Metabolic products of microorganisms, 271. Momofulvenone A and B, new benzo[b]fluorene quinones fromStreptomyces

New Polyketide and Sesquiterpenoid Derivatives from the Magellan Seamount-Derived Fungus Penicillium rubens AS-130

Rubenpolyketone A (1), a polyketide featuring a new carbon skeleton having cyclohexenone condensed with a methyl octenone chain and a new linear sesquiterpenoid, chermesiterpenoid D (2), together with seven known secondary metabolites (3-9) were isolated and identified from the Magellan Seamount-derived fungus Penicillium rubens AS-130. Their structures were determined based on detailed analysis of NMR and mass spectroscopic data and the absolute configurations of these two new compounds were elucidated by the combination of quantum mechanical (QM)-NMR and time-dependent density functional (TDDFT) ECD calculation approaches. Chermesiterpenoids B (3) and C (4) showed potent inhibitory activities against the aquatic pathogen Vibrio anguillarum with MIC values of 0.5 and 1 μg/mL, respectively, while chermesin F (6) exhibited activity against Escherichia coli with MIC value of 1 μg/mL.

Konamycins A and B and Rubromycins CA1 and CA2, Aromatic Polyketides from the Tunicate-Derived Streptomyces hyaluromycini MB-PO13T

Four new aromatic polyketides, konamycins A (1) and B (2) and rubromycins CA1 (3) and CA2 (4), were isolated from the culture extract of the tunicate-derived Streptomyces hyaluromycini MB-PO13^T. Compounds 1 and 2 possess a benzo[ b]fluorene aglycon modified by C-glycosylation with l-amicetose. Compounds 3 and 4 are the new congeners of rubromycin in which a naphthoquinone and carboxylated isocoumarin are joined through a spiroketal carbon. The structures of these compounds were determined by extensive analysis of 1D and 2D NMR spectroscopic data. Compound 1 showed radical scavenging activity in DPPH and superoxide quenching assays, and 3 and 4 displayed antimicrobial activity against Gram-positive bacteria.

Direct access to benzo[b]fluorenes via a gold-catalysed A3-coupling strategy

A one-pot combination of gold catalysis and thermal cyclization provides a fast convergent route to benzo[b]fluorenes.

Quinone methide chemistry of prekinamycins: 13C-labeling, spectral global fitting and in vitro studies

In this article, we address the presence of the prekinamycin quinone methide using the techniques of spectral global fitting and the 13C-labeling of the reactive centre. Two-electron reduction of a prekinamycin affords a long-lived quinone methide species that was characterised spectrally. A correlation was made between the calculated DeltaE (kcal/mol) values for quinone methide tautomerisation and cytostatic activity to support the postulate that the quinone methide plays a role in prekinamycin biological activity. We also prepared a stable quinone methide of prekinamycin and studied its solution chemistry directly.