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A Novel Peptide Stapling Strategy with Built-in Fluorescence via Direct Late-stage C(sp2)-H Olefination of Tryptophan.

Fluorescent stapled peptides are important chemical tools for detecting intracellular distribution, protein/protein interactions and localization of target proteins. These peptides are usually labelled with bulky-sized fluorophores through reactive functional groups, which may alter the physical properties and biological activities of peptides. Herein, we developed a unique strategy for synthesizing novel stapled peptides with built-in fluorescence. The stapled peptides were prepared through Rh-catalyzed C(sp2)-H olefination in tryptophan (Trp) residues using pyridine/pyrimidine as the directing groups under mild conditions. This method displays good regioselectivity and high efficiency. Furthermore, as a proof of concept for its biological applications, stapled peptides without additional fluorophore 9a and 9b were constructed for cell imaging study. These peptides displayed strong binding affinity toward integrin αvβ3 in A549 cells by cell imaging experiments. Notably they demonstrated even better anticancer activity than commercial antagonist cyclic (RGDfK). The method will provide robust tools to peptide macrocyclization field.