Sulfonyl-γ-AAs as Turn Templates Inducing β-Sheet Conformation in Macrocyclic Peptides

β-hairpins are minimal antiparallel β-sheets and essential protein secondary structures, critical for diverse biological functions, yet designing synthetic β-sheet mimics remains challenging due to sequence-dependent folding. Here, we report sulfonyl-γ-AAs (γ-substituted-N-sulfonyl-N-aminoethyl amino acids) as artificial β-turn inducers that drive stable β-sheet conformations in macrocyclic peptides, leading to a class of protein antiparallel β-sheet mimetics. Single-crystal X-ray diffraction of sulfonyl-γ-AAs B1 and a macrocyclic peptide BS-1 containing sulfonyl-γ-AA residues reveals that sulfonyl-γ-AAs adopt a β-turn-like conformation stabilized by both intramolecular hydrogen bonding and intrinsic curvature of the sulfonamido moiety, thereby facilitating the formation of a folded β-sheet structure with defined amino acid residues. To the best of our knowledge, this is also the first report of the crystallographic validation of a polyalanine β-sheet structure enforced by a β-turn mimic. Additionally, circular dichroism (CD) spectroscopy displayed characteristic minima between 208-214 nm in BS-6 to BS-9, consistent with robust β-sheet signatures. 2D-NMR studies revealed the well-folded solution structures consistent with X-ray crystal structures. These results establish sulfonyl-γ-AAs as a versatile class of β-turn templates that drive β-sheet formation, enabling the creation of novel macrocyclic antiparallel β-sheet mimics with broad potential in therapeutic development and biomaterials design.