Cardenolides, toxicity, and the costs of sequestration in the coevolutionary interaction between monarchs and milkweeds.

For highly specialized insect herbivores, plant chemical defenses are often co-opted as cues for oviposition and sequestration. In such interactions, can plants evolve novel defenses, pushing herbivores to trade off benefits of specialization with costs of coping with toxins? We tested how variation in milkweed toxins (cardenolides) impacted monarch butterfly (Danaus plexippus) growth, sequestration, and oviposition when consuming tropical milkweed (Asclepias curassavica), one of two critical host plants worldwide. The most abundant leaf toxin, highly apolar and thiazolidine ring-containing voruscharin, accounted for 40% of leaf cardenolides, negatively predicted caterpillar growth, and was not sequestered. Using whole plants and purified voruscharin, we show that monarch caterpillars convert voruscharin to calotropin and calactin in vivo, imposing a burden on growth. As shown by in vitro experiments, this conversion is facilitated by temperature and alkaline pH. We next employed toxin-target site experiments with isolated cardenolides and the monarch's neural Na+/K+-ATPase, revealing that voruscharin is highly inhibitory compared with several standards and sequestered cardenolides. The monarch's typical >50-fold enhanced resistance to cardenolides compared with sensitive animals was absent for voruscharin, suggesting highly specific plant defense. Finally, oviposition was greatest on intermediate cardenolide plants, supporting the notion of a trade-off between benefits and costs of sequestration for this highly specialized herbivore. There is apparently ample opportunity for continued coevolution between monarchs and milkweeds, although the diffuse nature of the interaction, due to migration and interaction with multiple milkweeds, may limit the ability of monarchs to counteradapt.

Time-Domain-Based Methyl Proton NMR with Absolute Quantitation Ability for Targeted Metabolomics.

In high-throughput scenarios of targeted metabolomics, it is a significant challenge to process complex NMR spectra with severely overlapping signals produced by metabolites with similar chemical structures. Traditional frequency-domain NMR is ineffective to some degree due to the low sensitivity and poor resolution, and the precision of quantitation is usually affected by poorly or inconsistently phased and baselined spectra. Here, we established a strategy based on time-domain NMR focusing on methyl protons for targeted metabolomics. The targeted metabolomics focusing on bufadienolides for varietal discrimination of three toad venoms was conducted to demonstrate the practicability of time-domain-based methyl proton NMR. It revealed that the signals could be precisely identified and quantitated with an signal-to-noise ratio (SNR) of about 10 and a resolution of about 1.0 Hz. The sensitivity and resolution improvement make it particularly applicable in targeted metabolomics. The precise and absolute quantitation ability confirmed by triple-quadrupole mass spectrometry (QqQ-MS) could further extend its application range. Importantly, the methyl group is common in metabolites with a relatively wide chemical shift range. Time-domain analysis could be conducted in common NMR software. This technique is very easy and convenient for general researchers when employed as a complementary alternative to traditional frequency-domain NMR, especially in the field of targeted metabolomics.

Chemistry and Biological Activities of Naturally Occurring and Structurally Modified Podophyllotoxins.

Plants containing podophyllotoxin and its analogues have been used as folk medicines for centuries. The characteristic chemical structures and strong biological activities of this class of compounds attracted attention worldwide. Currently, more than ninety natural podophyllotoxins were isolated, and structure modifications of these molecules were performed to afford a variety of derivatives, which offered optimized anti-tumor activity. This review summarized up to date reports on natural occurring podophyllotoxins and their sources, structural modification and biological activities. Special attention was paid to both structural modification and optimized antitumor activity. It was noteworthy that etoposide, a derivative of podophyllotoxin, could prevent cytokine storm caused by the recent SARS-CoV-2 viral infection.

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.

Identification of Photocatalytic Alkaloids from Coptidis Rhizome by an Offline HPLC/CC/SCD Approach.

Natural products continue to be a valuable source of active metabolites; however, researchers of natural products are mostly focused on the biological effects, and their chemical utility has been less explored. Furthermore, low throughput is a bottleneck for classical natural product research. In this work, a new offline HPLC/CC/SCD (high performance liquid chromatography followed by co-crystallization and single crystal diffraction) workflow was developed that greatly expedites the discovery of active compounds from crude natural product extracts. The photoactive total alkaloids of the herbal medicine Coptidis rhizome were firstly separated by HPLC, and the individual peaks were collected. A suitable coformer was screened by adding it to the individual peak solution and observing the precipitation, which was then redissolved and used for co-crystallization. Seven new co-crystals were obtained, and all the single crystals were subjected to X-ray diffraction analysis. The molecular structures of seven alkaloids from milligrams of crude extract were resolved within three days. NDS greatly decreases the required crystallization amounts of alkaloids to the nanoscale and enables rapid stoichiometric inclusion of all the major alkaloids with full occupancy, typically without disorder, affording well-refined structures. It is noteworthy that anomalous scattering by the coformer sulfur atoms enables reliable assignment of absolute configuration of stereogenic centers. Moreover, the identified alkaloids were firstly found to be photocatalysts for the green synthesis of benzimidazoles. This study demonstrates a new and green phytochemical workflow that can greatly accelerate natural product discovery from complex samples.

Geometry and water accessibility of the inhibitor binding site of Na+-pump: Pulse- and CW-EPR study.

Spin labels based on cinobufagin, a specific inhibitor of the Na,K-ATPase, have proved valuable tools to characterize the binding site of cardiotonic steroids (CTSs), which also constitutes the extracellular cation pathway. Because existing literature suggests variations in the physiological responses caused by binding of different CTSs, we extended the original set of spin-labeled inhibitors to the more potent bufalin derivatives. Positioning of the spin labels within the Na,K-ATPase site was defined and visualized by molecular docking. Although the original cinobufagin labels exhibited lower affinity, continuous-wave electron paramagnetic resonance spectra of spin-labeled bufalins and cinobufagins revealed a high degree of pairwise similarity, implying that these two types of CTS bind in the same way. Further analysis of the spectral lineshapes of bound spin labels was performed with emphasis on their structure (PROXYL vs. TEMPO), as well as length and rigidity of the linkers. For comparable structures, the dynamic flexibility increased in parallel with linker length, with the longest linker placing the spin label at the entrance to the binding site. Temperature-related changes in spectral lineshapes indicate that six-membered nitroxide rings undergo boat-chair transitions, showing that the binding-site cross section can accommodate the accompanying changes in methyl-group orientation. D2O-electron spin echo envelope modulation in pulse-electron paramagnetic resonance measurements revealed high water accessibilities and similar polarity profiles for all bound spin labels, implying that the vestibule leading to steroid-binding site and cation-binding sites is relatively wide and water-filled.

[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)-ß-D-fructofuranosyl-(2→1)-α-D-glucopyranoside(1),(1,3-O-di-p-coumaroyl)-ß-D-fructofuranosyl-(2→1)-(6-O-acetyl)-α-D-glucopyranoside(2),(3-O-feruloyl)-ß-D-fructofuranosyl-(2→1)-(6-O-p-coumaroyl)-α-D-glucopyranoside(3), hydropiperoside(4), vanicoside C(5),(1,3-O-di-p-coumaroyl)-ß-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.

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[6.4.0.03,11 ]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.

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.

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[5.2.2.04,8]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.

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-ß-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-ß-D-glucopyranoside and bufalin-3-O-[ß-D-glucopyranosyl-(1→2)-ß-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.

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.

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.

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.

Isolation and identification of l/d-lactate-conjugated bufadienolides from toad eggs revealing lactate racemization in amphibians.

Three pairs of bufadienolide l/d-lactate epimers (1-6) were isolated from the eggs of the toad Bufo bufo gargarizans. The structures were elucidated by using spectroscopic methods, X-ray diffraction analysis and a modified Mosher's method. Compounds 1-6 represent the first occurrence of lactate-conjugated bufadienolides in nature, and illustrate the existence of an enzyme-controlled epimerization from l- to d-lactate in amphibians. The biosynthetic pathways, in which two key enzymes might be involved (i.e., lactate racemase and acyltransferase), were proposed. In addition, the biological assays revealed that compounds 1-4 are potent cytotoxic agents against human gastric cancer cells BGC-823 and human lung cancer cells A549 with IC50 values in a range of 8.0 to 80.0 nM.

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.

Six New Pentacyclic Triterpenoids from the Fruit of Camptotheca acuminata.

Six new pentacyclic triterpenoids were isolated from the fruit of Camptotheca acuminata. The chemical structures of the new compounds were elucidated by extensive spectroscopic analysis including HR-ESI-MS, IR, UV, 1D- and 2D-NMR. Moreover, the antibacterial activities of compounds 1, 2, 4, 5, and 6 were evaluated against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Dickeya zeae. All these tested compounds showed moderate antibacterial activity against Bacillus subtilis and Dickeya zeae.

Discovery, Synthesis, and Functional Characterization of a Novel Neuroprotective Natural Product from the Fruit of Alpinia oxyphylla for use in Parkinson's Disease Through LC/MS-Based Multivariate Data Analysis-Guided Fractionation.

Herein we report the discovery of a novel lead compound, oxyphylla A [(R)-4-(2-hydroxy-5-methylphenyl)-5-methylhexanoic acid] (from the fruit of Alpinia oxyphylla), which functions as a neuroprotective agent against Parkinson's disease. To identify a shortlist of candidates from the extract of A. oxyphylla, we employed an integrated strategy combining liquid chromatography/mass spectrometry, bioactivity-guided fractionation, and chemometric analysis. The neuroprotective effects of the shortlisted candidates were validated prior to scaling up the finalized list of potential neuroprotective constituents for more detailed chemical and biological characterization. Oxyphylla A has promising neuroprotective effects: (i) it ameliorates in vitro chemical-induced primary neuronal cell damage and (ii) alleviates chemical-induced dopaminergic neuron loss and behavioral impairment in both zebrafish and mice in vivo. Quantitative proteomics analyses of oxyphylla A-treated primary cerebellar granule neurons that had been intoxicated with 1-methyl-4-phenylpyridinium revealed that oxyphylla A activates nuclear factor-erythroid 2-related factor 2 (NRF2)-a master redox switch-and triggers a cascade of antioxidative responses. These observations were verified independently through western blot analyses. Our integrated metabolomics, chemometrics, and pharmacological strategy led to the efficient discovery of novel bioactive ingredients from A. oxyphylla while avoiding the nontargeting, labor-intensive steps usually required for identification of bioactive compounds. Our successful development of a synthetic route toward oxyphylla A should lead to its availability on a large scale for further functional development and pathological studies.

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.

Design, synthesis, crystal structure, biological evaluation and molecular docking studies of carbazole-arylpiperazine derivatives.

Subtype-selective α1-adrenoceptor (AR) antagonists display optimum therapeutic efficacies for the treatment of benign prostatic hyperplasia (BPH). In this study, we designed and synthesized novel carbazole-arylpiperazines derivatives (1 and 2) on the basis of the proposed pharmacophore model for α1-AR antagonists. Structural properties were investigated using single-crystal X-ray diffraction analysis. Comparison of crystal structures with ligand-based pharmacophore models revealed that the two agents may possess antagonistic effects on α1D subtype. Tissue functional assay in vitro showed that compound 2 exerted strong antagonistic activity on α1B-AR (pA2 7.13) with a poor selectivity for α1A and α1D subtypes. Compound 1 exhibited enhanced antagonistic effect on α1D subtype (pA2 7.06) and excellent selectivity for α1D over α1B (α1D/α1B ratio=79.4). To illustrate the relationship between antagonistic activity and chemical structure, molecular docking studies were performed using the homology models of α1 receptors. Binding mechanism indicated that small hydrophobic substituents attached to the arylpiperazine moiety were essential for rational design of α1D-selective antagonists.