New Ecotoxicologically and Biogenetically Relevant Terpenes of the tropical green seaweed Caulerpa taxifolia which is invading the Mediterranean

The tropical green seaweed Caulerpa taxifolia (V AHL ) C. A GARDH (Caulerpales) which is invading the Mediterranean is shown to contain trace amounts of two further novel terpenes, 7,7‐ C ‐didehydro‐6‐hydroxy‐6,7‐dihydrocaulerpenyne (= (4 S , 6 S ,1 E )‐3‐[( Z )‐acetoxymethylidene]‐6‐hydroxy‐11‐methyl‐7‐methylidenedodeca‐1,10‐dien‐8‐yne‐1,4‐diyl diacetate; 3a ) and taxifolione (= 6‐methylhept‐5‐en‐3‐yn‐2‐one; 4 ). The former is the most active of the toxins so far isolated from this seaweed, both as an in vitro inhibitor of the growth of marine bacteria and as a cytotoxic agent toward marine ciliate protists. This suggests a central ecotoxicological role for triacetate 3a as an adjuvant factor in the invasion of the Mediterranean by this seaweed. Moreover, the almost equally toxic 10,11 ‐epoxycaulerpenyne ( 2 ) which is scarcely available from Nature for bioassays can now be obtained by peroxy‐acid epoxidation of caulerpenyne ( 1 ), along with the 6,7‐epoxycaulerpenynes 6b and 6a . The latter are very labile, 6a giving triacetate 3a , suggesting epoxides to be late biogenetic intermediates in C. taxifolia .