Gallic Acid and Its Metabolites

Abstract

The biosynthesis of a wide range of derivatives of gallic acid in higher plants is a classic example of secondary metabolism. The formation of a majority of these polyphenolic metabolites (gallotannins and ellagitannins) may be rationalised in terms of further transformations of the key intermediate β-l,2,3,4,6-pentagalloyl-D-glucose. Four principal pathways have been identified. One involves the synthesis of depside derivatives by the addition of further galloyl groups to the galloyl glucose core (gallotannins), and the remainder are associated with dehydrogenation reactions and the formation of intra- and inter-molecular C-C and C-O bonds (ellagitannins). These biosynthetic pathways are illustrated and methods of isolation, identification and structure determination for this group of polyphenols are outlined.