A dihydroflavonol with taxonomic significance from the fern Notholaena sulphurea.

A new flavonoid, 2,3-trans-5,2'-dihydroxy-7,8-dimethoxy-dihydroflavonol-3-O-acetate, was isolated from the farinose coating on the lower leave surface of the fern, Notholaena sulphurea. The 2,3-cis diastereoisomer was isolated as a co-constituent. This novel acylated flavonoid is characteristic for the chemotype of N. sulphurea exhibiting yellow frond exudate. Its orrurrence underlines the affiliation of the species with the genus Notholaena.

Exudate flavonoid aglycones in the alpine species of Achillea sect. Ptarmica: Chemosystematics of A. moschata and related species (Compositae-Anthemideae).

In completion of our studies on Achillea exudate flavonoids, 11 alpine species of Achillea sect. Ptarmica were analyzed for their aglycone profiles. The study focuses on species commonly associated with A. moschata. The major flavonoid constituents found in exudates of most taxa were 6-hydroxyflavonol 3,6,4'-trimethyl ethers, except in A. ageratifolia and its subspecies, which are characterized by the accumulation of the 3,6,7-trimethoxy and 6-hydroxyflavones. Infraspecific variation was particularly high in A. abrotanoides and A. moschata. Results are discussed in relation to published data for related species and within the context of evolutionary aspects in the genus Achillea. The 3,6,4'-trimethoxy substitution is regarded as a basic chemical trend within the genus Achillea. Geographical and ecological aspects are briefly addressed, and a summary on known exudate aglycone composition of species from all sections of Achillea is included.

Epicuticular waxes and flavonol aglycones of the European mistletoe, Viscum album L.

Cuticular waxes of Viscum album ssp. album contain oleanolic acid as main constituent, accompanied by aliphatic compounds like alkanes, esters and primary alcohols. A number of flavonol aglycones (methyl ethers of quercetin and kaempferol) have also been identified. Seasonal changes in amount and composition of cuticular waxes and the presence of flavonol aglycones are described and the ecophysiological significance of flavonoids on the surface of the mistletoe is briefly discussed.

New constituents of the leaf and stem exudate of Ozothamnus hookeri (Asteraceae).

The exudate of Ozothamnus hookeri has been investigated for its non-flavonoid constituents. A new natural C6-C3 ester of a long chain fatty acid and seven structurally related kaurane-diterpenoids were isolated. Three of the latter are new natural products, too. A rare 8-methoxy flavonol was also identified.

Lipophilic exudates of Pteridaceae - chemistry and chemotaxonomy.

A number of fern species, belonging to several genera of Pteridaceae, exhibit a more or less conspicuous farinose wax, which is mostly located on the lower leaf surface. Production of these waxes is often correlated with the presence of glandular trichomes. Particularly during the past two decades, a series of publications appeared on the chemical composition of these exudates. The major components were found to be flavonoids (chalcones, dihydrochalcones, flavanones, dihydroflavonols, flavones, flavonols), some of them with a complex substitution pattern, including esters and C-methyl derivatives, and even bisflavonoids. Diterpenoids and triterpenoids can also occur in such exudates. It is the purpose of this paper to survey the chemical composition of Pteridaceae exudates and their occurrence within the genera of the family. The chemotaxonomic significance of the flavonoid aglycones at the generic, specific and populational level is briefly discussed.

A new oxyprenyl coumarin and highly methylated flavones from the exudate of Ozothamnus lycopodioides (Asteraceae).

A new oxyprenyl coumarin was isolated from the lipophilic exudate of Ozothamnus lycopodioides. Its structure was established as 7-(3,3'-dimethylallyloxy)-5-hydroxy-6-methoxycoumarin from its UV, MS and NMR spectral data, especially two dimensional experiments. In addition to six earlier reported flavonols, we found four highly substituted flavones, including two rare methylenedioxyflavones.

Epicuticular flavonoids of some Scrophulariaceae.

Twenty-two species of Scophulariaceae have been found to accumulate flavonoid aglycones externally on their leaves and stems. They belong to the genera Anarrhinum, Antirrhinum, Asarina, Calceolaria, Mimulus, and Odontites. Most of the flavonoids are methylated flavones and flavonols, some with 6-O and/or 8-O-substitution. One of them is the natural isobutyryl ester of a rare flavone.

C-methyl-flavonoids from the leaf waxes of some Myrtaceae.

The thin waxy coatings on leaves of nine species of Callistemon, two of Melaleuca and one species of Metrosideros, have been studied for the occurrence of leaf surface flavonoids. The Callistemon species and Metrosideros robusta exhibit only C-methylated flavonoids, while O-methyl flavonoids were detected in Melaleuca huegelii. The new natural C-methyl flavonol, 5,7-dihydroxy-3,8,4'-trimethoxy-6-C-methylflavone, was isolated from Metrosideros robusta. The leaf wax of Callistemon coccineus contains the novel C-methylflavonoid, 5,4'-dihydroxy-8-C-methyl-7-methoxy flavanone.

A novel 2-hydroxyflavanone from collinsonia canadensis

A new flavonoid, 2,5-dihydroxy-6,7-dimethoxyflavanone (1), was isolated from the leaf and stem exudates of Collinsonia canadensis along with three known flavones, baicalein-6,7-dimethyl ether (2), norwogenin-7,8-dimethyl ether (3), and tectochrysin (5-hydroxy-7-methoxyflavone).

Propolis allergy (IV). Studies with further sensitizers from propolis and constituents common to propolis, poplar buds and balsam of Peru.

26 different compounds have been investigated experimentally for their sensitizing capacity in guinea pigs. 19 of these occur in propolis as well as in poplar bud exudates, and 14 of them are also found in balsam of Peru. 4 caffeates and benzyl isoferulate were found to be strong sensitizers. 7 compounds were moderate, and 13 compounds showed only weak sensitizing potency. Methyl cinnamate was negative. Patch tests in 11 propolis-sensitive patients once more revealed 3-methyl-2-butenyl caffeate and phenylethyl caffeate as the major sensitizers. In addition to the 8 compounds already known to occur in propolis as well as in balsam of Peru, we detected 5 further substances that both materials have in common. Among these, benzyl isoferulate is considered a noteworthy sensitizer. Coniferyl benzoate, which was shown to be a moderate sensitizer, is present in fresh samples of balsam of Peru, while in propolis it has been detected only once so far. The flavonoid aglycones occurring in poplar bud exudates, and hence also in propolis, are weak sensitizers which play only a minor role in propolis hypersensitivity.

Structure of 2',6'-dihydroxy-4,4'-dimethoxychalcone.

1-(2,6-Dihydroxy-4-methoxyphenyl)-3-(4-methoxyphenyl)-2-propen-1-o ne, C17H16O5, Mr = 300.31, orthorhombic, Pbca, a = 27.903 (3), b = 13.958 (2), c = 7.662 (1) A, V = 2984 (1) A3, Z = 8, D chi = 1.337 Mg m-3, lambda(Cu K alpha) = 1.5418 A, mu = 0.729 mm-1, F(000) = 1264, T = 295 K, R = 0.040 for 1702 observed reflections. Two intramolecular hydrogen bonds are observed. The hydroxyl H atom at O(6A) is hydrogen bonded to the C(9) carbonyl group with short distances O(6A)...O(9) = 2.406 (3) and O(9)...H(6A) = 1.38 (3), O(6A)--H(6A) = 1.09 (3) A, the angle O(6A)--H(6A)...O(9) is 153 (4) degrees. The other hydrogen bond is of the C--H...O type with distances C(8)...O(2A) = 2.778 (4), H(8)...O(2A) = 2.09 (3) A and the angle around H(8) is 124 (2) degrees. Conjugation is observed between the aromatic rings and the central enone system. The molecule is not planar, the angle between the planes of the phenyl rings being 13.1 (4) degrees. Intermolecular O--H...O bonds with distances O(6A)...O(2A) = 2.689 (2), H(2A)...O(6A) = 1.86 (4) A and angle O(2A)--H...O(6A) = 176 (4) degrees form endless chains of molecules along b.

Propolis allergy. (III). Sensitization studies with minor constituents.

87% of the propolis product "LB-1", originally reported to be 1,1-dimethyl-allyl caffeic acid ester, was shown by GC/MS analysis to consist of 3 isomeric pentenyl caffeates, 63% of which are 1,1-dimethylallyl caffeate. These pentenyl caffeates proved to be the major sensitizers of propolis and of poplar bud secretion in our previous study. In addition, 3 further minor allergens have now been investigated. Experimental sensitization indicates that phenylethyl caffeate is as strong a sensitizer as the major allergen "LB-1", while benzyl salicylate is a moderate sensitizer. Benzyl cinnamate plays only a subordinate role. At least 3 further esters of caffeic acid or cinnamic acid remain to be studied. Interestingly, relationships between propolis and balsam of Peru were found. 8 compounds are common to both materials. Thus "cross-reactions" or concomitant reactions in propolis-sensitive individuals to balsam of Peru are explainable.

Synthesis of two allergenic constituents of propolis and poplar bud excretion.

The prenyl ester and the phenylethyl ester of caffeic acid, formed in the bud excretion of poplar species, were shown recently to be the major contact allergens in bee-glue. An unambiguous synthesis of these compounds, based on the reaction of caffeic acid with 1-bromo-3-methyl-2-butene and with beta-bromoethylbenzene, respectively, is reported. The synthetic products confirm the previously described structures of the natural products and allow further testing of their allergenic properties.

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

As shown in the preceding paper, propolis or bee-glue is the cause of an increasing number of allergic reactions in persons using it in external preparations and cosmetics. Propolis and its main contact allergen, 1,1-dimethylallyl caffeic acid ester, designated LB-1, show strong sensitizing properties in patients 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 bud extracts reveal that LB-1 is always present. Poplar bud secretion is the bee's major source for propolis and 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.

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.

Leaf Gland Flavonoids in Comptonia peregrina and Myrica pensylvanica (Myricaceae).

Natural products are formed in some Myricaceae by secretory glands on leaves, young twigs, and fruits. Leaf glands of Myrica pensylvanica and Comptonia peregrina produce flavonoid aglycones along with terpenoid material. This is the first study on exudate flavonoids of the two species. In M. pensylvanica rare C-methylated flavonones and chalcones, such as cryptostrobin, desmethoxymatteucinol, aurentiacin, and myrigalon-D, are the major constituents. In C. peregrina chrysin, galangin, pinocembrin, and their methyl ethers are dominant. They are accompanied by some of the C-methyl flavonoids found in M. pensylvanica. A novel natural flavanone, 7-hydroxy-5-methoxy-6-C-methyl flavanone (comptonin) was isolated from C. peregrina, where it was encountered along with trace amounts of the corresponding 2',4'-dihydroxy-6'-methoxy-5'-C-methyl chalcone.