Crystal structure of N-(tert-but-oxy-carbon-yl)phenyl-alanylde-hydro-alanine isopropyl ester (Boc-Phe-ΔAla-OiPr)

In the crystal structure of the de­hydro­dipeptide (Boc-Phe-ΔAla-OiPr), the mol­ecule has a trans configuration of the N-methyl­amide group. Its geometry is different from saturated peptides but is in excellent agreement with other de­hydro­alanine compounds. In the crystal, an N—H⋯O hydrogen bond links the mol­ecules in a herringbone packing arrangement.

In the title compound, the de­hydro­dipeptide (Boc–Phe–ΔAla–OiPr, C₂₀H₂₈N₂O₅), the mol­ecule has a trans conformation of the N-methyl­amide group. The geometry of the de­hydro­alanine moiety is to some extent different from those usually found in simple peptides, indicating conjugation between the H₂C=C group and the peptide bond. The bond angles around de­hydro­alanine have unusually high values due to the steric hindrance, the same inter­action influencing the slight distortion from planarity of the de­hydro­alanine. The mol­ecule is stabilized by intra­molecular inter­actions between the isopropyl group and the N atoms of the peptide main chain. In the crystal, an N—H⋯O hydrogen bond links the mol­ecules into ribbons, giving a herringbone head-to-head packing arrangement extending along the [100] direction. In the stacks, the mol­ecules are linked by weak C—H⋯O hydrogen-bonding associations.