In a bioassay-guided search for acetylcholinesterase inhibitors from Korean natural resources, four isoquinoline alkaloids, corynoxidine (1), protopine (2), palmatine (3), and berberine (4) have been isolated from the methanolic extract of the aerial parts of Corydalis speciosa. Structures of these
Three new tetrahydroprotoberberine N-oxide alkaloids, (-)- cis-corydalmine N-oxide, (-)- trans-corydalmine N-oxide, and (-)- trans-isocorypalmine N-oxide, along with three known benzo[ C]phenanthridine alkaloids, norsanguinarine, dihydrosanguinarine, and oxysanguinarine, six known berberine