Unusual immunosuppressive pyridine-containing bisnor - (c 23 ), tetranor - (c 21 ) and pentanor - (c 20 ) sesterterpenoids from Tibetan Leucosceptrum canum .

An unusual pyridine-containing sesterterpenoid, leucosceptrodine (1), and five new nor -leucosceptrane sesterterpenoids, including bisnor - (C 23 , 2), tetranor - (C 21 , 3) and pentanor - (C 20 , 4-6) skeletons, were isolated from the leaves of Tibetan Leucosceptrum canum . Their structures including their absolute configurations were determined by extensive spectroscopic analyses and quantum chemical calculations. A single crystal of one epimer (5) was crystallized from a pair of inseparable epimers, and its structure including its absolute configuration was determined by X-ray crystallographic analysis. The immunosuppressive activities of compounds 1-4 with different potencies were evaluated by inhibiting the secretion of cytokines TNF-α and IL-6 in LPS-induced RAW264.7 macrophages.