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Nanolobatone A, featuring an unprecedented tricyclo[10.3.0.01,2]pentadecane carbon skeleton, along with four new polyoxygenated and four unusual endoperoxide‐bridged casbane‐type diterpenoids were isolated from the Hainan soft coral Sinularia nanolobata. The structures of the new compounds were established by extensive spectroscopic analysis, X‐ray diffraction analysis, and time‐dependent density functional theory/electronic circular dichroism calculations. A plausible biosynthetic pathway of new isolates was proposed. Bioassays revealed that nanolobatone A showed weak antibacterial activity against the Gram‐positive bacteria Streptococcus pyogenes. [ABSTRACT FROM AUTHOR]

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]