Flavonoids: Flavones, Flavonols, Anthocyanins, and Related Compounds
Flavonoids
At least 4000 flavonoids are known; they are common in all higher plants
the glycosides accumulate in the vacuoles of higher plants
flavonoids are often pigments in higher plants
there are 14 major classes which are usually determined by the oxidation patterns of the C-ring
only 8 flavonoid aglycones are widely distributed and common
over 60% of all plants sampled had quercetin, kaempferol, or myricetin
but they are often components of glycosides, e.g., rutin
acetate, p-hydroxycoumarate, malonate, and other esters also occur
Biosynthesis
most major biosynthetic enzymes now isolated and studied
the gene sequences responsible for many have been determined
cell cultures and cell-free extracts - phytoalexins - were of major importance for doing this
Flavones/flavonols
there are 5 common flavones and flavonols: apigenin, luteolin, quercetin, kaempferol, and myricetin
biosynthesis
methylation/glycosylation requires specific methyltransferase or glycosyltransferase enzymes
methylated compounds generally are more biologically active than non-methylated compounds; aglycones are generally more active than glycosides
Chalcones
chalcone synthase. This enzyme is analogous to stilbene synthase
chalcones go to aurones in some plants
they are converted to flavanones either spontaneously or enzymatically. These compounds co-exist in many plants
Flavanones
about 320 are known;
most are (2S)-configuration
Flavones
about 650 known. They are formed by oxidation of flavanones.
the enzymes of parsley have been studied extensively; induction of flavone biosynthesis can be induced by fungal attack
Dihydroflavonols
Flavonols
Flavonols can be derived in two different ways. Which pathway is used depends on the plant.
Secondary changes in substitution patterns occur after the compounds are formed.
Glycosides and methylated compounds common
Flavonol sulfates are common, but usually not accumulated in quantity
C-Glycosylflavones
Attempts to hydrolyze these compounds cause C-6 and C-8 isomerization.
Anthocyanins
flavanones ----> dihydroflavonols ----> flavan-3,4-diols ----> anthocyanins
proanthocyanidins related
Systematic studies
hybrids
Biological activity
sunscreens
human diet
plant/insect interactions
flavones and flavonols can inhibit IAA oxidase and the electron transport chain in phytosynthesis and respiration
flavonoids are involved as chemical signals in nitrogen fixation
luteolin
Anthocyanins
biological activity
260 known
factors responsible for color
co-pigmentation
Biflavonoids
sweet-bitter flavonones
Common Flavones, Flavonols, and Anthocyanidins
Chalcone-Flavanone Isormerization
Biosynthesis of major flavonoid types
Flavone and Flavonol Biosynthesis
3-Hydroxyflavans, 4-hydroxyflavans, and 3,4-Dihydroxyflavans
Biflavonoid biosynthesis - the radical precursors
Biflavonoid biosynthesis - structural types
Flavanones and dihydrochalcones
Bioactive dihydroflavonols and dihydrochalcones
Bioactive flavonoids - Miscellaneous types 1
Bioactive flavonoids - Miscellaneous types 2
Flavan-3-ols and Flavan-3,4-diols
Anthocyanidin and Proanthocyanidin Biosynthesis
Cyanidin-3-p-coumaroylsophoroside-5-glucoside
Catechins and Catechin Derivatives
© David S. Seigler, Integrative Biology 425, Plant Secondary Metabolism, Department
of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana,
Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.
