Enantioselective epoxidation of α,β-unsaturated ketones catalyzed by stapled helical L-Leu-based peptides

Stapled helical L-leucine-based heptapeptides were synthesized and used as catalysts for the enantio-selective epoxidation of alpha,beta-unsaturated ketones. All N-terminal free stapled peptides were successfully used as chiral catalysts. Among them, the use of H-hS(3,7)hS-10 gave epoxide products with high enantioselectivities of up to 99% ee. Furthermore, the dominant conformations of the N-terminal protected stapled peptides R3,7R-10 and hS(3,7)hS-10 were investigated by H-1 NMR, IR, CD spectra, and X-ray crystallographic analysis. The peptide R3,7R-10 formed a right-handed (P) alpha-helix in solution and in the crystalline state, while fiS(3,7)hS-10 formed a right-handed (P) 3(10)-helix in solution. (C) 2011 Elsevier Ltd. All rights reserved.