Polyoxygenated Cembranoids from Soft Coral Lobophytum Crassum and Their Anti‐tumoral Activities.

Main observation and conclusion: Four new cembranoids, 6‐oxo‐cembrene‐A (1), lobocrassins G—H (2—3), and 14‐epi‐lobophytolide B (4), along with eight known related compounds (5—12), were isolated from the South China Sea soft coral Lobophytum crassum. Their structures were established by extensive spectroscopic analysis and by comparison of the spectral data with those reported in the literatures. The absolute stereochemistry of 14‐epi‐lobophytolide B (4) was established by time‐dependent density functional theory electronic circular dichroism (TDDFT‐ECD) calculations, whereas that of three known metabolites (6, 11 and 12) was also determined, for the first time, by using modified Mosher's method and/or X‐ray diffraction analyses. In bioassay, the cembranoids 6, 7 and 12 showed significant anti‐tumoral activity against A549, HT‐29, SNU‐398 and Capan‐1 tumor cell lines with IC50 values ranging from 1.5 to 7.4 μmol/L. A preliminary structure‐activity relationship was also discussed. [ABSTRACT FROM AUTHOR]