Synthesis and Conformational Study of Monosubstituted Aminoferrocene-Based Peptides Bearing Homo- and Heterochiral Pro-Ala Sequences

Abstract

The synthesis and conformational analysis of a series of the monosubstituted aminoferrocene-based peptides bearing homo- and heterochiral Pro-Ala sequences are described. A change of the Pro amino acid chirality can affect the secondary structure. The homochiral derivatives of tBuCO–AA2–AA1–NHFc (Fc = ferrocene; AA = Pro, Ala) favour β-turns, and a disruption of the secondary structure is observed for the heterochiral analogues in solution. A detailed computational study suggested that γ-turns form in the heterochiral derivatives. The X-ray-determined crystal structures of the heterochiral compounds show a preference for β-turns. The calculated interaction energies indicate the significance of the intermolecular hydrogen bonds, which are favourable enough to overcome the rearrangement of a single molecule from the most stable conformer to that adopted in the solid state. The current research indicates the potential of the investigated compounds for the fine tuning of their conformational properties by variation of the chirality of the constituent amino acids.