New norclerodane diterpenoids from bulbils of Dioscorea bulbifera L.

Investigation of extracts from bulbils of Dioscorea bulbifera L. yielded two new norclerodane diterpenoids, diosbulbin N acetate (1) and epi-diosbulbin B (3), together with eleven known compounds. Their structures were established based on spectroscopy. The absolute configurations of 1 and diosbulbin B (2) were determined by X-ray crystallographic analysis using Cu Kα radiation. The absolute configuration of 3 was determined by comparison of its ECD spectrum to that of 2. Isolated phenanthrenes 7, 9 and 10 exhibited moderate cytotoxicity against the HelaS3 cell line with IC50 values of 9.03 ± 0.04, 27.13 ± 6.86 and 10.88 ± 2.75 µM, respectively. In addition, 7-9 and 11 showed potent inhibition of NO production by LPS-induced RAW 264.7 macrophages.

Cytotoxic and α-glucosidase inhibitory metabolites from twigs and leaves of Phyllanthus mirabilis, a species endemic to limestone mountains.

The first investigation of Phyllanthus mirabilis Müll.Arg. led to the isolation of six undescribed compounds including two tyramine derivatives: phyllatyramines A and B; three butenolide analogues, phyllantenolide, phyllantenocoside-O-gallate and epi-phyllantenocoside-O-gallate; and a flavanonol gallate, (-)-taxifolin-3-O-gallate; as well as two first isolated natural products, phyllatyramine C and phyllantenocoside; together with twenty-three known compounds. Their structures were elucidated by spectroscopic means. ECD spectra of all isolated butenolides were compared and assigned the configurations. Phyllatyramine A displayed weak cytotoxicity against the KB cell line, while phyllatyramines B and C showed weak cytotoxicity against KB and HeLa cell lines. In addition, phyllatyramine B and (-)-taxifolin-3-O-gallate showed more potent α-glucosidase inhibitory activity than the standard acarbose 3.4 and 5.8 fold, respectively.

Inhibition of nitric oxide production by clerodane diterpenoids from leaves and stems of Croton poomae Esser.

Chromatographic separation of crude extracts from the leaves and stems of Croton poomae Esser led to the isolation of two new clerodane diterpenes crotonolide K (1) and furocrotinsulolide A acetate (2) and six known clerodane diterpenes (3-8), together with twelve known compounds (9-20). Their structures were established from spectroscopic analysis. The clerodane diterpenoids 1-8 were evaluated for inhibition of nitric oxide (NO) production in LPS-activated RAW 264.7 macrophages. Compounds 1, 2, 5, 7 and 8 showed potent inhibitory effects, with IC50 values ranging from 32.19 to 48.85 µM, which is better than both the standard drugs indomethacin (154.5 µM) and dexamethasone (56.28 µM).

Spirosteroids and α-glucosidase inhibitory norlignans from Asparagus racemosus Willd. roots.

Three undescribed spirosteroids, asparacemosones A-C, an undescribed spiro-21-norsteroid, asparacemosone D, along with seven known compounds were isolated from Thai herbal plant Asparagus racemosus Willd. roots. Their structures were elucidated by spectroscopic analysis including NMR, UV, IR and mass spectrometry. The absolute configurations of asparacemosones A, B, and D were determined by single crystal X-ray diffraction using CuKα radiation. Among the isolated compounds, the norlignan nyasol and three acetylenic norlignans demonstrated potent α-glucosidase inhibition, with IC50 values ranging from 0.003 to 0.004 µM which is 5 × 104 fold more potent than the standard acarbose.