Syntheses and mucosal adjuvant activity of simplified oleanolic acid saponins possessing cinnamoyl ester

Base-Promoted Glycosylation Allows Protecting Group-Free and Stereoselective O-Glycosylation of Carboxylic Acids

Here we report a simple and general method to achieve fully unprotected, stereoselective glycosylation of carboxylic acids, employing bench-stable allyl glycosyl sulfones as donors. Running the glycosylation reaction under basic conditions was crucial for the efficiencies and selectivities. Both the donor activation stage and the glycosidic bond forming stage of the process are compatible with free hydroxyl groups, thereby allowing for the use of fully unprotected glycosyl donors. This transformation is stereoconvergent, occurs under mild and metal-free conditions at ambient temperature with visible light (455 nm) irradiation, and displays remarkable scope with respect to both reaction partners. Many natural products and commercial drugs, including an acid derived from the complex anticancer agent taxol, were efficiently glycosylated. Experimental studies provide insights into the origin of the stereochemical outcome.

Synthesis of immunostimulatory saponins: A sweet challenge for carbohydrate chemists

Saponins are a large family of natural glycosides showing a wide range of biological activities. Current research efforts on saponins as vaccine adjuvants have been mainly focused on the development of synthetic analogs. By mimicking the immunomodulatory saponins from Quillaja saponaria (QS), less complex and readily accessible analogs have been synthesized to improve the industrial applicability and efficacy of saponins as vaccine adjuvants. Through the exploration of several structural modifications on the skeleton of QS saponins, including changes in the sugar and aglycone compositions as well as in the nature and configuration of the glycosidic bonds, structure-activity relationship (SAR) studies developed by Pr. Gin in the early 2010s were taken as a starting point for the development of a new generation of immunomodulatory candidates. In this review, the recent synthetic strategies and SAR studies of mono- and bidesmosidic QS saponins are discussed. Original concepts of vaccination including self-adjuvanticity and the development of saponin-based glycoconjugates are described. The synthesis and semi-synthesis of saponin alternatives to QS, such as Momordica saponin and onjisaponin derivatives, are also discussed in this review.

Potentials of saponins-based adjuvants for nasal vaccines

Respiratory infections are a major public health concern caused by pathogens that colonize and invade the respiratory mucosal surface. Nasal vaccines have the advantage of providing protection at the primary site of pathogen infection, as they induce higher levels of mucosal secretory IgA antibodies and antigen-specific T and B cell responses. Adjuvants are crucial components of vaccine formulation that enhance the immunogenicity of the antigen to confer long-term and effective protection. Saponins, natural glycosides derived from plants, shown potential as vaccine adjuvants, as they can activate the mammalian immune system. Several licensed human vaccines containing saponins-based adjuvants administrated through intramuscular injection have demonstrated good efficacy and safety. Increasing evidence suggests that saponins can also be used as adjuvants for nasal vaccines, owing to their safety profile and potential to augment immune response. In this review, we will discuss the structure-activity-relationship of saponins, their important role in nasal vaccines, and future prospects for improving their efficacy and application in nasal vaccine for respiratory infection.

Preparation of Tenuifolin from Polygala senega L. Root Using a Hydrolytic Continuous Flow System under High-Temperature, High-Pressure Conditions

An improved process for preparing tenuifolin (presenegenin 3-β-d-glucopyranoside) from the root of Polygala senega L. was developed. A crude saponin mixture extracted from P. senega was subjected to hydrolysis, and the reactivity of compounds in the extract was controlled by utilizing the combination of a flow reactor and experimental design. In addition, column chromatography with HP 20, a synthetic polystyrenic adsorbent, allowed the gram-scale preparation of tenuifolin in a continuous manner with fewer steps. This approach shortens the total time required for gram-scale preparation from 16 to 5 h in a continuous manner while improving the yield from 0.59% to 2.08% (w/w).

Efficient synthesis of diverse C-3 monodesmosidic saponins by a continuous microfluidic glycosylation/batch deprotection method

Triterpene and steroid saponins have various pharmacological activities but the synthesis of C-3 monodesmosidic saponins remains challenging. Herein, a series of C-3 glycosyl monodesmosidic saponins was synthesized via the microfluidic glycosylation of triterpenoids or steroids at the C-3 position, without the formation of orthoester byproducts, and subsequent deprotection of the benzoyl (Bz) group. This microfluidic glycosylation/batch deprotection sequence enabled the efficient synthesis of C-3 saponins with fewer purification steps and a shorter reaction time than conventional batch synthesis and stepwise microfluidic glycosylation. Furthermore, this system minimized the consumption of the imidate donor. Using this reaction system, 18 different C-3 saponins and 13 different C-28-benzyl-C-3 saponins, including 8 new compounds, were synthesized from various sugars and triterpenes or steroids. Our synthetic approach is expected to be suitable for further expanding the C-3 saponin library for pharmacological studies.

Biological and Pharmacological Effects of Synthetic Saponins

Saponins are amphiphilic molecules consisting of carbohydrate and either triterpenoid or steroid aglycone moieties and are noted for their multiple biological activities-Fungicidal, antimicrobial, antiviral, anti-inflammatory, anticancer, antioxidant and immunomodulatory effects have all been observed. Saponins from natural sources have long been used in herbal and traditional medicines; however, the isolation of complexed saponins from nature is difficult and laborious, due to the scarce amount and structure heterogeneity. Chemical synthesis is considered a powerful tool to expand the structural diversity of saponin, leading to the discovery of promising compounds. This review focuses on recent developments in the structure optimization and biological evaluation of synthetic triterpenoid and steroid saponin derivatives. By summarizing the structure-activity relationship (SAR) results, we hope to provide the direction for future development of saponin-based bioactive compounds.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Oleanolic acid 3-glucoside, a synthetic oleanane-type saponin, alleviates methylmercury toxicity in vitro and in vivo

Methylmercury (MeHg) is one of the most toxic environmental pollutants, presenting a serious health hazard worldwide. In this study, we examined the potential of derivatives of oleanolic acid (OA), such as OA 3-glucoside, OA 28-glucoside, and OA 3,28-diglucoside, to mitigate MeHg toxicity in vitro and in vivo. We found that OA 3-glucoside suppressed the cellular MeHg uptake by 63.4% compared with that of the control and improved the cell viability from 75.4% to 107.9% upon exposure to cytotoxic MeHg in Caco-2 cells. To verify the anti-MeHg activity of OA 3-glucoside, mice were orally administered MeHg (0, 1.0, or 5.0 mg kg^-1·d^-1), with or without OA 3-glucoside, and then mercury accumulation was measured in various organs of the mice. The mice co-treated with MeHg and OA 3-glucoside showed significantly lower mercury content in organs such as the cerebrum, cerebellum, liver, kidney, and spleen, with 83.1%, 68.7%, 71.7%, 82.1%, and 18.2% of those in the OA 3-glucoside-untreated group, respectively. This suggested OA 3-glucoside had the potential as an anti-MeHg compound, owing to its ability to suppress the distribution of MeHg into organs. Supporting this hypothesis, the mice treated with MeHg and OA 3-glucoside showed a tendency to survive one day longer than the control mice. Our findings suggest OA 3-glucoside administration alleviates the toxicity of MeHg by suppressing MeHg accumulation in organs.

Mucosal immunomodulatory evaluation and chemical profile elucidation of a classical traditional Chinese formula, Bu-Zhong-Yi-Qi-Tang

ETHNOPHARMACOLOGICAL EVIDENCE

With fast development and high pace life in modern society, autoimmune diseases like inflammatory bowel disease had become increasingly common. Bu-Zhong-Yi-Qi-Tang (BZYQT), a famous traditional Chinese medicine prescription (TCMP), has been used for 700 years mainly in Eastern Asia countries for the treatment of gastrointestinal and respiratory disorder, and weakness after serious diseases. These diseases were proved to be closely related to human immune system, among which, mucosal immune system is the largest immune system. So it is necessary to discover the mucosal immune related bioactive components of BZYQT.

AIM OF THE STUDY

To evaluate the mucosal immunomodulatory bioactivity of BZYQT and ingredients.

MATERIALS AND METHODS

Peyer's patches were collected from mice administrated orally with BZYQT, its related Octadecylsilane (ODS) fractions and polysaccharide part. Productions of several cytokines including IL-2, IL-4, IL-5, and IFN-γ from T lymphocytes were tested with enzyme linked immunosorbent assay (ELISA) by Peyer's patch cells ex vivo experiments. Chemical profile including low molecular part and polysaccharide part were investigated. Low molecular part of BZYQT and related ODS fractions were analyzed by ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC-Q/TOF-MS) based on LC-MS information from self-established compound library. exclusion chromatography, and chemical property has been analyzed.

RESULT

Three-days' administration of BZYQT enhanced productions of IL-4 and IFN-γ in T lymphocytes of Peyer's patches in addition to IL-2. Some hydrophobic low molecular weight fractions (30%, 70% and 100% MeOH ODS fraction), which were fractionated from BZYQT by ODS column chromatography, showed enhancing or suppressive effects on productions of IL-2, IL-4 or IL-5 in T lymphocytes of Peyer's patches after oral administration. Besides, 161 components from hydrophobic low molecular weight fractions of BZYQT were unequivocally identified or tentatively characterized by UPLC-Q/TOF-MS according to retention time behaviors and fragments, and most of them were flavonoids and saponins from Glycyrrhizae Radix, Citri Reticulatae Pericarpium, and Cimicifugae Rhizoma. Polysaccharide part was separated and purified both by anion-exchange and size. BZYQT also contained at least one neutral and three weakly or strongly acidic polysaccharides, and analysis of their chemical properties indicated that a neutral polysaccharide was glucan, and acidic polysaccharides possessed heteroglycan and pectic arabinogalactan features. Murine administration of polysaccharide fractions of BZYQT induced different changes on functions of T lymphocytes in Peyer's patches from hydrophobic low molecular weight fractions. By experiment using intranasally-immunized mice, BZYQT negatively regulated antibody response in lung as combinatorial actions of its low molecular weight ingredients and polysaccharides.

CONCLUSION

BZYQT contains several low and macromolecular weight ingredients, which affect to immune-function of T lymphocytes in Peyer's patches, and the formula expresses its regulative activity on lower respiratory immune system through combinatorial actions of these ingredients on immunocompetent cells in Peyer's patches.

Synthesis of (E)-cinnamyl ester derivatives via a greener Steglich esterification

Cinnamic acid derivatives are known antifungal, antimicrobial, antioxidant, and anticancer compounds. We have developed a facile and mild methodology for the synthesis of (E)-cinnamate derivatives using a modified Steglich esterification of (E)-cinnamic acid. Using acetonitrile as the solvent, rather than the typical chlorinated solvent, and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the coupling agent enables ester conversion in 45 min with mild heating (40-45 °C) and an average yield of 70% without need for further purification. These conditions were used to couple (E)-cinnamic acid with 1° and 2° aliphatic alcohols, benzylic and allylic alcohols, and phenols. This work demonstrates a facile and greener methodology for Steglich esterification reactions.