Eckhard Wollenweber

Occurrence and distribution of free flavonoid aglycones in plants

Abstract Flavonoids are widely present in plants as water-soluble glycosides but the lipophilic free aglycones are far less abundant. The 462 flavonoids reported so far to be present in the free state and their plant sources are listed. Evaluation of these data reveals a correlation in most cases between the occurrence of flavonoid aglycones, the presence of secretory structures and the production of other lipophilic plant products. Their accumulation in some plant organs and in certain taxa is discussed. Special attention is given to their occurrence in materials deposited externally on leaves and buds.

Flavones and flavonols

Most reports on the identification of known flavonoids in new plant sources as well as those on novel flavonoids naturally deal with the two most abundant classes, the flavones and flavonols. For this chapter we have listed all references to the occurrence of flavone and flavonol aglycones which have appeared from 1975 to 1980, and also include such earlier references as were overlooked in the relevant chapters of The Flavonoids’ (1975). Emphasis is given to the natural distribution of these compounds. The data are collected in Tables 4.1 and 4.2 which cite substances, plant sources and references. Since 1974, some 50 flavones and 60 flavonols with common substitution patterns have been described as novel compounds. Many are simply new methyl ethers of known compounds. The structures are arranged throughout the Tables by number and arrangement of substituents in ring A, followed by ring B. Wherever possible, the plant organs from which the compounds have been isolated are cited. In cases where authors have extracted the ‘whole plant’ or ‘aerial parts’, it does not necessarily follow that the compound is present in all parts, since these substances are often specifically located in certain organs only. In all cases where free aglycones are encountered, especially highly methylated flavonoids, it is likely that they occur externally, or are associated with secretory structures and are correlated with the production of other lipophilic secondary compounds, mainly of terpenoid origin.

Propolis allergy. (I). Origin, properties, usage and literature review.

Propolis or bee‐glue, a resinous bee‐hive product, is the cause of an increasing number of cases of allergic contact dermatitis. Formerly only observed in bee‐keepers, propolis allergy today is mainly seen in individuals who use propolis in bio‐cosmetics and self treatment of various diseases. Nearly 200 cases are summarized in an overview, including the first description of ‘poplar bud’ contact, dermatitis from 1887. As practically all flavonoid aglycones and most of the other phenolics present in propolis are identical with the bud secretion of poplars, evidence is given that the poplar bud constituents are responsible for propolis hypersensitivity.

Sur l'analyse qualitative des aglycones flavoniques dans une optique chimiotaxinomique

Abstract A qualitative method is described for the analysis of flavonols and flavones in hydrolysed extracts of plant organs; the procedure involves thin layer and column chromatography of plant extracts on polyamide. Physicochemical data are given for about eighty flavonoids.

External flavones in sweet basil, Ocimum basilicum, and related taxa

Abstract Sixteen accessions of Ocimum basilicum L. belonging to different cultivars and varieties, and one accession each of O. x citriodorum Vis. and O. minimum L., were examined for their external leaf flavonoids. The O. basilicum samples showed the presence of one or two major flavone aglycones, which were identified as salvigenin and nevadensin, and up to 10 minor ones: cirsileol, cirsilineol, eupatorin, apigenin, acacetin, genkwanin, apigenin 7,4′-dimethyl ether, cirsimaritin, ladenein and gardenin B. No trace was found of xanthomicrol, the only lipophilic flavone so far reported from O. basilicum . There were appreciable differences amongst the accessions in total flavonoid concentration and in their nevadensin / salvigenin ratios, which, on the whole, were not correlated with morphological characters. The surface flavonoid profile of O. x citriodorum was very similar to those of the O. basilicum plants studied, but that of O. minimum was significantly different. Only 4′-methyl ethers of apigenin derivatives were detected in the latter taxon, whereas apigenin and luteolin derivatives in which the 4′-hydroxyls are free were absent. Furthermore, the ratio of nevadensin / salvigenin was much higher in O. minimum than in O. basilicum or O. x citriodorum . These differences support the treatment of O. minimum as a separate species rather than as a variety of O. basilicum .

Propolis allergy. (II). The sensitizing properties of 1,1-dimethylallyl caffeic acid ester.

As shown in the preceding paper, propolis or bee‐pine is the cause of an increasing number of allergic reactions in persons using it in external preparations and cosmetics. Propolis und its main contact allergen, 1,1‐dimethylallyl caffeic acid ester, designated LB‐1, show strong sensitizing properties in properties as well as in guinea pig experiments. 9 patients have been patch tested with this compound, 8 of whom reacted strongly. Chemical separation of different propolis samples and poplar and extracts reveal that LB‐1 is always present. Poplar bud secretion is the bees major source for propolis und hence the origin of LB‐1. A warning is indicated, in agreement with several other authors, that propolis should not be used in topical products because of its strong sensitizing properties.

Exudate flavonoids of Inula viscosa

Abstract Aerial parts of Inula viscose exhibit a resinous exudate of terpenoid nature, containing flavonoid aglycones. Nine flavonoids are reported in addition to 13 previously known components. The.study of samples collected in France, Spain and Turkey indicates the existence of a qualitatively constant exudate flavonoid profile in this species.

Chemodiversity of exudate flavonoids in some members of the Lamiaceae

Several newly studied species and further accessions of the Lamiaceae have been analyzed for their exudate flavonoid profiles. The principal compounds accumulated were flavones and their 6-methoxy derivatives, whereas flavonols were rarely encountered. The chemodiversity observed was relatively low, with only some 15 derivatives being found. The new data are discussed in relation to published data, and chemosystematic aspects are briefly addressed. Of the studied species, Salvia arizonica yielded only a rare diterpene quinone, demethylfruticulin A. Glandular hair diversification and different qualities of their secretions are briefly discussed.

Flavonoidmuster als systematisches Merkmal in der Gattung Populus

Abstract Buds of almost every species of popular excrete lipophilic “coating” which contains many flavonoid and related derivatives. The compounds found in this “bud coat” of eighty taxa of Populus have been examined and nearly 30 compounds have been identified and their distribution related to the taxonomy of the genus. In sections Aigeiros and Tacamahaca and hybrids of these, chrysin, galangin and pinocembrin form the major components which, in most cases, are accompanied by lesser amounts of tectochrysin, izalpinin, pinostrobin, galangin-3-methylether and pinobanksin-3-acetate. Variations are shown by presence of apigenin and its monomethyl ethers, kaempferol methyl ethers, rhamnetin, quercetin-3,7- and 3,3′-dimethylether, the unusual flavanone “P4” and two chalcones. Myricetin, genkwanin and kaempferol-7.4′-dimethylether are each found only in one species. In the sections Leuce and Leucoides, the major compounds are cinnamic acid derivatives. Flavonoid patterns, as analysed on polyamide TLC, allow species of the sections Aigeiros and Tacamahaca and some hybrids to be characterized, provided several individuals are examined, It is not possible by this method to differentiate clones within a species.

Leaf surface flavonoids of Chrysothamnus

Twenty-six flavonoid aglycones have been identified from eight plants covering three species of Chrysothamnus that were collected in eastern Oregon. The flavonoids were identified by NMR spectroscopy, tandem mass spectrometry and co-TLC with authentic markers. Chrysothamnus nauseosus yielded methyl ethers of apigenin, isoscutellarein, luteolin, kaempferol, herbacetin and quercetin. O-Methylated kaempferol and quercetin derivatives were isolated from the leaf exudate of C. humilis. The flavonoid chemistry of C. viscidiflorus was found different from the other two species by the presence of methyl ethers of quercetin, eriodictyol and taxifolin-3-acetate. Although the flavonoid profiles proved of diagnostic value at the species level, they provided little further evidence in favour of inclusion of Chrysothamnus into Ericameria as proposed earlier on the basis of morphological similarities.