title: [Design and synthesis of non-proteinogenic amino acids and secondary structures of their peptides].
abstract: Replacement of the alpha-hydrogen atom of L-alpha-amino acids with an alkyl substituent results in alpha,alpha-disubstituted amino acids. The modification changes the properties of the amino acids. Incorporation of alpha,alpha-disubstituted amino acids into oligopeptides restricts the conformational freedom of their peptides. The author developed a synthetic route for optically active alpha-ethylated alpha,alpha-disubstituted amino acids using chiral cyclic 1,2-diol, and disclosed that the preferred conformation of peptides composed of chiral alpha-ethylated disubstituted amino acids is a fully planar conformation, whereas that of chiral alpha-methylated disubstituted amino acids is a 3(10)-helical structure. Furthermore, the author designed and synthesized two chiral cyclic alpha,alpha-disubstituted amino acids, i.e., (3S,4S)-1-amino-3,4-di(methoxy)cyclopentanecarboxylic acid {(S,S)-Ac5cdOM}, and (1R,6R)-8-aminobicyclo-[4.3.0]non-3-ene-8-carboxylic acid {(R,R)-Ab5,6=c}. They do not have a chiral center at the alpha-position, but do have chiral centers on the side-chain cyclopentane or the bicyclic skeleton. The preferred secondary structure of the (S,S)-Ac5cdOM homopeptides was the left-handed (M) 3(10)-helical structure (hexapeptide) and the left-handed (M) alpha-helical structure (octa- and decapeptides), while that of the (R,R)-Ab5,6=c hexapeptide was both the right-handed (P) and left-handed (M) 3(10)-helices. These results indicate that the side-chain chiral centers affect the secondary structure of their peptides, and the side-chain chiral environment is important for the control of the helical-screw direction of peptides.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka City, Japan. mtanaka@phar.kyushu-u.ac.jp
authors.forename: Masakazu
authors.initials: M
authors.lastname: Tanaka
mesh_terms: D000596:Amino Acids / Q000138:chemical synthesis* / Q000737:chemistry*; D018257:Helix-Loop-Helix Motifs; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D010455:Peptides