Genome-Driven Discovery of Antiviral Atralabdans A-C from the Soil-Dwelling Streptomyces atratus.

Heterologous expression of an atr terpenoid gene cluster derived from Streptomyces atratus Gö66 in S. albus J1074 led to the discovery of three novel labdane diterpenoids featuring an unprecedented 6/6/5-fused tricyclic skeleton, designated as atralabdans A-C (1-3), along with a known compound, labdanmycin A. Compounds 1-3 were identified through extensive spectroscopic analysis, including NMR calculations with DP4+ probability analysis, and a comparative assessment of experimental and theoretical electronic circular dichroism (ECD) spectra. A plausible biosynthetic pathway for these compounds was proposed. Compounds 1-3 exhibited inhibitory activity against the human neurotropic coxsackievirus B3 (CVB3); 1 was the most potent, surpassing the positive control ribavirin with a higher therapeutic index.

The Structure of Cyclodecatriene Collinolactone, its Biosynthesis, and Semisynthetic Analogues: Effects of Monoastral Phenotype and Protection from Intracellular Oxidative Stress.

Recently described rhizolutin and collinolactone isolated from Streptomyces Gö 40/10 share the same novel carbon scaffold. Analyses by NMR and X-Ray crystallography verify the structure of collinolactone and propose a revision of rhizolutin's stereochemistry. Isotope-labeled precursor feeding shows that collinolactone is biosynthesized via type I polyketide synthase with Baeyer-Villiger oxidation. CRISPR-based genetic strategies led to the identification of the biosynthetic gene cluster and a high-production strain. Chemical semisyntheses yielded collinolactone analogues with inhibitory effects on L929 cell line. Fluorescence microscopy revealed that only particular analogues induce monopolar spindles impairing cell division in mitosis. Inspired by the Alzheimer-protective activity of rhizolutin, we investigated the neuroprotective effects of collinolactone and its analogues on glutamate-sensitive cells (HT22) and indeed, natural collinolactone displays distinct neuroprotection from intracellular oxidative stress.

Investigations into the biosynthesis of the antifungal strobilurins.

The strobilurins are important antifungal metabolites isolated from a number of basidiomycetes and have been valuable leads for the development of commercially important fungicides. Isotopic labelling studies with early and advanced intermediates confirm for the first time that they are produced via a linear tetraketide, primed with the rare benzoate starter unit, itself derived from phenylalanine via cinnamate. Isolation of a novel biphenyl metabolite, pseudostrobilurin B, provides evidence for the involvement of an epoxide in the key rearrangement to form the ß-methoxyacrylate moiety essential for biological activity. Formation of two bolineol related metabolites, strobilurins Y and Z, also probably involves epoxide intermediates. Time course studies indicate a likely biosynthetic pathway from strobilurin A, with the simplest non-subsubstituted benzoate ring, to strobilurin G with a complex dioxepin terpenoid-derived substituent. Precursor-directed biosynthetic studies allow production of a number of novel ring-halogenated analogues as well as a new pyridyl strobilurin. These studies also provide evidence for a non-linear biosynthetic relationship between strobilurin A and strobilurin B.

First Evidence of Dehydroabietic Acid Production by a Marine Phototrophic Gammaproteobacterium, the Purple Sulfur Bacterium Allochromatium vinosum MT86.

The production of secondary metabolites by a new isolate of the purple sulfur bacterium Allochromatium vinosum, which had shown antibiotic activities during a preliminary study, revealed the production of several metabolites. Growth conditions suitable for the production of one of the compounds shown in the metabolite profile were established and compound 1 was purified. The molecular formula of compound 1 (C20H28O2) was determined by high resolution mass spectra, and its chemical structure by means of spectroscopic methods. The evaluation of these data revealed that the structure of the compound was identical to dehydroabietic acid, a compound known to be characteristically produced by conifer trees, but so far not known from bacteria, except cyanobacteria. The purified substance showed weak antibiotic activities against Bacillus subtilis and Staphylococcus lentus with IC50 values of 70.5 µM (±2.9) and 57.0 µM (±3.3), respectively.

Structure and Biosynthesis of Isatropolones, Bioactive Amine-Scavenging Fluorescent Natural Products from Streptomyces†Gö66.

The natural products isatropolone A-C (1-3) were reisolated from Streptomyces Gö66, with 1 and 3 showing potent activity against Leishmania donovani. They contain a rare tropolone ring derived from a type II polyketide biosynthesis pathway. Their biosynthesis was elucidated by labeling experiments, analysis of the biosynthesis gene cluster, its partial heterologous expression, and structural characterization of various intermediates. Owing to their 1,5-diketone moiety, they can react with ammonia, amines, lysine, and lysine-containing peptides and proteins, which results in the formation of a covalent bond and subsequent pyridine ring formation. Their fluorescence properties change upon amine binding, enabling the simple visualization of reacted amines including proteins.

Insights into the bioactivity of mensacarcin and epoxide formation by MsnO8.

Mensacarcin, a potential antitumour drug, is produced by Streptomyces bottropensis. The structure consists of a three-membered ring system with many oxygen atoms. Of vital importance in this context is an epoxy moiety in the side chain of mensacarcin. Our studies with different mensacarcin derivatives have demonstrated that this epoxy group is primarily responsible for the cytotoxic effect of mensacarcin. In order to obtain further information about this epoxy moiety, inactivation experiments in the gene cluster were carried out to identify the epoxy-forming enzyme. Therefore the cosmid cos2, which covers almost the complete type II polyketide synthase (PKS) gene cluster, was heterologously expressed in Streptomyces albus. This led to production of didesmethylmensacarcin, due to the fact that methyltransferase genes are missing in the cosmid. Further gene inactivation experiments on this cosmid showed that MsnO8, a luciferase-like monooxygenase, introduces the epoxy group at the end of the biosynthesis of mensacarcin. In addition, the protein MsnO8 was purified, and its crystal structure was determined to a resolution of 1.80 Å.

Cloning and heterologous expression of three type II PKS gene clusters from Streptomyces bottropensis.

Mensacarcin is a potent cytotoxic agent isolated from Streptomyces bottropensis. It possesses a high content of oxygen atoms and two epoxide groups, and shows cytostatic and cytotoxic activity comparable to that of doxorubicin, a widely used drug for antitumor therapy. Another natural compound, rishirilide A, was also isolated from the fermentation broth of S. bottropensis. Screening a cosmid library of S. bottropensis with minimal PKS-gene-specific primers revealed the presence of three different type II polyketide synthase (PKS) gene clusters in this strain: the msn cluster (mensacarcin biosynthesis), the rsl cluster (rishirilide biosynthesis), and the mec cluster (putative spore pigment biosynthesis). Interestingly, luciferase-like oxygenases, which are very rare in Streptomyces species, are enriched in both the msn cluster and the rsl cluster. Three cosmids, cos2 (containing the major part of the msn cluster), cos3 (harboring the mec cluster), and cos4 (spanning probably the whole rsl cluster) were introduced into the general heterologous host Streptomyces albus by intergeneric conjugation. Expression of cos2 and cos4 in S. albus led to the production of didesmethylmensacarcin (DDMM, a precursor of mensacarcin) and the production of rishirilide A and B (a precursor of rishirilide A), respectively. However, no product was detected from the expression of cos3. In addition, based on the results of isotope-feeding experiments in S. bottropensis, a putative biosynthesis pathway for mensacarcin is proposed.

Resistoflavine, cytotoxic compound from a marine actinomycete, Streptomyces chibaensis AUBN1/7.

In our systematic screening programme for marine actinomycetes, a bioactive Streptomycete was isolated from marine sediment samples of Bay of Bengal, India. The taxonomic studies indicated that the isolate belongs to Streptomyces chibaensis and it was designated as S. chibaensis AUBN1/7. The isolate yielded a cytotoxic compound. It was obtained by solvent extraction followed by the chromatographic purification. Based on the spectral data of the pure compound, it was identified as quinone-related antibiotic, resistoflavine (1). It showed a potent cytotoxic activity against cell lines viz. HMO2 (Gastric adenocarcinoma) and HePG2 (Hepatic carcinoma) in vitro and also exhibited weak antibacterial activities against Gram-positive and Gram-negative bacteria.

Fogacin, a novel cyclic octaketide produced by Streptomyces strain Tü 6319.

A new octaketide named fogacin (1) was isolated from Streptomyces sp. (strain Tü 6319). Furthermore two shunt metabolites, SEK4b (2) and anhydroSEK4b (3), were detected and identified as non-enzymatically cyclized products of polyketide intermediates built during the biosynthesis of actinorhodin. SEK4b (2) as well as anhydroSEK4b (3) were previously described as metabolites of genetically engineered strains.

New aminophenoxazinones from a marine Halomonas sp.: fermentation, structure elucidation, and biological activity.

The addition of anthranilic acid to the culture medium of the marine derived Halomonas sp. strain GWS-BW-H8hM completely altered the secondary metabolite pattern relative to the standard conditions. The red-orange color of the culture filtrate extract was the result of the production of 2-aminophenoxazin-3-one (1), chandrananimycin C (5) and three new derivatives of 1 with a previously unknown substitution pattern: 2-amino-, 2-amino-8-benzoyl-, and 2-amino-8-(4-hydroxybenzoyl)-6-hydroxyphenoxazin-3-one (2-4). The compounds were determined to have antibacterial and cytotoxic activities; a mode of action other than DNA intercalation is discussed.

Archazolid and apicularen: novel specific V-ATPase inhibitors.

BACKGROUND: V-ATPases constitute a ubiquitous family of heteromultimeric, proton translocating proteins. According to their localization in a multitude of eukaryotic membranes, they energize many different transport processes. Since their malfunction is correlated with various diseases in humans, the elucidation of the properties of this enzyme for the development of selective inhibitors and drugs is one of the challenges in V-ATPase research. RESULTS: Archazolid A and B, two recently discovered cytotoxic macrolactones produced by the myxobacterium Archangium gephyra, and apicularen A and B, two novel benzolactone enamides produced by different species of the myxobacterium Chondromyces, exerted a similar inhibitory efficacy on a wide range of mammalian cell lines as the well established plecomacrolidic type V-ATPase inhibitors concanamycin and bafilomycin. Like the plecomacrolides both new macrolides also prevented the lysosomal acidification in cells and inhibited the V-ATPase purified from the midgut of the tobacco hornworm, Manduca sexta, with IC50 values of 20-60 nM. However, they did not influence the activity of mitochondrial F-ATPase or that of the Na+/K+-ATPase. To define the binding sites of these new inhibitors we used a semi-synthetic radioactively labelled derivative of concanamycin which exclusively binds to the membrane Vo subunit c. Whereas archazolid A prevented, like the plecomacrolides concanamycin A, bafilomycin A1 and B1, labelling of subunit c by the radioactive I-concanolide A, the benzolactone enamide apicularen A did not compete with the plecomacrolide derivative. CONCLUSION: The myxobacterial antibiotics archazolid and apicularen are highly efficient and specific novel inhibitors of V-ATPases. While archazolid at least partly shares a common binding site with the plecomacrolides bafilomycin and concanamycin, apicularen adheres to an independent binding site.

Retymicin, galtamycin B, saquayamycin Z and ribofuranosyllumichrome, novel secondary metabolites from Micromonospora sp. Tü 6368. II. Structure elucidation.

A detailed screening of the secondary metabolite pattern from Micromonospora sp. strain Tü 6368 resulted in the isolation of ten compounds belonging to five different structural families. The structures of the novel compounds 1-(alpha-ribofuranosyl)-lumichrome (3), retymicin (7), galtamycin B (11) and saquayamycin Z (14) were assigned by spectroscopic methods and chemical transformations. This strain fits our hypothesis that the metabolite analysis of biosynthetically talented strains leads readily to novel compounds.

Retymicin, galtamycin B, saquayamycin Z and ribofuranosyllumichrome, novel secondary metabolites from Micromonospora sp. Tü 6368. I. Taxonomy, fermentation, isolation and biological activities.

A new xanthone compound named retymicin (1) was isolated together with galtamycin B (2) and saquayamycin Z (3), new members of the galtamycin and saquayamycin families, respectively, and the new lumichrome derivative 1-(alpha-ribofuranosyl)-lumichrome (4) from Micromonospora strain Tü 6368, isolated from a soil sample collected in Romania. Retymicin, galtamycin B and saquayamycin Z show cytostatic effects to various human tumor cell lines whereas saquayamycin Z is also active against Gram-positive bacteria.

1-Hydroxy-1-norresistomycin, a new cytotoxic compound from a marine actinomycete, Streptomyces chibaensis AUBN1/7.

In our systematic screening programme for marine actinomycetes, a bioactive streptomycete was isolated from marine sediment samples of the Bay of Bengal, India. The isolate yielded a new cytotoxic compound. This was obtained by solvent extraction followed by chromatographic purification. The pure compound was identified from spectroscopic data as a quinone-related antibiotic, 1-hydroxy-1-norresistomycin (1). It showed a potent cytotoxic activity against cell lines viz. HMO2 (gastric adenocarcinoma) and HePG2 (hepatic carcinoma) in vitro. It also exhibited antibacterial activities against Gram-positive and Gram-negative bacteria.

Screening for biologically active metabolites with endosymbiotic bacilli isolated from arthropods.

Endosymbiotic bacteria from the genus Bacillus were isolated from different compartments of the gut of various members of insects (Hexapoda) and millipedes (Diplopoda). They were grown in submerged culture and investigated by biological assays and HPLC-diode array analysis regarding their production of bioactive metabolites, which were isolated and determined in structure. Known compounds and yet unknown derivatives from the primary metabolism were detected, as well as antibacterially and antifungally acting peptide antibiotics.

Glucosides from Vitex agnus-castus.

The methanolic extract of the flowering stems of Vitex agnus-castus yielded three new iridoids: 6'-O-foliamenthoylmussaenosidic acid (agnucastoside A), 6'-O-(6,7-dihydrofoliamenthoyl)mussaenosidic acid (agnucastoside B) and 7-O-trans-p-coumaroyl-6'-O-trans-caffeoyl-8-epiloganic acid (agnucastoside C) in addition to four known iridoids (aucubin, agnuside, mussaenosidic acid and 6'-O-p-hydroxybenzoylmussaenosidic acid) and one known phenylbutanone glucoside (myzodendrone). The structure elucidations were mainly done by spectroscopic methods (1D and 2D NMR spectra) and MS data interpretation. The purified compounds were tested for biological activities against various microorganisms and cancer cell lines.

4'-deoxy iridoid glycosides from Centranthus longiflorus.

The new iridoid glycosides, 4'-deoxykanokoside A and 4'-deoxykanokoside C, were isolated from the methanolic root extract of Centranthus longiflorus ssp. longiflorus. They were accompanied by the three known iridoid glycosides, kanokoside A, kanokoside C and valerosidatum, and two known phenylpropanoid glycosides, coniferin and isoconiferinoside. The structures were elucidated mainly by spectroscopic methods. The presence of 4-deoxy glucose as a part of plant glycosides is rather unusual. Cytotoxic effects of the isolated compounds were also investigated.

Simocyclinones, novel cytostatic angucyclinone antibiotics produced by Streptomyces antibioticus Tü 6040 II. Structure elucidation and biosynthesis.

The simocyclinones D4 (1) and D8 (2), members of a novel class of antibiotics, were isolated from the mycelial extract of Streptomyces antibioticus Tü 6040 and consist of angucyclinone, deoxysugar, octatetraene dicarboxylate and aminocoumarin structural elements. The structure elucidation was done by one and two dimensional NMR experiments, and other spectroscopic methods in combination with incorporation experiments using 13C labelled precursors.

Endophenazines A-D, new phenazine antibiotics from the athropod associated endosymbiont Streptomyces anulatus II. Structure elucidation.

A detailed screening of the secondary metabolite pattern produced by different athropod associated strains of the species Streptomyces anulatus resulted in the isolation and structure elucidation of the endophenazines A-D (2, 4-6). The structures were assigned by spectroscopic methods and chemical transformations. 4 represents a chromophoric system based on a phenazin-7-one, 5 and 6 are new 5,10-dihydrophenazine derivatives.

Structure and biosynthesis of cetoniacytone A, a cytotoxic aminocarba sugar produced by an endosymbiontic Actinomyces.

Cetoniacytone A (1) and some related minor components (2, 6, 7) were produced by Actinomyces sp. (strain Lu 9419), which was isolated from the intestines of a rose chafer (Cetonia aureata). The structures of the novel metabolites were established by detailed spectroscopic analysis. The absolute configuration of 1 was determined by X-ray analysis and derivatisation with chiral acids. 1 exhibits a significant cytotoxicity against selected tumor cell lines. The biosynthesis of 1 was studied by feeding 13C labelled precursors. The results suggest that the characteristic p-C7N skeleton of the aminocarba sugar is formed via the pentose phosphate pathway by cyclisation of a heptulose phosphate intermediate.