Anti-complementary activity-guided fractionation led to the isolation of a new abietane diterpene (1) and twenty-five known compounds (2-26) from the twigs and leaves of Juniperus tibetica. All the compounds were isolated from J. tibetica for the first time. The structure of 1 was assigned by spectroscopic data and X-ray crystallography analysis. Five lignans (2, 3, 7, 9 and 10), two flavones (19 and 22), and one coumarin (23) exhibited anti-complementary activity with CH50 values ranging from 0.3 to 3.69 mM.
Keywords: Juniperus tibetica; abietane diterpene; anti-complementary activity.