NEW ECOTOXICOLOGICALLY AND BIOGENETICALLY RELEVANT TERPENES OF THE TROPICAL GREEN SEAWEED CAULERPA-TAXIFOLIA WHICH IS INVADING THE MEDITERRANEAN

The tropical green seaweed Caulerpa taxifolia (VAHL) C. AGARDH (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 (=(4S,6S,1E)-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 nitro 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.