Structure of an α,β-unsaturated dipeptide, racemic N-[(phenylmethoxy)carbonyl]phenylalanyl-Δ2-phenylalanine

C2_6H24N2Os, M r = 444.49, m.p. 466-469 K, triclinic, P1, a=6.418 (1), b= 13.223 (2), c=14.153(2)A, a=104.73 (1), fl=94.33(2), y=96.54 (2) °, V= 1147.2 (3) A 3, Z = 2, Dx=1.287 Mg m -3, 2(Mo K~) = 0.71069 A,/z = 0.01 mm -~, F(000)=468. Final R =0.039 for 2806 observed 1I _> 3o(I)1 reflections measured on a diffractometer at 293 K. The molecules in the crystal form compact 'hydrophilic columns' consisting of intermolecular hydrogen-bonded double chains surrounded by a hydrophobic space composed of phenyl substituents. The conformation of the phenylalanyl residue is close to parallel fl-sheet (tp=-89.3, ~,= 114.4 °) while the unsaturated residue adopts a left-handed or-helix conformation (~ = 50.4, ~, = 21.2°).