A Left-Handed 9-Helix in gamma-Peptides: Synthesis and Conformational Studies of Oligomers with Dipeptide Repeats of C-Linked Carbo-gamma~4-amino Acids and gamma-Aminobutyric Acid

摘要

The design of nonnatural oligomers that form diversified secondary structures is an active area of research.An extensive search of the beta-peptide class of foldamers has provided several new secondary structures,while the gamma-peptides,despite the possibility of having and traversing a larger conformational space,have received less attention.Dado and Gellman identified the H-bonding of the nearest neighbor in gamma-amino acid derivatives by FTIR and NMR studies.Seebach and co-workers and Hanessian et al.reported 14-helices in gamma-peptides,while a 9-membered H-bonded ring was also observed by Seebach et al.in the crystal structure of a dipeptide.Recently,Farrera-Sinfreu el al.reported 9-membered sheets in gamma-peptides from cyclic gamma-amino acids,while Balaram and co-workers reported 9-helices and ribbons in gamma-peptides from constrained acyclic gamma-amino acids.