Four isocoumarins have been isolated from the terrestrial Streptomyces sp. ANK302, namely 6,8-dimethoxy-3-methylisocoumarin (1), 6,8-dihydroxy-3-methylisocoumarin (2), 6,8-dihydroxy-7-methoxy-3-methylisocoumarin (3), and 6,7,8-trimethoxy-3-methylisocoumarin (4). Compound 1 is a new naturally-occurring isocoumarin, and 2 was isolated as a new bacterial product. The structures 1-4 were deduced from high resolution mass, 1D and 2D NMR spectra and by comparison with related compounds from the literature. Compound 2 showed a strong zoosporicidal activity at a concentration of 5 μg/mL against a phytopathogenic oomycete, Plasmopara viticola, and 1 was active against Candida albicans.
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M2 medium: Glucose (4 g), yeast extract (4 g), malt extract (10 g) were dissolved in 1 L of tap water. The pH of the solution was adjusted to 7.8 and sterilized by autoclaving for 30 minutes at 121°C and 1.2 bar.
