New Cytotoxic Cembranes from the Sea Pen <i>Gyrophyllum </i><i>s</i><i>ibogae</i>

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