Cytotoxic Flavonoids from the Leaves and Twigs of Murraya tetramera

Cytotoxic flavonoids of Murraya tetramera were investigated in this study. A novel flavonoid and twelve known flavonoids, including seven flavones (1–7), three flavanones (8–10), and three chalcones (11–13) were isolated from the leaves and twigs of Murraya tetramera. Chemical structures were elucidated by NMR combined with MS spectral analysis, and the new compound (6) was confirmed as 3′,5′-dihydroxy-5,6,7,4′-tetramethoxyflavone. Furthermore, all the isolated flavonoids were evaluated for their cytotoxicities against murine melanoma cells (B16), and human breast cancer cells (MDA-MB-231) by CCK-8 assay. Among them, compounds 7, 13, and 5 exhibited potent cytotoxic activities against B16 cell lines (IC₅₀ = 3.87, 7.00 and 8.66 μg/mL, respectively). Compounds 5, 13, and 12 displayed potent cytotoxicities against MDA-MB-231 cell lines (IC₅₀ = 3.80, 5.95 and 7.89 μg/mL, respectively). According to the correlation of the structure and activity analysis, 5-hydroxyl and 8-methoxyl substituents of the flavone, 8-methoxyl substituent of the flavanone, and 3′,5′-methoxyl substituents of the chalcone could be critical factors of the high cytotoxicity. The results indicated that the active flavonoids have potential to be developed as leading compounds for treating cancers.