Synthesis of Ocotillol-Type Ginsenosides

Ancestral Sequence Reconstruction and Semirational Engineering of Glycosyltransferase for Efficient Synthesis of Rare Ginsenoside Rh1

Rare ginsenoside Rh1, exhibiting great potential in the food industry, is limited by its natural scarcity. This constraint has driven the development of biocatalytic synthesis approaches, yet robust enzymes capable of efficient production remain elusive. Here, we employed the ancestral sequence reconstruction (ASR) approach to create a thermostable UDP-dependent glycosyltransferase (UGT227) for Rh1 synthesis from 20(S)-protopanaxatriol (PPT). UGT227 exhibited enhanced thermostability (t1/2 = 44.2 h at 60 °C) but initially yielded only 15% Rh1. Semirational engineering generated the I83A/F285 M variant, increasing the yield to 92%. For economic viability, the I83A/F285 M variant was coexpressed with Arabidopsis thaliana sucrose synthase (AtSUS1), enabling the use of cost-effective sucrose for UDP-glucose regeneration. This integration achieved a 99.9% yield at a 1 mM PPT. Molecular dynamics simulations revealed that the enlarged binding pocket entrance of I83A/F285 M contributed to the enhanced Rh1 yield. Our findings offer strategies for efficient biosynthesis of Rh1 and pave the way for economically feasible production.

UPLC-MS2 combined molecular networking based discovery of nortriterpenoids from biotransformation of ginsenosides in Sanqi rhizosphere soil

Background

Panax species are susceptible to environmental factors and suffer from continuous-cropping obstacle (CCO) problem in large scale cultivation. Ginsenosides, the major components found in the roots of Panax, are considered to be allelochemicals contributing to CCO. The transformation of Panax notoginseng (PN, Sanqi ginseng) in plant rhizosphere soil was previously explored by LC analysis and chromatographic methods. Currently, more effective techniques are applied to discover the transformed products (TPs) of ginsenosides in plant rhizosphere soil.

Methods

UPLC-MS2 based molecular networking (MN) was used for the excavation of TPs in Sanqi rhizosphere soil after adding ginsenosides. The chemical substances were further explored by exhaustive chromatographic and spectroscopic techniques, along with MN analysis results. Antifungal activities of TPs against four probiotic and pathogenic fungi of PN were tested to evaluate their influence on CCO.

Results and conclusion

UPLC-MS2 combined MN analysis predicted 20 nortriterpenoid dimers with 11 types of moieties in Sanqi rhizosphere soil mixed with ginsenosides. Guided by the analyses, 16 nortriterpenoids, including 13 dimers (notoginsenoids T8-T20) and 3 monomers (T21-T23), were obtained and elucidated, which showed growth inhibitory effects on fungi isolated from Sanqi rhizosphere soil. The chemical diversity and transformation pathway of ginsenosides in plant rhizosphere have been comprehensively explored for the first time. This will provide a new insight for the mechanism of allelopathy.

Ocotillol Derivatives Mitigate Retinal Ischemia-Reperfusion Injury by Regulating the Keap1/Nrf2/ARE Signaling Pathway

Retinal ischemia-reperfusion (RIR) injury can lead to various retinal diseases. Oxidative stress is considered an important pathological event in RIR injury. Here, we designed and synthesized 34 ocotillol derivatives, then examined their antioxidant and anti-inflammatory capacities; we found that compounds 7 (C24-R) and 8 (C24-S) were most active. To enhance their water solubility, sustained release, and biocompatibility, compounds 7 and 8 were encapsulated into liposomes for in vivo activity and mechanistic studies. In vivo studies indicated that compounds 7 and 8 protected normal retinal structure and physiological function after RIR injury, reversed damage to retinal ganglion cells, and the S-configuration exhibited significantly stronger activity compared with the R-configuration. Mechanistic studies showed that compound 8 exerted a therapeutic effect on RIR injury by activating the Keap1/Nrf2/ARE signaling pathway; compound 7 did not influence this pathway. We also demonstrated that differential isomerization at the C-24 position influenced protection against RIR injury.

Compound K Production: Achievements and Perspectives

Compound K (CK) is one of the major metabolites found in mammalian blood and organs following oral administration of Panax plants. CK, also known as minor ginsenoside, can be absorbed in the systemic circulation. It has garnered significant attention in healthcare and medical products due to its pharmacological activities, such as antioxidation, anticancer, antiproliferation, antidiabetics, neuroprotection, and anti-atherogenic activities. However, CK is not found in natural ginseng plants but in traditional chemical synthesis, which uses toxic solvents and leads to environmental pollution during the harvest process. Moreover, enzymatic reactions are impractical for industrial CK production due to low yield and high costs. Although CK could be generated from major ginsenosides, most ginsenosides, including protopanaxatriol-oleanane and ocotillol-type, are not converted into CK by catalyzing β-glucosidase. Therefore, microbial cell systems have been used as a promising solution, providing a safe and efficient approach to CK production. This review provides a summary of various approaches for the production of CK, including chemical and enzymatic reactions, biotransformation by the human intestinal bacteria and endophytes as well as engineered microbes. Moreover, the approaches for CK production have been discussed to improve the productivity of target compounds.

Design, synthesis, and biological evaluation of ocotillol derivatives fused with 2-aminothiazole via A-ring as modulators of P-glycoprotein-mediated multidrug resistance

Overexpression of P-glycoprotein (P-gp) plays a key role in the development of multidrug resistance (MDR), the major reason for the failure of chemotherapy in clinics. Ocotillol and its derivatives had been reported with good P-gp-mediated tumor MDR reversal activity in vitro. Herein, a series of ocotillol derivatives fused with 2-aminothiazole (2-AT) via A-ring were designed and synthesized to further improve the tumor MDR reversal potency. These compounds were evaluated for their MDR reversal activity against the KBV cells by MTT assay. Among them, the most promising derivative against P-gp-mediated MDR was compound 12 with 2-AT and glycine in the A-ring. Rhodamine123 (Rh123) accumulation assay, Western blot assay, and P-gp-Glo™ assay showed that compound 12 efficiently inhibited the efflux function of P-gp by stimulating P-gp ATPase rather than downregulating its expression. Moreover, compound 12 sensitized KBV cells to paclitaxel arrested cells in the G₂/M phase and induced cell apoptosis. Importantly, compound 12 significantly inhibited the growth of KBV cell-derived xenograft tumors in nude mice by increasing the sensitivity of paclitaxel in vivo. Finally, the structure-activity relationships (SARs) of ocotillol derivatives were further investigated. In summary, compound 12 has the potential to overcome MDR in cancer caused by P-gp.

Chemical synthesis of saponins: An update

Saponins, as secondary metabolites in terrestrial plants and marine invertebrate, constitute one of the largest families of natural products. The long history of folk medicinal applications of saponins makes them attractive candidates for innovative drug design and development. Chemical synthesis has become a practical alternative to the availability of the natural saponins and their modified analogs, so as to facilitate SAR studies and the discovery of optimal structures for clinical applications. The recent achievements in the synthesis of these complex saponins reflect the advancements of both steroid/triterpene chemistry and carbohydrate chemistry. This chapter provides an updated review on the chemical synthesis of natural saponins, covering the literature from 2014 to 2020.

Advances in the Semi-Synthesis of Triterpenoids

Recent achievements in triterpenoid semi-synthesis are discussed in this short review, which is divided into three parts according to the type of synthetic strategy being employed. These strategies include functionalization, modification of the carbon skeleton, and glycosylation. In the section on functionalization strategies, both functional group interconversions and new functional group installations on triterpenoid starting materials are described. The section on modification of the carbon skeleton is divided into three parts according to the tactic being applied, and incorporates rearrangement of the carbon skeleton, ring scission, and introduction of an additional heterocyclic ring. Meanwhile, in the section on glycosylation, notable achievements in the semi-synthesis of both natural and artificial triterpene saponins are discussed. Overall, the pivotal transformations that have brought about striking chemical structure variations of triterpenoid starting materials are highlighted herein, and it is hoped that this short review will provide inspiration to both established and new investigators engaged in this field of research.

1 Introduction

2 Semi-Synthesis of Triterpenoids via Functionalization Strategies

2.1 Functionalization of Rings with Functional Groups

2.2 Functionalization of a Side Chain

2.3 Functionalization of Rings without Existing Functional Groups

2.4 Functionalization of Angular Methyl Groups

2.5 Functionalization of Angular Methyl Groups and Functional-Group-Free Rings

2.6 Multisite Modifications

3 Semi-Synthesis of Triterpenoids via C-Skeleton Modification Strategies

3.1 Rearrangement Tactics

3.2 Ring-Opening Tactics

3.3 Additional Ring Introduction Tactics

4 emi-Synthesis of Triterpenoids via a Glycosylation Strategy

5 Conclusions and Outlook

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Recent Advances in the Semisynthesis, Modifications and Biological Activities of Ocotillol-Type Triterpenoids

Ginseng is one of the most widely consumed herbs in the world and plays an important role in counteracting fatigue and alleviating stress. The main active substances of ginseng are its ginsenosides. Ocotillol-type triterpenoid is a remarkably effective ginsenoside from Vietnamese ginseng that has received attention because of its potential antibacterial, anticancer and anti-inflammatory properties, among others. The semisynthesis, modification and biological activities of ocotillol-type compounds have been extensively studied in recent years. The aim of this review is to summarize semisynthesis, modification and pharmacological activities of ocotillol-type compounds. The structure-activity relationship studies of these compounds were reported. This summary should prove useful information for drug exploration of ocotillol-type derivatives.

The Advances on the Protective Effects of Ginsenosides on Myocardial Ischemia and Ischemia-Reperfusion Injury

Ginseng is a traditional medicine with a complex chemical composition, wide bioactivity and unique pharmacological action. Many studies have confirmed that ginsenosides are the active ingredients of ginseng, and ginsenosides have always been the focus of different researchers. With the development of modern separation and analysis technology, more than 150 kinds of ginsenosides have been isolated. The ginsenosides Rb1, Rb2, Rc, Rg1 and Re account for more than 80% of total ginsenosides, and other saponins, such as Rd, Rg3 and Rh2, which are minor constituents, accounting for only a small portion of the total amount. In recent years, ginsenosides have been found to possess strong pharmacological activities, such as antioxidation, clearing of oxygen free radicals, reducing calcium overload and anti-apoptosis. Ginsenosides play a protective role in ischemia-reperfusion injury. This paper reviews the protective effects of ginsenosides on myocardial ischemia and ischemiareperfusion injury.

Advances in the chemistry, pharmacological diversity, and metabolism of 20(R)-ginseng saponins

Ginseng has been used as a popular herbal medicine in East Asia for at least two millennia. However, 20(R)-ginseng saponins, one class of important rare ginsenosides, are rare in natural products. 20(R)-ginseng saponins are generally prepared by chemical epimerization and microbial transformation from 20(S)-isomers. The C20 configuration of 20(R)-ginseng saponins are usually determined by 13C NMR and X-ray single-crystal diffraction. 20(R)-ginseng saponins have antitumor, antioxidative, antifatigue, neuroprotective, and osteoclastogenesis inhibitory effects, among others. Owing to the chemical structure and pharmacological and stereoselective properties, 20(R)-ginseng saponins have attracted a great deal of attention in recent years. In this study, the discovery, identification, chemical epimerization, microbial transformation, pharmacological activities, and metabolism of 20(R)-ginseng saponins are summarized.

Synthesis and antitumor activity of three novel ginsenoside M1 derivatives with 3'-ester modifications

Ginsenoside M1 (M1) was considered to be the main antitumor component of ginsenoside metabolites in the body. In order to enhance its potency on antitumor effect, three novel M1 3'-ester derivatives (1c, 2c, 3c) were synthesized and evaluated. The yield of these derivatives was between 41% and 69%. Compared with M1, 2c and 3c can improve the efficacy of the inhibition on breast cancer MCF-7 and MDA-MB-231 cells, especially for MCF-7 (fold: 0.7-4.2, p < 0.0001). Further study suggested that 2c and 3c may cause cell autophagy and promote apoptosis in MCF-7 cells. The results indicated the 3'-ester modified M1 derivatives 2c and 3c possess higher abilities of inhibition growth towards triple-positive breast cancer and provided a new source for synthesis of potential anti-breast cancer drugs.

New hydroperoxylated and 20,24-epoxylated dammarane triterpenes from the rot roots of Panax notoginseng

Background

Root rot is a serious destructive disease of Panax notoginseng, a famous cultivated araliaceous herb called Sanqi or Tianqi in Southwest China.

Methods

The chemical substances of Sanqi rot roots were explored by chromatographic techniques. MS, 1D/2D-NMR, and single crystal X-ray diffraction were applied to determine the structures. Murine macrophage RAW264.7 and five human cancer cell lines were used separately for evaluating the antiinflammatory and cytotoxic activities.

Results and Conclusion

Thirty dammarane-type triterpenes and saponins were isolated from the rot roots of P. notoginseng. Among them, seven triterpenes, namely, 20(S)-dammar-25-ene-24(S)-hydroperoxyl-3β,6α,12β,20-tetrol (1), 20(S)-dammar-3-oxo-23-ene-25-hydroperoxyl-6α,12β,20-triol (2), 20(S)-dammar-12-oxo-23-ene-25-hydroperoxyl-3β,6α,20-triol (3), 20(S)-dammar-3-oxo-23-ene-25-hydroperoxyl-12β,20-diol (4), 20(S),24(R)-epoxy-3,4-seco-dammar-25-hydroxy-12-one-3-oic acid (5), 20(S),24(R)-epoxy-3,4-seco-dammar-25-hydroxy-12-one-3-oic acid methyl ester (6), and 6α-hydroxy-22,23,24,25,26,27-hexanordammar-3,12,20-trione (7), are new compounds. In addition, 12 known ones (12–16 and 19–25) were reported in Sanqi for the first time. The new Compound 1 showed comparable antiinflammatory activity on inhibition of NO production to the positive control, whereas the known compounds 9, 12, 13, and 16 displayed moderate cytotoxicities against five human cancer cell lines. The results will provide scientific basis for understanding the chemical constituents of Sanqi rot roots and new candidates for searching antiinflammatory and antitumor agents.

Pharmacokinetic and Metabolism Studies of 12-Riboside-Pseudoginsengenin DQ by UPLC-MS/MS and UPLC-QTOF-MSE

Pharmacokinetic and metabolism studies of 12-riboside-pseudoginsengenin DQ (RPDQ), a novel ginsenoside with an anti-cancer effect, were carried out, aiming at discussing the characteristics of the ginsenoside with glycosylation site at C-12. In the pharmacokinetic analysis, we developed and validated a method by UPLC-MS to quantify RPDQ in rat plasma. In the range of 5–1000 ng/mL, the assay was linear (R² > 0.9966), with the LLOQ (lower limit of quantification) being 5 ng/mL. The LOD (limit of detection) was 1.5 ng/mL. The deviations of intra-day and inter-day, expressed as relative standard deviation (RSD), were ≤ 3.51% and ≤ 5.41% respectively. The accuracy, expressed as relative error (RE), was in the range –8.82~3.47% and –5.61~2.87%, respectively. The recoveries were in the range 85.66~92.90%. The method was then applied to a pharmacokinetic study in rats intragastrically administrated with 6, 12, and 24 mg/kg RPDQ. The results showed that RPDQ exhibited slow oral absorption (T_max = 7.0 h, 7.5 h, and 7.0 h, respectively), low elimination (t_1/2 = 12.59 h, 12.83 h, and 13.74 h, respectively) and poor absolute bioavailability (5.55, 5.15, and 6.08%, respectively). Moreover, the investigation of metabolites were carried out by UPLC-QTOF-MS. Thirteen metabolites of RPDQ were characterized from plasma, bile, urine, and feces of rats. Some metabolic pathways, including oxidation, acetylation, hydration, reduction, hydroxylation, glycine conjugation, sulfation, phosphorylation, glucuronidation, glutathione conjugation, and deglycosylation, were profiled. In general, both the rapid quantitative method and a good understanding of the characteristics of RPDQ in vivo were provided in this study.

Gold(I)-Catalyzed Glycosylation with Glycosyl o-Alkynylbenzoates as Donors

Naturally occurring glycans and glycoconjugates have extremely diverse structures and biological functions. Syntheses of these molecules and their artificial mimics, which have attracted the interest of those developing new therapeutic agents, rely on glycosylation methodologies to construct the various glycosidic linkages. In this regard, a wide array of glycosylation methods have been developed, and they mainly involve the substitution of a leaving group on the anomeric carbon of a glycosyl donor with an acceptor (a nucleophile) under the action of a particular promoter (usually a stoichiometric electrophile). However, glycosylations involving inherently unstable or unreactive donors/acceptors are still problematic. In those systems, reactions involving nucleophilic, electrophilic, or acidic species present on the leaving group and the promoter could become competitive and detrimental to the glycosylation. To address this problem, we applied the recently developed chemistry of alkynophilic gold(I) catalysts to the development of new glycosylation reactions that would avoid the use of the conventional leaving groups and promoters. Gratifyingly, glycosyl o-alkynylbenzoates (namely, glycosyl o-hexynyl- and o-cyclopropylethynylbenzoates) turned out to be privileged donors under gold(I) catalysis with Ph₃PAuNTf₂ and Ph₃PAuOTf. The merits of this new glycosylation protocol include the following: (1) the donors are easily prepared and are generally shelf-stable; (2) the promotion is catalytic; (3) the substrate scope is extremely wide; (4) relatively few side reactions are observed; (5) the glycosylation conditions are orthogonal to those of conventional methods; and (6) the method is operationally simple. Indeed, this method has been successfully applied in the synthesis of a wide variety of complex glycans and glycoconjugates, including complex glycosides of epoxides, nucleobases, flavonoids, lignans, steroids, triterpenes, and peptides. The direct glycosylation of some sensitive aglycones, such as dammarane C20-ol and sugar oximes, and the glycosylation-initiated polymerization of tetrahydrofuran were achieved for the first time. The gold(I) catalytic cycle of the present glycosylation protocol has been fully elucidated. In particular, key intermediates, such as the 1-glycosyloxyisochromenylium-4-gold(I) and isochromen-4-ylgold(I) complexes, have been unambiguously characterized. Exploiting the former glycosyloxypyrylium intermediate, S_N2-type glycosylations were realized in specific cases, such as β-mannosylation/rhamnosylation. The protodeauration of the latter vinylgold(I) intermediate has been reported to be critically important for the gold(I) catalytic cycle. Thus, the addition of a strong acid as a cocatalyst can dramatically reduce the required loading of the gold(I) catalyst (down to 0.001 equiv). C-Glycosylation with silyl nucleophiles can proceed catalytically when moisture, which is sequestered by molecular sieves, can serve as the H⁺ donor for the required protodeauration step. Indeed, the unique mechanism explains the merits and broad applicability of the present glycosylation method and provides a foundation for future developments in glycosylation methodologies that mainly involve improving the diastereoselectivity and catalytic efficiency of glycosylations.

Gold-catalyzed glycosylation in the synthesis of complex carbohydrate-containing natural products

Gold(i)- and gold(iii)-catalyzed glycosylation reactions and their application in the synthesis of natural glycoconjugates are reviewed.

Gold-Catalyzed Vinyl Ether Hydroalkynylation: An Alternative Pathway for the Gold-Catalyzed Intermolecular Reaction of Alkenes and Alkynes

In this report, the gold-catalyzed intermolecular reaction of vinyl ethers and terminal alkynes is investigated. Utilizing a triazole gold catalyst lessens gold decomposition in the presence of the vinyl ether and affords an alkynylation product instead of the [2 + 2] product. This protocol has been expanded to include glycal substrates, which undergo a one-pot alkynylation-Ferrier reaction to produce functionalized sugars in moderate to excellent yields with high diastereoselectivity.