Bulky Dehydroamino Acids Enhance Proteolytic Stability and Folding in β‑Hairpin Peptides

The bulky dehydroamino acids dehydrovaline (ΔVal) and dehydro­ethyl­norvaline (Δ<i>E</i>nv) can be inserted into the turn regions of β-hairpin peptides without altering their secondary structures. These residues increase proteolytic stability, with ΔVal at the (<i>i</i> + 1) position having the most substantial impact. Additionally, a bulky dehydroamino acid can be paired with a d-amino acid (i.e., d-Pro) to synergistically enhance resistance to proteolysis. A link between proteolytic stability and peptide structure is established by the finding that a stabilized ΔVal-containing β-hairpin is more highly folded than its Asn-containing congener.