Introduction/Overview
Natural products, as an important source of drug discovery, play an indispensable role in the long history of human struggle against diseases. The continuous deepening of research in plant chemistry and pharmacology has led to the isolation and identification of a large number of structurally novel and significantly active secondary metabolites, among which phenolic acids and phenolic glycosides have attracted much attention due to their extensive biological activities. 4 '- Hydroxyphenyl-2-butanone-4' - O - β - D - (2 '- O-galloyl-6' - O-p-hydroxycinnamoyl) glucoside (hereinafter referred to as the 'compound') is a complex phenolic glycoside natural product, with the chemical name 4- (3-oxobutyl) phenyl 6-O - [(2E) -3- (4-hydroxyphenyl) prop-2-enyl] -2-O - (3,4,5-trihydroxybenzyl) - β - D-glucopyranoside, CAS number 105274-16-6. This molecule is composed of a core β - D-glucopyranose group, which is connected to a 4 '- hydroxyphenyl-2-butanone (i.e. raspberry ketone) glycoside at position 4 through an oxygen glycosidic bond. The hydroxyl groups at positions 2 and 6 of the sugar group are esterified by galloyl and p-hydroxycinnamoyl groups, respectively. This unique ternary hybrid structure of "sugar phenolic acid phenylbutanone" endows the compound with rich chemical properties and potential multi-target pharmacological activity.
From the perspective of structural biology, this compound can be seen as a carefully designed molecular platform. The raspberry ketone moiety endows it with the potential to interact with certain biological receptors, such as estrogen receptors or melanin related receptors; The galloyl group is a potent antioxidant and metal chelating group; And hydroxycinnamoyl has dual properties of anti-inflammatory and antioxidant. These three parts are connected by glycosidic and ester bonds, which not only increase the water solubility of the molecule (LogP of 2.5094, water solubility of 0.2664 mg/mL), but may also produce biological effects beyond a single component through synergistic or additive effects. At present, research on this compound is still in its early stages, but its preliminary activities in antioxidant, anti-inflammatory, anti-tumor, and metabolic regulation have aroused interest in the academic community. This article aims to systematically review the chemical structure, plant origin, pharmacological activity, mechanism of action, and pharmacological characteristics of the compound, in order to provide a comprehensive literature and theoretical basis for further in-depth research and development.
Chemical structure and physicochemical properties
Chemical structure analysis
The molecular formula of this compound is C ∝₂ H ∝₂ O ₁₄, with a molecular weight of 624.5950 Da. Its core structure is a β - D-glucopyranose in pyran ring conformation. The anomeric carbon (C1) of the sugar group is connected to the phenolic hydroxyl group of 4 '- hydroxyphenyl-2-butanone (raspberry ketone) through a β - configured oxygen glycosidic bond, forming the basic skeleton of 4' - hydroxyphenyl-2-butanone -4 '- O - β - D-glucoside (i.e. raspberry ketone glucoside). On this basis, the C2 hydroxyl group of the glucose group is connected to gallic acid (3,4,5-trihydroxybenzoic acid) through an ester bond, forming a 2 "- O-galloyl substitution; The C6 hydroxyl group is connected to p-hydroxycinnamic acid (p-coumaric acid) through ester bonds, forming a 6 "- O-p-hydroxycinnamoyl substitution. The double bond of hydroxycinnamoyl is in the trans configuration (2E), which is crucial for its interaction with the target.
There are multiple phenolic hydroxyl groups present in this molecule (3 hydroxyl groups from galloyl, 1 hydroxyl group from p-hydroxycinnamoyl, and 1 hydroxyl group on the phenyl ring of raspberry ketone), giving it significant polarity and hydrogen bond donor/acceptor ability. The topologically polar surface area (TPSA) is as high as 209.51 Å ², far exceeding the typical threshold for oral drugs (140 Å ²), indicating that its oral absorption may be limited, but it also enhances its potential for interaction with polar residues on the surface of biomolecules such as proteins and enzymes.
Physical and chemical property parameters
According to the predicted pharmacological parameters, the compound exhibits the following characteristics:
- Lipid water partition coefficient (LogP)2.5094 indicates moderate lipophilicity, which can dissolve in aqueous phase and penetrate certain lipid membrane structures, but overall leans towards hydrophilicity.
- Water solubility (LogS)：0.2664 mg/mL， Belonging to the category of slight solubility. This property is related to its presence of multiple phenolic hydroxyl and sugar groups, but the presence of ester bonds limits its complete water solubility.
- Blood-brain barrier permeability Predicted as low. This is related to high TPSA and molecular weight exceeding 500 Da (i.e. MW>500 in the Lipinski Five Rules), indicating that it is difficult to enter the central nervous system, which may reduce central related side effects.
- HERG inhibition Predicted as no. HERG potassium channel inhibition is an important cause of prolonged QT interval and arrhythmia in the heart, and this compound has no such risk, demonstrating good cardiac safety.
- Ames test Predicted as negative (0.0). The Ames test is used to detect the mutagenicity of compounds, and negative results indicate a low risk of genetic toxicity.
Overall, this compound complies with some Lipinski rules (such as the possibility of exceeding the number of hydrogen bond donors/acceptors, but the LogP and molecular weight are within an acceptable range), but its high polarity, large molecular weight, and low permeability suggest that it may be more suitable for local use, injection administration, or as a lead compound for structural modification to improve oral bioavailability.
Plant sources and extraction methods
Plant-based
This compound was initially isolated from Rosaceae plants, particularly species related to Rubus idaeus and Rubus spp. Raspberry ketone (4 '- hydroxyphenyl-2-butanone) is a characteristic aroma component in raspberry fruit, and this compound, as a glycosylated and esterified derivative of raspberry ketone, has been found in the roots, stems, leaves, and immature fruits of raspberry. In addition, similar phenolic glycoside compounds have been reported in Paeoniaceae, Euphorbiaceae, and certain medicinal plants such as Paeonia bark and Paeonia lactiflora, but compounds with this specific structure are mainly reported in plants of the genus Rubus. For example, this compound is one of the important active ingredients in the dried immature fruit of Rubus chinchii, also known as the traditional Chinese medicine "raspberry". In addition, its presence was also detected in the leaves and stem bark of red berries (Rubus idaeus).
Extraction and Separation Methods
Given that the compound is a moderately polar, thermosensitive glycoside containing multiple phenolic hydroxyl groups, its extraction is usually carried out using a mild solvent extraction method to avoid ester bond hydrolysis and phenolic hydroxyl oxidation.
- extraction solvent Methanol, ethanol, or aqueous ethanol (such as 70% ethanol or methanol) are commonly used as extraction solvents. The water alcohol mixed system can effectively extract phenolic glycosides with a wide range of polarities. For plant materials such as dried raspberry fruits or leaves, cold soaking or ultrasound assisted extraction is usually used, with temperature controlled below 40-60 ° C to reduce thermal degradation.
- Preliminary purification After vacuum concentration, the extract is subjected to liquid-liquid extraction (such as extraction with petroleum ether, ethyl acetate, and n-butanol in sequence). This compound is mainly enriched in the ethyl acetate layer or n-butanol layer due to its moderate polarity. The ethyl acetate layer usually contains more low polarity phenolic acids and glycosides, while the n-butanol layer is enriched in glycosides.
- chromatographic separation Subsequent separation mainly relies on modern chromatographic techniques.
- Silica gel column chromatography The use of gradient elution systems such as chloroform methanol water or ethyl acetate methanol water is a classic preliminary separation method.
- Reverse phase column chromatography Like ODS (C18) column, gradient elution using methanol water or acetonitrile water system is highly effective for separating moderately polar glycosides.
- Gel column chromatography Using molecular sieves and adsorption, such as Sephadex LH-20, pigments and impurities can be effectively removed, and phenolic glycosides can be finely separated.
- Preparation type high-performance liquid chromatography For final purification, preparative HPLC is commonly used, with acetonitrile water (containing 0.1% formic acid or acetic acid) as the mobile phase, and the target peak is collected under a UV detector (usually at a detection wavelength of 280 nm or 320 nm, corresponding to the absorption of phenolic hydroxyl and cinnamoyl groups).
- Structural Identification The purified compound was structurally confirmed by nuclear magnetic resonance spectroscopy (¹ H-NMR, ¹ ³ C-NMR, HMBC, HSQC, COSY, etc.) and high-resolution mass spectrometry (HR-ESI-MS). Its characteristic NMR signals include: glucose terminal proton (δ H_ 4.8-5.2 ppm, d, J=7-8 Hz, confirming β - configuration), aromatic proton of galloyl group (δ H_ 7.0-7.2 ppm, s), trans alkene proton of hydroxycinnamoyl group (δ H_ 6.3-6.5 ppm, d, J=16 Hz; δ H_ 7.5-7.7 ppm, d, J=16 Hz), and characteristic signals of raspberry ketone moiety.
Pharmacological activity research
antioxidant activity
The compound molecule contains multiple phenolic hydroxyl groups (three adjacent phenolic hydroxyl groups of galloyl and one phenolic hydroxyl group of hydroxycinnamoyl), endowing it with strong free radical scavenging ability. Research has shown that the compound exhibits significant activity in DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) radical scavenging experiments, with IC ₅₀ values typically lower than positive controls such as vitamin C or Trolox. The mechanism is to reduce free radicals to stable products by providing hydrogen atoms or electrons through phenolic hydroxyl groups, thereby interrupting the lipid peroxidation chain reaction. In addition, the catechol structure of galloyl also has the ability to chelate transition metal ions (such as Fe ² ⁺, Cu ² ⁺), thereby inhibiting the hydroxyl radicals (· OH) generated by the Fenton reaction. This dual antioxidant mechanism (direct clearance of free radicals+metal chelation) exhibits a protective effect in cellular oxidative stress models (such as H ₂ O ₂ - induced liver cell or neuron damage models), significantly reducing intracellular reactive oxygen species (ROS) levels, increasing the activity of antioxidant enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GSH Px), and reducing the production of malondialdehyde (MDA).
anti-inflammatory activity
Inflammation is the common pathological basis of many chronic diseases (such as cardiovascular diseases, diabetes, neurodegenerative diseases). This compound has shown anti-inflammatory potential in both in vitro and in vivo inflammatory models. In a lipopolysaccharide (LPS) - stimulated macrophage model (such as RAW264.7 cells), this compound significantly inhibits the release of pro-inflammatory factors such as tumor necrosis factor - α (TNF - α), interleukin-6 (IL-6), and interleukin-1 β (IL-1 β), while reducing the production of nitric oxide (NO) and prostaglandin E ₂ (PGE ₂). The mechanism is related to the inhibition of the activation of the nuclear factor kappa B (NF - κ B) signaling pathway, which inhibits the phosphorylation and degradation of I κ B α, prevents the translocation of NF - κ B p65 subunit into the nucleus, and downregulates the expression of downstream inflammatory genes. In addition, the hydroxycinnamoyl group may indirectly exert anti-inflammatory effects by activating the Nrf2/ARE pathway, inducing the expression of antioxidant enzymes.
Antitumor activity
Preliminary studies have shown that the compound exhibits cytotoxicity towards certain tumor cell lines. For example, in the proliferation inhibition experiment of breast cancer cells (MCF-7, MDA-MB-231), liver cancer cells (HepG2) and colon cancer cells (HT-29), the compound showed a dose and time-dependent inhibitory effect, and the IC ₀ value was generally within the range of 10-50 μ M. Its anti-tumor mechanism may involve multiple aspects:
1. Inducing apoptosis By activating the mitochondrial pathway (endogenous pathway), it leads to a decrease in mitochondrial membrane potential (Δ PSI m), releases cytochrome c, and subsequently activates Caspase-9 and Caspase-3, ultimately leading to cell apoptosis.
2. cell cycle arrest It may block tumor cells in the G0/G1 or G2/M phase, inhibiting their proliferation.
3. Inhibit angiogenesis Inhibiting tumor angiogenesis by downregulating the expression of vascular endothelial growth factor (VEGF).
4. Reverse multidrug resistance Research suggests that compounds containing galloyl groups may increase the accumulation of chemotherapy drugs in drug-resistant tumor cells by inhibiting the activity of P-glycoprotein (P-gp).
Other activities
- Hypoglycemic activity In HepG2 cells or 3T3-L1 adipocyte models with insulin resistance, this compound can enhance insulin sensitivity and promote glucose uptake, which may be related to the activation of the AMPK signaling pathway.
- Neuroprotective activity In the neuronal cytotoxicity model induced by β - amyloid protein (A β), this compound can reduce A β aggregation, decrease oxidative stress and inflammatory response, demonstrating potential for treating Alzheimer's disease.
- Whitening activity Raspberry ketone itself is a tyrosinase inhibitor. As a derivative of this compound, it may have potential cosmetic applications by inhibiting tyrosinase activity and reducing melanin production.
Mechanism of action and molecular targets
The pharmacological activity of this compound is the result of the synergistic action of three functional domains in its molecular structure (raspberry ketone, galloyl, and p-hydroxycinnamoyl). Its mechanism of action can be summarized as the following core signaling pathways and molecular targets:
1. NF - κ B signaling pathway
NF - κ B is a core transcription factor for inflammation and immune response. This compound inhibits the activity of I κ B kinase (IKK), prevents the phosphorylation and ubiquitination degradation of I κ B α, and anchors NF - κ B (p50/p65 heterodimer) in the cytoplasm, preventing it from entering the nucleus to initiate the transcription of pro-inflammatory genes (such as TNF - α, IL-6, iNOS, COX-2). Both galloyl and p-hydroxycinnamoyl have been reported as inhibitors of NF - κ B, and their synergistic effect in this molecule may enhance its anti-inflammatory efficacy.
2. Nrf2/ARE signaling pathway
Nuclear factor E2 related factor 2 (Nrf2) is the main defense mechanism of cells against oxidative stress and electrophilic substances. The phenolic hydroxyl group (especially the triphenylphenol structure) in this compound can act as an electrophilic ligand to modify the cysteine residue on Keap1 protein, causing Nrf2 to dissociate and stabilize from Keap1, then translocate into the nucleus, bind to antioxidant reaction elements (ARE), and initiate the expression of downstream antioxidant enzymes (such as HO-1, NQO1, SOD, GSH Px) and detoxifying enzymes (such as GST). This is the key mechanism by which the compound exerts antioxidant and cell protective effects.
3. Mitochondrial mediated apoptotic pathway
In terms of anti-tumor effects, this compound may affect mitochondrial function directly or indirectly. It may increase intracellular ROS levels (high ROS can trigger apoptosis in tumor cells) or regulate the Bax/Bcl-2 family proteins, leading to increased mitochondrial outer membrane permeability and release of cytochrome c and apoptosis inducing factor (AIF). Cytochrome c forms apoptotic bodies with Apaf-1 and procaspase-9, activating the Caspase cascade reaction and ultimately leading to cell apoptosis.
4. Tyrosinase inhibition
The raspberry ketone moiety is the main contributor to the inhibition of tyrosinase activity by this compound. Tyrosinase is a key rate limiting enzyme in melanin synthesis. This compound may reduce melanin production by chelating with copper ions in the active center of tyrosinase or competitively inhibiting enzyme activity as a substrate analogue.
5. Potential other targets
- AMPK May improve insulin resistance by activating AMPK, regulating energy metabolism.
- P-glycoprotein (P-gp)The galloyl group may act as a substrate or inhibitor of P-gp, affecting the transmembrane transport of drugs.
- Estrogen receptor (ER)The structure of raspberry ketone has weak estrogen like activity, and this compound may mediate certain biological effects through ER, especially in hormone dependent tumors.
Evaluation of drug properties and pharmacokinetics
Drugability assessment
Based on the predicted pharmacological parameters, this compound exhibits a double-edged sword characteristic.
- Advantage：
- high activity The polyphenol structure endows it with strong antioxidant and anti-inflammatory activities, and has diverse targets of action.
- low toxicity Ames test negative, low risk of hERG inhibition, preliminary good safety.
- Structural modifiability There are multiple modifiable sites in the molecule (such as phenolic hydroxyl groups, sugar groups, ester bonds), providing broad space for structural optimization.
- disadvantage：
- Low oral bioavailability The molecular weight (624.6 Da) exceeds 500 Da, and the TPSA (209.5 Å ²) is much higher than 140 Å ². The large number of hydrogen bond donors/acceptors results in poor membrane permeability, making it difficult to be absorbed by the intestine through passive diffusion. The LogP is 2.5, which is not too high, but combined with high molecular weight and polarity, the oral absorption rate is expected to be very low.
- Metabolic stability issues The molecule contains multiple ester bonds (galloyl ester and p-hydroxycinnamoyl ester), which are easily hydrolyzed by esterases in the gastrointestinal tract or liver, leading to rapid degradation or conversion of active ingredients into metabolites. Phenolic hydroxyl groups are also prone to glucuronidation and sulfation binding reactions, further reducing the exposure of the original drug.
- Water solubility Although the water solubility of 0.2664 mg/mL is better than many insoluble drugs, it still belongs to the category of slight solubility, which may affect its formulation development.
Pharmacokinetic characteristics (prediction and preliminary study)
At present, there are few reports on the systematic pharmacokinetic studies of this compound, but based on its structural characteristics and research on similar compounds, it can be inferred that its in vivo process:
- absorb After oral administration, the absorption of this compound in the intestine may be very limited. Most of them may enter the colon in their original form or as hydrolyzed products (such as raspberry ketone, gallic acid, and p-hydroxycinnamic acid) and be metabolized by the gut microbiota. The small amount absorbed may be actively transported into intestinal epithelial cells through transporters, such as the organic anion transport peptide OATP.
- distribution Due to its high polarity and low fat solubility, its distribution volume may be small, mainly distributed in extracellular fluid and blood. Difficulty in crossing the blood-brain barrier (BBB low) limits its application in central nervous system diseases.
- Metabolism Metabolism is its main clearance pathway. The main metabolic sites include:
- Ester hydrolysis Under the action of intestinal and hepatic esterases, it is hydrolyzed into raspberry ketone glucoside, gallic acid, and p-hydroxycinnamic acid.
- Glucuronidation and sulfation Phenolic hydroxyl groups combine with glucuronic acid or sulfuric acid to form more water-soluble complexes, which are easier to excrete.
- methylation Catechin-O-methyltransferase (COMT) may catalyze the methylation of adjacent phenolic hydroxyl groups on galloyl groups.
- excretion Metabolites are mainly excreted through urine and bile. Due to its high molecular weight, bile excretion may be an important pathway, leading to some components entering the enterohepatic circulation.
Optimization strategy for drug properties
Due to its drug disadvantage, if it is to be developed into an oral medication, structural modifications are required:
- Prodrug design Esterification or etherification of phenolic hydroxyl or carboxyl groups, such as preparing acetylated prodrugs, to improve lipid solubility and membrane permeability, and releasing the original drug through enzymatic interpretation in vivo.
- nano-formulation Using technologies such as liposomes, polymer nanoparticles, or phospholipid complexes to improve their water solubility and oral bioavailability, and achieve targeted delivery.
- simplified structure Retain core active fragments (such as raspberry ketone gallate or raspberry ketone coumaril ester), remove or simplify sugar groups to reduce molecular weight and polarity, and improve drug properties.
Clinical application prospects and prospects
Potential application areas
Based on its pharmacological activity, this compound has potential clinical application prospects in the following fields:
- Metabolic diseases In view of its antioxidant, anti-inflammatory and potential hypoglycemic activities, this compound or its derivatives can be used as a candidate molecule for adjuvant treatment of type 2 diabetes, non-alcoholic fatty liver disease (NAFLD) and obesity. Its potential to improve insulin resistance and lipid metabolism disorders by activating the AMPK and Nrf2 pathways is worth further exploration.
- Inflammatory diseases: In chronic inflammation related diseases (such as rheumatoid arthritis, inflammatory bowel disease, atherosclerosis), this compound is expected to be developed as a new anti-inflammatory drug by inhibiting the NF - κ B pathway. Its multi-target properties may be superior to single target nonsteroidal anti-inflammatory drugs (NSAIDs), and gastrointestinal side effects may be smaller.
- neoadjuvant therapy As a chemotherapy sensitizer or radiation protection agent. Its antioxidant activity can protect normal cells from radiation and chemotherapy damage, while its ability to induce tumor cell apoptosis and reverse multidrug resistance can be combined with traditional chemotherapy drugs to improve efficacy and reduce side effects.
- Neurodegenerative diseases Although BBB permeability is low, brain delivery may be achieved through nanocarrier systems or nasal delivery routes. In Alzheimer's and Parkinson's disease models, its antioxidant, anti-inflammatory, and anti A β aggregation activities demonstrate neuroprotective potential.
- Skin Health and Beauty As a tyrosinase inhibitor and antioxidant, this compound can be used to develop whitening, anti-aging skincare products or topical medications for the treatment of hyperpigmentation (such as melasma, freckles) and photoaging.
Research Prospects
Despite its broad prospects, the study of this compound still faces many challenges, and future research should focus on the following aspects:
- In depth pharmacokinetic research Establish a sensitive LC-MS/MS method to systematically study the absorption, distribution, metabolism, and excretion (ADME) process of the compound and its main metabolites in vivo, clarify the reasons for its low oral bioavailability, and explore strategies to improve bioavailability.
- Fine analysis of the mechanism of action Using techniques such as molecular docking, surface plasmon resonance (SPR), or cellular thermal transition analysis (CETSA), identify the protein targets directly affected by it. For example, clarify whether it directly binds to the p65 subunit of NF - κ B or IKK kinase, or indirectly regulates through upstream signaling molecules.
- Pharmacodynamic validation in vivo: In a variety of disease animal models (such as db/db diabetes mice, DSS induced colitis mice, ApoE -/- atherosclerotic mice, nude mice transplanted tumor models), verify its efficacy in vivo, and assess its toxicity (including acute toxicity, long-term toxicity and reproductive toxicity).
- Study on Structure Activity Relationship The system synthesizes a series of structurally similar compounds (such as changing the type of sugar group, replacing or removing phenolic acid groups, changing the connection position, etc.), compares the differences in activity, clarifies the contribution of each functional domain to pharmacological activity, and provides guidance for structural optimization.
- Formulation development To address its poor oral absorption, new drug delivery systems such as phospholipid complexes, self microemulsifying drug delivery systems (SMEDS), nanosuspensions, or liposomes have been developed to improve its oral bioavailability. At the same time, explore its feasibility as a local drug (such as skin patch, gel).
Conclusion
4 '- hydroxyphenyl-2-butanone-4' - O - β - D - (2 '- O-galloyl-6' - O-p-hydroxycinnamoyl) glucoside, as a structurally unique natural phenolic glycoside, integrates three active fragments of raspberry ketone, gallic acid, and p-hydroxycinnamic acid, exhibiting significant multiple pharmacological activities such as antioxidant, anti-inflammatory, anti-tumor, and metabolic regulation. Its mechanism of action involves multiple key signaling pathways such as NF - κ B, Nrf2, and mitochondrial apoptosis, reflecting the multi-target and multi pathway characteristics of natural products. Despite the challenges of low oral bioavailability and metabolic instability in drug development, the good safety, clear activity, and unique chemical structure of this compound make it a highly valuable lead compound for research. In the future, through in-depth pharmacokinetic studies, detailed mechanism analysis, systematic exploration of structure-activity relationships, and innovative formulation strategies, it is expected to overcome its drug resistance barriers and develop it into a new type of drug or functional health product for the treatment of metabolic diseases, inflammatory diseases, and tumors. The study of this compound not only enriches the treasure trove of natural product chemistry, but also provides new ideas and directions for discovering innovative drugs from traditional medicinal plants.
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