Rubiyunnanins C-H, cytotoxic cyclic hexapeptides from Rubia yunnanensis inhibiting nitric oxide production and NF-κB activation.

Six new (rubiyunnanins C-H, 1-6) and five known (7-11) cyclic hexapeptides were isolated from the roots of Rubiayunnanensis (Franch.) Diels. The structures and stereochemistry of 1-6 were established by extensive spectroscopic analyses and chemical methods. All compounds (1-11) not only exhibited cytotoxic activities against a panel of eleven cancer cell lines with IC₅₀ values ranging from 0.001 to 56.24 μM, but also exerted inhibitory activities against nitric oxide (NO) production in LPS and IFN-γ-induced RAW 264.7 murine macrophages with IC₅₀ values ranging from 0.05 to 12.68 μM. Furthermore, this is the first time it is being reported that compounds 2 and 7-10 significantly inhibited TNF-α-induced NF-κB activation in HEK-293-NF-κB luciferase stable cells with IC₅₀ values of 35.07, 0.03, 1.69, 12.64 and 1.18 μM, respectively.