Fig. 7.

Strategies of peptide cyclization and stabilization of α-helices, β-sheets, and β-strands. The establishment of intramolecular cross-links can stabilize different secondary structures of peptides. Side chain cross-links between i and i + 4 or/and i + 7 and hydrogen bond surrogate cross-links can stabilize α-helices. Side chain-to-side chain, head-to-tail, and side chain-to-tail cyclization can stabilize turn, loop and β structures (β-sheets and β-strands). The D-Pro-L-Pro scaffold can specifically stabilize antiparallel β-hairpins