- Studies of the selective O-alkylation and dealkylation of flavonoids. XXII. A convenient method for synthesizing 3,5,7-trihydroxy-6-methoxyflavones
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The demethylation of 3,4-dioxygenated 6-methoxy-2- isopropoxyacetophenones was studied and it was found that 4-benzyloxy-6- hydroxy-3-methoxy-2-isopropoxyacetophenone was easily obtained from 4- benzyloxy-3,6-dimethoxy-2-isopropoxyacetophenone by selective demethylation with anhydrous aluminum bromide-sodium iodide in acetonitrile. The acetophenone was converted into 7-benzyloxy-3-hydroxy-6-methoxy-5- isopropoxyflavones by cyclization followed by oxidation with dimethyldioxirane. The isopropoxy group in the flavones was selectively cleaved with anhydrous aluminum chloride via the corresponding tosylates to give 7-benzyloxy-3,5-dihydroxy-6-methoxyflavones, which were converted into the desired 3,5,7-trihydroxy-6-methoxyflavones by hydrogenolysis. The process was suitable as a general method for synthesizing 3,5,7-trihydroxy-6- methoxyflavones and five flavones were synthesized. We also examined the 13C-NMR spectra of twelve kinds of 3,5,6,7-tetraoxygenated 4'- methoxyflavones and revised the proposed structure of a natural flavone.
- Horie, Tokunaru,Shibata, Kenichi,Yamashita, Kazuyo,Kawamura, Yasuhiko,Tsukayama, Masao
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p. 446 - 451
(2007/10/03)
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- Potential antitumor agents from Lantana camara: Structures of flavonoid-, and phenylpropanoid glycosides
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Besides the known glycosides, verbascoside and a flavone glycoside, a novel flavonol glycoside named camaraside and a new phenylpropanoid glycoside, lantanaside have been isolated from the leaves of Lantana camara and defined as 3,5-dihydroxy-4',6-dimethoxyflavonol-7-O-glucopyranoside and 3,4-dihydroxy-β-phenylethyl-O-α-L-rhamnopyranosyl (1 → 3)-4-O-cis-caffeoyl-β-D-glucopyranoside respectively by spectroscopic methods and chemical transformations.
- Mahato,Sahu,Roy,Sharma
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p. 9439 - 9446
(2007/10/02)
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