title: Biomimetic cyclization of epoxide precursors of indole mono-, sesqui- and diterpene alkaloids by Lewis acids.
abstract: Cyclization of the synthesized epoxide precursors of indole mono-, sesqui- and diterpene alkaloids was performed to elucidate the mechanism for biomimetic cationic cyclization to polycyclic structures. 3-(6,7-Epoxygeranyl)indole (11), 3-(10,11-epoxyfarnesyl)indole (2) and 3-(14,15-epoxygeranylgeranyl)indole (3) were respectively synthesized from geraniol, farnesol and geranylgeraniol in 6 or 7 steps. Four Lewis acids (MeAlCl(2), BF(3)·OEt(2), TiCl(4) and SnCl(4)) were applied for biomimetic cyclization of the synthesized epoxide precursors. The cyclization products (one product from 11, four products from 2, and three products from 3) were isolated after separation by chromatography. Their structures were determined by using NMR (COSY, HSQC, HMBC, NOESY, etc.) and HRMS analyses. The results show that biomimetic cyclization gave new polycyclic compounds similar to natural indole terpene alkaloids. We conclude that the stability of cation intermediates should determine the preference for product formation by biomimetic cyclization when using a Lewis acid.
authors: United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo, Japan.
authors: Tetsuya
authors: T
authors: Isaka
authors: Morifumi
authors: M
authors: Hasegawa
authors: Hiroaki
authors: H
authors: Toshima
mesh_terms: D032701:Biomimetics; D002845:Chromatography; D003500:Cyclization; D004224:Diterpenes / Q000737:chemistry*; D004852:Epoxy Compounds / Q000138:chemical synthesis; D026121:Indole Alkaloids / Q000138:chemical synthesis; D058116:Lewis Acids / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D039821:Monoterpenes / Q000138:chemical synthesis*; D011083:Polycyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D012717:Sesquiterpenes / Q000138:chemical synthesis*; D013237:Stereoisomerism
chemical_list: D004224:Diterpenes; D004852:Epoxy Compounds; D026121:Indole Alkaloids; D058116:Lewis Acids; D039821:Monoterpenes; D011083:Polycyclic Compounds; D012717:Sesquiterpenes