Novel meroditerpenes from the brown alga Cystoseira sp.

Five new meroditerpenes have been isolated from a brown alga of the genus Cystoseira collected around the Canary Islands. One, cystoseirone diacetate (3), possesses a new rearranged structure with an unusual ether linkage in the diterpene side chain. Its biogenetic origin was explained as derived from the oxidation of amentol chromane diacetate (2) and subsequent cyclization. Structures were determined through the interpretation of the spectral data and by means of chemical transformations. The relative stereochemistry was proposed on the basis of ROESY correlations.