Synthesis, Crystal and Molecular Structure of Boc‐Pro‐ ΔPhe‐Ala‐ ΔPhe‐ Ala‐OMe; A Pentapeptide with a Novel β‐Bend Ribbon Structure

Neither a helical structure nor a spiral β‐bend ribbon structure, but a flat β‐bend ribbon is formed by the title compound. Peptides with 2,3‐didehydroamino acid esters (α,β‐didehydroamino acid esters) such as dehydrophenylalanine (ΔPhe) are of great interest as model compounds for the study of structure–function relationships, since the dehydroamino acids strongly influence the conformation and the enzymatic degradation of peptides. The comparison of the structure of the title compound with that of corresponding Aib‐containing peptides is informative.