Flavonol glycosides of Phlomis spectabilis

Four flavonol glucosides, one new, have been isolated from a methanolic extract of Phlomis spectabilis. Their structures were established as the 3-glucosides and 3-(6″-(E)-p-coumaroyl)glucosides of kaempferol and of kaempferol 7,4′-dimethyl ether.     

Flavone C-Glycosides of Almeidea guyanensis

From the stem and the root bark of Almeidea guyanensis were identified isoswertisin, 6,8-di-C-arabinosylapigenin and two new compounds 2″-O-xylosyl-8-C-arabinosylgenkwanin, and 6-C-glucosyl-8-C-arabinosylgenkwanin.     

Rhynchospermin. A prenylated flavanol from Rhynchosia cyanosperma

A new flavanol has isolated from the leaves of Rhynchosia cyanosperma and identified as 8-C-prenylquercetin 7,4′-dimethyl ether (rhynchospermin).     

Flavonoids of the flowers of tamarix nilotica

The ethyl ester of kaempferol 3-O-β-D-glucuronide, the methyl and ethyl esters of quercetin 3-O-β-D-glucuronide have been isolated from an aqueous acetone extract of the flowers of Tamarix nilotica. In addition kaempferol 3-O-sulphate-7,4′-dimethyl ether and the free aglycones were isolated. The structures were established by routine methods, by FAB-MS and by ¹³C NMR spectral measurements.     

5-Methyl ether flavone glucosides from the leaves of Bruguiera gymnorrhiza

Two new 5-methyl ether flavone glucosides (7,4′,5′-trihydroxy-5,3′-dimethoxyflavone 7-O-β-D-glucopyranoside and 7,4′-dihydroxy-5-methoxyflavone 7-O-β-D-glucopyranoside) were isolated from the leaves of Thai mangrove Bruguiera gymnorrhiza together with 7,3′,4′,5′-tetrahydroxy-5-methoxyflavone, 7,4′,5′-trihydroxy-5,3′-dimethoxyflavone, luteolin 5-methyl ether 7-O-β-D-glucopyranoside, 7,4′-dihydroxy-5,3′-dimethoxyflavone 7-O-β-D-glucopyranoside, quercetin 3-O-β-D-glucopyranoside, rutin, kaempferol 3-O-rutinoside, myricetin 3-O-rutinoside and an aryl-tetralin lignan rhamnoside. The structure of a lignan rhamnoside was found to be related to racemiside, an isolated compound from Cotoneaster racemiflora, and also discussed. Structure determinations were based on analyses of physical and spectroscopic data including 1D- and 2D-NMR.     

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.     

Flavonoids of Wyethia angustifolia and W. helenioides

Seventeen flavonoids, including seven new natural products, were isolated from a dichloromethane extract of Wyethia angustifolia. Known compounds are:8-C-prenyleriodictyol, 6-C-prenyleriodictyol, 8-C-prenylnaringenin, 6-C-prenylnaringenin, orobol 7-methyl ether, orobol 3′-methyl ether, naringenin 4′-methyl ether, orobol, eriodictyol and naringenin. The new compounds are 6-C-prenylorobol, 6-C-prenylorobol 3′-methyl ether, orobol 7,3′-dimethyl ether, 8-C-prenyldihydroisorhamnetin, 7,8-dihydrooxepinocriodictyol, 7,8-dihydrooxepinodihydroquercetin and 3′,4′-dihydrooxepino-6′-hydroxybutein. A dichloromethane extract of Wyethia heleniodes yielded eleven compounds only five of which were previously reported from the species. All these compounds appear to occur on the leaf surface.     

Puerarin 6″-O-β-apiofuranoside,a C-glycosylisoflavone O-glycoside from Pueraria mirifica

In addition to puerarin (7,4′-dihydroxyisoflavone 8-C-β-glucopyranoside), the air-dried tuberous roots of Pueraria mirifica have been found to contain a second, previously unreported, isoflavone C-glycoside. This new compound (mirificin), which has now been identified by chemical and spectroscopic (UV, ¹H NMR, ¹³C NMR including GASPE) procedures as puerarin 6″-O-β-apiofuranoside is the first O″-glycoside of an isoflavone C-glycoside to be discovered in nature. Mirificin contains a rare 1 → 6 interglycosidic linkage between apiose and the glucose unit which is unique in flavonoids. It is proposed that 1 → 2 and 1 → 6 linked apioglucosides can be distinguished by ¹H NMR spectroscopy in the same manner as used for the equivalent rhamnoglucosides.     

Biflavones from the leaves of Araucaria excelsa

Eight biflavones have been isolated from the leaf extracts of Araucaria excelsa. 7″-O-Methylamento-flavone, 7,7″-di-O-methylamentoflavone, 4′ or 4″', 7-di-O-methylcupressuflavone, 7,7″,4″'-tri-O-methyl agathisflavone and 7,4′,7″-tri-O-methylamentoflavone are new compounds and are being reported for the first time. The others are 7,7″-di-O-methylagathisflavone,7,4′,7″,4″'-tetra-O-methylamentoflavone and 7,4′,7″,4″'-tetra-O-methyl-cupressuflavone. Mass and NMR spectral studies are used for structural elucidation. In addition, the presence of several other biflavones has been indicated by TLC examination of methylated products.     

Acetylated allose-containing flavonoid glucosides from Stachys anisochila

In continuation of our chemosystematic study of Stachys (Labiatae) we have isolated the previously reported isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (1) and 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (4) and four new allose-containing flavonoid glycosides from S. anisochila. The new glycosides are hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranside] (6) as well as the three corresponding diacetyl analogues of 1, 4 and 6, isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside], 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside] and hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside]. Extensive two-dimensional NMR studies (proton-carbon correlations, COSY experiments) allowed assignment of all ¹H NMR sugar signals and a correction of the ¹³C NMR signal assignments for C-2 and C-3 of the allose.     

Triterpenoid saponins and C-glycosyl flavones from stem bark of Erythrina abyssinica Lam and their cytotoxic effects.

Six new compounds including two oleanane-type triterpenoid saponins (1, 2) and four C-glycosyl flavones (3–6), along with a known saponin (7), three di-C-glycosyl flavones (8–10) and a glycosyl auronol (11), were isolated from the stem bark of Erythrina abyssinica Lam. The structures of the new compounds, identified as 3-O-[α-l-rhamnopyranosyl-(1 → 2)-β-d-galactopyranosyl-(1 → 2)-β-d-glucuronopyranosyl]-22-O-β-d-glucopyranosyl sophoradiol (1), 3-O-[α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl-(1 → 2)-β-d-glucuronopyranosyl]-22-O-β-d-glucopyranosyl sophoradiol (2), 6-C-β-glucopyranosyl-8-C-β-quinovopyranosyl apigenin (3), 6-C-β-quinovopyranosyl-8-C-β-glucopyranosyl apigenin (4), 8-C-[6″-O-α-l-rhamnopyranosyl-(1‴ → 6″)]-β-glucopyranosyl 7,4′-dihydroxyflavone (5) and 8-C-[6″-O-β-d-xylopyranosyl-(1‴ → 6″)]-β-glucopyranosyl 7,4′-dihydroxyflavone (6), were determined by comprehensive spectroscopic analysis, including 1D and 2D NMR techniques, mass spectrometry and acid hydrolysis. These new compounds together with the known saponins 7 were evaluated for their cytotoxic activity against MCF-7 (estrogen dependent) and MDA-MB-231 (estrogen independent) cell lines. The new saponin 2 exhibited the highest cytotoxic activity among tested compounds, exerting a selective inhibitory effect against the proliferation of MCF-7 cells, with lower IC₅₀ value (12.90 μM) than that of the positive control, resveratrol (13.91 μM). Structure–activity relationship of these compounds is also discussed.     

6-methoxyflavonoids from Brickellia laciniata (compositae)

One new and fourteen known flavonoids, including thirteen containing 6-methoxy groups, were isolated from Brickellia laciniata. The new flavonol is quercetagetin 6,4′-dimethyl ether. Among the known compounds identified were the 4′-methyl and 7,4′-dimethyl ethers of eupafolin and luteolin 4′-methyl ether, and the flavonols: patuletin, spinacetin, eupatolitin, eupatin, centaureidin, casticin, patuletin 3-glucoside and 3-galactoside, eupatolitin 3-galactoside, patuletin 3-SO₃K and eupatin 3-SO₃Ca_1/2.     

Flavonoid glycosides from needles of Pinus massoniana

Seven flavonoids have been isolated from Pinus massoniana needles and identified as taxifolin and its 3′-O-β-D-glucopyranoside, (+)-catechin, naringenin-7-O-β-D-glucopyranoside and three new flavonoid glycosides, 6-C-methylaromadendrin 7-O-β-D-glucopyranoside, taxifolin 3′-O-β-D-(6″-O-phenylacetyl)-glucopyranoside and eriodictyol 3′-O-β-D-glucopyranoside.     

Flavonoids of four species of Parthenium (compositae)

Kaempferol and quercetin 3-O-glycosides were found in the closely related species, Parthenium hysterophorus, P. bipinnatifidum and P. glomeratum; the major aglycone flavonols in P. hypterophorus are quercetagetin 3,7-dimethyl ether and a new flavonoid, 6-hydroxykaempferol 3,7-dimethyl ether. The North-South American species-pair P. glomeratum (Argentina) and P. bipinnatifidum (Mexico) yielded quercetagetin 3,7,3′-trimethyl ether as the major aglycone. The desert species P. rollinsianum yielded five methylated flavonols: quercetin 3,3′-dimethyl ether, penduletin, quercetagetin 3,6,7-trimethyl ether, polycladin and artemetin.     

Anthraquinone,anthrone and phenylpyrone components of Aloe nyeriensis var. kedongensis leaf exudate

The leaf exudate of Aloe nyeriensis var. kedongensis yielded six compounds which were identified on the basis of spectral data and inter-conversions as two groups of three allied compounds. These were (a) 4-methoxy-6(2′,4′-dihydroxy-6′- methylphenyl)-pyran-2-one, its 2′-O-β-D-glucopyranoside (aloenin) and the 2″-O-p-coumaroyl ester of aloenin, (b) the anthracene derivatives l,2,8-trihydroxy- 6-methylanthraquinone (nataloe-emodin), its 2-O-β-D-glucopyranosyl ester and the corresponding 10-C -β-D-glucopyranoside nataloin.     

Biflavonoids from Ochna lanceolata

Two new biflavonoids, 7,4′,7″,4‴-tetramethylisochamaejasmin (1) and 2,3-dihydroochnaflavone 7″-O-methyl ether (2), together with six known flavonoids (3–8) were isolated from the stem bark of Ochna lanceolata. Their structures were established on the basis of spectral studies.     

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.     

An acylated allose-containing 8-hydroxyflavone glycoside from Veronica filiformis

A novel flavone glycoside has been obtained from the whole plant of Veronica filiformis and identified by means of ¹³C NMR spectroscopy as isoscutellarein 4′-methyl ether 7-O-β-(6?-O-acetyl-2″-O-allosylglucoside). The related isoscutellarein glycoside is also present. This is the first report of 2-allosylglucose as a disaccharide unit of flavonoids. ¹³`C NMR data on some A-ring trioxygenated flavonoids are also presented.     

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.     

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.