Isofusidienols: Novel chromone-3-oxepines produced by the endophytic fungus Chalara sp.

Abstract

Four novel metabolites, named isofusidienol A, B, C, and D (1-4), were produced by cultures of Chalara sp. (strain 6661), an endophytic fungus isolated from Artemisia vulgaris. The unprecedented chromone-3-oxepine structure of the compounds was established by detailed spectroscopic analysis and in the case of isofusidienol A (1) verified by an X-ray analysis. Additionally, two xanthones, known 5 and its 8-chloro derivative 6, were isolated. Presumably, 5 is the biosynthetic precursor of the isofusidienols. The isofusidienols exhibit antifungal activity against Candida albicans and antibacterial activity against gram-positive and gram-negative bacteria. Inhibition of Bacillus subtilis could be achieved with less than 0.625 μg of 1 on 6-mm filter disks in plate diffusion assays. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.