Applying Metallo-Organic Ligand Design Principles to the Stereoselective Synthesis of a Peptide-Based Pd2L4X4 Cage

The rational and controlled synthesis of metallo-organic cages using polyaromatic ligands is well established in the literature. There is a strong interest to advance this field towards the use of chiral ligands capable of yielding cages in a stereoselective manner. Herein, we demonstrate that the classical approach for designing metallo-organic cages can be translated to polyproline peptides, a biocompatible class of chiral ligands. We have successfully designed a series of polyprolines, which mimic the topology of ditopic polyaromatic ligands, to achieve the stereoselective synthesis of a novel Pd lantern cage. This cage exhibits excellent stability in water and demonstrates the stabilization of a highly reactive species in solution. This work will pave the way towards the stereospecific synthesis of more complex, functionalized peptide-based metallo-cages.