Two new metabolites, (4S)‐(+)‐ascochin (1a) and (S,S)‐(+)‐ascodiketone (3), together with the known compounds (3R,4R)‐(–)‐4‐hydroxymellein (2), ent‐α‐cyperone (4) and (3S,4R)‐(–)‐dihydroxy‐(6S)‐undecyl‐α‐pyranone (5) were isolated from cultures of the of the endophytic fungus Ascochyta sp. The biologically active isocoumarin derivative, (4S)‐(+)‐ascochin (1a), has an unusual substitution pattern which was confirmed by X‐ray diffraction. Its absolute configuration was determined by our solid‐state TDDFT CD methodology using the X‐ray coordinates as input for the calculation. By catalytic hydrogenation, (4S)‐(+)‐ascochin was converted into the corresponding (3S,4S)‐dihydroisocoumarin derivative 1b. The measured and TDDFT calculated CD spectra enabled studies on the correlation between absolute configuration and n‐π* transition Cotton effect. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
To determine the best sources of novel, biologically active metabolites, both endophytic fungi (plant isolates) and fungi associated with algae were isolated from plants and algae from marine habitats of the North, Baltic and Mediterranean Seas, Atlantic Ocean, and Gulf of Mexico. Following preselection of the isolates according to taxon and metabolic profiles, almost all were active in at least one of the tests for antibacterial, antifungal, and/or herbicidal activities. Metabolites isolated from the culture extracts belonged to diverse structural groups; 42% were previously unknown structures. Compared to fungi associated with algae, endophytic fungi were a better source of novel metabolites and antifungal culture extracts; they produced a higher number of metabolites per fungus. Microsphaeropsis spp. and Coniothyrium spp. synthesized the highest numbers of novel metabolites per isolate, and Geniculosporium, Nodulisporium and Phomopsis the greatest numbers of metabolites per isolate. Based on the proportion of novel to known metabolites, endophytic fungi from marine environments equalled endophytes from terrestrial habitats. Metabolic profiles (HPLC-DAD) of the saprophytic, marine fungi belonging to Dendryphiella spp. from diverse temperate and subtropical locations revealed that geographical source of the isolates had little qualitative effect on secondary metabolite production in this genus.
Two new isochromans named pseudoanguillosporin A (2a) and B (3), together with the known cephalochromin (1), were isolated from Pseudoanguillospora sp. The C‐2 absolute configuration of 2a and 3 was deduced from its CD spectrum by the isochroman helicity rule, supported by TDDFT CD calculations. The absolute configuration of the sec‐hydroxyl group of 3 was determined by the Mosher NMR method from the MPA esters of its methylated derivative. The axial chirality of 1 was assigned through exciton analysis of its CD spectrum and confirmed by ZINDO CD calculations. The metabolites showed broad antimicrobial activities.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Thirteen new metabolites, namely oblongolides B–M (2–13) and 4‐[5‐(1‐hydroxyethyl)furan‐2‐yl]‐4‐oxobutanoic acid (14), together with the six known compounds phomopsolide B (15), alternariol dimethyl ether (16), alternariol monomethyl ether (17), the mycotoxin alternariol (18), ergosterol (19), and 5α,8α‐epidioxyergosterol (20) were isolated from the endophytic fungus Phomopsis sp. The new biologically active norsesquiterpene γ‐lactones differ in their degree of substitution, saturation, and substituent pattern from the known oblongolide 1. Their structures were determined by means of spectroscopic data including HREIMS, 1H NMR, 13C NMR, 2D NMR (HMQC, HMBC, NOESY) and X‐ray single crystal analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Cultivation of the marine-derived streptomycete isolate B8005 delivered three known antibiotics, resistomycin (1), resistoflavin (3a) and tetracenomycin (4), and a further member of the rare resistomycin class, the weakly antibiotically active 1-hydroxy-1-norresistomycin (2). From a related marine strain B4842, 1 and resistoflavin methyl ether (3b) have been isolated. The formation of 2 is of interest from a biosynthetic point of view.Keywords resistomycin, 1-hydroxy-1-norresistomycin, marine streptomycetes, natural product, structure elucidationIn the course of our screening of streptomycetes for new bio-active secondary metabolites, extracts of the marine Streptomyces isolate B8005 showed inhibitory activity against Escherichia coli, Staphylococcus aureus, Streptomyces viridochromogenes (Tü 57), Mucor miehei, Candida albicans, and the microalga Chlorella vulgaris. Additionally it possessed cytotoxic activity against Artemia salina. In the TLC screening, the extract showed moderately polar yellow and red spots. Work-up delivered three known antibiotics, resistomycin (1) [1,2], resistoflavin (3a) [1,3] and tetracenomycin (4) [4], and a new resistomycin derivative, 1-hydroxy-1-norresistomycin (2), as a further active principle. From a second marine Streptomyces isolate B4842, resistoflavin methyl ether (3b) has been isolated, along with 1. Resistomycin (1) is a quinone-related antibiotic with unique structure and possesses bactericidal and vasoconstrictive activity. It inhibits RNA and protein synthesis, but has no effect on DNA synthesis [5]. It was so far the only further member of this type of compounds.The Streptomyces strain B8005 has been derived from sediment of the Laguna de Terminos at the Gulf of Mexico and was isolated on M3-medium [6]. The partial 16S rRNA gene sequence of the strain B8005 is identical with that of the strain Streptomyces albogriseolus (DSM 40003) and Streptomyces viridodiastaticus (DSM 40249). However, the strain B8005 differs from both strains in forming a chocolate brown substrate mycelium. The spore mass is gray, spore chains are spiral; the surface of spores is spiny. Melanin pigment is neither produced on peptone -yeastextract iron agar [7] nor on tyrosine agar [7] but a chocolate brown pigment is found in media like yeast -extract maltextract agar [8] and chitin agar [8]. The optimum growth temperature is at about 30°C. The strain does not grow at 10°C but shows growth at 45°C. Growth occurred in media from 0% up to 10% seawater salinity. Chitin, cellulose, starch, casein, gelatine, and esculin are degraded. The strain is catalase and nitrate reductase positive. The use of
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