Peptide Bioconjugates of Electron-Poor Metallocenes: Synthesis, Characterization, and Anti-Proliferative Activity.

We report the synthesis of metallocene compounds Cp2 M with two different electron-withdrawing substituents on both cyclopentadienyl rings (hexafluoroacetone (HFA) and chlorobenzoyl (1-5); HFA and COOH (6 and 7), M=Fe or Ru). The COOH-containing derivatives were used to synthesize peptide bioconjugates with enkephalin (8 and 9) and neurotensin (10 and 11) as well as fluorescein-labeled neurotensin (12). All the molecules were fully characterized, including X-ray structures for 6 and 7.