Lipoxygenase inhibitory constituents from rhubarb.
Phytochemical study on the ethanol extract of rhubarb led to the isolation of fifteen compounds, including five anthraquinones: chrysophanol (1), physcion (2), emodin (7), chrysophanol-8-O-beta-D: -glucopyranoside (9) and emodin-8-O-beta-D: -glucopyranoside (15), and ten stilbenes: desoxyrhaponticin (3), rhaponticin (4), resveratrol (5), desoxyrhapotigenin (6), rhapontigenin (8), piceatannol-3'-O-beta-D: -glucopyranoside (10), piceid (11), epsilon-viniferin (12), ampelopsin B (13) and isorhaponticin (14). Their structures were identified by comparing the physicochemical data with those of published papers. Among the isolated compounds, stilbene derivatives (3-6, 8 and 10-14) showed remarkable inhibitory effect on lipoxygenase with IC(50) values ranging from 6.7 to 74.1 microM. The inhibition kinetics analyzed by Lineweaver-Burk plots found that they were competitive inhibitors with the linoleic acid at the active site of lipoxygenase. In addition, stilbenes exhibited significantly free radical scavenging activity against ABTS(.+) with trolox equivalent activity capacity (TEAC) values ranging from 1.16 to 4.64. Whereas, anthraquinone derivatives (1-2, 7, 9 and 15) neither inhibited lipoxygenase nor scavenged free radical ABTS(.+). These results indicated that stilbene derivatives were considerate to be mainly lipoxygenase inhibitor and free radical scavenger constituents of rhubarb.
Ngoc
Tran Minh
TM
College of Pharmacy, Chungnam National University, Daejeon, 305-764, Korea.
Minh
Pham Thi Hong
PT
Hung
Tran Manh
TM
Thuong
Phuong Thien
PT
Lee
IkSoo
I
Min
Byung-Sun
BS
Bae
KiHwan
K
D000880:Anthraquinones / Q000737:chemistry / Q000302:isolation & purification*; D016166:Free Radical Scavengers / Q000737:chemistry / Q000302:isolation & purification; D016859:Lipoxygenase Inhibitors / Q000737:chemistry / Q000302:isolation & purification*; D010936:Plant Extracts / Q000737:chemistry; D012250:Rheum; D013267:Stilbenes / Q000737:chemistry / Q000302:isolation & purification*
D000880:Anthraquinones; D016166:Free Radical Scavengers; D016859:Lipoxygenase Inhibitors; D010936:Plant Extracts; D013267:Stilbenes