Uncommon, but emerging, alpha-peptide conformations

Compared with the classical secondary structural elements of proteins [alpha-helix, beta-pleated sheets, isolated beta-turns, and Poly(Pro)(n) helix] other types of helical conformations [3(10)-helix and beta-turn ribbon spiral, gamma-helix, and 2.0(5)-helix] of peptides based on alpha-amino acids are currently emerging particularly from detailed analyses of appropriately designed model compounds. Their 3D-structural characterizations offer fascinating issues of precise control of probe-probe distances and relative orientations. Therefore, they present real potential to play a significant role as rigid, but easily tunable, spacers and templates in various areas of organic chemistry, supramolecular chemistry, and physical chemistry.