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Chemical investigation on the soft coral Sarcophyton ehrenbergi collected from the Xisha Islands of the South China Sea have led to the isolation of eight cembranoids including five new ones, sarcophytonoxides A–E (1–5). The structures of new cembranoids (1–5) were determined by spectroscopic analysis and comparison of the NMR data with those of related analogues. The cytotoxicities of compounds 1–8 against human ovarian cancer cell line A2780 were also evaluated.

Two novel biscembranoids, sarelengans A and B (1 and 2), five new cembranoids, sarelengans C–G (3–7), along with two known cembranoids (8 and 9) were isolated from the South China Sea soft coral Sarcophyton elegans. Their structures were determined by spectroscopic and chemical methods, and those of 1, 4, 5, and 6 were confirmed by single crystal X-ray diffraction. Compounds 1 and 2 represent the first example of biscembranoids featuring a trans-fused A/B-ring conjunction between the two cembranoid units. Their unique structures may shed light on an unusual biosynthetic pathway involving a cembranoid-Δ8 rather than the normal cembranoid-Δ¹ unit in the endo-Diels-Alder cycloaddition. Compounds 2 and 3 exhibited potential inhibitory effects on nitric oxide production in RAW264.7 macrophages, with IC50 values being at 18.2 and 32.5 μM, respectively. [ABSTRACT FROM AUTHOR]