Isolation and structures of sixteen new asbestinin diterpenes from the Caribbean gorgonian Briareum asbestinum.

Sixteen new diterpenoids, representative of the asbestinane skeletal class, have been isolated from shallow water colonies of the Caribbean gorgonian octocoral Briareum asbestinum. The structures of these secondary metabolites, named asbestinin-11 [1], asbestinin-12 [3], asbestinin-13 [4], asbestinin-14 [5], asbestinin-15 [7], asbestinin-16 [8], asbestinin-17 [9], asbestinin-18 [10], asbestinin-19 [11], asbestinin-20 [12], asbestinin-21 [13], asbestinin-22 [14], asbestinin-23 [15], 11-acetoxy-4-deoxyasbestinin E [16], 11-acetoxy-4-deoxyasbestinin F [17] and 4-deoxyasbestinin G [18], were defined by chemical and spectroscopic methods. These specimens of B. asbestinum, collected in Puerto Rico, yielded almost exclusively diterpenoids possessing the asbestinane carbon skeleton thus suggesting minor biosynthetic variations for this gorgonian. In this paper, we also revise the structures of the known asbestinin-6 and asbestinin-7 to asbestinanes 2 and 6, respectively.