Marine Bacteria, XLVII - Psychrotolerant Bacteria from Extreme Antarctic Habitats as Producers of Rare Bis- and Trisindole Alkaloids.

From the gastrointestinal tract of a fish dredged near the South Orkney Islands in Antarctica, we isolated the psychrotolerant bacterial strain T262, which belongs to the species Vibrio splendidus. Investigation of this strain led to the isolation of a series of 15 bis- and trisindole derivatives. Among them, six new indole alkaloids, namely, turbomycin C [4'-n-butoxyphenyl-bis(1H-indol-3-yl)methane, 1a], turbomycin D [4'-n-propoxyphenyl-bis(1H-indol-3-yl)methane, 1b], turbomycin E [4'-ethoxyphenyl-bis(1H-indol-3-yl)methane, 1c], turbomycin F [4'-methoxy-3',5'-dinitrophenyl-bis(1H-indol-3-yl)methane, 2], trisindolal (3a), and 4-(1H-indol-3-yl-sulfanyl)phenol (4). Another new bisindole derivative elucidated as 2-(indol-3-ylmethyl)-indol-3-ylethanol (7a) was obtained together with six known compounds from the psychrotolerant Arthrobacter psychrochitiniphilus strain T406, isolated from the excrement of penguins. Some of the isolated compounds showed activity against both gram-positive and gram-negative bacteria at 10 µg/paper disk. Trisindolal (3a) was active against the peronosporomycetes Botrytis cinerea and Phytophthora infestans, and some of the indole derivatives indicated promising cytotoxicity towards human tumor cell lines. By exhibiting a mean IC50 of 0.45 µg/mL (1.17 µM), trisindolal (3a) showed pronounced potency and selectivity in a panel of 11 human tumor cell lines derived from 10 different tumor histotypes.