Studies of Australian Soft Corals. XXXX.1 The Natural Products Chemistry of Alcyonacean Soft Corals with Special Reference to the Genus Lobophytum

The eggs of the alcyonacean soft coral Lobophytum microlobulatum contain the known cembranoid diterpene 3,4‐epoxynephthenol (9). This compound was not detected in the soft coral colony from which the eggs were released, although decaryiol (10), which is derived from (9) by acid treatment, was present in the eggs and coral tissue. The new diterpene decaryiol acetate (11) was a natural product in the eggs and coral. Several new non‐cembranoid diterpenes based on known eudesmane, germacrene and elemene sesquiterpene skeletons were isolated. Investigation of the chemistry of two Lobophytum species afforded diterpenes which are prenylated examples of cubebol and germacrene‐type ses‐quiterpenes (12, 18). In the course of studies of the overgrowth of soft corals by filamentous algae, a new eudesmane‐based diterpene (20) was identified. The related diterpene (19) which co‐occurs with (20), was shown to inhibit the growth of the algae Ceramium codii even at 12.5 ppm. Lobophytum chemistry is of interest because of the frequent co‐occurrence of different diterpene skeletons in the same colony, a relatively infrequent observation in other genera.