Selective cleavage of peptides and proteins is one of the most important procedures in analytical biochemistry. However, the extreme inertness of the amide bond with a half-life estimated to be up to 600 years at physiological pH and temperature makes this task highly challenging. Several proteolytic enzymes are available, but they are usually not regioselective and cleave proteins in short fragments which are difficult to identify. The few existing synthetic reagents require harsh conditions and even when applied in great excess over the substrate, they tend to cleave proteins with partial selectivity and low yields. In our lab metal-substituted polyoxometalates (POMs) have been developed as promising reagents for amide bond hydrolysis.¹ In this study, monolacunary Lindqvist anions [W₅O₁₈]^6- were used as ligands for Zr(IV). The hydrolysis of various dipeptides in the presence of the complex (Me₄N)₂[W₅O₁₈Zr(H₂O)₃] was studied by ¹H and ¹³C NMR spectroscopy and based on detailed kinetic experiments the molecular mechanism of the peptide bond cleavage was elucidated.