Natural diaryl ethers
In this review, on the basis of an analysis of voluminous literature material on natural phenolic compounds belonging to various structural types, the interrelationship between the dimeric molecules formed as the result of the oxidative coupling of the corresponding monomeric compounds is considered.
Constituents of tabebuia guayacan—II
Abstract A unique oxalactone dibenzxanthone, guayin, has been isolated from the heartwood of T. guayacan and structurally identified. A biomimetic synthesis of the dihydro derivative of guayin, based upon the probable biosynthetic origin of guayin from the dibenzxanthene guayacanin, has been successfully achieved.
The formation of xanthylium salts from proanthocyanidins
Abstract Acid treatment of monomeric and condensed natural leucoanthocyanidins yields red anthocyanidins and hitherto unidentified yellow pigments. Model leucocyanidin-polyphenol condensation products also yield yellow pigments with acids, and spectral evidence is now presented which indicates that these yellow compounds are xanthylium salts. The possible significance of these observations in relation to the structures and acid degradation of condensed tannins and phlobaphenes is discussed.