Poster Presentation 10th Australian Peptide Conference 2013

Synthesis of cyclic ɑ,ɑ-disubstituted amino acids bearing a pendent chiral center and conformational analysis of heteropeptides containing their amino acids (#185)

Makoto Oba 1 , Ikumi Kato 1 , Yosuke Demizu 2 , Masaaki Kurihara 2 , Mitsunobu Doi 3 , Yukiko Takano 4 , Hiroshi Suemune 4 , Masakazu Tanaka 1
  1. Nagasaki University, Nagasaki, Japan
  2. National Institute of Health Sciences, Tokyo, Japan
  3. Osaka University of Pharmaceutical Sciences, Osaka, Japan
  4. Kyushu University, Fukuoka, Japan

Cyclic ɑ,ɑ-disubstituted amino acids, in which the side chain becomes a cyclic structure, have attracted considerable attention because of their characteristic properties, such as chemical stability, metabolic stability, and conformational restriction.  We recently reported that side-chain chiral centers of amino acids affect the secondary structures of their peptides.  Herein, we wish to report the synthesis of chiral cyclic ɑ,ɑ-disubstituted amino acids; (S)-PipMe,Ph and (S)-oPipMe,Ph, and also the preparation of heteropeptides containing them in dimethylglycine sequence. Amino acids Cbz-(S)-PipMe,Ph-OMe and Cbz-(S)-oPipMe,Ph-OMe were prepared using dimethyl malonate and 2-bromomethyl-1,3-dioxolane as starting materials.  The synthesis of heteropeptides was carried out according to solution-phase methods by using EDC•HCl and HOBt as coupling reagents.  FT-IR and NOESY 1H NMR spectra indicated that (S)-PipMe,Ph heteropeptide preferentially formed a 310-helical structure in CDCl3 solution.  X-ray crystallographic analyses indicated that (S)-PipMe,Ph heteropeptide formed both right-handed (P) and left-handed (M) 310-helical structures, while (S)-oPipMe,Ph heteropeptide formed (P) 310-helical structure.