Crystal structure of tert.‐butyloxycarbonyl‐L‐prolyl‐D‐alanyl‐D‐alanyl‐N‐methylamide Dimeric β‐sheet formation
Journal Articles
Overview
Research
Identity
Additional Document Info
View All
Overview
abstract
The crystal structure of the tripeptide t‐Boc‐L‐Pro‐D‐Ala‐D‐Ala‐NHCH3, monohydrate, (C17H30N4O5·H2O, molecular weight = 404.44) has been determined by single crystal X‐ray diffraction. The crystals are mono‐clinic, space group P21, a = 9.2585(4), b = 9.3541(5). c = 12.4529(4) Å, β= 96.449(3)°, Z = 2. The peptide units are in the trans and the tBoc‐Pro bond in the cis orientation. The first and third peptide units show significant deviations from planarity (Δω=5.2° and Δω=3.7°, respectively). The backbone torsion angles are: φ1, = ‐60°, ψ1/= 143.3°, ω1= ‐174.8°, φ2= 148.4°, ψ2= ‐143.1°, ω2= ‐179.7°, φ3= 151.4°, ψ3= ‐151.9°, ω3= ‐176.3°. The pyrrolidine ring of the proline residue adopts the C2— Cγ conformation. The molecular packing gives rise to an antiparallel β‐sheet structure formed of dimeric repeating units of the peptide. The surface of the dimeric β‐sheet is hydrophobic. Water molecules are found systematically at the edges of the sheets interacting with the urethane oxygen and terminal amino groups. Surface catalysis of an L‐Ala to D‐Ala epimerization process by water molecules adsorbed on to an incipient β‐sheet is suggested as a mechanism whereby crystals of the title peptide were obtained from a solution of tBoc‐Pro‐D‐Ala‐Ala‐NHCH3.
