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

The widespread seagrass Zostera marina contains a new diarylheptanoid heterodimer, zosterabisphenone C ( 1 ), 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 1 was selectively cytotoxic against HCT 116 adenocarcinoma colon cancer cells, reducing their viability by 73% at 10 μM (IC ₅₀ of 7.6 ± 1.1 μM). The biosynthetic origin of zosterabisphenone C ( 1 ) from an oxidative rearrangement of zosterabisphenone A ( 4 ) is proposed.