Four New Iridoids isolated from the stem of Neonauclea reticulate

Neonauclea reticulate (Rubiaceae) is a large evergreen tree and only one species found in Taiwan. It was an important Lanyu folk plant for built traditional canoe in Tao people culture. Previous investigations of some Neonauclea plants resulted in the isolation of alkaloids, anthraquinones, iridoids, triterpenes and saponins. Iridoid was a cyclic monoterpene type structure and exhibited a wide range of bioactivity in previous study, such as: antihepatotoxic, anti-inflammatory, antispasmodic, antitumor, anti-diabetes and antiviral et al. In this study, stem of Neonauclea reticulate extracted with methanol. The methanol extracts suspended in water and partition with ethyl acetate. The water suspension partition with butanol. Each steps repeat three times. Four different layers assay for lung and liver tumor cells cytotoxicity ability. The result showed that the methanol extract owning a dose-dependent cytotoxicity against to the human hepatoma (Hep3B) cell line (IC₅₀ = 500 µg/mL). Investigation of the active layer of N.reticulate led to the isolation of three new dimeric iridoids:reticunin C (1) reticunin D (2) and reticunin E (3) and one new iridoid: neonanin D (4), along with four known iridoids including siphonosetegiol (5), isoboonein (6), floribundano B (7) and alyxialactone (8).The structure of these compounds were determined through spectral analyses including extensive 2D-NMR data and the new compounds were identify by ESI-MS. In this symposium we described the four structural elucidations of 1, 2, 3 and 4. Biological activities of pure compounds were all in progress.