Novel Extracellular Diterpenoids with Biological Activity from the Cyanobacterium Nostoc commune

Five novel extracellular metabolites with an unprecedented diterpenoid skeleton, 5-[(5-carboxy-2-hydroxy)benzyl]-11-hydroxymethyl-2,5,6,8a, 11-pentamethyldodecahydrocyclopentanaphthalene (1), 5-[(5-carboxy-2-hydroxy)benzyl]-11-formyl-2,5,6,8a, 11-pentamethyl-dodecahydrocyclopentanaphthalene (2), 5-[(5-carboxy-2-hydroxy)benzyl]-11-carboxy-2,5,6,8a, 11-pentamethyl-dodecahydrocyclopentanaphthalene (3), 5-[(5-carboxy-2-hydroxy)benzyl]-11-dihydroxymethyl-2,5,6,8a, 11-pentamethyldodecahydrocyclopentanaphthalene (4), and 5-[(5-carboxy-2-hydroxy)benzyl]-11-acetyl-2,5,6, 8a-tetramethyldodecahydrocyclopentanaphthalene (5), have been isolated from the culture medium of the terrestrial cyanobacterium Nostoc commune by means of bioguided isolation. The molecules were designated as comnostins A-E. The structures were determined by spectroscopic methods, mainly NMR and mass spectrometry. The relative stereochemistry of comnostin A was confirmed by single-crystal X-ray structure analysis. All comnostins showed antibacterial activities. Additionally, cytotoxic and molluscicidal activities were found for comnostin B.