En Route to a Heterogeneous Catalytic Direct Peptide Bond Formation by Zr-Based Metal-Organic Framework Catalysts

The catalytic activity of Zr6-based metal-organic frameworks (Zr-MOFs) toward peptide bond formation is investigated using dipeptide cyclization as a model reaction. Unlike previous catalysts, Zr-MOFs largely tolerate water, reactions are carried out under ambient conditions, the catalyst is recyclable and no additives to activate the COOH group are necessary. The reaction mechanism was assessed by detailed mechanistic and computational studies and features a Lewis acid activation of carboxylate groups by Zr centers toward amine addition in which an alkoxy ligand on adjacent Zr sites assists in lowering the barrier of key proton transfers. The proposed concepts were also used to study the formation of intermolecular peptide bond formation.