Compatibility of the thioamide functional group with beta-sheet secondary structure: incorporation of a thioamide linkage into a beta-hairpin peptide.

[structure: see text]. We report the incorporation of a thioamide linkage between the i + 2 and i + 3 residues of the type II' beta-turn of a peptide known to fold into a beta-hairpin conformation. Two-dimensional NMR spectroscopy and circular dichroism spectroscopy indicate that the thioxo peptide adopts a hairpin conformation similar to that of the oxo peptide and that the hairpin conformation persists at elevated temperatures. The results show that a thioamide linkage is compatible with beta-sheet secondary structure.