A systematic study of the solid state and solution phase conformational preferences of β-peptides derived from C(3)-alkyl substituted transpentacin derivatives

Abstract

The solid state and solution phase conformational preferences of a homologous series of β-peptides derived from a range of 2-amino-3-alkylcyclopentanecarboxylic acid residues have been investigated using a variety of spectroscopic and crystallographic techniques. These studies indicate that C(3)-alkyl substitution trans to the amino group on the cyclopentane backbone is tolerated by the established 12-helix secondary structural preference of the parent pentamer and hexamer derived from 2-aminocyclopentanecarboxylic acid (transpentacin) residues in both the solid state and solution phase. Evidence for the alternative turn type conformation identified for the C(3)-unsubstituted tetramer was not observed in the C(3)-alkyl substituted derivatives, consistent with the alkyl substituent anti to the amino functionality destabilising this motif. These results suggest that oligomers based around the transpentacin scaffold may be amenable to further elaboration at C(3) anti to the amino group with retention of the secondary structure.