Structural Revision of Aromadendrane Diterpenoids and Sesquiterpenoids from Olibanum Based on DFT Calculations and X-ray Crystallography.

The structural revision of aromadendrane diterpenoids and sesquiterpenoids derived from olibanum is reported. Boscartols Q-T (4-7), four new aromadendrane diterpenoids and sesquiterpenoids along with five previously described analogues (1-3, 8-9), were isolated from the gum resin of Boswellia sacra. Configurational revision assigned boscartols O, N, and P to compounds 1-3, respectively. Their structures were determined by the analysis of spectroscopic data, GIAO NMR/DP4+ analyses, ECD calculations, and a single-crystal X-ray diffraction study. Among these compounds, 1-3 and 6 showed moderate inhibitory activity against lipopolysaccharide (LPS)-induced NO production in RAW 264.7 monocyte macrophages relative to the positive control. Meanwhile, compounds 1, 5, and 7 demonstrated cytoprotective activity in L929 mouse fibroblast cells against H2O2-induced oxidative damage at 50 μM.