Thiodiketopiperazines produced by the endophytic fungus Epicoccum nigrum

Synthesis and toxicity of monothiooxalamides against human red blood cells, brine shrimp (Artemia salina), and fruit fly (Drosophila melanogaster)

A new family of monothiooxalamides derived from 2-aminobenzimidazole was synthesized, and their structures were confirmed by 1H and 13C one-dimensional and 2D NMR experiments (COSY, HSQC, and HMBC). The antioxidant capacity was evaluated by free radical scavenging assays: 1,1-diphenyl-2-picrylhydrazyl (DPPH•), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS•+), ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), and the Fe(II) chelating ability. Our work group has previously reported the synthesis and antioxidant activity of monothiooxalamides derived from 2-aminopyridine (I). In this study, the in vitro hemolytic activity of compounds from the 2-aminopyridine (I) and 2-aminobenzimidazole (II) families was evaluated against human red blood cells (RBCs). The concentration at which monothiooxalamides showed no hemolytic activity was chosen to assess their ability to inhibit free radical-induced membrane damage in human RBCs, acute toxicity in brine shrimp, and in vivo toxicity against Drosophila melanogaster. Compounds with morpholine fragments (1g, 1h, 2g, and 2h) showed time- and concentration-dependent protective effects against radical-induced oxidative hemolysis. Moreover, they had the lowest acute toxicity in the brine shrimp lethality assay and a significant increase in chelating activity compared with the other molecules. In particular, monothiooxalamide 2g showed lower toxicity and can be considered for further biological screening and application trials.

Stimulating Novel and Bioactive Metabolite Production by Cocultivation of Two Fungi─Aspergillus oryzae and Epicoccum dendrobii

Fungi produce various bioactive secondary metabolites (SMs) as protective and weaponized tools to enhance survival in shared ecological niches. By mimicking a competitive ecosystem, cocultivation has been proven to be particularly successful in stimulating SM discovery. Here, we reported the identification of four novel metabolites, epiclactones A and B, epioxochromane and aoergostane, from the coculture of two biotechnologically important strains, Aspergillus oryzae and Epicoccum dendrobii. Transcriptome and metabolome analyses revealed widespread silent gene activation during fungal-fungal interaction. The majority of differentially expressed gene clusters were summarized for both strains. Based on these highly activated biosynthetic pathways, we suggested that a bidirectional chemical defense occurred under cocultivation. E. dendrobii enhanced the production of the spore inhibitor, fumigermin. Moreover, A. oryzae highly accumulated the antifungal agent kojic acid with a yield of up to 1.10 g/L. This study provides an excellent example for the discovery of hidden natural products by cocultivation.

Construction of Hydroindole Skeleton by Photocatalytic Oxidative Dearomatization and Cyclization Sequence, and a Concise Synthesis of Melodamide A and (±)-Toussaintine C

A method of synthesizing hydroindole skeletons has been developed by using photocatalytic oxidative dearomatization and an aza-Michael addition sequence. Using this method, optically active hydroindoles, which are often used in natural product synthesis as chiral building blocks, can be easily prepared with >99% ee. Furthermore, the synthesis of melodamide A and (±)-toussaintine C was achieved using this method as a key step.

Cytotoxic naphtho- and benzofurans from an endophytic fungus Epicoccum nigrum Ann-B-2 associated with Annona squamosa fruits

Chemical exploration of the total extract derived from Epicoccum nigrum Ann-B-2, an endophyte associated with Annona squamosa fruits, afforded two new metabolites, epicoccofuran A (1) and flavimycin C (2), along with four known compounds namely, epicocconigrone A (3), epicoccolide B (4), epicoccone (5) and 4,5,6-trihydroxy-7-methyl-1,3-dihydroisobenzofuran (6). Structures of the isolated compounds were elucidated using extensive 1D and 2D NMR along with HR-ESI-MS. Flavimycin C (2) was isolated as an epimeric mixture of its two diastereomers 2a and 2b. The new compounds 1 and 2 displayed moderate activity against B. subtilis, whereas compounds (2, 3, 5, and 6) showed significant antiproliferative effects against a panel of seven different cancer cell lines with IC50 values ranging from 1.3 to 12 µM.

Lecanicilliums A-F, Thiodiketopiperazine-Class Alkaloids from a Mangrove Sediment-Derived Fungus Lecanicillium kalimantanense

Six new thiodiketopiperazine-class alkaloids lecanicilliums A-F were isolated from the mangrove sediment-derived fungus Lecanicillium kalimantanense SCSIO41702, together with thirteen known analogues. Their structures were determined by spectroscopic analysis. The absolute configurations were determined by quantum chemical calculations. Electronic circular dichroism (ECD) spectra and the structure of Lecanicillium C were further confirmed by a single-crystal X-ray diffraction analysis. Lecanicillium A contained an unprecedented 6/5/6/5/7/6 cyclic system with a spirocyclic center at C-2'. Biologically, lecanicillium E, emethacin B, and versicolor A displayed significant cytotoxicity against human lung adenocarcinoma cell line H1975, with IC50 values of 7.2~16.9 μM, and lecanicillium E also showed antibacterial activity against four pathogens with MIC values of 10~40 μg/mL. Their structure-activity relationship is also discussed.

Transition-metal catalyzed C-H activation as a means of synthesizing complex natural products

Over the past few decades, the advent of C-H activation has led to a rethink among chemists about the synthetic strategies employed for multi-step transformations. Indeed, deploying innovative and masterful tricks against the numerous classical organic transformations has been the need of the hour. Despite this, the immense importance of C-H activation remains unfulfilled unless the methodology can be deployed for large-scale industrial processes and towards the concise, step-economic synthesis of prodigious natural products and pharmaceutical drugs. Lately, the growing potential of C-H activation methodology has indeed driven the pioneers of synthetic organic chemists into finding more efficient methods to accelerate the synthesis of such complex molecular scaffolds. This review aims to draw a general overview of the various C-H activation procedures that have been adopted for synthesizing these vast majority of structurally complicated natural products. Our objective lies in drawing a complete picture and taking the readers through the synthesis of a series of such complex organic compounds by simplified techniques, making it step-economic on a larger scale and thus instigating the readers to trigger the use of such methodology and uncover new, unique patterns for future synthesis of such natural products.

Epipolythiodioxopiperazine-Based Natural Products: Building Blocks, Biosynthesis and Biological Activities

Epipolythiodioxopiperazines (ETPs) are fungal secondary metabolites that share a 2,5-diketopiperazine scaffold built from two amino acids and bridged by a sulfide moiety. Modifications of the core and the amino acid side chains, for example by methylations, acetylations, hydroxylations, prenylations, halogenations, cyclizations, and truncations create the structural diversity of ETPs and contribute to their biological activity. However, the key feature responsible for the bioactivities of ETPs is their sulfide moiety. Over the last years, combinations of genome mining, reverse genetics, metabolomics, biochemistry, and structural biology deciphered principles of ETP production. Sulfurization via glutathione and uncovering of the thiols followed by either oxidation or methylation crystallized as fundamental steps that impact expression of the biosynthesis cluster, toxicity and secretion of the metabolite as well as self-tolerance of the producer. This article showcases structure and activity of prototype ETPs such as gliotoxin and discusses the current knowledge on the biosynthesis routes of these exceptional natural products.

Screening for broad-spectrum antimicrobial endophytes from Rosa roxburghii and multi-omic analyses of biosynthetic capacity

Plants with certain medicinal values are a good source for isolating function-specific endophytes. Rosa roxburghii Tratt. has been reported to be a botanical source of antimicrobial compounds, which may represent a promising candidate for screening endophytic fungi with antimicrobial potential. In this study, 54 endophytes were isolated and molecularly identified from R. roxburghii. The preliminary screening using the plate confrontation method resulted in 15 different endophytic strains showing at least one strong inhibition or three or more moderate inhibition against the 12 tested strains. Further re-screening experiments based on the disc diffusion method demonstrated that Epicoccum latusicollum HGUP191049 and Setophoma terrestris HGUP190028 had excellent antagonistic activity. The minimum inhibitory concentration (MIC) test for extracellular metabolites finally indicated that HGUP191049 had lower MIC values and a broader antimicrobial spectrum, compared to HGUP190028. Genomic, non-target metabolomic, and comparative genomic studies were performed to understand the biosynthetic capacity of the screened-out endophytic fungus. Genome sequencing and annotation of HGUP191049 revealed a size of 33.24 megabase pairs (Mbp), with 24 biosynthetic gene clusters (BGCs), where the putative antimicrobial compounds, oxyjavanicin, patulin and squalestatin S1 were encoded by three different BGCs, respectively. In addition, the non-targeted metabolic results demonstrated that the strain contained approximately 120 antimicrobial secondary metabolites and was structurally diverse. Finally, comparative genomics revealed differences in pathogenicity, virulence, and carbohydrate-active enzymes in the genome of Epicoccum spp. Moreover, the results of the comparative analyses presumed that Epicoccum is a promising source of antimicrobial terpenes, while oxyjavanicin and squalestatin S1 are antimicrobial compounds shared by the genus. In conclusion, R. roxburghii and the endophytic HGUP191049 isolated from it are promising sources of broad-spectrum antimicrobial agents.

Four new fatty acid derivatives from Diaporthe sp. T24, an endophytic fungus isolated from Ligularia fischer

The endophytic fungus Diaporthe sp. is known to contain many secondary metabolites, but fatty acid derivatives have rarely been found. In this study, four new fatty acid derivatives (1-4), together with four known compounds (5-8), were isolated from Diaporthe sp., which was obtained from the stem of Ligularia fischeri. The absolute configurations of the new compounds 1-4 were deduced based on spectroscopic technique and J-based coupling constant analysis. Moreover, compound 1 exhibited cytotoxic activities against HCT-8 and MCF-7 cancer cells, and compounds 3 and 4 showed modest selectivity for HCT-8 cells by MTT assay.

Sulfur-Containing Compounds from Endophytic Fungi: Sources, Structures and Bioactivities

Endophytic fungi have attracted increasing attention as an under-explored source for the discovery and development of structurally and functionally diverse secondary metabolites. These microorganisms colonize their hosts, primarily plants, and demonstrate diverse ecological distribution. Among endophytic fungal natural products, sulfur-containing compounds feature one or more sulfur atoms and possess a range of bioactivities, e.g., cytotoxicity and antimicrobial activities. These natural products mainly belong to the classes of polyketides, nonribosomal peptides, terpenoids, and hybrids. Here, we reviewed the fungal producers, plant sources, chemical structures, and bioactivities of 143 new sulfur-containing compounds that were reported from 1985 to March 2022.

A copper-catalyzed three-component reaction of dithioacetals with diazo ketones and ketimines

An efficient protocol for the synthesis of various acyclic thioacetal derivatives and medium-size sulfur-containing heterocycles via copper-catalyzed three-component reaction of dithioacetals with diazo-ketones and ketimines was reported.

Investigation of Thiocarbamates as Potential Inhibitors of the SARS-CoV-2 Mpro

In the present study we tested, using the microscale thermophoresis technique, a small library of thionocarbamates, thiolocarbamates, sulfide and disulfide as potential lead compounds for SARS-CoV-2 Mpro drug design. The successfully identified binder is a representative of the thionocarbamates group with a high potential for future modifications aiming for higher affinity and solubility. The experimental analysis was extended by computational studies that show insufficient accuracy of the simplest and widely applied approaches and underline the necessity of applying more advanced methods to properly evaluate the affinity of potential SARS-CoV-2 Mpro binders.

Antimicrobial and Antibiofilm Activities of the Fungal Metabolites Isolated from the Marine Endophytes Epicoccum nigrum M13 and Alternaria alternata 13A

Epicotripeptin (1), a new cyclic tripeptide along with four known cyclic dipeptides (2-5) and one acetamide derivative (6) were isolated from seagrass-associated endophytic fungus Epicoccum nigrum M13 recovered from the Red Sea. Additionally, two new compounds, cyclodidepsipeptide phragamide A (7) and trioxobutanamide derivative phragamide B (8), together with eight known compounds (9-16), were isolated from plant-derived endophyte Alternaria alternata 13A collected from a saline lake of Wadi El Natrun depression in the Sahara Desert. The structures of the isolated compounds were determined based on the 1D and 2D NMR spectroscopic data, HRESIMS data, and a comparison with the reported literature. The absolute configurations of 1 and 7 were established by advanced Marfey's and Mosher's ester analyses. The antimicrobial screening indicated that seven of the tested compounds exhibited considerable (MIC range of 2.5-5 µg/mL) to moderate (10-20 µg/mL) antibacterial effect against the tested Gram-positive strains and moderate to weak (10-30 µg/mL) antibacterial effect against Gram-negative strains. Most of the compounds exhibited weak or no activity against the tested Gram-negative strains. On the other hand, four of the tested compounds showed considerable antibiofilm effects against biofilm forming Gram-positive and Gram-negative strains.

Electroreductive Nickel-Catalyzed Thiolation: Efficient Cross-Electrophile Coupling for C-S Formation

Sulfur-containing molecules are of utmost topical importance towards the effective development of pharmaceuticals and functional materials. Herein, we present an efficient and mild electrochemical thiolation by cross-electrophile coupling of alkyl bromides with functionalized bench-stable thiosulfonates to access alkyl sulfides with excellent efficacy and broad functional group tolerance. Cyclic voltammetry and potentiostatic analysis were performed to elucidate mechanistic insights into this electrocatalytic thiolation reaction.

Selective cytotoxicity of marine-derived fungal metabolite (3S,6S)-3,6-dibenzylpiperazine-2,5-dione against cancer cells adapted to nutrient starvation

The cancer cells that are adapted to the hypoxic and nutrient-starved conditions of the tumor microenvironment have become a key target for anticancer therapies. In the course of search for selective cytotoxic substances against cancer cells adapted to nutrient starvation, (3S,6S)-3,6-dibenzylpiperazine-2,5-dione (1) was isolated from culture extract of marine-derived Paecilomyces formous 17D47-2. Compound 1 showed cytotoxic activity on the human pancreatic carcinoma PANC-1 cells adapted to glucose-starved conditions with IC50 value of 28 µM, whereas no effect was observed against PANC-1 cells under general culture conditions up to 1000 µM. Further studies on the mechanism of the selective cytotoxicity of 1 against the glucose-starved PANC-1 cells suggest that it may function via uncoupling of mitochondrial oxidative phosphorylation.

Divergent Synthesis of Bioactive Dithiodiketopiperazine Natural Products Based on a Double C(sp3 )-H Activation Strategy

This article provides a detailed report of our efforts to synthesize the dithiodiketopiperazine (DTP) natural products (-)-epicoccin G and (-)-rostratin A using a double C(sp³ )-H activation strategy. The strategy's viability was first established on a model system lacking the C8/C8' alcohols. Then, an efficient stereoselective route including an organocatalytic epoxidation was secured to access a key bis-triflate substrate. This bis-triflate served as the functional handles for the key transformation of the synthesis: a double C(sp³ )-H activation. The successful double activation opened access to a common intermediate for both natural products in high overall yield and on a multigram scale. After several unsuccessful attempts, this intermediate was efficiently converted to (-)-epicoccin G and to the more challenging (-)-rostratin A via suitable oxidation/reduction and protecting group sequences, and via a final sulfuration that occurred in good yield and high diastereoselectivity. These efforts culminated in the synthesis of (-)-epicoccin G and (-)-rostratin A in high overall yields (19.6 % over 14 steps and 12.7 % over 17 steps, respectively), with the latter being obtained on a 500 mg scale. Toxicity assessments of these natural products and several analogues (including the newly synthesized epicoccin K) in the leukemia cell line K562 confirmed the importance of the disulfide bridge for activity and identified dianhydrorostratin A as a 20x more potent analogue.

Azacoccones F-H, new flavipin-derived alkaloids from an endophytic fungus Epicoccum nigrum MK214079

Three new flavipin-derived alkaloids, azacoccones F-H (1-3), along with six known compounds (4-9) were isolated from the endophytic fungus Epicoccum nigrum MK214079 associated with leaves of Salix sp. The structures of the new compounds were established by analysis of their 1D/2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectroscopy (HRESIMS) data. The absolute configuration of azacoccones F-H (1-3) was determined by comparison of experimental electronic circular dichroism (ECD) data with reported ones and biogenetic considerations. Epicocconigrone A (4), epipyrone A (5), and epicoccolide B (6) exhibited moderate antibacterial activity against Staphylococcus aureus ATCC 29213 with minimal inhibitory concentration (MIC) values ranging from 25 to 50 μM. Furthermore, epipyrone A (5) and epicoccamide A (7) displayed mild antifungal activity against Ustilago maydis AB33 with MIC values of 1.6 and 1.8 mM, respectively. Epicorazine A (8) showed pronounced cytotoxicity against the L5178Y mouse lymphoma cell line with an IC₅₀ value of 1.3 μM.

New Antibacterial Thiodiketopiperazines from the Deep Sea Sediment-Derived Fungus Epicoccum nigrum SD-388

Two new antibacterial thiodiketopiperazine derivatives (TDKPs), 7-dehydroxyepicoccin H and 7-hydroxyeutypellazine F, along with seven known TDKP analogs, were isolated and identified from Epicoccum nigrum SD-388, a deep-sea-sediment-derived fungus. The structures of these compounds were elucidated on the basis of detailed spectroscopic analysis. The absolute configuration of 7-dehydroxyepicoccin H was established by X-ray crystallographic analysis, while 7-hydroxyeutypellazine F was determined by ECD experiment and TDDFT-ECD calculation. The antibacterial activities against human and aquatic pathogens were evaluated. 7-Dehydroxyepicoccin H and 7-hydroxyeutypellazine F displayed inhibitory activities against aquatic pathogens Vibrio vulnificus, V. alginolyticus, and Edwardsiella tarda, with MIC values ranging from 4.0 to 8.0 μg/mL.

Irregularly Bridged Epipolythiodioxopiperazines and Related Analogues: Sources, Structures, and Biological Activities

Epipolythiodioxopiperazines (ETPs) are a class of biologically active fungal secondary metabolites characterized by a bridged polysulfide piperazine ring. Regularly, the sulfide functionality is attached in the α-positions of the dioxopiperazine scaffold. However, ETPs possessing irregular sulfur bridges have rarely been explored. This review summarizes that 83 compounds of this subtype have been isolated and characterized since the discovery of gliovirin in 1982. Herein, particular emphasis is given to the isolation, chemistry, and biological activity of this subtype. For a better understanding, a relevant summary focusing on the source microorganisms and their taxonomy is provided and will help elucidate the fascinating chemistry and biology of these unusual ETPs.

Anti-inflammatory, Antiplatelet Aggregation, and Antiangiogenesis Polyketides from Epicoccum sorghinum: Toward an Understating of Its Biological Activities and Potential Applications

The ethyl acetate extract of an endophyte Epicoccum sorghinum exhibited anti-inflammatory activity at a concentration of <10 μg/mL. By bioassay-guided fractionation, one new compound, named epicorepoxydon A (1), and one unusual bioactive compound, 6-(hydroxymethyl)benzene-1,2,4-triol (6), together with six known compounds, were isolated from E. sorghinum. The structures of all isolates were established by spectroscopic analyses. The relative configuration of 1 was deduced by the NOESY spectrum and its absolute configuration was determined by X-ray single-crystal analysis. The biological activities of all isolates were evaluated using four types of bioassays including cytotoxicity, anti-inflammatory, antiplatelet aggregation, and antiangiogenesis activities. Compounds 4 and 6 showed potent anti-inflammatory activity, compound 2 possessed potent antiplatelet aggregation and antiangiogenesis activities, and compound 6 demonstrated antiangiogenesis activity. This fungal species can cause a human hemorrhagic disorder known as onyalai. In this study, we identified the active components with antiplatelet aggregation and antiangiogenesis activities, which may be related to the hemorrhagic disorder caused by this fungus. Moreover, we proposed a biosynthetic pathway of the isolated polyketide secondary metabolites and investigated their structure-activity relationship (SAR). Our results suggested that E. sorghinum is a potent source of biologically active compounds that can be developed as antiplatelet aggregation and anti-inflammatory agents.

Copper-catalyzed diastereoselective hydrothioetherification of oxa(aza)benzonorbornadienes

A novel copper-catalyzed hydrothioetherification of oxa(aza)bicyclic alkenes with potassium thioacetate and aryl or alkyl iodides to synthesize unsymmetrical thioethers has been developed. Notably, the reaction with complete diastereoselectivity went through a syn-selective addition process to give exo-adducts. In addition, this protocol exhibited high efficiency and good functional group tolerance to afford the target thioethers in moderate to good yields. Based on the results of mechanistic investigations, a plausible mechanism was proposed.

Amphiepicoccins A-J: Epipolythiodioxopiperazines from the Fish-Gill-Derived Fungus Epicoccum nigrum HDN17-88

Ten new epipolythiodioxopiperazines (ETPs), namely, amphiepicoccins A-J (1-10), were isolated from the fish-gill-derived fungus Epicoccum nigrum HDN17-88. Their structures were deduced from extensive spectroscopic data and electronic circular dichroism (ECD) calculations. Amphiepicoccin A (1) which contains an aromatic indole motif is unprecedented among the epicoccin type of ETPs. Compounds 1, 3, and 6 displayed anti-HSV-2 activities, with IC₅₀ values of 70, 64, and 29 μM, respectively (acyclovir as positive control with an IC₅₀ value of 31 μM), while 5 and 6 also revealed inhibitory activity against Bacillus subtilis with minimum inhibitory concentration (MIC) values of 13 and 25 μM, respectively.

A general method for site-selective Csp3-S bond formation via cooperative catalysis

Herein, we report a copper-catalysed site-selective thiolation of Csp³-H bonds of aliphatic amines. The method features a broad substrate scope and good functional group compatibility. Primary, secondary, and tertiary C-H bonds can be converted into C-S bonds with a high efficiency. The late-stage modification of biologically active compounds by this method was also demonstrated. Furthermore, the one-pot preparation of pyrrolidine or piperidine compounds via a domino process was achieved.

Efficient and Divergent Total Synthesis of (-)-Epicoccin G and (-)-Rostratin A Enabled by Double C(sp3)-H Activation

Dithiodiketopiperazines are complex polycyclic natural products possessing a variety of interesting biological activities. Despite their interest, relatively few total syntheses have been completed. We herein report the enantioselective, scalable, and divergent total synthesis of two symmetrical pentacyclic dithiodiketopiperazines, (-)-epicoccin G and (-)-rostratin A. A common intermediate was synthesized on a multigram scale from inexpensive, commercially available starting materials using an enantioselective organocatalytic epoxidation and a double C(sp³)-H activation as key steps, with the latter allowing the efficient simultaneous construction of the two five-membered rings. In addition to the cis,cis-fused target (-)-epiccocin G, the more challenging (-)-rostratin A, possessing two trans ring junctions, was obtained for the first time on a 500 mg scale through the optimization of each step and validation on multigram quantities. Both natural products were synthesized with high overall yields (13-20%). This study should facilitate access to this fascinating and yet understudied family of biologically active natural products.

The Purification, Characterization, and Biological Activity of New Polyketides from Mangrove-Derived Endophytic Fungus Epicoccum nigrum SCNU-F0002

Six new polyketides, including one coumarin (1), two isocoumarins (2 and 3), dihydroradicinin (4), and two benzofuranone derivatives (7 and 8), together with seven known analogues (5–6 and 9–13) were isolated from the culture of the mangrove endophytic fungus Epicoccum nigrum SCNU-F0002. The structures were elucidated on the interpretation of spectroscopic data. The absolute configuration of Compounds 2 and 3 were determined by comparison of their ECD spectra with the data of their analogue dihydroisocoumarins described in the literature. The absolute configuration of 4 was determined by single-crystal X-ray diffraction. All the compounds were screened for their antioxidant, antibacterial, anti-phytopathogenic fungi and cytotoxic activities. Using a DPPH radical-scavenging assay, Compounds 10–13 showed potent antioxidant activity with IC₅₀ values of 13.6, 12.1, 18.1, and 11.7 μg/mL, respectively. In addition, Compounds 6 and 7 showed antibacterial effects against Bacillus subtilis (ATCC 6538), Escherichia coli (ATCC 8739), and Staphylococcus aureus (ATCC 6538), with MIC values in the range of 25–50 μg/mL.

Dithiodiketopiperazine derivatives from endophytic fungi Trichoderma harzianum and Epicoccum nigrum

A new epidithiodiketopiperazine (ETP), pretrichodermamide G (1), along with three known (epi)dithiodiketopiparazines (2-4) were isolated from cultures of Trichoderma harzianum and Epicoccum nigrum, endophytic fungi associated with medicinal plants Zingiber officinale and Salix sp., respectively. The structure of the new compound (1) was established on the basis of spectroscopic data, including 1D/2D NMR and HRESIMS. The isolated compounds were investigated for their antifungal, antibacterial and cytotoxic potential against a panel of microorganisms and cell lines. Pretrichodermamide A (2) displayed antimicrobial activity towards the plant pathogenic fungus Ustilago maydis and the human pathogenic bacterium Mycobacterium tuberculosis with MIC values of 1 mg/mL (2 mM) and 25 µg/mL (50 µM), respectively. Meanwhile, epicorazine A (3) exhibited strong to moderate cytotoxicity against L5178Y, Ramos, and Jurkat J16 cell lines with IC₅₀ values ranging from 1.3 to 28 µM. Further mechanistic studies indicated that 3 induces apoptotic cell death.

The biotechnological potential of Epicoccum spp.: diversity of secondary metabolites

Epicoccum is a genus of ubiquitous fungi typically found in air, in soil, and on decaying vegetation. They also commonly display an endophytic lifestyle and are isolated from diverse plant tissues. The fungi from the genus Epicoccum are mainly known for their use as biocontrol agents against phytopathogens and for their ability to produce many secondary metabolites with potential biotechnological applications, such as antioxidant, anticancer,r and antimicrobial compounds. Among the bioactive compounds produced by Epicoccum spp., epicocconone is a commercially available fluorophore, D8646-2-6 is a patented telomerase inhibitor, and taxol is an anticancer drug originally isolated from Taxus brevifolia. Epicoccum spp. also produces epicolactone, an antimicrobial compound with a unique and complex structure that has aroused considerable interest in the chemical-synthesis community. The main goal of the present review is to discuss the diversity of secondary metabolites produced by Epicoccum spp., their biotechnological applications, and proposed hypothetical biosynthesis. In addition, the use of Epicoccum spp. as biocontrol agents and the pigments produced by these fungi are also discussed.

FeCl3-Catalyzed Regio-Divergent Carbosulfenylation of Unactivated Alkenes: Construction of a Medium-Sized Ring

A FeCl₃-catalyzed regio-divergent carbosulfenylation of unactivated alkenes with electrophilic N-sulfenophthalimides has been developed. This protocol provides a straightforward and efficient access to various medium-sized rings, especially strained 7- and 8-membered carborings with a sulfur atom attached. The endo/exo selectivity in the reaction depends on the atom number of the chain between arene and alkene. Broad substrate scope, high yields, and gram-scale synthesis exemplified the utility and practicability of this protocol. In addition, this methodology can be extended to the carboselenylation of isolated alkenes.

Bis-Indolyl Benzenoids, Hydroxypyrrolidine Derivatives and Other Constituents from Cultures of the Marine Sponge-Associated Fungus Aspergillus candidus KUFA0062

A previously unreported bis-indolyl benzenoid, candidusin D (2e) and a new hydroxypyrrolidine alkaloid, preussin C (5b) were isolated together with fourteen previously described compounds: palmitic acid, clionasterol, ergosterol 5,8-endoperoxides, chrysophanic acid (1a), emodin (1b), six bis-indolyl benzenoids including asterriquinol D dimethyl ether (2a), petromurin C (2b), kumbicin B (2c), kumbicin A (2d), 2″-oxoasterriquinol D methyl ether (3), kumbicin D (4), the hydroxypyrrolidine alkaloid preussin (5a), (3S, 6S)-3,6-dibenzylpiperazine-2,5-dione (6) and 4-(acetylamino) benzoic acid (7), from the cultures of the marine sponge-associated fungus Aspergillus candidus KUFA 0062. Compounds 1a, 2a-e, 3, 4, 5a-b, and 6 were tested for their antibacterial activity against Gram-positive and Gram-negative reference and multidrug-resistant strains isolated from the environment. Only 5a exhibited an inhibitory effect against S. aureus ATCC 29213 and E. faecalis ATCC29212 as well as both methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococci (VRE) strains. Both 1a and 5a also reduced significant biofilm formation in E. coli ATCC 25922. Moreover, 2b and 5a revealed a synergistic effect with oxacillin against MRSA S. aureus 66/1 while 5a exhibited a strong synergistic effect with the antibiotic colistin against E. coli 1410/1. Compound 1a, 2a-e, 3, 4, 5a-b, and 6 were also tested, together with the crude extract, for cytotoxic effect against eight cancer cell lines: HepG2, HT29, HCT116, A549, A 375, MCF-7, U-251, and T98G. Except for 1a, 2a, 2d, 4, and 6, all the compounds showed cytotoxicity against all the cancer cell lines tested.

Structural Diversity and Biological Activities of the Cyclodipeptides from Fungi

Cyclodipeptides, called 2,5-diketopiperazines (2,5-DKPs), are obtained by the condensation of two amino acids. Fungi have been considered to be a rich source of novel and bioactive cyclodipeptides. This review highlights the occurrence, structures and biological activities of the fungal cyclodipeptides with the literature covered up to July 2017. A total of 635 fungal cyclodipeptides belonging to the groups of tryptophan-proline, tryptophan-tryptophan, tryptophan-Xaa, proline-Xaa, non-tryptophan-non-proline, and thio-analogs have been discussed and reviewed. They were mainly isolated from the genera of Aspergillus and Penicillium. More and more cyclodipeptides have been isolated from marine-derived and plant endophytic fungi. Some of them were screened to have cytotoxic, phytotoxic, antimicrobial, insecticidal, vasodilator, radical scavenging, antioxidant, brine shrimp lethal, antiviral, nematicidal, antituberculosis, and enzyme-inhibitory activities to show their potential applications in agriculture, medicinal, and food industry.

Elemental sulfur as a sulfuration agent in the copper-catalyzed C-H bond thiolation of electron-deficient arenes

By utilizing elemental sulfur as the thiolation agent and oxidant, a copper-catalyzed direct C-H bond thiolation of electron-deficient arenes was demonstrated. Various electron-deficient arenes were proved to be suitable for this transformation. Preliminary mechanistic studies indicated that this reaction underwent a radical pathway, in which the trisulfur radical anion (S₃˙^-) might play a vital role. Meanwhile, KIE experiments suggested that C-H bond cleavage was not involved in the rate-determining step.

(±)-Uncarilins A and B, Dimeric Isoechinulin-Type Alkaloids from Uncaria rhynchophylla

(±)-Uncarilins A and B (1a/1b and 2a/2b), two pairs of unusual dimeric isoechinulin-type enantiomers with a symmetric four-membered core, were isolated from Uncaria rhynchophylla driven by LCMS-IT-TOF analyses. Their structures were elucidated by extensive 1D and 2D NMR spectra, X-ray diffraction, and ECD spectroscopic data. (-)-Uncarilin B (2a) showed activities on MT₁ and MT₂ receptors with agonistic rates of 11.26% and 52.44% at a concentration of 0.25 mM.

Eutypellazines A–M, thiodiketopiperazine-type alkaloids from deep sea derived fungus Eutypella sp. MCCC 3A00281

Bioassay and NMR/MS guided fractionation resulted in the isolation of 13 new alkaloids from marine fungus Eutypella sp.

Endophytic fungi associated with Taxus fuana (West Himalayan Yew) of Pakistan: potential bio-resources for cancer chemopreventive agents

CONTEXT

Endophytic fungi, being a prolific source of bioactive secondary metabolites, are of great interest for natural product discovery.

OBJECTIVE

Isolation and partial characterization of endophytic fungi inhabiting the leaves and woody parts of Taxus fuana Nan Li & R.R. Mill. (Taxaceae) and evaluation of biological activity.

MATERIALS AND METHODS

Endophytic fungal isolates were identified by molecular analysis of internal transcribed spacer (ITS) regions of 18S rDNA. Extracts of the endophytic fungi cultured on potato dextrose agar and modified medium were evaluated using cancer chemoprevention bioassays [inhibition of TNF-α-induced NFκB, aromatase and inducible nitric oxide synthase (iNOS); induction of quinone reductase 1 (QR1)] and growth inhibition with MCF-7 cells.

RESULTS

Nine of 15 fungal isolates were identified as belonging to Epicoccum, Mucor, Penicillium, Chaetomium, Paraconiothriym, Plectania or Trichoderma. Five of the 15 extracts inhibited NFκB activity (IC₅₀ values ranging between 0.18 and 17 μg/mL) and five inhibited iNOS (IC₅₀ values ranging between 0.32 and 12.9 μg/mL). In the aromatase assay, only two isolates mediated inhibition (IC₅₀ values 12.2 and 10.5 μg/mL). With QR1 induction, three extracts exhibited significant activity (concentrations to double activity values ranging between 0.20 and 5.5 μg/mL), and five extracts inhibited the growth of MCF-7 cells (IC₅₀ values ranging from 0.56 to 17.5 μg/mL). Six active cultures were derived from woody parts of the plant material.

CONCLUSION

The endophytic fungi studied are capable of producing pharmacologically active natural compounds. In particular, isolates derived from the wood of Taxus fuana should be prioritized for the isolation and characterization of bioactive constituents.