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OPhPh(E)-chalconeR-{L-Leu-L-Leu-dAA} n -OMe(R = Boc, or H)urea-H 2 O 2 , DBUroom temp., THF, 24 hr.OOPhPh(2R,3S)-epoxideFig. 2. Epoxidation of chalcone using helical oligopeptides.N(2)H, N(3)H and N(4)H protons are crucial for asymmetric induction, and the N(1)Hproton is less important. In Boc-protected α-helical peptides, the N(4)H proton forms anintramolecular hydrogen bond with the C=O of the protecting group, and thus, the N(4)Hproton may not be available for interaction with chalcone intermediate. Thus, next weexamined epoxidation using 5 mol % of N-terminal free oligomers.Except for hexamers having Aib and (R,R)-Ac 5 c dOM , N-terminal free peptides gavebetter enantiomeric excesses than Boc-protected ones. In particular, the reaction by (S,S)-Ac 5 c dOM and (1S,3S)-Ac 5 c OM containing nonamers and dodecamers afforded epoxides of>95% ee in good yield. Furthermore, the (1S,3S)-Ac 5 c OM containing α-helical nonamer canbe applied to epoxidation of various α,β-unsaturated ketones.AcknowledgmentsThis work was supported in part by a Grant-in-Aid (B) from JSPS, by a Grant-in-Aid for ScientificResearch on Priority Areas (No. 20037054, “Chemistry of Concerto Catalysis”) from MEXT, and alsoby a Grant-in-Aid from the ASAHI GLASS Foundation.References1. (a) Juliá, S., Masana, J., Vega, J.C. Angew. Chem., Int. Ed. 19, 929 (1980); (b) Juliá, S., Colonna, S.,et al. J. Chem. Soc. Perkin Trans. 1 1317 (1982).2. (a) Porter, M.J., Roberts, S.M., Skidmore, J. Bioorg. Med. Chem. 7, 2145 (1999); (b) Roberts, S.M.,et al. TRENDS in Biotechnology 23, 507 (2005); (c) Kelly, D.R., Roberts, S.M. Biopolymers(Peptide Sci.) 84, 74 (2006); (d) Toniolo, C., et al. Biopolymers (Peptide Sci.) 84, 90 (2006); (e)Geller, T., Roberts, S.M. J. Chem. Soc., Perkin Trans. I. 1397 (1999); (f) Roberts, S.M., et al.Tetrahedoron Lett. 45, 3885 (2004). Also, references cited therein.3. (a) Ohkata, K., et al. Chem. Lett. 366 (2000); (b) Toniolo, C., Scrimin, P., et al. Biopolymers(Peptide Sci.) 84, 97 (2006).4. (a) Demizu, Y., Tanaka, M., et al. Chem. Pharm. Bull. 55, 840(2007); (b) Nagano, M., Tanaka, M.,et al. Org. Lett. 11, 1135 (2009).5. Nagano, M., Tanaka, M., et al. Org. Lett. 12, 3564 (2010).623