Structure and conformation of peptides involving prolyl residue

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Abstract
The dipeptide, L-procyl-L-leucine monohydrate (C11H20N2O3.cntdot.H2O, molecular weight, 246.3) crystallizes in the mononclinic space group P21, with cell constants: a = 6.49 (2) .ANG., b = 5.417(8) .ANG., c = 20.49 (5) .ANG., .beta. = 96.59(2).degree., Z = 2, Do = 1.15 g/cm3, and Dc = 1.142 g/cm3. The structure was solved by SHELX-86 and refined by full matrix least squares methods to a final R-factor of 0.081 for 660 unique reflections (1 > 2 .sigma. (I)) measured on an Enraf Nonius CAD-4 diffractometer (CuK2, .lambda. = 1.5418 .ANG., T = 293 K). The peptide linkage exists in the trans conformation. The pyrroliding ring exists in the envelope conformation. The values of the sidechain torsion angles are: .chi.1 =- 59.3(13).degree., .chi.21 =- 63.1(16).degree. and .chi.22 = 174.8(15).degree. for leucine (C-terminal). The crystal structure is stabilised by a three-dimensional network of N .fwdarw. H .cntdot..cntdot..cntdot. O, O .fwdarw. H .cntdot..cntdot..cntdot. O, and C .fwdarw. H .cntdot..cntdot..cntdot. O hydrogen bonds.