Immunosuppressive sesquiterpene phenols from the marine sponge <i>Dactylospongia elegans</i>

Two new sesquiterpene phenols, dactyltone A (<b>1</b>) and dactyltone B (<b>2</b>), were isolated from the marine sponge <i>Dactylospongia elegans</i> collected from the South China Sea. Their structures were elucidated by comprehensive spectroscopic analysis (including NMR and HRESIMS) combined with experimental and calculated electronic circular dichroism (ECD) data. Notably, the carbonylation at C-2 observed in ring A of marine sponge-derived sesquiterpene phenols represents an uncommon structural feature. Biological evaluation revealed that both compounds showed selective immunosuppressive activity, specifically inhibiting ConA-induced T-cell proliferation with IC₅₀ values of 6.53 μM and 9.85 μM for <b>1</b> and <b>2</b>, respectively, while demonstrating no significant antibacterial or cytotoxic effects at tested concentrations.