Fragmentation pattern of permethyl 6-C-glycosylflavones in electron impact mass spectrometry

A mass spectral fragmentation pattern of permethyl 6-C-glycosylflavones is proposed from the MS data of permethyl derivatives mono-O-deuteriomethylated in the 2″-, 3″-, 4″- or 6″-positions. The synthesis of these compounds via O″-glycosyl-6-C-glucosylflavones is described.     

Structural determination of C-glycosylflavones by mass spectrometry of their permethyl ethers

Permethylated C-glycosylflavones give well defined MS, including in all cases an important molecular peak. The observed fragmentations are characteristic for the nature and position of the sugar. The 6-C and 8-C glycosylated derivatives are clearly differentiated. In dissymmetrical 6,8-di-C-glycosylflavones, the natures of the sugar in both the 6- and 8- positions can be determined. The structures of several natural compounds are discussed.     

New C-glycosylflavones from Cerastium arvense

Three C-glycosylflavones isolated from Cerastium arvense have been identified as 6-C-xylosyl-apigenin (cerarvensin), its 7-O-glucoside and isovitexin 7,2″-di-O-glucoside.     

C-glycosylanthocyanidins synthesized from C-glycosylflavones

Nine C-glycosyldeoxyanthocyanidins, 6-C-β-glucopyranosyl-7-O-methylapigeninidin, 6-C-β-glucopyranosyl-7-O-methylluteolinidin, 6-C-β-(2″-O-β-glucopyranosylglucopyranosyl)-7-O-methylapigeninidin, 6-C-β-(2″-O-β-glucopyranosylglucopyranosyl)-7,4′-di-O-methylapigeninidin, 8-C-β-glucopyranosylapigeninidin, 8-C-β-(2″-O-α-rhamnopyranosylglucopyranosyl)apigeninidin, 8-C-β-(2″-O-α-(4″′-O-acetylrhamnopyranosyl)glucopyranosyl)apigeninidin, 6,8-di-C-β-glucopyranosylapigeninidin (8), 6,8-di-C-β-glucopyranosyl-4′-O-methylluteolinidin (9), have been synthesized from their respective C-glycosylflavones (yields between 14% and 32%) by the Clemmensen reduction reaction using zinc-amalgam. The various precursors (C-glycosylflavones) of the C-glycosylanthocyanidins were isolated from either flowers of Iris sibirica L., leaves of Hawthorn ‘Crataegi Folium Cum Flore’, or lemons and oranges. This is the first time C-glycosylanthocyanidins have been synthesized. The structures of all flavonoids including the flavone rotamers were elucidated by 2D NMR techniques and high-resolution electrospray MS. The distribution of the various structural forms of 8 and 9 are different at pH 1.1, 4.5, and 7.0, however, the two pigments undergoes similar structural transformations at the various pH values. Pigments 8 and 9 with C-C linkages between the sugar moieties and the aglycone, were found to be far more stable towards acid hydrolysis than pelargonidin 3-O-glucoside, which has the typical anthocyanidin C-O linkage between the sugar and aglycone. This stability may extend the present use of anthocyanins as nutraceuticals, pharmaceuticals or colorants.     

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.     

C-glycosylflavones from roots of glycine max

Chemical investigation of the roots of Glycine max yielded six C-glycosylflavones identified on the basis of spectral data as carlinoside, isocarlinoside, vitexin, vitexin 2″-O-rhamnoside, isoschaftoside and a new compound 6,8-di-C-hexosylgenkwanin.     

New C-glycosylflavones from Mollugo distica

Four C-glycosylflavones isolated from Mollugo distica were identified as 8-C-β-d-glucopyranosyl-genkwanin, 8-C-α-l-arabinopyranosylgenkwanin and their 2″-rhamnosides.     

Nouvelles C-glycosylflavones extraites de Spergularia rubra

Three 6,8-di-C-glucosylflavones: 6,8-di-C-β-d-glucopyranosylapigenin, luteolin and chrysoeriol were isolated from the whole plant of Spergularia rubra. Two new compounds, 7,2″-di-O-β-d-glucopyranosyl-6-C-α-l-arabinopyranosylapigenin and 6-C-α-l-arabinopyranosylapigenin (isomollupentin), were also characterized. Structural assignments were based on ¹H NMR and MS spectra and on comparison with synthetic samples. MS fragmentation patterns of the new di-O-glucosyl compound PM derivative and of its acid hydrolysis product are given.     

Effect of conformation and configuration of arabinose residues on the circular dichroism of C-glycosylflavones

Examination of a variety of arabinose containing C-glycosylflavones has shown that the sign and intensity of the CD band at 250–275 nm (charge-transfer band) reflect not only the point of attachment of the sugar to the flavone but also depend upon the absolute and anomeric configuration, ring-size and ring-conformation in addition to the preferred rotameric conformation of the sugar about the C-aryl, C-l″ bond. A change in stereochemistry of arabinose from the α to β anomer resulted in sign inversion of the 250–275 nm CD band for 6-C-l-arabinosylflavones. Furthermore, a 6-C-arabinosylflavone containing α-l-arabinose exhibited an oppositely signed charge-transfer CD band in comparison to one which contained α-d-arabinose. 6,8-Di-C-glycosylflavones containing arabinose and glucose exhibited CD bands resulting from contributions due to both sugars, if the arabinose was not present as the β-pyranose form (¹C₄, conformation).     

C-glycosylflavones from Oryza sativa

Eight flavone C-glycosides isolated from rice plant were found to act as probing stimulants for planthoppers. They have been identified as the known compounds schaftoside, neoschaftoside, carlinoside, isoorientin 2″-glucoside and the new constituents neocarlinoside (6-C-β-D-glucopyranosyl-8-C-β-L-arabinopyranosylluteolin), isoscoparin 2″-glucoside (chrysoeriol 6-C-β-D-(2-O-β-D-glucopyranosyl)glucopyranoside) and its 6?-p-coumaric and ferulic acid esters.     

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.     

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.     

Determination of O-glycosidic bond position in 6-C-glycosylglucosylflavones by mass spectrometry

2″,3″,4″ and 6″-O-glycosides of 6-C-glucosylflavones can be differentiated by the MS of the hydrolysis products of their permethyl ethers.     

Flavonoid glycoside accumulation trends of Achillea nobilis L. and related species

More than 50 collections of five species forming the Achillea nobilis group were analysed for their leaf flavonoid complement. Major accumulation trends were found to be C-glycosylflavones and flavonol 3-O-glycosides. The most common pattern consisted of the C-8-glycosylfiavones (vitexin and orientin), the C-6-glycosylflavone (isoörientin) together with minor amounts of di-C-glycosylapigenins and quercetin 3-O-glycosides. Additionally, C-6-glycosylflavones (isovitexin) and their 7-methyl ethers swertisin and swertiajaponin were sporadically accumulated, characterizing particularly two subspecies of A. nobilis. Whereas C-glycosylflavone dominated profiles were typical of most species, two taxa exhibited a flavonol dominated profile (A. ligustica; A. virescens p.p.). Regarding the infraspecific and interpopulational variations of flavonoid accumulation trends, their systematic and ecological significance is briefly discussed.     

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.     

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.     

Antinociceptive activity of the HPLC- and MS-standardized hydroethanolic extract of Pterodon emarginatus Vogel leaves

Several studies have demonstrated the analgesic and anti-inflammatory effects of fruit and seed extracts from Pterodon emarginatus Vogel (Fabaceae). The objective of this study was to evaluate the antinociceptive activity of the hydroethanolic extract of P. emarginatus leaves in mice and characterize its chemical composition using HPLC coupled to UV–vis diode array detection and mass spectrometry with electrospray ionization. Our results showed that the doses of 500 and 1000 mg/kg produced an antinociceptive effect, as observed in the hot plate test and writhing induced by acetic acid. The chromatographic profile and spectral mass data suggest the presence of di-C-glycosylflavones (e.g., vicenin-2 and schaftoside), C,O-glycosylflavones (e.g., chrysoeriol-8-C-glucosyl-2″-O-glucuronide-6-C-arabinoside) and luteolin-7-O-rutinoside as the main constituents. Lower levels of oleanane-type saponins, such as soyasaponin Bb and Be, and the saponin derivatives hederagenin and aglycone B, which are typical of Fabaceae family, were also found. From this study, it is suggested that the analgesic effect observed is not due to the terpenoids previously reported from fruit and seed extracts, but could be attributed to flavones and the hederagenin derivatives that were identified as main constituents of the hydroethanolic extract from the leaves.     

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.     

Arbutin derivatives from the buds of Vaccinium dunalianum and their MS/MS spectrometric fragmentations

Four arbutin derivatives were isolated from the buds of Vaccinium dunalianum in which 4-hydroxyphenyl-6′-(3''-O-β-D-glucopyranosyl-4''-hydroxycinnamoyl)-O-β-D-glucopyranoside (1) was a new compound. The structure of the new compound was determined on the basis of NMR and HR-ESI-MS data. All the arbutin derivatives were subjected to the MS/MS analyses from which the MS/MS spectrometric fragmentations were summarized.     

Two new neoflavonoids and C-glycosylflavones from Passiflora serratodigitata

The aerial parts of Passiflora serratodigitata yielded 5,7-dihydroxy-4-phenylcoumarin, its 7-β-glucoside and the known C-glycosylflavones 2″-xylosylvitexin, 2″-xylosylisovitexin, vitexin, isovitexin, a vicenin, and orientin. The known flavone chrysin was also isolated. This is the first report of neoflavonoids in the family Passifloraceae.