Benzofuranyl 3,5-bis-polyamine derivatives as time-dependent inhibitors of trypanothione reductase

Toward a Drug Against All Kinetoplastids: From LeishBox to Specific and Potent Trypanothione Reductase Inhibitors

Leishmaniasis, Chagas disease, and sleeping sickness affect millions of people worldwide and lead to the death of about 50 000 humans per year. These diseases are caused by the kinetoplastids Leishmania, Trypanosoma cruzi, and Trypanosoma brucei, respectively. These parasites share many general features, including gene conservation, high amino acid identity among proteins, the presence of subcellular structures as glycosomes and the kinetoplastid, and genome architecture, that may make drug development family specific, rather than species-specific, i.e., on the basis of the inhibition of a common, conserved parasite target. However, no optimal molecular targets or broad-spectrum drugs have been identified to date to cure these diseases. Here, the LeishBox from GlaxoSmithKline high-throughput screening, a 192-molecule set of best antileishmanial compounds, based on 1.8 million compounds, was used to identify specific inhibitors of a validated Leishmania target, trypanothione reductase (TR), while analyzing in parallel the homologous human enzyme glutathione reductase (GR). We identified three specific highly potent TR inhibitors and performed docking on the TR solved structure, thereby elucidating the putative molecular basis of TR inhibition. Since TRs from kinetoplastids are well conserved, and these compounds inhibit the growth of Leishmania, Trypanosoma cruzi, and Trypanosoma brucei, the identification of a common validated target may lead to the development of potent antikinetoplastid drugs.

Total synthesis of diptoindonesin G and its analogues as selective modulators of estrogen receptors

We have developed a versatile synthetic strategy for the synthesis of the natural product diptoindonesin G and its analogues as selective modulators of estrogen receptors. The strategy involves a regioselective dehydrative cyclization of arylacetals, a regioselective bromination of benzofurans, a sequential cross-coupling of bromo-benzofurans with aryl boronic acids, and a BBr₃-mediated tandem cyclization and demethylation. Preliminary biological studies uncovered the critical and dispensable phenolic hydroxyl groups in the natural product and also revealed unexpected selectivity for isoforms of estrogen receptor.

Hydrazone–Pd-catalyzed direct intermolecular reaction of o-alkynylphenols with allylic acetates

The hydrazone–palladium catalyzed direct intermolecular reaction of o-alkynylphenols with allylic acetates gave the corresponding 2-substituted-3-allylbenzofuran derivatives at room temperature.

Antiprotozoal glutathione derivatives with flagellar membrane binding activity against T. brucei rhodesiense

A new series of N-substituted S-(2,4-dinitrophenyl)glutathione dibutyl diesters were synthesized to improve in vitro anti-protozoal activity against the pathogenic parasites Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. The results obtained indicate that N-substituents enhance the inhibitory properties of glutathione diesters whilst showing reduced toxicity against KB cells as in the cases of compounds 5, 9, 10, 16, 18 and 19. We suggest that the interaction of N-substituted S-(2,4-dinitrophenyl) glutathione dibutyl diesters with T. b. brucei occurs mainly by weak hydrophobic interactions such as London and van der Waals forces. A QSAR study indicated that the inhibitory activity of the peptide is associated negatively with the average number of C atoms, N_C and positively to S_ZX, the ZX shadow a geometric descriptor related to molecular size and orientation of the compound. HPLC-UV studies in conjunction with optical microscopy indicate that the observed selectivity of inhibition of these compounds against bloodstream form T. b. brucei parasites in comparison to L. donovani under the same conditions is due to intracellular uptake via endocytosis in the flagellar pocket.

Hydrazone–palladium catalyzed annulation of 1-cinnamyloxy-2-ethynylbenzene derivatives

The annulation of 1-cinnamyloxy-2-ethynylbenzene derivatives using a hydrazone–palladium catalyst system proceeded smoothly and gave the corresponding 2-substituted-3-cinnamylbenzofurans in good-to-excellent yields.

Mini review on tricyclic compounds as an inhibitor of trypanothione reductase

Trypanosomiasis and leishmaniasis are two most ruinous parasitic infectious diseases caused by Trypanosoma and Leishmania species. The disease affects millions of people all over the world and associated with high morbidity and mortality rates. The review discuss briefly on current treatment of these parasitic diseases and trypanothione reductase (TryR) as potential targets for rational drug design. The enzyme trypanothione reductase (TryR) has been identified as unique among these parasites and has been proposed to be an effective target against for developing new drugs. The researchers have selected this enzyme as target is due to its substrate specificity in contrast to human analogous glutathione reductase and its absence from the host cell which makes this enzyme an ideal target for drug discovery. In this review we have tried to present an overview of the different tricyclic compounds which are potent inhibitors of TryR with their inhibitory activities against the parasites are briefly discussed.

Design and synthesis of pyrido[3,2-α]carbazole derivatives and their analogues as potent antitumour agents

A series of pyrido[3,2-α]carbazole derivatives and their analogues have been prepared and evaluated for their antitumour activity against human lung cancer A549 cells and colon cancer HT29 cells. The intermediates 4a-4k are successfully synthesized from 1a-1k and ethyl 2-(3-bromopyridin-2-yl)acetate by Knoevenagel condensation and intramolecular Heck-type reaction, and this is a novel and efficient synthetic approach to the core scaffold of the target compounds. These target compounds have shown an interesting antitumour profile towards the tested cell lines with IC50 values ranging from 0.07 μM to 4.45 μM. Among all the compounds synthesized, 8 compounds show higher potency than R16, 12 compounds are as potent as R16, and 6 compounds are less potent than R16. The best compound 24 is 7 times and approximately 10 times as potent as R16 against A549 and HT29 cells, respectively.

Investigation of trypanothione reductase as a drug target in Trypanosoma brucei

There is an urgent need for new drugs for the treatment of tropical parasitic diseases such as human African trypanosomiasis, which is caused by Trypanosoma brucei. The enzyme trypanothione reductase (TryR) is a potential drug target within these organisms. Herein we report the screening of a 62,000 compound library against T. brucei TryR. Further work was undertaken to optimise potency and selectivity of two novel-compound series arising from the enzymatic and whole parasite screens and mammalian cell counterscreens. Both of these series, containing either a quinoline or pyrimidinopyrazine scaffold, yielded low micromolar inhibitors of the enzyme and growth of the parasite. The challenges of inhibiting TryR with druglike molecules is discussed.

Antimycobacterial flavonoids from the leaf extract of Galenia africana

The bioassay-guided fractionation of the EtOH extract of the leaves of Galenia africana led to the isolation of three known flavonoids, (2S)-5,7,2'-trihydroxyflavanone (1), (E)-3,2',4'-trihydroxychalcone (2), and (E)-2',4'-dihydroxychalcone (3), and the new (E)-3,2',4'-trihydroxy-3'-methoxychalcone (4). Compounds 1 and 3 exhibited moderate antituberculosis activity. During synergistic studies, a combination of compound 4 and an existing antituberculosis drug, isoniazid, reduced their original MICs 4-fold, resulting in a fractional inhibitory concentration of 0.50. The most pronounced effect was demonstrated by compound 1 and isoniazid reducing their MICs 16-fold and resulting in an FIC of 0.12. Both EtOH extract and isolated compounds failed to exhibit any NADPH oxidase activity at 800.0 muM concentrations, indicating that mycothiol disulfide reductase is not the target for their antituberculosis activity.

Trypanocidal drugs: mechanisms, resistance and new targets

The protozoan parasitesTrypanosoma bruceiandTrypanosoma cruziare the causative agents of African trypanosomiasis and Chagas disease, respectively. These are debilitating infections that exert a considerable health burden on some of the poorest people on the planet. Treatment of trypanosome infections is dependent on a small number of drugs that have limited efficacy and can cause severe side effects. Here, we review the properties of these drugs and describe new findings on their modes of action and the mechanisms by which resistance can arise. We further outline how a greater understanding of parasite biology is being exploited in the search for novel chemotherapeutic agents. This effort is being facilitated by new research networks that involve academic and biotechnology/pharmaceutical organisations, supported by public–private partnerships, and are bringing a new dynamism and purpose to the search for trypanocidal agents.

Mycothiol disulfide reductase: a continuous assay for slow time-dependent inhibitors

Mycothiol (MSH) is the principal low-molecular-weight thiol, unique to mycobacteria and other actinomycetes, that performs a role analogous to glutathione found in other organisms. MSH plays a key role in oxidative stress management and is oxidized to the dimeric mycothiol disulfide (MSSM) in the process. NADPH-dependent mycothiol disulfide reductase (Mtr) helps to maintain an intracellular reducing environment by reducing MSSM back to MSH. Mtr inhibition studies are currently impaired by limited availability of MSSM. Substrate demands are particularly high in time-dependent inhibition assays. Here we report an assay that chemically recycles a mixed disulfide substrate analogue in situ, thereby greatly reducing the substrate quantities needed for such assays. This has enabled the development of a continuous assay where linear reaction rates can be maintained for 40 min or longer using minimal substrate concentrations (5 microM versus a substrate K(m) value of 268 microM). In this manner, substrate requirements are reduced by orders of magnitude. Characterization of a novel time-dependent inhibitor, 2-(5-bromo-2-methoxyphenyl)acrylonitrile, is also demonstrated using these procedures.

Time-dependent inhibitors of trypanothione reductase: analogues of the spermidine alkaloid lunarine and related natural products

The macrocyclic spermidine alkaloid lunarine 1 from Lunaria biennis is a competitive, time-dependent inhibitor of the protozoan oxidoreductase trypanothione reductase (TryR), a promising target in drug design against tropical parasitic diseases. Various molecules related to 1 and the alkaloid itself have been synthesized in racemic form and evaluated against TryR in order to determine the key features of 1 that are associated with time-dependent inhibition. Kinetic data are consistent with an inactivation mechanism involving a conjugate addition of an active site cysteine residue onto the C-24-C-25 double bond of the tricyclic nucleus of 1. Comparison of data for synthetic (+/-)-1, the natural product, and other derivatives 7-10 from L. biennis confirms the importance of the unique structure of the tricyclic core as a motif for inhibitor design and reveals that the non-natural enantiomer may be a more suitable scaffold upon which thiophilic groups may be presented.

Dithiol Proteins as Guardians of the Intracellular Redox Milieu in Parasites: Old and New Drug Targets in Trypanosomes and Malaria-Causing Plasmodia

Parasitic diseases such as sleeping sickness, Chagas' heart disease, and malaria are major health problems in poverty-stricken areas. Antiparasitic drugs that are not only active but also affordable and readily available are urgently required. One approach to finding new drugs and rediscovering old ones is based on enzyme inhibitors that paralyze antioxidant systems in the pathogens. These antioxidant ensembles are essential to the parasites as they are attacked in the human host by strong oxidants such as peroxynitrite, hypochlorite, and H2O2. The pathogen-protecting system consists of some 20 thiol and dithiol proteins, which buffer the intraparasitic redox milieu at a potential of -250 mV. In trypanosomes and leishmania the network is centered around the unique dithiol trypanothione (N1,N8-bis(glutathionyl)spermidine). In contrast, malaria parasites have a more conservative dual antioxidative system based on glutathione and thioredoxin. Inhibitors of antioxidant enzymes such as trypanothione reductase are, indeed, parasiticidal but they can also delay or prevent resistance against a number of other antiparasitic drugs.