New tetrahydroprotoberberine N-oxide alkaloids and cytotoxic constituents of Corydalis tashiroi

Three new tetrahydroprotoberberine N-oxide alkaloids, (-)-cis-corydalmine N-oxide (1), (-)-trans-corydalmine N-oxide (2), and (-)-trans-isocorypalmine N-oxide (3), along with three known benzo[c]phenanthridine alkaloids, norsanguinarine (4), dihydrosanguinarine (5), and oxysanguinarine (6), six known berberine alkaloids, (-)-tetrahydropalmatine (7), (-)-corydalmine (8), (-)-scoulerine (9), (-)-corynoxidine (10), (-)epicorynoxidine (11), palmatine (12), and protopine (13), have been isolated from the herb Corydalis tashiroi. The structures of these compounds were elucidated by spectroscopic analysis. Three of the isolated compounds show significant cytotoxic activities (ED50 values < 4 mu g/ml) against P-388, KB16, A549, and HT-29 cell lines.