Lipophilic conformationally constrained spiro carbocyclic 2,6‐diketopiperazine‐1‐acetohydroxamic acid analogues as trypanocidal and leishmanicidal agents: An extended SAR study

We have previously described a number of lipophilic conformationally constrained spiro carbocyclic 2,6‐diketopiperazine (2,6‐DKP)‐1‐acetohydroxamic acids as potent antitrypanosomal agents. In this report, we extend the SAR analysis in this class of compounds with respect to in vitro growth inhibition of Trypanosoma and Leishmania parasites. Introduction of bulky hydrophobic substituents at the vicinal position of the basic nitrogen atom in the spiro carbocyclic 2,6‐DKP ring system can provide analogues which are potently active against bloodstream form Trypanosoma brucei and exhibit significant activities toward Trypanosoma cruzi epimastogotes and Leishmania infantum promastigotes and intracellular amastigotes. In particular, compounds possessing a benzyl or 4‐chlorobenzyl substituent were found to be the most active growth inhibitors, with activities in the low nanomolar and low micromolar ranges for T. brucei and L. infantum, respectively. The benzyl‐substituted (S)‐enantiomer was the most potent derivative against T. brucei (IC₅₀ = 6.8 nm ), T. cruzi (IC₅₀ = 0.21 μm ), and L. infantum promastigotes (IC₅₀ = 2.67 μm ) and intracellular amastigotes (IC₅₀ = 2.60 μm ). Moreover, the (R)‐chiral benzyl‐substituted derivative and its racemic counterpart displayed significant activities against L. donovani. Importantly, the active compounds show high selectivity in comparison with two mammalian cell lines.     

Discovery of benzimidazole‐based Leishmania mexicana cysteine protease CPB2.8ΔCTE inhibitors as potential therapeutics for leishmaniasis

Chemotherapy is currently the only effective approach to treat all forms of leishmaniasis. However, its effectiveness is severely limited due to high toxicity, long treatment length, drug resistance, or inadequate mode of administration. As a consequence, there is a need to identify new molecular scaffolds and targets as potential therapeutics for the treatment of this disease. We report a small series of 1,2‐substituted‐1H‐benzo[d]imidazole derivatives ( 9a–d ) showing affinity in the submicromolar range (K_i = 0.15–0.69 μM) toward Leishmania mexicanaCPB2.8ΔCTE, one of the more promising targets for antileishmanial drug design. The compounds confirmed activity in vitro against intracellular amastigotes of Leishmania infantum with the best result being obtained with derivative 9d (IC₅₀ = 6.8 μM), although with some degree of cytotoxicity (CC₅₀ = 8.0 μM on PMM and CC₅₀ = 32.0 μM on MCR‐5). In silico molecular docking studies and ADME‐Tox properties prediction were performed to validate the hypothesis of the interaction with the intended target and to assess the drug‐likeness of these derivatives.     

Design,synthesis, antileishmanial,and antifungal biological evaluation of novel 3,5-disubstituted isoxazole compounds based on 5-nitrofuran scaffolds

Nineteen 3,5-disubstituted-isoxazole analogs were synthesized based on nitrofuran scaffolds, by a [3 + 2] cycloaddition reaction between terminal acetylenes and 5-nitrofuran chloro-oxime. The compounds were obtained in moderate to very good yields (45–91%). The antileishmanial activity was assayed against the promastigote and amastigote forms of Leishmania (Leishmania) amazonensis. Alkylchlorinated compounds 14p–r were active on both the promastigote and amastigote forms, with emphasis on compound 14p , which showed strong activity against the amastigote form (IC₅₀ = 0.6 μM and selectivity index [SI] = 5.2). In the alkyl series, compound 14o stands out with an IC₅₀ = 8.5 μM and SI = 8.0 on the amastigote form. In the aromatic series, the most active compounds were those containing electron-donor groups, such as trimethoxy isoxazole 14g (IC₅₀ = 1.2 μM and SI = 20.2); compound 14h , with IC₅₀ = 7.0 μM and SI = 6.1; and compound 14j containing the 4-SCH₃ group, with IC₅₀ = 5.7 μM and SI = 10.2. In addition, the antifungal activity of 19 nitrofuran isoxazoles was evaluated against five strains of Candida (C. albicans, C. parapsilosis, C. krusei, C. tropicalis, and C. glabrata). Eleven isoxazole derivatives were active against C. parapsilosis, and compound 14o was found to be the most active (minimal inhibitory concentration [MIC] = 3.4 μM) for this strain. Compound 14p was active against all the strains tested, with an MIC = 17.5 μM for C. glabrata, lower than that of the fluconazole used as the reference drug.     

Synthesis and Antileishmanial Activity of Lipidic Amino Alcohols

In this work, a number of lipidic amino alcohols wereas synthesized and evaluated in vitro on cultures of Leishmania amazonensis and Leishmania chagasi. Nine amino alcohols showed inhibition of L. chagasi growth, and seven of them showed inhibition of L. amazonensis with IC₅₀ below 10 μm . Compound 11f was more active than the reference drug amphotericin B against L. chagasi promastigote forms.     

Effect of Vigna radiata, Tamarix ramosissima and Carthamus lanatus extracts on Leishmania major and Leishmania tropica: An in vitro study

Objective: Current therapy strategies of leishmaniasis have some problems such as high cost, toxicity and side effects. Plant extracts can be a source of drugs to control leishmaniasis. In this study, the effect of hydroalcoholic and chloroformic extracts of Vigna radiata, Tamarix ramosissima, and Carthamus lanatus on Leishmania major and L. tropica was studied. Methods: The plant samples were collected from west of Iran and their extracts were prepared. Anti-promastigote activity assay of all extracts was done using tetrazolium-dye assay. Results: Only high concentrations of V. radiata and C. lanatus were able to inhibit Leishmania, while both high and low concentrations of T. ramosissima had antileishmanial effect. No difference was observed between hydroalcoholic with chloroformic extract of each plant. Conclusion: Altogether, the results revealed the antileishmanial activity of T. ramosissima extracts against L. major and L. tropica, indicating its potential as an antileishmanial agent.     

Synthesis and Biological Evaluation of Tricyclic Guanidine Analogues of Batzelladine K for Antimalarial,Antileishmanial, Antibacterial,Antifungal, and Anti‐HIV Activities

Fifty analogues of batzelladine K were synthesized and evaluated for in vitro antimalarial (Plasmodium falciparum), antileishmanial (Leishmania donovani), antimicrobial (panel of bacteria and fungi), antiviral (HIV‐1) activities. Analogues 14h and 20l exhibited potential antimalarial activity against chloroquine‐sensitive D6 strain with IC₅₀ 1.25 and 0.88 μm and chloroquine‐resistant W2 strain with IC₅₀ 1.64 and 1.07 μm , respectively. Analogues 12c and 14c having nonyl substitution showed the most potent antileishmanial activity with IC₅₀ 2.39 and 2.78 μm and IC₉₀ 11.27 and 12.76 μm , respectively. Three analogues 12c , 14c, and 14i were the most active against various pathogenic bacteria and fungi with IC₅₀ < 3.02 μm and MIC/MBC/MFC <6 μm . Analogue 20l having pentyl and methyl substituents on tricycle showed promising activities against all pathogens. However, none was found active against HIV‐1. Our study demonstrated that the tricyclic guanidine compounds provide new structural class for broad spectrum activity.     

Identification of dehydroxy isoquine and isotebuquine as promising antileishmanial agents

Traditional antimalarial drugs based on 4‐aminoquinolines have exhibited good antiproliferative activities against Leishmania parasites; however, their clinical use is currently limited. To identify new 4‐aminoquinolines to combat American cutaneous leishmaniasis, we carried out a full in vitro evaluation of a series of dehydroxy isoquines and isotebuquines against two Leishmania parasites such as Leishmania braziliensis and Leishmania mexicana. First, the antiproliferative activity of the quinolines was studied against the promastigote forms of L. braziliensis and L. mexicana parasites, finding that five of them exhibited good antileishmanial responses with micromolar IC₅₀ values ranging from 3.84 to 10 μM. A structure‐activity relationship analysis gave evidence that a piperidine or a morpholine attached as N‐alkyamino terminal substituent as well as the inclusion of an extra phenyl ring attached at the aniline ring of the isotebuquine core constitute important pharmacophores to generate the most active derivatives, with antileishmanial responses by far superior to those found for the reference drug, glucantime. All compounds showed a relatively low toxicity on human dermis fibroblasts, with CC₅₀ ranging from 69 to >250 μM. The five most active compounds displayed moderate to good antileishmanial activity against the intracellular amastigote form of L. braziliensis, compared to the reference drug. In particular, compound 2j was identified as the most potent agent against antimony‐resistant amastigotes of L. braziliensis with acceptable biological response and selectivity, emerging as a promising candidate for further in vivo antileishmanial evaluation. Diverse mechanism‐of‐action studies and molecular docking simulations were performed for the most active 4‐aminoquinoline.     

Thiopurine derivatives containing triazole and steroid: Synthesis, antimalarial and antileishmanial activities

A series of novel 6-thiopurine derivates containing 1,2,3-triazole were synthesized and their in vivo antimalarial activity and in vitro antileishmanial activity were examined. The compounds 10, 11, 12 and 14 presented higher values of inhibition of parasite multiplication than chloroquine. For antileishmanial activity, the compound 14 showed activity against the three species of Leishmania tested. None of compounds showed cytotoxicity against mammalian cells.     

In Vitro Assessment of Plants Growing in Cuba Belonging to Solanaceae Family Against Leishmania amazonensis

In this study, an in vitro antileishmanial assessment of plant extracts from 12 genera and 46 species growing in Cuba belonging to Solanaceae family was performed. A total of 226 extracts were screened against promastigotes of Leishmania amazonensis, and cytotoxicity of active extracts [median inhibitory concentration (IC₅₀) promastigotes <100 µg/mL] was determined on peritoneal macrophage from BALB/c mice. Extracts that showed selective index >5 were then assayed against intracellular amastigote. Metabolomics analysis of promissory extracts was performed using chemical profile obtained by ultra performance liquid chromatography. Only 11 extracts (4.9%) from nine plants were selected as potentially actives: Brunfelsia cestroides A. Rich, Capsicum annuum L., Capsicum chinense Jacq., Cestrum nocturnum L., Nicotiana plumbaginifolia Viv., Solanum havanense Jacq., Solanum myriacanthum Dunal, Solanum nudum Dunal and Solanum seaforthianum And., with IC₅₀ < 50 µg/mL and selectivity index >5. Metabolomics analysis demonstrated significant differences in the chemical profiles with an average of 42.8 (range 31–88) compounds from m/z 104 to 1477, which demonstrated the complex mixture of compounds. In addition, no common markers among active extracts were identified. The results demonstrate the importance of the Solanaceae family to search new antileishmanial agents, particularly in unexplored species of this family. Copyright © 2016 John Wiley & Sons, Ltd.