Studies of Australian soft corals. XXV. Several caryophyllene-based diterpenes from a Nephthea species

Two new caryophyllene-based diterpenes (5) and (6) are reported from the soft coral Nephthea chabrolii. The structures were deduced spectroscopically and the compounds were converted into several known diterpenes by chemical transformation. The presence of the caryophyllene ring system was based on 13C n.m.r. data and confirmed by conversion into the known clovane ring system by an acid-catalysed hydration-rearrangement of the endocyclic epoxide (12).