Crystal and molecular structure of the dehydropeptide Ac-ΔPhe-Val-ΔPhe-NH-Me

The dehydropeptide Ac-ΔPhe-l-Val-ΔPhe-NH-Me, containing two dehydrophenylalanine (ΔPhe) residues, crystallizes from methanol/water in space group P212121 with a= 12.622 (1), b= 12.979 (1), and c= 15.733 (1) Å. In the solid state, the molecular structure is characterized by the presence of two intramolecular hydrogen bonds which form two consecutive β-bends. The (φ,Ψ) torsion angles of the three residues are very similar and close to the standard values of type III β-bends, so the molecular conformation corresponds to an incipient right-handed 310 -helix, only slightly distorted. In the crystal, the molecules are linked by head-to-tail hydrogen bonds, thus forming continuous helical columns packed in antiparallel mode. There are no lateral hydrogen bonds; the only interactions are hydrophobic contacts between the apolar side chains of neighboring helical columns.