Flavonoid diversification in Achillea ptarmica and allied taxa

More than 50 collections of 12 species forming the A. ptarmica group have been analysed for their leaf flavonoids. C-Glycosylflavones (iso-orientin and derivatives, vicenins and lucenins) were found to be the main components, whereas flavonol 3-O-glycosides (based on quercetin and kaempferol) and flavone 7-O-glycosides (based on luteolin and diosmetin) were of restricted distribution. Infraspecific variability regarding C-glycosylflavones was observed in most of the taxa investigated. By contrast, flavonol 3-O-glycosides appeared to be stable characters and were sometimes accumulated instead of C-glycosylflavones. In addition to the flavonoids, the geographical distribution patterns and the possible origin of the A. sibirica in Eastern Asia are briefly discussed.     

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.     

Flavonoid pattern and systematics of the genus Leucocyclus

The flavonoid pattern of the monotypic Turkish genus Leucocyclus consists of C-glycosylflavones (isovitexin; isoorientin and derivatives; several di-C-glycosylapigenins; schaftoside, isoschaftoside and vicenin-3; lucenin-2), of flavonol 3-O-glycosides (quercetin and kaempferol 3-O-rhamnoglucoside) and trace amounts of luteolin 7-O-rhamnoglucoside. The systematic significance of the flavonoid diversification within Leucocyclus as well as possible relationships to other genera of the Anthemideae are discussed.     

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.     

Leaf flavonoid glycosides as chemosystematic characters in Ocimum

Thirty-one accessions of nine species belonging to three subgenera of Ocimum (basil, family Lamiaceae) were surveyed for flavonoid glycosides. Substantial infraspecific differences in flavonoid profiles of the leaves were found only in O. americanum, where var. pilosum accumulated the flavone C-glycoside, vicenin-2, which only occurred in trace amounts in var. americanum and was not detected in cv. Sacred. The major flavonoids in var. americanum and cv. Sacred, and also in all other species investigated for subgenus Ocimum, were flavonol 3-O-glucosides and 3-O-rutinosides. Many species in subgenus Ocimum also produced the more unusual compound, quercetin 3-O-(6″-O-malonyl)glucoside, and small amounts of flavone O-glycosides. The level of flavonol glycosides produced was reduced significantly in glasshouse-grown plants, but levels of flavone glycosides were unaffected. A single species investigated from subgenus Nautochilus, O. lamiifolium, had a different flavonoid glycoside profile, although the major compound was also a flavonol O-glycoside. This was identified as quercetin 3-O-xylosyl(1‴→2″)galactoside, using NMR spectroscopy. The species investigated from subgenus Gymnocimum, O. tenuiflorum (=O. sanctum), was characterised by the accumulation of flavone O-glycosides. These were isolated, and identified as the 7-O-glucuronides of luteolin and apigenin. Luteolin 5-O-glucoside was found in all nine species of Ocimum studied, and is considered to be a key character for the genus.     

Uniformity and distinctness of phyllocladus as evidenced by flavonoid accumulation

The conifer genus Phyllocladus is shown by comparative flavonoid chemistry to be remarkably homogeneous and quite distinct from other studied genera in the Podocarpaceae. It is characterized by the accumulation (in the foliage) of a predominance of flavone O-glycosides, and in particular, luteolin 7- and 3′-O-glycosides. Lower levels of flavonol O-glycosides are also evident. Two flavone glycosides are reported for the first time, luteolin 3′-O-α-L-rhamnopyranoside and luteolin 7-O-α-L-rhamnoside.     

Structural determination of 6-C-diglycosyl-8-C-glycosyl-flavones and 6-C-glycosyl-8-C-diglycosylflavones by mass spectrometry of their permethyl ethers

Permethylated 6-C-diglycosyl-8-C-glycosylflavones and 6-C-glycosyl-8-C-diglycosylflavones gave well defined EIMS including the molecular peak and a fragmentation pattern characteristic of the 6-C-glycosyl residue. X″′-O-glycosides (8-C-disaccharides) are thus easily distinguished from X″-O-glycosides (6-C-disaccharides) and, in the latter, the position of the O-glycosidic bond should be deduced from the MS, after acid hydrolysis. Three new C-glycosylflavones have been characterized in this way from Spergularia rubra and Stellaria holostea.     

Intra- and interspecific variations in vacuolar flavonoids among Ficus species from the Budongo Forest,Uganda

Leaves of 14 species of Ficus growing in the Budongo Forest, Uganda, were analysed for vacuolar flavonoids. Three to six accessions were studied for each species to see whether there was intraspecific chemical variation. Thirty-nine phenolic compounds were identified or characterised, including 14 flavonol O-glycosides, six flavone O-glycosides and 15 flavone C-glycosides. In some species the flavonoid glycosides were acylated. Ficus thonningii contained in addition four stilbenes including glycosides. Most of the species could be distinguished from each other on the basis of their flavonoid profiles, apart from Ficus sansibarica and Ficus saussureana, which showed a very strong intraspecific variation. However, on the whole flavonoid profiles were sufficiently distinct to help in future identifications.     

Flavonoids in the leaves of Hillebrandia and Begonia species (Begoniaceae)

The fresh leaves of Hillebrandia sandwicensis and 126 Begonia taxa were chemotaxonomically surveyed for flavonoids. Of their taxa, H. sandwicensis and 119 species, one variety and three hybrids were analyzed for flavonoids for the first time. Ten flavonols and eleven C-glycosylflavones were isolated and characterized as quercetin 3-O-rutinoside (1), kaempferol 3-O-rutinoside (2), isorhamnetin 3-O-rutinoside (3), quercetin 3-O-glucoside (4), quercetin 3-methyl ether 7-O-rhamnosylglucoside (5), quercetin 3,3'-dimethyl ether 7-O-rhamnosylglucoside (6), quercetin glycoside (13), quercetin glycoside (acylated) (14), kaempferol glycoside (17) and quercetin 3-O-rhamnoside (18) as flavonols, and isovitexin (7), vitexin (8), isoorientin (9), orientin (10), luteolin 6-C-pentoside (11), luteolin 8-C-pentoside (12), schaftoside (15), isoschaftoside (16), chrysoeriol 6,8-di-C-pentoside (19), apigenin 6,8-di-C-arabinoside (20) and isovitexin 2''-O-glucoside (21) as C-glycosylflavones. Quercetin 3-O-rutinoside (1) alone was isolated from H. sandwicensis endemic to Hawaii. Major flavonoids of almost Begonia species was also 1. Begonia species were divided into two chemotypes, i.e. flavonol containing type and C-glycosylflavone containing type. Of 14 section of the Begonia, almost species of many section, i.e. sect. Augustia, Coelocentrum, Doratometra, Leprosae, Loasibegonia, Monopteron and Ruizoperonia, were flavonol types. On the other hand, C-glycosyflavone type was comparatively most in sect. Platycentrum.     

Flavonoids of Mayaca fluviatilis (Mayacaceae)

Mayaca is an aquatic monocot of the monogeneric family Mayacaceae. The flavonol glycosides quercetin 3-O-glucoside, quercetin 3-O-rutinoside, and kaempferol 3-O-glucoside, and the flavone luteolin 5-O-glucoside were found in methanolic leaf extracts. The presence of flavonol and flavone O-glycosides sets the Mayacaceae apart from the Commelinaceae, which accumulates predominantly flavone C-glycosides.     

Anthocyanins and flavonols from the blue flowers of six Meconopsis species in Bhutan

Blue flowers of six Bhutani Meconopsis species, M. bhutanica, M. bella, M. horridula, M. simplicifolia, M. primulina and M. polygonoides, were surveyed for anthocyanins and other flavonoids. Four anthocyanins were isolated and identified as cyanidin 3-O-sambubioside-7-O-glucoside (1), cyanidin 3-O-[xylosyl-(1 → 2)-(6″-malonylglucoside)]-7-O-glucoside (2), cyanidin 3-O-sambubioside (4) and cyanidin 3-O-[xylosyl-(1 → 2)-(6″-malonylglucoside)] (5). On the other hand, 12 flavonols were isolated from their Meconopsis species with various combination and characterized as kaempferol 3-O-glycosides (8–12), kaempferol 3,7-O-glycosides (13–16), quercetin 3-O-glycosides (17 and 18) and isorhamnetin 3-O-glycoside (19). Of six Meconopsis species which were surveyed in this experiment, anthocyanin and flavonol composition of five species except for M. horridula was clarified for the first time. Their Meconopsis species showed the different flavonoid profiles, respectively, and flavonoid diversity within the glycosylation level of Meconopsis flowers were indicated.     

Flavonoids of the primitive liverwort Takakia and their taxonomic and phylogenetic significance

The flavonoid chemistry of Takakia is described for the first time. T. lepidozioides, thought to be amongst the most primitive of extant liverworts, contains a high level and wide variety of flavone C- and O-glycosides, many of which are unique. New flavonoids include the 8-O-glucuronide and 8-O-xylosylglucoside of takakin (8-hydroxyacacetin), luteolin 6-C-arabinoside-8-C-pentoside, kaempferol 3-O-glucoside-7-O-xyloside and a number of tricetin C-glycosides. The only other known Takakia species, T. ceratophylla, contains the same 4 major constituents but significantly lacks flavonols. The often suggested relationship of Takakia with the order Calobryales is not supported by the available flavonoid data. Biochemical affinities of Takakia with all major liverwort orders are noted and the flavonoid data are interpreted as supporting the concept of Takakia as an isolated branch among the ancestors of modern bryophytes.     

Flavonoids in the species of Cyrtomium (Dryopteridaceae) and related genera

Flavonoids in 19 Cyrtomium, three Cyrtogonellum and two Phanerophlebia taxa were surveyed. Major flavonoids were flavonol O-glycosides based on kaempferol, quercetin, and sometimes myricetin, and C-glycosylflavones, such as isovitexin, vitexin, isoorientin, orientin and their O-glycosides. The C-methylflavanones, farrerol and cyrtominetin, and their 7-O-glucosides were isolated from Cyrtomium devexiscapulae and Cyrtomium laetevirens. Flavanones have been reported from Cyrtomium falcatum sensu lato. Though C. falcatum sensu lato is divided into four taxa, i.e. C. falcatum subsp. falcatum, C. falcatum subsp. australe, C. falcatum subsp. littorale, and C. devexiscapulae, the occurrence of the flavanones was restricted to C. devexiscapulae, and they did not occur in C. falcatum sensu stricto.     

Flavonoid chemistry of the generic segregates Ascyrum and Crookea of Hypericum

Leaf flavonoids were isolated and characterized from the seven taxa of Hypericum, formerly segregated as Ascyrum and Crookea. These included flavonol 3-glycosides based on quercetin and kaempferol and flavone-O-glycosides and C-glycosides based on apigenin and luteolin. The flavonoid data do not indicate that the taxe of Ascyrum and Crookea form a single coherent group and hence support their merger with Hypericum.     

Apigenin and amentoflavone glycosides in the psilotaceae and their phylogenetic significance

Documentation of amentoflavone O-glucosides as the predominant flavonoid glycosides in both genera of the Psilotaceae clearly distinguishes this family from all other families of vascular plants. Psilotum and Tmesipteris also possess apigenin C- and O-glycosides as common flavonoid types. Apigenin 7-O-rhamnoglucoside occurs in both genera and the previously undocumented apigenin 7-O-rhamnoglucoside-4′-O-glucoside, although identified only in Tmesipteris, may also be present in Psilotum. The existence of flavone C-glycosides in both genera may provide a phytochemical relationship between the Psilotaceae and some ferns. The phylogenetic significance of these results is discussed.     

C-Glycosylflavones from Avena sativa

Avena sativa leaves, stems and inflorescences contain a range of new C-glycosylflavone 2″-O-glycosides, including vitexin and isoswertisin 2″-rhamnosides, isovitexin and isoorientin 2″-arabinosides. The structure of ‘vitexin 4′-rhamnoside’ from Crataegus oxyacantha is revised in vitexin 2″-rhamnoside.     

Flavonoids of Lupinus texensis and L. subcarnosus

Lupinus texensis and L.- subcarnosus exhibit very similar flavonoid profiles based on O-glycosylflavones, Cglycosylflavones, an isoflavone and a flavanone. Differences between the two species amount to the presence of a diglucoside of diosmetin in L. texensis and comparatively higher concentrations of C-glycosylflavones in L. subcarnosus. The two species have a higher degree of flavonoid pigment similarity than any other pair of lupines examined in our studies. The similar profiles support the view that these two endemic Texan species are closely related.     

Advances in the biotechnological glycosylation of valuable flavonoids

The natural flavonoids, especially their glycosides, are the most abundant polyphenols in foods and have diverse bioactivities. The biotransformation of flavonoid aglycones into their glycosides is vital in flavonoid biosynthesis. The main biological strategies that have been used to achieve flavonoid glycosylation in the laboratory involve metabolic pathway engineering and microbial biotransformation. In this review, we summarize the existing knowledge on the production and biotransformation of flavonoid glycosides using biotechnology, as well as the impact of glycosylation on flavonoid bioactivity. Uridine diphosphate glycosyltransferases play key roles in decorating flavonoids with sugars. Modern metabolic engineering and proteomic tools have been used in an integrated fashion to generate numerous structurally diverse flavonoid glycosides. In vitro, enzymatic glycosylation tends to preferentially generate flavonoid 3- and 7-O-glucosides; microorganisms typically convert flavonoids into their 7-O-glycosides and will produce 3-O-glycosides if supplied with flavonoid substrates having a hydroxyl group at the C-3 position. In general, O-glycosylation reduces flavonoid bioactivity. However, C-glycosylation can enhance some of the benefits of flavonoids on human health, including their antioxidant and anti-diabetic potential.     

Distribution of charged flavones and caffeylshikimic acid in Palmae

Identification of the phenolic constituents in flowers of nine palm species has revealed that charged C-glycosylflavones and caffeylshikimic acid are characteristically present. Flavonol glycosides are also common; the 3-glucosides, 3-rutinosides and 3,4′-diglucosides of quercetin and isorhamnetin and the 7-glucoside and 3,7-diglucoside of quercetin are all variously present. Tricin 7-glucoside, luteolin 7-rutinoside and several unchanged C-glycosylflavones were also detected. Male flowers of Phoenix canariensis differ from female flowers in having flavonol glycosides. As expected, in most species studied, flavonoid patterns in the flowers vary considerably from those found in the leaves.     

Structural determination of C-glycosylflavones by mass spectrometry of their permethyl ethers: O-glycosyl-6-C-glycosylflavones

Permethylated O-glycosyl-C-glycosylflavones give well defined MS including an important molecular peak. Permethyl 6-C-glycosylflavones O-glycosylated on a phenolic hydroxyl group are easily distinguished from the isomeric permethyl 6-C-diholosylflavones. In both types, the position of the O-glycosidic bond can be deduced from the MS, eventually after acid hydrolysis. 2″-O-glycosyl-6-C-glycosylflavones can be differentiated from their 8-C isomers.