Abstract Five new briarane derivatives, briaexcavatins V–Z (1–5), have been isolated from a cultured octocoral Briareum excavatum. The structures of compounds 1–5 were established by spectroscopic methods. Single-crystal X-ray diffraction data for 2 confirmed the structure. Briarane 4 possesses an unprecedented 8,9-epoxy moiety. The relationships between 13C NMR chemical shifts and the conformations of briaranes possessing an 11,12-epoxy group are described. Briaranes 1, 3, and 4 have displayed weak inhibitory effects on superoxide anion generation by human neutrophils. Briarane 1 was found to show mild inhibitory effects on human neutrophil elastase release and 5 exhibited mild activity to enhance human neutrophil elastase release.