Synthesis, structure and electrochemistry of ferrocene–peptide macrocycles

Abstract

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.