Acacetin glycosides as taxonomic markers in Calamintha and Micromeria.

A new acetylated flavone glycoside, acacetin 7-O-[6""-O-acetylglucosyl(1""-->2")]rhamnosyl(1"'-->6")glucoside, has been isolated from the leaves of Calamintha glandulosa together with the known compound acacetin 7-O-rhamnosyl(1"'-->6")glucoside. The occurrence of these flavonoids in the closely related genera Satureja, Micromeria, Acinos and Clinopodium indicates that their distribution may be of taxonomic significance.

The role of lipophilic and polar flavonoids in the classification of temperate members of the Anthemideae.

Lipophilic and vacuolar flavonoids were separately identified in representative temperate species of the genera Anthemis, Chrysanthemum, Cotula, Ismelia, Leucanthemum and Tripleurospermum. The four Anthemis species investigated variously produced four main surface constituents, in leaf and flower: santin, quercetagetin 3,6,3'-trimethyl ether, scutellarein 6,4'-dimethyl ether and 6-hydroxyluteolin 6,3'-dimethyl ether. By contrast, surface extracts of disc and ray florets of the species of Chrysanthemum, Cotula, Ismelia, Leucanthemum and Tripleurospermum surveyed yielded five common flavones in the free state: apigenin, luteolin, acacetin, apigenin 7-methyl ether and chrysoeriol. Polar flavonoids were isolated and identified in leaf, ray floret and disc floret of all the above plants. Anthemis species were distinctive in having flavonol glycosides in the leaves, whereas the leaf flavonoids of the other taxa were generally flavone O-glycosides. The 3-glucoside and 3-rutinoside of patuletin were characterised for the first time from Anthemis tinctoria ssp. subtinctoria. Two new flavonol glycosides, the 5-glucuronides of quercetin and kaempferol, were obtained from the leaf of Leucanthemum vulgare, where they co-occur with the related 5-glucosides and with several flavone glycosides. The ray florets of these Anthemideae generally contain apigenin and/or luteolin 7-glucoside and 7-glucuronide, whereas disc florets have additional flavonol glycosides, notably the 7-glucosides of quercetin and patuletin and the 7-glucuronide of quercetin. A comparison of the flavonoid pattern encountered here with those previously recorded for Tanacetum indicate some chemical affinity between Anthemis and Tanacetum. Flavonoid patterns of the other five genera are more distinct from those of Tanacetum and suggest that those genera form a related group. All 14 species surveyed for their flavonoid profiles have distinctive constituents and the chemical data are in harmony with modern taxonomic treatments of the "Chrysanthemum complex" as a series of separate genera.

A distinctive flavonoid chemistry for the anomalous genus Biebersteinia.

Leaf surface extracts of Biebersteinia orphanidis have yielded a complex mixture of five flavones with the unusual 5,7-dihydroxy-6,8-dimethoxy A ring substitution pattern. They are acerosin, hymenoxin, nevadensin, sudachitin and 5,7,4'-trihydroxy-6,8-dimethoxyflavone. Also present at the leaf surface are gardenin B, luteolin, apigenin, acacetin and the coumarin umbelliferone. The internal leaf flavonoids include the 7-glucosides of apigenin, luteolin and tricetin, together with the 7-rutinosides of apigenin and luteolin. This profile differs from those of B. heterostemon and B. odora. It appears that B. orphanidis is as highly distinctive in its flavonoid pattern as it is phytogeographically. The data also confirm the conclusion of other studies, including rbcL and atpB gene sequence analysis, that Biebersteinia is completely unrelated to the Geraniaceae, where it was once placed.

Advances in flavonoid research since 1992.

Some of the recent advances in flavonoid research are reviewed. The role of anthocyanins and flavones in providing stable blue flower colours in the angiosperms is outlined. The contribution of leaf flavonoids to UV-B protection in plants is critically discussed. Advances in understanding the part played by flavonoids in warding off microbial infection and protecting plants from herbivory are described. The biological properties of flavonoids are considered in an evaluation of the medicinal and nutritional values of these compounds.

The flavonoids of Tanacetum parthenium and T. vulgare and their anti-inflammatory properties.

The lipophilic flavonoids in leaf and flower of Tanacetum parthenium and T. vulgaris have been compared. While those of T. parthenium are methyl ethers of the flavonols 6-hydroxykaempferol and quercetagetin, the surface flavonoids of T. vulgare are methyl ethers of the flavones scutellarein and 6-hydroxyluteolin. Apigenin and two flavone glucuronides are surprisingly present in glandular trichomes on the lower epidermis of the ray florets of T. parthenium. The opportunity has been taken to revise the structures of the four 6-hydroxyflavonol methyl ethers of T. parthenium based on NMR measurements. These are now shown to be uniformly 6- rather than 7-O-methylated. Tanetin, previously thought to be a new structure, is now formulated as the known 6-hydroxykaempferol 3,6,4'-trimethyl ether. The vacuolar flavonoids of both plants are dominated by the presence of apigenin and luteolin 7-glucuronides; nine other glycosides were present, including the uncommon 6-hydroxyluteolin 7-glucoside in T. vulgare. When the major flavonol and flavone methyl ethers of the two plants were tested pharmacologically, they variously inhibited the major pathways of arachidonate metabolism in leukocytes. There were significant differences in potency, with the tansy 6-hydroxyflavones less active than the feverfew 6-hydroxyflavonols as inhibitors of cyclo-oxygenase and 5-lipoxygenase.

Condensed tannins and sugars in the diet of chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda.

Fruits, leaves and bark forming part of the diet of chimpanzees were collected and it was noted whether samples were of a kind being eaten or not eaten. Samples were dried and analysed for condensed tannin content and for three sugars, glucose, sucrose and fructose. It was found that chimpanzees did not select foods according to the level of tannins but did so according to the levels of sugars, preferring the higher levels. Fig seeds contained higher tannin levels than fig pulp, and the chimpanzees made oral boli ("wadges") of fig seeds which they spat out. Two fig species were compared: the one with lower tannin and higher sugar content was preferred. The bark of one tree species often eaten contained high levels of tannins but also contained sugars. Young leaves with lower tannin levels were preferred to mature leaves with higher levels. Chimpanzees appear to be able to tolerate higher tannin levels than three monkey species in this forest, and considerably higher levels than marmosets (Callitrichidae).

Chrysin and other leaf exudate flavonoids in the genus Pelargonium.

In a chemotaxonomic survey of 57 Pelargonium species, leaf exudate flavonoids were detected in 35% of the sample, mostly in trace amounts. However, chrysin and a related C-methylflavanone were identified as major leaf surface constituents of P. crispum, and a mixture of quercetin and kaempferol mono-, and di- and trimethyl ethers of P. quercifolium. In two other species, P. fulgidum and P. exstipulatum, methylated flavones were the only lipophilic flavonoids present. This is the first report of leaf surface flavonoids from the genus Pelargonium.

A biologically active lipophilic flavonol from Tanacetum parthenium.

A new lipophilic flavonol, 6-hydroxykaempferol 3,7,4'-trimethyl ether, called tanetin, has been characterized in the leaf, flower and seed of feverfew, Tanacetum parthenium. It co-occurs with the known 6-hydroxykaempferol 3,7-dimethyl ether, quercetagetin 3,7-dimethyl ether and quercetagetin 3,7,3'-trimethyl ether. Pharmacological tests indicate that tanetin could contribute to the anti-inflammatory properties of feverfew by inhibiting the generation of pro-inflammatory eicosanoids, although it is unlikely to be the only biologically active compound within the plant. Water soluble flavone glycosides were detected in the leaves and identified as apigenin 7-glucuronide, luteolin 7-glucuronide, luteolin 7-glucoside and chrysoeriol 7-glucuronide.

Methylated C-glycosylflavones as taxonomic markers in orchids of the subtribe Ornithocephalinae.

In a leaf flavonoid survey of 15 Brazilian orchid species from the subtribe Ornithocephalinae, flavone C-glycosides were found to be the major constituents in all except two Ornithocephalus taxa. In Zygostates cornuta a rare glycoside, apigenin 7,4'-dimethyl ether 6-C-glucoside-2"-O-rhamnoside, was identified. This also occurred in Z. alleniana, Z. lunata, Z. pellucida and Z. pustulata. Two further similar apigenin 7,4'-dimethyl ether C-glycoside-O-rhamnosides, possibly with different C-linked sugars, were detected in Z. multiflora and Z. grandiflora. In Z. cornuta, apigenin 4'-methyl ether 6-C-glucoside-2"-O-rhamnoside was found to co-occur with the apigenin 7,4'-dimethyl ether derivative. Ornithocephalus myrticola was distinguished by the presence of an apigenin 8-C-methylpentoside and three apigenin 7-methyl ether 8-C-glycoside derivatives. In O. bicornis and O. kruegeri, another apigenin 7,4'-dimethyl ether C-glycoside was found, while from Phymatidum falcifolium, apigenin 7,4'-dimethyl ether and apigenin 7-methyl ether C-glycosides and their O-arabinosides were isolated. Chytroglossa marileoniae also contained an apigenin 7,4'-dimethyl ether C-glycoside, which appeared to be the same as that in P. falcifolium. Rauhiella silvana, on the other hand, could be distinguished from all the other taxa studied by the absence of methylated C-glycosylflavones and presence of isovitexin. 6-Hydroxyflavone O-glycosides, which are characteristic leaf constituents of some Oncidium species in the related subtribe Oncidinae were not detected in the present sample.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of secondary metabolites in chemical defence mechanisms in plants.

The classic view that secondary constituents are waste products in plants has been replaced by one in which their value is assumed to be as a protection against herbivorous and microbial attack. However, secondary pathways may still be physiologically important as a means of channelling and storing carbon compounds, accumulated from photosynthesis, during periods when nitrogen is limiting or whenever leaf growth is curtailed. Large increases in the amount of secondary metabolites can occur in stressed plants and those subject to mechanical damage or that caused by insects. In order to establish a protective role for a given metabolite, it is necessary to monitor concentrations over the life cycle of the plant, to survey plant populations, to determine specific localization within tissues and to carry out bioassays against insects and microorganisms. Synergy between toxins of the same class or of different classes is likely. Changes in secondary chemistry may also occur during ontogeny, and protection may be restricted to the most vulnerable plant organs. Finally, toxins may vary indiscriminately in their distribution within the plant or within populations and still provide protection.