title: Asymmetric synthesis of Ampelomin A and ent-Epiampelomin A.
abstract: We synthesized the naturally occurring carbasugar ampelomin A and its epimer from a common starting material. The enantiomerically pure starting material was obtained by base-catalyzed asymmetric Diels-Alder reaction of 3-hydroxy-2-pyrone and chiral acrylate. The total yield of ampelomin A was 14% in seven synthetic steps. The key step of the synthesis of ampelomin A was inversion of the stereochemistry at the C-6 position, which was achieved by stereoselective catalytic hydrogenation of the corresponding methylidene group. Further synthesis of the epimer was straightforward, because all stereogenic centers had already been introduced on the starting material; the total yield was 44% in four synthetic steps. Both the final products were obtained in pure form without contamination with undesired isomers. The reported (1)H NMR chemical shift of the C-7 methyl protons and the H-5axial coupling pattern of natural ampelomin A were inconsistent with those of our synthetic product. After careful comparison of the spectra and examination of the stable conformation obtained through MM2 calculations, we present revised NMR data for ampelomin A.
authors.affiliation: Department of Chemistry and Bioscience, Graduate School of Kagoshima University.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Koyanagi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Hamada
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Iwagawa
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Okamura
mesh_terms: D000179:Acrylates / Q000737:chemistry; D054329:Carbasugars / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D061565:Cycloaddition Reaction / Q000379:methods*; D003510:Cyclohexanes / Q000138:chemical synthesis* / Q000737:chemistry; D006865:Hydrogenation; D009682:Magnetic Resonance Spectroscopy; D011753:Pyrones / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000179:Acrylates; D054329:Carbasugars; D003510:Cyclohexanes; D011753:Pyrones; C550397:ampelomin A