Epoxycaulerpenynes: Reactivity, and Diastereoselective and Highly Regioselective Synthesis by Dimethyldioxirane Oxidation of Caulerpenyne

Abstract

Caulerpenyne (1), the abundant sesquiterpene of the green seaweed Caulerpa taxifolia, has been epoxidized with dimethyldioxirane. The reaction proceeds with significant regioselectivity and moderate diastereoselectivity, the addition of oxygen occurring preferentially at the C(6)C(7) double bond thereby giving (6S,7S)‐ and (6R,7R)‐epoxycaulerpenynes 10 and 12 in an approximately 2:1 molar ratio besides a small amount of 10,11‐epoxycaulerpenyne as an equimolecular diastereomeric mixture 8. The epoxides underwent rearrangement under acidic conditions; the 6,7‐epoxides were easily converted into allylic alcohols, whereas the 10,11 isomers required more drastic acidic conditions and gave complex mixtures containing two diastereoisomeric 1,4‐dioxanes and an enynone. The high reactivity of 6,7‐epoxycaulerpenynes suggests their involvement in the biogenetic pathways of the alga.

Palatability of Macroalgae that Use Different Types of Chemical Defenses

“…The secondary metabolite caulerpenyne can be converted through activation, degradation, and oxidation to a variety of additional compounds that may have greater toxicity than the precursor, including oxytoxins (1 and 2), epoxycaulerpenynes (6, 7, and 10, 11), 7,7-C-didehydro-6-hydroxy-6,7-dihydrocaulerpenyne, taxifolials (A-D), and taxifolione Guerriero and D'Ambrosio, 1999;Jung and Pohnert, 2001). During activation, the 1,4-diacetoxybuta-1,3-diene(bis-enol acetate) moiety is hydrolyzed by esterases in seconds and is replaced with 1,4 dialdehydes, which are suggested to be responsible for significant bioactivity.…”

New Caulerpenyne-derived Metabolites of an Elysia Sacoglossan from the South Indian Coast

“…This finding raises the question of whether compounds 4 and 5 may be the result of transformation of 1 by the sacoglossan or whether the molluscs may simply accumulate very minor algal compounds. A series of caulerpenyne-derived products related to compounds 4 and 5, have in fact been reported from several tropical Caulerpa algae [19][20][21][22]. However, in contrast to the majority of Caulerpa-feeder sacoglossans, the defensive toxins, oxytoxin-1 (2) and oxytoxin-2 (3), were not found in Elysia cf.…”