Two pentadehydropeptides with different configurations of the ΔPhe residues

Comparison of the crystal structures of two pentadehydropeptides containing ΔPhe residues, namely (Z,Z)-N-(tert-butoxycarbonyl)glycyl-α,β-phenylalanylglycyl-α,β-phenylalanylglycine (or Boc⁰–Gly¹–Δ^ZPhe²–Gly³–Δ^ZPhe⁴–Gly⁵–OH) methanol solvate, C₂₉H₃₃N₅O₈·CH₄O, (I), and (E,E)-N-(tert-butoxycarbonyl)glycyl-α,β-phenylalanylglycyl-α,β-phenylalanylglycine (or Boc⁰–Gly¹–Δ^EPhe²–Gly³–Δ^EPhe⁴–Gly⁵–OH), C₂₉H₃₃N₅O₈, (II), indicates that the Δ^ZPhe residue is a more effective inducer of folded structures than the Δ^EPhe residue. The values of the torsion angles ϕ and ψ show the presence of two type-III′β-turns at the Δ^ZPhe residues and one type-II β-turn at the Δ^EPhe residue. All amino acids are linked trans to each other in both peptides. β-Turns present in the peptides are stabilized by intramolecular 4→1 hydrogen bonds. Molecules in both structures form two-dimensional hydrogen-bond networks parallel to the (100) plane.