The Australian sea pen Anthoptilum cf. kukenthali has afforded five new briarane-type diterpenes, anthoptilides A-E. Their structures were determined on the basis of their spectroscopic data. Single-crystal X-ray determination was performed on anthoptilide A. Anthoptilides B and C inhibited the binding of [(3)H]1, 3-dipropyl-8-cyclopentylxanthine ([(3)H]DPCPX) on adenosine A(1) receptors.