For flavone

With the establishment of clear-cut flavone races, the next obvious question was how the pattern became established. One possibility discussed by Mastenbroek (1983) involved selection for flavone profiles in response to some environmental factor or factors, climatological or edaphic being the most obvious ones. Alternatively, the present-day distribution pattern may be the result of historical factors (1) migration involving long- or intermediate-distance dispersal (2) range extension... 

Lee, M.S. et ak. Rapid screening of fermentation broths for flavones using tandem mass spectrometry, Biol. Mass Spectrom., 22, 84, 1993. 

A comprehensive and critical review of food flavonoid literature has led to the development of a food composition database for flavonols, flavones, procyanidins, catechins, and flava-nones. This database can now be used and continuously updated to estimate flavonoid intake of populations, to identify dietary sources of flavonoids, and to assess associations between flavonoid intake and disease. However, there is a need for better food composition data for flavones, procyanidins, and flavanones as current literature is sparse particularly for citrus fruits, fruit juices, and herbs. In addition, anthocyanin food composition data are lacking although validated methods of determination are becoming available. 

Electron densities and bond orders for pyran-2-one, pyran-4-one and eight benzologues or dibenzologues have been calculated using the simple Hiickel, the Hiickel autocoherent and the semi-empirical Pople methods (74BSF538). Similar properties have been obtained for flavone and the electronic absorption spectra of some substituted flavones have been examined in detail (74CHE1218). Excitation is accompanied by a transfer of charge from the... 

Based on three-bond carbon-hydrogen coupling constants, specific selective proton decoupling experiments and investigations of specifically deuterated compounds, the resonances of C-6 and C-8 in 5,7-dihydroxyflavonoids appear in the range of 90 to 100 ppm and C-8 is always more shielded compared to C-6. The chemical shift differences found are small for flavanones ( 1 ppm) and larger for flavones and flavonols ( 5 ppm). 

The 13C chemical shifts of the carbonyl resonances of 5,7-dihydroxyflavonoids are characteristic of the different types of flavonoid compounds For flavones and iso-flavones the C-4 resonance generally appears around 181 ppm, for dihydroflavones around 196 ppm and for flavonols around 176 ppm. 

Set detector at 280 nm for catechins (flavan-3-ols), naringin, and benzoic acid derivatives 320 nm for chlorogenic acid, resveratrol, and hydroxycinnamic acids 370 nm for flavones and flavonols and 520 nm for anthocyanins and anthocyanidins (see Table 11.3.1). 

For flavones in citrus peel oils, separations were accomplished with isocratic mobile phases of 38% and 40% acetonitrile in H20 (1). The extracts of peel and cold-pressed peel oils were diluted in ethanol and analyzed by reversed-phase on various C18 columns with good results. For the dilute citrus oils, gradient elution was preferred, to prevent the accumulation of terpenes on the column. With normal-phase chromatography, the elution order is reversed terpenes elute with the solvent front and are not a problem. 

A retrosynthetic analysis for flavone (118) reveals o-benzoyloxyacetophe-none (122), readily formed by the benzoylation of o-hydroxyacetophenone. 

Whilst on-line desorption chemical ionisation mass spectrometry (MS) has been used to analyse fermentation biosuspensions for flavones [11], the majority of MS applications during fermentations have been for the analysis of gases and volatiles produced over the reactor [12-15], or by employing a membrane inlet probe for volatile compounds dissolved in the biosuspensions [16-22]. It is obvious that more worthwhile information would be gained by measuring the non-volatile components of fermentation biosuspensions, particularly when the product itself is non-volatile, which is usually the case. 

The most frequently used solvent for flavones is hexadeuterodi-methylsulfoxide (DMSO- 56) and tetradeuteromethanol (CD3OD). For lypophilic flavone aglycones, solvents such as carbontetrachloride (CCI4) are recommended. 

Figure 15.1 Basic structures of the six main classes of flavonoids. Ring nomenclature for all classes is indicated for flavonone. Caibon numbering and C-ring bonds for all classes except chalcones is indicated for flavone and flavonol, respectively.

Song, G.-Y., Ahn, B.-Z. Synthesis of dibenzoylmethanes as intermediates for flavone synthesis by a modified Baker-Venkataraman rearrangement. Arch. Pharm. Res. 1994, 17, 434 37. 

As for flavones, or isoflavones, mentioned previously, the prefix iso- signifies a similarity or, more exactly, the same chemical composition but a different structure, with different physical and chemical properties. According to a letter and litraature search presented by Sally Fallon and Mary G. Enig in the July 2004 Townsend Letter for Doctors Patients, cited elsewhere, the soy isoflavone genistein has been found to act as an inhibitor for tyrosine kinase. However, it has also been found to damage the DNA and to have adverse estrogen-like effects. Apparently, there is a trade-off. 

However, the relatively simpler two-step s3mthesis for FLAVONE shall be discussed in the sections that follow ... 

Fig. 8. LC/UV chromatogram of G. ottonis with UV spectra and main FSP/LC-MS ions of the major constituents. HPLC Column, RP-18 NovaPak (4 im, 150 x 3.9 mm i.d.) gradient, CH3CN-H2O (0.05% TFA) 5 95 ->65 35 in 50 min (1.0 ml/min). UV spectra of 14 and 16 were characteristic for flavones, while those of 15 and 17-19 were indicative of xanthones and those of 5 of a secoiridoid glycoside.

However, the flavanone naringenin (10) [but not dihydro-kaempferol (13)] is the substrate for flavone formation in snapdragons. Antirrhinum majus (Scrophulariaceae) (flavone synthase II) (Fig. 11.10). In this plant, flavones arise from dehydrogenation of flavanones and not from dehydration of dihydroflavonols (Britsch et al., 1981). A similar enzyme system converts dihydroflavonols to flavonols (Britsch et al., 1981). In other work, the enzyme responsible for oxidation of flavanones to flavones in snapdragon Antirrhinum majus) was isolated from a microsomal fraction and shown to require NADPH and molecular oxygen (Britsch et al., 1981 Dewick, 1989 Forkmann and Stotz, 1981). The system appears to be a cytochrome P-450-dependent monooxygenase. This system also is known from Glycine max... 

The TLC systems presented for flavone and flavonol aglycones (Table 2) reveal different separation mechanisms. Thus, a combination of various systems gives valuable information during the analysis of these pigments. 

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