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A novel highly oxygenated norbisabolane sesquiterpene, namely phyllanthacidoid U (1), along with nine known sesquiterpenes (2–10) was isolated from the roots and stems of Phyllanthus acidus (L.) Skeels (Phyllanthaceae), collected from Xishuangbanna, Yunnan province, China. Their structures were elucidated by means of extensive spectroscopic analysis and by comparison of their data with reported values in literatures. Instead of the C-13 ester O-glycosyl found mostly in the titled plant growing in Thailand, compound 1 possessed a rare N-β-glucosamine-2-N-acetate moiety linked directly to the carbonyl at C-13 through an amido bond. Moreover, the acyl group at C-10 in 1 was (Z)-2-(2-hydroxyethyl)-pent-2-enedioyl group, instead of benzoic or p-hydroxybenzoic moieties found commonly in the reported norbisabolane sesquiterpenes. The known sesquiterpene 5 displayed stronger anti hepatitis B virus (HBV) activity with IC50 values of 1.69 ± 0.22 and 2.79 ± 0.69 μM towards HBV surface antigen (HBsAg) and HBV excreted antigen (HBeAg) secretion, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four new rare dichapetalins (1–4) were isolated from Phyllanthus acidus. • Their structures were elucidated by extensive spectroscopic data and X-ray diffraction analysis. • The isolated dichapetalins showed cytotoxicity against seven human cancer or normal cell lines. The young leaves of Phyllanthus acidus (Euphorbiaceae) are commonly used as edible vegetables in Indonesia, Thailand, and India, and their water infusions as dieting aids for people trying to remain slim. However, it is regarded as a poisonous plant in Malaya, and current researches are insufficient to provide a conclusion on its toxicity and safety under large doses. In this study, we firstly found that the refined nonpolar extracts of P. acidus leaves showed significant cytotoxic effect against BEAS-2B and L02 normal cell lines with IC 50 values of 2.15 and 1.64 mg/mL, respectively. Further bioactivity-guided isolation produced four new rare dichapetalins (pacidusins A – D) from the most active fraction. Their structures including absolute configurations were elucidated by extensive spectroscopic data and X-ray diffraction analysis. All the isolated dichapetalins exhibited moderate cytotoxicity against, BEAS-2B and L02 normal cell lines with IC 50 values ranging from 12.44 to 22.55 μM, as well as five human cancer cell lines with IC 50 values ranging from 3.38 to 22.38 μM. Furthermore, the content of the main dichapetalins in the leaves were determined by analytical HPLC, which showed that the leaves contained a very high amount of the four isolated dichapetalins with a total yield of 0.488 mg/g of dry plant material. These toxic dichapetalins may lead to adverse health effects in higher doses. Our findings indicate that the dichapetalin containing leaves may not be suitable for consumption in large quantities as food, but demonstrate their potency as anti-cancer agents for new drug discovery. [ABSTRACT FROM AUTHOR]