Boronic Acid‐Assisted Cellular Delivery of Pallado‐Fingers for Enhanced Pd(II)‐Mediated De‐Propargylation in Mammalian Cells

Transition‐metal catalysis in living cells offers a valuable tool in chemical biology for intracellular transformations; however, it is hindered by insufficient catalyst uptake and rapid deactivation in the intracellular environment. This study introduces “Pallado‐fingers”: Pd(II) complexes derived from a minimal Cys2His2 zinc finger domain, engineered into a His2 scaffold (ZFP2H) to facilitate precise metal coordination and catalysis. Using a fluorogenic propargylated dye, this work demonstrates efficient Pd(II)‐mediated de‐propargylation in buffer solutions, with activity modulated by the co‐ligand/counterion in the order PPh 3 > OAc − > Cl − . Notably, this trend is reversed within mammalian cells (A549, HeLa, U2OS), with ZFP2H–PdCl 2 emerging as the most effective intracellular catalyst, highlighting the significant influence of the cellular environment on catalyst performance. To address limitations associated with peptide internalization, 4‐carboxyphenylboronic acid units were installed to lysine residues, yielding ZFP2HBA that exhibits markedly improved cellular uptake. The complexation of ZFP2HBA with PdCl 2 induces a tenfold increase in intracellular de‐propargylation, as quantified by flow cytometry and visualized through fluorescence microscopy, followed by an exploration of the internalization pathway using different endocytosis inhibitors. This research establishes boronic acid–assisted delivery of Pallado‐fingers as a straightforward, modular strategy to enhance transition metal complex catalysis in living mammalian cells.