Xanthone Inhibitors of Unfolded Protein Response Isolated from Calophyllum caledonicum.

The unfolded protein response (UPR) is a key component of fungal virulence. The prenylated xanthone γ-mangostin isolated from Garcinia mangostana (Clusiaceae) fruit pericarp, has recently been described to inhibit this fungal adaptative pathway. Considering that Calophyllum caledonicum (Calophyllaceae) is known for its high prenylated xanthone content, its stem bark extract was fractionated using a bioassay-guided procedure based on the cell-based anti-UPR assay. Four previously undescribed xanthone derivatives were isolated, caledonixanthones N-Q (3, 4, 8, and 12), among which compounds 3 and 8 showed promising anti-UPR activities with IC50 values of 11.7 ± 0.9 and 7.9 ± 0.3 µM, respectively.

CANPA: Computer-Assisted Natural Products Anticipation.

Traditional natural products discovery workflows implying a combination of different targeting strategies, including structure- and/or bioactivity-based approaches, afford no information about new compound structures until late in the discovery pipeline. By integrating a MS/MS prediction module and a collaborative library of (bio)chemical transformations, we have developed a new platform, coined MetWork, that is capable of anticipating the structural identity of metabolites starting from any identified compound. In our quest to discover new monoterpene indole alkaloids, we demonstrate the utility of the MetWork platform by anticipating the structures of five previously undescribed sarpagine-like N-oxide alkaloids that have been targeted and isolated from the leaves of Alstonia balansae using a molecular networking-based dereplication strategy fueled by computer-generated annotations. This study constitutes the first example of nonpeptidic molecular networking-based natural product discovery workflow, in which the targeted structures were initially generated, and therefore anticipated by a computer prior to their isolation.

Natural Inhibitors of the RhoA-p115 Complex from the Bark of Meiogyne baillonii.

In an effort to find potent natural inhibitors of RhoA and p115 signaling G-proteins, a systematic in vitro evaluation using enzymatic and plasmonic resonance assays was undertaken on 11 317 plant extracts. The screening procedure led to the selection of the New Caledonian endemic species Meiogyne baillonii for a chemical investigation. Using a bioguided isolation procedure, three enediyne-γ-butyrolactones (1-3) and two enediyne-γ-butenolides (4 and 5), named sapranthins H-L, respectively, two enediyne carboxylic acid (6 and 7), two depsidones, stictic acid (8) and baillonic acid (9), aristolactams AIa and AIIa (10 and 11), and two aporphines, dehydroroemerine (12) and noraristolodione (13), were isolated from the ethyl acetate extract of the bark. The structures of the new compounds (1-6, 9, and 11) and their relative configurations were established by NMR spectroscopic analysis and by X-ray diffraction analysis for compound 9. Only stictic acid (8) exhibited a significant inhibiting activity of the RhoA-p115 complex, with an EC50 value of 0.19 ± 0.05 mM. This is the first time that a natural inhibitor of the complex RhoA-p115's activity was discovered from an HTS performed over a collection of higher plant extracts. Thus, stictic acid (8) could be used as the first reference compound inhibiting the interaction between RhoA and p115.

Dual Beam Depth Profiling and Imaging with Argon and Bismuth Clusters of Prenylated Stilbenes on Glandular Trichomes of Macaranga vedeliana.

Using a time-of-flight secondary ion mass spectrometer equipped with an argon cluster ion for sputtering and a bismuth liquid metal ion source for analysis, both surfaces of leaves and fruits of Macaranga vedeliana, an endemic New Caledonian species, have been for the first time analyzed by a dual beam depth profiling. To prevent in-vacuum evaporation of the liquid content of the small glandular trichomes covering fruits and leaves surfaces and also to be able to analyze their liquid content while preventing any sublimation of the latter, the samples were kept frozen during the whole experiment using a nitrogen cooled sample holder. Thus, it was possible to demonstrate that vedelianin, an active metabolite of the family of prenylated stilbenes named schweinfurthins, is only located in these glandular trichomes.

Fast & easy preparation of 3D scaffolds from methyl benzoate by a diversity oriented synthesis strategy based on Diels-Alder and ene-reactions.

Thermic dimerization of methyl 1,3-cyclohexadiene 2-carboxylate gave original 3D-shape compounds by Diels-Alder cycloaddition and original [6 + 4]-ene reaction. Further selective modifications on an endo [4 + 2] cycloadduct via a diversity oriented synthesis (DOS) strategy quickly led to the preparation of a small library of original 3D scaffolds, providing access to a larger and unexplored chemical space for drug discovery processes.

(+)- and (-)-Ecarlottones, Uncommon Chalconoids from Fissistigma latifolium with Pro-Apoptotic Activity.

Four new compounds, (+)- and (-)-ecarlottone (1), (±)-fislatifolione (5), (±)-isofislatifolione (6), and (±)-fislatifolic acid (7), and the known desmethoxyyangonin (2), didymocarpin-A (3), and dehydrodidymocarpin-A (4) were isolated from the stem bark of Fissistigma latifolium, by means of bioassay-guided purification using an in vitro affinity displacement assay based on the modulation of Bcl-xL/Bak and Mcl-1/Bid interactions. The structures of the new compounds were elucidated by NMR spectroscopic data analysis, and the absolute configurations of compounds (+)-1 and (-)-1 were assigned by comparison of experimental and computed ECD spectra. (-)-Ecarlottone 1 exhibited a potent antagonistic activity on both protein-protein associations with Ki values of 4.8 µM for Bcl-xL/Bak and 2.4 µM for Mcl-1/Bid.

Anacardic Acids from Knema hookeriana as Modulators of Bcl-xL/Bak and Mcl-1/Bid Interactions.

Proteins of the Bcl-2 family are key targets in anticancer drug discovery. Disrupting the interaction between anti- and pro-apoptotic members of this protein family was the approach chosen in this study to restore apoptosis. Thus, a biological screening on the modulation of the Bcl-xL/Bak and Mcl-1/Bid interactions permitted the selection of Knema hookeriana for further phytochemical investigations. The ethyl acetate extract from the stem bark led to the isolation of six new compounds, three acetophenone derivatives (1-3) and three anacardic acid derivatives (4-6), along with four known anacardic acids (7-10) and two cardanols (11, 12). Their structures were elucidated by 1D and 2D NMR analysis in combination with HRMS experiments. The ability of these compounds to antagonize Bcl-xL/Bak and Mcl-1/Bid association was determined, using a protein-protein interaction assay, but only anacardic acid derivatives (4-10) exhibited significant binding properties, with Ki values ranging from 0.2 to 18 µM. Protein-ligand NMR experiments further revealed that anacardic acid 9, the most active compound, does not interact with the anti-apoptotic proteins Bcl-xL and Mcl-1 but instead interacts with pro-apoptotic protein Bid.

Advanced Structural Determination of Diterpene Esters Using Molecular Modeling and NMR Spectroscopy.

Three new jatrophane esters (1-3) were isolated from Euphorbia amygdaloides ssp. semiperfoliata, including an unprecedented macrocyclic jatrophane ester bearing a hemiketal substructure, named jatrohemiketal (3). The chemical structures of compounds 1-3 and their relative configurations were determined by spectroscopic analysis. The absolute configuration of compound 3 was determined unambiguously through an original strategy combining NMR spectroscopy and molecular modeling. Conformational search calculations were performed for the four possible diastereomers 3a-3d differing in their C-6 and C-9 stereocenters, and the lowest energy conformer was used as input structure for geometry optimization. The prediction of NMR parameters ((1)H and (13)C chemical shifts and (1)H-(1)H coupling constants) by density functional theory (DFT) calculations allowed identifying the most plausible diastereomer. Finally, the stereostructure of 3 was solved by comparison of the structural features obtained by molecular modeling for 3a-3d with NMR-derived data (the values of dihedral angles deduced from the vicinal proton-proton coupling constants ((3)JHH) and interproton distances determined by ROESY). The methodology described herein provides an efficient way to solve or confirm structural elucidation of new macrocyclic diterpene esters, in particular when no crystal structure is available.

Pro-apoptotic meiogynin A derivatives that target Bcl-xL and Mcl-1.

The biological evaluation of a natural sesquiterpene dimer meiogynin A 1, is described as well as that of five non-natural analogues. Although active on a micromolar range on the inhibition of Bcl-xL/Bak and Mcl-1/Bid interaction, meiogynin A 1 is not cytotoxic on three cell lines that overexpress Bcl-xL and Mcl-1. Contrarily, one of its analogues 6 with an inverted configuration on the side chain and an aromatic moiety replacing the cyclohexane ring was active on both target proteins, cytotoxic on a micromolar range and was found to induce apoptosis through a classical pathway.

Endiandric acid analogues from Beilschmiedia ferruginea as dual inhibitors of Bcl-xL/Bak and Mcl-1/Bid interactions.

A rapid screening by (1)H and (1)H-(13)C HSQC NMR spectroscopy of EtOAc extracts of Endiandra and Beilschmiedia species allowed the selection of Beilschmiedia ferruginea leaves and flowers extract for a chemical investigation, leading to the isolation of 11 new tetracyclic endiandric acid analogues, named ferrugineic acids A-K (1-11). Their structures were determined by 1D and 2D NMR spectroscopic analysis in combination with HRMS data. These compounds were assayed for Bcl-xL and Mcl-1 binding affinities. Ferrugineic acids B, C, and J (2, 3, and 10) exhibited significant binding affinity for both antiapoptotic proteins Bcl-xL (Ki = 19.2, 12.6, and 19.4 µM, respectively) and Mcl-1 (Ki = 14.0, 13.0, and 5.2 µM, respectively), and ferrugineic acid D (4) showed only significant inhibiting activity for Mcl-1 (Ki = 5.9 µM).

Jatrophane diterpenes as inhibitors of chikungunya virus replication: structure-activity relationship and discovery of a potent lead.

Bioassay-guided purification of an EtOAc extract of the whole plant of Euphorbia amygdaloides ssp. semiperfoliata using a chikungunya virus-cell-based assay led to the isolation of six new (1-4, 9, and 10) and six known (5-7, 8, 11, and 12) jatrophane esters. Their planar structures and relative configurations were determined by extensive spectroscopic analysis, and their absolute configurations by X-ray analysis. These compounds were investigated for selective antiviral activity against chikungunya virus (CHIKV), Semliki Forest virus, Sindbis virus, and HIV-1 and HIV-2 viruses. Compound 3 was found to be the most potent and selective inhibitor of the replication of CHIKV and of HIV-1 and HIV-2 (EC50 = 0.76, IC50 = 0.34 and 0.043 µM, respectively). A preliminary structure-activity relationship study demonstrated that potency and selectivity are very sensitive to the substitution pattern on the jatrophane skeleton. Although replication strategies of CHIK and HIV viruses are quite different, the mechanism of action by which these compounds act may involve a similar target for both viruses. The present results provide additional support for a previous hypothesis that the anti-CHIKV activity could involve a PKC-dependent mechanism.

Antioxidant and α-amylase inhibitory activities of extract and isolates from Zygogynum pancheri subsp. arrhantum.

One new sesquiterpenoid (5R(*),8R(*),9R(*),10R(*))-cinnamolide (8), and seven known compounds, 5-hydroxy-7-methoxyflavonone (1), 8-hydroxy-3-(4'-hydroxyphenyl)-6,7-(2″,2″-dimethylchromene)-tetralone (2), 8-hydroxy-3-(3',4'-dihydroxyphenyl)-6,7-(2″,2″-dimethylchromene)-tetralone (3), 1ß-E-O-p-methoxycinnamoyl-bemadienolide (4), 1ß-O-(E-cinnamoyl)-6α-hydroxy-9-epi-polygodial (5), 1ß-O-(E-cinnamoyl)-6α-hydroxypolygodial (6), and 1ß-O-E-cinnamoylpolygodial (7) were isolated from the ethyl acetate extract of barks of Zygogynum pancheri subsp. arrhantum (Winteraceae). The structures of these molecules were assigned predominantly based on spectral data. The structure of compound 8 was confirmed by X-ray crystallographic analysis. Compounds 2 and 3 exhibited significant antioxidant activity, whereas compounds 1 and 4-7 showed significant α-amylase inhibitory activity.

Trigocherrierin A, a potent inhibitor of chikungunya virus replication.

Trigocherrierin A (1) and trigocherriolide E (2), two new daphnane diterpenoid orthoesters (DDOs), and six chlorinated analogues, trigocherrins A, B, F and trigocherriolides A-C, were isolated from the leaves of Trigonostemon cherrieri. Their structures were identified by mass spectrometry, extensive one- and two-dimensional NMR spectroscopy and through comparison with data reported in the literature. These compounds are potent and selective inhibitors of chikungunya virus (CHIKV) replication. Among the DDOs isolated, compound 1 exhibited the strongest anti-CHIKV activity (EC50 = 0.6 ± 0.1 µM, SI = 71.7).

Kingianic acids A-G, Endiandric acid analogues from Endiandra kingiana.

A phytochemical investigation of the methanolic extract of the bark of Endiandra kingiana led to the isolation of seven new tetracyclic endiandric acid analogues, kingianic acids A-G (1-7), together with endiandric acid M (8), tsangibeilin B (9) and endiandric acid (10). Their structures were determined by 1D- and 2D-NMR analysis in combination with HRMS experiments. The structure of compounds 9 and 10 were confirmed by single-crystal X-ray diffraction analysis. These compounds were screened for Bcl-xL and Mcl-1 binding affinities and cytotoxic activity on various cancer cell lines. Compound 5 showed moderate cytotoxic activity against human colorectal adeno-carcinoma (HT-29) and lung adenocarcinoma epithelial (A549) cell lines, with IC50 values in the range 15-17 µM, and compounds 3, 6 and 9 exhibited weak binding affinity for the anti-apoptotic protein Mcl-1.

Natural aristolactams and aporphine alkaloids as inhibitors of CDK1/cyclin B and DYRK1A.

In an effort to find potent inhibitors of the protein kinases DYRK1A and CDK1/Cyclin B, a systematic in vitro evaluation of 2,500 plant extracts from New Caledonia and French Guyana was performed. Some extracts were found to strongly inhibit the activity of these kinases. Four aristolactams and one lignan were purified from the ethyl acetate extracts of Oxandra asbeckii and Goniothalamus dumontetii, and eleven aporphine alkaloids were isolated from the alkaloid extracts of Siparuna pachyantha, S. decipiens, S. guianensis and S. poeppigii. Among these compounds, velutinam, aristolactam AIIIA and medioresinol showed submicromolar IC50 values on DYRK1A.

Structure elucidation of an aspidofractinine-type monoterpene indole alkaloid from Melodinus reticulatus.

The structure and complete NMR assignments of aspidoreticulofractine, an aspidofractinine N-oxide, are reported. Its structure was elucidated based on a combination of spectroscopic techniques including 1D and 2D NMR, high-resolution mass spectrometry, and electronic circular dichroism.

In vitro evaluation of NA1-115-7-loaded nanoemulsions, an MCL-1-specific inhibitor of natural origin, intended to treat B-cell lymphoproliferative disorders after oral administration.

MCL-1, an anti-apoptotic member of the BCL-2 protein family, is overexpressed in many types of cancer and contributes to chemotherapy resistance. The drimane derivative NA1-115-7 is a natural compound isolated from Zygogynum pancheri that can be considered as a very promising lead for treating MCL-1-dependent hematological malignancies. As this drug suffers from low stability in acidic conditions and poor aqueous solubility, we evaluated the potential oral use of NA1-115-7 by encapsulating it in lipid nanoemulsions (NA-NEs) prepared by spontaneous emulsification. NA-NEs showed a particle size of 41.9 ± 2.2 nm, PDI of 0.131 ± 0.016, zeta potential of -5.8 ± 3.4 mV, encapsulation efficiency of approximately 100 % at a concentration of 24 mM. The stability of NA-1-115-7 was sixfold higher than that of the unencapsulated drug in simulated gastric fluid. NA-NEs significantly restored apoptosis and halved the effective doses of NA1-115-7 on BL2, a Burkitt lymphoma cell line, without toxicity in normal cells. Such a drug-delivery system appears to be particularly interesting for the oral administration of NA1-115-7, as it improves its solubility and stability, as well as efficacy, by reducing the therapeutic dose, making it possible to further consider in-vivo studies of this promising drug in BL2 xenografted mice.

Acetylcholinesterase inhibitors from the leaves of Macaranga kurzii.

Bioassay-guided fractionation of an extract of leaves of Macaranga kurzii yielded four new compounds, a stilbene (furanokurzin, 1) and three flavonoids (macakurzin A-C, 2-4). Nine known compounds were also isolated (5-13). Their structures were determined by spectroscopic analyses including MS and 2D NMR. The isolates were all evaluated for acetylcholinesterase inhibitory activity. Compound 6 (trans-3,5-dimethoxystilbene) exhibited the greatest activity (IC50 9 µM). Cytotoxic evaluation against KB cells showed that compound 7 had an IC50 of 4 µM, followed by 11 (IC50 10 µM) and 3 (IC50 13 µM).

NA1-115-7, from Zygogynum pancheri, is a new selective MCL-1 inhibitor inducing the apoptosis of hematological cancer cells but non-toxic to normal blood cells or cardiomyocytes.

The overexpression of antiapoptotic members (BCL-2, BCL-xL, MCL-1, etc.) of the BCL-2 family contributes to tumor development and resistance to chemotherapy or radiotherapy. Synthetic inhibitors targeting these proteins have been developed, and some hematological malignancies are now widely treated with a BCL-2 inhibitor (venetoclax). However, acquired resistance to venetoclax or chemotherapy drugs due to an upregulation of MCL-1 has been observed, rendering MCL-1 an attractive new target for treatment. Six MCL-1 inhibitors (S64315, AZD-5991, AMG-176, AMG-397, ABBV-467 and PRT1419) have been evaluated in clinical trials since 2016, but some were affected by safety issues and none are currently used clinically. There is, therefore, still a need for alternative molecules. We previously described two drimane derivatives as the first covalent BH3 mimetics targeting MCL-1. Here, we described the characterization and biological efficacy of one of these compounds (NA1-115-7), isolated from Zygogynum pancheri, a plant belonging to the Winteraceae family. NA1-115-7 specifically induced the apoptosis of MCL-1-dependent tumor cells, with two hours of treatment sufficient to trigger cell death. The treatment of lymphoma cells with NA1-115-7 stabilized MCL-1, disrupted its interactions with BAK, and rapidly induced apoptosis through a BAK- and BAX-mediated process. Importantly, a similar treatment with NA1-115-7 was not toxic to erythrocytes, peripheral blood mononuclear cells, platelets, or cardiomyocytes. These results highlight the potential of natural products for use as specific BH3 mimetics non-toxic to normal cells, and they suggest that NA1-115-7 may be a promising tool for use in cancer treatment.

Benzofurans from Styrax agrestis as acetylcholinesterase inhibitors: structure-activity relationships and molecular modeling studies.

An extract of Styrax agrestis fruits, collected in Vietnam, significantly inhibited acetylcholinesterase (AChE) in vitro. Bioassay-guided fractionation revealed three new egonol-type benzofurans: egonol-9(Z),12(Z) linoleate (1), 7-demethoxyegonol-9(Z),12(Z) linoleate (2), and 7-demethoxyegonol oleate (4). Ten known egonol-type benzofurans were also isolated (3, 5, 6-13). In order to better understand structure-activity relationships in this series, egonol derivatives 14-19 were prepared by chemical modifications and evaluated for their inhibition of AChE, butyrylcholinesterase (BChE), and AChE-induced Aß aggregation. Compounds 1-4 were the most potent inhibitors of the series, which exhibited inhibitory activity against AChE (IC50 1.4-3.1 µM) and, for 1, Aß aggregation (77.6%). Molecular docking studies were also performed to investigate interaction of these compounds with the active site of AChE.