Polyoxygenated cembranoids from the Hainan soft coral Lobophytum crassum.

Five new uncommon cembranoids, named lobophycrasins A–D (1 and 3 – 5) and (−)-humilisin A (2), together with a known related one (6), have been isolated from Hainan soft coral Lobophytum crassum. Their structures were elucidated by extensive spectroscopic analysis, NMR calculation with DP4+ probability analysis, TDDFT-ECD (time-dependent density functional theory-electronic circular dichroism) calculations and comparison with the reported data. Further, with the aid of X-ray diffraction analysis, the structure of lobocrasol (6), which was announced possessing novel unprecedented skeleton, was firmly revised as 6a. In addition, a plausible biogenetic connection among these isolates was also proposed. [Display omitted] • Five new cembranoids have been isolated from Hainan soft coral Lobophytum crassum. • Their structures were elucidated by DP4+ calculation and/or TDDFT-ECD calculation. • With the aid of X-ray diffraction analysis, the structure of lobocrasol (6) was firmly revised as 6a. [ABSTRACT FROM AUTHOR]