Peptide Stapling by Crosslinking Two Amines with α-Ketoaldehydes through Diverse Modified Glyoxal-Lysine Dimer Linkers

Solvent-Dependent Chemoselectivity Switch to Arg-Lys Imidazole Cross-Links

Herein, we report a trifluoroethanol-mediated, chemoselective method for the formation of Arg-Lys imidazole cross-links with methylglyoxal and its application in the selective macrocyclization of peptides between Lys and Arg and the late-stage diversification of Lys-containing peptides with guanidine. Our findings highlight the critical role of solvent choice in controlling chemoselectivity, providing valuable insights into solvent-dependent peptide modification.

Rhodium(I)-Catalyzed Cascade Annulation of 1,n-Diynyl Nitrones to 3,4-Fused Fully Substituted Furans

A method for the assembly of fully substituted furans containing a 3,4-fused 5-8-membered carbocycle, heterocycle, or spirocycle from rhodium(I)-catalyzed and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP)-assisted cascade annulation of 1,n-diynyl nitrones has been developed.

Synthesis of N-H Aziridines from Unactivated Olefins Using Hydroxylamine-O-Sulfonic Acids as Aminating Agent

Herein, we presented a practical methodology for the intermolecular aziridination of alkenes, using HOSA as the aminating agent, alongside pyridine or piperidine as the base, within HFIP solvent system. Notably, this approach showcases excellent reactivity, especially with nonactivated alkenes, and facilitates the transformation of various alkenes substrates, including mono-, di-, tri, and tetra-substituted alkenes, into aziridines with moderate to excellent yield. This method presents a promising avenue for synthesizing aziridines from a wide range of alkenes, featuring the benefits of straightforward operation, mild reaction conditions, extensive substrate compatibility, and scalability.

Formaldehyde-Mediated Hydride Liberation of Alkylamines for Intermolecular Reactions in Hexafluoroisopropanol

The ability of alkylamines to spontaneously liberate hydride ions is typically restrained, except under specific intramolecular reaction settings. Herein, we demonstrate that this reactivity can be unlocked through simple treatment with formaldehyde in hexafluoroisopropanol (HFIP) solvent, thereby enabling various intermolecular hydride transfer reactions of alkylamines under mild conditions. Besides transformations of small molecules, these reactions enable unique late-stage modification of complex peptides. Mechanistic investigations uncover that the key to these intermolecular hydride transfer processes lies in the accommodating conformation of solvent-mediated macrocyclic transition states, where the aggregates of HFIP molecules act as dexterous proton shuttles. Importantly, negative hyperconjugation between the lone electron pair of nitrogen and the antibonding orbital of amine's α C-H bond plays a critical role in the C-H activation, promoting its hydride liberation.