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Two new bisindole alkaloids, bisnaecarpamines A (1) and B (2), possessing a vobasine-sarpagine type skeleton were isolated from the bark of Tabernaemontana macrocarpa Jack. Their structures were elucidated by extensive spectroscopic methods and chemical correlation. The absolute configurations of compounds 1 and 2 were established using TDDFT-ECD calculation of the selected isomers. Bisnaecarpamine A exhibited potent antimalarial activity against Plasmodium falciparum 3D7 strain with IC 50 value of 28.8 µM.

Three new alkaloids, cassiarins C-E (1-3), and a new chromone, 10,11-dihydroanhydrobarakol (4), which showed moderate antiplasmodial activity against Plasmodium falciparum 3D7, were isolated from flowers of Cassia siamea, and the structures of 1-4 were elucidated by 2D NMR analysis and chemical transformation. Cassiarin D (2) was a dimeric compound consisting of 5-acetonyl-7-hydroxy-2-methylchromone and cassiarin C (1), and cassiarin E (3) was a dimer of cassiarins A and C (1).

Two new bisindole alkaloids, biscarpamontamine A (1), possessing an aspidosperma-iboga-type skeleton, and biscarpamontamine B (2), having an aspidosperma-aspidosperma-type skeleton, were isolated from stems of Tabernaemontana sphaerocarpa, and their structures were elucidated on the basis of spectroscopic data analysis. The absolute configuration of biscarpamontamine B (2) was established by comparison of its CD spectrum and with that of vobtusine (3). Biscarpamontamine B (2) showed potent cytotoxicity against various human cancer cell lines.

Four new alkaloids, alstiphyllanines A-D (1-4), were isolated from Alstonia macrophylla, and their structures were determined by MS and 2D NMR analyses. Alkaloids 1-4 showed moderate antiplasmodial activity against Plasmodium falciparum and vasorelaxant activity against phenylephrine-induced contraction of isolated rat aorta.