Tamam El-Elimat

High-resolution MS, MS/MS, and UV database of fungal secondary metabolites as a dereplication protocol for bioactive natural products.

A major problem in the discovery of new biologically active compounds from natural products is the reisolation of known compounds. Such reisolations waste time and resources, distracting chemists from more promising leads. To address this problem, dereplication strategies are needed that enable crude extracts to be screened for the presence of known compounds before isolation efforts are initiated. In a project to identify anticancer drug leads from filamentous fungi, a significant dereplication challenge arises, as the taxonomy of the source materials is rarely known, and, thus, the literature cannot be probed to identify likely known compounds. An ultraperformance liquid chromatography-photodiode array-high-resolution tandem mass spectrometric (UPLC-PDA-HRMS-MS/MS) method was developed for dereplication of fungal secondary metabolites in crude culture extracts. A database was constructed by recording HRMS and MS/MS spectra of fungal metabolites, utilizing both positive- and negative-ionization modes. Additional details, such as UV-absorption maxima and retention times, were also recorded. Small-scale cultures that showed cytotoxic activities were dereplicated before engaging in the scale-up or purification processes. Using these methods, approximately 50% of the cytotoxic extracts could be eliminated from further study after the confident identification of known compounds. The specific attributes of this dereplication methodology include a focus on bioactive secondary metabolites from fungi, the use of a 10 min chromatographic method, and the inclusion of both HRMS and MS/MS data.

Antioxidant activity and total phenolic content of aqueous and methanolic extracts of Jordanian plants: an ICBG project

As part of an International Cooperative Biodiversity Groups (ICBG) program to study Jordans biodiversity, the relative levels of antioxidant activity and the total phenolic content of aqueous and methanolic extracts of a total of 95 plant species, all of Jordanian origin and those collected at random, have been measured. The total phenolic content of aqueous and methanolic extracts of the investigated plant species ranged from 4.4 to 78.3 mg and from 2.1 to 52.8 mg gallic acid equivalents g−1 dry weight, respectively, while the total antioxidant capacity ranged from 20.0 to 916.7 and from 15.1 to 915.6 μmol Trolox equivalents g−1 dry weight, respectively. Based on this collection, approximately 5% of assayed plants showed high levels of antioxidant activity. There was a significant linear correlation between antioxidant activity and total phenolic content for aqueous and methanolic extracts, suggesting that phenolic compounds were the predominant antioxidant components in the investigated plant species. Interestingly, a few of the collected plants had high-antioxidant activity yet “low” phenolic content includes Ceratonia siliqua and Viscum cruciatum. These plants may serve as sources of antioxidants with new chemotypes.

Polyhydroxyanthraquinones as Quorum Sensing Inhibitors from the Guttates of Penicillium restrictum and Their Analysis by Desorption Electrospray Ionization Mass Spectrometry

The endophytic fungus Penicillium restrictum was isolated from the stems of a milk thistle (Silybum marianum) plant. In culture, the fungus produced distinct red guttates, which have been virtually uninvestigated, particularly from the standpoint of chemistry. Hence, this study examined the chemical mycology of P. restrictum and, in doing so, uncovered a series of both known and new polyhydroxyanthraquinones (1–9). These compounds were quorum sensing inhibitors in a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA), with IC50 values ranging from 8 to 120 μM, suggesting antivirulence potential for the compounds. Moreover, the spatial and temporal distribution of the polyhydroxyanthraquinones was examined in situ via desorption electrospray ionization–mass spectrometry (DESI-MS) imaging, demonstrating the first application of this technique to a guttate-forming fungus and revealing both the concentration of secondary metabolites at the ventral surface of the fungus and their variance in colonies of differing ages.

ω-Hydroxyemodin Limits Staphylococcus aureus Quorum Sensing-Mediated Pathogenesis and Inflammation

ABSTRACT Antibiotic-resistant pathogens are a global health threat. Small molecules that inhibit bacterial virulence have been suggested as alternatives or adjuncts to conventional antibiotics, as they may limit pathogenesis and increase bacterial susceptibility to host killing. Staphylococcus aureus is a major cause of invasive skin and soft tissue infections (SSTIs) in both the hospital and community settings, and it is also becoming increasingly antibiotic resistant. Quorum sensing (QS) mediated by the accessory gene regulator (agr) controls virulence factor production essential for causing SSTIs. We recently identified ω-hydroxyemodin (OHM), a polyhydroxyanthraquinone isolated from solid-phase cultures of Penicillium restrictum, as a suppressor of QS and a compound sought for the further characterization of the mechanism of action. At concentrations that are nontoxic to eukaryotic cells and subinhibitory to bacterial growth, OHM prevented agr signaling by all four S. aureus agr alleles. OHM inhibited QS by direct binding to AgrA, the response regulator encoded by the agr operon, preventing the interaction of AgrA with the agr P2 promoter. Importantly, OHM was efficacious in a mouse model of S. aureus SSTI. Decreased dermonecrosis with OHM treatment was associated with enhanced bacterial clearance and reductions in inflammatory cytokine transcription and expression at the site of infection. Furthermore, OHM treatment enhanced the immune cell killing of S. aureus in vitro in an agr-dependent manner. These data suggest that bacterial disarmament through the suppression of S. aureus QS may bolster the host innate immune response and limit inflammation.

Flavonolignans from Aspergillus iizukae, a Fungal Endophyte of Milk Thistle (Silybum marianum)

Silybin A (1), silybin B (2), and isosilybin A (3), three of the seven flavonolignans that constitute silymarin, an extract of the fruits of milk thistle (Silybum marianum), were detected for the first time from a fungal endophyte, Aspergillus iizukae, isolated from the surface-sterilized leaves of S. marianum. The flavonolignans were identified using a UPLC-PDA-HRMS-MS/MS method by matching retention times, HRMS, and MS/MS data with authentic reference compounds. Attenuation of flavonolignan production was observed following successive subculturing of the original flavonolignan-producing culture, as is often the case with endophytes that produce plant-based secondary metabolites. However, production of 1 and 2 resumed when attenuated spores were harvested from cultures grown on a medium to which autoclaved leaves of S. marianum were added. The cycle of attenuation followed by resumed biosynthesis of these flavonolignans was replicated in triplicate.

Greensporones: Resorcylic Acid Lactones from an Aquatic Halenospora sp.

Fourteen new resorcylic acid lactones (1–14) were isolated from an organic extract of a culture of a freshwater aquatic fungus Halenospora sp. originating from a stream in North Carolina. The structures were elucidated using a set of spectroscopic and spectrometric techniques. The absolute configuration of one representative member of the compounds (7) was assigned using X-ray crystallography of an analogue that incorporated a heavy atom, whereas for compounds 8–11, a modified Mosher’s ester method was utilized. The relative configurations of compounds 12–14 were determined on the basis of NOE data. Compounds 12–14 were proposed as artifacts produced by intramolecular cycloetherification of the ε-hydroxy-α,β-unsaturated ketone moieties of the parent compounds during the purification processes. The isolated compounds, except for 8 and 12, were tested against the MDA-MB-435 (melanoma) and HT-29 (colon) cancer cell lines. Compound 5 was the most potent, with IC50 values of 2.9 and 7.5 μM, respectively. The compounds were evaluated as TAK1–TAB1 inhibitors but were found to be inactive.

Benzoquinones and Terphenyl Compounds As Phosphodiesterase-4B Inhibitors from a Fungus of the Order Chaetothyriales (MSX 47445)

Three bioactive compounds were isolated from an organic extract of an ascomycete fungus of the order Chaetothyriales (MSX 47445) using bioactivity-directed fractionation as part of a search for anticancer leads from filamentous fungi. Of these, two were benzoquinones [betulinan A (1) and betulinan C (3)], and the third was a terphenyl compound, BTH-II0204-207:A (2). The structures were elucidated using a set of spectroscopic and spectrometric techniques; the structure of the new compound (3) was confirmed via single-crystal X-ray diffraction. Compounds 1-3 were evaluated for cytotoxicity against a human cancer cell panel, for antimicrobial activity against Staphylococcus aureus and Candida albicans, and for phosphodiesterase (PDE4B2) inhibitory activities. The putative binding mode of 1-3 with PDE4B2 was examined using a validated docking protocol, and the binding and enzyme inhibitory activities were correlated.

Evaluation of culture media for the production of secondary metabolites in a natural products screening program

Variation in the growing environment can have significant impacts on the quantity and diversity of fungal secondary metabolites. In the industrial setting, optimization of growing conditions can lead to significantly increased production of a compound of interest. Such optimization becomes challenging in a drug-discovery screening situation, as the ideal conditions for one organism may induce poor metabolic diversity for a different organism. Here, the impact of different media types, including six liquid media and five solid media, on the secondary metabolite production of three fungal strains was examined in the context of the drug-discovery screening process. The relative production of marker compounds was used to evaluate the usefulness and reliability of each medium for the purpose of producing secondary metabolites.

Dereplicating and Spatial Mapping of Secondary Metabolites from Fungal Cultures in Situ.

Ambient ionization mass spectrometry techniques have recently become prevalent in natural product research due to their ability to examine secondary metabolites in situ. These techniques retain invaluable spatial and temporal details that are lost through traditional extraction processes. However, most ambient ionization techniques do not collect mutually supportive data, such as chromatographic retention times and/or UV/vis spectra, and this can limit the ability to identify certain metabolites, such as differentiating isomers. To overcome this, the droplet–liquid microjunction–surface sampling probe (droplet–LMJ–SSP) was coupled with UPLC–PDA–HRMS–MS/MS, thus providing separation, retention times, MS data, and UV/vis data used in traditional dereplication protocols. By capturing these mutually supportive data, the identity of secondary metabolites can be confidently and rapidly assigned in situ. Using the droplet–LMJ–SSP, a protocol was constructed to analyze the secondary metabolite profile of fungal cultures without any sample preparation. The results demonstrate that fungal cultures can be dereplicated from the Petri dish, thus identifying secondary metabolites, including isomers, and confirming them against reference standards. Furthermore, heat maps, similar to mass spectrometry imaging, can be used to ascertain the location and relative concentration of secondary metabolites directly on the surface and/or surroundings of a fungal culture.

Phytochemical studies and cytotoxicity evaluations of Colchicum tunicatum Feinbr and Colchicum hierosolymitanum Feinbr (Colchicaceae): Two native Jordanian meadow saffrons.

As a part of our continuing investigation of Jordanian Colchicum species, the biologically active components of Colchicum hierosolymitanum Feinbr and Colchicum tunicatum Feinbr (Colchicaceae) were pursued. The brine shrimp lethality test (BSLT) was used to direct the fractionation and isolation of active components. Five and four known colchicinoids were isolated and characterized from C. tunicatum and C. hierosolymitanum, respectively. The known colchicinoids, reported for the first time from these two species are: (−)-colchicine (I), 3-demethyl-(−)-colchicine (II), (−)-cornigerine (III), β-lumicolchicine (IV), and (−)-androbiphenyline (V) from C. tunicatum, and (−)-colchicine (I), 2-demethyl-(−)-colchicine (VI), (−)-cornigerine (III), and β-lumicolchicine (IV) from C. hierosolymitanum. The chemical structures of the isolated compounds have been elucidated using a series of spectroscopic and spectrometric techniques principally; 1D-NMR (1H and 13C) and low resolution EI-MS and APCIMS. All pure compounds were evaluated for cytotoxicity against three human cancer cell lines; MCF-7 human breast carcinoma, NCI-H460 human large cell lung carcinoma, and SF-268 human astrocytoma. (−)-Colchicine (I) and (−)-cornigerine (III) were found to be the most bioactive of the identified compounds with EC50 values in the range of 0.016–0.097 μM.