Galloylation of polyphenols alters their biological activity.

Polyphenols form one of the largest groups of natural compounds and possess a wide range of biological properties. These activities can be influenced by the galloyl moiety within their structures. A multitude of galloylated polyphenolic compounds occurs in nature, but galloylated phenols are also produced synthetically to influence their biological properties. This review provides a comprehensive summary of current knowledge about natural (galloylated catechins, theaflavins and proanthocyanidins, penta-O-galloyl-β-d-glucose, gallotannins, ellagitannins, ellagic acid and flavonols) and semisynthetic gallates with a focus on their biological activity and toxicity issues. The effects of tea catechins (epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate) and semisynthetic galloyl esters of the flavonolignans silybin and 2,3-dehydrosilybin from the milk thistle (Silybum marianum) on angiogenesis were used as examples of the structure-activity relationship (SAR) study.