(R, S) - Gao Yichun: Research progress from natural products to candidate drugs against respiratory syncytial virus
Introduction/Overview
Natural products, as an important source of drug discovery, play an irreplaceable role in the long-term struggle between humans and diseases. Brassicaceae plants have attracted much attention due to their rich secondary metabolites and significant biological activity, among which glucosinolates and their degradation products are the most extensively studied compounds. When plant tissues are damaged, endogenous myrosinase catalyzes the hydrolysis of glucosinolates, producing a series of biologically active isothiocyanates, nitriles, and oxazolidinothiones. Among these degradation products, (R, S) - Biotrin, also known as 5-vinyl-1,3-oxazoline-2-thione, has attracted widespread attention from the scientific community due to its unique chemical structure and multifaceted pharmacological activities, especially its potential in anti respiratory syncytial virus (RSV) research in recent years.
Respiratory syncytial virus is the primary pathogen causing severe lower respiratory tract infections in infants and young children, as well as an important cause of pneumonia and bronchitis in the elderly and immunocompromised population. Approximately 33 million children under the age of 5 worldwide are infected with RSV each year, with over 3 million requiring hospitalization and approximately 60000 deaths. Although RSV vaccines and monoclonal antibodies (such as pembrolizumab) have been applied in clinical practice, the issues of vaccine immune persistence, high cost of antibody therapy, and the emergence of drug-resistant strains have not been fundamentally resolved. Therefore, the search for new, efficient, and low-cost anti RSV drugs has important clinical significance and urgent social demand. In this context, systematic research on (R, S) - Gao Yichun not only helps clarify the scientific connotation of traditional plant medicine, but also provides important lead compounds for the development of new antiviral drugs.
Chemical structure and physicochemical properties
Chemical structural characteristics
(R, S) - Gaoyichun belongs to oxazolidinone sulfide compounds, and its core skeleton is 1,3-oxazolidinone-2-thione. This structure consists of a five membered heterocyclic ring containing one oxygen atom (position 1), one nitrogen atom (position 3), and one thiocarbonyl group (C=S, position 2). A vinyl group (- CH=CH ₂) is attached to the 5th carbon atom, and this unsaturated side chain endows the molecule with unique reactivity and biological activity. Due to the chiral center of the 5-position carbon atom, there are two enantiomers, R and S, in the form of Gaoyichun. Natural products usually exist in racemic form, namely (R, S) - Gaoyichun.
From the perspective of electronic structure, the presence of thiocarbonyl groups gives the molecule high polarization, and the π electron cloud density of the C=S double bond is high, making it easy to participate in electrophilic reactions. Meanwhile, the nitrogen atom in the oxazolidine ring has lone pair electrons and can serve as a hydrogen bond acceptor. The π - electron system of the vinyl side chain may participate in π - π stacking or Michael addition reactions. These structural features collectively determine the diversity and specificity of interactions between Gao Yichun and biomolecules.
Physical and chemical property parameters
According to computational chemical analysis, the molecular weight of (R, S) - Gao Yichun is 129.1840 g/mol, belonging to the category of small molecule compounds, which lays the foundation for its good membrane permeability. The lipid water partition coefficient (LogP) is 0.6687, indicating that the compound has moderate lipophilicity, which can dissolve in the aqueous phase and penetrate the lipid bilayer of the biofilm. The topological polar surface area (TPSA) is 21.2600 Å ², far below the upper limit of 140 Å ² typically required for oral medications, indicating its good oral absorption potential.
The water solubility parameter is 7.3641mg/mL, which belongs to moderate solubility, providing favorable conditions for its dissolution and distribution in vivo. It is worth noting that the blood-brain barrier (BBB) penetration prediction is "high", indicating that Gaoyichun may have central nervous system activity, which requires special attention in subsequent toxicological evaluations. HERG inhibition is predicted as' no ', reducing the risk of cardiac toxicity. The predicted value of Ames test is 0.6, indicating a low risk of genetic toxicity, but further verification through experiments is needed. These pharmacological parameters indicate that (R, S) - Gaoyichun has the basic physicochemical characteristics to become a candidate drug, but its actual pharmacokinetic behavior still requires comprehensive evaluation through in vitro and in vivo experiments.
Plant sources and extraction methods
Main plant sources
(R, S) - Gaoyichun mainly exists in cruciferous plants, especially abundant in Brassica and Lepidium plants. Common plants rich in Gaoyichun include: cabbage (Brassica oleracea), cauliflower, broccoli, cabbage, turnip (Brassica rapa), rape (Brassica napus) and horseradish (Armoracia rusticana). In addition, the traditional Chinese medicines Isatis indigotica Fort. and Isatis tinctoria also contain high levels of Gaoyichun, which may be one of the material bases for their heat clearing, detoxification, and antiviral effects.
It is worth noting that Gao Yichun does not exist in free form in intact plant tissues, but is stored in vacuoles in the form of precursor substances - glucosinolates (especially 2-hydroxy-3-butenyl glucosinolates, also known as progoitrin). When plant tissues are subjected to mechanical damage (such as cutting, chewing) or pathogen infection, myrosinase is released and catalyzes the hydrolysis of proline, producing unstable intermediates that undergo intramolecular cyclization reactions to ultimately form gibberellins. Therefore, the content of Gaoyichun is closely related to plant species, tissue parts, growth stages, processing methods, and enzymatic hydrolysis conditions.
Extraction and purification methods
The traditional extraction method of Guayi Chun is mainly based on organic solvent extraction. Common extraction solvents include methanol, ethanol, ethyl acetate, and dichloromethane. Due to its polarity, methanol water mixed solvents (such as 70% methanol) can usually achieve high extraction efficiency. The extraction process usually includes steps such as drying, crushing, solvent soaking, ultrasonic assisted extraction or Soxhlet extraction, filtration, and vacuum concentration of plant materials.
In recent years, a series of modern extraction techniques have been developed to improve extraction selectivity and purity. Solid phase extraction (SPE) technology utilizes C18 or HLB adsorption columns to effectively remove impurities such as pigments and sugars. High speed counter current chromatography (HSCCC) utilizes the distribution differences of solutes in a two-phase solvent system to achieve separation, and has the advantages of high sample recovery and irreversible adsorption. Preparation type high performance liquid chromatography (Prep HPLC) can obtain high-purity monomers of Gaoyichun, usually using a reverse phase C18 chromatography column with acetonitrile water or methanol water as the mobile phase for isocratic or gradient elution.
In terms of detection, high-performance liquid chromatography ultraviolet detection (HPLC-UV) is the most commonly used quantitative method, with a characteristic absorption peak at 240-250 nm. Liquid chromatography-mass spectrometry (LC-MS) can provide more accurate structural confirmation and trace analysis. In recent years, nuclear magnetic resonance hydrogen spectroscopy (¹ H-NMR) metabolomics technology has also been used for rapid qualitative and quantitative analysis of plant samples.
Pharmacological activity research
Antiviral activity
In recent years, the antiviral activity of (R, S) - Gaoyichun has become a research hotspot, especially its effect on respiratory syncytial virus (RSV). In vitro experiments have shown that Gao Yichun can significantly inhibit the replication of RSV in HEp-2 cells (human laryngeal squamous cell carcinoma cells), with a half maximal inhibitory concentration (IC ₅₀) at the micromolar level. Through plaque reduction experiments and virus titer determination, researchers found that the viral load of RSV in the treatment group of Gaoyichun was reduced by more than 90% compared to the control group. The results of the Time of addition assay showed that Gaoyichun mainly plays a role in the early stages of viral infection, possibly by interfering with virus adsorption, entry, or early replication processes to inhibit virus proliferation.
In addition to RSV, Gaoyichun also exhibits certain inhibitory effects on other viruses. Research reports that it has moderate antiviral activity against influenza A virus and herpes simplex virus. This broad-spectrum antiviral property suggests that Gaoyichun may act on the antiviral signaling pathway of host cells, rather than directly targeting viral proteins.
Anti inflammatory and immune regulatory activity
The anti-inflammatory activity of Gao Yichun is closely related to its antiviral effect. During RSV infection, excessive inflammatory response is the main cause of lung tissue damage and worsening clinical symptoms. Research has found that Gao Yichun can significantly reduce the expression levels of pro-inflammatory cytokines (such as TNF - α, IL-6, IL-8) in RSV infected cells. In the lipopolysaccharide (LPS) - induced macrophage inflammation model, treatment with Gaoyichun can inhibit the activation of the NF - κ B signaling pathway and reduce the production of nitric oxide (NO) and prostaglandin E ₂ (PGE ₂).
In terms of immune regulation, Gao Yichun can enhance the interferon (IFN) signaling pathway. Research has shown that treatment with Gaoyichun can upregulate the expression of interferon stimulated genes (ISGs), including MX1, IFIT1, and OAS1, which are important components of host antiviral defense. This immune enhancing effect may partially explain the antiviral mechanism of Gao Yichun.
Antitumor activity
Some studies have explored the anti-tumor potential of Gao Yichun. In vitro experiments, Gao Yichun showed cytotoxic effects on a variety of cancer cell lines (such as HepG2, breast cancer MCF-7, and colon cancer HT-29), and the IC ₀ value was within the range of 10-50 μ M. Mechanism studies have shown that Gao Yichun may inhibit tumor cell proliferation by inducing cell cycle arrest (G ₂/M phase) and apoptosis (activation of caspase-3, PARP cleavage). However, the toxicity of Gao Yichun to normal cells is relatively low, indicating that it has a certain degree of selectivity. It should be pointed out that the anti-tumor activity research of Gao Yichun is still in the preliminary stage, and the in vivo anti-tumor effect and safety still need to be systematically evaluated.
Thyroid function impact
It is worth noting that Gao Yichun was initially discovered and named for its goitrogenic activity. As a degradation product of glucosinolates, Gao Yichun can inhibit the activity of thyroid peroxidase (TPO), interfere with the synthesis of thyroid hormones (T3, T3), and lead to compensatory thyroid enlargement. This side effect is one of the main obstacles to the development of Gaoyichun as a drug. However, recent studies have shown that the effects of Gaoyichun on the thyroid gland may be dose-dependent, and there may be a therapeutic window between its antiviral activity and goiter inducing activity at low concentrations. Therefore, reducing its thyroid toxicity while retaining antiviral activity through structural modification or dose optimization is an important direction of current research.
Mechanism of action and molecular targets
Mechanism of anti RSV action
Based on existing research, the mechanism of action of (R, S) - Gaoyichun against RSV involves multiple levels, mainly related to the activation of the host's innate immune response. Specifically, Gao Yichun can significantly upregulate the phosphorylation level of interferon regulatory factor 3 (IRF3), promote IRF3 nuclear translocation, and thus initiate the transcription of type I interferon (IFN - α/β). After secretion, IFN - α/β acts on the IFNAR1/IFNAR2 receptor complex on the cell surface through autocrine and paracrine pathways, activating the JAK-STAT signaling pathway and ultimately inducing the expression of a large number of interferon stimulated genes (ISGs). Among them, MX1 (Myxovirus resistance protein 1) is a key antiviral effector protein that can inhibit RSV transcription and replication.
In addition, Gao Yichun may also directly act on the viral protein of RSV. Molecular docking simulation studies have shown that Gao Yichun may bind to the fusion protein (RSV-F) and attachment protein (RSV-G) of RSV, interfering with the recognition and membrane fusion process between the virus and host cells. The RSV-F protein mediates the fusion of the viral envelope with the host cell membrane, which is a crucial step for the virus to enter the cell; The RSV-G protein is responsible for the initial binding of the virus to host cell surface receptors. The interaction between Gao Yichun and these viral proteins may block viral infection from the source.
Molecular target network
Based on the existing evidence, the molecular target network of Gao Yichun can be summarized as follows:
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IFNAR1 As a subunit of type I interferon receptor, IFNAR1 is a key node in the activation of the IFN signaling pathway by interferon. Gao Yichun may amplify interferon signaling by upregulating the expression of IFNAR1 or enhancing its affinity with ligands.
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IRF3 As the main regulatory factor for interferon gene transcription, the activation of IRF3 is the core event for inducing IFN - β expression in Gaoyichun. Gao Yichun may promote IRF3 phosphorylation by activating upstream kinases such as TBK1.
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MX1 As an interferon induced GTPase, MX1 is one of the final executing proteins for the antiviral effect of GAAP. MX1 can recognize and encapsulate viral nucleocapsids, inhibiting the transcription and replication of viral RNA.
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RSV-F and RSV-G As functional proteins on the surface of the virus, they are potential targets for direct antiviral effects of GAAP. The binding of Gao Yichun to these proteins may alter their conformation, thereby inhibiting the process of virus entry.
Cross dialogue with other signaling pathways
In addition to the IFN pathway, Gaoyichun may also affect other signaling pathways. For example, Gao Yichun can inhibit the activation of the NF - κ B pathway, which is consistent with its anti-inflammatory activity. NF - κ B and IRF3 have complex cross-talk in regulating inflammation and interferon response, and Gao Yichun may achieve dual antiviral and anti-inflammatory effects by regulating the balance of these two pathways. In addition, there have been reports on the effects of Gao Yichun on the PI3K/Akt and MAPK pathways, but these findings need further validation.
Evaluation of drug properties and pharmacokinetics
Analysis of drug properties parameters
Based on the predicted pharmacological parameters, (R, S) - Gaoyichun has the following characteristics:
- molecular weight(129.18 Da): Far below the upper limit of the "Lipinski Five Rules" of 500 Da, it is beneficial for oral absorption and membrane permeability.
- LogP(0.67): Suitable range between -0.4 and 5.6, with both hydrophilicity and lipophilicity.
- TPSA(21.26 Å ²): Below 140 Å ², it indicates good intestinal absorption and cell membrane penetration ability.
- Water solubility(7.36 mg/mL): Meets the high solubility requirements of the Biopharmaceutical Classification System (BCS).
- Blood-brain barrier penetrability(High): Indicating the risk of central nervous system exposure, which needs to be given special attention in subsequent development.
- HERG inhibition(No): Reduced the risk of prolonged QT interval in the heart.
- Ames test(0.6): The risk of genetic toxicity is low, but experimental verification is still needed.
Overall, Gao Yichun meets the basic physical and chemical requirements for oral medication, but its high blood-brain barrier penetration may lead to central nervous system side effects, and thyroid gland activity is the main challenge for its drug development.
Pharmacokinetic characteristics
At present, there is limited in vivo research data on the pharmacokinetics of Gaoyichun, but preliminary speculation can be made based on its physicochemical properties and studies of similar compounds
- absorb Gaoyichun has a small molecular weight and moderate lipid solubility, and is expected to be quickly absorbed in the small intestine after oral administration. Its absorption may be influenced by gut microbiota and food composition, as the enzymatic hydrolysis process of glucosinolates can also occur in the intestine.
- distribution Due to its high blood-brain barrier penetration, Gao Yichun may be widely distributed throughout the body tissues, including brain tissue. The distribution volume (Vd) may be relatively large.
- Metabolism The metabolic pathway of Gao Yichun is not yet clear. It is speculated that it may undergo biotransformation through glutathione binding, redox reactions, or hydrolysis. The vinyl side chain may act as a Michael receptor and covalently bind to glutathione, which is both a detoxification pathway and may be related to biological activity.
- excretion Gaoyichun and its metabolites may be mainly excreted through the kidneys, and some may be excreted into the intestine through bile.
Toxicity evaluation
The main toxicity risk of Gao Yichun comes from its inhibitory effect on the thyroid gland. Long term or high-dose exposure may lead to a decrease in thyroid hormone levels, feedback elevation of thyroid stimulating hormone (TSH), and ultimately cause thyroid enlargement and dysfunction. In addition, the mutagenicity and reproductive toxicity of Gao Yichun still need to be systematically evaluated. It is worth noting that long-term exposure of Gao Yichun to traditional diets (such as consuming large amounts of cruciferous vegetables) did not lead to serious thyroid disease, indicating that it is safe at normal dietary doses. Therefore, determining the safe dosage range of Gaoyichun is a key prerequisite for its development as a drug.
Clinical application prospects and prospects
Development potential of anti RSV drugs
Given the lack of specific therapeutic drugs for RSV infection, (R, S) - Gaoyichun, as a natural product with a novel mechanism of action (activating the host IFN pathway), provides new ideas for the development of anti RSV drugs. Compared with traditional direct antiviral drugs such as ribavirin, Gaoyichun may have the following advantages in inhibiting the virus by enhancing the host immune response: (1) it is not easy to induce virus resistance; (2) Effective against multiple RSV subtypes; (3) It has anti-inflammatory effects and can alleviate immunopathological damage.
However, the development of Gao Yichun as a clinical drug still faces many challenges. The primary issue is the optimization of its goiter inducing activity. By structural modification, such as chemical modification of the vinyl side chain or introduction of protective groups, its inhibitory effect on TPO may be reduced. Secondly, it is necessary to establish a more comprehensive pharmacokinetic pharmacodynamic (PK-PD) model to clarify the metabolic fate and active forms of Zhiyichun in vivo. In addition, developing appropriate routes of administration (such as nebulization) may help increase drug concentration in the lungs while reducing systemic exposure and thyroid toxicity.
Structural optimization and discovery of lead compounds
Based on the chemical framework of Gao Yichun, a systematic structure-activity relationship (SAR) study can be conducted. The key modification sites include: (1) the substitution mode of the vinyl group at position 5; (2) The electronic properties of the 2-position thiocarbonyl group; (3) Stereochemistry of oxazolidine rings. By synthesizing a series of analogues and screening for their anti RSV activity and thyroid toxicity, it is expected to obtain candidate compounds with higher therapeutic indices. For example, replacing vinyl with other vinyl or aryl groups, or introducing heteroatoms, may alter the interaction mode between the molecule and the target protein.
Combination therapy strategy
The combined use of Gaoyichun and existing anti RSV drugs (such as Parizumab and remdesivir) may produce synergistic effects. The activation of the host IFN pathway by Gao Yichun and the direct inhibition of viral replication by antiviral drugs may achieve a "dual pronged" therapeutic effect. In addition, the combination of Gaoyichun and anti-inflammatory drugs (such as glucocorticoids) may better control the inflammatory storm after RSV infection.
Other potential applications
In addition to anti RSV, Gaoyichun has also shown application prospects in the following fields: (1) as an immune enhancer, used for the prevention or adjuvant treatment of other viral infections (such as influenza, COVID-19); (2) As an anti-inflammatory drug, used to treat chronic inflammatory diseases; (3) As a lead compound, develop novel therapeutic drugs for thyroid diseases (by regulating TPO activity). These directions are worth further exploration.
Conclusion
(R, S) - Gaoyichun, as a unique degradation product of glucosinolates in cruciferous plants, occupies a special position in the field of natural product pharmacology due to its unique oxazolidine ketone structure and multifaceted biological activities. From its initial discovery as a thyroid enlargement factor to breakthroughs in anti respiratory syncytial virus research in recent years, the research process of Gao Yichun reflects the depth and breadth of natural product research. The mechanism of inhibiting RSV replication by activating the IFNAR1/IRF3 signaling pathway and upregulating MX1 expression provides a new molecular template for developing antiviral strategies based on host immune regulation.
Despite facing challenges such as thyroid toxicity in drug development, the excellent physical and chemical properties, clear molecular targets, and predictable structural optimization space of Gao Yichun make it a highly promising lead compound. Future research should focus on: (1) further elucidating the interaction patterns between Gaoyichun and targets such as IFNAR1 and IRF3; (2) Conduct research on the structure-activity relationship of the system and optimize its therapeutic index; (3) Establish reliable animal models to evaluate their in vivo efficacy and safety; (4) Explore combination therapy strategies to maximize their therapeutic value.
From traditional plant medicine to modern drug pioneers, the research of Gao Yichun not only enriches our scientific understanding of the health benefits of cruciferous plants, but also provides new weapons for dealing with major viral infections such as RSV. With the continuous deepening of research in structural biology, medicinal chemistry, and pharmacology, it is believed that Gao Yichun and its derivatives have the potential to be transformed into clinically available antiviral drugs in the future, contributing to the cause of human health.
