Structural Variation of the Flavonoids of Asteraceae
We concern ourselves in this chapter with a moderately detailed view of the flavonoid chemistry of Asteraceae. Attention will be given to the individual flavonoid types that have been reported, flavones, flavonols, flavanones, chalcones, and the like, and
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Structural Variation of the Flavonoids of Asteraceae
We concern ourselves in this chapter with a moderately detailed view of the flavonoid chemistry of Asteraceae. Attention will be given to the individual flavonoid types that have been reported, flavones, flavonols, flavanones, chalcones, and the like, and to the diversity of substitution patterns that underlie the richness of the family's pigment profile. Adding to this richness are the various types of derivatives of each of the main structural types: O-methyl ethers, C-alkyl groups, both 0- and C-linked glycosides, acylated forms of the glycosides, sulphates, etc. Combinations of these features add further to the variety of structures known. Owing to the shear mass of data available much of the information will be presented in tabulated form whenever practicable. The order of presentation will be as follows: Flavones, flavonols, and flavonoid oxygenation patterns Flavanones Dihydroflavonols Chalcones, dihydrochalcones, and aurones Isoflavones Anthocyanins Glycosides and acylated glycosides Sulphates Flavans and C-ring hydroxyflavans Flavonolignans Biflavonoids The nomenclature used in the preceding outline, and in the rest of this book, should be familiar to anyone acquainted with the chemosystematic or phytochemical literature. It is not, however, the formal nomenclature used by Chemical Abstracts, and if one needs to search for a specific compound they should be aware that looking for "apigenin 7-0-glucoside" may not yield a very fruitful harvest. A general entry under the key word "flavone" would likely exist, but one would have to look at all entries under that lead
B. Bohm et al., Flavonoids of the Sunflower Family (Asteraceae) © Springer-Verlag Wien 2001
Structural Variation of the Flavonoids of Asteraceae
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in order to locate specific references to apigenin 7-0-glucoside. A more direct approach exists. A brief note on the formal conventions used by Chemical Abstracts will be useful for anyone not familiar with the official chemical rules of nomenclature. Chalcones are named as derivatives of 2-propen-l-one. Chalcone [4-1] itself would be properly known, as 1,3-diphenyl-2-propen-l-one, while isoliquiritigenin, more familiarly known as 2',4',4-trihydroxychalcone, becomes 1-(2, 4-dih ydroxyphenyl-3-( 4-hydroxypheny 1)-2-propen-I-one. Note that the phenyl group attached to the number-I, or carbonyl carbon, is the A-ring (biosynthetically speaking). Dihydrochalcones are based on 1,3diphenylpropan-l-one, with substituents located as with chalcones. By convention, the A-ring is written on the left and the carbonyl group at C-4 is written on the lower side. Aurones are found in Chemical Abstracts by looking under the general entry 3(2H)-benzofuranone. Aurone [4-2] itself would be 2-phenylmethylene3(2H)-benzofuranone. Sulfuretin, commonly referred to as 6,3',4'-trihydroxyaurone, would be found under 2-(3,4-dihydroxyphenyl)methylene-6-hydroxy3(2H)benzofuranone. The reader should be aware that at times aurones have also been referred to as benzalcoumarano
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