Neopetromin, a Cyclic Tripeptide with a C-N Cross-Link, from the Marine Sponge Neopetrosia sp., That Causes Vacuole Fragmentation in Tobacco BY-2 Cells.

HPLC-MS analysis revealed the presence of an unreported peptide in the extract of the marine sponge Neopetrosia sp. Its structure was determined as a tripeptide, named neopetromin (1), composed of two tyrosine and one tryptophan residues with a heteroaromatic C-N cross-link between side chains. The absolute configuration of amino acids was determined using Marfey's method after ozonolysis and hydrolysis of 1. Compound 1 promoted vacuole fragmentation in an actin-independent manner in tobacco BY-2 cells.

A new linear peptide, higapeptin, isolated from the mud flat-derived fungus Acremonium persicinum inhibits mitochondrial energy metabolism.

A combination of LC-MS/MS and feature-based molecular networking analyses led to the isolation of a new adenopeptin analog, higapeptin (1), and four known peptides, adenopeptin (2), adenopeptins B and C (3 and 4), and acremopeptin (5), from the rice culture of the fungus Acremonium persicinum (18F04103) isolated from a mud flat of the Ariake Sea in Kyushu, Japan. The structure of 1 was determined by NMR and MS/MS fragmentation analyses. The absolute configuration of the constituent amino acids was determined by Marfey's analysis after acid hydrolysis. The C-terminal residue was synthesized, and its absolute configuration was established by Marfey's analysis. Compounds 1 and 2 were found to inhibit mitochondrial energy metabolism, similar to efrapeptin D (6), a known mitochondrial ATPase inhibitor.

Syrosingopine Enhances 20S Proteasome Activity and Degradation of α-Synuclein.

Cellular proteins are degraded by the 26S proteasome in the ubiquitin-proteasome system in an ATP-dependent manner, whereas intrinsically disordered proteins (IDPs) are degraded by the 20S proteasome independent of ATP and ubiquitin. The accumulation and aggregation of IDPs are considered to be the etiology of neurodegenerative diseases. Notably, the 20S proteasome has a cylindrical structure, and its gate on the α-ring is closed in the inactive form. The compounds that open the gate promote the degradation of IDPs and prevent their accumulation, and therefore, such compounds may be promising therapeutic agents for neurodegenerative diseases. After screening the Prestwick Phytochemical Library, several yohimbine-type and ergot alkaloids were identified that enhance the 20S proteasome activity. Among them, syrosingopine was the most potent activator of the 20S proteasome and enhanced the degradation of fluorogenic substrates and α-synuclein, an IDP. Furthermore, in HeLa cells, syrosingopine enabled the binding of a membrane-permeable fluorescent probe to the catalytic site of the 20S proteasome by opening the gate.

Akanthomins A-C, aphidicolin analogs from a fungus Akanthomyces sp., that inhibit cell cycle.

Natural products that inhibit cell cycle progression may have potential as anticancer agents. In this study, cell cycle inhibition of microbial culture extracts was screened by fluorescent images using HeLa/Fucci2 cells. The culture extract of a fungus, Akanthomyces sp., inhibited the cell cycle progression at the S/G2/M phases, and bioassay-guided fractionation of the extract afforded three previously undescribed aphidicolin derivatives, namely akanthomins A-C, and an undescribed chromone glycoside, specifically 9-hydroxyeugenetin 9-O-ß-d-(4-O-methyl)glucopyranoside, in addition to aphidicolin. The chemical structures of these compounds were elucidated by spectroscopic analysis and chemical derivatization. Using a flow cytometer, akanthomin A and aphidicolin were found to inhibit cell cycle progression at the S phase.

Aaptocarbamates A-G, chlorinated terpene carbamates with antiosteoclastogenic activities from the marine sponge Aaptos sp.

Six undescribed chlorinated sesquiterpene carbamates, aaptocarbamates A-F, and a chlorinated tris-norsesquiterpene carbamate, aaptocarbamate G, were isolated from the marine sponge Aaptos sp. collected in Indonesia. Aaptocarbamates D-F and G possess tetrahydrofurans and a tetrahydrofuranone, respectively. The relative configurations of the tetrahydrofuran units were determined by the NOE correlations and DFT-based calculation of the 13C chemical shifts. This is the first time that chlorinated terpene carbamates have been reported from natural sources. Various aaptamine derivatives have been reported from the Aaptos sponges so far, the isolation of chlorinated terpene carbamates is very rare. Aaptocarbamates A, B, and D showed 60% inhibition of the RANKL-induced formation of multinucleated osteoclasts in RAW264 macrophages at 20 µM.

A monoacylglyceryltrimethylhomoserine, 21F121-A, containing a branched acyl group from Penicillium glaucoroseum.

A new monoacylglyceryltrimethylhomoserine, 21F121-A (1), was isolated from the culture of Penicillium glaucoroseum (21F00121) by LCMS-guided purification. The structure was elucidated by NMR and mass spectrometries. The absolute configuration of the homoserine moiety was analyzed by the ECD spectrum after acid hydrolysis, and the S-configuration of the glycerol moiety was determined based on the spectrum of the 1,2-dibenzoyl derivative after acid hydrolysis. Although a variety of diacylglyceryltrimethylhomoserine is distributed in lower plants and fungi, a limited number of studies on monoacyl derivatives have been reported. This is the fourth sample of monoacylglyceryltrimethylhomoserine discovered from a natural source, and the second sample isolated from a fungus. Compound 1 contains an unusual branched pentaene chain attached at the sn-1 position of glycerol and weakly inhibited the growth of HCT116 cells.

Divergent Total Syntheses of Hetero-Oligomeric Iridoid Glycosides.

Divergent total syntheses of the hetero-oligomeric iridoid glycosides mainly found in Dipsacus asper were achieved. Thus, loganin (1), which is important as a monomer unit, was efficiently synthesized by stereoselective reductive cyclization using secologanin (2) as a substrate. Sequential condensation reactions of derivatives of 1 and 2 as monomer units led to the first enantioselective total syntheses of the heterooligomers cantleyoside, (E)-aldosecologanin, dipsaperine, (3R, 5S)-5-carboxyvincosidic acid 22-loganin ester, and dipsanoside A.

Arteperoxides A-C, tris-normonoterpene-sesquiterpene conjugates with peroxide-bridges from Artemisia judaica exhibiting antiosteoclastogenic activity.

Antiosteoclastogenic-guided screening was conducted with 120 extracts of the medicinal plants collected in Egypt that led to the selection of Artemisia judaica L. (Asteraceae). Three undescribed davanone-related terpenoids, arteperoxides A-C, were isolated from the extract with two known derivatives, hydroxydavanone and davana acid. Structural analysis revealed that arteperoxides A-C were tris-normonoterpene-sesquiterpene conjugates with peroxide bridges. Although davanone derivatives with peroxides, such as a hydroperoxyl and peroxyhemiketal groups, have been isolated from Artemisia species, arteperoxides A-C are the first variations observed to contain peroxide bridges between two terpene-derived units. The absolute configurations of arteperoxides A and B were studied based on their spectroscopic data compared with those of the semisynthetic analogs that have ether linkages. The natural and synthetic compounds were tested for the antiosteoclastogenic activity, and arteperoxide C and hydroxydavanone were more potent than other compounds at 20 µM.

Combinatorial screening for therapeutics in ATTRv amyloidosis identifies naphthoquinone analogues as TTR-selective amyloid disruptors.

Hereditary ATTR amyloidosis is caused by the point mutation in serum protein transthyretin (TTR) that destabilizes its tetrameric structure to dissociate into monomer. The monomers form amyloid fibrils, which are deposited in peripheral nerves and organs, resulting in dysfunction. Therefore, a drug that dissolves amyloid after it has formed, termed amyloid disruptor, is needed as a new therapeutic drug. Here, we first established a high throughput screening system to find TTR interactors from the LOPAC1280 compound library. Among the hit compounds, thioflavin T-based post-treatment assay determined lead compounds for TTR amyloid disruptors, NSC95397 and Gossypol, designated as B and R, respectively. Because these compounds have naphthoquinone-naphthalene structures, we tested 100 naphthoquinone derivatives, and found 10 candidate compounds that disrupted TTR amyloid. Furthermore, to determine whether these 10 compounds are selective for TTR amyloid, we evaluated them against beta-amyloid (Aß1-42). We found two compounds that were selective for TTR and did not disrupt Aß-derived amyloid. Therefore, we succeeded in identifying TTR-selective amyloid disruptors, and demonstrated that naphthoquinone compounds are useful structures as amyloid disruptors. These findings contribute to the on-going efforts to discover new therapeutic tools for TTR amyloidosis.

Cyclopsammocinamides A and B, Enantiomeric Cyclic Peptides of Cyclocinamide A, from the Marine Sponge Psammocinia sp.

LC-MS and molecular networking analyses of the extract of the marine sponge Psammocinia sp. indicated the presence of two new compounds with multiple halogens. LC-MS-guided isolation yielded cyclic peptides, cyclopsammocinamides A (1) and B (2), in an enantiomeric relationship to cyclocinamide A (3). Planar structures of 1 and 2 were elucidated by NMR and mass spectroscopic analyses and the absolute configurations of the amino acid residues were determined using Marfey's method with their acid hydrolysates. The sponge extract exhibited cytotoxicity and the bioassay-guided isolation afforded a dimeric dilactone macrolide, swinholide A, as the cytotoxic compound.

Colletofragarone A2 Inhibits Cancer Cell Growth In Vivo and Leads to the Degradation and Aggregation of Mutant p53.

Mutant p53 not only loses its original tumor suppressor function but also acquires new abilities regarding oncogenic progression. Therefore, the strategy of targeting mutant p53 has attracted attention for cancer therapy. We isolated colletofragarone A2 (CF) from the fungus Colletotrichum sp. (13S020), which decreases mutant p53 levels in cells, and herein examine its effect on mutant p53. CF showed more potent cytotoxic activities on cells with p53R175H structural mutants than those with different p53 statuses such as a DNA-contact mutant, wild-type, and null cells. CF markedly decreased tumor cell growth in vivo using a mouse xenograft model with HuCCT1 (p53R175H) cells. Cotreatment of SK-BR-3 (p53R175H) cells with CF and cycloheximide decreased mutant p53 levels by promoting p53 degradation. In the presence of MG-132, CF induced the accumulation of the aggregated mutant p53. These results suggest that CF inhibits the function of molecular chaperones such as HSP90.

Isolation, Synthesis, and Structure-Activity Relationship Study on Daphnane and Tigliane Diterpenes as HIV Latency-Reversing Agents.

Three new diterpenes, stellejasmins A (1) and B (2) and 12-O-benzoylphorbol-13-heptanoate (3), were isolated from the roots of Stellera chamaejasme L. The structures of 1-3 were elucidated by extensive NMR and mass spectroscopic analyses. Compounds 1 and 2 are the first derivatives containing a hydroxy group at C-2 in the family of daphnane and tigliane diterpenes. The presence of a chlorine atom in 1 is unique in the plant metabolite. Compound 3 has an odd-number acyl group, which is biosynthetically notable. Human immunodeficiency virus (HIV) LTR-driven transcription activity was tested with 1-3 and 17 known diterpenes isolated from S. chamaejasme L. and Wikstroemia retusa A.Gray. Among these, gnidimacrin (4), stelleralide A (5), and wikstroelide A (20) were highly potent, with EC50 values of 0.14, 0.33, and 0.39 nM, respectively. The structure-activity relationship (SAR) was investigated using 20 natural and eight synthetic diterpenes. This is the first SAR study on natural daphnane and tigliane diterpenes.

Cell-based screening of extracts of natural sources to search for inhibitors of the ubiquitin-proteasome system and identification of proteasome inhibitors from the fungus Remotididymella sp.

The ubiquitin-proteasome system (UPS) regulates selective protein degradation to maintain protein homeostasis. Small molecules that inhibit the UPS-dependent protein degradation are promising anti-tumor agents. We report a cell-based luminescent assay using HeLa cells expressing luciferase-fused oxygen-dependent destruction domain (ODD) of hypoxia-inducible factor 1 α (HIF-1 α). ODD is degraded by the UPS and this assay system can aid in the identification of natural products that inhibit either process of the UPS, including ubiquitination/deubiquitination and proteasomal degradation. This reporter assay can exclude the influences of coloring or fluorescent compounds in extracts, thereby leading to effective high-throughput processing. The screening of 15,025 extracts of natural sources identified the culture extract of the fungus Remotididymella sp. (18F02908). Bioassay-guided isolation yielded two new polyketides, mellains A (1) and B (2), together with leptosphaerodione (3) and its acetone adduct 4. Compound 1 was revealed to have an unprecedented benzo[g]isoquinoline-8,10-dione skeleton. Evaluation of the biological activities demonstrated that these polyketides inhibit the proteasomal proteolysis. This is the first report of the identification of proteasome inhibitors from natural sources using a cell-based reporter assay targeting UPS inhibitors.

Colletofragarone A2 and Colletoins A-C from a Fungus Colletotrichum sp. Decrease Mutant p53 Levels in Cells.

p53 is frequently mutated in tumor cells. Mutant p53 (mut p53) accumulates in cells to promote cancer progression, invasion, and metastasis, and it is attracting attention as a target for cancer therapies. In this study, we used immunofluorescence staining of Saos-2 cells harboring doxycycline-inducible p53R175H [Saos-2 (p53R175H) cells] to search for compounds from natural sources that can target mut p53 and found an extract of Colletotrichum sp. (13S020) that was active. Bioassay-guided fractionation of the extract afforded a known polyketide, colletofragarone A2 (1), and three new analogues, colletoins A-C (2-4). The relative and absolute configurations of 1 were determined by the spectroscopic method and DFT calculation. Compounds 1 and 2 inhibited the growth of Saos-2 (p53R175H) cells and decreased mut p53 in the cells.

Neopetrosidines A-D, pyridine alkaloids isolated from the marine sponge Neopetrosia chaliniformis and their cell cycle elongation activity.

Natural products that inhibit cell cycle progression show promise as anticancer agents and chemical probes. In our research on biologically active natural products that affect cell cycle progression of HeLa/fluorescent ubiquitination-based cell cycle indicator (Fucci)2 cells, the extract of the marine sponge Neopetrosia chaliniformis was revealed to inhibit cell proliferation. Purification of the extract afforded four new pyridine alkaloids, neopetrosidines A-D (1-4). Their structures were elucidated by the interpretation of spectroscopic data and chemical degradation. Compounds 1-4 were found to inhibit cell proliferation of HeLa/Fucci2 cells, and time-lapse imaging showed that 1 exerts its effect by increasing the duration of the cell cycle. Furthermore, we show that 1 perturbs bioenergetics to exhibit a cytostatic effect by reducing the mitochondrial membrane potential.

Amakusamine from a Psammocinia sp. Sponge: Isolation, Synthesis, and SAR Study on the Inhibition of RANKL-Induced Formation of Multinuclear Osteoclasts.

A simple methylenedioxy dibromoindole alkaloid, amakusamine (1), was isolated from a marine sponge of the genus Psammocinia, and its structure was determined from spectroscopic data, time-dependent density-functional theory calculations, and synthesis. Compound 1 inhibited the receptor activator of nuclear factor-κB ligand (RANKL)-induced formation of multinuclear osteoclasts with an IC50 value of 10.5 µM in RAW264 cells. The structure-activity relationship of 1 was also investigated with synthetic derivatives.

Taichunins E-T, Isopimarane Diterpenes and a 20-nor-Isopimarane, from Aspergillus taichungensis (IBT 19404): Structures and Inhibitory Effects on RANKL-Induced Formation of Multinuclear Osteoclasts.

Fifteen new isopimarane-type diterpenes, taichunins E-S (1-15), and a new 20-nor-isopimarane, taichunin T (16), together with four known compounds were isolated from Aspergillus taichungensis (IBT 19404). The structures of these new compounds were determined by NMR and mass spectroscopy, and their absolute configurations were analyzed by NOESY and TDDFT calculations of ECD spectra. Taichunins G, K, and N (3, 7, and 10) completely inhibited the receptor activator of nuclear factor-κB ligand (RANKL)-induced formation of multinuclear osteoclasts in RAW264 cells at 5 µM, with 3 showing 92% inhibition at a concentration of 0.2 µM.

Halichonic Acid B, a Rearranged Nitrogenous Bisabolene-Type Sesquiterpene from a Marine Sponge Axinyssa sp.

A new rearranged nitrogenous bisabolone-type sesquiterpene, halichonic acid B (1), was isolated from a marine sponge Axinyssa sp. together with halichonic acid (2) and (6R,7S)-7-amino-7,8-dihydro-α-bisabolene (3). The structure of 1 was determined by extensive NMR and MS analyses, revealing an unprecedented carbon framework, and its absolute configuration was elucidated by time-dependent density-functional theory (TDDFT)-based electronic circular dichroism (ECD) spectrum calculation. We propose that 1 and 2 may be biosynthesized in the same pathway, involving the reaction between farnesyl pyrophosphate and glycine, followed by cyclization.

Fluorescent image-based high-content screening of extracts of natural resources for cell cycle inhibitors and identification of a new sesquiterpene quinone from the sponge, Dactylospongia metachromia.

Natural products are important sources for drug development. Discovery of natural products that inhibit cell cycle progression significantly contributes to the progress of cancer biology and the development of new antitumor agents. In this study, cell cycle inhibitory activity was evaluated with our extract library of natural resources, including marine invertebrates, fungi, and bacteria, using HeLa/Fucci2 cells which allow classification of the cell cycle phases of living cells. Screening of the extract library revealed that the extract of the marine sponge Dactylospongia metachromia inhibited cell cycle progression at S/G2/M phases. Bioassay-guided fractionation afforded a new sesquiterpene quinone, neoisosmenospongine (1), and four known compounds, nakijiquinone I, N, and Q (2-4) and (-)-dictyoceratin-C (5). The chemical structure of 1 was elucidated by interpretating the NMR and mass spectroscopic data, and the absolute configuration was determined by comparison of the experimental and calculated ECD spectra. Fluorescent imaging of HeLa/Fucci2 cells revealed that 1-4 inhibited the cell cycle progression at S/G2/M phases. This study demonstrated that fluorescent image-based high-content screening using HeLa/Fucci2 cells is an effective approach for isolating cell cycle inhibitors from natural resources.