Flavonoids Overview and Classification

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Questions and Answers

What is the primary structural backbone of flavonoids?

C6-C3-C6 skeleton (correct)

C6-C2-C6 skeleton

C6-C4-C6 skeleton

C7-C3-C7 skeleton

Which of the following statements is true regarding the glycosides of flavonoids?

They are usually water-soluble. (correct)

They can only be extracted using non-miscible solvents.

They are soluble in polar organic solvents.

They are typically lipophilic compounds.

Which of the following compounds lacks a central pyrone ring?

Isoflavones

Flavones

Chalcones (correct)

Flavonols

What technique is commonly used for the separation and purification of different flavonoids?

HPLC (High-Performance Liquid Chromatography) Signup and view all the answers

Which of the following extraction methods is suitable for lipophilic flavonoids?

Extraction with dichloromethane Signup and view all the answers

Which of the following flavonoid classifications is based on the oxidation level of the central pyran ring?

Anthocyanidins Signup and view all the answers

What is the typical color associated with most flavonoids due to their name?

Yellow Signup and view all the answers

Which compound is an oxidized form of flavonoids with a five-membered pyrone ring?

Aurone Signup and view all the answers

What occurs to flavonoids when they are treated with acid after dissolving in alkali?

They turn colorless. Signup and view all the answers

Which property is primarily associated with flavonoids and referred to as 'venoactivity'?

Ability to decrease capillary permeability. Signup and view all the answers

Which of the following solvents is preferred for extracting flavonoids from an aqueous solution?

Ethyl acetate Signup and view all the answers

What is the expected product of hydrolysis from diosmin?

Rhamnose, glucose, and diosmetin Signup and view all the answers

Which flavonoid glycoside is known to decrease capillary fragility?

Rutin Signup and view all the answers

What action do flavonoids have concerning free radicals?

They scavenge free radicals formed during various processes. Signup and view all the answers

Which of the following is a characteristic of flavonoidal glycosides?

Soluble in water and alcohol Signup and view all the answers

Which of the following is a diuretic action exerted by quercetin?

Promotion of diuresis Signup and view all the answers

What is the primary structural skeleton of flavonoids?

C6-C3-C6 Signup and view all the answers

Which statement accurately describes the solubility of glycosides?

They are soluble in water and alcohols. Signup and view all the answers

What type of extractions are typically used to isolate glycosides from plant materials?

Acetone or alcohol mixtures at high temperatures. Signup and view all the answers

Chalcones differ from traditional flavonoids in that they lack which structural component?

A central pyrone ring. Signup and view all the answers

Which of the following best describes the classification of flavonoids?

Based on the oxidation level of the central pyran ring. Signup and view all the answers

Which component is commonly found in the extraction process of lipophilic flavonoids?

Dichloromethane. Signup and view all the answers

What is the typical extraction sequence after evaporating a solvent under vacuum from glycoside extraction?

Perform liquid-liquid extraction with non-miscible solvents. Signup and view all the answers

Which of the following is an oxidized form of flavonoids resulting in a five-membered pyrone ring?

Aurones. Signup and view all the answers

What is the role of flavonoids in relation to free radicals?

They scavenge free radicals formed under conditions such as inflammation. Signup and view all the answers

Which flavonoid glycoside can yield rhamnose, glucose, and diosmetin upon hydrolysis?

Diosmin Signup and view all the answers

What effect do flavonoids have on capillary permeability?

They decrease capillary permeability and fragility. Signup and view all the answers

Which of the following statements about flavonoids is incorrect?

Flavonoids only become colorless when treated with alkali. Signup and view all the answers

Which flavonoid glycoside is referred to as a 3-rhamnoglucoside of quercetin?

Rutin Signup and view all the answers

What is the interaction of flavonoids with dehydroascorbic acid generally thought to involve?

Reduction involving glutathione as a carrier. Signup and view all the answers

Which of the following is a property of flavonoidal glycosides?

They are soluble in both water and alcohol. Signup and view all the answers

What is known about quercetrin upon acid hydrolysis?

It yields rhamnose and quercetin. Signup and view all the answers

What type of flavonoid glycosides are most commonly found in nature?

O-glycosides Signup and view all the answers

Which solvent is more likely to dissolve aglycones with a free phenolic group in alkaline solutions?

Water Signup and view all the answers

What distinguishes chalcones from traditional flavonoids?

They lack a central pyrone ring. Signup and view all the answers

Which flavonoid classification does NOT arise from the oxidation of the central pyran ring?

Chalcones Signup and view all the answers

Which component is crucial for the extraction of lipophilic flavonoids?

Dichloromethane Signup and view all the answers

Which of the following statements about flavonoid glycosides is correct?

They are generally water-soluble. Signup and view all the answers

Which term is used to describe the basic structural unit of flavonoids?

C6-C3-C6 skeleton Signup and view all the answers

What process is involved in the extraction of glycosides after solvent evaporation under vacuum?

Liquid-liquid extractions using non-miscible solvents Signup and view all the answers

What happens to flavonoids when a strong alkali is introduced?

They dissolve and give an intense yellow color. Signup and view all the answers

Which of the following substances is commonly studied for its antioxidant properties?

Flavonoids Signup and view all the answers

Which of the following describes the effect of flavonoids on capillary permeability?

They decrease capillary permeability. Signup and view all the answers

Which of the following is NOT a characteristic of flavonoidal glycosides?

They lack fluorescence under UV light. Signup and view all the answers

What product is formed when the flavonoid glycoside rutin is hydrolyzed?

Rhamnose and quercetin Signup and view all the answers

When studying the biological properties of flavonoids, which property is most recognized?

Venoactivity Signup and view all the answers

Which compound is an example of a flavonol glycoside?

Rutin Signup and view all the answers

What is the main biochemical effect of free radicals concerning cellular health?

Causing cellular damage and mutation. Signup and view all the answers

Study Notes

Flavonoids

The largest class of naturally occurring plant products
Polyphenolic compounds, often occurring as glycosides
Most are O-glycosides but a considerable number of flavonoid C-glycosides are known
Usually yellow-coloured compounds (flavus is Latin for yellow)
Found in fruits, vegetables, grains, bark, roots, stems, flowers, tea and wine
Have a basic C6-C3-C6 skeleton derived from the 2-phenyl-benzopyran (flavan) nucleus

Flavonoid Classification

Classified by the oxidation level of the central pyran ring:
- Flavones
- Flavonols
- Isoflavones
- Flavanones
- Anthocyanidins

Flavonoid Properties

Glycosides: Generally water-soluble and soluble in alcohols
Aglycones: Soluble in polar organic solvents and alkaline solutions when they have at least one free phenolic group
Lipophilic flavonoids: Extracted with medium polarity solvents (e.g., dichloromethane)
Glycosides: Often extracted at high temperatures using acetone or alcohol (ethanol, methanol) mixed with water

Flavonoid Purification

Separation and purification often achieved by chromatography techniques, such as HPLC

Flavonoid Variations

Chalcones: Lack a central pyrone ring, so they are not true flavonoid compounds
Aurones: Oxidized forms obtained by enzymatic processes, with a five-membered pyrone ring

Flavonoid Properties and Characteristics

Dissolved in alkali, they give an intense yellow colour solution, which becomes colourless upon adding acid
Exhibit strong fluorescence under UV light
Flavonoidal glycosides are soluble in water and alcohol
Ethyl acetate is the solvent of choice for extracting flavonoids from aqueous solutions
Characterized through UV spectra analysis

Biological Properties of Flavonoids

Venoactivity: Decrease capillary permeability and fragility
Vitamin P: Referred to as a "vitamin" due to its role in reducing capillary fragility, often more active in conjunction with vitamin C

Flavonoids and Free Radicals

Scavenging Action: Act as free radical scavengers, protecting against damage caused by:
- Anoxia
- Inflammation
- Lipidic autoxidation
Cellular Protection: Prevent damage to nucleic acids, mutations, carcinogenesis, and membrane phospholipids

Flavonoid Glycoside Examples

Flavone glycoside:
- Diosmin:
  - Found in Barosma crenulata (Rutaceae)
  - Has diuretic, diaphoretic, and anti-Helicobacter pylori activity
  - Upon hydrolysis, yields rhamnose, glucose, and diosmetin
Flavonol glycoside:
- Rutin:
  - 3-rhamnoglucoside (rutinose) of the genin quercetin
  - Decreases capillary fragility
  - Hydrolysis yields quercetin, glucose, and rhamnose
- Quercetrin:
  - Quercetin 3-O-rhamnoside
  - Hydrolysis yields rhamnose and quercetin
  - Quercetin (the aglycone) has diuretic properties
Flavanones:
- Hesperidin: A common flavanone

Flavonoid Glycosides

Flavonoids are a large class of naturally occurring plant compounds, often found as glycosides (sugar attached).
Most are O-glycosides, but C-glycosides exist.
Flavonoids are typically yellow (Latin: "flavus" means yellow).
Found in fruits, vegetables, grains, bark, roots, stems, flowers, tea, and wine.
Known for health benefits before their active compounds were isolated.
All flavonoids share a basic C6-C3-C6 skeleton structure, deriving from 2-phenyl-benzopyran (flavan).
Classified based on the oxidation level of the central pyran ring:
Flavonoid Classification
- Flavones
- Flavonols
- Isoflavones
- Flavanones
- Anthocyanidins

Flavonoid Properties and Extraction

Glycosides are generally water-soluble and soluble in alcohols.
Aglycones are usually soluble in polar organic solvents and alkaline solutions if they have free phenolic groups.
Lipophilic flavonoids are extracted with medium-polarity solvents (e.g., dichloromethane) and then separated from waxes and fats.
Glycosides are extracted at high temperatures using acetone or alcohol (ethanol, methanol) mixed with water.
Solvent evaporation under vacuum removes the solvent, leaving an aqueous phase.
Liquid-liquid extractions with non-miscible solvents (e.g., ethyl acetate) separate glycosides from the aqueous phase.
Chromatography techniques (e.g., HPLC) are used to separate and purify flavonoids.

Variations in Flavonoid Structure

Some flavonoids have a 5-membered heterocyclic ring (aurones) instead of the usual 6-membered pyrone ring.
Chalcones, which lack a central pyrone ring, are not considered true flavonoids.
Aurones are formed by enzymatic oxidation of flavonoids.

Properties of Flavonoids

Flavonoids dissolve in alkali, forming intense yellow solutions that turn colorless upon acid addition.
They exhibit strong fluorescence under UV light.
Flavonoid glycosides are soluble in water and alcohol.
Ethyl acetate is preferred for extracting flavonoids from aqueous solutions.
Their UV spectra are useful for characterization.

Biological Properties of Flavonoids

Known for their "venoactivity," reducing capillary permeability and fragility.
Referred to as "vitamin P" for their capillary-strengthening property.
Vitamin P is more effective when combined with vitamin C.
Flavonoids act as antioxidants and free radical scavengers.
They protect against damage caused by free radicals generated under various conditions:
- Anoxia
- Inflammation
- Lipid peroxidation
- Free radicals contribute to nucleic acid damage, mutations, and carcinogenesis by reacting with membrane phospholipids.
Research investigates flavonoids as potential preventative agents due to their antioxidant properties.

Flavonoid Glycoside Examples

Flavone Glycoside

Diosmin:
- Found in Barosma crenulata (Rutaceae family).
- Has diuretic, diaphoretic (inducing sweating) and anti-Helicobacter pylori activity.
- Hydrolysis produces rhamnose, glucose, and diosmetin.

Flavonol Glycoside

Rutin and quercetin:
- Rutin: 3-rhamnoglucoside (rutinose) of quercetin.
  - Hydrolysis yields quercetin, glucose, and rhamnose.
  - Used to reduce capillary fragility.
- Quercetin: A flavonol with diuretic action.
- Quercetrin: Quercetin 3-O-rhamnoside.
  - Hydrolysis yields rhamnose and quercetin.

Flavanones

Hesperidin:
- An example of a flavanone.

Flavonoids

The largest class of naturally occurring plant compounds.
Polyphenolic compounds - meaning they contain multiple phenol groups.
Can exist in both free and glycosidic forms.
Most are O-glycosides but C-glycosides are also known.
Named for their typically yellow color (flavus is Latin for yellow).
Found in fruits, vegetables, grains, bark, roots, stems, flowers, tea, and wine.
Beneficial health effects were known long before their isolation and identification.
Derived from a common parent nucleus: 2-phenyl-benzopyran (flavan) with the C6-C3-C6 skeleton.

Flavonoid Classification

Based on central pyran ring oxidation level:
- Flavones
- Flavonols
- Isoflavones
- Flavanones
- Anthocyanidins

Flavonoid Properties & Extraction

General Solubility:
- Glycosides: water-soluble and soluble in alcohols.
- Aglycones: soluble in polar organic solvents and alkaline solutions (if they have a free phenolic group).
Extraction:
- Lipophilic flavonoids: extracted with medium polarity solvents like dichloromethane.
- Glycosides: extracted with acetone or alcohol-water mixtures, often at high temperatures.
Further Purification:
- Solvent evaporation under vacuum.
- Liquid-liquid extractions with non-miscible solvents like ethyl acetate.

Chromatographic Techniques

Separation and purification of flavonoids relies on chromatographic techniques like HPLC.

Aurones & Chalcones

Aurones: 5-membered heterocyclic ring replaces the pyrone ring.
Chalcones: Open-chain isomeric forms of flavonoids without the central pyrone ring, not considered true flavonoids.
Formation:
- Aurones are formed by enzymatic oxidation of flavonoids.

Key Flavonoid Properties

Dissolves in alkali, giving an intense yellow solution that becomes colorless upon acid addition.
Strong fluorescence under UV light.
Glycosides are water-soluble and alcohol-soluble.
Ethyl acetate is the preferred solvent for extraction from aqueous solutions.
Characterization by UV spectroscopy.

Biological Properties

Venoactivity: Decreases capillary permeability and fragility.
"Vitamin P": Refers to this venotonic property.
Synergistic activity with Vitamin C.
Antioxidant Activity: Scavenge free radicals generated under various conditions like:
- Anoxia (lack of oxygen)
- Inflammation
- Lipid autoxidation (oxidation of fats).
Potential to prevent/treat:
- Nucleic acid alterations
- Mutations
- Carcinogenesis
- Cellular damage (by protecting membrane phospholipids).

Flavonoid Glycosides Examples

Flavone Glycosides

Diosmin:
- Found in Barosma crenulata (Rutaceae family).
- Diuretic, diaphoretic, and anti-Helicobacter pylori activity.
- Hydrolyzes to rhamnose, glucose, and diosmetin.

Flavonol Glycosides

Rutin:
- 3-rhamnoglucoside (rutinose) of the genin quercetin.
- Hydrolyzes into quercetin, glucose, and rhamnose.
- Decreases capillary fragility.
Quercetin:
- Diuretic action.

Flavanones

Hesperidin:
- A common flavanone.

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Description

Explore the fascinating world of flavonoids, the largest class of naturally occurring plant products characterized by their yellow color and diverse structures. This quiz covers their classification based on the oxidation level of the central pyran ring and delves into their properties, including glycosides and aglycones. Test your knowledge on these crucial compounds found in various edible plants and beverages!