Late‐stage C−H Functionalization of Tryptophan‐Containing Peptides with Thianthrenium Salts: Conjugation and Ligation

Abstract Bioorthogonal late‐stage diversification of structurally complex peptides bears enormous potential for drug discovery and molecular imaging, among other applications. Herein, we report on a palladium‐catalyzed C−H arylation of tryptophan‐containing peptides with readily accessible and modular arylthianthrenium salts. Under exceedingly mild reaction conditions, the late‐stage diversification of structurally complex peptides was accomplished. The tunability and ease of preparation of arylthianthrenium salts allowed the expedient stitching of tryptophan‐containing peptides with drug, natural product, and peptidic scaffolds by forging sterically congested biaryl linkages. The robustness of the palladium catalysis regime was reflected by the full tolerance of a plethora of sensitive and coordinating functional groups. Hence, our manifold enabled efficient access to highly decorated, labelled, conjugated, and ligated linear and cyclic peptides.