Three new alkaloids from the roots of Sophora tonkinensis

A new β-carboline alkaloid (1) and two new matrine-type alkaloids (2 and 3), together with two known alkaloids (4 and 5), were isolated from the roots of Sophora tonkinensis. The new structures were elucidated via extensive analyses of the spectroscopic data (IR, UV, HRESIMS, NMR) and X-ray crystallography. The absolute configuration of 1 was established by electronic circular dichroism data. Herein, is the first report of β-carboline alkaloid in the plant of genus Sophora. In addition, the cytotoxic activities against HepG2 cells of compounds 1–5 were evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Among them, compounds 1, 4 and 5 showed a weak cytotoxic activity with IC50 values of 87.4 ± 7.1, 91.8 ± 3.5 and 48.9 ± 5.2 μM, respectively.