Investigation of the ring-closing metathesis of peptides in water

Anionic Olefin Metathesis Catalysts Enable Modification of Unprotected Biomolecules in Water

Stability problems have limited the uptake of cationic olefin metathesis catalysts in chemical biology. Described herein are anionic catalysts that improve water-solubility, robustness, and compatibility with biomolecules such as DNA. A sulfonate tag is installed on the cyclic (alkyl)(amino) carbene (CAAC) ligand platform, chosen for resistance to degradation by nucleophiles, base, water, and β-elimination. Hoveyda-Grubbs catalysts bearing the sulfonated CAAC ligands deliver record productivity in metathesis of unprotected carbohydrates and nucleosides at neutral pH. Decomposed catalyst has negligible impact on metathesis selectivity, whereas N-heterocyclic carbene (NHC) catalysts degrade rapidly in water and cause extensive C=C migration.

Thioether analogues of the pituitary neuropeptide oxytocin via thiol–ene macrocyclisation of unprotected peptides

A radical mediated approach to macrocyclisation of unprotected peptides via Thiol-Ene Click for synthesis of disulfide analogues is reported.

Macrocyclization strategies for cyclic peptides and peptidomimetics

Peptides are a growing therapeutic class due to their unique spatial characteristics that can target traditionally "undruggable" protein-protein interactions and surfaces. Despite their advantages, peptides must overcome several key shortcomings to be considered as drug leads, including their high conformational flexibility and susceptibility to proteolytic cleavage. As a general approach for overcoming these challenges, macrocyclization of a linear peptide can usually improve these characteristics. Their synthetic accessibility makes peptide macrocycles very attractive, though traditional synthetic methods for macrocyclization can be challenging for peptides, especially for head-to-tail cyclization. This review provides an updated summary of the available macrocyclization chemistries, such as traditional lactam formation, azide-alkyne cycloadditions, ring-closing metathesis as well as unconventional cyclization reactions, and it is structured according to the obtained functional groups. Keeping peptide chemistry and screening in mind, the focus is given to reactions applicable in solution, on solid supports, and compatible with contemporary screening methods.

Ring-closing metathesis of unprotected peptides in water

Ring-closing metathesis (RCM) is an attractive reaction for the preparation of artificially designed peptides. Until now, RCM has been used for fully or partially protected peptides. Herein, the first RCM of unprotected peptides in water was achieved using a water-soluble Ru catalyst.

Rational design of new cyclic analogues of the antimicrobial lipopeptide tridecaptin A1

Cyclization of tridecaptin A₁ imparts stability to the d-peptidase TriF.

Non-ribosomal peptides (NRPs) are a rich source of antibiotic candidates. However, it was recently discovered that resistance to NRPs can be mediated by d-stereoselective peptidases. The tridecaptins, a class of NRPs that selectively target Gram-negative bacteria, are degraded by the d-peptidase TriF. Through analysis of a solution NMR structure of tridecaptin A₁, we have rationally synthesized new cyclic tridecaptin analogues that retain strong antimicrobial activity and are resistant to TriF.

Allyl Sulfides: Reactive Substrates for Olefin Metathesis

Allyl sulfides have gained traction in recent years as promoters for olefin metathesis. The high reactivity of allyl sulfides in olefin metathesis is remarkable, given that many sulfur-containing substrates are incompatible with ruthenium-based olefin metathesis catalysts. In stark contrast, allyl sulfides actually enhance the rate of metathesis in comparison with other alkenes, when matched with a suitable catalyst. This review examines how the high reactivity of allyl sulfides in olefin metathesis has been harnessed in diverse areas of synthesis. In the cases examined, allyl sulfides have been explicitly incorporated into substrates to promote olefin metathesis. Recent insights into catalyst considerations, applications in chemical and biochemical synthesis, and future opportunities are discussed.

Allyl sulphides in olefin metathesis: catalyst considerations and traceless promotion of ring-closing metathesis

Allyl sulphides provoke rapid olefin metathesis when matched with an appropriate catalyst. In relay metathesis, allyl sulphides can serve as traceless promoters that facilitate the synthesis of non-sulphide targets.

Bioorthogonal chemistry: strategies and recent developments

The use of covalent chemistry to track biomolecules in their native environment-a focus of bioorthogonal chemistry-has received considerable interest recently among chemical biologists and organic chemists alike. To facilitate wider adoption of bioorthogonal chemistry in biomedical research, a central effort in the last few years has been focused on the optimization of a few known bioorthogonal reactions, particularly with respect to reaction kinetics improvement, novel genetic encoding systems, and fluorogenic reactions for bioimaging. During these optimizations, three strategies have emerged, including the use of ring strain for substrate activation in the cycloaddition reactions, the discovery of new ligands and privileged substrates for accelerated metal-catalysed reactions, and the design of substrates with pre-fluorophore structures for rapid "turn-on" fluorescence after selective bioorthogonal reactions. In addition, new bioorthogonal reactions based on either modified or completely unprecedented reactant pairs have been reported. Finally, increasing attention has been directed toward the development of mutually exclusive bioorthogonal reactions and their applications in multiple labeling of a biomolecule in cell culture. In this feature article, we wish to present the recent progress in bioorthogonal reactions through the selected examples that highlight the above-mentioned strategies. Considering increasing sophistication in bioorthogonal chemistry development, we strive to project several exciting opportunities where bioorthogonal chemistry can make a unique contribution to biology in the near future.