A variety of approaches to controlling the conformations of peptides have been investigated, and the incorporation of α,α–disubstituted α–amino acids (dAAs) and cross–linked side chains into peptide sequences is of vital importance for constructing stable helical structures. Thus, we speculated that stable helical structures could be constructed using a combination of dAAs and a covalent cross–linking system. Here, we have designed and synthesized four L–leucine (L–Leu) based heptapeptides containing an aα–aminoisobutyric acid at the 4th position as a helical promoter and L/D–(homo)serine derivatives at the 3rd and 7th positions to produce a cross–linked subunit. N–terminal free peptides were used for enantioselective epoxidation of α,β–unsaturated ketones, which is known as the Julià–Colonna asymmetric reaction.
