The chemical investigation of the rarely studied soft coral Sinularia tumulosa resulted in the discovery of five oxygenated cembrane diterpenes 1-5, including two new compounds situmulins A (1) and B (2). The structures of 1 and 2 were established through the extensive analyses of 1D and 2D NMR spectral data together with the comparisons with the known compounds. Furthermore, the absolute configuration of 1 was determined by the time-dependent density functional theory (TDDFT) ECD approach, while the relative configuration of 2 was assigned via the quantum mechanical-NMR (QM-NMR) calculations. It might be worth to point out it is the first time to disclose the presence of cembrane diterpenes in the title species. In the bioassays, compound 2 not only showed strong antibacterial activities against fish pathogenic bacteria Streptococcus parauberis FP KSP28 and Phoyobacterium damselae FP2244 with both minimum inhibitory concentration for 90 % (MIC90 ) values of 25 μM, but also demonstrated substantial inhibitory efficacy against vancomycin-resistant Enterococcus faecium bacteria G1, G4, G7, G8 and G13 from several individuals, with MIC90 values of 25, 50, 100, 50 and 25 μM, respectively.
Keywords: Sinularia tumulosa; antibacterial activity; cembrane diterpene; soft coral; structural elucidation.
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