Afzelin

Abstract: Nine flavonoids were isolated and characterized from the leaves of Zanthoxylum bungeanum. Their structures were elucidated by spectroscopic techniques as quercetin (1), afzelin (2), quercitrin (3), trifolin (4), quercetin-3-O-β-D-glucoside (5), isorhamnetin 3-O-α-L-rhamnoside (6), hyperoside (7), vitexin (8) and rutin (9). All compounds were isolated from the leaves of Z. bungeanum for the first time. Five compounds (2, 4, 5, 6 and 8) were found for the first time in the genus Zanthoxylum. To learn the mechanisms underlying its health benefits, in vitro (DPPH, ABTS, FRAP and lipid peroxidation inhibition assays) and in vivo (protective effect on Escherichia coli under peroxide stress) antioxidant activities of the nine flavonoids were measured. Quercetin and quercetin glycosides (compounds 1, 3, 5, 7, 9) showed the highest antioxidant activity. Structure-activity relationships indicated that the -OH in 4′ position on the B ring and the -OH in 7 position on the A ring possessed high antioxidant activity; B ring and/or A ring with adjacent -OH groups could greatly increase their antioxidant ability. Also, due to the different structures of various flavonoids, they will certainly exhibit different antioxidant capacity when the reactions occur in solution or in oil-in-water emulsion. These findings suggest that Z. bungeanum leaves may have health benefits when consumed. It could become a useful supplement for pharmaceutical products and functional food ingredients in both nutraceutical and food industries as a potential source of natural antioxidants.

Abstract: The objective of this study was to examine the biological activity of kaempferol and its rhamnosides. We isolated kaempferol (1), a-rhamnoisorobin (2), afzelin (3), and kaempferitrin (4) as pure compounds by far-infrared (FIR) irradiation of kenaf (Hibiscus cannabinus L.) leaves. The depigmenting and anti-inflammatory activity of the compounds was evaluated by analyzing their structure-activity relationships. The order of the inhibitory activity with regard to depigmentation and nitric oxide (NO) production was kaempferol (1) > a-rhamnoisorobin (2) > afzelin (3) > kaempferitrin (4). However, a-rhamnoisorobin (2) was more potent than kaempferol (1) in NF-kB-mediated luciferase assays. From these results, we conclude that the 3-hydroxyl group of kaempferol is an important pharmacophore and that additional rhamnose moieties affect the biological activity negatively.

Abstract: Rosa damascena has been manufactured as various food products, including tea, in Korea. A new flavonoid glycoside, kaempferol-3-O-beta-D-glucopyranosyl(1-->4)-beta-D-xylopyranoside, named roxyloside A was isolated from the buds of this plant, along with four known compounds, isoquercitrin, afzelin, cyanidin-3-O-beta-glucoside, and quercetin gentiobioside. The chemical structures of these compounds were determined by spectroscopic analyses, including FAB-MS, UV, IR, (1)H and (13)C NMR, DEPT, and 2D NMR (COSY, HSQC, and HMBC). All the isolated compounds except cyanidin-3-O-beta-glucoside exhibited high levels of inhibitory activity against 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase with IC(50) values ranging from 47.1 to 80.6 microM. Cyanidin-3-O-beta-glucoside significantly suppressed angiotensin I-converting enzyme (ACE) activity, with an IC(50) value of 138.8 microM, while the other four compounds were ineffective. These results indicate that R. damascena and its flavonoids may be effective to improve the cardiovascular system.