Quercetin: Structure, Properties, and Therapeutic Potential

Quercetin is a naturally occurring flavonoid, specifically a flavonol, widely distributed in fruits, vegetables, leaves, seeds, and grains. It is chemically identified as 3,3',4',5,7-pentahydroxyflavone, with a molecular formula of C15H10O7 and a molar mass of 302.24 g/mol. Its structure features a 15-carbon skeleton with two benzene rings (A and B) connected by a three-carbon bridge forming a heterocyclic ring (C). This unique structure underpins quercetin’s biological activity and robust antioxidant properties.

Quercetin’s physical characteristics include its yellow crystalline form, a melting point of approximately 316°C, and practical insolubility in water, although it dissolves in organic solvents and aqueous alkaline solutions. It is highly abundant in foods such as capers, red onions, kale, apples, and berries like cranberries and blueberries. Quercetin’s content in these foods varies depending on factors such as cultivation conditions, storage, and processing methods.

In plants, quercetin is synthesized via the phenylpropanoid pathway, beginning with the amino acid phenylalanine. Phenylalanine is converted into 4-coumaroyl-CoA, which undergoes a series of enzymatic reactions involving chalcone synthase and flavonol synthase to produce quercetin. This pathway not only highlights the complexity of plant metabolism but also underscores quercetin’s role in plant defense mechanisms, such as UV protection and pathogen resistance.

Quercetin’s antioxidant properties stem from its ability to scavenge free radicals, chelate metal ions, and inhibit lipid peroxidation, thus mitigating oxidative stress. These properties are pivotal in reducing the risk of chronic diseases like cardiovascular diseases, diabetes, neurodegenerative disorders, and certain types of cancer. Recent studies have also suggested quercetin’s potential role in modulating the immune response and reducing inflammation, making it a subject of interest in combating viral infections, including SARS-CoV-2. Preliminary research indicates that quercetin may inhibit viral entry and replication, though more clinical studies are required to substantiate these findings.

Quercetin’s bioavailability, however, is relatively low due to poor absorption, rapid metabolism, and systemic elimination. To address this, various strategies, such as using quercetin glycosides or nanoformulations, are being explored to enhance its effectiveness as a dietary supplement and therapeutic agent.
Quercetin: Structure, Properties, and Therapeutic Potential

Quercetin: A polyphenolic flavonoid compound

Quercetin (3, 5, 7, 3′, 4′- pentahydroxyflavone) is classified as a flavonol which is one of the five subclasses and major dietary flavonoids distributed in both cultivated and wild plants.

Quercetin is a polyphenolic flavonoid compound derived food compounds and is present in various mangos.

Quercetin generally exists in edible plants and is among the most efficient antioxidants of the flavonoids. These compounds have pivotal role in treatment of diabetes, cancers and some cardiovascular diseases.

The antioxidant activity of quercetin is mainly manifested through its effect on glutathione (GSH), enzymatic activity, signal transduction pathways, and reactive oxygen species (ROS) caused by environmental and toxicological factors.

Quercetin is a yellow, crystalline solid with a bitter taste, which is insoluble in water, slightly soluble in alcohol, and soluble in glacial acetic acid and aqueous alkaline solutions.

Quercetin is a member of a group of naturally occurring compounds, the flavonoids, which have a common flavone nucleus composed of two benzene rings linked through a heterocyclic pyrone ring.

A hydroxyl group in third carbon, a double bond between second and third carbon, a carbonyl group in fourth carbon and polyhydroxylated A and B aromatic rings have main role in antioxidant proprieties of these compounds.

Quercetin is found in various food products and plants, including fruits, seeds, vegetables, tea, coffee, bracken fern, and natural dyes. Quercetin is usually obtained from the hydrolysis of rutin (quercetin-3- rutinoside), a naturally occurring flavonoid glycoside although it can also be synthesized.
Quercetin: A polyphenolic flavonoid compound

Quercetin in mango

Mangos are very healthy treat. A strong source of beta-carotene quercetin, and astragalin, they help neutralize free radicals that can damage cells. 

Quercetin-3-galctoside, quercetin-3-glucosode and quercetin-3-arabinose have been detected in mangos. 

Quercetin has gained the attention of the supplement industry and is now widely promoted as a natural anti-inflammatory and antioxidant magic bullet.

In human body quercetin helps to keep bones from dissolving away. Quercetin inhibits osteoclasts form taken away calcium from bones, which was causing the formation pits in the bones.

Quercetin also can reduce the risk of atherosclerosis.

It is a flavonoid well-known to inhibit growth and heat shock protein synthesis of cancer cells. The heat shock reduced the cell viability of the quercetin-treated cells only.

Quercetin reduces inflammation by inhibiting the production of cytokines such as interleukin-6, interleukin-8 and tumor necrosis factor through the inhibition of the promoter nuclear factor-kB.
Quercetin in mango