Reversal activity of the naturally occurring chemosensitizer malagashanine in Plasmodium malaria

Highly diastereoselective cascade dearomatization of 3-(2-isocyanoethyl)indoles with nitrile imines: a facile access to unexpected polycyclic indolines

A novel cascade annulation between 2-isocyanoethylindoles and hydrazonyl chlorides has been realized to assemble a variety of unexpected polycyclic indoline derivatives with excellent diastereoselectivities under simple reaction conditions.

Squaramide-catalysed asymmetric Michael addition/cyclization cascade reaction of 4-arylmethylidene-2,3-dioxopyrrolidines with 2-isothiocyanato-1-indanones

A highly efficient cinchona alkaloid-derived squaramide catalysed asymmetric Michael/cyclization cascade reaction of 4-arylmethylidene-2,3-dioxopyrrolidines with 2-isothiocyanato-1-indanones was successfully developed. This protocol provides an efficient and mild access to indanone-derived spiropyrrolidone scaffolds containing three contiguous stereocenters with two spiroquaternary stereocenters in excellent yields (up to 99%) with high enantio- and diastereoselectivities (up to 99% ee and up to >20 : 1 dr). This method provides an economical and practical approach for the asymmetric synthesis of medicinally relevant molecules.

New solutions using natural products

Most antibiotics are derived from natural products, like penicillin, as well as recent insecticides, like pyrethroids. Secondary metabolites are produced by plants as ecological chemical mediators, and can therefore possess intrinsic physiological properties against other organisms. These benefits are far from being fully explored. In particular, attention is here focused on the multipurpose neem tree (Azadirachta indica), reporting several experiments of applications in the field of seed oil and neem cake. The latter product seems to be promising because of the low cost, the possible production on a large scale, and the selection of effects in favor of beneficial organisms. Neem cake is able to act on different sites, as required by integrated pest management. Several utilizations of neem products are reported and their potentiality evidenced. Some considerations in this chapter may appear distant from the title of the book, but only by applying the general natural rules can the reason of the single phenomenon be understood. Other studies on resistance mechanisms of Plasmodium are enabling new possible methods of control always based on natural products activity.

Total synthesis of malagashanine: a chloroquine potentiating indole alkaloid with unusual stereochemistry

The first total synthesis of malagashanine, a chloroquine potentiating indole alkaloid, is presented. A highly stereoselective cascade annulation reaction was developed to generate the tetracyclic core of the Malagasy alkaloids. This chemistry is likely to be broadly applicable to the synthesis of other members of this stereochemically unique family of natural products.

Nucleolin is important for Epstein-Barr virus nuclear antigen 1-mediated episome binding, maintenance, and transcription

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is essential for EBV episome maintenance, replication, and transcription. These effects are mediated by EBNA1 binding to cognate oriP DNA, which comprise 20 imperfect copies of a 30-bp dyad symmetry enhancer and an origin for DNA replication. To identify cell proteins essential for these EBNA1 functions, EBNA1 associated cell proteins were immune precipitated and analyzed by liquid chromatography-tandem mass spectrometry. Nucleolin (NCL) was identified to be EBNA1 associated. EBNA1's N-terminal 100 aa and NCL's RNA-binding domains were critical for EBNA1/NCL interaction. Lentivirus shRNA-mediated NCL depletion substantially reduced EBNA1 recruitment to oriP DNA, EBNA1-dependent transcription of an EBV oriP luciferase reporter, and EBV genome maintenance in lymphoblastoid cell lines. NCL RNA-binding domain K429 was critical for ATP and EBNA1 binding. NCL overexpression increased EBNA1 binding to oriP and transcription, whereas NCL K429A was deficient. Moreover, NCL silencing impaired lymphoblastoid cell line growth. These experiments reveal a surprisingly critical role for NCL K429 in EBNA1 episome maintenance and transcription, which may be a target for therapeutic intervention.

Molecular aspects on the specific interaction of cytotoxic plant alkaloid palmatine to poly(A)

The interaction of the protoberberine alkaloid palmatine with single and double stranded structures of poly(A) was studied by various biophysical techniques. Comparative binding studies were also performed with double stranded DNA, t-RNA, poly(C).poly(G), poly(U) and poly(C). The results of competition dialysis, fluorescence, and absorption spectral studies converge to reveal the molecular aspects of the strong and specific binding of palmatine to single stranded poly(A). The binding affinity of palmatine to natural DNA, t-RNA and double stranded poly(A) was weaker while no binding was apparent with single stranded poly(U), poly(C) and double stranded poly(C).poly(G). The strong affinity of the alkaloid to single stranded poly(A) in comparison to the double stranded structure was also revealed from circular dichroic and viscometric studies. The effect of [Na+] ion concentration on the binding process revealed the significant role of electrostatic forces in the complexation. The presence of bound alkaloid also remarkably affected denaturation-renaturation of stacked helical poly(A). The energetics of the strong binding to poly(A) was studied from thermodynamic estimation from van Hoff' analysis of the temperature dependent binding constants and ultra sensitive isothermal titration calorimertry, both suggesting the binding to be exothermic and enthalpy driven. This study provides detailed insight into the binding specificity of the natural alkaloid to single stranded poly(A) over several other single and double stranded nucleic acid structures suggesting its potential as a lead compound for RNA based drug targeting.

Exploiting a basic chemosensitizing pharmacophore hypothesis. Part 1: Synthesis and biological evaluation of novel arylbromide and bicyclic chemosensitizers against drug-resistant malaria parasites

An exploratory series of novel arylbromide and bicyclic chemosensitizers (modulators) against chloroquine-resistant Plasmodium falciparum were designed and synthesized on the basis of a basic chemosensitizing pharmacophore hypothesis in malaria. ortho-Substituted bromo and biphenyl ether compounds displayed the best activity from the series.

Synthesis and chloroquine-enhancing activity of Na-deacetyl-ferrocenoyl-strychnobrasiline

Several strychnobrasiline derivatives have been synthesized to overcome the lack of in vivo reversal activity of the parent compound. In the present study, N(a)-deacetyl-ferrocenoyl-strychnobrasiline was synthesized by condensing N(a)-deacetyl-strychnobrasiline with ferrocenic acid previously treated with oxalyl chloride. While the in vitro antiplasmodial activity of the test compound (IC(50)=4.83 microg/mL) was increased 15-fold compared to that of strychnobrasiline, and the in vitro enhancing activity was found to be similar to that of the parent compound, the compound was devoid of any in vivo potentiating effect, and an antagonistic effect was even observed at higher doses. Based on the overall results on the hemisynthesis of strychnobrasiline derivatives for better reversal activity, this strategy has appeared to be of little value for useful drugs.

Cytotoxicity and DNA binding properties of the plant alkaloid burasaine

Burasaine is a plant alkaloid isolated from the roots of several species of the Burasaia genus endemic to Madagascar. It exhibits in vitro antiplasmodial activities but the molecular basis of this biological activity is not known. The strong structural similarity with the alkaloid berberine prompted us to postulate that burasaine could interact with DNA. To test this hypothesis, we investigated the mode of binding of burasaine to DNA and tested its cytotoxic potential toward human HL-60 leukemia cells. Its inhibitory activity toward topoisomerases I and II was also studied. Absorption and melting temperature measurements attested that burasaine forms stable complexes with DNA. The results of electric linear dichroism (ELD) spectroscopy may be interpreted either by an intercalation or by an external stacking parallel to the base pairs. The affinity of burasaine for DNA is slightly lower than that of berberine and this translates at the cellular level by a reduced cytotoxicity. Burasaine does not promote DNA cleavage by human topoisomerases I or II and this likely accounts for its very weak cytotoxic potential and its very modest effects on the cell cycle progression observed at high concentrations. The study identifies DNA as a potential bioreceptor for burasaine and contributes to a better understanding of the mechanism of action of benzoquinolizine alkaloids.

Biological activities of the plant-derived bisindole voacamine with reference to malaria

The in vivo antiplasmodial activity of voacamine was assessed in a 4-day test. It was shown to exhibit in vivo activity with 25.4% and 43.4% inhibition of parasitaemia with 2.5 and 10 mg/kg, respectively. In synchronized cultures, it was found to act on trophozoite and schizont stages of Plasmodium falciparum. Using the FMC29 strain of Plasmodium falciparum as parasite and the isobologram curve as a method to assess interaction in drug combination, it was shown to lack any chloroquine-enhancing activity and its in vitro antiplasmodial effect was not potentiated by the chemosensitizer malagashanine.