Chemical and biological perspectives of ellagitannin oligomers from medicinal plants

The phytoehemical study of hydrolyzable tannins, naturally occurring complex polyphenols, has been facilitated by recent developments in modern analytical and spectroscopic techniques. Among numerous tannins characterized during the last two decades, those classified as oligomeric ellagitannins have attracted widespread attention as to their diverse structures and biological activities including antioxidative, antitumor and antiviral effects. We describe herein the molecular structures of representative oligomeric hydrolyzable tannins and general methods for their extraction, separation, and structural elucidation based on MS, NMR and CD spectra. Biological activities specific to each oligomer structure are also summarized.