Susanne Grabley

Benzopyrenomycin, a Cytotoxic Bacterial Polyketide Metabolite with a Benzo[a]pyrene‐Type Carbocyclic Ring System

Polyketides form a major class of secondary metabolites of bacteria, fungi, and plants with broad structural diversity as a result of dense functionalization and spatial properties. Many polyphenolic derivatives have found considerable interest as pharmaceuticals, biological tools, and dyes. A hallmark of aromatic polyketides is their common biogenesis from simple acyl and malonyl units through the action of different types of iterative polyketide synthases. The orchestrated assembly and processing of the biosynthetic intermediates gives rise to polyphenolic compounds that differ widely in the number of carbocycles they contain, their topology, and the substitution of the rings. From a structural point of view, it is remarkable that only a limited number of carbocyclic (aromatic) polyketide frameworks occur naturally. Linear and monoangular polyphenolic ring systems are found almost exclusively (Scheme 1); perifused carbocycles, in which rings are fused through more than one face, are rarities. A possible rationale for this observation is the preferred U-shaped folding of a nascent poly-b-keto chain. S-shaped cyclization patterns, as in the biosynthesis of the pentacyclic “discoid” Streptomyces naphthanthrene metabolites resistomycin and resistoflavin, are clear exceptions. Some phenalenes and benz[d,e]anthracenes from plants and fungi are probably also formed by an alternating polyketide folding pattern, whereas the biosynthesis of phenylphenalenones involves intramolecular cycloaddition with a cinnamoyl-derived moiety. Homologous tetracyclic pyrenes thought to be derived from phenanthrenes have been isolated from Uvaria and Juncus spp. An important example of a perylene is altertoxin, which is formed by naphthol dimerization in analogy with the hypericin biosynthetic pathway. To date, however, a significant gap has remained between the pentacyclic pentangular and discoid polyketide structures: the benzo[a]pyrene scaffold. Benzo[a]pyrenes are only known as notorious products of the pyrolysis of organic matter which are transformed into carcinogens upon epoxidation. No example of the biogenesis of a related carbocyclic system has been described. Herein, we report the first discovery of a natural product with a benzo[a]pyrene framework. During the course of metabolic profiling of the ketalin producer Streptomyces lavendulae (strain T< 1668), we noted the formation of minute amounts of a novel aromatic compound with UVabsorptions at lmax= 417, 251, and 217 nm when the strain was cultured on a large scale (2 > 50 L). Highresolution EIMS provided sufficient evidence that the compound had not been described previously. The crude extract was subjected to purification first with amberlite XAD16, then by reversed-phase flash chromatography (RP18) and subsequent open-column chromatography on Sephadex LH20 and silica gel. The new compound 1 (7 mg in total) was isolated as a yellow solid. A series of biological assays with 1 revealed inhibitory activity against various tumor-cell lines. Compound 1 showed strong antiproliferative activity against the cell lines L-929 and K562 with GI50 values of 3.2 mgmL 1 (8.2 mm) and 4.2 mgmL 1 (10.8 mm), respectively, and moderate cytotoxicity against HeLa cells with a CC50 value of 26.4 mgmL 1 (68.0 mm). The structure of the cytotoxic metabolite was resolved fully by MS and NMR spectroscopy. High-resolution EIMS Scheme 1. Structure-based phylogeny of fundamental dito pentacyclic ring systems found in natural aromatic polyketides; no natural product with a benzo[a]pyrene-type skeleton was known previously. Shared faces are highlighted in bold.

Direct detection of Kitasatospora species with a chaperone oligonucleotide microarray method lacking PCR amplification.

Identification of members of the genus Kitasatospora from soil samples has been introduced to evaluate occurrence of potential natural compound producers in different habitats. The microarray hybridization usually involves PCR amplification of the target DNA. Since PCR might lead to biased amplification, a diagnostic Kitasatospora microarray technique was improved by a protocol lacking PCR amplification prior to hybridization. The described advanced hybridization method used chaperone oligonucleotides for direct co‐hybridization with genomic DNA on an oligonuclotide microarray with optical readout. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)