Van Hung Nguyen

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.

Structure and total synthesis of (-)-myrionidine and (-)-schoberine, antimalarial alkaloids from Myrioneuron nutans.

Two new alkaloids, (5S,9S,10R)-myrionidine (1) and (5S,9S,10R,13S)-myrionamide (2), along with the known schoberine (3), were isolated from the leaves of Myrioneuron nutans (Rubiaceae), and their structures were determined from spectral analysis, including mass spectrometry and 2D NMR. The total asymmetric syntheses of (-)-myrionidine (1), (-)-schoberine (3), their enantiomers as well as their 9-epimers derivatives were performed, allowing the determination of their absolute configuration together with that of myrionamide (2). (-)-Myrionidine (1) and its synthetic enantiomer (18) showed a significant antimalarial activity on Plasmodium falciparum.

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 Aβ 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, Aβ aggregation (77.6%). Molecular docking studies were also performed to investigate interaction of these compounds with the active site of AChE.

Antiplasmodial, antitrypanosomal, and cytotoxic activities of prenylated flavonoids isolated from the stem bark of Artocarpus styracifolius.

In continuation of our efforts to find new antimalarial drugs, a systematic IN VITRO evaluation using a chloroquine resistant strain of PLASMODIUM FALCIPARUM (FcB1) was undertaken on extracts prepared from various parts of Vietnamese plants. The ethyl acetate extract obtained from the stem bark of ARTOCARPUS STYRACIFOLIUS (Moraceae) exhibited strong antiplasmodial activity (87 % at 10 µg/mL) whereas weak cytotoxicity was observed in a human fibroblast cell line (MRC-5). Phytochemical investigation of this extract led to isolation of two new prenylated flavonoids, styracifolins A and B ( 1 and 2), as well as the known artoheterophyllin A ( 3) and B ( 4), artonins A ( 5), B ( 6), and F ( 7), and heterophyllin ( 8). Structures of 1 and 2 were elucidated by spectroscopic methods and through comparison with data reported in the literature. Compounds 1- 8 exhibited antiplasmodial activities with IC (50) values ranging from 1.1 µM to 13.7 µM, and compounds 1, 2, 6, and 8 showed significant antitrypanosomal activities.

Cytotoxic pentacyclic triterpenoids from Combretum sundaicum and Lantana camara as inhibitors of Bcl-xL/BakBH3 domain peptide interaction.

In an effort to discover potent inhibitors of the antiapoptotic protein Bcl-xL, a systematic in vitro evaluation was undertaken on extracts prepared from various parts of Vietnamese plants. The ethyl acetate extracts obtained from the leaves and flowers of Combretum sundaicum and the leaves of Lantana camara were selected for their interaction with the Bcl-xL/Bak association. Bioassay-guided purification of these species led to the isolation of 15 pentacyclic triterpenoids (1-15) possessing olean-12-en-28-oic acid and olean-12-en-29-oic acid aglycons, of which compounds 1-6 and 8-10 are new. Five compounds exhibited binding activity with K(i) values between 5.3 and 17.8 microM. The cytotoxic activity of 1-15 was also evaluated on various cancer cell lines.

Preparative Isolation, Fast Centrifugal Partition Chromatography Purification and Biological Activity of Cajaflavanone from Derris ferruginea Stems

INTRODUCTION The Derris genus is known to contain flavonoid derivatives, including prenylated flavanones and isoflavonoids such as rotenoids, which are generally associated with significant biological activity. OBJECTIVE To develop an efficient preparative isolation procedure for bioactive cajaflavanone. METHODOLOGY Fast centrifugal partition chromatography (FCPC) was optimised to purify cajaflavanone from Derris ferruginea stems in a single step as compared to fractionation from the cyclohexane extract by successive conventional solid-liquid chromatography procedures. The purification yield, purity, time and solvent consumption per procedure are described. The anti-fungal, anti-bacterial, anti-leishmanial, anti-plasmodial, anti-oxidant activities and the inhibition of advanced glycation end-products (AGEs) by cajaflavanone accumulation are described. RESULTS FCPC enabled cajaflavanone purification in a single separation step, yielding sufficient quantities to perform in vitro biological screening. Interestingly, cajaflavanone had an inhibitory effect on the formation of AGEs, without displaying any in vitro anti-oxidant activity. CONCLUSION A simple and efficient procedure, in comparison with other preparative methods, for bioactive cajaflavone purification has been developed using FCPC.

Antiplasmodial alkaloids from Desmos rostrata.

Two new alkaloids, desmorostratine (1) and discretine N-oxide (2), were isolated from the stem bark of Desmos rostrata, together with five known alkaloids, discretine (3), dehydrodiscretine (4), pseudocolumbamine (5), predicentrine (6), and aristolactam AII (7). The structures were established on the basis of spectroscopic data, including mass spectrometry and 2D-NMR. Compound 1 was cytotoxic against KB cells (IC(50) 2.4 microM), while 2, 3, and 4 inhibited Plasmodium falciparum (IC(50) of 4.2, 1.6, and 0.9 microM, respectively).

Artemisinin Analogues as Potent Inhibitors of In Vitro Hepatitis C Virus Replication

We reported previously that Artemisinin (ART), a widely used anti-malarial drug, is an inhibitor of in vitro HCV subgenomic replicon replication. We here demonstrate that ART exerts its antiviral activity also in hepatoma cells infected with full length infectious HCV JFH-1. We identified a number of ART analogues that are up to 10-fold more potent and selective as in vitro inhibitors of HCV replication than ART. The iron donor Hemin only marginally potentiates the anti-HCV activity of ART in HCV-infected cultures. Carbon-centered radicals have been shown to be critical for the anti-malarial activity of ART. We demonstrate that carbon-centered radicals-trapping (the so-called TEMPO) compounds only marginally affect the anti-HCV activity of ART. This provides evidence that carbon-centered radicals are not the main effectors of the anti-HCV activity of the Artemisinin. ART and analogues may possibly exert their anti-HCV activity by the induction of reactive oxygen species (ROS). The combined anti-HCV activity of ART or its analogues with L-N-Acetylcysteine (L-NAC) [a molecule that inhibits ROS generation] was studied. L-NAC significantly reduced the in vitro anti-HCV activity of ART and derivatives. Taken together, the in vitro anti-HCV activity of ART and analogues can, at least in part, be explained by the induction of ROS; carbon-centered radicals may not be important in the anti-HCV effect of these molecules.

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).

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).