Nitrogenous Sesquiterpenoids from the South China Sea Nudibranch <i>Hexabranchus sanguineus</i> and Its Possible <scp>Sponge‐Prey</scp><i>Acanthella cavernosa</i>: Chiral Separation, Stereochemistry and Chemical Ecology
Shou‐Mao Shen, Zaiyong Zhang, Li‐Gong Yao, Jian‐Rong Wang, Yue‐Wei Guo, Xu‐Wen Li
Abstract
Comprehensive Summary A detailed chemical investigation of the South China Sea nudibranch Hexabranchus sanguineus , as well as its possible sponge‐prey Acanthella cavernosa , led to the isolation of fifteen new nitrogenous sesquiterpenoids, namely ximaocavernosins A−O, including seven cadinanes (1—7), seven spiroaxanes (12—18) and one aromadendrane (19), together with thirteen known related compounds (8—11 and 20—28). Compounds (±)‐1—9 (except for 4 and 6) were further separated by chiral‐phase HPLC to their corresponding unequal enantiomers, respectively. Their structures and absolute configurations were determined by a combination of extensive spectroscopic data analysis, quantum mechanical nuclear magnetic resonance (QM‐NMR) methods, Mosher's method, X‐ray diffraction analysis and/or time‐dependent density functional theory/electronic circular dichroism (TDDFT‐ECD) calculation. The commonly existed nitrogenous sesquiterpenoids in these two animals are suggested to be chemical markers for their prey‐predator relationship.