Spirofused tetrahydroisoquinoline-oxindole hybrids as a novel class of fast acting antimalarial agents with multiple modes of action

Molecular hybridization of privileged scaffolds may generate novel antiplasmodial chemotypes that display superior biological activity and delay drug resistance. In the present study, we describe the in vitro activities and mode of action of 3′,4′-dihydro-2′H-spiro[indoline-3,1′-isoquinolin]-2-ones, a novel class of spirofused tetrahydroisoquinoline–oxindole hybrids, as novel antimalarial agents. Whole cell phenotypic screening of these compounds identified (14b), subsequently named (±)-moxiquindole, as the most potent compound in the current series with equipotent antiplasmodial activity against both chloroquine sensitive and multidrug resistant parasite strains with good selectivity. The compound was active against all asexual stages of the parasite including inhibition of merozoite egress. Additionally, (±)-moxiquindole exhibited significant inhibitory effects on hemoglobin degradation, and disrupted vacuolar lipid dynamics. Taken together, our data confirm the antiplasmodial activity of (±)-moxiquindole, and identify 3′4′-dihydro-2′H-spiro[indoline-3,1′-isoquinolin]-2-ones as a novel class of antimalarial agents with multiple modes of action.

3',4'-Dihydro-2'H-spiro[indoline-3,1'-isoquinolin]-2-ones as potential anti-cancer agents: synthesis and preliminary screening

Both tetrahydroisoquinolines (THIQs) and oxindoles (OXs) display a broad range of biological activities including anti-cancer activity, and are therefore recognized as two privileged scaffolds in drug discovery. In the present study, 24 3',4'-dihydro-2'H-spiro[indoline-3,1'-isoquinolin]-2-ones, designed as molecular hybrids of THIQ and OX, were synthesized and screened in vitro against 59 cell lines in the NCI-60 screen. Twenty compounds displayed weak to moderate inhibition of cell proliferation; among them, three compounds displayed at least 50% inhibition of cell proliferation. The compounds appeared to target primarily renal cell cancer lines; however, leukaemia, melanoma, non-small cell lung cancer, prostate, ovarian and even breast cancer cell lines were also affected. Therefore, this class of spirooxindoles may provide useful leads in the search for new anti-cancer agents.

Antiparasitic Sesquiterpenes from the Cameroonian Spice Scleria striatinux and Preliminary In Vitro and In Silico DMPK Assessment

The antiparasitic activity and preliminary in vitro and in silico drug metabolism and pharmacokinetic (DMPK) assessment of six isomeric sesquiterpenes (1-6), isolated from the Cameroonian spice Scleria striatinux De Wild (Cyperaceae) is reported. The study was prompted by the observation that two of the compounds (1 and 2) exhibited varying levels of antiparasitic activity on Plasmodium falciparum, Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. The in silico method employed a total of 46 descriptors, calculated using Schrödinger QikProp software. 18 of these molecular descriptors that are often used to predict DMPK profiles of drug-like molecules have been selected for discussion. In vitro experimental assessment of metabolic stability made use of human liver microsomes, which was used to correlate theoretical predictions with experimental findings. Overall, the test compounds have been found to have acceptable physicochemical properties and fall within the ranges associated with "drug-like" molecules. Moreover, the compounds exhibited minimal degradation in incubations with human liver microsomes. Although some of these compounds have been reported previously (1, 2, 4 and 5), this is the first report on their antiparasitic activities, as well as assessment of their DMPK profiles. These results have therefore provided a window for further development of this novel class of sesquiterpene molecules as potential antiparasitic drugs.

4-aroylpiperidines and 4-(α-hydroxyphenyl)piperidines as selective sigma-1 receptor ligands: synthesis, preliminary pharmacological evaluation and computational studies

Background

Sigma (σ) receptors are membrane-bound proteins characterised by an unusual promiscuous ability to bind a wide variety of drugs and their high affinity for typical neuroleptic drugs, such as haloperidol, and their potential as alternative targets for antipsychotic agents. Sigma receptors display diverse biological activities and represent potential fruitful targets for therapeutic development in combating many human diseases. Therefore, they present an interesting avenue for further exploration. It was our goal to evaluate the potential of ring opened spipethiane (1) analogues as functional ligands (agonists) for σ receptors by chemical modification.

Results

Chemical modification of the core structure of the lead compound, (1), by replacement of the sulphur atom with a carbonyl group, hydroxyl group and 3-bromobenzylamine with the simultaneous presence of 4-fluorobenzoyl replacing the spirofusion afforded novel potent sigma-1 receptor ligands 7a–f, 8a–f and 9d–e. The sigma-1 receptor affinities of 7e, 8a and 8f were slightly lower than that of 1 and their selectivities for this receptor two to threefold greater than that of 1.

Conclusions

It was found that these compounds have higher selectivities for sigma-1 receptors compared to 1. Quantitatitive structure–activity relationship studies revealed that sigma-1 binding is driven by hydrophobic interactions.Graphical abstract

Isolation and Characterization of Sclerienone C from Scleria striatinux

Herein, we report the isolation and characterization of sclerienone C, a novel sesquiterpene isolated from the methylene chloride/methanol (1:1) extract of Scleria striatinux that we have deduced to have structure 1. This medicinal spice of Cameroon has been shown to display antimicrobial and antiplasmodial activities. The isolation and purification involved a combination of methods including silica gel column chromatography, Sephadex LH-20, and semi-prep HPLC separations. Structure elucidation was carried-out by means of spectroscopic analysis and comparison with previously isolated sesquiterpene derivatives from the plant.

1-Aryl-1,2,3,4-tetrahydroisoquinolines as potential antimalarials: synthesis, in vitro antiplasmodial activity and in silico pharmacokinetics evaluation

In the present study, twenty-one 1-aryl-6-hydroxy-1,2,3,4-tetrahydroisoquinoline (THIQ) analogues were synthesized by base-catalyzed Pictet–Spengler reaction, and testedin vitroagainstP. falciparumusing the [³H]hypoxanthine incorporation assay.

AfroDb: a select highly potent and diverse natural product library from African medicinal plants

Computer-aided drug design (CADD) often involves virtual screening (VS) of large compound datasets and the availability of such is vital for drug discovery protocols. We assess the bioactivity and "drug-likeness" of a relatively small but structurally diverse dataset (containing >1,000 compounds) from African medicinal plants, which have been tested and proven a wide range of biological activities. The geographical regions of collection of the medicinal plants cover the entire continent of Africa, based on data from literature sources and information from traditional healers. For each isolated compound, the three dimensional (3D) structure has been used to calculate physico-chemical properties used in the prediction of oral bioavailability on the basis of Lipinski's "Rule of Five". A comparative analysis has been carried out with the "drug-like", "lead-like", and "fragment-like" subsets, as well as with the Dictionary of Natural Products. A diversity analysis has been carried out in comparison with the ChemBridge diverse database. Furthermore, descriptors related to absorption, distribution, metabolism, excretion and toxicity (ADMET) have been used to predict the pharmacokinetic profile of the compounds within the dataset. Our results prove that drug discovery, beginning with natural products from the African flora, could be highly promising. The 3D structures are available and could be useful for virtual screening and natural product lead generation programs.

In silico drug metabolism and pharmacokinetic profiles of natural products from medicinal plants in the Congo basin

Purpose

Drug metabolism and pharmacokinetics (DMPK) assessment has come to occupy a place of interest during the early stages of drug discovery today. The use of computer modelling to predict the DMPK and toxicity properties of a natural product library derived from medicinal plants from Central Africa (named ConMedNP). Material from some of the plant sources are currently employed in African Traditional Medicine.

Methods

Computer-based methods are slowly gaining ground in this area and are often used as preliminary criteria for the elimination of compounds likely to present uninteresting pharmacokinetic profiles and unacceptable levels of toxicity from the list of potential drug candidates, hence cutting down the cost of discovery of a drug.

In the present study, we present an in silico assessment of the DMPK and toxicity profile of a natural product library containing ~3,200 compounds, derived from 379 species of medicinal plants from 10 countries in the Congo Basin forests and savannas, which have been published in the literature. In this analysis, we have used 46 computed physico-chemical properties or molecular descriptors to predict the absorption, distribution, metabolism and elimination and toxicity (ADMET) of the compounds.

Results

This survey demonstrated that about 45% of the compounds within the ConMedNP compound library are compliant, having properties which fall within the range of ADME properties of 95% of currently known drugs, while about 69% of the compounds have ≤ 2 violations. Moreover, about 73% of the compounds within the corresponding “drug-like” subset showed compliance.

Conclusions

In addition to the verified levels of “drug-likeness”, diversity and the wide range of measured biological activities, the compounds from medicinal plants in Central Africa show interesting DMPK profiles and hence could represent an important starting point for hit/lead discovery.

Electronic supplementary material

The online version of this article (doi:10.1186/2193-9616-1-12) contains supplementary material, which is available to authorized users.

Bioactive natural products derived from the Central African flora against neglected tropical diseases and HIV

This review discusses the medicinal potential of bioactive metabolites isolated from medicinal plants in Central Africa for the treatment of neglected tropical diseases and HIV. A correlation is established between the biological activities of the isolated compounds and the uses of the plants in traditional medicine. Insight is provided on how secondary metabolites from medicinal plants in Central Africa could be exploited for drug discovery.

Cameroonian medicinal plants: a bioactivity versus ethnobotanical survey and chemotaxonomic classification

Background

In Cameroon herbs are traditionally used to meet health care needs and plans are on the way to integrate traditional medicine in the health care system, even though the plans have not been put into action yet. The country however has a rich biodiversity, with ~8,620 plant species, some of which are commonly used in the treatment of several microbial infections and a range of diseases (malaria, trypanosomiasis, leishmaniasis, diabetes and tuberculosis).

Methods

Our survey consisted in collecting published data from the literature sources, mainly from PhD theses in Cameroonian university libraries and also using the author queries in major natural product and medicinal chemistry journals. The collected data includes plant sources, uses of plant material in traditional medicine, plant families, region of collection of plant material, isolated metabolites and type (e.g. flavonoid, terpenoid, etc.), measured biological activities of isolated compounds, and any comments on significance of isolated metabolites on the chemotaxonomic classification of the plant species. This data was compiled on a excel sheet and analysed.

Results

In this study, a literature survey led to the collection of data on 2,700 secondary metabolites, which have been previously isolated or derived from Cameroonian medicinal plants. This represents distinct phytochemicals derived from 312 plant species belonging to 67 plant families. The plant species are investigated in terms of chemical composition with respect to the various plant families. A correlation between the known biological activities of isolated compounds and the ethnobotanical uses of the plants is also attempted. Insight into future direction for natural product search within the Cameroonian forest and Savanna is provided.

Conclusions

It can be verified that a phytochemical search of active secondary metabolites, which is inspired by knowledge from the ethnobotanical uses of medicinal plants could be very vital in a drug discovery program from plant-derived bioactive compounds.

Synthesis and in vitro and in vivo evaluation of 18F-labeled positron emission tomography (PET) ligands for imaging the vesicular acetylcholine transporter

A new class of vesicular acetylcholine transporter inhibitor that incorporates a carbonyl group into the benzovesamicol structure was synthesized, and analogues were evaluated in vitro. (+/-)-trans-2-Hydroxy-3-(4-(4-[(18)F]fluorobenzoyl)piperidino)tetralin (9e) has K(i) values of 2.70 nM for VAChT, 191 nM for sigma(1), and 251 nM for sigma(2). The racemic precursor (9d) was resolved via chiral HPLC, and (+/-)-[(18)F]9e, (-)-[(18)F]9e, and (+)-[(18)F]9e were respectively radiolabeled via microwave irradiation of the appropriate precursors with [(18)F]/F(-) and Kryptofix/K(2)CO(3) in DMSO with radiochemical yields of approximately 50-60% and specific activities of >2000 mCi/micromol. (-)-[(18)F]9e uptake in rat brain was consistent with in vivo selectivity for the VAChT with an initial uptake of 0.911 %ID/g in rat striatum and a striatum/cerebellum ratio of 1.88 at 30 min postinjection (p.i.). MicroPET imaging of macaques demonstrated a 2.1 ratio of (-)-[(18)F]9e in putamen versus cerebellum at 2 h p.i. (-)-[(18)F]9e has potential to be a PET tracer for clinical imaging of the VAChT.

Synthesis and in vitro biological evaluation of carbonyl group-containing inhibitors of vesicular acetylcholine transporter

To identify selective high-affinity inhibitors of the vesicular acetylcholine transporter (VAChT), we have interposed a carbonyl group between the phenyl and piperidyl groups of the prototypical VAChT ligand vesamicol and its more potent analogues benzovesamicol and 5-aminobenzovesamicol. Of 33 compounds synthesized and tested, 6 display very high affinity for VAChT (K(i), 0.25-0.66 nM) and greater than 500-fold selectivity for VAChT over sigma(1) and sigma(2) receptors. Twelve compounds have high affinity (K(i), 1.0-10 nM) and good selectivity for VAChT. Furthermore, 3 halogenated compounds, namely, trans-3-[4-(4-fluorobenzoyl)piperidinyl]-2-hydroxy-1,2,3,4-tetrahydronaphthalene (28b) (K(i) = 2.7 nM, VAChT/sigma selectivity index = 70), trans-3-[4-(5-iodothienylcarbonyl)piperidinyl]-2-hydroxy-1,2,3,4-tetrahydronaphthalene (28h) (K(i) = 0.66 nM, VAChT/sigma selectivity index = 294), and 5-amino-3-[4-(p-fluorobenzoyl)piperidinyl]-2-hydroxy-1,2,3,4,-tetrahydronaphthalene (30b) (K(i) = 2.40 nM, VAChT/sigma selectivity index = 410) display moderate to high selectivity for VAChT. These three compounds can be synthesized with the corresponding radioisotopes so as to serve as PET/SPECT probes for imaging the VAChT in vivo.

Okundoperoxide, a bicyclic cyclofarnesylsesquiterpene endoperoxide from Scleria striatinux with antiplasmodial activity

Okundoperoxide (1) was isolated by bioassay-guided fractionation of extracts from Scleria striatinux (syn. S. striatonux). The compound contains a cyclic endoperoxide structural moiety and possesses moderate antimalarial activity.

In vitro anti-Helicobacter pylori activity of extracts of selected medicinal plants from North West Cameroon

ETHNOPHARMACOLOGICAL RELEVANCE

Helicobacter pylori, a gram negative microaerophilic bacterium is a major etiological agent in duodenal, peptic and gastric ulcers. The growing problem of antibiotic resistance by the organism demands the search for novel compounds from plant based sources.

AIM OF STUDY

The present study is aimed at evaluating the antimicrobial activity of some selected medicinal plants on clinical isolates of H. pylori circulating in Cameroon in a bid to identify potential sources of cheap starting materials for the synthesis of new drugs.

MATERIALS AND METHODS

Gastric biopsy samples were obtained from patients presenting with gastroduodenal complications. H. pylori was isolated from the specimens following standard microbiology procedures. The disk diffusion method was used to determine the susceptibility of 15 isolates to ten methanol plant extracts (Ageratum conyzoides, Scleria striatinux, Lycopodium cernua, Acanthus montanus, Eryngium foetidium, Aulutandria kamerunensis, Tapeinachilus ananassae, Euphorbia hirta, Emilia coccinea and Scleria verrucosa). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for the most active plant extracts were also determined by the agar dilution method. Results were analyzed statistically by the Fisher's exact test.

RESULTS

All the plants tested demonstrated antimicrobial activity with zone diameters of inhibition ranging from 0-30mm. Of these, A. conyzoides, S. striatinux and L. cernua showed very potent antibacterial activity on the isolates. The lowest MIC and MBC recorded were 0.032mg/mL and 0.098mg/mL respectively. However, the MIC of the extracts ranged from 0.032-1.0mg/mL for S. striatinux; 0.063-0.5mg/mL for L. cernua and 0.063-1.0mg/mL for A. conyzoides. The MBC of the extracts ranged from 0.098-15.0mg/mL for S. striatinux; 0.098-12.5mg/mL for A. conyzoides, and 0.195-12.5mg/mL for L. cernua. The extracts had a wide spectrum of activity. The three most potent extracts possessed significant (P<0.05) inhibitory activities.

CONCLUSION

The plant extracts may contain compounds with therapeutic activity.

Nature-inspired indolyl-2-azabicyclo[2.2.2]oct-7-ene derivatives as promising agents for the attenuation of withdrawal symptoms: synthesis of 20-desethyl-20-hydroxymethyl-11-demethoxyibogaine

Microwave assisted Diels-Alder cycloaddition of 5-Br-N-benzylpyridinone (2) with methyl acrylate is described to gain an easy access to 7-bromo-2-benzyl-3-oxo-2-aza-5 or 6-carbomethoxy bicyclo[2.2.2]oct-7-enes (3)-(6). The preparation of the ibogaine analogue 20-desethyl-(20-endo)-hydroxymethyl-11-demethoxyibogaine (17) is described by stereoselective hydrogenation of the C(7)-C(8) double bond. Biological evaluation showed an interesting in vitro binding profile toward dopamine transporter, serotonin transporter and opioid receptor systems accompanied by an antiwithdrawal effect in mice for hydroxymethyl 7-indolyl-2-aza-bicyclo[2.2.2]oct-2-ene (14). The simplification of the ibogaine structure appears as a promising approach toward the design of compounds that could reduce the withdrawal symptoms.

Constituents of Peucedanum zenkeri seeds and their antimicrobial effects

The methanol extract of Peucedanum zenkeri L. seeds showed antimicrobial activity which is concentrated in the n-hexane fraction. Bioactivity-guided chromatographic fractionation of the seeds of P. zenkeri led to the isolation and characterization of five major coumarins, umbelliprenin, imperatorin, bergapten, isopimpinellin and byakangelicin, as well as two minor coumarins, 7-methoxy coumarin and 5-hydroxy-8-methoxy psoralen. Amongst the isolated compounds only imperatorin, bergapten and isopimpinellin were found to possess anti-microbial activity.

Ibogaine analogues. Synthesis and preliminary pharmacological evaluation of 7-heteroaryl-2-azabicyclo[2.2.2]oct-7-enes

Synthesis of 7-heteroaryl-2-azabicyclo[2.2.2]oct-7-enes by cycloaddition and subsequent cross-coupling reaction is described. Binding affinity of these novel compounds towards the characteristic receptorial targets of ibogaine is illustrated.

Chromaproline and Chromaperidine, nicotine agonists, and Donepezil, cholinesterase inhibitor, enhance performance of memory tasks in ovariectomized rats

Chromaproline and Chromaperidine, two recently synthesized and pharmacologically characterized nicotinic agonists, and Donepezil (Aricept), an acetylcholinesterase inhibitor approved for the treatment of memory loss, were evaluated for effects on performance of a visual recognition memory task (object recognition) and a spatial memory task (object placement). Ovariectomized female rats received the drugs chronically via subcutaneous Alzet minipumps. None of the drugs altered activity in the open field or the time spent exploring objects in the field. One week following initiation of treatment, all three drugs enhanced performance of the visual recognition task, but only Donepezil enhanced performance of the spatial memory task. With a longer period of treatment (3 weeks), the nicotinic agonist Chromaproline also enhanced object placement performance. Current results show the memory-enhancing efficacy of Donepezil in two additional memory tasks in rats and suggest that the novel nicotinic agonists, Chromaproline and Chromaperidine, may also be useful new drugs for the treatment of memory impairments/loss.