α,ε-Hybrid Peptide Foldamers: Self-Assembly of Peptide with Trans Carbon–Carbon Double Bonds in the Backbone and Its Saturated Analogue

Abstract

The effect of geometrically rigid trans α,β-unsaturated ε-amino acids on the structure, folding, and assembly of α,ε-hybrid peptide foldamers has been reported. From single-crystal diffraction analysis, the unsaturated tetrapeptide 1 has stapler-pin-like structure but without intramolecular hydrogen bond. The asymmetric unit has two molecules that are stabilized by multiple intermolecular hydrogen bonding interactions as well as π–π stacking interactions between the aromatic rings of 3-aminocinnamic acid. Peptide 1 does not form organogel. But on hydrogenation, peptide 1 provides the saturated α,ε-hybrid peptide foldamer 2 , which forms instant gel in most of the aromatic solvents. The gel exhibits high stability. The unsaturated peptide 1 has porous microsphere morphology, but saturated analogue 2 has ribbonlike morphology. The gel has been used efficiently for removal of cationic organic pollutants from waste water.

Exploring Helical Folding in Oligomers of Cyclopentane‐Based ϵ‐Amino Acids: A Computational Study

“…designed an α/ϵ‐hybrid hexapeptide containing l ‐Ala and ( S )‐C‐linked carbo‐ϵ‐amino acid [( S )‐ϵ‐Caa (x) ; Figure 1c] constituents in 1 : 1 alteration and suggested its structure as a novel mixed H 14/12 helix by 1 H NMR experiments [39] . The synthesis and structural characterization of another α/ϵ‐hybrid tetrapeptide composed of Aib and 3‐(3‐aminophenyl)propanoic acid (Figure 1d) in 1 : 1 alteration were reported by Haldar and his co‐workers [40] . Temperature‐dependent 1 H NMR experiments of the α/ϵ‐hybrid tetrapeptide supported the formation of a ribbon‐like structure in CDCl 3 .…”

The Diverse World of Foldamers: Endless Possibilities of Self-Assembly

“…The absence of intramolecular hydrogen bonding characterized a peculiar organogel-forming α,ε-hybrid tetrapeptide, showing alternating residues of Aib and the aromatic ε-amino acid AcaH (3-(3-aminophenyl)propionic acid, indicated as the hydrogenated form of its precursor Aca, ( E )-3-aminocinnamic acid), as shown in Figure 22 e [ 254 ]. According to UV–vis and FT-IR spectroscopies, in organic solvents (e.g., p -xylene, toluene and 1,2-dichlorobenzene) intermolecular hydrogen bonding, and possibly also the π–π stacking interactions observed by single-crystal XRD, drove the fast formation of highly stable organogels, also called xerogels, containing ribbon-like fibers (ca.…”

“…[ 252 ]); ( e ) Structure of Boc-(Aib-Aca) 2 -OMe α/ε-foldamer (Ref. [ 254 ]); ( f ) General structure of Boc-Gpn-Aib-Xaa-Aib-OMe α/γ-foldamers (Ref. [ 256 ]); ( g ) SEM images of (left) microspheres formed by the unsaturated α,ε-hybrid tetrapeptide and (right) ribbon-like entangled fibers formed in p -xylene by the saturated α,ε-hybrid tetrapeptide (adapted with permission from Ref.…”

“…[ 256 ]); ( g ) SEM images of (left) microspheres formed by the unsaturated α,ε-hybrid tetrapeptide and (right) ribbon-like entangled fibers formed in p -xylene by the saturated α,ε-hybrid tetrapeptide (adapted with permission from Ref. [ 254 ]); ( h ) General structure of Boc-Aic n -OEt γ-foldamers (Ref. [ 257 ]).…”

“…[250]); (d) General structure of Aib-Amb α/γ-foldamers (n = 0, 1, 3 and 7) (Ref. [252]); (e) Structure of Boc-(Aib-Aca) 2 -OMe α/ε-foldamer (Ref [254][256]…”