Naturally produced isocoumarins: inhibitors of calmodulinsensitive cyclic guanosine 3′,5′-monophosphate phosphodiesterase

Three isocoumarins have been isolated from a strain ofStreptoverticillium sp. and all inhibit the calmodulin-sensitive cyclic guanosine 3′,5′-monophosphate phosphodiesterase (EC 3.1.4.17, Boehringer Mannheim). Two of the compounds, 6,8-dihydroxy-7-methoxy-3-methyl isocoumarin and 6,7,8-trihydroxy-3-methyl isocoumarin have previously been isolated fromStreptomyces. The third fermentation product, 6,8-dihydroxy-3-methyl isocoumarin, was also found as a metabolite ofCeratocystis minor, a fungal species associated with the blue stain disease of pine [2,3].