Iboga-type alkaloids from the leaves of Tabernaemontana penduliflora (Apocynaceae)

Isolation studies on the leaves of Tabernaemontana penduliflora afforded two undescribed indole alkaloids, 7,10-dihydroxyindolenine (1a) and pendulifloramine (2), together with four known compounds, 10-hydroxyheyneanine (4), 10-hydroxycoronaridine (5), vobasine (6), and voacristine (7). The structures 1a and 2 were determined based on NMR and mass spectra, together with database mining and computer-assisted structure elucidation. Their absolute and relative configurations were deduced by comparison of their CD spectra with those of known compounds and of the ab initio calculated spectra. Compounds 1a and 2 displayed moderate radical-trapping activity towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) with 50 % scavenging capacity activity (SC50) values of 34 µg/mL and 46 µg/mL, respectively, and good ability to reduce the TPTZ-Fe(III) complex to TPTZ-Fe(II) (TPTZ = 2,4,6-Tri-(2-pyridyl)-s-triazin) with 133 µg EGA/mg and 186 µg EGA/mg of dry weight, respectively. Both compounds also have anti-inflammatory activity with IC50 values of 9 µg/mL and 5 µg/mL for 1a and 2, respectively.