Flavonoids: Structure and Occurrence

Study Notes

Over 9000 different flavonoids occur naturally, with a basic nucleus of 15 carbon atoms in a C6-C3-C6 structural core.
Biosynthesized from shikimate (C6-C3) and acetate (C6) biosynthetic pathways.

Found in all plant organs, including flowers, leaves, stems, and roots, mostly as glycosides in vacuoles.
Abundant in foods and beverages of plant origin, such as fruits, vegetables, tea, cocoa, and wine.
Occur as aglycones, glycosides, and methylated derivatives.
Soluble in water and organic solvents, with glycosides being readily soluble in water, methanol, and ethanol.

Contribute to flower and fruit colors and aroma, attracting pollinators and aiding in fruit dispersion, growth, and development.
Protect plants from biotic and abiotic stressors, functioning as antimicrobial compounds, detoxifying agents, and signal molecules.
Combat oxidative stress by absorbing solar wavelengths, inhibiting ROS generation, and quenching ROS.
Act as growth regulators, regulating auxin and influencing plant morphoanatomical features.

Used as antioxidants, suppressing ROS formation, scavenging ROS, and upregulating antioxidant defenses.
Used as antimicrobial agents, effective against a wide array of microorganisms.
Used as anti-inflammatory agents, inhibiting enzymes and proinflammatory mediators.
Used as hepatoprotective agents, with reported activities against catechin, apigenin, quercetin, naringenin, and rutin.
Influence food quality and stability, acting as flavorings, colorants, and antioxidants.

Indispensable component in nutraceutical, pharmaceutical, medicinal, and cosmetic applications due to antioxidative, anti-inflammatory, anti-mutagenic, and anti-carcinogenic properties.

Major classes include flavones, flavonols, flavanones, isoflavanones, anthocyanins, and chalcones.
Differ in the level of oxidation and pattern of substitution of the C ring, while individual compounds within a class differ in the pattern of substitution of the A and B rings.
Flavonoids are often hydroxylated in positions 3, 5, 7, 2, 3′, 4′, and 5′.