Structure and conformation of linear peptides

Abstract
The crystal structure of t-Boc-glycyl-L-phenylalanine (C14H22N2O5, molecular weight = 298) has been determined. Crystals, are monoclinic, space group P21, with a = 7.599(1).ANG., b = 9.576(2), c = 12.841(2), .beta. = 97.21(1).degree., Z = 2, Dm = 1.149, Dc = 1.168 g .cntdot. cm-3. Trial structure was obtained by direct methods and refined to a final R-index of 0.064 for 1465 reflections with I > 1 .sigma.. The peptide unit is trans planar and is nearly perpendicular to the plane containing the urethane moiety. The plane of the carboxyl group makes a dihedral angle of 16.0.degree. with the peptide unit. The backbone torsion angles are .omega.o = -176.9.degree., .vphi.1 = -88.0.degree., .psi.1 = -14.5.degree., .omega.1 = 176.4.degree., .vphi.2 = -164.7.degree. and .psi.2 = 170.3.degree.. The phenylalanine side chain conformation is represented by the torsion angles .chi.1 = 52.0.degree., .chi.2 = 85.8.degree.

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