@-tide-stabilized β-hairpins

(Chemical Equation Presented) As minimalist versions of β-structure, two-stranded β-hairpins are commonly employed as platforms for assessing the interactions that stabilize β-sheets in proteins. We have found that the presence of a 1,6-dihydro-3(2H)-pyridinone moiety (the "@-unit") as an amino acid replacement at the i - 1 or i + 4 positions relative to a β-turn strongly stabilizes the hairpin conformation. Hybrids of this type bridge the gap between natural β-hairpins and unnatural β-sheets because the @-unit only replaces one residue in a peptide while stabilizing the hairpin conformation to a greater extent than a normal amino acid. In this report, we describe the synthesis of a variety of @-tide-templated hairpins and the NMR and CD characterization of their conformations in both polar and nonpolar solvents.