Oligomeric stilbenes

Other methods have also been successfully employed in the isolation procedure of stilbenoids, including MPLC [209,299,326], preparative TLC [208,277,299], centrifugal partition chromatography (CPC) [359,360] and the support-free technique of multilayer coil countercurrent chromatography (MLCCC) [32]. A method based on capillary electrophoresis with electrochemical detection (CE-ED) was employed for the determination of oligomeric stilbenes found in the roots of Caragana species [361]. 

Wine, phenoHc constHuents of. Besides the volatile constituents of wine flavor, alcohols, tartaric acid and tartrates, especially red wines contain phenolic constituents stilbenes, e.g. resveratrol, the vitisins, tannins and other polyphenols like ellagic acid and the viniferins, and other oligomeric stilbenes, e.g. e-viniferin. Mainly to these phenolic compounds, the anti-atherosclerotic and infarction-prophylactic activity is attributed, explaining the so-called French Para-... 

Resveratrol 1 is the most famous representative of this group and occurs in Polygonum cuspidatum root and Vitis species. It is a phytotoxin produced by several plants in response to infection or other stresses and attracted attention for its cardioprotective effect in red wine. In addition, it is the most important unit for the construction of oligomeric stilbenes. 

Liu HX, Lin WH, Yang IS (2004) Oligomeric stilbenes from the root of Caragana stenophylla. Chem Pharm Bull 52 1339-1341... 

Due to its mildness and efficiency the Heck reaction has been explored for polymerization chemistry. For example, oligomeric stilbenes, such as 87 were successfully prepared and studied in the context of photochemically induced reactions. ... 

Stilbenes can also occur in oligomeric and polymeric forms, so-called viniferins. They are induced by oxidative polymerization of the monomer resveratrol through the activity of a peroxidase (Jean-Denis et al. 2006). Figure 9C.7 shows the biosynthesis of trans-s-mmfcxm. 

Studies have demonstrated that 1 plays a vital defensive role in plants. It has been shown that 1 possesses modest in vitro antimicrobial properties [2,7]. In addition, several oligomeric metabolites of 1 are known to exhibit greater antimicrobial activity [8]. Further evidence for the important defensive role of 1 in plants comes from studies in which transgenic barley, wheat, and tobacco plants containing a stilbene synthase gene exhibit enhanced resistance to fungal infection [9,10],... 

In some plant species, the production of stilbene monomers and oligomers has been shown to be associated with a variety of stress factors [2,112,120,121,122,123,124]. The stilbene 1 is one of the most commonly encountered of these stress metabolites. While 1 has been shown to exhibit rather modest antimicrobial properties, some of its oligomeric derivatives have demonstrated more potent phytoalexin activity [2,8,125,126]. 

Some interesting plant phenolics of stilbene and 2-phenylbenzofuran types have been identified as phytoalexins of the mulberry tree (Moms alba) (19, 107, 112, 113). Of particular interest are the oligomeric compounds chalcomoracin (10) and dimoracin (12), which may be considered to be Diels-Alder adducts of morachal-cone (11) and dehydromoracin (9). However, the adducts are optically active, unlike some other natural products that are proposed to be Diels-Alder adducts. 

The many stilbenic compounds found in various parts of grapevine are derived from fran -resveratrol (3,5,4 -trihydroxystilbene) and occur as glucosylated derivatives or oligomeric forms of this compound called viniferins (Figure 4.8). The most common among the latter is the dimer s-viniferin [111] however, some trimers (a-viniferin) [112] and tetramers have also been isolated and characterized [113]. 

In 1996, Yamamoto and coworkers reported that organolithium (t-BuLi, n-BuLi, PhLi)-initiated oligomerization of hydrocinnamaldehyde tran -l-amino-2,3-diphenylaziridine hydrazone 22 afforded oligo(phenylpropylidene) with M = 1,500 2,500 in 43 --67% yield [78], The polymerization proceeded as shown in Scheme 59, where the nucleophilic attack of a carbanion to C = N bond in 22 followed by elimination of N2 and stilbene generated a secondary carbanion as a propagating chain end. 

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