Cytotoxic 5-Hydroxyindole Alkaloids from the Marine Sponge Scalarispongia sp.

Three new 5-hydroxyindole alkaloids (1, 2, 3) along with seven known analogs (4, 5, 6, 7, 8, 9, 10) were isolated from a Dokdo marine sponge Scalarispongia sp. The elucidation of the structures of the new compounds by spectroscopic analyses indicated that these compounds were an indole glyoxylate (1), a mono-indole analog of hyrtinadine A (2), and a symmetrical bis-indole with pyridine linker (3). The comparison of IC50 values for obtained compounds against a human leukemia cell line revealed that the bis-indole structure is a requirement for cytotoxicity.