Stilbene derivatives piceid

Addition. Resveratrol. The biosynthetic pathway to resveratrol diverges from the flavonoid pathway after the third malonyl-CoA condensation. Cyclization of the common polyketide intermediate catalyzed by resveratrol synthase yields the stilbene derivative resveratrol, whereas the same intermediate catalyzed by chal-cone synthase yields the common flavonoid precursor chalcone (Fig. 6.8). Resveratrol, well known as a functional food ingredient (e.g., grape skin, red wine) with strong antioxidant properties (cardiovascular protection), and its 3-glucopyranoside piceid turned out to be also present in the skin of tomato fruits, S. lycopersicum (Ragab et al. 2006). 

The green grape skin is also capable of synthesizing phytoalexins in response to an infection (Langcake and Pryce, 1977). These stilbenic derivatives (trans-resveratrol and its glycoside, trans-piceid, dimer e-viniferin, a-viniferin trimer, /S-viniferin tetramer) have fungicidal properties (Figure 10.24). 

Stilbenes have a 1,2-diphenylethylene as their basic structure (C6-C2-C6). Resve-ratrol, the most widely known compound, contains three hydroxyl groups in the basic structure and is called 3,4, 5-trihydroxystilbene. In plants, piceid, the glucoside of resveratrol, is the major derivative of resveratrol. Stilbenes are present in plants as cis or trans isomers. Trans forms can be isomerized to cis forms by UV radiation (Lamuela-Raventos and others 1995). 

The difference in the chemical structure of fraws-resveratrol and cis-piceid is that the latter has a glucose at the Rj position while the former has a hydroxyl group. This implies that the presence of the hydroxyl substituent is necessary for antitumor activity of the stilbene. The difference in activity may also be due to geometric stereochemical differences between the cis and trans double bonds and/or the poor solubility of the glucoside derivative in water which inhibits the interaction of this compound with cellular components. 

The stilbenes that have been reported for several varieties from peanuts Arachis hypogaea), in leaves, roots and seeds, seem to be derived mainly from (E)-resveratrol (10-146). Examples of peanut stilbenes are (E)-piceatannol (10-146), (E)-piceid (10-147),... 

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