Sesquiterpenoids and Cytochalasins with Immunosuppressive Activity from Sonchus wightianus.

The plant species, Sonchus wightianus DC., was historically used in China for both medicinal and dietary uses. In present study, seven new guaiane sesquiterpenoids (1-7) and one cytochalasin (8), along with five known guaianes (9-13) and two known cytochalasins (14 and 15), were isolated from the whole plants of S. wightianus. These guaianes showed structural variations in the substituents at C-8 and/or C-15, and compounds 6 and 7 are two sesquiterpenoid glycoside derivatives. Their structures were determined by extensive analysis of spectroscopic, electronic circular dichroism, and X-ray diffraction data, and chemical method. Biological tests revealed that compounds 5 and 8 are potent and selective immunosuppressive reagents.

Chae-type cytochalasans from coculture of Aspergillus flavipes and Chaetomium globosum.

Cocultivation of the high cytochalasan-producing fungi Aspergillus flavipes and Chaetomium globosum resulted in the isolation of 11 undescribed Chae-type cytochalasans. Their structures were determined by spectroscopic data and NMR data calculations. Asperchaetoglobin A (1) was the first Chae-type cytochalasan possessing an unprecedented nitrogen bridge between C-17 and C-20 to generate a surprising 5/6/12/5 multiple ring system; asperchaetoglobins B and C (2 and 3) displayed higher oxidation with an additional epoxide at the thirteen-member ring; asperchaetoglobin D (4) was the second Chae-type cytochalasin featuring a 5/6/12 tricyclic ring system. The cytotoxic activities against five human cancer cell lines and antibacterial activities against Staphylococcus aureus and Colon bacillus of selected compounds were evaluated in vitro.

Boerechalasins A-G, cytochalasans from the fungus Boeremia exigua with anti-inflammatory and cytotoxic activities.

Seven previously undescribed cytochalasans, namely, boerechalasins A-G, together with one analogue, were characterized from the solid culture of the fungus Boeremia exigua. Their structures and absolute configurations were elucidated on the basis of extensive spectroscopic analysis as well as electronic circular dichroism calculations. Remarkably, boerechalasin F possessed an unusual sulfoxide moiety that might be derived from methionine, while boerechalasin G had an unusual 5-methylcyclohexane-1,2,3-triol substituent at N-2 position. Boerechalasins A and E exhibited inhibitory activities against nitric oxide production in LPS-induced RAW264.7 macrophages with IC50 values of 21.9 and 5.7 µM, respectively. Boerechalasin F displayed cytotoxicity against human MCF‒7 cells with an IC50 value of 22.8 µM.

Cytochalasans produced by Xylaria karyophthora and their biological activities.

The recent description of the putative fungal pathogen of greenheart trees, Xylaria karyophthora (Xylariaceae, Ascomycota), prompted a study of its secondary metabolism to access its ability to produce cytochalasans in culture. Solid-state fermentation of the ex-type strain on rice medium resulted in the isolation of a series of 19,20-epoxidated cytochalasins by means of preparative high-performance liquid chromatography (HPLC). Nine out of 10 compounds could be assigned to previously described structures, with one compound being new to science after structural assignment via nuclear magnetic resonance (NMR) assisted by high-resolution mass spectrometry (HRMS). We propose the trivial name "karyochalasin" for the unprecedented metabolite. The compounds were used in our ongoing screening campaign to study the structure-activity relationship of this family of compounds. This was done by examining their cytotoxicity against eukaryotic cells and impact on the organization of networks built by their main target, actin-a protein indispensable for processes mediating cellular shape changes and movement. Moreover, the cytochalasins' ability to inhibit the biofilm formation of Candida albicans and Staphylococcus aureus was examined.

Cytochalasans with Inhibitory Activity against NPC1L1 from the Endophytic Fungus Chaetomium nigricolor F5.

Mass spectrometry (MS)-based metabolic profiling of the endophytic fungus Chaetomium nigricolor F5 guided the isolation of five novel cytochalasans, chamisides B-F (1-5), and two known ones, chaetoconvosins C and D (6 and 7). Their structures including stereochemistry were unambiguously determined by MS, nuclear magnetic resonance, and single-crystal X-ray diffraction analyses. Compounds 1-3 share a new 5/6/5/5/7-fused pentacyclic skeleton in cytochalasans and are appropriately proposed to be the key biosynthetic precursors of co-isolated cytochalasans with a 6/6/5/7/5, 6/6/5/5/7, or 6/6/5 ring system. Remarkably, compound 5 with a relatively flexible side chain showed promising inhibition activity against the cholesterol transporter protein Niemann-Pick C1-like 1 (NPC1L1), expanding the function of cytochalasans.

New cytochalasans from an endophytic Xylaria species associated with Costa Rican Palicourea elata (Rubiaceae).

Four new leucine-derived cytochalasans, possessing a 5,6,5,8-ring (1) and a 5,6,11-ring core (2-4), were isolated from a cultivated endophytic fungus Xylaria sp. strain WH2D4 (Xylariaceae). This fungus was isolated from leaves of the neotropical tree species Palicourea elata (Sw.) Borhidi (Rubiaceae) collected in Costa Rica. The chemical structures were determined by employing IR, MS as well as 1D- and 2D-NMR experiments. The stereochemistry at C-15 of compound 4 was determined by quantum calculations. The isolated compounds did not affect germination and growth of Trichoderma reesei and the opportunistic human fungal pathogen T. longibrachiatum.

Cytochalasans from the endophytic fungus Diaporthe ueckerae associated with the fern Pteris vittata.

Six previously undescribed cytochalasans, ueckerchalasins A-E and 4'-hydroxycytochalasin J3, together with eight known congeners, were isolated from solid cultures of the endophytic fungus Diaporthe ueckerae SC-J0123 which was originally isolated from the leaves of Pteris vittata L. Their structures were elucidated by extensive spectroscopic analysis, single-crystal X-ray diffraction, and theoretical simulations of ECD spectra and 13C NMR shifts. Ueckerchalasins A-C have a carbon-carbon bridge between C-14 and C-20, forming a rare 5/6/6/7-fused heterocyclic core. Ueckerchalasins C and D displayed selective activity against human carcinoma HeLa and HepG2 cells. Ueckerchalasins C was also active against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA).

New Cytochalasin Derivatives from Deep-Sea Cold Seep-Derived Endozoic Fungus Curvularia verruculosa CS-129.

Two new antimicrobial cytochalasin derivatives, 6ß,7ß-epoxydeoxaphomin C (1) and 12-hydroxydeoxaphomin C (2), a new natural occurring product 24-nor-cytochalasin B (3), together with two related known analogs (4-5) were isolated and identified from an endozoic fungus Curvularia verruculosa CS-129, isolated from the deep-sea squat lobster Shinkaia crosnieri which was collected in cold seep region of south China sea. The structures of new compounds were elucidated on the basis of detailed spectroscopic analysis and ECD calculation. The spectroscopic data of 24-nor-cytochalasin B (3) were reported for the first time. All compounds were tested for their antibacterial activities against human and aquatic pathogenic bacteria.

Cytotoxic Bromine- and Iodine-Containing Cytochalasins Produced by the Mangrove Endophytic Fungus Phomopsis sp. QYM-13 Using the OSMAC Approach.

Twelve new cytochalasins, phomopchalasins D-O (1-3, 5-12, and 14), including one brominated (2) and two iodinated cytochalasins (3 and 6), together with six known analogues (4, 13, and 15-18) were isolated from the mangrove-derived fungus Phomopsis sp. QYM-13 treated with 3% NaBr or 3% KI in potato liquid medium. Their structures and absolute configurations were established by extensive spectroscopic analysis (1D and 2D NMR, HRESIMS), electronic circular dichroism calculations, and a single-crystal X-ray diffraction experiment. Compounds 3 and 6 represent the first iodinated cytochalasins. Compounds 2, 15, 17, and 18 exhibited significant cytotoxicity against human cancer cell line MDA-MB-435 with IC50 values ranging from 0.2 to 8.2 µM.

Cytochalasins from coastal saline soil-derived fungus Aspergillus flavipes RD-13 and their cytotoxicities.

Chemical investigation of coastal saline soil-derived fungus Aspergillus flavipes RD-13 led to the isolation of two new seco-cytochalasins (1) and (2) along with nine known analogs. Their structures were elucidated by comprehensive spectral analysis, and the absolute configurations of these two new ones were determined through Rh2(OCOCF3)4-induced CD experiment and chemical interconversions. Moreover, the absolute configuration of a known compound named cytochalasins Z18 (3) was also determined for the first time. Structurally, compounds 1, 2 and 3 were the open ring derivatives of compounds 5, 8, and 4, respectively. All compounds were evaluated for their cytotoxic activities on A549, H1299 and H520 cells and 4 exhibited the strongest inhibitory activities towards the above cell lines with IC50 values of 0.15, 0.23 and 0.43 µg/mL, respectively. Preliminary structure-activity relationship analysis suggested the importance of macrocyclic ring in cytochalasins to confer cytotoxicity.

Berberine bridge enzyme-like oxidase-catalysed double bond isomerization acts as the pathway switch in cytochalasin synthesis.

Cytochalasans (CYTs), as well as their polycyclic (pcCYTs) and polymerized (meCYTs) derivatives, constitute one of the largest families of fungal polyketide-nonribosomal peptide (PK-NRP) hybrid natural products. However, the mechanism of chemical conversion from mono-CYTs (moCYTs) to both pcCYTs and meCYTs remains unknown. Here, we show the first successful example of the reconstitution of the CYT core backbone as well as the whole pathway in a heterologous host. Importantly, we also describe the berberine bridge enzyme (BBE)-like oxidase AspoA, which uses Glu538 as a general acid biocatalyst to catalyse an unusual protonation-driven double bond isomerization reaction and acts as a switch to alter the native (for moCYTs) and nonenzymatic (for pcCYTs and meCYTs) pathways to synthesize aspochalasin family compounds. Our results present an unprecedented function of BBE-like enzymes and highly suggest that the isolated pcCYTs and meCYTs are most likely artificially derived products.

TRAIL-sensitizing Cytochalasins from the Endophytic Fungus Phoma multirostrata.

Seven undescribed cytochalasins, multirostratins K - Q (2: -8: ), together with one known analogue, cytochalasin Z3 (1: ), were isolated from the culture of Phoma multirostrata XJ-2-1, an endophytic fungus obtained from the root of Parasenecio albus. Their structures with absolute configurations were determined by 1D and 2D NMR, high-resolution electrospray ionization mass spectrometry (HRESIMS), electronic circular dichroism (ECD), single-crystal X-ray crystallography, and chemical methods. The structure of ascochalasin was revised from Δ 13 to Δ 21 by detailed analysis of the NMR data and by comparison with the data for 7: . In a TRAIL (tumor necrosis factor related apoptosis inducing ligand)-resistance-overcoming experiment, co-treatment of 2: or 6: with TRAIL reduced the cell viability of A549 cells by 30.3% and 27.5% at 10 µM, respectively.

Rare cytochalasans isolated from the mangrove endophytic fungus Xylaria arbuscula.

Four new cytochalasans, arbuschalasins A-D (1-4), along with thirteen known analogues (5-17), were isolated from the solid rice medium of endophytic fungus Xylaria arbuscula. Arbuschalasins A-B feature a rare 5/6/6/6 fused ring system while arbuschalasin D was characterized as the first example of natural cytochalasans that possesses a 5/5/11 fused scaffold. The structures of 1-4 were assigned by spectroscopic data, with their absolute structures being determined by electronic circular dichroism (ECD) calculations. All of the isolates were evaluated against the human colorectal adenocarcinoma cell lines (HCT15). Compounds 6 and 7 showed significant inhibitory effects (IC50 values were 13.5 and 13.4 µM, respectively), being more active than those of the positive control, fluorouracil (103.1 µM).

Cytochalasan Alkaloids as TRAIL Sensitizers from an Endophytic Fungus Chaetomium sp.

Two new cytochalasans with a rare 6/6/5/5/7 pentacyclic ring system, named chaetoconvosins C-D (1: -2: ), together with two known congeners (3: -4: ), were isolated from the fermentation of an endophytic fungus, Chaetomium sp. SG-01, harbored in the fibrous roots of Schisandra glaucescens Diels. Their structures including the absolute configuration were elucidated by extensive spectroscopic (HRESIMS, NMR, and ECD) and X-ray crystallographic analyses. The TRAIL-resistance-overcoming activity of 1: -4: in a TRAIL-resistant HT29 colorectal cancer cell line was evaluated, which revealed that co-treatment of 1: -4: at 50 µM with TRAIL (150 ng/mL) reduced the HT29 cell viability by 19.0%, 24.1%, 17.9%, and 15.5%, respectively, compared to treatment with 1: -4: alone.

Armochaetoglasins J and K: new cytochalasans from Chaetomium globosum.

Two novel cytochalasans, armochaetoglasin J (1) and armochaetoglasin K (2), along with 14 known analogues (3-16) were isolated from Chaetomium globosum. Their structures were elucidated by HRESIMS, NMR spectroscopy, single-crystal X-ray crystallography, and ECD spectra. Armochaetoglasins J and K were found to be inactive against the HepG2, HT-29, K562, HL-60, and A549 cancer cell lines.

Rubichaetoglobin A, a new cytochalasan alkaloid isolated from the plant endophytic fungus Chaetomium tectifimeti S104.

Rubichaetoglobin A (1), a new cytochalasan alkaloid, together with nine closely related known ones (2-10), were isolated from the ethyl acetate extracts of the endophytic fungus Chaetomium tectifimeti S104 harbored in the root of Rubia podantha Diels. Their structures were elucidated based on comprehensive spectroscopic analysis. All isolated compounds were tested for cytotoxic, antibacterial, and nitric oxide inhibitory activities. The results showed that 2, 4, and 5 possessed moderate cytotoxicity against MDA-MB-231 cells with the IC50 values of 19.14, 11.43, and 10.27 µM, respectively.

Cytochalasin Derivatives from the Endozoic Curvularia verruculosa CS-129, a Fungus Isolated from the Deep-Sea Squat Lobster Shinkaia crosnieri Living in the Cold Seep Environment.

A new cytochalasin dimer, verruculoid A (1), three new cytochalasin derivatives, including 12-nor-cytochalasin F (2), 22-methoxycytochalasin B6 (3), and 19-hydroxycytochalasin B (4), and 20-deoxycytochalasin B (5), a synthetic product obtained as a natural product for the first time, together with four known analogues (6-9), were isolated and identified from the culture extract of Curvularia verruculosa CS-129, an endozoic fungus obtained from the inner fresh tissue of the deep-sea squat lobster Shinkaia crosnieri, which was collected from the cold seep area of the South China Sea. Structurally, verruculoid A (1) represents the first cytochalasin homodimer containing a thioether bridge, while 12-nor-cytochalasin F (2) is the first 12-nor-cytochalasin derivative. Their structures were elucidated by detailed interpretation of the NMR spectroscopic and mass spectrometric data. X-ray crystallographic analysis and ECD calculations confirmed their structures and absolute configurations. Compound 1 displayed activity against the human pathogenic bacterium Escherichia coli (MIC = 2 µg/mL), while compounds 4, 8, and 9 showed cytotoxicity against three tumor cell lines (HCT-116, HepG-2, and MCF-7) with IC50 values from 5.2 to 12 µM. The structure-activity relationship was briefly discussed.

Pentacyclic Cytochalasins and Their Derivatives from the Endophytic Fungus Phomopsis sp. xz-18.

Eight new cytochalasins 1-8 and ten known analogs 9-18 were isolated from the endophytic fungus Phomopsis sp. xz-18. The planar structures of the cytochalasins were determined by HR-ESI-MS and NMR analysis. Compounds 1, 2, 9 and 10 were 5/6/6/7/5-fused pentacyclic cytochalasins; compounds 3 and 4 had conjugated diene structures in the macrocycle; and compound 6 had a ß,γ-unsaturated ketone. The absolute configuration of 6 was confirmed for the first time by the octant rule. The acid-free purification process proved that the pentacyclic system was a natural biosynthetic product and not an acid-mediated intramolecular cyclized artifact. The new compounds did not exhibit activities against human cancer cell lines in cytotoxicity bioassays or antipathogenic fungal activity, but compounds 1, 3 and 4 showed moderate antibacterial activity in disk diffusion assays.

Zopfiellasins A-D, Two Pairs of Epimeric Cytochalasins from Kiwi-Associated Fungus Zopfiella sp. and Their Antibacterial Assessment.

In our continuous search for antibacterial agents against Pseudomonas syringae pv. actinidiae (Psa) from kiwi-associated fungi, two pairs of epimeric cytochalasins, zopfiellasins A-D (1-4), were characterized from the fungus Zopfiella sp. The structures were established on the basis of spectroscopic data analysis, while the absolute configurations were determined by single-crystal X-ray diffraction. Compounds 1 and 3 exhibited antibacterial activity against Psa with MIC values of 25 and 50 µg/mL, respectively. This is the first report of anti-Psa activity of cytochalasin derivatives.

New Cytotoxic Cytochalasans from a Plant-Associated Fungus Chaetomium globosum kz-19.

Four new cytochalasans, phychaetoglobins A-D (1-4), together with twelve known cytochalasans (5-16), were isolated from a mangrove-associated fungus Chaetomium globosum kz-19. The new structures were elucidated on the basis of extensive 1D and 2D NMR, HR ESIMS spectroscopic analyses, and electronic circular dichroism (ECD) calculations. The absolute configuration of 2 was established by application of Mosher's method. Compounds 4-8 exhibited moderate cytotoxicities against A549 and HeLa cell lines with the IC50 values less than 20 µM.