Bioactive indole alkaloids isolated from Alstonia angustifolia.

Bioassay-guided fractionation was conducted on a CHCl ₃ -soluble extract of the stem bark of Alstonia angustifolia (Apocynaceae) collected in Vietnam using the HT-29 human colon cancer cell line, and led to the isolation of a new sarpagine-type indole alkaloid ( 1 ), together with nine known alkaloids, including four macroline-derived alkaloids ( 2-5 ), a sarpagine-type alkaloid ( 6 ), and four macroline-pleiocarpamine bisindole alkaloids ( 7-10 ). The structure of the new compound ( 1 ) was determined on the basis of spectroscopic data interpretation. Compounds 1-10 were evaluated in vitro for their NF-κB (p65) inhibitory activity against the Hela cells in an ELISA assay. The new sarpagine alkaloid, N (4)-methyltalpinine ( 1 ), was found to show significant NF-κB inhibitory activity (ED ₅₀ = 1.2 µM). Furthermore, all the isolates ( 1-10 ) were evaluated in vitro for their antileishmanial activity, and compounds ( 1-4, 6 and 8-10 ) exhibited leishmaniacidal activity against promastigotes of Leishmania mexicana .