Ervatamines A–I, Anti-inflammatory Monoterpenoid Indole Alkaloids with Diverse Skeletons from Ervatamia hainanensis

Nine new monoterpenoid indole alkaloids, ervatamines A–I (1–9), and five known ones (10–14), were isolated from Ervatamia hainanensis. The new structures were elucidated by extensive spectroscopic analysis and comparison to known compounds. Their absolute configurations were determined by various methods including computational methods, X-ray diffraction analysis, and electronic circular dichroism spectroscopy, as well as chemical transformations. Ervatamine A (1) is a ring-C-contracted ibogan-type monoterpenoid indole alkaloid with an unusual 6/5/6/6/6 pentacyclic rearranged ring system. Ervatamines B–E (2–5) display a nitrogen-containing 9/6 ring system, which is rarely observed in nature. The epimeric ervatamines B (2) and C (3) possess a 22-nor-monoterpenoid indole alkaloid carbon skeleton, which was only found in deformylstemmadenine. Compounds 10 and 14 exhibited significant anti-inflammatory activities, with IC50 values of 25.5 and 41.5 μM, respectively, while the IC50 value of indomethacin as a positive control was found to be 42.6 μM. Additionally, compound 9 showed mild activity against 786-O and HL-60 cell lines.