Isoquinolone and protoberberine alkaloids from Stephania rotunda.

Chemical investigation of Stephania rotunda Lour. growing in Viet Nam led to the isolation and structural elucidation of three new alkaloids, 5-hydroxy-6,7-dimethoxy-3,4-dihydroisoquinolin-1(2H)-one (1), thaicanine 4-O-beta-D-glucoside (6), as well as (-)-thaicanine N-oxide (4-hydroxycorynoxidine) (8), along with 23 known alkaloids. These structures were determined on the basis of MS and NMR spectroscopic data.