Chlorinated polyketide obtained from a Daldinia sp. treated with the epigenetic modifier suberoylanilide hydroxamic acid

Chromic properties of dibenzo[j,l]fluoranthenes exhibiting different resonance contributions

Chromic molecules change colour in response to external stimuli and are utilized in applications such as food additive detection, light dimmers, and biological probes. One of the common design strategies for organic chromic molecules is based on changes in the π-conjugation. We have hypothesized that non-alternant polyaromatic hydrocarbon (PAH) skeletons can be used as backbones for chromic molecules. Herein, we synthesized hydroxy-substituted dibenzo[j,l]fluoranthenes, a class of non-alternant PAHs, as novel chromic compounds and evaluated their halochromic properties by UV-vis and fluorescence spectroscopy. Under basic conditions, the 1-hydroxy derivatives show a hyperchromic shift, whereas the 9-hydroxy derivatives show a bathochromic shift and fluorescence although the skeleton of the chromophore is the same. Density functional theory calculations indicated that the different chromic properties are attributed to the differences in their resonance structures.

Epigenetic modifiers as inducer of bioactive secondary metabolites in fungi

Scientists are making efforts to search for new metabolites as they are essential lead molecules for the drug discovery, much required due to the evolution of multi drug resistance and new diseases. Moreover, higher production of known drugs is required because of the ever growing population. Microorganisms offer a vast collection of chemically distinct compounds that exhibit various biological functions. They play a crucial role in safeguarding crops, agriculture, and combating several infectious ailments and cancer. Research on fungi have grabbed a lot of attention after the discovery of penicillin, most of the compounds produced by fungi under normal cultivation conditions are discovered and now rarely new compounds are discovered. Treatment of fungi with the epigenetic modifiers has been becoming very popular since the last few years to boost the discovery of new molecules and enhance the production of already known molecules. Epigenetic literally means above genetics that actually does not alter the genome but alter its expression by altering the state of chromatin from heterochromatin to euchromatin. Chromatin in heterochromatin state usually doesn't express because it is closely packed by histones in this state. Epigenetic modifiers loosen the packing of chromatin by inhibiting DNA methylation and histone deacetylation and thus permit the expression of genes that usually remain dormant. This study delves into the possibility of utilizing epigenetic modifying agents to generate pharmacologically significant secondary metabolites from fungi.

Recent advances in the synthesis and applications of fluoranthenes

As an important subclass of polycyclic aromatic hydrocarbons (PAHs), fluoranthenes continue to attract significant attention in synthetic organic chemistry and materials science. In this article, an overview of recent advances in the synthesis of fluoranthene derivatives along with selected applications is provided. First, methods for fluoranthene synthesis with a classification based on strategic bond disconnections are discussed. Then, the total syntheses of natural products featuring the benzo[j]fluoranthene skeleton are covered. Finally, examples of important applications of a variety of fluoranthenes are summarized.

Dearomative Intramolecular Diels-Alder/Sulfur Extrusion Reaction of Thiophenes with Alkynes Using peri-Substituted Naphthalene as a Tether

Dearomative intramolecular Diels-Alder/sulfur extrusion reaction of thiophenes with alkynes successfully afforded fluoranthenes in moderate to excellent yields. The proximity of both reactive sites fixed at the peri-position of naphthalene would play an important role in the progress of this reaction. Tri(o-tolyl)phosphine effectively suppressed the side reactions as a sulfur scavenger.

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.

Benzo[j]fluoranthene-Derived Natural Products

In this overview the literature on benzo[j]fluoranthene-derived toxins produced by fungi is discussed with a view on isolation, structure, biological activities, biosynthesis, and total syntheses of the natural products. This class of compounds consists until now of 33 naturally occurring compounds, where 25 are chiral and eight contain no stereogenic centers. The relative configuration of xylarenol was clarified by comparison of experimental and calculated ECD spectra, and absolute configurations of four toxins were corrected. The compounds show various biological activities including antibiotic and cytotoxic properties.

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.

Synthesis of azafluoranthenes by iridium-catalyzed [2 + 2 + 2] cycloaddition and evaluation of their fluorescence properties

We report a method for the synthesis of azafluoranthenes under neutral reaction conditions in a highly atom-economical manner by the iridium-catalyzed [2 + 2 + 2] cycloaddition of 1,8-dialkynylnaphthalenes with nitriles. A variety of nitriles react with methyl- or phenyl-substituted 1,8-dialkynylnaphthalenes to give a wide range of azafluoranthenes. Azafluoranthenes bearing an amino group show intense fluorescence at around 500 nm. Comparison of the fluorescence properties of amine-substituted azafluoranthenes with related compounds revealed the importance of the amine moiety for obtaining a high fluorescence quantum yield. The choice of the solvent affected the emission maxima and the fluorescence quantum yield. Azafluoranthenes bearing pyrrolidine exhibited blue-shifted emission bands in a non-polar solvent and gave a fluorescence quantum yield of 0.76 in toluene. A Lippert-Mataga plot and computational studies provide insight into the origin of the fluorescence of azafluoranthenes. Furthermore, cellular experiments using human breast adenocarcinoma cells SK-BR-3 demonstrated the feasibility of using azafluoranthenes as fluorescent probes.

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.

Metabolomic Strategy to Characterize the Profile of Secondary Metabolites in Aspergillus aculeatus DL1011 Regulated by Chemical Epigenetic Agents

Chemical epigenetic regulation (CER) is an effective method to activate the silent pathway of fungal secondary metabolite synthesis. However, conventional methods for CER study are laborious and time-consuming. In the meantime, the overall profile of the secondary metabolites in the fungi treated by the CER reagent is not well characterized. In this study, suberohydroxamic acid (SBHA), a histone deacetylase inhibitor, was added to a culture of Aspergillus aculeatus DL1011 and a new strategy based on LC-MS/MS analysis integrated with various metabolomic tools (MetaboAnalyst, MS-DIAL, SIRIUS and GNPS) was developed to characterize the profile of induced metabolites. As a result, 13.6%, 29.5% and 27.2% of metabolites were identified as newly biosynthesized, increasing and decreasing in abundance by CER, respectively. The structures of the 18 newly induced secondary metabolites were further identified by the new strategy to demonstrate that 72.2% of them (1 novel compound and 12 known compounds) were first discovered in A. aculeatus upon SBHA treatment. The accuracy of the new approach was confirmed by purification and NMR data analysis of major newly biosynthesized secondary metabolites. The bioassay showed that the newly biosynthesized compounds, roseopurpurin analogues, showed selective activities against DPPH scavenging, cytotoxicity and SHP1 inhibition. Our research demonstrated that CER was beneficial for changing the secondary metabolic profile of fungi and was an effective means of increasing the diversity of active metabolites. Our work also supplied a metabolomic strategy to characterize the profile changes and determine the newly induced compounds in the secondary metabolites of fungi treated with the chemical epigenetic regulator.

Rapid Access to Hydroxyfluoranthenes via a Domino Suzuki-Miyaura/Intramolecular Diels-Alder/Ring-Opening Reactions Sequence

In this work, we developed an efficient method for the rapid construction of fluoranthene skeleton to access a variety of substituted hydroxyfluoranthenes. The 1-iodo-8-alkynylnaphthalene derivatives, which serve as substrates for the key fluoranthene-forming step, were prepared via selective monoalkynylative Sonogashira reactions of 1,8-diiodonaphthalene. The domino reaction sequence which involves a sequential Suzuki–Miyaura coupling, an intramolecular Diels–Alder reaction, and an aromatization-driven ring-opening isomerization has been shown to give substituted hydroxyfluoranthenes in up to 92% yield. This work demonstrates the utility of designing new domino reactions for rapid access to substituted polycyclic aromatic hydrocarbons (PAHs).

Straightforward One-Pot Synthesis of New 4-Phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one Derivatives: X-ray Single Crystal Structure and Hirshfeld Analyses

A straightforward one-pot route for the synthesis of a new 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one is reported form the direct hydrazinolysis of triketo ester and hydrazine hydrate in ethanol. 4-Phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one was subjected to aza-Michael addition and N-alkylation on reaction with a set of alkylating agents in the presence of K2CO3. Hydrazinolysis of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one ester to hydrazide and conversion of hydrazide to thiosemicarbazide were successful. X-Ray single crystals analysis and 1H, 13C NMR were used for unambiguous structure confirmation. The O…H, N…H, C…N and C…C in 2, and the N…H, C…N, C…C, C…O and H…H interactions in 6 are the most important in the molecular packing based on Hirshfled analysis. Moreover, the presence of short C…C and C…N contacts in both compounds revealed the presence of π–π stacking interactions.

Building Natural Product Libraries Using Quantitative Clade-Based and Chemical Clustering Strategies

The success of natural product-based drug discovery is predicated on having chemical collections that offer broad coverage of metabolite diversity. We propose a simple set of tools combining genetic barcoding and metabolomics to help investigators build natural product libraries aimed at achieving predetermined levels of chemical coverage. It was found that such tools aided in identifying overlooked pockets of chemical diversity within taxa, which could be useful for refocusing collection strategies. We have used fungal isolates identified as Alternaria from a citizen-science-based soil collection to demonstrate the application of these tools for assessing and carrying out predictive measurements of chemical diversity in a natural product collection. Within Alternaria, different subclades were found to contain nonequivalent levels of chemical diversity. It was also determined that a surprisingly modest number of isolates (195 isolates) was sufficient to afford nearly 99% of Alternaria chemical features in the data set. However, this result must be considered in the context that 17.9% of chemical features appeared in single isolates, suggesting that fungi like Alternaria might be engaged in an ongoing process of actively exploring nature's metabolic landscape. Our results demonstrate that combining modest investments in securing internal transcribed spacer (ITS)-based sequence information (i.e., establishing gene-based clades) with data from liquid chromatography-mass spectrometry (i.e., generating feature accumulation curves) offers a useful route to obtaining actionable insights into chemical diversity coverage trends in a natural product library. It is anticipated that these outcomes could be used to improve opportunities for accessing bioactive molecules that serve as the cornerstone of natural product-based drug discovery. IMPORTANCE Natural product drug discovery efforts rely on libraries of organisms to provide access to diverse pools of compounds. Actionable strategies to rationally maximize chemical diversity, rather than relying on serendipity, can add value to such efforts. Readily implementable biological (i.e., ITS sequence analysis) and chemical (i.e., mass spectrometry-based feature and scaffold measurements) diversity assessment tools can be employed to monitor and adjust library development tactics in real time. In summary, metabolomics-driven technologies and simple gene-based specimen barcoding approaches have broad applicability to building chemically diverse natural product libraries.

Media and strain studies for the scaled production of cis-enone resorcylic acid lactones as feedstocks for semisynthesis

Resorcylic acid lactones (RALs) with a cis-enone moiety, represented by hypothemycin (1) and (5Z)-7-oxozeaenol (2), are fungal secondary metabolites with irreversible inhibitory activity against protein kinases, with particularly selective activity for inhibition of TAK1 (transforming growth factor beta-activated kinase 1). Gram-scale quantities of these compounds were needed as feedstock for semi-synthesizing RAL-analogues in a step-economical fashion. To do so, this study had three primary goals: identifying fungi that biosynthesized 1 and 2, enhancing their production by optimizing the fermentation conditions on the lab scale, and developing straight forward purification processes. After evaluating 536 fungal extracts via an in-house dereplication protocol, three strains were identified as producing cis-enone RALs (i.e., MSX78495, MSX63935, MSX45109). Screening these fungal strains on three grain-based media revealed enhanced production of 1 by strain MSX78495 on oatmeal medium, while rice medium increased the biosynthesis of 2 by strain MSX63935. Furthermore, the purification processes were improved, moving away from HPLC purification to utilizing two to four cycles of resuspension and centrifugation in small volumes of organic solvents, generating gram-scale quantities of these metabolites readily. In addition, studying the chemistry profiles of strains MSX78495 and MSX63935 resulted in the isolation of ten other RALs (3-12), two radicinin analogues (13-14), and six benzopyranones (15-20), with 19 and 20 being newly described chlorinated benzopyranones.

Transition metal-free approach to azafluoranthene scaffolds by aldol condensation/[1+2+3] annulation tandem reaction of isocyanoacetates with 8-(alkynyl)-1-naphthaldehydes

A transition metal-free aldol condensation/[1+2+3] annulation reaction of isocyanoacetates with 8-(alkynyl)-1-naphthaldehydes has been developed for the general synthesis of azafluoranthenes. This domino reaction enables successive formation of three new bonds and two rings from readily accessible starting materials in a single operation. Furthermore, this methodology can also be utilized to construct chromeno[4,3-c]pyridines and benzo[c][2,6]naphthyridines in moderate yields.

Thielavins: tuned biosynthesis and LR-HSQMBC for structure elucidation

A series of thielavins I, V, and Q (1-3) and the previously undescribed thielavin Z₈ (4) were isolated from cultures of a fungal Shiraia-like sp. (strain MSX60519) that were grown under a suite of media and light conditions, with enhanced biosynthesis noted using rice as a substrate with 12:12 h light:dark cycles. Conversely, oatmeal medium and continuous white light-emitting diode light exposure negatively affected the production of these compounds, at least by strain MSX60519. The structure of 4 was determined using NMR spectroscopic data and mass fragmentation patterns. Of note, the utility of LR-HSQMBC and NOESY NMR experiments in the structural elucidation of these hydrogen-deficient natural products was demonstrated. Compounds 1-4 exhibited cytotoxic activity at the micromolar level against human breast, ovarian, and melanoma cancer cell lines.

Enhanced Production and Anticancer Properties of Photoactivated Perylenequinones

Hypocrellins and hypomycins are naturally occurring fungal perylenequinones with potential photodynamic activity against cancer and microbial diseases. This project pursued three lines of research. First, the production of perylenequinones was enhanced by investigating the effect of culture medium and light exposure on their biosynthesis. Solid-fermentation cultures on rice medium allowed for enhanced production of hypocrellins as compared to Cheerios or oatmeal medium. Alternatively, increased production of hypomycins, which are structurally related to the hypocrellins, was observed on oatmeal medium. In both cases, light exposure was an essential factor for the enhanced biosynthesis. In addition, this led to the discovery of two new perylenequinones, ent-shiraiachrome A (5) and hypomycin E (8), which were elucidated based on spectroscopic data. Finally, the photocytotoxic effects of both classes of compounds were evaluated against human skin melanoma, with EC50 values at nanomolar levels for hypocrellins and micromolar levels for hypomycins. In contrast, both classes of compounds showed reduced dark toxicity (EC50 values >100 μM), demonstrating promising phototherapeutic indices.

Expeditious Green Synthesis of Novel 4-Methyl-1,2,5,6-tetraazafluoranthen-3(2H)-one Analogue from Ninhydrin: N/S-Alkylation and Aza-Michael Addition

A straightforward green synthesis of 4-methyl-1,2,5,6-tetraazafluoranthen-3(2H)-one 6 is reported from ninhydrin 1 via condensation with ethyl acetoacetate, followed by cyclization with hydrazine hydrate in water as a benign solvent. Tetraazafluoranthen-3-thione 7 was obtained using Lawesson's reagent. N-alkylated tetraazafluoranthen-3-one 8-12 and S-alkylated analogues 13-15 were synthesized via alkylation. The investigation of the unique reactivity of 4-methyl-1,2,5,6-tetraazafluoranthen-3(2H)-one/thione toward the alkylation and aza-Michael additions was explored.

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.

Epigenetic modification, co-culture and genomic methods for natural product discovery

Fungi and bacteria are encountered in many habitats where they live in complex communities interacting with one another mainly by producing secondary metabolites, which are organic compounds that are not directly involved in the normal growth, development, or reproduction of the organism. These organisms appear as a promising source for the discovery of novel bioactive natural products that may find their application in medicine. However, the production of secondary metabolites by those organisms when cultured axenically is limited as only a subset of biosynthetic genes is expressed under standard laboratory conditions leading to the search of new methods for the activation of the silent genes including epigenetic modification and co-cultivation. Biosynthetic gene clusters which produce secondary metabolites are known to be present in a heterochromatin state in which the transcription of constitutive genes is usually regulated by epigenetic modification including DNA methylation and histone deacetylation. Therefore, small-molecule epigenetic modifiers which promote changes in the structure of chromatin could control the expression of silent genes and may be rationally employed for the discovery of novel bioactive compounds. Co-cultivation, which is also known as mixed-fermentation, usually implies two or more microorganisms in the same medium in which the resulting competition is known to enhance the production of constitutively present compounds and/or to lead to the induction of cryptic metabolites that were not detected in axenic cultures of the considered axenic microorganism. Genomic strategies could help to identify biosynthetic gene clusters in fungal genomes and link them to their products by the means of novel algorithms as well as integrative pan-genomic approaches. Despite that all these techniques are still in their infancy, they appear as promising sources for the discovery of new bioactive compounds. This chapter presents recent ecological techniques for the discovery of new secondary metabolites that might find application in medicine.

Synthesis of a Diastereomer of the Marine Macrolide Lytophilippine A

The synthesis of a diastereomer of lytophilippine A required 22 longest linear steps using known building blocks. Cross-metathesis/asymmetric aldol addition and regioselective esterification/ring-closing metathesis served as efficient combi tools for scaffold construction. Detailed NMR investigations in different solvent (systems) provide evidence for a deep-seated configurational misassignment of the molecule named lytophilippine A.

Hydrogen-Bond-Controlled Formal Meta-Selective C-H Transformations and Regioselective Synthesis of Multisubstituted Aromatic Compounds

The meta-selective introduction of functional groups into aromatic substrates was successfully achieved by hydrogen-bond-controlled meta-selective C-H borylation and successive conversion of the boryl group to other functional groups. By this method a wide range of functional groups could be introduced without isolation of the borylated intermediates. The desired meta-functionalized aromatic products were obtained in a one-pot manner even on a gram scale. Regioselective synthesis of multisubstituted aromatic compounds was also achieved.

Exploring Structural Diversity of Microbe Secondary Metabolites Using OSMAC Strategy: A Literature Review

Microbial secondary metabolites (MSMs) have played and continue to play a highly significant role in the drug discovery and development process. Genetically, MSM chemical structures are biologically synthesized by microbial gene clusters. Recently, however, the speed of new bioactive MSM discovery has been slowing down due to consistent employment of conventional cultivation and isolation procedure. In order to alleviate this challenge, a number of new approaches have been developed. The strategy of one strain many compounds (OSMAC) has been shown as a simple and powerful tool that can activate many silent biogenetic gene clusters in microorganisms to make more natural products. This review highlights important and successful examples using OSMAC approaches, which covers changing medium composition and cultivation status, co-cultivation with other strain(s), adding enzyme inhibitor(s) and MSM biosynthetic precursor(s). Available evidences had shown that variation of cultivation condition is the most effective way to produce more MSMs and facilitate the discovery of new therapeutic agents.

On top of biosynthetic gene clusters: How epigenetic machinery influences secondary metabolism in fungi

Fungi produce an abundance of bioactive secondary metabolites which can be utilized as antibiotics and pharmaceutical drugs. The genes encoding secondary metabolites are contiguously arranged in biosynthetic gene clusters (BGCs), which supports co-regulation of all genes required for any one metabolite. However, an ongoing challenge to harvest this fungal wealth is the finding that many of the BGCs are 'silent' in laboratory settings and lie in heterochromatic regions of the genome. Successful approaches allowing access to these regions - in essence converting the heterochromatin covering BGCs to euchromatin - include use of epigenetic stimulants and genetic manipulation of histone modifying proteins. This review provides a comprehensive look at the chromatin remodeling proteins which have been shown to regulate secondary metabolism, the use of chemical inhibitors used to induce BGCs, and provides future perspectives on expansion of epigenetic tools and concepts to mine the fungal metabolome.

Bortezomib-induced new bergamotene derivatives xylariterpenoids H–K from sponge-derived fungus Pestalotiopsis maculans 16F-12

The addition of the proteasome inhibitor, bortezomib, to the fermentation broth of a sponge-derived fungus Pestalotiopsis maculans 16F-12 led to the isolation of four new bergamotene derivatives xylariterpenoids H–K (1–4).

Omics based approach for biodiscovery of microbial natural products in antibiotic resistance era

The need for a new antibiotic pipeline to confront threat imposed by resistant pathogens has become a major global concern for human health. To confront the challenge there is a need for discovery and development of new class of antibiotics. Nature which is considered treasure trove, there is re-emerged interest in exploring untapped microbial to yield novel molecules, due to their wide array of negative effects associated with synthetic drugs. Natural product researchers have developed many new techniques over the past few years for developing diverse compounds of biopotential. Taking edge in the advancement of genomics, genetic engineering, in silico drug design, surface modification, scaffolds, pharmacophores and target-based approach is necessary. These techniques have been economically sustainable and also proven efficient in natural product discovery. This review will focus on recent advances in diverse discipline approach from integrated Bioinformatics predictions, genetic engineering and medicinal chemistry for the synthesis of natural products vital for the discovery of novel antibiotics having potential application.

Bioactive halogenated dihydroisocoumarins produced by the endophytic fungus Lachnum palmae isolated from Przewalskia tangutica

Guided by the UPLC-ESIMS profile, seven previously undescribed halogenated dihydroisocoumarins, palmaerones A-G, along with eleven known dihydroisocoumarins, were isolated from Lachnum palmae, an endophytic fungus from Przewalskia tangutica by exposure to a histone deacetylase inhibitor SAHA. Structures of the isolates were elucidated by analysis of their NMR, MS and optical rotation values. The antimicrobial, anti-inflammatory and cytotoxic activities of palmaerones A-G were evaluated. Palmaerones A-G showed antimicrobial activities against the strains (C. neoformans, Penicillium sp., C. albicans, B. subtilis and S. aureus), and palmaerone E exhibited potential antimicrobial activities against all the test strains with the MIC value in the range of 10-55 μg/mL. Palmaerones A and E exhibited moderate inhibitory effects on NO production in LPS-induced RAW 264.7 cells, with the IC₅₀ values of 26.3 and 38.7 μM, respectively and no obvious toxicities were observed at 50 μM. Palmaerone E showed weak cytotoxicity against HepG2 with the IC₅₀ value of 42.8 μM. This work provides an effective strategy for expanding natural product resource.

Dynamics of Metabolite Induction in Fungal Co-cultures by Metabolomics at Both Volatile and Non-volatile Levels

Fungal co-cultivation has emerged as a promising way for activating cryptic biosynthetic pathways and discovering novel antimicrobial metabolites. For the success of such studies, a key element remains the development of standardized co-cultivation methods compatible with high-throughput analytical procedures. To efficiently highlight induction processes, it is crucial to acquire a holistic view of intermicrobial communication at the molecular level. To tackle this issue, a strategy was developed based on the miniaturization of fungal cultures that allows for a concomitant survey of induction phenomena in volatile and non-volatile metabolomes. Fungi were directly grown in vials, and each sample was profiled by head space solid phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS), while the corresponding solid culture medium was analyzed by liquid chromatography high resolution mass spectrometry (LC-HRMS) after solvent extraction. This strategy was implemented for the screening of volatile and non-volatile metabolite inductions in an ecologically relevant fungal co-culture of Eutypa lata (Pers.) Tul. & C. Tul. (Diatrypaceae) and Botryosphaeria obtusa (Schwein.) Shoemaker (Botryosphaeriaceae), two wood-decaying fungi interacting in the context of esca disease of grapevine. For a comprehensive evaluation of the results, a multivariate data analysis combining Analysis of Variance and Partial Least Squares approaches, namely AMOPLS, was used to explore the complex LC-HRMS and GC-MS datasets and highlight dynamically induced compounds. A time-series study was carried out over 9 days, showing characteristic metabolite induction patterns in both volatile and non-volatile dimensions. Relevant links between the dynamics of expression of specific metabolite production were observed. In addition, the antifungal activity of 2-nonanone, a metabolite incrementally produced over time in the volatile fraction, was assessed against Eutypa lata and Botryosphaeria obtusa in an adapted bioassay set for volatile compounds. This compound has shown antifungal activity on both fungi and was found to be co-expressed with a known antifungal compound, O-methylmellein, induced in solid media. This strategy could help elucidate microbial inter- and intra-species cross-talk at various levels. Moreover, it supports the study of concerted defense/communication mechanisms for efficiently identifying original antimicrobials.

Synthesis of Fluoranthene Derivatives via Tandem Suzuki-Miyaura and Intramolecular C-H Arylation Reactions under Both Homogeneous and Heterogeneous Catalytic Conditions

A catalytic method for the synthesis of substituted fluoranthenes that operates via tandem Suzuki-Miyaura and intramolecular C-H arylation reactions is reported. The overall reaction sequence works effectively with homogeneous catalysis using Pd(dppf)Cl₂ as well as heterogeneous catalysis using reduced graphene oxide (rGO)-CuPd nanocatalysts with low catalyst loadings. High functional group tolerance is observed under both catalytic conditions where arylboronic acids and esters having electron-withdrawing and electron-donating substituents afforded fluoranthene products in good yields (up to 78%). Moreover, the rGO-CuPd nanocatalysts are demonstrated to be reusable by preserving almost 90% of their initial activity after the third cycle.

NAD+-dependent HDAC inhibitor stimulates Monascus pigment production but inhibit citrinin

Monascus species are edible fungi due to the production of food colorant and other beneficial compounds. Hence, it has been an attractive thesis to improve their productivities. Increasing numbers of investigations revealed that regulating the activities of histone deacetylases can significantly perturb secondary metabolites (SM) production at a global level. In this study, dihydrocoumarin (DHC, an inhibitor of the Sirtuin family of NAD⁺-dependent deacetylases) was used to treat Monascus ruber for evaluating its effects on organism growth and SM production. The results revealed that the variation trends of colonial sizes, biomass and mycotoxin were in a dose-dependent manner. Generally, they decreased with the increased DHC concentrations in the designed range. But the variation trend of pigment was different. Comparison of SM profile, three new peaks occurred to the mycelia extractions from DHC-treated strain corresponding to molecular weights 402, 416 and 444, respectively. These three compounds were identified as Monasfluol B, Monascus azaphilone C and acetyl-monasfluol B (a new Monascus chemical pigment structure). In short, DHC can stimulate M. ruber strain to produce more pigment-like polyketides but inhibition of mycotoxin (citrinin).

Unexpected Biotransformation of the HDAC Inhibitor Vorinostat Yields Aniline-Containing Fungal Metabolites

The diversity of genetically encoded small molecules produced by filamentous fungi remains largely unexplored, which makes these fungi an attractive source for the discovery of new compounds. However, accessing their full chemical repertoire under common laboratory culture conditions is a challenge. Epigenetic manipulation of gene expression has become a well-established tool for overcoming this obstacle. Here, we report that perturbation of the endophytic ascomycete Chalara sp. 6661, producer of the isofusidienol class of antibiotics, with the HDAC inhibitor vorinostat resulted in the production of four new modified xanthones. The structures of chalanilines A (1) and B (2) and adenosine-coupled xanthones A (3) and B (4) were determined by extensive NMR spectroscopic analyses, and the bioactivities of 1-4 were tested in antibiotic and cytotoxicity assays. Incorporation studies with deuterium-labeled vorinostat indicate that the aniline moiety in chalalanine A is derived from vorinostat itself. Our study shows that Chalara sp. is able to metabolize the HDAC inhibitor vorinostat to release aniline. This is a rare report of fungal biotransformation of the popular epigenetic modifier vorinostat into aniline-containing polyketides.

Halogenated Compounds from Directed Fermentation of Penicillium concentricum, an Endophytic Fungus of the Liverwort Trichocolea tomentella

One new chlorinated xanthone, 6-chloro-3,8-dihydroxy-1-methylxanthone (1), a new 2-bromo-gentisyl alcohol (2), and a mixture of 6-epimers of 6-dehydroxy-6-bromogabosine C (3a and 3b), together with 19 previously identified compounds, epoxydon (4), norlichexanthone (5), 2-chlorogentisyl alcohol (6), hydroxychlorogentisyl quinone (7), 6-dehydroxy-6α-chlorogabosine C (8a), 6-dehydroxy-6β-chlorogabosine C (8b), gentisyl alcohol (9), gentisyl quinone (10), (R,S)-1-phenyl-1,2-ethanediol (11), dehydrodechlorogriseofulvin (12), dechlorogriseofulvin (13), dehydrogriseofulvin (14), griseofulvin (15), ethylene glycol benzoate (16), alternariol (17), griseoxanthone C (18), drimiopsin H (19), griseophenone C (20), and griseophenone B (21), were isolated from cultures of Penicillium concentricum, a fungal endophyte of the liverwort Trichocolea tomentella. The structures of the new compounds (1, 2, 3a, and 3b) were elucidated by interpretation of spectroscopic data including one- and two-dimensional NMR techniques. Among these, compounds 2-4 displayed modest cytotoxicity to the MCF-7 hormone-dependent breast cancer cell line with IC₅₀ values of 8.4, 9.7, and 5.7 μM, respectively, whereas compound 9 exhibited selective cytotoxicity against the HT-29 colon cancer cell line with an IC₅₀ value of 6.4 μM. During this study we confirmed that the brominated gentisyl alcohol (2) was formed by chemical conversion of 4 during bromide salt addition to culture media.

Daldinone derivatives from the mangrove-derived endophytic fungus Annulohypoxylon sp

Three new benzo[j]fluoranthene metabolites, including an isolation artefact which induces intrinsic apoptosis and blocks autophagy, were isolated fromAnnulohypoxylonsp.

High-yielding aqueous synthesis of chloroacetophenones and aroyl chlorohydrins

Two new reactions for preparing chloroacetophenones and aroyl chlorohydrins promoted by sulfonyl chloride and mediated by water are reported.