Triple C–H\nActivation/Annulation: In Situ Construction\nof Fluorescent Peptides

Herein, we report a Rh(III)-catalyzed triple C–H\nactivation–annulation\nof Phe-based peptides with alkynes for the preparation of fluorescent\npeptides. The robustness of this protocol is reflected by a broad\nsubstrate scope, high atom- and step-economy, and excellent chemo-\nand site-selectivity. An in situ generated polycyclic aromatic hydrocarbon\ncarbocation as a fluorophore exhibits good fluorescence properties\n(maximum emission wavelength up to 628 nm) and low cell cytotoxicity.\nThe synthetic utility of this method is further demonstrated by versatile\nproduct applications in bioconjugation with the protein BSA and specifically\ntargeting lysosomes and mitochondria of live mammalian cells.