Synthesis and conformational analysis of new troponyl aromatic amino acid

Synthetic peptides are in huge demand in expansion of potential peptide mimics, which may have improved or comparable function as natural one. With these concerns, phenyl bearing aromatic amino acids and peptides has extensively explored, because phenyl residue has high probability in forming stable secondary structure, owing to the presence of an extra stabilizing factor as π–π non-covalent interactions. Apart from phenyl bearing benzenoid aromatic amino acids, a few non-benzenoid aromatic derivatives such as tropolone and related compounds are also occurred in nature, but troponyl containing amino acids and peptides are very poorly understood. Tropolonyl derivatives also contain carbonyl functional group, which may play an important role to provide stable conformation in peptide. Herein we report the synthesis, and conformational analysis of rationally designed new unnatural δ-amino acid, troponyl aminoethylglycine (Tr-aeg), which contains troponyl residue as side chain in flexible aminoethylglycine (aeg) amino acid backbone. We also demonstrate the role of troponyl carbonyl of Tr-aeg residue in hydrogen bonding with adjacent amide NH of their hybrid di/tri-peptides with NMR methods and DFT calculations. In future, Tr-aeg amino acid would be a potential building block in development of promisable peptide mimics.