Antimalarial β-Carboline and Indolactam Alkaloids from Marinactinospora thermotolerans, a Deep Sea Isolate

Four new beta-carboline alkaloids, designated marinacarbolines A D (1-4), two new indolactam alkaloids, 13-N-demethyl-methylpendolmycin (5) and methylpendolmy-cin-14-O-alpha-glucoside (6), and the three known compounds 1-acetyl-beta-carboline (7), methylpendolmycin (8), and pendolmycin (9) were obtained from the fermentation broth of Marinactinospora thermotolerans SCSIO 00652, a new actinomycete belonging to the family Nocardiopsaceae. Their structures were elucidated by extensive MS and ID and 2D NMR spectroscopic data analyses. The structure of compound I was further confirmed by single-crystal X-ray crystallography. The new compounds 1-6 were inactive against a panel of eight tumor cell lines (IC50 > 50 mu M) but exhibited antiplasmodial activities against Plasmodium falciparum lines 3D7 and Dd2, with IC50 values ranging from 1.92 to 36.03 mu M.