Cladobotric acids A-F: new cytotoxic polyketides from a New Zealand Cladobotryum sp

[reaction: see text] Cladobotric acids A-F (1-6), fungal-derived polyketides, were isolated from the fermentation broth of a New Zealand Cladobotryum species. Structures were determined by extensive spectral analysis and X-ray crystallography, and the polyketide origin of 1-6 was concluded from feeding experiments with (13)C-labeled precursors. The observed folding pattern for the polyketide chain is unusual for fungi. Cladobotric acids A-F (1-6) exhibited notable cytotoxicity against the murine P388 leukemia cell line and were also active against Bacillus subtilis and Candida albicans.     

Chemistry and cytotoxic activities of polyketides produced by the mangrove endophytic fungus <Emphasis Type="Italic">Phomopsis</Emphasis> SP. ZSU-H76

A new polyketide, 2-(7′-hydroxyoxooctyl)-3-hydroxy-5-methoxybenzeneacetic acid ethyl ester (1), together with three known compounds dothiorelone A (2), B (3), and C (4) were isolated from the mangrove endophytic fungus Phomopsis sp. ZSU-H76 obtained from the South China Sea. Their structures were elucidated by spectroscopic methods, mainly 1D and 2D NMR spectroscopic techniques. Primary bioassays showed that 1 exhibited cytotoxicity against HEp-2 and HepG2 cells with IC₅₀ values of 25 and 30 μg/mL, respectively.     

Chaetominine, a cytotoxic alkaloid produced by endophytic Chaetomium sp. IFB-E015

Chaetominine (1), an alkaloidal metabolite with a new framework, was characterized from the solid-substrate culture of Chaetomium sp. IFB-E015, an endophytic fungus on the apparently healthy Adenophora axilliflora leaves. Its structure was determined by a combination of its spectral data and single-crystal X-ray diffraction analysis, with its absolute configuration elucidated by Marfey's method. Chaetominine was more cytotoxic than 5-fluorouracil against the human leukemia K562 and colon cancer SW1116 cell lines. [structure: see text]     

Emericelactones A-D: Four novel polyketides produced by Emericella sp. XL 029, a fungus associated the leaves of Panax notoginseng

The application of an OSMAC approach on an endophytic fungus Emericella sp. XL 029 has yielded four novel polyketides, emericelactones A-D (1–4).The structures and stereochemistry of 1–4 were elucidated by NMR and MS data analyses, computational methods, as well as by comparison with known compounds. Compound 1 contained an unprecedented linear pentaene substructure ending in an oxabicyclo[2.2.1]heptane moiety, while compounds 2–4 are epimers possessing an unprecedented linear triene structures ending in two cyclic moieties of an oxabicyclo[2.2.1]heptane and a cyclopentan-1-one. Compounds 1–4 showed moderate antimicrobial activities against three agricultural pathogenic fungi (Verticillium dahliae Kleb, Rhizoctonia solani and Gibberella saubinetii) and two human pathogenic bacteria (Micrococcus lysodeikticus and Salmonella typhi) with MIC values of 25–50?μg/mL.     

Enzymatic formation of unnatural novel polyketides from alternate starter and nonphysiological extension substrate by chalcone synthase

[reaction: see text] In the chalcone synthase (CHS) enzyme reaction, both the starter molecule and the extension unit of the polyketide chain elongation reaction were simultaneously replaced with nonphysiological substrates. When incubated with benzoyl-CoA and methylmalonyl-CoA as substrates, recombinant CHS from Scutellaria baicalensis afforded an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-phenyl-pyran-2-one, along with a tetraketide, 4-hydroxy-3,5-dimethyl-6-(1-methyl-2-oxo-2-phenyl-ethyl)-pyran-2-one. On the other hand, the enzyme also accepted hexanoyl-CoA and methylmalonyl-CoA as substrates to produce an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-pentyl-pyran-2-one.     

Alkaloids produced by endophytic fungi: a review

In recent years, a number of alkaloids have been discovered from endophytic fungi in plants, which exhibited excellent biological properties such as antimicrobial, insecticidal, cytotoxic, and anticancer activities. This review mainly deals with the research progress on endophytic fungi for producing bioactive alkaloids such as quinoline and isoquinoline, amines and amides, indole derivatives, pyridines, and quinazolines. The biological activities and action mechanisms of these alkaloids from endophytic fungi are also introduced. Furthermore, the relationships between alkaloid-producing endophytes and their host plants, as well as their potential applications in the future are discussed.     

Proline-catalyzed asymmetric assembly reactions: enzyme-like assembly of carbohydrates and polyketides from three aldehyde substrates

Directed asymmetric assembly of simple achiral building blocks into stereochemically complex molecules like triketides has been described for the first time using l-proline catalyzed asymmetric double aldol reactions. The product pyranoses contain four asymmetric centers constructed under proline catalysis in a highly diastereoselective and modestly enantioselective fashion from three aldehyde molecules. These results suggest that the construction of complex products from simple starting materials is within the realm of organocatalysis involving the simple naturally occurring amino acid l-proline. Our successful assembly of pyranoses from simple aldehydes under proline catalysis suggests that this approach may warrant consideration as a prebiotic route to sugars and polyketides.     

Aspergiolides C and D: spirocyclic aromatic polyketides with potent protein kinase c-Met inhibitory effects

Variation of the cultivation conditions for Aspergillus glaucus led to the discovery of two novel spirocyclic aromatic polyketides, aspergiolides C (3) and D (4). Their constitutions were elucidated by a combination of spectroscopic methods and isotope-labeling experiments. Aspergiolides C (3) and D (4) occur as racemic mixtures, the resolution of which was succeeded by HPLC on a chiral phase. The absolute configurations of their enantiomers were assigned online, from the peaks in the chromatogram, by a combination of HPLC-CD and quantum chemical CD calculations. Both compounds were found to inhibit the kinase activities of the receptor tyrosine kinases (RTKs) c-Met, Ron, and c-Src with low-micromolar IC(50)s. The enantiomers of 3 were resolved by HPLC on a chiral phase. Both enantiomers showed a comparable inhibition of the HGF-induced autophosphorylation of c-Met and of subsequent cell migration.     

Absolute stereostructures of cytotoxic metabolites, chaetomugilins A-C, produced by a Chaetomium species separated from a marine fish

Chaetomugilins A-C were isolated from a strain of Chaetomium globosum originally isolated from the marine fish Mugil cephalus, and their absolute stereostructures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques, some chemical transformations, and an X-ray analysis. This compound exhibited significant cytotoxicity against cultured P388 cells and HL-60 cells.     

The marine sponge Plakortis zyggompha: a source of original bioactive polyketides

Three new spiculoic acids 1-3 and two members of a new closely related family of natural products named zyggomphic acids 4 and 5 were isolated from the very little studied marine sponge Plakortis zyggompha. Both families of compounds share a unique trans-hydrindan-2-one skeleton with six stereogenic centers. A total of 15 new metabolites were isolated from this sponge, all are of polyketide origin. The structures were elucidated using LC-MS, 1D, and 2D NMR methods. The absolute stereochemistry was determined by circular dichroism. The large number of close bioactive analogues allowed us to propose preliminary structure-activity relationships as antitumoral and antimycobaterial agents.     

Tetrahydrolipstatin: Degradation products produced by human carboxyl-ester lipase

The fate of tetrahydrolipstatin ( 1 ) incubated with human carboxyl-ester lipase (HCEL) was investigated. The primary metabolite was identified as δ-(N-formyl-L -leucyloxy)-β-hydroxy acid 2a with conserved configuration. It is formed by attack of the active-site serine of HCEL at the carbonyl C-atom of the β-lactone ring of 1 followed by hydrolysis of the intermediate serine ester. Further products isolated were identified and a complete degradation scheme is proposed.     

Analysis of immunosuppressive drugs and their pharmaceuticals by micellar electrokinetic chromatography

Summary A simple and practical micellar electrokinetic capillary chromatography (MEKC) method is proposed for the quantitation of immunosuppressive drugs such as azathioprine (AZA), mycophenolate mofetil (MMF), cyclosporine A (CyA) and tacrolimus (FK 506). The electrophoretic separation of the analytes was performed with a background electrolyte containing 20 mM phosphate buffer at pH 7.5, 50 mM SDS and methanol as an organic modifier. Fused silica capillaries 75 μm i.d. and 60 cm in length were employed and detection of analytes was performed at 214 nm. Thorough validation according to international guidelines showed that the proposed method is reliable and appropiate for the routine analysis of immunosuppressants. Moreover, it may be an advantageous alternative to the traditional chromatographic methodologies currently employed in the pharmaceutical and bioanalysis fields.     

A unified synthetic approach to polyketides having both skeletal and stereochemical diversity

An efficient systematic approach to the diversity-oriented synthesis of polyketides has been developed to provide both skeletal and stereochemical diversity. Each synthetic intermediate is also a desired polyketide fragment and no protecting group manipulations are required. A first-generation synthesis provides a 74-membered polyketide library comprising six different skeletal classes, each in one to five steps from propargylic alcohol precursors. A study of epoxyol opening reactions revealed unusual reactivity trends based on epoxide configuration.     

Synthesis of isoxazoles en route to semi-aromatized polyketides: dehydrogenation of benzonitrile oxide-para-quinone acetal cycloadducts

A variety of highly functionalized polycyclic isoxazoles are prepared by a two-step protocol: (1) 1,3-dipolar cycloaddition of o,o'-disubstituted benzonitrile oxides to para-quinone mono-acetals, then (2) dehydrogenation. The cycloaddition proceeds in a regioselective manner, favouring the formation of the 4-acyl cycloadducts, which are suitable intermediates for the synthesis of semi-aromatized polycyclic targets derived from polyketide type-II biosynthesis.     

Tributyltin speciation in aquatic matrices by CGC-FPD and CGC-MS confirmation

An analytical procedure for the determination of tributyltin (TBT) in seawater, sediments and biota is described. Extraction of TBT as chloride is achieved by hydrochloric acid treatment followed by a liquid extraction using a modified solvent with a metal coordinating ligand, and a Grignard derivatization (CH₃MgCl). The organotin fraction was isolated from the derivatized extract by column chromatography. The final determination was accomplished by on-column capillary gas chromatography (CGC) coupled to a flame photometric detector (FPD) and mass spectrometry (MS) confirmation. The relative detection limits of the analytical procedure were dependent of the environmental compartment, 0.5 ng 1^–1 (as TBT) for seawater, and 0.1 ng g^–1 and 0.4 ng g^–1 for sediments and biota, respectively. The TBT recovery of fortified samples was in the range of 90% for water and biota, and of 60% in case of sediments. The reproducibility (RSD) of the whole procedure for three independent replicates was around 15%.     

Size fractionation of aquatic colloids and particles by cross-flow filtration: analysis by scanning electron and atomic force microscopy

The suitability of the combined application of environmental scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the evaluation of the ability of cross-flow filtration (CFF) to perform adequate size fractionation of freshwater colloids and particles was examined. ESEM and SEM imaging provided reference images of the CFF-generated fractions and, in estimating the experimental cut-off diameter of the membrane, provided evidence that separation was not consistent with nominal pore sizes of the membranes. However, analysis of the images showed that size distribution of CFF-generated fractions and the estimated cut-off diameter of the membranes were dependent on the advantages and limitations of the two imaging techniques. With both ESEM and SEM, best estimates of size cut-offs were lower than the nominal pore size of the membrane in the case of 0.45 μm membranes, but roughly accurate in the case of 0.1 μm pore size membranes. The results also suggested that the effectiveness of CFF may benefit from a pre-separation step using a minimally perturbing technique such as split thin-flow fractionation. AFM demonstrated the presence of colloids smaller than 50 nm in all fractions including the retentates, showing that CFF fractionation is not fully quantitative and not based on size alone. The results indicate that previous studies investigating trace element partitioning using CFF may need re-evaluation as the importance of particles and large colloids may be over-estimated.     

New methods for stereochemical determination of complex polyketides: configurational assignment of novel metabolites from myxobacteria

An overview on recently developed methods for the stereochemical determination of complex polyketides is given and NMR-spectroscopic, computational, biosynthetic and synthetic methods are discussed. These methods are presented in their applications to structurally novel polyketide classes from myxobacteria.     

A new polyketide purpurogenic acid: the activated production of polyketides by the diethyl sulphate mutagenesis of marine-derived Penicillium purpurogenum G59

A new polyketide, purpurogenic acid (1), and two known polyketides, (-)-mitorubrin (2) and (-)-mitorubrinol (3), were isolated from a fungal mutant derived from the diethyl sulphate (DES) mutagenesis of marine-derived Penicillium purpurogenum G59. The planar structure of new 1 was elucidated by spectroscopic methods and the absolute configuration was assigned on the basis of [α]_D and CD data. In our preliminary MTT assay, 1 inhibited human cancer K562, HL-60, HeLa and BGC-823 cells with the inhibition rates of 52.7, 78.8, 38.4 and 35.3% at the 100 μg/mL, respectively.     

Antimicrobial and allelopathic metabolites produced by Penicillium brasilianum

Six known compounds, isoroquefortine C (1), griseofulvin (2), ergosterol peroxide (3), 3β-hydroxy-(22E,24R)-ergosta-5,8,22-trien-7-one (4), cerevisterol (5) and (22E,24R)-6β-methoxyergosta-7,22-diene-3β,5α-diol (6), were produced by the fungus Penicillium brasilianum, and their structures were elucidated by spectroscopic methods. This is the first report on isoroquefortine C as naturally occurring compound. Their bioactivities against five phytopathogenic fungi (Gibeberalla saubinetti, Fusarium solani, Botrytis cinerea, Colletotrichum gloeosporioides and Alternaria solani) and four pathogenic bacteria (Escherichia coli, Bacillus subtilis, Staphyloccocus aureus and Bacillus cereus), as well as allelopathic activities on Raphanus sativus were tested. Compound 1 exhibited a remarkable antifungal activity with minimum inhibitory concentration (MIC) of 12.5 μM against C. gloeosporioides, in comparison with positive control hymexazol (MIC 25 μM). Compound 2 displayed strong inhibitory effects on the growth of A. solani and S. aureus with MIC of 3.13 μM for each. Compounds 2 and 3 displayed a significant growth-inhibition activity on R. sativus.