Klaus-Dieter Menzel

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.

Hygrobafilomycin, a cytotoxic and antifungal macrolide bearing a unique monoalkylmaleic anhydride moiety, from Streptomyces varsoviensis

A new bafilomycin-type macrolide, named hygrobafilomycin (6), was isolated by a bioassay-guided selection and fractionation from a terrestrial actinomycete, Streptomyces varsoviensis, along with three known derivatives, bafilomycin D (3), C1 (4) and C2 (5). The structure of hygrobafilomycin was fully established by MS and NMR analyses, revealing a hygrolidin–bafilomycin hybrid with an unusual monoalkylmaleic anhydride moiety. Hygrobafilomycin (6) shows strong antifungal, antiproliferative and cytotoxic activities. In a panel of 40 tumor cell lines, compound 6 shows high cytotoxic potency (mean IC50=5.3 n).

Pyrrole and indole alkaloids from an endophytic Fusarium incarnatum (HKI00504) isolated from the mangrove plant Aegiceras corniculatum

Two new pyrrole alkaloids, N-[4-(2-formyl-5-hydroxymethyl-pyrrol-1-yl)-butyl]-acetamide (1) and N-[5-(2-formyl-5-hydroxymethyl-pyrrol-1-yl)-pentyl]-acetamide (2), and a new indole derivative (3aR,8aR)-3a-acetoxyl-1,2,3,3a,8,8a-hexahydropyrrolo-[2,3-b]indol (3) were isolated, together with ( − )-3a-hydroxyfuroindoline, (3aR,8aS)-1-acetyl-1,3,3a,8,8a-hexahydropyrrolo-[2,3-b]indol-3a-ol, and N-acetyltryptamine A, from an endophytic ascomycetous fungus, Fusarium incarnatum (HKI00504), which was isolated from the mangrove plant Aegiceras corniculatum. The structures of compounds 1–3 were determined on the basis of extensive spectroscopic data analyses.

Production and derivate composition of trisporoids in extended fermentation of Blakeslea trispora

Trisporic acid, its precursors and derivatives are used within zygomycete fungi as communication signals and sexual regulators, and also influence the production rate of the parent compound, β-carotene. Cultivation parameters during growth and the trisporoid production phase of Blakeslea trispora were studied in two-step shake flask cultures and up-scaled fermentations. Comparison of various fermentation protocols allowed the definition of parameters governing trisporoid production. Highest yields were obtained when the initial growth phase allowed for both rapid growth and fast exhaustion of nitrogen and phosporous sources. Onset of trisporoid production is accompanied by a pH drop in the medium and triggered by nutrient limitation, nitrogen depletion being the most important factor. Supplementation of cultures with carbon at low concentration after onset of trisporoid production led to prolonged growth and higher final product accumulation. B. trispora produces trisporoids in two major series, B and C. During a first peak in trisporic acid accumulation, production of trisporic acid B exceeds that of trisporic acid C, which later accumulates at the expense of the trisporic acid B, indicating a variable regulation of the ratio between these metabolites. These data are valuable for tailoring production systems for enrichment of specific intermediates of this complex signal family.