Indoloquinazoline alkaloids from Araliopsis tabouensis

Three new indoloquinazolidine-type alkaloids, 8,13-dihydro-2-methoxyindolo[2',3': 3,4]pyrido[2,1-b]quinazolin-5(7H)-one (1), 8,13-dihydro-2-methoxy-13-methylindolo[2',3':3,4]pyrido[2,1-b]quinazolin-5(7H)-one (2), and 5,8,13,14-tetrahydro-2-methoxy-14-methyl-5-oxo-7H-indolo[2',3':3,4]pyrido[2,1-b]quinazolim-6-iun chloride (3) were isolated from Araliopsis tabouensis, together with three known compounds. The structures of the new compounds were determined primarily from 1D- and 2D-NMR analysis. The antimalarial activities of compounds 1-5 were evaluated against Plasmodium falciparum D6 and W2 clones. The IC50 values in antimalarial bioassay for compounds 2-5 varied from 1.8 to 4.7 mug/ml.