in protein structures nucleating type I β-turns. By bridging the amino acid side chain in position i with a nitrogen substituent in position i+2 by ring-closing olefin metathesis (RCM), peptide mimetics of type 1 could be developed. NMR based conformational investigations indicated a stable intramolecular H-bond constraining a U-turn conformation that was predicted to simulate a type I β-turn.