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Phyllaciduloids E (1) and F (2), two new cleistanthane diterpenoids, were isolated from the leaves of Phyllanthus acidus (L.) Skeels (Phyllanthaceae). Their planar structures were established by spectroscopic analysis and comparison with literature values. The relative configurations of phyllaciduloids E and F were confirmed by DFT-NMR chemical shift calculations and subsequent CP3 probability methods. Phyllaciduloids E and F were evaluated for their cytotoxicity. However, no significant activities were detected at concentrations up to 40 μM.

Phytochemical investigation on the nonpolar extracts of P. acidus leaves afforded three new cleistanthane diterpenoids, named phyllanacidins A–C (1–3), in addition to three known ones (4–6). Among them, compounds 2 and 3 represent the first examples of 17-nor cleistanthane diterpenoids. Their structures including absolute configurations were elucidated on the basis of extensive spectroscopic data and single crystal X-ray diffraction analysis. All the isolated cleistanthane diterpenoids were evaluated for their cytotoxic activities against five human cancer cell lines. Compounds 4–6 exhibited moderate cytotoxicity with IC50 values ranging from 16.11 to 30.82 μM.

Salviyunnanone A (1), a cytotoxic diterpenoid possessing an unprecedented 7/5/6/3 ring system derived from a normal abietane skeleton, was characterized from Salvia yunnanensis. Its structure was established by extensive MS and NMR spectroscopic analyses and its absolute configuration was defined by the comparison of experimental and calculated ECDs. The synthetic study of 1 was carried out and its 6-epi-isomer (12) was achieved in 9 steps involving the conjugated addition of an aryl boronic acid as a key step.

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 IC50 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 IC50 values ranging from 12.44 to 22.55 μM, as well as five human cancer cell lines with IC50 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.

Scopariusins A-C (1-3), three novel rearranged ent-halimanoids with a bicycle[5.4.0]undecane ring system, two new normal ent-halimanoids (4 and 5), and a new ent-clerodanoid (6) were isolated from Isodon scoparius. Moreover, a biomimetic transformation from the ent-clerodanoid to the normal and the rearranged ent-halimane diterpenoids was successfully accomplished, which not only validated the biogenetic hypothesis in this plant but also confirmed the absolute configurations of 1 and 5.