Bioactive terpenoids and guggulusteroids from Commiphora mukul gum resin of potential anti-inflammatory interest

Guggulu, the gum resin from Commiphora mukul, is one of the components of various formulations of traditional Ayurvedic medicine to treat inflammation, obesity, and lipid disorders. In most preparations of Ayurvedic medicine in India, guggulu is boiled prior to its use. Therefore, guggulu was boiled with H2O prior to extractions in our study. Bioassay-guided isolation of compounds from the hexane-soluble portion of the MeOH extract of guggulu yielded cembrenoids, 1-6, a bicyclic diterpene, 7, guggulusterone derivatives, 8-11, myrrhanone derivatives, 12, myrrhanol derivative, 13, and a lignan, 14. The structures of these compounds were confirmed by spectroscopic methods. Compounds 5, 6, 7, 10, and 12-14 are novel. These compounds were assayed for lipid peroxidation and cyclooxygenase (COX) enzyme inhibitory activities. At 100 ppm, compounds 3, 6, and 14 inhibited the lipid peroxidation by 79, 57, and 58%, respectively, and the rest of isolated compounds showed 20-40% inhibitory activity with respect to the controls. In COX-1 and COX-2 enzyme inhibitory assays, compound 3 showed 79 and 83%, and compound 8 gave 67 and 54% of inhibition, respectively, at 100 ppm. All fourteen compounds inhibited COX-1 enzyme at 100 ppm. The lipid peroxidation and COX enzyme inhibitory activities exhibited by compounds isolated from C. mukul may substantiate its use in traditional medicine.     

Antioxidant properties of flavonol glycosides from tea

We have determined the antioxidant activity of the major flavonols found in tea: a monoglycoside, a diglycoside and two triglycosides of kaempferol and three monoglycosides, a diglycoside and two triglycosides of quercetin. The Trolox equivalent antioxidant capacity (TEAC) and inhibition of iron/ascorbate-induced lipid peroxidation of phosphatidyl choline vesicles were measured. In the aqueous phase TEAC assay, the quercetin monoglycosides and diglycoside were approximately half as effective as quercetin aglycone. The quercetin triglycosides were much less effective than the monoglycosides and the diglycoside. The kaempferol glycosides were 32-39% less effective in the aqueous phase antioxidant assay compared to the kaempferol aglycone. Quercetin monoglycosides and diglycoside were potent inhibitors of lipid peroxidation, in contrast to the triglycoside which was much less effective. All the kaempferol glycosides were significantly less potent inhibitors of lipid peroxidation compared to the kaempferol aglycone. The compounds described herein demonstrate the antioxidant activity of the major flavonols in tea and indicate the effect of substituting a range of sugar moieties in the phenolic C ring.     

Antioxidant properties of flavonol glycosides from tea

Abstract

We have determined the antioxidant activity of the major flavonols found in tea: a monoglycoside, a diglycoside and two triglycosides of kaempferol and three monoglycosides, a diglycoside and two triglycosides of quercetin. The Trolox equivalent antioxidant capacity (TEAC) and inhibition of iron/ascorbate-induced lipid peroxidation of phosphatidyl choline vesicles were measured. In the aqueous phase TEAC assay, the quercetin monoglycosides and diglycoside were approximately half as effective as quercetin aglycone. The quercetin triglycosides were much less effective than the mono-glycosides and the diglycoside. The kaempferol glycosides were 32–9% less effective in the aqueous phase antioxidant assay compared to the kaempferol aglycone. Quercetin monoglycosides and diglycoside were potent inhibitors of lipid peroxidation, in contrast to the triglycoside which was much less effective. All the kaempferol glycosides were significantly less potent inhibitors of lipid peroxidation compared to the kaempferol aglycone. The compounds described herein demonstrate the antioxidant activity of the major flavonols in tea and indicate the effect of substituting a range of sugar moieties in the phenolic C ring.     

Stemodin-derived analogues with lipid peroxidation, cyclooxygenase enzymes and human tumour cell proliferation inhibitory activities

A series of analogues, derived from the antiviral and cytotoxic diterpene stemodin, were prepared and evaluated for their lipid peroxidation (LPO), cyclooxygenase enzyme-1 (COX-1) and -2 (COX-2), and tumour cell proliferation inhibitory activities. Oxidation of stemodin produced stemodinone, which was then converted to stemod-12-en-2-one. Reaction of the latter under Petrow conditions (bromine; silver acetate/pyridine) yielded mainly dibrominated abeo-stachanes. Solvolysis of the dibromo compounds gave products of hydrolysis, some with rearranged skeleta. In the lipid peroxidation inhibitory assay three of the compounds exhibited prominent activity. Interestingly, all the analogues showed higher COX-1 enzyme inhibition than COX-2. Although a few of the diterpenes limited the growth of some human tumour cell lines, most compounds induced proliferation of such cells.     

Quantification and characterisation of cyclo-oxygenase and lipid peroxidation inhibitory anthocyanins in fruits of Amelanchier

The levels of bioactive anthocyanins in the fruits of Amelanchier alnifolia, A. arborea and A. canadensis have been determined by HPLC. Cyanidin 3-galactoside (1) was present in the fresh fruit of the three species at concentrations of 155, 390 and 165 mg/100 g, respectively. Cyanidin 3-glucoside (2) was present only in A. alnifolia and A. canadensis at concentrations of 54 and 48 mg/100 g, respectively. The anthocyanins were confirmed by LC-ESI/MS and NMR studies. At 100 ppm, anthocyanin mixtures from the three species inhibited cyclo-oxygenase (COX)-1 and -2 enzymes at 66 and 67%, 60 and 72%, and 51 and 76%, respectively. The positive controls used in the COX assays were aspirin, Celebrex and Vioxx at 180, 1.67 and 1.67 ppm, respectively, and showed 74 and 69%, 5 and 82% and 0 and 85% COX-1 and COX-2 inhibition, respectively. Anthocyanins 1 and 2 and cyanidin (3) inhibited COX-1 enzyme 50.5, 45.62 and 96.36%, respectively, at 100 ppm, whereas COX-2 inhibition was the highest for 3 at 75%. In the lipid peroxidation inhibitory assay, anthocyanin mixtures at 10 ppm from the three species showed activities of 72, 73 and 68%, respectively, compared with 89, 87 and 98% for commercial anti-oxidants butylated hydoxyanisole, butylated hydroxytoluene, and tert-butylhydroxyquinone at 1.67, 2.2 and 1.67 ppm, respectively. At 10 ppm, compounds 1-3 inhibited lipid peroxidation by 70, 75 and 78%, respectively.     

Lipid peroxidation inhibitory compounds from daylily (Hemerocallis fulva) leaves

Daylilies (Hemerocallis spp.) have been used as food and in traditional medicine for thousands of years in eastern Asia. The leaves of the plant are used in the treatment of inflammation and jaundice. In studies of the aqueous methanol extracts of fresh Hemerocallis fulva leaves, 1',2',3',4'-tetrahydro-5'-deoxy-pinnatanine (1), pinnatanine (2), roseoside (3), phlomuroside (4), lariciresinol (5), adenosine (6), quercetin 3-O-beta-D-glucoside (7), quercetin 3,7-O-beta-D-diglucopyranoside (8), quercetin 3-O-alpha-L-rhamnopyransol-(1-->6)-beta-D-glucopyranosol-7-O-beta-D-glucopyranoside (9), isorhamnetin-3-O-beta-D-6'-acetylglucopyranoside (10) and isorhamnetin-3-O-beta-D-6'-acetylgalactopyranoside (11) were isolated. All of these compounds were tested for their in vitro lipid peroxidation inhibitory activities. Compounds 3-5 and 7-11 were found to possess strong antioxidant properties, inhibiting lipid oxidation by 86.4, 72.7, 90.1, 79.7, 82.4, 89.3, 82.2, and 93.2%, respectively at 50 microg/mL. Compound 1 is novel and compounds 3-6 and 8-11 described here in are isolated for the first time from daylily leaves.     

Antioxidant activity of compounds from the medicinal herb Aster tataricus

A number of compounds were isolated from the medicinal plant Aster tataricus including shionone, epifriedelinol, quercetin, kaempferol, scopoletin, emodin, aurantiamide acetate and 1,7-dihydroxy-6-methyl-anthraquinone. The compounds were compared with regard to their ability in inhibiting hemolysis of rat erythrocytes induced by 2'-2' azobis (2-amidinopropane) dihydrochloride, lipid peroxidation using the FeSO(4)-ascorbic acid system, and generation of superoxide radicals using a phenazine methosulfate-nicotinamide adenine dinucleotide system. The effects on the Fe-bleomycin-induced DNA damage reflected pro-oxidant activity. Quercetin and kaempferol were most potent in inhibiting hemolysis, lipid peroxidation and superoxide radical generation. Scopoletin and emodin were similar to quercetin and kaempferol in inhibiting superoxide radical generation and second to them in inhibiting lipid peroxidation. Aurantiamide acetate exhibited some inhibitory activity toward superoxide radical generation. 1,7-dihydroxy-6-methyl-anthraquinone exerted an inhibitory activity only on superoxide radical generation. Shionone and epifriedelinol did not display any antioxidant activity. Quercetin and kaempferol, but not the remaining compounds, exhibited some pro-oxidant activity.     

Antioxidant constituents of Nymphaea caerulea flowers

As part of an ongoing search for antioxidants from medicinal plants, 20 constituents were isolated from the Nymphaea caerulea flowers, including two 2S,3S,4S-trihydroxypentanoic acid (1), and myricetin 3-O-(3'-O-acetyl)-alpha-L-rhamnoside (2), along with the known myricetin 3-O-alpha-L-rhamnoside (3), myricetin 3-O-beta-D-glucoside (4), quercetin 3-O-(3'-O-acetyl)-alpha-L-rhamnoside (5), quercetin 3-O-alpha-L-rhamnoside (6), quercetin 3-O-beta-D-glucoside (7), kaempferol 3-O-(3'-O-acetyl)-alpha-L-rhamnoside (8), kaempferol 3-O-beta-D-glucoside (9), naringenin (10), (S)-naringenin 5-O-beta-D-glucoside (11), isosalipurposide (12), beta-sitosterol (13), beta-sitosterol palmitate (14), 24-methylenecholesterol palmitate (15), 4alpha-methyl-5alpha-ergosta-7,24(28)-diene-3beta,4beta-diol (16), ethyl gallate (17), gallic acid (18), p-coumaric acid (19), and 4-methoxybenzoic acid (20). The structures were determined by spectroscopic means. Compounds were tested for antioxidant activity and nine compounds 2-7, 11, 12 and 18 were considered active with IC(50) of 1.16, 4.1, 0.75, 1.7, 1.0, 0.34, 11.0, 1.7 and 0.95 microg/ml, respectively, while 1 was marginally active (IC(50)>31.25 microg/ml). The most promising activity was found in the EtOAc fraction (IC(50) 0.2 microg/ml). This can be attributed to the synergistic effect of the compounds present in it.     

Characterisation of new oligoglycosidic compounds in two Chinese medicinal herbs

A series of caffeic acid derivatives (3,5-dicaffeoyl-quinic acid, 3,4-dicaffeoyl-quinic acid, and 4,5-dicaffeoyl-quinic acid), and the new compound beta,3,4-trihydroxyphenethyl-O-[beta-apiofuranosyl-(1-->4)-alpha- rhamnopyranosyl-(1-->3)]-(4-O-caffeoyl)-beta-glucopyranoside (wedelosin), as well as three known flavonoid glycosides (quercetin 3-O-beta-glucoside, kaempferol 3-O-beta-apiosyl-(1-2)-beta-glucoside, and astragalin or kaempferol 3-O-beta-glucoside) were isolated from the Chinese medicinal herb Wedelia chinensis. Wedelosin showed an inhibitory activity on both the classical and the alternative activation pathway of the complement system. Another Chinese medicinal herb, Kyllinga brevifolia, yielded two known flavonoid glycosides [kaempferol 3-O-beta-apiosyl-(1-2)-beta-glucoside and isorhamnetin 3-O-beta-apiosyl-(1-2)-beta-glucoside], and a new quercetin triglycoside [quercetin 3-O-beta-apiofuranosyl-(1-->2)-beta-glucopyranoside 7-O-alpha-rhamnopyranoside]. The latter compound showed a moderate anti-viral activity.     

Stilbenes from the roots of Pleuropterus ciliinervis and their antioxidant activities

Two stilbene glycosides, pieceid-2"-O-gallate and pieceid-2"-O-coumarate, were isolated from the MeOH extract of the roots of Pleuropterus ciliinervis Nakai (Polygonaceae), together with two known compounds, resveratrol and pieceid. Their structures were determined spectroscopically, particularly by 2D NMR spectroscopic analysis. The antioxidant activities of stilbenes isolated were determined in vitro against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, superoxide radicals and by determining their lipid peroxidation inhibitory activities. Among the compounds isolated, pieceid-2"-O-gallate had the most potent inhibitory scavenging effect on DPPH, superoxide radicals and upon lipid peroxidation inhibition with IC50 values of 16.5, 23.9 and 5.1 microM, respectively.     

Novel lipid-peroxidation- and cyclooxygenase-inhibitory tannins from Picrorhiza kurroa seeds

From the AcOEt extract of the seeds of Picrorhiza kurroa were isolated picrorhiza acid (1), picrorhizoside A (2), picrorhizoside B (3), picrorhizoside C (4), (-)-shikimic acid (5), gallic acid (6), ellagic acid (7), isocorilagin (8), 1-O-galloyl-beta-D-glucose (9), 1-O,3-O,6-O-trigalloyl-beta-D-glucose (10), and 1-O,2-O,3-O,4-O,6-O-pentagalloyl-beta-D-glucose (11), and their structures were established by extensive NMR and chemical studies. Constituents 1-4 are novel compounds, and the known compounds 5-11 have been isolated for the first time from the seeds of P. kurroa. Compounds 2 and 3 were hydrolyzed and yielded 12, isochebulic acid. Compounds 1-12 showed 89.6, 77.3, 56.1, 50.5, 11.0, 86.4, 50.5, 29.2, 70.9, 50.5, 56.5, and 86.1% inhibition of lipid peroxidation at 5 microg/ml, respectively. The commercial antioxidants BHA (1.8 microg/ml), BHT (2.2 microg/ml), and TBHQ (1.66 microg/ml) inhibited lipid peroxidation at 85.6, 87.1, and 81.1%, respectively. The inhibition of cyclooxygenase-1 (COX-1) by 2-5, 7, 8, and 10-12 at 100 microg/ml was 41.9, 28.4, 32.9, 9.3, 70.7, 34.7, 16.0, 89.6, and 53.4%, respectively. Similarly, compounds 1-8 and 11 and 12, at 100 microg/ml, inhibited COX-2 by 12.6, 15.3, 25.1, 5.3, 13.2, 21.7, 2.0, 42.4, 43.4, and 36.9%, respectively.     

Antioxidant Properties of the Major Polyphenolic Compounds in Broccoli

We have examined the antioxidant activity of the major phenolic compounds in Broccoli: two flavonol glycosides (quercetin 3-O-sophoroside and kaemp-ferol 3-O-sophoroside) and four hydroxycinnamic acid esters (1,2'-disinapoyl-2-feruloyl gentiobiose, 1-sinapoyl-2-feruloyl gentiobiose, 1,2,2'-trisinapoyl gentiobiose and 1,2-disinapoyl gentiobiose). The Trolox C equivalent antioxidant capacity (TEAC) and inhibition of iron/ascorbate-induced lipid per-oxidation of phosphatidyl choline vesicles were measured. In the aqueous phase TEAC assay, the two flavonol glycosides were less active than their respective aglycones. TEAC values for the hydroxycinnamic acid esters were less than the sum of their constituent hydroxycinnamic acids on a molar basis. Quercetin 3-O-sophoroside was a potent inhibitor of lipid peroxidation, in contrast to kaempferol 3-O-sophoroside. The hydroxycinnamic acid esters were highly effective at preventing lipid damage with the exception of 1,2,2'-trisinapoyl gentiobiose. The six compounds analysed herein demonstrate the antioxidant activity of the major phenolics in broccoli and indicate the effect on antioxidant activity of sugar substitutions in the phenolic B ring.     

Inhibitory effects of flavonol glycosides from Cinnamomum osmophloeum on inflammatory mediators in LPS/IFN-gamma-activated murine macrophages

Four kaempferol glycosides were isolated from the leaves of Cinnamomum osmophloeum Kaneh, a Taiwan endemic tree. These compounds namely, kaempferitrin (1), kaempferol 3-O-beta-D-glucopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-7-O-alpha-L-rhamnopyranoside (2), kaempferol 3-O-beta-D-apiofuranosyl-(1-->2)-alpha-L-arabinofuranosyl-7-O-alpha-L-rhamnopyranoside (3), and kaempferol 3-O-beta-D-apiofuranosy-(1-->4)-alpha-L-rhamnopyranosyl-7-O-alpha-L-rhamnopyranoside (4). The structure of compound 2 was determined by spectroscopic analyses and acid hydrolysis. The isolates 1-4 were evaluated as inhibitors of some macrophage functions involved in the inflammatory process. These four compounds inhibited lipopolysaccharide (LPS) and interferon (IFN)-gamma-induced nitric oxide (NO), and cytokines [tumor necrosis factor (TNF)-alpha and interleukin (IL)-12] in a dose-dependent manner. The concentration of 50% inhibition (IC(50)) of NO by compounds 1, 3, 4 were 40, 15, 20microM, respectively. In parallel, these concentrations were approximately in a similar manner to that observed for TNF-alpha and IL-12 production. However, compound 2 inhibited NO and cytokines production by 30% at 100microM concentration. On the other hand, compounds 3 and 4 showed no inhibitory effect on the production of NO from macrophages, when inducible NO synthase was already expressed by the stimulation with LPS and IFN-gamma. Taken together, our results provide evidence that isolates of C. osmophloeum possess an anti-inflammatory potential which constitutes a previously unrecognized biological activity.     

Flavonol and drimane-type sesquiterpene glycosides of Warburgia stuhlmannii leaves

An investigation of methanolic extract of Warburgia stuhlmannii leaves has led to the isolation of two new drimane-type sesquiterpene glycosides characterized as mukaadial 6-O-beta-D-glucopyranoside, mukaadial 6-O-alpha-L-rhamnopyranoside together with two other novel flavonol glycosides identified as 3',5'-O-dimethylmyricetin 3-O-beta-D-2",3"-diacetylglucopyranoside and 3'-O-methylquercetin 3-O-beta-D-2",3",4"-triacetylglucopyranoside. The known compounds; mukaadial, deacetylugandensolide, quercetin, kaempferol, kaempferol 3-O-alpha-L-rhamnopyranoside, quercetin 3-O-beta-D-glucopyranoside, kaempferol 7-O-beta-D-glucopyranoside, myricetin 3-O-alpha-L-rhamnopyranoside, quercetin 3-O-alpha-L-rhamnopyranoside, quercetin 3-O-sophoroside and isorhamnetin 3-O-beta-D-glucopyranoside were also isolated from the same extract.     

Enzymatic hydrolysis of green tea seed extract and its activity on 5alpha-reductase inhibition

Two kaempferol glycosides were isolated from green tea seed extract (GTSE). After conducting a structure analysis, these two compounds were identified as kaempferol-3-O-[2-O-beta-D-galactopyranosyl-6-O-alpha-L-rhamnopyranosyl]-beta-D-glucopyranoside (compound 1) and kaempferol-3-O-[2-O-beta-D-xylopyranosyl-6-O-alpha-L-rhanmopyranosyl]-beta-D-glucopyranoside (compound 2). These two compounds were hydrolysed by o-glycolytic enzymes for the production of kaempferol. After performing several reactions, we found the optimum enzyme combination, a reaction with beta-galactosidase and hesperidinase. Finally, we produced kaempferol of above 95% purity. The 5alpha-reductase inhibition activities of GTSE hydrolysate (GTSE-H) containing kaempferol were evaluated by the contact cell-based metabolic method using a stable HEK 293 cell line. GTSE-H showed a good inhibition effect on HEK 293 cell lines both type 1 and type 2 on 5alpha-reductase. Especially, GTSE-H inhibited type 2 with kaempferol content dependency. The results indicate that the inhibition activity of hydrolysate on 5alpha-reductase type 2 increases in accordance with kaempferol content.     

Metabolic profiling of flavonoids in Lotus japonicus using liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry

Flavonoids detected from a model legume plant, Lotus japonicus accessions Miyakojima MG-20 and Gifu B-129, were profiled using liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR/MS). Five flavonols and two anthocyanidins were detected as aglycones. LC-FTICR/MS facilitated simultaneous detection of 61 flavonoids including compounds that have not been reported previously. Chemical information of the peaks such as retention time, lambdamax, m/z value of the quasi-molecular ion, m/z value of MS/MS fragment ions, and relative intensity of MS/MS fragments was obtained, along with the molecular formulas and conjugate structures. Fourteen were completely identified by comparison with authentic compounds. The high accuracy of m/z values, being 0.081 ppm between observed and theoretical values, allowed prediction of molecular formulas of unknown compounds with the help of isotope peak information for determination of chemical composition. Based on a predicted elemental composition, the presence of a novel nitrogen-containing flavonoid was proposed. A comparison of flavonoid profiles in flowers, stems, and leaves demonstrated that the flowers yielded the most complex profile, containing 30 flower-specific flavonoids including gossypetin glycosides and isorhamnetin glycosides. A comparison of flavonoid profiles between MG-20 and B-129 grown under the same conditions revealed that the accumulation of anthocyanins was higher in B-129 than MG-20, particularly in the stem. Developmental changes in the flavonoid profiles demonstrated that kaempferol glycosides increased promptly after germination. In contrast, quercetin glycosides, predominant flavonoids in the seeds, were not detectable in growing leaves.     

Malonylated flavonol glycosides from the petals of Clitoria ternatea

Three flavonol glycosides, kaempferol 3-O-(2"-O-alpha-rhamnosyl-6"-O-malonyl)-beta-glucoside, quercetin 3-O-(2"-O-alpha-rhamnosyl-6"-O-malonyl)-beta-glucoside, and myricetin 3-O-(2",6"-di-O-alpha-rhamnosyl)-beta-glucoside were isolated from the petals of Clitoria ternatea cv. Double Blue, together with eleven known flavonol glycosides. Their structures were identified using UV, MS, and NMR spectroscopy. They were characterized as kaempferol and quercetin 3-(2(G)- rhamnosylrutinoside)s, kaempferol, quercetin, and myricetin 3-neohesperidosides, 3-rutinosides, and 3-glucosides in the same tissue. In addition, the presence of myricetin 3-O-(2"-O-alpha-rhamnosyl-6"-O-malonyl)-beta-glucoside was inferred from LC/MS/MS data for crude petal extracts. The flavonol compounds identified in the petals of C. ternatea differed from those reported in previous studies.     

Flavonol glycosides from distilled petals of Rosa damascena Mill

Flavonol glycosides were extracted from petals of Rosa damascena Mill. after industrial distillation for essential oil recovery and characterized by high-performance liquid chromatography-electrospray ionization mass spectrometry. Among the 22 major compounds analyzed, only kaempferol and quercetin glycosides were detected. To the best of our knowledge, the presence of quercetin 3-O-galactoside and quercetin 3-O-xyloside has so far not been reported within the genus Rosa. In addition, based on their fragmentation patterns, several acylated quercetin and kaempferol glycosides, some of them being disaccharides, were identified for the first time. The kaempferol glycosides, along with the kaempferol aglycone, accounted for 80% of the total compounds that were quantified, with kaempferol 3-O-glucoside being the predominant component. The high flavonol content of approximately 16 g/kg on a dry weight basis revealed that distilled rose petals represent a promising source of phenolic compounds which might be used as functional food ingredients, as natural antioxidants or as color enhancers.     

金花茶花化学成分的研究

采用反复硅胶柱色谱法、Sephadex LH-20柱色谱法、ODS柱色谱法、反复重结晶等方法对金花茶花的化学成分进行分离纯化,并通过理化常数测定和波谱分析等方法进行结构鉴定.从金花茶花的乙醇提取物中分离得到13个化合物,分别鉴定为:槲皮素(1)、槲皮素-7-O-β-D-葡萄糖苷(2)、槲皮素-3-O-β-D-葡萄糖苷(...     

Inhibition of human low density lipoprotein oxidation by flavonols and their glycosides

Antioxidative effects of the flavonols and their glycosides, i.e., quercetin (Q), quercetin galactopyranoside (QG), quercetin rhamnolpyranoside (QR), rutin (R), morin (MO), myrecetin (MY), kaempferol (K) and kaempferol glucoside (KG), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either by a water-soluble initiator 2,2'-azobis(2-amidino propane hydrochloride) (AAPH), or by cupric ion (Cu2+). The reaction kinetics were monitored either by the uptake of oxygen and the depletion of alpha-tocopherol (TOH) presented in the native LDL, or by the formation of thiobarbituric acid reactive substances (TBARS). Kinetic analysis of the antioxidation process demonstrates that these flavonols and their glycosides are effective antioxidants against AAPH- and Cu(2+)-initiated LDL peroxidation, the flavonols bearing ortho-dihydroxyl groups possess significantly higher antioxidant activity than those bearing no such functionalities, and the glycosides are less active than their parent aglycones.