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

The co-ordination of dipeptides modified with a phosphine group to the Re=O3+ core has been studied, and the new donor sets PN2X (X = O or S) achieved. N-{N-[3-(Diphenylphosphino)propionyl]glycy}-L-S-benzylcysteine (H3L2) and its methyl ester derivative (H2L1) have been used for preparing six-co-ordinated oxorhenium(V) complexes, providing a new chelating system for targeting Re-186/188 to protein bioactive molecules. The complexes have been characterized by means of UV/VIS, IR, FAB and H-1 NMR spectroscopy. The crystal structures of [ReO(L-2)(OH2)]. H2O . 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 Re=O3+ 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 PN2S donor set.