Palladium peptide complexes

The interaction of palladium(II) complexes with sulfur-containing peptides was studied by electrospray mass spectrometry.331... 

Kostic el al. discovered that Pd11 complexes, when attached to tryptophan residues, can rapidly cleave peptides in acetone solutions to which a stoichiometric amount of water is added, for hydrolysis.436 The indole tautomer in which a hydrogen has moved from the nitrogen to C(3) is named indolenine. Its palladium(II) complexes that are coordinated via the nitrogen atom have been characterized by X-ray crystallography and spectroscopic methods.451 Binuclear dimeric complexes between palladium(II) and indole-3-acetate involve cyclopalladation.452 Bidentate coordination to palladium(II) through the N(l) and the C(2) atoms occurs in binuclear complexes.453 Reactions of palladium(II) complexes with indole-3-acetamide and its derivatives produced new complexes of unusual structure. Various NMR, UV, IR, and mass spectral analyses have revealed bidentate coordination via the indole carbon C(3) and the amide oxygen.437... 

The highly regioselective hydrolysis of tryptophan-containing peptides with the [Pd(en)]2+ (en = H2NC2H4NH2) complex has been reported by Kostic and co-workers.436 The hydrolysis does not proceed without the palladium(II) complex. However, when equimolar amounts of a... 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

Kostic, N. M. Catalysis of selective cleavage of peptides and proteins with palladium(II) complexes, American Chemical Society, Washington, D. C. In Book of Abstracts, 212th ACS National Meeting, Orlando, FL, August 25-29, 1996. 

Peptide hydrolysis by platinum(II) (436) and palladium(II) complexes (437). In the latter case there is selective hydrolysis of the unactivated peptide bond in iV-acetylated L-histidylglycine the hydrolysis rate depends on the steric bulk of the catalyst. 

L. Zhu and N. M. Kostic, Toward artificial metallopeptidases mechanisms by which platinum(II) and palladium(II) complexes promote selective, fast hydrolysis of unactivated amide bonds in peptides, Inorganic Chemistry, vol. 31, no. 

D.xi.a. Hydrolysis and Hydration. The electrophilicity of cationic palladium(II) complexes has been taken advantage of in an interesting biomimetic method of selective cleavage of peptide bonds at histidine, methionine, or tryptophane residues. Further discrimination is possible as peptides with two former amino acids are cleaved in aqueous solution but not cleaved in acetone, while those with tryptophane are cleaved only in acetone in the presence of water. The mechanism of cleavage at tryptophane is particularly interesting as it involves the electrophilic ip o-paUadation of indole ring, while the remaining coordination site of Pd in the ip/ro-cyclopalladated complex is used for the electrophilic activation of carbonyl (Scheme 91). 

Complex formation between palladium(II) and amino acids, peptides and related ligands. L. D. Pettit and M. Bezer, Coord. Chem. Rev., 1985, 61, 97 (90). 

Selective cleavage of peptides and proteins is an important procedure in biochemistry and molecular biology. The half-life for the uncatalyzed hydrolysis of amide bonds is 350 500 years at room temperature and pH 4 8. Clearly, efficient methods of cleavage are needed. Despite their great catalytic power and selectivity to sequence, proteinases have some disadvantages. Peptides 420,423,424,426 an(j proteins428 429 can be hydrolytically cleaved near histidine and methionine residues with several palladium(II) aqua complexes, often with catalytic turnover. 

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