# The Crystal Structure of Benzyloxycarbonyl-${(\alpha-aminoisobutyryl)}_2$-L-Alanyl Methyl Ester

Prasad, Venkataram BV and Shamala, N and Nagaraj, R and Balaram, P (1980) The Crystal Structure of Benzyloxycarbonyl-${(\alpha-aminoisobutyryl)}_2$-L-Alanyl Methyl Ester. In: Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry, 36 (1). pp. 107-110.

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Crystals of the title compound, $C_{20}H_{29}N_3O_6$, are monoclinic, space group ${P2}_1$, with a = 8.839 (3), b = 10.818 (3), c = 11.414 (2) A, \beta = 95.69 (2) deg, Z = 2; final R = 0.053. The molecular conformation is defined by the following angles (\phi, \psi): Aib-1 58.1, 36.8; Aib-2 68.3, 18.6; Ala-3 (\phi) = 136.2 deg. The molecule adopts a type III' \beta-turn conformation stabilized by an intramolecular hydrogen bond between the CO of the benzyloxycarbonyl group and the NH of the alanyl residue. The hydrogen-bond parameters are N . . . O 2.904 A and \angle NH . . . O 156.9 deg.