Flavonoids and Dihydrochalcones

Chart 37. Flavonoid and dihydrochalcones found in the Hepaticae Ara arabinoside, GA glucuronide, GalA galacturonide, Glc glucoside, Gly glycoside, Hex hexoside, P pentoside, Rha rhamnoside, Xyl xyloside 

In Chart 37 and Table I, structures of the flavonoids from Hepaticae and their distribution are listed. Representative flavonoids of the Hepaticae are apigenin and luteolin glycosides. Flavanones and flavonols are very rare. The most primitive liverworts, Takakia species, contain the same 

Variabilin (775), a unique dihydrochalcone with a dihydrooxepin skeleton has been isolated as its methyl ether from Radula variabilis. The structure assignment was based on spectroscopic correlation with the methylated bibenzyls prepared from the co-metabolites, (614) and (616) (61), A 3, 5 -Di-C-glycosylated dihydrochalcone (776) has also been detected in Hymenophyton species (203), 

More recently, the flavonoid pattern found in the Hepaticae and the Musci has been discussed by Zinsmeister and Mues (348), Chromatographic characteristics of the flavonoids detected in the Hepaticae and a chemosystematic study of the Marchantiales by use of flavonoids have been reported in a recent review (199), 

Structure Number Name of Compound m.p.°C Plant Source Order References Comments  

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Table If. Aromatic Compounds (Flavonoids and Dihydrochalcones) Found in the Hepaticae...

S. Kazuno, M. Yanagida, N. Shindo and K. Murayama, Mass spectrometric identification and quantification of glycosyl flavonoids, including dihydrochalcones with neutral loss scan mode, Anal. Biochem., 347, 182 192 (2005). 

Chalcones Chalcones and dihydrochalcones can be considered as flavonoids with an open structure (see Fig. 5.1). Although dihydrochalcones such as phloretin glycosides and 3-hydroxyphloretin glycosides have been found in many fruits and vegetables (Tsao and others 2003 Arabbi and others 2004), the occurrence in general is rare (Tomas-Barberan and Clifford 2000). Prenylated chalcones such as xanthohumol are found in hops (Zhao and others 2005) (see Fig. 5.2). 

In three of the volumes of The Flavonoids, Advances in Research, published between 1975 and 1993, flavanones and dihydroflavonols were part of the chapter on Minor Flavonoids, expertly written by Professor Bruce Bohm. These Minor Flavonoid chapters also included chalcones, dihydrochalcones, and aurones. The term Minor Flavonoids was first used by Harborne in 1967 to encompass not only flavanones, chalcones, and aurones, but also isoflavonoids, biflavonyls, and leucoanthocyanidins, because so few compounds belonging to each of these flavonoid classes were known at that time. For example, only about 30 flavanone and dihydroflavonol aglycones, 19 chalcones, and 7 aurones were known in 1967. The number of known minor flavonoids increased considerably in the next two decades, so that when the checklist for The Flavonoids, Advances in Research Since 1980 was published in 1988, 429 known flavanones and dihydroflavonols (including glycosides) were listed, 268 chalcones and dihydrochalcones, and 29 aurones. In the last 15 years, the total number of known compounds in these flavonoid classes has more than doubled, so that the term minor flavonoids is no longer appropriate. Consequently, it has been decided that separate chapters should be devoted to the flavanones and dihydroflavonols (this chapter), and chalcones, dihydrochalcones, and aurones (Chapter 16). 

The farinose exudate of the frond of the fern Pityrogramma calomelanos (Adiantaceae) has been the source of complex flavonoids characterized by a novel Ce-Cs-Ce-Cs-Ce skeleton (Table 15.7). This group includes four flavanones, calomelanols G (238), H (239), I (240), and J (241) (Figure 15.10). In these compounds, a molecule of p-coumaric or cinnamic acid appears to be fused with the A-ring of the flavanone. Biosynthetic pathways for these complex flavanones and related flavones, chalcones, and dihydrochalcones in P. calomelanos and other Pityrogramma species have been proposed by the authors. 

It has also been found to contain antibacterial flavonoids which are responsible for the beer preserving activity. One of these, myrigalone B (MyB), is assigned to a rare class of flavonoids, C-methylated dihydrochalcones. As far as is known no further work has been done to identify the potential of these flavonoids and their antibacterial properties. 

Fig. (14). Two flavonoids and a novel dunmeric dihydrochalcone from Iryanthera sagoliana.

HPLC is the method of choice for the separation of complex mixtures containing non-volatile compounds such as various flavonoids in extracts prepared from different samples. A survey of literatures revealed that most researchers have used Cjg-reversed stationary phases, which proved to be superior to the normal phase technique. The reversed phases are suitable for separating flavonoids in a wide range of polarities, as Vande Casteele et al. have demonstrated the separation of 141 flavonoids from polar triglycosides to relatively non-polar polymetoxy-lated aglycones belonging to the classes of flavones, flavonols, flavanones, dihydroflavonols, chalcones, and dihydrochalcones. 

The only other types of flavonoid substances which have to be considered are benzalcoumaranones (aurones, c/., Bate-Smith and Geissman, 1951), e.g., sulphuretin (XIII, R = H) and aureusidin (XIII, R = OB), chalcones, e.g., butein (XIV), and dihydrochalcones, e.g., phloretin (XV). The relationships between these types are admirably illustrated by Geissman and Hinreiner (1952). Table II is a somewhat modified... 

Bohm A B 1975 Chalcones, aurones and dihydrochalcones. In Harborne J B, Mabry T J, Mabry H (eds) The flavonoids. Chapman and Hall London, 466-492... 

Figure 6. Kumquats are rich in flavonoids (flavanones and dihydrochalcones), carotenoids (beta carotene) and phenolic acids (cinnamic acids). These dietary polyphenols actually exhibit a dual effect through indirect neuroprotection against oxidative stress and indirect protection through suppression of gha-mediated inflammation.

The chalcones, dihydrochalcones, and aurones are three distinctive classes of compound that comprise more than 900 of all the naturally occurring flavonoids reported in the literature to... 

Chalcones are unsaturated and, along with dihydrochalcones, contain an open pyronic cycle and a carbon skeleton numbered in a way different from other flavonoids, Fig. (8, 9). Native chalcone glycosides tend to transform into flavanone glycosides during extraction procedures. Chalcones per se are therefore of restricted occurence in foods [35]. 

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