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.
Highlights
The genus Salacia (Celastraceae) has a great variety of species spread throughout Brazil and other regions of South America [1]
In order to accomplish our initial aim, i.e., establish the complete chemical shifts assignments of 4, the NMR experiments were repeated, but using pyridine-D5 as solvent, and, the results showed that no rearrangement was observed
The structural elucidation, including the stereochemistry of compounds 4 and 7, was based on the chemical shifts assignments obtained from 1D (1H, 13C and DEPT-135) and 2D (HMQC, HMBC, correlation spectroscopy (COSY) and NOESY) NMR
Summary
The genus Salacia (Celastraceae) has a great variety of species spread throughout Brazil and other regions of South America [1]. NMR spectral data are reported for compounds 4 and 7. The analysis of 2D NMR spectral data contributed to establish the correct chemical shift assignments of all carbons and hydrogens of compound 4.
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