Total syntheses of pongaflavone and its natural analogues.

The efficient total synthesis of anti-tumor natural product pongaflavone (1) was described starting from commercially available 2,4-dihydroxyacetophenone (9) via seven steps and in 16% overall yield. Its two natural analogues pongachromene (2) and 7,8-(2",2"-dimethylpyrano)-5,3',4'-trihydroxy-3-methoxyflavone (3) were also synthesized following the similar procedure with the yields of 11% and 18%, respectively. Their preliminary anti-tumor activities were evaluated by the inhibition effect on A549 cells. The result showed that this kind of natural products exhibited different levels of anti-tumor activity. Among them, pongachromene (2) displayed the best anti-tumor activity.

Sugar easters and xanthones from the roots of Polygala tenuifolia Willd. and their cytoprotective activity.

Six new sugar esters (1-6), named tenuifolisides F-G (1-2) and tenuifolioses W-Z (3-6), together with 16 known compounds (7-22) were isolated from the roots of Polygala tenuifolia. The chemical structures of the new compounds were elucidated by 1D, 2D NMR and HRESIMS techniques together with chemical methods. All the compounds were evaluated for the cytoprotective activity against hydrogen peroxide (H2O2)-induced oxidative stress in human keratinocyte HaCaT cells. Compounds 4, 5, 13, 20 and 22 showed strong cytoprotective effect.

Flavonoid glycosides and alkaloids from the embryos of Nelumbo nucifera seeds and their antioxidant activity.

Chemical investigation of the embryos of Nelumbo nucifera afforded four new flavone C-glycosides, named nelumbosides A-D (1-4), together with nine known ones, comprising five flavonoids (5-9) and four alkaloids (10-13). The chemical structures of the new compounds were elucidated by 1D, 2D-NMR and HR-ESI-MS techniques, together with chemical methods. Nelumbosides A-D (1-4) are rarely present in naturally occurring flavone C-glycosides featuring a 4-hydroxystyrene unit connected to the flavonoid skeleton. Compounds 2-13 were evaluated for their antioxidant activity by ABTS and DPPH radical-scavenging assay. Among them, compounds 2, 6, 7 and 11 exhibited strong scavenging activity with SC50 values ranging from 12.07 to 25.68µM compared with the positive control l-ascorbic acid.

Homo-aro-cholestane, furostane and spirostane saponins from the tubers of Ophiopogon japonicus.

Phytochemical investigation of the tubers of Ophiopogon japonicus led to the isolation of five previously undescribed steroidal saponins, ophiojaponins A-E, together with twelve known ones. The structures of these isolated compounds were elucidated by detailed spectroscopic analyses and chemical methods. Ophiojaponins A-C are rare naturally occurring C29 steroidal glycosides possessing a homo-cholestane skeleton with an aromatized ring E. Ruscogenin 1-O-α-L-rhamnopyranosyl-(1 â†’ 2)-4-O-sulfo-ß-D-fucopyranosido-3-O-ß-D-glucopyranoside was isolated as single component and its full spectroscopic data was reported for the first time. The isolated steroidal saponins were evaluated for their cytotoxicities against two human tumor cell lines MG-63 and SNU387. Among them, five known spirostane-type glycosides showed cytotoxic activity against both MG-63 and SNU387 cell lines with IC50 values ranging from 0.76 to 27.0 µM.