Phytochemical Constituents from the Aerial Parts of Acanthus ebracteatus Vahl. and Their Cytotoxic Activity.

Objective: Acanthus ebracteatus Vahl. (family Acanthaceae) is distributed in the mangrove areas of northern Vietnam. The whole plant has the effect of dissolving blood stasis, reducing swelling, relieving pain, dissolving phlegm, and is often used to treat back pain, numbness, cough, and asthma. In our screening program for seeking cytotoxic active compounds, the methanol extract of this plant significantly showed activity and was selected for further study. In this paper we report the chemical constituents of A. ebracteatus and their cytotoxic activity towards two cancer cell lines, HepG2 and SK-LU1 in vitro. Methods: The dried and powdered aerial parts of A. ebracteatus were ultrasonically extracted with methanol. This extract was suspended in water and successively partitioned with n -hexane, dichloromethane, and ethyl acetate to give n -hexane, dichloromethane, ethyl acetate, and water-soluble extracts. These extracts were fractionated and purified by column and HPLC chromatographic methods. The chemical structures of the isolates were determined by analysis of HRESIMS, and 1D and 2D NMR, and CD spectra. The isolates were screened for their in vitro cytotoxic activity by SRB assay. Results: One new flavone glycoside (1) and ten known compounds (2 - 11), including five flavones (2 - 6), three alkaloids (7 - 9), and two phenolic glycosides (10 and 11), were isolated from the aerial parts of A. ebracteatus. Compounds 7 – 9 showed moderate cytotoxic activity against HepG2 and SK-LU1 cell lines with IC₅₀ values ranging from 28.2 to 31.1 µM. Compounds 2 – 6, 8, 9, and 11 are reported herein from A. ebracteatus for the first time. Conclusion: One new (1) and five known flavonoids (2 - 6), together with three alkaloids (7 - 9) and two phenolic glycosides (10 and 11) were recorded from A. ebracteatus. Our results preliminarily revealed that alkaloids may be cytotoxic ingredients of A. ebracteatus. [ABSTRACT FROM AUTHOR]