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

[GRAPHICS] 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 b eta -hairpin conformation. Two-dimensional NMR spectroscopy and circular di chroism spectroscopy indicate that the thioxo peptide adopts a hairpin conf ormation similar to that of the oxo peptide and that the hairpin conformati on persists at elevated temperatures. The results show that a thioamide lin kage is compatible with beta -sheet secondary structure.