Abstract
New isolates of Streptomyces champavatii were isolated from marine sediments of the Gotland Deep (Baltic Sea), from the Urania Basin (Eastern Mediterranean), and from the Kiel Bight (Baltic Sea). The isolates produced several oligopeptidic secondary metabolites, including the new octapeptide champacyclin (1a) present in all three strains. Herein, we report on the isolation, structure elucidation and determination of the absolute stereochemistry of this isoleucine/leucine (Ile/Leu = Xle) rich cyclic octapeptide champacyclin (1a). As 2D nuclear magnetic resonance (NMR) spectroscopy could not fully resolve the structure of (1a), additional information on sequence and configuration of stereocenters were obtained by a combination of multi stage mass spectrometry (MSn) studies, amino acid analysis, partial hydrolysis and subsequent enantiomer analytics with gas chromatography positive chmical ionization/electron impact mass spectrometry (GC-PCI/EI-MS) supported by comparison to reference dipeptides. Proof of the head-to-tail cyclization of (1a) was accomplished by solid phase peptide synthesis (SPPS) compared to an alternatively side chain cyclized derivative (2). Champacyclin (1a) is likely synthesized by a non-ribosomal peptide synthetase (NRPS), because of its high content of (d)-amino acids. The compound (1a) showed antimicrobial activity against the phytopathogen Erwinia amylovora causing the fire blight disease of certain plants.
Highlights
The actinobacterial genus Streptomyces is widely distributed in both terrestrial and aquatic ecosystems
Spore forming actinobacteria were isolated from sediments of the Gotland Deep (Baltic Sea), from the eastern Mediterranean (Urania Basin) and from the Kiel Bight, respectively
Based on the genotypic data of multilocus sequence analysis (MLSA) and DNA-DNA hybridization (DDH), combined with key phenotypic properties, it was proposed that these Streptomyces species of the S. albidoflavus clade, including S. champavatii, should be merged into a single genomic species, for which the name
Summary
The actinobacterial genus Streptomyces is widely distributed in both terrestrial and aquatic ecosystems. These bacteria exhibit diverse physiological and metabolic properties, such as the production of extracellular enzymes and the synthesis of a large variety of secondary metabolites, a number of which are exploited by the pharmaceutical industries. Many of these antimicrobials are of low molecular weights (≤2000 Da) and belong to macrolides, polyenes, tetracyclines, amino glycosides, or other compound classes with heterogeneous chemical structures. The structural complexity can be dramatically increased if fatty acids and/or carbohydrate moieties are present in these molecules [1]
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