Prenylemestrins A and B: Two Unexpected Epipolythiodioxopiperazines with a Thioethanothio Bridge from Emericella sp. Isolated by Genomic Analysis

Bioactivity-Based Molecular Networking-Guided Isolation of Epicolidines A-C from the Endophytic Fungus Epicoccum sp. 1-042

Bioactivity-based molecular networking-guided fractionation enabled the isolation of three new polycyclic tetramic acids bearing cis-decalin, epicolidines A-C (1-3), along with one known compound, PF 1052 (4), from the endophytic fungus Epicoccum sp. 1-042 collected in Tibet, China. Their structures were assigned on the basis of extensive spectroscopic data, partial hydrolysis, advanced Marfey's method, quantum chemistry calculations, and X-ray diffraction analysis. Compounds 2-4 displayed promising activities against Gram-positive bacteria in vitro. Particularly, compound 4 displayed remarkable potential against vancomycin-resistant Enterococcus faecium (VRE) with an MIC value of 0.25 μg/mL, lower than the MIC (0.5 μg/mL) of the antibiotic combination quinupristin/dalfopristin (Q/D). In a further in vivo study, compound 4 increased the survival rate to 100% in the VRE-G. mellonella infection model at a concentration of 10 mg/kg.

Quinomycins with an unusual N-methyl-3-methylsulfinyl-alanine residue from a Streptomyces sp

Four new echinomycin congeners, quinomycins M-P (1-4) were isolated from the cultures of the soil-derived Streptomyces sp. CPCC205575. The planar structures were determined by comprehensive analyses of NMR and HRESIMS/MS data. The absolute configurations were elucidated by the advanced Marfey's method combined with biosynthetic gene analysis. Compounds 1-4 represent the first examples of quinomycin-type natural products with the sulfur atom at the N,S-dimethylcysteine residue oxidized as a sulfoxide group forming the unusual N-methyl-3-methylsulfinyl-alanine residue. Bioassay results revealed that the oxidation of the sulfur atom at the Cys or Cys' residues led to dramatic decrease of cytotoxicity and antimicrobial activity.

Unexpected Noremestrin with a Sulfur-Bearing 15-Membered Macrocyclic Lactone from Emericella sp. 1454

Two previous unreported epipolythiodioxopiperazines of the emestrin family, namely, noremestrin A (1) and secoemestrin E (2), were successfully isolated from the fungal source Emericella sp. 1454. Employing comprehensive spectroscopic techniques, such as high-resolution electrospray ionization mass spectrometry, infrared, and nuclear magnetic resonance (NMR), along with NMR and electronic circular dichroism calculations, the chemical structures of compounds 1 and 2 were elucidated. Particularly noteworthy is the distinctive nature of noremestrin A, representing the inaugural instance of a noremestrin variant incorporating a sulfur-bearing 15-membered macrocyclic lactone moiety. Compounds 1 and 2 exhibited weak cytotoxic activities against the human chronic myelocytic leukemia cell lines MEG-01 and K562.

Cytotoxic Epipolythiodioxopiperazines from the Deep-Sea-Derived Fungus Exophiala mesophila MCCC 3A00939

Four new aranotin-type epipolythiodioxopiperazines, graphiumins K-N (1-4), along with four known analogues (5-8), were isolated from the deep-sea-derived fungus Exophiala mesophila MCCC 3A00939. Their structures were elucidated by detailed interpretation of NMR and mass spectrometric data. The absolute configuration of the isolates was deduced by a single-crystal X-ray diffraction analysis and the comparisons of experimental electronic circular dichroism (ECD) data with calculated ECD spectra. Graphiumins K (1) and L (2) exhibited cytotoxic activities against the K562, H69AR, and MDA-MB-231 cancer cells with IC50 values ranging from 2.3 to 5.9 μM.

Nocaviogua A and B: two lipolanthines from root-nodule-associated Nocardia sp

Nocaviogua A (1) and B (2), two lipolanthines featuring a non-canonical avionin (Avi)-containing macrocycle and a long acyl chain, were identified from the mutualistic actinomycete Nocardia sp. XZ19_369, which was isolated from the nodules of sea buckthorn collected in Tibet. Their planar structures were elucidated via extensive analyses of 1D and 2D NMR, as well as HRMS data. The absolute configurations were fully elucidated by advanced Marfey's analysis and GIAO NMR calculations, representing the first time that the configurations of this family of lipolanthines have been determined. Nocaviogua A (1) exhibited weak cytotoxicity against human chronic uveal melanoma cells (UM92-1), non-small cell lung cancer (NCI-H2170), and breast cancer (MDA-MB-231). Our work provides valuable information on this burgeoning class of lipolanthines for further investigations.

Four Undescribed Pyranones from the Scutellaria formosana-Derived Endophytic Fungi Ascomycota sp. FAE17

Four undescribed pyranone derivatives, named ascomycopyrones A-D (1-4), as well as one known analogue simplicilopyrone (5) (this is the first study to report the absolute configuration), were isolated from the endophytic fungus Ascomycota sp. FAE17 derived from the flowers of Scutellaria formosa. The structures of these pyranones were identified by comprehensive spectroscopic and MS analyses, and the absolute configurations were determined by their experimental and quantum chemical electronic circular dichroism (ECD) calculations. All isolated compounds were tested for various bioactivities, including antibacterial, cytotoxic activity, and NO inhibitory activity. Unfortunately, none of the compounds showed significant bioactivities.

Quadristerols A-G: Seven undescribed ergosterols from Aspergillus quadrilineata

Quadristerols A-G, seven undescribed ergosterols, were obtained from Aspergillus quadrilineata. Their structures and absolute configurations were determined based on HRESIMS, NMR, quantum-chemical calculations, and single-crystal X-ray diffraction analyses. Quadristerols A-G featured ergosterol skeletons with different attachments; quadristerols A-C were three diastereoisomers possessing a 2-hydroxy-propionyloxy group at C-6, and quadristerols D-G were two pairs of epimers with a 2,3-butanediol group at C-6. All of these compounds were evaluated for their immunosuppressive activities in vitro. Quadristerols B and C showed excellent inhibitory effects against concanavalin A-induced T lymphocyte proliferation with IC₅₀ values of 7.43 and 3.95 μM, respectively, and quadristerols D and E strongly inhibited lipopolysaccharide-induced B lymphocyte proliferation with IC₅₀ values of 10.96 and 7.47 μM, respectively.

Natural epidithiodiketopiperazine alkaloids as potential anticancer agents: Recent mechanisms of action, structural modification, and synthetic strategies

Cancer has become a grave health crisis that threatens the lives of millions of people worldwide. Because of the drawbacks of the available anticancer drugs, the development of novel and efficient anticancer agents should be encouraged. Epidithiodiketopiperazine (ETP) alkaloids with a 2,5-diketopiperazine (DKP) ring equipped with transannular disulfide or polysulfide bridges or S-methyl moieties constitute a special subclass of fungal natural products. Owing to their privileged sulfur units and intriguing architectural structures, ETP alkaloids exhibit excellent anticancer activities by regulating multiple cancer proteins/signaling pathways, including HIF-1, NF-κB, NOTCH, Wnt, and PI3K/AKT/mTOR, or by inducing cell-cycle arrest, apoptosis, and autophagy. Furthermore, a series of ETP alkaloid derivatives obtained via structural modification showed more potent anticancer activity than natural ETP alkaloids. To solve supply difficulties from natural resources, the total synthetic routes for several ETP alkaloids have been designed. In this review, we summarized several ETP alkaloids with anticancer properties with particular emphasis on their underlying mechanisms of action, structural modifications, and synthetic strategies, which will offer guidance to design and innovate potential anticancer drugs.

Neuropyrones A-E, five undescribed α-pyrone derivatives with tyrosinase inhibitory activity from the endophytic fungus Neurospora dictyophora WZ-497

Five undescribed α-pyrone derivatives, named neuropyrones A-E, were isolated from the endophytic fungus Neurospora dictyophora WZ-497 derived from the stems of Aster tataricus L. f. The structures of these α-pyrones with absolute configurations were determined by comprehensive spectroscopic analysis and computational calculations. All isolated compounds were tested for various bioactivities, including tyrosinase inhibitory activity. The results showed that neuropyrones A-C displayed potent inhibitory effects on tyrosinase with IC₅₀ values of 0.38 ± 0.07, 0.49 ± 0.06, and 0.12 ± 0.01 mM, respectively, which were comparable to that of the positive control, kojic acid (IC₅₀ = 0.14 ± 0.021 mM). A molecular docking study revealed the interaction between 3 and the His263, His85, Val283, Asn260, Phe264, and Val248 residues of tyrosinase.

Cytotoxic hexadepsipeptides and anti-coronaviral 4-hydroxy-2-pyridones from an endophytic Fusarium sp

Three new hexadepsipeptides (1-3), along with beauvericin (4), beauvericin D (5), and four 4-hydroxy-2-pyridone derivatives (6-9) were isolated from the endophytic fungus Fusarium sp. CPCC 400857 that derived from the stem of tea plant. Their structures were determined by extensive 1D and 2D NMR, and HRESIMS analyses. The absolute configuration of hexadepsipeptides were elucidated by the advanced Marfey's method and chiral HPLC analysis. Compounds 4, and 7-9 displayed the cytotoxicity against human pancreatic cancer cell line, AsPC-1 with IC₅₀ values ranging from 3.45 to 29.69 μM, and 7 and 8 also showed the antiviral activity against the coronavirus (HCoV-OC43) with IC₅₀ values of 13.33 and 6.65 μM, respectively.

Asperemestrins A-D, Emestrin Hybrid Polymers with Bridged Skeletons from the Endophytic Fungus Aspergillus nidulans

Four emestrin hybrid polymers, asperemestrins A-D (1-4, respectively), were isolated from the fungus Aspergillus nidulans. Asperemestrins A-C are the first examples of emestrin-sterigmatocystin heterodimers bearing a 7/5/6/6/5/5/6/6/6 nonacyclic system with a 2,5-diazabicyclo[2.2.2]octane-3,6-dione core, while asperemestrin D features an unprecedented 2,15-dithia-17,19-diazabicyclo[14.2.2]icosa-4,8-diene-12,18,20-trione core skeleton. Their structures were determined by extensive spectroscopic data, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Asperemestrin B showed moderate cytotoxicity against cancer cell lines, including SU-DHL-2, HEPG2, and HL-60.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as hyjapone A from Hypericum japonicum.