CEMBRANE AND PSEUDOPTERANE DITERPENOIDS OF THE OCTOCORAL PSEUDOPTEROGORGIA-ACEROSA

The diterpenoid metabolites isolated from Pseudopterogorgia acerosa collected off the coast of Tobago have been investigated. Collections made in the month of March showed a different distribution of these metabolites from a collection made in July. The dominant constituents in March were acidic diterpenoids which were converted by reaction with diazomethane to deoxypseudopterolide (1), a pseudopterane, and acerosolide (2), a cembrane. Esters 1 and 2 were isolated directly from the July collection, which also afforded the novel nitrogenous pseudopteranoid tobagolide (3). Tobagolide undergoes a novel reaction with acetic anhydride that leads to the displacement of Me2N by OAc. Tobagolide reacts with diazomethane to form a pyrazoline. Structural assignments have depended heavily on 2-D NMR spectroscopy; in particular, the value of our FLOCK pulse sequence for establishing two-bond and three-bond C-13-H-1 shift correlations is illustrated.