Alpinoblonoids A and B, Two 16-<i>nor</i>-Labdane-Related Diterpenoids with a Tricyclic Carbon Skeleton from <i>Alpinia oblongifolia</i>

Alpinoblonoids A (<b>1</b>) and B (<b>2</b>), two 16-<i>nor</i>-labdane related diterpenoids featuring 2,6,6,10,11-pentamethyl­tricyclo­[8.4.0.0^2,7]­tetradecane and 11-ethyl-2,6,6,10-tetramethyl­tricyclo­[8.3.0.0^2,7]­tridecane skeletons, respectively, along with their biosynthetic precursor (<b>3</b>), were isolated from the rhizomes of <i>Alpinia oblongifolia</i>. Their structural elucidation was achieved by a variety of techniques, including spectroscopic and chemical methods, ECD calculations, as well as single-crystal X-ray diffraction. Compounds <b>1</b> and <b>2</b> exhibited antihepatic fibrosis activity by inhibiting the expressions of fibronectin, collagen I, and α-smooth muscle actin.