Methanol-mediated, modular self-assembly of antiparallel β-dimers. Crystal structure of C^α backbone-modified tripeptide Bz-Aib-NHCOCO-Aib-OMe

Abstract

The backbone-modified tripeptide Bz-Aib-NHCOCO-Aib-OMe (l), in which the central Cα has been replaced with CO, self-assembles in the solid state into highly ordered two-dimensional arrays through MeOH mediated intermolecular stacking of dimeric 'disk' modules formed by an antiparallel β-sheet-type arrangement of tripeptide molecules. The Cα(C'O)N(C'O) (C'O)NC segment is nearly coplanar (average deviation from a mean least-square plane is ±0.037 Å). The oxalyl moiety forms two pseudo-C₅ intramolecular hydrogen bonds. Crystal parameters are as follows: C₁₈H₂₃N₃O⁶CH₃OH, triclinic space group P1 a = 9.796(4), b = 10.348(3), c = 11.836(4) Å, α= 78.28(3), β= 73.72(3), γ = 69.45(3), R = 0.082 for 1747 reflections measured with ||Fo||3σ(F).