Natural Indoles From The Bacterium Pseudovibrio Denitrificans P81 Isolated From A Marine Sponge, Aaptos Species

A new natural indole, vibrindole B (1), together with known analogs, vibrindole A (2), trisindoline (3), norharmane (4), and 3- (hydroxyacetyl)indole (5), produced by the bacterium Pseudovibrio denitrificans P81, were isolated from a sponge, Aaptos species. The structures of indoles 1 to 5 were established by spectroscopic methods. The proposed biosynthetic pathway of 1 to 5 is also discussed, starting from tryptophan. Moreover, indoles 1 to 3 were found to exhibit cytotoxicity toward T24 tumor cells with IC50 values of 1.71 +/- 0.11, 4.53 +/- 0.14, and 2.26 +/- 0.26 mu M, respectively.