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Mimics of protein secondary and tertiary structure offer rationally‐designed inhibitors of biomolecular interactions. β‐Sheet mimics have a storied history in bioorganic chemistry and are typically designed with synthetic or natural turn segments. We hypothesized that replacement of terminal inter‐β‐strand hydrogen bonds with hydrogen bond surrogates (HBS) may lead to conformationally‐defined macrocyclic β‐sheets without the requirement for natural or synthetic β‐turns, thereby providing a minimal mimic of a protein β‐sheet. To access turn‐less antiparallel β‐sheet mimics, we developed a facile solid phase synthesis protocol. We surveyed a dataset of protein β‐sheets for naturally observed interstrand side chain interactions. This bioinformatics survey highlighted an over‐abundance of aromatic–aromatic, cation‐π and ionic interactions in β‐sheets. In correspondence with natural β‐sheets, we find that minimal HBS mimics show robust β‐sheet formation when specific amino acid residue pairings are incorporated. In isolated β‐sheets, aromatic interactions endow superior conformational stability over ionic or cation‐π interactions. Circular dichroism and NMR spectroscopies, along with high‐resolution X‐ray crystallography, support our design principles. [ABSTRACT FROM AUTHOR]

RNA, unlike DNA, folds into a multitude of secondary and tertiary structures. This structural diversity has impeded the development of ligands that can sequence‐specifically target this biomolecule. We sought to develop ligands for double‐stranded RNA (dsRNA) segments, which are ubiquitous in RNA tertiary structure. The major groove of double‐stranded DNA is sequence‐specifically recognized by a range of dimeric helical transcription factors, including the basic leucine zippers (bZIP) and basic helix‐loop‐helix (bHLH) proteins; however, such simple structural motifs are not prevalent in RNA‐binding proteins. We interrogated the high‐resolution structures of DNA and RNA to identify requirements for a helix fork motif to occupy dsRNA major grooves akin to dsDNA. Our analysis suggested that the rigidity and angle of approach of dimeric helices in bZIP/bHLH motifs are not ideal for the binding of dsRNA major grooves. This investigation revealed that the replacement of the leucine zipper motifs in bHLH proteins with synthetic crosslinkers would allow recognition of dsRNA. We show that a model bHLH DNA‐binding motif does not bind dsRNA but can be reengineered as an RNA ligand. Based on this hypothesis, we rationally designed a miniature synthetic crosslinked helix fork (CHF) as a generalizable proteomimetic scaffold for targeting dsRNA. We evaluated several CHF constructs against a set of RNA and DNA hairpins to probe the specificity of the designed construct. Our studies reveal a new class of proteomimetics as an encodable platform for sequence‐specific recognition of dsRNA. [ABSTRACT FROM AUTHOR]

Radical addition to dehydroalanine (Dha) represents an appealing, modular strategy to access non‐canonical peptide analogues for drug discovery. Prior studies on radical addition to the Dha residue of peptides and proteins have demonstrated outstanding functional group compatibility, but the lack of stereoselectivity has limited the synthetic utility of this approach. Herein, we address this challenge by employing chiral nickel catalysts to control the stereoselectivity of radical addition to Dha on oligopeptides. The conditions accommodate a variety of primary and secondary electrophiles to introduce polyethylene glycol, biotin, halo‐tag, and hydrophobic and hydrophilic side chains to the peptide. The reaction features catalyst control to largely override substrate‐based control of stereochemical outcome for modification of short peptides. We anticipate that the discovery of chiral nickel complexes that confer catalyst control will allow rapid, late‐stage modification of peptides featuring nonnatural sidechains. [ABSTRACT FROM AUTHOR]

The design of a stimuli‐responsive peptide whose conformation is controlled by wavelength‐specific light and metal coordination is described. The peptide adopts a defined tertiary structure and its conformation can be modulated between an α‐helical coiled coil and β‐sheet. The peptide is designed with a hydrophobic interface to induce coiled coil formation and is based on a recently described strategy to obtain switchable helix dimers. Herein, we endowed the helix dimer with 8‐hydroxyquinoline (HQ) groups to achieve metal coordination and shift to a β‐sheet structure. It was found that the conformational shift only occurs upon introduction of Zn2+; other metal ions (Cu2+, Fe3+, Co2+, Mg2, and Ni2+) do not offer switching likely due to non‐specific metal‐peptide coordination. A control peptide lacking the metal‐coordinating residues does not show conformational switching with Zn2+ supporting the role of this metal in stabilizing the β‐sheet conformation in a defined manner. [ABSTRACT FROM AUTHOR]

Protein secondary and tertiary structure mimics have served as model systems to probe biophysical parameters that guide protein folding and as attractive reagents to modulate protein interactions. Here, we review contemporary methods to reproduce loop, helix, sheet, and coiled‐coil conformations in short peptides. [ABSTRACT FROM AUTHOR]

The article reviews the book "Organic Chemistry: Principles in Context: A Story Telling Historical Approach" by Mark M. Green.

The novel coronavirus SARS-CoV-2, which in humans leads to the disease COVID-19, has caused global disruption and more than 2 million fatalities since it first emerged in late 2019. As we write, infection rates are at their highest point globally and are rising extremely rapidly in some areas due to more infectious variants. The primary target of SARS-CoV-2 is the cellular receptor angiotensin-converting enzyme-2 (ACE2). Recent sequence analyses of the ACE2 gene predict that many nonhuman primates are also likely to be highly susceptible to infection. However, the anticipated risk is not equal across the Order. Furthermore, some taxonomic groups show high ACE2 amino acid conservation, while others exhibit high variability at this locus. As an example of the latter, analyses of strepsirrhine primate ACE2 sequences to date indicate large variation among lemurs and lorises compared to other primate clades despite low sampling effort. Here, we report ACE2 gene and protein sequences for 71 individual strepsirrhines, spanning 51 species and 19 genera. Our study reinforces previous results while finding additional variability in other strepsirrhine species, and suggests several clades of lemurs have high potential susceptibility to SARS-CoV-2 infection. Troublingly, some species, including the rare and endangered aye-aye (Daubentonia madagascariensis), as well as those in the genera Avahi and Propithecus, may be at high risk. Given that lemurs are endemic to Madagascar and among the primates at highest risk of extinction globally, further understanding of the potential threat of COVID-19 to their health should be a conservation priority. All feasible actions should be taken to limit their exposure to SARS-CoV-2., (© 2021 Wiley Periodicals LLC.)