Trichodermatides A-D, novel polyketides from the marine-derived fungus Trichoderma reesei

Four new polyketide derivatives, Trichodermatides A-D (1-4) were isolated from the marine-derived fungus Trichoderma reesei. Trichodermatide A (1) is an unprecedented example of a polyketide with a ketal-containing pentacyclic skeleton. The chemical structures and absolute configurations of compounds 1-4 were elucidated by extensive spectroscopic methods, especially 2D NMR and CD spectral analysis, and supported by their proposed biosynthesis pathway. The cytotoxicity of 1-4 was evaluated against A375-S2 human melanoma cell line.     

Metabolites from fungi 15. New isocoumarins from an endophytic fungus isolated from the Canadian thistle Cirsium arvense

One known (1) and five new polyketide metabolites (2-6) were isolated from the culture extract of an endophytic fungus, Mycelia sterila, from the Canadian thistle Cirsium arvense. Compounds 1-4 are members of the isocoumarin family, whereas metabolite 5 is a dihydrobenzofuran and 6 has an open chain structure. All compounds have an unusual methyl group at the aromatic ring that does not fit into the usual polyketide pattern.     

Amphidinolides T2, T3, and T4, new 19-membered macrolides from the dinoflagellate Amphidinium sp. and the biosynthesis of amphidinolide T1.

Three new 19-membered macrolides, amphidinolides T2 (2), T3 (3), and T4 (4), structurally related to amphidinolide T1 (1) have been isolated from two strains of marine dinoflagellates of the genus Amphidinium. The structures of 2-4 were elucidated on the basis of spectroscopic data. The absolute configurations at C-7, C-8, and C-10 of 1-4 were determined by comparison of NMR data of their C-1-C-12 segments with those of synthetic model compounds for the tetrahydrofuran portion. The biosynthetic origins of amphidinolide T1 (1) were investigated on the basis of 13C NMR data of a 13C enriched sample obtained by feeding experiments with [1-(13)C], [2-(13)C], and [1,2-(13)C2] sodium acetates and 13C-labeled sodium bicarbonate in the cultures of the dinoflagellate. These incorporation patterns suggested that amphidinolide T1 (1) was generated from four successive polyketide chains, an isolated C1 unit formed from C-2 of acetates, and three unusual C2 units derived only from C-2 of acetates. Furthermore, it is noted that five oxygenated carbons of C-1, C-7, C-12, C-13, and C-18 were not derived from the C-1 carbonyl, but from the C-2 methyl of acetates.     

Polyketide analysis using mass spectrometry,evaporative light scattering,and charged aerosol detector systems

In this study, a mass spectrometer (MS), an evaporative light scattering detector (ELSD), and a charged aerosol detector (CAD) were used to analyze an erythromycin precursor (termed 6-deoxyerythronolide B). The work highlights the capabilities of each detector to analyze a representative polyketide compound that does not possess a natural chromophore, and presents the first comparison to include a charged aerosol system. Each detector was evaluated based upon limit of detection (LOD), dynamic range, and precision in the context of polyketide analysis. Due to its low LOD, wide dynamic range, and ability to provide molecular weight information, the MS was deemed the best detection option for the analysis of low-concentration, poorly identified polyketide compounds. Alternatively, both the CAD and ELSD systems studied showed better precision and accuracy. The ELSD demonstrated the best precision at 3%, but its LOD was limited to concentrations primarily greater than or equal to 1 mg/L. The Corona CAD demonstrated a LOD (0.012 mg/L) and dynamic range comparable to mass spectroscopy and therefore serves as a more cost-efficient alternative for polyketide production schemes with low titers.     

Characterization of the lnmKLM genes unveiling key intermediates for β-alkylation in leinamycin biosynthesis

Leinamycin (LNM, 1) biosynthesis is proposed to involve β-alkylation of the polyketide intermediate, catalyzed by LnmKLM. Inactivation of lnmK, lnmL, or lnmM afforded mutant strains that accumulated LNM K-1 (2), K-2 (3), K-3 (4), and isomers LNM K-1' (5), K-2' (6), and K-3' (7) whose polyketide origin was established by feeding experiments with sodium [1-(13)C]acetate. These findings confirm the indispensability of LnmKLM in 1 biosynthesis and suggest that β-alkylation proceeds on the growing polyketide intermediate while bound to the LNM polyketide synthase.     

A novel tricyclic polyketide and its biosynthetic precursor azaphilone derivatives from the endophytic fungus Dothideomycete sp

Azaphilone derivatives 1 and 2 and a novel tricyclic polyketide 3, together with a known azaphilone, austdiol (4), were isolated from the endophytic fungus Dothideomycete sp., which was isolated from a Thai medicinal plant, Tiliacora triandra. Compound 3 is the first polyketide having a tricyclic 6,6,6 ring system, which is similar to that of a terpenoid skeleton. The absolute configurations of stereogenic centers in 1-3 were addressed by Mosher's method and biosynthetic analogy with a known azaphilone isolated from the same fungus. Cytotoxic and antimicrobial activities of the isolated compounds were evaluated.     

Botrylactone: new interest in an old molecule—review of its absolute configuration and related compounds

The absolute configuration of botrylactone, a unique compound with an interesting polyketide lactone skeleton with two oxirane bridges previously isolated from Botrytis cinerea and described as a powerful antibiotic, has been reviewed on the basis of sign of the optical rotation, NOE experiments and NMR method. The isolation of 7-deoxybotrylactone and 5-hydroxy-7-(4-hydroxydec-2(3)-enoyl) botrylactone enables us to characterize an intriguing new family of compounds with this interesting polyketide skeleton. A common biosynthetic origin with botcinin derivatives is proposed.     

Biosynthesis of spiro-mamakone A, a structurally unprecedented fungal metabolite

Biosynthetic studies on spiro-mamakone A (1), a potently cytotoxic and antimicrobial compound from an endophytic fungus isolated from the New Zealand native tree Knightia excelsa (rewarewa), confirm the polyketide origins of this unique compound belonging to the spirobisnaphthalene class of compounds. The biosynthesis proceeds via an unprecedented symmetric enedione with the two halves of the molecule being formed from two separate pentaketide units connected by oxidative coupling.     

Simplextones A and B, unusual polyketides from the marine sponge Plakortis simplex

Two novel polyketides, simplextones A (1) and B (2), were isolated from the sponge Plakortis simplex. Their structures were established by spectroscopic methods. The absolute configurations were assigned by modified Mosher's method, X-ray crystallographic analysis, and quantum mechanical calculation of the electronic circular dichroism (ECD) spectrum. Compounds 1 and 2 featured an unprecedented polyketide skeleton via the connection of a single carbon-carbon bond to form a cyclopentane. These compounds also exhibited moderate cytotoxicity.     

Biosynthesis of furanochromones in Pimpinella monoica

During a search for bioactive compounds from indigenous plants,Pimpinella monoica (Umbelliferae) was found to contain furocoumarin, isopimpenellin (3) and five biogenetically related furocoumarins viz khellin (1), visnagin (2), visamminol (4), ammiol (5) and khellol (6). Labelled (i) and (2) were isolated from [1−¹⁴C]- and [2−¹⁴C]-acetates. Labelling pattern, determined by degradation of biosynthesised compounds, establishes the polyketide origin of their aromatic and pyrone rings while the furan ring originates via an acetate-mevalonate pathway. The plant also utilises glycine and leucine as substratevia acetate. Biotransformation of [3−³H]-visnagin to (6) but not to (2) was also observed.     

Stereochemical determination of tetrahydropyran-substituted xanthones from fungus Chaetomium murorum

Chaetoxanthone D (1), a new tetrahydropyran-substituted xanthone originated from polyketide pathway, together with the four known natural products chaetoxanthone C (2), alternariol methyl ether (3), alternariol (4) and 2,5-dimethyl-7-hydroxychromone (5) was isolated from a strain of Chaetomium murorum. The structures of these compounds were elucidated based on extensive spectroscopic analyses. The absolute configurations of 1 and 2 were determined by using quantum chemical electronic circular dichroism (ECD) calculations.     

One metabolite, two pathways: convergence of polypropionate biosynthesis in fungi and marine molluscs

Structural similarity or even the identity of polyketide compounds does not necessarily imply unique biosynthesis. Feeding experiments with a (13)C labeled precursor establish that the C(3) units in 7-methyl-cyercene-1 (1) are derived from intact propionate in the marine mollusc Ercolania funerea. The same compound in the terrestrial fungus Leptosphaeria maculans/Phoma lingam is synthesized by an acetate/SAM pathway thus proving for the first time metabolic convergence of polyketide biosynthesis in eukaryotes. Traditional (1)H-(13)C NMR correlation spectroscopy has been successfully applied to estimate (13)C incorporation in biosynthetic experiments.     

Enzymatic formation of an unnatural C(6)-C(5) aromatic polyketide by plant type III polyketide synthases

[reaction: see text] Substrate specificities of plant polyketide synthases (PKSs) were investigated using analogues of malonyl-CoA, the extension unit of the polyketide chain elongation reactions. When incubated with methylmalonyl-CoA and 4-coumaroyl-CoA, plant PKSs (chalcone synthase from Scutellaria baicalensis, stilbene synthase from Arachis hypogaea, and benzalacetone synthase from Rheum palmatum) afforded an unnatural C(6)-C(5) aromatic polyketide, 1-(4-hydroxyphenyl)pent-1-en-3-one, formed by one-step decarboxylative condensation of the two substrates. In contrast, succinyl-CoA was not accepted as a substrate by the enzymes.     

Biosynthesis of tetrapetalones

The biosynthesis of tetrapetalones (tetrapetalones A, B, C, and D) in Streptomyces sp. USF-4727 was studied by feeding experiments with [1-13C] sodium propanoate, [1-13C] sodium butanoate, [carbonyl-13C] 3-amino-5-hydroxybenzoic acid (AHBA) hydrochloride, and [1-13C] glucose, followed by analysis of the 13C-NMR spectra. These feeding experiments revealed that the four tetrapetalones were polyketide compounds constructed from propanoate, butanoate, AHBA, and glucose. The tetrapetalone biosynthetic pathway was also suggested in this study. In this pathway, tetrapetalone A (1) is synthesized by polyketide synthase (PKS) using AHBA as a starter unit, then the side chain of 1 is subjected to acetoxylation to produce tetrapetalone B (2). Additionally, 1 is oxidized and transformed into tetrapetalone C (3). In a similar way, 2 is converted to tetrapetalone D (4). Therefore, the biosynthetic relationship of the four tetrapetalones was indicated.     

An iterative type I polyketide synthase PKSN catalyzes synthesis of the decaketide alternapyrone with regio-specific octa-methylation

A biosynthetic gene cluster containing five genes, alt1-5, was cloned from Alternaria solani, a causal fungus of early blight disease to tomato and potato. Homology searching indicated that the alt1, 2, and 3 genes code for cytochrome P450s and the alt4 gene for a FAD-dependent oxygenase/oxidase. The alt5 gene encodes a polyketide synthase (PKS), named PKSN, that was found to be an iterative type I complex reduced-type PKS with a C-methyltransferase domain. To identify the PKSN function, the alt5 gene was introduced into the fungal host Aspergillus oryzae under an alpha-amylase promoter. The transformant produced a polyketide compound, named alternapyrone, whose structure is shown to be 3,5-dimethyl-4-hydroxy-6-(1,3,5,7,11,13-hexamethyl-3,5,11-pentadecatrienyl)-pyran-2-one. Labeling experiments confirmed that alternapyrone is a decaketide with octa-methylation from methionine on every C(2) unit except the third unit.     

Cytotoxic metabolites from the soil-derived fungus Exophiala pisciphila

A new polyketide compound 1 and a new naturally occurring chromone derivative 2, along with two known indole alkaloids 3-4 were characterized from the ethyl acetate extract of a soil-derived fungal strain, Exophiala pisciphila PHF-9. The structures of compounds 1-4 were established by detailed spectroscopic analysis and comparison with literature data. The absolute configuration of 1 was determined by a modified Mosher's method. Compound 1 exhibited moderate cytotoxicity against A-549, Hela, PANC-28 and BEL-7402 cell lines.     

Further studies on the biosynthesis of the manumycin-type antibiotic, asukamycin, and the chemical synthesis of protoasukamycin

Asukamycin (2), a metabolite of Streptomyces nodosus ssp. asukaensis ATCC 29757 and a member of the manumycin family of antibiotics, is assembled from three components, an "upper" polyketide chain initiated by cyclohexanecarboxylic acid, a "lower" polyketide chain initiated by the novel starter unit, 3-amino-4-hydroxybenzoic acid (3,4-AHBA), and a cyclized 5-aminolevulinic acid moiety, 2-amino-3-hydroxycyclopent-2-enone (C(5)N unit). To shed light on the order in which these components are assembled, we synthesized in labeled form various potential intermediates and evaluated their incorporation into 2. The assembly of the molecular framework of 2 from 3,4-AHBA and cyclohexanecarboxylic acid apparently does not involve free, unactivated intermediates. However, protoasukamycin (12), the total synthesis of which is reported, was efficiently converted into 2, demonstrating that the modification of the aromatic ring to the epoxyquinol structure is the terminal step in the biosynthesis. The results suggest that the two polyketide chains are synthesized separately and that the "upper" chain must be connected to the "lower" polyketide chain before the C(5)N unit.     

Two new antimicrobial metabolites from the endophytic fungus, Seimatosporium sp

Two new acaranoic acids, named seimatoporic acid A and B (1, and 2), together with six known compounds, R-(-)-mellein (3), cis-4-hydroxymellein (4), trans-4-hydroxymellein (5), 4R-hydroxy-5-methylmellein (6), (-)-5-hydroxymethylmellein (7), and ergosterol (8) were isolated from an endophytic fungus, Seimatosporium sp, by a bioassay-guided procedure. The structures of the new compounds have been assigned from analysis of the 1H and 13C NMR spectra, DEPT, and by 2D COSY, HMQC, HMBC and NOESY experiments. A mixture of compounds 1 and 2 showed strong antifungal activity against Botrytis cinerea, Septoria tritici, and Pyricularia oryzae.     

The type I rat fatty acid synthase ACP shows structural homology and analogous biochemical properties to type II ACPs

While X-ray and NMR structures are now available for most components of the Type II fatty acid synthase (FAS), there are no structures for Type I FAS domains. A region from the mammalian (rat) FAS, including the putative acyl carrier protein (ACP), has been cloned and over-expressed. Here we report multinuclear, multidimensional NMR studies which show that this isolated ACP domain contains four alpha-helices (residues 8-16 [1]; 41-51 [2]; 58-63 [3] and 66-74 [4]) and an overall global fold characteristic of ACPs from both Type II FAS and polyketide synthases (PKSs). The overall length of the structured ACP domain (67 residues) is smaller than the structured regions of the Eschericia coli FAS ACP (75 residues), the actinorhodin PKS ACP (78 residues) and the Bacillus subtilis FAS ACP (76 residues). We further show that the rat FAS ACP is recognised as an efficient substrate by enzymes known to modify Type II ACPs including phosphopantetheinyl and malonyl transferases, but not by the heterologous S. coelicolor minimal polyketide synthase.     

Synthesis and characterization of Ru2(DMBA)4X2 (X = CN, N3, N(CN)2, I): controlling structural, redox, and magnetic properties with axial ligands

Metathesis reactions between Ru(2)(DMBA)(4)Cl(2) (DMBA = N,N'-dimethylbenzamidinate) and MX (M = Na and K) yielded bis-adduct derivatives Ru(2)(DMBA)(4)X(2) (X = CN (1), N(3) (2), N(CN)(2) (3)). Metathesis reactions between Ru(2)(DMBA)(4)(NO(3))(2) and KI resulted in Ru(2)(DMBA)(4)I(2) (4). Compound 1 is diamagnetic, while compounds 2-4 are paramagnetic (S = 1). Both compounds 1 and 2 undergo two reversible one-electron processes, an oxidation and a reduction, while compound 3 features a quasireversible reduction. Single-crystal X-ray diffraction studies revealed that the Ru-Ru bond lengths are 2.4508(9), 2.3166(7), 2.304[1], and 2.328(1) A for compounds 1-4, respectively. Structural and electrochemical data clearly indicate that the axial ligands impart a significant influence on the electronic structures of diruthenium species.