Polymethylated flavonoids

The polymethylated flavonoids 5-hydroxy-3,6,7,8,4 -pentamethoxyflavone (353), 5-hydroxy-3,6,7,8,-tetramethoxyflavone (354), and 5,6-dihydroxy-3,7-dimethoxyflavone (355) and a chalcone, 4,4, 6 -trihydroxy-2 -methoxychalcone 356, have all been isolated from cudweed, Gnaphalium affine Compositae).153 Although the flavonoids were present in small amount in the plant, they all exhibit high antifeedant activity against the common cutworm (S. litura) with ED50 values of 1.1 x 10-7 mol cm-2 for 353, 2.0 x 10-8 mol cm-2 for 354, and 2.5 x 10 8 mol cm-2 for 355. The chalcone 356 was present in higher amounts, but had less activity (3.8 x 10 7 mol cm-2).153... 

Losses of small nentrals snch as HjO and CO are observed in the negative-ion mode as well. Again, the loss of CHj can be observed from methoxylated flavonoids, as was stndied in detail by Justesen [22-23], [M-H] of monomethyl-flavonoids show the loss of CHj and subseqnent losses of CO or HCO, while polymethyl-flavonoids show losses of CHj and snbseqnent losses of CHj, or CHj and CO. It is not clear whether the loss of two CH3 radicals was checked by accurate-mass determination. Alternatively, the loss of 30 Da conld be explained by the loss of H2C=0, which is frequently observed in the fragmentation of polymethoxylated compounds. Isomeric methoxylated flavonoids showed different fragmentation behaviour, but standards were still needed for determination of the methoxy-position. The product-ion MS-MS spectra of rhanmetin and isorhamnetin are shown in Figure 15.3. No loss of the prenyl substitnent is observed for prenyl flavonoids in negative-ion mode [14],... 

Polymethylated Flavonoids Cancer Preventive and Therapeutic Potentials Derived from Antiinflammatory and Drug Metabolism—Modifying... 

Chapters 8-11 are devoted to consideration of two main classes of phytochemicals Chapter 8 centers on organosulfur compounds from the Allium genus, and their role in cancer prevention, while subsequent chapters are devoted to polyphenols and their wide-ranging effects against cancers, cataracts, and cardiovascular disease. Chapter 9 examines the cancer-protective and therapeutic potential of polymethylated flavonoids such as occur in citras, while Chapter 10 summarizes recent cancer chemopievention research in an area particularly relevant to the British and Chinese backgrounds of the editors, notably tea. A much less well-studied area, that of cataracts and their prevention by dietary flavonoids, is presented in Chapter 11. 

The antimicrobial polymethylated flavones, 5-hydroxy-3,6,7,8,4 -pentamethoxyflavone, 5-hydroxy-3,6,7,8-tetramethoxyflavone and 5,6-dihydroxy-3,7-dimethoxyflavone, have been isolated from Gnaphalium affine D Don. [229,230], These flavonoids showed antimicrobial activity against Spodoptera litura. Structure-activity studies suggested the importance of the 6-position substitution of the flavonoid however, hydrophilic substituents decreased the activity. The flavonoid 8-0-(2-methyl-2-butenoyl)-5,7-dihydroxy-3-methoxyflavone isolated from Gnaphalium robustum L. also inhibited the growth of Escherichia coli [231]. 

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