Atramacronoids A−C, three eudesmanolide sesquiterpene-phenol hybrids with an unprecedented C−C linkage from the rhizomes of Atractylodes macrocephala

Three eudesmanolide sesquiterpene-phenol hybrids, atramacronoids A−C (1−3), featuring an unusual 6/6/5/5/6 skeleton furnished by forming an unexpected C-8−C-16 linkage, were obtained from the rhizomes of Atractylodes macrocephala. Their structures and absolute configurations were elucidated by spectroscopic data analysis, chemical calculations, combined with X-ray diffractions. The plausible biosynthetic pathways for compounds 1−3 are proposed. Surprisingly, compound 1 exhibited cytotoxicity against SGC-7901 cells by inducing cells apoptosis, which might relate to the promotion of synthesis of neutrophil elastase.