Stabilized short helical heptapeptides containing a combination of an α-aminoisobutyric acid as a helical promoter and l/d-serine derivatives to produce cross-linked units were synthesized. The cyclic peptide R 3 , 7 R-2, which had d-serine derivatives at its 3rd and 7th positions, formed a stable right-handed (P) α-helix in solution and the crystalline state. Furthermore, its N-terminal free helical peptide catalyzed the enantioselective epoxidation of (E)-chalcone to afford the epoxide in a high yield and moderate enantioselectivity.