Andrew Pelter

Oxidation experiments with flavonoids

Abstract It is proposed that phenolic oxidation of a 4(2)-hydroxychalcone(4′[2′]-hydroxyflavanone) serves to initiate transformations to aurone, flavone, dihydroflavonol and isoflavone. Flavonols could be produced by phenolic oxidation of either a 4′-hydroxydihydroflavonol or a 4′-hydroxyflavone. The production of 4-hydroxyphenylcoumarins and derived products could follow a similar pathway from isoflavones. Simple model flavanones and chalcones have been synthesized and their oxidation by potassium ferricyanide studied. The 4′-hydroxy and 2′-hydroxy compounds rapidly give flavone or aurone in high yield, in sharp distinction to the 3′-hydroxy derivatives. The fully methylated flavanones or corresponding chalcones are not oxidized after long periods. The results provide excellent analogies for the proposed biosynthetic pathway. The hydroxyaurone is produced as a metal complex, in which form it is protected from further oxidation, a situation that may have biochemical analogies.

Biflavonyls from guttifereae—garcinia livingstonII

Abstract Moarelloflavone (BGH-II) and a new biflavonyl, BGH-111 along with optically active amentoflavone and podocarpusflavone A have been isolated from the phenolic extractives ofheartwood, bark and leaves of Garcinia livingstonii. Two members of a new series of 3,8-linked biflavones have been produced from BGH-II and BGH-111. Mass spectral and NMR studies including solvent dependent shifts ofOMe resonances are used for structure elucidation. An anomaly in the method ofOMe proton shifts is pointed out.

Cinnamylidenbutenolide aus Piper sanctum

Zusammenfassung Aus den Wurzeln von Piper sanctum (Miq) Schlecht haben wir eine Substanz isoliert, fur die wir die Bezeichnung Piperolid vorschlogen. Die Konstitution wurde ermittelt. Es handelt sich um 5-(γ-Methoxy)-cinnamyliden-4-methoxy-but-3-enolid und damit um den ersten Vertreter einer substituierten Tetronsaure (5-Yliden- O -methyltetronsaure), die in hoheren Pflanzen gefunden wurde. Begleitet wird Piperolid (III) von einer zweiten Substanz, dem Methylendioxyderivat von III (= MDO-III).

Zur struktur des silybins: synthese von unsymmetrisch substituierten 2.3-trans-benzdioxanen

Zusammenfassung The synthesis of model trans -2-aryl-3-hydroxymethyl-1,4-benzdioxanes is described. These substances are very similar in p.m.r. spectra and fragmentation patterns to the aliphatic residue of silybin, dehydrosilybin and their derivatives, thus confirming the presence of a 1,4-benzdioxane ring in these compounds. Neither cis- nor trans-chroman-3,4-diols show any similarity in p.m.r. spectra to silybin or its derivatives, showing the structural proposal incorporating this unit to be untenable.

Obtusifolin, ein Flavanon mit einem biogenetisch unüblichen C9-Baustein / Obtusifolin, a Flavonone with a Biogenetically Unusual C9-unit

From the overground parts of Gnaphalium obtusifolium (Compositae) there was isolated a flavanone substituted by a biogenetically unusual C9-unit (= obtusifolin). Mass-, UV-, IR-, PMR-spectra are correlated on the basis of a structure previously established by X-ray analysis CHOPPE et al. 12).