Gerhard Schlingmann

Diepoxins, novel fungal metabolites with antibiotic activity

Abstract Diepoxins ( 1-4 ), unique, spiroketal-linked bisepoxides have been isolated from a filamentous fungus. Structures were assigned to these compounds primarily on the basis of NMR data.

New α-pyrones produced by fungal culture LL-11G219 function as androgen receptor ligands

Abstract This report describes the isolation and characterization of several closely related compounds, produced by fungal culture LL-11G219, with androgen-like activity. Bioassay-guided isolation yielded four novel fermentation products of the α-pyrone class: 11G219α, β, γ, and δ. Structures were assigned to these compounds on the basis of spectroscopic data, particularly those from 1D and 2D NMR experiments. α-Pyrones bearing an olefinic side chain in conjunction with a 6-alkyl substitution were hitherto unknown.

Biosynthesis of Diazepinomicin/ECO-4601, a Micromonospora Secondary Metabolite with a Novel Ring System

The novel microbial metabolite diazepinomicin/ECO-4601 (1) has a unique tricyclic dibenzodiazepinone core, which was unprecedented among microbial metabolites. Labeled feeding experiments indicated that the carbocyclic ring and the ring nitrogen of tryptophan could be incorporated via degradation to the 3-hydroxyanthranilic acid, forming ring A and the nonamide nitrogen of 1. Genomic analysis of the biosynthetic locus indicated that the farnesyl side chain was mevalonate derived, the 3-hydroxyanthranilic acid moiety could be formed directly from chorismate, and the third ring was constructed via 3-amino-5-hydroxybenzoic acid. Successful incorporation of 4,6-D2-3-hydroxyanthranilic acid into ring A of 1 via feeding experiments supports the genetic analysis and the allocation of the locus to this biosynthesis. These studies highlight the enzymatic complexity needed to produce this structural type, which is rare in nature.

Isolation and identification of antifungal polyesters from the marine fungus Hypoxylon oceanicum LL-15G256

Abstract Cultures of the marine fungus Hypoxylon oceanicum (LL-15G256) were found to have potent antifungal activity in assays designed to detect inhibitors of fungal cell wall biosynthesis. Bio-activity guided isolation provided the macrocyclic polyesters 15G256α ( 1 ), 15G256α-1 ( 2 ) and 15G256β ( 3 ) that were partially responsible for the antifungal activity. In addition, fermentation beers contained a series of related, but unreported metabolites designated 15G256ι ( 4 ), 15G256ω ( 5 ), 15G256ο ( 6 ), 15G256α-2 ( 7 ), 15G256β-2 ( 8 ), 15G256ν ( 9 ) and 15G256π ( 10 ). Their isolation, characterization and structures are described here and a biosynthetic sequence is proposed.

Absolute Stereochemistry of the Diepoxins

Abstract The exciton coupled CD method has been applied to determine the absolute configuration of the diepoxins, spiroketal-linked naphthodiepoxydecalinones of fungal origin. The CD spectra of the bis-dimethylaminobenzoate derivatives of the diepoxins η, ι and κ, reveal a positive chiral twist between the two substituted hydroxyl groups and thus infer theS configuration at both of these stereogenic centers. The absolute configuration of the remaining chiral centers is deduced from their relative configurations as established by X-ray diffraction of diepoxin κ. The twist boat conformation of the epoxycyclohexanone ring and the continued axial orientation of the substituents at C-4 and C-5 after dimethylaminobenzoate derivatization was corroborated by1H-NMR coupling constants.

Evaluating Indole-Related Derivatives as Precursors in the Directed Biosynthesis of Diazepinomicin Analogues

The effectiveness of precursor-directed biosynthesis to generate diazepinomicin (1) analogues with varied ring-A substitutents was investigated by feeding commercially available, potential ring-A precursors such as fluorinated tryptophans, halogenated anthranilates, and various substituted indoles into growing actinomycete culture DPJ15 (genus Micromonospora). Two new monofluorinated diazepinomicin analogues (2 and 3) were identified and characterized by spectroscopic methods. Both derivatives showed modest antibacterial activity against the Gram-positive coccus Staphylococcus aureus with MIC values in the range 8-32 microg/mL.

Fumaquinone, a New Prenylated Naphthoquinone from Streptomyces fumanus

A new prenylated naphthoquinone antibiotic, fumaquinone (5,7-dihydroxy-2-methoxy-3-methyl-6-(3-methyl-but-2-enyl)[1,4]naphthoquinone) was isolated from cultures of Streptomyces fumanus (LL-F42248). Its chemical structure was determined primarily by NMR spectroscopy. Preliminary feeding experiments indicated the naphthoquinone is of polyketide origin, while the O-methyl and aromatic C-methyl groups are derived from methionine.

Strevertenes, antifungal pentaene macrolides produced by Streptoverticillcum LL-30F848

Abstract This report describes new polyenes isolated from fermentations with Streptoverticillium sp. LL-30F848. Structure elucidation using a variety of spectroscopic techniques, including extensive NMR studies, revealed that these pentaene macrolides lacked the otherwise common hemiketal-tetrahydropyran and aminoglycoside moieties, but still carried a carboxylic acid group. The unambiguous assignment of NMR signals attributed to the olefinic region of the pentaenes was possible for the first time, and the relative stereochemistry of the macrolide was established according to ROESY correlations. Strevertene A is the principal pentaene of the antibiotic polyene complex produced.

Probing natural product biosynthetic pathways using Fourier transform ion cyclotron resonance mass spectrometry.

Two natural products, diazepinomicin (1) and dioxapyrrolomycin (2), containing stable isotopic labels of (15)N or deuterium, were used to demonstrate the utility of Fourier transform ion cyclotron resonance mass spectrometry for probing natural product biosynthetic pathways. The isotopic fine structures of significant ions were resolved and subsequently assigned elemental compositions on the basis of highly accurate mass measurements. In most instances the mass measurement accuracy is less than one part per million (ppm), which typically makes the identification of stable-isotope labeling unambiguous. In the case of the mono-(15)N-labeled diazepinomicin (1) derived from labeled tryptophan, tandem mass spectrometry located this (15)N label at the non-amide nitrogen. Through the use of exceptionally high mass resolving power of over 125,000, the isotopic fine structure of the molecular ion cluster of 1 was revealed. Separation of the (15)N(2) peak from the isobaric (13)C(15)N peak, both having similar abundances, demonstrated the presence of a minor amount of doubly (15)N-labeled diazepinomicin (1). Tandem mass spectrometry amplified this isotopic fine structure (Deltam=6.32 mDa) from mDa to 1 Da scale thereby allowing more detailed scrutiny of labeling content and location. Tandem mass spectrometry was also used to assign the location of deuterium labeling in two deuterium-labeled diazepinomicin (1) samples. In one case three deuterium atoms were incorporated into the dibenzodiazepine core; while in the other a mono-D label was mainly incorporated into the farnesyl side chain. The specificity of (15)N-labeling in dioxapyrrolomycin (2) and the proportion of the (15)N-label contained in the nitro group were determined from the measurement of the relative abundance of the (14)NO(2)(1-) and (15)NO(2)(1-) fragment ions.

Absolute stereochemistry of the strevertenes

The CD exciton chirality method was applied to determine the absolute stereochemistry of the strevertenes, antifungal pentaene macrolides produced by Streptoverticillium sp. LL-30F848. The CD difference spectrum of strevertene A methyl ester 15-dimethylaminobenzoate showed a positive couplet between the dimethylaminobenzoate and the pentaene chromophores, and therefore established the 15R configuration. Thus, by considering the relative configurations of the remaining stereogenic centers as derived from X-ray crystallography and ROESY experiments, the absolute stereochemistry of the strevertenes is established as 2R, 3S, 5S, 7S, 11R, 13R, 14R, 15R, 26S and 27R.