Spiroaxillarone A, a Symmetric Spirobisnaphthalene with an Original Skeleton from Cyanotis axillaris

The first representative of a new type of spirobisnaphthalene with a previously unknown skeletal system, Spiroaxillarone A ( 1 ), was isolated from Cyanotis axillaris . The planar structure was determined through analysis of spectroscopic evidence, while electronic circular dichroism (ECD) calculations were used to determine its absolute configuration. The structure of 1 was further confirmed through X-ray diffraction studies of its tetrabromobenzoate derivative ( 1a ). Spiroaxillarone A exhibited significant antimalarial activity against resistant Plasmodium falciparum (IC 50 = 2.32 μM).