A Left-Handed 9-Helix in γ-Peptides: Synthesis and Conformational Studies of Oligomers with Dipeptide Repeats of C-Linked Carbo-γ4-amino Acids and γ-Aminobutyric Acid

✍ Scribed by Gangavaram V. M. Sharma; Pagadala Jayaprakash; Kongari Narsimulu; Ampapathi Ravi Sankar; Kondreddy Ravinder Reddy; Palakodety Radha Krishna; Ajit C. Kunwar

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 236 KB
• Volume: 118
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/ange.200504380

✦ Synopsis

The design of nonnatural oligomers that form diversified secondary structures is an active area of research. [1] An extensive search of the b-peptide class of foldamers has provided several new secondary structures, while the gpeptides, despite the possibility of having and traversing a larger conformational space, have received less attention. Dado and Gellman [2] identified the H-bonding of the nearest neighbor in g-amino acid derivatives by FTIR and NMR studies. Seebach and co-workers [3] and Hanessian et al. [4] reported 14-helices in g-peptides, while a 9-membered Hbonded ring was also observed by Seebach et al. [3b] in the crystal structure of a dipeptide. Recently, Farrera-Sinfreu et al. [5] reported 9-membered sheets in g-peptides from cyclic g-amino acids, while Balaram and co-workers [6] reported 9helices and ribbons in g-peptides from constrained acyclic gamino acids. Theoretical predictions by Hofmann and coworkers [7] for g-peptides revealed that structures with 14-and 9-helices are most stable. Herein, we report a left-handed 9helix in a novel class of mixed g-peptides, derived from dipeptide repeats with alternating C-linked carbo-g 4 -amino acids (g-Caas) and g-aminobutyric acid (GABA), in CDCl 3 .

Our earlier findings [8] on mixed b-peptides derived from alternating C-linked carbo-b 3 -amino acids (b-Caas) and bhomoglycine (b-hGly) revealed a switching of the handed-