New Indole Alkaloids from the Sponge Plakortis sp.

Marine organisms are rich sources of a variety of natural products possessing unique skeletons with many functional groups. Marine sponges have proved to be sources of bioactive compounds [1, 2]. Among them, indole alkaloids are commonly found in marine organisms and terrestrial plants as well as in microorganisms [3]. The bis-indole alkaloids belong to a class of marine natural products that may serve as a promising candidate for new drug leads. Some examples are staurosporine [4, 5], coscinamide [6], and chondriamide [7]. They exhibit a wide range of biological activities such as protein kinase inhibition [4, 5], anti-HIV [6], and cytotoxicities [7]. The sponge genus Plakortis usually produces major cyclic peroxide compounds [8], highly volatile ketone or acid [9], alkaloid [10], aromatic compounds [11], and fatty acids [12]. In the course of our studies on the bioactive molecules of marine organisms, we found two novel indole alkaloid compounds (1, 2) together with the known indole compounds penaresin (3), indolecarbaldehyde (4), and plakohypaphorine D (5) whose structures (for the new ones) and biological activities are described herein.