flavonol

Flavonol is a class of flavonoids, a group of polyphenolic compounds found in many plants. They share a 3-hydroxyflavone backbone with a carbonyl group at position 4 and an unsaturated bond between positions 2 and 3, forming the C6-C3-C6 flavonoid skeleton. Flavonols occur as aglycones and predominantly as glycosides in nature.

Common flavonols and sources: The most abundant dietary flavonols are quercetin, kaempferol, and myricetin. Other members include fisetin, galangin, and morin. They are widely distributed in fruits, vegetables, tea, and wine. Typical food sources include onions, apples, berries, grapes, citrus, broccoli, and leafy greens. In plants these compounds commonly exist as glycosides such as rutin (quercetin-3-O-rutinoside) and other conjugates.

Biosynthesis and chemical features: Flavonols are produced via the plant phenylpropanoid pathway, with enzymes that convert dihydroflavonols to flavonols (flavonol synthase). This pathway yields aglycones that are often glycosylated, affecting solubility, stability, and bioavailability. The presence of the 3-hydroxyl group and the 4-oxo function contributes to their UV absorption and redox properties.

Biological activity and relevance: Flavonols exhibit antioxidant activity through radical scavenging and metal chelation. They can modulate inflammatory processes and enzymes, and may influence cell signaling and apoptosis. Epidemiological and experimental data suggest potential cardiovascular and anticancer benefits, but clinical evidence is variable. Bioavailability is influenced by glycoside forms, digestion, and rapid metabolism to glucuronides, sulfates, and methylated metabolites.