Total synthesis of cladocorans A and B: a structural revision

Cladocorans A and B, isolated from the Mediterranean coral Cladocora cespitosa, are novel sesterterpenoids whose structures were initially proposed as 1 and 2, respectively. These designations, however, subsequently came under doubt. In the present study, the synthesis of compounds 5 and 6 was undertaken. The physical properties of 5 and 6 were found to be identical to those of natural cladocorans A and B, whose structures were thus concluded to be 5 and 6, respectively. Cladocoran B is thus clearly shown to be an olefinic regioisomer of dysidiolide and cladocoran A as its acetate.