Summary Amataine (1) was isolated from the roots of Hedranthera barteri (HOOK. F.) PICHON (Apocynaceae). In comparison to the alkaloid vobtusine (5), which was isolated from the same plant, 1 contains two hydrogen atoms less. By reduction of 1 with H2/Pt02 or with NaBH4 dihydroamataine (= isovobtusine, 13) was formed which is isomeric to 5. Acid catalysed water addition to 1 afforded hydratoamataine (15), which was reduced to 5 with ...