Discovery of 2-iminobenzimidazoles as a new class of trypanothione reductase inhibitor by high-throughput screening

A high-throughput screening campaign of a library of 100,000 lead-like compounds identified 2-iminobenzimidazoles as a novel class of trypanothione reductase inhibitors. These 2-iminobenzimidazoles display potent trypanocidal activity against Trypanosoma brucei rhodesiense, do not inhibit closely related human glutathione reductase and have low cytotoxicity against mammalian cells.     

Antitrypanosomal cycloartane glycosides from Astragalus baibutensis

Baibutoside (5), a new cycloartane-type triterpene glycoside, has been isolated from the roots of Astragalus baibutensis along with four known glycosides, acetylastragaloside I (1), and astragalosides I, II, and IV (2-4, resp.). The structure elucidation of the compounds were achieved by a combination of one- and two-dimensional NMR techniques (DQF-COSY, HSQC, HMBC, and ROESY), and mass spectrometry (ESI-MS), where all the compounds were shown to have cycloastragenol (=(20R,24S)-3beta,6alpha,16beta,25-tetrahydroxy-20,24-epoxy-9,19-cyclolanostane) as aglycone. All compounds were tested for in vitro antiprotozoal activity. Compounds 1-4 displayed notable activity vs. Trypanosoma brucei rhodesiense, with acetylastragaloside I (1) being the most potent (IC50 9.5 microg/ml). Acetylastragaloside I (1) was also lethal to T. cruzi (IC50 5.0 microg/ml), and it is the first cycloartane-type triterpene with remarkable trypanocidal activity against both T. brucei rhodesiense and T. cruzi. However, it exhibits some cytotoxicity on mammalian cells.     

Discovery of nitroheterocycles active against African trypanosomes. In vitro screening and preliminary SAR studies

A selection of 76 nitroheterocycles and related compounds from our in-house compound library was screened in vitro against the parasite Trypanosoma brucei rhodesiense, causative agent of human African trypanosomiasis (HAT). The unspecific cytotoxicity of the compounds was also evaluated against rat myoblast L6-cells to measure the selectivity of the compounds towards the parasite. This screening revealed some preliminary structure-activity relationships (SAR) among the series, and six hit compounds showing interesting activity (IC(50)≤10μM) and fair selectivity (SI>17). The 7-nitroquinoxalin-2-one and 5-nitroindazole scaffold derivatives 58 and 35, respectively, are particularly interesting because of their established oral bioavailability in mice. These hits represent interesting starting points for a medicinal project aimed at identifying the SAR behind this class of compounds.     

Minor cytotoxic and antibacterial compounds from the rhizomes of Amomum aculeatum.

A new cytotoxic 1,7-dioxa-dispiro[5.1.5.2]pentadeca-9,12-dien-11-one derivative, aculeatin D, and a new alkenone, 5-hydroxy-hexacos-1-en-3-one, have been isolated as minor compounds from the rhizomes of Amomum aculeatum. Their structures have been determined mainly by NMR spectroscopy and mass spectrometry. Aculeatin D showed high cytotoxicity against the KB and the L-6 cell line with IC(50) of 0.38 microg/ml and 1 microg/ml, respectively. Additionally, it revealed remarkable activity against two Plasmodium falciparum strains, as well as against Trypanosoma brucei rhodesiense and Trypanosoma cruzi. 5-Hydroxy-hexacos-1-en-3-one exhibited neither cytotoxic nor antiprotozoal activity, whereas antibacterial testing against Bacillus cereus, Escherichia coli and Staphylococcus epidermidis showed moderate to strong activity for both compounds.     

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).     

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.     

Leishmanicidal cycloartane-type triterpene glycosides from Astragalus oleifolius

Two new cycloartane-type glycosides oleifoliosides A (1) and B (2) were isolated from the lower stem parts of Astragalus oleifolius. Their structures were identified as 3-O-[beta-xylopyranosyl-(1 --> 2)-alpha-arabinopyranosyl]-6-O-beta-xylopyranosyl-3beta,6alpha,16beta,24(S),25-pentahydroxycycloartane and 3-O-[beta-xylopyranosyl-(1 --> 2)-alpha-arabinopyranosyl]-6-O-beta-glucopyranosyl-3beta,6alpha,16beta,24(S),25-pentahydroxycycloartane, respectively, by means of spectroscopic methods (IR, 1D and 2D NMR, ESI-MS). Three known cycloartane glycosides cyclocanthoside E (3), astragaloside II (4) and astragaloside IV (5) were also isolated and characterized. All five compounds were evaluated for in vitro trypanocidal, leishmanicidal and antiplasmodial activities as well as their cytotoxic potential on primary mammalian (L6) cells. Except for the compound 5, all compounds showed notable growth inhibitory activity against Leishmania donovani with IC50 values ranging from 13.2 to 21.3 microg/ml. Only weak activity against Trypanosoma brucei rhodesiense was observed with the known compounds astragaloside II (4, IC50 66.6 microg/ml) and cyclocanthoside E (3, IC50 85.2 microg/ml), while all compounds were inactive against Trypanosoma cruzi and Plasmodium falciparum. None of the compounds were toxic to mammalian cells (IC50's > 90 microg/ml). This is the first report of leishmanicidal and trypanocidal activity of cycloartane-type triterpene glycosides.     

Design, synthesis and evaluation of 2,4-diaminoquinazolines as inhibitors of trypanosomal and leishmanial dihydrofolate reductase

This paper describes the design, synthesis and evaluation of a series of 2,4-diaminoquinazolines as inhibitors of leishmanial and trypanosomal dihydrofolate reductase. Compounds were designed by a generating virtual library of compounds and docking them into the enzyme active site. Following their synthesis, they were found to be potent and selective inhibitors of leishmanial dihydrofolate reductase. The compounds were also found to have potent activity against Trypanosoma brucei rhodesiense, a causative organism of African trypanosomiasis and also against Trypanosoma cruzi, the causative organism of Chagas disease. There was significantly lower activity against Leishmania donovani, one of the causative organisms of leishmaniasis.     

Triterpenic acids and flavonoids from Satureja parvifolia. Evaluation of their antiprotozoal activity

Bioassay-guided fractionation of a Satureja parvifolia MeOH extract led to the isolation of eriodictyol, luteolin and ursolic and oleanolic acids as its active components against Plasmodium falciparum K1. This is the first time these compounds are reported as constituents of S. parvifolia. Ursolic acid showed an IC50 of 4.9 microg/ml, luteolin 6.4 microg/ml, oleanolic acid 9.3 microg/ml and eriodictyol 17.2 microg/ml. Antiplasmodial activity of eriodictyol and luteolin is reported here for the first time. Besides, the four compounds showed activity against P. falciparum 3D7 strain and Trypanosoma brucei rhodesiense. Eriodictyol showed moderate activity on all the parasites but was the most selective compound as a result of its rather low cytotoxicity (IC50 174.2 microg/ml) on the mammalian KB cell line.     

Biological evaluation of glycosyl-isoindigo derivatives against the pathogenic agents of tropical diseases (malaria, Chagas disease, leishmaniasis and human African trypanosomiasis)

The biological activities of diversely substituted glycosyl-isoindigo derivatives against the causative agents of tropical diseases (malaria, Chagas disease, leishmaniasis and human African trypanosomiasis) are reported. Some of the compounds tested showed interesting activities with good selectivity indices, particularly against Trypanosoma brucei rhodesiense. These results suggested, for the first time, that glycosyl-isoindigo derivatives could be of interest for the discovery of new lead compounds to treat tropical diseases.     

Antitrypanosomal activity of quaternary naphthalimide derivatives

Sleeping sickness caused by Trypanosoma brucei gambiense and rhodesiense is fatal if left untreated. Due to the toxicity of drugs currently used and the emerging resistance against these drugs new lead compounds are urgently needed. Within the frame of a broad screening program for drugs with antitrypanosomal activity, some highly potent tertiary and quaternary mono- and bisnaphthalimides being active in the lower micromolar and nanomolar range of concentration have been identified. These compounds are easily available via a two- or three-step microwave-driven synthesis with high yield.     

Novel bisbenzimidazoles with antileishmanial effectiveness

A small library of 2,2'-[(alpha,omega-alkanediylbis(oxyphenylene)]bis-1H-benzimidazoles has been prepared and screened in vitro against Pneumocystis carinii, Trypanosoma brucei rhodesiense, and Leishmania donovani. Among the six tested compounds two derivatives emerged as promising hits characterized by IC(50) values lower than that determined for pentamidine against L. donovani.     

Preparation of transition-state analogues of sterol 24-methyl transferase as potential anti-parasitics

There is an urgent need for new drugs to treat leishmaniasis and Chagas disease. One important drug target in these organisms is sterol biosynthesis. In these organisms the main endogenous sterols are ergosta- and stigmata-like compounds in contrast to the situation in mammals, which have cholesterol as the sole sterol. In this paper we discuss the design, synthesis and evaluation of potential transition state analogues of the enzyme Delta24(25)-methyltransferase (24-SMT). This enzyme is essential for the biosynthesis of ergosterol, but not required for the biosynthesis of cholesterol. A series of compounds were successfully synthesised in which mimics of the S-adenosyl methionine co-factor were attached to the sterol nucleus. Compounds were evaluated against recombinant Leishmania major 24-SMT and the parasites L. donovani and Trypanosoma cruzi in vitro, causative organisms of leishmaniasis and Chagas disease, respectively. Some of the compounds showed inhibition of the recombinant Leishmania major 24-SMT and induced growth inhibition of the parasites. Some compounds also showed anti-parasitic activity against L. donovani and T. cruzi, but no inhibition of the enzyme. In addition, some of the compounds had anti-proliferative activity against the bloodstream forms of Trypanosoma brucei rhodesiense, which causes African trypanosomiasis.     

Antiprotozoal activities of new bis-chlorophenyl derivatives of bicyclic octanes and aza-nonanes

The in vitro activity of newly synthesized bis-(chlorophenyl)-azabicyclo[3.2.2]nonanes and bis-(chlorophenyl)-bicyclo[2.2.2]octanes against Plasmodium falciparum K(1) (resistant to chloroquine and pyrimethamine) and Trypanosoma brucei rhodesiense was investigated. Especially the bis-(chlorophenyl)-azabicyclo[3.2.2]nonanes exhibit promising antitrypanosomal activity and were tested in vivo against Trypanosoma brucei brucei featuring moderate activities.     

Cissampeloflavone,a chalcone-flavone dimer from Cissampelos pareira

From the aerial parts of Cissampelos pareira L. (Menispermaceae), a chalcone-flavone dimer has been isolated which, mainly from NMR spectroscopic and MS data, was proved to be 2-(4-hydroxy-3-methoxyphenyl)-7-(4-methoxyphenyl)-6-(2-hydroxy-4,6-dimethoxybenzoyl)-furano[3,2-g]benzopyran-4-one. This has been assigned the trivial name cissampeloflavone. The compound has good activity against Trypanosoma cruzi and T. brucei rhodesiense and has a low toxicity to the human KB cell line.     

Augustamine type alkaloids from Crinum kirkii

Sixteen more Amaryllidaceae alkaloids have been isolated from bulbs of Crinum kirkii Baker of which noraugustamine and 4a,N-dedihydronoraugustamine are hitherto unknown. Their structures and those of earlier known alkaloids have been established by physical and spectroscopic analysis. Application of 2D NMR techniques was used for complete characterization of the alkaloids as well as of 3-O-acetylsanguinine. 1,2-Diacetyllycorine and 3-O-acetylsanguinine showed activity against Trypanosoma brucci rhodesiense, the parasite associated with sleeping sickness. 3-O-acetylsanguinine also showed some activity against Trypanosoma cruzi.     

Alkaloids from Narcissus angustifolius subsp. transcarpathicus (Amaryllidaceae)

Seven alkaloids have been isolated from fresh bulbs of Narcissus angustifolius subsp. transcarpathicus (Amaryllidaceae). Nangustine, reported here for the first time, is the first 5,11-methanomorphanthridine alkaloid with a C-3/C-4 substitution. The structure and stereochemistry of this new alkaloid, as well as those previously known, have been determined by physical and spectroscopic methods. Spectroscopic data of pancracine have been completed. The in vitro assay activity against the parasitic protozoa Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum was carried out with the compounds nangustine and pancracine.     

Synthesis and biological evaluation of substrate-based inhibitors of 6-phosphogluconate dehydrogenase as potential drugs against African trypanosomiasis

The synthesis and biological evaluation of three series of 6-phosphogluconate (6PG) analogues is described. (2R)-2-Methyl-4,5-dideoxy, (2R)-2-methyl-4-deoxy and 2,4-dideoxy analogues of 6PG were tested as inhibitors of 6-phosphogluconate dehydrogenase (6PGDH) from sheep liver and also Trypanosoma brucei where the enzyme is a validated drug target. Among the three series of analogues, seven compounds were found to competitively inhibit 6PGDH from T. brucei and sheep liver enzymes at micromolar concentrations. Six inhibitors belong to the (2R)-2-methyl-4-deoxy series (6, 8, 10, 12, 21, 24) and one is a (2R)-2-methyl-4,5-dideoxy analogue (29b). The 2,4-dideoxy analogues of 6PG did not inhibit both enzymes. The trypanocidal effect of the compounds was also evaluated in vitro against T. brucei rhodesiense as well as other related trypanosomatid parasites (i.e., Trypanosoma cruzi and Leishmania donovani).     

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.