Ainsliadimer A, a new sesquiterpene lactone dimer with an unusual carbon skeleton from Ainsliaea macrocephala.

A phytochemical investigation of Ainsliaea macrocephala led to the isolation of a new dimeric sesquiterpene lactone, ainsliadimer A (1). The structure of 1 was elucidated by spectroscopic analysis, and confirmed by single crystal X-ray diffraction. Ainsliadimer A represents an unusual carbon skeleton with a cyclopentane system connecting the two monomeric sesquiterpene lactone units. This unique molecule exerted potent inhibitory activity against the production of nitric oxide in RAW264.7 stimulated by LPS.