Structure and conformation of n‐ (t‐butoxycarbonyl)‐l‐valine‐l‐phenylalanine‐methyl ester (Boc‐Val‐Phe‐OMe)

The crystal structure of N‐ (t‐butoxycarbonyl) ‐ L‐valine‐L‐phenylalanine‐methyl ester (Boc‐Val‐Phe‐OMe), C₂₀H₃₀N₂O₅ was determined by X‐ray diffraction methods. The dipeptide crystallizes in orthorhombic space group P2₁2₁2₁, with cell parameters a = 5.0680(1) Å, b = 13.8650(1) Å and c = 28.2630(1) Å, V = 2143.8(5) ų, F.W. = 378.46, Z = 4, D_calc = 1.173 Mg/m³, μ = 0.687 mm^‐1, F₀₀₀ = 816, CuKα = 1.5418 Å. The structure was solved by direct methods and final R1 and wR2 are 0.0659 and 0.1654, respectively. The peptide unit is in trans conformation [ω = 177.4(9)°]. The conformation angles ϕ₁, ψ₁, ϕ₂ and ψ₂ for the peptide backbone are: ‐96.5(13)°, 101.2(13)°, ‐123.9(12)° and 34.0(15)°. The N‐H…O and C‐H…O hydrogen bondings influence the packing of the molecules in the dipeptide crystal. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)