Stilbene structural skeleton

The essential structural skeleton of stilbene comprises two aromatic rings joined by a methylene bridge. Since the double bond doesn t allow free... 

Phenolics and their functional derivatives are widely found throughout the plant kingdom. One defining characteristic of these compounds is that their aromatic ring usually contains at least one hydroxyl substituent. In a broad sense, phenolics, which are classified according to their structural skeleton, are basically derivatives from simple phenols and phenolic acids, phenylpropanoids including coumarins and lignans, flavonoids and related compounds, and stilbenes. Some of these compounds which show anti-inflammatory activity are reviewed in this section. 

The stilbene-dihydrophenanthrene photocycllsatlon reaction continues to find synthetic applications. The tetra-oxygenated methyl phenanthrene skeleton (161) has been prepared by photocyclisation of the stilbene (162) aromatisation of the intermediate dihydrophenanthrene occurs by elimination of methanol. 2 nq photocyclisation was observed In the absence of the cyano group in this compound 2 although the closely related structures (163) and (164) are said to cyclise to the phenanthrenes (165) and (166). Triarylethylenes are important... 

Besides compounds 110 and 111, two new compounds (119, 120) representing a novel carbon skeleton having a new stilbene-coumarin nucleus, were isolated from the root bark of Ekebergia benguelensis. The structure of 119 was elucidated by 2D spectral methods and confirmed by single X-ray analysis [65]. 

The optical inactive stilbenolignan, maackoline (791) [344], has the same planar structure as cararosin A (790) [345], but the latter is optically active [a]D-3.71°. Lehmbachol D (792) isolated from Salacia lehmbachii, has the same planar structure but the stereochemistry has not been established [269]. Other stilbenolignans include compounds 117, 118, 124 and 125. As they all possess a stilbene skeleton, so they are all classified into the group E of stilbenes. 

Replacement of the phenyl group by a thiophene unit results in structure 50. These chromophores exhibit less TPA amplitude compared to the similar structures of 49. 6 of 50 decreases to about half that for comparable compounds 49, as shown by the data in Table 3.5. Thus, incorporation of thiophene in the 7r-bridge results in less efficient chromophores compared to corresponding compounds bearing stilbene in the main molecular skeleton. These findings agree well with the results disclosed for 45. 

Comparison of the structures of the 2-arylbenzofuran and stilbene derivatives suggests that the latter compounds are biogenetic precursors of the former. The skeletons of the 2-arylbenzofuran and stilbene derivatives could formally be regarded as a 1,2-diphenylethane biogeneti-cally the skeleton would be derived from cinnamoylpolyketide produced from cinnamic acid and acetate (70). 

With a basic skeleton of Q, there are simple phenols and benzoquinones with C -Ci structure, there are hydroxyben-zoic acids such as gallic acid corresponds to pheny-lacetic acids and with C -C skeleton there is a larger class including hydroxycinnamic acids, coumarines, and chro-mones. Sometimes these strucmres appear dupUcated, giving rise to lignoids. Naphthoquinones have a C6-C4 stmcmre, while xanthones exhibit a Ce-Ci-Cg one. Stilbenes and anthraquinones are Cg-Ca-Ce compounds. 

Nonflavonoid compounds comprise simple phenols, phenolic acids, coumarins, xanthones, stilbenes, lignins, and lignans. Phenolic acids are further divided into benzoic acid derivatives, based on a C6-C1 skeleton and cinnamic acid derivatives, which are based on a C6-C3 skeleton [6], The conmarins are phenolic acid derivatives composed of a benzene ring fnsed with an oxygen heterocycle. Xanthones consist of a C6-C1-C6 basic structure, and stilbenes are composed of a C6-C2-C6 skeleton with various hydroxylation patterns [13], Lignins are polymers of C6-C3 units, whereas lignans are made up of two phenylpropane units [13]. The structures of each of these classes are shown in Table 16.1. 

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