Mucronine J a 14-membered cyclopeptide alkaloid from Zizyphus mucronata

Chemical Elicitors Induce Rare Bioactive Secondary Metabolites in Deep-Sea Bacteria under Laboratory Conditions

Bacterial genome sequencing has revealed a vast number of novel biosynthetic gene clusters (BGC) with potential to produce bioactive natural products. However, the biosynthesis of secondary metabolites by bacteria is often silenced under laboratory conditions, limiting the controlled expression of natural products. Here we describe an integrated methodology for the construction and screening of an elicited and pre-fractionated library of marine bacteria. In this pilot study, chemical elicitors were evaluated to mimic the natural environment and to induce the expression of cryptic BGCs in deep-sea bacteria. By integrating high-resolution untargeted metabolomics with cheminformatics analyses, it was possible to visualize, mine, identify and map the chemical and biological space of the elicited bacterial metabolites. The results show that elicited bacterial metabolites correspond to ~45% of the compounds produced under laboratory conditions. In addition, the elicited chemical space is novel (~70% of the elicited compounds) or concentrated in the chemical space of drugs. Fractionation of the crude extracts further evidenced minor compounds (~90% of the collection) and the detection of biological activity. This pilot work pinpoints strategies for constructing and evaluating chemically diverse bacterial natural product libraries towards the identification of novel bacterial metabolites in natural product-based drug discovery pipelines.

Opuntisines, 14-membered cyclopeptide alkaloids from fruits of Opuntia stricta var. dillenii isolated by high-performance countercurrent chromatography

Extracts of Opuntia stricta var. dillenii fruits were fractionated by semi-preparative high-performance countercurrent chromatography (HPCCC) to study the secondary metabolite formation, whereby HPCCC showed a superior separation capacity to fractionate minor metabolites compared to HPLC. A family of new peptides was detected in semi-polar fractions when monitoring the HPCCC separation by off-line injections of fractions to ESI-MS/MS. Planar structures of the major compounds, two 14-ring-membered cyclopeptide alkaloids, which were named opuntisines A and B, were elucidated by 1D- and 2D-NMR spectroscopy and HR-ESI-MS/MS spectrometry, while a combination of chemical derivatisation and degradation revealed the stereo-configurations. Specifically, the methods of Marfey and Mosher indicated l-Glu, l-Ile, l-Phe and 1S-configurations, respectively; ROESY correlations revealed 8S, 9S. The novel opuntisine A showed moderate activity against the Gram-negative bacterium Escherichia coli, but no further antibacterial, antifungal nor cytotoxic effects. This bioactive natural product class is reported for the first time in the plant family Cactaceae.

Ziziphus mucronata Willd. (Rhamnaceae): it's botany, toxicity, phytochemistry and pharmacological activities

Ziziphus mucronata is an important multi-purpose plant species that has been used in African traditional medicine for ages in the treatment of various devastating human and animal infections. The current paper is aimed at providing an overview of uses, toxicology, pharmacological properties and phytochemistry of Z. mucronata. The information used in the current work was retrieved using various search engines, including Pubmed, Science Direct, Google Scholar, Scielo, SciFinder and Scopus. The key words used included Ziziphus mucronata, secondary metabolites, chemistry, biological activity and pharmacology, anti-inflammatory, antimicrobial, antifungal, antiviral, ethnobotanical survey, medicinal uses, safety, toxicology and other related words. Out of the 46 infections which the plant species is used to treat, the most common uses includes sexually transmitted infections, skin infections, diarrhoea and dysentery, respiratory and chest complaints and gynaecological complaints (citations ≥6). Pharmacologically, the plant species exhibited a potential antimicrobial activity yielding a minimum inhibitory concentration of <1 mg/ml against important pathogens which includes Mycobacterium tuberculosis, Moraxella catarrhalis, Staphylococcus aureus, Escherichia coli, Propionibacterium acnes, Candida albicans, Cryptoccoos neoformans amongst other microorganisms. Furthermore, the extracts and compounds from Z mucronata revealed potent antiviral, antioxidant, anti-inflammatory and other activities in vitro. Phytochemically, cyclo-peptide alkaloids (commonly called mucronines) dominates and in conjunction with triterpenes, flavonoids, phenolic acids and anthocyanins. Besides these compounds, the plant species exhibited the presence of important in minerals. These phytoconstituents may well explain the reported biological activities. Although the extracts revealed no cytotoxic effect to Vero cells, further toxicological characteristics of the plant species still needs to be explored. There is also a need to carry out the comprehensive safety profiles of the plant species, including heavy metal detection. Although the plant species revealed important biological activities, which includes antimicrobial, antiviral, anti-diabetic, anti-inflammatory, anti-oxidant, anti-plasmodial, anthelmintic, and anti-anaemic activity in vitro, further research is needed to explore the in vivo studies, other compounds responsible for such activities and the mechanisms of action thereof. Such activities validates the use of the plant species in traditional medicine. The data on the possible use of the plant species in the treatment of diarrhoea, sexually transmitted infections, skin related and gynaecological complaints are scant and still needs to be explored and validated both in vitro and in vivo. Furthermore, the anticancer and anthelmintic activity of the plant species also needs to be explored.

Direct Amination of α-Hydroxy Amides

A TiCl4-mediated reaction for the direct amination of α-hydroxy amides has been developed. This simple, general, additive/base/ligand-free reaction is mediated by economical TiCl4. The reaction runs under mild conditions. This highly efficient C-N bond formation protocol is valid for diverse amines, including primary, secondary and heterocyclic amines, and even a primary amide and indole.

α-Glucosidase and α-Amylase Inhibitory Compounds from three African Medicinal Plants: An Enzyme Inhibition Kinetics Approach

The quest to find new lead compounds with anti-diabetic effects via the inhibition of α-glucosidase and α-amylase had led us to conduct bioassay guided isolation of three African medicinal plants which resulted in the identification of bicyclo[2.2.0]hexane-2,3,5-triol (1), 3β- O-acetyl betulinic acid (2) and 2,7-dihydroxy-4 H-1-benzopyran-4-one (3), as the bioactive compounds. The compounds demonstrated a significant (P < 0.05) inhibitory effect on α-glucosidase and α-amylase activities than acarbose. Steady state kinetic analysis revealed that compounds 1 and 2 inhibited both α-amylase and α-glucosidase in non-competitive patterns whilst compound 3 was an uncompetitive inhibitor of α-glucosidase and a non-competitive inhibitor of α-amylase. In conclusion, the study has identified three new active α-glucosidase and α-amylase inhibitory compounds that could have the potential to retard postprandial hyperglycemia.

Cyclopeptide Alkaloids from Ziziphus apetala

Six novel Ia₃-type cyclopeptide alkaloids (1-6) were isolated from stems of Ziziphus apetala. Compound 5 and the known compounds mauritine A (7) and mauritine F (8) were isolated from the roots. Their structures were determined by spectroscopic analyses and chemical methods. The total alkaloids from the roots and the isolated cyclopeptide alkaloids were tested for antidepressant behavior on mice, cytotoxicity, and 11β-hydroxysteroid dehydrogenase (11β-HSD) inhibition in vitro. Only mauritine A (7) showed inhibitory activity on 11β-HSD1, with IC₅₀ values of 52.0 (human) and 31.2 μg/mL (mouse).

Ziziphus mucronata: an underutilized traditional medicinal plant in Africa

In Africa, rural people depend heavily, if not exclusively, on medicinal plants and indigenous healthcare knowledge to meet their medical needs. Over 80000 flowering plant species are used medicinally worldwide. Amongst them are the underutilized Ziziphus species in the Rhamnaceae family. In terms of abundance and economic value, Z. jujuba and Z. mauritiana are currently the most important, especially in China and India where they are cultivated and exploited for medicinal use and their edible fruits. We examined a related common species widely distributed in Africa, Z. mucronata, whose economic value has not, as yet, been explored. Local people in various African countries use its different parts to cure a large number of diseases, many of which are similar to those treated with Z. jujuba and Z. mauritiana. Several studies have shown that Z. mucronata has cyclopeptide alkaloids, i.e., mucronines F, G and H, with antibacterial properties. Conservation strategies to sustain and maximize the benefits of Z. mucronata to people are proposed.

Anthelmintic screening of Sub-Saharan African plants used in traditional medicine

AIM OF STUDY

This study screened for anthelmintic activity of plant species traditionally used in the treatment of intestinal parasites and their symptoms in Sub-Saharan Africa in an effort to confirm their local use and aid in the search for new compounds since resistance is a growing concern.

MATERIALS AND METHODS

Aqueous and organic extracts of 33 plant parts from 17 plant species traditionally used in the treatment of intestinal infections in Sub-Saharan Africa were evaluated for their anthelmintic activity. This activity was assessed using a standard motility assay against a levamisole resistant strain of the nematode Caenorhabditis elegans.

RESULTS AND CONCLUSIONS

Anthelmintic activity was confirmed in 12 plant species. Of these, eight showed strong evidence of activity (p<0.0001), one exhibited moderate evidence of activity (p<0.001), three demonstrated weak evidence of activity (p<0.05), and five plants showed no evidence of activity. The eight species with the strongest evidence of activity were Acacia polyacantha, Anogeissus leiocarpus, Bridelia micrantha, Cassia sieberiana, Combretum nigricans, Grewia bicolor, Strychnos spinosa and Ziziphus mucronata. In only two cases, Anogeissus leiocarpus and Cassia sieberiana, anthelmintic activity has been previously confirmed. The activity demonstrated against the levamisole resistant strain of Caenorhabditis elegans and the presence of molecules in these plants known or suspected of having a broad spectrum of activity provide support for further study of these plants and their compounds as possible treatments for parasitic worm infections.

Total Synthesis of the Cyclopeptide Alkaloid Abyssenine A. Application of Inter- and Intramolecular Copper-Mediated Coupling Reactions in Organic Synthesis

The first total synthesis of the 15-membered ring cyclopeptide alkaloid abyssenine A 1 has been achieved with a longest linear sequence of 15 steps. Central to the synthetic approach was an efficient copper-mediated Ullmann coupling/Claisen rearrangement sequence allowing for both ipso and ortho functionalization of aromatic iodide 4. This sequence was used for the synthesis of the aromatic core. The synthetic utility of copper-catalyzed coupling reactions was further demonstrated to install the enamide with a concomitant straightforward macrocyclization starting from acyclic alpha-amido-omega-vinyl iodide 13.

In vitro evaluation of the cytotoxic and trypanocidal activities of Ampelozizyphus amazonicus (Rhamnaceae)

Ampelozizyphus amazonicus Ducke is a tree commonly found in the Amazon region and an extract of its stem bark is popularly used as an antimalarial and anti-inflammatory agent and as an antidote to snake venom. Ursolic acid; five lupane type triterpenes: betulin, betulinic acid, lupenone, 3beta-hydroxylup-20(29)-ene-27,28-dioic acid, and 2alpha,3beta-dihydroxylup-20(29)-ene-27,28-dioic acid, and three phytosteroids: stigmasterol, sitosterol and campesterol, have been isolated from stem extracts of A. amazonicus Ducke. Their structures were characterized by spectral data including COSY and HMQC. In an in vitro biological screening of the isolated compounds, 3beta-hydroxylup-20(29)-ene-27,28-dioic acid was cytotoxic against the SKBR-3 human adenocarcinoma cell line (1 to 10 mg/mL), while 2alpha,3beta-dihydroxylup-20(29)-ene-27,28-dioic acid exhibited cytotoxicity against both SKBR-3 human adenocarcinoma and C-8161 human melanoma tumor cell lines (>0.1 mg/mL). In the present study, different extracts and some fractions of this plant were also investigated for trypanocidal activity due to the presence of pentacyclic triterpenes. The triterpene classes are potent against Trypanosoma cruzi. The bioassays were carried out using blood collected from Swiss albino mice by cardiac puncture during the parasitemic peak (7th day) after infection with the Y strain of T. cruzi. The results obtained showed that A. amazonicus is a potential source of bioactive compounds since its extracts and fractions isolated from it exhibited in vitro parasite lysis against trypomastigote forms of T. cruzi at concentrations >100 microg/mL. Fractions containing mainly betulin, lupenone, 3beta-hydroxylup-20(29)-ene-27,28-dioic acid, and 2alpha,3beta-dihydroxylup-20(29)-ene-27,28-dioic acid showed more activity than crude extracts.