Sesquiterpenoids with antibacterial and cytotoxic activities from the soft coral Litophyton arboreum

A chemical investigation of the CH 2 Cl 2 /MeOH extract of the Red Sea soft coral Litophyton arboreum led to the isolation of a new eudesmane-type sesquiterpenoid, 11-acetoxy-5 β ,8 β -epidioxy-6-eudesmene ( 1 ), together with three known analogues ( 2 – 4 ) . The structures of the isolated metabolites were elucidated using comprehensive spectroscopic techniques, including NMR and HRESIMS, supported by detailed comparison with reported data of related analogues. The antiproliferative properties of metabolites 1 – 4 were evaluated against Hep G2 and NCI-H1299 human cancer cell lines. Among them, compounds 1 and 4 exhibited weak cytotoxic activity against NCI-H1299, with IC 50 values of 39.8 ± 0.93 and 43.1 ± 0.61 μM, respectively, compared to doxorubicin as a reference. The antibacterial screening revealed that the isolated sesquiterpenoids displayed weak to moderate activity, with inhibition observed at relatively high concentrations (50–150 µg/mL). Compounds 1 , 3 , and 4 showed selective inhibition of Bacillus cereus and Staphylococcus aureus , whereas Gram-negative bacteria were less affected. Although MIC values could not be determined owing to limited sample availability, the results suggest a weak but measurable antibacterial potential consistent with other eudesmane-type sesquiterpenoids. The combined cytotoxic and antibacterial data indicate that these metabolites may serve as useful scaffolds for future structure–activity and mechanistic studies. ● A new eudesmane-type sesquiterpenoid was isolated from Litophyton arboreum . ● Structures of metabolites were elucidated by NMR and HRESIMS analyses. ● Compound 1 showed antibacterial activity against S. aureus and B. cereus . ● Compounds 1 and 4 displayed weak cytotoxic activity against NCI-H1299 cells. ● Results highlight L. arboreum as a promising source of bioactive metabolites.