title: Stereochemistry of 16a-hydroxyfriedelin and 3-Oxo-16-methylfriedel-16-ene established by 2D NMR spectroscopy.
abstract: Friedelin (1), 3beta-friedelinol (2), 28-hydroxyfriedelin (3), 16alpha-hydroxyfriedelin (4), 30-hydroxyfriedelin (5) and 16alpha,28-dihydroxyfriedelin (6) were isolated through fractionation of the hexane extract obtained from branches of Salacia elliptica. After a week in CDCl(3) solution, 16alpha-hydroxyfriedelin (4) reacted turning into 3-oxo-16-methylfriedel-16-ene (7). This is the first report of a dehydration followed by a Nametkin rearrangement of a pentacyclic triterpene in CDCl(3) solution occurring in the NMR tube. These seven pentacyclic triterpenes was identified through NMR spectroscopy and the stereochemistry of compound 4 and 7 was established by 2D NMR (NOESY) spectroscopy and mass spectrometry (GC-MS). It is also the first time that all the (13)C-NMR and 2D NMR spectral data are reported for compounds 4 and 7.
authors.affiliation: NEPLAM - Departamento de Química, ICEx, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Pampulha, CEP 31270-901, Belo Horizonte, Minas Gerais, Brazil. lupadu@netuno.lcc.ufmg.br
authors.forename: Lucienir Pains
authors.initials: LP
authors.lastname: Duarte
authors.forename: Roqueline Rodrigues
authors.initials: RR
authors.lastname: Silva de Miranda
authors.forename: Salomão Bento Vasconcelos
authors.initials: SB
authors.lastname: Rodrigues
authors.forename: Grácia Divina
authors.initials: GD
authors.lastname: de Fátima Silva
authors.forename: Sidney Augusto
authors.initials: SA
authors.lastname: Vieira Filho
authors.forename: Vagner Fernandes
authors.initials: VF
authors.lastname: Knupp
mesh_terms: D004365:Drugs, Chinese Herbal / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008968:Molecular Conformation; D015394:Molecular Structure; D049918:Salacia / Q000737:chemistry; D013237:Stereoisomerism; D014315:Triterpenes / Q000737:chemistry*; D000094042:Lupanes
chemical_list: D004365:Drugs, Chinese Herbal; D014315:Triterpenes; C060796:friedelin; D000094042:Lupanes