Multiple convergence in polyketide biosynthesis: a third folding mode to the anthraquinone chrysophanol.

The polyketide chrysophanol is shown to be formed, in an organism-specific way, by a third folding mode, involving a remarkable cyclization of a bicyclic diketo precursor, thus establishing the first example of multiple convergence in polyketide biosynthesis.

Genoketides A1 and A2, new octaketides and biosynthetic intermediates of chrysophanol produced by Streptomyces sp. AK 671.

The new aromatic polyketides genoketide A1, genoketide A2 and prechrysophanol glucuronide are biosynthetic intermediates of the octaketide chrysophanol. They were isolated from the alkaliphilic strain Streptomyces sp. AK 671 together with the new metabolite chrysophanol glucuronide. The structures of the compounds were elucidated by mass spectrometry and NMR methods. Genoketide A2 exhibited a slight and prechrysophanol glucuronide a more pronounced inhibition of the proliferation of L5178y lymphoma cells.

Gephyromycin, the first bridged angucyclinone, from Streptomyces griseus strain NTK 14.

The new, highly oxygenated angucyclinone gephyromycin was isolated from an extract of a Streptomyces griseus strain. Its unprecedented ether-bridged structure was elucidated by NMR methods and substantiated by single crystal X-ray analysis. The absolute configuration was evidenced by quantum chemical CD calculations. Gephyromycin exhibits glutaminergic activity towards neuronal cells. Furthermore, the known compounds fridamycin E and dehydrorabelomycin were identified.

Pyrocoll, an antibiotic, antiparasitic and antitumor compound produced by a novel alkaliphilic Streptomyces strain.

A new secondary metabolite was detected in the culture extract of Streptomyces sp. AK 409 by HPLC-diode-array screening. The metabolite was identified as pyrocoll, which is known to be a constituent of cigarette smoke. Pyrocoll is known as a synthetic compound, but until now had not been isolated as a natural product from a microorganism. The compound showed biological activity against various Arthrobacter strains, filamentous fungi, several pathogenic protozoa, and some human tumor cell lines.

Atroposelective biaryl coupling with chiral catalysts: total synthesis of the antileishmanial naphthylisoquinoline alkaloids ancistrotanzanine B and ancistroealaine A.

[reaction: see text] The first total synthesis of the naphthylisoquinoline alkaloid ancistrotanzanine B and its atropo-diastereomer, ancistroealaine A, is described. The key step is the construction of the rotationally hindered and thus stereogenic biaryl axis by Suzuki coupling. While only weak internal asymmetric inductions by the stereogenic center in the dihydroisoquinoline part were observed, much better atropisomeric ratios in favor of ancistrotanzanine B were achieved by the use of chiral catalysts. Both alkaloids, in particular ancistrotanzanine B, show high antileishmanial activities.

Nepenthes insignis uses a C2-portion of the carbon skeleton of L-alanine acquired via its carnivorous organs, to build up the allelochemical plumbagin.

Tropical pitcher plants (Nepenthes) catch animals in their specialized cup-shaped leaves, digest the prey by secreting enzymes, and actively take up the resulting compounds. The benefit of this behaviour is the ability to grow and compete in nutrient-poor habitats. Our present in vitro study shows that not only the nitrogen of alanine fed to the carnivorous organs is used by the plant but that in addition intact C2-units derived from C-2 and C-3 of stable isotope labelled L-alanine serve as building blocks, here exemplarily for the synthesis of the secondary metabolite plumbagin, a potent allelochemical. This result adds a new facet to the benefit of carnivory for plants. The availability of plumbagin by a de novo synthesis probably enhances the plants' fitness in their defence against phytophagous and pathogenic organisms. A missing specific uptake or CoA activation mechanism might be the reason that acetate fed to the pitchers was not incorporated into the naphthoquinone plumbagin. The dihydronaphthoquinone glucosides rossoliside and plumbaside A, here isolated for the first time from Nepenthes, by contrast, showed no incorporation after feeding of any of the two precursors, suggesting these compounds to be storage forms with probably very low turnover rates.