Hasubanan alkaloids with delta-opioid binding affinity from the aerial parts of Stephania japonica.

Two new (1 and 2) and six known hasubanan alkaloids (3-8) and one morphinane alkaloid (9) were isolated from the leaves of the North Queensland rainforest vine Stephania japonica. The structures of 1 and 2 were determined by interpretation of their 1D and 2D NMR spectra. The hasubanan alkaloids showed affinity for the human delta-opioid receptor with IC(50) values ranging from 0.7 to 46 microM. The compounds were also tested for their affinity to micro- and kappa-opioid receptors and shown to be inactive against kappa-opioid receptors, but were of similar potency against the micro-opioid receptor.