Publikationen

The isolation and structure elucidation of malettinins A?C (1?3) along with the new malettinin E (4) are described. The compounds were produced by the fungus Cladosporium sp. strain KF501, which was isolated from the German Wadden Sea. The malettinins are built up of tropolone/dihydropyran ring structures linked to a furan ring. The structure elucidation of the isolated compounds was achieved by means of one- and two-dimensional NMR spectroscopy supported by mass and UV data. The relative configuration of 4 was determined on the basis of single-crystal X-ray diffraction analysis. 1?4 exhibited antibacterial and antifungal activities when profiled against Xanthomonas campestris and Trichophyton rubrum. The influence of the chemical structure of the furan ring and of configurational changes on biological activities was observed.

The isolation and structure elucidation of the novel calcaripeptides A (1), B (2), and C (3) and studies on their biosynthetic origin are described. The calcaripeptides were identified from Calcarisporium sp. strain KF525, which was isolated from the German Wadden Sea. Compounds 1?3 are macrocyclic structures composed of a proline and a phenylalanine residue as well as a nonpeptidic substructure. Structure elucidation was achieved by applying one- and two-dimensional NMR spectroscopy supported by high-resolution mass spectrometry. X-ray crystallography was performed to determine the relative configuration of 1. The absolute configuration of 1 was assigned by HPLC of the amino acids after hydrolysis of the molecule and derivatization with chiral agents. Studies on the biosynthesis by feeding 13C-labeled substrates revealed that the nonpeptidic part of 1 originates from acetate and l-methionine. The involvement of a hybrid between a polyketide synthase and a nonribosomal peptide synthetase in the biosynthesis of the calcaripeptides is discussed.