Flavone C-glycosides from Coronilla varia

One new and 5 known flavone C-glycosides were isolated from leaves and stems of Coronilla varia. The new compound was shown to be isoorientin 2″-O-rhamnoside. The known compounds were isovitexin, isoorientin, isovitexin 4′-O-glucoside, isoorientin 4′-O-glucoside, and isoorientin 7-O-glucoside.     

Isomollupentin-O-glucosides from Cerastium arvense

Eight C-glycosylflavone O-glycosides including three new compounds: isomollupentin 7-O-glucoside, isomollupentin 4′-O-glucoside and isomollupentin 2″-O-glucoside have been isolated from the leaves and flowers of Cerastium arvense. The 27 C-glycosylflavones identified in this plant are tabulated.     

Flavonoid diversification in different leaf compartments of Primula auricula (Primulaceae)

Populations of Primula auricula L. subsp. auricula from Austrian Alps were studied for flavonoid composition of both farinose exudates and tissue of leaves. The leaf exudate yielded Primula-type flavones, such as unsubstituted flavone and its derivatives, while tissue flavonoids largely consisted of flavonol 3-O-glycosides, based upon kaempferol (3, 4) and isorhamnetin (5–7). Kaempferol 3-O-(2″-O-β-xylopyranosyl-[6″-O-β-xylopyranosyl]-β-glucopyranoside) (3) and isorhamnetin 3-O-(2″-O-β-xylopyranosyl-[6″-O-β-xylopyranosyl]-β-glucopyranoside) (6) are newly reported as natural compounds. Remarkably, two Primula type flavones were also detected in tissues, namely 3′-hydroxyflavone 3′-O-β-glucoside (1) and 3′,4′-dihydroxyflavone 4′-O-β-glucoside (2), of which (1) is reported here for the first time as natural product. All structures were unambiguously identified by NMR and MS data. Earlier reports on the occurrence of 7,2′-dihydroxyflavone 7-O-glucoside (macrophylloside) in this species could not be confirmed. This structure was now shown to correspond to 3′,4′-dihydroxyflavone 4′-O-glucoside (2) by comparison of NMR data. Observed exudate variations might be specific for geographically separated populations. The structural diversification between tissue and exudate flavonoids is assumed to be indicative for different ecological roles in planta.     

Flavonol tetraglycosides from the leaves of Prunus cerasus and P. Avium

Four new flavonol glycosides have been identified from fresh leaves and fruits of sweet and sour cherries (Prunus avium and P. cerasus) as minor flavonoids: quercetin 3-O-rutinosyl-7,3′-O-bisglucoside; two quercetin 3-O-rutinosyl-4′-di-O-glucosides; kaempferol 3-O-rutinosyl-4′-di-O-glucoside.     

New 8-hydroxyflavonoids from Solanum section Androceras

Five new 8-hydroxyflavonoids have been identified from leaves of Solanum section Androceras: 8-methoxymyricetin 3,7,4′-trimethyl ether; 8-hydroxymyricetin 3,7,4′-trimethyl ether; 8-hydroxymyricetin 8-O-glucosylxyloside 3,7,4′-trimethyl ether; 8-hydroxychrysoeriol 7-methyl ether; 8-hydroxychrysoeriol 7-O-glucoside.     

Apigenin 4′-O-β-d-glucoside 7-O-β-d)- glucuronide: The copigment in the blue pigment of Centaurea cyanus

The copigment present in the crystalline blue pigment isolated from Blue Boy cornflowers (Centaurea cyanus L.) was identified as apigenin 4′-O-β-glucoside 7-O-β-d-glucuronide. The NMR spectra of aryl glucuronides are discussed.     

Chalcones and other flavonoids from Asarum sensu lato (Aristolochiaceae)

Seventy-five taxa belonging to the genus Asarum sensu lato were studied for their composition of flavonoids. Three chalcones and an aurone were found as major components. The chalcones were identified as chalcononaringenin 2′,4′-di-O-glucoside, 4,2′,4′-tri-O-glucoside, 4-O-glucoside, and the aurone as aureisidin 4,6-di-O-glucoside. The glycoside, 2′,4′-di-O-glucoside was detected in all taxa examined, and is a chemotaxonomical feature of Asarum sensu lato. 4,2′,4′-Tri-O-glucoside was found from the taxa classified into the genera Asiasarum, Geotaenium and Heterotropa by Maekawa's system. On the other hand, the glycoside was not detected from three Asarum sensu stricto species, A. caudigerum, A. caulescens and A. leptophyllum. In contrast, aurone, aureusidin 4,6-di-O-glucoside occurred in two Asarum s.s., A. caulescens and A. leptophyllum. Thus, the Asarum s.s. and other Maekawa's genera, Asiasarum, Geotaenium and Heterotropa could distinguish by the presence or absence of some anthochlor pigments. Other flavonoids were isolated from the selected 18 Asarum species. They were characterized as some flavonol 3- or 3,7-O-glycosides based on kaempferol, quercetin and isorhamnetin, flavone, apigenin 6,8-di-C-glycoside, flavanone, naringenin 5,7-di-O-glucoside, and xanthone, mangiferin.     

Flavonoide aus salix alba. Die struktur des Terniflorins und eines weiteren acylflavonoides

Eight flavonoids were isolated from the leaves of Salix alba. One, apigenin 7-O-(4-p-coumarylglucoside), is a new natural compound; another, terniflorin, the 6-isomer, is an artefact. The others are quercetin 3-O-glucoside, quercetin 3-O-rutinoside, isorhamnetin 3-O-glucoside, isorhamnetin 3-O-rutinoside and quercetin 7,′3-dimethylether 3-O-glucoside.     

Biologically-active flavonoids from Gossypium arboreum

A new flavonol glycoside, gossypetin 8-O-rhamnoside, was isolated from flower petals of Gossypium arboreum along with quercetin 7-O-glucoside, quercetin 3-O-glucoside and quercetin 3′-O-glucoside. These compounds showed antibacterial activity against Pseudomonas maltophilia and Enterobacter cloacae.     

The flavonoids of phragmites australis flowers

The major flavonoid constituents of Phragmites australis flowers are the C-glycosylflavones swertiajaponin, isoswertiajaponin and two new O-glycosides, the 3′-O-gentiobioside and the 3′-O-glucoside of swertiajaponin. Two unusual flavonol glycosides, rhamnetin 3-O-rutinoside and rhamnetin 3-O-glucoside, were also characterized from the same tissue.     

Localization of partially methylated flavonol glucosides in Chrysosplenium americanum. I. Preparation and some properties of a trimethyl flavonol glucoside antibody

5,2′,5′-Trihydroxy-3,7,4′-trimethoxyflavone-2′-O-glucoside, a major flavonoid constituent of Chrysosplenium americanum Schwein. ex Hooker was conjugated to bovine serum albumin (BSA) by the diazo reaction in good yield and with a molar ratio of 11.5:1. Antibody raised against the latter conjugate had a titer value of 1:1600 and was found to be specific for the 2′-O-glucosides of tri- and tetramethoxyflavones. Some cross reactivity (about 55%) was observed against the pentamethoxyflavone-5′-O-glucoside; but almost none with the parent hydroxyflavone, quercetin, or any of its partially methylated (3,7,4′-tri- or 3,7,3′,4′-tetramethyl-) derivatives. The specificity of antibodies raised against the 2′-O-glucosides of Chrysosplenium makes them useful for the intracellular localization of these natural constituents.     

Further flavonol glycosides from Anthyllis onobrychioides

The new triglycoside rhamnetin 3-O-β-d-galactopyranoside-3′,4′-di-O-β-d-glucopyranoside has been isolated from the aerial parts of Anthyllis onobrychioides. Two other new flavonol glycosides, rhamnazin 3-O-galactoside and rhamnazin 3-O-galactoside-4′-O-glucoside, were identified but not isolated as pure substances.     

The flavonoids of tetragonotheca (compositae)

Fifteen flavonols, five aglycones and ten glucosides were isolated from the four species of Tetragonotheca, T. repanda, T. helianthoides, T. texana and T. ludoviciana. Included among the isolated flavonols are four previously unreported 7-O-glucosides, 6-hydroxykaempferol 7-O-glucoside, 6-hydroxykaempferol 6-methyl ether 7-O-glucoside, quercetagetin 6,3′-dimethyl ether 7-O-glucoside and quercetagetin 3,6-dimethyl ether 7-O-glucoside.     

Evidence of biosynthetic simplicity in the flavonoid chemistry of the ricciaceae

The major flavonoids in Riccia crystallina are naringenin and its 7-O-glucoside, apigenin 7-O-glucoside and apigenin 7-O-glucuronide and derivatives. Ricciocarpus natans is a rich source of luteolin 7,3′-di-O-glucuronide and also contains the 7-O-glucuronides of apigenin and luteolin and the 3′-O-glucuronide of luteolin. A parallel between the production of biosynthetically simple flavonoids and reduced morphology is evident among these liverworts.     

Three acylated anthocyanins and a flavone glycoside in violet-blue flowers of Saintpaulia ‘Thamires’

Three new acylated anthocyanidin 3-rutinoside-5-glucosides were isolated from the violet-blue flowers of Saintpaulia ‘Thamires’ (Saintpaulia sp.) along with a known flavone glycoside. Three new acetylated anthocyanins were determined to be 3-O-[6-O-(4-O-(acetyl)-α-rhamnopyranosyl)-β-glucopyranoside]-5-O-(β-glucopyranoside)s of malvidin (pigment 1), peonidin (pigment 2), and pelargonidin (pigment 3) by chemical and spectroscopic methods. HPLC analysis revealed that malvidin 3-O-acetylrutinoside-5-O-glucoside existed as a dominant pigment in the violet-blue flowers. Moreover, the isolated flavone was identified to be apigenin 4′-O-β-glucuronopyranoside (pigment 4).On the visible absorption spectral curves of fresh violet-blue petals and in their crude extracts in pH 5.0 buffer solution, two characteristic absorption maxima at 547 and 577 nm, with a shoulder near 620 nm, were observed. In contrast, the absorption curves of malvidin 3-O-acetylrutinoside-5-O-glucoside and its deacyl anthocyanin exhibited only one maximum at 535 nm in pH 5.0 buffer solution, and its color was violet and soon fell into decay.However, by addition of apigenin 4′-O-glucuronide, the color of malvidin 3-O-acetylrutinoside-5-O-glucoside changed from violet to violet-blue, similar to that of the fresh flower in pH 5.0 buffer solution. The absorption curve of its violet-blue solution exhibited two similar absorption maxima at 547 and 577 nm, with a shoulder near 620 nm. These results suggest that intermolecular copigmentation between malvidin 3-O-acetylrutinoside-5-O-glucoside and apigenin 4′-O-glucuronide may be responsible for the violet-blue flower color of S. ‘Thamires’.     

Flavonoids from the leaves and flowers of the Himalayan Cathcartia villosa (Papaveraceae)

Five flavonols, four flavones and one C-glycosylflavone were isolated from the leaves of Cathcartia villosa which is growing in the Himalayan Mountains. They were characterized as quercetin 3-O-vicianoside (1), quercetin 7,4′-di-O-glucoside (3), quercetin 3-O-rutinoside (4), quercetin 3-O-glucoside (5), quercetin 3-O-arabinosylarabinosylglucoside (6) (flavonols), luteolin (7), luteolin 7-O-glucoside (8), apigenin (9), chrysoeriol (10) (flavones), and vicenin-2 (11) (C-glycosylflavone) by UV, LC-MS, acid hydrolysis, NMR and/or HPLC and TLC comparisons with authentic samples. On the other hand, two flavonols 1 and kaempferol 3-O-vicianoside (2) were isolated and identified from the flowers of the species. Flavonoids were reported from the genus Cathcartia in this survey for the first time. Their chemical characters were chemotaxonomically compared with those of related Papaveraceous genera, Meconopsis and Papaver.     

Flavonoids and the chemotaxonomy of three Sophora species

Sophora microphylla, S. prostrata and S. tetraptera are distinguishable from one another by their leaf flavonoids. S. microphylla is distinguished by the present of rhamnosylvitexin and rhamnosylisovitexin and S. tetraptera by the presence of apigenin-7-O-rhamnosylglucoside-4′-O-glucoside and the 7-O-glucosides of apigenin, 7,4′-dihydroxyflavone, luteolin and 7,3′,4′-trihydroxyflavone. Sophora prostrata lacks all these flavonoids, but has several pigments which are common to all three species.     

Molecular cloning and characterization of genistein 4′-O-glucoside specific glycosyltransferase from Bacopa monniera

Health related benefits of isoflavones such as genistein are well known. Glycosylation of genistein yields different glycosides like genistein 7-O-glycoside (genistin) and genistein 4′-O-glycoside (sophoricoside). This is the first report on isolation, cloning and functional characterization of a glycosyltransferase specific for genistein 4′-O-glucoside from Bacopa monniera, an important Indian medicinal herb. The glycosyltransferase from B. monniera (UGT74W1) showed 49 % identity at amino acid level with the glycosyltransferases from Lycium barbarum. The UGT74W1 sequence contained all the conserved motifs present in plant glycosyltransferases. UGT74W1 was cloned in pET-30b (+) expression vector and transformed into E. coli. The molecular mass of over expressed protein was found to be around 52 kDa. Functional characterization of the enzyme was performed using different substrates. Product analysis was done using LC–MS and HPLC, which confirmed its specificity for genistein 4′-O-glucoside. Immuno-localization studies of the UGT74W1 showed its localization in the vascular bundle. Spatio-temporal expression studies under normal and stressed conditions were also performed. The control B. monniera plant showed maximum expression of UGT74W1 in leaves followed by roots and stem. Salicylic acid treatment causes almost tenfold increase in UGT74W1 expression in roots, while leaves and stem showed decrease in expression. Since salicylic acid is generated at the time of injury or wound caused by pathogens, this increase in UGT74W1 expression under salicylic acid stress might point towards its role in defense mechanism.     

Effects of drought stress on phenolic accumulation in greenhouse-grown olive trees (Olea europaea)

The present study evaluates the effects of severe drought stress on the content of phenolic compounds in olive leaves, namely hydroxytyrosol, tyrosol, p-hydroxybenzoic acid, catechin, luteolin 7-O-rutinoside, luteolin 7-O-glucoside, apigenin 7-O-glucoside, quercetin, apigenin, pinoresinol, oleuropein and verbascoside in greenhouse-grown plantlets. The results showed that oleuropein, verbascoside, luteolin 7-O-glucoside and apigenin 7-O-glucoside were the most important phenolic compound of stressed olive plants and can represent up to 84% of the total amount of the identified phenolic compounds. Application of drought stress caused a significant increase in the level of oleuropein (87%), verbascoside (78%), luteolin 7-O-glucoside (72%) and apigenin 7-O-glucoside (85%), when compared to the control. The elevated values of these phenolic compounds can help controlling the water status of olive plants and avoiding serious oxidative damage induced by water deficit stress. To our knowledge, this is the first report to show the boost in the concentrations of verbascoside, luteolin 7-O-glucoside and apigenin 7-O-glucoside in the leaves of olive trees after water deficit stress.     

Dihydrochalcone glucosides and antioxidant activity from the roots of Anneslea fragrans var. lanceolata

Bioassay-guided fractionation of the roots of Anneslea fragrans var. lanceolata led to the isolation of four dihydrochalcone glucosides, davidigenin-2′-O-(6″-O-4″′-hydroxybenzoyl)-β-glucoside (1), davidigenin-2′-O-(2″-O-4″′-hydroxybenzoyl)-β-glucoside (2), davidigenin-2′-O-(3″-O-4″′-hydroxybenzoyl)-β-glucoside (3), and davidigenin-2′-O-(6″-O-syringoyl)-β-glucoside (4), and 13 known compounds. The structures were identified by means of spectroscopic analysis. Davidigenin-2′-O-(6″-O-syringoyl)-β-glucoside (4), 1-O-3,4-dimethoxy-5-hydroxyphenyl-6-O-(3,5-di-O-methylgalloyl)-β-glucopyranoside (5), lyoniresinol (10), and syringic acid (13) showed ABTS [2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)] cation radical scavenging activity, with SC₅₀ values of 52.6 ± 5.5, 26.0 ± 0.7, 6.0 ± 0.2, and 27.5 ± 0.6 μg/mL in 20 min, respectively. Lyoniresinol (10), isofraxidin (12), and syringic acid (13) also showed DPPH [1,1-diphenyl-2-picrylhydrazyl] radical scavenging activity, with SC₅₀ values of 8.4 ± 1.8, 51.6 ± 2.2, and 4.3 ± 0.7 μg/mL in 30 min, respectively.