Paralemnanoids A–K, new norsesquiterpenoids and sesquiterpenoids with hepatoprotective activity from the soft coral Paralemnalia sp.

Abstract Eleven nardosinane-type compounds, including a norsesquiterpenoid featuring a novel carbon skeleton designated as paralemnanoid A ( 1 ), and ten additional norsesquiterpenoids identified as paralemnanoids B − K ( 2 − 11 ), were isolated from the South China Sea soft coral Paralemnalia sp.. Comprehensive structural elucidation of compounds 1 − 11 was achieved through an integrated analytical approach, combining including NMR spectroscopy, HRESIMS, single-crystal X-ray diffraction analysis, DP4 + probability assessments, ECD calculations, and literature comparisons. Furthermore, we proposed that the novel poly-isoprenoid scaffold paralemnanoid A ( 1 ) originates from paralemnanoid B ( 2 ) through sequential oxidative modifications followed by non-enzymatic skeletal rearrangements. The hepatoprotective effects of compounds 1 − 11 were assessed through bioassays, revealing that paralemnanoids A ( 1 ) and E ( 5 ) exhibited moderate hepatoprotective activity at a concentration of 20 μmol/L in the zebrafish model. This study expands the chemical diversity of marine-derived nardosinane-type terpenoids and provides new insights into their potential therapeutic applications.