Induction of Apoptosis and Anti-HIV Activity by Tannin- and Lignin-Related Substances

Tannins and lignins are two major classes of polyphenolic compounds widely distributed in the plant kingdom. Tannins are largely classified into hydrolyzable and condensed tannins.1 Hydrolyzable tannins have structures in which a polyalcohol (mainly glucose) is esterified with polyphenolic carboxylic acids, such as galloyl, hexahydroxydiphenoyl (HHDP) (a dimer of the galloyl group), valoneoyl (a trimer of the galloyl group), or dehydrohexahydroxydiphenoyl groups (an oxidized metabolite of the HHDP group). Condensed tannins are composed of flavan units, mostly (+)-catechin, (−)-epieatechin, or their analogues, condensed with each other via carbon-carbon bonds.