Monoterpenoid indole alkaloids from the aerial parts of Tabernaemontana divaricata (L.) R. Br. ex Roem. & Schult. and their anti-inflammatory activity and cytotoxicity on acute leukaemia cells.

The species Tabernaemontana divaricata of Apocynaceae has a long history of application in folk medicine. Previous phytochemical studies have revealed that it is abundant in monoterpenoid indole alkaloids (MIAs). To support the comprehensive development and utilisation of active compounds from T. divaricata, an undescribed monoterpenoid indole alkaloid named 6α-hydroxy-20-epi-ervatamine (1), together with twelve known MIAs (2-13), were isolated from its aerial parts. Their structures were elucidated based on extensive spectroscopic analyses, including NMR, UV, IR, and MS techniques. The biological evaluation showed significant anti-inflammatory and inhibitory effects against leukaemia cell proliferation. Compounds 1 and 7 exhibited the strongest anti-inflammatory effects, comparable to the positive control dexamethasone (DXM) at a concentration of 20 μM. Furthermore, compounds 2 and 8 exhibited inhibitory effects against all three acute leukaemia cell lines, with IC50 values ranging from 0.84 ± 0.06 μM to 18.75 ± 0.73 μM, highlighting their potential biological activities.