Antitussive stemoninine alkaloids from the roots of Stemona tuberosa.

Investigation of the roots of Stemona tuberosa afforded five minor constituents, stemoenonine (1), 9a- O-methylstemoenonine (2), oxystemoenonine (3), 1,9a- seco-stemoenonine (4), and oxystemoninine (5), along with the known compound stemoninoamide (6). Their structures were elucidated by 1D and 2D NMR spectra and other spectroscopic studies. Alkaloids 1, 2, and 6, as well as the representative stemoninine-type alkaloid, stemoninine (7), were screened for antitussive activity in the citric acid-induced guinea pig cough model. Compounds 6 and 7 exhibited strong antitussive activity after oral and intraperitoneal administrations.