Myrcaulones A–C, Unusual Rearranged Triketone–Terpene Adducts from <i>Myrciaria</i> <i>cauliflora</i>

Three rearranged triketone–terpene adducts, myrcaulones A–C (<b>1</b>–<b>3</b>), were isolated from the leaves of <i>Myrciaria cauliflora</i>. Myrcaulones A (<b>1</b>) and B (<b>2</b>) feature a new carbon skeleton with an unprecedented spiro­[bicyclo[3.1.1]­heptane-2,2′-cyclopenta­[<i>b</i>]­pyran] core. Myrcaulone C (<b>3</b>) possesses an unusual cyclobuta­[6,7]­cyclonona­[1,2-<i>b</i>]­cyclopenta­[<i>e</i>]­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 (<b>1</b>) and B (<b>2</b>) exhibited inhibitory effects against tumor necrosis factor-α and nitric oxide generation induced by lipopolysaccharide in RAW 264.7 macrophages.