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 (<b>4</b>-<b>7</b>), four new aromadendrane diterpenoids and sesquiterpenoids along with five previously described analogues (<b>1</b>-<b>3</b>, <b>8</b>-<b>9</b>), were isolated from the gum resin of <i>Boswellia sacra</i>. Configurational revision assigned boscartols O, N, and P to compounds <b>1</b>-<b>3</b>, 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, <b>1</b>-<b>3</b> and <b>6</b> showed moderate inhibitory activity against lipopolysaccharide (LPS)-induced NO production in RAW 264.7 monocyte macrophages relative to the positive control. Meanwhile, compounds <b>1</b>, <b>5</b>, and <b>7</b> demonstrated cytoprotective activity in L929 mouse fibroblast cells against H₂O₂-induced oxidative damage at 50 μM.