X-ray structure of 16mer 7 reveals a compact, multiturn helix having a 9 Å inner pore.

Conformationally Programmable Chiral Foldamers with Compact and Extended Domains Controlled by Monomer Structure

Foldamers are an important class of abiotic macromolecules, with potential therapeutic applications in the disruption of protein–protein interactions. The majority adopt a single conformational motif such as a helix. A class of foldamer is now introduced where the choice of heterocycle within each monomer, coupled with a strong conformation‐determining dipole repulsion effect, allows both helical and extended conformations to be selected. Combining these monomers into hetero‐oligomers enables highly controlled exploration of conformational space and projection of side‐chains along multiple vectors. The foldamers were rapidly constructed via an iterative deprotection‐cross‐coupling sequence, and their solid‐ and solution‐phase conformations were analysed by X‐ray crystallography and NMR and CD spectroscopy. These molecules may find applications in protein surface recognition where the interface does not involve canonical peptide secondary structures.