Minor sesquiterpene lactones from Centaurea pullata and their antimicrobial activity

Feature-Based Molecular Networking for the Exploration of the Metabolome Diversity of Common Egyptian Centaurea Species in Relation to Their Cytotoxic Activity

Centaurea is a genus compromising over 250 herbaceous flowering species and is used traditionally to treat several ailments. Among the Egyptian Centaurea species, C. lipii was reported to be cytotoxic against multidrug-resistant cancer cells. In this context, we aimed to explore the metabolome of C. lipii and compare it to other members of the genus in pursuance of identifying its bioactive principles. An LC-MS/MS analysis approach synchronized with feature-based molecular networks was adopted to offer a holistic overview of the metabolome diversity of the Egyptian Centaurea species. The studied plants included C. alexandrina, C. calcitrapa, C. eryngioides, C. glomerata, C. lipii, C. pallescens, C. pumilio, and C. scoparia. Their constitutive metabolome showed diverse chemical classes such as cinnamic acids, sesquiterpene lactones, flavonoids, and lignans. Linking the recorded metabolome to the previously reported cytotoxicity identified sesquiterpene lactones as the major contributors to this activity. To confirm our findings, bioassay-guided fractionation of C. lipii was adopted and led to the isolation of the sesquiterpene lactone cynaropicrin with an IC₅₀ of 1.817 µM against the CCRF-CEM leukemia cell line. The adopted methodology highlighted the uniqueness of the constitutive metabolome of C. lipii and determined the sesquiterpene lactones to be the responsible cytotoxic metabolites.

Onopordopicrin from the new genus Shangwua as a novel thioredoxin reductase inhibitor to induce oxidative stress-mediated tumor cell apoptosis

Isolation and identification of natural products from plants is an essential approach for discovering drug candidates. Herein we report the characterization of three sesquiterpene lactones from a new genus Shangwua, e.g. onopordopicrin (ONP), C2, and C3, and evaluation of their pharmacological functions in interfering cellular redox signaling. Compared to C2 and C3, ONP shows the most potency in killing cancer cells. Further experiments demonstrate that ONP robustly inhibits thioredoxin reductase (TrxR), which leads to perturbation of cellular redox homeostasis with the favor of oxidative stress. Knockdown of the TrxR sensitizes cells to the ONP treatment while overexpression of the enzyme reduces the potency of ONP, underpinning the correlation of TrxR inhibition to the cytotoxicity of ONP. The discovery of ONP expands the library of the natural TrxR inhibitors, and the disclosure of the action mechanism of ONP provides a foundation for the further development of ONP as an anticancer agent.

Terpene core in selected aromatic and edible plants: Natural health improving agents

Aromatic plants synthesize and produce aromatic molecules, among these compounds some of them belong to terpenes and terpenoids. Plant species have specific genes involved in secondary metabolism which allows them to synthesize various compounds with terpene core. These kinds of plant species are also known as herbal drugs and they are primarily used as components in medicinal products or simply as health foods. This chapter will focus on terpene and terpenoid compounds found in selected edible and aromatic plants belonging to several plant families. Selected plant species are briefly discussed. Biologically active compounds with terpene core are most frequently found in essential oils of the edible and aromatic species, as well as they are separately isolated and identified from the extracts. Health beneficial effects coming from terpene compounds found in edible and aromatic plants are further presented and include antimicrobial, antiviral, cytotoxic, anticancer, anti-inflammatory and many other pharmacological activities.

Minor Nortriterpenoids from the Twigs and Leaves of Rhododendron latoucheae

A hyphenated NMR technique (analytical HPLC with a DAD connected to MS, SPE, and NMR) has proven effective for the full structural analysis and identification of minor natural products in complex mixtures. Application of this hyphenated technique to the CH₂Cl₂-soluble fraction of Rhododendron latoucheae led to the identification of 15 new minor ursane-type 28-nortriterpenoids (1-15). Compounds 1 and 12 inhibited HSV-1 with IC₅₀ values of 6.4 and 0.4 μM, respectively.

Differentiation between 3,4- and 4,15-Epoxyeudesmanolides by Electrospray Ionization Tandem Mass Spectrometry

We investigated the fragmentation of the eudesmanolide-type sesquiterpene lactones 1α-(4-hydroxymethacryloyloxy)-3α,4α-epoxy-8α-hydroxyeudesm-11(13)-6α,12-olide (1) and 1α-(2,3-epoxyangeloyloxy)-4α,15-epoxy-8α-hydroxyeudesm-11(13)-6α,12-olide (2) by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The elimination of the different ester substituent at C(1) directly from protonated 1 and 2 (A) led to the formation of two regioisomer product ions B (A - RCO2H). Further fragmentation of B resulted from consecutive eliminations of H2O and CO molecules. However, we identified four product ions that allowed for the differentiation between 3,4- and 4,15-epoxyeudesmanolides. The formation of these diagnostic ions was associated with the C(3)-O bond of compound 1, which propitiates the participation of the lone pair of the oxygen epoxide in the formation of B through a Grob-Wharton-type fragmentation, then resulting in an alternative fragmentation pathway. These data can be useful for the fast differentiation between epoxyeudesmanolide regioisomers directly from Dimerostemma extracts by liquid chromatography-tandem mass spectrometry (LC-MS/MS), as an alternative to NMR, or even for quantitation studies of these compounds using multiple reaction monitoring (MRM) scan.

Rhodoterpenoids A‒C, Three New Rearranged Triterpenoids from Rhododendron latoucheae by HPLC‒MS‒SPE‒NMR

Rhodoterpenoids A‒C (1‒3), three new rearranged triterpenoids, together with one new biogenetically related compound, rhodoterpenoid D (4), were isolated and efficiently elucidated from Rhododendron latoucheae by high-performance liquid chromatography−mass spectrometry−solid-phase extraction−nuclear magnetic resonance (HPLC‒MS‒SPE‒NMR). Compounds 1 and 2 possess an unprecedented skeleton with a 5/7/6/6/6-fused pentacyclic ring system, while compound 3 contains a unique 6/7/6/6/6-fused pentacyclic carbon backbone. Their structures were determined by extensive spectroscopic methods and electronic circular dichroism (ECD) analyses. Plausible biogenetic pathways for 1‒4 were proposed. Compounds 1 and 4 showed potential activity against herpes simplex virus 1 (HSV-1) with IC₅₀ values of 8.62 and 6.87 μM, respectively.

Chemical constituents, cytotoxic, antifungal and antimicrobial properties of Centaurea diluta Ait. subsp. algeriensis (Coss. & Dur.) Maire

OBJECTIVE

To investigate the chemical composition of a moderately polar extract (CHCl3 soluble part of the MeOH-H2O extract) obtained from the aerial parts (leaves and flowers) of Centaurea diluta Ait. subsp. algeriensis (Coss. & Dur.) Maire, a species endemic to Algeria and Morocco on which no reports are available to date. To evaluate in vitro the cytotoxic, antifungal and antimicrobial activities of this extract and the cytotoxic and antimicrobial activities of its isolated secondary metabolites.

METHODS

The cytotoxic effects of the extract were investigated on 3 human cancer cell lines i.e. the A549 non-small-cell lung carcinoma (NSCLC), the MCF7 breast adenocarcinoma and the U373 glioblastoma using a MTT colorimetric assay. Biological data allowed to guide the fractionation of the extract by separation and purification on silica gel 60 (CC and TLC). The isolated compounds which were characterized by spectral analysis, mainly HR-ESIMS, HR-EIMS, UV and NMR experiments ((1)H, (13)C, COSY, ROESY, HSQC and HMBC) and comparison of their spectroscopic data with those reported in the literature, were evaluated for cytotoxic activities on six cancer cell lines (A549, MCF7, U373, Hs683 human glioma, PC3 human prostate and B16-F10 murine melanoma). The direct and indirect antibacterial and antifungal activities were determined using microdilution methods for the raw extract and TLC-bioautography and microdilution methods against standard and clinical strains for the isolated compounds.

RESULTS

The raw extract reduced cell viability with IC50s of 27, 25 and 21 μg/mL on A549, MCF7 and U373, respectively. Five secondary metabolites: two phenolic compounds (vanillin 1, paridol 3), a lignan [(-)-arctigenin 2] and two flavonoid aglycones (eupatilin 4 and jaceosidin 5), were then isolated from this extract. Moderate cytotoxic effects were observed for (-)-arctigenin 2 (IC50s: 28 and 33 μM on Hs683 and B16-F10, respectively), eupatilin 4 (IC50s: 33 and 47 μM on B16-F10 and PC3, respectively) and jaceosidin 5 (IC50s: 32 and 40 μM on PC3 and B16-F10, respectively).

CONCLUSIONS

All the isolated compounds were described for the first time from this species. Although inactive against 7 tested microorganisms (fungi, bacteria and yeast, human or plant pathogens), the raw extract was able to potentiate the effect of beta-lactam antibiotics on methicillin-resistant Staphylococcus aureus (MRSA), reducing the minimal inhibitory concentrations (MICs) by a factor of 2-32-fold. No synergy was found between the extract and streptomycin. From the five isolated compounds only jaseosidin 5 showed a moderate antimicrobial activity.

Sesquiterpenoids in subtribe Centaureinae (Cass.) Dumort (tribe Cardueae, Asteraceae): distribution, (13)C NMR spectral data and biological properties

Asteraceae Bercht. & J. Presl is one of the biggest and most economically important plant families. The taxonomy and phylogeny of Asteraceae is rather complex and according to the latest and most reliable taxonomic classification of Panero & Funk, based on the analysis of nine chloroplast regions, the family is divided into 12 subfamilies and 35 tribes. One of the largest tribes of Asteraceae is Cardueae Cass. with four subtribes (Carlininae, Echinopinae, Carduinae and Centaureinae) and more than 2500 species. Susanna & Garcia-Jacas have organized the genera of Centaureinae (about 800 species) into seven informal groups, which recent molecular studies have confirmed: 1. Basal genera; 2. Volutaria group; 3. Rhaponticum group; 4. Serratula group; 5. Carthamus group; 6. Crocodylium group; 7. Centaurea group. This review summarizes reports on sesquiterpenoids from the Centaureinae subtribe of the Asteraceae family, as well as the (13)C NMR spectral data described in the literature. It further reviews studies concerning the biological activities of these metabolites. For this work, literature data on sesquiterpenes from the Centaureinae subtribe were retrieved with the help of the SciFinder database and other similar data banks. All entries from 1958 until the end of 2011 were considered. This review is addressed to scientists working in the metabolomics field such as chemists, botanists, etc., the spectroscopic data reported make this work a good tool for structural elucidation, the biological section gives useful information to those who wish to study the structure activity relationships.

Efficacy of some natural compounds as antifungal agents

Natural sources have been important for the development of new active molecules for many years. Various small molecules with unique chemical skeleton and potent bioactivities were discovered through various sources like plants, marine products, and microorganisms, etc., which are considered as very important part of the nature. A number of potent antifungals have been originated from various natural sources. This account describes structure and activities of selected agents isolated from various natural sources.

Antimicrobial activity of secondary metabolites isolated from Centaurea spruneri Boiss.& Heldr

Two coumarins, scopoletin (1) and isoscopoletin (2), two simple phenolic acids, protocatechuic acid (3) and isovanillic acid (4) and one flavonoid, eriodictyol (5) were isolated from the aerial parts of Centaurea spruneri. The structure of the compounds was established by spectroscopic methods. The in vitro antimicrobial activity of the isolated compounds was tested against eight bacteria and eight fungal species, using a microdilution method. All compounds tested showed moderate antibacterial and antifungal activities. Their minimum inhibitory concentrations were in the range 0.655 - 2.38 ?mol ml-1 and their minimal bactericidal concentrations ranged from 0.694 to 4.15 ?mol ml-1 against the tested bacterial species. All compounds showed fungistatic activity at 0.259 - 2.38 ?mol ml-1 and fungicidal at 0.69 - 2.6 ?mol ml-1 against all fungi tested.

New Improvements in Automatic Structure Elucidation Using the LSD (Logic for Structure Determination) and the SISTEMAT Expert Systems

This article describes the integration of the LSD (Logic for Structure Determination) and SISTEMAT expert systems that were both designed for the computer-assisted structure elucidation of small organic molecules. A first step has been achieved towards the linking of the SISTEMAT database with the LSD structure generator. The skeletal descriptions found by the SISTEMAT programs are now easily transferred to LSD as substructural constraints. Examples of the synergy between these expert systems are given for recently reported natural products.

Natural sesquiterpenoids

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. 423 references are cited.