Redetermination and absolute configuration of (+)-7-epiclusianone

Abstract

The absolute configuration of 3-benzoyl-4-hydroxy-6,6-dimethyl-1,5,7- tris(3-methylbut-2-enyl)bicyclo[3.3.1]non-3-ene-2,9-dione, C33H 42O4, isolated from Hypericum hypericoides, has been determined. The previous study [Xiao et al. (2007). J. Nat. Prod. 70, 1779-1782] gave only the established relative configuration. The three stereogenic centers are now established as 1R, 5R and 7S on the basis of the refinement of the Flack absolute structure parameter against Cu Kα data and correspond to a specific rotation of [α] D 20 = +66°. The enol-hydroxy group forms an intramolecular O-H⋯O hydrogen bond to close an S(6) ring.