Monatshefte f€ ur Chemie 135, 1445–1453 (2004) DOI 10.1007/s00706-004-0232-4 Hydrolysis of the Peptide Bond in N-Acetylated L-Methionylglycine Catalyzed by Various Palladium(II) Complexes: Dependence of the Hydrolytic Reactions on the Nature of the Chelate Ligand in cis-[Pd(L)(H 2 O) 2 ] 21 Complexes Darko P. As ˇanin 1 , Snez ˇana Rajkovic ´ 1 , Dora Molnar-Gabor 2 , and Milos ˇ I. Djuran 1; 1 Department of Chemistry, University of Kragujevac, Faculty of Science, P.O. Box 60, 34000 Kragujevac, Serbia and Montenegro 2 Department of Chemistry, University of Novi Sad, Faculty of Science, 21000 Novi Sad, Serbia and Montenegro Received March 31, 2004; accepted (revised) June 2, 2004 Published online September 30, 2004 # Springer-Verlag 2004 Summary. Hydrolytic reactions between various palladium(II) complexes of the type cis- [Pd(L)(H 2 O) 2 ] 2þ in which L is ethylenediamine (en), 1,2-propylenediamine (1,2-pn), iso- butylenediamine (ibn), 1,2-diaminocyclohexane (1,2-dach), N-methylethylenediamine (Meen), N,N,N 0 ,N 0 -tetramethylethylenediamine (Me 4 en), S-methyl L-cysteine (MeS-L-HCys), L-methionine (L-HMet), and 2,5-dithiahexane (dth) and dipeptide N-acetylated L-methionylglycine (MeCOMet-Gly) were studied by 1 H NMR spectroscopy. The reactions were carried out in the pH range 2.0–2.5 and at 50  C. In all these reactions, palladium(II) complex bound to a methionine residue effects the regiose- lective cleavage of the amide bond involving the carboxylic group of methionine. We found that the rate of hydrolysis and mechanism of this reaction are strongly dependent from the nature of the chelate ligand L in palladium(II) complexes of the type cis-[Pd(L)(H 2 O) 2 ] 2þ . Keywords. Palladium(II) complexes; Hydrolysis; Methionine-containing peptides. Introduction Many biological processes involve hydrolysis of peptides and proteins, but rela- tively little is known about the mechanism of this reaction. The extreme inertness  Corresponding author. E-mail: djuran@knez.uis.kg.ac.yu