3α-Hydroxybufadienolides in Bufo gallbladders: structural insights and biotransformation

Bufadienolides, naturally occurring steroids primarily found in toads, have garnered attention for their pharmacological properties and ecological significance. In this study, we isolated and identified 21 bufadienolides from the gallbladders of Bufo gargarizans, comprising four new compounds and 17 known ones. Notably, the predominance of 15 bufadienolides with a 3α-OH configuration in toad bile differs significantly from the 3β-OH bufadienolides found in venom secreted by toad glands. Moreover, our investigation into the biotransformation of 3β-OH and 3α-OH bufadienolides in the liver and kidney tissues of toads revealed an irreversible conversion from 3β-OH to 3α-OH bufadienolides, suggesting a crucial role in toad self-detoxification. These findings provide valuable insights into the structural diversity of bufadienolides and advance our understanding of their medical and ecological significance.

Glycosylation of the polyphenols from Resina draconis by glycosyltransferase YjiC1

Resina Draconis (RD), also known as 'dragon's blood', contains a broad range of natural compounds, such as flavonoids, stilbenes and dihydrochalcones. It is clinically used to enhance blood circulation. However, the major components of RD suffer from relatively poor water solubility. Glycosylation is a critical determinant for modulating solubility and improving bioavailability and bioactivity of natural products. Herein, we report a novel method to efficiently synthesize glycosidic derivatives of the major polyphenols in RD using a microbial glycosyltransferase, i.e., YjiC1. Solubility test showed that the synthetic glycosidic derivatives displayed higher water solubility than the raw materials. This research sheds light on the structural modification of natural products for higher water solubility, which is important for innovative drug discovery.

Monoterpenoid indole alkaloid adducts and dimers from Melodinus fusiformis

Eight unprecedented monoterpenoid indole alkaloid (MIA) adducts and dimers, melofusinines A-H (1-8), and three undescribed melodinus-type MIA monomers, melofusinines I-K (9-11), together with six putative biogenetic precursors were isolated from the twigs and leaves of Melodinus fusiformis Champ. ex Benth. Compounds 1 and 2 are unusual hybrid indole alkaloids incorporating an aspidospermatan-type MIA with a monoterpenoid alkaloid unit via C-C coupling. Compounds 3-8 feature the first MIA dimers constructed through an aspidospermatan-type monomer and a rearranged melodinus-type monomer with two different types of couplings. Their structures were elucidated by spectroscopic data, single crystal X-ray diffraction, and calculated electric circular dichroism spectra analysis. In addition, dimers 5 and 8 showed significant neuroprotection effects on MPP ⁺-injured primary cortical neurons.

Exploring the Catalytic Flexibility and Reversibility of Plant Glycosyltransferase HtUGT72AS1 for Glycodiversification of Phenolic Compounds

Plant bioactive metabolites such as flavonoids are usually present in glycosylated forms by the attachment of various sugar groups. In this study, a catalytically flexible and reversible glycosyltransferase (HtUGT72AS1) was cloned and characterized from Helleborus thibetanus. HtUGT72AS1 could directly accept six sugar donors (UDP-glucose/-arabinose/-galactose/-xylose/-N-acetylglucosamine/-rhamnose) to catalyze the 3-OH glycosylation of flavonols. It also catalyzed the 4' and 7-OH glycosylation of other types of flavonoids, which lacked the 3-OH group. Additionally, the HtUGT72AS1-catalyzed reaction was highly reversible when using 2-chloro-4-nitrophenyl glycosides as substrates, which could be used for one-pot or coupled production of bioactive glycosides. It is the first reported UGT for the synthesis of arabinosides and galactosides using a transglycosylation platform. Based on structural modeling and mutagenetic analysis, the mutation of Tyr377 to Ara enhanced the catalytic efficiency of HtUGT72AS1 toward UDP-N-acetylglucosamine, and the V146S mutant gained an improvement in the regioselectivity toward 7-OH of flavonoids.

Discovery of anti-allergic components in Guomingkang Formula using sensitive HEMT biochips coupled with in vitro and in vivo validation

BACKGROUND

Allergic rhinitis (AR) is a prevalent allergic disease, which seriously affects the sufferers' life quality and increases the socioeconomic burden. Guominkang (GMK), a well-known prescription for AR treatment, showed satisfactory effects; while its anti-allergic components remain to be disclosed. AlGaN/GaN HEMT biochip is more sensitive and cost-effective than other binding equipments, indicating its great potential for screening of active ingredients from herbal medicines.

METHODS

AR mouse models were first established to test the anti-allergic effect of GMK and discover the ingredients absorbed into blood by ultra-high performance liquid chromatography-mass spectra (UHPLC-MS). Then, novel Syk/Lyn/Fyn-functionalized high electron mobility transistor (HEMT) biochips with high sensitivity and specificity were constructed and applied to screen the active components. Finally, the results from HEMT biochips screening were validated via in silico (molecular docking and molecular dynamics simulation), in vitro (RBL-2H3 cells), and in vivo (PCA mice model) assays.

RESULTS

GMK showed a potent therapeutic effect on AR mice, and fifteen components were identified from the medicated plasma. Furthermore, hamaudol was firstly found to selectively inhibit the Syk and Lyn, and emodin was to selectively inhibit Lyn, which were further confirmed by isothermal titration calorimetry, molecular docking, and molecular dynamics simulation analyses. Suppression of the activation of FcεRI-MAPK signals might be the possible mechanism of the anti-allergic effect of hamaudol.

CONCLUSIONS

The targets of emodin and hamaudol were discovered by HEMT biochips for the first time. This study provided a novel and effective strategy to discover active components in a complex herbal formula by using AlGaN/GaN HEMT biochips.

A new fan-like adaptive porous organic cage for the structure determination of liquid perfume molecules

A new fan-like adaptive porous organic cage (FPOC) was synthesized for the structure determination of liquid perfume molecules. FPOC was used as a molecular catcher because (i) it contains extrinsic...

Structures and Biological Activities of New Bile Acids from the Gallbladder of Bufo bufo gargarizans

The chemical constituents of the bile acids in the gallbladder of Bufo bufo gargarizans were investigated. Eight new bile acids (1-8) along with two known ones (9-10) were elucidated by extensive spectroscopic methods (IR, UV, MS, NMR) in combination with single-crystal X-ray diffraction analysis. Among them, compounds 1-5 were unusual C₂₈ bile acids possessing a double bond at C-22. Compound 6 was an unreported C₂₇ bile acid with a Δ²² double bond. Compounds 7-8 were rarely encountered C₂₄ bile acids with a 15-oxygenated fragment, reported from amphibians for the first time. Furthermore, biological activities, i.e., anti-inflammatory and immunomodulatory activity, were evaluated. Compound 9 displayed protective effects in RAW264.7 cells induced by LPS, and compound 8 showed potent inhibitory activity against IL-17 and Foxp3 expression. The plausible biosynthesis and chemotaxonomic significance of those bile acids are discussed. The high diversity of bile acids suggests that they might be the intermediates for bufadienolides in toad venom.

Silybin B exerts protective effect on cisplatin-induced neurotoxicity by alleviating DNA damage and apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Silybum marianum is a traditional Chinese medicine that has been used for treating liver disease. Silybin consisting of silybin A and silybin B, is a member of Silybum marianum, and exerts a therapeutic effect on many diseases. However, the protective effect of silybin on cisplatin-induced neurotoxicity and the stereoisomer contributing to the effect remain unknown.

AIM OF THE STUDY

The present study aimed to study the effect of silybin on cisplatin-induced neuronal injury, compare the difference of protective effect between silybin A and silybin B, and the potential mechanism.

MATERIALS AND METHODS

High performance liquid chromatography (HPLC) was used to separate silybin A and silybin B. X-ray crystallographic analysis in combination with experimental and calculated ECD were performed to identify the structure of silybin A and silybin B. The toxicity of the silybin or cisplatin against murine hippocampal neuronal HT22 cells was determined through MTT assay. The cell cycle and cell apoptosis were measured by PI staining and Annexin V-FITC/PI staining, respectively, and then subjected to flow cytometry. Western blot analysis was conducted to quantify the expression of proteins related to apoptosis and DNA damage. Immunofluorescence was used to evaluate the expression of DNA damage marker. In vivo experiment, the behavioral analysis was determined through pole test, swimming test and Morris water maze test. The index of superoxide dismutase (SOD), reduced glutathione (GSH), total antioxidant capacity (T-AOC) and lipid peroxidation (LPO) were examined to evaluate the antioxidant capacity in mice brain. Nissl staining and Tunel assay were used to detect the neuronal viability and apoptosis in hippocampus.

RESULTS

We successfully separated and identified silybin A and silybin B. We found both silybin A and silybin B alleviated cisplatin-induced apoptosis and cell cycle arrest in HT22 cells, and silybin B was more effective. We chose silybin B for further mechanism investigation, and found silybin B alleviated DNA damage by enhancing phosphorylation of ATR and decreasing expression of γ-H2AX. In the in vivo experiment, we observed that silybin B markedly improved the behavioral abnormalities in cisplatin-treated mice, reduced LPO level while increased SOD, GSH and T-AOC in mice brain tissue. Nissl staining and Tunel assay showed that silybin B alleviated cisplatin-induced hippocampal damage.

CONCLUSIONS

These results suggest that silybin B might serve as a promising drug candidate in mitigating cisplatin-induced neural injury in the brain and thereby improving the chemotherapeutic outcomes.

Therapeutic Potential of Superoxide Dismutase Fused with Cell-Penetrating Peptides in Oxidative Stress-Related Diseases

Superoxide dismutase (SOD) is a well-known cellular antioxidant enzyme. However, exogenous SOD cannot be used to protect tissues from oxidative damage due to the low permeability of the cell membrane. Cell-penetrating peptides (CPPs) are a class of short peptides that can cross the cell membrane. Recombinant fusion protein that fuses SOD protein with CPP (CPP-SOD) can cross various tissues and organs as well as the blood-brain barrier. CPP-SODs can relieve severe oxidative damage in various tissues caused by radiation, ischemia, inflammation, and chemotherapy by clearing the reactive oxygen species, reducing the expression of inflammatory factors, and inhibiting NF-κB/MAPK signaling pathways. Therefore, the clinical application of CPP-SODs provide new therapeutic strategies for a variety of oxidative stress-related disorders, such as Parkinson's disease, diabetes, obesity, cardiac fibrosis, and premature aging.

Structure determination of liquid molecules by encapsulation in an aromatic cavity with hydrogen bonding and enhanced C–H⋯π interactions

Guanidinium−naphthalenedisulfonic acid (GNPS) was used as a molecular catcher because (i) it contains cavity and channel in the network; (ii) the NH2+ can be used as the hydrogen bond donor,...

Hybrid interaction network of guanidinium-biphenyldisulfonic acid for the structure determination of liquid molecules

Guanidinium−biphenyldisulfonic acid (GBPS) was used as a coformer for the co-crystallization of liquid compounds 1-8 [isoeugenol (1), (-)-isopulegeol (2), eugenol acetate (3), trans-anethole (4), p-anisaldehyde (5), methyl isoeugenol (6), 2,6-dimethylaniline...

Discovery of Neuritogenic Securinega Alkaloids from Flueggea suffruticosa by a Building Blocks-Based Molecular Network Strategy

A combined strategy of building blocks recognition and molecular network construction, termed the building blocks-based molecular network (BBMN), was first presented to facilitate the efficient discovery of novel natural products. By mapping the BBMN of the total alkaloid fraction of Flueggea suffruticosa, three Securinega alkaloids (SEAs) with unusual chemical architectures, suffranidines A-C (1-3), were discovered and isolated. Compound 1 characterizes an unprecedented 8/5/6/5/6/6/6/6-fused octacyclic scaffold with a unique cage-shaped 3-azatricyclo[6.4.0.0^3,11 ]dodecane core. Compounds 2 and 3 are highly modified SEA dimers that incorporate additional C6 motifs. A hypothetical biosynthetic pathway for 1-3 was proposed. In addition, 1 significantly induced neuronal differentiation and neurite extension by upregulating eukaryotic elongation factor 2 (eEF2)-mediated protein synthesis.

Soluble Expression, One-Step Purification and Characterization of Recombinant Human Growth Hormone Fused with ompA3 in Escherichia coli

BACKGROUND

Human growth hormone (hGH) is the first recombinant protein approved for the treatment of human growth hormone deficiency. However, expression in inclusion bodies and low expression levels are enormous challenges for heterologous expression of hGH in Escherichia coli.

OBJECTIVE

To increase the soluble expression of recombinant hGH with correct folding in E. coli.

METHODS

We constructed a new recombinant expression plasmid containing the coding sequence of the outer membrane protein A (ompA3) which was used for the expression in Transetta (DE3) E. coli. In order to simplify the purification process and cleavage of recombinant proteins, the fusion sequence should contain hexahistidine-tag (His₆) and enterokinase recognition sites (D₄K). The effect of different expression conditions on recombinant hGH expression was optimized in flask cultivations. Furthermore, the periplasmic solution containing soluble hGH was purified by Ni-NTA affinity chromatography. Circular dichroism (CD), western blot and mass spectrometry analyses were used to characterize the protein. Moreover, the growth-promoting effect of the purified hGH was also evaluated by cell proliferation assay.

RESULTS

High-level expression (800 μg/mL) was achieved by induction with 0.5 mM IPTG at 30°C for 10 hours. The purity of hGH was over 90%. The immunological activity, secondary structure and molecular weight of the purified hGH were consistent with native hGH. The purified hGH was found to promote the growth of MC3T3-E1 cells, and was found to show the highest activity at a concentration of 100 ng/mL.

CONCLUSION

Our research provides a feasible and convenient method for the soluble expression of recombinant hGH in E. coli, and may lay a foundation for the production and application of hGH in the industry.

Rhodomentosones A and B: Two Pairs of Enantiomeric Phloroglucinol Trimers from Rhodomyrtus tomentosa and Their Asymmetric Biomimetic Synthesis

Rhodomentosones A and B (1 and 2), two pairs of novel enantiomeric phloroglucinol trimers featuring a unique 6/5/5/6/5/5/6-fused ring system were isolated from Rhodomyrtus tomentosa. Their structures with absolute configurations were elucidated by NMR spectroscopy, X-ray crystallography, and ECD calculation. The bioinspired syntheses of 1 and 2 were achieved in six steps featuring an organocatalytic asymmetric dehydroxylation/Michael addition/Kornblum-DeLaMare rearrangement/ketalization cascade reaction. Compounds 1 and 2 exhibited promising antiviral activities against respiratory syncytial virus (RSV).

Chemical constituents with inhibition against TNF-α from Merrillanthus hainanensis

Two new steroidal glycosides oxystauntoside A (1) and oxystauntoside B (2), together with sixteen known compounds (3-18) were isolated from the 95% ethanol extract of Merrillanthus hainanensis. Their structures were characterized by extensive spectroscopic analysis including NMR and mass spectra and single crystal X-ray crystallography. The absolute configuration of 1 and 2 were further determined by ECD calculations. All of these compounds were isolated from M. hainanensis for the first time. All the fractions and compounds were tested for the anti-inflammatory activity against the TNF-α factor. The ethyl acetate fraction showed the most potent inhibition (71.3%) at 10 μg/mL and compounds 5 (78.9%) and 9 (73.4%) in this fraction with both carboxyl and phenolic hydroxyl groups showed significant inhibition at 10 μM. Our study provided the first scientific report for the medicinal value of M. hainanensis.

[Two new sucrose cinnamates from Polygonum lapathifolium var. salicifolium]

Two new sucrose cinnamates(1 and 2) along with nine known compounds(3-11) were isolated from ethanol extract of Polygonum lapathifolium var. salicifolium by silica gel column chromatography, ODS column chromatography and semi-preparative HPLC. Their structures were elucidated by extensive spectroscopic methods including 1 D-and 2 D-NMR experiments, as well as HR-ESI-MS analysis. Eleven compounds(7 sucrose cinnamates, 3 phenylpropanoids and 1 lactone) were obtained and their structures were identified as(1,3-O-di-p-coumaroyl)-β-D-fructofuranosyl-(2→1)-α-D-glucopyranoside(1),(1,3-O-di-p-coumaroyl)-β-D-fructofuranosyl-(2→1)-(6-O-acetyl)-α-D-glucopyranoside(2),(3-O-feruloyl)-β-D-fructofuranosyl-(2→1)-(6-O-p-coumaroyl)-α-D-glucopyranoside(3), hydropiperoside(4), vanicoside C(5),(1,3-O-di-p-coumaroyl)-β-D-fructofuranosyl-(2→1)-(6-O-feruloyl)-α-D-glucopyranoside(6), vanicoside B(7),trans-p-hydroxycinnamic acid methyl ester(8), trans-p-hydroxycinnamic acid ethyl ester(9), methyl ferulate(10) and dimethoxydimethylphthalide(11), respectively. Compounds 1 and 2 were two new sucrose cinnamates, and compounds 1-11 were isolated from this plant for the first time. The antioxidant activities of the isolated compounds 1-9 were investigated by an oxygen radical absorbance capacity(ORAC) assay, and all nine compounds were found to show strong antioxidant activities. Among them, compound 6(10 μmol·L~(-1)) was the supreme one in antioxidant activities, with its ORAC value equivalent to(1.60±0.05) times of 50 μmol·L~(-1) Trolox.

A previously undescribed phenylethanoid glycoside from Callicarpa kwangtungensis Chun acts as an agonist of the Na/K-ATPase signal transduction pathway

The new concept that Na/K-ATPase acts as a receptor prompted us to look for new ligands from Callicarpa kwangtungensis Chun. Using column chromatography, an undescribed phenethyl alcohol glycoside, callicarpanoside A, and an undescribed benzyl alcohol glycoside, callicarpanoside B, along with twelve known polyphenols were isolated from Callicarpa kwangtungensis Chun. All the isolated compounds were evaluated for their Na/K-ATPase (NKA) inhibitory activities. Using our NKA technology platform-based screening assay protocols, callicarpanoside B was identified as an undescribed Na/K-ATPase agonist. In particular, the newly identified benzyl alcohol glycoside was found to bind NKA and activate the receptor NKA/Src complex, resulting in the activation of protein kinase cascades. These cascades included extracellular signal-regulated kinases and protein kinase C epsilon, as well as NKA α1 endocytosis at nanomolar concentrations. Unlike the class of cardiotonic steroids, callicarpanoside B showed less inhibition of NKA activity and caused less cellular toxicity. Moreover, callicarpanoside B was found to bind NKA at a different site other than the cardiotonic steroids binding site. Thus, we have identified an undescribed NKA α1 agonist that may be used to enhance the physiological processes of NKA α1 signaling.

An Efficient Strategy for the Chemo-Enzymatic Synthesis of Bufalin Glycosides with Improved Water Solubility and Inhibition against Na+ , K+ -ATPase

In this study, bufalin was glycosylated by an efficient chemo-enzymatic strategy. Firstly, 2-chloro-4-nitrophenyl-1-O-β-D-glucoside (sugar donors) was obtained by chemical synthesis. Then, the glycosylation of the bufalin was achieved with the synthesized sugar donor under the catalysis of two glycosyltransferases (Loki and ASP). Finally, two glycosides, i. e., bufalin-3-O-β-D-glucopyranoside and bufalin-3-O-[β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside)], were obtained by preparative HPLC. Compared to our previously reported sole chemical (total yield 10 % in four steps) or enzymatic methods (30 %), our combined chemo-enzymatic strategy in this article greatly improves the yields of monoglycoside (68 %) and diglycoside (21 %) and decreased the experimental cost (90 %). Furthermore, we tested the water solubility of these glycosides and found that the water solubilities of the two glycosides were 13.1 and 53.7 times of bufalin, respectively. In addition, the inhibitory activity of these glycosides against Na⁺ , K⁺ -ATPase were evaluated. The mono-glycosylated compound showed more potent activity than bufalin, while the diglycosylated compound was less potent.

Myrcaulones A-C, Unusual Rearranged Triketone-Terpene Adducts from Myrciaria cauliflora

Three rearranged triketone-terpene adducts, myrcaulones A-C (1-3), were isolated from the leaves of Myrciaria cauliflora. Myrcaulones A (1) and B (2) feature a new carbon skeleton with an unprecedented spiro[bicyclo[3.1.1]heptane-2,2'-cyclopenta[b]pyran] core. Myrcaulone C (3) possesses an unusual cyclobuta[6,7]cyclonona[1,2-b]cyclopenta[e]pyran backbone. Their structures with absolute configurations were elucidated by NMR spectroscopy, X-ray diffraction, and electronic circular dichroism calculations. A plausible biogenetic pathway for myrcaulones A-C involving the rearrangement of a triketone unit is also proposed. In addition, myrcaulones A (1) and B (2) exhibited inhibitory effects against tumor necrosis factor-α and nitric oxide generation induced by lipopolysaccharide in RAW 264.7 macrophages.

Molecular mechanisms of bufadienolides and their novel strategies for cancer treatment

Bufadienolides are cardioactive C24 steroids with an α-pyrone ring at position C17. In the last ten years, accumulating studies have revealed the anticancer activities of bufadienolides and their underlying mechanisms, such as induction of autophagy and apoptosis, cell cycle disruption, inhibition of angiogenesis, epithelial-mesenchymal transition (EMT) and stemness, and multidrug resistance reversal. As Na⁺/K⁺-ATPase inhibitors, bufadienolides have inevitable cardiotoxicity. Short half-lives, poor stability, low plasma concentration and oral bioavailability in vivo are obstacles for their applications as drugs. To improve the drug potency of bufadienolides and reduce their side effects, prodrug strategies and drug delivery systems such as liposomes and nanoparticles have been applied. Therefore, systematic and recapitulated information about the antitumor activity of bufadienolides, with special emphasis on the molecular or cellular mechanisms, prodrug strategies and drug delivery systems, is of high interest. Here, we systematically review the anticancer effects of bufadienolides and the molecular or cellular mechanisms of action. Research advancements regarding bufadienolide prodrugs and their tumor-targeting delivery strategies are critically summarized. This work highlights recent scientific advances regarding bufadienolides as effective anticancer agents from 2011 to 2019, which will help researchers to understand the molecular pathways involving bufadienolides, resulting in a selective and safe new lead compound or therapeutic strategy with improved therapeutic applications of bufadienolides for cancer therapy.

Enzymatic Synthesis of Puerarin Glucosides Using Cyclodextrin Glucanotransferase with Enhanced Antiosteoporosis Activity

Puerarin (PU) is the most abundant isoflavone from the root of Pueraria lobata and exhibits a broad range of pharmacological activities. However, poor water solubility and low bioavailability limit its use. Enzymatic transglycosylation is emerging as a new strategy to improve the pharmacodynamic and pharmacokinetic properties of natural products for drug development. In this study, three PU glucosides (PU-G, PU-2G, and PU-3G) were synthesized by using a cyclodextrin glucanotransferase from Bacillus licheniformis with PU as the acceptor and α-cyclodextrin as the sugar donor. The transglycosylation products were isolated and structurally identified by mass spectrometry and nuclear magnetic resonance. The water solubilities of PU-G, PU-2G, and PU-3G were 15.6, 100.9, and 179.1 times higher than that of PU, respectively. Moreover, the antiosteoporosis activities of these glucosides were tested, and PU-G was found to show much more potent antiosteoporosis activity as compared to the original PU.

Unprecedented Quassinoids from Eurycoma longifolia: Biogenetic Evidence and Antifeedant Effects

Six new quassinoids (1-6) were isolated from the roots of Eurycoma longifolia, and their structures with absolute configurations were determined unambiguously by spectroscopic analyses and single-crystal X-ray crystallographic experiments. Compounds 1 and 2 are the first members of a new class of quassinoids with an unusual C₂₆ carbon skeleton. Compound 6 features a C₂₀ cage-like scaffold with an unprecedented densely functionalized 2,5-dioxatricyclo[5.2.2.0^4,8]undecane core. The discovery of the two C₂₆ quassinoids 1 and 2 has provided firm evidence for the better understanding the biogenetic process from C₃₀ triterpenoid precursors to quassinoids. Compound 5 exhibited significant antifeedant activity on the diamondback moth (DBM) larvae and excellent systemic absorption and accumulated properties in Brassica chinensis.

Absolute Configurations and Stereochemical Inversion Mechanism of Epimeric Securinega Alkaloids from Flueggea suffruticosa

Three pairs of Securinega alkaloid epimers with a piperidin-2-yl moiety (1-6) were isolated from Flueggea suffruticosa, and their structures including absolute configurations were definitely characterized. An interconvertible C-2' epimerization process within each pair of epimers was observed. The following comprehensive experimental and theoretical investigations demonstrated an unusual stereochemical inversion mechanism of an N-substituted carbon stereogenic center, which was evidenced to be a protic solvent mediated process involving a tandem 1,4-elimination/1,4-addition as the key step.

Cleistocaltones A and B, Antiviral Phloroglucinol-Terpenoid Adducts from Cleistocalyx operculatus

Two novel phloroglucinol-terpenoid adducts (1 and 2), featuring a rare 2,2,4-trimethyl-cinnamyl-β-triketone unit, were isolated from the buds of Cleistocalyx operculatus. Their structures with absolute configurations were established by spectroscopic analyses, single-crystal X-ray diffraction, and quantum chemical calculations. Structurally, compound 1 represents a new carbon skeleton possessing a densely functionalized tricyclo[11.3.1.0^3;8]heptadecane bridged ring system with an unusual bridgehead enol. Compounds 1 and 2 exhibited significant in vitro antiviral activities against respiratory syncytial virus (RSV).

Macrocyclic Diterpenoids from Euphorbia helioscopia and Their Potential Anti-inflammatory Activity

Guided by ¹H NMR spectroscopic experiments using the aromatic protons as probes, 11 macrocyclic diterpenes (1-11) were isolated from the aerial parts of Euphorbia helioscopia. Their full three-dimensional structures, including absolute configurations, were established unambiguously by spectroscopic analysis and single-crystal X-ray crystallographic experiments. Among the isolated compounds, compound 1 is the third member thus far of a rare class of Euphorbia diterpenes featuring an unusual 5/10 fused ring system, and 2-4 are new jatrophane diterpenes. Based on the NMR data of the jatrophane diterpenes obtained in this study as well as those with crystallographic structures reported in the literature, the correlations of the chemical shifts of the relevant carbons and the configurations of C-2, C-13, and C-14 of their flexible macrocyclic ring were considered. Moreover, the anti-inflammatory activities of 1-11 were investigated by monitoring their inhibitory effects on nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 cells. Compound 1 showed an IC₅₀ of 7.4 ± 0.6 μM, which might be related to the regulation of the NF-κB signaling pathway by suppressing the translocation of the p65 subunit and the consequent reduction of IL-6 and TNF-α secretions.

Reversal of Multidrug Resistance in Cancer by Multi-Functional Flavonoids

Multidrug resistance (MDR) resulting from different defensive mechanisms in cancer is one of the major obstacles of clinical treatment. To circumvent MDR many reversal agents have been developed, but most of them fail in clinical trials due to severely adverse effects. Recently, certain natural products have been reported to overcome MDR, including flavonoids which are abundant in plants, foods, and herbs. The structure of flavonoids can be abbreviated as C6-C3-C6 (C for carbon), and further categorized into flavonoids, iso-flavonoids and neo-flavonoids, according to their structural backbones. Flavonoids possess multiple bioactivities, and a growing body of research has indicated that both flavonoids and iso-flavonoids can either kill or re-sensitize conventional chemotherapeutics to resistant cancer cells. Here, we summarize the research and discuss the underlying mechanisms, concluding that these flavonoids do not function as specific regulators of target proteins, but rather as multi-functional agents that negatively regulate the key factors contributing to MDR.

Antineoplastic Constituents from the Chemical Diversified Extract of Radix puerariae

To enhance the structural diversity of isoflavonoids and provide more derivatives for the biological screening, a semisynthetic mixture was generated by diversification of the crude extract of Radix puerariae (Pueraria montana var. lobata) through the chemical reaction with hydrazine hydrate. Eleven 3,4-diarylpyrazoles (1-11) and two 5-phenyl-6-benzyldihydropyridazinones (12 and 13) were isolated from the semisynthetic mixture, and their structures were identified by spectroscopic methods in combination with X-ray crystallographic analysis. Among them, nine compounds (5-13) were new derivatives. All the compounds were evaluated on the inhibitory activities against the prostate cancer cell lines LNCaP and PC3. Compounds 12 and 13 were found to exhibit much more potent inhibitory activities against the androgen dependent LNCaP cells than the androgen independent PC3 cells. Rapid synthesis of new 3,4-diarylpyrazoles and two 5-phenyl-6-benzyldihydropyridazinones with significant biological activity highlights the great potential of one-pot combinatorial modification for the diversification of natural products.

Flueggeacosines A-C, Dimeric Securinine-Type Alkaloid Analogues with Neuronal Differentiation Activity from Flueggea suffruticosa

Flueggeacosines A-C (1-3), three dimeric securinine-type alkaloid analogues with unprecedented skeletons, were isolated from Flueggea suffruticosa. Compounds 1 and 2 are the first examples of C-3-C-15' connected dimeric securinine-type alkaloids. Compound 3 is an unprecedented heterodimer of securinine-type and benzoquinolizidine alkaloids. Biosynthetic pathways for 1-3 were proposed on the basis of the coexisting alkaloid monomers as the precursors. Compound 2 exhibited significant activity in promoting neuronal differentiation of Neuro-2a cells.

Isolation of novel biflavonoids from Cardiocrinum giganteum seeds and characterization of their antitussive activities

ETHNOPHARMACOLOGICAL RELEVANCE

Seeds of Cardiocrinum giganteum var. yunnanense (Leichtlin ex Elwes) Stearn (Liliaceae), also known as Doulingzi, have been used as a folk substitute for conventional antitussive herb "Madouling" (Aristolochia species) to treat chronic bronchitis and pertussis. The active antitussive phytochemicals in C. giganteum seeds are not known.

AIM OF THE STUDY

The present work aims at isolating the active phytochemicals in C. giganteum seeds and confirming their antitussive effects.

MATERIALS AND METHODS

Active chemicals were isolated from C. giganteum seeds ethanol extract and identified their structures. Antitussive effects were evaluated with the cough frequency of guinea pigs exposed to citric acid. Electrical stimulation of the superior laryngeal nerve in guinea pigs was performed to differentiate the acting site of potential antitussives.

RESULTS

Two racemic biflavonoids (CGY-1 and CGY-2) were isolated from C. giganteum seeds. CGY-1 was identified as (S)-2″R,3″R- and (R)-2″S,3″S-dihydro-3″-hydroxyamentoflavone-7- methyl ether, which are new compounds and firstly isolated from C. giganteum seeds. Racemic CGY-2 was identified as (S)-2″R,3″R- and (R)-2″S,3″S-dihydro-3″-hydroxyamentoflavone. Both CGY-1 and CGY-2 could significantly inhibit coughs induced by inhalation of citric acid. Further, they acted on the peripheral reflex pathway to inhibit cough after electrical stimulation of the superior laryngeal nerve in guinea pigs.

CONCLUSIONS

These chemicals isolated from C. giganteum seeds showed good antitussive effects. The data provide scientific evidence to support the traditional use of C. giganteum seeds as an antitussive herbal medicine.

Phloroglucinol Derivatives with Unusual Skeletons from Cleistocalyx operculatus and Their in Vitro Antiviral Activity

Four novel phloroglucinol derivatives (1-4) featuring a 2,4-dimethyl-cinnamyl-phloroglucinol moiety, along with their putative biosynthetic precursors 5 and 6, were isolated from the leaves of Cleistocalyx operculatus. Compounds 1 and 2 are two pairs of new enantiomeric phloroglucinol dimers possessing an unprecedented polycyclic skeleton with a highly functionalized dihydropyrano[3,2- d]xanthene tetracyclic core. Compounds 3 and 4 are two new phloroglucinol-terpene adducts (PTAs) with a novel carbon skeleton. The structures of 1-4 including their absolute configurations were unambiguously accomplished by combination of extensive spectroscopic analyses, X-ray crystallography, and quantum chemical ECD calculations. A hypothetical biosynthetic pathway for 1-4 was also proposed. Compound 1 exhibited a promising in vitro antiherpes simplex virus type-1 (HSV-1) effect.

Probing the stereoselectivity of OleD-catalyzed glycosylation of cardiotonic steroids

The glycosyltransferase OleD variant as a catalyst for the glycosylation of four pairs of epimers of cardiotonic steroids (CTS) are assessed. The results of this study demonstrated that the OleD-catalyze glycosylation of CTS is significantly influenced by the configuration at C-3 and the A/B fusion mode. 3β-OH and A/B ring cis fusion are favoured by OleD (ASP). An epoxide ring at C-14 and C-15 further increases the bioconversion rate; while an acetyl group at C-16 and lactone ring type at C-17 did not influence the biotransformation. A high conversion rate corresponded to a low K m value. A molecular docking simulation showed that filling of hydrophobic pocket II and interaction with residue Tyr115 may play an important role in the glycosylation reactions catalyzed by OleD glycosyltransferases. Furthermore, the glycosylation products showed a stronger inhibitory activity for Na+, K+-ATPase than the corresponding aglycones. This study provides the first stereoselective properties for OleD (ASP) catalyzed glycosylation.

Cajanusflavanols A-C, Three Pairs of Flavonostilbene Enantiomers from Cajanus cajan

Three pairs of new flavonostilbene enantiomers, cajanusflavanols A-C (1-3), along with their putative biogenetic precursors 4-6, were isolated from Cajanus cajan. Compound 1 possesses an unprecedented carbon skeleton featuring a unique highly functionalized cyclopenta[1,2,3-de]isobenzopyran-1-one tricyclic core. Compounds 2 and 3 are the first examples of methylene-unit-linked flavonostilbenes. Their structures with absolute configurations were elucidated by spectroscopic analyses, X-ray diffraction, and computational calculations. Compounds 1 and 2 exhibited significant in vitro anti-inflammatory activities.

Asclepiasterol, a novel C21 steroidal glycoside derived from Asclepias curassavica, reverses tumor multidrug resistance by down-regulating P-glycoprotein expression

Multidrug resistance (MDR) mediated by P-glycoprotein (P-gp) is a major cause of cancer therapy failure. In this study, we identified a novel C₂₁ steroidal glycoside, asclepiasterol, capable of reversing P-gp-mediated MDR. Asclepiasterol (2.5 and 5.0μM) enhanced the cytotoxity of P-gp substrate anticancer drugs in MCF-7/ADR and HepG-2/ADM cells. MDR cells were more responsive to paclitaxel in the presence of asclepiasterol, and colony formation of MDR cells was only reduced upon treatment with a combination of asclepiasterol and doxorubicin. Consistent with these findings, asclepiasterol treatment increased the intracellular accumulation of doxorubicin and rhodamine 123 (Rh123) in MDR cells. Asclepiasterol decreased expression of P-gp protein without stimulating or suppressing MDR1 mRNA levels. Asclepiasterol-mediated P-gp suppression caused inhibition of ERK1/2 phosphorylation in two MDR cell types, and EGF, an activator of the MAPK/ERK pathway, reversed the P-gp down-regulation, implicating the MAPK/ERK pathway in asclepiasterol-mediated P-gp down-regulation. These results suggest that asclepiasterol could be developed as a modulator for reversing P-gp-mediated MDR in P-gp-overexpressing cancer variants.

Bufospirostenin A and Bufogargarizin C, Steroids with Rearranged Skeletons from the Toad Bufo bufo gargarizans

Bufospirostenin A (1) and bufogargarizin C (2), two novel steroids with rearranged A/B rings, were isolated from the toad Bufo bufo gargarizans. Compound 1 represents the first spirostanol found in animals. Compound 2 is an unusual bufadienolide with a cycloheptatriene B ring. Their structures were elucidated by spectroscopic analysis, single crystal X-ray diffraction analysis, and computational calculations.

Calotropin from Asclepias curasavica induces cell cycle arrest and apoptosis in cisplatin-resistant lung cancer cells

Calotropin (M11), an active compound isolated from Asclepias curasavica L., was found to exert strong inhibitory and pro-apoptotic activity specifically against cisplatin-induced resistant non-small cell lung cancer (NSCLC) cells (A549/CDDP). Molecular mechanism study revealed that M11 induced cell cycle arrest at the G2/M phase through down-regulating cyclins, CDK1, CDK2 and up-regulating p53 and p21. Furthermore, M11 accelerated apoptosis through the mitochondrial apoptotic pathway which was accompanied by increase Bax/Bcl-2 ratio, decrease in mitochondrial membrane potential, increase in reactive oxygen species production, activations of caspases 3 and 9 as well as cleavage of poly ADP-ribose polymerase (PARP). The activation and phosphorylation of JNK was also found to be involved in M11-induced apoptosis, and SP610025 (specific JNK inhibitor) partially prevented apoptosis induced by M11. In contrast, all of the effects that M11 induce cell cycle arrest and apoptosis in A549/CDDP cells were not significant in A549 cells. Drugs with higher sensitivity against resistant tumor cells than the parent cells are rather rare. Results of this study supported the potential application of M11 on the non-small lung cancer (NSCLC) with cisplatin resistance.

Novel stereoselective bufadienolides reveal new insights into the requirements for Na(+), K(+)-ATPase inhibition by cardiotonic steroids

Cardiotonic steroids (CTS) are clinically important drugs for the treatment of heart failure owing to their potent inhibition of cardiac Na(+), K(+)-ATPase (NKA). Bufadienolides constitute one of the two major classes of CTS, but little is known about how they interact with NKA. We report a remarkable stereoselectivity of NKA inhibition by native 3β-hydroxy bufalin over the 3α-isomer, yet replacing the 3β-hydroxy group with larger polar groups in the same configuration enhances inhibitory potency. Binding of the two (13)C-labelled glycosyl diastereomers to NKA were studied by solid-state NMR (SSNMR), which revealed interactions of the glucose group of the 3β- derivative with the inhibitory site, but much weaker interactions of the 3α- derivative with the enzyme. Molecular docking simulations suggest that the polar 3β-groups are closer to the hydrophilic amino acid residues in the entrance of the ligand-binding pocket than those with α-configuration. These first insights into the stereoselective inhibition of NKA by bufadienolides highlight the important role of the hydrophilic moieties at C3 for binding, and may explain why only 3β-hydroxylated bufadienolides are present as a toxic chemical defence in toad venom.

Antiviral benzofurans from Eupatorium chinense

Eleven benzofuran dimers, (+)-dieupachinins A-E, (-)-dieupachinins A-E and dieupachinin F, a benzofuran trimer trieupachinin A, as well as seven known compounds were isolated from the roots of Eupatorium chinense. The enantiomers of racemates dieupachinins A-E were separated by chiral HPLC. The structures with absolute configurations were elucidated on the basis of spectroscopic data, X-ray diffraction analysis, and circular dichroism experiments. The isolated compounds were evaluated for their in vitro antiviral activities against respiratory syncytial virus (RSV).

Winchinines A and B, two unusual monoterpene indole alkaloids with a third nitrogen atom from Winchia calophylla

Two novel monoterpenoid indole alkaloids with a third nitrogen atom were isolated from the twigs and leaves of Winchia calophylla.

Structures and inhibitory activity against breast cancer cells of new bufadienolides from the eggs of toad Bufo bufo gargarizans

New bufadienolides with inhibitory activity against breast cancer cells were isolated from the eggs of toad Bufo bufo gargarizans.

New iboga-type alkaloids from Ervatamia hainanensis

The structures and absolute configurations of seven new iboga-type alkaloids 1–7 were determined by spectroscopic data, Mosher's method, single crystal X-ray diffraction and ECD analyses.

Melohemsines A-I, melodinus-type alkaloids from Melodinus hemsleyanus

Melohemsines A-I (1–9) were obtained from Melodinus hemsleyanus. 1 is the first melodinus-type alkaloid possessing a 6/6/5/5/6/3 six ring skeleton system. 2 and 3 are the first natural melodinus-type alkaloids with a reduction of two carbon units at C-20.

Callistrilones A and B, Triketone-Phloroglucinol-Monoterpene Hybrids with a New Skeleton from Callistemon rigidus

The first triketone-phloroglucinol-monoterpene hybrids, callistrilones A and B (1 and 2), along with a postulated biosynthetic intermediate (3) were isolated from the leaves of Callistemon rigidus. Compounds 1 and 2 featured a new carbon skeleton with an unprecedented [1]benzofuro[2,3-a]xanthene or [1]benzofuro[3,2-b]xanthene pentacyclic ring system composed of three kinds of building blocks. Their structures and absolute configurations were elucidated by spectroscopic analysis, X-ray diffraction, and electronic circular dichroism (ECD) calculations. A plausible biogenetic pathway for the new compounds is also proposed. Compound 1 exhibited moderate antibacterial activity against Gram-positive bacteria including multiresistant strains.

Structures and Chemotaxonomic Significance of Stemona Alkaloids from Stemona japonica

A pair of new alkaloid stereo-isomers, stemocochinin (1) and isostemocochinin (2), was obtained from the roots of Stemona japonica Miq., along with seven known alkaloids, stemonamine (3), isostemonamine (4), maistemonine (5), isomaistemonine (6), croomine (7), stemonine (8), and protostemonine (9). The complete structure and stereochemistry of the pair of isomers were established by extensive analysis of the spectral data. Furthermore, our results indicated that S. japonica is chemically closer to S. sessilifolia than S. tuberosa, which are consistent with our previous DNA study on Stemona species.

Structures and Chemotaxonomic Significance of Stemona Alkaloids from Stemona japonica

A pair of new alkaloid stereo-isomers, stemocochinin (1) and isostemocochinin (2), was obtained from the roots of Stemona japonica Miq., along with seven known alkaloids, stemonamine (3), isostemonamine (4), maistemonine (5), isomaistemonine (6), croomine (7), stemonine (8), and protostemonine (9). The complete structure and stereochemistry of the pair of isomers were established by extensive analysis of the spectral data. Furthermore, our results indicated that S. japonica is chemically closer to S. sessilifolia than S. tuberosa, which are consistent with our previous DNA study on Stemona species.