New Terpenoids and Lignans from Phyllanthus acidus Fruits with Antioxidant Activity

The fruits of Phyllanthus acidus, rich in various secondary metabolites and possessing significant antioxidant activity, have been consumed widely by many Southeast Asian people, including the Thai, Vietnamese, Burmese, Laotians, and Cambodians. An extensive investigation of the secondary metabolites of the fruits resulted in our obtaining 17 compounds, including four new compounds (1–4). The absolute configurations of 1, 3, and 4 were determined by comparing their experimental electronic circular dichroism (ECD) spectra with both reference data and computed ECD profiles. At a concentration of 40μM, terpenoids (1 and 5–9) showed no cytotoxic activity against five strains of human tumor cells and one of normal cells. Notably, the known lignan 13 and phenylpropanoid 15 showed obvious ABTS+ radical scavenging activities with IC50 values of 203.7 and 232.9 μM, which have a comparable impact to the positive control, Trolox (IC50 = 176.5 ± 2.0 μM). The results indicated that P. acidus fruits could be a promising sources of antioxidant food supplement.