Building Proficient Enzymes with Foldamer Prostheses

α-Amino-iso-butyric acid foldamers terminated with rhodium(I) N-heterocyclic carbene catalysts

To investigate how remotely induced changes in ligand folding might affect catalysis by organometallic complexes, dynamic α‐amino‐iso‐butyric acid (Aib) peptide foldamers bearing rhodium(I) N‐heterocyclic carbene (NHC) complexes have been synthesized and studied. X‐ray crystallography of a foldamer with an N‐terminal azide and a C‐terminal Rh(NHC)(Cl)(diene) complex showed a racemate with a chiral axis in the Rh(NHC) complex and a distorted 3₁₀ helical body. Replacing the azide with either one or two chiral L‐α‐methylvaline (L‐αMeVal) residues gave diastereoisomeric foldamers that each possessed point, helical and axial chirality. NMR spectroscopy revealed an unequal ratio of diastereoisomers for some foldamers, indicating that the chiral conformational preference of the N‐terminal residue(s) was relayed down the 1 nm helical body to the axially chiral Rh(NHC) complex. Although the remote chiral residue(s) did not affect the stereoselectivity of hydrosilylation reactions catalysed by these foldamers, these studies suggest a potential pathway towards remote conformational control of organometallic catalysts.

Desolvation of Peptide Bond by O to S Substitution Impacts Protein Stability

Amino acid side chains are key to fine-tuning the microenvironment polarity in proteins composed of polar amide bonds. Here, we report that substituting an oxygen atom of the backbone amide bond with sulfur atom desolvates the thioamide bond, thereby increasing its lipophilicity. The impact of such local desolvation by O to S substitution in proteins was tested by synthesizing thioamidated variants of Pin1 WW domain. We observe that a thioamide acts in synergy with nonpolar amino acid side chains to reduce the microenvironment polarity and increase protein stability by more than 14 °C. Through favorable van der Waals and hydrogen bonding interactions, this single atom substitution significantly stabilizes proteins without altering the amino acid sequence and structure of the native protein.

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.

Interfacing native and non-native peptides: using Affimers to recognise α-helix mimicking foldamers

Selection methods are used to identify Affimers that recognise α-helix mimicking N-alkylated aromatic oligoamides thus demonstrating foldamer and natural α-amino acid codes are compatible.

An α-Helix-Mimicking 12,13-Helix: Designed α/β/γ-Foldamers as Selective Inhibitors of Protein-Protein Interactions

A major current challenge in bioorganic chemistry is the identification of effective mimics of protein secondary structures that act as inhibitors of protein-protein interactions (PPIs). In this work, trans-2-aminocyclobutanecarboxylic acid (tACBC) was used as the key β-amino acid component in the design of α/β/γ-peptides to structurally mimic a native α-helix. Suitably functionalized α/β/γ-peptides assume an α-helix-mimicking 12,13-helix conformation in solution, exhibit enhanced proteolytic stability in comparison to the wild-type α-peptide parent sequence from which they are derived, and act as selective inhibitors of the p53/hDM2 interaction.

Metallopeptoids as efficient biomimetic catalysts

Metallopeptoid catalysts incorporating phenanthroline–copper and TEMPO, and at least one non-catalytic group perform in the oxidation of various benzylic, allylic and aliphatic primary alcohols with a TON of up to 16 times higher than a mixture of the two catalytic groups or the peptoid dimer that is lacking the non-catalytic group.