Lingaoamide (1), a new cyclic heptapeptide natural product, was isolated from a freshwater Oscillatoria cyanobacterium. The producing organism was collected in Chinese water spinach paddy farm fields in Lingao County, Hainan, China. The structure of 1 was determined by conventional mass spectrometry, NMR spectroscopy, and chemical degradation studies. Lingaoamide concentration-dependently up-regulates the biogenesis of pro-pathogenic melanin pigments (melanogenesis) in the rice blast fungus, Magnaporthe grisea, when tested in vitro. This molecule also exhibits weak in vitro inhibition (MIC 32 μg/mL) of Gram-negative Pseudomonas aeruginosa and Gram-positive Bacillus pumilus, and does not appear to impact plant growth or immune response in vivo using the model organism, Arabidopsis thaliana.
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