In Situ Generation of Quinoliziniums for Dual Visible Light-Induced Gold(III)-Catalyzed Alkynylation and Peptide Modification

A new approach of dual visible light-induced gold(III)-catalyzed alkynylation and its application in selective modification of alkyne-linked peptides has been developed. The bis-cyclometalated gold(III) complex exhibited dual roles of (1) in situ generation of quinolizinium-based photosensitizer (λ_em=500 – 594 nm) and (2) alkynylation of iminium ions. Under optimized conditions, alkynylated products were afforded in good yields up to 73 %. The application of this strategy in selective modification of alkyne-linked peptides gave modified peptides in up to 67 % conversion. Our dual visible light/gold(III) catalysis exemplifies the potential of merging photocatalysis and transition metal catalysis to develop novel bioconjugation.