Synthesis, structure and electrochemistry of ferrocene-peptide macrocycles

Redox active cyclopeptides Fc[CSA](2) (5), Fc[Gly-CSA](2) (6), Fc[Ala-CSA](2) (7), Fc[Val-CSA](2) (8) and Fc[Leu-CSA](2) (9) (CSA=cysteamine) which are formed by the reaction of ferrocenedicarboxylic acid with peptide cystamines at high dilutions. These systems exhibit H-bonding involving the amide NH in solution as shown by their temperature dependent NMR spectra. With the exception of 5, the ferrocene macrocycles display intramolecular N...O cross-ring H-bonding in the solid state involving the amino acids proximal to the ferrocene.