CAULERPENYNE-AMINE REACTING SYSTEM AS A MODEL FOR IN-VIVO INTERACTIONS OF ECOTOXICOLOGICALLY RELEVANT SESQUITERPENOIDS OF THE MEDITERRANEAN-ADAPTED TROPICAL GREEN SEAWEED CAULERPA-TAXIFOLIA

Caulerpenyne (1), the most abundant of the ecotoxicologically relevant sesquiterpenoids of the Mediterranean-adapted tropical green seaweed Caulerpa taxifolia, was found to react with Et(3)N or pyridine in MeOH by initial deprotection of C(I)HO to give oxytoxin 1 (2a), previously isolated from the sacoglossan mollusc Oxynoe olivacea. With BuNH(2), without any precaution to exclude light, 1 gave the series of racemic 3 and 4, and achiral (4E,6E)-5, (4E,6Z)-5, (4Z,6E)-5, and (4Z,6Z)-5 pyrrole compounds, corresponding to formal C(4) substitution, 4,5-beta-elimination, and (E/Z)-isomerization at the C(4)=C(5) and C(6)=C(7) bonds. Changing to CDCl3 as solvent in the dark, 1 gave cleanly, via 2a as an intermediate, 3 and (4E,6E)-5. The latter proved to be prone to (E/Z)-photoisomerization. Under standard acetylation conditions, 3 gave (4E,6E)-5 via acetamide 7 as an intermediate. Particular notice is warranted by selective deprotection of 1 at C(1), mimicking enzyme reactions, and unprecedented formation of pyrrole compounds from freely-rotating, protected 1,4-dialdehyde systems.