X-ray Crystallographic Structure of α-Helical Peptide Stabilized by Hydrocarbon Stapling at , + 1 Positions.

Hydrocarbon stapling is a useful tool for stabilizing the secondary structure of peptides. Among several methods, hydrocarbon stapling at , + 1 positions was not extensively studied, and their secondary structures are not clarified. In this study, we investigate , + 1 hydrocarbon stapling between -4-allyloxy-l-proline and various olefin-tethered amino acids. Depending on the ring size of the stapled side chains and structure of the olefin-tethered amino acids, or -selectivities were observed during the ring-closing metathesis reaction (/ was up to 8.5:1 for 17-14-membered rings and up to 1:20 for 13-membered rings). We performed X-ray crystallographic analysis of hydrocarbon stapled peptide at , + 1 positions. The X-ray crystallographic structure suggested that the , + 1 staple stabilizes the peptide secondary structure to the right-handed α-helix. These findings are especially important for short oligopeptides because the employed stapling method uses two minimal amino acid residues adjacent to each other.