Karin Mann

5,2′,5′-trihydroxyflavone and 2′,β-dihydroxychalcone from Primula pulverulenta

Abstract A new flavone, 5,2′,5′-trihydroxyflavone and 2′,β-dihydroxychalcone (β-diketone) were isolated from the farinose exudate of Primula pulverulenta . These structures were established on the basis of spectral data and confirmed by total synthesis. A transformation experiment suggests that the β-diketone is converted into flavone during isolation procedures.

8,2'-dihydroxyflavone from Primula pulverulenta

Abstract A novel flavone, isolated from the farinose exudate of Primula pulverulenta , was identified as 8,2′-dihydroxyflavone. This is the first naturally occurring flavone, in which ring A is oxygenated only at C-8. The structure was deduced from spectral comparisons with the structurally related flavones: 5,2′-, 3,2′- and 2′,3′-dihydroxyflavone and confirmed by total synthesis. The spectral properties of other flavones oxygenation with a simple pattern are discussed in relation to 8,2′-dihydroxyflavone.

Exudate flavonoids from two australian asteraceae, Bracteantha viscosa and cassinia quinquefaria

Abstract Nineteen flavonoids were identified in the leaf and stem exudates of Bracteantha viscosa : 12 flavones and seven flavanones. Two flavones and four flavanones are rare 6-methoxyflavonoids. The resinous exudate accumulating on aerial parts of Cassinia quinquefaria contains six flavonoid aglycones. One of them is a novel natural flavonol: 6-hydroxygalangin.

Flavonoid aglycones excreted by three Calceolaria species

Abstract The lipophilic exudate produced by Calceolaria irazuensis leaf glands was shown to contain small amounts of three rare 8-methoxy flavonoids and one new one: gossypetin 7,8,3′-trimethyl ether. The leaf exudates of C. chelidonioides and C. scabiosifolia also contain trace amounts of flavonoid aglycones.

Flavonoid Aglycones in the Leaf Resin of Some Cistus Species

Members of the genus Cistus excrete a leaf resin that consists mainly of terpenoids. This resin also contains methylated flavonoids as aglycones. Rare methyl derivatives of myricetin have been isolated from C. monspeliensis, along with uncommon methyl derivatives of quercetin. Further flavonoids encountered in the leaf resin of this and six further species are methyl derivatives of kaempferol and quercetin, some of apigenin and in one species also of luteolin. The results indicate that there might exist species-specific flavonoid patterns

Flavonoids and terpenoids from the leaf resin of Pluchea odorata

Abstract The chemical composition of the leaf resin of Pluchea odorata has been studied from material collected in Tamaulipas, Mexico. It mostly consists of triterpenes and phytosterols and an eudesmane type sesquiterpene. Very small amounts of ten different flavonol aglycones occur, dissolved in this resin; most of them are 6-methoxy compounds. A comparison with previous results on material from El Salvador shows that the latter contains a lesser number of triterpenes and especially of flavonoids, but more sesquiterpenes, while the n-alkane composition varies only quantitatively between both populations.

2′,5′-Dihydroxyflavone and its 5′-Acetate — Novel Compounds from the Farinose Exudate of Primula

2′,5′-Dihydroxyflavone and its 5′-acetate were isolated from the farinose exudate of Primula japonica and P. pulverulenta. Their structures were elucidated by spectroscopic methods and confirmed by synthesis. Both flavones are novel natural products.

Internal and external leaf flavonoids of Pericome caudata

Abstract Pericome caudata accumulates four flavonol aglycones externally on leaf and stem surfaces. The glycosides present in the leaf tissue are based on eight further flavonols. This preponderance of tissue flavonoids over exudate flavonoids is unusual.

New Flavonoids from the Farina of Pityrogramma Species

Abstract 2′,6′,4-OH, 4′-OMe-chalcone (neosakuranetin) and 2′,6′,4-OH, 4′-OMe-dihydrochalcone (asebogenin) were found as major constituents of the frond exudate on one in dividual plant of Pityrogramma calomelanos. Galangin-5,7-dimethyl ether was isolated from the farina on fronds of a certain population of Pityrogramma triangularis as a novel natural flavonol.

Exudate flavonoids in three Ambrosia species

Abstract Three species of Ambrosia (Asteraceae) were studied for leaf and stem exudate flavonoids. Among these, A. bidentata contained 5,7-dihydroxy-8,4′-dimethoxyflavanone and other rare flavonoids, whereas A. chamissonis and A. trifida were shown to contain a number of trivial flavonoids.