HYDROLYSIS OF METHIONINE-CONTAINING PEPTIDES IN BINUCLEAR AND MONONUCLEAR PALLADIUM(II) COMPLEXES

The diaqua complexes of trans-[Pd(py)(2)Cl-2] (Py-pyridine), cis-[Pd(e dta)Cl-2] (edta-ethylene diamine tetraacetic acid) (complex A), cis-[P d(temed)Cl-2] (temed-N,N,N',N'-tetramethylethylene diamine) and cis-1, 2-bis(2-formylglycinebenzenesulfenyl)ethane Pd(II) dichloride (complex C) react with methionine-containing dipeptides (AcMet-aa) (aa-amino a cid) via the thioether group in the methionyl sidechain. The trans-Pd( py)(2)(H2O)(2)](2+) and cis-[Pd(temed)(H2O)(2)](2+) yield binuclear co mplex [Pd-2(mu-AcMet-aa)(2)(H2O)(4)](4+), the diaqua complexes of comp lex A and complex C yield mononuclear complexes, [PdL(AcMet-aa)(H2O)]( 2+) (L-edta, 1,2-bis(2-formylglycinebenzenesulfenyl)ethane). These rea ctions and hydrolytic cleavage of the Met-aa amide band in the coordin ated AcMet-aa are conveniently monitored by H-1 NMR spectroscopy. The trans-Pd(py)(2)(H2O)(2)](2+) is a very efficient promoter. The hydroly tic rate promoted by it is almost equal to that promoted by [Pd(H2O)(3 )(OH)](+), the fastest one up to now. Although reaction of trans-[Pd(p y)(2)(H2O)(2)](2+) and cis-[Pd(temed)(H2O)(2)](2+) with AcMet-aa yield the same binuclear complex, [Pd-2(mu-AcMet-aa)(2)(H2O)(2)](4+), the k inetic data showed that the hydrolytic rate promoted by cis-[Pd(temed) (H2O)(2)](2+) was actually controlled by temed release. The new mononu clear complexes, [PdL(AcMet-aa)(H2O](2+), observed for the first time, are also hydrolytically active. It is of interest because they are cl osely associated with protein cleavage promoted by simple mononuclear Pd(II) complexes. (C) 1998 Elsevier Science Ltd. All rights reserved.