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Main observation and conclusion: A detailed chemical study on the Hainan soft coral Sinularia crass has resulted in the isolation and characterization of eleven casbane‐type diterpenoids, named sinucrassins A—K (1—11), along with six known related ones (12—17). Their structures were elucidated by extensive spectroscopic analyses and comparison with the reported data. The absolute configurations of new compounds were determined by the X‐ray diffraction analysis and computer‐assisted structural elucidation including 13C NMR data calculation and time‐dependent density functional theory/electronic circular dichroism calculation. [ABSTRACT FROM AUTHOR]

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]