Structure Revision of Heptacyclic Naphthoquinone Dimer Arnebidin Based on NMR Spectroscopic Analysis and X-ray Crystallography.

Arnebidin, a heptacyclic naphthoquinone dimer with a tricyclo[3.3.0.0]octane core, which was first isolated from and later found from . Its structure was identified by the analysis of NMR and EI-MS data. In the present work, a heptacyclic naphthoquinone dimer ((±)-) was obtained from the petroleum ether portion of the ethanol extract of . By comparing the NMR data of with the literatures, compound should be identified as arnebidin. However, the single-crystal X-ray diffraction analysis followed by reinterpretation of the NMR data revealed that the structure of was a heptacyclic naphthoquinone dimer with a tricyclo[3.2.1.0]octane core. Thus, we proposed that arnebidin should be revised to .