Chengdu Push-Bio Technology Co., Ltd.

Phytochemical investigation of the peels of Citrus reticulata "Dahongpao" resulted in the isolation and characterization of six polymethoxyflavones. Their structures were elucidated as 5,6,7,3'-tetrahydroxy-8,4'-dimethoxyflavone (1), 5,6,7-trihydroxy-8,3',4'-trimethoxyflavone (2), 5,7,8-trihydroxy-6,3',4'-trimethoxyflavone (3), 5,8-dihydroxy -6,7,3',4'-tetramethoxyflavone (4), 5,6,7,8-tetrahydroxy-3',4'-dimethoxyflavone (5), and nobiletin (6) by analysis of their spectroscopic data. They feature a characteristic fully substituted A-ring and a 3',4'-disubstituted B-ring, analogous to nobiletin. Among them, compounds 1 and 2 are new compounds. Full assignment of NMR data for compounds 3 and 5 is presented here for the first time. Furthermore, the discrepancies in the previously reported NMR spectroscopic data of compound 4 are discussed.