New Bioactive Eudesmane‐type Sesquiterpenoids From the Red Sea Soft Coral Nephthea sp.

Two previously unreported eudesmane‐class sesquiterpenes, ( 4R *,5 S *,6 Z ,10 R *)‐11‐hydroperoxy‐8‐oxo‐eudesm‐6‐en‐5α‐ol ( 1 ) and (4R *,5 S *,6 Z ,10 R *)‐5‐acetoxy‐11‐methoxy‐8‐oxo‐eudesm‐6‐en ( 2 ), were obtained through fractionation of the CH 2 Cl 2 /MeOH (1:1) extract derived from the Red Sea‐derived soft coral Nephthea sp., along with three known sesquiterpenes ( 3 – 5 ). The structural determination of the new compounds was achieved through comprehensive analysis of spectroscopic data, including one‐ and two‐dimensional nuclear magnetic resonance techniques and high‐resolution electrospray ionisation mass spectrometry measurements. The cytotoxic activities of the newly isolated compounds ( 1 and 2 ) were evaluated using the Sulforhodamine B assay against three human carcinoma cell lines: MCF‐7, HT‐29 and HepG2, with doxorubicin serving as the reference drug. Metabolite 2 showed moderate cytotoxicity towards MCF‐7 and HT‐29 cell lines, with IC 50 values of 51.5 ± 2.1 and 64.1 ± 1.9 µM, respectively, and weak activity against HepG2 (IC 50 = 71.3 ± 2.5 µM). In contrast, compound 1 displayed weak cytotoxic effects across all tested cell lines, with IC 50 values of 72.8 ± 2.3 µM (MCF‐7), 85.4 ± 2.7 µM (HT‐29) and 95.6 ± 3.2 µM (HepG2). These findings contribute to the chemical and biological characterisation of Nephthea sp. metabolites and support further exploration of eudesmane‐type sesquiterpenes as potential anticancer agents.