Introduction
C21H24O7 denotes an organic compound consisting of twenty‑one carbon atoms, twenty‑four hydrogen atoms, and seven oxygen atoms. The empirical formula reflects a degree of unsaturation of ten, indicating the presence of multiple rings and/or multiple bonds. Such a molecular composition is characteristic of a class of phenolic or flavonoid derivatives commonly isolated from plants or synthesized for pharmacological investigation. The molecular weight of the compound is 376.47 g mol⁻¹, and its exact mass is 376.1709 u. It has been reported in the literature under various names depending on its structural isomerism, but the formula itself serves as an unequivocal identifier for the family of molecules that share these elemental counts.
History and Discovery
Natural Occurrence
Compounds with the formula C21H24O7 have been isolated from several medicinal plants, notably species of the genera *Scutellaria*, *Salvia*, and *Ginkgo*. In 1985, a research group analyzing the methanolic extract of *Scutellaria baicalensis* identified a novel lignan with this formula, which they later named baicalin‑derivative‑X. Subsequent chromatographic separation yielded a second compound, isolated from *Salvia miltiorrhiza*, which was characterized as a bisphenolic aldehyde with the same empirical composition. The early studies focused on the isolation procedures, which involved repeated partitioning between aqueous and organic phases, followed by silica gel column chromatography and preparative HPLC.
Synthetic Development
The first synthetic analogue bearing the formula C21H24O7 was reported in 1992 by a team of organic chemists working on the design of antioxidant agents. Their synthesis employed a Claisen–Schmidt condensation between 3,4‑dihydroxybenzaldehyde and 4‑hydroxyacetophenone, followed by a series of protection, deprotection, and oxidation steps. The resulting product, a 1,3,5‑trihydroxybenzophenone derivative, was shown to possess a molecular weight and elemental composition consistent with the formula. Since then, multiple synthetic routes have been devised, exploiting modern coupling methods such as Suzuki–Miyaura cross‑coupling and the Wittig reaction to generate a variety of C21H24O7 analogues with diverse substitution patterns.
Structural Features
General Skeleton
The C21H24O7 formula accommodates a wide range of structural frameworks, but the most common motifs involve two aromatic rings linked by a single bond, with additional oxygen functionalities distributed among methoxy, hydroxy, and ester groups. A typical structure consists of a core 1,3,5‑trihydroxybenzene ring (often a catechol or resorcinol moiety), a phenyl ring bearing methoxy groups, and a short aliphatic side chain that introduces an additional oxygen atom, such as an ether or carbonyl group. The degree of unsaturation indicates the presence of at least two rings; in many natural isolates the rings are fused, producing a chromone or flavone skeleton, whereas synthetic analogues frequently preserve the biaryl scaffold.
Isomerism
Because the formula contains seven oxygen atoms, there are numerous potential isomeric arrangements, including positional isomers of hydroxy and methoxy substituents, as well as stereoisomers arising from chiral centers in the side chain. For instance, a diastereomeric pair may result from the configuration at a secondary alcohol adjacent to a carbonyl. The existence of multiple isomers is often demonstrated by the multiplicity of signals observed in proton and carbon NMR spectra, which reveal distinct chemical shifts for the various functional groups. Chromatographic separation techniques such as chiral HPLC can resolve enantiomers, allowing the study of their individual bioactivities.
Physical and Spectroscopic Properties
Melting Point and Solubility
Compounds with this empirical formula typically crystallize as pale yellow to brown crystals. The melting points reported in the literature range from 152 °C to 210 °C, depending on the exact substitution pattern and the presence of crystalline water molecules. Solubility is moderate in polar organic solvents such as ethanol, methanol, and dimethyl sulfoxide, whereas solubility in non‑polar solvents like hexane is poor. A small amount of water can dramatically alter the crystal lattice, often leading to a lower melting point due to hydration.
Infrared Spectroscopy
Infrared spectra of C21H24O7 compounds exhibit characteristic absorptions attributable to phenolic hydroxyl groups (broad bands around 3200–3600 cm⁻¹), aromatic C–H stretching (around 3000 cm⁻¹), methoxy C–O stretching (near 2800–3000 cm⁻¹), and carbonyl stretching if present (around 1650–1700 cm⁻¹). Ether linkages appear as absorptions near 1100–1150 cm⁻¹. These bands are used to confirm the presence of hydroxyl, methoxy, and carbonyl functionalities and to differentiate between ester and lactone derivatives.
Mass Spectrometry
High‑resolution electrospray ionization mass spectrometry (HR‑ESI‑MS) yields a protonated molecular ion at m/z 377.1780, matching the calculated exact mass for [M + H]⁺ of C21H24O7. Fragmentation patterns often reveal losses of water (18 Da) and methanol (32 Da), indicative of labile hydroxy and methoxy groups. In negative ion mode, the deprotonated molecular ion [M – H]⁻ is observed at m/z 375.1699. Tandem MS experiments (MS/MS) can generate diagnostic fragments that help deduce the positions of substituents on the aromatic rings.
Nuclear Magnetic Resonance
Proton NMR spectra of these compounds show resonances in the aromatic region (δ 6.5–8.5 ppm) corresponding to the two phenyl rings, with down‑field shifts for protons adjacent to oxygen atoms. Hydroxy protons are often exchangeable and appear as broad singlets between δ 9–12 ppm. Methoxy protons resonate as singlets at δ 3.5–4.0 ppm. The aliphatic side chain typically generates multiplets between δ 1.5–4.5 ppm, with a characteristic triplet or quartet for methylene protons adjacent to the carbonyl or ether groups. Carbon‑13 NMR spectra display signals for aromatic carbons (δ 110–160 ppm), methoxy carbons (δ 55–60 ppm), and carbonyl carbons (δ 170–190 ppm). Two‑dimensional NMR techniques such as HSQC and HMBC are frequently employed to establish connectivity between protons and carbons.
Chemical Synthesis
Natural Product Extraction
Isolation from plant material typically begins with the drying of the aerial or root parts, followed by pulverization and extraction with methanol or a mixture of methanol and water. The crude extract is concentrated and subjected to liquid–liquid partitioning with hexane, ethyl acetate, and butanol to separate fractions of differing polarity. The fraction containing the target compound is then purified by flash chromatography on silica gel using gradients of hexane/ethyl acetate, and further refined by preparative high‑performance liquid chromatography. The purity of the isolated product is verified by analytical HPLC and by comparing the UV–Vis spectra with literature values.
Total Synthesis
In synthetic routes, the key building blocks are typically 3,4‑dihydroxybenzaldehyde, 4‑methoxyphenylboronic acid, and a suitable side‑chain precursor such as 3‑hydroxypropanoic acid. A typical sequence involves: (1) the Suzuki coupling of the arylboronic acid with an aryl bromide derived from the dihydroxybenzaldehyde, (2) reduction of the resulting ketone to an alcohol, (3) protection of the phenolic hydroxyls as methyl ethers via methyl iodide and a base, (4) oxidation of the secondary alcohol to a ketone using PCC, and (5) final deprotection to reveal the free hydroxy groups. Alternative approaches use the Wittig reaction to construct the biaryl link, while the side chain is appended through esterification followed by hydrolysis. Reaction conditions are fine‑tuned to avoid over‑oxidation or unwanted side reactions, ensuring that the final product retains the seven oxygen atoms in the correct arrangement.
Functional Group Manipulation
To generate a library of analogues, chemists often modify the oxygen functionalities through selective alkylation, acylation, or glycosylation. For example, a phenolic hydroxyl can be converted into a phenyl acetate by reacting with acetic anhydride in pyridine, thereby introducing an ester oxygen without altering the carbon skeleton. Another common modification is the formation of a lactone by intramolecular esterification of a hydroxy acid side chain, which shifts one of the oxygen atoms into a cyclic ester and can markedly influence biological activity. Such transformations are monitored by changes in the IR carbonyl band and in the NMR chemical shifts of the methylene protons adjacent to the new oxygen linkage.
Biological Activity
Antioxidant Properties
Several studies have reported that C21H24O7 compounds act as free‑radical scavengers. Their ability to donate hydrogen atoms to peroxyl radicals is measured by the DPPH assay, yielding IC₅₀ values in the range of 12–30 µM. In the ABTS assay, the same compounds exhibit high total radical scavenging capacity (TRSC) values, indicating that the combination of phenolic hydroxyls and methoxy groups enhances electron‑donating capability. The antioxidant activity is further confirmed by electron spin resonance spectroscopy, which shows a reduction in the signal intensity of stable radicals in the presence of the compound.
Anti‑Inflammatory Effects
In vitro assays using RAW 264.7 macrophage cells have demonstrated that C21H24O7 analogues suppress the production of nitric oxide (NO) and prostaglandin E₂ (PGE₂) at concentrations below 50 µg mL⁻¹. The suppression is attributed to down‑regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase‑2 (COX‑2) expression, as confirmed by Western blotting. In vivo studies in carrageenan‑induced paw edema models in rats showed significant inhibition of edema formation, with dose‑dependent reductions reaching 65 % at 20 mg kg⁻¹. These anti‑inflammatory effects appear to be linked to the ability of the compound to modulate the NF‑κB signaling pathway.
Cytotoxicity and Anticancer Activity
Screening against a panel of human cancer cell lines (A549, MCF‑7, and HeLa) revealed selective cytotoxicity at micromolar concentrations. The most potent analogue, referred to as 3‑methoxy‑1,3,5‑trihydroxy‑bis‑phenyl‑acrylic acid, exhibited an IC₅₀ of 18 µM against MCF‑7 cells, while sparing normal fibroblasts at concentrations up to 100 µM. Mechanistic studies suggest that apoptosis is induced via the mitochondrial pathway, with an increase in the Bax/Bcl‑2 ratio and release of cytochrome c. Additionally, DNA fragmentation assays indicated a late apoptotic phase, corroborated by annexin V/propidium iodide staining. These findings have motivated further investigation into combination therapies, where the compound is paired with standard chemotherapeutic agents to assess synergistic effects.
Photocatalytic Activity
Compounds with a chromone or flavone core have been studied for their ability to act as photosensitizers. In photodynamic therapy (PDT) models, the C21H24O7 derivative is activated by blue light (λ = 470 nm) to produce singlet oxygen, which in turn induces selective tumor cell death. The photostability of the compound is influenced by the number and position of hydroxyl groups; a higher density of electron‑rich phenolic groups generally enhances singlet oxygen generation while also increasing susceptibility to photobleaching. In vitro PDT studies have shown a dose‑dependent increase in reactive oxygen species production, which is attenuated by the addition of radical scavengers such as N‑acetyl‑cysteine.
Pharmacological Potential
Antioxidant and Neuroprotective Effects
Because of their phenolic structure, C21H24O7 compounds have been extensively evaluated for neuroprotective activity. In models of amyloid‑β toxicity, the compound reduces oxidative stress markers such as malondialdehyde (MDA) and restores glutathione (GSH) levels. The antioxidant mechanism involves both radical scavenging and up‑regulation of endogenous antioxidant enzymes, including superoxide dismutase (SOD) and catalase. Furthermore, in the rotenone‑induced Parkinson’s disease model in mice, treatment with the compound mitigates dopaminergic neuron loss, suggesting a potential therapeutic role in neurodegenerative disorders.
Anti‑Cancer Effects
Multiple studies have demonstrated that the compound can inhibit proliferation of colorectal, breast, and lung cancer cell lines. The inhibition is largely mediated through cell‑cycle arrest at the G₂/M phase, accompanied by up‑regulation of p21 and down‑regulation of cyclin B1. In addition to cytostatic effects, the compound induces apoptosis through the intrinsic mitochondrial pathway, as evidenced by increased Bax expression and caspase‑9 activation. Combination studies with cisplatin have shown additive cytotoxic effects, indicating that the compound may serve as an adjuvant to existing chemotherapeutics.
Anti‑Inflammatory Activity
Beyond its direct effects on inflammatory mediators, the compound also modulates the expression of adhesion molecules such as VCAM‑1 and ICAM‑1 in endothelial cells. These actions reduce leukocyte adhesion and transmigration, thereby attenuating inflammatory responses in vitro. In an in vivo model of acute lung injury, oral administration of the compound reduced infiltration of neutrophils into the alveolar space and decreased lung wet/dry weight ratios. The anti‑inflammatory effects are considered to result from the combined action of phenolic hydroxyls and methoxy groups, which modulate signaling pathways including MAPK and JAK‑STAT.
Other Biological Activities
Additional pharmacological properties reported for C21H24O7 compounds include hepatoprotective, antimicrobial, and antiviral activities. In hepatic injury models induced by carbon tetrachloride, the compound reduces serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, while increasing antioxidant enzyme activity. Antimicrobial assays against Gram‑positive and Gram‑negative bacteria have shown moderate inhibition, with MIC values ranging from 64 to 128 µg mL⁻¹. A study on influenza A virus revealed that the compound interferes with viral replication by inhibiting neuraminidase activity, though the effect was less potent than standard neuraminidase inhibitors.
Applications
Pharmaceutical Development
Given its multiple bioactivities, derivatives of C21H24O7 are actively pursued as lead compounds for drug discovery. In the context of chronic diseases such as atherosclerosis and diabetes, the antioxidant properties of the compound are harnessed to reduce oxidative damage in vascular tissues. Ongoing clinical trials in Japan have tested a formulated version of the compound as an oral supplement aimed at lowering LDL oxidation markers. The trials evaluate safety, tolerability, and pharmacokinetic parameters, with a particular focus on the compound’s metabolic stability and its ability to reach therapeutic concentrations in plasma.
Nutraceuticals and Functional Foods
Food‑grade extracts containing the compound are incorporated into dietary supplements marketed for cardiovascular health. The inclusion of the compound in functional beverages often relies on its solubility in aqueous media, allowing for easy dispersion into drinks. Consumer reports indicate that ingestion of 250 mg of the compound daily for eight weeks leads to measurable decreases in plasma lipid peroxidation levels. Regulatory agencies in the European Union have classified the compound as “generally regarded as safe” (GRAS) when used at concentrations below 1 g kg⁻¹ in food products.
Cosmetic Formulations
Due to its light‑stabilizing and anti‑aging effects, the compound is used in topical formulations such as creams and serums. Cosmetic manufacturers combine the compound with other phenolic antioxidants, including resveratrol and quercetin, to produce synergistic protection against ultraviolet (UV)‑induced skin damage. In vitro studies on keratinocytes demonstrate that the compound reduces the expression of matrix metalloproteinase‑1 (MMP‑1) after UVB irradiation, suggesting a role in preventing collagen degradation. Formulation scientists note that the compound’s moderate water‑solubility permits its inclusion in aqueous emulsions, while its aromatic nature confers a characteristic fragrance profile that is considered desirable in high‑end cosmetics.
Analytical Methodologies
Chromatographic Techniques
High‑performance liquid chromatography (HPLC) coupled with diode‑array detection (DAD) is the primary method for quantifying the compound in complex matrices. A typical HPLC method employs a C18 column, with a gradient elution of methanol and water containing 0.1 % formic acid. The detection wavelength is set at 280 nm to capture the absorbance of phenolic groups. Calibration curves generated from purified standards yield limits of detection (LOD) of 0.2 µg mL⁻¹ and limits of quantitation (LOQ) of 0.6 µg mL⁻¹. This method is suitable for both biofluid analysis and plant extracts.
Mass Spectrometry
Liquid chromatography–tandem mass spectrometry (LC‑MS/MS) is employed for structural elucidation and for determining the compound’s metabolic fate. The compound exhibits a characteristic [M+H]⁺ ion at m/z = 353.15. Fragmentation patterns reveal neutral loss of 18 Da (water) and 28 Da (CO₂), corresponding to hydroxy and carboxyl groups. In pharmacokinetic studies, LC‑MS/MS is used to track the compound’s plasma concentration over time, revealing a half‑life (t½) of approximately 4.5 hours in rats.
Spectroscopic Characterization
UV‑Vis spectroscopy provides insights into the electronic transitions associated with the chromone core, with λmax values around 290 nm. Infrared spectroscopy confirms the presence of phenolic OH (≈ 3500 cm⁻¹) and aromatic C=C bonds (≈ 1600 cm⁻¹). The NMR spectra, both ¹H and ¹³C, are used to verify the substitution pattern of methoxy groups, with characteristic signals at δ 3.8 ppm for methoxy protons and δ 122–130 ppm for aromatic carbons. The combination of these spectroscopic techniques ensures accurate structural assignment and purity assessment.
Safety and Toxicological Profile
Acute Toxicity
Animal studies have determined that the compound exhibits low acute toxicity. A single oral dose of 2000 mg kg⁻¹ in mice results in no observable adverse effects (NOAEL). The compound’s hepatotoxic potential is minimal, with histological examinations revealing no signs of hepatic necrosis after repeated dosing.
Chronic Toxicity
Long‑term administration (six months) in rats at 50 mg kg⁻¹ shows no significant changes in body weight, food intake, or organ weights. Blood chemistry panels remain within normal ranges, including renal markers such as blood urea nitrogen (BUN) and creatinine. The compound’s metabolism predominantly involves conjugation reactions - glucuronidation and sulfation - followed by renal excretion. These pathways reduce the potential for bioaccumulation.
Allergenicity
Skin‑prick tests performed on 100 volunteers demonstrate a low incidence (3 %) of mild itching at the application site, suggesting that the compound is largely non‑allergenic. Dermatological studies confirm that the compound does not interfere with skin barrier function or increase transepidermal water loss (TEWL). Regulatory oversight in the United States requires that any new cosmetic formulation containing the compound provide allergenicity data before market approval.
Future Research Directions
Structure–Activity Relationship (SAR) Studies
Researchers aim to delineate the influence of methoxy versus hydroxyl substitution on pharmacological outcomes. Systematic modification of the methoxy groups (e.g., converting to ethoxy or isopropoxy) has been proposed to enhance lipophilicity and potentially improve membrane permeability. Comparative assays will assess whether such changes alter the compound’s ability to inhibit iNOS or to generate singlet oxygen in PDT models.
Formulation for Targeted Delivery
Encapsulation technologies, including liposomes and polymeric nanoparticles, are being explored to deliver the compound to specific tissues. For instance, loading the compound into PEG‑coated liposomes can increase its circulation time and reduce hepatic clearance. Studies on pulmonary delivery via inhalation are underway, where the compound is incorporated into dry‑powder formulations for targeted lung disease therapy.
Mechanistic Studies
Further molecular investigations are needed to clarify how the compound interacts with signaling pathways at the receptor and post‑translational levels. Proteomic profiling using mass spectrometry could identify novel protein targets, while CRISPR‑based gene editing may delineate the pathways essential for its anti‑cancer effects. Additionally, metabolomic analyses could uncover how the compound’s metabolic intermediates contribute to its pharmacological profile.
Conclusion
In summary, the C21H24O7 compound represents a versatile scaffold with a broad spectrum of potential applications. Its complex arrangement of phenolic and methoxy groups endows it with antioxidant, anti‑inflammatory, and cytotoxic activities that can be harnessed across pharmaceutical, nutraceutical, and cosmetic sectors. While the current body of evidence supports its safety and efficacy at therapeutic doses, continued research into structure‑activity relationships, targeted delivery systems, and comprehensive toxicological assessments will be essential to fully realize its commercial and clinical potential.
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