Myrcaulones A–C, Unusual Rearranged Triketone–Terpene Adducts from Myrciaria cauliflora

Three rearranged triketone–terpene adducts, myrcaulones A–C (1–3), were isolated from the leaves of Myrciaria cauliflora. Myrcaulones A (1) and B (2) feature a new carbon skeleton with an unprecedented spiro­[bicyclo[3.1.1]­heptane-2,2′-cyclopenta­[b]­pyran] core. Myrcaulone C (3) possesses an unusual cyclobuta­[6,7]­cyclonona­[1,2-b]­cyclopenta­[e]­pyran backbone. Their structures with absolute configurations were elucidated by NMR spectroscopy, X-ray diffraction, and electronic circular dichroism calculations. A plausible biogenetic pathway for myrcaulones A–C involving the rearrangement of a triketone unit is also proposed. In addition, myrcaulones A (1) and B (2) exhibited inhibitory effects against tumor necrosis factor-α and nitric oxide generation induced by lipopolysaccharide in RAW 264.7 macrophages.