Two new koumine-type indole alkaloids from Gelsemium elegans Benth.

Two new indole alkaloids, 21-oxokoumine (1) and furanokoumine (2), were isolated from the roots of Gelsemium elegans Benth together with three known compounds. The structures of the two novel compounds were elucidated by spectroscopic methods, including NMR, HR-ESI-MS, UV, IR, CD and molecular modeling. Compound 1 is the first instance of a koumine-type alkaloid with a carbonyl at the C-21 position, while compound 2 possesses a tetrahydrofuran ring located on C-20 and C-21.