Chapter X - Flavonoid Compounds, Tannins, Lignins and, Related Compounds

Publisher Summary The limitless abilities of plants to synthesize aromatic substances, most of which are phenols or their oxygen-substituted derivatives, affords structurally varied a group of substances to defy the attempts to classify them in summary form. Their range of structural complexity runs from simple substances as hydroquinone to such complex ones as the polycyclic dianthrone, hypericin. Any attempt to erect a system of a priori classification based upon biosynthetic origin is hazardous because few biosynthetic pathways in the field of the natural phenols have been established by experimental means. The idea of the origin of many phenolic plant products by the cyclization of linear polyketomethylene precursors, derived by the condensation of —CH 2 —CO— units, had been developed along speculative and experimental lines. In its simplest form, it can be represented by the formation of orcinol and orsellinic acid from four “acetate units.”