Simone Keller

Labyrinthopeptins: A New Class of Carbacyclic Lantibiotics

Lantibiotics are peptides that are ribosomally synthesized from bacteria such as staphylococci, lactobacilli, and actinomycetes. The common structural characteristic of lantibiotics is the noncanonical amino acid lanthionine (Lan, 1; Figure 1), which confers conformational stability to the peptide. The most prominent representative is nisin, which is a lipid II binder, and has been known for its use as an antimicrobial food preservative for over 40 years. The majority of studies on molecular targets and bioactivities are focused on potential applications of lantibiotics as anti-infectives. Duramycin (Moli1901) is in phase II clinical trials for the treatment of cystic fibrosis because of its ability to increase chloride transport in airway epithelium. Biosurfactant function in the life cycle of streptomycetes has been elucidated for some members such as SapB. Herein, we present the structures, the biosynthesis gene cluster, and the bioactivities of labyrinthopeptins, which are lantibiotics that contain labionin, an unprecedented carbacyclic, posttranslationally modified amino acid. The culture extracts of the novel actinomycete Actinomadura namibiensis DSM 6313 attracted our attention because of their activity against the Herpes simplex virus. Active fractions of the extracts contained a peptide that was isolated by chromatographic methods. The high-resolution ESI-FTICR mass spectrum showed a mass of 984.3333 Da for the doubly charged sodium adduct of the compound, corresponding to a neutral monoisotopic mass of 1922.6872 Da and the molecular formula C85H110N20O24S4 (Dm/m= 0.7 ppm). Amino acid analysis revealed Gly and the l-enantiomers of Ala, Thr, Leu, Asx, Cys, Phe, Glx, Trp (ratio 1:1:1:2:1:2:1:1:2). However, the total molecular mass of the detected amino acids indicated a considerable mass difference, which could not be correlated with known peptidic or lantibiotic posttranslational modifications. Resolution of the structure by H NMR spectroscopy was impeded by broad signals in parts of the spectrum. The X-ray structure at 1.0 resolution (Figure 1) enabled interpretation of the analytical data and displayed several unique structural features. In view of its labyrinthine structure, the compound was named labyrinthopeptin A2 (2). Labyrinthopeptin A2 has a globular structure that consists primarily of hydrophobic amino acids. Formally, the structure can be dissected into two nonapeptides. Each peptide bears a C-terminal Cys residue that forms a disulfide bond, which is a comparatively rare modification in lantibiotics, but is found for sublancin 168 from B. subtilis. Each nonapeptide contains a tetrapeptide (ring A) and a pentapeptide (ring B) that share a quaternary aC atom; labyrinthopeptin A rings are formed by a methylene group between the aC atoms of Lab1/ Lab10 and Lab4/Lab13 (Figure 1). A carbacyclic side-chain linkage is unprecedented in peptides and proteins. We propose the name labionin (Lab) for the corresponding amino acid (Figure 1). Labionin 3 represents an aC quaternary substituted amino acid with a subtle structural resemblance to a-aminoisobutyric acid (Aib) or isovaline (Iva), which are incorporated in fungal peptaibol-type antibiotics. The stereocenters of 3 can be assigned to (2S,4S,8R)-labionin (Lab), which is consistent with the configuration of (2S,6R)lanthionine of other lantibiotics. The formation of the 11membered ring that involves 3 forces the peptide backbone into a conformation with cis-amide bonds between Asp2– Trp3 and Thr11–Gly12, respectively (Figure 1). The presence of cis-amide bonds and the absence of a hydrogen bond between Lab1–Lab4 and Lab10–Lab13, respectively, show that the turn motif in 2 is clearly different from a b-turn motif. Subsequent identification of the biosynthetic gene cluster was performed from a cosmid library of A. namibiensis by means of degenerated primer probes, followed by sequencing [*] Dr. T. Schmiederer, Dr. K. Schneider, Dr. A. Reicke, Dr. D. Butz, Dr. S. Keller, Prof. Dr. R. D. S ssmuth Technische Universit t Berlin, Fakult t II—Institut f r Chemie Strasse des 17. Juni 124, 10623 Berlin (Germany) Fax: (+49)30-314-24205 E-mail: suessmuth@chem.tu-berlin.de Homepage: http://www2.tu-berlin.de/fb5/Suessmuth/ contact.html Dr. K. Meindl, Prof. Dr. G. M. Sheldrick Universit t G ttingen (Germany)

Proximicins A, B, and C—Antitumor Furan Analogues of Netropsin from the Marine Actinomycete Verrucosispora Induce Upregulation of p53 and the Cyclin Kinase Inhibitor p21

Netropsin (1) and distamycin (2) are naturally occurring gpeptides with antiviral and antibacterial activity (Figure 1). Netropsin, formerly named congocidine, was isolated from S. netropsis in 1951, while distamycin was isolated from S. distallicus in 1964. Both compounds bind in the minor groove of DNA, and they were arguably the first compounds for which AT-selective DNA binding was demonstrated. The design of synthetic derivatives capable of addressing a specific sequence of DNAwould allow the selective inhibition of gene expression and thus result in compounds that act as antitumor agents. As a consequence, netropsin and distamycin were used as the basic structures for the synthesis of numerous analogues to enable the investigation and modulation of their minor-groove binding. This was also achieved by using combinatorial approaches. A particular challenge was to generate selective binders for GC base pairs. One approach was based on the assumption that the introduction of a hydrogen-bond acceptor in the pyrrole

Structure Elucidation of Auxofuran, a Metabolite Involved in Stimulating Growth of Fly Agaric, Produced by the Mycorrhiza Helper Bacterium Streptomyces AcH 505

Mycorrhiza helper bacterium Streptomyces strain AcH 505 stimulates ectomycorrhiza formation between spruce and fly agaric by supporting fungal growth whereas growth of pathogenic fungi is suppressed. A fungal growth promoting substance was isolated and the chemical structure elucidated by mass spectrometry and NMR spectroscopy. The absolute configuration of the novel fungal growth promoting compound auxofuran (1) was deduced from NMR data with the help of Mosher esters.

Bendigoles A approximately C, new steroids from Gordonia australis Acta 2299.

Bendigoles A~C are the first secondary metabolites to be isolated from a member of the actinomycete genus Gordonia. They were detected in a culture filtrate extract of Gordonia australis Acta 2299 by HPLC-diode array analysis and characterized as new steroids by mass spectrometry and NMR experiments. Bendigole C show binding affinity to the human progesterone and A~C to androgen receptor but are inactive at mineralocorticoid and estrogen receptors. In in vitro transactivation studies bendigoles A and C showed moderate and weak androgenic activities.