Tropolone-Bearing Sesquiterpenes from Juniperus chinensis: Structures, Photochemistry and Bioactivity.

The tropolone-bearing sesquiterpenes juniperone A (1) and norjuniperone A (2) were isolated from the folk medicinal plant Juniperus chinensis, and their structures were determined by a combination of spectroscopic and crystallographic methods. Photojuniperones A1 (3) and A2 (4), bearing bicyclo[3,2,0]heptadienones derived from tropolone, were photochemically produced and structurally identified by spectroscopic methods. Predicted by the machine learning-based assay, 1 significantly inhibited the action of tyrosinase. The new compounds also inhibited lipid accumulation and enhanced the extracellular glycerol excretion.

Tropolone derivatives with hepatoprotective and antiproliferative activities from the aerial parts of Chenopodium album Linn.

Chenopodium album Linn is used as the traditional Chinese medicine for treating cough, anorexia, piles, dysentery, diarrhea, and kills small worms in China. Nine new tropolones (1-9), and fourteen known tropolone derivatives (10-23) were elucidated by comprehensive spectroscopic data analysis and references from C. album Linn for the first time. Compounds (1-4) and compounds (13-14) displayed notably hepatoprotective activities in intro for lowering AST levels (19.63 ± 2.34 to 29.87 ± 1.27 U•L-1) and ALT levels (15.21 ± 1.18 to 20.29 ± 2.11 U•L-1) in HepG2 cells treated with H2O2. Compounds (8-9) and compounds (15-17) exhibited moderate antiproliferative activities in vitro against the human tumor cell lines with IC50 values ranging from 0.5 ± 0.2 to 15.5 ± 2.7 µM. A preliminary structure activity relationship was summarized and discussed scientifically, which provided new clues to design novel hepatoprotective and antiproliferative drugs based on the tropolone derivatives.

Isarubrolones Containing a Pyridooxazinium Unit from Streptomyces as Autophagy Activators.

Isarubrolones are bioactive polycyclic tropoloalkaloids from Streptomyces. Three new isarubrolones (2-4), together with the known isarubrolone C (1) and isatropolones A (5) and C (6, 3( R)-hydroxyisatropolone A), were identified from Streptomyces sp. CPCC 204095. The structures of these compounds were determined using a combination of mass spectrometry, 1D and 2D NMR spectroscopy, and ECD. Compounds 3 and 4 feature a pyridooxazinium unit, which is rarely seen in natural products. Compound 6 could conjugate with amino acids or amines to expand the structural diversity of isarubrolones with a pentacyclic or hexacyclic core. Importantly, 1 and 3-6 were found to induce complete autophagy.

A sesquiterpenoid tropolone and 1,2,3,4-tetrahydronaphthalene derivatives from Olax imbricata roots.

The methanol extract of Olax imbricata roots afforded one new sesquiterpenoid tropolone and three new 1,2,3,4-tetrahydronaphthalene derivatives, olaximbrisides A-D (1-4). Their structures were determined by 1D and 2D NMR experiments in combination of HRESIMS. The relative configurations were assigned by the NOESY experiments. The absolute configurations were established by a combination of X-ray diffraction analysis and electronic circular dichroism (ECD) experiments. All isolated compounds were evaluated for their cytotoxic effects against some cancer cell lines. Among them, compound 1 exhibited the cytotoxicities against MCF-7, HepG2 and LU cell lines with IC50 values of 16.3, 34.3 and 8.0 µM, respectively.

A Novel Tropoloisoquinoline Alkaloid, Neotatarine, from Acorus calamus L.

A novel tropoloisoquinoline alkaloid, neotatarine (1), was isolated from the 95% ethanol extract of the rhizome parts of Acorus calamus L. The chemical structure was unambiguously elucidated by spectroscopic and single-crystal X-ray diffraction analysis. Neotatarine (1) exhibited significantly inhibitory activity against Aß25 - 35 induced PC12 cell death with 2, 4 and 8 µm comparing with the assay control (P < 0.01).

Cytotoxic Effects of Tropodithietic Acid on Mammalian Clonal Cell Lines of Neuronal and Glial Origin.

The marine metabolite tropodithietic acid (TDA), produced by several Roseobacter clade bacteria, is known for its broad antimicrobial activity. TDA is of interest not only as a probiotic in aquaculture, but also because it might be of use as an antibacterial agent in non-marine or non-aquatic environments, and thus the potentially cytotoxic influences on eukaryotic cells need to be evaluated. The present study was undertaken to investigate its effects on cells of the mammalian nervous system, i.e., neuronal N2a cells and OLN-93 cells as model systems for nerve cells and glia. The data show that in both cell lines TDA exerted morphological changes and cytotoxic effects at a concentration of 0.3-0.5 µg/mL (1.4-2.4 µM). Furthermore, TDA caused a breakdown of the mitochondrial membrane potential, the activation of extracellular signal-regulated kinases ERK1/2, and the induction of the small heat shock protein HSP32/HO-1, which is considered as a sensor of oxidative stress. The cytotoxic effects were accompanied by an increase in intracellular Ca(2+)-levels, the disturbance of the microtubule network, and the reorganization of the microfilament system. Hence, mammalian cells are a sensitive target for the action of TDA and react by the activation of a stress response resulting in cell death.

Identification and bioactivity of compounds from the fungus Penicillium sp. CYE-87 isolated from a marine tunicate.

In the course of our continuous interest in identifying bioactive compounds from marine microbes, we have investigated a tunicate-derived fungus, Penicillium sp. CYE-87. A new compound with the 1,4-diazepane skeleton, terretrione D (2), together with the known compounds, methyl-2-([2-(1H-indol-3-yl)ethyl]carbamoyl)acetate (1), tryptamine (3), indole-3-carbaldehyde (4), 3,6-diisobutylpyrazin-2(1H)-one (5) and terretrione C (6), were isolated from Penicillium sp. CYE-87. The structures of the isolated compounds were established by spectral analysis, including 1D (1H, 13C) and 2D (COSY, multiplicity edited-HSQC and HMBC) NMR and HRESIMS, as well as comparison of their NMR data with those in the literature. The compounds were evaluated for their antimigratory activity against the human breast cancer cell line (MDA-MB-231) and their antiproliferation activity against HeLa cells. Compounds 2 and 6 showed significant antimigratory activity against MDA-MB-231, as well as antifungal activity against C. albicans.

Butyrolactone and cycloheptanetrione from mangrove-associated fungus Aspergillus terreus.

A new butyrolactone, 7″-hydroxybutyrolactone III (1) and three new cycloheptanetriones, terretrione A-C (2-4), together with five known compounds, butyrolactone I, cyclo(Leu-Pro), cyclo(Val-Pro), cyclo(Ile-Pro), cyclo(Phe-Pro), were isolated from mangrove-associated marine fungus Aspergillus terreus. The structures of these compounds were elucidated on the basis of physical data analysis (NMR, high resolution-electrospray ionization (HR-ESI)-MS), especially by 2D-NMR techniques. These compounds showed weak cytotoxicity in vitro against HCT-8, Bel-7402, BGC-823, A2780 cell lines.

Potentiation of bleomycin in Jurkat cells by fungal pycnidione.

Most cancer cells have mutations in genes at the G1 checkpoint and repair DNA only in the G2 phase; therefore, the G2 checkpoint is a potential target to develop novel therapy. In the course of screening, a known compound, pycnidione, was isolated from the fungal culture broth of Gloeotinia sp. FKI-3416. Pycnidione irreversibly abrogated bleomycin-induced G2 arrest in Jurkat cells and synergically potentiated the cytotoxicity of bleomycin. To elucidate the mechanism of action, the effect of pycnidione on the signal transduction of the G2 checkpoint was analyzed, showing that the increased phospho-cyclin dependent kinase-1 (CDK1) level caused by bleomycin was abrogated in the presence of pycnidione, indicating that cells did not arrest at the G2 phase. Moreover, under these conditions, Chk1 and Chk2 levels were markedly down-regulated. Thus, we concluded that pycnidione abrogated bleomycin-induced G2 arrest by decreasing Chk1 and Chk2.

Biological activity of beta-dolabrin, gamma-thujaplicin, and 4-acetyltropolone, hinokitiol-related compounds.

Beta-dolabrin, gamma-thujaplicin, and 4-acetyltropolone, the components of Aomori Hiba (Thujopsis dolabrata SIEB. et ZUCC. var. hondai MAKINO), showed antifungal activity on seven kinds of plant-pathogenic fungi, antibacterial activity against two kinds of Legionella sp., and in vitro cytotoxic effect on murine P388 lymphocytic leukemia cell line. Firstly, beta-dolabrin, gamma-thujaplicin and 4-acetyltropolone had clear antifungal activity against seven kinds of plant-pathogenic fungi tested. In particular, beta-dolabrin and 4-acetyltropolone showed strong antifungal activity against Pythium aphanidermatum IFO 32440, with minimum inhibitory concentration (MIC) values of 6.0 microg/ml. Secondly, beta-dolabrin, gamma-thujaplicin and 4-acetyltropolone had obvious growth-inhibitory effect on two kinds of Legionella sp. 4-Acetyltropolone especially had strong antibacterial activity toward Legionella pneumophila SG 1, and its MIC value was 3.1 microg/ml. These three compounds showed cytotoxic effects against murine P388 lymphocytic leukemia cell line in vitro. The cytotoxic effect of three compounds in the murine P388 lymphocytic leukemia cell line were clear when cell growth was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. At 48 h after treatment, gamma-thujaplicin and 4-acetyltropolone at 0.63 microg/ml inhibited cell growth of murine P388 lymphocytic leukemia by 85% and 65%, respectively. At the same time after treatment, the growth of the murine P388 lymphocytic leukemia cell line was completely suppressed by the three compounds at concentrations higher than 5.0 microg/ml. Among these three compounds, gamma-thujaplicin had the strongest cytotoxic activity on the growth of this tumor cell line in vitro.

Biological activity of alpha-thujaplicin, the minor component of Thujopsis dolabrata SIEB. et ZUCC. var. hondai MAKINO.

Alpha-thujaplicin, a minor component of Thujopsis dolabrata SIEB. et ZUCC. var. hondai MAKINO, which was synthesized, showed the antibacterial activity, phytogrowth-inhibitory effect, inhibition of carboxypeptidase A and cytotoxic effect. Antibacterial activity of alpha-thujaplicin on Enterococcus faecalis IFO-12965 [minimum inhibitory concentration (MIC): 1.56 microg/ml] was higher than that of gentamicin (MIC: 6.25 microg/ml) used as a positive control. Inhibitory activity of alpha-thujaplicin on carboxypeptidase A [50% inhibitory concentration (IC50): 3.24 x 10(-5) M] was higher than that of 1,10-phenanthroline used as a positive control. Alpha-thujaplicin showed germination inhibition toward the seed of Echinochloa utilis Ohwi et Yabuno even at the low concentration of 10 ppm and its growth inhibitory effect was stronger than that of sodium 2,4-dichlorophenoxyacetate used as a standard. Alpha-thujaplicin at 1.25 microg/ml inhibited cell growth of human stomach cancer KATO-IIl by 86%, and Ehrlich's ascites carcinoma by 87%, respectively. This compound even at the low concentration of 0.32 microg/ml also inhibited cell growth of the former by 66%, and the latter by 75%, respectively. The acute toxicity of alpha-thujaplicin [50% lethal dose (LD50) value: 256 mg/kg] in mice was as strong as those of beta-dolabrin (LD50 value: 232 mg/kg) and gamma-thujaplicin (LD50 value: 277 mg/kg).

Structures and solid state tautomeric forms of two novel antileukemic tropoloisoquinoline alkaloids, pareirubrines A and B, from Cissampelos pareira.

Two novel tropoloisoquinoline alkaloids, Pareirubrines A and B, have been isolated as antileukemic substances from Cissampelos pareira (Menispermaceae), together with the same skeleton alkaloids, grandirubrine and isoimerubrine. Their structures were elucidated by nuclear magnetic resonance (NMR) studies, and their solid state tautomeric forms were examined by X-ray crystallographic analysis.

Eupenifeldin, a novel cytotoxic bistropolone from Eupenicillium brefeldianum.

Eupenifeldin was isolated from cultures of Eupenicillium brefeldianum ATCC 74184 by extraction and crystallization. The compound was identified as a pentacyclic bistropolone on the basis of spectral data and its complete structure was established by single-crystal X-ray analysis. The compound is cytotoxic against the HCT-116 cell line and has in vivo antitumor activity in the P388 leukemia model.

BMY-28438 (3,7-dihydroxytropolone), a new antitumor antibiotic active against B16 melanoma. I. Production, isolation, structure and biological activity.

A new antitumor antibiotic BMY-28438 was isolated from the cultured broth of Streptomyces tropolofaciens No. K611-97. The antibiotic showed potent cytotoxicity against cultured B16 melanoma cells and remarkable prolongation of life span of mice bearing B16 melanoma. The structure of BMY-28438 was determined as 3,7-dihydroxytropolone on the basis of spectral analyses and direct comparison with the authentic compound synthesized.

Studies on lipoxygenase inhibitors. I. MY3-469 (3-methoxytropolone), a potent and selective inhibitor of 12-lipoxygenase, produced by Streptoverticillium hadanonense KY11449.

Streptoverticillium hadanonense KY11449 was found to produce a 12-lipoxygenase inhibitor MY3-469. The compound was purified by chromatography on Diaion HP-10, charcoal, Sephadex LH-20 and crystallization. The chemical structure of MY3-469 was determined to be 3-methoxytropolone on the basis of its physico-chemical properties. The half maximal inhibitory concentration (IC50) of MY3-469 against bovine platelet 12-lipoxygenase was 1.8 X 10(-6)M. The compound did not inhibit bovine platelet cyclooxygenase at 10(-3)M and showed weak inhibition (IC50 2.8 X 10(-4)) against 5-lipoxygenase of rat basophilic leukemia cells. The results indicate that MY3-469 is a potent and selective inhibitor of 12-lipoxygenase.

Thujaplicins from Thuja plicata as iron transport agents for Salmonella typhimurium.

Strains of Salmonella typhimurium which are unable to synthesize their normal iron transport agent, enterobactin, and which must be supported with an exogenous chelator (siderophore) on certain media, were used to examine various types of wood for the presence of chelators. Western red cedar wood, Thuja plicata, was observed to contain large amounts of three substances that in low concentration would serve as chelators for S. typhimurium. The chelators from T. plicata were characterized and found to be alpha-, beta-, and gamma-thujaplicin. Other planar cyclic alpha-hydroxyketones were examined, and several were found to function as chelators for S. typhimurium.