Cytotoxic aryltetralin lignans from fruits of Cleistanthus indochinensis.

Eight new aryltetralin lignans, cleisindosides A-F (1-6), picroburseranin (7), and 7-hydroxypicropolygamain (8), were isolated from the fruits of Cleistanthus indochinensis (Euphorbiaceae). The structures of the isolates were established on the basis of their one- and two-dimensional NMR spectral data, as well as their mass spectrometric data. Compound 7 was found to have potent cytotoxicity against oral epidermoid carcinoma cells with an IC50 value of 0.062 µM, whereas glycosylation to 3 (IC50 7.5 µM) and stereochemical changes to 8 (IC50 10.8 µM) led to marked decreases in biological activity. Thus, it was determined that the C-7 and C-8' positions are critical for the biological activity of the lignans from this plant.

Tigliane diterpenes from Croton mauritianus as inhibitors of chikungunya virus replication.

A bioassay-guided purification of an EtOAc extract of the leaves of Croton mauritianus using a chikungunya virus-cell-based assay led to the isolation of 12-O-decanoylphorbol-13-acetate (1) and the new 12-O-decanoyl-7-hydroperoxy-phorbol-5-ene-13-acetate (2), along with loliolide, vomifoliol, dehydrovomifoliol, annuionone D and bluemol C. The planar structure and the relative configuration of compound 2 were elucidated based on spectroscopic analysis, including 1D- and 2D-NMR experiments, mass spectrometry, and comparison with literature data. Compounds 1 and 2 inhibited chikungunya virus-induced cell death in cell culture with EC50s of 2.4±0.3 and 4.0±0.8 µM, respectively.

Styryllactones and acetogenins from the fruits of Goniothalamus macrocalyx.

Two new styryllactones, macrocalactone (1) and 3-deoxycardiobutanolide (2), were isolated from the fruits of Goniothalamus macrocalyx Ban (Annonaceae), together with seven known compounds including four acetogenins, annonacin (3), solamin (4), isoannonacin (5), trans-murisolinone (6), and three other compounds, 7-acetylaltholactone (7), beta-caryophyllene-8R,9R-oxide (8) and 2-(2'-hydroxytetracosanoylamino)-octadecane-1,3,4-triol (9). Their structures were determined by spectroscopic and MS analysis. The absolute configuration of 1 was determined by X-ray crystallographic analysis. The structures of the acetogenins were confirmed by liquid chromatography coupled to a hybrid quadrupole-time of flight mass spectrometer, using post-column lithium infusion. The results were compared with the fragmentation obtained with a hybrid linear trap-orbitrap mass spectrometer. Compound 7 had cytotoxicity against KB, HepG2, Lu, and MCF7 cell lines with IC50 values of 13.1, 23.7, 26.3 and 60.2 microM, respectively, whereas annonacin (3) was selectively active against KB cells (IC50 value of 6.5 microM). The discovery of 3-deoxycardiobutanolide (2) from the fruits of this plant revealed that G. macrocalyx could be a valuable natural resource to obtain this compound as it has been previously reported to have a significant cytotoxicity against different cancer cell lines, especially HL-60 cells.

One-pot synthesis of vinca alkaloids-phomopsin hybrids.

Hybrids of vinca alkaloids and phomopsin A have been elaborated with the aim of interfering with the "vinca site" and the "peptide site" of the vinca domain in tubulin. They were synthesized by an efficient one-pot procedure that directly links the octahydrophomopsin lateral chain to the velbenamine moiety of 7'-homo-anhydrovinblastine. In their modeled complexes with tubulin, these hybrids were found to superimpose nicely on the tubulin-bound structures of vinblastine and phomopsin A. This good matching can account for the fact that two of them are very potent inhibitors of microtubules assembly and are cytotoxic against four cancer cell lines.

Cycloartane triterpenes from the leaves of Neoboutonia macrocalyx L.

Neoboutonia macrocalyx is used by people in south western Uganda around Kibale National Park in the treatment of malaria. Phytochemical investigation on the leaves of this plant led to the isolation of nine cycloartane triterpenes (1-9) and one phenanthrene; 7-methoxy-2,8 dimethyl-9,10-dihydrophenantherene-3,6 diol (10) along with three known compounds which included 22-de-O-acetyl-26-deoxyneoboutomellerone (11), mellerin B (12) and 6-hydroxystigmast-4-en-3-one (13). The chemical structures of the compounds were established mainly through a combination of spectroscopic techniques. The isolated compounds were evaluated for antiplasmodial activity against the chloroquine-resistant FcB1/Colombia strain of Plasmodium falciparum and for cytotoxicity against the KB (nasopharyngeal epidermoid carcinoma) and MRC-5 (human diploid embryonic lung) cells. Seven out of 13 compounds exhibited good antiplasmodial activity with IC50 of ⩽5µg/ml with two compounds exhibiting low cytotoxicity and five compounds having significant cytotoxicity.

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.

Synthesis and biological evaluation of a new series of highly functionalized 7'-homo-anhydrovinblastine derivatives.

Sixteen new 7'-homo-anhydrovinblastine derivatives were prepared in one or two steps from vinorelbine by means of an original and regiospecific rearrangement and subsequent diastereoselective reduction. This strategy has allowed fast access to a family of vinca alkaloid derivatives with an enlarged and functionalized ring C'. Their synthesis and biological evaluation are reported. One compound (compound 35) is 1.7 times more active than vinorelbine as a tubulin assembly inhibitor. Moreover, some of these compounds are highly cytotoxic, and two of them are more potent than vinorelbine on HCT116 and K562 cell lines. Molecular modeling studies, carried out with two of the new vinca derivatives, provide useful hints about how a given functionalization introduced at positions 7' and 8' of the C' ring results in improved binding interactions between one of the new derivatives and the interdimer interface when compared to the parent compound vinblastine.

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.

Prostratin and 12-O-tetradecanoylphorbol 13-acetate are potent and selective inhibitors of Chikungunya virus replication.

A chemical study of the Vietnamese plant species Trigonostemon howii led to the isolation of a new tigliane-type diterpenoid, trigowiin A (1), along with several known coumarins and phenylpropanoids. The planar structure and the relative configuration of compound 1 were elucidated based on spectroscopic analysis, including 1D- and 2D-NMR experiments, mass spectrometry, and comparison with literature data. Trigowiin A (1) exhibited moderate antiviral activity in a virus-cell-based assay for Chikungunya virus (CHIKV). Since the structure of compound 1 is closely related to those of well-known tigliane diterpenoids such as prostratin (2), phorbol (3), 12-O-tetradecanoylphorbol 13-acetate (TPA) (4), and 4α-TPA (5), the antiviral activity of the latter compounds was also evaluated against CHIKV, as well as in virus-cell-based assays of two additional members of the genus Alphavirus (Sindbis virus, SINV, and Semliki forest virus, SFV). Whereas prostratin inhibited CHIKV replication with a moderate EC(50) of 2.6 µM and a selectivity index (SI) approximating 30, compound 4 proved to be an extremely potent inhibitor, with an EC(50) of ∼3 nM and a SI near 2000. Interestingly, no or very little activity was observed on the replication of SINV and SFV.

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).

Cytotoxic lignans from fruits of Cleistanthus indochinensis: synthesis of cleistantoxin derivatives.

Two new aryl-tetralin lignans, 1 and 2, were isolated from the fruits of Cleistanthus indochinensis by bioassay-guided purification. Their structures were determined by spectroscopic analysis including MS and 2D NMR. The absolute configurations of 1 and 2 were established from examination of their CD spectra. Compound 1 was cytotoxic against KB cells with an IC(50) value of 0.022 µM, while compound 2 had weaker cytotoxicity, with an IC(50) value of 1.4 µM. When tested against other cancer cell lines (MCF-7, MCF-7R, and HT29), 1 showed an IC(50) of 0.014 against MCF-7R cells and an IC(50) of 0.036 µM against MCF-7 cells. A series of amide derivatives of a new lactone, homoderivatives of 1, were prepared. Of these derivatives, only compound 3 had weak cytotoxicity against KB cells.

Antiviral chlorinated daphnane diterpenoid orthoesters from the bark and wood of Trigonostemon cherrieri.

The chemical study of the bark and the wood of Trigonostemon cherrieri, a rare endemic plant of New Caledonia, led to the isolation of a series of highly oxygenated daphnane diterpenoid orthoesters (DDO) bearing an uncommon chlorinated moiety: trigocherrins A-F and trigocherriolides A-D. Herein, we describe the isolation and structure elucidation of the DDO (trigocherrins B-F and trigocherriolides A-D). We also report the antiviral activity of trigocherrins A, B and F (1, 2 and 6) and trigocherriolides A, B and C (7-9) against various emerging pathogens: chikungunya virus (CHIKV), Sindbis virus (SINV), Semliki forest virus (SFV) and dengue virus (DENV).

Goniomedines A and B: unprecedented bisindole alkaloids formed through fusion of two indole moieties via a dihydropyran unit.

Two novel bisindole alkaloids, goniomedines A (1) and B (2), possessing an unprecedented quebrachamine-pleioarpamine-type skeleton, in which indole moieties are fused via a dihydropyran unit, were isolated from the stem bark of Gonioma malagasy. The structures were elucidated by comprehensive analysis of MS and NMR spectroscopic data. Their absolute configurations were deduced following the comparison of experimental and theoretically calculated ECD spectra and through biogenetic considerations. Goniomedine B (2) exhibited moderate activity against Plasmodium falciparum.

Chemical constituents of Anacolosa pervilleana and their antiviral activities.

In an effort to identify novel inhibitors of Chikungunya (CHIKV) and Dengue (DENV) virus replication, a systematic study with 820 ethyl acetate extracts of Madagascan plants was performed in a virus-cell-based assay for CHIKV and a DENV NS5 RNA-dependant RNA polymerase (RdRp) assay. The extract obtained from the leaves of Anacolosa pervilleana was selected for its significant activity in both assays. One new (E)-tridec-2-en-4-ynedioic acid named anacolosine (1), together with three known acetylenic acids, the octadeca-9,11,13-triynoic acid (2), (13E)-octadec-13-en-9,11-diynoic acid (3), (13E)-octadec-13-en-11-ynoic acid (4), two terpenoids, lupenone (5) and ß-amyrone (6), and one cyanogenic glycoside, (S)-sambunigrin (7) were isolated. Their structures were elucidated by comprehensive analyses of NMR spectroscopy and mass spectrometry data. The inhibitory potency of these compounds was evaluated on CHIKV, DENV RdRp and West-Nile polymerase virus (WNV RdRp). Both terpenoids showed a moderate activity against CHIKV (EC(50) 77 and 86 µM, respectively) and the acetylenic acids produced IC(50) values around 3 µM in the DENV RdRp assay.

Flacourtosides A-F, phenolic glycosides isolated from Flacourtia ramontchi.

In an effort to identify novel inhibitors of chikungunya (CHIKV) and dengue (DENV) virus replication, a systematic study with 820 ethyl acetate extracts of madagascan plants was performed in a virus-cell-based assay for CHIKV, and a DENV NS5 RNA-dependent RNA polymerase (RdRp) assay. The extract obtained from the stem bark of Flacourtia ramontchi was selected for its significant activity in both assays. Six new phenolic glycosides, named flacourtosides A-F (1-6), phenolic glycosides itoside H, xylosmin, scolochinenoside D, and poliothrysoside, and betulinic acid 3ß-caffeate were obtained using the bioassay-guided isolation process. Their structures were elucidated by comprehensive analyses of NMR spectroscopic and mass spectrometric data. Even though several extracts and fractions showed significant selective antiviral activity in the CHIKV virus-cell-based assay, none of the purified compounds did. However, in the DENV RNA polymerase assay, significant inhibition was observed with betulinic acid 3ß-caffeate (IC(50) = 0.85 ± 0.1 µM) and to a lesser extent for the flacourtosides A and E (1 and 5, respectively), and scolochinenoside D (IC(50) values ~10 µM).

Synthesis, biological evaluation, and molecular modeling of natural and unnatural flavonoidal alkaloids, inhibitors of kinases.

The screening of the ICSN chemical library on various disease-relevant protein kinases led to the identification of natural flavonoidal alkaloids of unknown configuration as potent inhibitors of the CDK1 and CDK5 kinases. We thus developed an efficient and modular synthetic strategy for their preparation and that of analogues in order to determine the absolute configuration of the active natural flavonoidal alkaloids and to provide further insights on the structure-activity relationships in this series. The structural determinants of the interaction between some flavonoidal alkaloids with specific kinases were also evaluated using molecular modeling.

High resolution crystal structure of rat long chain hydroxy acid oxidase in complex with the inhibitor 4-carboxy-5-[(4-chlorophenyl)sulfanyl]-1, 2, 3-thiadiazole. Implications for inhibitor specificity and drug design.

Long chain hydroxy acid oxidase (LCHAO) is responsible for the formation of methylguanidine, a toxic compound with elevated serum levels in patients with chronic renal failure. Its isozyme glycolate oxidase (GOX), has a role in the formation of oxalate, which can lead to pathological deposits of calcium oxalate, in particular in the disease primary hyperoxaluria. Inhibitors of these two enzymes may have therapeutic value. These enzymes are the only human members of the family of FMN-dependent l-2-hydroxy acid-oxidizing enzymes, with yeast flavocytochrome b(2) (Fcb2) among its well studied members. We screened a chemical library for inhibitors, using in parallel rat LCHAO, human GOX and the Fcb2 flavodehydrogenase domain (FDH). Among the hits was an inhibitor, CCPST, with an IC(50) in the micromolar range for all three enzymes. We report here the crystal structure of a complex between this compound and LCHAO at 1.3 Å resolution. In comparison with a lower resolution structure of this enzyme, binding of the inhibitor induces a conformational change in part of the TIM barrel loop 4, as well as protonation of the active site histidine. The CCPST interactions are compared with those it forms with human GOX and those formed by two other inhibitors with human GOX and spinach GOX. These compounds differ from CCPST in having the sulfur replaced with a nitrogen in the five-membered ring as well as different hydrophobic substituents. The possible reason for the ∼100-fold difference in affinity between these two series of inhibitors is discussed. The present results indicate that specificity is an issue in the quest for therapeutic inhibitors of either LCHAO or GOX, but they may give leads for this quest.

Toxicarioside M, a new cytotoxic 10ß-hydroxy-19-nor-cardenolide from Antiaris toxicaria.

A new 10ß-hydroxy-19-nor-cardenolide, named toxicarioside M (1), was isolated from the trunk bark of Antiaris toxicaria (Pers.) Lesch (Moraceae), along with six known cardenolides (convallatoxin (2), convallatoxol (3), convalloside (4), 3-O-ß-D-xylopyranosylstrophanthidin (5), glucostrophanthidin (6) and strophanthidin (7)). Their structures were elucidated on the basis of HR-MS(n) analysis, spectroscopic methods (IR, UV, 1D and 2D NMR) and by comparison with data reported in the literature. The cardenolides were evaluated for their cytotoxic activity against KB, HCT-116, SF-268, MCF-7, HL-60, PC-3 and MRC-5 cell lines.

Trigocherrin A, the first natural chlorinated daphnane diterpene orthoester from Trigonostemon cherrieri.

Trigocherrin A, a chlorinated and highly oxygenated daphnane diterpenoid orthoester (DDO), was isolated from the bark of Trigonostemon cherrieri. Trigocherrin A is the first example of a naturally occurring halogenated DDO. Its structure was elucidated by comprehensive analysis of NMR spectroscopic data, and its absolute configuration was determined by comparison of experimental and theoretically calculated ECD spectra. Trigocherrin A exhibited a potent and selective effect against Chikungunya virus in Vero cells.

Alkylated flavanones from the bark of Cryptocarya chartacea as dengue virus NS5 polymerase inhibitors.

An in vitro screening of New Caledonian plants allowed the selection of several species with a significant dengue virus NS5 RNA-dependent RNA polymerase (RdRp) inhibiting activity. The chemical investigation of Cryptocarya chartacea led to the isolation of a series of new mono- and dialkylated flavanones named chartaceones A-F (1-6), along with pinocembrin. They were isolated as racemic mixtures and characterized using extensive one- and two-dimensional NMR spectroscopy. Four diastereomers of chartaceone A (1) were separated using chiral HPLC, and their absolute configurations were established by comparison of their experimental and calculated ECD spectra. The dialkylated flavanones, chartaceones C-F (3-6), exhibited the most significant NS5 RdRp inhibiting activity, with IC(50) ranging from 1.8 to 4.2 µM. Chartaceones represent a new class of non-nucleosidic inhibitors of the DENV NS5 RdRp.