Absolute Stereostructures of New Arborinane-Type Triterpenoids and Inhibitors of Nitric Oxide Production from Rubia yunnanensis

The aqueous acetone extract from the roots of a Chinese herbal medicine, Rubia yunnanensis, showed a potent inhibitory effect on nitric oxide production in lipopolysaccharide-activated macrophages. Five new arborinane-type triterpenes, rubianols-a (1), -b (2), -c (3), -d (4), and -e (5), and a new arborinane-type triterpene glycoside, rubianoside I (6), were isolated from the herbal crude extract together with 10 known compounds. The absolute stereostructures of 1-6 were determined on the basis of chemical and physicochemical evidence, including the application of the modified Mosher's method. The effects of the isolated constituents on nitric oxide production in lipopolysaccharide-activated macrophages were examined, and several triterpenes were found to show inhibitory activity.