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

Four new β-carboline alkaloids, designated marinacarbolines
A–D (1–4), two new indolactam
alkaloids, 13-N-demethyl-methylpendolmycin (5) and methylpendolmycin-14-O-α-glucoside
(6), and the three known compounds 1-acetyl-β-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 1D and 2D NMR spectroscopic data
analyses. The structure of compound 1 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 μM) but exhibited antiplasmodial
activities against Plasmodium falciparum lines 3D7 and Dd2, with IC50 values ranging from 1.92
to 36.03 μM.