| Abstract
| - Five novel extracellular metabolites with an unprecedented diterpenoid skeleton, 5-[(5-carboxy-2-hydroxy)benzyl]-11-hydroxymethyl-2,5,6,8a,11-pentamethyldodecahydrocyclopenta〈a〉naphthalene (1), 5-[(5-carboxy-2-hydroxy)benzyl]-11-formyl-2,5,6,8a,11-pentamethyl-dodecahydrocyclopenta〈a〉naphthalene (2), 5-[(5-carboxy-2-hydroxy)benzyl]-11-carboxy-2,5,6,8a,11-pentamethyl-dodecahydrocyclopenta〈a〉naphthalene (3),5-[(5-carboxy-2-hydroxy)benzyl]-11-dihydroxymethyl-2,5,6,8a,11-pentamethyldodecahydrocyclopenta〈a〉naphthalene (4), and 5-[(5-carboxy-2-hydroxy)benzyl]-11-acetyl-2,5,6,8a-tetramethyldodecahydrocyclopenta〈a〉naphthalene (5), have been isolated from the culture medium of the terrestrial cyanobacterium Nostoccommune by means of bioguided isolation. The molecules were designated as comnostins A−E. Thestructures were determined by spectroscopic methods, mainly NMR and mass spectrometry. The relativestereochemistry of comnostin A was confirmed by single-crystal X-ray structure analysis. All comnostinsshowed antibacterial activities. Additionally, cytotoxic and molluscicidal activities were found for comnostinB.
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