Late-stage functionalization of peptides via a palladium-catalyzed C(sp³)-H activation strategy

Peptides hold great promise in proteomics, diagnostics and drug discovery. While natural peptides continue to be of key importance, chemically modified unnatural peptides have been found to show enhanced biological activities and improved therapeutic capabilities compared to their natural counterparts. Therefore, the development of efficient and versatile strategies to enable easy access to unnatural peptides is in high demand. In recent years, palladium-catalyzed direct functionalization of inert C(sp³)-H bonds has emerged as a powerful and straightforward synthetic strategy for late-stage modification of peptides. In this review, we summarize recent progress in this emerging field. For clarity, this review is organized into three sections according to the functionalization of the peptide side-chains at β-, γ-, and δ-positions.