Condensed vegetable tannins: Biodiversity in structure and biological activities

Proanthocyanidins, as an important class of secondary plant metabolites, ar e in many cases the active principles of the medicinal plants from which th ey are isolated. The structural complexity and conformational properties of the lower molecular weight oligomers have been investigated thoroughly, wh ile the chemistry of the polymers still remains a difficult topic. Shikimat e-derived phenolics like flavonoids and tannins are widely distributed in p lant kingdom and are thus not of interest as classificatory tool; oxidation levels however are indicative in the attribution of evolutionary status am ong phyla and within each phylum. The main biological and pharmacological e ffects reported for condensed tannins can be classified into antibacterial and antiviral activities, enzyme inhibition, anti-oxidative effects, antimu tagenic and antitumoral properties, next to some more specific interactions e.g. with vascular and cardial systems and inflammation processes. Their a nticipated interaction with biological systems originates in principle dire ctly from the physical and chemical properties of the polyphenolic skeleton , although prominent individual differences have been observed. (C) 1999 El sevier Science Ltd. All rights reserved.