14,15-Secopregnane-type C₂₁-steriosides from the roots of Cynanchum stauntonii

Nine 14,15-secopregnane-type C₂₁-steriosides, stauntosides U, V, V₁-V₃, W and C₁-C₃, as well as two known C₂₁-steriosides, were isolated from the roots of Cynanchum stauntonii. Stauntosides U, V and V₁-V₃ share the same basic structural features of 8α:14α,14:16,15:20,18:20-tetraepoxy-14,15-secopregn-6-ene-3β,5α,9α-triol, with the numbering system following that of C₂₁-pregnanes. The aglycones of stauntosides U, V and V₁-V₃ are classified into two subcategories, the 5,9-dihydroxy groups and 5α:9α-peroxy bridge, according to the oxidative states of the two hydroxy groups at the C-5 and C-9 positions. The anti-inflammatory activity of the major compounds was assessed in an in vitro inflammatory model of mouse peritoneal macrophages using IC₅₀ values of the inhibition of nitric oxide (NO) production as an indicator. Stauntosides V₁ and V₃ exhibited target activity with IC₅₀ values of 9.3 μM and 12.4 μM, respectively, compared with dexamethasone, which was used as a positive control.