PREPARATION AND CHARACTERIZATION OF A NEW RHENIUM(V) COMPLEX CONTAINING THE ENYLPHOSPHINOPROPIONYLGLYCYL-L-(S-BENZYL)CYSTEINYL METHYL-ESTERLIGAND

A new phosphine derivatized peptide tetradentate ligand containing the PN2S donor atom set, 3-diphenylphosphinepropionylglycyl-L-(S-benzyl) cysteinyl methyl ester, was synthesized in good yields by coupling a p hosphine group to protected Gly-L-Cys dipeptide. Complexation of the n ew ligand with rhenium proceeded in satisfactory yields by substitutio n reaction on (ReOCl3)-O-v(PPh(3))(2) in a 1.2:1 molar ratio. The resu lting rhenium complex was characterized by IR, FAB-MS, H-1 and P-31 NM R spectroscopy and was found to be neutral and diamagnetic. These stud ies revealed, that rhenium(V) in a trans-ReOCl2+ core coordinates with the PN2S2- donor atom set formed by one neutral phosphine, one neutra l thioether and two deprotonated amide groups of the ligand forming a neutral complex. High performance liquid chromatography tests verified the purity and high stability of the complex in solution for long per iods of time. In alkaline organic media the complex transforms to an e qually stable, more hydrophilic analogue, in which the methyl ester gr oup of cysteine is hydrolyzed to the free carboxylate.