Methylated flavonoids

Schroder, G. et al., Flavonoid methylation a novel 4 -0-methyltransferase from Catharanthus roseus, and evidence that partially methylated flavanones are substrates of four different flavonoid dioxygenases. Phytochemistry, 65, 1085, 2003. 

Masayuki, S., D. DiFeo JR., N. Nakatani, B. Timmermann, and T. J. Mabry Flavonoid Methyl Ethers on the External Leaf Surface of Larrea tridentata and L. divaricata. Phytochemistry 15, 727 (1976). 

The 5-OH signal of prenylated flavonols (3-hydroxyflavones) is observed between 5 11.9 and 12.6 in acetone-ds when the 3-hydroxyl group is free (276). The substituent parameters of flavonols are listed in Table 8. It should be noted that the 5-OH signal of flavonols is sometimes shifted due to chelation with metals. When a flavonol fluoresces under irradiation with UV light, the sample needs further purification. The shift upon prenylation at C-6 or C-8 of flavonols (parameters i and ii) is almost identical with that of the other flavonoids. Methylation of 3-OH causes a downfield shift of 0.64-0.67 ppm. However, the 5-OH signal of 3-0-methylflavonols appears still further upfield (about 0.2 ppm) than that of flavones having the same A and B rings. 

Phlomis consists of about 100 species, a dozen of which occur in Mediterranean Europe (Mabberley, 1997, p. 549). The study of interest here involves a study of the flavonoids of R lychnitys L., a small plant native to Mediterranean Spain (Tomas et ah, 1986). Those workers identified the common flavones apigenin, luteolin, and luteolin 3 -methyl ether (chrysoeriol) 7-0-glucosides and their respective /7-coumaroyl derivatives. A brief review of the literature revealed that Mediterranean species of Phlomis are characterized by the presence of the flavone methyl ether, whereas continental species appear to lack 0-methylated flavones. Species from India have been reported to lack flavones but accumulate flavonols. The suggestion was made that accumulation of flavonols represents an ancestral feature of the genus. 

Returning to the chemotaxonomic aspect of the stndy, however, it is interesting to note that recent work by Bakker et al. (1998) on rfccL and atpB sequences of Bieber-steinia place the genus close to Rutaceae. This position is fully supported by the flavonoids reported by Greenham et al. (2001), which are very similar to 0-methylated flavones known from well-studied members of Rutaceae, such as Citrus. 

Additional information on chemical variation within this species came from studies of exudate and internal (vacuolar) pigments based on broader collections of the fern (Star et al., 1975a, b). Exudate flavonoids, identified from specimens representing the range of the species, were identified as ceroptene [221], the C-methylflavonol pityrogrammin [222], and two derivatives of kaempferol, the 4 -methyl ether [223] and the 7,4 -dimethyl ether [224] (see Fig. 2.69 for stmctures 221-224). 

In addition to the bitter acids and essential oils, the flowers of hops offer a rich array of polyphenolic compounds, primarily chalcones and their accompanying flavanones, many of which are prenylated derivatives (Stevens et al., 1997,1999a, b). The most prominent flavonoid in all plants studied was xanthohumol [342] (3 -prenyl-6 -0-methylchalconaringenin chalconaringenin is 2, 4, 6, 4-tetrahydroxychalcone) (see Fig. 4.11 for structures 342-346). Several additional chalcones—variously adorned with 0-methyl and/or C-prenyl functions—were also encountered, along with their respective flavanones. Three new compounds were described in the Stevens et al. 

Haberlein, H. and Tschiersch, K.-P. 1998. On the occurrence of methylated and methoxylated flavonoids in Leptospermum scoparium. Biochem. Syst. Ecol. 26 97-103. 

Tea flavonoids, or tea extracts, are increasingly being added to foods. However, interactions with food and drink components remain unclear, and thus need to be carefully assessed in order that the full potential benefits from consuming tea, in whatever form, can be achieved. Meanwhile, tea catechins themselves undergo extensive O-methylation, glucuronidation, sulphation and ring fission... 

PEDRIELLI p, PEDULLi G F and SKIBSTED L H (2001a) Antioxidant mechanism of flavonoids. Solvent effect on rate constant for chain-braining reaction of quercetin and epicatechin in autoxidation of methyl linoleate, JAgric Food Chem, 49, 3034-40. 

ROGINSKY v A, BARSUKOVA T K, REMOROVA A A and BORS w (1996) Moderate antioxidative efficiencies of flavonoids during peroxidation of methyl linoleate in homogeneous and micellar solutions, J Am Oil Chem, Ti, 777-86. 

The shikimate pathway is the major route in the biosynthesis of ubiquinone, menaquinone, phyloquinone, plastoquinone, and various colored naphthoquinones. The early steps of this process are common with the steps involved in the biosynthesis of phenols, flavonoids, and aromatic amino acids. Shikimic acid is formed in several steps from precursors of carbohydrate metabolism. The key intermediate in quinone biosynthesis via the shikimate pathway is the chorismate. In the case of ubiquinones, the chorismate is converted to para-hydoxybenzoate and then, depending on the organism, the process continues with prenylation, decarboxylation, three hydroxy-lations, and three methylation steps. - ... 

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