Targeting malaria and leishmaniasis: Synthesis and pharmacological evaluation of novel pyrazole-1,3,4-oxadiazole hybrids. Part II

In continuance with earlier reported work, an extension has been carried out by the same research group. Mulling over the ongoing condition of resistance to existing antimalarial agents, we had reported synthesis and antimalarial activity of certain pyrazole-1,3,4-oxadiazole hybrid compounds. Bearing previous results in mind, our research group ideated to design and synthesize some more derivatives with varied substitutions of acetophenone and hydrazide. Following this, derivatives 5a–r were synthesized and tested for antimalarial efficacy by schizont maturation inhibition assay. Further, depending on the literature support and results of our previous series, certain potent compounds (5f, 5n and 5r) were subjected to Falcipain-2 inhibitory assay. Results obtained for these particular compounds further strengthened our hypothesis. Here, in this series, compound 5f having unsubstituted acetophenone part and a furan moiety linked to oxadiazole ring emerged as the most potent compound and results were found to be comparable to that of the most potent compound (indole bearing) of previous series. Additionally, depending on the available literature, compounds (5a–r) were tested for their antileishmanial potential. Compounds 5a, 5c and 5r demonstrated dose-dependent killing of the promastigotes. Their IC₅₀ values were found to be 33.3 ± 1.68, 40.1 ± 1.0 and 19.0 ± 1.47 μg/mL respectively. These compounds (5a, 5c and 5r) also had effects on amastigote infectivity with IC₅₀ of 44.2 ± 2.72, 66.8 ± 2.05 and 73.1 ± 1.69 μg/mL respectively. Further target validation was done using molecular docking studies. Acute oral toxicity studies for most active compounds were also performed.     

New 5-(nitroheteroaryl)-1,3,4-thiadiazols containing acyclic amines at C-2: synthesis and SAR study for their antileishmanial activity

A novel series of 5-(5-nitrofuran-2-yl)-and 5-(5-nitrothiophen-2-yl)-1,3,4-thiadiazole-2-amines bearing acyclic amine at C-2 position of thiadiazole ring were synthesized and evaluated in vitro against promastigote and amastigote forms of Leishmania major. The structure-activity of series was investigated by studying 40 compounds. The most active derivatives were hydroxypropylamino- and methoxypropylamino- analogs of 5-(5-nitrothiophen-2-yl)-1,3,4-thiadiazole (compounds 29 and 32, respectively) with highest selectivity index (SI >12).     

Evaluation of a diospyrin derivative as antileishmanial agent and potential modulator of ornithine decarboxylase of Leishmania donovani

World health organization has called for academic research and development of new chemotherapeutic strategies to overcome the emerging resistance and side effects exhibited by the drugs currently used against leishmaniasis. Diospyrin, a bis-naphthoquinone isolated from Diospyros montana Roxb., and its semi-synthetic derivatives, were reported for inhibitory activity against protozoan parasites including Leishmania. Presently, we have investigated the antileishmanial effect of a di-epoxide derivative of diospyrin (D17), both in vitro and in vivo. Further, the safety profile of D17 was established by testing its toxicity against normal macrophage cells (IC₅₀ ∼ 20.7 μM), and also against normal BALB/c mice in vivo. The compound showed enhanced activity (IC₅₀ ∼ 7.2 μM) as compared to diospyrin (IC₅₀ ∼ 12.6 μM) against Leishmania donovani promastigotes. Again, D17 was tested on L. donovani BHU1216 isolated from a sodium stibogluconate-unresponsive patient, and exhibited selective inhibition of the intracellular amastigotes (IC₅₀ ∼ 0.18 μM). Also, treatment of infected BALB/c mice with D17 at 2 mg/kg/day reduced the hepatic parasite load by about 38%. Subsequently, computational docking studies were undertaken on selected enzymes of trypanothione metabolism, viz. trypanothione reductase (TryR) and ornithine decarboxylase (ODC), followed by the enzyme kinetics, where D17 demonstrated non-competitive inhibition of the L. donovani ODC, but could not inhibit TryR.     

Antileishmanial activity and cytotoxicity of ent-beyerene diterpenoids

We describe the in vitro activity of two natural isomeric ent-beyerene diterpenes, several derivatives and synthetic intermediates. Beyerenols 1 and 2 showed EC₅₀ of 4.6?±?9.4 and 5.3?±?9.4?μg/mL against amastigotes of L. (V) brazilensis, with SI of 5.1 and 7.7, respectively. Beyerenol 1 was synthesized from stevioside. In vivo experiments with bereyenols showed cure in 50% of hamsters infected with L. (V) brazilensis topically applied as Cream I (beyerenol 1, 0.81%, w/w) and Cream III (beyerenol 2, 1.96%, w/w). These results suggest that beyerenols are potential candidates for cutaneous leishmaniasis chemotherapy by topical application. In vitro assays of amastigotes of L. (V) brazilensis showed EC₅₀ of 1.1?±?0.1 and 1.3?±?0.04?μg/mL, with SI of 3.1 and 3.5 for hydrazone intermediates 10 and 11, respectively.     

Antileishmanial activity and ultrastructural changes of sesquiterpene lactones isolated from Calea pinnatifida (Asteraceae)

Bioactivity-guided fractionation of antileishmanial active CH₂Cl₂ phase of MeOH extract from leaves of Calea pinnatifida led to isolation of two sesquiterpene lactones calein C (1) and calealactone C (2), which structures were stablished on the basis of spectroscopic analysis. Compounds 1 and 2 displayed potent activity against Leishmania amazonensis promastigotes with EC₅₀ of 1.7 and 4.6 µg mL⁻¹, respectively. Compound 2 presented low cytotoxicity for J774 macrophages and displayed activity against amastigote forms of L. amazonensis similar to miltefosine with CC₅₀ values of 31.73 and 27.18 µg mL⁻¹, respectively. Additionally, compounds 1 and 2 caused ultrastructural changes in promastigotes leading to a loss of their classical structural morphology, as evidenced by electron microscopy. Also compound 2 decreased the mitochondria membrane potential. To the best of our knowledge, this is the first occurrence of 1 and 2 in C. pinnatifida. The results obtained highlighted the importance of studying sesquiterpene lactones isolated from Calea pinnatifida in terms of antileishmanial activity, in order to understand the mechanism of action of the isolated compounds in promastigotes forms of L. amazonensis.     

Klaivanolide, an antiprotozoal lactone from Uvaria klaineana

Bioguided-fractionation of a CH(2)Cl(2) extract of the stems of Uvaria klaineana (Annonaceae) led to isolation of klaivanolide, a novel bisunsaturated 7-membered lactone (5-acetoxy-7-benzoyloxymethyl-7H-oxepin-2-one), together with benzyl benzoate. Klaivanolide showed potent in vitro antileishmanial activity against both sensitive and amphotericin B-resistant promastigote forms of Leishmania donovani with IC(50) values of 1.75 and 3.12 microM, respectively. The compound also showed in vitro trypanocidal activity against trypomastigote forms of Trypanosoma brucei brucei GVR 35. Its structure was established by 1D and 2D NMR and other spectroscopic techniques.     

<Emphasis Type="Italic">In vitro</Emphasis> antileishmanial activity of <Emphasis Type="Italic">Aloe vera</Emphasis> leaf exudate: A potential herbal therapy in leishmaniasis

Aloe vera has wide spread use in health products, and despite several reports on the whole plant and inner gel, little work has been performed on the leaf exudate. Our aim was to evaluate the in vitro efficacy of Aloe vera leaf exudate (AVL) in leishmaniasis. Irrespective of the disease manifestation, promastigotes from strains responsible for cutaneous, mucocutaneous, and visceral leishmaniasis were susceptible to AVL and their IC₅₀ ranged from 100 to 180 μg/ml. In axenic amastigotes cultured from a L. donovani strain 2001 responsible for visceral leishmaniasis, the IC₅₀ was 6.0 μg/ml. AVL caused activation of host macrophages evident by an increased release of members of reactive oxygen species that was attenuated by preincubation with free radical scavengers. Collectively, our data indicates that AVL, via its direct leishmanicidal activity which can be further enhanced by activation of host macrophages, is an effective antileishmanial agent meriting further pharmacological investigations.     

The living library of The Cotapata National Park in Bolivia: an example of application of Bolivian law on the access to genetic resources

Developing countries with a rich biodiversity want to control the use of this natural patrimony, especially in the research of natural compounds of pharmaceutical interest. Here we present the organization of six permanent plots in a mountain tropical forest on the east side of the Andean Cordillera in Bolivia, and their role in the discovery of plants with antiplasmodial or antileishmanial activities. Permanent plots are widely used in ecological survey, but rarely in bioprospecting. This set-up allows Bolivian authorities to control the bioprospecting, and facilitates further chemical studies on the bioactive plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Lucia Acebey and Amira Apaza have contributed equally to this work.     

gem-Dithioacetylated indole derivatives as novel antileishmanial agents

In this communication we report a serendipitously discovered hybrid molecule 1, combining fragment of 3 (an in vivo active antileishmanial molecule) with H₂S donor moiety (known for bimodal behavior of cytoprotection and apoptosis), as antileishmanial agent. Compound 1 suppresses 99.82% parasitemia of L. donovani infected macrophages at 12.5 μg/ml without even deforming them (CC₅₀ > 100 μg/ml). This compound appears cytotoxic for intracellular amastigotes while cytoprotective to host macrophages. The concept can be utilized to develop high therapeutic index NCE (New Chemical Entities) for other macrophage mediated diseases like tuberculosis and cancer.     

Antitumoral and antileishmanial dioncoquinones and ancistroquinones from cell cultures of Triphyophyllum peltatum (Dioncophyllaceae) and Ancistrocladus abbreviatus (Ancistrocladaceae)

From the methanolic extracts of solid callus cultures from two species of the closely related palaeotropical plant families Dioncophyllaceae and Ancistrocladaceae seven new natural naphthoquinones were isolated, dioncoquinones A (4) and B (5) from Triphyophyllum peltatum, and ancistroquinones B (6), C (7), D (9), E (10), and F (12) from Ancistrocladus abbreviatus. Their structures were elucidated by spectroscopic, chemical, and computational methods. Furthermore, the already known naphthoquinones plumbagin (2), droserone (3), malvone A (8), and nepenthone A (11) were found in the extract of A. abbreviatus. Dioncoquinones A (4) and B (5) showed good - and specific - activity against Leishmania major, while they were not active against other protozoic parasites. Moreover, treatment with 4 and 5 strongly induced apoptosis in human tumor cells derived from two different B cell malignancies, B cell lymphoma and multiple myeloma, without any significant toxicity towards normal peripheral mononuclear blood cells.