New cytotoxic cembranes from the sea pen Gyrophyllum sibogae

Two new cembrane-type diterpenoids have been isolated from the 2-propanol extract of the sea pen Gyrophyllum sibogae collected in South Africa: 7,8-dihydroflabellatene A (1) and 7,8-dihydroflabellatene B (2). Their structures were determined on the basis of detailed spectroscopic analysis and by single-crystal X-ray analysis of the major metabolite 1, which showed strong in vitro cytotoxicity against a panel of 13 tumor cell lines.