Hydrogen Bonded Squaramide-Based Foldable Module Induces Both β- and α‑Turns in Hairpin Structures of α‑Peptides in Water

A novel
tertiary squaramido-based reverse-turn module SQ is reported,
and its conformational properties are evaluated. This module is easily
incorporated into a α-peptide sequence by conventional solid-phase
peptide synthesis. The structure characterization of the hybrid squaramido-peptide 4 is described, showing that the turn segment induces the
formation of hairpin structures in water through the formation of
both αSQ- and βSQ-turns.