Stilbenoids structure

As indicated above, acidic and alkaline treatments of lignin may, under appropriate conditions, lead to the formation of stilbenoid structures. The amount of such groups in kraft Bjorkman lignin has been estimated by UV spectroscopy (Falkehag 1961, Falkehag et al. 1966). Specifically, the procedure... 

The carexanes (794-796) with a tetracyclic skeleton have been isolated from the leaves of Carex distachya. They seem to be derived from the coupling of the prenyl moiety with a stilbenoid structure. A plausible biogenetic pathway for the formation of carexanes has been proposed (Scheme 5) [346],... 

Hernandez-Romero Y Rojas J-I, Castillo R, Rojas A, MataR, Spasmolytic effects, mode of action, and structure-activity relationships of stilbenoids from Nidema boothii, J Nat Prod 67 160—167, 2004. 

The most comprehensive studies on shape-persistent Hekates have been performed on stilbenoid star-shaped molecules. Structures and mesomorphic properties are collected in Table 1. Core building blocks with only one repeating unit per arm and one flexible chain 26a,b, 28a-d, 30a did not show any liquid crystal properties [56-58]. In the series of two chain derivatives 28e, 30b,c the formation of meso-phases depend on the core [57-59]. The electron deficient triazine and the dicyanopyridine building block induced obviously columnar mesophases. The pyridine derivative 30b showed only a crystalline phase [58]. In the series of nine chain stars 26c-g [60-62] and 28f-n [57], the compounds formed columnar phases depending on the chain length of the peripheral chains. Propyloxy chains are too short but hexyloxy and dodecyloxy chains are sufficient for the formation of liquid crystal phases by nanosegregation [60-62]. This can be rationalised by a dense... 

Structurally, dendrimers of type 5 are best compared with rigid dendrimers made up of tolan building blocks. However, neither the form of aggregation observed in stilbenoid dendrimers, nor the phase behaviour or the photochemistry of these compounds have so far been found to occur in similar form in tolan systems. 

Invention Significance Stilbenoid tubulin-binding agents structurally... 

Stilbenoids are derived from cinnamic acid and three acetate units from mal-onyl coenzym A. The first part of the biosynthesis is in common to flavonoids. The two biosynthetic routes are diverging at the point of cyclization of a styryl-3,5,7-triketoheptanoic acid. A C-acylation produces a chalcone and subsequent modifications lead to the flavonoids. An aldol condensation of the same intermediate polyketide produces a stilbene-2-carboxylic acid that is unstable and constitutes a range of structures known as stilbenoids. Figure 9C.5 shows an overview of the biosynthetic pathway (Gorham 1995). 

In addition, stilbenes are fluorescent compounds which are easily detected by flu-orometry. For resveratrol, fluorescence detection is highly selective and even twice as sensitive as UV detection (Stecher et al. 2001). Due to this potential, methods by using HPLC coupled with absorbance and fluorescence detection were developed (Jeandet et al. 1997 Vitrac et al. 2002). Otherwise identification of stilbenes in wine by HPLC-DAD can be limited by coelution of two or more compounds. Therefore application of modern mass-spectrometry techniques is important to confirm the structure of stilbenes and to detect novel compounds in wine (Monagas et al. 2005b Buiarelli et al. 2007 Careri et al. 2004 Jean-Denis et al. 2006 Kammerer et al. 2004 Mark et al. 2005 Piissa et al. 2006 Stecher et al. 2001). Table 9C. 1 shows an overview on stilbenoid molecular ions and fragments identified in wine and grapevine by mass spectrometry. 

This model of an onion internal structure of the columns was supported by molecular dynamics on the homolithic stilbenoid system (Fig. 48, X = Y = r1 = r2 = OC12H25, = H). It showed good segregation at the molecular... 

Stilbenoid-like dendrimers possessing an analogous molecular structure were reported by Meier to be mesomorphic too [273]. The five generations of stilbene-based dendrimers (Fig. 57) [274,275] and the first two gener-... 

Fig. 57 Chemical structures of the stilbenoid-like dendrimers (R = OC3H7, OCgH, ...

The work on stilbenoids was reviewed by Gorham in 1995 [4]. Herein, we review the recent progress in the studies of stilbenoids with respect to their structure, distribution, extraction and isolation, technologies used in structure identification, synthesis and biosynthesis, and the last but not the least, bioactivities. The coverage of the new structures is from 1994 (especially those that have not been covered by Gorham [4]) to June 2006 (the references in 2006 may not be collected thoroughly as some of them might have not been included in the databases yet). 

In the past 12 years, about 800 novel Stilbenoids have been isolated and identified. According to their structural characteristics, they are classified into six types, namely, stilbenes, bibenzyls, bisbibenzyls, phenanthrenoids, stilbene oligomers and other stilbenoids. 

Apart from the structures mentioned above, there are other stilbenoids with some unique structural characteristics so they can not be easily classified into the above five types. We describe these stilbenoids in Table 19 and Fig. (47)-Fig. (49). These stilbenoids usually are hybrids of stilbenes conjugated with flavanoids or lignans, or are oligostilbene-related derivatives. 

It is the development of separation and identification techniques that makes the isolation and elucidation of the stilbenoids applicable. Silica gel is still the most commonly used material of the stationary phase. However, many other materials possessing better resolution or different isolation mechanisms have also been widely applied, e.g. Sephadex LH-20 [299 etc.], ODS Cis [208,299 etc.], MCI gel CHP20P, Toyopearl HW-40F [20,27,114,242,354], especially the former two. The combination use of the materials is efficient for the separation of the structures with high similarity and high polarity such as stilbene glucoside sulfates (34—43) [27]. 

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