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.

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.

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.

Drimane Derivatives as the First Examples of Covalent BH3 Mimetics that Target MCL-1.

Drimane sesquiterpenoid dialdehydes are natural compounds with antiproliferative properties. Nevertheless, their mode of action has not yet been discovered. Herein, we demonstrate that various drimanes are potent inhibitors of MCL-1 and BCL-xL, two proteins of the BCL-2 family that are overexpressed in various cancers, including lymphoid malignancies. Subtle changes in their structure significantly modified their activity on the target proteins. The two most active compounds are MCL-1 selective and bind in the BH3 binding groove of the protein. Complementary studies by NMR spectroscopy and mass spectrometry analyses, but also synthesis, showed that they covalently inhibit MCL-1 though the formation of a pyrrole adduct. In addition, cytotoxic assays revealed that these two compounds show a cytotoxic selectivity for BL2, a MCL-1/BCL-xL-dependent cell line and induce apoptosis.

A method to assess algicidal activity of microalgal extracts coupling microalgae produced in stirred closed photobioreactor operating in continuous with pulse amplitude modulated (PAM) fluorometry.

We describe in the present study a quick and reliable method based on chlorophyll a fluorescence to assess putative algicidal effect of different microalgal extracts. We couple microalgal production under chemostat cultivation mode to continuously produce a given microalgae species (e.g. Dunaliella salina in this study) at a stable physiological state to ease comparison between extracts tested; with a non-destructive method based on chlorophyll a fluorescence. Pulse amplitude modulated (PAM) fluorometry was used to assess over time the effect of different microalgal crude extracts on the efficiency of the photosystem II (PSII) of a tested microalgae (Dunaliella salina). • Microalgal production at stationary phase in stirred closed photobioreactor (PBR) operating in continuous have stable photophysiological parameters, which is a prerequisite to compare the impact of different algicidal compounds. • The combination of both methods, allows to quickly assess the algicidal effect of diverse microalgal (crude) extracts on the PSII efficiency of a tested microalgae. • The method may be used to identify and isolate algicidal molecules affecting algal PSII using a bio-guided isolation protocol.

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.

(+)- 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.

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.

Unified biomimetic assembly of voacalgine A and bipleiophylline via divergent oxidative couplings.

Bipleiophylline is a highly complex monoterpene indole alkaloid composed of two pleiocarpamine units anchored on an aromatic spacer platform. The synthesis of bipleiophylline is considered as a mountain to climb by the organic chemistry community. Here, a unified oxidative coupling protocol between indole derivatives and 2,3-dihydroxybenzoic acid, mediated by silver oxide, has been developed to produce the core of bipleiophylline. This method also allows the independent preparation of benzofuro[2,3-b]indolenine and isochromano[3,4-b]indolenine scaffolds, depending only on the nature of the aromatic platform used. The procedure has been applied to simple indole derivatives and to more challenging monoterpene indole alkaloids, thereby furnishing natural-product-like structures. The use of scarce pleiocarpamine as the starting indole allows the first syntheses of bipleiophylline and of its biosynthetic precursor, voacalgine A. The structure of the latter has been reassigned in the course of our investigations by 2D NMR and displays an isochromano[3,4-b]indolenine motif instead of a benzofuro[2,3-b]indolenine.

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.

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.

Triterpenes from the exudate of Gardenia urvillei.

A cycloartane gardurvilleic acid, three 3,4-seco-cycloartanes securvienol, secodienurvilleic acid, securvitriol, a 3,4;9,10-seco-cycloartane gardheptlactone, two dammaranes urvilone, urvilol, along with eight known cycloartanes and 3,4-seco-cycloartanes and four known dammaranes have been isolated from the bud exudate of Gardenia urvillei, an endemic tree to the New Caledonian dry forest. Two other dammarane derivatives have been obtained by semisynthesis. The structures of the original compounds were determined by spectroscopic methods and chemical correlations. In association with previously published data, the description of oxidized side-chains in position 17 are now available for two couples of diastereoisomers. Evaluation of anti-parasite activity and cytotoxicity has shown noticeable results for some of the isolated triterpenes.

A New Polycyclic Polyprenylated Acylphloroglucinol Derivative from Garcinia verrucosa.

In our continuing phytochemical screening program aimed at finding major constituents. of endemic Madagascar plants as potential templates for semisynthesis, we investigated the ethyl acetate extract of stem bark of Garcinia verrucosa. Fractionation of the extract led to the isolation of the major compound named garcicosin. -Its structure was elucidated by spectroscopic methods including ID and 2D homo- and heteronuclear NMR techniques (COSY, HSQC, HMBC and NOESY), and HR-mass spectromnetry.

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.

LC-MS²-Based dereplication of Euphorbia extracts with anti-Chikungunya virus activity.

Recently, phorbol esters from Euphorbiaceae have been shown to elicit potent and selective antiviral activity on the replication of Chikungunya virus (CHIKV) in cell culture. With the objective to found new compounds with anti-CHIKV activities, 45 extracts from various plant parts of 11 Mediterranean Euphorbia and one Mercurialis species were evaluated for selective inhibition of CHIKV replication. All EtOAc extracts, especially those prepared from latex, exhibited significant and selective antiviral activity in a Chikungunya virus-cell-based assay. An LC-MS(2) dereplication method was then developed to investigate whether known diterpenoids with anti-CHIKV activity, such as the potent anti-CHIKV 12-O-tetradecanoylphorbol-13-acetate (TPA), phorbol-12,13-didecanoate, and prostratin as well as 24 other commercially available diterpenoids of tigliane-, ingenane-, and daphnane-type for which the anti-CHIKV activity have been established in advance (Nothias-Scaglia et al. 2015), were present in the Euphorbia extracts. Only ingenol-3-mebutate, 13-O-isobutyryl-12-deoxyphorbol-20-acetate, and ingenol-3,20-dibenzoate, all exhibiting weak anti-CHIKV activities, were detected in the EtOAc extracts of Euphorbia peplus, Euphorbia segetalis ssp. pinea, and Euphorbia pithyusa ssp. pithyusa. Given the potent anti-CHIKV activities of these Euphorbia extracts, the present study suggested that their antiviral activities are probably due to untargeted diterpenoids.

Antivascular and anti-parasite activities of natural and hemisynthetic flavonoids from New Caledonian Gardenia species (Rubiaceae).

A series of 16 flavonoids were isolated and prepared from bud exudate of Gardenia urvillei and Gardenia oudiepe, endemic to New Caledonia. Most of them are rare polymethoxylated flavones. Some of these compounds showed noticeable activity against Leishmania (Leishmania) amazonensis, Plasmodium falciparum and Trypanosoma brucei gambiense, in addition to tubulin polymerization inhibition at low micromolar concentration. We also provide a full set of NMR data as some of the flavones were incompletely described.

Triterpenoid glycosides from the leaves of Meliosma henryi.

Seven triterpenoid glycosides, named meliosmosides A-G, were isolated from the leaves of Meliosma henryi Diels (Sabiaceae). Their structures were elucidated by different spectroscopic methods including 1D and 2D NMR experiments as well as HRESIMS analysis. Isolated compounds were evaluated for their cytotoxic activity against KB cell line.