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

Six previously undescribed methyl ester cembranoids, namely sarcoehrenolides L-Q (<b>1</b>-<b>6</b>), along with three known related ones (<b>7</b>-<b>9</b>), were isolated from the soft coral <i>Sarcophyton ehrenbergi</i> 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 <b>2</b>, <b>8</b>, and <b>9</b> exhibited moderate antibacterial activity against <i>Streptococcus parauberis</i> with MIC values of 38.8, 37.4 and 31.6 μg/mL, respectively.