Syntheses and structures of technetium(V) and rhenium(V) oxo complexes of peptide having KYC-sequence

Technetium(V) and rhenium(V) oxo complexes of a peptide having a KYC-sequence such as KYCAR (H₃L⁵) and KYCAREPPTRTNAYWGQG-NH₂ (H₃L¹⁸) were synthesized, and structures of the complexes were characterized by spectroscopic techniques. All of the complexes were synthesized by the ligand exchange reaction of [(n-C₄H₉)₄N] [MOCl₄] (M = ⁹⁹Tc, Re) with peptide in methanol or dimethylformamide solution. These complexes have a square pyramidal structure with an oxo ligand at the apical position. The peptide is coordinated to a metal atom through N(amine) of lysine, S(thiol) of cysteine, and N(amide) of tyrosine and cysteine in the equatorial plane. A lysine (CH₂)₄NH₂ group of the L⁵ ligand has the syn conformation with respect to metal-oxo bonding in the complex. The syn isomer was selectively formed in the ligand exchange reaction. The conversion of the syn isomer to the anti isomer was observed only for syn-[ReO(L⁵)], in which the coordination of water to the trans position of the oxo ligand was involved.