Two New Alkaloids from Stemona tuberosa

Two new alkaloids, named tuberostemoninol A (1) and tuberostemoninol B (2), along with the known compounds tuberostemoninol (3) and bisdehydroneotuberostemonine (4), were isolated from Stemona tuberosaLour. The structures were elucidated by means of spectroscopic analyses, including 1D- and 2D-NMR experiments. The four alkaloids 1–4 were analyzed by on-line high-performance liquid chromatography/electrospray-ionization mass spectrometry (HPLC/ESI-MS), and their fragmentation pathways were found to be similar. Compounds 1, 2, and 3 are isomers with the same molecular mass but which eluted at different retention times.