Atrachinenynes A–D, four diacetylenic derivatives with unprecedented skeletons from the rhizomes of Atractylodes chinensis†
Atrachinenynes A–D (1–4), four novel diacetylenic derivatives, were isolated for the first time from the rhizomes of Atractylodes chinensis. Compound 1 features a new C26 skeleton with an unusual 8/6/6/5 tetracyclic ring system bearing a diacetylene sidechain. Compounds 2–4 are three novel diacetylenic terpenoids with an additional six-membered ring between terpenes and diacetylenes formed via a Diels–Alder reaction. The structures and the absolute configurations of 1–4 were elucidated by spectroscopic methods, electronic circular dichroism (ECD) calculations, and 13C quantum chemical calculations. Their plausible biogenetic pathways were also proposed.