6-c-β-d-glucopyranosyl-8-c-β-d-galactopyranosylapigenin from cerastium arvense

The new C-glycosyiflavone, 6-C-β-d-glucopyranosyl-8-C-β-d-galactopyranosylapigenin, has been isolated from Cerastium arvense and identified on the basis of UV, MS and ¹³C NMR spectral data and comparison with the product obtained from 6-C-galactosylation of vitexin.     

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-galactosylflavones from Polygonatum multiflorum

8-C-Galactosylapigenin and 6-C-galactosyl-8-C-arabinosylapigenin were isolated from the leaves of Polygonatum multiflorum (L.) All. Structural assignments for the latter compound were made on the basis of mass, CD and ¹³C-NMR spectra.     

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.     

Corymboside,nouvelle di-C-glycosylflavone des racines de Carlina corymbosa

Corymboside, a new di-C-glycosylflavone from Carlina corymbosa roots, was shown to be 6-C-α-l-arabinopyranosyl-8-C-β-d-galactopyranosylapigenin by MS, CD, ¹H and ¹³C NMR.     

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.     

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.     

Flavone C-glycosides of two Metzgeria species

Six known tricin and apigenin di-C-glycosides, including 2″-O-ferulylisoschaftoside, have been identified in gametophytic material of Metzgeria conjugata. M. leptoneura contains a new di-C-glycoside, tricin 6-C-xyloside-8-C-hexoside. The chemotaxonomic relevance of the flavonoid patterns is briefly discussed.     

New syntheses of 2′-C-methylnucleosides starting from d-glucose and d-ribose

Effective general methods have been developed for the synthesis of 2′-C-methylnucleosides starting from d-glucose and d-ribose. 3-O-benzyl-1,2-O-isopropylidene-3-C-methyl-α-d-allofuranose was prepared in 5 steps from d-glucose and converted into 1,2,3-tri-O-acetyl-2-C-methyl-5-O-p-methylbenzoyl-d-ribofuranose (5), the starting compound for nucleoside synthesis. Compound 5 was also synthesised from 2-C-hydroxymethyl-2,3-O-isopropylidene-5-O-trityl-d-ribofuranose, prepared in 3 steps from d-ribose. Condensation of 5 with the bis-trimethylsilyl derivatives of uracil, N⁴-benzoylcytosine, and N⁶-benzoyladenine in the presence of F₃CSO₃OSiMe₃ followed by removal of the protecting acyl groups yielded the corresponding 2′-C-methylnucleosides.     

Sugar ring isomerization in C-arabinosylflavones

6-C-α-l-Arabinopyranosyl- and furanosylacacetins have been synthesized. They are isomerized by short acid treatment to give a mixture of the four anomer/ring size combinations without any Wessely-Moser isomerization. In the same conditions molludistin (8-C-α-l-arabinopyranosylgenkwanin) led only to a mixture of molludistin and 8-C-α-l-arabinofuranosylgenkwanin. This is the first demonstration of ring sugar isomerization in C-glycosylflavones. In usual solvent systems, α-anomers are easily separated from β-anomers, whereas corresponding pyranosyl and furanosyl anomers are not. However, they are easily separated after permethylation and characteristic features are found in the mass spectra of PM 6-C-arabinofuranosyl isomers.     

Flavone C-glycosides of Apometzgeria pubescens

Eleven flavone di-C-glycosides, including nine which are new, have been identified in gametophytic material of Apometzgeria pubescens. Tricetin 6,8-di-C-glucoside and tricin 6-C-arabinoside-8-C-pentoside are the major compounds. Another identified was ferulylisoschaftoside. The chemotaxonomic relevance of the flavonoid pattern of Apometzgeria pubescens is briefly discussed.     

Removal of the acetate-moiety of 2,4-dichlorophenoxyacetic acid in Ribes sativum

Ten minutes after uptake of 2,4-dichlorophenoxyacetic acid-1-¹⁴C(2,4-D-1-¹⁴C) by excised Ribes sativum leaves, 37·8 % of the radioactivity in water-soluble metabolites was in glyoxylic acid. When 2,4-D- 2-¹⁴C was supplied under the same conditions, 23·0 % of the radioactivity of the water-soluble rnetabolites was in glyoxylic acid. Radioactive glycine and glyoxylic acid, isolated from Ribes sativum 6 hr after uptake of 2,4-D-1-¹⁴C, contained essentially all of the ¹⁴C in the carboxyl-carbon atoms. When 2,4-D-2-¹⁴C was the precursor, the glycine isolated contained 64·8 % of its radioactivity in C₂, while 60·0 % of the radioactivity in glyoxylic acid was in C₂. The side-chain label of 2,4-D-2-¹⁴C-4-³⁶Cl was more efficiently incorporated into ethanol-insoluble plant residue than the ring-label. The metabolism of glyoxylic acid-1-¹⁴C and 2,4-D-1-¹⁴C in excised Ribes sativum leaves were compared. The data suggest a cleavage of the acetate-moiety of 2,4-D resulting in a C₂ compound, perhaps glyoxylate.     

The influence of hydrogen bonding on the rate of thiolate alkylation in tripod-zinc thiolate complexes

A series of new thioimidazolylborate zinc thiolate complexes Tti^xylZnSR (2)-(5) (where R = C₆H₄-o-OH, C₆H₄-o-CH₂OH, C₆H₄-o-NH₂, and C₆H₄-p-OH, respectively) have been synthesized and characterized as structural and functional models of the active site of the Ada repair protein. Structural determination of complexes 2-4 reveals intramolecular N/O-H?S hydrogen-bonding interactions. The influence of these hydrogen bonding interactions on the methylation of the thiolate ligands is evident from the fact that the rate of methylation for these complexes is reduced ca. 2 orders of magnitude compared to that found in the case of the non-hydrogen bonding-containing complex, Tti^xylZnSC₆H₅ (1).     

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.     

Unprecedented furan-2-carbonyl C-glycosides and phenolic diglycosides from Scleropyrum pentandrum

Five unprecedented furan-2-carbonyl C-glycosides, scleropentasides A–E, and two phenolic diglycosides, 4-hydroxy-3-methoxybenzyl 4-O-β-d-xylopyranosyl-(1 → 6)-β-d-glucopyranoside and 2,6-dimethoxy-p-hydroquinone 1-O-β-d-xylopyranosyl-(1 → 6)-β-d-glucopyranoside, were isolated from leaves and twigs of Scleropyrum pentandrum together with potalioside B, luteolin 6-C-β-d-glucopyranoside (isoorientin), apigenin 8-C-β-d-glucopyranoside (vitexin), apigenin 6,8-di-C-β-d-glucopyranoside (vicenin-2), apigenin 6-C-α-l-arabinopyranosyl-8-C-β-d-glucopyranoside (isoschaftoside), apigenin 6-C-β-d-glucopyranosyl-8-C-β-d-xylopyranoside, adenosine and l-tryptophan. Structure elucidations of these compounds were based on analyses of chemical and spectroscopic data, including 1D and 2D NMR. In addition, the isolated compounds were evaluated for their radical scavenging activities using both DPPH and ORAC assays.     

Sur le sterol a 26 atomes de carbone de l'algue rouge Rhodymenia palmata

Triterpene alcohols and sterols of the red alga Rhodymenia palmata have been investigated. Cycloartanol, 31-nor-cycloartanol and the C₂₆ sterol 24-dimethylchola-5,22-diene-3β-ol (1) have been identified. Feeding experiments have been performed using 1-¹⁴C-acetate, 5-¹⁴C-mevalonic acid or ¹⁴C-methylmethionine. The C₂₇, C₂₈ and C₂₉ sterols incorporate radioactivities but the C₂₆ sterol is unlabelled after each experiment; its possible origin is discussed.     

Reactivity study of arene(azido)ruthenium N∩O-base complexes with activated alkynes

Substitution reaction of chloro η⁶-arene ruthenium N∩O-base complexes [(η⁶-arene)Ru(N∩O)Cl] [N∩O = pyrazine-2-carboxylic acid (pca-H), 8-hydroxyquinoline (hq-H); arene = p-ⁱPrC₆H₄Me, N∩O = hq (1); arene = C₆Me₆, N∩O = hq (2)] with NaN₃ yield the neutral arene ruthenium azido complexes of the general formula [(η⁶-arene)Ru(N∩O)N₃] [N∩O = pca, arene = p-ⁱPrC₆H₄Me (3), arene = C₆Me₆ (4); N∩O = hq, arene = p-ⁱPrC₆H₄Me (5), arene = C₆Me₆ (6)]. These complexes undergo [3 + 2] dipolar cycloaddition reaction with activated alkynes dimethyl and diethyl acetylenedicarboxylates to yield the arene triazole complexes [(η⁶-arene)Ru(N∩O){N₃C₂(CO₂R)₂}] [N∩O = pca, R = Me, arene = p-ⁱPrC₆H₄Me (7), C₆Me₆ (8); R = Et, arene = p-ⁱPrC₆H₄Me (9), C₆Me₆ (10); N∩O = hq, R = Me, arene = p-ⁱPrC₆H₄Me (11) C₆Me₆ (12); R = Et, arene = p-ⁱPrC₆H₄Me (13), C₆Me₆ (14)]. On the bases of proton NMR study, in the above triazole complexes N(2) isomers are assigned with dimethylacetylenedicarboxylate whereas N(1) isomers with diethylacetylenedicarboxylate. All complexes have been characterized by IR and NMR spectroscopy as well as by elemental analysis. The molecular structures of the azido complexes [(η⁶-p-ⁱPrC₆H₄Me)Ru(pca)N₃] (3), [(η⁶-p-ⁱPrC₆H₄Me)Ru(hq)N₃] (5) and [(η⁶-C₆Me₆)Ru(hq)N₃] (6) have been established by single crystal X-ray diffraction studies.     

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.     

Studies of carbohydrate derivatives having the -CH2F function

The following primary sulphonates have been converted into the corresponding deoxyfluoro derivatives by reaction with potassium fluoride in ethylene glycol:1,2:3,4-di-O-isopropylidene-6-O-tosyl α-D-galactopyranose (1), methyl 2,3-O2-isopropyliden-5-O-tosyl-α,β-D-ribofuranoside (2), 1,2:3,4-di-O-methylene-6-O-tosyl-α-D-glucofuranose (3), 3,5-di-O-benzylidene-1,2-O-isopropylidene-6-O-tosyl-α-D-glucofuranose (4), and 1,2:3,5-di-O-isopropylidene-6-O-tosyl-α-D-glucofuranose (5). The yields were generally poor; in the reaction of 1, a major by-product was 6-O-(2-hydroxyethyl)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (11). The reaction of the primary hydroxyl precursor of each of the above tosylates with N2-(2-chloro- 1,1,2-trifluoroethyl)-N,N-diethylamine generally yielded the O-chlorofluoroacetyl derivative; however, 1,2:3,5-di-O-methylene-α-D-glucofuranose (12) was converted into the 6-deoxy-6-fluoro derivative (8). The ¹⁹F resonances of compounds containing the CH₂F moiety fall between φ_C +213 and φ_C +235 p.p.m. The differences between the vicinal¹⁹F-¹H couplings of compounds having the D-gluco and D-galacto configurations clearly reflect the influence of the C-4O-4 substitutents on the populations of the C-5C-6 rotamers. A novel type of noise-modulated, heteronuclear decoupling experiment is described.     

Coordination chemistry of molybdenum relevant to hydrodenitrogenation: Reactivity of Mo(PMe3)6 towards 6-membered heterocyclic aromatic nitrogen compounds involving C-H bond cleavage and η-coordination

The reactivity of Mo(PMe₃)₆ towards 6-membered heterocyclic aromatic nitrogen compounds, namely pyridine, pyrazine, pyrimidine and triazine, has been investigated as part of an effort to define the coordination chemistry of molybdenum relevant to hydrodenitrogenation. For example, Mo(PMe₃)₆ reacts with pyridine to yield initially (η²-N,C-pyridyl)Mo(PMe₃)₄H, an uncommon example of an η²-pyridyl-hydride complex. The formation of (η²-N,C-pyridyl)Mo(PMe₃)₄H is reversible and treatment with PMe₃ regenerates Mo(PMe₃)₆ and pyridine. At elevated temperatures, (η²-N,C-pyridyl)Mo(PMe₃)₄H dissociates PMe₃ and converts to the η⁶-pyridine complex (η⁶-pyridine)Mo(PMe₃)₃. Pyrazine, pyrimidine and 1,3,5-triazine likewise react with Mo(PMe₃)₆ to yield (η²-N,C-pyrazinyl)Mo(PMe₃)₄H, (η²-N,C-pyrimidinyl)Mo(PMe₃)₄H and (η²-N,C-triazinyl)Mo(PMe₃)₄H, respectively. At elevated temperatures (η²-N,C-pyrazinyl)Mo(PMe₃)₄H and (η²-N,C-pyrimidinyl)Mo(PMe₃)₄H dissociate PMe₃ and convert to (η⁶-pyrazine)Mo(PMe₃)₃ and (η⁶-pyrimidine)Mo(PMe₃)₃ in which the heterocycle coordinates to molybdenum in an unprecedented η⁶-manner.