Hemoprotein models based on a covalent helix-heme-helix sandwich. 1. Design, synthesis, and characterization

In this paper we describe the design, synthesis, and spectroscopic characterization of a covalent helix-heme-helix sandwich named FeIII mimochrome I. It contains deuterohemin bound through both propionyl groups to two identical N-and C-terminal protected nonapeptides as ?-helical scaffolds. Each peptide moiety bears a His residue in the central position, which acts as axial ligand to the metal ion. The newly developed synthetic strategy is based on a combination of solution and solid-phase methodologies. It represents a powerful method for obtaining a large variety of analogues containing two symmetric or unsymmetric peptide chains covalently bound to the deuteroporphyrin ring. UV/Visible spectroscopic characterization in buffered 2,2,2-trifluoroethanol/water solution proves low-spin bis(his-tidine) iron(III) coordination; circular dichroism (CD) measurements show an ?-helical conformation for the peptide moieties. Thus, all the data are in agreement with the designed hypothetical model regarding both the iron(III) coordination and the peptide chain structural organization.