Isolation of Isoquinoline Alkaloids from the Tuber of Corydalis turtschaninovii and their Inhibition Activity on Low Density Lipoprotein Oxidation

The dried and powdered tubers of Corydalis turtschaninovii (C. turtschaninovii) were extracted with 80% aqueous MeOH, and the concentrated extracts were partitioned using the acidity and polarity of the solvents. From the alkaloid fraction, nine alkaloids were isolated through repeated SiO2 column chromatography. Based on NMR, MS and IR spectroscopic data, the chemical structures of the compounds were determined to be (+/-)-demethylcorydalmine (1), (+)-isocorydine (2), (+)-stylopine (3), (-)-alpha-N-methylcanadine (4), pseudoprotopine (5), tetrahydroprotopapaverine (6), allocryptopine (7), berberine (8), and pseudocoptisine (9). This was the first report in which compounds 1, 2, 4, 6, and 7 were isolated from the tuber of C turtschaninovii. And because the NMR data for some compounds have been incorrectly or incompletely identified in previous literature, they were revised on the basis of 2D NMR experiments. Compounds 1, 2, and 3 showed inhibition activity on LDL oxidation with IC50 values of 2.1 +/- 0.2, 2.4 +/- 0.1, and 2.0 +/- 0.2 mu M, respectively, which are higher activities than that of the positive control, probucol (6.8 +/- 0.1 mu M).