Flavone: Properties, Biochemistry & Research Applications

Flavone is the parent aromatic compound of the flavonoid family, defined by a 2-phenylchromen-4-one skeleton, and serves as an indispensable reference scaffold in plant biochemistry, pharmacological research, and the synthesis of bioactive natural-product analogues.

IUPAC Name

2-phenylchromen-4-one

Molecular Formula

C₁₅H₁₀O₂

Molecular Weight

222.24 g/mol

CAS Number

525-82-6

Appearance

White to pale yellow crystalline powder

Solubility

Sparingly soluble in water; soluble in DMSO, ethanol, and acetone

Biological Role

Parent scaffold of flavonoid natural products; antioxidant, anti-inflammatory reference compound

Chemical Structure and Physicochemical Properties

Flavone (CAS 525-82-6) is the simplest and most structurally fundamental member of the flavonoid class. Its core is the 2-phenylchromen-4-one (2-phenyl-4H-1-benzopyran-4-one) skeleton, comprising two fused aromatic rings (A and B rings) connected through a central γ-pyrone ring (C ring). The planar, fully conjugated structure confers strong UV absorption, typically around 250 nm and 300–350 nm, which is exploited analytically for detection and quantification by HPLC-UV and spectrophotometric methods.

Flavone is a white to pale yellow crystalline solid with a molecular weight of 222.24 g/mol and a melting point reported in the range of 97–100 °C. It is sparingly soluble in water but readily dissolves in polar organic solvents including dimethyl sulfoxide (DMSO), ethanol, methanol, and acetone. Stock solutions for cell-based assays are commonly prepared in DMSO at concentrations of 10–50 mM, with subsequent dilution into aqueous buffers. Researchers should note that extensive aqueous dilution may cause precipitation and recommend the use of sonication or gentle warming to aid dissolution.

The absence of hydroxyl substituents on the flavone parent structure distinguishes it from most naturally occurring flavonoids (e.g., apigenin, luteolin, quercetin), making it a chemically stable, non-polar benchmark reagent ideal for structure–activity relationship (SAR) studies where hydroxylation patterns are systematically varied.

Biosynthesis and Natural Occurrence

In plants, the flavonoid biosynthetic pathway originates from phenylalanine via the general phenylpropanoid pathway. Phenylalanine ammonia-lyase (PAL) catalyses the first committed step, converting phenylalanine to trans-cinnamic acid. Subsequent enzymatic reactions produce 4-coumaroyl-CoA, which condenses with three molecules of malonyl-CoA under the action of chalcone synthase (CHS)—the key gateway enzyme—to form naringenin chalcone. Chalcone isomerase (CHI) then cyclises this intermediate to naringenin (a flavanone). The oxidative conversion of flavanones to flavones is catalysed by flavone synthase (FNS), which exists as two distinct types: the cytosolic, 2-oxoglutarate-dependent dioxygenase FNS I (found predominantly in Apiaceae) and the membrane-bound cytochrome P450-type FNS II (widespread across angiosperms).

Flavone itself, lacking hydroxyl or methoxy substituents on its aromatic rings, is relatively rare in nature compared with its hydroxylated congeners. Hydroxylated flavones such as apigenin (4′,5,7-trihydroxyflavone), luteolin (3′,4′,5,7-tetrahydroxyflavone), and chrysin (5,7-dihydroxyflavone) are widely distributed in fruits, vegetables, herbs, and medicinal plants. Flavone is therefore more commonly encountered as a synthetic reference standard and biosynthetic precursor analogue in laboratory settings than as an abundant dietary constituent.

The distribution of flavones across plant taxa is strongly linked to ecological functions, including UV photoprotection of foliar tissues, attraction of pollinators, defence against herbivores and pathogens, and regulation of symbiotic nitrogen fixation through interaction with Nod factor signalling in legumes.

Biological Activities and Pharmacological Research

Although flavone itself is the unsubstituted parent compound, it retains measurable intrinsic bioactivity and is extensively used as the negative or baseline control in SAR studies that probe the contributions of specific hydroxyl, methoxy, or prenyl substituents to pharmacological potency. Key biological activities attributed to or studied via the flavone scaffold include:

• Antioxidant activity: The conjugated 2-phenylchromen-4-one system contributes to radical-scavenging capacity through electron delocalisation. Hydroxylated derivatives greatly amplify this activity relative to the parent flavone, making flavone the appropriate zero-substitution reference.
• Anti-inflammatory effects: Flavone and its hydroxylated congeners have been shown to modulate NF-κB signalling and inhibit cyclooxygenase (COX) enzymes in cell-based models. These properties underpin interest in flavones as potential leads for anti-inflammatory agent development.
• Inhibition of cytochrome P450 enzymes: Flavone is a well-documented inhibitor of CYP1A1 and CYP1A2 enzymes, and is used experimentally to dissect metabolic pathways and herb–drug interactions. This interaction is relevant to researchers studying xenobiotic metabolism.
• Anxiolytic and neuroactive properties: The flavone scaffold shows affinity for GABA_A receptors, and certain substituted flavones (e.g., 6,3′-dibromoflavone) have been investigated as benzodiazepine-site ligands. Unsubstituted flavone serves as the structural comparator in such neurochemical studies.
• Anticancer research: Flavone has been employed in mechanistic studies examining cell-cycle arrest, apoptosis induction, and kinase inhibition. Its role is primarily as a scaffold for medicinal chemistry rather than as a direct clinical candidate.

Researchers should note that biological activity data for flavone vary across assay systems and cell lines. All cited activities should be independently verified within the specific experimental context.

Laboratory Handling, Storage, and Preparation Guidelines

Flavone (Aladdin SKU: F156758) is supplied as a solid. The following guidelines support reliable experimental use:

Storage: Store at room temperature (15–25 °C) in a tightly sealed container, protected from light and moisture. The compound is stable under these conditions for an extended period when handled appropriately.

Stock solution preparation: Dissolve flavone in DMSO to prepare a concentrated stock (e.g., 10–50 mM). Vortex thoroughly and sonicate if necessary to ensure complete dissolution. For ethanol-based stocks, warming to 40–50 °C with agitation aids solubility. Avoid preparing aqueous solutions directly from solid, as the low aqueous solubility leads to incomplete dissolution and variable dosing.

Working solution dilution: Dilute stock solutions into the appropriate aqueous buffer or cell culture medium immediately before use. Maintain the final DMSO concentration at ≤0.1% (v/v) in cell-based assays to avoid solvent toxicity artefacts; include a DMSO vehicle control at the same concentration.

Analytical verification: Confirm identity and purity by HPLC or TLC before use in quantitative studies. UV absorbance at ~300 nm (in ethanol) can serve as a rapid identity check.

Safety: Handle in accordance with standard laboratory safety practices. Consult the Safety Data Sheet (SDS) for full hazard information. Avoid inhalation of dust; use appropriate PPE including gloves and eye protection.

Waste disposal: Dispose of flavone-containing waste in accordance with applicable local regulations for organic chemical waste.

Applications in Research and Industry

Flavone finds application across several domains of chemical biology, pharmacology, and food science research:

1. Structure–Activity Relationship (SAR) Studies: As the unsubstituted parent compound, flavone is the essential starting reference for systematic SAR investigations across the flavonoid family. Researchers introduce defined substituents (hydroxyl, methyl, halogen, prenyl) at specific ring positions and compare resulting bioactivities against the flavone baseline.

2. Enzyme Inhibition Studies: Flavone is employed as a tool compound and positive/negative control in assays targeting cytochrome P450 isoforms (particularly CYP1A1/CYP1A2), kinases, and oxidoreductases. Its use as a CYP1A inhibitor is well-established in metabolic phenotyping workflows.

3. Biosynthetic Pathway Research: As the simplest flavone, it is used as a substrate or analogue to characterise the activity and substrate specificity of plant biosynthetic enzymes including FNS I, FNS II, and various hydroxylases and methyltransferases.

4. Analytical Standards: Flavone serves as a chromatographic reference standard for HPLC method development and validation in natural product analysis, enabling retention time calibration and detector response assessment.

5. Medicinal Chemistry: The flavone scaffold is a privileged structure in medicinal chemistry, informing the design of synthetic libraries targeting inflammation, neurological disorders, metabolic diseases, and oncology indications. Flavone itself anchors such libraries as the unmodified lead.

6. Food Science and Nutraceutical Research: Although dietary flavone intake is primarily from hydroxylated congeners, flavone is used as a reference compound in studies characterising the absorption, distribution, metabolism, and excretion (ADME) of flavonoids, as well as in food authentication and adulteration studies.

Frequently asked questions

What is the difference between flavone and other flavonoids such as quercetin or apigenin?

Flavone is the unsubstituted parent compound of the flavone subclass, carrying no hydroxyl or other substituents on its A or B rings. Apigenin is the 4′,5,7-trihydroxylated derivative of flavone, while quercetin belongs to the flavonol subclass and bears an additional 3-hydroxyl group on the C ring. These hydroxyl substituents substantially alter polarity, antioxidant capacity, protein-binding affinity, and bioavailability relative to the parent flavone.

How should I prepare a working solution of flavone for cell-based assays?

Prepare a concentrated stock solution by dissolving flavone in DMSO (e.g., 10–50 mM), vortexing and sonicating to ensure complete dissolution. Dilute the stock into cell culture medium immediately before use to the desired working concentration, keeping the final DMSO content at or below 0.1% (v/v). Always include a DMSO vehicle control at the equivalent concentration to account for any solvent effects.

Why is flavone used as a CYP1A inhibitor in metabolic studies?

Flavone is a well-characterised inhibitor of the cytochrome P450 isoforms CYP1A1 and CYP1A2, which are involved in the metabolism of numerous xenobiotics and endogenous substrates. Researchers use flavone as a pharmacological tool to selectively inhibit CYP1A activity in cell or microsomal assays, helping to attribute specific metabolic transformations to these enzyme isoforms and to study potential herb–drug interactions involving CYP1A-metabolised drugs.

Is flavone found naturally in foods, and can it be obtained from dietary sources?

The unsubstituted flavone is relatively rare as a free compound in food; most dietary exposure to flavones comes from hydroxylated derivatives such as apigenin (found in parsley, celery, and chamomile) and luteolin (found in thyme, peppers, and olive oil). Flavone itself is primarily relevant as a laboratory reference standard rather than a significant dietary component.

What analytical methods are recommended for confirming the identity and purity of flavone?

Reverse-phase HPLC with UV detection (monitoring at 254 nm or 300–310 nm) is the standard method for purity assessment of flavone. TLC on silica gel with UV visualisation provides a rapid identity check. NMR spectroscopy (¹H and ¹³C) in deuterated DMSO or CDCl₃ confirms structural identity. Mass spectrometry (ESI-MS) showing [M+H]⁺ at m/z 223 further corroborates identity.

References

1. Harborne, J.B. & Williams, C.A. (2000). Advances in flavonoid research since 1992. Phytochemistry, 55(6), 481–504. doi:10.1016/S0031-9422(00)00235-1
2. Martens, S. & Mithöfer, A. (2005). Flavones and flavone synthases. Phytochemistry, 66(20), 2399–2407. doi:10.1016/j.phytochem.2005.07.013
3. Middleton, E., Kandaswami, C. & Theoharides, T.C. (2000). The effects of plant flavonoids on mammalian cells: implications for inflammation, heart disease, and cancer. Pharmacological Reviews, 52(4), 673–751. PMID:11121511
4. Pelkonen, O. et al. (2008). Inhibition and induction of human cytochrome P450 enzymes: current status. Archives of Toxicology, 82(10), 667–715. doi:10.1007/s00204-008-0332-8
5. Kumar, S. & Pandey, A.K. (2013). Chemistry and biological activities of flavonoids: an overview. The Scientific World Journal, 2013, 162750. doi:10.1155/2013/162750

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