C15 acetogenins and terpenes of the dictyoceratid sponge Spongia zimocca of Il Rogiolo: A case of seaweed-metabolite transfer to, and elaboration within, a sponge?

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Abstract 1. 1. In the narrow Mediterranean area of Il Rogiolo, the acetates of the secondary alcohols of β-chamigrene (−)-1b, branched lauroxepane (−)-2b, and isopimarane (+)-3b are found in the dictyoceratid sponge Spongia zimocca , whereas the corresponding free alcohols (+)-1a, (−)-2a, and probably also (+)-3a, are found in the red seaweed Laurencia microcladia . 2. 2. No one of these acetylated metabolites could be detected either in this seaweed or in the global algal mass of Il Rogiolo. 3. 3. Terpenes bearing tertiary alcoholic functionalities of either L. microcladia (−)-4E, (−)-4Z or another red seaweed of the same area, Sphaerococcus coronopifolius [(+)-5, (−)-6], are found unaltered also in S. zimocca . 4. 4. These findings imply transfer of the hydroxyl-bearing metabolites from the seaweeds to the sponge and it is tempting to speculate that the secondary alcoholic function is acetylated in the sponge while tertiary alcohols and the secondary alcohol (+)-7 escape acetylation, the first ones as sterically-hindered alcohols and the latter one as a sponge metabolite residing in a special cell compartment.