Streptomonospora litoralis sp. nov., a halophilic thiopeptides producer isolated from sand collected at Cuxhaven beach

Antonie van Leeuwenhoek - Strain M2T was isolated from the beach of Cuxhaven, Wadden Sea, Germany, in course of a program to attain new producers of bioactive natural products. Strain M2T produces...     

Iromycins from Streptomyces sp. and from synthesis: new inhibitors of the mitochondrial electron transport chain

Two new alpha-pyridone metabolites, iromycins E and F, were isolated from cultures of strain Streptomyces sp. Dra 17, thus expanding the recently discovered iromycin family. The inhibitory potential on the mitochondrial respiratory chain was examined and revealed that iromycin metabolites block NADH oxidation in beef heart submitochondrial particles with different efficacy, yet remarkably show only very low cytotoxicity. Difference spectroscopic studies indicated that iromycins inhibit the electron transport at the site of complex I (NADH-ubiquinone oxidoreductase). Derivatives of the natural products were semisynthetically prepared and provided detailed insights into structure-activity relationships. Drawn from these results, there are strong similarities with the piericidins, which are among the most potent complex I inhibitors of the mitochondrial electron transport chain. Furthermore, total synthesis afforded new analogues, and the non-natural iromycin S (IC50 = 58 ng/mL) emerged as the most active compound, thus opening avenues of future studies with the iromycins as new valuable biochemical tools.     

Hypoxyvermelhotins A–C,new pigments from Hypoxylon lechatii sp. nov

A new species of Hypoxylon was discovered, based on material collected in French Guiana and recognised on the basis of new combination of morpholological characters in comparison with type and authentic material of macroscopically similar taxa. These findings were corroborated by the rather isolated positions of its ITS-nrDNA and beta-tubulin DNA sequences in molecular phylogenies. However, the most salient feature of this fungus only became evident by a comparison of its stromatal HPLC profile, revealing several secondary metabolites that were hitherto not observed in stromata of any other member of the Xylariaceae. Part of the stromata were subsequently extracted to isolate these apparently specific components, using preparative chromatography. Five metabolites were obtained in pure state, and their chemical structures were elucidated by means of high resolution mass spectrometry and nuclear magnetic resonance spectroscopy. They turned out to be tetramic acid derivatives of the so-called vermelhotin type. Aside from vermelhotin, previously isolated from cultures of endophytic fungi, we identified three novel congeners, for which the trivial names hypoxyvermelhotins A–C were proposed. Like vermelhotin, they constitute orange-red pigments and a preliminary biological characterisation revealed them to have rather strong cytotoxic and moderate to weak antimicrobial effects. These results further illustrate the high diversity of unique secondary metabolites in stromata of the hypoxyloid Xylariaceae, a family in which biological diversity seems to parallel the chemical diversity of their bioactive principles to a great extent.