Klyflaccicembranols A–I, New Cembranoids from the Soft Coral Klyxum flaccidum

New cembranoids klyflaccicembranols A–I (1–9), along with gibberosene D (10), have been isolated from the organic extract of a Formosan soft coral Klyxum flaccidum. Their structures were established by extensive spectroscopic analyses, including 2D NMR spectroscopy, and spectral data comparison with related structures. The cytotoxicity of the isolated metabolites, as well as their nitric oxide (NO) inhibitory activity, were evaluated and reported. Metabolites 2, 4, 6, 8 and 9 were found to exhibit variable activities against a limited panel of cancer cell lines in a range of IC50 16.5–49.4 μM. Among the tested cembranoids, compounds 4, 5, 6, and 9 significantly inhibited NO production in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages at a dose of 50 μg/mL.