The Chemical Ecology Approach to Reveal Fungal Metabolites for Arthropod Pest Management

Biorational insecticides (for instance, avermectins, spinosins, azadirachtin, and afidopyropen) of natural origin are increasingly being used in agriculture. The review considers the chemical ecology approach for the search for new compounds with insecticidal properties (entomotoxic, antifeedant, and hormonal) produced by fungi of various ecological groups (entomopathogens, soil saprotrophs, endophytes, phytopathogens, and mushrooms). The literature survey revealed that insecticidal metabolites of entomopathogenic fungi have not been sufficiently studied, and most of the well-characterized compounds show moderate insecticidal activity. The greatest number of substances with insecticidal properties was found to be produced by soil fungi, mainly from the genera Aspergillus and Penicillium. Metabolites with insecticidal and antifeedant properties were also found in endophytic and phytopathogenic fungi. It was noted that insect pests of stored products are mostly low sensitive to mycotoxins. Mushrooms were found to be promising producers of antifeedant compounds as well as insecticidal proteins. The expansion of the number of substances with insecticidal properties detected in prospective fungal species is possible by mining fungal genomes for secondary metabolite gene clusters and secreted proteins with their subsequent activation by various methods. The efficacy of these studies can be increased with high-throughput techniques of extraction of fungal metabolites and their analysis by various methods of chromatography and mass spectrometry.

The Biological and Chemical Diversity of Tetramic Acid Compounds from Marine-Derived Microorganisms

Tetramic acid (pyrrolidine-2,4-dione) compounds, isolated from a variety of marine and terrestrial organisms, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities. In the past decade, marine-derived microorganisms have become great repositories of novel tetramic acids. Here, we discuss the biological activities of 277 tetramic acids of eight classifications (simple 3-acyl tetramic acids, 3-oligoenoyltetramic acids, 3-decalinoyltetramic acid, 3-spirotetramic acids, macrocyclic tetramic acids, N-acylated tetramic acids, α-cyclopiazonic acid-type tetramic acids, and other tetramic acids) from marine-derived microbes, including fungi, actinobacteria, bacteria, and cyanobacteria, as reported in 195 research studies up to 2019.

Biological and Chemical Diversity of Marine Sponge-Derived Microorganisms over the Last Two Decades from 1998 to 2017

Marine sponges are well known as rich sources of biologically natural products. Growing evidence indicates that sponges harbor a wealth of microorganisms in their bodies, which are likely to be the true producers of bioactive secondary metabolites. In order to promote the study of natural product chemistry and explore the relationship between microorganisms and their sponge hosts, in this review, we give a comprehensive overview of the structures, sources, and activities of the 774 new marine natural products from sponge-derived microorganisms described over the last two decades from 1998 to 2017.

Design and Application of a High-Throughput, High-Content Screening System for Natural Product Inhibitors of the Human Parasite Trichomonas vaginalis

It is estimated that Trichomonas vaginalis affects an astonishing 3.9% of the world's population, and while many of those infected are asymptomatic, progression of the disease can lead to serious health problems. Currently, the nitroimidazoles constitute the only drug class approved to treat trichomoniasis in the United States, which makes the spread of drug resistance a realistic concern. We developed a new image-based, high-throughput, and high-content assay for testing natural products (purified compounds and extracts) for antitrichomonal activity. Applying this assay system to a library of fungal natural product extracts led to the identification of three general classes of natural product inhibitors that exhibited moderate to strong activities against T. vaginalis: anthraquinones, xanthone-anthraquinone heterodimers, and decalin-linked tetramic-acid-containing metabolites. The tetramate natural products emerged as the most promising candidate molecules with pyrrolocin A (51) exhibiting potent activity against the parasite (EC50 = 60 nM), yet this metabolite showed limited toxicity to mammalian cell lines (selectivity index values of 100 and 167 versus 3T3 fibroblast and Ect1 normal cervical cells, respectively). The imaging-based assay system is a powerful tool for the bioassay-guided purification of single-component antitrichomonal biomolecules from complex natural product mixtures.

Marilones A-C, phthalides from the sponge-derived fungus Stachylidium sp

The marine-derived fungus Stachylidium sp. was isolated from the sponge Callyspongia sp. cf. C. flammea. Culture on a biomalt medium supplemented with sea salt led to the isolation of three new phthalide derivatives, i.e., marilones A-C (1-3), and the known compound silvaticol (4). The skeleton of marilones A and B is most unusual, and its biosynthesis is suggested to require unique biochemical reactions considering fungal secondary metabolism. Marilone A (1) was found to have antiplasmodial activity against Plasmodium berghei liver stages with an IC(50) of 12.1 µM. Marilone B (2) showed selective antagonistic activity towards the serotonin receptor 5-HT(2B) with a K(i) value of 7.7 µM.

Spartinoxide, a New Enantiomer of A82775C with Inhibitory Activity toward HLE from the Marine-derived Fungus Phaeosphaeria spartinae

The fungus Phaeosphaeria spartinae is an endophyte of the marine alga Ceramium sp. Investigation of this marine-derived fungus led to the isolation of spartinoxide (1), which is the enantiomer of the known compound A82775C (2). Additionally, the known metabolites 4-hydroxy-3-prenyl-benzoic acid (4) and anofinic acid (5) were obtained. The structures of all compounds were established from extensive spectroscopic investigations. Compounds 1, 4 and 5 were assayed against the enzymes human leukocyte elastase (HLE), trypsin, acetylcholinesterase and cholesterolesterase. Compounds 1 and 4 showed potent inhibition of HLE with IC50 values of 1.71 ± 0.30 μg/mL (6.5 μM) and 1.67 ± 0.32 μg/mL (8.1 μM), respectively.

Novel Bisabolane Sesquiterpenes from the Marine-derived Fungus Verticillium tenerum

Chemical investigations of the marine-derived fungus Verticillium tenerum yielded two new hydroxylated bisabolane-type sesquiterpenes verticinol A (1) and B (2). The planar structures of the new compounds were elucidated by employing spectroscopic (NMR, UV, and IR) and mass spectrometric techniques. The absolute configuration of the cyclohexenyl moiety was deduced by a combination of CD spectroscopy and NOESY measurements.