An unusual pyridine-containing sesterterpenoid, leucosceptrodine (1), and five new nor-leucosceptrane sesterterpenoids including bisnor- (C23, 2), tetranor- (C21, 3) and pentanor- (C20, 4−6) skeletons, were isolated from the leaves of Tibetan Leucosceptrum canum. Their structures including the absolute configurations were determined by extensive spectroscopic analyses and quantum chemical calculations. Single crystal of one epimer (5) was crystallized from a pair of inseparable epimers, and its structure including absolute configuration was determined by X-ray crystallographic analysis. Immunosuppressive activity of compounds 1−4 with different potencies through inhibiting the secretion of cytokines TNF-α and IL-6 in LPS-induced macrophages RAW264.7 was observed.

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