Immunosuppresive Sesterterpenoids and Norsesterterpenoids from Colquhounia coccinea var. mollis

A pair of new C-14 epimeric sesterterpenoids, colquhounoid D (1) and 14-epi-colquhounoid D (2), and five degradation products featuring new C₂₀ and C₂₁ frameworks, norcolquhounoids A-E (3-7), were isolated from Colquhounia coccinea var. mollis. Their structures were elucidated by comprehensive spectroscopic analysis and single-crystal X-ray diffraction. Degradation of the C₂₅ skeleton to the C₂₁ skeleton was also achieved using aqueous NaIO₄ and RuCl₃. Compounds 1 and 2 showed significant immunosuppressive activity on the cytokine IFN-γ secretion of mouse splenocytes induced by anti-CD3/CD4 monoclonal antibodies, with IC₅₀ of 8.38 and 5.79 μM, respectively, and compounds 5 and 6 were moderately active.