Isolation and Identification of Polymethoxyflavones from the Hybrid Citrus, Hallabong

Seven polymethoxyflavones (PMFs) were isolated from the dried peels of hallabong, the hybrid Citrus, by a repeated column chromatography. The structures of PMFs were identified as 5,6,7,3',4'-pentamethoxyflavone (1), 6,7,8,3',4'-pentamethoxyflavone (2), 3-hydroxy-5,6,7,4'-tetramethoxyflavone (3), 5,6,7,8,3',4'-hexamethoxyflavone (4), 3,6,7,4'-tetramethoxyflavone (5), 3,5,6,7,8,3',4'-heptamethoxyflavone (6), and 5,6,7,8,4'-pentamethoxyflavone (7) using H-1 and C-130 NMR in combination with mass spectrometry. Among these compounds, 5 was isolated for the first time from nature. The content of PMFs 1-7 in hallabong was determined by HPLC-UV. The major PMFs of hallabong are 5 in the dried peels (15.4 mg/g) and 7 in the dried leaves (12.2 mg/g).