Oligomers of β-amino acid bearing non-planar amides form ordered structures

In this report, we explore the feasibility of using bicyclic chiral beta-amino acids, (1R,2R,4S)- and (1S,2S,4R)-7-azabicyclo[2.2.1]-heptane-2-carboxylic acid (R-Ah2c and S-Ah2c, respectively), to prepare novel peptides with unique properties. Facile cis-trans isomerization of the non-planar amide bonds of these beta-amino acids should result in great flexibility of the backbone structure of beta-peptides containing them. Indeed, oligomers of these amino acids showed thermostability and characteristic CD absorptions, which were not concentration-dependent, suggesting that the oligomers remained monomeric. The results indicated the formation of self-organized monomeric structures with chain-length-dependent stabilization. Energy calculations suggested that the peptides can take helical structures in which the energy barriers to cis-trans isomerization are greater for the central amide bonds than for the terminal amides. (c) 2006 Elsevier Ltd. All rights reserved.