# Structure of tert-ButyloxycarbonyI-L-alanyI-L-proline Monohydrate (t-Boc-Ala-Pro)

Kamwaya, ME and Oster, O and Bradaczek, H and Ponnuswamy, MN and Parthasarathy, S and Nagaraj, R and Balaram, P (1982) Structure of tert-ButyloxycarbonyI-L-alanyI-L-proline Monohydrate (t-Boc-Ala-Pro). In: Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry, 38 (1). pp. 172-176.

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## Abstract

$C_{13}H_{22}N_2O_5.H_2O$, $M_r$ = 304.37, is orthorhombic, space group ${P2}_12_12_l$, with a = 20.751 (2), b = 13.457 (1), c = 5.875 (1) A, V = 1640.49 $A^3$, $D_o$ = 1.20, $D_c$ = 1.231 Mg $m^{-3}$; Z = 4; \lambda(Cu Ka) = 1.5418 A; Z = 4; F(000) = 656. Final R = 3.9% for 1664 observed reflexions. There is one molecule of water as well as an N-H...O hydrogen bond, rendering high stability to the crystal packing. The water-bridge bond is of the same type as that of a triple helix: $O_w...O$ = 2.78, $O_w...O'$ = 2.69 and $O_w...OH$ = 2.50 A. $C^{\alpha}$ is in the trans configuration. The absolute configuration of the non-centro-symmetric structure and, therefore, of the molecular conformation was determined by anomalous dispersion. The $N'C^{\alpha}C^{\gamma}C^{\delta}$ group in the pyrrolidine ring is fairly planar. $C^{\beta}$ is readily displaced from this best plane of the five-membered ring and deviates by 0.489 A. N' and $C^{\gamma}$ are on the same side of this plane in relation to the carboxyl C'. Thus t-Boc-Ala-Pro is $C_s-C^{\gamma}-endo(C^{\beta}-exo)$. This derivative belongs to conformation B, since the dihedral angle $x_1$ = 28.55 deg takes a positive value, and it has collagen-like characteristics, with $N'-C^{\alpha}-C'-O$ , that is, the dihedral angle ${\psi}_1$ Pro, equal to 161 deg. The $C^{\alpha}$ atoms of the prolyl and alanyl residues are trans with respect to the peptide bond.

Item Type: Journal Article http://dx.doi.org/10.1107/S0567740882002... Copyright for this article belongs to International Union of Crystallography. Division of Biological Sciences > Molecular Biophysics Unit 29 Mar 2005 19 Sep 2010 04:18 http://eprints.iisc.ernet.in/id/eprint/2969