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

Alpinoblonoids A (1) and B (2), two 16-nor-labdane related diterpenoids featuring 2,6,6,10,11-pentamethyltricyclo[8.4.0.02,7]tetradecane and 11-ethyl-2,6,6,10-tetramethyltricyclo[8.3.0.02,7]tridecane skeletons, respectively, along with their biosynthetic precursor (3), were isolated from the rhizomes of Alpinia oblongifolia. 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 1 and 2 exhibited antihepatic fibrosis activity by inhibiting the expressions of fibronectin, collagen I, and α-smooth muscle actin.