Volker H. Dietz

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.

Flavonoids from chemotypes of the goldback fern, Pityrogramma triangularis

Abstract More than 20 flavonoid aglycones were identified from the frond exudate of various collections of Pityrogramma triangularis . Ten of them are novel natural products; most of the others are rare flavonoids. They are substituted at C-8; many are C -methylated. They mostly occur only as trace constituents in var. triangularis . Two compounds come from var. viscosa . One population of P. triangularis var. triangularis exhibits a unique flavonoid pattern not encountered before in any other chemotype studied.

Flavonoid patterns in the farina of goldenback and silverback ferns

Most species of the fern genus Pityrogramma show a farinose indument caused by a deposit of exuded flavonoid aglycones. Some 220 samples, comprising 14 species, have been studied for the chemical composition of their farinas. Flavones, flavonols and C-methylated flavonoid are rarely found. The presence of certain chalcones and dihydrochalcones, however, appears to be to some extent characteristic for the genus. In some cases the farina flavonoid pattern is species-specific; in one species also variety-specific patterns and even chemotypes are observed. In general, the flavonoid chemistry in Pityrogramma parallels frond morphology to a great extent. This supports the concept that around a core of generalized species a few variant species exist which are best treated as belonging to Pityrogramma.

The occurrence of aurentiacin and flavokawin B on Pityrogramma triangularis var. pallida and Didymocarpus species

Abstract The two chalcones, aurentiacin and flavokawin B, were isolated from the frond exudate of Pityrogramma triangularis var. pallida. In addition, flavokawin B was obtained from the leaf exudate of Didymocarpus corchorifolia.

C-Methyl-Flavanones as Farina on the Fronds of Pityrogramma pallida

Summary Pityrogramma pallida , an endemic silver fern of California, is characterised by very rich production of a white farinose exudate on its fronds. Such material normally consists of methoxy-flavonoids, occuring as aglycones. The present fern, however, produces C-methylated flavonoids. It can be shown that the major constituent of the farina is strobopinin, followed by desmethoxymatteucinol and cryptostrobin in decreasing quantities.

A Novel C-Methylated Dihydrochalcone from Pityrogramma triangularis var. viscosa

Abstract Pityrogramma triangularis var. viscosa is one of the clearly defined varieties within the Pityrogramma triangularis complex. The flavonoid constituents of its frond exudate show a pattern characteristic for this taxon. The major component of the exudate could now be isolated. By spectroscopic methods it has been shown to be 2′,6′,4-trihydroxy,4′-m ethoxy,3′-m ethyl dihydrochalcone, a novel natural compound.

A Series of Novel Flavanones from Fern Exudates

Abstract The white farinose exudate on the fronds of Cheilanthes argentea contains a series of flavanones as minor constituents. These were identified by spectroscopic methods as: 5,4′-diOH,6,7-diOMe flavanone and its 4′-OMe derivative, 5,4′-diOH,7,8-diOMe flavanone and its 4′-OMe derivative, 5,6-diOH,7,8,4′-triOMe flavanone, 5,4′-diOH, 6,7,8-triOMe flavanone and its 4′-OMe derivative. The farina of Notholaena limitanea var. mexicana contains eriodictyol-7,4′-di-methyl ether and eriodictyol-7,3′, 4′-trimethyl ether as minor components. Both compounds were also identified in the exudate of N. fendleri, together with naringenin-7-OMe and naringenin-4′-OMe. In N. lemmonii var. lemmonii trace amounts of 5-OH,7,3′,4′,5′-tetra-OMe flavanone were detected. Nine of these substances are novel natural flavanones.

Leaf surface terpenoids of the tree fernLophosoria quadripinnata

Abstract Fronds of the fernLophosoria quadripinnata exhibit a thin waxy coating on their lower surface. Five major components of this lipophilic material have been identified by spectroscopic methods as hopane type triterpenes, one of which is a novel natural product.

A Novel Class of Complex Flavonoids from the Frond Exudate of Pityrogramma trifoliata

Abstract Fronds of the neotropical fern Pityrogram m a trifoliata produce a farinose exudate which consists mainly of a dihydrochalcone. The structure of som e minor constituents has been elucidated by spectroscopic m ethods. They are shown to be representatives of a novel class of complex flavonoids, com posed of a flavonoid and a neoflavonoid moiety. In other terms, they are 5,7-di-hydroxy-8-cinnamoyl-4-phenyl-dihydrocoumarins. The occurence of these and closely related compounds in this fern’s exudate supports its inclusion in the genus Pityrogramma.

Scale Insects Feeding on Farinose Species of Pityrogramma

Several well known species of the fern genus Pityrogramma are called Silverback Ferns or Goldback Ferns because of the conspicuous white or yellow farinose deposit on the abaxial surface of their fronds. This material is composed of flavonoid aglycones, mostly of dihydrochalcones and chalcones (Wollenweber, 1978; Wollenweber & Dietz, 1980). The correct structural formulae of these compounds are shown in Fig. 1; the formulae in both cited papers are incorrect. These lipophilic phenolic compounds are secreted by glandular trichomes and form quasi-crystalline rods or filaments on the surface of the enlarged terminal cell of the capitate glands (Wollenweber, 1978, pp. 13-15).