Introduction/Overview
Natural products have always been an important source of innovative drug discovery, and their unique chemical structures and diverse biological activities provide valuable clues for addressing clinical challenges. Among numerous natural compounds with medicinal value, Pseudolaric acid B-O-beta-D-glucopyranoside (CAS number: 98891-41-9), as a diterpenoid acid glycoside isolated from traditional medicinal plants, has attracted the attention of pharmacological researchers in recent years due to its significant antifungal activity. With the increase of incidence rate of invasive fungal infections and the emergence of drug-resistant strains worldwide, the development of new, efficient and low toxic antifungal drugs has become an urgent clinical need. Tujingpi acetic acid glycoside exhibits broad-spectrum and potent antifungal potential by acting on multiple key targets such as the ergosterol synthesis pathway, efflux pumps, and cell wall synthesis in fungal cell membranes, particularly exhibiting good inhibitory activity against clinically challenging drug-resistant fungi such as Candida albicans and Candida albicans. The purpose of this article is to systematically review the chemical properties, plant sources, pharmacological activities, mechanisms of action, pharmacological evaluation, and clinical application prospects of acetic acid glycosides in the bark of Sophora japonica, in order to provide comprehensive scientific references for the in-depth research of this compound and the development of future antifungal drugs.
Chemical structure and physicochemical properties
Tujingpi acetic acid glycoside is a glycosylated derivative of Pseudolaric acid B. Its chemical structure consists of a highly oxidized rosin alkyl diterpenoid acid core (Tujingpi acid B) connected to a β - D-glucopyranose unit via an O-glycosidic bond. This glycosylation modification significantly alters the polarity and biological activity spectrum of the parent compound.
Its molecular formula is C31H38O12 and its molecular weight is 594.6100. From the analysis of parameters related to drug properties, the compound exhibits the following key physicochemical properties: the calculated lipid water partition coefficient (LogP) is 0.6070, indicating moderate lipophilicity, but overall leaning towards hydrophilicity. The topologically polar surface area (TPSA) is as high as 195.35 Å ², mainly attributed to the presence of multiple hydroxyl, carboxyl, and oxygen atoms on the sugar ring in the molecule, which provide abundant hydrogen bond donor and acceptor sites. The high TPSA and moderate LogP together determine its relatively good water solubility, with a calculated value of 0.5729 mg/mL, which is beneficial for its dissolution and distribution in organisms. However, its high polarity also limits its ability to penetrate the blood-brain barrier, and predictions indicate low blood-brain barrier permeability. In early safety screening, the compound did not show significant hERG potassium channel inhibitory activity (predicted as' no '), indicating a low potential risk of arrhythmia. In addition, the Ames test predicted a value of 0.0, indicating that it may not have direct genetic toxicity. These physicochemical and preliminary safety parameters have laid a foundation with certain advantages for its subsequent development.
Plant sources and extraction methods
The main source of acetic acid glycosides in the bark of Platycodon grandiflorus comes from the genus Platycodon in the Pinaceae family（Pseudolarix amabilis The root bark or near root bark of Nelson Rehder, also known as "soil bark" in traditional Chinese medicine, has been used to treat skin diseases such as scabies and eczema.
Its extraction and separation is a multi-step refinement process. Usually, the dried soil bark raw material is first crushed and subjected to reflux extraction or ultrasound assisted extraction using medium polarity organic solvents such as ethanol, methanol, or acetone to fully extract the diterpenoid acid components. After the crude extract was concentrated under reduced pressure, it was preliminarily enriched using solvent partitioning method (such as partitioning in different proportions of ethyl acetate water system), and the acetic acid glycoside of Fructus Sophorae tended to be enriched in the more polar regions due to its glycoside structure. Further purification mainly relies on modern chromatographic techniques. Silica gel column chromatography is commonly used for preliminary separation, using solvent systems of different polarities (such as chloroform methanol gradient elution) for elution. Subsequently, fine purification was carried out by combining reverse phase medium pressure or high pressure liquid chromatography (such as C18 packing, methanol water or acetonitrile water as mobile phase), and finally high-purity acetic acid glycoside monomers were obtained by preparative high-performance liquid chromatography. Structural identification is accomplished through the comprehensive use of techniques such as nuclear magnetic resonance (NMR, including 1H-NMR, 13C-NMR, 2D-NMR), mass spectrometry (MS), and infrared spectroscopy (IR). In recent years, there have also been studies exploring the use of efficient separation techniques such as high-speed countercurrent chromatography to optimize its preparation process.
Pharmacological activity research
The core pharmacological activity of acetic acid glycosides in the bark of Polygonatum sibiricum is focused on its excellent antifungal effect, while also showing regulatory potential for other pathological processes.
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Antifungal activity A large number of in vitro studies have confirmed that the acetic acid glycosides of Sophora japonica have broad-spectrum inhibitory activity against various clinically relevant pathogenic fungi. It is effective against Candida albicans（Candida albicans）Smooth Candida albicans（C. glabrata）Candida krusei（C. krusei）And Cryptococcus neoformans（Cryptococcus neoformans）The minimum inhibitory concentration (MIC) value of yeast is usually in the micromolar range, with activity stronger than or equivalent to some commonly used antifungal drugs in clinical practice. It is worth noting that it also exhibits good inhibitory effects on azole (such as fluconazole) and polyene (such as amphotericin B) resistant strains, making it uniquely valuable in combating drug-resistant fungal infections. In addition, it also has an inhibitory effect on some skin fungi, such as Trichophyton rubrum.
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Antitumor activity The parent compound of resveratrol B has been widely reported to have significant anti proliferative and apoptosis inducing activities. Although there is relatively little research on the direct anti-tumor effects of acetic acid glycoside in Sophora flavescens, some studies suggest that it may exhibit certain growth inhibitory activity on certain cancer cell lines (such as liver cancer and leukemia cells) by affecting the cell cycle, inducing tumor cell apoptosis, and other pathways. However, its activity is usually weaker than its glycoside, Sophora flavescens B, suggesting that glycosylation may alter its targeting.
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Anti inflammatory and immune regulatory activity Preliminary studies have shown that the acetic acid glycosides of Sophora japonica may exhibit anti-inflammatory effects in vitro models by inhibiting inflammatory signaling pathways such as NF - κ B and downregulating the expression of pro-inflammatory factors such as TNF - α and IL-6. This is consistent with its traditional use for treating inflammatory skin diseases.
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Other activities Occasional reports also involve potential activities such as anti angiogenesis and anti parasitic effects, but further research is needed to verify them.
Mechanism of action and molecular targets
The antifungal mechanism of acetic acid glycosides in Turmeric bark is complex and involves multi-target effects, which may be the key to its ability to overcome or delay the development of drug resistance.
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Inhibition of ergosterol biosynthesis This is one of its core mechanisms of action. Ergosterol is a key sterol component of fungal cell membranes, equivalent to cholesterol in mammalian cells. The acetic acid glycosides in the bark of Eucommia ulmoides can significantly inhibit the synthesis pathway of ergosterol. Its main targets include:
- ERG11/CYP51A1 This is the coding gene for lanosterol 14 α - demethylase (ERG11) and its product (CYP51), which are the main targets of azole drugs. The acetic acid glycosides in the bark of Polygonatum sibiricum may directly or indirectly inhibit the enzyme activity, leading to the accumulation of 14 α - methylsterols, ergosterol deficiency, and disruption of membrane integrity.
- CYP51 Generalized sterol 14 α - demethylase target.
- MLS1 Possible involvement of enzymes related to sterol metabolism, but the specific mechanism of action remains to be clarified.
The inhibition of ergosterol synthesis leads to a decrease in fungal cell membrane fluidity, an increase in permeability, and dysfunction of membrane-bound enzymes, ultimately resulting in leakage of cell contents and cell death.
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Affects cell wall synthesis The fungal cell wall is another important target. Research has shown that acetic acid glycosides from the bark of Polygonatum sibiricum can interfere with the synthesis of cell wall β -1,3-glucan.
- FKS1 This gene encodes the catalytic subunit of β -1,3-glucan synthase and is a target of echinocandin drugs. Tujingpi acetic acid glycoside may weaken the cell wall structure by affecting the function or expression of FKS1, making it more sensitive to osmotic pressure and producing a synergistic lethal effect with membrane damage.
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Inhibit drug efflux pump One of the important mechanisms of fungal drug resistance is overexpression of drug efflux pump proteins, which expel drugs from the extracellular space. Tujingpi acetic acid glycoside has been proven to be an effective inhibitor of efflux pumps.
- CDR1 and MDR1 These two genes encode ABC transporters and major chemokine superfamily transporters, respectively, and are the most important efflux pumps for azole drugs in Candida. Tujingpi acetate glycoside can inhibit the function of these pumps, reduce the efflux of self and other antifungal drugs (such as fluconazole), thereby reversing drug resistance and improving the efficacy of combination therapy.
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Inducing the accumulation of reactive oxygen species (ROS) and cell apoptosis In addition to directly targeting the cell membrane and cell wall, resveratrol can also induce a sharp increase in intracellular ROS levels in fungal cells, leading to oxidative stress, mitochondrial damage, and possibly triggering programmed cell death like processes.
In summary, the acetic acid glycosides in the bark of Polygonatum sibiricum attack fungi through a "multi pronged" approach, while also acting on membrane sterol synthesis, cell wall construction, and drug efflux systems. This multi-target characteristic makes it less prone to drug resistance and has the potential for synergistic enhancement.
Evaluation of drug properties and pharmacokinetics
Based on its physical and chemical parameters and preliminary research, a preliminary evaluation of the pharmacological properties of acetic acid glycosides in Sophora japonica was conducted
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Absorption, distribution, metabolism, excretion (ADME)：
- absorb Moderate LogP and good water solubility are beneficial for its oral absorption, but larger molecular weight and higher TPSA may limit its transmembrane passive diffusion efficiency, and its oral bioavailability needs to be confirmed by in vivo experiments.
- distribution The predicted blood-brain barrier permeability is low, which means it may not be suitable for fungal infections in the central nervous system, but it also reduces the potential risk of central neurotoxicity. The distribution characteristics of its organization need to be further studied through animal experiments.
- Metabolism As a glycoside compound, it may be hydrolyzed by β - glucosidase in the intestine or liver, releasing quercetin B glycoside. The metabolic pathways, main metabolites, and enzyme systems involved in metabolism (such as CYP450) of aglycones and glycoside forms are not yet clear, which is the focus of their pharmacokinetic studies.
- excretion Glycosides with higher polarity may be mainly excreted through the kidneys, while aglycones may be excreted through bile or the kidneys.
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Preliminary evaluation of safety The calculated toxicology prediction shows no risk of hERG inhibition and Ames mutagenicity, which is a positive signal. However, the potential hepatotoxicity, nephrotoxicity, or gastrointestinal irritation of natural diterpenoids need to be comprehensively evaluated through systematic in vitro cytotoxicity experiments and in vivo acute and long-term toxicity experiments. The parent compound, oxalic acid B, has a certain degree of irritation, and it is worth noting whether the toxicity decreases after glycosylation.
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Pharmaceutical considerations Due to its acceptable water solubility, the development of injections (such as freeze-dried powder injections) is technically feasible. If the oral bioavailability is low, it may be necessary to improve its absorption and stability through formulation techniques (such as solid dispersions, liposomes, nanoparticles) or structural modifications (prodrugs).
At present, there is still a lack of research reports on the pharmacokinetics of the acetic acid glycoside system in Sophora japonica, which is a key data gap that must be filled in order to move towards drug development.
Clinical application prospects and prospects
Tujingpi acetate glycoside has shown broad clinical application prospects, but also faces a series of challenges.
prospect：
1. New antifungal drug candidates Especially suitable for treating invasive infections caused by drug-resistant Candida (such as Candida albicans, Candida auricula), such as candidemia, peritonitis, etc. Its multi-target mechanism of action provides a new strategy to overcome the problem of drug resistance in existing drugs.
2. Synergistic agents for combination therapy Based on its efflux pump inhibitory activity, when combined with azole drugs such as fluconazole and voriconazole, it can effectively reverse drug resistance, reduce the dosage and toxic side effects of existing drugs, and has important clinical synergistic value.
3. Development of topical preparations for local use: For fungal infections of skin and mucous membrane (such as vaginal candidiasis, tinea pedis), develop cream, gel, suppository and other external dosage forms, use their direct and local strong antifungal effects, and may avoid the pharmacokinetics and toxicity problems brought by the system.
4. Lead compounds for structural optimization Using it as the parent nucleus, systematic medicinal chemical modifications (such as glycosylation and side chain modifications) are expected to obtain derivatives with stronger activity, lower toxicity, and better pharmacokinetic properties.
Challenges and Prospects：
1. In depth mechanism research More precise elucidation of its direct interaction mode with targets such as ERG11 and FKS1 is needed (such as eutectic structure analysis), and exploration of whether there are other unknown targets.
2. Systematic evaluation of drug properties It is necessary to conduct comprehensive preclinical pharmacokinetic and toxicological studies as soon as possible to clarify their in vivo fate and safety window.
3. Resources and Synthesis The resources of Jinqiansong are limited, and the full chemical synthesis route has multiple steps and low yield. In the future, it is necessary to develop efficient and green synthetic or semi synthetic methods, or explore biosynthetic pathways such as microbial fermentation, to meet the needs of large-scale drug development.
4. Clinical translational research After completing sufficient preclinical research, gradually advance formulation research and pharmacological validation, and ultimately enter the clinical trial stage to verify its safety and efficacy in humans.
Conclusion
As a natural diterpenoid glycoside derived from traditional Chinese medicine, Tujingpi acetic acid glycoside has become an attractive lead compound in the field of antifungal drug development due to its unique multi-target antifungal mechanism, significant anti drug resistance activity, and relatively good initial pharmacological parameters. It not only provides new candidate molecules to address the increasingly severe threat of drug-resistant fungal infections, but also provides an example for understanding the pleiotropy mode of action of natural products. However, the road from lead compounds to successful drugs is still long, and interdisciplinary research teams urgently need to carry out collaborative research in deep analysis of the mechanism of action, systematic evaluation of pharmacokinetics and toxicology, efficient preparation processes, and innovative formulation development. With the continuous deepening of research and the development of technology, the acetic acid glycoside in the bark of Sophora japonica is expected to achieve a breakthrough from basic research to clinical application in the field of antifungal therapy in the future, benefiting patients worldwide.
