Crystal Structure and Conformation of N-(t-Butoxycarbonyl)-L-Isoleucyl-L-Valine Methyl Ester (Boc-Ile-Val-OMe)

ABSTRACT

N-(t-Butoxycarbonyl)-L-Isoleucyl-L-Valine Methyl ester, C₁₇H₃₂N₂O₅, F.W.=344.46, crystallizes in hexagonal space group P6₅ with parameters, a=b = 20.285(5), c=27.160(5) A˚, V=9679.1(6) A˚ ³, Z = 18, Dcal=1.064 Mg cm⁻³, λ(CuKα) = 1.5418 A˚, μ (CuKα). The dipeptide Boc-Ile-Val-OMe has three crystallographically independent molecules (A, B, and C) in the asymmetric unit. The peptide units are in trans conformation and the three molecules adopt an extended conformation. The side chains of isoleucine and valine for the three molecules A, B, and C take up g⁻ t, g⁻ g⁻, and g⁻ t; and g⁻ g⁺, g⁺ t, and tg⁻ conformations, respectively. The molecules form an infinite ribbon of β-sheet structure, which in turn forms helical arrangement along the c-direction. They are stabilized by N − H … O and C − H … O types of intermolecular interactions.

Keywords:

• conformation
• crystal
• dipeptide
• hydrogen bonds
• isoleucine
• valine

Notes

†CDB Reference Number CCDC 227928.

*D=Donor; H=Hydrogen; Ac=Acceptor. A, B, and C in parentheses represent molecules A, B, and C respectively.