Heterocyclic pseudoguaianolide oligomers and seco-pseudoguaianolide derivatives from the inflorescence of Ambrosia artemisiifolia.

Two heterocyclic sesquiterpenoid oligomers (1, 2) and four previously undescribed seco-pseudoguaianolide derivatives (3-6) were isolated from the inflorescence of Ambrosia artemisiifolia. Ambrosiadimer A (1) is an unprecedented dimer featuring a hexahydropyrrolizine core scaffold and two pseudoguaianolide units. Ambrosiatrimer A (2) is a trimer formed from three pseudoguaianolide units via a pyrrolidine ring. The structures and absolute configurations of these compounds were determined through NMR, MS, and Cu Kα X-ray crystallographic analysis. A plausible cycloaddition reaction was proposed for 1 and 2. Moreover, compounds 2 and 7 exhibited moderate cytotoxicities in human cancer cell lines, with IC values ranging from 7.22 to 27.45 μM and 9.32-33.45 μM, respectively.