Isolation and identification of new polymethoxyflavonoids from Dancy tangerine leaves

Ten highly oxygenated flavonoids, including four new compounds, were isolated from the leaves of Dancy tangerine. Six were identified as 5,6,7,3',4'-pentamethoxyflavone (sinensetin) (1), 5,6,7,8,4'-pentamethoxyflavone (tangeretin) (2), 5,6,7,8,3',4'-hexamethoxyflavone (nobiletin) (3), 5-hydroxy-6,7,3',4'-tetramethoxyflavone (4), 5,7-dihydroxy-6,8,3',4'-tetramethoxyflavone (5), and 5-hydroxy-6,7,8,3',4'-pentamethoxyflavone (5-O-desmethylnobiletin) (6) by direct comparison with authentic samples, comparing their spectroscopic data with those reported in the literature or by simply interpreting their spectral data. The new compounds were elucidated as 5,7,8,3',4'-pentamethoxyflavanone (7), 5,6,7,8,3',4'-hexamethoxyflavanone (8), 7-chloro-3,5,6,8,3',4'-hexamethoxyflavone (9), and 7-chloro-3,5,6,8,4'-pentamethoxyflavone (10) on the basis of chemical and spectroscopic studies.