Antimalarial activity and structure-activity relationships of protoberberine alkaloids

Discovery of natural AMPK activator from the fruits of Xanthium sibiricum Patr.: Xanthiumine A, protoberberine alkaloid with unique C28 skeleton

Two protoberberine alkaloids with a unique C28 skeleton, named xanthiumines A (1) and B (2), respectively, were isolated from the fruits of Xanthium sibiricum Patr. Their structures including absolute configurations were unequivocally established by the comprehensive NMR and MS spectroscopic data analysis together with gauge-independent atomic orbital (GIAO) NMR calculations, and electronic circular dichroism (ECD) calculations. Compounds 1 and 2 are the first examples of natural protoberberine alkaloid with a phenolic acid group at C-13a. Their plausible biosynthetic pathway was proposed on the basis of the coexisting alkaloid monomer as the precursor. Furthermore, the effects and related molecular mechanism of compound 1 on hepatic lipid accumulation were also investigated in oleic acid (OA)-treated HepG2 cells.

Metal-catalyzed B-H acylmethylation of pyridylcarboranes: access to carborane-fused indoliziniums and quinoliziniums

Metal-catalyzed mono-acylmethylation of pyridylcarboranes has been realized using α-carbonyl sulfoxonium ylides as a coupling partner. The reaction features high efficiency, excellent site-selectivity and good functional group tolerance. In the presence of pyridyl and enolizable acylmethyl groups, a post-coordination mode has been proposed and validated by in situ high resolution mass spectroscopy (HRMS) to rationalize the unique mono-substitution. Post-functionalization at the newly incorporated alkyl site provides additional utility of this method, including the construction of carborane-fused indoliziniums and quinoliziniums. We believe that these mono-alkylated carboranes, together with their post-functionalized derivatives, may find applications in luminescent materials and drug discovery in the near future.

Synthesis and Evaluation of the Antibacterial Activities of 13-Substituted Berberine Derivatives

The biological activities of berberine, a natural plant molecule, are known to be affected by structural modifications, mostly at position 9 and/or 13. A series of new 13-substituted berberine derivatives were synthesized and evaluated in term of antimicrobial activity using various microorganisms associated to human diseases. Contrarily to the original molecule berberine, several derivatives were found strongly active in microbial sensitivity tests against Mycobacterium, Candida albicans and Gram-positive bacteria, including naïve or resistant Bacillus cereus, Staphylococcus aureus and Streptococcus pyogenes with minimal inhibitory concentration (MIC) of 3.12 to 6.25 µM. Among the various Gram-negative strains tested, berberine's derivatives were only found active on Helicobacter pylori and Vibrio alginolyticus (MIC values of 1.5-3.12 µM). Cytotoxicity assays performed on human cells showed that the antimicrobial berberine derivatives caused low toxicity resulting in good therapeutic index values. In addition, a mechanistic approach demonstrated that, contrarily to already known berberine derivatives causing either membrane permeabilization, DNA fragmentation or interacting with FtsZ protein, active derivatives described in this study act through inhibition of the synthesis of peptidoglycan or RNA. Overall, this study shows that these new berberine derivatives can be considered as potent and safe anti-bacterial agents active on human pathogenic microorganisms, including ones resistant to conventional antibiotics.

Fabrication, characterization and optimization of berberine-loaded PLA nanoparticles using coaxial electrospray for sustained drug release

BACKGROUND

Berberine (BBR) broadly found in medicinal plants has a major application in pharmacological therapy as an anticancer drug. Clinical applications of this promising natural drug are limited due to its poor water solubility and low bioavailability.

OBJECTIVE

In this study, for the first time, we synthesized core-shell BBR-loaded PLA nanoparticles (NPBs) by using coaxial electrospray (CES) to solve the poor bioavailability of BBR.

METHODS

Three-factor (feeding rate, polymeric solution concentration and applied voltage), three-level, Box-Behnken design was used for optimization of the size and particle size distribution of the prepared NPBs.

RESULTS

Based on the results of response surface methodology, the NPBs with the mean size of 265 nm and particle size distribution of 43 nm were synthesized. A TEM image was used to well illustrate the core-shell structure of the NPBs. Encapsulation efficiency and BBR loading capacity for the optimized NPBs were determined at about 81% and 7.5%, respectively. Release of NPBs was examined at pH 7.4 and 5.8. NPBs had a slower release profile than free BBR in both pH values, and the rate of BBR release was more and faster in acidic pH than in physiological one. Effects of the NPBs on the drug release were confirmed by data fitting with six kinetic models. NPBs showed an increased cytotoxic efficacy against HCT116 cells (IC₅₀ = 56 μM), while NIH3T3 cells, non-neoplastic fibroblast cells, (IC₅₀ > 150 μM) were less affected by NPBs. Flow cytometry demonstrated that the cellular uptake of NPBs were higher than BBR at different concentrations.

CONCLUSIONS

A new approach was developed in this study to prepare NPBs using the CES process for improving the efficiency and controlled BBR release. It is concluded that nano-scaled NPBs prepared by CES can improve toxicity and chemotherapeutic properties of BBR against cancerous cells. We believe that these NPBs can exhibit further potential in cancer drug delivery systems. Graphical abstract.

Synthesis of hydrophobically modified berberine derivatives with high anticancer activity through modulation of the MAPK pathway

Linoleic acid-modified berberine derivative induces apoptosis of A549 cells and affects the expression of proteins associated with the MAPK pathway.

Methanol extracts of Fagara zanthoxyloides leaves possess antimalarial effects and normalizes haematological and biochemical status of Plasmodium berghei-passaged mice

Context: The resistance of Plasmodium species to many available antimalarials calls for a continuous search for newer antimalarial agents. One possible source of new antimalarials is from natural sources such as Fagara zanthoxyloides Lam (Rutaceae), a medicinal plant used traditionally for treating malaria in South-Eastern Nigeria, Uganda and Asia. Objectives: To investigate the application of methanol extracts of F. zanthoxyloides in combating malaria infection and its associated disorders. Materials and methods: Methanol extracts of F. zanthoxyloides leaves (MEFZ) were evaluated for in vivo antimalarial activity. MEFZ at doses of 200, 400, and 600 mg/kg/d were administered orally for 4 consecutive days (days 0-4) to P. berghei-infected mice. The possible ameliorative effects of MEFZ on malaria-associated organ malfunctions were also assessed. Results: At 200, 400 and 600 mg/kg b.w., respectively, MEFZ produced 82.37% and 68.39%, 84.84%, and 90.75%, 95.95% and 92.67% chemosuppression and inhibition of P. berghei, respectively, comparable to 98.67% and 97.29% by combisunate, a standard antimalarial. The IC₅₀ of MEFZ was estimated to be 235.23 mg/kg b.w. Similarly, treatment of parasitized mice with MEFZ significantly restored the malaria-modified haematological and biochemical status of the parasitized-MEFZ-treated mice compared with parasitized-untreated mice. MEFZ was tolerable up to 5000 mg/kg b.w dose; hence, the LD₅₀ is above 5000 mg/kg b.w. Discussion and conclusions: The results of this curative assay demonstrated that MEFZ has antimalarial effects and normalized haematological and biochemical aberrations generated by malaria. The isolation of the antimalarial principles in MEFZ is warranted; they could be lead molecules for the development of new antimalarials.

A Unified Strategy for the Syntheses of the Isoquinolinium Alkaloids Berberine, Coptisine, and Jatrorrhizine

Total syntheses of the antibacterial alkaloids berberine, coptisine, and jatrorrhizine have been achieved in four steps through a unified route. The key step of this strategy is an efficient intramolecular Friedel-Crafts alkoxyalkylation which, following oxidation, establishes the isoquinolinium core of these natural products. Herein, the design and development of this synthetic strategy, which has enabled the shortest and most efficient syntheses of these alkaloids reported to date, is described.

Screening of a library of traditional Chinese medicines to identify anti-malarial compounds and extracts

BACKGROUND

Malaria is a major infectious disease in the world. In 2015, approximately 212 million people were infected and 429,000 people were killed by this disease. Plasmodium falciparum, which causes falciparum malaria, is becoming resistant to artemisinin (ART) in Southeast Asia; therefore, new anti-malarial drugs are urgently needed. Some excellent anti-malarial drugs, such as quinine or ART, were originally obtained from natural plants. Hence, the authors screened a natural product library comprising traditional Chinese medicines (TCMs) to identify compounds/extracts with anti-malarial effects.

METHODS

The authors performed three assays: a malaria growth inhibition assay (GIA), a cytotoxicity assay, and a malaria stage-specific GIA. The malaria GIA revealed the anti-malarial ability and half-maximal inhibitory concentrations (IC₅₀) of the natural products, whereas the malaria stage-specific GIA revealed the point in the malaria life cycle where the products exerted their anti-malarial effects. The toxicity of the products to the host cells was evaluated with the cytotoxicity assay.

RESULTS

Four natural compounds (berberine chloride, coptisine chloride, palmatine chloride, and dehydrocorydaline nitrate) showed strong anti-malarial effects (IC₅₀ < 50 nM), and low cytotoxicity (cell viability > 90%) using P. falciparum 3D7 strain. Two natural extracts (Phellodendri cortex and Coptidis rhizoma) also showed strong antiplasmodial effects (IC₅₀ < 1 µg/ml), and low cytotoxicity (cell viability > 80%). These natural products also demonstrated anti-malarial capability during the trophozoite and schizont stages of the malaria life cycle.

CONCLUSIONS

The authors identified four compounds (berberine chloride, coptisine chloride, palmatine chloride, and dehydrocorydaline nitrate) and two extracts (Phellodendri cortex and Coptidis rhizoma) with anti-malarial activity, neither of which had previously been described. The IC₅₀ values of the compounds were comparable to that of chloroquine and better than that of pyrimethamine. These compounds and extracts derived from TCMs thus show promise as potential future anti-malarial drugs.

Evolution of two routes for asymmetric total synthesis of tetrahydroprotoberberine alkaloids

Two routes were developed for the catalytic asymmetric total synthesis of tetrahydroprotoberberine alkaloids.

A Facile and Diastereoselective access to Functionalised Benzopyrano[3,4-a] Quinolizines via a Pyridine-Based Three-Component Reaction

The reaction of 2-oxo-2 H-chromene-3-carbonitriles with dialkyl acetylenedicarboxylates and pyridines results in a three-component condensation reaction in which the 2-oxo-2 H-chromene-3-carbonitrile group acts as a dipolarophile to produce benzopyrano[3,4- a] quinolizines under mild conditions in good yield.

The synthesis and antistaphylococcal activity of 9, 13-disubstituted berberine derivatives

A series of novel 9, 13-disubstituted berberine derivatives have been synthesized and evaluated for the antibacterial activities against Staphylococcus aureus, including Newman strain and multidrug-resistant strains (NRS-1, NRS-70, NRS-100, NRS-108, and NRS-271). Compound 20 shows the most potent activity against the growth of Newman strain, with a MIC value of 0.78 μg/mL, which is comparable with the positive control vancomycin. In addition, compound 20, 21, and 33 are highly antistaphylococcal active against five strains of multidrug-resistant S. aureus, with MIC values of 0.78-1.56 μg/mL. Of note, theses antibacterial active compounds have no obvious toxicity to the viability of human fibroblast (HAF) cells at the MIC concentration.

Benzo[b]quinolizinium Derivatives Have a Strong Antimalarial Activity and Inhibit Indoleamine Dioxygenase

The heme-containing enzymes indoleamine 2,3-dioxygenase-1 (IDO-1) and IDO-2 catalyze the conversion of the essential amino acid tryptophan into kynurenine. Metabolites of the kynurenine pathway and IDO itself are involved in immunity and the pathology of several diseases, having either immunoregulatory or antimicrobial effects. IDO-1 plays a central role in the pathogenesis of cerebral malaria, which is the most severe and often fatal neurological complication of infection with Plasmodium falciparum. Mouse models are usually used to study the underlying pathophysiology. In this study, we screened a natural compound library against mouse IDO-1 and identified 8-aminobenzo[b]quinolizinium (compound 2c) to be an inhibitor of IDO-1 with potency at nanomolar concentrations (50% inhibitory concentration, 164 nM). Twenty-one structurally modified derivatives of compound 2c were synthesized for structure-activity relationship analyses. The compounds were found to be selective for IDO-1 over IDO-2. We therefore compared the roles of prominent amino acids in the catalytic mechanisms of the two isoenzymes via homology modeling, site-directed mutagenesis, and kinetic analyses. Notably, methionine 385 of IDO-2 was identified to interfere with the entrance of l-tryptophan to the active site of the enzyme, which explains the selectivity of the inhibitors. Most interestingly, several benzo[b]quinolizinium derivatives (6 compounds with 50% effective concentration values between 2.1 and 6.7 nM) were found to be highly effective against P. falciparum 3D7 blood stages in cell culture with a mechanism independent of IDO-1 inhibition. We believe that the class of compounds presented here has unique characteristics; it combines the inhibition of mammalian IDO-1 with strong antiparasitic activity, two features that offer potential for drug development.

Annickia affinis and A. chlorantha (Enantia chlorantha)--A review of two closely related medicinal plants from tropical Africa

ETHNOPHARMACOLOGICAL RELEVANCE

Annickia affinis (Exell) Versteegh & Sosef, closely related to A. chlorantha Setten & P.J.Maas (both species also referred to as Enantia chlorantha Oliv.), from the Annonaceae family, are multi-purpose medicinal plants used widely across tropical Africa. The two Annickia species are morphologically distinct from each other and have different distribution patterns, but are frequently confused. Furthermore, the name Enantia chlorantha is an illegitimate name, but is still used today.

MATERIALS AND METHODS

A review of the literature was undertaken and an in-depth analysis of previous research and future prospectives are considered. While a myriad of publications cite the species "Enantia chlorantha", this is not the case for A. affinis and A. chlorantha, and no reviews are available for any of the species to date. Consequently, a summary of their ethnobotany, phytochemistry and biological properties is presented here (for the period 1933 - November 2014) in order to substantiate their traditional importance as medicines for rural people in Africa.

RESULTS

To this effect, these species seem to be the preferred traditional treatments for malaria in tropical Africa, an area suffering heavily under the malaria pandemic. Their chemical composition is dominated particularly by various isoquinoline alkaloids, as well as by acetogenins and sesquiterpenes, which have been isolated from the bark and leaves. All three of these classes of compounds have been reported to exhibit noteworthy biological activity.

CONCLUSIONS

Due to their widespread use, especially of the bark, these species have already been categorized as threatened with extinction. Consequently this study further aims to identify areas where more research needs to be conducted involving these important species, and also to suggest possible means of increasing the biological activities of their extracts as a way to conserve the species.

Naturally occurring plant isoquinoline N-oxide alkaloids: their pharmacological and SAR activities

The present review describes research on novel natural isoquinoline alkaloids and their N-oxides isolated from different plant species. More than 200 biological active compounds have shown confirmed antimicrobial, antibacterial, antitumor, and other activities. The structures, origins, and reported biological activities of a selection of isoquinoline N-oxides alkaloids are reviewed. With the computer program PASS some additional SAR (structure-activity relationship) activities are also predicted, which point toward new possible applications of these compounds. This review emphasizes the role of isoquinoline N-oxides alkaloids as an important source of leads for drug discovery.

A room-temperature protocol to access isoquinolines through Ag(i) catalysed annulation of o-(1-alkynyl)arylaldehydes and ketones with NH4OAc: elaboration to berberine and palmatine

A silver catalysed protocol for the synthesis of a wide range of isoquinolines from o-(1-alkynyl)arylaldehydes has been developed under mild conditions and elaborated to the synthesis of berberine and palmatine.

Short and efficient syntheses of protoberberine alkaloids using palladium-catalyzed enolate arylation

A concise synthesis of the biologically active alkaloid berberine is reported, and a versatile palladium-catalyzed enolate arylation is used to form the isoquinoline core. The overall yield of 50 % is a large improvement over the single, previous synthesis. By design, this modular route allows the rapid synthesis of other members of the protoberberine family (e.g., pseudocoptisine and palmatine) by substitution of the readily available aryl bromide and ketone coupling partners. Moreover, by combining enolate arylation with in situ functionalization, substituents can be rapidly and regioselectively introduced at the alkaloid C13 position, as demonstrated by the total synthesis of dehydrocorydaline. The avoidance of electrophilic aromatic substitution reactions to make the isoquinoline allows direct access to analogues possessing more varied electronic properties, such as the fluorine-containing derivative synthesized here.

Binding of novel 9-O-N-aryl/arylalkyl amino carbonyl methyl berberine analogs to poly(U)-poly(A)·poly(U) triplex and comparison to the duplex poly(A)-poly(U)

Interaction of the 9-O-N-aryl/arylalkyl amino carbonyl methyl substituted analogs of the anticancer isoquinoline alkaloid berberine with RNA triplex, poly(U)-poly(A) · poly(U) has been studied in comparison to the duplex poly(A)-poly(U), using multiple biophysical techniques. Spectrophotometric and spectrofluorimetric studies established the non-cooperative binding mode of all the analogs with both the duplex and the triplex. However, berberine exhibited cooperative binding with poly(A)-poly(U) and non-cooperative binding with poly(U)-poly(A) · poly(U). Analog BER1 showed the highest affinity to both the duplex and the triplex followed by BER2 and BER3. The overall binding affinity varied as BER1 > BER2 > BER3 > BER. The magnitude of the quantum efficiency values (Q > 1) revealed that energy was transferred from the bases of the triplex and the duplex to the analogs. Comparative ferrocyanide quenching and viscosity studies unambiguously established a stronger intercalative geometry of the analogs to both the triplex and the duplex in comparison to berberine. Circular dichroism studies revealed that the alkaloids perturbed the conformation of both RNA helices. The binding of all the alkaloids was found to be exothermic from isothermal titration studies. Binding of the analogs was highly entropy driven while that of berberine was enthalpy dominated. The results presented here reveal strong and specific binding of these new berberine analogs to the RNA triplex and duplex and highlight the remarkable influence of the 9-substitution on the interaction profile.

Berberine and its metabolites: relationship between physicochemical properties and plasma levels after administration to human subjects

Berberine (1) is an alkaloid used widely in the treatment of several diseases. However, its physicochemical properties, pharmacokinetics, and metabolism remain unclear, and conflicting data have been reported. In this study, the main physicochemical properties of 1 and its metabolites were evaluated, including lipophilicity, solubility, pKa, and albumin binding. A sensitive HPLC-ESIMS/MS method was developed and validated to identify 1 and its main metabolites in human plasma. This method was used to quantify their levels in the plasma of healthy volunteers and hypercholesterolemic patients following a single dose and chronic administration, respectively. In both cases, berberrubine (2) was found to be the main metabolite. Surprisingly, 2 is more lipophilic than 1, which suggests that this compound tautomerizes to a highly conjugated, electroneutral quinoid structure. This was confirmed by NMR studies. These results indicate that the higher plasma concentration of 2 was a consequence of a more efficient intestinal absorption, suggesting that berberrubine is potentially more pharmacologically active than berberine.

Interaction of 9-O-N-aryl/arylalkyl amino carbonyl methyl berberine analogs with single stranded ribonucleotides

Studies on the molecular aspects of alkaloid-RNA complexation are of prime importance for the development of rational RNA targeted drug design strategies. Towards this goal, the binding aspects of three novel 9-O-N-aryl/arylalkyl amino carbonyl methyl substituted berberine analogs to four single stranded ribonucleotides, poly(G), poly(I), poly(C) and poly(U), were studied for the first time employing multifaceted biophysical tools. Absorbance and fluorescence studies revealed that these analogs bound non-cooperatively to poly(G) and poly(I) with binding affinities remarkably higher than berberine. The binding of these analogs to poly(U) and poly(C) was weaker in comparison to poly(G) and poly(I) but were one order higher in comparison to berberine. Quantum efficiency values revealed that energy transfer occurred from the RNA bases to the analogs upon complexation. The binding was dominated by large positive entropic contributions and small but favorable enthalpic contributions. Salt dependent studies established that the binding was dominated by hydrophobic forces that contributed around 90% of the total standard molar Gibbs energy. The chain length of the substitution at the 9-position was found to be critical in modulating the binding affinities. These results provide new insights into the binding efficacy of these novel berberine analogs to single stranded RNA sequences.

Flow-injection post-chemiluminescence method for the determination of palmatine

A post-chemiluminescence (PCL) phenomenon was observed when palmatine was injected in a mixture of N-bromosuccinimide (NBS) and alkaline dichlorofluorescein (DCF) after the chemiluminescence (CL) reaction of NBS-alkaline DCF had finished. Based on the PCL reaction, a rapid and sensitive method for the determination of palmatine was established. Under optimum conditions, the CL intensity was linear, with the concentration of palmatine in the range of 5.0 × 10(-9) to 1.0 × 10(-6) M. The detection limit was 6.0 × 10(-10) M for palmatine. The relative standard deviation for 11 parallel measurements of 1.0 × 10(-7) M palmatine was 1.5%. This method was applied to the determination of palmatine in pharmaceutical samples and biological fluids, with satisfactory results. The possible reaction mechanism is discussed briefly.

Binding of the 9-O-N-aryl/arylalkyl amino carbonyl methyl substituted berberine analogs to tRNA(phe.)

Background

Three new analogs of berberine with aryl/arylalkyl amino carbonyl methyl substituent at the 9-position of the isoquinoline chromophore along with berberrubine were studied for their binding to tRNA^phe by wide variety of biophysical techniques like spectrophotometry, spectrofluorimetry, circular dichroism, thermal melting, viscosity and isothermal titration calorimetry.

Methodology/Principal Findings

Scatchard binding isotherms revealed that the cooperative binding mode of berberine was propagated in the analogs also. Thermal melting studies showed that all the 9-O-N-aryl/arylalkyl amino carbonyl methyl substituted berberine analogs stabilized the tRNA^phe more in comparison to berberine. Circular dichroism studies showed that these analogs perturbed the structure of tRNA^phe more in comparison to berberine. Ferrocyanide quenching studies and viscosity results proved the intercalative binding mode of these analogs into the helical organization of tRNA^phe. The binding was entropy driven for the analogs in sharp contrast to the enthalpy driven binding of berberine. The introduction of the aryl/arylalkyl amino carbonyl methyl substituent at the 9-position thus switched the enthalpy driven binding of berberine to entropy dominated binding. Salt and temperature dependent calorimetric studies established the involvement of multiple weak noncovalent interactions in the binding process.

Conclusions/Significance

The results showed that 9-O-N-aryl/arylalkyl amino carbonyl methyl substituted berberine analogs exhibited almost ten folds higher binding affinity to tRNA^phe compared to berberine whereas the binding of berberrubine was dramatically reduced by about twenty fold in comparison to berberine. The spacer length of the substitution at the 9-position of the isoquinoline chromophore appears to be critical in modulating the binding affinities towards tRNA^phe.

Synthesis and cytotoxicity evaluation of 13-n-alkyl berberine and palmatine analogues as anticancer agents

By introducing long carbon-chain alkyl groups at the C-13 position of berberine and palmatine, 13-n-hexyl/13-n-octyl berberine and palmatine chloride analogues 4a–d were synthesized and examined by MTT assays for cytotoxic activity in seven human cancer cell lines (7701QGY, SMMC7721, HepG2, CEM, CEM/VCR, KIII, Lewis), yielding IC₅₀ values of 0.02 ± 0.01–13.58 ± 2.84 μM. 13-n-Octyl palmatine (compound 4d) gave the most potent inhibitor activity, with an IC₅₀ of 0.02 ± 0.01 μM for SMMC7721. In all cases, the 13-n-alkyl berberine and palmatine analogues 4a–d were more cytotoxic than berberine and palmatine. In addition, compounds 4a–d also exhibited more potent cytotoxicity than berberine and palmatine in mice with S180 sarcoma xenografted in vivo. The primary screening results indicated that the 13-n-hexyl/13-n-octyl berberine and palmatine analogues might be valuable source for new potent anticancer drug candidates.

HPLC enantioseparation of alkaloid malacitanine using fluorimetric/polarimetric detection

This work reports two methods developed for the separation and determination of the enantiomers of the new alkaloid malacitanine (MLC) and the determination of the enantiomeric purity in mixtures. First, the isomers were separated using a Chirex 3020 (250 mm × 4.6 mm, 5 μm) chiral column with a mobile phase of cyclohexane-1,2-dichloroethane-ethanol-trifluoroacetic acid (64:30:6:0.6, v/v/v/v) at a flow rate of 1 mL/min and fluorimetric detection. Obtained retention times were 12.4 and 15.9 min (+ and -) with a resolution Rs of 1.13. Relative standard deviations (RSDs) were 2.5 and 2.4% at the 0.5-μg level (four determinations). Second, a nonenantioselective procedure for the determination of enantiomeric purity of MLC using a Lichrospher ® Si-60 (250 mm × 5 mm, 5 μm) normal phase with a mobile phase of 100% ethanol at a flow rate of 0.9 mL/min coupled to two detectors in series, fluorimetric and polarimetric. RSD of 3.3% was obtained. Calculated enantiomeric purity by chiral chromatography gave 48.6% (-)-MLC in the near racemic product. Using polarimetric signal of the nonseparated enantiomers and comparing the slopes of the calibration curves (enantiomers) from the racemic product gave 47.8% (-)-MLC content. A study of accuracy of (-)-MLC gave recoveries from 98.3 to 100.7%.

Spontaneous formation of fluorescent nanofibers and reticulated solid from berberine palmitate: a new example of aggregation-induced emission enhancement in organic ion pairs

The salt formed between the large aromatic berberine cation and the long-chain palmitate anion was synthesized and used to prepare aqueous suspensions of particles owing to a solvent-exchange method. Under these conditions, elongated particles were readily obtained. They were studied by transmission microscopy with polarized light, as well as by fluorescence and electron microscopy. They were shown to be probably crystallized nanofibers, which were stable in suspension. Unexpectedly, upon filtration and drying, these fibers evolved to give a reticulated solid. The fluorescence properties of the compound were analyzed in solution, in aqueous suspension and in the powder crystalline state. Interestingly, berberine palmitate is virtually not fluorescent in aqueous solution because of the quenching effect of water, but transition to the solid state was accompanied by a strong increase in fluorescence intensity. This phenomenon was explained by the original molecular arrangement in the solid state. Actually, in the crystal, the anions form a distinct layer, which limits parallel-stacking of the fluorescent cations. Moreover, the berberine cations are protected from the access of water molecules, and so no quenching effect can take place. This example confirms that the newly introduced concept of ion-pair aggregation-induced fluorescence enhancement can be extended to a variety of structures. It also shows the interest of ion pairs for preparing fluorescent nanofibers and reticulated solids using a solvent-exchange method that is particularly easy to implement.

9-O-Ethyl-berberrubinium iodide monohydrate

In the title compound (systematic name: 9-eth­oxy-10-meth­oxy-5,6-dihydro-1,3-dioxolo[4,5-g]isoquinolino­[3,2-a]isoquin­olin-7-ium iodide monohydrate), 2C₂₁H₂₀NO₄⁺·2I⁻·H₂O, two independent mol­ecules pack in the unit cell, where interactions between the molecules are stabilized by weak inter­molecular π–π stacking inter­actions [centroid–centroid distances in the range 3.571 (4) to 3.815 (4)Å]. Inter­molecular C—H⋯O inter­actions are also observed. The iodide anions are disordered with occupancy ratios of 0.94 (1):0.06 (1) and 0.91 (1):0.09 (1). The cationic molecule is planar in structure with a small torsion resulting from the dihydropyridine ring.

In vitro antimalarial activity of traditionally used Western Ghats plants from India and their interactions with chloroquine against chloroquine-resistant Plasmodium falciparum

Malaria is a major global public health problem, and the alarming spread of drug resistance and limited number of effective drugs now available underline how important it is to discover new antimalarial compounds. An ethnopharmacological investigation was undertaken on Western Ghats plants traditionally used to treat malaria in India; 50 plants were very carefully selected from a total of 372 plants, and 200 extracts were prepared and tested for in vitro antiplasmodial activity alone and in combination with chloroquine (CQ) against CQ-resistant Plasmodium falciparum (strain MRC-Pf-43). In in vitro antiplasmodial activity, when plant extract alone is used, 29 extracts (or 14.5%) showed significant high in vitro antiplasmodial activity with IC(50) values ranging from 3.96 to 4.85 μg/ml, 53 extracts (or 26.5%) showed significant good in vitro antiplasmodial activity with IC(50) values ranging from 5.02 to 9.87 μg/ml, and 28 extracts (or 14%) showed significant moderate in vitro antiplasmodial activity with IC(50) values ranging from 10.87 to 14 μg/ml, respectively. In combination with CQ, 103 extracts (or 51.5%) showed significant synergistic in vitro antiplasmodial activities with synergistic factor values ranging from 1.03 to 1.92, and these activities were up to a fold higher with CQ, suggesting synergistic interactions of the two drugs. Our investigation has confirmed that above 62.1% of the plant extracts showed moderate to high in vitro antiplasmodial activity when used alone, and in combination with CQ, 55.7% of the extracts showed borderline to good synergistic activity.

Novel 2H-isoquinolin-3-ones as antiplasmodial falcipain-2 inhibitors

A series of 1-aryl-6,7-disubstituted-2H-isoquinolin-3-ones (2-10) was synthesized and evaluated for their inhibition against Plasmodium falciparum cysteine protease falcipain-2, as well as against cultured P. falciparum strain FCBR parasites. All compounds displayed inhibitory activity against recombinant falcipain-2 and against in vitro cultured intraerythrocytic P. falciparum, with the exception of 9. The new compounds exhibited no selectivity against human cysteine proteases such as cathepsins B and L. The inhibitory activity of the synthesized compounds was also evaluated against another protozoal cysteine protease, namely rhodesain of Trypanosoma brucei rhodesiense.

One-Pot, Multicomponent Route to Pyrazoloquinolizinones

[reaction: see text] An efficient synthesis of 5a-hydroxy-4,5,5a,6,7,8-hexahydropyrazolo[4,3-c]quinolizin-9-ones based on the three-component condensation of 5-aminopyrazoles, aromatic aldehydes, and cyclic 1,3-diketones is described. The multicomponent reaction is performed under strongly basic conditions applying controlled microwave heating in a sealed vessel and involves an unusual base-mediated ring-opening/recyclization of the cyclic 1,3-diketone moiety.

Antimalarial and cytotoxic activities of ethnopharmacologically selected medicinal plants from South Vietnam

Malaria is a major global public health problem and the alarming spread of drug resistance and limited number of effective drugs now available underline how important it is to discover new antimalarial compounds. An ethnopharmacological investigation was undertaken of medicinal plants traditionally used to treat malaria in the South Vietnam. Forty-nine plants were identified, 228 extracts were prepared and tested for their in vitro activity against Plasmodium falciparum, and assessed for any cytotoxicity against the human cancer cell line HeLa and the embryonic lung MRC5 cell line. In a first screening at a concentration of 10 microg/ml, 92 extracts from 46 plants showed antiplasmodial activity (parasite growth inhibition >30%). The IC(50) values of the most active extracts were determined as well as their selectivity towards Plasmodium falciparum in comparison to their cytotoxic effects against the human cell lines. Six plants showed interesting antiplasmodial activity (IC(50) ranging from 0.4 to 8.6 microg/ml) with a good selectivity: two Menispermaceae, Arcangelisia flava (L.) Merr. and Fibraurea tinctoria Lour., and also Harrisonia perforata (Blanco) Merr. (Simaroubaceae), Irvingia malayana Oliv. ex Benn. (Irvingiaceae), Elaeocarpus kontumensis Gagn. (Elaeocarpaceae) and Anneslea fragrans Wall. (Theaceae).

Quaternary protoberberine alkaloids

This contribution reviews some general aspects of the quaternary iminium protoberberine alkaloids. The alkaloids represent a very extensive group of secondary metabolites with diverse structures, distribution in nature, and biological effects. The quaternary protoberberine alkaloids (QPA), derived from the 5,6-dihydrodibenzo[a,g]quinolizinium system, belong to a large class of isoquinoline alkaloids. Following a general introduction, the plant sources of QPA, their biosynthesis, and procedures for their isolation are discussed. Analytical methods and spectral data are summarized with emphasis on NMR spectroscopy. The reactivity of QPA is characterized by the sensitivity of the iminium bond CN(+) to nucleophilic attack. The addition of various nucleophiles to the protoberberine skeleton is discussed. An extended discussion of the principal chemical reactivity is included since this governs interactions with biological targets. Quaternary protoberberine alkaloids and some related compounds exhibit considerable biological activities. Recently reported structural studies indicate that the QPA interact with nucleic acids predominantly as intercalators or minor groove binders. Currently, investigations in many laboratories worldwide are focused on the antibacterial and antimalarial activity, cytotoxicity, and potential genotoxicity of QPA.

Molecular aspects on the interaction of protoberberine, benzophenanthridine, and aristolochia group of alkaloids with nucleic acid structures and biological perspectives

Alkaloids occupy an important position in chemistry and pharmacology. Among the various alkaloids, berberine and coralyne of the protoberberine group, sanguinarine of the benzophenanthridine group, and aristololactam-beta-d-glucoside of the aristolochia group have potential to form molecular complexes with nucleic acid structures and have attracted recent attention for their prospective clinical and pharmacological utility. This review highlights (i) the physicochemical properties of these alkaloids under various environmental conditions, (ii) the structure and functional aspects of various forms of deoxyribonucleic acid (DNA) (B-form, Z-form, H(L)-form, protonated form, and triple helical form) and ribonucleic acid (RNA) (A-form, protonated form, and triple helical form), and (iii) the interaction of these alkaloids with various polymorphic DNA and RNA structures reported by several research groups employing various analytical techniques like absorbance, fluorescence, circular dichroism, and NMR spectroscopy; electrospray ionization mass spectrometry, thermal melting, viscosity, and DNase footprinting as well as molecular modeling and thermodynamic studies to provide detailed binding mechanism at the molecular level for structure-activity relationship. Nucleic acids binding properties of these alkaloids are interpreted in relation to their biological activity.