First total synthesis and antileishmanial activity of (Z)-16-methyl-11-heptadecenoic acid, a new marine fatty acid from the sponge Dragmaxia undata

The first total synthesis for the (Z)-16-methyl-11-heptadecenoic acid, a novel fatty acid from the sponge Dragmaxia undata, was accomplished in seven steps and in a 44% overall yield. The use of (trimethylsilyl)acetylene was key in the synthesis. Based on a previous developed strategy in our laboratory the best synthetic route towards the title compound was first acetylide coupling of (trimethylsilyl)acetylene to the long-chain protected 10-bromo-1-decanol followed by a second acetylide coupling to the short-chain 1-bromo-4-methylpentane, which resulted in higher yields. Complete spectral data is also presented for the first time for this recently discovered fatty acid and the cis double bond stereochemistry of the natural acid was established. The title compound displayed antiprotozoal activity against Leishmania donovani (IC₅₀ = 165.5 ± 23.4 μM) and inhibited the leishmania DNA topoisomerase IB enzyme (LdTopIB) with an IC₅₀ = 62.3 ± 0.7 μM.     

Antituberculotic and antiprotozoal activities of primin, a natural benzoquinone: in vitro and in vivo studies

Primin (=2-methoxy-6-pentylcyclohexa-2,5-diene-1,4-dione), a natural benzoquinone synthesized in our laboratory, was investigated for its in vitro antiprotozoal, antimycobacterial, and cytotoxic potential. Primin showed very potent activity against Trypanosoma brucei rhodesiense (IC50 0.144 microM) and Leishmania donovani (IC50 0.711 microM), and revealed low cytotoxicity (IC50 15.4 microM) on mammalian cells. Only moderate inhibitory activity was observed against Mycobacterium tuberculosis, Trypanosoma cruzi, and Plasmodium falciparum. When tested for in vivo efficacy in a Trypanosoma b. brucei rodent model, primin failed to cure the infection at 20 mg/kg given intraperitoneally. Primin was too toxic in vivo at a higher concentration (30 mg/kg, injected i.p. route) in mice infected with L. donovani. Taken together, primin can serve as a lead compound for the rational design of more potent and less toxic antiprotozoal agents.     

Synthesis and in vitro antiprotozoal activities of 5-phenyliminobenzo[a]phenoxazine derivatives

A series of 5-phenyliminobenzo[a]phenoxazine derivatives were synthesized. The in vitro antiprotozoal activities were evaluated against Plasmodium falciparum K1, Trypanosoma cruzi, Leishmania donovani and Trypanosoma brucei rhodesiense. N,N-Diethyl-5-((4-methoxyphenyl)imino)-5H-benzo[a]phenoxazin-9-amine shows IC(50)=0.040 μmol L(-1) with a selective index of 1425 against Plasmodium falciparum K1.     

Synthesis of a small library of 2-phenoxy-1,4-naphthoquinone and 2-phenoxy-1,4-anthraquinone derivatives bearing anti-trypanosomal and anti-leishmanial activity

Taking advantage of the structural features of natural products showing anti-trypanosomatid activity, we designed and synthesized a small library of 2-phenoxy-1,4-naphthoquinone and 2-phenoxy-1,4-anthraquinone derivatives. The library was obtained following a parallel approach and using readily available synthons. All the derivatives showed inhibitory activity toward either Trypanosoma or Leishmania species, with 8, 10, and 16 being the most active compounds against Trypanosoma brucei rhodesiense, Leishmania donovani, and Trypanosoma cruzi cells (IC(50)=50nM, IC(50)=0.28microM, and IC(50)=1.26microM, respectively).     

First total synthesis and antiprotozoal activity of (Z)-17-methyl-13-octadecenoic acid, a new marine fatty acid from the sponge Polymastia penicillus

The first total synthesis for the (Z)-17-methyl-13-octadecenoic acid was accomplished in seven steps and in a 45% overall yield. The use of (trimethylsilyl)acetylene was key in the synthesis. Based on a previous developed strategy in our laboratory the best synthetic route towards the title compound was first acetylide coupling of (trimethylsilyl)acetylene to the long-chain protected 12-bromo-1-dodecanol followed by a second acetylide coupling to the short-chain 3-methyl-1-bromobutane, which resulted in higher yields. Complete spectral data is also presented for the first time for this recently discovered fatty acid. The title compound displayed antiprotozoal activity against Leishmania donovani (EC₅₀ = 19.8 μg/ml) and inhibited the leishmania DNA topoisomerase IB at concentrations of 50 μM.     

Evaluation of antileishmanial activity of South Indian medicinal plants against Leishmania donovani

Infections due to protozoa of the genus Leishmania are a major worldwide health problem, with high endemicity in developing countries. The aim of this study was to evaluate the in vitro antileishmanial activity of the acetone and methanol leaf extracts of Anisomeles malabarica, flower of Gloriosa superba, leaf of Ocimum basilicum, leaf and seed of Ricinus communis against promastigotes form of Leishmania donovani. Antiparasitic evaluations of different plant crude extracts were performed on 96 well plates at 37°C for 24-48h. Out of the 10 experimental plant extracts tested, the leaf methanol extracts of A. malabarica, and R. communis showed good antileishmanial activity (IC(50)=126±19.70 and 184±39.33μg/mL), respectively against promastigotes. Effective antileishmanial activity was observed making these plants as good candidates for isolation of antiprotozoal compounds which could serve as new lead structures for drug development.     

Turkish freshwater and marine macrophyte extracts show in vitro antiprotozoal activity and inhibit FabI, a key enzyme of Plasmodium falciparum fatty acid biosynthesis.

The ethanolic extracts of a number of Turkish freshwater macrophytes (Potamogeton perfoliatus, Ranunculus tricophyllus and Cladophora glomerata) and marine macroalgae (Dictyota dichotoma, Halopteris scoparia, Posidonia oceanica, Scinaia furcellata, Sargassum natans and Ulva lactuca) were assayed for their in vitro antiprotozoal activity. Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum were used as test organisms. The cytotoxicity of the extracts was also assessed against primary rat skeletal myoblasts (L6 cells). Whereas none of the extracts were active against T. cruzi, all crude extracts displayed appreciable trypanocidal activity against T. brucei rhodesiense, with S. natans being the most active one (IC(50) 7.4microg/ml). Except for the marine alga H. scoparia, all extracts also possessed leishmanicidal potential. The best antileishmanial activity was exerted by U. lactuca and P. oceanica (IC(50)'s 5.9 and 8.0microg/ml, respectively). Five extracts that demonstrated inhibitory activity towards P. falciparum (IC(50)'s 18.1-48.8microg/ml) were simultaneously assayed against FabI, a crucial enzyme of the fatty acid system of P. falciparum, to find out whether FabI was their target. The extracts of C. glomerata and U. lactuca efficiently inhibited the FabI enzyme with IC(50) values of 1.0 and 4.0microg/ml, respectively. None of the extracts were cytotoxic towards mammalian L6 cells. This work reports for the first time antiprotozoal activity of some Turkish marine and freshwater algae, as well as a target-based antiplasmodial screening for the identification of P. falciparum FabI inhibitors from aquatic and marine macrophytes.     

An insight into the mechanism of inhibition of unusual bi-subunit topoisomerase I from Leishmania donovani by 3,3'-di-indolylmethane, a novel DNA topoisomerase I poison with a strong binding affinity to the enzyme

DIM (3,3'-di-indolylmethane), an abundant dietary component of cruciferous vegetables, exhibits a wide spectrum of pharmacological properties. In the present study, we show that DIM is a potent inhibitor of Leishmania donovani topoisomerase I with an IC50 of 1.2 microM. Equilibrium dialysis shows that DIM binds strongly to the free enzyme with a binding constant of 9.73x10(-9) M. The binding affinity of DIM to the small subunit is 8.6-fold more than that of the large subunit of unusual LdTOP1LS (bi-subunit L. donovani topoisomerase I). DIM stabilizes topoisomerase I-DNA cleavage complexes in vitro and also in vivo. Like CPT (camptothecin), DIM inhibits the religation step when the drug was added to preformed topoisomerase I-DNA binary complex. Hence, DIM is similar to CPT with respect to its ability to form the topoisomerase I-mediated 'cleavable complexes' in vitro and in vivo. But unlike CPT, DIM interacts with both free enzyme and substrate DNA. Therefore DIM is a non-competitive class I inhibitor of topoisomerase I. DIM also inhibits the relaxation activity of the CPT-resistant mutant enzyme LdTOP1Delta39LS (N-terminal deletion of amino acids 1-39 of LdTOP1LS). The IC50 values of DIM in simultaneous and enzyme pre-incubation relaxation assays were 3.6 and 2.9 muM respectively, which are higher than that of wild-type topoisomerase I (LdTOP1LS), indicating that the affinity of DIM to LdTOP1Delta39LS is less than that for LdTOP1LS. This is the first report on DIM as an L. donovani topoisomerase I poison. Our study illuminates a new mode of action of enzyme inhibition by DIM that might be exploited for rational drug design in human leishmaniasis.     

Antiprotozoal and cytotoxic naphthalene derivatives from Diospyros assimilis

Chemical investigation of the roots of Diospyros assimilis had led to the isolation and characterization of six naphthalene derivatives, two 2-naphthaldehyes, namely 4-hydroxy-3,5-dimethoxy-2-naphthaldehyde 1, 4-hydroxy-5-methoxy-2-naphthaldehye 2, its related isomer 5-hydroxy-4-methoxy-2-naphthaldehyde 3 and three commonly occurring naphthoquinones, diospyrin 4, 8'-hydroxyisodiospyrin 5 and the simple monomer, plumbagin 6. Their chemical structures were established by detailed NMR investigations including 1H and 13C NMR, HSQC, HMBC and NOESY experiments. In addition, the naphthalene derivatives 1-5 were evaluated for their in vitro antiprotozoal activity against protozoan parasites belonging to the genera Trypanosoma, Leishmania and Plasmodium. Among the tested compounds, naphthaldehyde 1 showed moderate inhibition of the growth of the parasites, T. brucei, T. cruzi, L. donovani with IC50 values of 19.82, 12.28 and 38.78 microM and displayed cytotoxicity towards rat skeletal myoblasts (L-6 cells) with IC50 of 174.94 microM, while 2 and 3 were found to be comparatively less active to 1. The dimeric quinones 4 and 5 exhibited good activity against T. brucei and L. donovani with IC50 of 1.12 and 8.82 microM and 12.94 and 16.66 microM respectively.     

Anti-protozoal and plasmodial FabI enzyme inhibiting metabolites of Scrophularia lepidota roots

The ethanolic root extract of Scrophularia lepidota, an endemic plant of the Turkish flora, has been investigated for its anti-protozoal and inhibitory effect towards plasmodial enoyl-ACP reductase (FabI), a key enzyme of fatty acid biosynthesis in Plasmodium falciparum. Chromatographic separation of the extract yielded 10 iridoids (1-10), two of which are new, and a known phenylethanoid glycoside (11). The structures of the new compounds were determined as 3,4-dihydro-methylcatalpol (8) and 6-O-[4'-O-trans-(3,4-dimethoxycinnamoyl)-alpha-L-rhamnopyranosyl]aucubin (scrolepidoside, 9) by spectroscopic means. The remaining metabolites were characterized as catalpol (1), 6-O-methylcatalpol (2), aucubin (3), 6-O-alpha-L-rhamnopyranosyl-aucubin (sinuatol, 4), 6-O-beta-D-xylopyranosylaucubin (5), ajugol (6), ajugoside (7), an iridoid-related aglycone (10) and angoroside C (11). Nine isolates were active against Leishmania donovani, with the new compound 9 being most potent (IC50 6.1 microg/ml). Except for 4, all pure compounds revealed some trypanocidal potential against Trypanosoma brucei rhodesiense (IC50 values 29.3-73.0 microg/ml). Only compound 10 showed moderate anti-plasmodial (IC50 40.6 microg/ml) and FabI enzyme inhibitory activity (IC50 100 microg/ml). 10 is the second natural product inhibiting the fatty acid biosynthesis of Plasmodium falciparum.     

Antileishmanial activity, cytotoxicity and QSAR analysis of synthetic dihydrobenzofuran lignans and related benzofurans

A series of synthetic dihydrobenzofuran lignans and related benzofurans were evaluated for their cytotoxicity in a screening panel consisting of various human tumour cell lines, and for their antiprotozoal activity against L. donovani (axenic amastigotes), chloroquine resistant Plasmodium falciparum (strain K1), Trypanosoma brucei rhodesiense and T. cruzi, and for cytotoxicity on L6 cells. No promising cytotoxicities against human tumour cell lines were observed for newly synthesised compounds, but the dimerisation product of some lipophylic esters of caffeic acid, such as compound 2g, showed a high activity against chloroquine-resistant P. falciparum (strain K1) (IC50 0.43 microg/mL) and L. donovani (axenic amastigotes) (IC50 0.12 microg/mL), which was confirmed in an infected macrophage assay (IC50 0.19 microg/mL). QSAR models for the cytotoxic and antileishmanial activity were generated using Quasar receptor surface modelling.     

2-Octadecynoic acid as a dual life stage inhibitor of Plasmodium infections and plasmodial FAS-II enzymes

The malaria parasite Plasmodium goes through two life stages in the human host, a non-symptomatic liver stage (LS) followed by a blood stage with all clinical manifestation of the disease. In this study, we investigated a series of 2-alkynoic fatty acids (2-AFAs) with chain lengths between 14 and 18 carbon atoms for dual in vitro activity against both life stages. 2-Octadecynoic acid (2-ODA) was identified as the best inhibitor of Plasmodium berghei parasites with ten times higher potency (IC₅₀ = 0.34 μg/ml) than the control drug. In target determination studies, the same compound inhibited three Plasmodium falciparum FAS-II (PfFAS-II) elongation enzymes PfFabI, PfFabZ, and PfFabG with the lowest IC₅₀ values (0.28–0.80 μg/ml, respectively). Molecular modeling studies provided insights into the molecular aspects underlying the inhibitory activity of this series of 2-AFAs and a likely explanation for the considerably different inhibition potentials. Blood stages of P. falciparum followed a similar trend where 2-ODA emerged as the most active compound, with 20 times less potency. The general toxicity and hepatotoxicity of 2-AFAs were evaluated by in vitro and in vivo methods in mammalian cell lines and zebrafish models, respectively. This study identifies 2-ODA as the most promising antiparasitic 2-AFA, particularly towards P. berghei parasites.     

Lipophilic amines as potent inhibitors of N-acylethanolamine-hydrolyzing acid amidase

N-Acylethanolamines (NAEs) including N-arachidonoylethanolamine (anandamide) and N-palmitoylethanolamine are endogenous lipid mediators. These molecules are degraded to the corresponding fatty acids and ethanolamine by fatty acid amide hydrolase (FAAH) or NAE-hydrolyzing acid amidase (NAAA). Lipophilic amines, especially pentadecylamine (2c) and tridecyl 2-aminoacetate (11b), were found to exhibit potent NAAA inhibitory activities (IC(50)=5.7 and 11.8μM), with much weaker effects on FAAH. These simple structures would provide a scaffold for further improvement in NAAA inhibitory activity.     

Synthesis, biological evaluation, and molecular modeling of 3,5-substituted-N1-phenyl-N4,N4-di-n-butylsulfanilamides as antikinetoplastid antimicrotubule agents

Dinitroanilines are of interest as antiprotozoal lead compounds because of their selective activity against the tubulin of these organisms, but concern has been raised due to the potentially mutagenic nitro groups. Analogues of N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (GB-II-150, compound 2b), a selective antimitotic agent against African trypanosomes and Leishmania, have been prepared where the nitro groups are replaced with amino, chloro, cyano, carboxylate, methyl ester, amide, and methyl ketone moieties. Dicyano compound 5 displays IC(50) values that are comparable to 2b against purified leishmanial tubulin assembly (6.6 vs 7.4 microM), Trypanosoma brucei brucei growth in vitro (0.26 vs 0.18 microM), Leishmania donovani axenic amastigote growth in vitro (4.4 vs 2.3 microM), and in vitro toxicity against Vero cells (16 vs 9.7 microM). Computational studies provide a rationale for the antiparasitic order of activity of these analogues and further insight into the role of the substituents at the 3 and 5 positions of the sulfanilamide ring.     

Synthesis and antimalarial and antituberculosis activities of a series of natural and unnatural 4-methoxy-6-styryl-pyran-2-ones, dihydro analogues and photo-dimers

Previous studies have identified the 3,6-dialkyl-4-hydroxy-pyran-2-one marine microbial metabolites pseudopyronines A and B to be modest growth inhibitors of Mycobacterium tuberculosis and a range of tropical diseases including Plasmodium falciparum and Leishmania donovani. In an effort to expand the structure-activity relationship of this compound class towards infectious diseases, a library of natural product and natural product-like 4-methoxy-6-styryl-pyran-2-ones and a subset of catalytically reduced examples were synthesized. In addition, the photochemical reactivity of several of the 4-methoxy-6-styryl-pyran-2-ones were investigated yielding head-to-head and head-to-tail cyclobutane dimers as well as examples of asymmetric aniba-dimer A-type dimers. All compounds were evaluated for cytotoxicity and activity against M. tuberculosis, P. falciparum, L. donovani, Trypanosoma brucei rhodesiense and Trypanosoma cruzi. Of the styryl-pyranones, natural product 3 and non-natural styrene and naphthalene substituted examples 13, 18, 21, 22 and 23 exhibited antimalarial activity (IC(50) <10 μM) with selectivity indices (SI) >10. Δ(7) Dihydro analogues were typically less active or lacked selectivity. Head-to-head and head-to-tail photodimers 5 and 34 exhibited moderate IC(50)s of 2.3 to 17 μM towards several of the parasitic organisms, while the aniba-dimer-type asymmetric dimers 31 and 33 were identified as being moderately active towards P. falciparum (IC(50) 1.5 and 1.7 μM) with good selectivity (SI ~80). The 4-tert-butyl aniba-dimer A analogue 33 also exhibited activity towards L. donovani (IC(50) 4.5 μM), suggesting further elaboration of this latter scaffold could lead to the identification of new leads for the dual treatment of malaria and leishmaniasis.     

N-terminal region of the large subunit of Leishmania donovani bisubunit topoisomerase I is involved in DNA relaxation and interaction with the smaller subunit

Leishmania donovani topoisomerase I is an unusual bisubunit enzyme. We have demonstrated earlier that the large and small subunit could be reconstituted in vitro to show topoisomerase I activity. We extend our biochemical study to evaluate the role of the large subunit in topoisomerase activity. The large subunit (LdTOP1L) shows a substantial degree of homology with the core DNA binding domain of the topoisomerase IB family. Two N-terminal truncation constructs, LdTOP1Delta39L (lacking amino acids 1-39) and LdTOP1Delta99L (lacking amino acids 1-99) of the large subunit were generated and mixed with intact small subunit (LdTOP1S). Our observations reveal that residues within amino acids 1-39 of the large subunit have significant roles in modulating topoisomerase I activity (i.e. in vitro DNA relaxation, camptothecin sensitivity, cleavage activity, and DNA binding affinity). Interestingly, the mutant LdTOP1Delta99LS was unable to show topoisomerase I activity. Investigation of the loss of activity indicates that LdTOP1Delta99L was unable to pull down glutathione S-transferase-LdTOP1S in an Ni(2+)-nitrilotriacetic acid co-immobilization experiment. For further analysis, we co-expressed LdTOP1L and LdTOP1S in Escherichia coli BL21(DE3)pLysS cells. The lysate shows topoisomerase I activity. Immunoprecipitation revealed that LdTOP1L could interact with LdTOP1S, indicating the subunit interaction in bacterial cells, whereas immunoprecipitation of bacterial lysate co-expressing LdTOP1Delta99L and LdTOP1S reveals that LdTOP1Delta99L was significantly deficient at interacting with LdTOP1S to reconstitute topoisomerase I activity. This study demonstrates that heterodimerization between the large and small subunits of the bisubunit enzyme appears to be an absolute requirement for topoisomerase activity. The residue within amino acids 1-39 from the N-terminal end of the large subunit regulates DNA topology during relaxation by controlling noncovalent DNA binding or by coordinating DNA contacts by other parts of the enzyme.     

Antileishmanial and trypanocidal activity of Brazilian Cerrado plants

The side effects and the emerging resistance to the available drugs against leishmaniasis and trypanosomiasis led to the urgent need for new therapeutic agents against these diseases. Thirty one extracts of thirteen medicinal plants from the Brazilian Cerrado were therefore evaluated in vitro for their antiprotozoal activity against promastigotes of Leishmania donovani, and amastigotes of Trypanosoma cruzi. Among the selected plants, Casearia sylvestris var. lingua was the most active against both L. donovani and T. cruzi. Fifteen extracts were active against promastigotes of L. donovani with concentrations inhibiting 50% of parasite growth (IC50) between 0.1-10 microg/ml, particularly those of Annona crassiflora (Annonaceae), Himatanthus obovatus (Apocynaceae), Guarea kunthiana (Meliaceae), Cupania vernalis (Sapindaceae), and Serjania lethalis (Sapindaceae). With regard to amastigotes of T. cruzi, extracts of A. crassiflora, Duguetia furfuracea (Annonaceae), and C. sylvestris var. lingua were active with IC50 values between 0.3-10 microg/ml. Bioassay fractionations of the more active extracts are under progress to identify the active antiparasite compounds.     

The activity of diguanidino and 'reversed' diamidino 2,5-diarylfurans versus Trypanosoma cruzi and Leishmania donovani

The in vitro activity of 20 dicationic molecules containing either diguanidino or reversed amidine cationic groups were evaluated versus Trypanosoma cruzi and Leishmania donovani. The most active compounds were in the reversed amidine series and six exhibited IC(50) values of less than 1 micro mol versus T. cruzi and five gave similar values versus L. donovani.     

Design, synthesis, and biological evaluation of novel (1-thioxo-1,2,3,4-tetrahydro-β-carbolin-9-yl)acetic acids as selective inhibitors for AKR1B1

New substituted (1-thioxo-1,2,3,4-tetrahydro-β-carbolin-9-yl)acetic acids were designed as the inhibitor of AKR1B1 based upon the structure of rhetsinine, a minor alkaloidal component of Evodia rutaecarpa, and twenty derivatives were synthesized and evaluated. The most active compound of the series was (2-benzyl-6-methoxy-1-thioxo-1,2,3,4-tetrahydro-β-carbolin-9-yl)acetic acid (7m), which showed comparable inhibitory activity for AKR1B1 (IC(50)=0.15μM) with clinically used epalrestat (IC(50)=0.1μM). In the view of activity and selectivity, the most potent compound was (2-benzyl-6-carboxy-1-thioxo-1,2,3,4-tetrahydro-β-carbolin-9-yl)acetic acid (7t), which showed strong inhibitory effect (IC(50)=0.17μM) and very high selectivity for AKR1B1 against AKR1A1 (311:1) and AKR1B10 (253:1) compared with epalrestat.     

Comparative antiplasmodial, leishmanicidal and antitrypanosomal activities of several biflavonoids

The antiplasmodial, leishmanicidal and antitrypanosomal activities of eight natural biflavonoids were estimated in vitro on a chloroquine-resistant strain of Plasmodium falciparum, axenically grown Leishmania donovani amastigotes and Trypanosoma cruzi trypomastigotes and Trypanosoma brucei rhodesiense bloodstream forms. Lanaroflavone showed the highest antiplasmodial activity (IC(50) = 0.48 microM), isoginkgetin was the most active leishmanicidal compound (IC(50) = 1.9 microM), whereas ginkgetin (IC(50) = 11 microM) and isoginkgetin (IC(50) = 13 microM) showed the best antitrypanosomal activity in our assays. The cytotoxicity and the selectivity indices for the most active compounds were also estimated. Lanaroflavone exhibited a high selectivity index value (SI = 159), indicating selective antiplasmodial activity.