A Cytotoxic Heterodimeric Cyclic Diarylheptanoid with a Rearranged Benzene Ring from the Seagrass .

The widespread seagrass contains a new diarylheptanoid heterodimer, zosterabisphenone C (), featuring an unprecedented rearrangement of one of its benzene rings to a cyclopentenecarbonyl unit. The planar structure and absolute configuration of zosterabisphenone C were elucidated by a combination of spectroscopic (MS, ECD, and low-temperature NMR) and computational (DFT-NMR and DFT-ECD) evidence. Consistent with the previously isolated zosterabisphenones, compound was selectively cytotoxic against HCT 116 adenocarcinoma colon cancer cells, reducing their viability by 73% at 10 μM (IC of 7.6 ± 1.1 μM). The biosynthetic origin of zosterabisphenone C () from an oxidative rearrangement of zosterabisphenone A () is proposed.