Acridone Alkaloids. VI.1)The Constituents of Citrus depressa. Isolation and Structure Elucidation of New Acridone Alkaloids from Citrus genus

Five new acridone alkaloids, citracridone-I (1a), -II (1b), citpressine-I (2a), -II (2b), and prenylcitpressine (3) along with a known acridone alkaloid, 5-hydroxynoracronycine (5), and three known coumarins, clausarin (6), suberosin (7a), and xanthyletin (8) were isolated from the root bark of Citrus depressa (Rutaceae) collected in Taiwan and characterized. This is the first report of isolation of acridone alkaloids from Citrus species. In the structure elucidations, the use of nuclear Overhauser effect (NOE) experiment on the O-methoxymethyl derivatives of phenolic acridone alkaloids was shown to be useful for the determination of the location of the phenolic hydroxyl groups.