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 Et₃N or pyridine in MeOH by initial deprotection of C(1)HO to give oxytoxin 1 ( 2a ), previously isolated from the sacoglossan mollusc Oxynoe olivacea. With BuNH₂, 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-β-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.