Varitatin A, a Highly Modified Fatty Acid Amide from Penicillium variabile Cultured with a DNA Methyltransferase Inhibitor

The biosynthetic logic and enzymatic machinery of approved fungi-derived pharmaceuticals and agricultural biopesticides

Covering: 2000 to 2023The kingdom Fungi has become a remarkably valuable source of structurally complex natural products (NPs) with diverse bioactivities. Since the revolutionary discovery and application of the antibiotic penicillin from Penicillium, a number of fungi-derived NPs have been developed and approved into pharmaceuticals and pesticide agents using traditional "activity-guided" approaches. Although emerging genome mining algorithms and surrogate expression hosts have brought revolutionary approaches to NP discovery, the time and costs involved in developing these into new drugs can still be prohibitively high. Therefore, it is essential to maximize the utility of existing drugs by rational design and systematic production of new chemical structures based on these drugs by synthetic biology. To this purpose, there have been great advances in characterizing the diversified biosynthetic gene clusters associated with the well-known drugs and in understanding the biosynthesis logic mechanisms and enzymatic transformation processes involved in their production. We describe advances made in the heterogeneous reconstruction of complex NP scaffolds using fungal polyketide synthases (PKSs), non-ribosomal peptide synthetases (NRPSs), PKS/NRPS hybrids, terpenoids, and indole alkaloids and also discuss mechanistic insights into metabolic engineering, pathway reprogramming, and cell factory development. Moreover, we suggest pathways for expanding access to the fungal chemical repertoire by biosynthesis of representative family members via common platform intermediates and through the rational manipulation of natural biosynthetic machineries for drug discovery.

Structural diversity of microbial secondary metabolites based on chemical epigenetic manipulation

Fungi are microorganisms with biosynthetic potential that are capable of producing a wide range of chemically diverse and biologically interesting small molecules. Chemical epigenetic manipulation has been increasingly explored as a simple and powerful tool to induce the production of additional microbial secondary metabolites in fungi. This review focuses on chemical epigenetic manipulation in fungi and summarizes 379 epigenetic manipulation products discovered from 2008 to 2022 to promote the discovery of their medicinal value.

A new steroid with potent antimicrobial activities and two new polyketides from Penicillium variabile EN-394, a fungus obtained from the marine red alga Rhodomela confervoides

Three new compounds, including one steroid named penivariod A (1) and two polyketides penivarides A and B (2 and 3), as well as six known derivatives (4-9) were isolated from Penicillium variabile EN-394, a fungus afforded from the marine red alga Rhodomela confervoides. Their structures were elucidated by analysis of the HRESIMS, 1D and 2D NMR. The absolute stereochemistry was determined by X-ray crystallographic data, gauge-independent atomic orbital (GIAO) NMR shift calculation followed by DP4+ analysis combined with calculated electronic circular dichroism (ECD). Antimicrobial activities for the new compounds (1-3) were evaluated against human- and aquatic-pathogenic bacteria as well as plant pathogenic fungi. Compound 1 exhibited potent antimicrobial activity against most of the pathogenic strains, especially for Escherichia coli and Pseudomonas aeruginosa, with MIC values of 1.0 and 2.0 μg ml-1, respectively.

Discovery of Novel Terpenoids from the Basidiomycete Pleurotus ostreatus through Genome Mining and Coculture Optimization

In our previous work, postredienes A-C, three unusual linear sesterterpenes with high antifungal activities, were isolated from Pleurotus ostreatus SY10 when cocultured with Trametes robiniophila SY636. However, their titers were low, and exploration of newly biosynthesized trace analogues is required. Herein, genome mining analysis predicted that 17 gene clusters are involved in terpenoid biosynthesis in P. ostreatus. Thus, coculture conditions for strains SY10 and SY636 were optimized using a single-factor test and Box-Behnken design. As a result, the titers of postredienes A-C were increased by over 2.5-fold, reaching 1.28 to 8.40 mg/L. Moreover, five new terpenoids, named postredienes D-H (1-5), were successfully isolated. Compound 1 exhibited activities against the human pathogenic fungi Candida albicans and Cryptococcus neoformans comparable to those of amphotericin B. Compound 2 represents a novel sesterterpene with a five-membered ring at C-7. The absolute configurations of 1-5 were elucidated by making the methoxyphenylacetic acid esters and acetonide derivatives, combined with ECD and NMR calculation. Two potential gene clusters and relevant biosynthetic pathways for 1-5 were subsequently proposed based on real-time reverse transcription-quantitative PCR (RT-qPCR) analysis. The current study provides new insights into the research of terpenoid biosynthesis genes in P. ostreatus and other basidiomycetes.

Recent Advances in Search of Bioactive Secondary Metabolites from Fungi Triggered by Chemical Epigenetic Modifiers

Genomic analysis has demonstrated that many fungi possess essential gene clusters for the production of previously unobserved secondary metabolites; however, these genes are normally reduced or silenced under most conditions. These cryptic biosynthetic gene clusters have become treasures of new bioactive secondary metabolites. The induction of these biosynthetic gene clusters under stress or special conditions can improve the titers of known compounds or the production of novel compounds. Among the inducing strategies, chemical-epigenetic regulation is considered a powerful approach, and it uses small-molecule epigenetic modifiers, which mainly act as the inhibitors of DNA methyltransferase, histone deacetylase, and histone acetyltransferase, to promote changes in the structure of DNA, histones, and proteasomes and to further activate cryptic biosynthetic gene clusters for the production of a wide variety of bioactive secondary metabolites. These epigenetic modifiers mainly include 5-azacytidine, suberoylanilide hydroxamic acid, suberoyl bishydroxamic acid, sodium butyrate, and nicotinamide. This review gives an overview on the method of chemical epigenetic modifiers to trigger silent or low-expressed biosynthetic pathways to yield bioactive natural products through external cues of fungi, mainly based on the research progress in the period from 2007 to 2022. The production of about 540 fungal secondary metabolites was found to be induced or enhanced by chemical epigenetic modifiers. Some of them exhibited significant biological activities such as cytotoxic, antimicrobial, anti-inflammatory, and antioxidant activity.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Bioactive pulvinones from a marine algicolous fungus Aspergillus terreus NTU243

Marine fungi are regarded as an under-explored source of structurally interesting and bioactive natural products with the potential to provide attractive lead compounds for drug discovery. In this study, several fungal strains were isolated from marine algae collected from the northeastern coast of Taiwan. In the preliminary antimicrobial screening against bacteria and fungi, the ethyl acetate extract of the fermented products of Aspergillus terreus NTU243 derived from a green alga Ulva lactuca was found to exhibit significant antimicrobial activities. Therefore, bioassay-guided separations of the active principle from liquid and solid fermented products of A. terreus NTU243 were undertaken, which resulted in the isolation and purification of 16 compounds. Their structures were elucidated by spectroscopic analysis to be four previously undescribed aspulvinones S-V as well as twelve known compounds. All the isolates were assessed for anti-inflammatory activity by measuring the amount of nitric oxide (NO) production in lipopolysaccharide (LPS)-induced BV-2 cells, and aspulvinone V, butyrolactone I, and (+)-terrein inhibited 45.0%, 34.5%, and 49.2% of NO production, respectively, at 10 μM concentration. Additionally, zymography showed that the conditioned medium of THP-1 cells post-LPS challenged significantly enhanced matrix metalloproteinase (MMP)-9-mediated gelatinolysis, and pretreatment with aspulvinones U and V significantly attenuated MMP-9-mediated gelatinolysis by 56.0% and 67.8%, separately.

Microbiological Aspects of Unique, Rare, and Unusual Fatty Acids Derived from Natural Amides and Their Pharmacological Profile

In the proposed review, the pharmacological profile of unique, rare, and unusual fatty acids derived from natural amides is considered. These amides are produced by various microorganisms, lichens, and fungi. The biological activity of some natural fatty acid amides has been determined by their isolation from natural sources, but the biological activity of fatty acids has not been practically studied. According to QSAR data, the biological activity of fatty acids is shown, which demonstrated strong antifungal, antibacterial, antiviral, antineoplastic, anti-inflammatory activities. Moreover, some fatty acids have shown rare activities such as antidiabetic, anti-infective, anti-eczematic, antimutagenic, and anti-psoriatic activities. For some fatty acids that have pronounced biological properties, 3D graphs are shown that show a graphical representation of unique activities. These data are undoubtedly of both theoretical and practical interest for chemists, pharmacologists, as well as for the pharmaceutical industry, which is engaged in the synthesis of biologically active drugs.

Natural products from mangrove sediments-derived microbes: Structural diversity, bioactivities, biosynthesis, and total synthesis

The mangrove forests are a complex ecosystem, and the microbial communities in mangrove sediments play a critical role in the biogeochemical cycles of mangrove ecosystems. Mangrove sediments-derived microbes (MSM), as a rich reservoir of natural product diversity, could be utilized in the exploration of new antibiotics or drugs. To understand the structural diversity and bioactivities of the metabolites of MSM, this review for the first time provides a comprehensive overview of 519 natural products isolated from MSM with their bioactivities, up to 2021. Most of the structural types of these compounds are alkaloids, lactones, xanthones, quinones, terpenoids, and steroids. Among them, 210 compounds are obtained from bacteria, most of which are from Streptomyces, while 309 compounds are from fungus, especially genus Aspergillus and Penicillium. The pharmacological mechanisms of some representative lead compounds are well studied, revealing that they have important medicinal potentials, such as piericidins with anti-renal cell cancer effects, azalomycins with anti-MRSA activities, and ophiobolins as antineoplastic agents. The biosynthetic pathways of representative natural products from MSM have also been summarized, especially ikarugamycin, piericidins, divergolides, and azalomycins. In addition, the total synthetic strategies of representative secondary metabolites from MSM are also reviewed, such as piericidin A and borrelidin. This review provides an important reference for the research status of natural products isolated from MSM and the lead compounds worthy of further development, and reveals that MSM have important medicinal values and are worthy of further development.

Cryptic Metabolites from Marine-Derived Microorganisms Using OSMAC and Epigenetic Approaches

Marine microorganisms have proven to be a source of new natural products with a wide spectrum of biological activities relevant in different industrial sectors. The ever-increasing number of sequenced microbial genomes has highlighted a discrepancy between the number of gene clusters potentially encoding the production of natural products and the actual number of chemically characterized metabolites for a given microorganism. Homologous and heterologous expression of these biosynthetic genes, which are often silent under experimental laboratory culture conditions, may lead to the discovery of new cryptic natural products of medical and biotechnological interest. Several new genetic and cultivation-based strategies have been developed to meet this challenge. The OSMAC approach (one strain—many compounds), based on modification of growth conditions, has proven to be a powerful strategy for the discovery of new cryptic natural products. As a direct extension of this approach, the addition of chemical elicitors or epigenetic modifiers have also been used to activate silent genes. This review looks at the structures and biological activities of new cryptic metabolites from marine-derived microorganisms obtained using the OSMAC approach, the addition of chemical elicitors, and enzymatic inhibitors and epigenetic modifiers. It covers works published up to June 2021.

Extremophilic Fungi from Marine Environments: Underexplored Sources of Antitumor, Anti-Infective and Other Biologically Active Agents

Marine environments are underexplored terrains containing fungi that produce a diversity of natural products given unique environmental pressures and nutrients. While bacteria are commonly the most studied microorganism for natural products in the marine world, marine fungi are also abundant but remain an untapped source of bioactive metabolites. Given that their terrestrial counterparts have been a source of many blockbuster antitumor agents and anti-infectives, including camptothecin, the penicillins, and cyclosporin A, marine fungi also have the potential to produce new chemical scaffolds as leads to potential drugs. Fungi are more phylogenetically diverse than bacteria and have larger genomes that contain many silent biosynthetic gene clusters involved in making bioactive compounds. However, less than 5% of all known fungi have been cultivated under standard laboratory conditions. While the number of reported natural products from marine fungi is steadily increasing, their number is still significantly lower compared to those reported from their bacterial counterparts. Herein, we discuss many varied cytotoxic and anti-infective fungal metabolites isolated from extreme marine environments, including symbiotic associations as well as extreme pressures, temperatures, salinity, and light. We also discuss cultivation strategies that can be used to produce new bioactive metabolites or increase their production. This review presents a large number of reported structures though, at times, only a few of a large number of related structures are shown.

Epigenetic Manipulation to Trigger Production of Guaiane-Type Sesquiterpenes from a Marine-Derived Spiromastix sp. Fungus with Antineuroinflammatory Effects

Epigenetic manipulation of a deep-sea sediment-derived Spiromastix sp. fungus using suberoylanilide hydroxamic acid (SAHA) induction resulted in the activation of a terpene-related biosynthetic gene cluster, and nine new guaiane-type sesquiterpenes, spiromaterpenes A-I (1-9), were isolated. Their structures were determined using various spectroscopic techniques, in association with the modified Mosher's method, computed electronic circular dichroism (ECD) spectra, and chemical conversion for configurational assignments. Compounds 4-6 exhibited significant effects against the NO production on lipopolysaccharide (LPS)-induced microglia cells BV2, and the preliminary SAR analyses demonstrated that a 2(R),11-diol unit is favorable. The most active 5 abolished LPS-induced NF-κB translocation from the cytosol to the nucleus in BV-2 microglial cells, accompanied by the marked reduction of the transcription levels of pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α dose-dependently in both LPS-induced BV-2 and BV-2 cells, as well as the protein and mRNA levels of iNOS and COX-2. This study complements the gap in knowledge regarding the anti-neuroinflammatory activity of guaiane-type sesquiterpenoids at the cellular level and suggests that 5 is promising for further optimization as a multifunctional agent for antineuroinflammation.

Penipyrols C-G and methyl-penipyrol A, α-pyrone polyketides from the mangrove derived fungus Penicillium sp. HDN-11-131

Six new α-pyrone polyketides, penipyrols C-G (1-5) and methyl-penipyrol A (6), together with one biogenetically related known compound, penipyrol A (7), were isolated from the extract of fungus Penicillium sp. HDN-11-131. Their structures including the absolute configurations were established by extensive spectroscopic analysis, Mosher's method, and ECD calculations as well as biogenic considerations. Compounds 1-4 possess a rare skeleton featuring γ-butyrolactone linked to α-pyrone ring through double bond. Compound 1 can induce pancreatic β-cell regeneration in zebrafish at 10 μM, which demonstrated promising anti-diabetes potential.

Inducing new bioactive metabolites production from coculture of Pestalotiopsis sp. and Penicillium bialowiezense

Coculturing two or more fungi is a useful strategy to awaken the silent genes to produce structurally diverse and bioactive natural products. Through the coculture of Pestalotiopsis sp. and Penicillium bialowiezense, six new isoprenylated chromane derivatives, including two pairs of enantiomeric ones (1a/1b-2a/2b) and two optical pure ones (3-4), two new isoprenylated phenol glucoside derivatives (6-7), as well as eight known structural analogues (5 and 8-14), were obtained. The structures of these new compounds were characterized by NMR spectroscopy, single-crystal X-ray crystallography, and ECD calculation. The Δ^10,11 double bond of pestaloficin D (5) was revised to E-configurated based on the extensive spectroscopic analyses. Compounds 1a/1b and 2a/2b were the first examples of enantiomeric isoprenylated chromane derivatives, which were successfully separated by chiral HPLC. Additionally, all the isolated compounds were evaluated for the in vitro β-glucuronidase (GUS) and butyrylcholinesterase (BChE) inhibitory activities. Compounds 1a and 1b showed significant β-glucuronidase inhibitory potency with IC₅₀ values of 7.6 and 10.3 μM, respectively. Compound 14 exhibited moderate BChE inhibitory activity with an IC₅₀ value of 21.3 μM. In addition, the structure-enzyme inhibitory activity relationship of compounds 1-14 is discussed.

Distinct Roles of Two DNA Methyltransferases from Cryphonectria parasitica in Fungal Virulence, Responses to Hypovirus Infection, and Viral Clearance

Two DNA methyltransferase (DNMTase) genes from Cryphonectria parasitica have been previously identified as CpDmt1 and CpDmt2, which are orthologous to rid and dim-2 of Neurospora crassa, respectively. While global changes in DNA methylation have been associated with fungal sectorization and CpDmt1 but not CpDmt2 has been implicated in the sporadic sectorization, the present study continues to investigate the biological functions of both DNMTase genes. Transcription of both DNMTases is regulated in response to infection with the Cryphonectria hypovirus 1 (CHV1-EP713). CpDmt1 is upregulated and CpDmt2 is downregulated by CHV1 infection. Conidium production and response to heat stress are affected only by mutation of CpDmt1, not by CpDmt2 mutation. Significant changes in virulence are observed in opposite directions; i.e., the CpDmt1-null mutant is hypervirulent, while the CpDmt2-null mutant is hypovirulent. Compared to the CHV1-infected wild type, CHV1-transferred single and double mutants show severe growth retardation: the colony size is less than 10% that of the parental virus-free null mutants, and their titers of transferred CHV1 are higher than that of the wild type, implying that no defect in viral replication occurs. However, as cultivation proceeds, spontaneous viral clearance is observed in hypovirus-infected colonies of the null mutants, which has never been reported in this fungus-virus interaction. This study demonstrates that both DNMTases are significant factors in fungal development and virulence. Each fungal DNMTase affects fungal biology in both common and separate ways. In addition, both genes are essential to the antiviral responses, including viral clearance which depends on their mutations.

Regulation of Secondary Metabolism in the Penicillium Genus

Penicillium, one of the most common fungi occurring in a diverse range of habitats, has a worldwide distribution and a large economic impact on human health. Hundreds of the species belonging to this genus cause disastrous decay in food crops and are able to produce a varied range of secondary metabolites, from which we can distinguish harmful mycotoxins. Some Penicillium species are considered to be important producers of patulin and ochratoxin A, two well-known mycotoxins. The production of these mycotoxins and other secondary metabolites is controlled and regulated by different mechanisms. The aim of this review is to highlight the different levels of regulation of secondary metabolites in the Penicillium genus.

Newly reported alkaloids produced by marine-derived Penicillium species (covering 2014-2018)

Alkaloids, especially heterocyclic alkaloids, have received remarkable attention due to their intriguing structures and potential pharmacological activities. The marine fungi residing in extreme environmental conditions are among the richest sources of these basic nitrogen-containing compounds. Fungal species belonging to the genus Penicillium have been studied worldwide for their biosynthetic potential for generating bioactive alkaloids. This paper offers a systematic review of the newly reported alkaloids produced by marine-derived Penicillium species over the past five years (covering the literature from the beginning of 2014 through the end of 2018) and describes the structural diversity, biological activities, and plausible biosynthetic pathway of the reported compounds. A total of 106 alkaloids and 81 references are included in this review, which is expected to be beneficial for drug development and biosynthesis in the near future.

Epigenetic Agents Trigger the Production of Bioactive Nucleoside Derivatives and Bisabolane Sesquiterpenes From the Marine-Derived Fungus Aspergillus versicolor

Epigenetic agents, histone deacetylase inhibitor (SAHA) and DNA methyltransferase inhibitor (5-Aza), were added to Czapek-Dox medium to trigger the chemical diversity of marine-derived fungus Aspergillus versicolor XS-20090066. By HPLC and 1H NMR analysis, the diversity of fungal secondary metabolites was significantly increased compared with the control. With the aid of MS/MS-based molecular networking, two new nucleoside derivatives, kipukasins K (1) and L (2) were obtained. Meanwhile, the yields of four known nucleoside derivatives were significantly enhanced. In addition, one new bisabolane sesquiterpene, aspergillusene E (7), along with ten known derivatives were also isolated. The structures were elucidated by comprehensive spectroscopic methods of NMR and HRESIMS analysis. Compounds 1 and 7 displayed antibacterial activities against Staphylococcus epidermidis and Staphylococcus aureus with the MIC values of 8-16 μg/mL. Our study revealed that the fungus A. versicolor XS-20090066 has been effectively induced by chemical epigenetic manipulation with a combination of SAHA and 5-Aza to produce new metabolites.

Chromosome-Level Comprehensive Genome of Mangrove Sediment-Derived Fungus Penicillium variabile HXQ-H-1

Penicillium is an ascomycetous genus widely distributed in the natural environment and is one of the dominant fungi involved in the decomposition of mangroves, which can produce a variety of antitumor compounds and bioactive substances. However, in mangrove ecosystems there is no complete genome in this genus. In this study, we isolated a fungus strain named Penicillium variabile HXQ-H-1 from coast mangrove (Fujian Province, China). We generated a chromosome-level genome with total size of 33.32 Mb, scaffold N50 of 5.23 Mb and contig N50 of 96.74 kb. Additionally, we anchored about 95.91% assembly sequences into the longest seven scaffolds, and predicted 10,622 protein-coding genes, in which 99.66% could be annotated by eight protein databases. The secondary metabolites analysis reveals the strain has various gene clusters involving polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS) and terpene synthase that may have a largely capacity of biotechnological potential. Comparison genome analysis between Penicillium variabile and Talaromyces islandicus reveals a small difference in the total number of genes, whereas HXQ-H-1 has a higher gene number with COG functional annotation. Evolutionary relationship of Penicillum based on genome-wide data was carried out for the first time, showing the strain HXQ-H-1 is closely related to Talaromyces islandicus. This genomic resource may provide a new resource for development of novel bioactive antibiotics, drug candidates and precursors in Penicillium variabile.

Antimicrobial Metabolites Produced by Penicillium mallochii CCH01 Isolated From the Gut of Ectropis oblique, Cultivated in the Presence of a Histone Deacetylase Inhibitor

Three chemical epigenetic modifiers [5-azacytidine, nicotinamide, and suberoylanilide hydroxamic acid (SAHA)] were applied to induce the metabolites of Penicillium mallochii CCH01, a fungus isolated from the gut of Ectropis oblique. Metabolite profiles of P. mallochii CCH01 were obviously changed by SAHA treatment. Four metabolites (1-4), including two new natural sclerotioramine derivatives, isochromophilone XIV (1) and isochromophilone XV (2), and two known compounds, sclerotioramine (3) and (+)-sclerotiorin (4), were isolated and purified from P. mallochii CCH01 treated with SAHA. Their structures were determined by spectroscopic analyzes. Anti-phytopathogenic activities of the isolated compounds 1-4 were investigated under laboratory conditions, and compound 4 showed broad and important inhibition activities against Curvularia lunata (IC₅₀ = 2.1 μg/mL), Curvularia clavata (IC₅₀ = 21.0 μg/mL), Fusarium oxysporum f. sp. Mornordica (IC₅₀ = 40.4 μg/mL), and Botryosphaeria dothidea (IC₅₀ = 27.8 μg/mL), which were comparable to those of referenced cycloheximide, with IC₅₀ values of 0.3, 5.0, 12.4, and 15.3 μg/mL, respectively. Ingredients 2 and 3 showed selective and potent activities against Colletotrichum graminicola with IC₅₀ values of 29.9 and 9.7 μg/mL, respectively. Furthermore, the antibacterial bioassays showed that compounds 3 and 4 exhibited strong inhibition activities against Bacillus subtilis, with disc diameters of zone of inhibition (ZOI) of 9.1 mm for both compounds, which were a bit weaker than that of referenced gentamycin with a ZOI of 10.8 mm. Additionally, the new metabolite 1 showed a promising activity against Candida albicans (ZOI = 10.5 mm), comparable to that of positive amphotericin B with a ZOI of 23.2 mm. The present results suggest that chemical epigenetic modifier induction was a promising approach to obtaining antimicrobial metabolites encoded by silent biosynthetic genes of P. mallochii.

Methylsulfonylated Polyketides Produced by Neosartorya udagawae HDN13-313 via Exogenous Addition of Small Molecules

Two new polyketides modified with a rare methylsulfonyl group, 3-methoxy-6-methyl-5-(methylsulfonyl)benzene-1,2,4-triol (1) and neosartoryone A (2), along with a biogenetically related compound (3), were isolated from Neosartorya udagawae HDN13-313 cultivated with the DNA methyltransferase inhibitor 5-azacytidine. The methylsulfonyl group of 1 and 2 was proven to be derived from DMSO, which was used as the solvent to dissolve 5-azacytidine. This is the first report of a fungus that can achieve a sulfonylation-like modification of natural products utilizing DMSO as a sulfur source. Compound 2 showed lipid-lowering activity in vitro comparable to simvastatin.

Enzyme-Catalyzed Inverse-Electron Demand Diels-Alder Reaction in the Biosynthesis of Antifungal Ilicicolin H

The pericyclases are a growing superfamily of enzymes that catalyze pericyclic reactions. We report a pericyclase IccD catalyzing an inverse-electron demand Diels-Alder (IEDDA) reaction with a rate acceleration of 3 × 10⁵-fold in the biosynthesis of fungal natural product ilicicolin H. We demonstrate IccD is highly periselective toward the IEDDA cycloaddition over a competing normal electron demand Diels-Alder (NEDDA) reaction from an ambimodal transition state. A predicted flavoenzyme IccE was identified to epimerize the IEDDA product 8- epi-ilicicolin H to ilicicolin H, a step that is critical for the observed antifungal activity of ilicicolin H. Our results reveal the ilicicolin H biosynthetic pathway and add to the collection of pericyclic reactions that are catalyzed by pericyclases.

Lead Compounds from Mangrove-Associated Microorganisms

The mangrove ecosystem is considered as an attractive biodiversity hotspot that is intensively studied in the hope of discovering new useful chemical scaffolds, including those with potential medicinal application. In the past two decades, mangrove-derived microorganisms, along with mangrove plants, proved to be rich sources of bioactive secondary metabolites as exemplified by the constant rise in the number of publications, which suggests the great potential of this important ecological niche. The present review summarizes selected examples of bioactive compounds either from mangrove endophytes or from soil-derived mangrove fungi and bacteria, covering the literature from 2014 to March 2018. Accordingly, 163 natural products are described in this review, possessing a wide range of potent bioactivities, such as cytotoxic, antibacterial, antifungal, α-glucosidase inhibitory, protein tyrosine phosphatase B inhibitory, and antiviral activities, among others.

Extending the "One Strain Many Compounds" (OSMAC) Principle to Marine Microorganisms

Genomic data often highlights an inconsistency between the number of gene clusters identified using bioinformatic approaches as potentially producing secondary metabolites and the actual number of chemically characterized secondary metabolites produced by any given microorganism. Such gene clusters are generally considered as “silent”, meaning that they are not expressed under laboratory conditions. Triggering expression of these “silent” clusters could result in unlocking the chemical diversity they control, allowing the discovery of novel molecules of both medical and biotechnological interest. Therefore, both genetic and cultivation-based techniques have been developed aimed at stimulating expression of these “silent” genes. The principles behind the cultivation based approaches have been conceptualized in the “one strain many compounds” (OSMAC) framework, which underlines how a single strain can produce different molecules when grown under different environmental conditions. Parameters such as, nutrient content, temperature, and rate of aeration can be easily changed, altering the global physiology of a microbial strain and in turn significantly affecting its secondary metabolism. As a direct extension of such approaches, co-cultivation strategies and the addition of chemical elicitors have also been used as cues to activate “silent” clusters. In this review, we aim to provide a focused and comprehensive overview of these strategies as they pertain to marine microbes. Moreover, we underline how changes in some parameters which have provided important results in terrestrial microbes, but which have rarely been considered in marine microorganisms, may represent additional strategies to awaken “silent” gene clusters in marine microbes. Unfortunately, the empirical nature of the OSMAC approach forces scientists to perform extensive laboratory experiments. Nevertheless, we believe that some computation and experimental based techniques which are used in other disciplines, and which we discuss; could be effectively employed to help streamline the OSMAC based approaches. We believe that natural products discovery in marine microorganisms would be greatly aided through the integration of basic microbiological approaches, computational methods, and technological innovations, thereby helping unearth much of the as yet untapped potential of these microorganisms.

Discovery of a new biphenyl derivative by epigenetic manipulation of marine-derived fungus Aspergillus versicolor

Cultivation of the marine-derived Aspergillus versicolor MCCC 3A00080 with the addition of a histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), significantly enhanced the diversity of secondary metabolites. From the culture treated, a new biphenyl derivative, named versiperol A (1), along with two known compounds, 2,4-dimethoxyphenol (2) and diorcinol (3) were isolated. The structures of 1-3 were established based on spectroscopic analysis and comparison with literature data. Among the isolates, versiperol A (1) exhibited modest inhibition of Staphylococcus aureus growth with MIC value of 8 μg/mL.

Inducing Secondary Metabolite Production by Combined Culture of Talaromyces aculeatus and Penicillium variabile

Four new polyketides, penitalarins A-C (1-3) and nafuredin B (4), together with the known biogenetically related nafuredin A (5) were isolated from a mixed culture of a deep-sea-derived fungus Talaromyces aculeatus and a mangrove-derived fungus Penicillium variabile. Liquid chromatography/mass spectrometry analysis showed that none of compounds 1-5 was produced by either of the two fungi when cultured alone under the same condition. The structures of 1-4, including absolute configurations, were deduced based on the interpretation of MS, NMR data, and time-dependent density functional theory calculations of specific electronic circular dichroism spectra. Compounds 1-3 possess a 3,6-dioxabicyclo[3.1.0]hexane ring, and 4 showed cytotoxicity with IC₅₀ values ranging from 1.2 to 9.8 μM against a panel of human cancer cell lines.

Varilactones and wortmannilactones produced by Penicillium variabile cultured with histone deacetylase inhibitor

Seven polyketides, including four new ones named as varilactones A-B (1-2) and wortmannilactones M-N (3-4), as well as three biogenetically related known wortmannilactones E, F and H (5-7), were isolated from the fungus Penicillium variabile HXQ-H-1, cultivated in potato-based medium with the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). Their structures (1-7) were established by analysis of NMR and MS data, and the absolute configuration of oxabicyclo[2.2.1]heptane unit was deduced from ¹H-NMR analyses on MPA esters after chemical reduction reaction. Among them, varilactones A and B (1 and 2), features a novel skeleton with a triene unit linking an oxabicyclo[2.2.1]heptane and an oxabicyclo[3.3.0]octane rings.

Marine-Derived Penicillium Species as Producers of Cytotoxic Metabolites

Since the discovery of penicillin, Penicillium has become one of the most attractive fungal genera for the production of bioactive molecules. Marine-derived Penicillium has provided numerous excellent pharmaceutical leads over the past decades. In this review, we focused on the cytotoxic metabolites * (* Cytotoxic potency was referred to five different levels in this review, extraordinary (IC₅₀/LD₅₀: <1 μM or 0.5 μg/mL); significant (IC₅₀/LD₅₀: 1~10 μM or 0.5~5 μg/mL); moderate (IC₅₀/LD₅₀: 10~30 μM or 5~15 μg/mL); mild (IC₅₀/LD₅₀: 30~50 μM or 15~25 μg/mL); weak (IC₅₀/LD₅₀: 50~100 μM or 25~50 μg/mL). The comparative potencies of positive controls were referred when they were available). produced by marine-derived Penicillium species, and on their cytotoxicity mechanisms, biosyntheses, and chemical syntheses.

Strategies to diversify natural products for drug discovery

Natural product libraries contain specialized metabolites derived from plants, animals, and microorganisms that play a pivotal role in drug discovery due to their immense structural diversity and wide variety of biological activities. The strategies to greatly extend natural product scaffolds through available biological and chemical approaches offer unique opportunities to access a new series of natural product analogues, enabling the construction of diverse natural product-like libraries. The affordability of these structurally diverse molecules has been a crucial step in accelerating drug discovery. This review provides an overview of various approaches to exploit the diversity of compounds for natural product-based drug development, drawing upon a series of examples to illustrate each strategy.

Gunnilactams A-C, Macrocyclic Tetralactams from the Mycelial Culture of the Entomogenous Fungus Paecilomyces gunnii

Three novel macrocyclic tetralactams, gunnilactam A (1), gunnilactam B (2), and gunnilactam C (3), were isolated from the submerged fermentation broth of Paecilomyces gunnii, an entomogenous fungus identified as the anamorph of Cordyceps gunnii. Their structures were determined using NMR data, HREIMS, and single-crystal X-ray crystallography. Gunnilactam A exhibited selective cytotoxic activity against human prostate cancer C42B cells with an IC₅₀ value of 5.4 μM.