Ellagitannins: Chemistry, biochemistry and applications

Abstract

Ellagitannins are complex polyphenols typically produced during heartwood formation in hardwood species such as chestnut, eucalyptus and oak. These compounds are characterized by bi-aryl-coupled gallic acid moieties esterified to a D-glucose core. In the case of the oaks, heartwood concentrations of ellagitannins can reach 10%, and these compounds are thought to be biosynthesized as a natural preservative to protect the inner core of a tree from pathogen attack. The mechanism for durability is theorized to be via inactivation of pathogen degratory enzymes and/or pathogen metal ion deprivation. Considering the importance of heartwood/ellagitannin formation in the growth and maturation of woody plants, the biogenesis and chemical reactivity of ellagitannins remain obscure. We have initiated a series of investigations into: 1, the relationship of ellagitannins to cell wall polymers; 2, the biochemical pathway associated with ellagitannin formation; 3, the chemical and enzymatic reactivity of ellagitannins; 4, and the potential use of ellagitannins as pharmaceutical products. These issues are being investigated via studies with woody tissue isolates as well as tissue cultures of White oak (Quercus alba) and American chestnut (Castanea dentata).