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

摘要

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.