Structure and Conformation of N-(t-BUTOXYCARBONYL)-L-ISOLEUCYL-L-Leucine Methyl Ester

Abstract

Boc-Ile-Leu-OMe: N-(t-butoxycarbonyl)-L-isoleucyl-L-leucine methyl ester, C18H34N2O5, F.W. = 358.47, hexagonal, P65, a = b = 11.775(2), c = 27.597(7)Å, V = 3313(1)Å3, Z = 6, Dcal = 1.078 Mg/m3, μ = 0.635 mm−1, λ(CuKα) = 1.5418 Å, final R1 and wR2 are 0.064 and 0.160, respectively.The peptide unit is in trans configuration and the molecule adopts and extended conformation. The boc group adopts the trans-trans conformation, and the isoleucine and leucine side chains are in (g−g−) and (tg−) configurations, respectively. The parallel β sheet in the dipeptide forms an infinite ribbon of β-sheet structure, which in turn form a herringbone arrangement. The molecules are stabilized by N–H…O and C–H…O types of intermolecular interactions.