Hydrazone-Tethered 5-(Pyridin-4-yl)-4H-1,2,4-triazole-3-thiol Hybrids: Synthesis, Characterisation, in silico ADME Studies, and in†vitro Antimycobacterial Evaluation and Cytotoxicity.

Compounds containing arylpyrrole-, 1,2,4-triazole- and hydrazone structural frameworks have been widely studied and demonstrated to exhibit a wide range of pharmacological properties. Herein, an exploratory series of new 1,2,4-triazole derivatives designed by amalgamation of arylpyrrole and 1,2,4-triazole structural units via a hydrazone linkage is reported. The synthesised compounds were tested in vitro for their potential activity against Mycobacterium tuberculosis (MTB) H37 Rv strain. The most promising compound 13 - the derivative without the benzene ring appended to the pyrrole unit displayed acceptable activity (MIC90 =3.99 µM) against MTB H37 Rv, while other compounds from the series exhibited modest to weak antimycobacterial activity with MIC90 values in the range between 7.0 and >125 µM. Furthermore, in silico results, predicated using the SwissADME web tool, show that the prepared compounds display desirable ADME profile with parameters within acceptable range.

Synthesis and in vitro antiprotozoal evaluation of novel metronidazole-Schiff base hybrids.

Herein we report the synthesis of 21 novel small molecules inspired by metronidazole and Schiff base compounds. The compounds were evaluated against Trichomonas vaginalis and cross-screened against other pathogenic protozoans of clinical relevance. Most of these compounds were potent against T. vaginalis, exhibiting IC50 values < 5 µM. Compound 20, the most active compound against T. vaginalis, exhibited an IC50 value of 3.4 µM. A few compounds also exhibited activity against Plasmodium falciparum and Trypanosomal brucei brucei, with compound 6 exhibiting an IC50 value of 0.7 µM against P. falciparum and compound 22 exhibiting an IC50 value of 1.4 µM against T.b. brucei. Compound 22 is a broad-spectrum antiprotozoal agent, showing activities against all three pathogenic protozoans under investigation.

Phytochemical, Antiplasmodial, and Cytotoxic Investigation of Euclea natalensis A.DC. subsp. natalensis Leaves.

Previous research shows that the root and bark extracts of Euclea natalensis have antiplasmodial activity, but the leaves have not been examined yet. This study investigated the phytochemical, antiplasmodial, and cytotoxic properties of the plant leaves. The activity against 3D7 Plasmodium falciparum was determined using the parasite lactate dehydrogenase assay, and the cytotoxicity against Vero and HeLa cells was evaluated using the MTT and resazurin assays, respectively. The bioactive compounds were isolated by chromatography, and their structures were established with spectroscopic and spectrometric techniques. The extract showed antiplasmodial activity (IC50 =25.6 µg/mL) and was not cytotoxic against Vero cells (IC50 =403.7 µg/mL). Purification of the extract afforded six flavonoid glycosides, four triterpenoids, and a coumarin. The glycosides showed antiplasmodial and cytotoxic activities, against HeLa cells, at 50 µg/mL, but the activity was reduced at 10 µg/mL. Naphthoquinones, which are among the predominant phytochemicals in the root and root bark of E. natalensis, were not detected in the leaves.

7H-Pyrrolo[2,3-d]pyrimidine-4-amines as Potential Inhibitors of Plasmodium falciparum Calcium-Dependent Protein Kinases.

A series of pyrrolo[2,3-d]pyrimidines were designed in silico as potential bumped kinase inhibitors targeting P. falciparum calcium dependent protein kinase 4 (PfCDPK4), with the potential to inhibit PfCDPK1 based on earlier studies of the two kinases. A small series of these compounds were prepared and assessed for inhibitory activity against PfCDPK4 and PfCDPK1 in vitro. Four of the compounds displayed promising inhibitory activity against either PfCDPK4 (IC50 =0.210-0.530 µM), or PfCDPK1 (IC50 =0.589 µM). These data will enable optimisation of the molecular model to better predict inhibitory activity against PfCDPK4.

Antiplasmodial Activity of Vachellia xanthophloea (Benth.) P.J.H. Hurter (African Fever Tree) and Its Constituents.

Vachellia xanthophloea is used in Zulu traditional medicine as an antimalarial remedy. A moderate antiplasmodial activity was previously reported for extracts of the plant against D10 Plasmodium falciparum. This study aimed to identify the phytochemicals responsible for the antiplasmodial activity of the leaf extract. The compounds were isolated by chromatography and their structures were determined using spectroscopic and spectrometric methods. The antiplasmodial activity was evaluated using a parasite lactate dehydrogenase assay and cytotoxicity was determined using a resazurin assay. The ethyl acetate fraction inhibited P. falciparum with IC50 = 10.6 µg/mL and showed minimal cytotoxicity (98% cell viability at 33 µg/mL). The chromatographic purification of this fraction afforded sixteen compounds, including two new flavonoids. A 1:1 mixture of phytol and lupeol was also isolated from the hexane fraction. All the compounds were reported from V. xanthophloea for the first time. Among the isolated metabolites, methyl gallate displayed the best activity against P. falciparum (IC50 = 1.2 µg/mL), with a 68% viability of HeLa cells at 10 µg/mL. Therefore, methyl gallate was responsible for the antiplasmodial activity of the V. xanthophloea leaf extract and its presence in the leaf extract might account for the folkloric use of the plant as an antimalarial remedy.

Phytochemical and antiplasmodial investigation of Gardenia thunbergia L. f. leaves.

Previous results indicated that the methanol extract of Gardenia thunbergia has antiplasmodial activity but no compounds have ever been isolated from the plant. Therefore, this study aimed to investigate the phytochemical and antiplasmodial properties of the plant. The methanol leaf extract of G. thunbergia inhibited Plasmodium falciparum at 50 µg/mL (> 80% inhibition) and was not cytotoxic against HeLa cells. Chromatographic purification of the extract afforded a new saponin and eight other known compounds. The saponin and two flavonoid glycosides displayed non-selective antiplasmodial activity at 50 µg/mL but the activities were diminished at 10 µg/mL. The presence of the isolated compounds in the leaf extract of G. thunbergia could account for the folkloric use of the plant in treating malaria.

Synthesis and in vitro antitrypanosomal evaluation of novel 6-heteroarylidene-substituted quinolone derivatives.

Human African trypanosomiasis is a vector-borne tropical disease of African origin. Presently, due to human migration and climate change, the disease might present global health and economic burdens as current chemotherapy of trypanosomiasis remains a challenge due to limited existing drugs, which are of poor efficacy, cause severe adverse events and are very costly. Recently, Beteck and co-workers identified a small library of 1,3,6-substituted non-fluoroquinolones that showed moderate to weak trypanocidal activity without cytotoxic effects. The current study further explored SARs of the quinolone scaffold in search for more potent trypanocidal agents. Fifteen novel quinolone derivatives bearing a heteroarylidene moiety at positon-6 and varied chemical entities at positions -1 and -3 of the quinolone scaffold were synthesized and evaluated in vitro for antitrypanosomal activity. The compounds exhibit exceptionally good antitrypanosomal activity with IC50 values in the low-micromolar to sub-micromolar range (0.08-15.26 µM), with compound 6d being the most active having an IC50 value of 80 nM against T.b. brucei. Compounds in this study generally have molecular weight less than 600Da, ClogP value of 2-4 and a BBB score of 1-5, hence they could be potentially effective against both stages of trypanosomiasis.

Virtual screening and in vitro validation identifies the first reported inhibitors of Salmonella enterica HPPK.

HPPK, which directly precedes DHPS in the folate biosynthetic pathway, is a promising but chronically under-exploited anti-microbial target. Here we report the identification of new S. enterica HPPK inhibitors, offering potential for new resistance circumventing S. enterica therapies as well as avenues for diversifying the current HPPK inhibitor space.

Antiplasmodial and Cytotoxic Flavonoids from Pappea capensis (Eckl. & Zeyh.) Leaves.

Ethnobotanical surveys indicate that the Masai and Kikuyu in Kenya, the Venda in South Africa, and the Gumuz people of Ethiopia use Pappea capensis for the treatment of malaria. The present study aimed to investigate the phytochemical and antiplasmodial properties of the plant leaves. The bioactive compounds were isolated using chromatographic techniques. The structures were established using NMR, HRMS, and UV spectroscopy. Antiplasmodial activity of P. capensis leaf extract and isolated compounds against chloroquine-sensitive 3D7 P. falciparum was evaluated using the parasite lactate dehydrogenase assay. Cytotoxicity against HeLa (human cervix adenocarcinoma) cells was determined using the resazurin assay. The extract inhibited the viability of Plasmodium falciparum by more than 80% at 50 µg/mL, but it was also cytotoxic against HeLa cells at the same concentration. Chromatographic purification of the extract led to the isolation of four flavonoid glycosides and epicatechin. The compounds displayed a similar activity pattern with the extract against P. falciparum and HeLa cells. The results from this study suggest that the widespread use of P. capensis in traditional medicine for the treatment of malaria might have some merits. However, more selectivity studies are needed to determine whether the leaf extract is cytotoxic against noncancerous cells.

Antiplasmodial and Cytotoxic Activities of Extract and Compounds from Ozoroa obovata (Oliv.) R. & A. Fern. var. obovata.

Ozoroa obovata (Oliv.) R. & A. Fern. var. obovata found in KwaZulu-Natal in South Africa was investigated for phytochemical constituents, and for antiplasmodial and cytotoxic effects. The plant leaves were collected from the University of KwaZulu-Natal (UKZN) arboretum on the Pietermaritzburg Campus, in March 2019. The inhibitory activity against 3D7 Plasmodium falciparum was determined using the parasite lactate dehydrogenase (pLDH) assay and cytotoxicity against HeLa cells was evaluated using the resazurin assay. The bioactive compounds were isolated by chromatographic purification and their structures were established with spectroscopic and spectrometric techniques. The plant leaf extract displayed significant antiplasmodial activity at 50 µg/mL and was also cytotoxic against HeLa cells. Chromatographic purification of the extract led to the isolation of two biflavonoids, four flavonoid glycosides, a steroid glycoside, and a megastigmene derivative. The compounds displayed antiplasmodial and antiproliferative activities at 50 µg/mL but the activity was substantially reduced at 10 µg/mL. The activities and compounds are being reported in O. obovata for the first time.

Coumarin-Annulated Ferrocenyl 1,3-Oxazine Derivatives Possessing In Vitro Antimalarial and Antitrypanosomal Potency.

A tailored series of coumarin-based ferrocenyl 1,3-oxazine hybrid compounds was synthesized and investigated for potential antiparasitic activity, drawing inspiration from the established biological efficacy of the constituent chemical motifs. The structural identity of the synthesized compounds was confirmed by common spectroscopic techniques: NMR, HRMS and IR. Biological evaluation studies reveal that the compounds exhibit higher in vitro antiparasitic potency against the chemosensitive malarial strain (3D7 P. falciparum) over the investigated trypanosomiasis causal agent (T. b. brucei 427) with mostly single digit micromolar IC50 values. When read in tandem with the biological performance of previously reported structurally similar non-coumarin, phenyl derivatives (i.e., ferrocenyl 1,3-benzoxazines and α-aminocresols), structure-activity relationship analyses suggest that the presence of the coumarin nucleus is tolerated for biological activity though this may lead to reduced efficacy. Preliminary mechanistic studies with the most promising compound (11b) support hemozoin inhibition and DNA interaction as likely mechanistic modalities by which this class of compounds may act to produce plasmocidal and antitrypanosomal effects.

Easy-To-Access Quinolone Derivatives Exhibiting Antibacterial and Anti-Parasitic Activities.

The cell wall of Mycobacterium tuberculosis (Mtb) has a unique structural organisation, comprising a high lipid content mixed with polysaccharides. This makes cell wall a formidable barrier impermeable to hydrophilic agents. In addition, during host infection, Mtb resides in macrophages within avascular necrotic granulomas and cavities, which shield the bacterium from the action of most antibiotics. To overcome these protective barriers, a new class of anti-TB agents exhibiting lipophilic character have been recommended by various reports in literature. Herein, a series of lipophilic heterocyclic quinolone compounds was synthesised and evaluated in vitro against pMSp12::GFP strain of Mtb, two protozoan parasites (Plasmodium falciparum and Trypanosoma brucei brucei) and against ESKAPE pathogens. The resultant compounds exhibited varied anti-Mtb activity with MIC90 values in the range of 0.24-31 µM. Cross-screening against P. falciparum and T.b. brucei, identified several compounds with antiprotozoal activities in the range of 0.4-20 µM. Compounds were generally inactive against ESKAPE pathogens, with only compounds 8c, 8g and 13 exhibiting moderate to poor activity against S. aureus and A. baumannii.

Synthesis of 2-(N-cyclicamino)quinoline combined with methyl (E)-3-(2/3/4-aminophenyl)acrylates as potential antiparasitic agents.

A rationally designed series of 2-(N-cyclicamino)quinolines coupled with methyl (E)-3-(2/3/4-aminophenyl)acrylates was synthesized and subjected to in vitro screening bioassays for potential antiplasmodial and antitrypanosomal activities against a chloroquine-sensitive (3D7) strain of Plasmodium falciparum and nagana Trypanosoma brucei brucei 427, respectively. Substituent effects on activity were evaluated; meta-acrylate 24 and the ortho-acrylate 29 exhibited the highest antiplasmodial (IC50 = 1.4 µM) and antitrypanosomal (IC50 = 10.4 µM) activities, respectively. The activity against HeLa cells showed that the synthesized analogs are not cytotoxic at the maximum tested concentration. The ADME (absorption, distribution, metabolism, and excretion) drug-like properties of the synthesized compounds were predicted through the SwissADME software.

Design, synthesis and biological evaluation of mono- and bisquinoline methanamine derivatives as potential antiplasmodial agents.

Several classes of antimalarial drugs are currently available, although issues of toxicity and the emergence of drug resistant malaria parasites have reduced their overall therapeutic efficiency. Quinoline based antiplasmodial drugs have unequivocally been long-established and continue to inspire the design of new antimalarial agents. Herein, a series of mono- and bisquinoline methanamine derivatives were synthesised through sequential steps; Vilsmeier-Haack, reductive amination, and nucleophilic substitution, and obtained in low to excellent yields. The resulting compounds were investigated for in vitro antiplasmodial activity against the 3D7 chloroquine-sensitive strain of Plasmodium falciparum, and compounds 40 and 59 emerged as the most promising with IC50 values of 0.23 and 0.93 µM, respectively. The most promising compounds were also evaluated in silico by molecular docking protocols for binding affinity to the {001} fast-growing face of a hemozoin crystal model.

Potential repurposing of four FDA approved compounds with antiplasmodial activity identified through proteome scale computational drug discovery and in vitro assay.

Malaria elimination can benefit from time and cost-efficient approaches for antimalarials such as drug repurposing. In this work, 796 DrugBank compounds were screened against 36 Plasmodium falciparum targets using QuickVina-W. Hits were selected after rescoring using GRaph Interaction Matching (GRIM) and ligand efficiency metrics: surface efficiency index (SEI), binding efficiency index (BEI) and lipophilic efficiency (LipE). They were further evaluated in Molecular dynamics (MD). Twenty-five protein-ligand complexes were finally retained from the 28,656 (36 × 796) dockings. Hit GRIM scores (0.58 to 0.78) showed their molecular interaction similarity to co-crystallized ligands. Minimum LipE (3), SEI (23) and BEI (7) were in at least acceptable thresholds for hits. Binding energies ranged from -6 to -11 kcal/mol. Ligands showed stability in MD simulation with good hydrogen bonding and favorable protein-ligand interactions energy (the poorest being -140.12 kcal/mol). In vitro testing showed 4 active compounds with two having IC50 values in the single-digit µM range.

Terminaliamide, a new ceramide and other phytoconstituents from the roots of Terminalia mantaly H. Perrier and their biological activities.

Terminaliamide (1), a new ceramide was isolated from the roots of Terminalia mantaly H. Perrier (Combretaceae) along with 4 known compounds (2-5). The structures of the compounds were elucidated using 1D and 2D NMR spectroscopy analysis and mass spectrometry. Compound 1 exhibited moderated antibacterial activity towards Staphylococcus aureus with MIC value of 62.5 µg/mL. The crude MeOH extract (TMr) highly reduced Plasmodium falciparum growth with an IC50 value of 10.11 µg/mL, while hexane fraction (F1) highly reduced Trypanosoma brucei brucei growth with an IC50 value of 5.60 µg/mL. All tested samples presented little or no in vitro cytotoxicity on HeLa cell line. The present work confirms that T. mantaly is medicinally important and may be used effectively as an antimicrobial, an antiplasmodial and an antitrypanosomial with promising therapeutic index.

A new indole alkaloid and other constituents from Monodora minor and Uvaria tanzaniae: their antitrypanosomal and antiplasmodial evaluation.

Phytochemical investigation of the methanolic extract of Monodora minor Engl. & Diels (Annonaceae) stem bark yielded a new indole (E)-4-(1H-indol-5-yl)-but-3-en-2-one (1), a known indole 5-formyl-1H-indole (2) and an ubiquitous steroid sitosterol (3). The investigations of the methanolic extract of Uvaria tanzaniae Verdc. (Annonaceae) root bark yielded two previously reported C-benzylated dihydrochalcones namely uvaretin (4) and diuvaretin (5). Structures of the isolated compounds were elucidated based on NMR spectroscopy and high resolution electron ionization mass spectrometry (HR-EI-MS) data. All compounds were tested against Trypanosoma brucei brucei and Plasmodium falciparum. At a single concentration (20 µM) in the antitrypanosomal and antiplasmodial assays, compound 4 exhibited remarkable activities against T. brucei brucei and P. falciparum with percentage inhibition of 97.3% and 83.0% respectively, whereas compounds 1, 2, 3 and 5 were inactive. In a dose response antiplasmodial assay compound 4 exhibited moderate activity against P. falciparum with an IC50 value of 7.20 µM.

Synthesis and anti-parasitic activity of N-benzylated phosphoramidate Mg2+-chelating ligands.

A series of N-benzylated phosphoramidate esters, containing a 3,4-dihydroxyphenyl Mg2+-chelating group, has been synthesised in five steps as analogues of fosmidomycin, a Plasmodium falciparum 1-deoxy-1-d-xylulose-5-phosphate reductoisomerase (PfDXR) inhibitor. The 3,4-dihydroxyphenyl group effectively replaces the Mg2+-chelating hydroxamic acid group in fosmidomycin. The compounds showed very encouraging anti-parasitic activity with IC50 values of 5.6-16.4 µM against Plasmodium falciparum parasites and IC50 values of 5.2 - 10.2 µM against Trypanosoma brucei brucei (T.b.brucei). Data obtained from in silico docking of the ligands in the PfDXR receptor cavity (3AU9)5 support their potential as PfDXR inhibitors.

In Vitro Studies on Antioxidant and Anti-Parasitic Activities of Compounds Isolated from Rauvolfia caffra Sond.

As part of an ongoing study of natural products from local medicinal plants, the methanol extract of stem bark of Rauvolfia caffra Sond was investigated for biological activity. Column chromatography and preparative thin-layer chromatography were used to isolate lupeol (1), raucaffricine (2), N-methylsarpagine (3), and spegatrine (4). The crude extract, fractions and isolated compounds were tested for anti-oxidant, antitrypanosomal and anti-proliferation activities. Two fractions displayed high DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity and reducing power with IC50 (The half maximal inhibitory concentration) and IC0.5 values of 0.022 ± 0.003 mg/mL and 0.036 ± 0.007 mg/mL, and 0.518 ± 0.044 mg/mL and 1.076 ± 0.136 mg/mL, respectively. Spegatrine (4) was identified as the main antioxidant compound in R. caffra with IC50 and IC0.5 values of 0.119 ± 0.067 mg/mL and 0.712 ± 0 mg/mL, respectively. One fraction displayed high antitrypanosomal activity with an IC50 value of 18.50 µg/mL. However, the major constituent of this fraction, raucaffricine (2), was not active. The crude extract, fractions and pure compounds did not display any cytotoxic effect at a concentration of 50 µg/mL against HeLa cells. This study shows directions for further in vitro studies on the antioxidant and antitrypanosomal activities of Rauvolfia caffra Sond.

Synthesis and anti-parasitic activity of achiral N-benzylated phosphoramidic acid derivatives.

Synthetic pathways have been developed to access a series of N-benzylated phosphoramidic acid derivatives as novel, achiral analogues of the established Plasmodium falciparum 1-deoxy-d-xylulose-5-phosphate reductase (PfDXR) enzyme inhibitor, FR900098. Bioassays of the targeted compounds and their synthetic precursors have revealed minimal antimalarial activity but encouraging anti-trypanosomal activity - in one case with an IC50 value of 5.4 µM against Trypanosoma brucei, the parasite responsible for Nagana (African cattle sleeping sickness). The results of relevant in silico modelling and docking studies undertaken in the design and evaluation of these compounds are discussed.