Rhenium complexes with phosphine-containing peptides. Synthesis and characterization of oxorhenium(V) complexes with N-{N -[3-(diphenylphosphino)propionyl]glycyl}-L-S -benzylcysteine and its methyl ester

Abstract

The co-ordination of dipeptides modified with a phosphine group to the ReO 3+ core has been studied, and the new donor sets PN 2 X (X = O or S) achieved. N-{N-[3-(Diphenylphosphino)propionyl]glycyl }-L-S-benzylcysteine (H 3 L 2 ) and its methyl ester derivative (H 2 L 1 ) have been used for preparing six-co-ordinated oxorhenium(V) complexes, providing a new chelating system for targeting 186/188 Re to protein bioactive molecules. The complexes have been characterized by means of UV/VIS, IR, FAB and 1 H NMR spectroscopy. The crystal structures of [ReO(L 2 )(OH 2 )]·H 2 O·MeOH and [ReO(L 1 )Cl] have been established. In both the complexes the co-ordination geometry is distorted octahedral. The ligands are tetradentate, co-ordinating the ReO 3+ moiety through the phosphine phosphorus, the two deprotonated amide nitrogens and the O or S atom from the carboxylate or thioether groups. When the cysteine carboxylic moiety is free, it can replace, in organic solvents, the thioether sulfur to give a stable complex, the fourth donor atom in the equatorial plane being a carboxylate oxygen. In basic medium [ReO(L 1 )Cl] underwent substitution of Cl - by OH - , evidence for the high stability of the PN 2 S donor set.