Stereochemistry of 16α-Hydroxyfriedelin and 3-Oxo-16-methylfriedel-16-ene Established by 2D NMR Spectroscopy

Author： Duarte Lucienir Pains Silva de Miranda Roqueline Rodrigues Rodrigues Salomão Bento Vasconcelos de Fátima Silva Grácia Divina Filho Sidney Augusto Vieira Knupp Vagner Fernandes

Publisher： MDPI

E-ISSN： 1420-3049|14|2|598-607

ISSN： 1420-3049

Source： Molecules, Vol.14, Iss.2, 2009-02, pp. : 598-607

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Abstract

Friedelin (1), 3β-friedelinol (2), 28-hydroxyfriedelin (3), 16α-hydroxyfriedelin (4), 30-hydroxyfriedelin (5) and 16α,28-dihydroxyfriedelin (6) were isolated through fractionation of the hexane extract obtained from branches of Salacia elliptica. After a week in CDCl₃ solution, 16α-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 CDCl₃ 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 ¹³C-NMR and 2D NMR spectral data are reported for compounds 4 and 7.