Indoline alkaloids from Tabernaemontana contorta with cancer chemopreventive activity

Two bisindoline alkaloids, contortarine A, 16-epi-pleiomutinine and a reaction product of pleiomutinine, namely N4-chloromethyl-pleiomutinine, were isolated from the roots of Tabernaemontana contorta Stapf. together with five known compounds: pleiomutinine, 1-carbomethoxy-β-carboline, strictosidine lactam, pleiocarpamine, and pleiocarpine. The structures and relative configuration of these alkaloids were determined by extensive 1D and 2D NMR, and MS measurements. The absolute configuration of these compounds was determined by comparison of experimental and calculated ECD spectra. Among the isolated compounds, contortarine A, 1-carbomethoxy-β-carboline and strictosidine lactam presented cancer chemopreventive properties through either quinone reductase (QR) induction with CD values of 16.0 ± 2.5, 30.2 ± 6.1 and 23.1 ± 4.6 μM, respectively, while pleiomutinine and 16-epi-pleiomutinine displayed the inhibition of TNF-α induced NF-κB activity with IC50 at 11.7 ± 2.6 and 3.4 ± 1.1 μM, respectively.