• Archives of Pharmacal Research
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• v.27 no.1
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• pp.44-47
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• 2004

Loranthus tanakae Fr. et Sav. (Loranthaceae) is a species of mistletoe, a semiparasitic plant growing on the branches of Quercus and Betula species as host trees. In our ongoing search for bioactive compounds from endemic species in Korea, we have investigated to isolate the chemical constituents responsible for the antitumor effect of the MeOH extract of L. tanakae. The ethyl acetate soluble part of the MeOH extract demonstrated a marginal inhibition on the proliferation of the tumor cell lines such as A549 (non small cell lung), SK-OV-3 (ovary), SK-MEL-2 (melanoma), XF498 (central nerve system), and HCT-15 (colon) in vitro. Thus, the activity-guided isolation procedure upon the ethyl acetate soluble part of the extract has been carried out and finally four flavonoid rhamnopyranosides (1-4) were isolated as active principle. The structures of 1-4 were elucidated by the physicochemical and spectral data as rhamnetin 3-O-$\alpha$-L-rhamnoside (1), quercetin 3-O-$\alpha$-L-rhamnoside (2), rhamnocitrin 3-O-$\alpha$rhamnoside (3), and kaempferol 3-O-$\alpha$-L-rhamnoside (4).

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2083-2086
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• 2009

Human vascular endothelial growth factor receptor 2 (hVEGFR2) is an important signaling protein involved in angiogenesis and attractive drug target in cancer therapy. It has been reported that flavonols, a class of flavonoids, have anti-angiogenic activity in various cancer cell lines. We performed receptor-oriented pharmacophore based in silico screening for identification of hVEGFR2 inhibitors from flavonol database. By comparing with three X-ray complex structures of hVEGFR2 and its inhibitors, we evaluated the specific interactions between inhibitors and receptors and determined a single pharmacophore map. This map consisted of four features, a hydrogen bonding acceptor (HBA) on Cys917, two hydrogen bonding donors on Glu917 (HBD1) and Glu883 (HBD2), and one hydrophobic interaction (Lipo) with Val846, Ala864, Val897, Val914 and Phe1045 of hVEGFR2. Using this map, we searched a flavonol database including 9 typical flavonols and proposed that five flavonols, kaempferol, quercetin, fisetin, morin, and rhamnetin can be potent inhibitors of hVEGFR2. 3-OH of C-ring and 4’-OH of B-ring of flavonols are the essential features for hVEGFR2 inhibition. This study will be helpful for understanding the mechanism of inhibition of hVEGFR2 by natural products.

• Korean Journal of Pharmacognosy
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• v.38 no.3 s.150
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• pp.263-269
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• 2007

Nelumbo nucifera (Nymphaeaceae) has been widely used in a traditional oriental medicine to treat bleeding, fever, diarrhea, hemorrhoid, sunstroke, dysentery and dizziness. The leaves of this plant were refluxed with methanol, and then fractionated with organic solvents to screen the antioxidant activity using DPPH radical. Ethyl acetate and n-butanol fractions showed good DPPH radical scavenging effects and were carried out column chromatographies to isolate nine compounds. Their chemical structures were characterized as p-hydroxybenzoic acid (1), uracil (2), luteolin (3), quercetin $3-O-{\beta}-D-glucopyranoside$ (4), $rhamnetin 3-O-{\beta}-D-glucopyranoside$ (5), $isorhamnetin 3-O-{\beta}-D-glucopyranoside$ (6), $quercetin 3-O-{\beta}-D-glucuropyranoside$ (7), $quercetin 3-O-{\beta}β-D-xylofuranosyl(1{\rightarrow}2)-{\beta}-D-galactopyranoside$ (8), and adenine (9) by comparison NMR spectral data and with those in references. Compounds 1, 2, 5 and 9 were firstly isolated from this plant. Compounds 1, 3 and 4 showed potent DPPH radical scavenging activity. Especially, compound 3, luteolin showed the higher effect than ascorbic acid used as a positive control.