Photoredox Ni-catalyzed peptide C(sp2)–O cross-coupling: from intermolecular reactions to side chain-to-tail macrocyclization
Ni/photoredox (4DPAIPN) dual catalysis enabled challenging peptide C(sp2)–O coupling reactions. Successful cross-coupling reactions were demonstrated with highly functionalized alcohols including side chains of amino acids (i.e., serine, threonine, tyrosine), trans-4-hydroxy-L-proline, alkyl alcohols, alkynylated alcohols, and carbohydrates. Coupling reactions between bromobenzoyl-capped peptides containing various side chains and either a protected serine building block or a serine-containing dipeptide also proceeded efficiently. Chemoselective C–O coupling (over C–N) was achieved in intermolecular reactions in the presence of a C-terminal primary amide. Furthermore, by judicious structural design in combination with computational modeling, we demonstrated side chain-to-tail macrocyclization of peptides containing a β-turn motif via C–O coupling. The methodology developed in this work brings new opportunities for late-stage diversification of complex linear and macrocyclic peptides.