Aqabamycins A-G: novel nitro maleimides from a marine Vibrio species. I. Taxonomy, fermentation, isolation and biological activities.

In a screening of marine bacteria, a Vibrio species isolated from the surface of the soft coral Sinularia polydactyla collected in the Red Sea was found to be a prolific producer of secondary metabolites with antibacterial and cytotoxic activities. Seven novel maleimide derivatives named aqabamycin A (1a), aqabamycin B (1b), aqabamycin C (1c), aqabamycin D (1d), aqabamycin E (1e and 1e'), aqabamycin F (1f) and aqabamycin G (2) were isolated together with several known metabolites such as 3-nitro-1H-indazole (3), indazole-3-carbaldehyde (4), phenyl-2-bis-indolylmethane (5a), turbomycin B (5b), vibrindole A (6), 1,4-dithiane (7), 3-(3-nitro-4-hydroxyphenyl)-2-propenoic acid (8), 3-nitro-4-hydroxybenzaldehyde (9), phenylacetic acid, benzoic acid, 3-hydroxybenzoic acid and 4-hydroxycinnamic acid. The aqabamycins, except aqabamycin A, bear a nitro group. Compounds 3, 4, 7 are described here for the first time from a natural source and vibrindole A was found to have cytotoxic activity.