Antibacterial Methyl Ester Cembranoids from the Soft Coral Sarcophyton ehrenbergi and Their Structural Elucidation

Six previously undescribed methyl ester cembranoids, namely sarcoehrenolides L-Q (1-6), along with three known related ones (7-9), were isolated from the soft coral Sarcophyton ehrenbergi collected off Weizhou Island in the South China Sea. Their structures and absolute configurations were unambiguously established in the light of extensive spectroscopic data analysis, X-ray diffraction analysis, chemical conversion, and TDDFT-ECD calculations. All isolated compounds were evaluated via in vitro bioassays to investigate their antibacterial activity against eighteen human and fish pathogens. Compounds 2, 8, and 9 exhibited moderate antibacterial activity against Streptococcus parauberis with MIC values of 38.8, 37.4 and 31.6 μg/mL, respectively.