Crystal structure and molecular conformation of the peptide N‐Boc‐ L ‐gly‐dehydro‐Phe‐NHCH 3

The peptide N‐Boc‐ L ‐Gly‐dehydro‐Phe‐NHCH 3 was synthesized by the combination of N‐Boc‐ L ‐Gly‐dehydro‐Phe azlactone and methylamine. The peptide crystallizes in orthorhombic space group P2 1 2 1 2 1 with a = 5.679(2) Å, b = 16.423(9) Å, c = 19.198(10) Å, V = 1791(2) Å 3 , Z = 4, dm = 1.212(5) Mg m −3 , dc = 1.237(1) Mg m −3 . The structure was determined by direct methods using SHELXS 86. The structure was refined by full‐matrix least squares procedure to an R value of 0.049 for 1509 observed reflections. The molecular dimensions are, in general, in good agreement with the standard values. The bond angle C α –C β –C γ in the dehydro‐Phe residue is 133.6(5)°. The peptide backbone torsion angles are θ 1 = −171.4(4)°, ω 0 = 178.2(4)°, ϕ 1 = −57.2(6)°, ψ 1 = 141.2(4)°, ω 1 = −174.4(4)°, ϕ 2 = 71.5(6)°, ψ 2 = 7.2(6)°, and ω 2 = −179.8(5)°. These values show that the backbone adopts the β‐bend type II conformation. The Boc group has a trans‐trans conformation. The side‐chain torsion angles in dehydro‐Phe are χ 2 = 1.6(9)°, χ   2 2,1= 0.5(9)°, and χ   2 2,2= 179.8(6)°. The plane of C   2 α – C   2 β – C   2 γis rotated with respect to the plane of the phenyl ring at 0.5(6)°, which indicates that the atoms of the side chain of the dehydro‐Phe residue are essentially coplanar. As a result of the β‐bend in the structure, an intramolecular hydrogen bond is formed between the oxygen of the i th residue and the NH of the ( i + 3)th residue at a distance of 2.940(5) Å. The crystal structure is stabilized by a network of hydrogen bonds and van der Waals interactions.