Aglycone flavonoids

Several complexes of [Bu2Sn(IV)] with flavonoid glycosides 3-[6-0-(6-deoxy-a-L-mannopyranosyl)-(jS-D-glucopyranosyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-H-l-benzopyran-4-one (rutin) and 2, 4, 3-trihydroxy-5, 4-dimetoxychalcone 4-rutinoside (hesperidin) and flavonoid aglycones (quercetin, morin, hesperitin, and other flavones) (Figure 5) were prepared. 

This example involves a smdy of free flavonoids (aglycones) present on the leaf surface of Mentha suaveolens Ehrh. (Lamiaceae) growing in Spain and in Algeria... 

Table 4.8 Percentage flavonoid aglycone occurrence in species of Rhododendron sect. Vireya (from Harborne, 1986)...

Table 7.1 Flavonoid aglycones from leaf surfaces of Larrea tridentata and L. divaricata (from Mabry et al., 1977)...

Zaidi, F., Voirin, B., Jay, M. and Viricel, M. R. 1998. Free flavonoid aglycones from leaves of Mentha pulegium and Mentha suavolens (Labiatae) Phytochemistry 48 991-994. 

VOIRIN, B., BAYET, C., Developmental variations in leaf flavonoid aglycones of Mentha x piperita, Phytochemistry, 1992, 31,2299-2304. 

Flavonoid aglycones (isolated by acid hydrolysis of the corresponding flavonoid glycosides)... 

Fig. 2.41. Flavonoid aglycones identified in flowerheads of Arnica angustifolia. Reprinted with permission from T. J. Schmidt et al. [119].

There have been many survey studies of citrus flavonoids, yet by no means has an exhaustive analysis been performed for all species and cultivars. Surveys often are initiated by hydrolysis of tissue extracts and identification of the flavonoid aglycones present in the tissues. This provides a basis for subsequent identification of the glycosylated compounds present... 

Kinetics of Glucosylation. The detailed kinetic analysis of the partially purified enzyme (44) was consistent with an ordered bi bi mechanism, where UDP-glucose binds to the enzyme first, followed by the flavonoid aglycone... 

A convenient and frequently used procedure is sequential solvent extraction. A first step, with dichloromethane, for example, will extract flavonoid aglycones and less polar material. A subsequent step with an alcohol will extract flavonoid glycosides and polar constituents. 

Normal phases (unmodified silica gel) are rarely employed, except for the occasional separation of weakly polar flavonoid aglycones, polymethoxylated flavones, flavanones, or isoflavones. The polymethoxylated flavones present in citrus fruits can, for example, be separated on silica gel columns. The big drawback is that solvent gradients cannot normally be run with normal phases. 

Schmidt, T.J., Merfort, I., and Matthiesen, U., Resolution of complex mixtures of flavonoid aglycones by analysis of gas chromatographic-mass spectrometric data, J. Chromatogr., 634, 350, 1993. 

The first conventional mode of MS involves El ionization, in which the neutral flavonoid is impacted in the gas phase with an electron beam of 70 to 100 eV. Resulting mass spectra of the flavonoid aglycones are characterized by molecular ion peaks (M ), and fragment ions from both the A and B rings. The use of a reactant gas in the ionization chamber. Cl, normally results in the production of a more abundant molecular ion and simpler fragmentation patterns. General information about mass spectra of flavonoids recorded by these methods has been published by several authors. More specific mass spectra analyses... 

The application of MS in structural elucidations of flavonoids has increased dramatically with recent developments related to soft ionization techniques, mass analyzers, and coupled MS techniques (see Sections 2.3.1 and 2.3.2). Based on relatively small flavonoid quantities, reports have provided the molecular mass in addition to structural information about the flavonoid aglycone attachment points of glycosidic res-... 

A considerable amount of information has been accumulated during the review period with respect to fragmentation studies of flavonoid aglycones and their glycosides using ionization techniques such as El and CID (Figure 2.17). Tandem mass spectrometry with soft ionization methods such as FAB, ESI, and APCI have been used for the structural characterization of a variety of flavonoids, and both deprotonation ° ° and... 

Lugasi, A. and Hovari, J., Flavonoid aglycons in foods of plant origin I. Vegetables, Acta Alimen., 29, 345, 2000. 

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