Flavonol derivatives of the genus Clibadium (compositae)

The flavonoids of eleven species of Clibadium are all based on the flavonols kaempferol, quercetin and quercetagetin. Glucose and galactose sugar substitutions occur in all taxa, while rhamnosides, arabinosides, xylosides, rutinosides and diglucosides are less widely distributed. O-Methylated compounds provide the most meaningful taxonomic information and serve to divide the species into two groups. Infraspecific variation of flavonoids is commonplace. This is the first report of flavonoids in Clibadium.     

Phenylpropanoid and flavonoid glycosides from the leaves of Clerodendrum infortunatum (Lamiaceae)

Clerodendrum infortunatum L. (syn.: Clerodendrum viscosum Vent.), a member of the Lamiaceae, yielded one undescribed jasmonic acid derivative, ten acteosides, and two flavonoids. The jasmonic acid derivative was identified as 6'-O-caffeoyl-12-glucopyranosyloxyjasmonic acid. The acteosides were identified as isoacteoside, acteoside, 2''-O-acetyl-martyonside, 3''-O-acetyl-martyonside, martynoside, brachynoside, leucosceptoside A, jionoside C, jionoside D, incanoside C. The flavonoids were identified as apigenin 7-O-glucuronide and acacetin 7-O-glucuronide. The structures of the isolated components have been identified by UHPLC-HRMS, 1D and 2D NMR spectroscopic analyses, spectrometric techniques, and in comparison with published NMR data. The absolute sugar configuration was determined by GLC-MS/MS analysis of the octylated derivative of the sugar moiety after hydrolysis. Among the known compounds, ten are reported for the first time from this species, while the acteoside leucosceptoside A and the two flavonoids have been isolated for the first time from the genus Clerodendrum. The chemophenetic significance of the compounds obtained from C. infortunatum is summarized in comparison to those found in other Clerodendrum species.     

Flavonoids of Penthorum sedoides

In an attempt to elucidate the familial affinities of Penthorum, the flavonoids and other phenolic compounds of P. sedoides were examined. The species is characterized by a relatively simple array of kaempferol and quercetin 3-O-mono-, di- and triglycosides. Flavonoid variation was detected between populations. Also present was a group of phenolic compounds that gave positive color reactions for the existence of gallic acid-like components. Although structures were not determined for these compounds, the presence of gallic acid-like moieties in two of the compounds was confirmed by ¹H NMR. The array of these compounds and flavonoids detected in P. sedoides does not readily support inclusion of Penthorum in the Saxifragaceae.     

Kaempferol and its glycosides from Equisetum silvaticum L. from the Khanty-Mansi autonomous area

Three flavonoids were isolated from the aerial part of the wood horsetail (Equisetum silvaticum L.); two of them were found for the first time. The compounds were identified as kaempferol, kaempferol 3-O-β-D-galactopyranosyl-7-O-α-L-rhamnopyranoside and kaempferol 3-O-rutinosyl-7-O-L-rhamnopyranoside on the basis of the chemical transformations and IR, UV, ¹H-NMR and mass spectra.     

Phenolic dimers and an indole alkaloid from Campylospermum flavum (Ochnaceae)

From the leaves and stem bark of Campylospermum flavum (Ochnaceae), three compounds, namely 4?-O-methylagathisflavone, flavumchalcone, and flavumindole have been isolated together with 10 known compounds, including three flavonoids, two biflavonoids, two alkaloids, two nitrile glucosides, and glucopyranosyl-β-sistosterol. The structures of these compounds and their relative configurations were established by 1D and 2D NMR experiments. The methanolic crude extracts of leaves and stem bark of C. flavum and compounds displayed a significant cytotoxicity towards Artemia salina larvae.     

Three flavonoid glycosides containing acetylated allose from stachys recta

By means of ¹³C and ¹H NMR spectroscopy three flavone glycosides, obtained from Stachys recta, were identified as 7-O-(2″-O-6″′-O-acetyl-β-D-allopyranosyl-β-D-glucopyranosides) of 4′-O-methylisoscutellarein, isoscutellarein and 3′-hydroxy-4′-O-methylisoscutellarein. The latter two compounds are isolated for the first time. Only mannose and glucose have been reported previously as sugar components of flavonoids of the genus Stachys.     

Characterization and quantification of flavonoid glycosides in the Prunus genus by UPLC-DAD-QTOF/MS

Widely distributed in plants, flavonoids reduce the incidence of cancer and cardiovascular disease. In this study, flavonoid content and composition in members of the Prunus genus were evaluated using liquid chromatography with diode array and electrospray ionization mass spectrometric detection (UPLC-DAD-ESI/QTOF-MS). Flavonoids in plants of the Prunus genus include the basic structures of kaempferol, quercetin, and catechin, and exist as mono-, di-, or tri-glycoside compounds mono-acylated with acetic acid. A total of 23 individual flavonoids were isolated and confirmed, three of which appear to be newly identified compounds: quercetin 3-O-(2″-O-acetyl)neohesperidoside, quercetin 3-O-(4″-O-acetyl)rutinoside, and kaempferol 3-O-(4″-O-acetyl)rutinoside. Japanese apricot and Chinese plum contained the highest amounts of flavonoids in the Prunus genus. During the ripening stage of Japanese apricot, the total flavonol content was reduced, while the catechin content was increased.     

Flavonol and dihydroflavonol glycosides of echinocereus triglochidiatus var. Gurneyi

Perianth parts, in particular, tepals of Echinocereus triglochidiatus var. gurneyi yielded a complex mixture of dihydroflavonols and dihydroflavonol 7-O-glucosides. Dihydroquercetin and its 7-O-glucoside were the predominant compounds while dihydrokaempferol and dihydromyricetin and their 7-O-glycosides were present in lesser amounts. Quercetin 7-O-glucoside was the principal flavonol glycoside: others present were quercetin and kaempferol 3-O-glucosides and 3-O-rhamnosylglucosides. The epidermis and spines yielded only traces of presumed flavonols as determined by two-dimensional TLC. No flavonoids were detected in the cortex tissue. This is the first report of dihydroflavonol derivatives from the Cactaceae and constitutes the first record of flavonoids from Echinocereus.     

Regioselective synthesis of flavonoid bisglycosides using Escherichia coli harboring two glycosyltransferases

Regioselective glycosylation of flavonoids cannot be easily achieved due to the presence of several hydroxyl groups in flavonoids. This hurdle could be overcome by employing uridine diphosphate-dependent glycosyltransferases (UGTs), which use nucleotide sugars as sugar donors and diverse compounds including flavonoids as sugar acceptors. Quercetin rhamnosides contain antiviral activity. Two quercetin diglycosides, quercetin 3-O-glucoside-7-O-rhamnoside and quercetin 3,7-O-bisrhamnoside, were synthesized using Escherichia coli expressing two UGTs. For the synthesis of quercetin 3-O-glucoside-7-O-rhamnoside, AtUGT78D2, which transfers glucose from UDP-glucose to the 3-hydroxyl group of quercetin, and AtUGT89C1, which transfers rhamnose from UDP-rhamnose to the 7-hydroxyl group of quercetin 3-O-glucoside, were transformed into E. coli. Using this approach, 67 mg/L of quercetin 3-O-glucoside-7-O-rhamnoside was synthesized. For the synthesis of quercetin 3,7-O-bisrhamnoside, AtUGT78D1, which transfers rhamnose to the 3-hydroxy group of quercetin, and AtUGT89C1 were used. The RHM2 gene from Arabidopsis thaliana was coexpressed to supply the sugar donor, UDP-rhamnose. E. coli expressing AtUGT78D1, AtUGT89C1, and RHM2 was used to obtain 67.4 mg/L of quercetin 3,7-O-bisrhamnoside.     

Eight flavonol glycosides in Pyrola (pyrolaceae)

As part of a general survey of the flavonoids of Pyrolaceae, the flavonoids of Pyrola virens and P. chlorantha were investigated. Eight flavonol glycosides based upon kaempferol, quercetin and rhamnetin were identified from each of the two species. Two of the glycosides, rhamnetin 3,3′,4′-tri-O-glucoside and rhamnetin 3-O-arabinoside-3′,4′-di-O-glucoside are previously unreported and further, represent an unusual pattern of glycosylation. The similarity of flavonoids and the presence of the unusual substitution pattern supports a conspecific status for the two taxa.     

Polyphenols isolated from antiradical extracts of Mallotus metcalfianus

Six flavonoids including two new flavones, luteolin 7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside), chrysoeriol-7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside) and a mixture of two pairs of diastereoisomeric flavonolignans, (±)-hydnocarpin 7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside)/(±)-hydnocarpin-D 7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside) with a 2:1 ratio were isolated from the whole plant of Mallotus metcalfianus Croizat, in addition to 10 known compounds. Their structures were evaluated on the basis of different spectroscopic methods, including extensive 1D and 2D NMR spectroscopy. Some extracts have moderate antimicrobial properties and interesting antiradical (DPPH) activity, as well as some compounds isolated from this species. Tannins were also identified in some active extracts.     

Flavonoid constituents of Ephedra alata

Two new flavonol glucosides have been identified in Ephedra alata, namely, herbacetin 8-methyl ether 3-O- glucoside-7-O-rutinoside and herbacetin 7-O-(6″-quinylglucoside). The known flavonoids vicenin II, lucenin III, kaempferol 3-rhamnoside, quercetin 3-rhamnoside and herbacetin 7-glucoside were also found. The structure of the isolated compounds was determined mostly by FABMS and ¹H NMR spectroscopy. The final structure of the new compounds and of herbacetin 7-glucoside was confirmed by ¹³C NMR spectroscopy.     

Flavonoids from Gutierrezia grandis

Thirteen flavonoids, including three new compounds, were isolated from Gutierrezia grandis. The structures of the new compounds were 3,5,7,3′,4′-pentahydroxy-6,8-dimethoxyflavone, 5,7,3′-trihydroxy-3,6,8,4′,5′-pentamethoxyflavone and 5,7,3′,5′-tetrahydroxy-3,6,8,4′-tetramethoxyflavone 3′-O-glucoside.     

Plant Flavonoid <Emphasis Type="Italic">O</Emphasis>-Methyltransferases: Substrate Specificity and Application

Flavonoids consist of a large family of compounds, which has been estimated to be more than 10,000 compounds. The structural diversity of these compounds comes from different modification reactions. The O-methylation reaction is one of the most important modification reactions of flavonoids and the resulting O-methylated flavonoids have been shown to display new biological activities. The regioselective and substrate specific O-methylation is mediated by O-methyltranferases (OMTs). To date, 30 flavonoid OMTs (FOMTs) have been biochemically characterized from various plants. FOMTs utilize common reaction mechanisms to transfer a methyl group to the hydroxyl group of the flavonoid. Phylogenetic tree analysis along with biochemical characterization of FOMTs provides clues about their substrate specificity and regioselectivity. FOMTs can be used for the production of O-methylated flavonoids that have a particular biological activity.     

Flavonoids of the Tiarella trifoliata complex

The flavonoids of the Tiarella trifoliata L. complex consists of kaempferol, quercetin and myricetin-3-O-mono-, di- and triglycosides, kaempferol and quercetin-7-O-monoglycosides, kaempferol-3,7-O-monoglycosides and luteolin. Infrapopulationa and interpopulational variations were seen in the distribution of several of these types of compounds. The flavonoid data do not support recognition of separate species for the three taxa.     

Characterization of the Intestinal Absorption of Seven Flavonoids from the Flowers of Trollius chinensis Using the Caco-2 Cell Monolayer Model

The human Caco-2 cell monolayer model was used to investigate the absorption property, mechanism, and structure-property relationship of seven representative flavonoids, namely, orientin, vitexin, 2”-O-β-L-galactopyranosylorientin, 2”-O-β-L-galactopyranosylvitexin, isoswertisin, isoswertiajaponin, and 2”-O-(2”‘-methylbutanoyl)isoswertisin from the flowers of Trollius chinensis. The results showed that these flavonoids were hardly transported through the Caco-2 cell monolayer. The compounds with 7-OCH₃ including isoswertisin, isoswertiajaponin and 2”-O-(2”‘-methylbutanoyl)isoswertisin were absorbed in a passive diffusion manner, and their absorbability was increased in the same order as their polarity. The absorption of the remaining compounds with 7-OH including orientin, vitexin, 2”-O-β-L-galactopyranosylorientin, and 2”-O-β-L-galactopyranosylvitexin involved transporter mediated efflux in addition to passive diffusion. Among the four compounds with 7-OH, those with a free hydroxyl group at C-2” such as orientin and vitexin were the substrates of P-glycoprotein (P-gp) and that with a free hydroxyl group at C-2’ such as 2”-O-β-L-galactopyranosylorientin was the substrate of multidrug resistance protein 2 (MRP2). The results of this study also implied that the absorbability of the flavonoids should be taken into account when estimating the effective components of T. chinensis.     

Foliar flavonoids of North American Solanum section Solanum

A total of ten flavonoids, all flavonols, were isolated from leaves of eleven species of Solanum sect. Solanum. Most species had relatively few compounds, primarily quercetin 3-O-glycosides. Little intraspecific variation in flavonoids was observed, except in S. americanum were it correlated with previously recognized races. Flavonoid data are of little help in determining ancestries of polyploid species, but do rule out S. sarrachoides as a progenitor of S. villosum and S. nigrum. Solanum sarrachoides is unique among species examined in having free flavonoid aglycones as well as extensive 3-O-methoxylation.     

Flavonoids and xanthones from the leaves of Amorphophallus titanum (Araceae)

The flavonoids and xanthones in the leaves of Amorphophallus titanum, which has the largest inflorescence among all Araceous species, were surveyed. Eight C-glycosylflavones, five flavonols, one flavone O-glycoside and two xanthones were isolated and characterized as vitexin, isovitexin, orientin, isoorientin, schaftoside, isoschaftoside, vicenin-2 and lucenin-2 (C-glycosylflavones), kaempferol 3-O-robinobioside, 3-O-rutinoside and 3-O-rhamnosylarabinoside, and quercetin 3-O-robinobioside and 3-O-rutinoside (flavonols), luteolin 7-O-glucoside (flavone), and mangiferin and isomangiferin (xanthones). Although the inflorescence of this species has been surveyed for flavonoids, those of the leaves were reported for the first time.     

Ginkgo biloba responds to herbivory by activating early signaling and direct defenses

Background

Ginkgo biloba (Ginkgoaceae) is one of the most ancient living seed plants and is regarded as a living fossil. G. biloba has a broad spectrum of resistance or tolerance to many pathogens and herbivores because of the presence of toxic leaf compounds. Little is known about early and late events occurring in G. biloba upon herbivory. The aim of this study was to assess whether herbivory by the generalist Spodoptera littoralis was able to induce early signaling and direct defense in G. biloba by evaluating early and late responses.

Methodology/Principal Findings

Early and late responses in mechanically wounded leaves and in leaves damaged by S. littoralis included plasma transmembrane potential (Vm) variations, time-course changes in both cytosolic calcium concentration ([Ca²⁺]_cyt) and H₂O₂ production, the regulation of genes correlated to terpenoid and flavonoid biosynthesis, the induction of direct defense compounds, and the release of volatile organic compounds (VOCs). The results show that G. biloba responded to hebivory with a significant Vm depolarization which was associated to significant increases in both [Ca²⁺]_cyt and H₂O₂. Several defense genes were regulated by herbivory, including those coding for ROS scavenging enzymes and the synthesis of terpenoids and flavonoids. Metabolomic analyses revealed the herbivore-induced production of several flavonoids and VOCs. Surprisingly, no significant induction by herbivory was found for two of the most characteristic G. biloba classes of bioactive compounds; ginkgolides and bilobalides.

Conclusions/Significance

By studying early and late responses of G. biloba to herbivory, we provided the first evidence that this “living fossil” plant responds to herbivory with the same defense mechanisms adopted by the most recent angiosperms.     

Chemotaxonomic consideration of flavonoids from the leaves of Chrysanthemum arcticum subsp. arcticum and yezoense,and related species

We examined the foliar flavonoids of Chrysanthemum arcticum subsp. arcticum and yezoense, and related Chrysanthemum species. Five flavonoid glycosides (luteolin 7-O-glucoside and 7-O-glucuronides of luteolin, apigenin, eriodictyol and naringenin) were isolated from these taxa. Luteolin 7-O-xylosylglucoside, luteolin, apigenin and quercetin 3-methyl ether were found in subsp. yezoense as very minor compounds that were not recognised by high-performance liquid chromatography/photodiode array (HPLC/PDA). The related species C. yezoense contained acacetin 7-O-rutinoside and some methoxylated flavone aglycones as major compounds. Thus, C. arcticum was distinguished from C. yezoense according to their flavonoid profiles.