Study On Chemical Constituents Of Ribes Nigrum L. From Xinjiang And Their Antioxidant Activity

Black currants (Ribes nigrum L.), which is used to be the most commonly prescribed drug by Uygur doctor, have been proved to exhibit various biological effect recorded in "TCM from Xin Jiang", such as activation of blood circulation and removing of blood stasis. The chemical constituents in seeds, fruits and leaves had been widely investigated by scholars around the world. However, the relative research on the chemical constituents in roots has never been reported yet. In order to find bioactive compounds with new types of structures, the chemistry and antioxidant activity evaluation were conducted in the present study.A variety of separation techniques, such as solvent partition and column chromatography, have been employed for isolation of compounds in Xin Jiang Black currants. Nineteen compounds were isolated and eighteen of them have been identified by the combination of MS, 1D-NMR, 2D-NMR, IR and UV methods. There are four new compounds: 3-methyl-4-nitro-2-butanol-2-O-β-D-glucopyranoside(1),3',4'-diacetoxyl-3,5-dihydroxystilbene-3-O-β-D -glucopyranoside(3), 2-[3-(β-D-glucopyranosyloxy)-5-hydroxy-4-methoxyphenyl]-2,3-dihydro-5,7-dihydroxy-4H-1-benzopyran-4-one(5),1-O-(3,4-dihydroxy-5-methoxy-benzoyl)-β-D-glucopyranose(9). There are five compounds firstly isolated from the plants of this Ribes: 3,4,5-trihydroxy-benzoicacid-(2E)-2-cyano-4-(β-D-glucopyranosyloxy)-2-butenylester(2), isorhaponti(4), 2-[3-(P-D-glucopyranosyloxy)-4,5-dihydroxyphenyl]-2,3-dihydro-5,7-dihydroxy-4H-1-benzopyran-4-one(6), dihydromyricetin(8), 2-acetyl-3-hydroxy-1-O-β-D-glucopyranoside(11).There are three compounds firstly isolated from the plant: pleoside(12), ethyl-O-β-D-glucopyranoside(13), 3,4-dihydroxy-5-methoxy-benzoic acid (15). gallocatechin (7),β-D-glucogallin(10), vanillic acid(14), gallic acid(16), dimethyl phthalate(17), dibutyl phthalate(18) are firstly isolated from root of this plant.The antioxidant capacity of different compounds and extracts were evaluated through DPPH (diphenylpicrylhydrazyl) assay. The compound antioxidant capacity test indicated that compounds 1,5, 11, 12 and 13 showed very weak antioxidant activity while 2,4,6,7,9,10,16 exhibited strong free radical scavenging activity.Compound 2 (IC5o=0.061μmol/ml) demonstrated excellent free radical scavenging rate, which was significantly stronger than Trolox (IC₅₀=0.252μmol/ml). In addition, Compounds 6, 7, 10 and 16 was proved to exhibit slightly higher antioxidant capacity than Trolox, with IC50 equals to 0.184μmol/ml, 0.122μmol/ml, and 0.196μmol/ml,0.123μmol/ml, respectively. Compared with Trolox (IC₅₀ =0.063mg/ml),the extract antioxidant capacity test indicated that Black currants total extract, petroleum ether extract, chloroform extract, ethyl acetate extract,n-butanol extract and water extract showed satisfiing antioxidant capacity with IC₅₀ at 0.224mg/ml, 0.425mg/ml, 0.440mg/ml, 0.121mg/ml, 0.197mg/ml, 0.231mg/ml, respectively.