New cytotoxic N-methylated beta-carboline alkaloids from the marine ascidian Eudistoma gilboverde.

Bioassay-guided fractionation of an extract of the marine ascidian Eudistoma gilboverde provided three new beta-carboline alkaloids identified as 2-methyleudistomin D (1), 2-methyleudistomin J (2), and 14-methyleudistomidin C (3). Six known metabolites, eudistomins C, D (4), E, J (5), K, and L, were also isolated and characterized. The structures of the new metabolites were elucidated by spectroscopic analyses and by comparison of their spectral data with related literature values. Of the three new compounds, 14-methyleudistomidin C (3) exhibited the most potent cytotoxic activity with IC(50)'s of < 1.0 microg/mL against four different human tumor cell lines.