From the soft bodied coral Sarcophytum glaucum a crystalline compound-sarcophine (1), which is believed to be one of the repellents protecting the coral against predators, was isolated. The functional groups of 1 have been deduced from detailed NMR study and the whole molecular structure has been determined by a single-crystal 3-dimensional X-ray diffraction study proceeding from direct methods. The compound crystallizes in orthorhombic crystals, space group P212121, and there are four molecules in each unit cell of dimensions a = 12·429(3), b = 13·766(3) and c = 10·750(1). The structure was found to be a new epoxy cembranolide. The mass spectrum and CD of 1 and several simple derivatives as well as the conformation of 1 in solution are discussed.