Structurally diverse diterpenoids and phenanthrene derivatives from the roots of Baliospermum solanifolium

Ten undescribed diterpenoids (1–10) and three undescribed phenanthrene derivatives (11–13), together with seven known compounds, were isolated from the roots of Baliospermum solanifolium. Their structures were determined by a combination of spectroscopic data analysis, electronic circular dichroism calculations and single-crystal X-ray diffraction studies. Compounds 1–7 (baliosperoids A–G) represent the examples of 20-nor-ent-podocarpane class first discovered in nature. In particular, compound 7 possesses a unique 2,3-seco ring system incorporating γ-butanolide moiety. All isolates were assessed for their cytotoxic activities against HT-29, HCT-116, HCT-15, MCF-7, and A549 cell lines as well as their inhibitory effects on lipopolysaccharide-induced NO production in RAW264.7 cells. Compound 1, a 20-nor-ent-podocarpane-type diterpenoid possessing a Δ^1,2 double bond, not only exhibited considerable proliferation inhibition against five human cancer cell lines, with IC₅₀ values ranging from 4.13 to 23.45 μM, but also displayed the most potent inhibitory activity on NO production with IC₅₀ value at the nanomolar level (0.63 ± 0.21 μM).