C₂₁ steroids from Streptocaulon juventas (Lour) Merr. induce apoptosis in HepG2

Three new C₂₁ steroids, i.e., (3β,17α,20S)-pregn-5(6)-ene-3, 17, 20-triol-3-O-β-d-digitalopyranosyl-(1 → 4)-β-d-digitalopyranoside (4), (3β,17α,20S)-pregn-5(6)-ene-3, 17, 20-triol-20-O-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl-(1 → 2)-β-d-digital-opyranoside (8), (3β, 20R)-pregn-14(15)-ene-3, 20, 21-triol-3-O-β-d-glucopy-ranoside (10), along with ten known C₂₁ steroids were isolated from Streptocaulon juventas. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopic techniques, mass spectrometry as well as comparison with the literature. All the isolated compounds were screened for their in vitro cytotoxicity against human liver cancer cells (HepG2) and the structure-activity relationships were also analyzed. Moreover, compounds 1-3, 5, 10-12, which displayed cytotoxic activities in HepG2 cells, were tested for the selective index (SI) by the ratio of cytotoxic effect on human hepatocytes (LO2) to that on HepG2. As a result, new compound 10 exhibited a good inhibitory activity against HepG2 with IC₅₀ value 11.7 μM as well as high SI value 3.5. Furthermore, compound 10 could induce HepG2 cells apoptosis by flow cytometry.