(±)-Melicolones A and B, Rearranged Prenylated Acetophenone Stereoisomers with an Unusual 9-Oxatricyclo[3.2.1.13,8]nonane Core from the Leaves of Melicope ptelefolia

Melicolones A (1) and B (2), a pair of rearranged prenylated acetophenone epimers with an unusual 9-oxatricyclo[3.2.1.1(3,8)]nonane core, were isolated from the leaves of Melicope ptelefolia. Further chiral high-performance liquid chromatography resolution gave enantiomers (+)- and (-)-1, as well as (+)- and (-)-2, respectively. The structures and absolute configurations of the pure enantiomers were determined by extensive spectroscopic data and single crystal X-ray diffraction. All the isolated enantiomers exhibited potent cell protecting activities against high glucose-induced oxidative stress in human vein endothelial cells.