Unusual immunosuppressive pyridine-containing - (c), - (c) and - (c) sesterterpenoids from Tibetan .

An unusual pyridine-containing sesterterpenoid, leucosceptrodine (1), and five new -leucosceptrane sesterterpenoids, including - (C, 2), - (C, 3) and - (C, 4-6) skeletons, were isolated from the leaves of Tibetan . 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.