We designed a chiral bicyclic α,α-disubstituted α-amino acid {(1R,6R)-8-aminobicyclo[4.3.0] non-3-ene-8-carboxylic acid; (R,R)-Ab5,6=c}, in which the α-carbon atom is not a chiral center but the asymmetric centers exist at the side-chain bicyclic skeleton. The amino acid (R,R)-Ab5,6=c has efficiently been synthesized starting from (S,S)-cyclohexa-4-en-1,2-dicarboxylic acid. The modification of olefin function in the side-chain by ozonolysis afforded several amino acid and peptide analogs, before and after the preparation of the peptides. The conformation of homopeptides composed of (R,R)-Ab5,6=c was studied by using X-ray crystallographic analysis, 1H NMR, IR, and CD spectra.
